Introduction to Food Engineering (eBook)

Front Cover 1
Introduction to Food Engineering 4
Copyright Page 5
Contents 12
About the Authors 6
Foreword 8
Preface 10
CHAPTER 1 Introduction 24
1.1 Dimensions 24
1.2 Engineering Units 25
1.2.1 Base Units 25
1.2.2 Derived Units 26
1.2.3 Supplementary Units 27
1.3 System 33
1.4 State of a System 34
1.4.1 Extensive Properties 35
1.4.2 Intensive Properties 36
1.5 Density 36
1.6 Concentration 38
1.7 Moisture Content 40
1.8 Temperature 43
1.9 Pressure 45
1.10 Enthalpy 49
1.11 Equation of State and Perfect Gas Law 49
1.12 Phase Diagram of Water 50
1.13 Conservation of Mass 52
1.13.1 Conservation of Mass for an Open System 53
1.13.2 Conservation of Mass for a Closed System 55
1.14 Material Balances 55
1.15 Thermodynamics 64
1.16 Laws of Thermodynamics 65
1.16.1 First Law of Thermodynamics 65
1.16.2 Second Law of Thermodynamics 65
1.17 Energy 66
1.18 Energy Balance 68
1.19 Energy Balance for a Closed System 68
1.19.1 Heat 68
1.19.2 Work 69
1.20 Energy Balance for an Open System 78
1.20.1 Energy Balance for Steady Flow Systems 79
1.21 A Total Energy Balance 79
1.22 Power 82
1.23 Area 82
Problems 83
List of Symbols 85
Bibliography 86
CHAPTER 2 Fluid Flow in Food Processing 88
2.1 Liquid Transport Systems 89
2.1.1 Pipes for Processing Plants 90
2.1.2 Types of Pumps 91
2.2 Properties of Liquids 94
2.2.1 Terminology Used in Material Response to Stress 95
2.2.2 Density 95
2.2.3 Viscosity 96
2.3 Handling Systems for Newtonian Liquids 104
2.3.1 The Continuity Equation 104
2.3.2 Reynolds Number 107
2.3.3 Entrance Region and Fully Developed Flow 111
2.3.4 Velocity Profile in a Liquid Flowing Under Fully Developed Flow Conditions 113
2.3.5 Forces Due to Friction 119
2.4 Force Balance on a Fluid Element Flowing in a Pipe—Derivation of Bernoulli Equation 123
2.5 Energy Equation for Steady Flow of Fluids 130
2.5.1 Pressure Energy 133
2.5.2 Kinetic Energy 133
2.5.3 Potential Energy 135
2.5.4 Frictional Energy Loss 135
2.5.5 Power Requirements of a Pump 138
2.6 Pump Selection and Performance Evaluation 142
2.6.1 Centrifugal Pumps 142
2.6.2 Head 144
2.6.3 Pump Performance Characteristics 144
2.6.4 Pump Characteristic Diagram 148
2.6.5 Net Positive Suction Head 149
2.6.6 Selecting a Pump for a Liquid Transport System 152
2.6.7 Affinity Laws 158
2.7 Flow Measurement 159
2.7.1 The Pitot Tube 163
2.7.2 The Orifice Meter 165
2.7.3 The Venturi Meter 169
2.7.4 Variable-Area Meters 169
2.7.5 Other Measurement Methods 170
2.8 Measurement of Viscosity 171
2.8.1 Capillary Tube Viscometer 171
2.8.2 Rotational Viscometer 173
2.8.3 Influence of Temperature on Viscosity 176
2.9 Flow Characteristics of Non-Newtonian Fluids 178
2.9.1 Properties of Non-Newtonian Fluids 178
2.9.2 Velocity Profile of a Power Law Fluid 184
2.9.3 Volumetric Flow Rate of a Power Law Fluid 185
2.9.4 Average Velocity in a Power Law Fluid 186
2.9.5 Friction Factor and Generalized Reynolds Number for Power Law Fluids 186
2.9.6 Computation of Pumping Requirement of Non-newtonian Liquids 189
2.10 Transport of solid foods 192
2.10.1 Properties of Granular Materials and Powders 193
2.10.2 Flow of Granular Foods 198
