The governing equations for diffusion mass transfer are [35]
![]() |
(367) |
and
![]() |
(368) |
where
![]() |
(369) |
and
![]() |
(370) |
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:
![]() |
(371) |
and
![]() |
(372) |
where
![]() |
(373) |
and
![]() |
(374) |
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
![]() |
(375) |
or
![]() |
(376) |
If and
are constant, these equations reduce to:
![]() |
(377) |
or
![]() |
(378) |
Accordingly, by comparison with the heat equation, the correspondence in Table (16) arises.