REFRIGERATION AND AIR CONDITIONING SECOND EDITION S.N. Sapali Professor of Mechanical Engineering College of Engineering, Pune Delhi-110092 2014
REFRIGERATION AND AIR CONDITIONING, Second Edition S.N. Sapali 2014 by PHI Learning Private Limited, 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-978-81-203-4872-1 The export rights of this book are vested solely with the publisher. Second Printing (Second Edition) January, 2014 Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli-131028, Sonepat, Haryana.
Foreword... xiii Preface... xv Preface to the First Edition... xvii 1. INTRODUCTION 1 34 1.1 Introduction... 1 1.2 SI Units... 2 1.3 Terms Used in Thermodynamics... 7 1.4 Types of Energy... 8 1.5 Work...10 1.6 Heat... 11 1.7 Work Done during a Quasi-static Process... 12 1.8 First Law of Thermodynamics... 15 1.9 Processes for Ideal Gases... 17 1.9.1 Constant Volume Process... 17 1.9.2 Constant Pressure Process... 18 1.9.3 Constant Temperature Process... 18 1.9.4 Adiabatic Process... 20 1.9.5 Polytropic Process... 21 1.10 Control Volume... 23 1.11 Limitations of the First Law of Thermodynamics... 25 1.12 Second Law of Thermodynamics... 27 1.13 Pure Substance... 28 1.14 Other Phase Diagrams... 31 Numericals... 33 2. METHODS OF REFRIGERATION 35 52 2.1 Introduction... 35 2.2 Applications of Refrigeration... 35 2.3 Refrigeration Systems... 39 2.3.1 Ice Refrigeration... 39 iii
iv 2.3.2 Evaporative Refrigeration... 40 2.3.3 Refrigeration by Dry Ice... 41 2.3.4 Liquid Gas Refrigeration... 42 2.3.5 Steam Jet Refrigeration... 43 2.3.6 Thermoelectric Refrigeration... 44 2.3.7 Vortex Tube... 44 2.3.8 Solar Refrigeration... 46 2.3.9 Magnetic Refrigeration... 48 2.3.10 Air Refrigeration Cycle... 49 2.3.11 Vapour Compression Refrigeration Cycle... 50 Exercises... 51 3. AIR REFRIGERATION SYSTEMS 53 114 3.1 Introduction... 53 3.2 Definitions... 53 3.3 Refrigeration Load... 54 3.4 Heating Load... 54 3.5 Concept of Heat Engine, Refrigerator and Heat Pump... 55 3.6 Air Refrigeration Systems... 57 3.6.1 Carnot Refrigerator... 57 3.6.2 Limitations of Reversed Carnot Cycle... 61 3.6.3 Modified Reversed Carnot Cycle... 61 3.6.4 Reversed Carnot Cycle with Vapour as Refrigerant... 62 3.6.5 Bell Colemann or Reversed Brayton or Joule Cycle... 63 3.6.6 Actual Bell Colemann Cycle... 67 3.6.7 Application of Aircraft Refrigeration... 68 3.7 Methods of Air Refrigeration Systems... 68 3.7.1 Simple Air-cooling System... 68 3.7.2 Simple Air Evaporative Cooling System... 84 3.7.3 Boot-strap Air Cooling System... 88 3.7.4 Boot-strap Air Evaporative Cooling System... 100 3.7.5 Reduced Ambient Air Cooling System... 101 3.7.6 Regenerative Air Cooling System... 106 3.8 Comparison of Various Air Cooling Systems Used for Aircraft... 111 Exercises... 112 Numericals... 112 4. SIMPLE VAPOUR COMPRESSION REFRIGERATION SYSTEMS 115 177 4.1 Introduction... 115 4.2 Advantages and Limitations of Air Refrigeration... 115 4.2.1 Advantages of Air Refrigeration... 115 4.2.2 Limitations of Air Refrigeration... 115 4.3 Vapour Compression Refrigeration System (VC Cycle)... 116 4.4 Vapour Compression Cycle when Vapour is Dry Saturated at the End of Compression... 131 4.5 Vapour Compression Cycle when Vapour is Wet at the End of Compression... 134
v 4.6 Deviations from the Simple Compression Cycle... 141 4.6.1 Suction Gas Superheating without Cooling... 143 4.6.2 Suction Gas Superheating with Cooling Effect... 145 4.7 Effect of Subcooling the Liquid... 146 4.7.1 Liquid-suction Heat Exchanger... 151 4.7.2 Effect of Evaporator Pressure... 152 4.7.3 Effect of Condenser Pressure... 154 4.8 Losses in Vapour Compression Refrigeration System... 156 Exercises... 174 Numericals... 175 5. REFRIGERANTS 178 205 5.1 Introduction... 178 5.2 Classification of Refrigerants... 179 5.2.1 Primary Refrigerants... 179 5.2.2 Secondary Refrigerants... 180 5.3 Designation of Refrigerants... 180 5.4 Desirable Properties of a Good Refrigerant... 181 5.4.1 Thermodynamic Properties of Refrigerants... 181 5.4.2 Chemical Properties of Refrigerants... 183 5.4.3 Physical Properties of Refrigerants... 