Refrigeration Systems and Applications
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Preface xvii
Acknowledgments xix
1 General Aspects of Thermodynamics 1
1.1 Introduction 1
1.2 Dimensions and Units 2
1.2.1 Systems of Units 2
1.2.1.1 Mass 2
1.2.1.2 Length 2
1.2.1.3 Force 3
1.2.1.4 Density and Specific Volume 3
1.2.1.5 Mass Flow Rate and Volumetric Flow Rate 3
1.2.1.6 Temperature 4
1.2.1.7 Pressure 6
1.3 Thermodynamics 9
1.3.1 Thermodynamic Systems 9
1.3.2 Thermodynamic Laws 10
1.3.3 First Law of Thermodynamics 10
1.3.4 Second Law of Thermodynamics 12
1.3.4.1 Exergy and its Importance 13
1.3.4.2 Reversibility and Irreversibility 15
1.3.4.3 Reversible Work and Exergy Destruction 15
1.3.5 Dincer's Six-step Approach 15
1.3.6 Pure Substances 25
1.3.6.1 State and Change of State 25
1.3.6.2 Vapor States 27
1.3.6.3 Sensible Heat, Latent Heat and Latent Heat of Fusion 27
1.3.6.4 Specific Heat 27
1.3.6.5 Specific Internal Energy 28
1.3.6.6 Specific Enthalpy 28
1.3.6.7 Specific Entropy 28
1.3.6.8 Energy Change and Energy Transfer 29
1.3.6.9 Flow Energy 29
1.3.6.10 Heat Transfer 29
1.3.6.11 Work 30
1.3.6.12 Thermodynamic Tables 30
1.4 Ideal and Real Gases 30
1.5 Refrigerators and Heat Pumps 36
1.5.1 The Carnot Refrigerators and Heat Pumps 38
1.6 Psychrometrics 49
1.6.1 Common Definitions in Psychrometrics 50
1.6.2 Balance Equations for Air and Water Vapor Mixtures 52
1.6.3 The Psychrometric Chart 53
1.7 Concluding Remarks 64
Nomenclature 64
Study Problems 67
References 70
2 Refrigerants 71
2.1 Introduction 71
2.2 Classification of Refrigerants 72
2.2.1 Halocarbons 72
2.2.2 Hydrocarbons 73
2.2.3 Inorganic Compounds 74
2.2.3.1 Ammonia (R-717) 74
2.2.3.2 Carbon dioxide (R-744) 75
2.2.3.3 Air (R-729) 75
2.2.4 Azeotropic mixtures 75
2.2.5 Nonazeotropic mixtures 76
2.3 Prefixes and Decoding of Refrigerants 76
2.3.1 Prefixes 76
2.3.2 Decoding the Number 77
2.3.3 Isomers 78
2.4 Secondary Refrigerants 79
2.5 Refrigerant-absorbent Combinations 80
2.6 Stratospheric Ozone Layer 82
2.6.1 Stratospheric Ozone Layer Depletion 84
2.6.2 Ozone Depletion Potential 85
2.6.3 Montreal Protocol 88
2.7 Global Warming 89
2.7.1 Global Warming Potential 93
2.8 Clean Air Act 94
2.8.1 Significant New Alternative Policies Program 94
2.8.2 Classification of Substances 96
2.9 Key Refrigerants 103
2.9.1 R-134a 103
2.9.2 R- 123 105
2.9.3 Nonazeotropic (Zeotropic) Mixtures 106
2.9.4 Azeotropic Mixtures 108
2.9.5 Ammonia (R-717) 110
2.9.6 Propane (R-290) 111
2.9.7 Carbon Dioxide (R-744) 113
2.10 Selection of Refrigerants 115
2.11 Thermophysical Properties of Refrigerants 116
2.12 Lubricating Oils and their Effects 120
2.13 Concluding Remarks 122
Study Problems 122
References 125
3 Refrigeration System Components 127
3.1 Introduction 127
3.2 History of Refrigeration 128
3.3 Main Refrigeration Systems 130
3.4 Refrigeration System Components 131
3.5 Compressors 132
3.5.1 Hermetic Compressors 133
3.5.2 Semi-hermetic Compressors 135
3.5.3 Open Compressors 136
3.5.4 Classification of Compressors 136
3.5.5 Positive Displacement Compressors 137
3.5.5.1 Reciprocating Compressors 137
3.5.5.2 Rotary Compressors 137
3.5.6 Dynamic Compressors 144
3.5.6.1 Centrifugal Compressors 144
