Sustainable Phase Change and Polymeric Water Absorbent Materials: Heat Stress Reduction in Helmets [1st ed.] 9789811557491, 9789811557507

Table of contents :
Front Matter ....Pages iii-ix
Introduction (Sinnappoo Kanesalingam, Rajkishore Nayak)....Pages 1-5
Review of Literature: Motorcycle Helmet (Sinnappoo Kanesalingam, Rajkishore Nayak)....Pages 7-61
Experimental Techniques (Sinnappoo Kanesalingam, Rajkishore Nayak)....Pages 63-80
Results and Discussion (Sinnappoo Kanesalingam, Rajkishore Nayak)....Pages 81-115
Conclusions (Sinnappoo Kanesalingam, Rajkishore Nayak)....Pages 117-119
Back Matter ....Pages 121-142

Citation preview

Sinnappoo Kanesalingam Rajkishore Nayak

Sustainable Phase Change and Polymeric Water Absorbent Materials Heat Stress Reduction in Helmets

Sustainable Phase Change and Polymeric Water Absorbent Materials

Sinnappoo Kanesalingam Rajkishore Nayak •

Sustainable Phase Change and Polymeric Water Absorbent Materials Heat Stress Reduction in Helmets

123

Sinnappoo Kanesalingam RMIT University Brunswick, VIC, Australia

Rajkishore Nayak RMIT University Vietnam Ho Chi Minh City, Vietnam

ISBN 978-981-15-5749-1 ISBN 978-981-15-5750-7 https://doi.org/10.1007/978-981-15-5750-7

(eBook)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Research Concept . . . . . . . . . . . . . . . . 1.2.1 Scope of the Current Research 1.2.2 Research Questions . . . . . . . . 1.2.3 Objectives of the Study . . . . . 1.3 Hypothesis . . . . . . . . . . . . . . . . . . . . . 1.4 Conclusions . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . .

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2 Review of Literature: Motorcycle Helmet . 2.1 Introduction . . . . . . . . . . . . . . . . . . . 2.2 Need for Motorcycle Helmet . . . . . . . 2.3 Motorcycle Helmet Regulations . . . . . 2.4 Components of Motorcycle Helmets . 2.5 Cooling the Motorcycle Helmet . . . . . 2.6 Types of Motorcycle Helmets . . . . . . 2.6.1 Full Face Helmet . . . . . . . . . 2.6.2 Off-Road/Motocross Helmet . 2.6.3 Modular/Flip-up Helmet . . . . 2.6.4 Open Face Helmet . . . . . . . . 2.6.5 Half Helmet . . . . . . . . . . . . . 2.7 Bicycle Helmets . . . . . . . . . . . . . . . . 2.8 The Effects of Discomfort in Helmets 2.8.1 Skin Temperature . . . . . . . . . 2.8.2 Sweating . . . . . . . . . . . . . . . 2.9 Heat Balance . . . . . . . . . . . . . . . . . . 2.10 Modes of Heat Transfer . . . . . . . . . . 2.10.1 Conduction . . . . . . . . . . . . . 2.10.2 Convection . . . . . . . . . . . . .

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Contents

2.10.3 Radiation . . . . . . . . . . . . . . . . . . . . . . . . . 2.10.4 Evaporation . . . . . . . . . . . . . . . . . . . . . . . 2.11 Heat Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12 Thermal Energy Storage Systems . . . . . . . . . . . . . . 2.13 Phase Change Materials . . . . . . . . . . . . . . . . . . . . 2.13.1 Classification of PCM . . . . . . . . . . . . . . . 2.13.2 Micro-PCM . . . . . . . . . . . . . . . . . . . . . . . 2.13.3 Applications of PCM . . . . . . . . . . . . . . . . 2.13.4 Selection of Suitable PCM . . . . . . . . . . . . 2.14 Microencapsulation . . . . . . . . . . . . . . . . . . . . . . . . 2.14.1 Classification of Microencapsulation . . . . . 2.14.2 Features of Microcapsules . . . . . . . . . . . . . 2.14.3 Techniques of Microencapsulation . . . . . . . 2.14.4 Chemical Techniques . . . . . . . . . . . . . . . . 2.14.5 Applications of Microencapsulation . . . . . . 2.14.6 Advantages and Disadvantages of Microencapsulation . . . . . . . . . . . . . . . 2.15 Super Absorbent Materials . . . . . . . . . . . . . . . . . . 2.15.1 Applications of Super Absorbent Materials 2.16 PCM Salt Hydrate . . . . . . . . . . . . . . . . . . . . . . . . 2.17 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Experimental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Materials, Experimental Design, Methodology and Methods 3.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Equipment Used for Experiments and Analysis of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Motorcycle Helmets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 Wind Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 Heated Head Form . . . . . . . . . . . . . . . . . . . . . . . . 3.6.3 Wind Tunnel Process . . . . . . . . . . . . . . . . . . . . . . 3.6.4 Data Analysis Method . . . . . . . . . . . . . . . . . . . . . 3.7 Differential Scanning Calorimetry . . . . . . . . . . . . . . . . . . . 3.7.1 DSC Measurement . . . . . . . . . . . . . . . . . . . . . . . . 3.8 Theoretical Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents

4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 SEM Images of the Samples . . . . . . . . . . . . . . . . . . . 4.1.1 Polymeric Water-Absorbent Textile Materials 4.1.2 Paraffinic Phase Change Material . . . . . . . . . 4.2 Temperature Drop in the Aluminium Head Form Without a Helmet . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Temperature Drop Using PWAT Material . . . . . . . . . 4.4 Amount of Heat Removed from the Head Form for Thermal Equilibrium . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Heat Absorbed by PWAT Material at Various Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Temperature Drop with PCM Materials . . . . . . . . . . . 4.5.1 Paraffinic PCM at Speed of 55 kph . . . . . . . . 4.5.2 Paraffinic PCM at Speed of 75 kph . . . . . . . . 4.6 Heat Absorbed by Paraffinic PCM Materials . . . . . . . 4.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5.1 Future Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Uncited Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Abbreviations

ASHRAE CFD DIT DSC DT EPS HDPE Kph MDIT MTW PCM PET PMV PPD PTMG PTWs PWAT SEM Temp TES WT

American Society of Heating, Refrigeration and Air-conditioning Engineers Computational fluid dynamics Drop in temperature Differential scanning calorimetry Datataker Expanded polystyrene High-density polyethylene Kilometre per hour Maximum drop in temperature Motorised two wheeler Phase change material Polyethylene terephthalate Predicted mean vote Predicted percentage of dissatisfaction Polytetramtehylene glycol Powered two wheelers Polymeric water-absorbent textile Scanning electron microscopy Temperature Thermal energy storage Wind tunnel

ix

Chapter 1

Introduction

1.1 Scope Motorcycle helmets are protective equipment used by motorcyclists to protect the head, to minimise injuries and to save life in the event of an accident. At present, this is the most effective intervention available to reduce head injuries to motorcyclists. Motorcycle helmets greatly reduce injuries and fatalities in motorcycle accidents. Thus, many countries have stringent legislation requiring the mandatory wearing of helmets by motorcyclists. Due to high speeds, motorcyclists require protection because of the risk of fatal accidents. Although there are laws enforcing the mandatory wearing of helmets, motorcyclists are often reluctant to wear helmets because they are perceived to be uncomfortable. Studies in Thailand [1] and in the USA [2] found that men are less likely to wear a helmet as compared to women; in contrast, research in Vietnam showed the reverse trend [3]. In Thailand, research [4] showed that an increase in motorcyclists’ education level increased the use of helmets and contributed to a reduction in accidents. The lack of comfort and inconvenience of helmets, particularly in relation to their storage while not in use, has contributed to less helmet use [5, 6]. Anecdotal evidence states that helmets are unpopular among riders of motorised two wheelers in India because of the discomfort they feel in tropical climatic conditions [7]. An increase in skin temperature is significant, as studies have shown that the temperature of the head is the key in terms of perceived thermal comfort [8, 9]. A study [10] showed that, in high-income countries, wearing a properly fitted helmet reduced the risk of head injury in an accident by 20–45%. In most lowincome countries, motorcycle helmets are infrequently worn by riders, for reasons of discomfort, expense and lack of effectiveness in preventing head injuries [11, 12]. Many helmets manufactured locally in low-income countries are poorly constructed and offer little or no effective protection to the head. The head being the main sensitive region influencing the thermal comfort of the human body, any disincentive for wearing protective headgear should be minimised [13, 14]. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7_1

1

2

1 Introduction

1.2 Research Concept This research investigates the fundamental problems surrounding the thermal regulation of a human head wearing a helmet for motorcycle riding. The objective is to define non-invasive processes that can be employed to ensure thermal comfort to the rider in a tropical or hot climate region. The outcomes of this research will provide fundamental knowledge to helmet and accessories designers to design and manufacture safety standard compliant helmets with good passive thermal comfort.

1.2.1 Scope of the Current Research The scope of this study is to investigate the problem of how to improve motorcyclists’ comfort in tropical and hot climatic conditions. The possible sources of investigation are: 1. The use of innovative fabrics for the reduction of temperature inside motorcycle helmets; 2. To utilise these fabrics to design and develop a new textile liner for motorcycle helmets; 3. To investigate the heat transfer from the interior of the motorcycle helmet; 4. To analyse the possibility of cooling inside the motorcycle helmet without compromising the safety compliance of the helmet; 5. The quantity of heat that needs to be removed from a motorcycle helmet to facilitate a comfortable ride for the motorcyclist. The research builds on the investigations of Ellis [15] and recent research advances in the development of microfibre textiles. The project will validate the fundamental understanding of textile cooling techniques and mechanisms for motorcycle helmets.

1.2.2 Research Questions The research questions to be addressed are: 1. How much heat needs to be transferred from the interior of the motorcycle helmet so that the rider is comfortable? 2. Is the use of innovative fabrics effective in the reduction of temperature inside the motorcycle helmet? 3. How can a new textile liner be designed and developed for the current application? 4. Could a prototype be developed from the present investigation to be used for motorcycle helmets? 5. What are the mechanisms involved in the heat transfer related to the current study?

1.2 Research Concept

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6. How can current motorcycle helmets be modified to obtain cooling inside the helmets without compromising safety compliance?

1.2.3 Objectives of the Study The aim of this research is to investigate the practicality of using paraffinic phase change materials (PCMs) and water absorbent polymeric textile (PWAT) materials as a means of cooling the wearers of motorcycle helmets. The basic theory and processes of head cooling within helmets will be examined with a view to developing criteria to assist motorcycle helmet designers and manufacturers to produce effective designs that maximise helmet ventilation and reduce heat stress inside the helmet, while not compromising the protective performance of the helmet. It is envisaged that the new developments would avoid modifying helmets, so that the new processes or techniques could be both incorporated into new helmets and retrofitted to the existing helmets. The two main objectives of this project are: 1. To investigate whether PCM textile materials and PWAT materials can be used as a textile liner inside the helmet to reduce the heat stress of a motorcyclist; 2. To evaluate the performance of PCM textile materials and water-absorbent materials to reduce heat stress. The research will enable the design and manufacture of safety standard compliant helmets that are comfortable in high heat and humidity regions. At present, there are no mechanisms to achieve this, other than to increase ventilation and thereby lower the safety standard (introducing more holes into the helmet decreases the safety of the helmet). This research will provide supporting data and a mechanism to enable the computer-aided design of cool helmets, which is at present not possible.

1.3 Hypothesis The current study aims to use paraffinic PCM and PWAT materials inside motorcycle helmets, which will result in the reduction of temperature. The hypotheses for this investigation are: 1. Paraffinic PCM materials and PWAT materials can be used to reduce the temperature by 2–3 °C inside the helmets (Fig. 1.1). 2. Application of these materials as a removable textile liner will facilitate the ventilation and reduce the heat stress of the existing helmets and new helmets without affecting the safety aspects of the helmets. Microencapsulated PCMs embedded in the textile substrate are expected to reduce the temperature inside the helmet [16]. PCM microcapsules are embedded in the

4

1 Introduction

Proposed textile liner

Fig. 1.1 Schematic diagram of PCM or PWAT materials inside the helmet

fibre in the spinning stage or injected into foams or coated onto the surface of textile materials. The PCMs inside the microcapsules gradually melt and absorb the heat that is inside the helmet, thus reducing the temperature inside the helmet. A large quantity of heat will be absorbed when the temperature reaches the melting point of the PCM or PWAT material absorbs the heat from the head by evaporation. The heat generated from the head (metabolic heat), which is retained inside the helmet, is absorbed by the PWAT material, resulting in a drop in temperature within the helmet.

1.4 Conclusions This chapter discussed the scope of the study, research concepts, objectives and hypothesis. This chapter also discussed on the research questions and the scope of the current research. It is essential to read this chapter before proceeding to other chapters. The major research gap in reducing the heat stress was the driving factor to perform this research. An attempt has been made throughout the book to make it simple so that it is understood easily.

References

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References 1. M. Ichikawa, W. Chadbunchachai, E. Marui, Effect of the helmet act for motorcyclist in Thailand: accident analysis and prevention. Accid. Analy. Prevention 35, 183–189 (2003) 2. J. Youngblood, Nationwide survey of rider attitude concerning safety helmets, in Proceedings of the International Motorcycle Safety Conference (1980), pp. 1435–1465 3. D.V. Hung, M.R. Stevensen, R.Q. Ivers, Prevalence of motorcycle helmet use among motorcyclist in Vietnam. Injury Prevention 12, 409–413 (2006) 4. W. Swaddiwudhipong, C. Boonmak, P. Nguntra, P. Mahasakpan, Effect of motorcyclist rider education on changes in risk behaviours and motorcycles related injuries in rural Thailand. Tropical Medicine Intl. Health 3, 767–770 (1998) 5. F.G. Grima, I.A. Ontoso, F.A. Ontoso, Helmet use by drivers and passengers of motorcycle in Pamplona (Spain). Eur. J. Epidemiology 11, 87–89 (1995) 6. World Health Organization, Helmets: a road safety manual for decision-makers and practitioners, World Health Organization Publications (2006) 7. R. Patel, D. Mohan, An improved motorcycle helmet design for tropical climates. Appl. Ergon. J. 24, 427–431 (1993) 8. R.J. Osczevski, Design and evaluation of a three-zone thermal manikin head, Defence and Civil Institute of Environmental Medicine, North York, Ontario, Rep. No. 96–R–60, pp. 1–12, 1996 9. S. Boutcher, G. Maw, N. Taylor, Forehead skin temperature and thermal sensation during exercise in cool and thermoncutral environments. Aviation Space Environ. Med. 66, 1058–1062 (1995) 10. D. Sosin, J. Sacks, P. Holmgren, Head injury: associated deaths from motorcycles crashes. J. Am. Med. Assoc. 264, 2395–2399 (1990) 11. D. Mohan, Road safety in less-motorised environments: future concerns. Intl. J. Epidemiology 31, 527–532 (2002) 12. P. Conrad, Y.S. Bradshaw, R. Lamsudin, N. Kasniyah, C. Costello, Helmets, injuries and cultural definitions: motorcycle injury in urban Indonesia. Accid. Analy. Prevention 28, 193–200 (1996) 13. A. Kissen, J. Hall, F. Klemm, Physiological responses to cooling the head and neck verses the trunk and the leg areas in severe hypothermic exposure. Aerosp. Med. 42, 882–888 (1971) 14. S. Nunneley, D.C. Reader, R.J. Maldonado, Head temperature effects on physiology, comfort and performance during hyperthermia. Aviat. Space Environ. Med. 53, 623–628 (1982) 15. A. Ellis, Development of fundamental theory and techniques for the design and Optimization of bicycle helmet ventilation, Ph.D. Thesis, RMIT University, Melbourne, Victoria, Australia, 2003 16. K. Sinnappoo, R. Nayak, L. Thompson, R. Padhye, Application of sustainable phase change materials in motorcycle helmet for heat-stress reduction. J. Text.E Inst, 1–9. https://doi.org/10. 1080/00405000.2020.1715606

Chapter 2

Review of Literature: Motorcycle Helmet

2.1 Introduction The motorcycle helmet’s primary purpose is to protect the head, retaining the strength and integrity of the helmet structure with a perfect fit and providing comfort to the wearer. To maintain the structural integrity and safety aspects of motorcycle helmets, no holes are allowed to be drilled in the helmet for ventilation. As a result, heat builds up inside the helmet and causes heat stress that affects the concentration and ability of the rider. Ensuing discomfort makes the rider impatient, resulting in taking risks on the road, thereby possibly causing accidents.

2.2 Need for Motorcycle Helmet The introduction of the compulsory wearing of motorcycle helmets in Australia in the 1960s resulted in a substantial decline in serious head injuries sustained by motorcyclists [1]. Contemporary analysis also addresses the efficiency of helmet usage in reducing the impacts to the head in case of an accident. Easing of the mandatory requirement to wear a helmet in the USA for motorcyclists led to a 40– 50% decrease in helmet wearing rates and a subsequent increase in the frequency of fatal head injuries [2]. Motorcyclists form a very high percentage of crash victims in road traffic accidents. Riders injured in crashes predominantly had injuries to their heads, which were the common cause of severe morbidity and mortality [3, 4]. This demonstrates that, to prevent serious head injury, it is essential to use protective headgear such as helmets. In Australia, there has been a reduction in general road accidents on average of 2.1% per year over the last five years. However, for motorcyclists, there was a yearly increase of 4.1% in fatalities over the same period. In 2005, the national road toll in Australia indicated that the death of motorcyclists and pillion passengers was 14% © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7_2

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2 Review of Literature: Motorcycle helmet 80 70 67

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48 39 41

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2006

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2003

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1992

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0 1987

Number of deaths (Motorcyclist)

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Year

Fig. 2.1 Motorcyclists killed on Victorian roads from 1987 to 2007

of total accident deaths [5]. Figure 2.1 shows the statistics for motorcyclist deaths from 1987 to 2007 [6]. Out of the 332 people killed in Victoria’s road accidents in 2007 [6], 45 of those killed, as shown in Fig. 2.1, were motorcyclists. This represents 14% of the road toll, and yet only 3% of vehicles registered in Victoria are motorcycles. Table 2.1 [6] shows the number of riders killed and seriously injured in 2007. It can be observed from the table that 3% of the riders killed and 6% of the riders seriously injured were not wearing motorcycle helmets. In addition, the following data show, of the riders killed or seriously injured and not wearing a helmet: • 9% were aged 5–15 years, 11% were aged 16–17 years, 29% were aged 18– 20 years, 18% were aged 21–25 years, 4% were aged 26–29 years, 11% were aged 30–39 years, 16% were aged 40–49 years, and 2% were aged 50–59 years; • 64% were in metropolitan areas; and • 96% were male. The report also revealed that, in 2005, the number of motorcyclists seriously injured was 891. In 2008, the number of motorcyclist deaths was 44, and in the last five years, the average number of motorcyclist deaths per year was 43 [6]. The most susceptible part of the human body to injury in case of an accident is the head and Table 2.1 Number of motorcyclists killed and seriously injured in 2007

Helmet usage

Killed

Seriously injured

No helmet

2

43

Wearing helmet

35

722

Unknown

8

233

Total

45

998

2.2 Need for Motorcycle Helmet

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specifically the brain. Head injuries are one of the most dramatic forms of mechanical trauma. Almost all head injuries occur near or in the central nervous system, which is extremely dangerous to the well-being of the injured person. According to the National Safety Council of the USA, the head was injured in 7% of all industrial accidents and 8% of all farm accidents in 1971 [7]. In more than 70% of automobile accidents, head injuries have been found to occur.

2.3 Motorcycle Helmet Regulations Many countries have strict regulations relating to the use of helmets by motorcyclists. These laws vary considerably depending upon the country. Many countries have their own sets of standards that are used to determine the effectiveness of motorcycle helmets; some of the standards are AS 1698 (Australia), CSA CAN3-D230-M85 (Canada), JIS T8133 (Japan), NZ 5430 (New Zealand), ECE 22.05 (Europe), DOT FMVSS 218 (United States of America), ANSI Z90.1 (United States of America), BS 6658:1985 (Britain), BIS 4151-1982, ISO/R 1511, Snell M 2005 (United States of America) [8]. There is a great deal of pioneering research in the field of motorcycle helmets, although the history of the helmet is very brief. Hugh Cairns [9] was one of the neurosurgeons who operated on Colonel TE Lawrence, who was fatally injured in a motorcycle accident in the early 1930s and was not wearing a helmet at the time of the accident. Cairns decided to investigate, analyse and solve the problem of head trauma prevention in motorcyclists. Cairns and Holbourn [10] also carried out a statistical survey of motorcycle accidents and the associated morbidity and mortality. Cairns [11] showed that wearing a crash helmet would enable considerable saving of life and time spent in hospitals but, before this, helmet effectiveness was anecdotal, and helmet design was based on intuition and armourers’ lore. Cairns also gave an account of the investigation of over 100 motorcyclist fatalities in which 92% had head injuries and 66% had multiple injuries. He did not discover the crash helmet, but he demonstrated conclusively that helmets reduce the risk of serious head injuries and the value of crash helmets for head protection. The motorcycle helmet has been in use for the last five decades, and the general trend is for a large amount of research to be done in relation to its protective ability in case of an accident, and good fit and thermal comfort, so that the motorcyclist is willing to wear the helmet based on the protection and comfort it provides. Most of the earlier research on motorcycle helmets appeared to utilise a trial and error approach within the helmet industry.

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2.4 Components of Motorcycle Helmets The primary purpose of a motorcycle helmet is to protect the head from injuries. Contemporary helmets protect the head against impact by having an outer shell bonded to an impact-absorbing liner, as shown in Figs. 2.2a, b [12]. The purpose of the outer shell is to widen the area of impact and allow the helmet to slide along the ground. The four main components of a motorcycle helmet are the outer shell, impactabsorbing liner, comfort padding and retention system. The outer shell is the part that we see first and is usually made from some form of fibre-reinforced composites or thermoplastics such as polycarbonate. This material is very tough and intended to compress when it hits any hard object. This action disperses energy from the impact and reduces the force before it can reach the head. More expensive helmets are reinforced with Kevlar or carbon fibres. Thermoplastics helmets are generally the lightest and least expensive. The thermoplastic helmet tends to have a shorter life expectancy. Its chemical composition may be changed if it is painted or decals are applied to its surface. Damage can occur if it is stored near gasoline, cleaning fluids or exhaust fumes. Helmet manufacturers are constantly working to develop cheaper, stronger and lighter materials for helmet shell construction. The hard-outer shell of the motorcycle helmet tries to stop the penetration of sharp objects and also acts as a safeguard for the shock-absorbing liner and prevents the liner from disintegrating if the helmet hits the road or other objects. The helmet liner is made of expanded polystyrene (EPS) foam of varying density and thickness ranging from 10 to 25 mm. Lombard et al. [13] were the first to introduce expanded polystyrene to be used in helmets. This is the important part of a motorcycle helmet, as polystyrene is non-resilient and evenly spreads the impact in an accident and thus reduces the shock energy that could reach the head and cause injury [14]. The impact-absorbing liner is housed inside the outer shell and is usually made of expanded polystyrene. The liner provides a cushioning effect and absorbs the shock in case of an accident, thus protecting the head. Both the shell and the liner are compressed if hit hard, spreading the forces of impact throughout the helmet material. Generally, the more the impact energy is deflected, the less it can reach the head and cause damage. Some helmet shells are designed to delaminate in case of impact, and others crack or break if severely hit and thus absorb the shock of the impact. The comfort padding that is responsible for proper fit and comfort is made of soft foam. In some helmets, the comfort padding can be taken out for cleaning. The retention system keeps the helmet on the head in case of impact, and this is usually achieved by chin straps that are held around the chin and clasped together by some form of buckle. These are connected to each side of the outer shell very firmly. While wearing the helmet, the straps should be fastened properly. Hickling [15] suggested that 12 parameters are required for the acceptability of a safety helmet to protect the head: weather protection; thermal properties; tactile properties; absorptivity/permeability; mass distribution; degree of fit; size and shape; retention performance and fit; helmet

2.4 Components of Motorcycle Helmets

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Fig. 2.2 a Schematic representation of visor closed helmet and its components. b Schematic representation of visor closed helmet and the functionalities of its components

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volume; visual factors; speech and sound factors and helmet compatibility. Thermal properties of industrial safety helmets are one of the important parameters for workers in a tropical or subtropical climate among these 12 factors.

2.5 Cooling the Motorcycle Helmet Generally, the cooling or ventilation system in a motorcycle helmet is minimal. The one-inch thickness of insulation liner in the interior of the helmet restricts and virtually eliminates heat exchange with the outside wall of the most efficient part of the skin. This creates an uncomfortably hot environment for the head of the wearer. The interior of the helmet can quickly rise to temperatures of 37–38 °C. When this occurs, the physiological and psychological effects on the rider are potentially dangerous, due to a decrease in the ability to concentrate. It has been observed that head cooling is the most efficient of any part of the body because it has the highest skin temperature as well as large constant-volume blood flow [16]. Head cooling has been perceived as a necessity to provide overall thermal comfort to an individual rider. A rough measure of the discomfort due to the wearing of helmets can be estimated by calculating the discomfort factor used in air conditioning [17]. The human head is represented as two thermal compartments with the inner one as the body core and the outer one as the skin layer. The metabolic rate and heat due to the sun on the head are measured as 6.7 W/m2 and 8.33 W/m2 , respectively, which corresponds approximately to 10% of total body values. The thermal discomfort can be quantified on a 0–5 grade scale, with grade 0 as comfortable and grade 5 as highly uncomfortable. The total energy balance of the head can be represented [18] as shown in Eq. (2.1): Metabolic heat + heat due to sun = sensible heat loss + evaporative heat loss + heat stored in the body

(2.1)

The helmets generally used are either open-faced or closed-faced helmets having the option of a visor which can be opened or closed as needed by the motorcyclist. Some form of motorcycle helmet has been used since the early twentieth century. Their widespread use, and ultimately their mandatory use, only developed from the late 1950s. The Snell Foundation firmly established a standard and demonstrated the benefits of wearing a helmet. With improved technology, the speed, power and numbers of motorcycles have increased in the last two decades. Therefore, it is now essential that an efficient and effective motorcycle helmet should be designed and developed that provides both adequate protection in case of an accident and adequate cooling to minimise the thermal stress that may compromise the performance of the rider. These features must be designed for performance and style, so as to appeal sufficiently to motorcyclist so that helmet use increases.

2.5 Cooling the Motorcycle Helmet

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Some practical solutions can be implemented to cool the head while wearing a motorcycle helmet. The popular and marketable techniques are using an air blower or vents [19]. The air-cooling system uses vents to allow natural air flow to pass through the interior of the helmet to remove heat. Although motorcycle riders may use these designs, it is debatable whether these systems are suitable for tropical countries that have high ambient temperatures. The cooling or ventilation system that is currently available in motorcycle helmets is almost exclusively in the form of forced convection and evaporation, the efficiency of which is influenced by the type of helmet worn and the speed of the air moving over the head and helmet. The current process of cooling inside a motorcycle helmet is by the ventilation provided by air passing the side of the ears, around the neck, over the head and helmet. Research so far has not clearly shown the principles responsible for forced convective cooling around the head or procedures to develop new designs or to connect these to the comfort needs of the motorcycle rider. Earlier research concentrated on isolated and special features of motorcycle helmet design and cooling by using human, manikin or wind tunnel testing. The efforts undertaken so far have not been very successful, because the results have not been amalgamated into a form so as to produce a complete system that could aid the design process. This indicates a major limitation in the knowledge available for motorcycle helmet manufacturers to design, prototype and produce an effective helmet that contributes to the safety and comfort of the motorcycle rider. Thus, more research is required to obtain information for the design, prototype and manufacture of a more comfortable motorcycle helmet.

2.6 Types of Motorcycle Helmets Five basic types of helmets are available for motorcycling. These helmets are secured by a chin strap, and if the chin strap is not securely fastened to give a snug fit, the chances of getting injured are increased. The various types of motorcycle helmets are full face; off-road/motocross; modular/flip-up; open face and half helmet. These are discussed below.