Problems 201
List of Symbols 206
Bibliography 208
CHAPTER 3 Energy and Controls in Food Processes 210
3.1 Generation of Steam 210
3.1.1 Steam Generation Systems 211
3.1.2 Thermodynamics of Phase Change 213
3.1.3 Steam Tables 217
3.1.4 Steam Utilization 223
3.2 Fuel Utilization 227
3.2.1 Systems 229
3.2.2 Mass and Energy Balance Analysis 230
3.2.3 Burner Efficiencies 232
3.3 Electric Power Utilization 233
3.3.1 Electrical Terms and Units 235
3.3.2 Ohm's Law 236
3.3.3 Electric Circuits 237
3.3.4 Electric Motors 239
3.3.5 Electrical Controls 240
3.3.6 Electric Lighting 241
3.4 Process Controls in Food Processing 243
3.4.1 Processing Variables and Performance Indicators 245
3.4.2 Input and Output Signals to Control Processes 247
3.4.3 Design of a Control System 247
3.5 Sensors 255
3.5.1 Temperature 255
3.5.2 Liquid Level in a Tank 257
3.5.3 Pressure Sensors 258
3.5.4 Flow Sensors 259
3.5.5 Glossary of Terms Important in Data Acquisition 260
3.6 Dynamic Response Characteristics of Sensors 260
Problems 264
List of Symbols 267
Bibliography 268
CHAPTER 4 Heat Transfer in Food Processing 270
4.1 Systems for Heating and Cooling Food Products 271
4.1.1 Plate Heat Exchanger 271
4.1.2 Tubular Heat Exchanger 275
4.1.3 Scraped-surface Heat Exchanger 276
4.1.4 Steam-infusion Heat Exchanger 278
4.1.5 Epilogue 279
4.2 Thermal Properties of Foods 280
4.2.1 Specific Heat 280
4.2.2 Thermal Conductivity 283
4.2.3 Thermal Diffusivity 285
4.3 Modes of Heat Transfer 287
4.3.1 Conductive Heat Transfer 287
4.3.2 Convective Heat Transfer 290
4.3.3 Radiation Heat Transfer 292
4.4 Steady-State Heat Transfer 293
4.4.1 Conductive Heat Transfer in a Rectangular Slab 294
4.4.2 Conductive Heat Transfer through a Tubular Pipe 297
4.4.3 Heat Conduction in Multilayered Systems 300
4.4.4 Estimation of Convective Heat-Transfer Coefficient 308
4.4.5 Estimation of Overall Heat-Transfer Coefficient 325
4.4.6 Fouling of Heat Transfer Surfaces 329
4.4.7 Design of a Tubular Heat Exchanger 335
4.4.8 The Effectiveness-NTU Method for Designing Heat Exchangers 343
4.4.9 Design of a Plate Heat Exchanger 348
4.4.10 Importance of Surface Characteristics in Radiative Heat Transfer 355
4.4.11 Radiative Heat Transfer between Two Objects 357
4.5 Unsteady-State Heat Transfer 360
4.5.1 Importance of External versus Internal Resistance to Heat Transfer 362
4.5.2 Negligible Internal Resistance to Heat Transfer (N[sub(Bi)] & lt
4.5.3 Finite Internal and Surface Resistance to Heat Transfer (0.1 & lt
4.5.4 Negligible Surface Resistance to Heat Transfer (N[sub(Bi) & gt
4.5.5 Finite Objects 371
4.5.6 Procedures to Use Temperature–Time Charts 373
4.5.7 Use of f[sub(h)] and j Factors in Predicting Temperature in Transient Heat Transfer 381
4.6 Electrical Conductivity of Foods 389
4.7 Ohmic Heating 392
4.8 Microwave Heating 394
4.8.1 Mechanisms of Microwave Heating 395
4.8.2 Dielectric Properties 396
4.8.3 Conversion of Microwave Energy into Heat 397
4.8.4 Penetration Depth of Microwaves 398
4.8.5 Microwave Oven 400
4.8.6 Microwave Heating of Foods 401
Problems 403
List of Symbols 420
Bibliography 422
CHAPTER 5 Preservation Processes 426