3.5.6.2 Axial Compressors 147
3.5.7 Thermodynamic Analysis of Compressor 147
3.5.8 Compressor Capacity and Performance Assessment 149
3.5.8.1 Compression Ratio 149
3.5.8.2 Compressor Efficiency 150
3.5.8.3 Compressor Capacity Control for Better Performance 151
3.6 Condensers 156
3.6.1 Water-cooled Condensers 157
3.6.2 Air-cooled Condensers 157
3.6.3 Evaporative Condensers 158
3.6.4 Cooling Towers 159
3.6.5 Thermodynamic Analysis of Condenser 160
3.7 Evaporators 165
3.7.1 Liquid Coolers 165
3.7.2 Air and Gas Coolers 166
3.7.3 Thermodynamic Analysis of Evaporator 167
3.8 Throttling Devices 172
3.8.1 Thermostatic Expansion Valves 172
3.8.2 Constant Pressure Expansion Valves 173
3.8.3 Float Valves 173
3.8.4 Capillary Tubes 174
3.8.5 Thermodynamic Analysis of Throttling Valve 174
3.9 Auxiliary Devices 177
3.9.1 Accumulators 177
3.9.2 Receivers 178
3.9.3 Oil Separators 178
3.9.4 Strainers 179
3.9.5 Dryers 179
3.9.6 Check Valves 179
3.9.7 Solenoid Valves 179
3.9.8 Defrost Controllers 179
3.10 Concluding Remarks 180
Nomenclature 180
Study Problems 182
References 187
4 Refrigeration Cycles and Systems 189
4.1 Introduction 189
4.2 Vapor-compression Refrigeration Systems 189
4.2.1 Evaporation 190
4.2.2 Compression 190
4.2.3 Condensation 190
4.2.4 Expansion 191
4.3 Energy Analysis of Vapor-compression Refrigeration Cycle 192
4.4 Exergy Analysis of Vapor-compression Refrigeration Cycle 195
4.5 Actual Vapor-compression Refrigeration Cycle 200
4.5.1 Superheating and Subcooling 201
4.5.1.1 Superheating 201
4.5.1.2 Subcooling 203
4.5.2 Defrosting 204
4.5.3 Purging Air in Refrigeration Systems 205
4.5.3.1 Air Purging Methods 206
4.5.4 Twin Refrigeration System 209
4.6 Air-standard Refrigeration Systems 210
4.6.1 Energy and Exergy Analyses of a Basic Air-standard Refrigeration Cycle 211
4.7 Absorption Refrigeration Systems 216
4.7.1 Basic Absorption Refrigeration Systems 218
4.7.2 Ammonia-water (NH3-H2O) Absorption Refrigeration Systems 219
4.7.3 Energy Analysis of an Absorption Refrigeration System 221
4.7.4 Three-fluid (Gas Diffusion) Absorption Refrigeration Systems 224
4.7.5 Water-lithium Bromide (H2O -LiBr) Absorption Refrigeration Systems 225
4.7.5.1 Single-effect Absorption Refrigeration Systems 226
4.7.5.2 Double-effect Absorption Refrigeration Systems 227
4.7.5.3 Crystallization 229
4.7.6 Steam Ejector Recompression Absorption Refrigeration Systems 230
4.7.7 Electrochemical Absorption Refrigeration Systems 231
4.7.8 Absorption-augmented Refrigeration System 232
4.7.9 Exergy Analysis of an Absorption Refrigeration System 239
4.7.10 Performance Evaluation of an Absorption Refrigeration System 243
4.8 Concluding Remarks 245
Nomenclature 245
Study Problems 247
References 258
5 Advanced Refrigeration Cycles and Systems 261
5.1 Introduction 261
5.2 Multistage Refrigeration Cycles 262
5.3 Cascade Refrigeration Systems 268
5.3.1 Two-stage Cascade Systems 269
5.3.2 Three-stage (Ternary) Cascade Refrigeration System 274
5.4 Multi-effect Absorption Refrigeration Systems 280
5.5 Steam-jet Refrigeration Systems 311
5.6 Adsorption Refrigeration 317
5.7 Stirling Cycle Refrigeration 322
5.7.1 Performance Assessment 325