2.6.1 Full Face Helmet A full face helmet (Fig. 2.3) covers the entire head, the base of the skull and the front of the chin. These helmets contain a transparent plastic face shield that can be moved up and down to allow access to the face. Even though these helmets give full protection to the head, some riders do not like these helmets due to the increased heat, sense of isolation, lack of wind and alleged reduction in hearing. It has been shown that full face helmets offer the most protection to motorcyclists’ heads, as 35% of all crashes showed major impact on the chin bar area [20]. Increased protection is

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Fig. 2.3 Full face helmet

provided by the chin bar in the full face helmets, and the cool tinted face shields are close fitting with snug padding around the bottom, minimising wind noise. However, the trade-off is that it promotes fogging.

2.6.2 Off-Road/Motocross Helmet Generally, an off-road or motocross helmet (Fig. 2.4) consists of elongated chin and visor portions, a chin bar and a partially open face to provide extra protection to the rider while wearing goggles. Current off-road helmets include a typically angular chin bar to provide some facial impact protection in addition to protection from flying dirt and debris. Off-road helmets, along with goggles, provide similar protective features to those of full face helmets. Fig. 2.4 Off-road/motocross helmet

2.6 Types of Motorcycle Helmets

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2.6.3 Modular/Flip-up Helmet The modular or flip-up helmet (Fig. 2.5) is considered to have some features of the full face and open face helmets when assembled. The chin bar can be either removed or pivoted upwards, and this allows the rider to reach most of the face, as in an open face helmet. Modular helmets are worn in the closed position during riding and, if worn in the open position, pose an increased risk of neck injury in a crash [21]. Fig. 2.5 Modular/flip-up helmet

Fig. 2.6 Open face helmet with face shield

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2.6.4 Open Face Helmet The open face helmet (Fig. 2.6) covers the back of the skull but does not have the lower chin bar like the full face helmet, and the face shield is optional. In many open face helmets, visors are used to reduce glare. Although an open face helmet is similar to a full face helmet in rear protection, it hardly provides facial protection even from non-crash events. An open face helmet, where it does not have a visor, limits protection to the rider from insects, dust particles or even wind to the face and eyes, resulting in injury or inconvenience. Face shields fitted to open face helmets protect the upper part of the face and the eyes,

2.6.5 Half Helmet The half helmet (Fig. 2.7) is similar to the open face helmet but has a raised back. The half helmet provides the least coverage of the five helmets. Unlike open face and full face helmets, half helmets are subject to shifting and sometimes come off the rider’s head during an accident.

2.7 Bicycle Helmets A bicycle helmet as shown in Fig. 2.8 is designed to protect the head of a bicyclist from impact [22], and this is its primary function. A bicycle helmet should be very light in weight and have sufficient ventilation for the head, as cycling is a strenuous activity which raises the body temperature, especially of the head. As a result, there Fig. 2.7 Half helmet

2.7 Bicycle Helmets

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Fig. 2.8 Bicycle helmet

is the need to regulate its temperature. The two main types of bicycle helmets are hard shell and soft shell. Both types of bicycle helmets are designed to reduce the acceleration of the head due to impact, as the stiff expanded polystyrene liner is crushed [23]. They should also spread the point of impact over a wider area of the skull. Even though hard shell helmets are heavier, with reduced ventilation, they give better protection in case of an impact. Ventilation holes or openings are made in the shell and liner of the bicycle helmet in order to provide cooling. In all modern bicycle helmets, there is a trend towards more or larger ventilation openings, and many helmet manufacturers differentiate themselves in the market by the design and number of these openings. Unfortunately, these holes are detrimental to the structural integrity and safety of the helmet. Although ventilated helmets have good potential for marketing, there are a limited number of scientific research publications in this area. In addition, no standard methods are available by which to compare the cooling of these helmets [24]. Heat transfer variations between bicycle helmets were studied by Brühwiler et al. [25]. It was observed that the heat transfer among the helmets varied up to 30% (scalp) and 10% (face). In recent years, the physiological aspects of bicycle helmets have drawn the attention of many researchers [26–28]. Although bicycle helmets have been in use since the 1920s, and the method of cooling has always been via these ventilation openings, no study has been made to properly understand the principles of the airflow responsible for forced convection cooling, or the techniques to model this, or to link it to the comfort needs of cyclists. Furthermore, previous research has concentrated on isolated and specific aspects of helmet design and cooling, such as human or wind tunnel testing. However, there has been a failure to bring these together so that they can be effectively and holistically used in the design process. This represents a major gap in the knowledge needed by bicycle helmet manufacturers to design and optimise their helmets with the best

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interests of the cyclist in mind. Research needs to be undertaken that facilitates an informed holistic approach to the design of bicycle helmets. In countries where helmet usage is mandatory, the thermal discomfort caused by wearing a helmet while cycling creates a barrier to helmet wearing [29]. The first published paper relating to the physiological effects of wearing a bicycle helmet was done by Gisolfi et al. [30]. Many researchers have investigated and measured the thermoregulatory responses experienced by the cyclist while cycling with or without a helmet [31–33]. Stern [31] found that there is a high statistical difference between scalp temperatures when cycling with and without a helmet. Maximum scalp temperature was found to be 36.13 °C without a helmet as compared to 37.58 °C with a helmet. Gisolfi et al. [30] observed that wearing a helmet produces a perceived thermal discomfort in the cyclist. Heat loss in bicycle helmets was found to have very large variations in the presence of forced convection [34, 35]. However, this is in part due to the fact that sweating and discomfort make the cyclist more sensitive (per unit surface area) to changes in the temperature of the head (especially the face) than to changes in the temperature of other skin regions [36, 37].

2.8 The Effects of Discomfort in Helmets Slater [38] defined comfort as ‘a pleasant state of physiological, psychological and physical harmony between a human being and the environment’. He also defined these three aspects of comfort and discussed the role of environment in comfort. All three aspects are equally important for comfort, and if any one of them is missing, the person will feel discomfort. Comfort is the perception of the human mind caused by the integration of impulses in the brain passed up by the nerves from peripheral receptors. This perception is mainly affected by the clothing between the human body and the environment. Comfort can also be defined as ‘freedom from pain and from discomfort as a neutral state’ [39]. Büttner [40] recognised that, for the assessment of the thermal influence of the environment on the human body, the integrated effects of all thermal parameters have to be taken into account. In this regard, empirical thermal indices, such as the discomfort index [41], apparent temperature [42], wind chill index [43] or similar ones considering some of the relevant meteorological parameters but not accounting for thermal physiology, have to be regarded as not being state of the art, yet they are used very often. Despite many limitations, these parameters are useful in very specific situations as they can be calculated easily. To be effective in tropical countries, helmets must be comfortable, affordable and provide protection in various traffic conditions. In addition, high humidity and temperature in tropical countries cause the temperature inside the helmet to rise to uncomfortable levels. This rise in temperature affects the concentration of the motorcyclist [44, 45]. Hence, it is necessary to find ways to reduce the temperature inside the helmet and thus minimise the heat stress of the motorcyclist.

2.8 The Effects of Discomfort in Helmets

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In South East Asia, excessive sweating and the resulting discomfort due to hot and humid weather conditions discourage motorcycle riders from using helmets even where it is mandatory by law. The space between the head and helmet is small, and air velocities in this gap are also low. Hence, the rider is very uncomfortable due to sweat, which is unable to evaporate and accumulates within the helmet.

2.8.1 Skin Temperature Skin temperature is dependent on air temperature and the time spent in that environment. Weather factors such as wind chill and humidity contribute to causing changes in skin temperature. The normal temperature of skin is about 37 °C. In general, the temperature range at which a person feels comfortable is 29–34 °C. Above a temperature of 40 °C, the person will start feeling discomfort, and below 20 °C, there will be loss of agility [46]. It is essential that the core body temperature is maintained at a certain level to establish thermoregulatory equilibrium. Although thermal equilibrium is a necessary condition for thermal comfort, it is not the only condition. Both skin-surface temperature (T sk ) and core temperature (T c ) affect thermoregulatory equilibrium. It was found that the ratio of the contribution of skin-surface temperature (T sk ) and core temperature (T c ) to thermal comfort is approximately 1:1 [47].

2.8.2 Sweating Perspiration or sweat is the production of a fluid from the body consisting primarily of water as well as various dissolved solids (chiefly chlorides) that is excreted by the sweat glands in the skin of mammals [48]. Sweat also contains the chemicals or odourants 2-methylphenol (o- cresol) and 4-methylphenol (p-cresol) as well as a small amount of urea. In humans, sweating is primarily a means of thermoregulation [49]. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. Hence, in hot weather or when the individual’s muscles heat up due to exertion, more sweat is produced. Sweating is also increased by nervousness or nausea and decreased by cold. There are two situations in which our nerves will stimulate sweat glands, making us sweat: during physical heat and during emotional stress. Emotionally induced sweating is generally restricted to palms, soles and sometimes the forehead, while physical heat induced sweating occurs throughout the body [50]. An increase in air velocity increases sweat evaporation and thus results in a reduction of discomfort felt by the rider. The air velocity inside the helmet can be improved by providing holes in the helmet (similar to bicycle helmets). However, these holes

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would affect the structural integrity of the helmet and increase the risk factor in case of accidents. Very few research studies have been carried out on the ventilation of air flow inside helmets. There is limited literature available on systematic investigation relating to the ventilation and comfort of motorcycle helmets [51]. Some factors that contribute to motorcycle accidents are fatigue, lack of concentration, behaviour and the environment. A study in 2003 revealed that around 40% of riders reported experiencing fatigue on at least half of their journeys [52]. Long periods seated in a fixed position while riding a motorcycle result in static muscle fatigue. Depending on the type of motorcycle, there are more ergonomic constraints in riding [53]. A high level of concentration is required while riding a motorcycle compared to driving a car [54]. It has been reported that 14% of total traffic fatalities in Europe are for powered two wheelers (PTW) [55]. Motorcyclists run 20 times more risk of fatal accidents than car drivers per travelled kilometre [56]. In low-income countries, users of bicycles and motorcycles are the commonest victims of traffic injuries. This is due to the higher number of PTW than cars on the road. A study [57] concerning the accidents of PTW revealed that approximately 10% of all riders were not wearing helmets while riding in traffic. Bianco et al. [58] investigated helmet usage among teenage PTW riders in south-eastern Italy in summer and found it to be approximately 35%. This investigation found that, due to thermal discomfort, PTW riders were prepared to risk an accident instead of wearing a helmet. A similar conclusion on thermal discomfort was drawn by Hickling [15] in regards to protective headgear. In Europe, 14% of total yearly traffic fatalities involve PTWs [55]. The risk of a fatal accident involving a PTW per travelled kilometre is 20 times higher than for a car [56]. The factors associated with higher PTW traffic accidents can be attributed to the reduced conspicuousness [57, 59] and higher vulnerability of PTW drivers [57]. Where comfort in helmets is concerned, the thermo-physiological wear comfort (i.e. the heat and moisture transport from the helmet to maintain the heat balance of the body, especially the head) is the most important. The sensational or tactile comfort is of less concern. The heat and moisture transport from the head into the adjacent air is a complex phenomenon and has long been recognised to be critically important for human survival [60]. A large amount of work has been done by researchers on the role of heat and moisture transfer on thermal comfort [61–64]. The moisture exchange depends on its state, i.e. whether the moisture is present as liquid on the fibre surface or as vapour stored internally. Although there are four modes of heat transfer, in all motorcycle helmets, the cooling is achieved mainly via the modes of forced convection and evaporation. These are affected by the amount of air moving over the head. The following section will highlight the various modes of heat transfer.

2.9 Heat Balance

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2.9 Heat Balance The core body temperature of any person is maintained constantly at about 37 °C, although the actual value varies slightly from person to person. In cold climates, the body temperature should be above that of the external environment, so there is an internal source of heat in order to maintain the temperature difference; in hot climates, the reverse phenomenon is required. The body must maintain thermal balance for comfort, i.e. the metabolic heat generated in addition to the heat received from the external environment must be matched to the heat loss from the body. If there is no balance between the heat gain and the heat loss, the body temperature will potentially either rise or fall, leading to a serious threat to life. Heat is generated in the human body by the process of metabolism. It is an established fact that, of the total energy extracted from food, only 15–30% is converted into useful work, and the remaining 70–85% is wasted as heat. Higher levels of physical activity will generate additional amounts of heat energy that must be dissipated; otherwise, the body temperature will rise. A lower level of or no physical activity leads to a fall in body temperature if the available heat is not conserved by insulation. If a person is in heat balance (i.e. comfortable) at rest, then a bit of hard work will produce excess heat and perspiration, which need to be dissipated. Similarly, if the person is in heat balance while doing strenuous exercise, then ceasing the work will lead to heat loss and feeling cold [65]. The heat exchange with the environment plays a key role in the thermal state of the human body [66]. Thermal comfort is defined as the condition of mind that expresses satisfaction with the thermal environment. Dissatisfaction is caused by a warm or cool environment. Discomfort for the body, in general, is expressed by the predicted mean vote (PMV) and predicted percentage of dissatisfaction (PPD) indices. However, thermal dissatisfaction may also be caused by unwanted heating or cooling of one particular part of the body (local discomfort). The PMV and PPD indices express warm and cool discomfort for the body as a whole [67]. Due to individual differences, it is impossible to specify a thermal environment that will satisfy everybody. A percentage of occupants can always be expected to be dissatisfied. Nevertheless, it may be possible to specify environments predicted to be experienced as acceptable by a certain percentage of occupants. In the new standards, comfort requirements are specified and predicted to be acceptable for at least 80% of occupants [68]. Heat loss through respiration is only around 10% of the total heat loss from the body. Humidity and temperature of the inhaled air have, therefore, only a small impact on the thermal sensation for the human body as a whole [69].

2.10 Modes of Heat Transfer Heat transfer or heat exchange occurs when an object or fluid is at a different temperature than its surroundings or another object. The heat transfer occurs until the body and the surrounding reach thermal equilibrium. Heat transfer always occurs from the

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2 Review of Literature: Motorcycle helmet Convection By motion of air

Evaporation By change of moisture into vapour

Skin and surrounding air temperature difference

Relative Humidity Wetted area of body (perspiration)

Area of body exposed to moving air Velocity of surrounding air

Velocity of surrounding air

Human Body Heat Loss

Radiation By electromagnetic waves

Conduction By physical contact

Mean radiant temperature

Skin and contacting surface temperature difference

Radiation area of body

Fig. 2.9 Basic methods of heat loss

object at higher temperature to the object at lower temperature, which is explained by the second law of thermodynamics. The modes of heat transfer are discussed in the following section. The basic methods of heat transfer, such as conduction, convection, radiation and evaporation in maintaining the body temperature, are illustrated in Fig. 2.9 [70].

2.10.1 Conduction Conduction is the spontaneous transfer of thermal energy by direct contact between two or more materials. In conduction, the flow of heat takes place from the object at a higher temperature to the object at a lower temperature. Conduction of heat is the only mechanism possible in opaque and stationary media. The rate of heat exchange is determined by the temperature difference between the two substances and by their thermal conductivities [65] Conduction is governed by Fourier’s law [71] which is given in Eq. (2.2): Q = −k A(T2 − T1 )/d

(2.2)

where Q is the rate of heat transfer by conduction (W m−2 ), k is the thermal conductivity of medium (J s−1 m–1 K–1 ), A is the cross-sectional area normal to conductive

2.10 Modes of Heat Transfer

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direction (m2 ), T 2 –T 1 is the temperature difference across the medium (K), and d is the distance (m) between points at temperatures T 2 and T 1 .

2.10.2 Convection Convection is the mode of heat transfer which takes place because of the bulk motion (observable movement) of fluids. Convective heat transfer can be classified into two categories: natural convection and forced convection, also known as heat advection. This can be contrasted with conduction, which is the transfer of energy by vibrations at a molecular level through a solid. As convection depends on the bulk movement of a fluid, it can only occur in fluids and multiphase mixtures. The convective heat loss [72] can be calculated from Eq. (2.3): convective heat loss(Hc ) = kc · A · (Tsk − Tdb )

(2.3)

where k c is the convective coefficient, T sk is the mean weighted skin temperature, T db is the dry bulb temperature, and A is the surface area of the body. Many researchers have investigated the natural convection of industrial helmets and observed large variations between helmets. They have also noticed that there is a significant effect of vents situated on the top of the helmet. Brühwiler [73] studied the role of visors in forced convective heat loss in bicycle helmets, using a thermal manikin head form in a climate chamber. He showed that visor design can help to optimise thermal comfort via convective heat loss. Depending upon the wind speed, forced convection can exchange 2–40 W of dry heat [74]. In addition, the sensitivity of the head region, especially the face, should be considered while considering thermal influences [75].

2.10.3 Radiation Radiation is the emittance of heat from the surface of an object which is at a very high temperature by way of electromagnetic waves. Thermal radiation is caused when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. The waves can pass through the air without imparting much heat to it, and when they strike an object, their energy is largely transformed into heat [65]. Radiation can largely be ignored as a mechanism of heat loss from the human body, as it is very dependent on the temperature of an object (varying as the fourth power of the temperature). It is basically a means of heat transfer from very hot bodies such as the sun, radiant heaters or fires. The colour of an object affects the amount of heat

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radiation and absorption from it, e.g. black is both the best absorber and radiator of heat, while white is a poor absorber and radiator of heat.

2.10.4 Evaporation Evaporation is the reverse of condensation, and it is the vaporisation of a liquid. Evaporation is similar to heat transfer by convection but also requires an initial change of state from liquid to vapour at the skin surface and the subsequent diffusion of vapour across the boundary layer into the ambient air. The driving force for diffusion is the concentration gradient, and the quantity transferred is mass. Evaporation is caused when liquid water is converted into vapour by absorbing large amounts of heat energy. Generally, one calorie of heat will raise the temperature of one gram of water by one degree centigrade, and 580 calories of heat are required to evaporate one gram of water at body temperature. When water is evaporated from the skin, the energy required for evaporation is removed from the skin, thus cooling it [65]. Liu and Holmer [76] investigated the evaporative heat transfer characteristics of industrial safety helmets. They analysed the effects of ambient humidity, solar radiation and wind on heat loss. The evaporative heat loss [72] can be calculated using the following equation: evaporative heat loss (He ) = ke · A · (Psk − Pab )

(2.4)

where ke is the evaporative coefficient, Psk is the saturated vapour pressure of water at skin temperature, Pab is the ambient vapour pressure, and A is the surface area of the body. The basic methods of heat loss from human body are shown in Fig. 2.9 [70].

2.11 Heat Stress The human body generates a large amount of heat during exercise and hard work. If this heat is not quickly released, it can produce heat stress, and while resting after exercise, less heat is produced by the body, thus leading to hypothermia. The acceptance of a motorcycle helmet or any other helmet for continuous wear depends on the degree of comfort it provides. In some tropical and subtropical countries, in spite of strict laws relating to the wearing of helmets while riding a motorcycle, many riders are unwilling to wear a helmet as they perceive it to be very uncomfortable. However, they are wearing helmets reluctantly, because of the strict regulations [51]. For the safety and comfort of the motorcyclist, the physiological and ergonomic properties of the helmet play a crucial part. The thermal discomfort involved in wearing headgear by workers has motivated several researchers to work on the topic.

2.11 Heat Stress

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A motorcycle helmet should be properly designed to provide good protection for the rider and minimise head injuries in case of accidents. Without a helmet, an impact with any object would lead to localised high pressure on the skull, resulting in brain injury. While designing helmets, the functional (penetration resistance, shockabsorbing capability, retention and reliability) and non-functional (thermal characteristics, cost, weight and comfort) aspects should be taken into consideration. If the design of a helmet is good but the non-functional aspects are not properly addressed, riders will be unwilling to wear the helmet. Patel and Mohan [77] in a survey of 200 riders of MTW in India observed that 72% of them did not want to wear helmets, as discomfort is caused in the tropical atmosphere. The cause of discomfort is attributed to heat, especially in summer conditions. Kim and Park [78] found that, although people are aware of the role of a safety hat in head protection, they are unwilling to wear a safety hat because of its pressure on the head, the feeling of perspiration and the lack of ventilation. Humidity increases inside the safety hat because of an increase in perspiration in a hot environment. Thus, it is advisable to wear a safety hat containing holes which will assist in reducing moisture and increase ventilation. The physiological aspects of safety helmets, which is the second most important parameter following head protection from accidents, has drawn the attention of many researchers [79–85]. Comfort is not considered important for helmets that are worn infrequently or for short periods such as fire-fighter helmets. People wearing motorcycle helmets often complain of headaches. It has been suggested that the reasons for the headache are the mechanical pressure of the headband and the high temperature inside the helmet leading to heat stress. The rigid headband on modern helmets could restrict the flow of blood if not comfortably adjusted, causing the headache [86]. Pinnoji et al. [18] investigated the airflow between the helmet and the head by using the computational fluid dynamics (CFD) technique and the wind tunnel. The air gap inside a helmet (between the head and the helmet) varied from 0 mm (approx.) to 10 mm. In order to check the effectiveness of the CFD in simulating the airflow in a gap of 10 mm, they used two concentric cylinders separated by 10 mm and simulated with CFD. It was shown that the grooves of higher dimensions give higher air velocities and, in addition, they result in higher stress in the brain if the groove dimension exceeds a certain level. Heat stress can be defined as the sum of all the internal and external heat factors that cause the body to become fatigued and stressed. It is caused by a high external temperature and a very high level of activity. Heat stress not only lowers the efficiency of a person but also leads to severe accidents in the case of industrial workers. In addition to this, heat stress also causes health problems and fatigue and affects performance [87]. Heat stress is caused both by internal factors (body temperature, acclimatisation, natural heat tolerance and metabolic heat generated by the workload) and external factors (ambient air temperature, radiant heat, air velocity and humidity) [88]. Additional heat load, which is inherent for the wearer of a helmet in hot conditions, has not been proven to affect health conditions [33]. However, there is some evidence of psychomotor performance being severely affected by it [79]. Buyan et al. [89]

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studied the effect of tinted helmet visors on facial warming and showed that visor tinting reduces the actual and perceived heat load of the motorcycle rider by reducing the transmission of solar radiation. It is a well-known fact that 30% of the body’s heat dissipation takes place through the head when the body is at rest. As the level of work is increased, the proportion of heat dissipation through the head is decreased. Still, heat dissipation in this manner has a considerable bearing on comfort. Up to now, very little research has been done to investigate the amount by which the helmets restrict the flow of heat. Nielsen [90] found the main cause of heat stress is a high core temperature, which affects the functioning of motor centres and decreases muscular activity. The subsequent response of the body to heat stress is known as heat strain, which can be evaluated by biomechanical, physiological and psychological factors. The size of these responses determines the degree of heat stress to which the body is subjected [91]. Heat stress due to a hot environment can lead to heat disorders from irritations and to fatal conditions [91]. Work in hot environments, in both dry and humid conditions, causes poor motor control function and degrades mental performance well in advance of any deterioration of physical performance [92]. Bogerd and Brühwiler [93] investigated the heat loss variations of full face motorcycle helmets by using head forms, which were electrically heated and placed at the exit of a wind tunnel. They observed a large variation in heat loss among the 27 helmets they investigated. They identified that the constructional features of helmets play an important role in heat loss. Fonseca [94] studied the heat transfer properties of military helmets and observed that the evaporation of sweat increased as the standoff distance of the helmet from the head was increased. Roszkowski [95] studied industrial helmets from different countries and concluded that the ability to allow sweat evaporation varied with the design of the helmets. Brühwiler studied the effect of wind on the heat loss of motorcycle helmets and observed that the heat loss from the scalp section of a manikin head was very low. However, it was observed that in the face there was a 20% variation in heat loss [35]. Chinn et al. [96] suggested that wearing a motorcycle helmet can influence the cognitive performance of a motorcyclist. The concentration of the motorcyclist can be affected by the heat, moisture and carbon dioxide (CO2 ) produced within a closed helmet. It has been proven that there is considerable thermal discomfort in bicycle helmets [26], similarly for industrial helmets [97], and the same can be expected for motorcycle helmets [89]. Kamin and Scalone [98] investigated the importance of comfort and found that, in the United States of America, the poor standard of comfort in industrial helmets was due to rigid suspension systems that did not fit the head properly. Proctor [99] reviewed industrial safety helmets with respect to comfort, stability, acceptability, statistics and impact considerations. He found that the area for development of these helmets was comfort and the durability of the injection-moulded plastics used in manufacturing the helmets. Various researchers have studied the thermal discomfort associated with wearing a helmet [100–102]. Kim and Park [78] studied safety hats and showed that the ventilation through the holes in the hats reduced the increase in temperature of the head. The temperature

2.11 Heat Stress

27

and humidity of the hats with holes were lower, as compared to safety hats without holes. Although the head covers only 7–10% of the total body surface, the head skin temperature is generally higher than in other parts of the body [103]. A large number of studies have shown that protective headgear in hot environments causes higher levels of thermal discomfort [97, 104]. This discomfort is related to the head, as the head is one of the most important parts of the body in determining the whole body’s thermal comfort [105]. Many researchers have investigated the relationship between heat transfer and thermal comfort by evaluating the heat transfer characteristics of industrial helmets [25, 106, 107]. None of these studies were in the context of moving vehicles and road safety. In a recent study, Bogerd and Brühwiler [108] investigated the roles of head tilt, hair and wind speed on forced convective heat loss through motorcycle helmets, utilising a thermal manikin under the following conditions: (i) a 30° forward head tilt angle (six helmets); (ii) a wig installed between the head form and helmet (six helmets) and (iii) applied wind speeds ranging from 0 to 80 kmh−1 (three helmets). It was found that: (i) by tilting the head forward, a reduction in heat loss in the face section was observed in many helmets; (ii) the heat loss was reduced by a factor of 2 by the wig; and (iii) heat loss is approximately linearly dependent on wind speed (0–80 kmh−1 ), with some exceptions below 30 kmh−1 . The flow of air over the head is reduced by wearing a helmet, and the heat loss from the head to the environment is thereby reduced, which can lead to an increase in heat-related stress in the case of hard physical work [109]. The effect of heat transfer from the human head, along with other relevant environmental factors (such as air speed and radiant heat), has been investigated by many researchers when studying the characteristics of helmets such as effective materials [110–112], colour [113], standoff distance [114] and general construction [115]. The human head has generally been simulated by the use of manikins for measuring heat transfer from the head when wearing an industrial safety helmet [13, 112]. Sometimes, human participants have been used for experiments [116]. However, there are disadvantages in using human participants because of variability between different participants, depending on their personal circumstances and the time of the day or the month. Hence, it might be necessary to use large numbers of participants to obtain results that have statistical significance. Osczevski [117] studied the effects of wind on the nude head by using manikins he designed. In these manikins, there were four separately monitored regions for simulation and measurement. The emphasis of solar radiation on the cooling effect of headgear was investigated by using head forms. In this study, lamps were used to simulate the effect of the sun, and the temperatures were measured at several places on the head form [104]. A metallic head form with a constant power source was placed in a wind tunnel, and a non-dimensional thermal resistance was defined by comparing it with a bare sphere simultaneously. The temperatures were measured at certain points on one half of a symmetrical head form [34]. Heat stress reduction when wearing a helmet has been achieved by either actively cooling the head or by using passive vents into the helmet structure. It has been observed that cooling the head area in order to reduce heat stress is more efficient

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than cooling the torso (at a temperature of 26–50 °C and a relative humidity of 45%) [118]. The effects of forced air [119] and water [120, 121] to cool helmets have been investigated, and it was found that both are effective in reducing thermal stress in hot conditions (40–50 °C under both humid and dry conditions 15–80 mm Hg). However, these systems are heavy and large and thus not convenient for use in environments such as forest harvesting. Heat transfer from the head to the helmet microclimate, in the case of helmets with passive ventilation, seems to be more than for helmets without vents of similar design and shape [76, 111, 115, 122]. Holland et al. [123] investigated forest harvesting helmets and found that the exchange of air between the helmet microclimate and the ambient environment was fastest in the helmets with top vents. Guan et al. [124] designed a test rig to evaluate the thermal/moisture mapping of industrial safety helmets with and without ventilation openings, which measured both temperature and relative humidity in various locations inside the helmet. They indicated that the ventilation openings were essential for thermal comfort inside the helmet. The psychophysical tests conducted by Davis et al. [125] showed that ventilation contributes to a greater extent to safety helmets’ comfort. In addition, the weight and fit are important factors in helmet design. Liu and Holmér [112] studied the evaporative heat transfer characteristics of helmets and concluded that wind simulation considerably increased heat loss in all helmets under various environmental conditions. In addition, they indicated that the cradle design and construction were important for successful heat loss from the head. Industrial helmets have been modified to provide increased ventilation to the head and also to reduce the weight so that they are widely accepted by users in a hot climate. This improved ventilation increased the convection that assists heat dissipation from the helmet shell and also provided better insulation against radiant heat. Hsu et al. [104] studied the thermal discomfort of industrial safety helmets and redesigned them to improve their thermal properties. The new helmet designed by Hsu et al. [104] was proven both subjectively and objectively to be superior to commercially available safety helmets.