5.1 Processing Systems 426
5.1.1 Pasteurization and Blanching Systems 427
5.1.2 Commercial Sterilization Systems 429
5.1.3 Ultra-High Pressure Systems 433
5.1.4 Pulsed Electric Field Systems 435
5.1.5 Alternative Preservation Systems 436
5.2 Microbial Survivor Curves 436
5.3 Influence of External Agents 441
5.4 Thermal Death Time F 445
5.5 Spoilage Probability 446
5.6 General Method for Process Calculation 447
5.6.1 Applications to Pasteurization 449
5.6.2 Commercial Sterilization 452
5.6.3 Aseptic Processing and Packaging 455
5.7 Mathematical Methods 463
5.7.1 Pouch Processing 467
Problems 470
List of Symbols 473
Bibliography 474
CHAPTER 6 Refrigeration 478
6.1 Selection of a Refrigerant 479
6.2 Components of a Refrigeration System 483
6.2.1 Evaporator 484
6.2.2 Compressor 486
6.2.3 Condenser 489
6.2.4 Expansion Valve 491
6.3 Pressure–Enthalpy Charts 493
6.3.1 Pressure–Enthalpy Tables 497
6.3.2 Use of Computer-Aided Procedures to Determine Thermodynamic Properties of Refrigerants 498
6.4 Mathematical Expressions Useful in Analysis of Vapor-Compression Refrigeration 501
6.4.1 Cooling Load 501
6.4.2 Compressor 503
6.4.3 Condenser 503
6.4.4 Evaporator 504
6.4.5 Coefficient of Performance 504
6.4.6 Refrigerant Flow Rate 504
6.5 Use of Multistage Systems 513
6.5.1 Flash Gas Removal System 514
Problems 518
List of Symbols 521
Bibliography 521
CHAPTER 7 Food Freezing 524
7.1 Freezing Systems 525
7.1.1 Indirect Contact Systems 525
7.1.2 Direct-Contact Systems 530
7.2 Frozen-Food Properties 533
7.2.1 Density 533
7.2.2 Thermal Conductivity 534
7.2.3 Enthalpy 534
7.2.4 Apparent Specific Heat 536
7.2.5 Apparent Thermal Diffusivity 536
7.3 Freezing Time 537
7.3.1 Plank's Equation 539
7.3.2 Other Freezing-Time Prediction Methods 543
7.3.3 Pham's Method to Predict Freezing Time 543
7.3.4 Prediction of Freezing Time of Finite-Shaped Objects 547
7.3.5 Experimental Measurement of Freezing Time 551
7.3.6 Factors Influencing Freezing Time 551
7.3.7 Freezing Rate 552
7.3.8 Thawing Time 552
7.4 Frozen-Food Storage 553
7.4.1 Quality Changes in Foods during Frozen Storage 553
Problems 557
List of Symbols 561
Bibliography 562
CHAPTER 8 Evaporation 566
8.1 Boiling-Point Elevation 568
8.2 Types of Evaporators 570
8.2.1 Batch-Type Pan Evaporator 570
8.2.2 Natural Circulation Evaporators 571
8.2.3 Rising-Film Evaporator 571
8.2.4 Falling-Film Evaporator 572
8.2.5 Rising/Falling-Film Evaporator 573
8.2.6 Forced-Circulation Evaporator 574
8.2.7 Agitated Thin-Film Evaporator 574
8.3 Design of a Single-Effect Evaporator 577
8.4 Design of a Multiple-Effect Evaporator 582
8.5 Vapor Recompression Systems 588
8.5.1 Thermal Recompression 588
8.5.2 Mechanical Vapor Recompression 589
Problems 589
List of Symbols 592
Bibliography 592
CHAPTER 9 Psychrometrics 594
9.1 Properties of Dry Air 594
9.1.1 Composition of Air 594
9.1.2 Specific Volume of Dry Air 595
9.1.3 Specific Heat of Dry Air 595
9.1.4 Enthalpy of Dry Air 595
9.1.5 Dry Bulb Temperature 596
9.2 Properties of Water Vapor 596
9.2.1 Specific Volume of Water Vapor 596
9.2.2 Specific Heat of Water Vapor 596
9.2.3 Enthalpy of Water Vapor 597
9.3 Properties of Air–Vapor Mixtures 597
