Table of Contents

1 Mixing in the food industry: trends and challenges (P.J. Cullen and Colm P. O’Donnell)

1.1 Role of mixing

1.2 Design criteria for mixing

1.3 Specific challenges in food mixing

1.3.1 Quality assurance compliance through mixing

1.3.2 Engineering texture through mixing

1.4 Advances in the science of mixing

1.5 Book objectives

2 Mixing fundamentals (Kasiviswanathan Muthukumarappan)

2.1 Introduction

2.2 Defining mixing

2.2.1 Macromixing

2.2.2 Mesomixing

2.2.3 Micromixing

2.3 Scale of scrutiny

2.4 Quantifying mixedness

2.4.1 Inference of mixing indices

2.5 Determining the end point of mixing

2.5.1 Solids mixing

2.5.2 Fluid mixing

2.5.3 Multi-phase mixing

2.5.4 Alternative measures of mixedness in industrial practice

2.6 Residence time distributions

2.6.1 Modelling of residence time distributions

3 Kinematics of flow and mixing mechanisms (Brijesh Tiwari and P.J. Cullen)

3.1 Introduction

3.2 Fluid mixing

3.2.1 Kinematics of fluid flow

3.2.2 Quantification of flow regimes

3.2.3 Chaotic advection

3.2.4 Fluid mixing mechanisms

3.3 Solids mixing

3.3.1 Mixing flow in solids

3.3.2 Solids mixing mechanism

3.4 Identification of mixing mechanisms

3.4.1 Solids

3.4.2 Fluids

4 Rheology and mixing (P.J. Cullen and Robin K. Connelly)

4.1 Introduction

4.2 Dispersion rheology

4.2.1 Forces acting on dispersed particles

4.2.2 Parameters affecting suspension rheology

4.3 Fluid rheology and mixing

4.3.1 Shear flow

4.3.2 Elongational flow

4.4 Effects of mixing on fluid rheology

4.5 Mixer rheometry

4.5.1 Theory

4.5.2 Mixer rheometry applications

4.6 Conclusion

5 Equipment design (David S. Dickey)

5.1 Introduction

5.2 Liquid mixing equipment

5.2.1 Portable mixers

5.2.2 General purpose liquid mixers

5.2.3 Mixer shafts design

5.2.4 Other mechanical design considerations

5.2.5 Special purpose liquid mixing equipment

5.2.6 Food specific mixing equipment

5.3 Powder mixing equipment

5.3.1 Ribbon blenders

5.3.2 Paddle blenders

5.3.3 Combination blenders

5.3.4 Tumble blenders

5.3.5 Loading and emptying blenders

5.3.6 Liquid addition to powders

5.3.7 Sampling

5.3.8 Safety

5.3.9 Blending systems

5.4 Equipment components

5.4.1 Electric motors

5.4.2 Speed reducers

5.4.3 Seals

6 Mixing scale-up (David S. Dickey)

6.1 Introduction

6.2 Scale-up for fluid mixing

6.2.1 Dimensional analysis

6.2.2 Scale-up with geometric similarity

6.2.3 Scale-up without geometric similarity

6.3 Scale-up for powder mixing

7 Monitoring and control of mixing operations (Colette C. Fagan, P.J. Cullen and Colm P. O’Donnell)

7.1 Introduction

7.2 Torque and power measurement

7.3 Flow measurement

7.3.1 Hot-wire anemometry

7.3.2 Laser Doppler anemometry

7.3.3 Phase Doppler anemometry

7.3.4 Flow visualization using computer vision

7.3.5 Particle image velocimetry

7.3.6 Planar laser-induced fluorescence

7.3.7 Tomography

7.4 Quantification of mixing time

7.4.1 NIR spectroscopy

7.4.2 Chemical imaging

8 Computational fluid mixing (Chris D. Rielly and Jolius Gimbun)

8.1 Introduction

8.1.1 History of CFD

8.1.2 Steps towards CFD simulation of mixing processes

8.2 Conservation equations

8.2.1 Mass conservation

8.2.2 Momentum conservation

8.2.3 Turbulence

8.2.4 Energy conservation

8.2.5 Species transport

8.2.6 Turbulent species and energy transport

8.2.7 Boundary conditions

8.3 Numerical methods

8.3.1 Discretised solution of the flow variables

8.3.2 Grid generation

8.3.3 Discretisation

8.3.4 Finite-volume discretisation methods

8.3.5 Solver methods

8.4 Application of CFD to stirred tank modelling

8.4.1 Mixing operations

8.4.2 Representation of the impeller

8.4.3 Prediction of mixer performance characteristics

8.4.4 Simulation of unbaffled or partially baffled stirred tanks

8.4.5 Simulation of single-phase flow in baffled stirred tanks

8.4.6 Mixing and blending simulations

8.4.7 Multi-phase simulations

8.5 Application to food mixing operations

8.5.1 Challenges for simulation of food processes

8.5.2 Examples of food applications

8.6 Closing remarks

9 Immiscible liquid–liquid mixing (Fotis Spyropoulos, P.W. Cox and Ian T. Norton)

9.1 Introduction

9.2 Emulsion types and properties

9.2.1 Kinetically trapped nano-emulsions

9.2.2 Pickering emulsions

9.2.3 Double emulsions

9.2.4 Air-filled emulsions

9.2.5 Water-in-water emulsions