2.12 Thermal Energy Storage Systems Thermal energy storage (TES) systems work as a tool for energy management by storing thermal energy at periods when it is abundantly available and then using it when and where it is required. The primary function of the TES system is to fill the gap between energy supply and energy demand that is caused by higher energy consumption or primary energy source variation or both, such as the periodic variations of solar radiation energy. There are three types of TES systems, namely sensible, chemical and latent [126]. Sensible heat storage is based on increasing the temperature of any substance without its phase change. In chemical systems, the thermal energy storage is based on the thermo-physics of the reactions. In latent TES systems, heat is absorbed or released when the substance changes from solid to liquid

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29

and back. A classification of energy storage materials was done by Abhat [127] in 1983 and is shown in Fig. 2.10. Among these, the latent heat storage system is more attractive because of its ability to provide high-energy storage density and to store heat at a constant phase change temperature [128]. In Table 2.2, the important characteristics of energy storage materials are shown. Phase change materials (PCM) fall under the category of a latent TES system. Latent heat storage systems using PCM have been studied by several researchers [129–131]. Important characteristics of energy storage materials are shown in Table 2.2 [132].

Fig. 2.10 Classification of energy storage materials

Table 2.2 Important characteristics of energy storage materials Thermal properties

Physical properties

Chemical properties

Economic properties

Phase change temperature fitted to application

Low density variation

Stability

Cheap and abundant

High change of enthalpy near temperature of use

High density small or no under cooling

No phase separation compatibility with container materials

High thermal conductivity in both liquid and solid phases (although not always)

–

–

–

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2.13 Phase Change Materials Phase change materials (PCM) are substances that undergo the process of phase change when the temperature changes [133]. PCM are also substances with a high heat of fusion which melt and solidify at a certain temperature and are also capable of storing and releasing large amounts of energy. NASA developed PCM technology in the late 1970s to early 1980s, in order to protect delicate instruments and astronauts from the extreme temperatures of space [134]. The further potential of PCM was developed by the Triangular Research and Development Co., who subsequently gave the licence to Outlast Technologies based in Boulder, Colorado. Outlast Technologies exploited the potential of PCM in textile fibres and fabric coatings; as a result, PCM capsules are now applied to all types of materials [135, 136]. Heat is absorbed or released when the material changes from solid to liquid and back. PCM are considered latent heat storage units [137]. The amount of heat required to melt a solid at a constant temperature is called the melting enthalpy or latent heat of fusion. The latent heat of fusion is greater than the sensible heat capacity of the material. Generally, PCM are solid at room temperature, and as the temperature increases, PCM absorb the heat and melt, cooling the surroundings. Conversely, when the temperature drops, the material will solidify and give off heat, warming the surroundings. These phase changes take place at constant temperatures, and for certain materials, the process of melting and freezing can be repeated over an unlimited number of cycles with no change to their physical or chemical properties. Figure 2.11 shows a graphical explanation of the phase change process [138–140]. A few PCM have been identified that undergo the phase change process very close to the temperature of human skin. This property of PCM enables them to be applied in all-season protective outfits and for abruptly changing climatic conditions. This inherent attribute of heat absorption and dissipation of PCM enables them to be incorporated into summer and winter clothing [141, 142]. The main aim of applying PCM to garments such as ski clothing, athletic clothing and diver dry suits is to keep the wearer warmer or cooler or, in some cases, over a longer period of time [143].

Fig. 2.11 Process of phase change of PCM

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31

Fig. 2.12 Heat capacity of various common materials

Apart from PCM, traditional materials such as water, gravel, wood and plastic can sometimes be used for heat storage. The physical properties of a material which determine how much heat can be stored are the specific heat capacity and specific density. Figure 2.12 indicates the heat capacity of various materials [138]. It can be observed that the heat capacity of paraffin wax is very high as compared to other materials.

2.13.1 Classification of PCM PCM can be designed to melt and freeze at a selected temperature by using various chemical formulations. They possess the ability to reduce the size of storage systems by using the latent heat of storage. Though PCM have been in use for various heat storage applications since the 1800s, the application for cool storage media is very recent. The PCM used in research during the last 40 years are basically made of organic and inorganic compounds. Various types of PCM, such as paraffins or waxes, hydrated salts, organic, inorganic and fatty acids are commercially available, and these are well known for their thermal characteristics. According to their chemical nature, PCM can be classified into three categories: organic; inorganic and eutectic [132, 137]. The potential usefulness of a large number of PCM such as organic and inorganic paraffins, salt hydrates, fatty acids and their eutectic mixtures have been explored for heating and cooling applications [144, 145].

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Organic PCM (Paraffins and Fatty Acids)

This class of PCM includes paraffins (Cn H2n+2 ) and fatty acids (CH3 (CH2 )2n COOH). Of these two materials, paraffins are widely used as PCM. Carl Reichenbach discovered paraffin [derived from the Latin parum (=barely) + affinis (=lacking affinity or reactivity)], which is the common name given to a group of alkane hydrocarbons with the general formula Cn H2n+2 , where n is greater than about 20. The alkane series with more than 15 carbon atoms per molecule is waxy solids at room temperature and is known as paraffin wax. Although in general, paraffin is a technical name for an alkane, in most cases, it refers specifically to a linear chain or normal alkane, whereas branched or isoalkanes are called iso-paraffins. These PCM are straight chain hydrocarbons with 2-methyl branching groups near the end of the chains [146]. The paraffins with an even number of carbon atoms are generally preferred, as these are cheap, more stable and more abundant. The heat of fusion and melting points of paraffins increase with the increase in molecular weight. The paraffins can be classified into two main groups: even-chained (n-paraffin) and odd-chained (isoparaffin). The classification of paraffins into even-chained or odd-chained groups depends on the content of alkanes within the substance (ranging from 75 to 100%) [147]. Kaygusuz and Sari [148] investigated the thermal performance and phase change stability of palmitic and stearic acids as a latent heat energy storage material. They found better stability of the stearic and palmitic acids, which was accomplished at low inlet water temperature when compared with the high inlet water temperature. The paraffins absorb much more heat than normal materials during the melting process. Use of paraffinic PCM in textiles substantially increases the heat storage capacities of the textiles. The temperature remains constant during the melting and crystallisation processes of paraffin, thus making it a good source of heat storage for textile applications. These paraffins are enclosed in very small spheres with diameters of only a few micrometres. The microencapsulated paraffins are not only permanently locked in the fibres but also coated onto the surface of a textile structure. Some of the paraffins are readily available for textile applications at lower cost, have a wide range of melting temperatures and are thermally reliable even after a large number of thermal cycles [149, 150]. Fatty acids are organic compounds having melting ranges and heat of fusion values similar to organic paraffins. Only a limited number of fatty acids have melting and freezing points in the range of 20–40 °C [151]. Therefore, fatty acids have limited applications in textiles as energy storage materials. Another disadvantage of fatty acids is their availability in only narrow temperature ranges. Feldman and Shapiro [152] found fatty acids and their binary mixtures are attractive candidates for latent heat thermal energy storage in space heating applications. They observed the melting point and latent heat of transition of the fatty acids range from 30 °C to 65 °C and 153 kJ/kg to 182 kJ/kg, respectively. Paraffins are the ideal candidate for PCM applications due to their large temperature range and their availability in various forms and structures. The storage capacity of paraffins is high as compared to other compounds, and these materials can be frozen without supercooling. The paraffins possess a wide range of melting points

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(–5 to 66 °C) and have a high heat of fusion per unit weight. They are non-toxic, non-corrosive, chemically inert and stable below 500 °C [153]. These PCM have minimal super cooling behaviour, low volume change on melting, low vapour pressure in the melt and in addition reasonable cost. The density of the paraffins ranges from 700 to 770 kg/m3 . The most widely used paraffins are hexadecane (C16 H34 ), octadecane (C18 H38 ) and eicosane (C20 H42 ), along with some of the other paraffinic hydrocarbons such as heptadecane (C17 H36 ) and nonadecane (C19 H40 ). In spite of the many advantages, there are some limitations of paraffins. The advantages and disadvantages of using paraffin PCM are described below. Advantages 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Availability in a large temperature range; Freeze without much super cooling; Ability to melt congruently; Self-nucleating properties; Compatibility with conventional materials of construction; No segregation; Chemically stable; High heat of fusion; Safe and non-reactive and Recyclability.

Disadvantages 1. 2. 3. 4. 5. 6.

Low thermal conductivity in solid state; Requirement of high heat transfer rates during the freezing cycle; Low volumetric latent heat storage capacity; Flammability; Chemically purified paraffins are expensive; and Due to cost considerations, only technical grade paraffins are used.

Experimental results have established that laboratory grade paraffin waxes, tetradecane, hexadecane and their binary mixtures, are excellent candidates as PCM for cool storage. However, due to the very high cost involved with laboratory grade materials, technical grade materials must be used for cool storage. Apart from the paraffin organics, non-paraffin organics are also a common type of PCM available for textile applications. The non-paraffin organic PCM such as polyethylene glycol have been applied to fibres and fabrics. Commercial paraffin waxes are available with a wide range of melting temperatures and are cheap with moderate thermal storage densities (200 kJ/kg or 150 MJ/m3 ). They are chemically inert and stable with no phase segregation and undergo negligible sub-cooling. However, their application is limited as they have low thermal conductivity (0.2 W/m °C), and within a small physical space, they can exist in all three phases. Metallic fillers, metal matrix structures, finned tubes and aluminium shavings have been used to improve their thermal conductivity [154]. As pure paraffin waxes are very costly, commercially only technical grade paraffins are

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Table 2.3 a List of paraffin waxes with latent heat of fusion. b List of paraffin waxes with melting and boiling points (a) Phase change material

Crystallisation point (°C)

Melting point (°C)

Latent heat of fusion (cal/gm)

Eicosane

30.6

36.1

59

Octadecane

25.4

28.2

58

Heptadecane

21.5

22.5

51

Hexadecane

16.2

18.5

57

(b) Phase change material

Melting point (°C)

n-Decane

−30

Boiling point (°C) 174

n-Dodecane

−9.5

216

n-Tetradecane

6

254

n-Hexadecane

18

287

n-Octadecane

28

316

n-Eicosane

37

343

used for PCM applications. Table 2.3 indicates the list of paraffin waxes with their thermal properties that are used as PCM [155].

2.13.1.2

Inorganic PCM (Salt Hydrates)

Inorganic PCM or salt hydrates are crystalline solids of general formula MnH2O where M is an inorganic compound with the capacity to hold a high volumetric latent storage density [156]. These PCM are considered to be the alloys of inorganic salts with a definite number of moles of water. The applicability of salt hydrates for latent heat storage as PCM has been explored by several researchers [157–160] as they have a wide range of melting points (0–120 °C) [161]. Salt hydrates are attractive candidates for TES systems because of their high volumetric storage density, relatively high thermal conductivity and moderate costs as compared to paraffin waxes [162]. The major problem in using salt hydrates as PCM is that most of them melt incongruently, i.e. they melt to a saturated aqueous phase and a solid phase which is generally a lower hydrate of the same salt. Another problem with salt hydrates is that they have poor nucleating properties, resulting in super cooling of the liquid salt hydrate prior to freezing. A third problem is corrosion, which has meant that they have short service lives or high packing and maintenance costs. The following highlights the advantages and disadvantages of inorganic PCM.

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Advantages 1. 2. 3. 4. 5. 6. 7.

High volumetric latent heat storage capacity; Low cost and easy availability; Sharp melting point; High thermal conductivity; High heat of fusion; Low volume change and Non-flammability. Disadvantages

1. Super cooling is a major problem in solid–liquid transition and 2. Requirement to use nucleating agents which become ineffective after repeated cycling. 2.13.1.3

Eutectics

Eutectic PCM are mixtures of two or more chemicals which, when mixed in a particular ratio, have a freezing/melting point below or above the freezing temperature of water (0 °C or 32 °F) and offer a thermal energy storage facility between –114 °C (–173 °F) and +164 °C (327 °F). These are mixtures of organic–organic, organic– inorganic and inorganic–inorganic compounds. The applications of eutectics date back to the late eighteenth century. As the separation and the life expectancy of these mixtures were unpredictable, their widespread usage was limited. The advantages and disadvantages of using eutectic PCM are described below. Advantages 1. Sharp melting point similar to a pure substance and 2. Higher volumetric storage density as compared to organic compounds. Disadvantages 1. Limited availability of data on thermo-physical properties and 2. These materials are very new to thermal storage applications. Out of the above classes of PCM discussed, the most commonly used PCM are salt hydrates, fatty acids and paraffins. Recently, ionic liquids were investigated as novel PCM. Bugaje [163] conducted experiments on methods for enhancing the thermal response of paraffin wax heat storage tubes by the incorporation of aluminium fins and star structures. The conclusion was that internal fins performed much better than star matrices, reducing the loading time on the order of 2.2 and the unloading time on the order of 4.2. Zalba et al. [164] used paraffin PCM and developed an empirical model that measured the performance of PCM.

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2.13.2 Micro-PCM The use of the special thermo-physical properties of PCM to improve the thermal insulation of textile materials only became possible by enclosing them in microcapsules. The diameter of the capsules varies between 1 and 60 µm. The PCM can be encapsulated by a polymeric cover to produce a capsule of micrometre range [165]. The PCM contained in the microcapsule is referred to as a micro-PCM. The microPCM can be incorporated into the fibres by a wet-spinning process, or it can be coated onto the surface of the fabric substrate by chemical finishing. Figure 2.13 shows the structure of a micro-PCM where ‘a’ and ‘b’ indicate the diameter of the PCM and the thickness of the cell wall, respectively. The size of ‘a’ and ‘b’ in paraffin PCM varies between 40 and 2 µm, respectively. In an earlier work, solution-spun acrylic fibres were incorporated with micro-PCM that was stable at low temperatures. These micro-PCM were unable to be used at melt-spinning temperatures (>200 °C) as they lose their core material. Later, microPCM was successfully produced in melt-spinning polymers such as polypropylene (PP), nylon 6 and polyethylene terephthalate (PET) [166, 167]. Mono-component melt-spun fibres containing micro-PCM have also been produced and applied [168] to clothing. Packets of micro-PCM encapsulated in coated nylon shells were used in a mesh vest contained inside a garment, to increase sweat evaporation and thermal recharging by marines in jungle and desert environments [169]. Gear et al. [170] explored the thermal storage and insulation properties of garments containing microPCM. They showed that the diver dry suit containing micro-PCM provides better thermal protection in comparison with the diver dry suit containing thinsulate material and enables the diver to work for longer periods in extreme temperature conditions. Thermo-regulated fibre, fabrics and foams have been manufactured by the use of micro-PCM [171]. Micro-PCM has been incorporated into acrylic fibres and polyurethane foams and embedded into a coating compound and utilised for garments and home furnishing products [172]. Many researchers have used micro-PCM technology for protective garments that are worn in extreme environments [173, 174]. The development of the Fig. 2.13 Micro-PCM with a core and b polymeric hard shell

2.13 Phase Change Materials

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Fig. 2.14 Micro- and macro-PCM

dynamic thermal insulation concept, together with the insulation value of micro-PCM fabrics, has also been investigated [175]. The effectiveness of micro-PCM applied to garments during environmental transients was evaluated by Shim et al. [176]. Wearer trials on garments containing micro-PCM and garments without micro-PCM revealed that changes in mean skin temperature and microclimate temperature were less in the former [177]. The rate of temperature increase in garments with different add-on levels of micro-PCM was compared by Yin et al. [178], and it was observed that, in the garments with lower amounts of micro-PCM, the rate of temperature increase was higher. Smart gloves have been designed to keep the hands warm using micro-PCM in order to replace very bulky gloves heated with batteries. Micro-PCM particles were incorporated into textile fibres to increase the thermal storage of the fabric [179]. Adding micro-PCM to foams and fabrics, resulting in increased thermal storage and insulation, has created many new materials. The latent heat release or absorption phenomenon of micro-PCM has been used to provide the thermal capacitance [180– 183]. Apart from micro-PCM, further research has produced garments applied with capsules of 2–3 mm diameter known as macro-PCM, to increase comfort and assist in reducing heat stress [184–188]. These macro-PCM has several applications in marines, fire fighting and patients with heat stress problems [189]. Macro-PCM can be applied to a certain extent to control body temperature by the suitable selection of the fusion temperature of the PCM [170]. Figure 2.14 shows microscopic pictures of micro-PCM and macro-PCM [190].

2.13.3 Applications of PCM PCM is mainly used for heat management of thermo-regulated fabrics, telecommunication installations, civil engineering, microprocessors and high-power electronics. As an example in textile applications, PCM utilises microencapsulated chemicals such as nonadecane and other medium-chain length alkanes for cooling purposes.

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When the ambient temperature increases above 32.1 °C (the melting point of nonadecane), the nonadecane melts, and latent heat is absorbed, thereby interrupting the increase in temperature of a garment. Once the ambient temperature falls, the PCM solidifies, and the latent heat is released, providing a heating effect. Thus, PCM can be used to provide a cooling or heating effect on the garment microclimate depending on the ambient temperature. The various applications of PCM are discussed in the following section.

2.13.3.1

Textile Applications

In the field of textiles, there are many applications of PCM such as casual clothing, sportswear, technical textiles (bulletproof vests, spacesuits and air suits), medical uses, automotive textiles and shoe linings. For textile applications, PCM can be applied to textile substrates by four methods, namely: spinning of fibres containing PCM; impregnation of the fibres with PCM; coating the fibres with micro-PCM and direct incorporation of PCM into polymer film [126]. In the first method, PCM are added to the liquid polymer (solution or melt) followed by fibre spinning by various conventional methods such as dry or wet spinning. The protection of micro-PCM is enhanced in this process as there are two walls covering the PCM. The first wall is the wall of the microcapsule, and the second wall is the fibre itself [179]. Also, composite fibre-spinning (such as polytetramtehylene glycol (PTMG) used as core and PET used as sheath) can be employed. Gateway Technologies Inc. (now Outlast) has produced acrylic fibres (Fig. 2.15) containing paraffinic PCM [155]. The second method is impregnation or filling of the fibres with PCM. Vigo and Frost [139] impregnated inorganic PCM such as LiNO3 ·3H2 O, Zn(NO3 )2 ·6H2 O, CaCl2 ·6H2 O/SrCl2 ·6H2 O and Na2 SO4 ·10H2 O/Na2 B4 O7 ·10H2O into hollow rayon and polypropylene fibres for thermal regulation applications. The third method is the coating method, which involves coating the fibres with encapsulated PCM in an appropriate foam or cross-linking agent. Pushaw [191, 192] suggested some recipes Fig. 2.15 Acrylic fibre containing PCM

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containing a suitable binder for textile application of micro-PCM by coating. Zuckerman et al. [193] also suggested one recipe and compared the properties of fabrics coated with micro-PCM and without PCM. They found that a knife-over-roll coating technique is appropriate for PCM application to foam, and some techniques (such as solvent-based gravure printing, thermoplastic gravure printing, thermoplastic spray and thermoplastic extrusion techniques) are not suitable for PCM coating. The direct incorporation of PCM into textiles was suggested by Pause [194]. In this method, PCM are directly incorporated into a polymer film which is then laminated on to the non-woven fabric system. Pause has claimed several advantages of this method as compared to other PCM application methods in garments. The advantages of this method are getting a high PCM concentration per unit area; elimination of the expensive microencapsulation procedure of the PCM and minimisation of any increase in the weight of the garment. In order to decrease heat stress, accidents and errors, Pause [195] incorporated PCM into a thin polymer film and laminated the film onto the inner side of the fabric of chemical and non-woven protective garments. The heat stress of these garments was found to be decreased substantially by the application of PCM. The analytical modelling of a diver dry suit applied with micro-PCM has been investigated [183]. It was shown that the foams containing micro-PCM could reduce the heat loss in a diver during the initial phase of a dive. The PCM helped to delay the penetration of cold through the diver’s suit until it solidified. In addition to making garments, PCM-treated fabrics can be used as linings for garments, where they are in closer contact with the skin to provide cooling or heating as required. A cooling garment consisting of two main parts was designed by Doherty [196]. The garment consisted of an outer metallic part that reflected the high intensity of light and heat, and an inner PCM-coated lining with pockets of fabrics made from various fibres. He also placed one pouch of n-alkane in each of the pockets for cooling purposes. Thermal barriers with PCM were designed by Payne et al. [197] for clothing worn by scuba divers, fire fighters, astronauts and mountaineers. Also, these barriers were found to be effective in other textile products such as blankets, sleeping bags and carpets. Pause [198] showed that PCM could be applied to textiles used in automotives to increase thermal comfort. These PCM can also be applied to other automotive textiles such as carpets and headliners. Pause [199] also investigated the potential of textiles with PCM in various medical applications such as surgical gowns, bed linen and fabrics used in intensive care. A mixture of PCM, silica and carbon black were used as a microwavable TES material in textiles [200].

2.13.3.2

Other Applications

The use of PCM in building applications by microencapsulation has been investigated by several researchers [201–203]. The application of PCM integrated with building materials without encapsulation has also been investigated [204]. PCM are also applied in the field of medicine, such as in antibiotics, hormones and other drugs [205].

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2.13.4 Selection of Suitable PCM While selecting an appropriate PCM for thermo-regulating action, many factors are taken into consideration such as cost, availability, toxicity, colour, heat storage capacity and durability. The selection of PCM for various applications mainly depends on the temperature range needed for the application. However, for textiles, the main criterion for selection is the temperature at which the PCM will function (i.e. the phase change temperature of the PCM) to keep the wearer comfortable. For textile applications, the PCM with melting temperatures of 20–40 °C (i.e. close to body temperature) are selected [176, 195]. In addition to this, the viability of producing the different types of micro-PCM and the production costs also should be taken into account. PCM can be used either in a pure form or as a mixture. For applications with wide temperature ranges, mixtures are more efficient than single chemicals. The temperature at which the solid/liquid transition takes place depends on the number of carbon atoms on the chain backbone. The quantity of PCM in a fabric is constrained by the weight and/or the duration for which it performs its function of cooling and the reverse process of heating. Further research is being carried out to enhance the performance of PCM and also to reduce the weight of the fabrics. In active sports, for cooling in a stationary position where weight is not an important criterion, the PCM can be enclosed as a gel in sealed capsules placed in pockets of the clothing. The appropriate melting temperature of PCM is selected according to the final applications, and it should lie within the practical range of operation, i.e. it should melt congruently with minimum sub-cooling and should be chemically stable. Materials with melting temperatures below 15 °C are used for storing coolness in airconditioning applications, and materials with melting temperatures above 90 °C are used for absorption refrigeration. All other materials with melting temperatures between these two temperature ranges can be used in solar heating and for heat load levelling applications. Paraffin waxes are one of the best materials suitable for PCM applications because of their low cost, non-toxicity, eco-friendliness and easy process of application by microencapsulation. The quantity of the material used for phase change effect determines the thermal insulation value. Shape-stabilised or form-stable composite PCM are one of the new developments in PCM technology, classified as solid–solid PCM and solid–liquid PCM [206– 209]. Paraffin/high-density polyethylene (HDPE) composites form a stable solidliquid PCM mixture for thermal energy storage for textile applications [210]. In the composite, the mass percentage of paraffins could go up to a maximum of 76% without any seepage of the paraffins in the melted state [211].

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2.14 Microencapsulation Fragrance compounds and essential oils are volatile substances. The most difficult task in preparing a fragrance-finished textile is how to prolong the fragrant effect in the finished textile product [212]. Microencapsulation is an effective and popular technique to solve this problem [213, 214]. Microencapsulation is the process of producing small capsules by encasing tiny particles of one material within another material. The dimension of the resulting capsules ranges from less than one micron to several hundred microns. Microcapsules are very tiny particles containing core material surrounded by a shell [215]. The shapes of microcapsules can be spherical, asymmetrical or variably shaped with droplets of core material embedded throughout the microcapsule. The material encapsulated is called the core or nucleus, while the encapsulating material is referred to as the shell or wall. Various types of core materials such as dyes, drugs, fragrances and biological shells can be coated by the shells of various materials such as wax, fat and polymers. By selecting appropriate materials for core and shell, microcapsules with a variety of functions can be prepared. Solids, liquids and gases may be microencapsulated. Microencapsulation allows liquid and gases to be processed similar to solids, and in addition, hazardous materials can be easily and safely processed [216]. For the successful application of PCM by microencapsulation, the following parameters need to be considered [134]. • • • • • •

Particle size; Uniformity of particle size; Particle size distribution; Stability to mechanical actions such as shear, abrasion and pressure; Stability to chemicals and Core-to-shell ratio (the proportion of the core with respect to the whole should be as high as possible, and the thickness of the shell should be sufficient to maintain capsule stability).

Microcapsules can be encased with core materials for any specific period of time and can be released gradually. The release of the core material can be achieved by breaking the capsule walls or when the external conditions cause the capsule walls to rupture, melt or dissolve. For the effectiveness of the PCM, it is necessary to encapsulate them in a physically and chemically stable shell. PCM were first incorporated into textile materials by microencapsulation technology in 1987 [217]. The application of PCM in different areas by microencapsulation has been studied by several researchers [218–221]. Various companies such as BASF [222] and Microtek [190] have modified and developed new PCM which can be applied by microencapsulation. The paraffin waxes as PCM for textiles cannot be directly into incorporated textile substrates because of their low melting points. Therefore, paraffin waxes need to be microencapsulated by a suitable polymer. Colvin and Mulligan [223] from Triangle Research and Development Corporation (TRDC) were the first to prove that paraffin PCM can be successfully microencapsulated and suspended in water. In addition to

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this, they can be pumped in a closed loop that can transport more heat than water alone. Subsequent work by them led to the development of the first non-toxic PCM coolant, which produced a tenfold increase in the system’s effective fluid capacitance and a twofold increase in the heat transfer coefficient under isothermal conditions [223]. Aqueous-based non-toxic micro-PCM coolant was used for the cooling of spacesuits used by NASA [224]. The thermal stability of microencapsulated n-octadecane was improved by using different mole ratios of urea-melamine-formaldehyde copolymers as shells [225]. It has been shown that 163 °C is the highest thermal stable temperature of microcapsules with a diameter range of 0.4–5.6 µm and with a ureamelamine-formaldehyde mole ratio of 0.2:0.8:3. The core material diffuses out of the shell due to the expansion of n-octadecane as the temperature continuously increases. To obtain microcapsules, which are thermally stable up to 200 °C, the microencapsulated n-octadecane is added with cyclohexane in the oil phase and heated at 160 °C for 30 min. According to the performance properties and end-use of the finished product, the proper treatment process for incorporating PCM microcapsules into textiles should be selected. Hittle and Andre [226] used a loading of 60-wt % for coated fabrics and observed that the properties of fabrics such as drape, breathability, softness and tensile strength are adversely affected as the loading increases.