5.8 Thermoelectric Refrigeration 328
5.8.1 Performance Assessment of Thermoelectric Coolers 329
5.9 Thermoacoustic Refrigeration 332
5.10 Metal Hydride Refrigeration 334
5.10.1 Operational Principles 335
5.10.2 Regeneration Process 336
5.10.3 Refrigeration Process 336
5.11 Magnetic Refrigeration 337
5.11.1 Magnetic Refrigeration Cycle 339
5.11.2 Active Magnetic Regenerators 340
5.12 Supermarket Refrigeration Practices 345
5.12.1 Direct Expansion Systems 346
5.12.2 Distributed Systems 347
5.12.3 Secondary Loop Systems 348
5.13 Concluding Remarks 349
Nomenclature 349
Study Problems 351
References 354
6 Renewable Energy-based Integrated Refrigeration Systems 357
6.1 Introduction 357
6.2 Solar-powered Absorption Refrigeration Systems 358
6.3 Solar-powered Vapor-compression Refrigeration Systems 364
6.4 Wind-powered Vapor-compression Refrigeration Systems 368
6.5 Hydropowered Vapor-compression Refrigeration Systems 371
6.6 Geothermal-powered Vapor-compression Refrigeration Systems 375
6.7 Ocean Thermal Energy Conversion Powered Vapor-compression Refrigeration Systems 379
6.8 Biomass-powered Absorption Refrigeration Systems 383
6.9 Concluding Remarks 393
Nomenclature 394
Study Problems 395
Reference 398
7 Heat Pipes 399
7.1 Introduction 399
7.2 Heat Pipes 400
7.2.1 Heat Pipe Use 403
7.3 Heat Pipe Applications 403
7.3.1 Heat Pipe Coolers 404
7.3.2 Insulated Water Coolers 404
7.3.3 Heat Exchanger Coolers 404
7.4 Heat Pipes for Electronics Cooling 405
7.5 Types of Heat Pipes 407
7.5.1 Micro Heat Pipes 408
7.5.2 Cryogenic Heat Pipes 408
7.6 Heat Pipe Components 408
7.6.1 Container 410
7.6.2 Working Fluid 411
7.6.3 Selection of Working Fluid 413
7.6.4 Wick or Capillary Structure 414
7.7 Operational Principles of Heat Pipes 417
7.7.1 Heat Pipe Operating Predictions 418
7.7.1.1 Gravity-aided Orientation 419
7.7.1.2 Horizontal Orientation 419
7.7.1.3 Against Gravity Orientation 420
7.7.2 Heat Pipe Arrangement 421
7.8 Heat Pipe Performance 421
7.8.1 Effective Heat Pipe Thermal Resistance 423
7.9 Design and Manufacture of Heat Pipes 424
7.9.1 Thermal Conductivity of a Heat Pipe 427
7.9.2 Common Heat Pipe Diameters and Lengths 427
7.10 Heat-transfer Limitations 428
7.11 Heat Pipes in Heating, Ventilating and Air Conditioning 429
7.11.1 Dehumidifier Heat Pipes 430
7.11.1.1 Working Principle 431
7.11.1.2 Indoor Dehumidifier Heat Pipes 432
7.11.2 Energy Recovery Heat Pipes 433
7.12 Concluding Remarks 436
Nomenclature 436
Study Problems 437
References 439
8 Food Refrigeration 441
8.1 Introduction 441
8.2 Food Deterioration 442
8.3 Food Preservation 443
8.4 Food Quality 444
8.5 Food Precooling and Cooling 446
8.6 Food Precooling Systems 448
8.6.1 Energy Coefficient 449
8.6.2 Hydrocooling 450
8.6.2.1 Hydrocooling using Ice or Ice-slush Cooling 453
8.6.2.2 Hydrocooling using Artificial Ice 453
8.6.2.3 Hydrocooling using Natural Ice 454
8.6.2.4 Hydrocooling using Natural Snow 455
8.6.2.5 Hydrocooling using Compacted Snow 455
8.6.3 Forced-air Cooling 456
8.6.3.1 Methods of Forced-air Cooling 459
8.6.3.2 Cold-wall-type Tunnel Forced-air Cooling 461
8.6.3.3 Serpentine Cooling 463
8.6.3.4 Single-pallet Forced-air Cooling 464
