Industrial Refrigeration

There is a tendency in our complex (and complexed) time, to discount simplicity.

People sometimes feel that a simple, straightforward solution to a problem, or a
simple, understandable down-to-earth answer to a question must be rejected. Their
basis for this surprising view appears to be that such a simple solution somehow
reduces the magnitude of their problem, and by reflection, tends to minimise their
own personal importance.

Brinsley Le Poer Trench

Temple of the Stars
 Industrial Refrigeration
Principles, Design and Applications

P. C. Koelet
with T. B. Gray

M
MACMILLAN
© P. C. Koelet 1992
Softcover reprint of the hardcover 1st edition 1992 978-0-333-52168-7
All rights reserved. No reproduction, copy or transmission of
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issued by the Copyright Licensing Agency, 90 Tottenham Court Road,
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Any person who does any unauthorised act in relation to this

publication may be liable to criminal prosecution and civil
claims for damages.

First published 1992 by

THE MACMILLAN PRESS LTD
Houndmills, Basingstoke, Hampshire RG21 2XS
and London
Companies and representatives
throughout the world

ISBN 978-1-349-11435-1 ISBN 978-1-349-11433-7 (eBook)

DOI 10.1007/978-1-349-11433-7
A catalogue record for this book is available
from the British Library.

Typeset by TecSet Ltd., Wallington, Surrey

Contents

Symbols and Units xiii

International Units xv

1 Principles of Refrigeration 1
1.1 History 1
1.2 Relationship between pressure and temperature 4
1.3 Energy 5
1.3.1 Internal energy 6
1.3.2 Internal energy in relation to compression and
expansion 7
1.4 Compression 8
1.5 Expansion 9
1.6 Enthalpy 10
1. 7 Principles of the refrigeration process 11
1.8 The Mollier diagram or chart for refrigerants 15

2 An Introduction to Psychrometries 22
2.1 Introduction 22
2.2 The gas laws 25
2.3 Relative humidity, RH or <!> 30
2.4 Humidity ratio, specific humidity or moisture content x
mg ~
2.5 Enthalpy of moist air 31
2.6 The factor dh/dx 31
2. 7 The wet-bulb temperature 31
2.8 The Mollier diagram for moist air 33
2.9 The slope of the cooling line 34

v
vi Contents
2.10 The Carrier chart 36
2.11 The sensible heat factor 38
2.12 The concept of bypassing 38
2.13 The concept of apparatus dew point 39

3 Refrigerants 41
3.1 Primary refrigerants 41
3.1.1 The refrigerant of the future 42
3.1.2 The choice of refrigerant 43
3.1.3 New refrigerants 46
3.2 Toxicity and other hazards 56
3.3 The advantages of ammonia 59
3.4 Oil and refrigerant relationships 61
3.4.1 Lubricating oils 63
3.4.2 Specific gravity 65
3.4.3 Viscosity 65
3.4.4 Viscosity index 65
3.4.5 Flash point 65
3.4.6 Pour point 66
3.4.7 Floc point 66
3.4.8 Colour number 66
3.4.9 Aniline point 66
3.4.10 Neutralization number 67
3.5 Water in refrigerants 67
3.6 Secondary refrigerants 69
3.7 Heat-transfer characteristics 70

4 Compressors 73
4.1 Open and semi-hermetic compressors 73
4.2 Compression action in the refrigeration process 74
4.3 Charge coefficient A - overall volumetric efficiency 79
4.4 Influence of compressor design on A 83
4.5 Power requirement of a piston compressor 84
4.6 Influence of compressor design on TJis 86
4. 7 Capacity control 89
4.8 Main design features of a piston compressor 93
4. 9 Effects of valve construction 94
4.10 Calculation of cylinder swept volume Vs and number of
cylinders a 94
4.11 Multi-stage compression with open and closed intercooling 95
4.12 Determination of the intermediate pressure 98
4.13 Determination of discharge temperature 100
 Contents vii
4.14 Determination of compressor speed and power
consumption 101
4.14.1 Single-stage compression 101
4.14.2 Two-stage compression 104
4.15 Effects of evaporating temperature, condensing
temperature, subcooling and superheating 106
4.16 Rotary compressors 109
4.16.1 Vane compressors 109
4.16.2 Screw compressors 110
4.16.3 Turbo-compressors 130