2.14.1 Classification of Microencapsulation The encapsulation method for PCM to be applied to textiles should be easy, cheap and robust. Microcapsules of PCM can be encased in one or several shells arranged in strata of varying thicknesses around the core. Up to now, the main methods employed for microencapsulation are polymerisation; emulsification; phase separation; spray drying and grinding, which are discussed in the following sections.

2.14.1.1

Polymerisation

The polymerisation method or chemical method can be classified into interfacial polymerisation, in situ polymerisation and matrix polymerisation. In the interfacial polymerisation process, the two reactants react rapidly in a polycondensation. This is based on the classical Schotten–Baumann reaction between an acid chloride and an active hydrogen containing compound such as polyurea or polyester. If the conditions are suitable, condensed polymer walls are formed at the interface of the emulsion droplets. Interfacial polymerisation was used to prepare the microcapsules of polyurea for finishing applications, which was stable at curing temperatures higher than 80 °C [177]. In situ polymerisation consists of the direct polymerisation of a single monomer on the particle surface. One example of this process is the encapsulation of cellulose fibres in polyethylene. In matrix polymerisation, a core

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material is imbedded in a polymeric matrix. In this method, the particles are formed by evaporation of the solvent from the matrix.

2.14.1.2

Emulsification

This is a physical process which involves the preparation and dispersion of a core material in a polymer solution, emulsification of the dispersion in water or other organic solvent and removal of liquid from the dispersed second phase by heating the system to solidify and to encapsulate the core material. This process has been employed for preparing polymer encapsulated particles for electrophoretic displays [227], pressure-fixable toner particles [228] and cosmetic applications [229]. When this process is employed with small particulates such as dye or pigment, diffusion of the core material from the dispersed second phase to the continuous phase can cause inefficient encapsulation.

2.14.1.3

Phase Separation

The phase separation process is used for encapsulating water-immiscible core materials in aqueous media. By this process, any pair of oppositely charged polyelectrolytes capable of forming a liquid complex coacervate can be used for encapsulation. One typical example of the phase separation process is complex coacervation. The complex coacervate adsorbs on the core material, forming microcapsules. The coating of complex coacervate is gelled by cooling and then cross-linked with glutaraldehyde or formaldehyde to form capsules. In this process, a core material insoluble in the solvent is dispersed in a solvent, and a polymer soluble in the solvent is preferentially adsorbed by the dispersed core material. The polymer encapsulates the dispersed core material and forms the microcapsules. The wall of the microcapsule is solidified by the addition of a non-solvent or a cross-linking agent. Hawlader et al. [230] have investigated the encapsulation of a PCM by the coacervation method.

2.14.1.4

Spray Drying

In spray drying, a coating material is dissolved in a carrier solvent such as water or any organic solvent. Then, the core material is dispersed in the carrier solution and emulsified using a surfactant that forms an oil-in-water emulsion. This emulsion in the form of small droplets with a high surface area is sprayed into a hot drying chamber. Dry powder is formed in the drying chamber by rapid evaporation of water from the droplets. This process was commercially employed to encapsulate flavours with gum arabic in 1927. Since then, it has become a low-cost process capable of producing a range of microcapsules with good yields.

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Grinding

In this process, a mixture of a core material and a coating material is plasticised, either by adding a solvent to form a solution or by heating the mixture to form a melt. Then, the solvent is removed from the solution to form a solid mass. Mechanical shearing is used to break the solid mass into small particles in which the core material is encapsulated. This is a very simple process and for many years has been used for manufacturing toners [231]. Apart from the five basic techniques described above, microencapsulation can be carried out by several other processes such as desolvation [232], vapour deposition [233], biliquid column process [234], fluidised-bed coating [235], electrostatic encapsulation [236], centrifugal encapsulation [237] and gelation encapsulation [238].

2.14.2 Features of Microcapsules A microcapsule (Fig. 2.16) is a tiny sphere with a small wall around it. Microcapsules are miniature containers varied in shapes such as spherical and irregular. The shape is spherical if it encloses a liquid or gas, and it is irregular if it contains a solid. Most microcapsules have diameters between a few micrometres and a few millimetres. In some cases, the microcapsules have multiple walls. There are three classes of microcapsules: mono-core; poly-core and matrix type, according to morphology as shown in Fig. 2.17 [239]. The microcapsules with a diameter between 1 and 60 µm enable the use of the special thermo-physical properties of PCM for improving the thermal insulation of textile materials. Fig. 2.16 Microcapsule with sheath and core

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Fig. 2.17 Types of microcapsules a mono-core, b poly-core and c matrix

The covering must be able to release the encapsulated material when required, either by mechanical action or external force. This property has enabled microcapsules to serve many useful functions and find applications in different fields of technology [240]. For example, the storage life of a volatile compound can be increased markedly by microencapsulating [241]. Substances may be microencapsulated so that the core compound within the capsules can last for a specific period. Core materials can be released either gradually through the capsule walls, which is known as controlled release, or by diffusion. External conditions triggering the capsule walls to rupture or melt or dissolve are the other possibilities of releasing the core material. For textile applications of microcapsules, particle size and size uniformity are the main factors [134]. Pause [220] used microencapsulated PCM of 1–60 µm diameter to improve the thermal insulation of textile materials. Colvin and Bryant [219] used PCM microcapsules of 30–100 µm diameter for textile fibres, composites and foams for thermo-regulating purpose. They showed that particles of much larger size (1– 3 mm) could be applied within clothing layers to improve breathability and cooling under high humidity conditions. The heat storage capacity of fabrics treated with microcapsules decreased with the increase in the number of laundering cycles [242]. After the first laundering cycle, the largest decrease occurred as the microcapsules loosely attached to the fabric fell off during laundering. Up to ten launderings, the heat storage capacity of the treated samples decreased, with no more reduction thereafter. The application of an appropriate binder can result in a higher retention of the heat storage capacity of treated fabrics after washing. Kim and Cho [177] used an acrylic binder for coating PCM microcapsules onto fabrics and obtained 52–70% retention of the heat storage capacity even after ten launderings. Also, mild washing conditions can retain the heat storage capacity of microencapsulated materials.

2.14.3 Techniques of Microencapsulation The techniques of microencapsulation can be categorised into two groups, namely: chemical techniques and mechanical or physical techniques. The two processes are discussed in the following sections.

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2.14.4 Chemical Techniques In this process of encapsulation, there is a reaction between the aqueous solutions of cationic and anionic polymers such as gelatine and gum arabic. These polymers generate a concentrated phase known as complex coacervate. The coacervate exists in equilibrium with a dilute supernatant phase. Thin films of the polymer coacervate coat the dispersed droplets of core material, when water-immiscible core material is introduced into the system. The capsules are then made harvestable by solidifying the thin films and can be used to produce capsules for carbonless paper and other similar applications.

2.14.4.1

Mechanical/Physical Techniques

The mechanical microencapsulation technique was developed in the 1930 s. In this technique, an emulsion is prepared by dispersing the core material, usually an oil or active ingredient immiscible with water, into a concentrated solution of wall material until the desired size of oil droplets is attained. The resultant emulsion is atomised into a spray of droplets by pumping the slurry through a rotating disc into the heated compartment of a spray dryer. There, the water portion of the emulsion is evaporated, yielding dried capsules of variable shapes containing scattered drops of core material. The capsules are collected through continuous discharge from the spray drying chamber. This method can also be used to dry from aqueous slurry small microencapsulated materials that are produced by chemical methods.

2.14.5 Applications of Microencapsulation There are numerous applications of microencapsulated materials in different areas such as agriculture [243], pharmaceuticals, cosmetics, heat storage systems for buildings [218, 244], textiles [175, 177, 183], paints, adhesives and many other industries. In the textile industry, the microencapsulation process is used to enhance the properties of finished materials. There are many applications of fibres and fabrics containing microencapsulated PCM such as active/outdoor wear, sports apparel, footwear for comfort and protection from cold, protective clothing, bedding and furnishing. Other applications include insect repellents, dyes, vitamins, antimicrobial agents, durable fragrances and skin softeners. Microcapsules are also used in various other applications such as carbonless copy paper, pesticides and scented strips [245]. In the food industry, microencapsulation is used to protect, isolate or control the release of a given substance [246]. Several researchers have applied the process of microencapsulation for the formation of inks for ink-jet printers [247, 248]. Hong and Park [249] prepared microencapsulated melamine-formaldehyde systems containing fragrant oil and applied to them cotton

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fabric. The microcapsules were able to withstand up to 15 laundering cycles. It was revealed by scanning electron microscopy (SEM) that the smaller capsules survived more effectively after laundering. Shin et al. [242] developed a thermo-regulating textile material with microencapsulated PCM and added this to polyester knit fabrics by a pad–dry–cure process. The microcapsules thus produced were spherical in shape with melamine-formaldehyde shells containing eicosane. The morphology, thermal properties and laundering properties were investigated. It was found that the microcapsules were stable under stirring in hot water and an alkaline solution. The heat storage capacity of the fabric was increased with increased concentration of the microcapsules. The heat storage capacity of the thermo-regulating fabrics was 0.09–4.44 J/g which was retained up to 40% even after five laundering cycles. Hawlader et al. [250] prepared encapsulated paraffin wax by complex coacervation and spray drying methods and characterised them. The results of a differential scanning calorimeter (DSC) showed that the microcapsules prepared by both coacervation and the spray drying method possess a thermal energy storage/release capacity of about 145–240 J/g. Therefore, encapsulated paraffin wax is a good candidate for solar-energy storage material. Rodrigues et al. [251] microencapsulated limonene for textile applications by interfacial polymerisation and characterised them. Accordis (formerly Courtaulds Fibres, in Bradford, UK) developed the technology of in-fibre incorporation of Outlast microcapsules, loading the fibre with 5–10% of microcapsules [155]. The process utilises late injection technology that is also used to produce the antimicrobial fibre Amicor. In this way, the PCM is permanently locked within the fibre, and no change is necessary in subsequent fibre processing (spinning, knitting, dyeing, etc.). The fibre exhibits its normal properties of drape, softness and strength.

2.14.6 Advantages and Disadvantages of Microencapsulation Although there are many advantages in fibres and fabrics that contain microencapsulated PCM, there are a few disadvantages of the process, which are discussed below.

2.14.6.1

Fibres

Advantages • The PCM is permanently embedded within the fibre. • The process parameters during spinning, knitting, dyeing, etc., are not altered for the fibres containing the microcapsules of PCM. • The fabrics produced from the yarn containing the microencapsulated PCM in the fibres show the normal properties of drape, softness, comfort, etc.

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Disadvantages • Very few fibres containing microencapsulated PCM are currently available such as acrylic and viscose. • The fibre properties are affected if there is a very large amount of PCM in the fibre. 2.14.6.2

Fabrics

Advantages • Many companies can use currently available equipment using standard processes for applying the coating containing PCM. • A wide range of PCM concentrations can be applied as coating. • This process is suitable for different types of fabrics such as woven, knitted, non-woven and laminates. • This process is also suitable for fabrics made from different types of fibres and their blends. Disadvantages • Fabric properties such as drape and softness can be affected by the coating. • The durability of washing, dry-cleaning and abrasion resistance is similar to other types of coated fabric, which depends on the type of resin binder and the degree of curing.

2.15 Super Absorbent Materials Super absorbent materials are materials with very high absorbency. For example, the chemical used in a disposable nappy is a synthetic polyacrylamide with a potassium salt base. It is a safe, non-toxic polymer and can hold over 200 times its weight in water. The same chemical can release water slowly over time in horticultural applications.

2.15.1 Applications of Super Absorbent Materials There are many applications of super absorbent materials such as disposable nappies to absorb a large amount of water, helping babies to stay dry for a longer time. It can be also used in buildings to cool them in summer and in clothing to cool the wearer. Clothing containing a water-absorbent material absorbs moisture and assists in reducing body temperature. The water-absorbent material can be applied to a wide variety of clothing articles such as hats, headbands, wristbands, gloves, shirts,

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shorts and pants. Many researchers have applied super absorbent materials in fabric to obtain a cooling effect [252–255]. Bumbarger et al. [256] used super absorbent material to produce a protective multilayered liquid-retaining composite to be used for protective garments, blankets and compressors. Thomas and Bumbarger [257] produced a composite absorbent material which when soaked in a liquid protects a person from extreme heat when the clothing is worn close to the skin. This can also help in controlling body temperature by providing warming or cooling as required. There are many companies such as Cooltek [258] applying super absorbent materials to get a cooling effect when garments are worn. Hydroweave is one of the super absorbents introduced by AquaTex Industries (USA). In Hydroweave, the fabric has a three-layer design consisting of hydrophilic fibres (fibres that attract water) and hydrophobic fibres (fibres that reject water) woven into a fibrous batting core. The batting is sandwiched between a breathable outer shell fabric and a thermally conductive inner lining. When the Hydroweave fabric is wet, the hydrophilic fibres become charged with moisture, and then, the hydrophobic fibres evenly distribute and surround the charged fibres with air, creating an ideal environment for evaporation. Figure 2.18 shows the way the super absorbent materials function. The Hydroweave material absorbs heat when the wearer’s skin is in contact with the Hydroweave fabric and transfers to the outside environment by evaporation of the water in the garment. As there is an even distribution of water-absorbent polymer throughout the batting, the garment provides uniform cooling, and this can last for several hours. This mainly depends upon the degree of garment contact with the skin, climatic conditions, the level of physical activity and the type of outer clothing worn. The cooling effect can be reduced by wearing underclothing that limits the contact of the vest with the wearer’s skin. Apart from the cooling function, Hydroweave provides the benefit of insulating the wearer from heat. Despite the predicted advantages of PCM and water-absorbent materials to cool the body, this investigation found no application of PCM or water-absorbent materials for the thermal regulation of motorcycle helmets. The absence of application to motorcycle helmets and their unique rider/user application in the tropics and high heat climates raises the research question: ‘Can these materials be employed to regulate heat transfer?’

2.16 PCM Salt Hydrate Tan and Fok [259] conducted a conceptual study for the cooling of helmets using salt hydrate PCM within the helmet. PCM materials were placed in a pouch with other components to absorb the heat and which was placed in the helmet by removing a large portion of the impact-absorbing polystyrene. It is acknowledged that this attempts to reduce the temperature inside the helmet and provide cooling for the rider. Though this work provides a potential solution to provide cooling to the wearer of the helmet,

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Fig. 2.18 Functioning of super absorbent materials

this modification weakens the structural integrity of the helmet and does not comply with safety standards. Thus, the safety and protection of the head are substantially reduced. This approach requires a major modification to current helmets to make use of the conceptual ideas. The alterations made to the helmet void the helmet with respect to regulatory requirements, making the use of helmet unacceptable. In addition, this concept study adds many components to the helmet, and as such, it will incur in additional manufacturing cost. The end result of following this concept results in a new helmet design to incorporate the concepts with additional compliance tests that were required to meet the safety standards. Heat transfer phenomenon and cooling of different types of ventilated helmets have been conducted by several researchers [17, 34, 50]. Ellis et al. [260] conducted research on bicycle helmets with a view to improving their performance. To the best of our knowledge, very few of these works have involved the heat stress reduction of motorcycle helmets. The work done by Ellis did not address non-ventilated helmet

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or fully enclosed helmet such as motorcycle helmet. The attempt by Tan and Fok [259] using salt hydrate PCM to cool the rider’s head would lead to the helmet being non-compliant to the regulatory safety standards. Also, in this concept, the amount of PCM required to provide effective cooling was calculated to be approximately 1 kg which would increase the weight of the helmet substantially. This leads to further research to investigate the possibility of using appropriate PCM in smaller amounts and in addition, without altering the helmet structure or compromising the safety standards of the helmet [261]. A review of motorcycle safety standards does not restrict the application of textile substrates or other similar items that could be retrofitted between the scalp and the helmet to provide thermal comfort. This raises the research question of whether these materials can be applied in an effective manner inside the helmet to manage the heat stress. The advantage of such an approach by using textile substrates is to facilitate the use of standards compliant helmets irrespective of the brand and manufacture. The fundamental utility of the textile substrates and their behaviour in such a new application is yet to be explored. This research sets out to establish the parameters that characterise the behaviour of the textile substrates. The outcome of this investigation provides the knowledge necessary to facilitate the design of such a textile substrate to be applied inside the helmet. The progressive developments of these materials in future can be easily incorporated without any difficulties and, in addition, may be applied to helmets in other fields.

2.17 Conclusions This chapter described the needs of motorcycle helmets and various types of helmets in use. Various regulations relating to motorcycle helmets are also described. Components of motorcycle helmets and cooling mechanisms used to reduce the heat stress have also been discussed. The application of phase change materials including their types and mechanism of cooling are also included in this chapter. This chapter is essential for the readers to understand the concept of motorcycle helmets and the mechanisms to cool them.

References 1. R.J. Nairn, Motorcycle Safety Research Literature Review: 1987–1991 (Federal Office of Road Safety, Canberra, 1993) 2. T.C. Chenier, L. Evans, Motorcyclist fatalities and the repeal of mandatory helmet wearing laws. Accid. Analy. Prevention 19, 133–139 (1997) 3. B.L. Bachulis, W. Sangster, G.W. Gorrell, W.B. Long, Patterns of injury in helmeted and non-helmeted motorcyclists. Am. J. Surgery 155, 708–711 (1988) 4. D. Sosin, J. Sacks, P. Holmgren, Head injury: associated deaths from motorcycles crashes. J. Am. Med. Assoc. 264, 2395–2399 (1990)

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5. Australia. Australian Transport Safety Bureau. Road Death Australia: 2005 statistical summary, Australian Transport Safety Bureau, 2006 6. (Online). Available: http://tacsafety.com.au/jsp/content/NavigationController.do?areaID= 12&tierID=1&navID=2B63301D7F0000010080CB01C9E47EBA&navLink=null&pag eID=162. Accessed 15 Mar 2010 7. United States of America, National Safety Council (Accident Facts, National Safety Council, 1972) 8. (Online). Available: http://en.wikipedia.org/wiki/Motorcycle_Helmet. Accessed 15 Mar 2010 9. H. Cairns, Head Injuries in motorcyclists: the importance of the crash helmet. Br. Med. J. 2, 465–483 (1941) 10. H. Cairns, A.H.S. Holbourn, Head injuries in motorcyclists with special reference to crash helmets. Br. Med. J. 4, 592–598 (1943) 11. H. Cairns, Crash helmets. British Med J. 2, 322–324 (1946) 12. (Online). Available: http://www.msf-usa.org/downloads/helmet_CSI.pdf. Accessed 20 Feb 2009 13. C.F. Lombard, W.A. Smith, H.P. Roth, S. Rosenfeld, Voluntary tolerance of the human to acceleration of the head. J. Aviat. Med. 22, 109–116 (1951) 14. (Online). Available: http://www.motorcycle-accessories-wiseguy.com/motorcycle-helmet. html. Accessed 23 Feb 2009 15. E.M. Hickling, Factors affecting the acceptability of head protection at work. J. Occup. Accid. 8, 193–206 (1986) 16. K.C. Paarson (ed.), Human Thermal Environments (Taylor and Francis, 1993) 17. ASHRAE Handbook, American Society of Heating, Refrigeration and Air-Conditioning Engineers Incorporation, Atlanta, 1993, pp. 8.1–8.29 18. P.K. Pinnoji, P. Mahajan, Impact analysis of helmets for improved ventilation with deformable head model, in IRCOBI Conference (2006), pp. 159–170 19. Fresh Air System Technologies, Helmets conversion and air flow improvement. (Online). Available: http://www.fastraceproducts.com/fresh_air_systems_helmets_conver sions.htm. Accessed 15 Mar 2010 20. (Online). Available: http://jeff.dean.home.att.net/swisher.htm. Accessed 15 Mar 2010 21. (Online). Available: http://www.motorcyclecruiser.com/accessoriesandgear/flip_face_hel met_comparison/index.html. Accessed 15 Mar 2010 22. R.G. Attwel, K. Glase, M. McFadden, Bicycle helmet efficacy: a meta-analysis. J. Accid. Analy. Prevention 33, 345–352 (2001) 23. B. Walker, Head Protection Evaluations, Heads Up Cycle Mag., pp. 42–45, 2005 24. (Online). Available: http://cdr.stanford.edu/html/me210/Projects/93–94/Specialised/home. html. Accessed 15 Mar 2010 25. P.A. Brühwiler, M. Buyan, R. Huber, C.P. Bogerd, J. Sznitman, S.F. Graf, T. Rösgen, Heat transfer variations of bicycle helmets. J. Sports Sc. 24, 999–1011 (2006) 26. C.V. Gisolfi, D.P. Rphlf, S.N. Navarude, C.L. Hayes, S.A. Sayeed, Effects of wearing a helmet on thermal balance while cycling in the heat (I). Physician Sports Medicine 16, 139–142 (1988) 27. S. Quanten, J.M. Aerts, A. Van Brecht, J. Welkenhuyzen, D. Nuyttens, D. Berckmans, Dynamic spatial three dimensional comfort analysis underneath of a cyclist helmet, in 9th International Conference on Air Distribution in Rooms (2004), pp. 378–380 28. J.G. Wood, An investigation of the relative thermal comfort of bicycle helmets,” B.Sc. thesis, University of Southampton, Southampton, UK 29. K. Spolander, Cykelhjälmars komfort och hanterbarhet (National Road and Traffic Research Institute, Linköping, Sweden, 1982) 30. C.V. Gisolfi, D.P. Rohlf, S.N. Navarude, C.L. Hayes, S.A. Sayeed, Effects of wearing a helmet on thermal balance while cycling in the heat (II). Physician Sports Medicine 16, 145–146 (1988) 31. R. Stern, Thermoregulatory responses of wearing a cycle helmet, 1999. (Online). Available: http://www.endureplus.com/helmets.htm. Accessed 10 Mar 2009

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224. D.P. Colvin, J.C. Mulligan, Enhanced heat transfer and storage materials for strategic defense systems (Final Rep, SDIO Phase I, 1988) 225. X.-X. Zhang, X.-M. Tao, K.-L. Yick, X.-C. Wang, Structure and thermal stability of microencapsulated phase-change materials. Colloid Polym. Sc. 282, 330–336 (2004) 226. D.C. Hittle, T.L. Andre, ASHRAE Trans. 107, 175 (2001) 227. F.J. Micale, Electrophoretic display particles and a process for their preparation, European Patent 0,238,035, 1987 228. N. Sugiyama, K. Funato, H. Nagase, S. Yamamoto, S. Miyamori, Process for producing pressure-fixable toners, European Patent 0,133,353, 1985 229. F.J. Micale, Pigment encapsulated latex aqueous colorant dispersions, U.S. Patent 4,665,107, 12 May 1987 230. M.N.A. Hawlader, M.S. Uddin, H.J. Zhu, Preparation and evaluation of a novel solar storage material: microencapsulated paraffin. Intl. J. Solar Energy 22, 227–238 (2000) 231. H. Vollmann, H. Herrmann, Liquid developer and charge control substance suitable therefore, U.S. Patent 4,594,305, 10 June 1986 232. E.E. Beck, Essential oil composition and method of preparing the same, U.S. Patent 3,704,137, 28 Nov 1972 233. W.D. Jayne, Microencapsulation: processes and applications, in ed. by J.E. Vandegaer (Plenum Press, New York, 1974) 234. R.H. Sudekum, Microencapsulation, in ed. by J.R. Nixon (Marcel Dekker Inc, New York, 1976) 235. H.S. Hall, K.D. Lillie, R.E. Pondell, Controlled Release Technologies: Methods, Theory and Applications, vol. 2 (CRC Press, Boca Raton, 1980) 236. G. Langer, G. Kamate, Encapsulation of liquid and solid aerosol particles to form dry powders. J. Colloid Interface Sc. 29, 450–455 (1969) 237. J.T. Goodwin, G.R. Somerville, Micro-encapsulation by physical methods. Chem. Technol. 4, 623–626 (1974) 238. F. Lim, R.D. Moss, Micro-encapsulation of living cells and tissue. J. Pharm. Sc. 70, 351–354 (1981) 239. H. Yoshizawa, Trends in micro-encapsulation research. KONA 22, 23–30 (2004) 240. C.B. Schaab, Impregnating nonwoven fabrics with microencapsulated components. Nonwovens Ind. 16, 14–19 (1985) 241. A.K. Aggarwal, Microencapsulation processes and applications in textile processing. Colourage 45, 15–24 (1998) 242. Y. Shin, D.-I. Yoo, K. Son, Development of thermoregulating textile materials with microencapsulated phase change materials (PCM). II: preparation and application of PCM microcapsules. J. Appl. Polym. Sc. 96, 2005–2010 (2005) 243. D.P. Colvin, N.C. Cary, D.K. Cartwright, Microclimate environmental control on vegetation and seeds employing microencapsulated water and phase change materials and method, U.S. Patent 6,057,266, 2 May 2000 244. R. Yang, H. Xu, Y. Zhang, Solar Energy Mater. Solar Cells 80, 405 (2003) 245. P.M.M. Schrooyen, R. van der Meer, C.G. De Kruif, Microencapsulation: its application in nutrition. Proc. Nutr. Soc. 60, 475–479 (2001) 246. F. Shahidi, X.-Q. Han, Encapsulation of food ingredients. Crit. Rev. Food Sci. Nutr. 33, 501–547 (1993) 247. M. Tanaka, K. Yasui, Y. Seki, Water-borne dispersions of microencapsulated pigments, in Proceedings of IS&Ts NIP 15: International Conference on Digital Printing Technologies (1999), pp. 82–84 248. N. Hiroto, M. Toshiyuki, Y. Masahiro, K. Hidehiko, Microencapsulated pigment, production process thereof, aqueous dispersion and ink jet recording ink, U.S. Patent 7,074,843, 11 July 2006 249. K. Hong, S. Park, Melamine resin microcapsules containing fragrant oil: synthesis and characterization. Mater. Chem. Phys. 58, 128–131 (1999)

References

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250. M.N.A. Hawlader, M.S. Uddin, M.M. Khin, Microencapsulated PCM thermal energy storage system. Appl. Energy 74, 192–202 (2003) 251. S.N. Rodrigues, I. Fernandes, I.M. Martins, V.G. Mata, F. Barreiro, A.E. Rodrigues, Microencapsulation of limonene for textile application. Ind. Engg. Chem. Res. 47, 4142–4147 (2008) 252. H. Tanaka, S. Ideguchi, Y. Hasegawa, Water absorbent material, U.S. Patent 6,653,399, 25 Nov 2003 253. D.M. Jackson, B.J. Matthews, High wicking liquid absorbent composite, U.S. Patent 5,350,370, 27 Sep 1994 254. B.A. Messner, W.-N. Hsu, M.C. Joy, Superabsorbent polymer fibres having improved absorption characteristics, U.S. Patent 6,482,344, 19 Nov 2002 255. P.A. Graef, F.B. Howard, Reticulated absorbent composite, U.S. Patent 6,969,781, 29 Nov 2005 256. S.A. Bumbarger, T.H. Bumbarger, Protective multi-layer liquid retaining composite,U.S. Patent 6,371,977, 16 Apr 2002 257. T.H. Bumbarger, Protective multi-layer liquid retaining composite,U. S. patent 5,885,912, 23 Mar 1999 258. (Online), Available: http://www.heatrelief.com/how_cooltek_provides_heat_relief.htm. Accessed 17 Mar 2009 259. F.L. Tan, S.C. Fok, Cooling of helmet with phase change material. Appl. Therm. Eng. 26, 2067–2072 (2006) 260. A. Ellis, Development of fundamental theory and techniques for the design and Optimization of bicycle helmet ventilation, Ph.D. Thesis, RMIT University, Melbourne, Victoria, Australia, 2003 261. K. Sinnappoo, R. Nayak, L. Thompson, R. Padhye, Application of sustainable phase change materials in motorcycle helmet for heat-stress reduction. J. Text.E Inst, 1–9. https://doi.org/ 10.1080/00405000.2020.1715606

Chapter 3

Experimental Techniques

3.1 Materials, Experimental Design, Methodology and Methods In this chapter, the materials used, experimental design, methodology and methods employed are described. A critical component of the motorcycle helmet ventilation and cooling development process is by the verification of the material design in a wind tunnel. The wind tunnel techniques used to test the effectiveness of helmet ventilation in cooling are discussed. The paraffinic PCM and PWAT materials used for cooling the helmets have also been illustrated. The use of heated head forms to objectively quantify the difference between different types of materials for cooling is explained. The head form is made of cast aluminium. This is the main method currently used by helmet manufacturers to test the ventilation of helmets [1]. This technique provides a tool for objective and quantitative comparison of the helmets, while wearer trials by using human beings are subjective and qualitative.

