Transverse dispersion through non-uniform porous media.

Abstract

A laboratory experiment was devised to measure the effect on transverse dispersion of a permeability interf ace. A layer of coarse sand was interposed within a matrix of fine sand at two different orientations: (1) at right angles, and (2) at an angle of 60 °, to the direction of flow. Dispersion was first measured in fine sand alone in order to obtain a base measurement unaffected by permeability changes. Calculations for the non-uniform cases were made assuming that increased dispersion could be accounted for by changes in medium particle size. Thus in the calculations it is assumed that the permeability interface does not affect transverse dispersion. With the coarse sand layer at right angles to the flow field, the standard deviation of the observed dispersion was about 27% greater than predicted. With the layer at a 60 ° angle to the flow field, the standard deviation of the observed dispersion was 79% greater than predicted. Thus it appears that a permeability interface in a porous medium does have an effect on dispersion and that the magnitude of the effect depends, in part, on the orientation of the interface to the direction of mean flow.