184 5.5 Properties of an Ideal Refrigerant... 185 5.6 Properties of Important Refrigerants... 185 5.7 Selection of a Refrigerant... 187 5.8 New Refrigerants... 189 5.9 Secondary Refrigerants... 191 5.9.1 Substances Used as Secondary Refrigerants... 193 5.10 Toxicity and Safe Handling of Refrigerants... 194 5.11 Oil and Refrigerant Relationship... 195 5.12 Lubricating Oils... 195 5.13 Effect of CFC on Ozone Depletion and Global Warming... 197 5.13.1 Ozone Depletion... 197 5.13.2 Global Warming... 199 5.14 Montreal Protocol... 200 5.15 Alternatives to CFC Refrigerants... 201 5.15.1 Certain Mixtures of Refrigerants as Replacement for HCFC R22... 202 5.15.2 Substitutes for CFC, R12 Refrigerant... 202 5.16 Kyoto Protocol and TEWI... 204 Exercises... 204 6. MULTIPRESSURE SYSTEMS 206 259 6.1 Introduction... 206 6.1.1 Limitations and Drawbacks of the Simple Vapour Compression... Refrigeration Cycle... 207 6.2 Multistage Vapour Compression System... 208 6.2.1 Multistage Compression with Intercooling between the Stages... 208 6.2.2 Intermediate Pressure for Minimum Work... 210
vi 6.3 Types of Multistage Vapour Compression System with Intercooler... 211 6.3.1 Two-stage Compression with Flash Gas Removal... 211 6.3.2 Two-stage Compression with Flash Intercooling... 212 6.3.3 Two-stage Compression with Flash Gas Removal and Additional Gas Cooler... 215 6.4 Multiple Evaporators and Compressors Systems... 224 6.4.1 Multiple Evaporators at the Same Temperature and a Single Compressor System... 225 6.4.2 Multiple Evaporators at Different Temperatures with a Single Compressor, Individual Expansion Valves and a Back Pressure Valve... 228 6.4.3 Multiple Evaporators at Different Temperatures with a Single Compressor, Multiple Expansion Valves and a Back Pressure Valve... 232 6.4.4 Multiple Evaporators with Individual Compressors and Individual Expansion Valves... 235 6.4.5 Multiple Evaporators with Individual Compressors and Multiple Expansion Valves... 239 6.4.6 Multiple Evaporators with Compound Compression and Individual Expansion Valves... 243 6.4.7 Multiple Evaporator System with Compound Compression, Individual Expansion Valves and Flash Intercoolers... 246 6.4.8 Refrigeration Unit with Multiple Evaporators with Compound Compression Multiple Expansion Valves and Flash Intercooler... 250 6.5 Cascade System... 253 Exercises... 257 Numericals... 257 7. VAPOUR ABSORPTION REFRIGERATION SYSTEMS 260 274 7.1 Introduction... 260 7.1.1 Refrigerant Solvent Properties... 261 7.2 Simple Vapour Absorption System... 262 7.3 Practical Vapour Absorption System... 263 7.4 Vapour Absorption Refrigeration System vs Vapour Compression Refrigeration System... 265 7.5 COP of an Ideal Vapour Absorption Refrigeration System... 265 7.6 Domestic Electrolux (Ammonia Hydrogen) Refrigerator... 269 7.7 Lithium Bromide Absorption Refrigeration System... 271 Exercises... 274 Numericals... 274 8. PSYCHROMETRY 275 319 8.1 Introduction... 275 8.2 Psychrometry... 277
vii 8.3 Psychrometric Chart... 296 8.4 Typical Air Conditioning Processes... 298 8.4.1 Sensible Heating of Air... 298 8.4.2 Sensible Cooling of Moist Air... 301 8.4.3 Cooling and Dehumidification of Moist Air... 302 8.5 Adiabatic Cooling or Cooling with Humidification Process... 305 8.6 Heating and Humidification... 307 8.6.1 Heating and Humidification by Steam Injection... 308 8.7 Adiabatic Mixing of Air Streams... 309 8.8 Air Washer... 312 8.9 Chemical Dehumidification or Sorbent Dehumidification... 313 Exercises... 317 Numericals... 318 9. COOLING LOAD ESTIMATION AND PSYCHROMETRIC ANALYSIS 320 358 9.1 Introduction... 320 9.2 Thermodynamics of Human Body and Mathematical Model... 321 9.3 Effective Temperature... 322 9.4 Human Comfort Chart... 323 9.5 Outside Design Conditions... 324 9.6 Sources of Heat Load... 325 9.7 Conduction through Exterior Structures... 326 9.7.1 Overall Heat Transfer Coefficient... 326 9.7.2 Cooling Load Estimation by CLTD Method... 327 9.8 Heat Gain through Glass... 327 9.8.1 Factors Affecting Solar Radiation at a Place... 328 9.8.2 Method of Estimation... 328 9.9 Infiltration... 