Refrigeration Systems, Design Technologies and Developments [1 ed.] 9781624172304, 9781624172298

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Copyright © 2013. Nova Science Publishers, Incorporated. All rights reserved. Refrigeration Systems, Design Technologies and Developments, Nova Science Publishers, Incorporated, 2013. ProQuest Ebook

Copyright © 2013. Nova Science Publishers, Incorporated. All rights reserved. Refrigeration Systems, Design Technologies and Developments, Nova Science Publishers, Incorporated, 2013. ProQuest

MANUFACTURING TECHNOLOGY RESEARCH

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REFRIGERATION SYSTEMS, DESIGN TECHNOLOGIES AND DEVELOPMENTS

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MANUFACTURING TECHNOLOGY RESEARCH

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REFRIGERATION SYSTEMS, DESIGN TECHNOLOGIES AND DEVELOPMENTS

DONATUS ALDA AND

DAVIDE CIARLO EDITORS

New York

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The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

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CONTENTS

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Preface

vii

Chapter 1

Adsorption Refrigeration Ahmed Rezk, Ahmed Elsayed, Saad Mahmoud and Raya AL-Dadah

Chapter 2

How to Improve the Performance of Heat Pumps in Air-Conditioning Plants by Using Membrane Contactor Dehumidification/Regeneration Systems Stefano Bergero and Anna Chiari

Chapter 3

Chapter 4

Chapter 5

Condensation Heat Transfer in Smooth and Enhanced Geometries: A Review of the Recent Literature A. S. Dalkilic and S. Wongwises Prototyping and Experimental Evaluation of an Air Filtration System Yucheng Liu, Safa Alidoust and Benny Qi Irreversible Estimation Possibilities of an Absorption Refrigeration Cycle A. M. Tsirlin and I. N. Grigorevskii

Index

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57

113

155

167 183

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PREFACE This book examines the design technologies and developments in refrigeration systems. Topics discussed include sorption refrigeration systems; improving the performance of heat pumps in air-conditioning plants by using membrane contactor dehumidification/regeneration systems; the correct size of the condenser as one of the significant issues for the optimal performance of refrigerating and air conditioning systems; prototyping and experimental evaluation of an air filtration system; and irreversible estimation possibilities of an absorption refrigeration cycle. Chapter 1 - The global demand for commercial and domestic refrigeration and air conditioning systems has dramatically increased; currently it takes around third of the total worldwide energy consumption. Mechanical vapour compression refrigeration systems use refrigerants with adverse environmental effects. Sorption refrigeration systems offer the potential for better alternative to the mechanical vapour compression systems, if their technology can be improved to overcome current limitations. Sorption refrigeration systems are driven using low grade energy, solar energy and waste heat, and can operate with environmentally friendly refrigerants and non corrosive materials. This chapter presents a comprehensive review for adsorption cooling systems, including adsorption principles, refrigerants used, adsorbent materials, working pairs, various bed designs, operating conditions, development techniques and their applications. Chapter 2 - This chapter deals with the studies carried out in recent years at the University of Genoa, Italy, concerning the use of membrane contactors for air dehumidification and their integration into air-conditioning plants in order to improve the performances of heat pumps, thereby saving energy.

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viii

Donatus Alda and Davide Ciarlo

In the first part of this chapter (sections 1-5) experimental and numerical studies regarding air dehumidification by means of hydrophobic membrane contactors and LiCl desiccant solutions are reported. Desiccant-membrane systems offer several potential benefits: large working membrane area per unit volume; no carryover of liquid-phase droplets; no pollution of the liquid phase by atmospheric dust; good dehumidification efficiency, and potential highefficiency control of the quality of the handled air. Specifically, experimental tests on a plane-plate cross-flow membrane contactor prototype, made up of composite PTFE membranes fixed to PP supports, are described. A FORTRAN computer code able to study the behaviour of the contactor has been developed. Theoretical analysis involves mass and energy equations for both air and liquid desiccant. Moreover, heat and vapour mass fluxes through the membrane have been analysed. The agreement between theoretical predictions and the experimental data has been discussed. The possibility of using membrane contactors in air-conditioning systems is discussed in the second part of the chapter (sections 6-9). Specifically, the performances of a hybrid air-conditioning system in which a vapourcompression inverse cycle is integrated with an air dehumidification system working with membrane contactors and a hygroscopic solution have been investigated. This plant may be a valid alternative to traditional summertime air-conditioning systems, in which the air is cooled to below its dew-point temperature and subsequently reheated. The advantage of the hybrid system lies in the fact that the refrigeration device operates at a higher evaporation temperature than that of a traditional system, in which dehumidification is achieved through condensation. The proposed hybrid system involves simultaneously cooling and dehumidifying the air conveyed to the conditioned space in an air-solution membrane contactor. An LiCl solution is cooled by means of a vapour-compression inverse cycle using the refrigerant KLEA 410A. The solution is regenerated in another membrane contactor by exploiting the heat exchanged by the condenser. A SIMULINK calculation programme was specially designed in order to simulate the system under examination in steady-state conditions. The performances of the system were analysed on varying the most significant operating parameters and were compared with those of a traditional airconditioning plant in a typical case-study of summertime air-conditioning. The results of the simulations revealed significant energy savings, which, in particular operating conditions, may exceed 50%.

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Preface

ix

Chapter 3 - The correct size of the condenser is one of the significant issues for the optimal performance of refrigerating and air conditioning systems. This paper reports on most of the condensation heat transfer literature; both occurred in-tubes and in-channels related to the use of smooth and enhanced surfaces. The peer reviewed papers published in citation index journals in 2010 and 2011 are selected for review in the paper. Classification of the papers is performed considering tube geometry. The critical information on the theoretical, experimental and numerical works is presented comprehensively for each paper. This paper presents the in-tube condensation papers published in 2010 and 2011. It is expected to be a starting point for researchers who are interested in in-tube condensation process. Generalization of the proposed theoretical, empirical and numerical models is still significant on the two-phase flow applications. The use of new techniques such as CFD programs and artificial intelligence which need the validation with a large number of experimental data is also required. Chapter 4 - A cost effective, portable air filtration system was developed, built, and evaluated at the University of Louisiana at Lafayette. Prototype of the presented system was developed for experimental assessment and its computational model was also created for CFD simulation. The experimental and computer simulation results showed that the developed system could efficiently and safely remove and dispose accumulated particulate matter (in the size range of 5 ~ 1000 μm), and be tolerant to the abrasive properties that the particulate matter may have. The developed air filtration system as well as the applied technology can be further optimized and extended to be applied in aerospace and space engineering to remove suspended particles out from the closed cabinet of aircrafts or spacecrafts. The outcome of this project will also impact other commercial sectors and industries. Chapter 5 - Based on thermodynamic energy and entropy balances, the relationship between energy consumption for cooling and the heat ratio for an absorption refrigerating machine with mode and construction variables has been obtained. The limiting refrigeration capacity of the machine and the corresponding value of the heat ratio have been found. The problem of the optimal distribution of heat-exchange surfaces has been solved.

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In: Refrigeration Systems, Design … Editors: D. Alda and D. Ciarlo

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Chapter 1

ADSORPTION REFRIGERATION Ahmed Rezk, Ahmed Elsayed, Saad Mahmoud and Raya AL-Dadah* School of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham, UK

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ABSTRACT The global demand for commercial and domestic refrigeration and air conditioning systems has dramatically increased; currently it takes around third of the total worldwide energy consumption. Mechanical vapour compression refrigeration systems use refrigerants with adverse environmental effects. Sorption refrigeration systems offer the potential for better alternative to the mechanical vapour compression systems, if their technology can be improved to overcome current limitations. Sorption refrigeration systems are driven using low grade energy, solar energy and waste heat, and can operate with environmentally friendly refrigerants and non corrosive materials. This chapter presents a comprehensive review for adsorption cooling systems, including adsorption principles, refrigerants used, adsorbent materials, working pairs, various bed designs, operating conditions, development techniques and their applications.

*

Corresponding Author: [email protected].

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1. INTRODUCTION Refrigeration and air conditioning systems are required for food and vaccines transportation, comfort cooling, cold storage application, supermarket display and retails. It is predicted that the global market of air conditioning to reach 78.8 million units in volume sales by 2015 and is expected to increase further due to warm climate and high capita income (The Freedonia Group Report, 2010). Currently, most of this demand is met by mechanical vapour compression systems driven by high grade electrical power sources, use refrigerants with high global warming potential (Hassan et al. 2011 and Verde et al. 2010) and consume around 30% of total worldwide energy consumption (Navarro-Esbr et al. 2007). Therefore there is a need for alternative refrigeration systems that can use low grade heat and environment friendly refrigerants. Sorption cooling technology compresses the refrigerant using thermal compressors where the affinity of certain material to an appropriate refrigerant can be used to form a sorption / desorption cycle and pump the refrigerant. The sorption phenomena can be classified as absorption or adsorption depending on the sorbent material. When the sorbent material is liquid, the term absorption is used and if the sorbent material is solid, it is called an adsorption. Table 1 shows the advantages of adsorption compared to absorption systems. Sorption refrigeration integrated with combined heating and power (CHP) plants have been used in many industrial and commercial applications (Li and Wu 2009, Tora and Elghawi 2011, Huangfu et al. 2007 and Wang and Oliveira 2006) as trigeneration systems, also in sustainable building climatisation using solar energy as heat source (Luo et al. 2010, Sarabia Escriva et al 2011, Lemmini and Errougani 2007, Wang et al. 2009).

2. ADSORPTION REFRIGERATION CYCLE The adsorption refrigeration cycle is two sources two sinks thermodynamic cycle, which operates using three temperature levels (evaporation, ambient and regeneration temperatures). Two of these temperatures drive the thermal compressor “Reactors” that replaces the mechanical compressor in vapour compression refrigeration cycle (Demir et al. 2009) as shown in Figures 1-2. The cycle also operates between two pressures (Pe and Pc) and two refrigerant/adsorbent concentration levels.

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Table 1. The advantages of adsorption over absorption refrigeration systems Attribute Heat source

Adsorption  It is powered by sources of wide temperature range.  Temperature as low as 50˚C can be used as heat source, while heat sources with temperature close to 500˚C can be used directly without producing any kind of corrosion problem.  There is no limitation for the low temperature reservoir.

Operating consideration





Maintenance

   

Lifetime

Chua et al. 2001, Zycon, 2012.



It is utilized by solid sorbents and hence it is suitable for conditions with serious vibration, such as in fishing boats and locomotives. It is almost noiseless system, where there are no many moving parts. Operation possibility over 8000hr per year. There are no special requirements for maintenance, where few used moving parts (vacuum pump). Annual cleaning of condenser tubes is required. Simple control system is required

It has relatively very long lifetime and there are no special disposal requirements.

