Unsteady-state diffusion often occurs in inorganic, organic, and biological solid materials. If the boundary conditions are constant with time, if they are the same on all sides or surfaces of the solid, and if the initial concentration profile is uniform throughout the solid, the methods described in Section 7.1 can be used. However, these conditions are not always fulfilled, in which case numerical methods must be used.
For unsteady-state diffusion in one direction, Eq. (7.1-9) becomes
Since this equation is identical mathematically to the unsteady-state ...