Introduction to Food Process Engineering

Preface 1 An introduction to food process engineering 2 Dimensions, quantities and units 2.1 Dimensions and units 2.2 Definitions of some basic physical quantities 2.2.1 Velocity and speed 2.2.2 Acceleration 2.2.3 Force and momentum 2.2.4 Weight 2.2.5 Pressure 2.2.6 Work and energy 2.2.7 Power 2.3 Dimensional analysis 2.3.1 Dimensional consistency 2.3.2 Dimensional analysis 3 Thermodynamics and equilibrium 3.1 Introduction 3.1.1 Temperature and the zeroth law of thermodynamics 3.1.2 Temperature scale 3.1.3 Heat, work and enthalpy 3.1.4 Other definitions 3.2 The gaseous phase 3.2.1 Kinetic theory of gases 3.2.2 Perfect gases 3.2.3 Pure component vapour pressure 3.2.4 Partial pressure and pure component volume 3.3 The liquid-vapour transition 3.3.1 Vaporisation and condensation 3.3.2 Isotherms and critical temperature 3.3.3 Definition of gas and vapour 3.3.4 Vapour-liquid equilibrium 3.4 First law of thermodynamics 3.5 Heat capacity 3.5.1 Heat capacity at constant volume 3.5.2 Heat capacity at constant pressure 3.5.3 The relationship between heat capacities for a perfect gas 3.5.4 The pressure, volume, temperature relationship for gases 3.6 Second law of thermodynamics 3.6.1 The heat pump and refrigeration 3.6.2 Consequences of the second law 4 Material and energy balances 4.1 Process analysis 4.2 Material balances 4.2.1 Overall material balances 4.2.2 Concentration and composition 4.2.3 Component material balances 4.2.4 Recycle and by-pass 4.3 The steady-flow energy equation 4.4 Thermochemical data 4.4.1 Heat capacity 4.4.2 Latent heat of vaporisation 4.4.3 Latent heat of fusion 4.4.4 Steam tables 4.5 Energy balances 5 The fundamentals of rate processes 5.1 Introduction 5.2 Heat transfer 5.3 Momentum transfer 5.4 Mass transfer 5.5 Transport properties 5.5.1 Thermal conductivity 5.5.2 Viscosity 5.5.3 Diffusivity 5.6 Similarities between heat, momentum and mass transfer 6 The flow of food fluids 6.1 Introduction 6.2 Fundamental principles 6.2.1 Velocity and flow rate 6.2.2 Reynolds' experiment 6.2.3 Principle of continuity 6.2.4 Conservation of energy 6.3 Laminar flow in a pipeline 6.4 Turbulent flow in a pipeline 6.5 Pressure measurement and fluid metering 6.5.1 The manometer 6.5.2 The orifice meter 6.5.3 The venturi meter 6.6. Pumping of liquids 6.6.1 The centrifugal pump 6.6.2 Positive displacement pumps 6.6.3 Net positive suction head 6.6.4 Hygienic design 6.7 Non-Newtonian flow 6.7.1 Introduction 6.7.2 Stress, strain and flow 6.8 Time-independent rheological models 6.8.1 Hookean solids 6.8.2 Newtonian fluids 6.8.3 Bingham fluids 6.8.4 The power law 6.8.5 Laminar flow of power law fluids 6.8.6 Other time-independent models 6.9 Time-dependent rheological models 6.10 Visco-elasticity 6.10.1 Introduction 6.10.2 Mechanical analogues 6.11 Rheological measurements 6.11.1 Measurement of dynamic viscosity 6.11.2 Rheological measurements for non-Newtonian fluids 7 Heat processing of foods 7.1 Introduction 7.2 Conduction 7.2.1 Steady-state conduction in a uniform slab 7.2.2 Conduction in a composite slab 7.2.3 Radial conduction 7.2.4 Conduction in a composite cylinder 7.2.5 Conduction through a spherical shell 7.3 Convection 7.3.1 Film heat transfer coefficient 7.3.2 Simultaneous convection and conduction 7.3.3 Radial convection 7.3.4 Critical thickness of insulation 7.3.5 Correlations for film heat transfer coefficients 7.3.6 Overall heat transfer coefficient 7.4 Heat exchangers 7.4.1 Types of industrial heat exchanger 7.4.2 Sizing of heat exchangers 7.5 Boiling and condensation 7.5.1 Boiling heat transfer 7.5.2 Condensation 7.6 Heat transfer to non-Newtonian fluids 7.7 Principles of radiation 7.7.1 Absorption, reflection and transmission 7.7.2 Black body radiation 7.7.3 Emissivity and real surfaces 7.7.4 Radiative heat transfer 7.7.5 View factors 7.8 Microwave heating of foods 7.8.1 Microwaves 7.8.2 Generation of microwaves 7.8.3 Energy conversion and heating rate 7.8.4 Microwave ovens and industrial plant 7.8.5 Advantages and