3.2 Materials 3.2.1 Fabrics Various fabric laminates and foams coated with paraffinic PCM were collected from Outlast Technologies (USA) and PWAT materials from AquaTex Industries (USA). The PCM used in the study fall under the paraffin classification, with the carbon chain containing 18–20 carbon atoms (i.e. octadecane to eikosane). The melting point of PCM ranges from 28 to 33 °C and the crystallisation point ranges from 22 to 30 °C. The specifications of the fabrics used are given in Table 3.1.

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7_3

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Table 3.1 Specifications of materials used in current study Name of material

Style no.

Active constituent

Weight (g/m2 )

Functional layer

PCM nonwoven

S7465

Paraffinic PCM

169

PCM in acrylic matrix coating

PCM foam

S6584

Paraffinic PCM

327

All-season coating

PCM fabric

S5545

Paraffinic PCM

307

All-season coating

PCM composite

N/A

Paraffinic PCM

634

All-season coating

Polymeric water absorbent textile (PWAT) material

N/A

Water absorbent polymer

364

Fibrous batting

The scanning electron microscopic (SEM) images of the fabrics and foams used for the study are discussed in the following section and are illustrated in Fig. 3.1a–e. An additional composite material was prepared by stitching the PCM foam and PCM fabric laminates around the borders and gluing them together around the edges. This composite was then used in the experiments to observe any variations in performance in relation to the above range of single PCM materials.

3.2.2 Equipment Used for Experiments and Analysis of Results The following equipment was used to perform the experiments in the current study; • • • • • • • • • • • • • •

METTLER PM4800 DELTARANGE measuring balance SARTORIUS BP100 measuring balance ERNST-BENZ Laboratory padding mangle Differential scanning calorimetry: Perkin-Elmer Pyris 1 Field Emission Scanning Electron Microscopy (FESEM Philips XL-30) Closed circuit wind tunnel Water heater system Water pump Datataker (DT800) software and associated equipment Aluminium head as heated head form Thermocouples for measuring the temperature Anemometer Motorcycle helmets: THH helmets Temperature controller.

3.2 Materials

65

(a)

(b)

(c)

(d)

(e) Fig. 3.1 SEM images of the cross sections: a PCM nonwoven, b PCM foam, c PCM fabric, d PCM composite and e PWAT fabric

3.3 Motorcycle Helmets The visor-open and visor-closed motorcycle helmets used in the current study were collected from the Tong Ho Hsing (THH) Helmet Company and are shown in Fig. 3.2a, b respectively. The visor-open helmet was only used for initial trials and

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(a)

(b)

Fig. 3.2 THH motorcycle helmets: a visor open and b visor closed

the final experiments were performed using the visor-closed helmet. The motorcycle helmet was chosen to properly fit the aluminium head form with the textile liner.

3.4 Experimental Design The experimental design was primarily based on the visor-closed motorcycle helmet. The experimental investigation was conducted by using two different materials, namely, paraffinic PCM and PWAT materials. The technologies used in the materials are different. Both materials were investigated for their performance in the reduction of heat-stress in the head of a motorcycle rider. To simulate on-road conditions, a closed-circuit wind tunnel was used to introduce different wind speeds of 0, 15, 35, 55 and 75 kph. The low velocities of 0, 15 and 35 kph were used as preliminary tests and the tests with higher velocities of 55 and 75 kph were performed to simulate the velocities of city and open-road riding conditions. PCM were tested at a temperature that was 10 °C above the ambient temperature (i.e. ambient +10 °C) which allowed the phase change temperature of the materials to be reached. The PWAT materials were tested at a temperature that was 20 °C above the ambient temperature (i.e. ambient +20 °C) that facilitated the evaporation of the water held in the fabric and the water absorbent polymer. The experimental design for the current study is illustrated in Fig. 3.3.

3.5 Methodology The methodology for the present study is summarised in Table 3.2. The current investigation was carried out using three paraffinic PCM, one composite PCM material

3.5 Methodology

67 Visor-closed helmet

Liner material PCM fabric

Liner material PCM foam

Liner material PCM nonwoven

Liner material PCM comp. (fabric + foam)

Liner material PWAT material

Closed circuit wind tunnel Ambient +200C

Ambient +100C Road velocity test

Low velocity tests* ● 0 kph ● 15 kph ● 35 kph

● 55 kph ● 75 kph

● 75 kph

Evaluation of results *Preliminary tests to frame the base parameters for the research PCM = Phase Change Material, PWAT = Polymeric Water Absorbent Textile

Fig. 3.3 Experimental design

and a PWAT material. The experiments were performed by selecting five different wind velocities and two different temperature ranges. Each test was performed for a specific period depending on the type of materials tested. A design for the textile liner was developed and a pattern was cut for the test samples (using computer-aided design) as discussed in Sect. 3.6.2.1 The liner dimensions were selected so that it covered the aluminum head form in the same area covered by the motorcycle helmet. Based on the above design, the experimental samples were cut to the same dimensions. The experiments were conducted with all the samples and each sample was tested three times. The results of each sample were averaged and analysed.

3.6 Methods 3.6.1 Wind Tunnel A wind tunnel was used to simulate conditions while riding a motorcycle with a helmet for testing the PCM and PWAT materials. Figure 3.4 gives a schematic diagram of the RMIT industrial wind tunnel. The wind tunnel is an octagonal chamber with dimensions of 1320 mm in width by 1070 mm in height and 2100 mm in length [2]. The tunnel has a closed-circuit design and is fitted with a 134 hp DC motor. A fan consisting of six blades is driven by the DC motor. It is a subsonic tunnel, where the air velocities can be varied from 1 ms−1 up to 45 ms−1 in the test chamber. The air entering the test chamber was conditioned by a honeycomb and an anti-turbulence

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Table 3.2 Methodology adopted for the study Methodology

Method

Outcome

• From background research

• All test parameters are defined • Test variables are controlled

Planning of experiment • Selection of the type of helmets • Selection of application materials • Setting process variables

Design of hood and experimental samples • Identify design parameters and materials • Select different materials

• Design and production of • Hood and fabric parameters hood and liner from selected are defined and produced • Samples from different design parameters fabrics as liners inside the helmet are evaluated

Testing of experimental samples Materials evaluation type of PCM • Foam • Fabric • Nonwoven Type of water absorbent material • PWAT material

• Closed circuit wind tunnel equipment • Thermocouples • Data Taker (DT800) incorporated with the wind tunnel • Differential Scanning Calorimetry (DSC)

• Collection of data of temperature drops (cooling curves) at various speeds for different materials

• Data processing software • Spreadsheets

• Graphical representation and comparative results within and between different materials

Results analysis • Collate results of control samples • Collate results of tested samples • Analysis of results • Identify key trends

screen. A contraction ratio of 4:1 was used to condition the airflow entering the test section. The wind tunnel consists of various sections such as the expansion, working section, contraction, settling chamber and fan, as shown in Fig. 3.4 [2]. The wind tunnel is situated on two levels in the laboratory. The main motor and ancillary equipment are on the lower level and the experimental set up and test chamber are on the upper level.

3.6.2 Heated Head Form For objective evaluation of the effectiveness of helmet ventilation, a heated aluminium head form (Fig. 3.5) was used in the wind tunnel. The hollow aluminium head used in this investigation was designed by Ellis [3]. The aluminium head form

3.6 Methods

69

Fig. 3.4 Schematic diagram of wind tunnel at RMIT Aerospace Engineering Fig. 3.5 Aluminium head form on stand with attachment

Aluminium head form

Metal stand

Plastic cover

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3 Experimental Techniques

consists of different components such as a hollow aluminium head with stand, a heating system and a temperature measurement system. Aluminium was used to produce the head form for the experiments since it is a light material and has higher thermal conductivity. The head form is symmetrical in relation to the centre line from the nose to the middle of the head and the back of the neck. The thermal conductivity (k) of cast aluminium is approximately 170 W/m.K [4]. The size of the aluminium head form together with the textile liner was appropriate to give a proper fit with a size E helmet. The aluminium head form was hollow, having a wall thickness of 6–10 mm. The head form was hollow in order to pump water inside to heat it. The aluminium head form was mounted to the floor of the wind tunnel by using a metal stand, which was then covered by a plastic sheet to obtain a streamline flow as shown in Fig. 3.5. Water was heated and circulated into the hollow aluminium head form to heat it. The method of heating by pumping hot water was selected because it would produce a more uniform heat distribution over the aluminium head surface than other, less uniform, heating methods. The heat supplied to the aluminium head form increase the temperature above the ambient wind tunnel temperature. Figure 3.6 illustrates the set up for the inlet and outlet for hot water circulation to the aluminium head form. A small electric pump was used to circulate the hot water. The water entered the head form via a filter and then a flexible hose and exited through the outlet hose into the hot water system. The heating and pumping of water was turned off after the Fig. 3.6 Hot water inlet and outlet tubes assembly attached to aluminium head form

Water inlet Water outlet

3.6 Methods

71

Temperature controller Water heating system

Water pump

Fig. 3.7 Assembly of water heating system, water pump and temperature controller

aluminium head reached a prescribed temperature above that of the ambient. Then the air was blown at a constant velocity over the aluminium head in the wind tunnel to cool it. The temperature of the aluminium head form initially dropped by a large amount and then the temperature drop was gradual until a steady state was reached. The higher the drop in the average temperature of the aluminium head form, the better ventilated and cooler the helmet will be. Figure 3.7 shows the assembly of the temperature controller and water heating system together with the electric pump. T-type thermocouples were used to measure the temperatures on the surface of the aluminium head form. Electrical tape was used to attach the thermocouples onto the aluminium head form. All thermocouple wires were collected at the back of the head and neck and then passed through the hollow pipe holding the aluminium head form and then attached to the Datataker (DT800) as shown in Fig. 3.8. This method of attachment prevents any upstream airflow onto the aluminium head form. Twelve thermocouples were attached to the aluminium head form, as indicated in Table 3.3. The thermocouples were distributed over different locations on the aluminium head form, as shown in Fig. 3.9. The mean of all the thermocouple readings was considered to be the temperature of the aluminium head form. Temperature measurements were displayed to two decimal places. Thermocouples 1–7 were attached on the centre line of the head, along with 8–12 on both sides, in the front and back of the ear and the lower side of the head.

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Fig. 3.8 Experimental set–up with Datataker (DT800)

Table 3.3 Different positions of thermocouples on aluminum head form

3.6.2.1

Thermocouples

Position

1

Nose

2

Forehead

3

Front-lobal

4

Middle of head

5

Back-lobal

6

Back of head

7

Back of neck

8

Back of lower head

9

Front of ear

10

Above ear

11

Back of ear

12

Ambient

Textile Liner

The textile liner (as shown in Fig. 3.10) used in the current study consisted of a hood together with the replaceable material inserts, which were either paraffinic PCM or PWAT material. This liner was used between the helmet and the aluminium head form depending on the type of the experiment.

3.6 Methods Fig. 3.9 Positions of thermocouples on aluminium head form

Fig. 3.10 Textile liner

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3 Experimental Techniques

3.6.3 Wind Tunnel Process Once the heated aluminum head form was prepared, the testing was conducted. Many different helmet testing procedures were experimented with by varying the test conditions until the optimum and final procedure was selected for comparing the effectiveness of helmet ventilation. In the selected test method, the aluminum head form was heated by circulating water for each test until the average thermocouple temperature was 10 °C or 20 °C above the temperature of the air in the tunnel. Then the heating and pumping of water was stopped and a helmet together with textile liner was placed on the aluminum head form. The velocity of the wind in the tunnel was then gradually increased until the required speed was achieved. After the required speed was reached, cooling began and the thermocouple temperatures were recorded. The temperature was recorded by the Datataker (DT800) which recorded all the temperatures from the 12 thermocouples, as shown in Fig. 3.11. These results were then downloaded for analysis. The data for each of the experiments were evaluated by spreadsheets and graphical representations were obtained, from which the drop-in temperatures over the duration of the experiments was evaluated. The results were analysed by taking the difference between the materials on their performance criteria, wind speed and drop in temperature of the aluminum head form. The fitting of the helmet to a head form played a crucial role in maintaining

Fig. 3.11 Datataker (DT800)

3.6 Methods

75

the temperature. The temperature was recorded using the Datataker continuously at 10 sec intervals for the duration of the experiments.

3.6.4 Data Analysis Method All the experiments were conducted for 60 min and the data recorded by the Datataker were converted to Microsoft Excel worksheets for graphical representations. These graphical representations were termed cooling curves. The data from each of the thermocouples (1–11) were averaged to get the mean temperature. Ambient temperature was recorded by thermocouple number 12, as indicated in Table 3.3. The ambient was subtracted from the mean (i.e. mean–ambient) and was tabulated for PWAT and PCM. Identical experiments were performed without any material (PWAT or PCM) inside the helmet and these experiments were termed the Control. For all the materials (i.e. PWAT and PCM) at different speeds, the drops in temperature were calculated by subtracting the values of (mean–ambient) of the control experiments from the values of (mean–ambient) of the materials (PWAT or PCM). This new value was termed the DIT (drop in temperature). The maximum value in every series of DIT was referred to as the MDIT (maximum drop in temperature).

3.7 Differential Scanning Calorimetry Differential Scanning Calorimetry (DSC) comprises an insulated chamber containing two individual calorimeters, namely, sample and reference calorimeters. Each calorimeter accommodates a platinum resistance sensor (thermometer) and a resistance heater. When an exothermic or endothermic change occurs in a sample, power is continuously and automatically removed or applied to one or both of the calorimeters to compensate for the change to either the sample or reference. Hence, the temperature of both calorimeters is identical and the system is in equilibrium. A Perkin-Elmer Pyris 1 DSC instrument was incorporated in the current study, utilising an ice-water slurry (2–5 °C) as a source of coolant. The instrument’s heat flow sensitivity was 0.2 μW, with a temperature precision of ±0.01 °C. The lower stable temperature for this system was 20 °C. The enclosed chamber was purged with pure nitrogen (99.99%) at a flow rate of 20 mL min−1 . During thermal scanning, a continuous nitrogen flow in the DSC sample chamber was maintained to ensure minimal sample degradation. High purity standard indium (T m = 156.60 °C) and zinc (T m = 419.47 °C) were used to calibrate the instruments for temperature and enthalpy 28.45 °C and 108.37 Jg−1 respectively. The calibration was periodically checked and maintained. Pyris™ software (Version 3.81) for Windows was used in conjunction with the Perkin-Elmer instrument for analysis of the results. The DSC experiments for the PCM samples used in the research, the endothermic approach was taken with a heating rate of 2 °C per minute.

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3.7.1 DSC Measurement Samples of 2–4 mg were weighed using a Perkin-Elmer microbalance (model AD2Z). The specimens were encapsulated in standard hermetically sealed aluminum pans of 30 μL volume. For a typical DSC experiment, a sample and a reference pan were placed in the DSC cell holders and were covered with platinum covers. For crystallisation and melting experiments, the sample was heated to the upper extreme temperature allocated and held isothermally until stable heat flow was observed. Once a stable temperature was achieved, the sample was cooled from a melt at a controlled rate to a lower temperature limit, usually 20 °C. Then it was followed by a heating scan to a temperature beyond the melting temperature. A schematic diagram of the type of graph from the DSC experiments is shown in Fig. 3.12. A baseline was obtained in a similar manner and used for specific heat calculation. The measurement was recorded and analysed to determine the properties of the polymer. Typically, the peak temperature obtained from such experiments for melting and crystallisation were denoted T m and T c respectively. The intersection of the extrapolated baseline before the transition and the linear portion of the curve approaching the baseline were used to calculate the onset of this transition. The enthalpy or heat of fusion (H c ) was proportional to the area of the peak, which has been referenced to a standard such as indium [5].

Fig. 3.12 DSC graph

3.8 Theoretical Basis

77

3.8 Theoretical Basis Fanger [6] developed quantitative relations between comfortable skin temperature and desired sweat rate and metabolic activity by performing detailed experiments. He established three conditions for the thermal equilibrium of the body. The first condition is that the body must be in thermal equilibrium so that the heat lost and heat gained must be equal. The second condition for thermal comfort is that the mean skin temperature must be lower when the metabolic rate is higher, and the third condition is that there is a preferred rate of sweating for comfort that depends on metabolic activity. He further derived equations that establish the conditions for thermal equilibrium. The equations are: H − E is − E sw − E res − Cres = R + C

(3.1)

where, H = metabolic rate, E is = evaporative heat loss by diffusion through the skin, E sw = heat loss due to regulatory sweating, E res = latent respiration heat loss, C res = dry respiration heat loss, R = heat loss by radiation and C = heat loss by convection. E sw = 0.36(H − 58)

(3.2)

where, E sw = sweat rate and H = metabolic activity. Tsk = 35.7 − 0.0275H

(3.3)

where, T sk = mean skin temperature and H = metabolic activity. The above equations for thermal comfort were based on the assumption that the subject was either at optimum thermal comfort level or not. Fanger [6] developed another equation for the condition when the above equations had failed to measure an uncomfortable situation. He also developed an index known as the Predicted Mean Vote (PMV) which was based on the mean vote of the American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) seven-point scale [7]. The equation that was developed is: Y = 4 + (0.303e−0.036M + 0.0275)L

(3.4)

where, Y = thermal sensation vote (running from 1 to 7), L (W/m2 ) = thermal load and M (W/m2 ) = metabolic free energy production. Though the PMV equations, similar to the comfort equations, give good results for sedentary activity levels and light clothing, they do not hold good for higher activity levels and various clothing factors. Fanger’s [6] main work was focused on the comfort of people in the workplace or an indoor climate, but not for high activity levels. Several revised and updated equations were also derived such as the overall energy equation, energy storage equation and metabolism equation. The

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overall energy equation was derived by the standard ASHRAE to model human thermoregulation and is given below: S = H −W ±K ±C ± R− E

(3.5)

where, S = rate of energy storage in the body, H = rate of internal energy production, W = mechanical work produced, K = rate of energy loss due to conduction, C = heat lost due to convection, R = heat lost to the environment by radiation and E = heat lost due to evaporation. Each of the individual terms is elaborated further in the following section. The amount of heat stored or dissipated by a person is related to core body temperature. The overall amount of energy retained by a person (S in joules) can be related to the mass (m), specific heat at constant pressure (C p ) and the core body temperature (T c ) of the person. The equation is given below: S = 1000 mc p (Tc )

(3.6)

The energy required for work is generated by the body from food by the process of metabolism. The rate of metabolism varies from person to person and can be explained by the sum of the exothermic chemical reactions within the body. The metabolic energy produced by the body can be calculated by using the equation derived by Thornton and Nair [8] as given below: H = 348VCO2

(3.7)

where H = metabolic energy produced and Vco2 = rate of carbon dioxide exhaled. The maximum amount of metabolic energy converted to mechanical work (W ) is approximately 20%. The importance of conduction in the heat transfer of the body can be neglected compared to the other modes, as the body rarely comes in contact with good thermal conductors with a high temperature difference. Thornton and Nair’s [8] conduction equation related to humans is given below: K = ( f cl Ad /0.155)((v/Rs ) + (ψ/(Icl + Rs ))(Tsk − Ta ))

(3.8)

where, K = thermal conductivity, f cl = ratio of surface area of the clothed body to the nude body, Ad = DuBois body area, v = decimal fraction of unclothed body area exposed to conduction, Rs = thermal resistance of the supporting object (= L/k), ψ = decimal fraction of clothed body area exposed to conduction, I cl = unit of overall thermal resistance in Clo(m2 Khr/kcal), T sk = temperature of the skin and T a = ambient temperature. The convection equation derived by Thornton and Nair [8] for the total convective heat loss is given below:   C = 0.0014(348VCO2 )(307 − Ta ) + h c f cl [ζ(Tsk − Ta ) + ξ(Tcl − Ta )] Ad (3.9)

3.8 Theoretical Basis

79

All the variables of the equation have been explained previously except for hc , which is the convective coefficient [9]. Radiation depends on the characteristics of the surfaces i.e. the emissivity and reflectivity. Surfaces with high reflectivity absorb little heat and objects with high emissivity will absorb large amounts of heat by radiation. The human body can be considered as a black body over most of the thermal spectrum. Thornton and Nair [8] described the total heat loss from a human body by the following equation: R = σ f eff f cl Ad {εsk ζ(Tsk4 − Ta4 ) + εcl ξ(Tcl4 − Ta4 )}

(3.10)

where, σ = Stefan-Boltzmann constant (5.67 × 10−8 W/m2 K4 ), f eff gives a more accurate result for the radiant heat transfer with the environment by adjusting the DuBois body area, εsk = emissivity of skin (normally 0.98 approx), ζ = proportion of the body that is unclothed, Ad = DuBois Body area, T sk = temperature of skin, T a = temperature of surroundings, εcl = emissivity of clothing, T cl = temperature of the outside surface of the clothing and ξ = decimal fraction of the clothed body exposed to radiation. The total evaporative energy loss from Thornton and Nair [8] is given below: E = 0.80 Ad Vco2 (10aTc +b − 10aTdp +b ) + (0.06 + 0.94ω)(2.2) · h c (ξ f pcl + ζ ) Ad (10aTsk +b − 10aTdp +b )

(3.11)

The new terms in the above equation are ω = decimal proportion of the body that is wet from perspiration, a and b are the Cox chart curve fit coefficients for vapour pressure and for the purposes of the case study were taken to be a = 0.014371 and b = –3.11244. In many of the above equations, the body area Ad has been used which is known as the DuBois area that is given below: Ad = 0.203w 0.425 h 0.725

(3.12)

where w = mass of the body in kilograms and h = height in metres. For additional clothing an adjusted body area calculation would need to be performed.

3.9 Conclusions This chapter described the types of motorcycle helmets and various textile materials used for the research. This chapter also described the characterization techniques used to investigate the properties and effective cooling achieved by applying the

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3 Experimental Techniques

PCM. Research methodology and experimental design are also discussed in this chapter. The working of wind tunnel and data collection techniques are discussed, which will help the readers to completely understand the experimental setup.

References 1. R. Swart, The History of Bicycle Helmets (1999). Available: http://www.helmets.org/webdocs/ history.htm. Accessed March 15, 2010 2. J. Creazzo, Interaction Between a Non-embedded Longitudinal Vortex and Turbulent Boundary Layer Under the Influence of Stream Wise Pressure Gradient, PhD Dissertation (RMIT University, Melbourne, Victoria, Australia, 1999) 3. Ellis, Development of Fundamental Theory and Techniques for the Design and Optimization of Bicycle Helmet Ventilation. PhD Thesis. RMIT University, Melbourne, Victoria, Australia (2003) 4. F.P. Incropera, D.P. De Witt, Fundamentals of Heat and Mass Transfer, 3rd edn. (Wiley, New York, 1990) 5. E. Gmelin, S.M. Sarge, Calibration of differential scanning calorimeters. Pure Appl. Chem. 67, 1789–1800 (1995) 6. P.O. Fanger, Thermal Comfort: Analysis and Applications in Environmental Engineering (Mcgraw Hill, New York, 1972) 7. ASHRAE Handbook: American Society of Heating, Refrigeration and Air-Conditioning Engineers Incorporation, Atlanta, pp. 8.1–8.29 (1993) 8. S.B. Thornton, S.S. Nair, Paramedic studies of human thermal mechanisms and measurements. IEEE Trans. Biomed. Eng 47(4) (April, 2000) 9. K. Sinnappoo, R. Nayak, L. Thompson, R. Padhye, Application of sustainable phase change materials in motorcycle helmet for heat-stress reduction. J. Text.E Inst, 1–9. https://doi.org/10. 1080/00405000.2020.1715606

Chapter 4

Results and Discussion

The surface characteristics of all the materials used in the experiments were obtained using scanning electron microscopy (SEM-Philips XL 30). Differential scanning calorimetry (DSC) was used for the phase change materials (PCM) to obtain the latent heat of fusion and the melting point of the individual paraffinic PCM. The cooling achieved by the application of various polymeric water-absorbent textile (PWAT) materials and paraffinic PCM is discussed. In addition, mathematical equations were obtained in the case of PWAT material for the drop in temperatures and heat absorption in relation to speed utilising regression analysis. Also, a mathematical equation was obtained in the case of PCM materials for the heat absorption by utilising the DSC software.

4.1 SEM Images of the Samples 4.1.1 Polymeric Water-Absorbent Textile Materials The cross section and the surface morphology as examined by utilising the SEM of the three-layer PWAT material are shown in Figs. 4.1, 4.2, 4.3 and 4.4. Figure 4.1 shows the cross section of the PWAT material as shown by the SEM. The PWAT material consists of the breathable outer shell (a); the intermediate layer of super-absorbent non-woven batting (b), consisting of hydrophilic fibres (fibres that attract water) and hydrophobic fibres (fibres that reject water) woven into a fibrous batting core; and the bottom layer of fabric (c), consisting of thermal conductive lining (1) on one side of it and a high moisture vapour transmission lining (2) on the other side. The hydrophilic fibres of the PWAT material become charged with moisture when water is added and the hydrophobic fibres evenly distribute and surround the charged © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7_4

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4 Results and Discussion

Heat transmission (1) Thermal conductive inner lining (a) Breathable outer shell – top layer (c) Bottom layer

(2) High moisture vapour transmission lining

82

(b)Super absorbent nonwoven batting (intermediate layer)

Fig. 4.1 SEM image of PWAT material (cross section)

Fig. 4.2 SEM image of breathable outer shell (top view of PWAT material)

fibres with air, creating an ideal environment for evaporation. The PWAT material absorbs heat when the wearer’s head is in contact with it. As there is an even distribution of water-absorbent polymer throughout the batting, the PWAT material provides uniform cooling. The SEM image of the breathable outer shell (top layer) of the PWAT material is shown in Fig. 4.2. The above figure shows the top view of PWAT material, which is a plain woven fabric.

4.1 SEM Images of the Samples

83

Fig. 4.3 SEM image of super-absorbent non-woven batting (intermediate layer of

Fig. 4.4 SEM image of high moisture vapour transmission lining (bottom view of PWAT material)

The SEM image of the super-absorbent intermediate layer of the PWAT material is shown in Fig. 4.3. In the intermediate layer of PWAT material, the hydrophilic and the hydrophobic fibres are randomly intermingled in the fibrous batting. Figure 4.4 shows the SEM image of the bottom layer of PWAT material. It was observed from the figure that the bottom layer is also a plain-woven fabric like the top

84

4 Results and Discussion

layer and it consists of a thermal conductive lining on one side and a high moisture vapour transmission lining on the other side.

4.1.2 Paraffinic Phase Change Material The SEM images of the cross section and the surface morphology of the PCM materials (i.e. PCM non-woven, PCM foam, PCM fabric and the PCM composite) are shown in Fig. 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15 and 4.16.

4.1.2.1

PCM-Coated Non-woven Material

The cross section of the PCM-coated non-woven material as obtained by the SEM is shown in Fig. 4.5. The PCM microcapsules were predominantly shown on the top of the non-woven layer. The cross section also shows the random distribution of the fibres in the non-woven structure. Figure 4.6 shows the SEM image (front view) of the PCM-coated non-woven material. The PCM microcapsules were distinctly observed in clusters on the surface of the non-woven material. Figure 4.7 shows the SEM image (back view) of the PCM-coated non-woven material. The PCM microcapsules were also observed on the back surface of the non-woven material, as the cross section of the material is very thin.