5 Evaporators and Condensers 132

5.1 Heat transfer 132
5 .1.1 Heat transfer by conduction 133
5.1.2 Heat transfer by convection 135
5.1.3 Nusselt number (and other numbers) 138
5.1.4 Biot number 139
5.2 Evaporators: technology, design, selection and applications 139
5.3 Condensers 177
5.3.1 Introduction 177
5.3.2 Water-cooled condensers 178
5.3.3 Evaporative condensers 181
5.3.4 Air-cooled condensers 184
5.4 U-values in daily practice 187
5.5 Modern developments in enhanced heat transfer for
evaporators and condensers 188

6 Vessel and Piping Design 191

6.1 Ammonia circuits 191
6.1.1 Two-phase flow 193
6.2 CFC circuits 194
6.3 Liquid separators, receivers, refrigerant pumps and
intercoolers 201
6.3.1 Pump circulation 205
6.3.2 Oil separation in CFC installations 205
6.3.3 Pump selection and cavitation problems 206
6.3.4 Intercoolers 208
6.3.5 Calculation of the liquid separator zone
dimensions 209
6.3.6 Separator liquid capacity 210
6.4 Air purging 215
6.5 Heat exchangers 217
viii Contents
6.6 Oil rectifiers 219
6. 7 Some practical calculations 219
6. 7.1 Capacity of a vessel 219
6.7.2 The overflow valve 220
6.7.3 The pressure relief valve 220
6.7.4 The hot-gas defrost line 220
6. 7.5 Calculation of an oil rectifier in a R22 pump
circulation 221

7 Controls 223
7.1 Applications in industrial refrigeration requiring
regulation and control 224
7.2 Devices and components available to perform regulation
and control 226
7 .2.1 Thermostatic expansion valves 227
7.2.2 Pressure and temperature controls 229
7.2.3 Pressure regulators 230
7.3 Condensing pressure control by flooding the condenser
with liquid refrigerant 231

8 Food Products and their Preservation by Refrigeration 234

8.1 What are food products? 234
8.2 Vegetable matter 236
8.3 How plants live 237
8.4 Storage diseases 242
8.5 Meat products 243
8.6 How refrigeration techiques can help to conserve food
products 246
8. 7 Refrigeration or cooling 247
8. 7.1 Determination of the cooling time 251
8.7.2 Half cooling time 253
8.8 Deep-freezing of food 254
8.8.1 Freezing spread 256
8.8.2 Freezing time calculation 258
8.8.3 Freezing equipment 263
8. 9 Defrosting of frozen food 273
8.10 Packaging methods 277

9 Special Food Preservation Methods and Other Applications 280

9.1 Controlled atmosphere storage 280
9 .1.1 Scrubbers 282
9.1.2 Burners 283
9.1.3 Controls 287
9.1.4 Ethylene scrubbing 289
 Contents lX

9.1.5 Vacuum cooling 290

9.1.6 Wet cooling system and flow-through cooling 292
9.1.7 Hypobaric cooling 295
9.2 Banana storage 296
9.3 Citrus fruit 299
9.4 Bakery products 300
9.5 Eggs 301
9.6 Ice cream 301
9.7 Chocolate products 305
9.8 Cheese 306
9.9 Beer 306
9.10 Deboned meat and prepared dishes (TV dinners) 309
9.11 Poultry 310
9.12 Fish 310
9.13 Refrigerated cargo 313
9.14 Ice plants 313
9.14.1 Block ice 313
9.14.2 Block ice storage 316
9.14.3 Slice or flake ice 316
9.14.4 Slice ice storage 316
9.15 Other applications of artificial cooling 316
9.16 Heat recovery 320

10 Insulation Techniques and Coldstore Construction 322

10.1 Background information 322
10.1.1 Heat transfer 322
10.1.2 Water vapour diffusion, vapour barrier and
material characteristics 327
10.2 Insulation of coldstores 335
10.2.1 Floor insulation 335
10.2.2 Roof insulation 339
10.2.3 Gas-tight insulation 340
10.2.4 Overpressure protection 345
10.2.5 Practical guidelines to coldstore dimensioning 349
10.3 Pipework and vessel insulation 371

11 The Heat Load Calculation 374

11.1 Thermal transmission, Q1 374
11.2 Air infiltration, Q2 374
11.3 Moisture load, Q 3 378
11.4 Product, Q4 379
11.5 Miscellaneous heat loads, Q 5 380
11.6 Sample heat load calculation 381
X Contents
12 Economic Considerations of Refrigeration 384

