Food Mixing Principles and Applications

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 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