AN EXACT SOLUTION OF THE DIFFUSION EQUATION WITH SHRINKING

An exact solution for diffusion from a shrinking slab of finite thickness, assuming a constant mutual diffusion coefficient, has been obtained. This has been accomplished by first casting the appropriate differential equation into the form of an equation describing diffusion in a semi-infinite slab with a fixed domain of integration but with a quadratic concentration dependence of the diffusivity and then making use of Fujita's analytical solution for that equation. The present results are of potential interest in the fields of drying, dyeing, ion exchange and solid-liquid extraction.