Food Mixing: Principles and Applications

by Editor: P. J. Cullen (Dublin Institute of Technology, Ireland ; )

• ISBN13: 9781444309881
• ISBN10: 1444309889
• Format: eBook
• Copyright: 2009-07-01
• Publisher: Wiley-Blackwell

Summary

The mixing of liquids, solids and gases is one of the most common unit operations in the food industry. Mixing increases the homogeneity of a system by reducing non-uniformity or gradients in composition, properties or temperature. Secondary objectives of mixing include control of rates of heat and mass transfer, reactions and structural changes. In food processing applications, additional mixing challenges include sanitary design, complex rheology, desire for continuous processing and the effects of mixing on final product texture and sensory profiles. Mixing ensures delivery of a product with constant properties. For example, consumers expect all containers of soups, breakfast cereals, fruit mixes, etc to contain the same amount of each ingredient. If mixing fails to achieve the required product yield, quality, organoleptic or functional attributes, production costs may increase significantly.This volume brings together essential information on the principles and applications of mixing within food processing. While there are a number of creditable references covering general mixing, such publications tend to be aimed at the chemical industry and so topics specific to food applications are often neglected. Chapters address the underlying principles of mixing, equipment design, novel monitoring techniques and the numerical techniques available to advance the scientific understanding of food mixing. Food mixing applications are described in detail.The book will be useful for engineers and scientists who need to specify and select mixing equipment for specific processing applications and will assist with the identification and solving of the wide range of mixing problems that occur in the food, pharmaceutical and bioprocessing industries. It will also be of interest to those who teach, study and research food science and food engineering.