9.3 Future challenges

9.3.1 Better mechanistic understanding of the emulsification process(es)

9.3.2 Improved emulsification processes

9.3.3 Designed emulsions for improved nutrition and health

9.3.4 Reduced use of surfactants for environmental reasons

10 Solid–liquid mixing (Mostafa Barigou)

10.1 Introduction

10.2 Regimes of solids suspension and distribution

10.2.1 State of nearly complete suspension with filleting

10.2.2 State of complete particle motion

10.2.3 State of complete off-bottom suspension

10.2.4 State of homogeneous or uniform suspension

10.3 Prediction of minimum speed for complete suspension

10.3.1 Influence of physical properties

10.3.2 Influence of solids concentration

10.3.3 Influence of geometric parameters

10.4 Hydrodynamics of particle suspension and distribution

10.4.1 Particle slip velocity

10.4.2 Particle settling and drag

10.5 Scale-up of solid–liquid mixing

10.6 Damage to food particles in suspension

10.7 Fine particle slurries

11 Gas–liquid mixing (J.K. Sahu and Keshavan Niranjan)

11.1 Introduction

11.2 Gas–liquid dispersion operations

11.2.1 Characteristics of dispersed phase—mean diameter

11.2.2 Gas dispersion—bubble behaviour

11.2.3 Gas dispersion in agitated vessels

11.3 Power input to turbine dispersers

11.4 Gas handling capacity and loading of turbine impeller

11.5 Bubbles in foods

11.6 Methods for mixing gas in liquid

11.6.1 Mixing by mechanical agitation under positive pressure

11.6.2 Mixing by mechanical agitation under vacuum

11.6.3 Steam-induced mixing

11.6.4 Other gas–liquid mixing methods

11.7 Characterization of bubble-containing structures

11.7.1 Gas hold-up

11.7.2 Bubble size distribution

11.7.3 Rheological characterization

11.8 Role of gases and specific ingredients in characterizing interfacial and rheological properties

11.9 Stability of foams and solidification of bubbly dispersions

11.10 Ultrasound in gas mixing and applications in food aeration

12 Evaluation of mixing and air bubble dispersion in viscous liquids using numerical simulations (Kiran Vyakaranam, Maureen Evans, Bharani Ashokan and Jozef L. Kokini)

12.1 Introduction

12.2 Measures of mixing and evaluation of flow

12.2.1 Efficiency of stretching

12.2.2 Dispersive mixing efficiency

12.2.3 Distributive mixing efficiency

12.3 Governing equations for calculation of flow

12.4 CFD approaches for simulation of mixing flows

12.4.1 Finite element method

12.4.2 Techniques to handle moving parts

12.5 FEM numerical simulation of batch mixer geometries

12.5.1 3D numerical simulation of flow in a Brabender Farinograph®

12.5.2 Analysis of mixing in 2D single-screw and twin-screw geometries

12.6 3D Numerical simulation of twin-screw continuous mixer geometries

12.6.1 Distributive mixing efficiency in a 3D mixing geometry

12.6.2 Evaluation of dispersive mixing in 3D continuous mixer geometry

12.7 Prediction of bubble and drop dispersion in a continuous mixer

12.8 Summary

13 Particulate and powder mixing (John J. Fitzpatrick)

13.1 Introduction

13.2 Characterisation of particulate mixtures

13.2.1 Types of mixtures

13.2.2 Mixture quality

13.3 Assessment of mixture quality

13.3.1 Sampling

13.3.2 Sample variance and standard deviation

13.3.3 Lacey and Poole indices of mixture quality

13.3.4 Relative standard deviation

13.3.5 Estimating the true variance (s2) from the random sample variance (S2)

13.3.6 Assessing if satisfactory mixture quality is achieved

13.3.7 ‘Baking a cake’ method of assessing mixture quality

13.3.8 Influence of particle size and powder cohesiveness on mixture quality

13.4 Mixing mechanisms

13.4.1 Convection or macromixing

13.4.2 Diffusion or micromixing

13.4.3 Shearing

13.5 Segregation or demixing

13.5.1 Segregation

13.5.2 Reducing segregation

13.6 Powder mixing equipment

13.6.1 Tumbling mixers

13.6.2 Convective mixers

13.6.3 High shear mixers

13.6.4 Sigma blade mixers

13.6.5 Continuous mixers

13.7 Mixer selection and process design

13.7.1 Specification of mixture quality requirement

13.7.2 Mixer selection

13.7.3 Process design

13.8 Other factors affecting mixing process design in dry food processing

13.8.1 Hygiene and cleaning

13.8.2 Addition of multiple ingredients with large variation in properties

13.8.3 Addition of ingredients in liquid form

13.8.4 Dust prevention and control

Index