8.6.3.5 Room Cooling (with Storage and Shipping) 464
8.6.3.6 Ice-bank Forced-air Cooling System 464
8.6.3.7 Forced-air Cooling with Winter Coldness 465
8.6.3.8 Technical Details of Forced-air Cooling Systems 466
8.6.3.9 Engineering/economic Model for Forced-air Cooling Systems 468
8.6.4 Hydraircooling 469
8.6.5 Vacuum Cooling 471
8.6.6 Hydrovac Cooling 475
8.6.7 Evaporative Cooling 475
8.6.8 Ice Cooling 476
8.7 Precooling of Milk 477
8.8 Food Freezing 479
8.9 Cool and Cold Storage 480
8.9.1 Chilling Injury 481
8.9.2 Optimum Storage Conditions 481
8.9.2.1 Optimum Temperature 481
8.9.2.2 Optimum Relative Humidity 482
8.9.3 Technical Aspects of Cold Stores 485
8.9.3.1 Shape and Size 486
8.9.3.2 Construction Methods 486
8.9.3.3 Insulation 487
8.9.3.4 Vapor Barriers 488
8.9.3.5 Floors 488
8.9.3.6 Cold-air Distribution 488
8.9.3.7 Defrosting 489
8.9.3.8 Cold Store Planning 489
8.9.3.9 Refrigeration 490
8.9.4 Calculation of Cold Store Refrigeration Loads 490
8.9.5 Energy-efficient Cold Store 492
8.9.6 Photovoltaic-powered Cold Store 493
8.10 Controlled Atmosphere Storage 496
8.10.1 Controlled Atmosphere Storage Ripening and Waxing 500
8.10.2 Container-controlled Atmospheres 501
8.10.2.1 Controlled Modified Atmosphere Systems 501
8.10.2.2 Modified Atmospheres in Containers 502
8.10.2.3 Modified Atmospheres in Packaging 502
8.10.2.4 Pressure Swing Absorption Systems 502
8.10.2.5 Membrane Separation Systems 502
8.10.3 Packaging 503
8.10.4 Definitions 503
8.10.5 Modified Atmosphere Packaging 503
8.10.6 Modified Atmosphere Cooling 505
8.11 Refrigerated Transport 506
8.11.1 Reefer Technology 507
8.11.1.1 Controlled-atmosphere Reefer Containers 507
8.11.2 Quality Aspects of Products 507
8.11.3 Effective Packaging for Quality 508
8.11.4 Transport Storage 509
8.11.5 Temperature Control 511
8.11.5.1 Temperature Control and Monitoring 512
8.11.5.2 Temperature Monitoring Systems 513
8.11.6 Transportation Aspects 513
8.11.7 Recommended Transit and Storage Procedures 514
8.11.8 Developments in Refrigerated Transport 514
8.11.8.1 Sea and Land Transport 515
8.11.8.2 Air Transport 515
8.12 Respiration (Heat Generation) 515
8.12.1 Measurement of Respiratory Heat Generation 516
8.13 Transpiration (Moisture Loss) 516
8.13.1 Shrinkage 521
8.14 Cooling Process Parameters 522
8.14.1 Cooling Coefficient 522
8.14.2 Lag Factor 523
8.14.3 Half Cooling Time 523
8.14.4 Seven-eighths Cooling Time 523
8.15 Analysis of Cooling Process Parameters 524
8.15.1 Lin et al.'s Model for Irregular Shapes 527
8.16 Fourier-Reynolds Correlations 529
8.16.1 Development of Fourier-Reynolds Correlations 530
8.17 Cooling Heat-transfer Parameters 533
8.17.1 Specific Heat 533
8.17.1.1 Some Correlations for Specific Heat 534
8.17.2 Thermal Conductivity 535
8.17.2.1 Some Correlations for Thermal Conductivity 536
8.17.3 Thermal Diffusivity 538
8.17.4 Effective Heat-transfer Coefficients 540
8.17.4.1 Smith et al.'s Model 543
8.17.4.2 Ansari's Model 544
8.17.4.3 Stewart et al.'s Model 544
8.17.4.4 Dincer and Dost's Models 545
8.17.4.5 Some Methods for Effective Heat-transfer Coefficients 546
8.17.5 Modeling for Thermal Diffusivity and Heat-transfer Coefficient 547
8.17.6 Effective Nusselt-Reynolds Correlations 555