Clusters of PCM microcapsules on top of the nonwoven material

Fibres in the nonwoven structure

Fig. 4.5 SEM image of PCM-coated non-woven material (cross section)

4.1 SEM Images of the Samples

85

Clusters of PCM microcapsules grafted on the surface of the nonwoven

Fig. 4.6 SEM image of PCM-coated non-woven material (front view)

Clusters of PCM microcapsules grafted on the back surface of the nonwoven material

Fig. 4.7 SEM image of PCM-coated non-woven material (back view)

4.1.2.2

PCM-Coated Foam Material

The cross section of the PCM-coated foam material as obtained by the SEM is shown in Fig. 4.8. The PCM microcapsules are visible on the top of the foam. The cross section also clearly indicates the cell-like structure of the foam.

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4 Results and Discussion

PCM microcapsules on the surface of the foam

The structure of the foam

Fig. 4.8 SEM image of PCM-coated foam material (cross section)

Clusters of PCM microcapsules on the surface of the foam

Fig. 4.9 SEM image of PCM-coated foam material (front view)

The SEM image (front view) of the PCM-coated foam material is shown in Fig. 4.9. The PCM microcapsules are distinctly visible in clusters on the surface of the foam. Figure 4.10 shows the SEM image (back view) of the PCM-coated foam material. The backside of the foam does not show the presence of microcapsules, as the foam cross section is thick and the PCM is only coated on the top surface.

4.1 SEM Images of the Samples

87

Fig. 4.10 SEM image of PCM-coated foam material (back view-non-coated side)

Random distribution of PCM microcapsules on the surface of the coated fabric

Fig. 4.11 SEM image of PCM-coated fabric material (cross section)

4.1.2.3

PCM-Coated Fabric Material

Figure 4.11 shows the cross section of the PCM-coated fabric material as observed by the SEM. It was observed from the figure that the PCM microcapsules are randomly distributed on the surface of the fabric.

88

4 Results and Discussion

Random distribution of PCM microcapsules on the surface of the coated fabric

Fig. 4.12 SEM image of PCM-coated fabric material (front view)

Paraffinic PCM microcapsules

Fig. 4.13 SEM image of PCM-coated fabric material (back view)

The surface morphology as obtained by the SEM (front view) of the PCM-coated fabric material is shown in Fig. 4.12. The PCM microcapsules are distinctly visible on the surface of the fabric as shown in the figure. The surface morphology as obtained by the SEM (back view) of the PCMcoated fabric material is shown in Fig. 4.13. The PCM microcapsules were observed sparingly on the back surface of the fabric, as the cross section is thin.

4.1 SEM Images of the Samples

89

Fabric layer of the composite material

Foam layer of the composite material

Fig. 4.14 SEM image of PCM composite material (cross section)

Random distribution of PCM microcapsules on the surface of the composite material

Fig. 4.15 SEM image of PCM composite material (front view)

4.1.2.4

PCM Composite Material

Figure 4.14 shows the cross section of the composite material as observed by the SEM. It was observed from the figure that the composite material consisted of the PCM-coated fabric and CM-coated foam materials.

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4 Results and Discussion

Fig. 4.16 SEM image of PCM composite material (back view)

The SEM image (front view) of the composite material is shown in Fig. 4.15. The PCM microcapsules are distinctly visible in clusters on the surface of the PCM-coated fabric material, which is the upper layer of the composite material. Figure 4.16 shows the SEM image of the composite material (back view) which is the PCM-coated foam material. The surface morphology shows the PCM foam structure.

4.2 Temperature Drop in the Aluminium Head Form Without a Helmet The aluminium head form was heated to reach a temperature which was 20 °C above the ambient temperature (i.e. ambient + 20 °C). Once the required temperature was reached, the heating was discontinued. The temperature readings from the thermocouples were recorded continuously and automatically at 10-s intervals by the Datataker (DT800) for the total experimental time of 60 min for all the experiments. The experiments were performed at the wind speeds of 0, 15, 35, 55 and 75 kph, and the necessary graphs were plotted showing the effects of cooling (by the drop in temperature) with time until the temperature reached the steady state. The low velocities of 0, 15 and 35 kph were used as preliminary tests, and the higher velocities of 55 and 75 kph were performed to simulate the velocities of city and open road conditions as mentioned in Sect. 3.4 and Fig. 3.3. The cooling curves (defined in Sect. 3.6.4) of the aluminium head form at different wind speeds are shown in Fig. 4.17. The X-axis shows the time in hours, minutes and

4.2 Temperature Drop in the Aluminium Head Form Without a Helmet

91

(Mean-Ambient) 0 kph (Mean-Ambient) 15 kph (Mean-Ambient) 35 kph

25.0

(Mean-Ambient) 55 kph

Temp. in Deg. C.

20.0

(Mean-Ambient) 75 kph

15.0

10.0

5.0

0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Time:h:mm:ss

Fig. 4.17 Cooling curves of aluminium head form without helmet at different speeds

seconds (h:mm:ss). The Y-axis shows the drop in temperature in degree centigrade. This figure indicated that as the wind speed increased, the drop in temperature was rapid due to the forced convection of the air in the closed-circuit wind tunnel and all the curves eventually attain the steady state. The effect of natural convection is minimal, and the observations at various wind speeds are described below: • In case of 0 kph speed as shown in Fig. 4.17 (blue), the drop in temperature is not significant as the heat loss is only due to radiation from the aluminium head form to the surroundings inside the closed-circuit wind tunnel with a minimal amount of natural convection. • In case of 15 kph speed, there is a gradual drop in temperature initially as shown in Fig. 4.17 (grey) and then it decreases to a lower temperature in the time interval set for the experiment, which is 60 min. This is due to radiation and a small contribution from forced convection. • For the speed of 35 kph as shown in Fig. 4.17 (red), the drop in temperature is greater than for 15 kph speed and the curve gradually decreases to a lower value in the duration of 60 min. This can be attributed to radiation and forced convection similar to 15 kph speed experiment. • In contrast, for the 55 kph speed the drop in temperature is sharp at the beginning as shown in Fig. 4.17 (turquoise), which then tapers off slowly. In addition to radiation, a fair amount of forced convection assists to drop the temperature sharply and then tapers off to a steady state. • The 75 kph speed graph shows the drop in temperature is very steep as shown in Fig. 4.17 (purple), and this drop is achieved in a very short period and further drop was similar compared to 55 kph speed graph. The short delay to attain the speed of 75 kph is shown as an initial lag in temperature before dropping sharply. In

92

4 Results and Discussion

this case compared to the radiation, the forced convection plays a dominant role in decreasing the temperature very steeply and then gradually reaches the steady state.

4.3 Temperature Drop Using PWAT Material In Figs. 4.18, 4.19, 4.20, 4.21 and 4.22, the comparison graphs for PWAT material at different speeds are shown. The control and the PWAT material curves are indicated by the blue and pink colours, respectively, which are obtained by subtracting the ambient from the mean (i.e. mean–ambient) as described in Sect. 3.6.4. The X-axis in the graphs (Figs. 4.18, 4.19, 4.20, 4.21 and 4.22) represents the time in hours, minutes and seconds (h:mm:ss). The Y-axis represents the drop in temperature in degree centigrade. The control curve represents the difference between the mean and the ambient (i.e. mean–ambient) for the helmet only. The PWAT material curve represents the difference between the mean and the ambient (i.e. mean–ambient) for the PWAT material used within helmet. The difference between the control curve and the PWAT material curve represents the resultant cooling curve (orange colour), which corresponds to the drop in temperature achieved by using the PWAT material inside the textile liner. The textile liner consists of a hood within which the PWAT material was inserted. The experimental data is given in Appendix A.1. Control (Mean-Ambient) PWAT material (Mean-Ambient) 25.0

Drop in temp.

20.0

Drop in temp. Deg.C

15.0 10.0 5.0 0.0 -5.0 -10.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

Time:h:mm:ss

Fig. 4.18 Comparison graph for PWAT material at 0 kph speed

0:50:24

0:57:36

1:04:48

4.3 Temperature Drop Using PWAT Material

93 Control (Mean-Ambient) PWAT material (Mean-Ambient)

25.0

Drop in temp. 20.0

Drop in temp. Deg.C

15.0

10.0

5.0

0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

0:57:36

1:04:48

-5.0

-10.0

Time:h:mm:ss

Fig. 4.19 Comparison graph for PWAT material at 15 kph speed Control (Mean-Ambient) PWAT material (Mean-Ambient) Drop in temp.

25.0 20.0

Drop in temp. Deg.C

15.0 10.0 5.0 0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

-5.0 -10.0

Time:h:mm:ss

Fig. 4.20 Comparison graph for PWAT material at 35 kph speed

0:50:24

94

4 Results and Discussion Control (Mean-Ambient) PWAT material (Mean-Ambient) 25.0 Drop in temp.

Drop in temp. Deg.C

20.0 15.0 10.0 5.0 0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

0:57:36

1:04:48

-5.0

Time:h:mm:ss

-10.0

Fig. 4.21 Comparison graph for PWAT material at 55 kph speed Control (Mean-Ambient) 25.0

PWAT material (Mean-Ambient) Drop in temp.

Drop in temp. Deg.C

20.0 15.0 10.0 5.0 0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

-5.0 -10.0

Time:h:mm:ss

Fig. 4.22 Comparison graph for PWAT material at 75 kph speed

0:50:24

4.3 Temperature Drop Using PWAT Material

95

Table 4.1 Maximum drop in temperature achieved by PWAT material at various speeds Speeds (kph)

Corresponding time of MDITa (h:mm:ss)

Control ‘A’ (Mean–Ambient) (°C)

Material ‘B’ (Mean–Ambient) (°C)

MDITa (B–A) (°C)

0

0:00:40

23.1

21.0

– 2.1

15

0:57:40

9.9

6.2

– 3.8

35

0:56:10

5.3

1.0

– 4.3

55

0:23:50

12.0

5.0

– 7.0

0:27:00

11.0

2.3

– 8.8

75 a Maximum

drop in temperature

Figure 4.18 indicates the drop in temperature with a wind speed of 0 kph. It was observed from the figure that both the control curve (blue) and the PWAT material curve (pink) start declining in temperature in a gradual and slow manner that is due to the radiant heat dissipation and conduction. The highest drop in temperature is only 2.1 °C over the total experimental time of 60 min. The PWAT material curve is always below the control curve because more heat is being absorbed by the PWAT material compared to the helmet alone. Also it was observed from the figure that as the time increases, there is only a slight drop in temperature. The drop in temperature achieved with 0 kph speed is the minimal amount as compared to the other speeds, which was observed from the cooling curve that is almost horizontal as shown in Fig. 4.18. This is because the wind inside the tunnel is stationary, and the heat loss is mainly due to radiation and a small amount due to conduction. The comparison graph for PWAT material at 15 kph speed is shown in Fig. 4.19. It was observed that the resultant cooling achieved at 15 kph speed is also very low. This is because at a low speed of 15 kph, sufficient water had not evaporated from the PWAT material to give adequate cooling inside the helmet. A maximum drop in temperature (MDIT) of 3.8 °C was achieved over the total experimental time of 60 min (Table 4.1). Figure 4.20 shows the comparison graph for PWAT material at 35 kph speed. It was observed that the resultant cooling achieved at 35 kph speed is also low which is because at a low speed of 35 kph speed sufficient water had not evaporated from the PWAT material. A maximum drop in temperature of 4.3 °C was achieved over the total experimental time of 60 min. Figure 4.21 shows the comparison graph for PWAT material at 55 kph speed. It was observed that the resultant cooling achieved at 55 kph speed is much higher as compared to the low-velocity tests. This was due to the increased speed and the fact that the amount of water evaporated from the PWAT material was high. The highest drop in temperature is 7.0 °C, over the total experimental time of 60 min. The comparison graph for PWAT material at 75 kph speed is shown in Fig. 4.22. It was observed that the resultant cooling achieved at the speed of 75 kph is very high as compared to the low-velocity tests, and also, it is higher than the value for

96

4 Results and Discussion

the speed of 55 kph. This was due to the forced convection at the speed of 75 kph contributing to increased evaporation of the water contained in the PWAT material. The maximum drop in temperature of 8.8 °C was achieved over the total experimental time of 60 min. It can be inferred from Figs. 4.18, 4.19, 4.20, 4.21 and 4.22 that, for low-velocity tests (i.e. 0, 15 and 35 kph) the (mean–ambient) temperature curves for both control and the PWAT material tend to be located above the X-axis which indicates less cooling has been achieved. However, for road velocity tests (i.e. 55 and 75 kph), these curves approach the X-axis much more closely which can be attributed to the cooling achieved by higher wind speeds in the closed-circuit wind tunnel due to the increased amount of the forced convection of air. It is evident from the high-velocity graphs that an appreciable amount of cooling was achieved by using PWAT material as an insert into the textile liner in the motorcycle helmet. Adding more water to the PWAT material as necessary can increase the cooling. In addition, a graph was plotted to compare the maximum drop in temperatures at different speeds as shown in Fig. 4.23. The correlation between the maximum drop in temperature and the wind speeds was established by this graph. It was observed from the above figure that the drop in temperature using the PWAT material as a textile liner in the helmet varied from 2.1 to a maximum of 8.8 °C depending on the wind speed. A gradual increase in temperature drop was observed as the wind speed increased from 0 to 75 kph. The maximum drop in temperature at various speeds was correlated by plotting an exponential trend line, which was established by the equation y = 2.4024e0.0181x

(4.1)

10.0

Maximum drop in temp.Deg.C

9.0

y = 2.4024e

0.0181x

2

R = 0.9531

8.0

(75.0, 8.8) (55.0, 7.0)

7.0 6.0 5.0 (15.0, 3.8)

4.0

(35.0, 4.3)

3.0 (0.0, 2.1)

2.0 1.0 0.0 0

10

20

30

40

50

Speed in kph

Fig. 4.23 Comparison graph at different speeds for PWAT material

60

70

80

4.3 Temperature Drop Using PWAT Material 0:00:00 0.0

0:07:12

0:14:24

0:21:36

97

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Time:h:mm:ss

Drop in temp. Deg.C

-2.0

-4.0

-6.0

-8.0

-10.0

Drop in temp. 0 kph Drop in temp. 15 kph Drop in temp. 35 kph Drop in temp. 55 kph Drop in temp. 75 kph

Fig. 4.24 Comparison of cooling curves at different speeds for PWAT material

The exponential trend line was selected because the drop in temperature was better correlated to the speed. The R2 value was found to be 0.9531. To show the effect of increase in the wind speed on the cooling achieved using PWAT material as a textile liner inside the helmet, a graph was plotted as shown in Fig. 4.24. Figure 4.24 indicates that, as the wind speed increases, the maximum drop in temperature tends to increase due to the forced convection of the air in the closedcircuit wind tunnel. The effect of natural convection at various wind speeds is a marginal amount. The observations at various wind speeds are described below: • In the case of 0 kph speed cooling curve, as shown in Fig. 4.24 (blue) the drop in temperature is not significant, as the heat loss was only caused by radiation from the aluminium head form to the surroundings inside the closed-circuit wind tunnel. • In the case of 15 kph speed cooling curve, there is a small drop in temperature initially as shown in Fig. 4.24 (grey) and then decreased to a lower temperature over the time interval of 60 min. • The 35 kph speed cooling curve, as shown in Fig. 4.24 (red), the drop in temperature is greater initially when compared to 15 kph speed and the curve gradually decreases to a lower value over the duration of 60 min. The drop in temperature was not significant, as a sufficient quantity of water did not evaporate. • In contrast, in the case of 55 kph speed cooling curve (turquoise), the drop in temperature is significant compared to the low velocities of 0, 15 and 35 kph that have been shown in Fig. 4.24. Initially, the curve appears to drop in temperature at a faster rate and then decreases slowly to reach the steady state.

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4 Results and Discussion

• In the 75 kph speed cooling curve, the drop in temperature was very steep as shown in Fig. 4.24 (brown), and this drop was achieved at a rapid rate initially. In relation to the 55 kph speed cooling curve, the 75 kph speed cooling curve shows significant further drop in temperature before it approaches the steady state. Significant drops in temperature for the road velocity experiments were achieved because the forced convection at higher speeds allows additional evaporation of water from the textile liner inside the helmet and contributes to more cooling, as indicated by the curve shown in the figure. In addition, it was observed from the figure that at the higher velocities (i.e. 55 and 75 kph) the respective cooling curves show a rapid drop in temperature and reach the maximum nearer to the half-an-hour mark. Then the drop in temperature gradually decreases and eventually approaches the steady state.

4.4 Amount of Heat Removed from the Head Form for Thermal Equilibrium To analyse and calculate the thermal equilibrium for a motorcyclist riding in tropical conditions by using the heat loss equations, some assumptions have been made which are described as shown: The ambient temperature (T a ) was taken to be 28 °C. The mean skin temperature (T sk ) was taken to be 34 °C. The dew point temperature (T dp ) was taken to be 15 °C. The core body temperature (T c ) was taken to be 37.15 °C Motorcyclists’ DuBois body area (Ad ) for an adult (of weight 70 kg and height 1.73 m) was taken to be 1.84 m2 The metabolic rate (H) for a motorcyclist in tropical conditions was considered to be 4 Met which is equivalent to 428.35 W (1 Met = 58.2 W/m2 × Ad , thus 1 Met = 107.08 W). The mechanical work output for an adult motorcyclist was considered to be approximately 10% of the metabolic rate (H) that is 42.84 W. The speed of the motorcyclist was taken as 55 kph (15.28 m/s); he is the evaporative coefficient (for 55 kph speed, he = 8.3 × v0.5 , v = 15.28 m/s) = 32.44 W/m2 K [1]; hc is the convective coefficient (for 55 kph speed, hc = 8.3 × v0.5 , v = 15.28 m/s) = 32.44 W/m2 K [1].

4.4.1 Calculations The equations used for the thermal equilibrium calculations are shown from Eqs. 3.5– 3.12.

4.4 Amount of Heat Removed from the Head Form for Thermal Equilibrium

4.4.1.1

99

Conduction (K)

According to Eq. 3.8 as given in Sect. 3.8 F cl = Ratio of surface area of clothed body to nude body Ad = DuBois body area for an adult (of weight 70 kg and height 1.73 m) ν = Decimal fraction of unclothed body area exposed to conduction ψ = Decimal fraction of clothing exposed to conduction Rs = Thermal resistance of the supporting object (approximated average) I cl = Overall clothing thermal resistance T sk = Temperature of the skin T a = Ambient temperature

1.05 1.84 m2 0.05 0.05 0.3125 m2 K/W 0.74 Clo 307 °K 301 °K

Using the above equation and the value of each parameter as shown above the calculated value for conduction (K) = 15.5 W.

4.4.1.2

Radiation (R)

According to Eq. 3.10 as given in Sect. 3.8 5.67 × 10−8 W/m2 K4 f eff = Adjusted DuBois body area to give more accurate result for the radiant 0.71 m2 heat transfer with the environment f cl = Ratio of surface area of clothed body to nude body 1.05 1.84 m2 Ad = DuBois body area for an adult (of weight 70 kg and height 1.73 m) ε sk = Emissivity of the skin 0.97 ζ = Proportion of the unclothed body exposed to radiation 0.05 ξ = Proportion of the clothed body exposed to radiation 0.95 0.97 ε cl = Emissivity of clothing 307 °K T sk = Temperature of the skin 301 °K T a = Ambient temperature 303 °K T cl = Temperature of the outside surface of the clothing σ = Stefan-Boltzmann constant

Using the above equation and the value of each parameter as shown above the calculated value for radiation (R) = 18.3 W.

4.4.1.3

Convection (C)

According to Eq. 3.9 as given in Sect. 3.8

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4 Results and Discussion

348VCO2 = H (Metabolic rate of the motorcyclist in tropical conditions)

428.35 W

hc = Convective coefficient (for 55 kph speed) f cl = Ratio of surface area of clothed body to nude body Ad = DuBois body area for an adult (of weight 70 kg and height 1.73 m) ε sk = Emissivity of the skin ζ = Proportion of the unclothed body exposed to convection ξ = Proportion of the clothed body exposed to convection T sk = Temperature of the skin T a = Ambient temperature T cl =Temperature of the outside surface of the clothing

32.44 W/m2 K 1.05 1.84 m2 0.97 0.05 0.95 307 °K 301 °K 303 °K

Using the above equation and the value of each parameter as shown above, the calculated value for convection (C) = 144.5 W.

4.4.1.4

Evaporation (E)

According to Eq. 3.11 as given in Sect. 3.8 VCO2 = Rate of CO2 respiration = H/348 [derived from the equation H = 348 V CO2] he = Evaporative coefficient (for 55 kph speed) Ad = DuBois body area for an adult (of weight 70 kg and height 1.73 m) ω = Decimal proportion of the body that is wet from perspiration ζ = Proportion of the unclothed body exposed to evaporation ξ = Proportion of the clothed body exposed to evaporation a = Cox chart curve fit coefficients for vapour pressure b = Cox chart curve fit coefficients for vapour pressure f pcl = Permeation efficiency of clothing (approx.) T sk = Temperature of the skin T c = Core body temperature T dp = Dew point

1.23 l/min 32.44 W/m2 K 1.84 m2 0.1 0.05 0.95 0.014371 – 3.11244 1 307 °K 310.15 °K 288 °K

Using the above equation and the value of each parameter as shown above, the calculated value for evaporation (E) = 208.6 W.

4.4.1.5

Thermal Balance

The thermal balance equation for human thermal regulation is given in Sect. 3.8 and Eq. 3.5 where, for tropical climates K, C and R values are taken to be negative. Therefore, the thermal balance equation becomes:

4.4 Amount of Heat Removed from the Head Form for Thermal Equilibrium

S = H −W −K −C − R− E

101

(4.2)

The parameters of the above equation have been explained in Sect. 3.8. The calculated values for the above thermal balance equations are as follows: K = 15.5, R = 18.3, C = 144.5, E = 208.6, W = 42.8 and H = 428.4 Using the above-calculated values of all the parameters in the thermal balance equation, the value of energy storage (S) was calculated to be −1.3 W which is close to zero, which implies that the motorcyclist is in thermal equilibrium under the stated conditions.

4.4.2 Heat Absorbed by PWAT Material at Various Speeds The amount of heat absorbed by PWAT material at various speeds was calculated from the amount of water evaporated using the following equation [2]:   E = 60Wt 0.68/Ad W/m2

(4.3)

where E is the evaporative heat loss, W t is the rate of change of body weight in g/min, 0.68 is the latent heat of sweat in J/g, and Ad is the DuBois body area in m2 . The amount of heat absorbed at various speeds and the amount of water evaporated in each speed are given in Table 4.2. A graph was plotted to compare the amount of heat absorbed at different speeds as shown in Fig. 4.25. The correlation between the heat absorbed and the wind speeds was established by this graph. It was observed from the figure that the heat absorbed using the PWAT material in the textile liner inside the helmet varied from 13.1 to 22.3 W/m2 depending on the wind speed. The heat absorbed at various wind speeds was correlated by plotting an exponential trend line, which was established by the equation: y = 12.986e0.0072x Table 4.2 Amount of heat absorbed by PWAT material at various speeds

(4.4)

Speed (kph)

Weight of water evaporated (g)

Heat absorbed (W/m2 )

0

35.4

13.1

15

38.7

14.3

35

45.2

16.7

55

52.8

19.5

75

60.3

22.3

102

4 Results and Discussion 25

(75, 22.3)

Heat absorbed in Watts

20 (55, 19.5) (35, 16.7)

15 (15, 14.3) (0, 13.1)

10

5

0 0

10

20

30

40

50

60

70

80

Speed in kph

Fig. 4.25 Amount of heat absorbed by PWAT material at various wind speeds

The R2 value was found to be 0.9984. In general, it has been shown that the amount of heat produced in the head [3, 4] by metabolism is 15 watts approximately for an average size head. It can be observed from Fig. 4.25 that the heat absorbed increases as the speed increases from 0 to 75 kph. Therefore, the motorcyclist would be comfortable while riding at higher speeds. The graphs in Figs. 4.23 and 4.25 can be used directly or extrapolated for various speeds to predict the drop in temperature and the amount of heat absorbed, respectively, based on the speed of the motorcyclist.

4.5 Temperature Drop with PCM Materials The wind tunnel experiments were performed at 55 and 75 kph speeds for different textile substrates containing the paraffinic PCM. In contrast to the PWAT material, the aluminium head form was heated to reach a temperature, which is 10 °C above the ambient temperature (i.e. ambient + 10 °C) for the paraffinic PCM materials. As the PCM selected for the study has lower melting points ranging from 25 to 35 °C, a temperature of (ambient + 10 °C) was selected for these experiments. However, if (ambient + 20 °C) was considered for the PCM, it could exceed the melting points resulting in all the latent heat been given out rapidly. Hence, there could be a sudden large drop in temperature initially with limited further cooling. Once the required temperature was reached in the aluminium head form, the heating was discontinued. The temperature readings from the thermocouples were recorded automatically at 10s intervals by the Datataker (DT800) continuously for 60 min for all the experiments, and the necessary graphs were plotted.

4.5 Temperature Drop with PCM Materials

103

The X-axis in the graphs (Figs. 4.26, 4.27, 4.28 and 4.29) represents the time in hours, minutes and seconds (h: mm:ss). The Y-axis represents the drop in temperature in degree centigrade. The control curve represents the difference between the mean and the ambient temperature (i.e. mean–ambient) for the helmet only, and each of the PCM material curves (non-woven, foam, fabric and composite) represents the difference between the mean and the ambient (i.e. mean–ambient) for the PCM materials together with the helmet. The difference between the control curve and the respective PCM material curve together with the helmet represents the cooling Control (Mean-Ambient) PCM nonwoven material (Mean-Ambient)

14.0

Drop in temp.

12.0

Drop in temp. Deg.C

10.0 8.0 6.0 4.0 2.0 0.0 0:00:00 -2.0

0:07:12

0:14:24

0:21:36

-4.0

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Time:h:mm:ss

-6.0

Fig. 4.26 Comparison graph for PCM non-woven material at 55 kph speed Control (Mean-Ambient) 14.0

PCM foam material (Mean-Ambient)

12.0

Drop in temp.

Drop in temp. Deg.C

10.0 8.0 6.0 4.0 2.0 0.0 0:00:00 -2.0

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

-4.0 -6.0

Time:h:mm:ss

Fig. 4.27 Comparison graph for PCM foam material at 55 kph speed

0:50:24

0:57:36

1:04:48

104

4 Results and Discussion Control (Mean-Ambient) PCM fabric material (Mean-Ambient)

14.0

Drop in temp.

12.0

Drop in temp. Deg.C

10.0 8.0 6.0 4.0 2.0 0.0 0:00:00 -2.0

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

-4.0

Time:h:mm:ss

-6.0

Fig. 4.28 Comparison graph for PCM fabric material at 55 kph speed Control (Mean-Ambient) PCM composite material (Mean-Ambient)

14.0

Drop in temp. 12.0

Drop in temp. Deg.C

10.0 8.0 6.0 4.0 2.0 0.0 0:00:00 -2.0

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

-4.0 -6.0

Time:h:mm:ss

Fig. 4.29 Comparison graph for PCM composite material at 55 kph speed

curve, which was shown in the negative scale as drop in temperature for the duration of the experiment. The experiments were carried out at 55 and 75 kph speeds for each of the above PCM materials in the closed-circuit wind tunnel.