9.3.1 Gibbs–Dalton Law 597
9.3.2 Dew-Point Temperature 597
9.3.3 Humidity Ratio (or Moisture Content) 598
9.3.4 Relative Humidity 599
9.3.5 Humid Heat of an Air–Water Vapor Mixture 599
9.3.6 Specific Volume 600
9.3.7 Adiabatic Saturation of Air 600
9.3.8 Wet Bulb Temperature 602
9.4 The Psychrometric Chart 605
9.4.1 Construction of the Chart 605
9.4.2 Use of Psychrometric Chart to Evaluate Complex Air-Conditioning Processes 607
Problems 612
List of Symbols 615
Bibliography 616
CHAPTER 10 Mass Transfer 618
10.1 The Diffusion Process 619
10.1.1 Steady-State Diffusion of Gases (and Liquids) through Solids 622
10.1.2 Convective Mass Transfer 623
10.1.3 Laminar Flow over a Flat Plate 627
10.1.4 Turbulent Flow Past a Flat Plate 631
10.1.5 Laminar Flow in a Pipe 631
10.1.6 Turbulent Flow in a Pipe 632
10.1.7 Mass Transfer for Flow over Spherical Objects 632
10.2 Unsteady-State Mass Transfer 633
10.2.1 Transient-State Diffusion 634
10.2.2 Diffusion of Gases 639
Problems 642
List of Symbols 644
Bibliography 645
CHAPTER 11 Membrane Separation 646
11.1 Electrodialysis Systems 648
11.2 Reverse Osmosis Membrane Systems 652
11.3 Membrane Performance 659
11.4 Ultrafiltration Membrane Systems 660
11.5 Concentration Polarization 662
11.6 Types of Reverse-Osmosis and Ultrafiltration Systems 668
11.6.1 Plate and Frame 669
11.6.2 Tubular 669
11.6.3 Spiral-Wound 669
11.6.4 Hollow-Fiber 672
Problems 672
List of Symbols 673
Bibliography 674
CHAPTER 12 Dehydration 676
12.1 Basic Drying Processes 676
12.1.1 Water Activity 677
12.1.2 Moisture Diffusion 680
12.1.3 Drying-Rate Curves 681
12.1.4 Heat and Mass Transfer 681
12.2 Dehydration systems 683
12.2.1 Tray or Cabinet Dryers 683
12.2.2 Tunnel Dryers 684
12.2.3 Puff-Drying 685
12.2.4 Fluidized-Bed Drying 686
12.2.5 Spray Drying 686
12.2.6 Freeze-Drying 687
12.3 Dehydration System Design 688
12.3.1 Mass and Energy Balance 688
12.3.2 Drying-Time Prediction 693
Problems 703
List of Symbols 708
Bibliography 709
CHAPTER 13 Supplemental Processes 712
13.1 Filtration 712
13.1.1 Operating Equations 712
13.1.2 Mechanisms of Filtration 718
13.1.3 Design of a Filtration System 719
13.2 Sedimentation 722
13.2.1 Sedimentation Velocities for Low-Concentration Suspensions 722
13.2.2 Sedimentation in High-Concentration Suspensions 725
13.3 Centrifugation 728
13.3.1 Basic Equations 728
13.3.2 Rate of Separation 728
13.3.3. Liquid-Liquid Separation 730
13.3.4 Particle-Gas Separation 732
13.4 Mixing 732
13.4.1 Agitation Equipment 734
13.4.2 Power Requirements of Impellers 737
Problems 741
List of Symbols 742
Bibliography 743
CHAPTER 14 Extrusion Processes for Foods 744
14.1 Introduction and Background 744
14.2 Basic Principles of Extrusion 745
14.3 Extrusion Systems 752
14.3.1 Cold Extrusion 753
14.3.2 Extrusion Cooking 754
14.3.3 Single Screw Extruders 755
14.3.4 Twin-Screw Extruders 757
14.4 Extrusion System Design 758
14.5 Design of More Complex Systems 763
Problems 764
List of Symbols 765
Bibliography 765
CHAPTER 15 Packaging Concepts 768
15.1 Introduction 768
15.2 Food Protection 769
15.3 Product Containment 770
15.4 Product Communication 771