Table of Contents

Contributors

Mixing in the food industry: trends and challenges

Role of mixing

Design criteria for mixing

Specific challenges in food mixing

Quality assurance compliance through mixing

Engineering texture through mixing

Advances in the science of mixing

Book objectives

Mixing fundamentals

Introduction

Defining mixing

Macromixing

Mesomixing

Micromixing

Scale of scrutiny

Quantifying mixedness

Inference of mixing indices

Determining the end point of mixing

Solids mixing

Fluid mixing

Multi-phase mixing

Alternative measures of mixedness in industrial practice

Residence time distributions

Modelling of residence time distributions

Kinematics of flow and mixing mechanisms

Introduction

Fluid mixing

Kinematics of fluid flow

Quantification of flow regimes

Chaotic advection

Fluid mixing mechanisms

Solids mixing

Mixing flow in solids

Solids mixing mechanism

Identification of mixing mechanisms

Solids

Fluids

Rheology and mixing

Introduction

Dispersion rheology

Forces acting on dispersed particles

Parameters affecting suspension rheology

Fluid rheology and mixing

Shear flow

Elongational flow

Effects of mixing on fluid rheology

Mixer rheometry

Theory

Mixer rheometry applications

Conclusion

Equipment design

Introduction

Liquid mixing equipment

Portable mixers

General purpose liquid mixers

Mixer shafts design

Other mechanical design considerations

Special purpose liquid mixing equipment

Food specific mixing equipment

Powder mixing equipment

Ribbon blenders

Paddle blenders

Combination blenders

Tumble blenders

Loading and emptying blenders

Liquid addition to powders

Sampling

Safety

Blending systems

Equipment components

Electric motors

Speed reducers

Seals

Mixing scale-up

Introduction

Scale-up for fluid mixing

Dimensional analysis

Scale-up with geometric similarity

Scale-up without geometric similarity

Scale-up for powder mixing

Monitoring and control of mixing operations

Introduction

Torque and power measurement

Flow measurement

Hot-wire anemometry

Laser Doppler anemometry

Phase Doppler anemometry

Flow visualization using computer vision

Particle image velocimetry

Planar laser-induced fluorescence

Tomography

Quantification of mixing time

NIR spectroscopy

Chemical imaging

Computational fluid mixing

Introduction

History of CFD

Steps towards CFD simulation of mixing processes

Conservation equations

Mass conservation

Momentum conservation

Turbulence

Energy conservation

Species transport

Turbulent species and energy transport

Boundary conditions

Numerical methods

Discretised solution of the flow variables

Grid generation

Discretisation

Finite-volume discretisation methods

Solver methods

Application of CFD to stirred tank modelling

Mixing operations

Representation of the impeller

Prediction of mixer performance characteristics

Simulation of unbaffled or partially baffled stirred tanks

Simulation of single-phase flow in baffled stirred tanks

Mixing and blending simulations

Multi-phase simulations

Application to food mixing operations

Challenges for simulation of food processes

Examples of food applications

Closing remarks

Immiscible liquid liquid mixing

Introduction

Emulsion types and properties

Kinetically trapped nano-emulsions

Pickering emulsions

Double emulsions

Air-filled emulsions

Water-in-water emulsions

Future challenges

Better mechanistic understanding of the emulsification process(es)

Improved emulsification processes

Designed emulsions for improved nutrition and health

Reduced use of surfactants for environmental reasons

Solid liquid mixing

Introduction

Regimes of solids suspension and distribution

State of nearly complete suspension with filleting

State of complete particle motion

State of complete off-bottom suspension

State of homogeneous or uniform suspension

Prediction of minimum speed for complete suspension

Influence of physical properties

Influence of solids concentration

Influence of geometric parameters

Hydrodynamics of particle suspension and distribution

Particle slip velocity

Particle settling and drag

Scale-up of solid liquid mixing

Damage to food particles in suspension

Fine particle slurries

Gas liquid mixing

Introduction

Gas liquid dispersion operations

Characteristics of dispersed phase-mean diameter

Gas dispersion-bubble behaviour

Gas dispersion in agitated vessels

Power input to turbine dispersers

Gas handling capacity and loading of turbine impeller

Bubbles in foods

Methods for mixing gas in liquid

Mixing by mechanical agitation under positive pressure

Mixing by mechanical agitation under vacuum

Steam-induced mixing

Other gas liquid mixing methods

Characterization of bubble-containing structures

Gas hold-up

Bubble size distribution

Rheological characterization

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

Stability of foams and solidification of bubbly dispersions

Ultrasound in gas mixing and applications in food aeration

Evaluation of mixing and air bubble dispersion in viscous liquids using numerical simulations

Introduction

Measures of mixing and evaluation of flow

Efficiency of stretching

Dispersive mixing efficiency

Distributive mixing efficiency

Governing equations for calculation of flow

CFD approaches for simulation of mixing flows

Finite element method

Techniques to handle moving parts

FEM numerical simulation of batch mixer geometries

3D numerical simulation of flow in a Brabender Farinograph“

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

3D Numerical simulation of twin-screw continuous mixer geometries

Distributive mixing efficiency in a 3D mixing geometry

Evaluation of dispersive mixing in 3D continuous mixer geometry

Prediction of bubble and drop dispersion in a continuous mixer

Summary

Particulate and powder mixing

Introduction

Characterisation of particulate mixtures

Types of mixtures

Mixture quality

Assessment of mixture quality

Sampling

Sample variance and standard deviation

Lacey and Poole indices of mixture quality

Relative standard deviation

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

Assessing if satisfactory mixture quality is achieved

Baking a cake method of assessing mixture quality

Influence of particle size and powder cohesiveness on mixture quality

Mixing mechanisms

Convection or macromixing

Diffusion or micromixing

Shearing

Segregation or demixing

Segregation

Reducing segregation

Powder mixing equipment

Tumbling mixers

Convective mixers

High shear mixers

Sigma blade mixers

Continuous mixers

Mixer selection and process design

Specification of mixture quality requirement

Mixer selection

Process design

Other factors affecting mixing process design in dry food processing

Hygiene and cleaning

Addition of multiple ingredients with large variation in properties

Addition of ingredients in liquid form

Dust prevention and control

Index

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