8.17.7 The Dincer Number 557
8.18 Conclusions 560
Nomenclature 561
Study Problems 563
References 565
9 Food Freezing 573
9.1 Introduction 573
9.2 Food Freezing Aspects 574
9.2.1 Enzymatic Reactions 575
9.2.2 Microbiological Activities 576
9.3 Quick Freezing 577
9.4 Enthalpy 577
9.5 Crystallization 578
9.6 Moisture Migration 579
9.7 Weight Loss 579
9.8 Blanching 580
9.9 Packaging 582
9.10 Quality of Frozen Foods 582
9.10.1 Objective Tests 583
9.10.2 Sensory Tests 583
9.10.3 Tests on the Kinetics of Quality Loss 583
9.11 Food Freezing Process 585
9.11.1 Freezing of Fruits 586
9.11.2 Freezing of Vegetables 586
9.12 Freezing Point 588
9.13 Freezing Rate 589
9.14 Freezing Times 590
9.14.1 Plank's Model 592
9.14.2 Mellor's Model 592
9.14.3 Pham's Model 593
9.14.4 Cleland and Earle's Model 594
9.14.5 Mannapperuma et al.'s Model 595
9.15 Freezing Equipment 598
9.15.1 Tunnel Freezers 599
9.15.1.1 Packaged Tunnel Freezers 600
9.15.1.2 Modular Tunnel Freezers 601
9.15.1.3 Multipass Tunnel Freezers 602
9.15.1.4 Contact Belt Tunnel Freezers 603
9.15.1.5 Drag Thru Doly Freezers 603
9.15.2 Spiral Freezers 604
9.15.2.1 Packaged Spiral Freezers 605
9.15.2.2 Site-built Spiral Freezers 606
9.15.3 Plate (Tray) Freezers 606
9.15.3.1 Packaged Tray Freezers 608
9.15.4 Impingement Jet Freezers 608
9.15.5 Cryogenic Freezers 609
9.15.5.1 Immersing Cryogenic Freezers 611
9.15.5.2 Tunnel Cryogenic Freezers 612
9.15.6 Control in Freezers 612
9.16 Ice Making 613
9.16.1 Block Ice Manufacture 613
9.16.2 Shell Ice Manufacture 614
9.16.3 Flake Ice Manufacture 614
9.16.4 Tube Ice Manufacture 614
9.16.5 Plate Ice Manufacture 615
9.16.6 Slush, Slurry or Binary Ice Manufacture 615
9.17 Thawing 615
9.18 Freeze-drying 616
9.18.1 Operation Principles 617
9.18.2 Freeze-drying Times 619
9.18.3 Freeze-dryers 621
9.18.3.1 Batch-type Freeze-dryers 622
9.18.3.2 Continuous-type Freeze-dryers 624
9.18.3.3 Microwave and Dielectric Freeze-dryers 625
9.18.4 Atmospheric Freeze-drying 625
9.19 Conclusions 625
Nomenclature 626
Study Problems 627
References 628
10 Environmental Impact and Sustainability Assessment of Refrigeration Systems 631
10.1 Introduction 631
10.2 Environmental Concerns 633
10.3 Energy and Environmental Impact 637
10.4 Dincer's Six Pillars 638
10.5 Dincer's 3S Concept 638
10.6 System Greenization 639
10.7 Sustainability 641
10.8 Energy and Sustainability 643
10.9 Exergy and Sustainability 645
10.10 Concluding Remarks 667
Study Problems 668
References 668
Appendix A Conversion Factors 671
Appendix B Thermophysical Properties 675
Appendix C Food Refrigeration Data 701
Index 719
Chapter 1
General Aspects of Thermodynamics
1.1 Introduction
Refrigeration has a diverse nature and covers a large number of processes ranging from cooling to air conditioning and from food refrigeration to human comfort. Refrigeration as a whole, therefore, appears complicated due to the fact that thermodynamics, fluid mechanics, and heat transfer are always encountered in every refrigeration process or application. For a good understanding of the operation of refrigeration systems and applications, an extensive knowledge of such topics is indispensable.