13 Plant Maintenance 396

13.1 Regular maintenance plans 396
13.2 Oil and refrigerant charges 398
13.2.1 Oillevel 398
13.2.2 Refrigerant in the lubricating oil 399
13.2.3 Checking the refrigerant charge of the plant 400
13.2.4 Conversion from R12 and R502 to R22 401
13.3 Fault-finding and correction 403
13.3.1 Compressors 403
13.3.2 Oil 411
13.3.3 Expansion valve 414
13.4 Standards 417

Epilogue 419

References 420

Bibliography 422

Glossary 423

Index 426
Preface

Refrigeration is an exciting application of science and technology. It

involves a range of subjects such as thermodynamics, mechanics, electrical
technology, civil engineering, hydraulics, aerodynamics, chemistry and,
last but not least, food technology. However, it must never be forgotten
that refrigeration is not an end in itself but the means to an end - in most
cases, to help condition man's environment and satisfy many of his
nutritional needs. During the past 100 years, refrigeration has become
indispensable to our society. Modern food processing, storage and
transportation, for instance, would be impossible without the help of
refrigeration.
I am convinced that all over the world engineers and technicians would
like to learn more about the subject, and for this reason I have written this
book in English. It is intended for those who, either as contractors or
consultants, are involved in the design of refrigeration plants, and for those
who are responsible for the purchasing or maintenance of these plants.
Industrial applications are generally larger than commercial applications
and normally require a qualified operator on duty. Industrial refrigeration
plants are found in the food processing, plastic, metallurgical and chemical
industries, and on board ship. Such systems are based on a centralized
design and normally use open-type compressors with high efficiency, long
lifetime and power consumption above 30 kW.
This book deals not only with the installation and its components, but
also with the products that are processed or stored in the refrigeration
installation; it also considers the building in which the system operates.
The first chapters contain some useful and relevant thermodynamic
background information. Later, a description of refrigeration and freezing
systems is provided, as well as the calculation methods necessary to
determine the refrigeration capacity and selection of the different compo-
nents for the plant. This book is also about the application of refrigeration
and therefore provides the reader with background information about the
xi
xii Preface
composition of and the optimum storage conditions for food products.
Finally, it deals with the economic aspects, maintenance procedures, fault
finding and repair.
Teachers and students in universities, polytechnics and technical colleges
or others who would simply like to study refrigeration should find this book
very useful.
I wish to thank everyone who was helpful in creating this book,
especially my wife Mrs Maria Teresa Koelet-Paranhos de Oliveira for the
extensive and difficult word processing and also Mrs Ilonka Perl-
Chatterjee who, together with my wife, spent many hours editing the text.
I should also like to express my grateful thanks to Tom Gray for his
painstaking work in helping to produce the final draft; his constructive
comments have made a significant contribution throughout. Nonetheless, I
remain ultimately responsible for any errors that may remain.
Last but not least I would like to acknowledge the assistance of all the
individuals and companies quoted in the References at the end of the
book.

PIETER C. KOELET
Meise, Belgium, 1991
Symbols and Units
Symbols

A m2 Surface
a m2/s Temperature conductivity coefficient
c, Cp, Cv kJ/(kg K) Specific heat
D m2/s Diffusion coefficient
E kJ Energy
E kJ/s(=kW) Energy flow
F Force
H kJ Enthalpy
h kJjkg Specific enthalpy
J g/m 2/m/s Water vapour diffusion coefficient
k Isentropic exponent
k Wj(m 2 K) Heat transmission coefficient
L kJjkg Specific evaporation enthalpy
l kJ/kg Specific melting enthalpy
M kJ/kmol Relative molecular mass
m kg Mass
m kg/s Mass flow
n Exponent of polytrop
n 1/s; 1/min Rotation number
n kmol Molecular quantity
P kW Power
p Pa = N/m 2 ; bar Pressure
Q kJ Heat load
Q0 kW Refrigeration flow
Qo kJ/s (= kW) Heat flow
q kJjkg Specific heat load
q 0 kJ/kg Specific refrigerating load
q0 , v kl/m 3 Volumetric refrigerant load
xiii
xiv Symbols and Units
R kJ/(kg K) Gas constant
R kJ/(kmol K) Universal or absolute gas constant
S kJ/K Entropy
s kJ/(kg K) Specific entropy
TK Absolute temperature
Tc K Condensation temperature
Te K Evaporation temperature
To K Room temperature
Tp K Product temperature
t oc Temperature
t h Time
U m/s Velocity
UkJ Internal energy
V m3 Volume
V' m3/s; m3/h Volume flow
v m 3/kg Specific volume
W kJ; kWh Work
a W/(m 2 K) Heat-transfer coefficient
J3 kgi(Pa/m 2/s) Matter transfer coefficient
8 m Thickness
E kg/kg;% Mass proportion
eo Cold factor
Efficiency coefficient
TJ Pa s = N s/m 2 Dynamic viscosity
A Filling ratio
A W/(m K) Thermal conductivity coefficient
v m2/s Kinematic viscosity
1T Pressure ratio
p kglm 3 Density
International Units

