REFRIGERATION AND AIR CONDITIONING

REFRIGERATION AND AIR CONDITIONING

About the Author Late (Dr.) Ramesh Chandra Arora served as Professor of Mechanical Engineering at Indian Institute of Technology Kharagpur from 1987 to 2005. He received his B.Tech. and M.Tech. degrees in mechanical engineering from Indian Institute of Technology Kanpur in 1967 and 1969, followed by a Ph.D. (Fluid Mechanics and Heat Transfer) in 1975 from Case Western Reserve University, Cleveland, Ohio, USA. His research areas included fluid mechanics, heat transfer, refrigeration and air conditioning, alternative refrigerants and thermodynamic cycles to highlight a few. Professor Arora had patents pending for Design of facility for generation of mono-disperse test aerosols with size control, Design of low temperature drying system for seed grains, and A novel methodology of energy optimization for variable-air-volume air conditioning systems. Professor Arora also held several administrative assignments during his 30 years of tenure at Indian Institute of Technology Kharagpur (1975 2005). These included Deputy Director (Acting); Founder member and Head of Department, School of Medical Science and Technology; Dean of Students Affairs; Chairman, Hall Management Committee; Coordinator, Master s programme in Medical Science and Technology; Professor-in-Charge, Refrigeration and Air Conditioning Laboratory of Mechanical Engineering Department; Chairman, Undergraduate Programme Evaluation Committee Mechanical Engineering Department; Coordinator, Postgraduate and Research Committee of Mechanical Engineering Department; Faculty Advisor, Mechanical Engineering Society of Mechanical Engineering Department. Professor Arora was a highly respected subject matter expert in academia and industry alike. A few of his responsibilities and associations included: Member, National Advisory Committee of ISHTM-ASME, Joint Heat and Mass Transfer Conference; Member, Engineering Science Committee of Council of Scientific and Industrial Research, New Delhi, Govt. of India; Member, Cryogenics Committee of the Department of Science and Technology, New Delhi, Govt. of India; Reviewer: J. of Institution of Engineers; Reviewer: Indian J. of Engineering and Material Science, CSIR, New Delhi; Member, Board of Governors, Regional Engineering College, Durgapur; Member, Expert Committee to suggest improvement in operation of cold storages, Govt. of West Bengal. Professor Arora was also the recipient of several outstanding teacher awards, national scholarships, merit awards, graduate fellowship. He is credited with 91 research publications, 8 technical reports, 19 industrial projects and 3 pending patents. He guided 12 researchers towards their Ph.D. degrees, and 29 students towards their M.Tech. degrees, apart from being a constant anchor and mentor for numerous undergraduate students across departments.

REFRIGERATION AND AIR CONDITIONING RAMESH CHANDRA ARORA Formerly Professor Department of Mechanical Engineering Indian Institute of Technology Kharagpur New Delhi-110001 2010

REFRIGERATION AND AIR CONDITIONING Ramesh Chandra Arora 2010 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-3915-6 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi-110001 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli-131028, Sonepat, Haryana.

Contents Preface Acknowledgements 1 History of Refrigeration 1 18 1.1 Introduction 1 1.2 Natural Cooling Processes 2 1.3 Mechanical Cooling Processes 3 References 17 Review Questions 17 2 Thermal Principles A Review of Fundamentals 19 96 2.1 Introduction 20 2.2 Thermodynamic Properties 20 2.3 Closed and Open Systems 21 2.4 Units 22 2.5 The Four Laws of Thermodynamics 28 2.6 Zeroth Law of Thermodynamics 28 2.7 First Law of Thermodynamics 29 2.8 First Law of Thermodynamics for Open Systems 31 2.9 Second Law of Thermodynamics 32 2.10 Fundamental Relations of Thermodynamics 36 2.11 Third Law of Thermodynamics 38 2.12 Perfect Gas 38 2.13 Mixture of Ideal Gases 39 2.14 Real Gas and Vapours 40 2.15 Dry Air 42 2.16 Properties of Pure Substance 43 v xiii xv

