The governing equations for diffusion mass transfer are [34]
![]() |
(327) |
and
![]() |
(328) |
where
![]() |
(329) |
and
![]() |
(330) |
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:
![]() |
(331) |
and
![]() |
(332) |
where
![]() |
(333) |
and
![]() |
(334) |
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
![]() |
(335) |
or
![]() |
(336) |
If and
are constant, these equations reduce to:
![]() |
(337) |
or
![]() |
(338) |
Accordingly, by comparison with the heat equation, the correspondence in Table (16) arises.