Food Process Engineering

The Second Edition of Food Process Engineering by Dr. Dennis Heldman, my former student, and co-author Paul Singh, his former student, attests to the importance of the previous edition. In the Foreword to the First Edition, I noted the need for people in all facets of the food processing industry to consider those variables of design of particular importance in engineering for the food processing field. In addition to recognizing the many variables involved in the biological food product being handled from production to consumption, the engi­ neer must oftentimes adapt equations developed for non-biological materials. As more and more research is done, those equations are appropriately modified to be more accurate or new equations are developed specifically for designing to process foods. This Edition updates equations used. This book serves a very important need in acquainting engineers and technologists, particularly those with a math­ ematics and physics background, with the information necessary to provide a more efficient design to accomplish the objectives. Of prime importance, at present and in the future, is to design for efficient use of energy. Now, it is often economical to put considerably more money into first costs for an efficient design than previously, when energy costs were a much smaller proportion of the total cost of process engineering.

1 Introduction.- 1.1 Thermodynamics Applied to Food Processing.- 1.2 Kinetics of Reactions Occurring in Processed Foods.- 1.3 Fundamentals of Mass Transfer in Food Processing.- Problems.- Comprehensive Problem—I.- Nomenclature.- 2 Rheology of Processed Foods.- 2.1 Introduction to Stress-Strain Behavior in Materials.- 2.2 Properties of Fluid Foods.- 2.2.1 Rheological Models.- 2.2.2 Measurement of Rheological Parameters.- 2.2.2a Capillary Tube Rheometers.- 2.2.2b Rotational Rheometers.- 2.2.2c Experimental Values.- 2.2.3 Friction.- 2.2.4 Laminar Flow.- 2.2.5 Turbulent Flow.- 2.2.6 Considerations in Pumping Fluid Foods.- 2.3 Properties of Suspensions and Concentrated Products.- 2.3.1 Viscosity.- 2.3.2 Flow in Pipes.- 2.3.2a Suspension Transport.- 2.3.2b Pneumatic Transport.- 2.4 Properties of Granular Foods and Powders.- 2.4.1 Density.- 2.4.2 Particle Size and Size Distributions.- 2.4.3 Flow of Food Powders.- 2.5 Properties of Solid Foods.- 2.5.1 Viscoelastic Models.- 2.5.2 Measurement of Viscoelastic Parameters.- 2.5.3 Food Texture.- Problems.- Comprehensive Problem—II.- Nomenclature.- 3 Heating and Cooling Processes.- 3.1 Modes of Heat Transfer.- 3.1.1 Conduction.- 3.1.2 Convection.- 3.1.2a Forced Convection.- 3.1.2b Free Convection.- 3.1.3 Radiation.- 3.1.4 Overall Heat Transfer.- 3.2 Thermal Properties of Foods.- 3.2.1 Specific Heat.- 3.2.2 Thermal Conductivity.- 3.3 Steady-State Heating and Cooling.- 3.3.1 Heat Transfer in Laminar Flow.- 3.3.1a Piston Flow.- 3.3.1b Fully Developed Parabolic Velocity Profile.- 3.3.1c Fully Developed Velocity Profile for a Power-Law Fluid.- 3.3.2 Heat Transfer in Turbulent Flow.- 3.3.3 Heat Exchangers.- 3.3.3a Tubular Heat Exchanger.- 3.3.3b Triple Tube Heat Exchanger.- 3.3.3c Plate Heat Exchanger.- 3.3.3d Plate Heat Exchangers for Non-Newtonian Fluids.- 3.3.3e Scraped Surface Heat Exchanger.- 3.3.3f Direct Contact Heat Exchangers.- 3.4 Unsteady-State Heating and Cooling.- 3.4.1 Negligible Internal Resistance.- 3.4.2 Negligible Surface Resistance.- 3.4.3 Finite Surface and Internal Resistance.- 3.4.4 Use of ‘f’ and ‘j’ Parameters.- 3.4.5 Finite Objects.- 3.4.6 Anomalous Objects and Ellipsoids.