Absorption  Very sensitive against source temperature and the variation must be tightly controlled between 82˚C and 100˚C.  Heat source must be higher than 70˚C to avoid the crystallization problem, even in two-stage cycle.  Sever corrosion would start to occur for temperatures above 200˚C.  Low temperature reservoir must be 18-29˚C  It is utilized by liquid sorbent and hence it is suitable for stationary units only, where unfavourable absorbent flow from the generator / absorber to the evaporator / condenser.  Daily shutdown due to the dilution of sorbent solution        

It needs regular monitoring and maintenance for: Liquid analysis - pumps Control system Back up boiler Air leakage Sorbent exchange Heat exchanger replacement due to salt corrosion. The maximum life time is 7-9 years, due to the problem of salt corrosion.

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Ahmed Rezk, Ahmed Elsayed, Saad Mahmoud et al.

In process 1-2 (as shown in Figure 2) the adsorbent bed of high concentration level is heated up by means of high temperature source (Tgeneration) to desorb the refrigerant which results in increasing the adsorbent bed pressure from low pressure level (Pe) to high pressure level (Pc). During process 2-3 the adsorbent bed is heated up using the same temperature level (Tgeneration) and connected to the condenser (2-3`) to allow the desorbed refrigerant to be condensed and passed back to the evaporator (3`-4`). The adsorbent bed reactor of low concentration level (3) is cooled down using intermediate temperature level (Tambient) and reducing the reactor pressure from high pressure level (Pc) to low pressure level (Pe) during process (3-4). The adsorbent bed of low concentration level and low pressure is then cooled (4-1) while being connected to the evaporator and adsorbing the refrigerant vapour to achieve the cooling effect at the evaporative temperature (Tevaporation) by means of evaporation (4`-1).

3. ADSORPTION REFRIGERATION CYCLES

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This section describes the various adsorption refrigeration cycles based on the number of adsorber beds used and their configuration in the cycle.

Thigh Generator / Desorber

Tambient Absorber / Adsorber

Qgeneration Qsorption Heat engine

Driving Energy

Refrigeration Cycle

Qcondensation Qevaporator Tambient Condenser

Tlow Evaporator

Figure 1. Sorption thermodynamic cycle.

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Qcondensation 3\

re Re f Flo riger ant w

2

Pu

Pressure

Pc

Pe

Qgeneration

Mi n con refri cen ger tra ant tio n

Ma x con refr cen iger tra ant tio n

Adsorption Refrigeration

3

Qgeneration Refrigeration Cycle

Qsorption

Heat Engine

4\ 1 Qevaporator

4 Qsorption Temperature

Figure 2. Sorption Clapeyron diagram.

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3.1. Simple Two-Bed Adsorption Refrigeration Cycle This cycle consists of four main parts namely: reactors (adsorber or desorber based on operating mode), evaporator, and condenser (Hamamoto et al. 2006 and Wang and Chua 2007). The reactors are packed with adsorbent material which has the capability of adsorbing or desorbing the adsorbate/refrigerant during the adsorption or desorption process. Interconnecting valves are used to control the refrigerant flow as shown in Figure 3. The adsorption is an exothermic process, so the heat of adsorption needs to be removed by means of continuous cooling. On the other hand, during the desorption process heating is required to desorb the refrigerant from the adsorbent pores. The aforementioned components are controlled to work sequentially through four modes shown in Figures 4 and 2 namely; isosteric heating (preheating switching) (1-2), isobaric desorption / condensation (2-3 / 2-3`), isosteric cooling (precooling switching) (3-4) and isobaric adsorption / evaporation (4-1 / 4`-1). In the isosteric heating/cooling also named switching periods, the refrigerant amount in the reactor chambers remains constant. During the switching modes all interconnected valves are closed to keep the amount of refrigerant in the reactors constant during preheating / precooling. As a result, during the preheating mode the reactor pressure increases from the evaporation pressure to the condensation pressure and vice versa during the

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precooling. During the isobaric cooling, one of the reactors is connected to the evaporator to adsorb the refrigerant vapor from the evaporator producing the cooling effect. During the isobaric heating process the other reactor is connected to the condenser to deliver the refrigerant to be condensed and then flow to the evaporator through the liquid line. Using two adsorption reactors is necessary to obtain continuous cooling by making both of them working in parallel, while one reactor in adsorption, the other one is in desorption mode. Table 2and Figure 4 present the cyclic operating modes and valving operating sequence for simple two-bed adsorption refrigeration cycle shown in Figure 3. Table 2. Two bed cyclic operation and valving operating sequence Component Mode Mode-A Switching Mode-B Ads/Des Mode-C Switching Mode-D Ads/Des

Bed-A

Bed-A

V1

V2

V3

V4

Heating Heating Cooling

Cooling Cooling Heating

X O X

X X X

X O X

X X X

Cooling

Heating

X

O

X

O

X = closed, O = Open

Cooling/Heating water in/out

V2

Adsorbent Reactor

V4 Evaporator

Liquid Refrigerant

Condenser V3 Cooling/Heating water in/out

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Cooling water in/out

V1

Chilled water in/out

Figure 3. Flow diagram of simple two-bed adsorption refrigeration cycle.

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Adsorption Refrigeration Cooling water in/out

Cooling water in/out

V4

V4

V1

Evaporator

B

Cooling water in/out

ADSORPTION

DESORPTION

V2

A

Heating water in/out

Liquid Refrigerant

Cooling water in/out

B

COOLING DOWN

HEATING UP

A

Heating water in/out

V3

V2

Liquid Refrigerant

Condenser

Condenser V3

V1

Evaporator

Chilled water in/out

Chilled water in/out

Mode-A

Mode-B

Cooling water in/out Cooling water in/out

V4

Evaporator

V1

V4

Chilled water in/out

Mode-C

B

Evaporator

Cooling water in/out

DESORPTION

A

ADSORPTION

V2

Liquid Refrigerant

Condenser V3

Heating water in/out

B

Heating water in/out

HEATING UP

COOLING DOWN

A

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V2

Liquid Refrigerant

Condenser V3

V1

Chilled water in/out

Mode-D

Figure 4. Two bed adsorption cycle operating modes.

During the switching mode heat and/or mass recovery can be used (Taylan et al 2010, Lu et al. 2012, Wang, R.Z. 2001). During mass recovery, the adsorber and desorber are connected to speed up the pressure reduction of hot bed and pressure increase of the cold bed and hence the mechanical equilibrium by means of pressure swing (Ng et al. 2006). During heat recovery period, the cooling water flows through the hot bed and then to cold bed, which reduces the heat required for generating the refrigerant and hence improve the cycle performance (Wang et al. 2005 and Baker, D. K. 2008).

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3.2. Integrated Adsorption Refrigeration Cycle

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The integrated adsorption refrigeration cycle consists of two units where each one consists of adsorbent bed, condenser and evaporator (Liu et al. 2005) as shown in Figure 5. The major difference between this cycle and the simple two-bed adsorption refrigeration cycle is the absence of the switching mode, which makes it more reliable (Chen et al. 2010). The cycle operation is based on two modes; adsorption / evaporation and desorption / condensation where each unit alternatively works in different mode. There is a group of control valves used to control the flow of secondary fluid to each unit. This cycle was modified to reduce the number of heat exchangers, where each unit consists of one adsorbent bed and one coil that is working either as condenser or evaporator depending on the operating mode (Chang et al. 2009). The integrated cycle was also enhanced by combining it with a third chamber of a different refrigerant which acts as a heat pipe (Di et al. 2007, Wu and Li (2009), Wang et al. 2005, Xia et al. 2008) as shown in Figure 6. The integrated adsorption cycle can also be enhanced by including heat and mass recovery methods. CW in/out

HW in/out

CHW in/out

Bed-A

Bed-B

Condenser-A

Condenser-B

Evaporator-A

Evaporator-B

CW = Cooling Water HW = Heating Water CHW = Chilled Water = Valve

Figure 5. Schematic diagram of integrated adsorption refrigeration cycle.

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Adsorption Refrigeration CW in/out HW in/out Bed-A

Bed-B

Condenser-A

Condenser-B

Isolator

Isolator

Methanol

Evaporator

CHW out

CW = Cooling Water HW = Heating Water CHW = Chilled Water = Valve

CHW in

Figure 6. Schematic diagram for the integrated adsorption refrigeration cycle combined with heat pipe.

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3.3. Three Bed Adsorption Heat Cycle Three-bed adsorption refrigeration cycle consists of three adsorbent beds (reactors) in addition to condenser and evaporator. The aim of using three-bed is to obtain continues evaporation and hence continues cooling. Three-bed adsorption cycle is controlled by four operating modes (preheating, desorption, precooling and adsorption) and 12 operating steps (Saha et al. 2003). During preheating and precooling modes, the interconnecting valves between the adsorbent bed and the evaporator / condenser are closed to change the reactor pressure level. During adsorption mode, a cooling water stream flows through the adsorbent bed, while the interconnecting valve between the bed and the evaporator is opened. The interconnecting valve between the bed and condenser is closed to avoid the reverse flow. During desorption mode, the interconnecting valve between the adsorbent bed and the condenser is opened to condense the desorbed refrigerant to flow through the liquid line to the evaporator. Table 3 presents the operating modes and steps of the three-bed adsorption refrigeration cycle shown in Figure 7. Mass recovery scheme can be applied in three-bed adsorption refrigeration cycle (Khan et al. 2007).

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CW out

Condenser

Bed-A

Liquid line

V-3 Bed-B

CW/HW in/out

V-4

V-1 Bed-C CW/HW in/out

V-2

Evaporator CHW out

CHW in

CW = Cooling Water HW = Heating Water CHW = Chilled Water V = Valve

Figure 7. Schematic diagram for three-bed adsorption cycle.

Table 3. Operating modes and steps of three-bed adsorption cycle

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Component Steps Step-1 Step-2 Step-3

Bed-A

Bed-B

Bed-C

Desorption Desorption Desorption

Adsorption Adsorption Adsorption

Desorption Precooling Adsorption

Step-4

Desorption

Preheating

Adsorption

Step-5

Desorption

Desorption

Adsorption

Step-6

Precooling

Desorption

Adsorption

Step-7

Adsorption

Desorption

Adsorption

Step-8

Adsorption

Desorption

Preheating

Step-9

Adsorption

Desorption

Desorption

Step-10

Adsorption

Precooling

Desorption

Step-11

Adsorption

Adsorption

Desorption

Step-12

Preheating

Adsorption

Desorption

3.3.1. Three Bed with Dual Evaporator Adsorption Refrigeration Cycle This adsorption refrigeration cycle was designed to achieve adsorption equilibrium uptake difference. That means more refrigerant flow rate and hence more cooling capacity (Miyazaki et al. 2010). This cycle consists of three adsorbent-bed reactors in addition to two evaporator heat exchangers as shown in Figure 8. One of the evaporators is working at low evaporative temperature, while the other one is working at higher evaporative temperature. There are five operating modes controlled by five steps and these operating

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Adsorption Refrigeration

modes namely; low pressure adsorption, high pressure adsorption, desorption, preheating and precooling as shown in Table 4. During low pressure adsorption, the adsorbent-bed reactors are connected to the low pressure evaporator via the interconnecting valves. During high pressure adsorption, the adsorbent-bed reactor is connected to the high pressure evaporator using the interconnecting valves. During preheating and precooling, the interconnecting valves are completely closed to change the adsorbent-bed reactor pressure level.

