Dispersion in Porous Media

The molecular diffusivity of a tracer species in a given medium is a measure of the average spread of the tracer due to fluctuations in its velocity on the molecular scale. In a medium that is heterogeneous on a macroscopic scale, a tracer will experience an additional spreading due to variations in its velocity as it moves through the heterogeneous medium. This spreading due to macroscale velocity fluctuations is known as dispersion and is the subject of this article