TRACER DISPERSION IN DOUBLE-POROSITY POROUS-MEDIA WITH NONLINEAR ADSORPTION

Tracer dispersion measurements in double porosity porous media with a nonlinear adsorption isotherm are reported. Thanks to a radioactive ta gging technique we obtained transit time distributions at different cr oss-sections along the porous medium. This tagging technique allows us to work in a linear adsorption regime where classical dispersion resu lts are used. The basic dispersion mechanisms are related to physicoch emical and geometrical properties of the porous medium. We obtained sa tisfactory comparison of these theoretical results with experimental v alues, We conclude that useful information about microscopic length an d time scales may be obtained from the mean tracer velocity dependence of the longitudinal dispersion coefficient. Finally, we show how the total solute concentration, due to the nonlinear adsorption isotherm, weights the trapping effects. (C) 1998 Elsevier Science B.V. All right s reserved.