 
 
 
 
 
 
 
  
The governing equations for diffusion mass transfer are [34]
|  | (277) | 
and
|  | (278) | 
where
|  | (279) | 
and
|  | (280) | 
In these equations 
 is the mass flux of species A,
 is the mass flux of species A, 
 is the mass diffusivity,
is the mass diffusivity,  is the mass fraction of species A and
 is the mass fraction of species A and  is the density of species A. Furthermore,
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:
 is the rate of increase
of the mass of species A per unit volume of the mixture. Another way of
formulating this is:
|  | (281) | 
and
|  | (282) | 
where
|  | (283) | 
and
|  | (284) | 
Here, 
 is the molar flux of species A,
 is the molar flux of species A, 
 is the mass diffusivity,
is the mass diffusivity,  is the mole fraction of species A and
 is the mole fraction of species A and  is the molar concentration of species A. Furthermore,
is the molar concentration of species A. Furthermore,  is the rate of increase
of the molar concentration of species A.
 is the rate of increase
of the molar concentration of species A.
The resulting equation now reads
|  | (285) | 
or
|  | (286) | 
If  and
 and  are constant, these equations reduce to:
 are constant, these equations reduce to:
|  | (287) | 
or
|  | (288) | 
Accordingly, by comparison with the heat equation, the correspondence in Table (16) arises.
 
 
 
 
 
 