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CW/HW in/out

CHW out

Condenser

Bed-2

CW out

Liquid line

Bed-1

Liquid line

CW in

Bed-3 CW/HW in/out

LP = Low pressure HP = High pressure CW = Cooling Water HW = Heating Water CHW = Chilled Water = Valve

LP Evaporator

HP Evaporator

CHW in

Figure 8. Schematic diagram for three-bed dual evaporator adsorption refrigeration cycle

Table 4. Operating modes and valving system of three-bed dual evaporator adsorption refrigeration cycle Component Step Step-1 Step-2 Step-3 Step-4 Step-5 Step-6

Bed-A

Bed-B

Bed-C

Desorption Precooling LP Adsorption LP Adsorption HP Adsorption Preheating

HP Adsorption Preheating Desorption Precooling LP Adsorption LP Adsorption

LP Adsorption LP Adsorption HP Adsorption Preheating Desorption Precooling

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3.4. Multi-Stages Adsorption Refrigeration Cycle Multistage adsorption refrigeration cycle is used to utilize low generation temperature sources 45-60˚C, heat sink temperature of 30˚C and evaporative temperature of 7˚C (Saha et al. 2006 and Hamamoto et al. 2005). These operating temperatures are not suitable for simple two-bed adsorption refrigeration cycle operation (Khan et al. 2008). In this cycle the pressure increases from evaporation pressure to condensation pressure through three progressive steps using the same adsorption / desorption temperatures. Figure 9 is a schematic diagram for three-stage adsorption refrigeration cycle. In this cycle three adsorbent-bed reactors are heated up in parallel with cooling down the other beds. Preheating / precooling are needed prior desorption / adsorption modes in order to change the pressure level. Table 5 presents the operating modes of three stage adsorption cycle. Table 6 summarises the main features of the various adsorption cycles described above. CW in

Condenser

CW out

V-1 Bed-2 CW/HW in/out

CW/HW in/out

Liquid line

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V-5

Bed-1

V-6 Bed-3 CW/HW in/out

V-2 Bed-4 CW/HW in/out V-3

V-7 Bed-5

Bed-6 CW/HW in/out

CW/HW in/out

V-4

V-8

Evaporator CHW out

CW = Cooling Water HW = Heating Water CHW = Chilled Water V = Valve

CHW in

Figure 9. Schematic diagram of three-stage adsorption refrigeration cycle.

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Adsorption Refrigeration Table 5. Cyclic operation and valving of three stages adsorption refrigeration cycle Component Steps Bad-1 Bed-2 Bed-3 Bed-4 Bed-5 Bed-6 V-1 V-2 V-3 V-4 V-5 V-6 V-7 V-8

Mode-A

Mode-B

Mode-C

Mode-D

Precooling Preheating Preheating Precooling Precooling Preheating X X X X X X X X

Adsorption Desorption Desorption Adsorption Adsorption Desorption O X O X X O X O

Preheating Precooling Precooling Preheating Preheating Precooling X X X X X X X X

Desorption Adsorption Adsorption Desorption Desorption Adsorption X O X O O X O X

Table 6. The features of different adsorption refrigeration cycles

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Cycle name Simple two-bed cycle Integrated cycle Three-bed cycle Three-bed with dual evaporator Multi-stages cycle

Main features  Simple and commonly commercially applied  Simple design  Compact  Reliable  More continuity in cooling compared by two-bed  Brings more cooling with the same operating temperature  Utilise low driving heat sources

4. ADSORBENTS The adsorbents are classified based on the adsorption process. There are mainly three types; physical adsorbents, chemical adsorbents and composite adsorbents. Figure 10 shows the main adsorbent categories and their types. This section presents the characteristics of each type of these adsorbents.

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Adsorbents

Physical Adsorbents

Chemical Adsorbents

Composite Adsorbent

Porous carbons

Metal chlorides

Hygroscopic salts/ silica gel composites

Mesoporous silicates

Salt and metal hydrides

Chlorides / porous media composite adsorbents

Zeolites

Metal oxides

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Metalaluminoph osphates

Metal organic frame work

Figure 10. Adsorbent material classification.

4.1. Physical Adsorbents Physical adsorbents are usually porous materials with different pore size; Figure 11 shows the classification of such adsorbents based on the pore size. Such adsorbents adsorb the refrigerant by intermolecular force “Van der Waals force” and retain their original properties during the adsorption and desorption processes. This advantage makes the physical adsorbent the most commonly used in practical application. However, most of the physical adsorbents suffer from low adsorption kinetics and hence low cyclic refrigerant flow rate. The main physical adsorbent classes are mesoporous silicates, zeolites, metalaluminophosphates, porous carbons and metal organic frameworks (Aristov Y. I.., 2011).

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Macroporous Pores Diameter>50 nm Microporous Pores DiameterPores Diameter>1nm Misoporous 50nm>Pores Diameter>2nm

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Figure 11. Porous materials classification.

4.1.1. Porous Carbons Activated carbon (AC) is another name of porous carbons with high degree of porosity (500-1500 m2/g). It is obtained by gasifying the char using an oxidizing agent and the raw material of wood, peat, coal, fossil oil, chark, bone, coconut shell or nut stone. It is usually applied in gas separation and liquid purification, and the potential of using it in adsorption refrigeration systems is promising too (Srivastava and Eams 1998 and Wang et al. 2012). The adsorption heat of the activated carbon pairs is relatively low compared to other types of physical adsorbent pairs (1800-2000 kJ/kgads) and its adsorption capacity is low (0.3-0.4 kgref/kgads) (Maggio et al. 2009). Critoph and his coworker studied the adsorption performance of 26 types of activated carbon with ammonia (Tamainot-Telto et al. 2009) indicating the availability of wide range of this adsorbent. Activated carbon fiber (ACF) is a fiber form of activated carbon that has many advantages over activated carbon in terms of mass and heat transfer performance. Compared by activated carbon, ACF surface area is larger and its pores are more uniform. The disadvantages of the activated carbon fiber are anisotropic thermal conductivity and high thermal resistance between the fibers and adsorbent-bed heat exchanger surface compared to granular activated carbon.

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4.1.2. Mesoporous Silicates The most commonly used mesoporous silicates are the synthetic amorphous silica gel which consists of rigid and continuous net of colloidal silica connected to very small grains of hydrated SiO4. It contains chemically bonded traces of water (about 5%) and loses its adsorbitivity by overheating (above 120°C) due to loss of this bond (Srivastava and Eams 1998). Silica gel porosity level is lower than activated carbon (100-1000 m2/g) while the adsorption heat is higher (2500-2800kJ/kg) (Loh et al. 2009). Based on pore dimension there are two types of silica gel named; regular density (silica gel RD) of 2 nm pore diameter and low density (silica gel LD) 15-20 nm pore diameter. Silica gel has large adsorption ability (kgref/kgads) and can be regenerated using low temperature sources (50-100°C). Recently, Super-microporous or high density (HD) silica gel has been developed with pore size of 1-2nm (Guo et al. 2005 and Lin et al. 2004). It reversibly adsorbs water vapour at pressure ratio lower than 0.3 providing the ability of operating the cycle at lower condensation / desorption temperature difference. As a result, it adsorbs 2.75 time that of silica gel RD using evaporation, cooling and generation temperatures of 10, 30 and 70°C respectively (Yano and Fukushima 2003). 4.1.3. Zeolites Zeolites are a crystalline microporous aluminasilicate minerals and well known physical adsorbents. There are more than 180 types of zeolite frameworks and most of them adsorb water vapour at different rates (McCusker, 2011). Zeolites hydrophilicity is related to the silicon / aluminum ratio, where the lower this ratio is the higher hydrophilicity is the zeolite. It adsorbs most of water vapor at low partial pressure, have heat of adsorption of 3300-4200kJ/kg, regeneration temperature of 250-300˚C and can withstand high temperature treatment (up to 800˚C). Zeolites are only applicable for systems where high generation temperature sources are available. 4.1.4. Metalaluminophosphates Examples of metalaluminophosphates are Silica-aluminophosphates (SAPOs) and aluminophosphates (AlPOs) have a pore system with threedimensional networks similar to zeolites. These adsorbents have good water vapour adsorption and perform better than silica gel and zeolite (Henninger et al. 2010). Many of the aluminophosphates exhibit good thermal stability against high temperature treatment as they undergo up to 400-600˚C during

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synthesis. These attractive features invited researchers to study its ability to be applied in adsorption refrigeration application (Henninger et al. 2011).

4.1.5. Metal Organic Frame Work Metal organic frameworks (MOFs) are new micro-porous materials with exceptional high porosity, uniform pore size, well-defined molecular adsorption sites and large surface area (up to 5500m2/g) (Saha and Deng 2010, Saha and Deng 2010). MOFs have two main components: the organic linkers considered as organic secondary building unit, act as struts that bridge metal centres known as inorganic primary building units and act as joints in the resulting MOF architecture. The two main components are connected to each other by coordination bonds, together with other intermolecular interactions, form a network with defined topology (Kusgen et al. 2009 and Qiu and Zhu 2009). MOFs are less hydrophilic than silica gel or zeolite thus it can release more water vapour at the same partial pressure (Henninger et al. 2009 and Rezk et al. 2012).

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4.2. Chemical Adsorbents Chemical adsorbents sorb the refrigerant chemically by Valence force, where one layer of refrigerant reacts with the surface molecules of the adsorbent. Chemical adsorbents sorb more refrigerant at higher rate compared to physical adsorbents (Li et al. 2009). However their stability is lower than physical adsorbents, where chemical pair molecules never keep their original state which limits their practical applications. Chemical adsorbents suffer from swelling and agglomeration which negatively affect the heat and mass transfer performance, especially in cycles that operate at low pressure (Li et al. 2009). Chemical adsorbents mainly include metal chlorides, metal hydrides and metal oxides.

4.2.1. Metal Chlorides Metal chlorides that are applied for adsorption refrigeration are calcium chloride, strontium chloride, barium chloride and magnesium chloride (Zhong et al. 2007). Metal chlorides have high adsorption capacity (up to 1 kgref/kgads), but swelling and agglomeration are the main problems of metal chlorides. Calcium chloride has a good potential for use as solid chemical adsorbent for methanol and ethanol vapours, however ammonia is the usual refrigerant used with metal chlorides (Srivastava and Eames 1998).

