EFFECTIVE DIFFUSION-COEFFICIENTS IN SQUARE ARRAYS OF FILAMENT BUNDLES

The effects of the polydispersity of the characteristic diffusion leng th of the pore space of fibrous media on the effective diffusion coeff icients of gases are studied by investigating the problem of gaseous d iffusion in the Knudsen, transition, and bulk regimes in square arrays of filament bundles, of cylindrical cross section consisting of unidi rectional, freely overlapping cylindrical filaments. Effective diffusi on coefficients are computed using a stochastic simulation method base d on the computation of the mean square displacement of a large number of molecules (random walkers) diffusing in the pore space. The depend ence of effective diffusivity on filament to bundle radius ratio, intr abundle porosity, interbundle porosity, and Knudsen number is investig ated in detail. The computed diffusivities are compared to the predict ions of analytical or semianalytical formulas based on expressions der ived in the literature for two-phase media or bidisperse pore structur es.