Diffusion in Inhomogeneous Media

Abstract

Methods are given for the calculation of effective diffusion coefficients for inhomogeneous media in which the actual diffusion coefficient varies from point to point in a random manner. An exact result is obtained in the form of an infinite series involving correlations between diffusion coefficients at n different points. A procedure for deriving approximate expressions involving only two-point correlations is also developed, and applied, in particular, to the important special case of diffusion through a porous material.