Hydrodynamic Dispersion in a Saturated Homogeneous Porous Medium at Low Peclet Numbers and Nonhomogeneous Solution

The coefficient of mechanical dispersion of a solute in a homogeneous porous medium saturated by a binary diluted solution is derived, taking into account nonuniform density and viscosity fields. It is shown that in the neighborhood of a vanishing macroscopic velocity, a nonuniform density field induces a macroscopic dispersion resulting from the variation of microscopic density gradients and from horizontal variations of the macroscopic density. Both together yield the macroscopic effect of density instability on solute redistribution phenomena in porous materials.