ANOMALOUS DISPERSION AND FINITE-SIZE EFFECTS IN HYDRODYNAMIC DISPERSION

Anomalous dispersion refers to concentration profiles that exhibit long-time tails as opposed to normal or Gaussian dispersion, which does not exhibit such tails. An original acoustic technique has enabled experimentally the demonstration that, in an unsaturated porous medium, the observed non-Gaussian dispersion is due only to finite-size effects: the sample length is set too small to achieve a statistical Gaussian random walk. An accurate fit to the data with a semiphenomenological model is suitable for comparison with a nonlocal theory concerning this transient effect. Thus, the mechanism involved in the dispersion process, and also the characteristic length of this dispersion, can be determined. © 1990 American Institute of Physics.