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Introduction to Food Process Engineering pp 397–436Cite as

Mixing and Separation

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Part of the book series: Food Science Text Series ((FSTS))

Abstract

The mixing and/or agitation of liquids, solids and (to a lesser extent) gases is one of the commonest of all operations in the food processing industries. Of the possible combinations of these states, those of principal interest are liquid–liquid mixtures, solid–solid mixtures and liquid–solid mixtures or pastes. However, it is important at this early stage to define exactly what is meant by the terms ‘agitation’ and ‘mixing’ and it is perhaps easiest to do this by considering liquid–liquid systems. The agitation of a liquid may be defined as the establishment of a particular flow pattern within the liquid, usually a circulatory motion within a container. On the other hand mixing implies the random distribution, throughout a system, of two or more initially separate ingredients.

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Abbreviations

a :

Coefficient

A :

Area

b :

Index in Eq. (14.44)

B :

Baffle width

C :

Molar concentration

C 1 :

Feed concentration

C 2 :

Permeate concentration

C g :

Concentration of solute in gel layer

C S :

Solute concentration

C W :

Solvent concentration

D :

Impeller diameter; diffusivity

D e :

Effective diffusivity

D T :

Vessel diameter

Fr :

Froude number

g :

Acceleration due to gravity

H :

Depth of liquid

k :

Rate constant; mass transfer coefficient

k e :

Effective mass transfer coefficient

K :

Consistency coefficient; Kozeny’s constant

L :

Depth of filter cake

L 0 :

Equivalent bed depth of filter medium

M :

Mixing index

n :

Population or number of samples; flow behaviour index; molar mass

N :

Rotation speed; permeate flux

N 0 :

Initial permeate flux

N p :

Power number

p :

Proportion (fraction)

P :

Power consumption; pressure

R :

Mass transfer resistance; universal gas constant; rejection factor

Re :

Reynolds number

s :

Standard deviation

s 0 :

Initial (unmixed) standard deviation

s ∞ :

Limiting value of standard deviation

s 2 :

Variance

\(s_{\infty} ^{2}\) :

Limiting value of variance

\(s_{0} ^{2}\) :

Initial (unmixed) variance

S :

Specific surface

t :

Time

T :

Absolute temperature

u :

Superficial velocity

V :

Volume; volume of filtrate

W :

Impeller blade depth

x :

Index

x i :

Local concentration

\(\bar x\) :

Average concentration

y :

Index

z :

Membrane thickness

Z :

Height of impeller from vessel bottom

α :

Specific cake resistance

\(\dot \gamma\) :

Shear rate

ΔP :

Pressure drop across filter press; transmembrane pressure

ΔΠ:

Osmotic pressure difference

ɛ :

Voidage

μ :

Viscosity

μ a :

Apparent viscosity

ν :

Volume fraction; volume of cake deposited per unit volume of filtrate

Π:

Osmotic pressure

ρ :

Density

1:

Feed

2:

Permeate

f :

Fouling

m :

Membrane

p :

Concentration polarisation

Further Reading

  • Cheryan, M. 1998. Ultrafiltration and microfiltration handbook. Lancaster, Pennsylvania: Technomic.

    Google Scholar 

  • Fryer, P. J., Pyle, D. L., and Rielly, C. D., (eds.). 1997. Chemical engineering for the food industry. London: Chapman and Hall.

    Google Scholar 

  • Harnby, N., Edwards, M. F., and Nienow, A. W. 1997. Mixing in the process industries. Oxford: Butterworth-Heinemann.

    Google Scholar 

  • Renner, E. and Abd El-Salam, M. H. 1991. Applications of ultrafiltration in the dairy industry. London: Elsevier.

    Google Scholar 

  • Scott, K. and Hughes, R. 1996. Industrial membrane separation technology. London: Blackie.

    Book  Google Scholar 

  • Uhl, V. W. and Gray, J. B. 1966. Mixing: theory and practice. New York, NY: Academic.

    Google Scholar 

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Author information

Authors and Affiliations

  1. School of Natural and Applied Sciences, University of Lincoln, Brayford Pool, LN6 7TS, Lincoln, UK

    P.G. Smith

Authors
  1. P.G. Smith
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© 2011 Springer Science+Business Media, LLC

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Smith, P. (2011). Mixing and Separation. In: Introduction to Food Process Engineering. Food Science Text Series. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-7662-8_14

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