When an engineer or an engineering student undertakes the analysis of a refrigeration system and/or its application, he or she should deal with several basic aspects first, depending upon the type of the problem being studied, that may be of thermodynamics, fluid mechanics, or heat transfer. In conjunction with this, there is a need to introduce several definitions and concepts before moving into refrigeration systems and applications in depth. Furthermore, the units are of importance in the analysis of such systems and applications. One should make sure that the units used are consistent to reach the correct result. This means that there are several introductory factors to be taken into consideration to avoid getting lost further on. While the information in some situations is limited, it is desirable that the reader comprehend these processes. Despite assuming that the reader, if he or she is a student, has completed necessary courses in thermodynamics, fluid mechanics, and heat transfer, there is still a need for him or her to review, and for those who are practicing refrigeration engineers, the need is much stronger to understand the physical phenomena and practical aspects, along with a knowledge of the basic laws, principles, governing equations, and related boundary conditions. In addition, this introductory chapter reviews the essentials of such principles, laws, etc., discusses the relationships between the aspects and provides some key examples for better understanding.
This chapter primarily focuses on general aspects of thermodynamics, ranging from dimensions and units to psychrometric processes, and specifically discusses systems of units, thermodynamic systems, thermodynamic laws, pure substances, ideal and real gases, refrigerators and heat pumps, Carmot cycles, and psychrometrics and its processes. We also introduce performance assessment criteria through energy and exergy efficiencies and energetic and exergetic coefficients of performance (COPs) by the thermodynamic laws. The chapter presents lots of examples to show how to utilize thermodynamic tools, particularly balance equations, for design, analysis, and assessment.
1.2 Dimensions and Units
In the area of refrigeration it is critical to employ dimensions and units correctly for analysis, design, and assessment. It is commonly accepted that any physical quantity can be characterized by dimensions. Their magnitudes are measured/recognized in units. There are numerous commonly accepted dimensions, namely mass (m), length (L), time (t), and temperature (T), which are treated as primary quantities. There are also several other quantities, such as force (F), pressure (P), velocity (V), energy (E), and exergy (Ex), which are treated as the derived dimensions. We discuss several of these in the following subsections.
1.2.1 Systems of Units
Units are accepted as the currency of science. There are two systems: the International System of Units (Le Système International d'Unitès), which is always referred to as SI units, and the English System of Units (the English Engineering System). SI units are the most widely used throughout the world, although the English System is utilized as the traditional system of North America. In this book, SI units are primarily employed. Appendix A contains some common conversions. The dimensions, such as mass, length, force, density, specific volume, mass flow rate, volumetric flow rate, temperature and pressure, are briefly described below.