15.5 Product Convenience 771
15.6 Mass Transfer in Packaging Materials 771
15.6.1 Permeability of Packaging Material to "Fixed" Gases 774
15.7 Innovations in Food Packaging 777
15.7.1 Passive Packaging 778
15.7.2 Active Packaging 778
15.7.3 Intelligent Packaging 779
15.8 Food Packaging and Product Shelf-life 781
15.8.1 Scientific Basis for Evaluating Shelf Life 781
15.9 Summary 789
Problems 789
List of Symbols 790
Bibliography 791
Appendices 794
A.1 System of Units and Conversion Factors 794
A.1.1 Rules for Using SI Units 794
Table A.1.1: SI Prefixes 794
Table A.1.2: Useful Conversion Factors 797
Table A.1.3: Conversion Factors for Pressure 799
A.2 Physical Properties of Foods 800
Table A.2.1: Specific Heat of Foods 800
Table A.2.2: Thermal Conductivity of Selected Food Products 801
Table A.2.3: Thermal Diffusivity of Some Foodstuffs 803
Table A.2.4: Viscosity of Liquid Foods 804
Table A.2.5: Properties of Ice as a Function of Temperature 805
Table A.2.6: Approximate Heat Evolution Rates of Fresh Fruits and Vegetables When Stored at Temperatures Shown 805
Table A.2.7: Enthalpy of Frozen Foods 807
Table A.2.8: Composition Values of Selected Foods 808
Table A.2.9: Coefficients to Estimate Food Properties 809
A.3 Physical Properties of Nonfood Materials 810
Table A.3.1: Physical Properties of Metals 810
Table A.3.2: Physical Properties of Nonmetals 811
Table A.3.3: Emissivity of Various Surfaces 813
A.4 Physical Properties of Water and Air 815
Table A.4.1: Physical Properties of Water at the Saturation Pressure 815
Table A.4.2: Properties of Saturated Steam 816
Table A.4.3: Properties of Superheated Steam 818
Table A.4.4: Physical Properties of Dry Air at Atmospheric Pressure 819
A.5 Psychrometric Charts 820
Figure A.5.1: Psychrometric chart for high temperatures 820
Figure A.5.2: Psychrometric chart for low temperatures 821
A.6 Pressure-Enthalpy Data 822
Figure A.6.1: Pressure–enthalpy diagram for Refigerant 12 822
Table A.6.1: Properties of Saturated Liquid and Vapor R-12 823
Figure A.6.2: Pressure–enthalpy diagram of superheated R-12 vapor 826
Table A.6.2: Properties of Saturated Liquid and Vapor R-717 (Ammonia) 827
Figure A.6.3: Pressure–enthalpy diagram of superheated R-717 (ammonia) vapor 830
Table A.6.3: Properties of Saturated Liquid and Vapor R-134a 831
Figure A.6.4: Pressure–enthalpy diagram of R-134a 834
Figure A.6.5: Pressure–enthalpy diagram of R-134a (expanded scale) 835
A.7 Symbols for Use in Drawing Food Engineering Process Equipment 836
A.8 Miscellaneous 841
Table A.8.1: Numerical Data, and Area/Volume of Objects 841
Figure A.8.1: Temperature at geometric center of a sphere (expanded scale) 842
Figure A.8.2: Temperature at the axis of an infinitely long cylinder (expanded scale) 843
Figure A.8.3: Temperature at the midplane of an infinite slab (expanded scale) 844
A.9 Dimensional Analysis 845
Table A.9.1: Dimensions of selected experimental variables 846
Bibliography 849
Index 852
A 852
B 852
C 852
D 853
E 853
F 854
G 855
H 855
I 855
J 856
K 856
L 856
M 856
N 856
O 857
P 857
R 858
S 859
T 860
U 860
V 860
W 861
Y 861
Z 861
Food Science and Technology: International Series 862