The governing equations for diffusion mass transfer are [35]
(385) |
and
(386) |
where
(387) |
and
(388) |
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:
(389) |
and
(390) |
where
(391) |
and
(392) |
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
(393) |
or
(394) |
If and are constant, these equations reduce to:
(395) |
or
(396) |
Accordingly, by comparison with the heat equation, the correspondence in Table (16) arises.