329 9.9.1 Sensible Heat Loss Effect of Infiltration Air... 329 9.9.2 Latent Heat Loss Effect of Infiltration Air... 329 9.10 Ventilation... 330 9.11 Outside Air Load... 331 9.12 Heat Load from People... 332 9.13 Lighting... 333 9.14 Heat Gain from Equipment and Appliances... 333 9.15 System Heat Gain... 334 9.16 Room Cooling Load... 335 9.17 Cooling Coil Load... 335 9.18 Psychrometric Analysis of the Air Conditioning System... 335 9.18.1 Determining Supply Air Conditions... 335 9.18.2 Room Sensible Heat Factor (RSHF)... 337 9.19 Summer Air Conditioning System Provided with Ventilation Air (Zero Bypass Factor)... 338 9.19.1 Grand Sensible Heat Factor (GSHF)... 339 9.19.2 Winter Air Conditioning... 340
viii 9.20 Effective Room Sensible Heat Factor (ERSHF)... 342 Exercises... 357 Numericals... 357 10. AIR CONDITIONING SYSTEMS AND EQUIPMENT 359 382 10.1 Introduction... 359 10.2 Classification of Air Conditioning Systems... 360 10.3 Unitary System... 361 10.3.1 Window Air Conditioner... 361 10.3.2 Split Air Conditioner... 362 10.4 Central Air Conditioning Systems... 362 10.5 Reheat System... 365 10.6 Multizone System... 365 10.7 Dual Duct System... 366 10.8 Variable Air Volume (VAV) System... 367 10.9 All-water System... 368 10.10 Air-water Systems... 369 10.11 Unitary vs. Central Systems... 369 10.12 Air Conditioning Equipment... 370 10.13 Cooling Coil... 370 10.13.1 Coil Selection... 371 10.14 Heating Coils... 371 10.15 Air Cleaning Devices (Filters)... 372 10.15.1 Types of Filters/Cleaners... 373 10.15.2 Types of Media... 373 10.15.3 Electronic Air Cleaners... 374 10.15.4 Choice of Filter... 375 10.16 Humidifiers... 375 10.17 Fan... 376 10.17.1 Types of Fans... 376 10.17.2 Performance Characteristics of Fans... 377 10.17.3 Fan Selection... 379 10.17.4 Fan Ratings... 379 10.17.5 System Characteristics... 380 10.17.6 Fan system Interaction... 380 10.17.7 Selection of Optimum Fan Conditions... 381 10.17.8 Fan Laws... 381 Exercises... 382 11. COMPRESSORS 383 414 11.1 Introduction... 383 11.2 Compression Process... 384 11.3 Indicator Diagrams... 387 11.3.1 Comparison of Indicator Diagrams... 388 11.4 Overall Volumetric Efficiency... 388 11.4.1 Clearance Volumetric Efficiency (h cv )... 390
ix 11.4.2 Effect of Heat Exchange Loss... 390 11.4.3 Effect of Valve Pressure Drops... 391 11.4.4 Leakage Loss... 391 11.5 Design Features of a Reciprocating Compressor... 394 11.6 Determination of Compressor Motor Power... 395 11.7 Performance of a Reciprocating Compressor... 395 11.7.1 Performance of Ideal Compressor... 396 11.7.2 Actual Performance... 397 11.7.3 Capacity of a Compressor... 398 11.8 Capacity Control of Reciprocating Compressor... 399 11.9 Rotary Compressors... 401 11.9.1 Rolling Piston Compressor... 401 11.9.2 Rotary Vane Type Compressor... 402 11.9.3 Screw Compressors... 403 11.9.4 Single Screw Compressor... 403 11.9.5 Oil-injected Compressor... 404 11.9.6 Oil-injection Free Compressor... 405 11.10 Centrifugal Compressor... 409 11.10.1 Work Done by Impeller... 410 11.10.2 Power Input... 411 11.10.3 Performance of Centrifugal Compressor... 411 11.11 Hermetically Sealed Compressor... 413 Exercises... 414 12. EVAPORATORS AND CONDENSERS 415 442 12.1 Introduction... 415 12.2 Conduction... 416 12.2.1 Steady State Heat Conduction through a Slab... 416 12.2.2 Steady State Heat Flow through a Cylindrical Wall... 417 12.2.3 Steady State Conduction through a Composite Wall... 417 12.2.4 Steady State Conduction through a Composite Cylinder... 418 12.2.5 Overall Heat Transfer Coefficient... 419 12.3 Convection Heat Transfer... 420 12.4 Evaporator... 423 12.4.1 Dry and Flooded Evaporators... 423 12.5 Frosting and Defrosting of Coolers... 427 12.5.1 Methods of Defrost... 427 12.5.2 Latent Heat Defrost... 428 12.5.3 Electric Defrost... 428 12.6 Selection from Manufacturer s Data Sheets... 429 12.7 Liquid Coolers (Chillers)... 430 12.7.1 Direct Expansion Type... 430 12.7.2 Flooded Shell-and-Tube Coolers... 431 12.7.3 Baudelot Cooler... 431 12.7.4 Shell-and-Coil Cooler... 431
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