vi Contents 2.17 Correlations for Properties of Refrigerants 49 2.18 Heat Transfer 50 2.19 Conduction 50 2.20 Fick s Law of Diffusion 53 2.21 Thermal Radiation 54 2.22 Convection 59 2.23 Condensation Heat Transfer 66 2.24 Boiling Heat Transfer 67 2.25 Reynolds Analogy 69 2.26 Analogy between Heat, Mass and Momentum Transfer 69 2.27 Heat Transfer through Composite Walls and Cylinder 70 2.28 Heat Exchangers 75 2.29 Fluid Flow 77 2.30 Cooling Processes 85 References 95 Review Questions 95 3 Mechanical Vapour Compression Cycles 97 170 3.1 Introduction 98 3.2 Vapour Compression Cycle 98 3.3 Refrigeration Capacity 99 3.4 Coefficient of Performance 99 3.5 Reversed Carnot Cycle or Carnot Refrigeration Cycle 100 3.6 External Regime and Internal Regime 106 3.7 Gas as Refrigerant 108 3.8 Pure Substance as Refrigerant 116 3.9 Standard Vapour Compression Cycle or Vapour compression Cycle or Single Stage Saturation (SSS) Cycle 121 3.10 Representation of Work as Areas on the T s Diagram 125 3.11 Comparison of Standard Refrigeration Cycle with Reversed Carnot Cycle 126 3.12 Refrigerant Tables Thermodynamic Properties 130 3.13 Subcooling and Superheating 132 3.14 Performance of Single Stage Saturation Cycle 137 3.15 Effect of Refrigerant Properties 141 3.16 Suction State for Optimum COP, Ewing s Construction 143 3.17 Actual Cycle Diagram 148 Review Questions 169 4 Compressors 171 241 4.1 Introduction 172 4.2 Thermodynamics of Compression 172 4.3 Reciprocating Compressors 177 4.4 Hermetic Compressors 197 4.5 Rotary Compressors 205 4.6 Centrifugal Compressors 214 4.7 Comparison with Reciprocating Compressor 235 4.8 Capacity Control 238

Contents vii 4.9 Selection of Compressors 239 References 240 Review Questions 241 5 Performance of Single Stage Saturation Cycle with Reciprocating Compressor 242 268 5.1 Introduction 243 5.2 Volumetric Efficiency and Mass Flow Rate 245 5.3 Work Requirement and HP/TR 246 5.4 Specific Refrigeration Effect and Refrigeration Capacity 247 5.5 Swept Flow Rate per TR 248 5.6 Adiabatic Discharge Temperature 249 5.7 Coefficient of Performance 250 5.8 Methods of Improving COP 250 5.9 Choice of Intermediate Pressure 254 5.10 Optimum Intermediate Pressure for Ideal Gas Compressor with Ideal Intercooling 255 5.11 Optimum Intermediate Pressure if Intercooling is Done Up to Temperature T w 258 5.12 Optimum Intermediate Pressures for Three-Stage Compression 259 Reference 267 Review Questions 267 6 Multistage Refrigeration Systems 269 349 6.1 Introduction 270 6.2 Two-stage NH 3 Cycle 270 6.3 Recommended Temperature Ranges for Multistage Systems 291 6.4 Multi-evaporator Systems 303 6.5 Two-stage Reversed Carnot Cycle 316 6.6 Limitations of Multistage Systems 318 6.7 Cascade Refrigeration System 320 6.8 Dry Ice Manufacture 337 6.9 Auto-cascade System 347 References 348 Review Questions 348 7 Absorption Refrigeration Systems 350 409 7.1 Introduction 351 7.2 Absorption Cycle of Operation 351 7.3 Maximum COP 353 7.4 Properties of Solutions 354 7.5 Aqua Ammonia Solution 360 7.6 Simple Absorption System 369 7.7 h x Diagram for Simple Absorption System 373 7.8 Drawbacks of Presence of Water Vapour in Evaporator and Condenser 379 7.9 Ammonia Enrichment Process 380 7.10 Water Lithum Bromide Absorption Refrigeration System 393 7.11 The Platen Munters System 404

