Accounting for apparatus‐induced dispersion in analyses of miscible displacement experiments

Investigators studying hydrodynamic dispersion in porous media have had some difficulty in theoretically predicting experimental breakthrough curves from laboratory columns. The greatest discrepancies occur for short‐column experiments or studies of unsaturated media. Some of the disagreement apparently can be eliminated by a quantitative treatment of apparatus‐induced dispersion. The experimental system is treated as a two‐layer construct in which the porous medium and the apparatus are considered as separate layers. The dispersion characteristics of the apparatus layer are determined independently in the absence of the porous material. The dispersion coefficient for the porous medium is obtained from a two‐layer dispersion equation. The hydrodynamic dispersion coefficients calculated in this manner were found to be as much as 40% lower than those obtained by the usual, one‐layer approach.