Unsteady-State Diffusion in Binary Systems

For a binary system with no convection perpendicular to the interface, Eq. 9.1.1, combined with Eq. 3.1.1 for /j, simplifies to 

We use the method of combination of variables, with the combined variable f = z/yf.  

Equation 9.2.2 can be integrated to give the concentration profiles as (Arnold, 1944 Bird et al., 1960) 

The molar diffusion flux at the interface z = 0 is obtained from the one-dimensional form of Eq. 3.1.1 

The composition derivative dx- /dx z= ) is obtained by differentiating Eq. 9.2.5, setting z = 0, and the resulting expression combined with Eq. 9.2.6 to give 

---