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4.2.2. Salt and Metal Hydrides Salt and metal hydrides used in adsorption refrigeration systems are lithium hydrides, calcium hydrides, covalent high polymerized hydrides and non-metal molecular hydrides. Salt and metal hydrides perform promisingly with hydrogen refrigerant. Metal hydrides / hydrogen working pair are different from physical and chemical adsorption pair where there is no refrigerant in saturation state. The cycle based on this pair is sensitive to the driving temperature where the COP changes from 0.2 to 0.45 with increasing the heat source temperature from 120 to 160˚C (Srivastava and Eames 1998). 4.2.3. Metal Oxides The metal oxides are usually employed as catalyst for oxidation and deoxidation reactions. Oxygen is the suitable refrigerant when the metal oxides are used as adsorbents. Metal oxides / oxygen pair is suitable for heat pumps with temperature below 120K because of the large enthalpy of reaction between oxides and oxygen (Srivastava and Eames 1998). Similar to most chemical adsorbents, metal oxides suffer from the swelling and agglomeration problems.

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4.3. Chemical / Physical Adsorbent Composites Adsorption and desorption are respectively exothermic and endothermic processes and the chemi-sorption heat is higher than the physi-sorption heat. A chemi-sorption using salt of poor heat and mass transfer due to low thermal conductivity and with agglomeration phenomenon is not practical especially in low pressure systems (Li et al. 2009). Also Physi-sorption adsorbents suffer from low adsorption rate. Therefore, the aim of using composite adsorbents is to enhance the performance of physical adsorbents (increase the adsorption capacity) and avoid the aforementioned drawbacks of the chemical adsorbents (swelling, agglomeration and poor conductivity) (Srivastava and Eames 1998). Examples of composite adsorbents are the combination between metal chloride and activated carbon fibers, expanded graphite, silica gel or zeolite.

4.3.1. Hygroscopic Salts/Silica Gel Composites Adding hygroscopic salts (LiCl, LiBr, MgCl2, etc) to silica gel increases its water vapour adsorbtivity and avoids the problem of poor mass transfer due to swelling and agglomeration (Aristov et al. 2002, Dawoud and Aristov, 2003, Freni et al. 2009). The adsorption characteristics of the silica gel

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composite adsorbents (selective water sorbents SWS) can be modified by changing the salt type and changing the percentage of salt in silica gel (San and Hsu, 2009, Freni et al. 2012, Daou et al. 2008 and Hai-Jun et al. 2008). Higher salt amount increases the agglomeration problem and decreases composite porosity; however it enhances the heat transfer in the bed and the adsorption capacity (Restuccia et al. 2004, Freni et al. 2010 and Freni et al. 2007). Using calcium chloride as a hygroscopic salt approximately doubles silica gel adsorption capacity and hence the cooling capacity of the adsorption refrigeration cycle (Tokarev et al. 2002, Daou et al 2006, Zuh et al. 2006, Daou et al. 2007).

4.3.2. Chlorides / Porous Media Composite Adsorbents Adding chloride salts to expanded graphite, activated carbon, activated carbon fiber, zeolite and vermiculite is used to enhance these materials adsorptivity. Chloride salts / expandable graphite composite showed enhanced heat and mass transfer performance without expansion during adsorption (Deshmukh and Joshi, 2012). Impregnating activated carbon and activated carbon fibres with chloride salts enhanced the adsorption capacity (up to 0.95 kgref/kgads), but activated carbon performs better than activated carbon fibres in term of not separating from the salt (Ghorrishi et al. 2002). The above mentioned composites utilized ammonia refrigerant. However, impregnation of zeolite with chloride salt showed unexpected low performance of water vapour adsorption (Cortes et al. 2012).

5. REFRIGERANTS There are many refrigerants utilized in adsorption refrigeration systems, but the appropriate refrigerant need to be selected based on a number of parameters such as;   

Latent heat of vaporization: where the higher the refrigerant latent heat of vaporization the better the performance of the cycle. Thermal stability: stable refrigerant thermophysical properties mean stable cycle over the operating temperature range. Environment friendly: most of adsorption refrigeration cycles utilize environmentally friendly refrigerants with no ozone depletion and low

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







global warming potential. Natural refrigerants such as water, ammonia are the most commonly used ones. Flammability: some of the refrigerants utilized in adsorption refrigeration systems are flammable within certain concentration. The flammability issue should be taken into account especially when high generation temperature is used in the cycle. Toxicity: some of the refrigerants applied in adsorption refrigeration cycle are toxic and hence stringent safety measures should be implemented which limit their application. Explosion: hydrogen refrigerant utilized with salt hydrides is an explosive one. This means more consideration of the cost of manufacturing of such type of cycle. Compatibility: some refrigerants are corrosive and need special material of relatively high cost. This increases the machines costs and hence limits its market potential.

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The commonly applied refrigerants in adsorption cycles are water, ammonia, methanol and ethanol. Some other refrigerants are used in the adsorption technology, but not commercially applied such as hydrogen, oxygen, methyl alcohol, R134a, R22, R732 and R407.

6. ADSORPTION PAIRS Evaluating adsorbent or refrigerant independently is not sufficient, where adsorption characteristics vary based on adsorption pairs. Table 7 presents the characteristics of the most commonly used adsorption pairs (Saha et al. 2012, Chua et al. 1999, Dieng and Wang, 2001, Banket et al. 2004, Cui et al. 2005, liu and Leong, 2006, San and Lin, 2008, Schicktanz et al. 2012). There are a number of parameters that should be considered when selecting a particular pair for a given application. Table 8 presents these parameters such as adsorption rate, adsorption heat and desorption temperature. A weighing factor with minimum of 1 and maximum of 5 was developed based on the properties given in Table 7. For example, the average desorption (regeneration) temperatures for AC/Amonia, AC/Methanol, AC/Ethanol, AC/R134a, silica gel/water and zeolite / water are 140, 100, 100, 90, 75 and 175˚C respectively. The worst pair with highest regeneration temperature is zeolite/water was given a weighting factor of 1. The best pair with lowest regeneration

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temperature is silica gel/water was given a weighting factor of 5. On the other hand, the latent heat of vaporization for Methanol, Ethanol, R134a and water are 1368, 1102, 842, 217 and 2258 respectively. As a result, the best refrigerant in terms of latent heat is water and was given a factor of 5, but the worst one is R134a and was given a factor of 1. The values between the best pair and the worst one are prorated. The same weighting process is used for each criterion due to their equal importance. For example, complex manufacturing techniques influence the capital cost and hence the commercialization of the system. On the other hand, the temperature and quantity of energy required for adsorption influence the energy savings and the range of industries that can benefit from such systems. Therefore they should be equally weighted. Table 7. Characteristics of commonly used adsorption pairs AC, ACF/ Amonia

AC, ACF/ Methanol

AC, ACF/ Ethanol

AC, ACF/ 134a

Silica gel/ water

zeolite/ water

Operating pressure

+ve

Vacuum

Vacuum

+ve

Vacuum

Vacuum

Generating temperature ˚C

80-200

80-100

80-120

80100

50-100

100-200

Adsorption capacity kgref/kgads

0.29

0.45

0.19

0.36

0.30

0.17

-34

65

79

-48

100

100

1368

1102

842

217

2258

2258

Adsorption heat kJ/kg

1800-2000

18002000

12001400

18302300

25002800

32004200

Cooling density

2000 W/kg

140-500 W/kg

118159kJ/kg

57 kJ/kg

190W/kg

90150W/kg

Refrigerant

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Characteristic

Refrigerant boiling point ˚C Refrigerant latent heat of vaporization kJ/kg

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Criteria

AC, AC, ACF/ ACF/ Methanol Ammonia

AC, ACF/ Ethanol

AC, ACF/ R134a

Silicagel/ Water

Zeolites/ Water

Adsorption rate

2.7

5

3.3

3.7

2.9

1

Adsorption heat

4

4

5

3.8

2.8

1

2.4

4

4

4.4

5

1

5

1

2.4

4.7

3.2

3.2

3.3

2.7

2.2

1

5

5

5

2.9

1.6

4.8

1

1

Thermal stability

5

1

5

5

5

5

ODP

5

5

5

5

5

5

GWP

5

5

5

1

5

5

Non-toxicity

1

4

4

5

5

5

Non-flammability

1

1

1

5

5

5

Non-explosive

2.2

1

1

1.9

5

5

4

4

5

4

4

5

2.6

4.8

1

1

3.9

4.4

1.2

5

5

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Desorption temperature Maximum recovered temp Vaporization Latent heat Manufacturing complexes

Refrigerant 1 compatibility Refrigerant 4.1 solidification Average COP and 1 SCE Cost

3

3

3

3

5

4

Sum

50.7

52.5

53.5

59.3

62.7

56.2

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7. ADSORBENT BED DESIGN AND IMPROVEMENT TECHNIQUES

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The adsorbent bed replaces the mechanically driven compressor in conventional vapour compression refrigeration system. Improving the adsorbent bed design positively affect the overall cycle performance. It increases the power density of the adsorption cycle to compete with the conventional vapour compression cycle. Both heat and mass transfer are the key parameters that affect the performance of adsorbent bed reactors. Mass transfer process influences both adsorption capacity and adsorption rate (kinetics), which influence the refrigerant flow rate of a given cycle time and hence the cooling capacity. However, the heat transfer from / to the adsorbent is an important process for extracting / delivering both the adsorption / desorption heat, that directly influence the adsorption kinetics (Eun et al. 2000). The adsorption kinetics significantly affect the adsorption / desorption cycle time, where a short cycle time is more preferable to obtain continuous cooling. The following parameters affect the heat and mass transfer of the adsorbent bed.

7.1. Adsorbent Porosity The adsorbent porosity measures the free spaces (voids) inside the adsorbent granule and is given as the ratio between the voids volume over the total volume. Figure 12 shows an SEM image of high porosity material. The heat transfer and the refrigerant concentration are influenced by adsorbent porosity. As the adsorbent porosity increases, the adsorption capacity increases and with time the adsorbent becomes saturated, hence the adsorption rate decreases with time. The cycle time should be within the time period of high adsorption kinetics, otherwise the cycle performance deteriorates. Inversely, the adsorbent thermal conductivity decreases as adsorbent porosity increases and hence the adsorption kinetics (adsorption rate) also decreases (Demir et al. 2009).

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7.2. Pore Size The pore size is linked to adsorbent porosity, where the pore size reduces as the adsorbent porosity increases and as a result the adsorption specific surface area of the granules increases. On the other hand, the smaller the pore diameter, the higher is the adsorption isosteric energy and subsequently the regeneration temperature increases (Yano and Fukushima, 2003). One of the selecting suitable working pair criteria is the compatibility between the pore size and refrigerant molecules average diameter. If the pore size is too small to accommodate the refrigerant, the adsorption kinetic will be significantly reduced.

