TAYLOR DISPERSION IN POROUS-MEDIA - DETERMINATION OF THE DISPERSION TENSOR

In homogeneous porous media, the analytical expression of the dispersion tensor D* can be calculated by the method of moments and by a multiple scale expansion; the symmetric component of this tensor is identical in both cases. Numerically, D* can be computed by two methods, namely the B equation and random walks. The porous media are modeled as being spatially periodic; D* is determined as a function of the Peclet number for four types of unit cells: deterministic, fractal, random, and reconstructed. A systematic comparison is made with existing numerical and experimental data. The long time behavior, and its Gaussian limit, is documented.