- 3.4.7 Numerical Methods.- 3.4.8 Unsteady-State Heat Transfer in Agitated Containers.- Problems.- Comprehensive Problem—III.- Nomenclature.- 4 Thermodynamics of Food Freezing.- 4.1 Properties of Frozen Foods.- 4.1.1 Freezing-Point Depression.- 4.1.2 Ice Crystal Formation.- 4.2 Enthalpy Change During Freezing.- 4.2.1 Experimental Investigations.- 4.3 Prediction of Food Product Freezing Rates.- 4.3.1 Plank’s Equation.- 4.3.2 Neumann Problem.- 4.3.3 Tao Solutions.- 4.3.4 Tien Solutions.- 4.3.5 Mott Procedure.- 4.3.6 Numerical Solutions.- 4.4 Design of Food Freezing Equipment.- 4.4.1 Air-Blast Freezers.- 4.4.2 Plate Freezers.- 4.4.3 Immersion Freezers.- 4.5 Storage of Frozen Foods.- 4.5.1 Changes During Freezing.- 4.5.2 Storage Temperature Fluctuations.- Problems.- Comprehensive Problem—IV.- Nomenclature.- 5 Evaporation for Fluid Food Concentration.- 5.1 Thermodynamics of Evaporation.- 5.1.1 Phase Change.- 5.1.2 Boiling Point Elevation.- 5.2 Heat Transfer During Evaporation.- 5.2.1 Heating Medium.- 5.2.2 Heating Surface.- 5.2.3 Product.- 5.2.4 Heat-Transfer Coefficient.- 5.3 Design of Evaporation Systems.- 5.3.1 Retention Time.- 5.3.2 Single-Effect Systems.- 5.3.3 Multiple-Effect Systems.- 5.4 Improving Evaporation Efficiency.- 5.4.1 Thermal Recompression Systems.- 5.4.2 Mechanical Recompression Systems.- 5.4.3 Low-Temperature Evaporator.- Problems.- Comprehensive Problem—V.- Nomenclature.- 6 Food Dehydration.- 6.1 Basic Principles of Dehydration.- 6.1.1 Psychrometrics.- 6.1.2 Rate-of-Drying Curve.- 6.1.2a Constant-Rate Period Dehydration.- 6.1.2b Falling-Rate Period Dehydration.- 6.2 Estimation of Drying Time.- 6.2.1 Experimental Approaches to Predict Drying Time.- 6.2.1a Constant Rate Period.- 6.2.1b Falling-Rate Period.- 6.2.2 Theoretical Expressions Useful to Predict Drying Time.- 6.2.2a Constant-Rate Period.- 6.2.2b Diffusion-Controlled Falling-Rate Period.- 6.2.2c Additional Expressions to Predict Falling-Rate Period.- 6.2.2d Use of Heat and Mass Balances in the Analysis of Continuous Dryers.- 6.2.3 Equilibrium Moisture Content and Water Activity.- 6.3 Fixed-Tray Dehydration.- 6.3.1 Cabinet Drying.- 6.3.2 Tunnel Drying.- 6.4 Moving-Bed Dehydration.- 6.4.1 Conveyor Drying.- 6.4.2 Belt Drying.- 6.5 Air-Suspended Product.- 6.5.1 Spray Drying.- 6.5.2 Pneumatic Drying.- 6.5.3 Fluidized Bed Drying.- 6.6 Drum Dehydration.- 6.6.1 Types of Drum Dryers.- 6.6.2 Design Parameters.- 6.7 Miscellaneous Dehydration Processes.- 6.8 Freeze Dehydration.- 6.8.1 Heat and Mass Transfer.- 6.8.2 Freeze-Drying Times.- 6.8.3 Influence of Parameters.- 6.8.4 Atmospheric Freeze-Drying.- Problems.- Comprehensive Problem—VI.- Nomenclature.- 7 Contact Equilibrium Processes.- 7.1 Basic Principles.- 7.1.1 General Description of Transport Processes.- 7.1.2 Material Balance.- 7.2 Extraction.- 7.2.1 Rate of Extraction.- 7.2.2 Leaching.- 7.2.3 Multiple-Stage Leaching.- Problems.- Comprehensive Problem—VII.- Nomenclature.- 8 Mechanical Separation Processes.- 8.1 Filtration.- 8.1.1 Operating Equations.- 8.1.1a Constant-Rate Filtration.- 8.1.1b Constant-Pressure Filtration.- 8.1.2 Mechanisms of Filtration.- 8.1.3 Design of a Filtration System.- 8.2 Sedimentation.- 8.2.1 Sedimentation Velocities for Low-Concentration Suspensions.- 8.2.2 Sedimentation in High-Concentration Suspensions.- 8.3 Centrifugation.- 8.3.1 Basic Equations.- 8.3.2 Rate of Separation.- 8.3.3 Liquid-Liquid Separation.- 8.3.4 Particle-Gas Separation 381 Problems.- Comprehensive Problem—VIII.- Nomenclature.- Appendix: Useful Tables and Figures.- Solutions.