7.3. Granular Size

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The granules size affects both the heat and mass transfer of the adsorbent bed (Glaznev and Aristov, 2010). Decreasing the adsorbent granular size reduces the contact thermal resistance between the granules and heat exchanger surface. The heat transfer continuity through the adsorbent bed of small granule size is higher than that of large granules, due to the reduction of voids between granules (Eun et al. 2000).

Figure 12. SEM for porous material shows the high porosity degree.

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There are two types of mass transfer resistances in adsorbent bed, the first is the mass transfer within the adsorbent granules (intra-particle) and the second is the mass transfer through the voids between the granules (interparticles). The intra-particle mass transfer performance of small granules is higher than that of large granules. This is because of the total surface area of the bulk granules is higher for the smaller size. The adsorbent bed of large granules size (larger voids) has higher permeability level and hence better inter-particle heat transfer performance, which is more critical in cycles using low pressure refrigerants such as water, methanol and ethanol (Freni et al. 2009).

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7.4. Adsorbent / Metal Ratio As the adsorbent mass increases, the amount of refrigerant uptake increases, but the thermal resistance of the adsorbent will increase due to the low thermal conductivity of porous materials. However, adopting some heat transfer enhancement techniques between the heat exchanger and the adsorbent such as reducing fins spacing and adding metal particles will increase the amount of metal. This enhances the specific cooling power but it reduces the adsorption refrigeration cycle COP, where more heat absorbed by metal compared to that absorbed by adsorbent during the regeneration process (Cacciola and Restuccia, 1994 and Saha et al. 1997). An optimum adsorbent to metal mass ratio needs to be determined in order to obtain the highest specific cooling power with maximum COP. Figure 13 presents the effect of fin spacing on the heat transfer performance for a rectangular finned tube bed with loose packed silica gel granules. The term (NTU) number of transfer unit is a dimensionless parameter that evaluates the heat transfer performance of the adsorbent bed. The term (HCR) heat capacity ratio is the ratio between the heat capacity of the packed adsorbent mass and its value for the metal mass. Results show that as the fin spacing reduces, the heat transfer performance of the adsorbent bed improves because of the increase of the total surface area of the adsorbent bed due to increasing the fin number. However, the heat capacity ratio reduces by decreasing the fin spacing which is due to the increase of the metal mass of the extra fins used.

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Figure 13. Effect of fin spacing on silica gel-RD2060 adsorber bed heat transfer performance.

7.5. Heat Transfer in the Adsorbent Bed In adsorbent beds the adsorption and regeneration heat are handled by means of secondary fluid, usually water. During the heat transfer from / to the secondary fluid there are four heat transfer resistances developing the temperature gradient shown in Figure 14. These resistances could vary depending on the heat exchanger design, but generally named;    

Metal / secondary fluid convective heat transfer resistance - R1. Conductive heat transfer resistance through the wall of heat exchanger - R2. Metal / adsorbent interface contact heat transfer resistance - R3. Conductive heat transfer resistance through the adsorbent material R4.

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Figure 14. Schematic diagram of the heat transfer resistances in the adsorbent bed.

The convective heat transfer resistance between the secondary fluid and the heat exchanger wall is inversely proportional to the fluid velocity. The conductive heat transfer resistance is directly proportional to the thickness of the heat transfer medium and inversely proportional to the wall thermal conductivity. The conductive heat transfer resistance is very small through the heat exchanger wall but relatively high through the adsorbent medium and has a strong effect on the heat transfer performance of the adsorption cycle (Tatlier and Erdem-Senatalar, 1999). Metal / adsorbent interface contact heat transfer resistance usually dominates the heat transfer process and strongly depends on the nature of the physical contact between the adsorbent and the heat exchanger metal.

7.6. GRANULAR PACKED ADSORBENT BED In most commercially available adsorption systems, the adsorbent granules are packed in circular finned or rectangular finned tube bundles. In

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those designs, adsorbent granules are packed between the fins to fill in the gaps. A stainless steel mesh is used to wrap the adsorbent bed to prevent granules falling as shown in Figure 15. Granular packed adsorbent bed has the drawbacks of poor heat transfer performance due to: high contact thermal resistance between adsorbent granules and heat exchanger metal surface (Restuccia et al. 2002), discontinuity of heat transfer through granules due to the voids in-between the granules (Eun et al. 2000) and poor thermal conductivity of the used physical adsorbents. Granular packed adsorbent bed has the advantage of high mass transfer performance due to the high permeability level (Freni et al. 2009). To enhance the thermal performance of adsorbent bed reactors, the heat exchanger design and the heat transfer performance of the adsorbent materials need to be optimized (Kubota et al. 2008). Therefore many methods were investigated to enhance the heat transfer performance of the adsorbent materials such as mixing adsorbent granules with metal additives to improve their thermal conductivity, coating the bed heat exchanger metal with all the adsorbent to eliminate the contact thermal resistance, covering adsorbent granules by polyaniline net, adsorbent deposition over metallic foam and using consolidated bed techniques (compressed granules and clay, using expandable graphite, moulding granules and binder addition and adsorbent granules and metal foam). The following sections broadly present these enhancement techniques.

Heat transfer contact points

Tube fins

Adsorbent granules

Secondary fluid (water)

Tube wall

Adsorber heat exchanger tube

Metallic mesh

Fin pitch

Figure 15. Schematic diagram for the granular packed adsorbent bed.

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7.6.1. Covering the Adsorbent Particles by Polyaniline Net Covering the adsorbent granules by thermally conductive polyaniline net increases its thermal conductivity and hence the overall thermal performance of the adsorbent bed. A thin conducting net on the surface of adsorbent particles are grown by chemical oxidative in situ polymerization of aniline onto the surface of adsorbent granules. This technique was applied using zeolite granules where the overall thermal conductivity of the adsorbent bed increased by 4.6 times compared to uncoated zeolite granular packed adsorbent bed (Wang et al. 1999). However, adsorbent bed mass transfer performance was reduced; due to the blockage of the pores by the polyaniline net thus reducing the adsorbent bed uptake by 10%. 7.6.2. Adding Metallic Particles to Adsorbent Granules Adding metal particles to the adsorbent bed granules increases its overall thermal conductivity and hence the heat transfer performance. This technique was experimentally applied by adding aluminum, graphite and copper particles to zeolite granules using 16 - 84 wt% (Wang et al. 1999). This has increased the thermal conductivity of the adsorbent bed by 2.2 times. This technique is easy to apply, but it has been reported that it does not significantly improve the adsorbent bed performance (Cacciola and Restuccia, 1994). Figure 16 shows the effect of adding various metal particles on the heat transfer performance of rectangular finned tube silica gel adsorber bed. It is clear from this figure that the addition of the metal particles improves the heat transfer performance (NTU Cooling and NTU Heating). 7.6.3. Coating the Heat Exchanger by the Adsorbent Material Generally, thermal contact resistance between adsorbent granules and heat exchanger metal surface contributes an average of 25% to the overall heat transfer resistance. This contact heat transfer resistance can be eliminated using adsorbent coating technique. Firstly the heat exchanger surface is cleaned using organic agent while the adsorbent granules are mixed with suitable binder to make slurry. The mixture is then pasted over the heat exchanger surface and then thermally treated to be dried and stabilized. The adsorbent coating technique has been investigated and its performance has been reported. The adsorbent / metal thermal contact resistance was eliminated (almost zero) and the thermal conductivity of the adsorbent bed increased averagely by 3.5 times. This heat transfer enhancement increased the adsorption kinetics and hence the cycle specific

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cooling power by more than 4 times and the cycle time was halved (Restuccia and Cacciola, 1999, Waszkiewicz et al. 2009, Ge et al. 2010).

Rezk et al. 2012. Figure 16. Effect of metal particles addition on rectangular finned tube silica gel adsorber bed.

The adsorbent coated layer is within few millimetres and does not exceed one centimetre to avoid reducing the permeability as shown in Figure 17. This result in higher metal / adsorbent mass ratio compared with granular packed adsorbent bed which increases the adsorbent bed dimensions to accommodate the same amount of adsorbent and reduces the cycle coefficient of performance due to the increase of metal heat capacity. Chang et al. 2005 reported the preferable thin coated layer of large particle size to compromise the contradictory effect of heat and mass transfer of the coated bed.

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Figure 17. Zeolite coated tube.

Figure 18, Effect of eliminating the contact ressistance on heat transfer performance of silica gel adsorber bed.

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Alternatively, it is possible to coat the first layer of adsorbent granules to the bed and pack the remaining. Rezk et al. 2012 predicted the effect of such technique on the performance of silica gel packed in a rectangular finned adsorber bed. It is observed that a significant average enhancement of the adsorbent bed heat transfer performance of 28% as shown in Figure 18.

7.6.4. Consolidated Adsorbent Bed Consolidated adsorbent bed reactors using (compressed granules and clay, using expandable graphite, moulding granules and binder addition and metal foam impregnated with adsorbent granules) have the advantage of high heat transfer performance. Compressed granules and clay adsorbent bed which is moulded in hollow column shape has been investigated by Wang et al. 1999. The bed effective thermal conductivity is 30% higher than that of the granular packed bed. The micro-porosity between particles did not contribute to the adsorption process, but the overall porosity was enough for the refrigerant molecules movement. Consolidated adsorbent bed using expandable graphite and silica gel as adsorbent has been investigated by Eun et al. 2000.The adsorbent bed was made through four sequential steps as; (1) heating up expandable graphite to 600°C for10 min (2) add silica gel powder to expanded graphite and water slurry of appropriate ratio (3) the mixture is moulded and dried at 80°C for one hour (4) completely remove the water in vacuum at 145˚C for 2 hours. Graphite fraction and moulding pressure control the composite block thermal conductivity and permeability, where the permeability increased by increasing the graphite fraction and the decrease of the moulding pressure. The bed thermal conductivity was increased 88 times that of granular packed bed and its cooling power was doubled. Fragmentation in the consolidated block was observed during strength test. Moulding activated carbon adsorbent granules with binder was investigated by Wang L.W. et al. 2003, Wang, S.G. et al. 2003 and Wang S.G. et al. 2005. That adsorbent bed was produced based on the steps of; (1) mixing the adsorbent granules with pitch binder and water (2) compression moulding the mixture (3) heating up the adsorbent block to 120°C for three hours. The overall heat transfer coefficient of the produced consolidated adsorbent bed is about 4.5 times of the granular packed bed. The adsorption heat pump that utilized this consolidated bed has specific cooling power and COP of 1.1 and 0.9 times of granular packed bed respectively. The observed problems were bed permeability and cracking, but the later problem can be avoided by dividing the adsorbent block into smaller segments.