4.5 Temperature Drop with PCM Materials

105

4.5.1 Paraffinic PCM at Speed of 55 kph The comparison graphs for different paraffinic PCM materials at 55 kph speed are shown from Figs. 4.26, 4.27, 4.28 and 4.29. It was observed from the figures that the difference in the maximum drop in temperature achieved by using different PCM materials are within a very close range of 3.1–3.7 °C. This was attributed to the melting point of the PCM materials, which are close to one another as indicated by the DSC graphs (Figs. 4.38, 4.39, 4.40 and 4.41). It can also be observed from Figs. 4.26, 4.27, 4.28 and 4.29 that the maximum drop in temperature achieved by using PCM materials such as non-woven, foam, fabric and composite were 3.1 °C, 3.6 °C, 3.7 °C and 3.6 °C, respectively, over the total experimental time of 60 min. These figures indicate that the drop in temperature is rapid for the initial part of the experiment and as the time elapses the drop in temperature gradually decreases reaching a steady state. Figure 4.26 indicates that the maximum drop in temperature achieved was 3.1 °C. Correspondingly, in the initial stage the drop in temperature curve shows a greater drop in temperature and then stabilises for a short period of time, and subsequently, the drop in temperature decreases after the 30 min mark. The experimental data is given in appendix A1. Figure 4.27 indicates that the maximum drop in temperature achieved was 3.6 °C. Similarly, in the initial stage the drop in temperature curve shows a higher drop in temperature and then stabilises for a short span and subsequently the drop in temperature decreases after the 25 min mark. Figure 4.28 indicates that the maximum drop in temperature achieved was 3.7 °C. Similarly, in case of the PCM fabric material, in the initial stages the drop in temperature curve shows a greater drop in temperature and then stabilises for a short period and subsequently the drop in temperature decreases after the 30 min mark. Figure 4.29 indicates that the maximum drop in temperature achieved was 3.6 °C. In the initial stage, the drop in temperature curve shows a greater drop in temperature and then stabilises for a short span and subsequently the drop in temperature decreases after the 26 min mark. In addition to these graphs (Figs. 4.26, 4.27, 4.28 and 4.29), another graph was plotted to compare the effect of drop in temperatures using different PCM at 55 kph speed as shown in Fig. 4.30. The values of maximum drop in temperature and the corresponding time are also shown in Table 4.3. It was observed from Fig. 4.30 that the effective drop in temperature achieved is highest with PCM fabric material and lowest with PCM non-woven material. The drop in temperature varied from 3.1 °C to a maximum of 3.7 °C depending on the type of material used. Also, a graph was plotted to compare the effective cooling achieved inside the helmet by using different PCM materials at 55 kph speed as shown in Fig. 4.31. It was observed from Fig. 4.31 that the drop in temperature is rapid for the initial duration of the experiment irrespective of the type of PCM material contained in the textile liner. This is because the amount of PCM microcapsules contained in

106

4 Results and Discussion

Maximum drop in temp. Deg C

5 4 3 2 1 0 PCM nonwoven

PCM foam

PCM fabric

PCM composite

Types of PCM materials Fig. 4.30 Comparison graph of different PCM materials at 55 kph speed Table 4.3 Drop in temperature achieved by various PCM materials at 55 kph speed Materials

Corresponding time Control ‘A’ of MDITa (Mean–Ambient) (°C) (h:mm:ss)

Material ‘B’ (Mean–Ambient) (°C)

MDITa (B–A) (°C)

PCM Non-woven

0:30:40

3.1

– 3.1

6.2

PCM foam

0:25:30

6.8

3.1

– 3.6

PCM fabric

0:30:40

6.2

2.5

– 3.7

PCM Composite

0:26:20

6.5

2.9

– 3.6

a Maximum

drop in temperature Time:h:mm:ss

0:00:00 0.0

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Drop in temp. for PCM nonwoven material -1.0

Drop in temp. for PCM foam material

Drop in temp. Deg.C

Drop in temp. for PCM fabric material Drop in temp. for PCM composite material -2.0

-3.0

-4.0

-5.0

Fig. 4.31 Comparison of cooling curves for PCM materials at 55 kph speed

4.5 Temperature Drop with PCM Materials

107

each material begins to absorb a large quantity of heat initially by the process of melting, thus causing a rapid drop in temperature. After reaching the lowest point in the cooling curve, the drop in temperature then decreases gradually, as shown by the rising of the individual curves towards the X-axis. The forced convection of air in the wind tunnel assists in further cooling of the helmet until the curves approach the steady state. After the PCM contained in the textile liner have melted (attaining the highest drop in temperature), there would not be further absorption of heat.

4.5.2 Paraffinic PCM at Speed of 75 kph The comparison graphs for PCM materials at 75 kph speed are shown from Figs. 4.32, 4.33, 4.34 and 4.35. It was observed from the experiment data that the drop in temperatures achieved by using different PCM materials is within a very close range of 3.1–3.8 °C. This can be attributed to the melting point of the PCM materials, which are very close to one another as indicated by the DSC graphs (Figs. 4.38, 4.39 and 4.40, Fig. 4.41). It was also observed from Figs. 4.32, 4.33, 4.34 and 4.35 that the drop in temperature achieved by PCM materials, non-woven, foam, fabric and composite, were 3.1 °C, 3.7 °C, 3.8 °C and 3.7 °C, respectively, over the total experimental time of 60 min. These figures indicate that the drop in temperature is rapid for the initial part of the experiment, and as the time elapses, the drop in temperature gradually decreases. Figure 4.32 shows the drop in temperature of PCM non-woven material. It was observed from the figure that the maximum drop in temperature achieved was 3.1 °C 12.00

Control (Mean-Ambient)

10.00

PCM nonwoven material (Mean-Ambient) Drop in temp.

Drop in temp. Deg.C

8.00 6.00 4.00 2.00 0.00 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

2.00 4.00 6.00

Time:h:mm:ss

Fig. 4.32 Comparison graph for PCM non-woven material at 75 kph speed

0:57:36

1:04:48

108

4 Results and Discussion Control (Mean-Ambient) 12.0

PCM foam material (Mean-Ambient) Drop in temp.

10.0

Drop in temp. Deg.C

8.0 6.0 4.0 2.0 0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

-2.0 -4.0

Time:h:mm:ss -6.0

Fig. 4.33 Comparison graph for PCM foam material at 75 kph speed Control (Mean-Ambient) PCM fabric material (Mean-Ambient) Drop in temp.

12.0 10.0

Drop in temp. Deg.C

8.0 6.0 4.0 2.0 0.0 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

-2.0 -4.0

Time:h:mm:ss

-6.0

Fig. 4.34 Comparison graph for PCM fabric material at 75 kph speed

for the experimental time of 60 min. The maximum drop in temperature was achieved at 30 min. Figure 4.33 shows a drop in temperature of 3.7 °C over the total experimental time of 60 min. The maximum drop in temperature was achieved at 25 min. Figure 4.34 shows a drop in temperature of 3.8 °C over the total experimental time of 60 min. The maximum drop in temperature was achieved at 23 min. Figure 4.35 shows a drop in temperature of 3.7 °C over the total experimental time of 60 min. The maximum drop in temperature was achieved at 25 min.

4.5 Temperature Drop with PCM Materials

109 Control (Mean-Ambient) PCM composite material (Mean-Ambient) Drop in temp.

12.0 10.0

Drop in temp. Deg.C

8.0 6.0 4.0 2.0 0.0 0:00:00 -2.0

0:07:12

0:14:24

0:21:36

-4.0

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Time:h:mm:ss

-6.0

Fig. 4.35 Comparison graph for PCM composite material at 75 kph speed

In addition to these graphs (Figs. 4.32, 4.33, 4.34 and 4.35), another graph was plotted to compare the effect of drop in temperatures using different PCM at 75 kph speed as shown in Fig. 4.36. The drop in temperature varied from 3.1 °C to a maximum of 3.8 °C depending on the type of materials used and the duration of the experiments. However, there is a possibility of further cooling before it reaches the steady state. The values of maximum drop in temperature and the corresponding time are also shown in Table 4.4. It was observed from Tables 4.3 and 4.4 that the maximum drop in temperature was achieved during the first half of the duration of the experiment for both the 55

Maximum drop in temp. Deg C

5 4 3 2 1 0 PCM nonwoven

PCM foam

PCM fabric

PCM composite

Types of PCM materials Fig. 4.36 Comparison graph of different PCM materials at 75 kph speed

110

4 Results and Discussion

Table 4.4 Drop in temperature achieved by various PCM materials at 75 kph speed Materials

Corresponding time of MDIT* (h:mm:ss)

Control ‘A’ (Mean–Ambient) (°C)

Material ‘B’ (Mean–Ambient) (°C)

MDIT* (B-A) (°C)

PCM Non-woven

0:30:00

5.09

2.0

– 3.1

PCM Foam

0:25:10

5.58

1.87

– 3.7

PCM Fabric

0:23:20

5.82

2.07

– 3.8

PCM Composite

0:24:40

5.64

1.94

– 3.7

* Maximum drop in temperature

and 75 kph speeds. This was attributed to the higher speeds of 55 and 75 kph in the wind tunnel. It was observed from Fig. 4.36 that the effective cooling achieved is highest with PCM fabric material and lowest with PCM non-woven material. The drop in temperature varied from 3.1 °C to a maximum of 3.8 °C depending on the type of material used. In addition, another graph was plotted to compare the effective cooling achieved inside the helmet by using different PCM materials at 75 kph speed which has been shown in Fig. 4.37. It was observed from Fig. 4.37 that the drop in temperature was rapid for the initial duration of the experiment irrespective of the type of PCM material contained in the textile liner. The amount of PCM microcapsules contained in each material began to absorb a large quantity of heat by the process of melting, resulting in a rapid drop in temperature initially. Having reached the lowest point in the cooling curve, the drop in temperature then decreased gradually towards the X-axis. Further Time:h:mm:ss 0.00 0:00:00

0:07:12

0:14:24

0:21:36

0:28:48

0:36:00

0:43:12

0:50:24

0:57:36

1:04:48

Drop in temp. for PCM nonwoven material

Drop in temp. Deg.C

1.00

Drop in temp. for PCM foam material Drop in temp. for PCM fabric material Drop in temp. for PCM composite material

2.00

3.00

4.00

5.00

Fig. 4.37 Comparison of cooling curves for PCM materials at 75 kph speed

4.5 Temperature Drop with PCM Materials

111

cooling was achieved by the forced convection of air in the wind tunnel at 75 kph speed. After the PCM contained in the textile liner is melted (attaining the highest drop in temperature), there would not be further absorption of heat. It can be observed from the individual results of paraffinic PCM as shown in Tables 4.3 and 4.4 that the differences in the readings of the maximum drop in temperature at the speed of 55 and 75 kph are not markedly different. This was due to the contribution of forced convection to achieve further cooling. In these experiments, the temperatures of the PCM were not near enough to the melting points of the PCM to obtain maximum heat absorption. To facilitate the maximum amount of heat absorption, the temperature should exceed the melting points of the PCM where all microcapsules present would have melted. It also depends upon the amount of microcapsules present in the PCM materials. All the PCM materials used in these experiments have the same surface area equivalent to the surface area of the head. But the density and thickness of the PCM materials are different, and hence, the amount of microcapsules also varies to a limited extent. In addition, the weights of the PCM materials are different even though they have the same surface area.

4.6 Heat Absorbed by Paraffinic PCM Materials The PCM materials were tested using DSC to investigate the thermal behaviour and to obtain the melting points, as described in Sect. 3.7.1. The DSC graphs are shown from Figs. 4.38, 4.39, 4.40 and 4.41. The graphs show the relationship between the heat flow and the temperature at a heating rate of 2 °C/min and were used to calculate the

Fig. 4.38 DSC graph for PCM non-woven material (Melting point 27.7 °C)

112

4 Results and Discussion

Fig. 4.39 DSC graph for PCM foam material (Melting point 33.2 °C)

Fig. 4.40 DSC graph for PCM fabric material (Melting point 33.2 °C)

total amount of heat absorbed by the PCM materials. The melting points of different PCM materials are indicated by the highest peaks of the respective curves. From the figures, it can be observed that they are in the range of 27.7–33.2 °C. The temperature ranges and the delta H values indicated in blue and red correspond to the temperature ranges used in the wind tunnel experiments for the speeds of 55 kph and 75 kph, respectively. The values of delta H were calculated by using the DSC software that

4.6 Heat Absorbed by Paraffinic PCM Materials

113

Fig. 4.41 DSC graph for PCM composite material (Melting point 32.5 °C)

indicates the area between the curve and the baseline. These values of delta H were used to calculate the amount of heat absorbed by different PCM materials. The DSC graph for PCM non-woven material is shown in Fig. 4.38. As shown in the figure, the melting point of the PCM non-woven is 27.7 °C. Figure 4.39 shows the DSC graph for PCM foam material. It was observed from the figure that the melting point of the specific paraffinic PCM is 32.2 °C. Figure 4.40 shows the DSC graph for PCM fabric material. The figure illustrates that the melting point of the specific paraffinic PCM is 33.2 °C. Figure 4.41 shows the DSC graph for PCM composite material. The highest temperature reached for the PCM composite material is 32.5 °C. The total amount of heat absorbed by PCM materials as shown in Table 4.5 was calculated based on the experimental results obtained from the DSC graphs (Figs. 4.38, 4.39, 4.40 and 4.41) using the following equation [5, 6]: Total amount of heat absorbed(W ) = (m × H )/ t

(4.5)

where m is the mass of the PCM material used in the experiments, H is the difference in the heat absorbed in J/g as shown by the DSC curves within each temperature range, and t is the calculated value of time taken for this temperature range at a heating rate of 2 °C/min. The detailed calculation of the total amount of heat absorbed is shown in Appendix A.2. From Table 4.5, it is evident that only the PCM non-woven material exceeds the 15 W requirement to reduce the heat stress within the helmet. To achieve the same amount of heat absorption from other PCM materials, the quantity of the PCM

114

4 Results and Discussion

Table 4.5 Total amount of heat absorbed by PCM materials Materials

Weight of Temperature Temperature PCM range (°C) difference materials ( T ) (°C) (m) (g)

Time span for Heat Total temperature absorbed amount of difference ( H) (J/g) heat ( t) (s) absorbed (W)

55 kph PCM 66 non-woven

20.68–28.01

7.33

219.9

59.10

17.8

PCM foam

43

24.27–32.06

7.79

234.0

46.70

9.0

PCM fabric 41

20.92–28.48

7.56

226.8

7.67

1.4

PCM composite

84

20.19–28.56

8.37

251.1

21.2

7.1

PCM 66 non-woven

19.23–25.27

6.04

181.2

21.2

7.7

PCM foam

75 kph

43

22.61–29.33

6.72

201.6

32.4

7.0

PCM fabric 41

21.14–27.57

6.43

192.9

5.98

1.3

PCM composite

22.49–30.23

7.74

232.2

23.6

8.6

84

materials has to be increased. In spite of this increase, the total weight of the textile liner in all cases excluding PCM fabric material would be below 350 g [7]. The amount of heat absorbed by the PCM materials depends on the start and end temperature of the experiments and whether the temperature rise is near enough or beyond the melting point. If the end temperature is close enough to the melting point, there are still some PCM microcapsules available to absorb the heat in the helmet when there is further increase in temperature. If the temperature exceeds the melting point of the PCM, then all the microcapsules would have melted, resulting in no further absorption of heat and hence no further cooling achieved. However, in reality, the temperature of the environment can change at any time and as such it is difficult to tailor the PCM materials to suit this type of situation. It was observed from Table 4.5 and Fig. 4.40 that the amount of heat absorbed by the PCM fabric material at both the speeds of 55 and 75 kph was lowest. This is because the fabric material contains microcapsules with a melting point of 33.2 °C. The start and end temperature of the experiments are much lower than its melting point. Hence, the value of the area covered in the DSC curve to obtain H is very low, giving a lower total heat absorbed value. Therefore, in this case, the fabric was considered to be unsuitable for this application for the specific temperature range used in this experiment. In addition, Table 4.5 and Fig. 4.38 suggest that, in case of PCM non-woven material at 55 kph speed, the melting temperature was within the start and end temperature of the DSC experiment. On the contrary, in the 75 kph experiment the melting point was found to be outside the range of the experiment. This was the reason

4.6 Heat Absorbed by Paraffinic PCM Materials

115

for a lower value of total heat absorbed at 75 kph by PCM non-woven material. In order to obtain maximum benefit for heat absorption, the temperature range should be inclusive of the melting point or very close to the melting point. However, in reality this depends on the thermal conditions encountered by the motorcyclist.

4.7 Conclusions This chapter has discussed the results obtained from experiments conducted in the wind tunnel. The cooling curves of aluminum head without helmet at different speeds are discussed. The comparisons of PWAT materials at different speeds are also included. In addition, the comparisons of PCM materials at different speeds are also included. The amount of heat absorbed by the sustainable textile materials to cool the helmet is also included in this chapter.

References 1. K.M.D. Kerslake, The Stress of Hot Environments (Cambridge University Press, 1972) 2. X. Liu, I. Holmer, Evaluation of evaporative heat transfer characteristics of helmets. Appl. Hum. Sci. 16(3), 107–113 (1997) 3. F.L. Tan, S.C. Fok, Cooling of helmet with phase change material. Appl. Thermal Eng. 26, 2067–2072 (2006) 4. Z.J. Kang, H. Xue, T.Y. Bong, Modeling of thermal environment and human response in a crowed space for tropical climate. Build. Environ. 36, 511–525 (2001) 5. Private communication from J. Arthur, Product Manager, Thermal Analysis (PerkinElmer, March 2010) 6. Private communication from Dr. M/ Huson, Project Leader, Materials Science and Engineering (CSIRO, Geelong, Victoria, March 2010) 7. K. Sinnappoo, R. Nayak, L. Thompson, R. Padhye, Application of sustainable phase change materials in motorcycle helmet for heat-stress reduction. J. Text.E Inst, 1–9. https://doi.org/10. 1080/00405000.2020.1715606

Chapter 5

Conclusions

This research adds new knowledge for developing an innovative textile liner containing a hood and replaceable inserts of either PWAT or PCM materials for helmets to reduce the heat stress of motorcyclists. Experimental evaluation of the heat stress reduction by application of textile substrates containing PWAT or PCM materials was analysed. This research has also shown that the PWAT and PCM materials along with forced convection provide a substantial benefit to the motorcyclist wearing a helmet by reducing heat stress. It has been the focus of this research to define the fundamental relationships of heat transfer for PCM or PWAT materials in the design of textile liner to be used in the motorcycle helmet. The research presents a mechanism to enable the computer-aided design of textile liners for cooling within motorcycle helmets. PWAT material is slow to evaporate water at lower temperatures and lower speeds, but cooling is achieved faster at higher temperatures and higher speeds. If larger quantities of water from the PWAT material had evaporated, then more heat would have been absorbed, resulting in further cooling. If too much water is added to the PWAT material, then it might lead to the feeling of wetness on the head. In addition, if the motorcyclist goes at a higher speed, there would be increased cooling that might lead to wind chill and discomfort. It has been found that the application of PWAT material can reduce the temperature by 2.1–8.8 °C depending on the wind speed. The maximum drop in temperature for PWAT material was achieved at 75 kph wind speed as the forced convection contributed to the increased evaporation of water contained in the PWAT material. Similarly, in the case of PCM materials, the drop in temperature ranged from 3.1– 3.8 °C depending on the wind speeds. The maximum drop in temperature for PCM material was also achieved at 75 kph wind speed because of the forced convection contributing to additional cooling. Generally, the heat is transferred by conduction, convection, radiation and evaporation. In this research, forced convection and evaporation play the major roles with a limited contribution from radiation and conduction. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7_5

117

118

5 Conclusions

In the case of PCM materials, at higher temperatures, heat absorbed is maximised when it reaches the melting point. When it is beyond the melting point, all the heat had been absorbed by the latent heat of fusion. No further cooling takes place after all the PCM microcapsules have melted, but forced convection might provide a small amount of cooling. If the temperature drops in the surrounding environment, the already melted PCM microcapsules would solidify and release heat, providing comfort to the motorcyclist. Thus, by the application of PCM materials, there would be benefits if the temperature rises or falls in the surroundings. The amount of heat absorbed by the application of PWAT or PCM materials is close enough to the metabolic heat produced by the average sized human head. This research indicates that a sufficient amount of heat is being absorbed by textile substrates containing PWAT or PCM materials to reduce the heat stress of the motorcyclist. The forced convection of the air at different speeds in the wind tunnel also contributes to a further drop in temperature within the helmet, depending on the speeds. At higher speeds, the temperature drop is much higher than at lower speeds. At the beginning of this study, it was expected that a drop in temperature of 2– 3 °C within the helmet would be obtained to achieve the cooling needed. However, by using these innovative approaches, the cooling achieved has been much greater, especially at higher speeds. Hence, the heat stress in the helmet has been reduced for the motorcyclist. In addition, no external power supply (from batteries or electrical source) is needed for cooling the helmet by this approach. The addition of materials (PWAT or PCM) can be included in the textile liner for achieving further cooling. In the case of the exhausted PWAT material, additional water can be added (dry after the experiments due to water being evaporated), or for the exhausted PCM (due to all the PCM microcapsules completing phase change after absorption of heat), additional PCM material can be included to achieve further cooling. The regression analysis curves for PWAT materials can directly be used up to 75 kph or extrapolated for higher speeds to predict the drop in temperature and the amount of heat absorbed, respectively, based on the speed of the motorcyclist. Two equations were derived from this research for PWAT materials. The first equation y = 2.4024e0.0181x deals with the calculation of maximum drop in temperature at various speeds. This equation can be used directly or extrapolated for various speeds to predict the maximum drop in temperature. The second equation y = 12.986e0.0072x deals with the amount of heat absorbed at various speeds. Similar to the first equation, this equation can also be used directly or extrapolated for various speeds to predict the amount of heat absorbed. In case of PCM materials, an approach was taken to calculate the total amount of heat absorbed considering the start and end temperatures at different speeds. This was based on the experimental results obtained from the DSC graphs using the equation W = (m × H)/t. This approach was specific to the experiments conducted in this research using various PCM materials. The extensive experimental data from this research established that, for enclosed motorcycle helmets, the behaviour of PWAT materials was better predicted by the equations derived in this study, rather than that previously published research. The

5 Conclusions

119

application of these equations has facilitated for the first time reliable means to predict and to size thermal comfort textile liners for the current production standards approved helmets. The outcomes of this research have facilitated a mean to size thermal comfort textile liners to suit a variety of climatic conditions. This has been achieved by the application of the improved PWAT equation in combination with the application of PCM in hybrid liners giving a liner that can provide comfort for a broader climatic condition. Finally, it was concluded that for alleviating the motorcyclist’s heat stress in the helmet, textile liner with the hood and replaceable inserts of either PWAT or PCM materials can be manufactured and fitted to new helmets or retrofitted to old helmets without any alterations to the helmet. The application of a PWAT or PCM inner fabric liner can be used without compromising the legal safety compliance of the helmet. This research provides a means to develop a product to improve rider comfort that is compatible with all standards compliant motorcycle helmets.

5.1 Future Recommendations Application of newly developed materials with more microcapsules per square metre or innovative developments in nano-encapsulation of PCM materials will provide more cooling due to the availability of larger surface area to absorb the heat, and this might lead to reducing the amount of PCM materials. Incorporating the PCM microcapsules within the helmet itself should be investigated. This will lead to the elimination of additional materials being placed inside the helmet or altering the helmet. The combination PWAT and PCM materials for the purpose of cooling should be explored. The behaviour of which can now be predicted using the equations derived in this research.

Appendixes

A.1 Cooling Curve Data from Wind Tunnel Experiments Here, representative experimental data for PWAT material at 75 kph are given. Experiments were performed in triplicates for the speeds of 0, 15, 35, 55 and 75 kph, and data for these speeds are also available.

Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:00:00

19.48

18.13

1.34

0:00:10

19.47

17.64

1.83

0:00:20

19.45

17.60

1.86

0:00:30

19.47

17.56

1.91

0:00:40

19.42

17.49

1.93

0:00:50

19.42

17.43

1.99

0:01:00

19.37

17.30

2.07

0:01:10

19.34

17.19

2.15

0:01:20

19.30

17.12

2.18

0:01:30

19.24

16.85

2.39

0:01:40

19.18

16.59

2.59

0:01:50

19.09

16.33

2.76

0:02:00

19.02

16.09

2.93

0:02:10

18.96

15.79

3.18

0:02:20

18.88

15.59

3.29

0:02:30

18.78

15.32

3.46

0:02:40

18.73

15.04

3.69

0:02:50

18.65

14.81

3.84 (continued)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7

121

122

Appendixes

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:03:00

18.57

14.53

4.04

0:03:10

18.50

14.31

4.18

0:03:20

18.44

14.09

4.34

0:03:30

18.34

13.89

4.45

0:03:40

18.28

13.72

4.56

0:03:50

18.20

13.42

4.78

0:04:00

18.12

13.31

4.81

0:04:10

18.05

13.19

4.85

0:04:20

17.99

12.96

5.03

0:04:30

17.93

12.74

5.19

0:04:40

17.84

12.57

5.28

0:04:50

17.78

12.39

5.39

0:05:00

17.72

12.25

5.47

0:05:10

17.66

12.10

5.56

0:05:20

17.57

11.87

5.70

0:05:30

17.52

11.73

5.79

0:05:40

17.42

11.57

5.86

0:05:50

17.36

11.47

5.88

0:06:00

17.28

11.29

5.99

0:06:10

17.21

11.16

6.05

0:06:20

17.15

11.01

6.14

0:06:30

17.06

10.85

6.21

0:06:40

16.99

10.73

6.26

0:06:50

16.94

10.59

6.35

0:07:00

16.86

10.38

6.48

0:07:10

16.82

10.31

6.50

0:14:20

14.34

6.06

8.28

0:14:30

14.29

5.98

8.30

0:14:40

14.25

5.99

8.26

0:14:50

14.19

5.97

8.21

0:15:00

14.14

5.84

8.29

0:15:10

14.08

5.73

8.34

0:15:20

14.02

5.71

8.31

0:15:30

13.98

5.69

8.30

0:15:40

13.94

5.64

8.30

0:15:50

13.89

5.51

8.38

0:16:00

13.84

5.48

8.37 (continued)

Appendixes

123

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:16:10

13.80

5.38

8.41

0:16:20

13.73

5.26

8.47

0:16:30

13.70

5.21

8.49

0:16:40

13.65

5.17

8.48

0:16:50

13.61

5.10

8.51

0:17:00

13.56

5.04

8.51

0:17:10

13.51

5.02

8.49

0:17:20

13.45

4.94

8.52

0:17:30

13.42

4.87

8.56

0:17:40

13.36

4.84

8.52

0:17:50

13.32

4.79

8.53

0:18:00

13.27

4.77

8.49

0:18:10

13.22

4.67

8.55

0:18:20

13.17

4.59

8.58

0:18:30

13.14

4.54

8.60

0:18:40

13.10

4.50

8.59

0:18:50

13.04

4.45

8.59

0:19:00

13.01

4.36

8.65

0:19:10

12.97

4.34

8.63

0:19:20

12.92

4.27

8.65

0:19:30

12.86

4.24

8.62

0:19:40

12.83

4.20

8.62

0:19:50

12.78

4.14

8.63

0:20:00

12.75

4.07

8.68

0:20:10

12.69

4.06

8.64

0:20:20

12.64

3.98

8.65

0:20:30

12.61

3.96

8.65

0:20:40

12.55

3.89

8.66

0:20:50

12.50

3.80

8.70

0:21:00

12.45

3.76

8.70

0:21:10

12.42

3.72

8.69

0:21:20

12.37

3.71

8.66

0:21:30

12.35

3.67

8.67

0:21:40

12.31

3.60

8.71

0:21:50

12.27

3.60

8.67

0:22:00

12.25

3.56

8.68

0:22:10

12.19

3.48

8.71 (continued)

