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Mass Transfer

  • P.G. Smith
Chapter
Part of the Food Science Text Series book series (FSTS)

Abstract

Mass transfer is concerned with the movement of material in fluid systems, that is both gases or liquids, under the influence of a concentration gradient. As we saw in Chapter 5, this is analogous to the movement of heat under the influence of a temperature gradient. For example, in drying operations water is removed in vapour form from either a liquid or a solid food into a warm gas stream (usually air). Thus the mass transfer of water occurs because there is a high concentration of water in the food and a lower concentration of water in the air. Most examples of mass transfer in food processes involve the transfer of a given component from one phase across an interface to a second phase. Some examples are listed in Table 8.1

Keywords

Mass Transfer Mass Transfer Coefficient Sherwood Number Convective Mass Transfer Molar Density 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

a

Coefficient

b

Index

c

Index

C

Molar concentration

\({C_{{{\textrm{A}}_{\textrm{i}}}}}\)

Concentration of A (liquid phase) at the interface

\({C_{{{\textrm{A}}_{\textrm{L}}}}}\)

Concentration of A in the bulk liquid

\(C_{\textrm{A}}^{\textrm{*}}\)

Concentration of A in equilibrium with the bulk gas partial pressure

d

Diameter

D

Diffusivity or diffusion coefficient

\({D_{{\textrm{AB}}}}\)

Diffusivity of A in B

DG

Diffusivity in the gas phase

DL

Diffusivity in the liquid phase

g

Acceleration due to gravity

Gr

Grashof number

H

Henry’s constant

JA

Molar flux of A

kg

Film gas mass transfer coefficient

kG

Film gas mass transfer coefficient

kL

Film liquid mass transfer coefficient

kx

Film liquid mass transfer coefficient

ky

Film gas mass transfer coefficient

KG

Overall gas mass transfer coefficient

KL

Overall liquid mass transfer coefficient

L

Characteristic length

MA

Molecular weight of component A

N

Molar flux

Nw

Molar flux of water vapour

pA

Partial pressure of A

\({p_{{{\textrm{A}}_{\textrm{G}}}}}\)

Partial pressure of A in bulk gas

\(p_{\textrm{A}}^{\textrm{*}}\)

Partial pressure in equilibrium with bulk liquid concentration

\({p_{{{\textrm{A}}_{\textrm{i}}}}}\)

Partial pressure of A at interface

pw

Partial pressure of water vapour

\({p_{{\textrm{wo}}}}\)

Partial pressure of water vapour at saturation

\({p_{{{\textrm{B}}_{{\textrm{lm}}}}}}\)

Logarithmic mean partial pressure difference in B

P

Pressure; permeability

r

Radius

R

Universal gas constant

Re

Reynolds number

Sc

Schmidt number

Sh

Sherwood number

T

Absolute temperature

x

Mass or mole fraction in liquid phase

y

Mass or mole fraction in gas phase

\({y_{{{\textrm{B}}_{{\textrm{lm}}}}}}\)

Logarithmic mean concentration difference in B

z

Dimension in the z-direction

zG

Thickness of gas film

zL

Thickness of liquid film

Greek Symbols

ΔC

Concentration difference

Δp

Partial pressure difference

Δx

Mole fraction difference (liquid phase)

Δy

Mole fraction difference (gas phase)

Δρ

Density difference

μ

Viscosity

ρ

Mass density

ρA

Mass density of A

ω

Molar rate of evaporation

Subscripts

A

Component A

B

Component B

w

Water

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • P.G. Smith
    • 1
  1. 1.School of Natural and Applied SciencesUniversity of LincolnLincolnUK

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