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Zeolite / aluminium foam consolidated adsorbent bed performance and its influence on the adsorption cycle overall performance have been investigated and reported. The thermal conductivity of the consolidated zeolite / aluminium foam adsorbent bed is about 32 times that of the granular packed bed and the specific cooling power of the heat pump containing that consolidated bed was doubled. Seven steps have been used to make the zeolite / aluminium foam consolidated bed (Hu, P. et al. 2009), as:    

 

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

Zeolite particles are put into a mould and tightly compressed. Sodium chloride particles are added and shaken to be distributed into the space between the zeolite particles. The whole mould was put into a furnace and preheated to 400-600°C. Pure aluminium was melted in a furnace and superheated to 700800°C, and then the molten aluminium is poured into the preheated mould. Under the gravity action of the aluminium, the molten aluminium flowed through the zeolite and salt bed. The mould is cooled and the cast is removed from the mould to be washed by water to dissolve the salt particles. The consolidated bed heated to 400°C for more than 4 hours to be dried.

7.6.5. Adsorbent Deposition over Metallic Foam Adsorbent bed heat transfer performance using adsorbent deposition over metallic foam technique was investigated, using zeolite and copper metal foam (Freni et al. 2009 and Bonaccorsi, et al. 2006). Using this technique, adsorbent / metal contact heat transfer coefficient was found to be 75 and 1.9 times that of granular packed and consolidated adsorbent bed respectively. The thermal conductivity of the coated metal foam adsorbent bed was 300 and 90 times that of granular packed and consolidated adsorbent bed. Results showed that adsorption cooling cycles using coated foam bed specific cooling power of 12 and 2 times that when granular packed and consolidated bed were used. However, the cycle COP was reduced to 0.6 and 0.7 that when granular packed and consolidated bed reactors were used. The adsorbent deposition over metallic foam can be produced using mainly two steps as:

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Ahmed Rezk, Ahmed Elsayed, Saad Mahmoud et al. 



Coating the commercial copper tubes by copper foam using three basic components: o Epoxy risen o Foaming agent o Metal powder Zeolite deposition using the colloidal seeds solutions passing through four steps: o Seeding o Hydrothermal synthesis o Washing o Drying

7.7. Adsorber Bed Configurations

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Various heat exchanger technologies have been utilized in the design of adsorber beds including plate, tubular and flat tube, and spiral type heat exchangers.

7.7.1. Plate Heat Exchanger Adsorber Plate heat exchanger concept shown in figure 19 has been tested by Tamainot-Telto et al. 2009 at Warick University, UK using activated carbon/

Tamainot-Telto, 2009. Figure 19. Plate Compact sorption generator (a) concept based on plate heat exchanger (b) first experimental prototype (SOPLATEX).

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ammonia working pair. The consolidated activated carbon is fitted to one side of the plates adsorbing ammonia vapour and oil flow on the other side of the plate where gaskets are used to generate the desired depth of the flow channel. Such configuration indicated a cooling COP of 0.12 and SCP of 150 W/kg-1.

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7.7.2. Flat Tube Adsorber Bed Figure 20 shows the flat tube heat exchanger adsorber bed designed by Tchernev and Emerson (Wang et al., 1998) where the adsorbent material is packed between the flat tubes so that the whole bed is fitted in shell. The heat transfer fluid flows through the flat tubes. This type of heat exchangers ensures good thermal conduction in the bed as the adsorbent is consolidated, however, the pressure drop in the heat transfer fluid (hot water or cooling water) is high and large temperature differences occurs in the bed. Vasta (2012), Sapienza (2011), Verde (2010), Chang (2007), Grisel et al. (2010) have investigated the flat tube adsorber bed configuration shown in figure 21. It is advanced design with the adsorbent packed between the corrugated fins with system cooling coefficient of performance between 0.45 and 0.6.

Wang et al., 1998 Figure 20. Flat-pipe type adsorber. 1, thermal fluid flow cbannel 2, adsorbent []

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Figure 21. Flat tube heat exchanger tested by Chang (2007).

Wang et al., 2003. Figure 22. Tested adsorber bed configuration.

7.7.3. Finned Tube Adsorber Bed Figure 22 shows various configurations of finned tubes and shell heat exchanger adsorber beds (Zhang, 2000, Wang et al., 2003). The first configuration is shell and tube filled with granular activated carbon, the second configuration is consolidated activated carbon plates with no internal mass

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diffusion gaps and the third one is consolidated activated carbon plates with internal diffusion gaps. Such configurations showed a cooling COP of 0.104 to 0.125 and SCP of 13.1 to 16 W/kg. Critoph and Metcalf (2011) tested carbon-ammonia adsorption gas-fired domestic heat pump using shell and tube configuration with micro tubes with1.2 mm tube diameter as shown in figure 23.

Figure 23. Microchannel adsrober tested by Critoph and Metcalf (2011).

7.7.4 Spiral Heat Exchanger Adsorber Beds Figure 24 shows spiral type heat exchanger adsorber bed with extended surfaces to increase the heat transfer areas. One passage of the spiral is used to fill the activated carbon and the other passage is used for the heat transfer fluid. The distinct advantages of this type of heat exchanger include the compact size, the small temperature difference between the sorbent and the heat transfer fluid, and a more uniform temperature distribution within the bed (Wang et al.,1998),( Kiplagat et al., 2012). Table 9 compares the performance of various bed configurations described above in terms of volumetric cooling power (VCP), specific cooling power (SCP) and coefficient of performance (COP). It can be concluded that flat tube concept using water/silica gel pair produced the highest COP of up to 0.6 and the largest specific cooling power (150-600 W/kg) compared to other tubular concepts ( 0, it is evident that qrc increases monotonically with increasing D. Meanwhile, as follows from (39), this expression reaches its maximum value for ∗ q+ =

ηc α+ T+ T1 α+ T+ T1(T+ − Te ) = . 2Te 2Te

(42)

At the same time, D∗ = N +

∗ ηc2 α+ T+ T1 ηc q+ =N+ . 4Te 2

(43)

Thus, the extreme possible refrigeration capacity of an absorption refrigeration cycle is limited and amounts to √ B 2 + 4AD∗ − B qx∗ = , (44) 2A

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while the correspondent heat ratio is √ B 2 + 4AD∗ − B ∗ ρ = . ∗ 2Aq+

(45)

The optimal allocation of contacting surfaces. The ratio obtained allows for the solving of the optimization problems of a refrigeration cycle. An example of such a problem is the allocation of contacting surfaces between the refrigeration chamber, generator, condenser, and absorber. For simplicity, let us assume that the value of a contacting unit for each heat exchanger is the same. Then, the problem is reduced to such a selection of heat transfer coefficients that during which the refrigeration capacity qrc is highest under the condition αc + αa + αrc + α+ = α,

(46)

where α is the specified value defined by the installation dimensions. Here, it should be considered that the first three summands in (46) are contained in A, while α+ enters C. The Lagrangian function for the qrc maximum problem under condition (46) appears as L = qrc (αc , αa , αrc , α+ ) − λ(αc + αa + αrc + α+ ).

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The optimum conditions are reduced to proportions ∂qrc ∂qrc ∂qrc ∂qrc = = = λ, = ∂αc ∂αa ∂αrc ∂α+

(48)

which, together with Eq. (46), determine the optimum distribution of the coefficients. Let us rewrite Eq. (48) in regards to (40) as ∂A ∂A ∂A = = = ∂αc ∂αa ∂αrc

∂qrc ∂D

!

∂D ∂qrc : = λ. ∂α+ ∂A

(49)

Using (37), we obtain h

∆h1 ∆h1 −C(T1 −T4 )

=

i2

Te α2rc Trc T4

T [ε∆sp +(1−ε)∆sq ]2 α2a ε2 [∆h1 −C(T1 −T4 )]2 q 2 Te rc /∂D − α2 +T+ T1 · ∂q = λ. ∂qrc /∂A +

1 α2c T1

=

=

=

(50)

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Let us introduce the notations ∆h1 Rc = √ , T1 (∆h1 − C(T1 − T4)) √ T (ε∆sp + (1 − ε)∆sg ) Ra = , ε (∆h1 − C(T1 − T4)) Rrc = R+

s

Te , Trc T4

v u u Te = q + t−

∂qrc/∂D . T+ T1 ∂qrc/∂A

(51) (52) (53) (54)

We calculate the partial differential coefficients ∂qrc/∂D and ∂qrc/∂A using expression (40). They amount to √ ∂qrc ∂qrc B − B 2 + 4AD 1 D , + =√ 2 = √ 2 . ∂D 2A2 B + 4AD ∂A A B + 4AD (55) In these notations, after λ is excluded we obtain the following conditions to choose the optimum heat transfer coefficients α∗c = α RRc ,

α∗a = α RRa , α∗rc = α RRrc , α∗+ = α RR+ , R = Rc + Ra + Rrc + R+ .

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Irreversible Estimation Possibilities ...

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5.

179

Calculation Example

We cite an example of using ratios obtained for the calculation of the refrigeration cycle. Let us plot the dependence of the refrigeration capacity qrc on the heat consumption q+ using formula (40) under the following parameters. Temperatures (K): Trc = 263, Te = 288, T1 = 300, T = 298, T+ = 373. Pressures: P1 = 8.74 kg/cm2 and P2 = 2.97 kg/cm2 . Concentrations: x1 = 0.3, x = 0.495, and y1 = 0.95. Supplementary parameters: r1 = 23 250 is the latent heat of evaporation for NH3 , J/mol; r2 = 40 660 is the latent heat of evaporation for N2 O, J/mol; v= 16.3 is the molar volume of the mixture, cm3/mol; C = 68.2 is the molar heat capacity of the mixture, J/(mol K); and g = 5 is the mixture flow from the absorber, mol/s. Heat transfer coefficients: αc = 2500 for the condenser, αa = 2000 for the absorber, αrc = 2000 for the refrigeration chamber, and α+ = 2500 for the supplied vapor. All values are given in W/K. ηc = 1 − TT+e – is the Carnot efficiency. Let us find the evaporation fraction  = 0.3 using formula (19). We calculate the heat consumption for the evaporation of one mole of the mixture using formula (21). In order to obtain the change in the molar entropy of the vapor in the absorber, ∆sp , and the increment of the molar entropy of the liquid, ∆sg , using formulas (30) and (31), respectively, it is necessary to calculate the temperature behind the throttle valve T4 using formula (29). Let us determine the coefficient values in Eq. (40) on the basis of formulas (37), (38), and (39), whereupon coefficient D depends on q+ . We substitute the initial data and the results of the calculations into expression (40) and obtain the target dependence. We use it to calculate the refrigeration capacity in the range of the variation of q+ from 20 to 200 kW. The resulting dependence is shown in Fig. 3. The value of the heat ∗ , that corresponds to the maximum refrigeration capacity agrees flow q+ with expression (42).

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Figure 3. Relationship between heat consumption and refrigeration capacity of the absorption refrigeration cycle.

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6.

Conclusion

It has been demonstrated that using thermodynamic balance equations allows for the obtainment of the proportions between the cycle parameters of an absorption refrigeration machine and the flows which determine its efficiency. The irreversibility factor sets the limit of the refrigeration capacity of the installation. The proportions obtained may be used to select design parameters and operational conditions for the cycle and its modernization.