124

Appendixes

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:22:20

12.15

3.41

8.74

0:22:30

12.11

3.43

8.68

0:22:40

12.05

3.37

8.68

0:22:50

12.02

3.29

8.73

0:23:00

11.99

3.24

8.75

0:23:10

11.94

3.19

8.75

0:23:20

11.89

3.16

8.73

0:23:30

11.85

3.15

8.69

0:23:40

11.81

3.04

8.76

0:23:50

11.77

3.10

8.67

0:24:00

11.74

3.02

8.72

0:24:10

11.69

2.97

8.72

0:24:20

11.65

2.88

8.77

0:24:30

11.62

2.92

8.70

0:24:40

11.56

2.81

8.75

0:24:50

11.54

2.77

8.76

0:25:00

11.52

2.81

8.71

0:25:10

11.49

2.73

8.75

0:25:20

11.44

2.75

8.69

0:25:30

11.40

2.68

8.72

0:25:40

11.36

2.58

8.77

0:25:50

11.32

2.56

8.76

0:26:00

11.29

2.55

8.74

0:26:10

11.24

2.47

8.77

0:26:20

11.21

2.43

8.78

0:26:30

11.18

2.41

8.77

0:26:40

11.14

2.42

8.73

0:26:50

11.11

2.38

8.73

0:27:00

11.06

2.27

8.79

0:27:10

11.03

2.29

8.74

0:27:20

10.99

2.21

8.77

0:27:30

10.95

2.19

8.76

0:27:40

10.94

2.20

8.73

0:27:50

10.89

2.11

8.78

0:28:00

10.84

2.09

8.75

0:28:10

10.82

2.09

8.73

0:28:20

10.78

2.07

8.71 (continued)

Appendixes

125

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:28:30

10.75

2.01

8.74

0:28:40

10.70

2.02

8.68

0:28:50

10.67

2.01

8.66

0:29:00

10.64

1.97

8.67

0:29:10

10.60

1.90

8.71

0:29:20

10.58

1.89

8.69

0:29:30

10.53

1.88

8.65

0:29:40

10.50

1.89

8.62

0:29:50

10.48

1.84

8.64

0:30:00

10.43

1.76

8.67

0:30:10

10.40

1.76

8.64

0:30:20

10.39

1.69

8.70

0:30:30

10.34

1.70

8.64

0:30:40

10.31

1.67

8.64

0:30:50

10.25

1.67

8.58

0:31:00

10.25

1.64

8.61

0:31:10

10.20

1.54

8.66

0:31:20

10.18

1.55

8.64

0:31:30

10.14

1.57

8.57

0:31:40

10.09

1.52

8.57

0:31:50

10.07

1.43

8.64

0:32:00

10.02

1.47

8.55

0:32:10

10.01

1.43

8.58

0:32:20

9.98

1.38

8.60

0:32:30

9.96

1.38

8.58

0:32:40

9.93

1.34

8.59

0:32:50

9.90

1.33

8.57

0:33:00

9.84

1.29

8.56

0:33:10

9.83

1.29

8.54

0:33:20

9.80

1.21

8.59

0:33:30

9.76

1.23

8.53

0:33:40

9.74

1.19

8.55

0:33:50

9.70

1.21

8.49

0:34:00

9.68

1.17

8.51

0:34:10

9.65

1.11

8.54

0:34:20

9.62

1.11

8.51

0:34:30

9.58

1.09

8.49 (continued)

126

Appendixes

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:34:40

9.57

1.08

8.49

0:34:50

9.52

1.06

8.47

0:35:00

9.50

0.97

8.53

0:35:10

9.48

1.03

8.45

0:35:20

9.45

0.97

8.48

0:35:30

9.42

0.97

8.45

0:35:40

9.41

0.91

8.50

0:35:50

9.37

0.91

8.46

0:36:00

9.31

0.90

8.41

0:36:10

9.30

0.95

8.35

0:36:20

9.29

0.83

8.46

0:36:30

9.25

0.82

8.42

0:36:40

9.20

0.80

8.41

0:36:50

9.19

0.79

8.41

0:37:00

9.16

0.78

8.38

0:37:10

9.16

0.77

8.39

0:37:20

9.11

0.73

8.38

0:37:30

9.08

0.66

8.42

0:37:40

9.06

0.71

8.34

0:37:50

9.03

0.63

8.40

0:38:00

9.00

0.70

8.30

0:38:10

8.97

0.63

8.34

0:38:20

8.97

0.59

8.37

0:38:30

8.94

0.63

8.31

0:38:40

8.85

0.53

8.32

0:38:50

8.86

0.51

8.35

0:39:00

8.82

0.56

8.26

0:39:10

8.82

0.49

8.33

0:39:20

8.77

0.44

8.33

0:39:30

8.76

0.46

8.30

0:39:40

8.71

0.47

8.25

0:39:50

8.71

0.47

8.24

0:40:00

8.68

0.45

8.23

0:40:10

8.66

0.46

8.20

0:40:20

8.64

0.35

8.28

0:40:30

8.60

0.34

8.26

0:40:40

8.58

0.28

8.29 (continued)

Appendixes

127

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:40:50

8.53

0.42

8.11

0:41:00

8.51

0.37

8.14

0:41:10

8.49

0.31

8.18

0:41:20

8.47

0.30

8.17

0:41:30

8.44

0.32

8.11

0:41:40

8.43

0.29

8.14

0:41:50

8.39

0.22

8.17

0:42:00

8.37

0.28

8.09

0:42:10

8.36

0.24

8.12

0:42:20

8.33

0.27

8.06

0:42:30

8.31

0.27

8.04

0:42:40

8.28

0.24

8.04

0:42:50

8.26

0.20

8.6

0:43:00

8.22

0.17

8.05

0:43:10

8.20

0.14

8.06

0:43:20

8.17

0.15

8.02

0:43:30

8.17

0.08

8.09

0:43:40

8.14

0.12

8.02

0:43:50

8.11

0.06

8.04

0:44:00

8.08

0.05

8.03

0:44:10

8.07

0.02

8.05

0:44:20

8.03

0.01

8.04

0:44:30

8.03

0.04

7.99

0:44:40

8.01

0.01

8.02

0:44:50

7.96

0.00

7.96

0:45:00

7.95

0.02

7.97

0:45:10

7.91

0.06

7.97

0:45:20

7.92

0.04

7.96

0:45:30

7.89

0.02

7.87

0:45:40

7.85

0.07

7.91

0:45:50

7.85

0.00

7.85

0:46:00

7.80

0.07

7.86

0:46:10

7.78

0.13

7.90

0:46:20

7.77

0.07

7.84

0:46:30

7.76

0.13

7.89

0:46:40

7.72

0.15

7.87

0:46:50

7.70

0.09

7.79 (continued)

128

Appendixes

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:47:00

7.66

0.18

7.84

0:47:10

7.63

0.17

7.80

0:47:20

7.63

0.16

7.79

0:47:30

7.63

0.17

7.80

0:47:40

7.60

0.17

7.77

0:47:50

7.58

0.22

7.80

0:48:00

7.53

0.16

7.69

0:48:10

7.53

0.30

7.83

0:48:20

7.51

0.22

7.73

0:48:30

7.48

0.27

7.74

0:48:40

7.46

0.32

7.78

0:48:50

7.46

0.25

7.71

0:49:00

7.44

0.25

7.70

0:49:10

7.43

0.29

7.72

0:49:20

7.40

0.30

7.70

0:49:30

7.37

0.32

7.69

0:49:40

7.34

0.31

7.65

0:49:50

7.35

0.30

7.65

0:50:00

7.31

0.30

7.61

0:50:10

7.29

0.39

7.69

0:50:20

7.28

0.32

7.61

0:50:30

7.26

0.39

7.65

0:50:40

7.24

0.38

7.62

0:50:50

7.24

0.38

7.62

0:51:00

7.20

0.44

7.64

0:51:10

7.20

0.40

7.60

0:51:20

7.19

0.39

7.59

0:51:30

7.14

0.41

7.55

0:51:40

7.13

0.46

7.59

0:51:50

7.10

0.47

7.58

0:52:00

7.08

0.45

7.53

0:52:10

7.08

0.43

7.52

0:52:20

7.04

0.48

7

0:52:30

7.03

0.50

7.53

0:52:40

7.02

0.51

7.53

0:52:50

7.00

0.50

7.50

0:53:00

6.98

0.48

7.45 (continued)

Appendixes

129

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:53:10

6.96

0.54

7.50

0:53:20

6.94

0.52

7.46

0:53:30

6.91

0.54

7.45

0:53:40

6.89

0.58

7.47

0:53:50

6.90

0.52

7.42

0:54:00

6.88

0.53

7.41

0:54:10

6.85

0.52

7.38

0:54:20

6.84

0.60

7.44

0:54:30

6.82

0.59

7.41

0:54:40

6.79

0.54

7.33

0:54:50

6.78

0.52

7.30

0:55:00

6.76

0.59

7.35

0:55:10

6.74

0.64

7.39

0:55:20

6.71

0.63

7.34

0:55:30

6.69

0.60

7.29

0:55:40

6.69

0.61

7.29

0:55:50

6.65

0.58

7.24

0:56:00

6.67

0.62

7.30

0:56:10

6.63

0.62

7.25

0:56:20

6.59

0.67

7.27

0:56:30

6.61

0.69

7.30

0:56:40

6.58

0.71

7.29

0:56:50

6.57

0.67

7.23

0:57:00

6.55

0.71

7.26

0:57:10

6.53

0.73

7.27

0:57:20

6.52

0.65

7.17

0:57:30

6.52

0.65

7.17

0:57:40

6.50

0.68

7.18

0:57:50

6.47

0.72

7.19

0:58:00

6.47

0.71

7.17

0:58:10

6.45

0.74

7.19

0:58:20

6.43

0.71

7.14

0:58:30

6.44

0.73

7.17

0:58:40

6.41

0.75

7.16

0:58:50

6.40

0.77

7.17

0:59:00

6.38

0.73

7.11

0:59:10

6.38

0.73

7.11 (continued)

130

Appendixes

(continued) Time

Control (Mean–Ambient)

PWAT material (Mean–Ambient)

Drop in temp

0:59:20

6.36

0.70

7.06

0:59:30

6.35

0.75

7.10

0:59:40

6.33

0.81

7.14

0:59:50

6.32

0.80

7.13

1:00:00

6.31

0.81

7.12

Here, a representative experimental data for PCM non-woven material at 75 kph are given. Experiments were performed in triplicates for the speed of 55 and 75 kph for different PCM materials such as foam, nonwoven, fabric and composite. Data for these materials are also available.

Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:00:00

9.54

9.33

0.21

0:00:10

9.53

9.33

0.20

0:00:20

9.50

9.27

0.23

0:00:30

9.50

9.26

0.24

0:00:40

9.50

9.28

0.22

0:00:50

9.46

9.23

0.23

0:01:00

9.48

9.28

0.19

0:01:10

9.44

9.20

0.23

0:01:20

9.42

9.21

0.21

0:01:30

9.41

9.12

0.29

0:01:40

9.36

9.05

0.31

0:01:50

9.32

9.00

0.31

0:02:00

9.28

8.89

0.39

0:02:10

9.27

8.71

0.56

0:02:20

9.22

8.66

0.56

0:02:30

9.20

8.54

0.65

0:02:40

9.16

8.44

0.72

0:02:50

9.13

8.30

0.83

0:03:00

9.09

8.22

0.87

0:03:10

9.04

8.02

1.02

0:03:20

9.00

7.98

1.02

0:03:30

8.96

7.92

1.05

0:03:40

8.93

7.75

1.19

0:03:50

8.91

7.66

1.24 (continued)

Appendixes

131

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:04:00

8.84

7.52

1.32

0:04:10

8.82

7.47

1.35

0:04:20

8.79

7.40

1.40

0:04:30

8.74

7.35

1.39

0:04:40

8.70

7.24

1.47

0:04:50

8.65

7.12

1.53

0:05:00

8.62

7.09

1.53

0:05:10

8.58

6.94

1.63

0:05:20

8.54

6.91

1

0:05:30

8.52

6.87

1.65

0:05:40

8.49

6.82

1.67

0:05:50

8.44

6.76

1.68

0:06:00

8.43

6.70

1.73

0:06:10

8.38

6.57

1.81

0:06:20

8.32

6.55

1.76

0:06:30

8.30

6.46

1.84

0:06:40

8.27

6.42

1.85

0:06:50

8.25

6.26

1.99

0:07:00

8.19

6.22

1.97

0:07:10

8.21

6.21

2.00

0:07:20

8.17

6.14

2.03

0:07:30

8.12

6.07

2.05

0:07:40

8.12

6.03

2.09

0:07:50

8.08

6.00

2.08

0:08:00

8.06

5.90

2.15

0:08:10

8.01

5.88

2.13

0:08:20

8.00

5.75

2.25

0:08:30

7.94

5.85

2.09

0:08:40

7.89

5.71

2.18

0:08:50

7.87

5.62

2.25

0:09:00

7.86

5.53

2.33

0:09:10

7.85

5.55

2.29

0:09:20

7.81

5.49

2.32

0:09:30

7.78

5.45

2.33

0:09:40

7.74

5.39

2.35

0:09:50

7.73

5.31

2.42 (continued)

132

Appendixes

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:10:00

7.70

5.30

2.40

0:10:10

7.68

5.22

2.46

0:10:20

7.66

5.25

2.41

0:10:30

7.62

5.10

2.51

0:10:40

7.55

5.07

2.48

0:10:50

7.54

5.13

2.40

0:11:00

7.53

5.06

2.47

0:11:10

7.49

5.03

2.46

0:11:20

7.48

4.95

2.53

0:11:30

7.45

4.91

2.54

0:11:40

7.42

4.87

2.55

0:11:50

7.39

4.81

2.58

0:12:00

7.36

4.76

2.60

0:12:10

7.35

4.76

2.58

0:12:20

7.31

4.76

2.55

0:12:30

7.29

4.67

2.62

0:12:40

7.27

4.61

2.67

0:12:50

7.21

4.57

2.64

0:13:00

7.23

4.55

2.68

0:13:10

7.17

4.52

2.65

0:13:20

7.16

4.45

2.71

0:13:30

7.14

4.47

2.67

0:13:40

7.11

4.42

2.70

0:13:50

7.08

4.38

2.70

0:14:00

7.06

4.32

2.73

0:14:10

7.04

4.32

2.72

0:14:20

7.02

4.32

2.70

0:14:30

6.97

4.26

2.71

0:14:40

6.98

4.22

2.75

0:14:50

6.92

4.19

2

0:15:00

6.90

4.17

2.73

0:15:10

6.89

4.16

2.73

0:15:20

6.85

4.03

2.83

0:15:30

6.83

4.05

2.78

0:15:40

6.81

4.06

2.75

0:15:50

6.80

4.00

2.80 (continued)

Appendixes

133

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:16:00

6.78

3.97

2.81

0:16:10

6.76

3.90

2.85

0:16:20

6.74

3.93

2.80

0:16:30

6.70

3.86

2.84

0:16:40

6.65

3.83

2.82

0:16:50

6.64

3.82

2.82

0:17:00

6.63

3.80

2.84

0:17:10

6.60

3.75

2.85

0:17:20

6.58

3.69

2.89

0:17:30

6.56

3.72

2.83

0:17:40

6.52

3.67

2.86

0:17:50

6.50

3.67

2.83

0:18:00

6.47

3.58

2.89

0:18:10

6.46

3.51

2.95

0:18:20

6.44

3.50

2.94

0:18:30

6.40

3.52

2.87

0:18:40

6.37

3.46

2.91

0:18:50

6.38

3.44

2.94

0:19:00

6.34

3.39

2.95

0:19:10

6.33

3.38

2.94

0:19:20

6.30

3.41

2.89

0:19:30

6.29

3.34

2.95

0:19:40

6.27

3.32

2.95

0:19:50

6.24

3.32

2.92

0:20:00

6.21

3.26

2.95

0:20:10

6.19

3.21

2.98

0:20:20

6.20

3.19

3.01

0:20:30

6.18

3.10

3.08

0:20:40

6.13

3.18

2.95

0:20:50

6.11

3.09

3.02

0:21:00

6.09

3.14

2.95

0:21:10

6.07

3.09

2.98

0:21:20

6.06

3.05

3.01

0:21:30

6.03

3.02

3.02

0:21:40

6.01

2.99

3.02

0:21:50

5.99

2.97

3.02 (continued)

134

Appendixes

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:22:00

5.95

2.98

2.98

0:22:10

5.95

2.96

2.99

0:22:20

5.92

2.93

2.99

0:22:30

5.91

2.87

3.04

0:22:40

5.89

2.87

3.02

0:22:50

5.88

2.82

3.06

0:23:00

5.85

2.85

3.00

0:23:10

5.82

2.81

3.00

0:23:20

5.82

2.68

3.14

0:23:30

5.79

2.77

3.02

0:23:40

5.75

2.75

2.99

0:23:50

5.74

2.71

3.03

0:24:00

5.72

2.66

3.06

0:24:10

5.74

2.63

3.11

0:24:20

5.70

2.68

3

0:24:30

5.66

2.59

3.07

0:24:40

5.64

2.58

3.06

0:24:50

5.63

2.63

3.00

0:25:00

5.62

2.63

2.98

0:25:10

5.58

2.56

3.02

0:25:20

5.54

2.54

2.99

0:25:30

5.55

2.53

3.02

0:25:40

5.52

2.47

3.05

0:25:50

5.53

2.52

3.01

0:26:00

5.48

2.44

3.05

0:26:10

5.49

2.36

3.13

0:26:20

5.45

2.42

3.03

0:26:30

5.44

2.38

3.05

0:26:40

5.42

2.39

3.03

0:26:50

5.40

2.31

3.09

0:27:00

5.39

2.32

3.07

0:27:10

5.37

2.34

3.03

0:27:20

5.34

2.37

2.97

0:27:30

5.35

2.31

3.04

0:27:40

5.30

2.27

3.03

0:27:50

5.31

2.27

3.05 (continued)

Appendixes

135

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:28:00

5.26

2.19

3.07

0:28:10

5.25

2.24

3.01

0:28:20

5.25

2.17

3.07

0:28:30

5.21

2.17

3.04

0:28:40

5.23

2.25

2.97

0:28:50

5.19

2.16

3.04

0:29:00

5.18

2.17

3.01

0:29:10

5.17

2.09

3.08

0:29:20

5.14

2.09

3.05

0:29:30

5.13

2.14

2.99

0:29:40

5.10

2.08

3.03

0:29:50

5.10

2.04

3.05

0:30:00

5.09

2.00

3.09

0:30:10

5.05

1.99

3.07

0:30:20

5.03

2.07

2.95

0:30:30

5.00

2.06

2.94

0:30:40

5.02

1.98

3.04

0:30:50

4.98

2.02

2.96

0:31:00

4.99

2.00

2.99

0:31:10

4.94

1.91

3.03

0:31:20

4.94

1.89

3.05

0:31:30

4.93

1.93

3.00

0:31:40

4.88

1.90

2.98

0:31:50

4.90

1.91

2.99

0:32:00

4.87

1.90

2.97

0:32:10

4.82

1.85

2.97

0:32:20

4.84

1.82

3.02

0:32:30

4.82

1.87

2.95

0:32:40

4.79

1.75

3.04

0:32:50

4.78

1.78

3.00

0:33:00

4.74

1.72

3.02

0:33:10

4.75

1.73

3.01

0:33:20

4.74

1.78

2.95

0:33:30

4.74

1.74

3.00

0:33:40

4.70

1.64

3.06

0:33:50

4.71

1.72

2.99 (continued)

136

Appendixes

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:34:00

4.68

1.69

2.99

0:34:10

4.66

1.70

2.95

0:34:20

4.66

1.65

3.00

0:34:30

4.64

1.61

3.04

0:34:40

4.64

1.65

2.99

0:34:50

4.61

1

3.00

0:35:00

4.61

1.61

2.99

0:35:10

4.58

1.63

2.96

0:35:20

4.57

1.63

2.93

0:35:30

4.56

1.58

2.97

0:35:40

4.56

1.57

2.98

0:35:50

4.53

1.56

2.97

0:36:00

4.52

1.52

3.00

0:36:10

4.49

1.53

2.96

0:36:20

4.49

1.51

2.98

0:36:30

4.44

1.52

2.92

0:36:40

4.42

1.44

2.99

0:36:50

4.44

1.49

2.95

0:37:00

4.42

1.51

2.91

0:37:10

4.42

1.50

2.92

0:37:20

4.40

1.47

2.92

0:37:30

4.41

1.39

3.01

0:37:40

4.35

1.40

2.96

0:37:50

4.35

1.45

2.90

0:38:00

4.34

1.38

2.97

0:38:10

4.33

1.42

2.90

0:38:20

4.32

1.40

2.92

0:38:30

4.30

1.39

2.91

0:38:40

4.29

1.36

2.92

0:38:50

4.27

1.36

2.91

0:39:00

4.28

1.37

2.91

0:39:10

4.26

1.33

2.93

0:39:20

4.24

1.35

2.89

0:39:30

4.25

1.37

2.88

0:39:40

4.22

1.32

2.90

0:39:50

4.23

1.22

3.01 (continued)

Appendixes

137

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:40:00

4.19

1.27

2.92

0:40:10

4.18

1.26

2.91

0:40:20

4.14

1.30

2.84

0:40:30

4.15

1.21

2.94

0:40:40

4.14

1.29

2.85

0:40:50

4.12

1.20

2.92

0:41:00

4.11

1.25

2.86

0:41:10

4.10

1.22

2.88

0:41:20

4.09

1.18

2.92

0:41:30

4.08

1.20

2.88

0:41:40

4.05

1.16

2.89

0:41:50

4.02

1.19

2.83

0:42:00

4.02

1.20

2.82

0:42:10

4.03

1.16

2.88

0:42:20

4.01

1.13

2.88

0:42:30

4.00

1.12

2.88

0:42:40

3.98

1.09

2.89

0:42:50

3.97

1.09

2.88

0:43:00

3.96

1.07

2.89

0:43:10

3.95

1.15

2.80

0:43:20

3.94

1.12

2.82

0:43:30

3.92

1.07

2.85

0:43:40

3.92

1.07

2.85

0:43:50

3.93

1.01

2.92

0:44:00

3.91

0.99

2.91

0:44:10

3.87

1.08

2.80

0:44:20

3.89

0.99

2

0:44:30

3.85

1.02

2.84

0:44:40

3.86

1.03

2.83

0:44:50

3.85

1.04

2.81

0:45:00

3.81

1.02

2.79

0:45:10

3.81

1.01

2.81

0:45:20

3.81

0.98

2.83

0:45:30

3.80

0.99

2.81

0:45:40

3.78

0.93

2.86

0:45:50

3.77

0.97

2.81 (continued)

138

Appendixes

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:46:00

3.78

0.94

2.84

0:46:10

3.75

0.92

2.83

0:46:20

3.74

0.87

2.88

0:46:30

3.75

0.93

2.82

0:46:40

3.73

0.90

2.82

0:46:50

3.73

0.93

2.80

0:47:00

3.70

0.86

2.84

0:47:10

3.71

0.91

2.80

0:47:20

3.66

0.91

2.75

0:47:30

3.67

0.92

2.75

0:47:40

3.65

0.90

2.75

0:47:50

3.65

0.87

2.78

0:48:00

3.64

0.86

2.79

0:48:10

3.66

0.89

2.77

0:48:20

3.61

0.82

2.79

0:48:30

3.62

0.85

2.77

0:48:40

3.61

0.82

2.79

0:48:50

3.60

0.87

2.72

0:49:00

3.56

0.84

2.72

0:49:10

3.55

0.81

2.74

0:49:20

3.57

0.85

2.72

0:49:30

3.55

0.80

2.75

0:49:40

3.56

0.80

2.77

0:49:50

3.52

0.81

2.70

0:50:00

3.55

0.81

2.74

0:50:10

3.50

0.75

2.75

0:50:20

3.51

0.80

2.71

0:50:30

3.49

0.79

2.70

0:50:40

3.48

0.82

2.66

0:50:50

3.48

0.70

2.78

0:51:00

3.48

0.78

2.70

0:51:10

3.47

0.76

2.71

0:51:20

3.44

0.75

2.69

0:51:30

3.44

0.76

2.68

0:51:40

3.43

0.71

2.72

0:51:50

3.43

0.70

2.73 (continued)

Appendixes

139

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:52:00

3.42

0.71

2.71

0:52:10

3.40

0.66

2.73

0:52:20

3.38

0.68

2.70

0:52:30

3.37

0.72

2.65

0:52:40

3.38

0.67

2.70

0:52:50

3.33

0.68

2.65

0:53:00

3.35

0.67

2.68

0:53:10

3.32

0.73

2.60

0:53:20

3.31

0.69

2.62

0:53:30

3.33

0.69

2.64

0:53:40

3.32

0.67

2.65

0:53:50

3.28

0.69

2.59

0:54:00

3.30

0.65

2.64

0:54:10

3.27

0.65

2.63

0:54:20

3.26

0.64

2.62

0:54:30

3.26

0.66

2.60

0:54:40

3.24

0.64

2.60

0:54:50

3.24

0.63

2.60

0:55:00

3.22

0.60

2.63

0:55:10

3.23

0.63

2.59

0:55:20

3.21

0.63

2.58

0:55:30

3.21

0.67

2.54

0:55:40

3.21

0.63

2.58

0:55:50

3.17

0.66

2.51

0:56:00

3.17

0.61

2.56

0:56:10

3.16

0.61

2.56

0:56:20

3.15

0.59

2.56

0:56:30

3.12

0.58

2.55

0:56:40

3.14

0.57

2.57

0:56:50

3.13

0.64

2.49

0:57:00

3.09

0.56

2.53

0:57:10

3.11

0.61

2.50

0:57:20

3.12

0.58

2.54

0:57:30

3.07

0.55

2.51

0:57:40

3.08

0.62

2.47

0:57:50

3.06

0.53

2.53 (continued)

140

Appendixes

(continued) Time

Control (Mean–Ambient)

PCM non-woven material (Mean–Ambient)

Drop in temp

0:58:00

3.07

0.54

2.53

0:58:10

3.06

0.59

2.47

0:58:20

3.06

0.55

2.51

0:58:30

3.04

0.55

2.48

0:58:40

3.04

0.52

2.53

0:58:50

3.03

0.58

2.45

0:59:00

3.01

0.58

2.43

0:59:10

3.01

0.55

2.46

0:59:20

2.99

0.54

2.45

0:59:30

2.97

0.51

2.46

0:59:40

2.98

0.48

2.50

0:59:50

2.98

0.51

2.47

1:00:00

2.98

0.51

2.47

A.2 Total Amount of Heat Absorbed by PCM Materials The total amount of heat absorbed by PCM materials was calculated based on the experimental results obtained from DSC graphs using the following equation: Total amount of heat absorbed (W ) = (m × H )/t where m is the mass of the PCM material used in the experiments, H is the difference in the heat absorbed in J/g as shown by the DSC curves within each temperature range and t is the calculated value of time taken for this temperature range at a heating rate of 2 °C/min. The calculation has been explained for the case of PCM non-woven material as shown below: Start temperature = 20.68 °C (coloured blue in the curve) End temperature = 28.01 °C (coloured blue in the curve) Drop in temperature = (28.01 – 20.68) °C = 7.33 °C Rate of heating is 2 °C/min. Hence, the time taken for this drop in temperature = 7.33 × 60/2 s = 219.9 s. The H values as shown in the DSC curves are: For temperature of 28.01 ◦ C(H ) = 75.8737 J/g

Appendixes

141

For temperature of 20.68 ◦ C(H ) = 16.7698 J/g Heat absorbed for this range (28.01–20.68) (H) = (75.8737 – 16.7698) J/g = 59.1039 J/g. Weight of the PCM non-woven material used in the experiments (m) = 66 g. Hence heat absorbed = 59.1039 × 66{(J/g) × g} = 3900.8574 J Heat absorbed in Watts = 3900.8574/219.9 J/s = 17.74 W

Similarly, the calculations can be done for the other PCM materials (i.e. foam, fabric and composite) as explained above.

Uncited Reference

1. X. Liu, I. Holmer, Evaluation of evaporative heat transfer characteristics of helmets. Appl. Hum. Sci. 16(3), 107–113 (1997)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 S. Kanesalingam and R. Nayak, Sustainable Phase Change and Polymeric Water Absorbent Materials, https://doi.org/10.1007/978-981-15-5750-7

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