Modelling ion diffusion mechanisms in porous media

The main features of a numerical model aiming at predicting the drift of ions in electrolytic solutions are presented. The mechanisms of ionic di usion are described by solving the Nernst{Planck system of equations. The electrical coupling between the various ionic uxes is accounted for by the Poisson equation. Two algorithms using the nite element method for spatial discretization are compared for simple test cases. One is based on the Picard iteration method while the other is based on the Newton{Raphson scheme. Test results clearly indicate that the range of application is broader for the algorithm based on the Newton{Raphson method. Selected examples of the application of the algorithm to more complex 1-D and 2-D cases are given