7.

Notation

C molar heat capacity, J/(mol K); g1 flow rate of vapor leaving the generator, mol/s; g2 , g flow rates of liquid leaving the generator and absorber, mol/s; h molar enthalpy. J/mol; N pump power, W; q+ , qrc , qa, qc heat flows that arrive from the hot source and refrigeration chamber and are drawn from the absorber and condenser, W; R universal gas constant, J/(mol K); r molar enthalpy of evaporation, J/mol;

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s molar entropy, J/(mol K); T+ , Te , Trc , T4 , T5, T1 temperature of the hot source, environment, refrigeration chamber, mixture after the throttle valve, steam exiting the generator, and mixture in the generator, K; v molar volume, m3/mol; x2, x concentration of volatile components in the liquid at the inlet and outlet of the absorber, mol fraction; y1 concentration of volatile components in the vapor in the generator, mol fraction; α heat transfer coefficient, W/K;  the fraction of evaporation in the generator; ηc Carnot efficiency; λ Lagrange factor; ρ heat ratio; σ, σ1, σ2 general entropy production, entropy production upon the transfer between the hot source and generator, entropy production upon the heat transfer to the surrounding, W/K.

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8.

Subscripts and superscripts ∗ values characterizing the limiting refrigeration capacity conditions; e parameters of the environment; r parameters corresponding to the reversible process; c values relating to the condenser; rc values relating to the refrigeration chamber; a values relating to the absorber; + values characterizing the heating steam flow.

References [1] Martynovskii, V.S., Cycles, Schemes and Characteristics of Heat Transformers, Moscow: Energiya, 1979.(In Russian) [2] Bosnjakovic, F., Technical Thermodynamics, Holt R&W: New York, 1965.

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[3] Popov, A.V., Absorption Refrigerating Machines and Thermal Pumps of New Generation, Kholodilnaya tekhnika, 2006, no. 6, p. 26.(In Russian) [4] Galimova, L.V., Slavin, R.B., and Popov, A.V., Energy Saving System on the Base of SteamGasTurbine Plant and Absorption BromideLithium Refrigerating Machine of New Generation, Kholodilnaya tekhnika, 2007, no. 2, p. 42.(In Russian) [5] Berry, R.S., Kasakov, V.A., Sienytich, S., Szwast, Z., and Tsirlin, A.M., Thermodynamic Optimization of Finite Time Processes, Chichester: John Wiley and Sons, Chichester, 1999. [6] Tsirlin, A.M., Irreversible Estimates of the Limiting Performance of Thermodynamic and Microeconomic Systems, Moscow: Nauka, Moscow, 2003.(In Russian)

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[7] Prigogine, I. and Kondepudi, D., Sovremennaya termodinamika (Modern Thermodynamics), Wiley, 1998.

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INDEX

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A ACF, 15, 21, 22 activated carbon, 15, 16, 18, 19, 32, 34, 35, 36, 37, 40, 45, 48, 49, 53, 54, 55 additives, 28, 116, 119 adduction, 67 adsorption, vii, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 32, 33, 37, 39, 40, 41, 42, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56 adsorption cooling systems, vii, 1, 40, 45 adsorption principles, vii, 1 aerospace, ix, 155, 156, 165 air conditioning systems, vii, ix, 1, 2, 45, 49, 113, 115, 123, 124 air quality, 58, 107 air temperature, 101 algorithm, 115, 134 aluminium, 33, 66 ambient air, 85, 86, 89, 90 ammonia, 15, 17, 19, 20, 35, 37, 38, 40, 46, 50, 53, 116, 127, 139, 143, 168, 171 aniline, 29 aqueous solutions, 59, 60, 108, 110 arsenic, 156, 166 artificial intelligence, ix, 114, 132, 134, 143 assessment, ix, 109, 149, 153, 155 atmosphere, 165

atmospheric pressure, 71 automobile, 50 automotive applications, 40

B bacteria, 61 Bangladesh, 156, 166 barium, 17 benign, 46 blends, 119, 149 bonds, 17 bone, 15

C calcium, 17, 18, 19, 41, 48, 108 candidates, 43 capillary, 108 carbon, 15, 19, 36, 37, 46, 55, 127, 149 carbon dioxide, 127, 149 case study, 84, 89 catalyst, 18, 156, 166 certification, 166 CFD simulation, ix, 155 chemical, 13, 17, 18, 29, 59, 61, 75, 106, 156, 165, 173 chemicals, 119 chemisorption, 51

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184

Index

China, 49, 51, 56 circulation, 159 classes, 14 classification, 14, 15 cleaning, 3, 164 climates, 2, 53 CO2, 39, 121, 122, 124, 147, 148, 149 coal, 15 cogeneration, 42, 43 combustion, 40, 42, 44, 49 commercial, vii, ix, 1, 2, 34, 60, 82, 155, 156 compatibility, 22, 24, 124 complexity, 89 composites, 19, 49 composition, 119, 137, 168, 170, 174, 175 compression, vii, viii, 1, 2, 23, 32, 43, 51, 58, 59, 61, 62, 80, 81, 82, 104, 109, 110, 146, 149, 168 computational fluid dynamics, 115, 164 computer, viii, ix, 58, 68, 78, 155, 164 condensation, viii, ix, 5, 8, 12, 16, 58, 59, 71, 77, 81, 82, 83, 93, 94, 96, 101, 113, 115, 116, 117, 118, 119, 123, 125, 126, 127, 128, 129, 130, 131, 132, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 148, 149, 150, 151, 152, 153, 154, 172, 173, 175 conditioning, vii, viii, ix, 1, 2, 39, 45, 46, 47, 48, 49, 52, 53, 57, 58, 61, 62, 64, 79, 80, 81, 82, 83, 84, 86, 87, 89, 94, 96, 104, 108, 109, 110, 113, 115, 119, 123, 124, 142, 148 conduction, 35, 71, 139 conductivity, 15, 18, 23, 25, 27, 28, 29, 32, 33, 78, 106 configuration, 4, 35, 36, 37, 38, 85, 104 Congress, 108, 110, 145 conservation, 70, 71, 72 construction, ix, 65, 66, 167 consumption, 59, 123, 168, 173, 179, 180 contact time, 60 contamination, 156, 165 cooling, vii, viii, ix, 1, 2, 4, 5, 7, 9, 10, 12, 13, 16, 19, 23, 25, 30, 32, 33, 35, 37, 39,

40, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 58, 61, 81, 82, 84, 96, 98, 108, 109, 124, 127, 130, 150, 157, 167, 175 copper, 29, 33, 34, 45, 48, 132, 141 ccorrelations, 78, 79, 116, 117, 119, 129, 131, 132, 135, 136, 137, 139, 140, 142, 143, 144, 150, 151, 153 corrosion, 3, 60, 64 cost, ix, 20, 21, 60, 155, 157, 159, 161, 164, 165 covering, 28, 116 crystalline, 16 crystallization, 3 current limit, vii, 1 cycles, 4, 12, 13, 17, 19, 20, 25, 33, 45, 51, 54, 59, 82, 88 cyclohexanone, 48

D DART, 166 database, 118 decision makers, 54 Department of Energy, 145 dependent variable, 73 deposition, 28, 33, 34 depth, 35, 119, 141 desorption, 2, 5, 8, 9, 11, 12, 14, 16, 18, 20, 23, 42 destruction, 166 deviation, 135 dew, viii, 58, 59 differential equations, 73, 130 diffusion, 37, 38, 71, 74, 75, 105 diffusivities, 53 discontinuity, 28 discretization, 137 distillation, 171 distribution, ix, 37, 125, 132, 156, 166, 167, 178 DME, 147, 148 domestic refrigeration, vii, 1 drainage, 116, 126, 142 dusts, 63

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185

Index

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E electric field, 115, 117, 129 emission, 156 endothermic, 18 energy, vii, viii, ix, 1, 2, 21, 24, 39, 42, 45, 47, 50, 53, 55, 57, 58, 59, 61, 70, 71, 79, 83, 104, 109, 110, 119, 126, 139, 145, 157, 167, 170, 171, 173, 176 energy conservation, 104, 109 energy consumption, vii, ix, 1, 2, 58, 61, 79, 119, 167, 176 energy input, 171 engineering, ix, 39, 52, 115, 118, 155, 165, 168 entropy, ix, 167, 169, 170, 171, 172, 174, 175, 179, 181 environment, 2, 59, 61, 83, 97, 119, 124, 161, 164, 165, 168, 181 environmental effects, vii, 1 environmental protection, 156, 165 environments, 43, 59 equilibrium, 7, 10, 76, 120, 124, 172 equipment, 108, 119, 145 ethanol, 17, 20, 25 ethylene, 124 ethylene glycol, 124 evaporation, viii, 2, 4, 5, 8, 9, 12, 16, 42, 58, 61, 82, 83, 87, 93, 94, 101, 105, 116, 118, 120, 126, 129, 145, 148, 172, 173, 174, 179, 180, 181 experimental condition, 69, 135 experimental design, 164 exposure, 60, 165 extraction, 63 extracts, 129

F fiber membranes, 108 fibers, 15, 18, 19, 49 film thickness, 114, 130, 131, 132 filters, 165

filtration, vii, ix, 155, 156, 157, 160, 162, 163, 164, 165, 166 fishing, 3, 54 flammability, 20, 22, 124 flexibility, 159, 164, 165 flooding, 117, 144 flue gas, 127 fluid, 8, 26, 27, 35, 37, 44, 68, 115, 119, 124, 126, 129, 137, 138, 148, 157, 165 foams, 45 food, 2, 39, 45 force, 14, 17, 118, 129, 142 formula, 179 FORTRAN computer code, viii, 58, 78 free energy, 168 friction, 61, 117, 135, 140, 142 frost, 110 fuel cell, 42 fuel consumption, 39

G gas sorption, 50 gel, 16, 17, 18, 20, 21, 22, 25, 26, 29, 30, 31, 32, 37, 38, 40, 41, 44, 46, 47, 48, 50, 51, 53, 56, 59 geometrical parameters, 116 geometry, ix, 114, 115, 117, 154 Georgia, 45, 52 geothermal heat pump, 42 global demand, vii, 1 global warming, 2, 20, 119, 124 glycol, 60, 107, 124 grain size, 48 granules, 24, 25, 27, 28, 29, 32 graphite, 18, 19, 28, 29, 32, 47, 50 gravitational constant, 114 gravitational force, 139 gravity, 33, 117, 123, 125, 129, 130, 142, 150 greenhouse, 130, 150 groundwater, 156 guidelines, 55