1.2.1.1 Mass
Mass is defined as a quantity of matter forming a body of indefinite shape and size. The fundamental unit of mass is the kilogram (kg) in SI and its unit in the English System is the pound mass (lbm). The basic unit of time for both unit systems is the second (s). The following relationships exist between the two unit systems:
In thermodynamics the unit mole (mol) is commonly used and defined as a certain amount of substance containing all the components. The related equation is defined as
1.1where if m and M are given in grams and gram/mol, we get n in mol. If the units are kilogram and kilogram/kilomol, n is in kilomol (kmol). For example, one mol of water, having a molecular weight of 18 (compared to 12 for carbon-12), has a mass of 0.018 kg and for one kmol it becomes 18 kg.
1.2.1.2 Length
The basic unit of length is the meter (m) in SI and the foot (ft) in the English System, which additionally includes the inch (in) in the English System and the centimeter (cm) in SI. Here are some interrelations:
1.2.1.3 Force
A force is a kind of action that brings a body to rest or changes the direction of motion (e.g., a push or a pull). The fundamental unit of force is the Newton (N):
The four aspects, that is, mass, time, length and force, are interrelated by Newton's second law of motion, which states that the force acting on a body is proportional to the mass and acceleration in the direction of the force, as given below:
1.2Equation (1.2) shows the force required to accelerate a mass of one kilogram at a rate of one meter per square second as 1 N = 1 kg m/s2.
It is important to note the value of the earth's gravitational acceleration as 9.80665 m/s2 (generally taken as 9.81 m/s2) in the SI system and 32.174 ft/s2 in the English System, which indicates that a body falling freely toward the surface of the earth is subject to the action of gravity alone. Some common conversion factors are listed in Appendix in A.
1.2.1.4 Density and Specific Volume
Specific volume is defined as the volume per unit mass of a substance, usually expressed in cubic meters per kilogram (m3/kg) in the SI system and in cubic feet per pound (ft3/lb) in the English System. The density of a substance is defined as the mass per unit volume, and is therefore the inverse of the specific volume:
1.3Its units are kg/m3 in the SI system and lbm/ft3 in the English System. Specific volume is also defined as the volume per unit mass, and density as the mass per unit volume, that is,
1.4 1.5Both specific volume and density are intensive properties and affected by temperature and pressure. The related interconversions are
1.2.1.5 Mass Flow Rate and Volumetric Flow Rate
Mass flow rate is defined as the mass flowing per unit time (kg/s in the SI system and lb/s in the English System). Volumetric flow rates are given in m3/s in the SI system and ft3/s in the English System. The following expressions can be written for the flow rates in terms of mass, specific volume, and density:
1.6 1.71.2.1.6 Temperature
Temperature is an indication of the thermal energy stored in a substance. In other words, we can identify hotness and coldness with the concept of temperature. The temperature of a substance may be expressed in either relative or absolute units. The two most common temperature scales are Celsius (°C) and Fahrenheit (°F). Normally, the Celsius scale is used with the SI unit system and the Fahrenheit scale with the English System. There are also two more scales, the Kelvin scale (K) and the Rankine scale (R), which are sometimes employed in thermodynamic applications. The relations between these scales are summarized as follows:
1.8 1.9 1.10 1.11Furthermore, the temperature differences result in
Here, Kelvin is a unit of temperature measurement: zero Kelvin (0 K) is the absolute zero and is equal to -273.15 °C. Both K and °C are equal increments of temperature. For instance, when the temperature of a product is decreased to -273.15 °C (or 0 K), known as absolute zero, the substance contains no heat energy and supposedly all molecular movement stops. The saturation temperature is the temperature of a liquid or vapor at saturation conditions.
Temperature can be measured in many ways by many devices. In general, the following devices are in common use:
- Liquid-in-glass thermometers. It is known that in these thermometers the volume of the fluid expands when subjected to heat, thereby raising its temperature. It is important to note that in practice all thermometers, including mercury ones, only work over a certain range of temperature. For example, mercury becomes solid at -38.8 °C and its properties change dramatically.
- Resistance thermometers. A resistance thermometer (or detector) is made of resistance wire wound on a suitable former. The wire used has to be of known, repeatable, electrical characteristics so that the relationship between the temperature and resistance value can be predicted precisely. The measured value of the resistance of the...