applications of microwave heating 7.9 Temperature measurement 7.9.1 Principles of temperature measurement 7.9.1 Expansion thermometers 7.9.3 Electrical methods 7.9.4 Radiation pyrometry 8 Mass Transfer 8.1 Introduction 8.2 Molecular diffusion 8.2.1 Fick's law 8.2.2 Diffusivity 8.2.3 Concentration 8.3 Convective mass transfer 8.3.1 Whitman's theory 8.3.2 Film mass transfer coefficients 8.3.3 Overall mass transfer coefficients 8.3.4 Addition of film mass transfer coefficients 8.3.5 Resistances to mass transfer in food processing 8.3.6 Effect of solubility on mass transfer coefficients 8.3.7 Alternative units for mass transfer coefficients 8.3.8 Units of Henry's constant 8.4 Binary diffusion 8.4.1 General diffusion equation 8.4.2 Other forms of the general diffusion equation 8.4.3 Diffusion through a stagnant gas film 8.4.4 Particles, droplets and bubbles 8.5 Correlations for mass transfer coefficients 8.6 Mass transfer and food packaging 9 Psychrometry 9.1 Introduction 9.2 Definitions of some basic quantities 9.2.1 Absolute humidity 9.2.2 Saturated humidity 9.2.3 Percentage saturation 9.2.4 Relative humidity 9.2.5 Relationship between percentage saturation and relative humidity 9.2.6 Humid heat 9.2.7 Humid volume 9.2.8 Dew point 9.3 Wet bulb and dry bulb temperatures 9.3.1 Definitions 9.3.2 The wet bulb equation 9.3.3 Adiabatic saturation temperature 9.3.4 Relationship between wet bulb temperature and adiabatic saturation temperature 9.4 The psychrometric chart 9.4.1 Principles 9.4.2 Mixing of humid air streams 9.5 Application of psychrometry to drying 10 Thermal processing of foods 10.1 Unsteady-state heat transfer 10.1.1 Introduction 10.1.2 The Biot number 10.1.3 Lumped analysis 10.2 Unsteady-state conduction 10.2.1 Fourier's first law of conduction 10.2.2 Conduction in a flat plate 10.2.3 The Fourier number 10.2.4 Gurney-Lurie charts 10.2.5 Heisler charts 10.3 Food preservation techniques using heat 10.3.1 Introduction to thermal processing 10.3.2 Pasteurisation 10.3.3 Commercial sterilisation 10.4 Kinetics of microbial death 10.4.1 Decimal reduction time and thermal resistance constant 10.4.2 Process lethality 10.4.3 Spoilage probability 10.5 The general method 10.6 The mathematical method 10.6.1 Introduction 10.6.2 The procedure to find total process time 10.6.3 Heat transfer in thermal processing 10.6.4 Integrated value 10.7 Retorts for thermal processing 10.7.1 The batch retort 10.7.2 Design variations 10.7.3 Continuous retorts 10.8 Continuous flow sterilisation 10.8.1 Principles of UHT processing 10.8.2 Process description 11 Low temperature preservation 11.1 Principles of low temperature preservation 11.2 Freezing rate and freezing point 11.3 The frozen state 11.3.1 Physical properties of frozen food 11.3.2 Food quality during frozen storage 11.4 Freezing equipment 11.4.1 Plate freezer 11.4.2 Blast freezer 11.4.3 Fluidised bed freezer 11.4.4 Scraped surface freezer 11.4.5 Cryogenic and immersion freezing 11.5 Prediction of freezing time 11.5.1 Plank's equation 11.5.2 Nagaoka's equation 11.5.3 Stefan's model 11.5.4 Plank's equation for brick-shaped objects 11.6 Thawing 11.7 Principles of vapour compression refrigeration 11.7.1 Introduction 11.7.2 The refrigerant 11.7.3 The evaporator 11.7.4 The compressor 11.7.5 The condenser 11.7.6 The valve or nozzle 11.7.7 The refrigeration cycle 12 Evaporation and drying 12.1 Introduction to evaporation 12.2 Equipment for evaporation 12.2.1 Natural circulation evaporators 12.2.2 Forced circulation evaporators 12.2.3 Thin film evaporators 12.3 Sizing of a single effect evaporator 12.3.1 Material and energy balances 12.3.2 Evaporator efficiency 12.3.3 Boiling point elevation 12.4 Methods of improving evaporator efficiency 12.4.1 Vapour recompression 12.4.2 Multiple effect evaporation 12.4.3 An example of multiple effect evaporation: the concentration of tomato juice 12.5 Sizing of multiple effect evaporators 12.6 Drying 12.6.1 Introduction 12.6.2 Water activity 12.6.3 Effect of water activity on microbial growth 12.6.4 