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Index

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H habitat, 165 heat capacity, 25, 30, 173, 179, 180 heat pumps, vii, 18, 42, 45, 47, 49, 52, 53, 57, 61, 79, 123, 148 heat removal, 127, 168 heat transfer, ix, 15, 19, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 35, 37, 44, 60, 73, 77, 78, 79, 106, 110, 111, 113, 114, 115, 116, 117, 118, 119, 123, 125, 126, 127, 129, 130, 132, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 170, 171, 172, 177, 178, 181 host, 46, 47, 56 humidity, 59, 61, 68, 69, 70, 83, 85, 88, 89, 94, 97, 98, 99, 105, 106, 108 hybrid, viii, 58, 61, 62, 64, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 103, 104, 109, 110 hydrides, 17, 18, 20 hydrocarbons, 118, 119, 144 hydrogen, 18, 20 hydrophilicity, 16

I ideal, 49, 54, 74, 75, 163, 165 identification, 131, 132, 150, 151 independent variable, 73 industries, ix, 21, 39, 45, 142, 155, 156, 165 industry, 119, 156, 164, 165 inertia, 116 integration, vii, 40, 42, 57 interdependence, 175 interface, 26, 27, 69, 71, 74, 76, 77, 78 intermolecular interactions, 17 interphase, 116, 117, 139 in-tube condensation process, ix, 114 isobutane, 124, 146, 147 Italy, vii, 40, 57, 146

J Japan, 42, 56

K kinetics, 14, 23, 29

L lactose, 156 laminar, 78, 116, 117, 130, 131, 143, 150, 152 laws, 172 lead, 71 leakage, 3, 64, 160, 161 legislation, 59 lifetime, 3, 164 liquid phase, viii, 58, 61, 63, 64, 68, 74, 106, 119, 158, 174 lithium, 18, 51, 60, 64, 107, 108, 111 Louisiana, ix, 155 LPG, 121, 147 lubricating oil, 120 Luo, 2, 41, 51

M magnesium, 17 management, 45, 53, 165, 166 manufacturing, 20, 21, 159 mapping, 116 mass, viii, 7, 8, 15, 17, 18, 19, 23, 24, 25, 28, 29, 30, 36, 38, 46, 47, 49, 50, 51, 52, 53, 54, 55, 58, 59, 61, 63, 65, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 83, 95, 96, 97, 100, 102, 104, 105, 106, 108, 114, 125, 126, 127, 129, 130, 131, 132, 135, 136, 137, 139, 140, 141, 151, 167, 170, 173 materials, vii, 1, 15, 19, 28, 45, 64, 165 matrix, 56, 59 matter, ix, 116, 155, 157, 165

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Index measurements, 68, 69, 127, 157, 166 medical, 156, 166 membranes, viii, 58, 62, 64, 65, 66, 71, 73, 85, 104, 108, 111, 156, 166 mercury, 48 metal oxides, 17, 18 metals, 60, 64, 115, 143 methanol, 17, 20, 25, 38, 41, 53, 54, 55 methodology, 126 microclimate, 110 missions, 165 mixing, 28, 32, 79, 80, 163, 172, 175 modelling, 52, 116, 117, 123, 130 models, ix, 114, 117, 118, 123, 127, 130, 131, 132, 135, 136, 141, 142, 150, 151, 156, 164 modernization, 180 modules, 66, 78, 108 moisture, 71 molar volume, 171, 174, 179, 181 mole, 127, 173, 179 molecular mass, 106 molecules, 17, 24, 32 momentum, 132 Morocco, 50 Moscow, 145, 181, 182 moulding, 28, 32

N NaCl, 68 naphthalene, 129, 150 NCV, 73, 78 neglect, 116 Netherlands, 40, 55 neural network, 52, 115, 132, 151 novel materials, 49

O oil, 15, 35, 44, 117, 124, 137, 152 operations, 156, 165 optimal performance, vii, ix, 113 optimization, 116, 127, 134, 149, 177

oxidation, 18 oxygen, 18, 20, 156 ozone, 19, 115, 119, 124 ozone layer, 119, 124

P parallel, 6, 12, 141, 153, 161 partial differential equations, 73 particle mass, 25 permeability, 25, 28, 30, 32, 65, 75, 106, 165 petroleum, 155, 166 pharmaceutical, 156, 165 phosphate, 156 physical properties, 124 pitch, 32, 153 plants, vii, 2, 57, 59, 62, 79, 83, 115 pollutants, 59, 63, 107 pollution, viii, 58, 63 polymer, 48, 165 polymerization, 29 polymers, 163 porosity, 15, 16, 17, 19, 23, 24, 32, 47, 65, 165 porous materials, 14, 17, 25 potential benefits, viii, 57 power plants, 123 precipitation, 156, 166 pressure gradient, 79, 127 project, ix, 83, 86, 92, 94, 97, 99, 105, 155, 165, 166 propane, 118, 124, 146, 147, 148, 149 propylene, 124 protection, 124 prototype, viii, 34, 49, 50, 58, 64, 65, 67, 78, 85, 104, 160, 164, 165 prototypes, 64 PTFE, viii, 58, 65 pumps, 3, 83 pure water, 78 purification, 15

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Index

R

Copyright © 2013. Nova Science Publishers, Incorporated. All rights reserved.

radiation, 42 recovery, 7, 8, 9, 49, 50, 51, 52, 55 recovery process, 51 redistribution, 130 reduced-order models, 157 refrigeration capacity, ix, 40, 167, 175, 177, 179, 180, 181 regenerate, 59, 60, 61, 80, 85, 86, 89, 105 regeneration, vii, 2, 16, 20, 24, 25, 26, 45, 50, 62, 80, 81, 85, 86, 87, 89, 90, 92, 94, 105 regression, 115, 133 requirements, 3, 159 resistance, 26, 27, 29, 65, 75, 79, 85, 106, 110, 158 restrictions, 143, 169, 172 retail, 39 reverse osmosis, 156 rings, 64 rods, 64, 66, 115 rubber, 66 Russia, 167

S safety, 20, 124 salt concentration, 60, 88, 105 salts, 18, 19, 46, 60, 156 saturation, 18, 68, 89, 107, 114, 129, 132, 138, 140, 141 savings, viii, 21, 58, 59, 61, 89, 92 science, 45 scope, 45 SCP, 35, 37, 38, 41 semi-permeable membrane, 62, 63 sensing, 44 sensors, 68 shape, 32, 115, 124, 139, 140, 164 shear, 114, 116, 123, 125, 135, 139, 142, 156

silica, 16, 17, 18, 20, 25, 26, 29, 30, 31, 32, 37, 38, 40, 41, 44, 46, 47, 48, 50, 51, 54, 55, 56, 59 silicon, 16, 139, 140, 153 simulation, ix, 52, 54, 152, 155, 164 simulations, viii, 58, 64, 78, 85, 89, 92, 94, 98, 102, 104, 108 SIMULINK calculation, viii, 58, 83, 104 solar collectors, 42, 62 solid phase, 68 solid surfaces, 115 solidification, 22 solubility, 120 solution, viii, 3, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 77, 78, 79, 80, 81, 83, 85, 86, 87, 88, 89, 92, 93, 94, 98, 99, 101, 102, 104, 105, 106, 107, 119, 150, 169, 176 sorption, vii, 2, 18, 34, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56 sorption materials, 49 specific heat, 73, 105 specific surface, 24 specifications, 116, 124 stability, 17, 19, 22, 49, 53, 124 state, viii, 17, 18, 58, 70, 74, 80, 81, 83, 101, 107, 110, 120, 130, 139, 172 states, 85, 86, 87, 88, 96, 97, 99, 157 steel, 28, 67, 68 storage, 2, 46, 49 stress, 114, 116, 135 strontium, 17 structure, 63, 64, 168 substitutes, 145 Sun, 50, 148 suppression, 125 surface area, 15, 17, 25, 41, 60, 123, 128 surface tension, 123, 139, 142 swelling, 17, 18 synthesis, 17, 34, 51 synthetic polymers, 59 system level phenomena, 52

Refrigeration Systems, Design Technologies and Developments, Nova Science Publishers, Incorporated, 2013. ProQuest

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Copyright © 2013. Nova Science Publishers, Incorporated. All rights reserved.

T techniques, vii, ix, 1, 21, 25, 28, 45, 114, 116, 119, 134, 141, 143, 151, 164 technologies, vii, 34, 47, 156 technology, vii, ix, 1, 2, 20, 45, 47, 155, 156, 164, 165 TEG, 59, 60 temperature, viii, 2, 3, 4, 10, 12, 13, 16, 18, 19, 20, 21, 22, 24, 26, 35, 37, 39, 40, 42, 43, 46, 47, 52, 58, 59, 60, 61, 68, 69, 76, 79, 81, 82, 83, 84, 85, 87, 88, 89, 92, 93, 94, 96, 100, 101, 105, 106, 114, 119, 123, 124, 126, 127, 129, 132, 135, 137, 138, 139, 140, 141, 156, 168, 169, 171, 172, 174, 175, 179, 181 testing, 48, 56, 142 Thailand, 113, 143 thermal energy, 59, 61, 80 thermal resistance, 15, 24, 25, 28, 106, 114, 119 thermal stability, 16 thermodynamic cycle, 2, 4, 87 thermodynamic equilibrium, 170 thermodynamics, 169 thermosyphons, 129, 150 titanium, 68 toxicity, 22, 124 transfer performance, 17, 19, 25, 27, 28, 29, 46, 115, 141 transformation, 45, 49, 84, 87, 95 transmission, 65, 75, 79, 85, 106, 156 transport, 45, 63, 111, 117 transportation, 2 treatment, 16, 132, 156 turbulence, 142 Turkey, 113

universal gas constant, 180

V vacuum, 3, 32, 51 valve, 9, 50, 158, 159, 161, 168, 169, 174, 175, 179, 181 vapor, 6, 42, 48, 53, 119, 130, 132, 142, 144, 146, 150, 168, 169, 174, 175, 179, 180, 181 variables, ix, 134, 167 variations, 69, 89, 120 velocity, 27, 68, 71, 106, 114, 123, 124, 132, 136, 138, 140, 141, 158 ventilation, 165 vibration, 3, 119 viscosity, 60, 130, 163

W wall temperature, 73, 77, 116, 125 waste, vii, 1, 39, 46, 50, 52, 54, 55, 56, 156, 166 waste heat, vii, 1, 39, 46, 50, 52, 54, 55, 56 waste incineration, 166 water, 7, 9, 16, 17, 18, 19, 20, 21, 25, 26, 32, 33, 35, 37, 38, 40, 42, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 60, 65, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 78, 81, 82, 84, 105, 106, 107, 110, 124, 127, 130, 150, 156, 160, 161, 163, 166, 168, 173 water sorption, 48 water vapor, 16, 47, 130 welding, 66 wells, 44 working conditions, 84, 85, 99, 105, 142

U UK, 1, 34, 40 UL, 163, 166

Z zeolites, 14, 16, 59

Refrigeration Systems, Design Technologies and Developments, Nova Science Publishers, Incorporated, 2013. ProQuest