Modification of classical approximations for diffusion in fluids with density gradients

Abstract

An analysis of classical approximations is performed for diffusion in fluids with density gradients. This approach gives a new diffusion equation taking into account the asymmetry of molecular mean-free paths and the velocity distribution in the flux term. It is shown that new model is consistent with Einstein's evolution equation for an asymmetric distribution of spatial displacements and with molecular dynamic simulations for hard spheres.