A NEW ALGORITHM FOR REPRESENTING TRANSPORT IN POROUS-MEDIA IN ONE-DIMENSION, INCLUDING CONVECTION, DISPERSION, AND INTERACTION WITH THE IMMOBILE PHASE WITH 1ST-ORDER KINETICS

The model uses, in one-dimensional flow, the random-walk method on par ticles and integrates them into a discretized representation of space which eliminates the individual management of each particle. The metho d of computing allows a simulation of mass transfer in adsorbing media by dissociating the roles of convection, dispersion, and the exchange occurring between the mobile and immobile phases. This gives the para meters that have to be fitted, such as the dispersivity or the exchang e rate, a meaning which is closer to their physical reality than that defined by global models (e.g., apparent dispersivity without consider ing exchange between phases). The model was tested first on analytical solutions and also on data from laboratory experiments on a double po rosity chalk column and showed that, with the same limited set of para meters, it could fit concentration/time restitutions at different dist ances from the injection point. Because of its structure, the algorith m can easily be modified so as to simulate distributed injections and transfers in a regime of variable flow rates.