Introduction to Food Process Engineering (eBook)

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