Moisture content 12.6.5 Isotherms and equilibrium 12.7 Batch drying 12.7.1 Rate of drying 12.7.2 Batch drying time 12.8 Types of drier 12.8.1 Batch and continuous operation 12.8.2 Direct and indirect driers 12.8.3 Cross-circulation and through-circulation 12.8.4 Tray drier 12.8.5 Tunnel drier 12.8.6 Rotary drier 12.8.7 Fluidised bed drier 12.8.8 Drum drier 12.8.9 Spray drier 12.9 Freeze drying 12.9.1 Stages in the freeze drying process 12.9.2 Prediction of freeze-drying time 13 Solids processing and particle manufacture 13.1 Characterisation of particulate solids 13.1.1 Particle size distribution 13.1.2 Mean particle size 13.1.3 Particle shape 13.1.4 Methods of determining particle size 13.1.5 Mass distributions 13.1.6 Other particle characteristics 13.2 The motion of a particle in a fluid 13.2.1 Terminal falling velocity 13.2.2 Particle drag coefficient 13.2.3 Effect of increasing Reynolds number 13.3 Packed beds: the behaviour of particles in bulk 13.4 Fluidisation 13.4.1 Introduction 13.4.2 Minimum fluidising velocity in aggregative fluidisation 13.4.3 Gas-solid fluidised bed behaviour 13.4.4 Bubbles and particle mixing 13.4.5 Heat and mass transfer in fluidisation 13.4.6 Applications of fluidisation to food processing 13.4.7 Spouted beds 13.4.8 Particulate fluidisation 13.5 Two-phase flow: pneumatic conveying 13.5.1 Introduction 13.5.2 Mechanisms of particle movement 13.5.3 Pneumatic conveying regimes 13.5.4 Pneumatic conveying systems 13.5.5 Safety issues 13.6 Food particle manufacturing processes 13.6.1 Classification of particle manufacturing processes 13.6.2 Particle-particle bonding 13.6.3 Fluidised bed granulation 13.6.4 Other particle agglomeration methods 13.7 Size reduction 13.7.1 Mechanisms and material structure 13.7.2 Size reduction equipment 13.7.3 Operating methods 13.7.4 Energy requirement for size reduction 14 Mixing and separation 14.1 Mixing 14.1.1 Definitions and scope 14.1.2 Mixedness 14.1.3 Mixing index and mixing time 14.1.4 Mixing of liquids 14.1.5 Power consumption in liquid mixing 14.1.6 Correlations for the density and viscosity of mixtures 14.1.7 Mixing of solids 14.1.8 Equipment for solids mixing 14.2 Filtration 14.2.1 Introduction 14.2.2 Analysis of cake filtration 14.2.3 Constant pressure filtration 14.2.4 Filtration equipment 14.2.5 Filter aids 14.3 Membrane separations 14.3.1 Introduction 14.3.2 Osmosis and reverse osmosis 14.3.3 General membrane equation 14.3.4 Osmotic pressure 14.3.5 Ultrafiltration 14.3.6 Membrane properties and structure 14.3.7 Membrane configurations 14.3.8 Permeate flux 14.3.9 Prediction of permeate flux 14.3.10 Some applications of membrane technology 15 Mass transfer operations 15.1 Introduction to distillation 15.2 Batch distillation 15.2.1 Linear equilibrium relationship 15.2.2 Constant relative volatility 15.3 Ideal stages and equilibrium 15.4 Continuous fractionation: McCabe-Thiele method 15.4.1 Material and energy balances 15.4.2 Derivation of operating lines 15.4.3 Minimum reflux ratio 15.5 Steam distillation 15.6 Leaching 15.6.1 Introduction 15.6.2 Process description 15.6.3 Types of equipment 15.6.4 Counter-current leaching: representation of three-component systems 15.6.5 Procedure to calculate the number of ideal stages 15.7 Supercritical fluid extraction 15.7.1 Introduction 15.7.2 The supercritical state 15.7.3 Process description 15.7.4 Advantages of SCFE 15.7.5 Food applications of SCFE 16 Minimal processing technology 16.1 Introduction 16.2 Ohmic heating 16.3 Radio frequency heating 16.4 Pulsed electric field heating 16.5 High pressure processing 16.6 Food irradiation 16.7 Ultrasound Appendix A List of unit prefixes; Greek alphabet Appendix B Fundamental and derived SI units; Conversion factors Appendix C Derivation of a dimensionless correlation for film heat transfer coefficients Appendix D Properties of saturated water and water vapour Appendix E Derivation of logarithmic mean temperature difference Appendix F Derivation of Fourier's first law of conduction Answers to problems Index