viii Contents 7.12 Properties of Refrigerant Pairs for Absorption Systems 407 7.13 Comparison of Absorption System with Mechanical Vapour Compression Refrigeration System 408 References 408 Review Questions 409 8 Refrigerants 410 471 8.1 Introduction 410 8.2 Designation of Refrigerants 411 8.3 Some Commonly Used Refrigerants 414 8.4 Desirable Properties of Refrigerants 415 8.5 Reaction with Lubricating Oil 423 8.6 Reaction with Moisture 425 8.7 Thermodynamic Properties 426 8.8 Alternative Refrigerants 432 8.9 Mixtures 436 8.10 Alternatives to Various Popular Refrigerants 456 8.11 Natural Refrigerants 462 8.12 Secondary Refrigerants 465 References 468 Review Questions 470 9 Expansion Valves 472 504 9.1 Introduction 473 9.2 Capillary Tube 473 9.3 Automatic Expansion Valve 486 9.4 Thermostatic Expansion Valve 492 9.5 Float Type Expansion Valve 499 9.6 Electronic Type Expansion Valve 501 9.7 Some Practical Problems in Operation of Expansion Valves 502 References 503 Review Questions 503 10 Condensers 505 548 10.1 Introduction 505 10.2 Heat Rejection Ratio 506 10.3 Types of Condensers 506 10.4 Comparison of Water-cooled and Air-cooled Condensers 507 10.5 Comparison of Water-cooled and Evaporative Condensers 508 10.6 Air-cooled Condenser 508 10.7 Mean Temperature Difference for Crossflow Heat Exchanger 510 10.8 Fin Efficiency 514 10.9 Heat Transfer Areas 520 10.10 Overall Heat Transfer Coefficient 522 10.11 Heat Transfer Coefficients 523 10.12 Water Cooled Condensers 530 References 547 Review Questions 548

Contents ix 11 Evaporators 549 570 11.1 Introduction 549 11.2 Classification of Evaporators 549 11.3 Natural Convection Coils 550 11.4 Flooded Evaporator 551 11.5 Shell-and-Tube Liquid Chillers 552 11.6 Direct Expansion Coil 556 11.7 Plate Surface Evaporators 556 11.8 Finned Evaporators 558 11.9 Boiling Heat Transfer Coefficients 567 Reference 570 Review Questions 570 12 Complete Vapour Compression System 571 582 12.1 Introduction 571 12.2 Reciprocating Compressor Performance Characteristics 572 12.3 Condenser Performance Characteristics 573 12.4 Evaporator Performance Characteristics 576 12.5 Expansion Valve Characteristics 577 12.6 Condensing Unit characteristics 577 12.7 Performance of Complete System Condensing Unit and Evaporator 579 12.8 Effect of Expansion Valve 581 12.9 Conclusion 581 Reference 582 Review Questions 582 13 Gas Cycle Refrigeration 583 658 13.1 Introduction 583 13.2 Ideal Gas Behaviour 584 13.3 Temperature Drop Due to Work Output 584 13.4 Temperature Drop in Steady Flow Due to Change in Kinetic Energy 585 13.5 Temperature Drop in Closed System Due to Change in Kinetic Energy 586 13.6 Reversed Carnot and Joule Cycles for Gas Refrigeration 586 13.7 Aircraft Refrigeration Cycles 608 13.8 Vortex Tube Refrigeration 633 13.9 Pulse Tube 637 13.10 Stirling Cycle 641 13.11 Air Liquefaction Cycles 648 Review Questions 656 14 Water Steam Ejector Refrigeration System and Thermoelectric Refrigeration System 659 688 14.1 Introduction 659 14.2 Principle of Operation 660 14.3 Centrifugal Compressor-Based System 661 14.4 Steam-Jet Ejector System 664

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