The unit in which heat was expressed in the past was the calorie. 1 kcal of
heat was the quantity necessary to raise the temperature of 1 kg of water
by 1 degree. This unit was used until the 1970s in continental Europe.
Often the British Thermal Unit (Btu) was used in English-speaking
countries, and 'tons of refrigeration' in the USA. There is now an
internationally agreed system of units called the SI (Systeme International).
In this system a quantity of heat is expressed in joules (1 calorie = 4.1868
joules). The capacity of an installation is no longer expressed in calories/h,
or in Btu, but in kW. The International System defines the unit of
temperature as the kelvin, rather than oc or op (1 oc is equivalent to
1 kelvin, ooc is 273.15 kelvin).
The SI or International System is based on six basic units plus two
supplementary units. These are:

Unit of length = metre (symbol m)

Unit of mass = kilogram (symbol kg)
Unit of time = second (symbols)
Unit of electric current = ampere (symbol A)
Unit of temperature = kelvin (symbol K)
Unit of luminous intensity = candela (symbol cd)
Unit of plane angle = radian (symbol rad)
Unit of solid angle = steradian (symbol sr)

The system uses the same units for energy, no matter what kind of
energy is being considered. 150 years ago Newton propounded his laws of
motion: his 'second law' is often expressed by force is equal to mass
multiplied by acceleration, or F = m x a. In honour of his achievement
XV
xvi International Units
the new unit of force is called the newton (symbol N). It is the force
required to accelerate a body of 1 kg mass at 1 m/s2 . Previously, the unit of
force was the pound or the kg:

1 kg is the force that a body of 1 kg weight is subjected to by the pull

of gravity at a certain point in Paris
1 kg force = kg mass x 9.807/s2 = 9.807 N
The old system was confusing in as much as force and mass were both
expressed in kg. Also in an age of space exploration, units based on
gravitational force at a certain point of a certain planet are not logical.
Pressure = force/m 2 • The unit of pressure is now 1 N/m 2 , also called
1 Pascal (1 Pa). As this unit is small, for liquids and gases we use the unit
1 bar = 105 Pa = 105 N/m 2 . 1 kg/cm 2 in the old metric
system = 9.807 x 10 N/m = 0.9807 x 105 Pa.
4 2

The unit of energy is derived from work = force X distance. Thus the
unit of energy is 1 N x 1 m = 1 N m. This unit is now called 1 joule (1 J).
1 joule is the work done by a force of 1 N when it moves 1 m in the
direction of the force. The old 1 kg (force) = 9.807 N.

1 kg m = 1m X (1 kg force X 9.807 N/kg force)

1 kg m = 9.807 N m = 9.807 J

1 kcal was 427 kg m, which is 427 X 9.807 J or 4,187 J. Related to time,

the old system used the unit of kcaVh. In the SI system, the unit of effort is
the energy required to do work of 1 N m = 1 J in 1 second. The J/s is
however called the watt (symbol W). We think J/s but say 'W'.

4187
1 kcaVh = - J/s = 1.163 J/s or 1.163 W
3600

1 kcaVkg = 4187 J/kg = 4.187 kJ/kg

Specific heat is now expressed in J/ (kg K). Remember also that it is no

longer permissible to use the metric unit of horse power (HP) but rather W
or kW (1 HP was 75 kg m or 0.736 kW).

Kinematic viscosity v: 1 centistoke = 1 m m2/s

Dynamic viscosity TJ: 1 centipoise = 1 m Pa s
 International Units xvii
Speeds of revolution are no longer expressed as revolutions per minute
(rpm):

1 rpm = -rr/30 rad/s

1 rad/ s = 30/ -rr rpm

Notwithstanding this, however, rpm are still used in this book. Experience
has shown that few people in refrigeration technology use the new unit. In
general, however, new units are being used routinely in many countries by
refrigeration engineers.