Computational Experiments on Three-Dimensional Molecular Diffusion in Porous Media

Estimations of apparent diffusion coefficients usually consist of curve-fitting the output of one-dimensional models to experimental laboratory-measured data from porous aggregates shaped in different forms. In this research a computational exploration is presented on the alternative use of three-dimensional models for the same purpose. Saturated conditions and absence of retention mechanisms for the solute were assumed. The outputs of the three dimensional models were averaged and compared to the results generated by the one-dimensional formulations. The comparison showed that there are significant discrepancies in the concentration values output by the models. Percent differences ranging from 30 to 90% were calculated. Those different estimations suggest that different values of the apparent diffusion coefficient may be obtained if the three-dimensional solution of the diffusion equation would be used to match experimental results.