CONVECTION-DIFFUSION TRANSPORT IN DISORDERED STRUCTURES - NUMERICAL-ANALYSIS BASED ON THE EXIT-TIME EQUATION

The problem of biased diffusion in disordered media (percolation clust ers) is analysed by means of the exit-time equation. Numerical simulat ions show that for percolation lattices tending to criticality, the vo lume-averaged exit time as a function of the Peclet number, Pe, deviat es from the regular 1/Pe-behaviour and for high Pe grows monotonically with Pe. Numerical simulations on DLA-clusters and deterministic frac tals indicate the applicability of the exit-time approach to singular fractal structures. Finally, exit-time analysis is adopted in explaini ng standard and non-standard features of dispersion of solute particle s in highly heterogeneous porous packings.