The governing equations for diffusion mass transfer are [15]
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(34) |
and
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(35) |
where
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(36) |
and
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(37) |
In these equations
is the mass flux of species A,
is the mass diffusivity,
is the mass fraction of species A and
is the density of species A. Furthermore,
is the rate of increase
of the mass of species A per unit volume of the mixture. Another way of
formulating this is:
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(38) |
and
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(39) |
where
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(40) |
and
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(41) |
Here,
is the molar flux of species A,
is the mass diffusivity,
is the mole fraction of species A and
is the molar concentration of species A. Furthermore,
is the rate of increase
of the molar concentration of species A.
The resulting equation now reads
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(42) |
or
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(43) |
If and
are constant, these equations reduce to:
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(44) |
or
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(45) |
Accordingly, by comparison with the heat equation, the correspondence in Table (7) arises.
heat | mass diffusion | |
T | ![]() |
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