Knudsen Diffusion in parallel, multidimensional or randomly oriented capillary structures

Monte Carlo computations of transmission probabilities of test molecules and the mean-square displacement of a large number of molecules in finite pore network samples are used to compute effective Knudsen diffusivities in two- and three-dimensional parallel random pore structures (consisting of two or three mutually perpendicular bundles of parallel capillaries), and in structures of randomly oriented pores. The orientationally averaged effective diffusivities, which are obtained either directly from the mean-square displacement method or indirectly by orientational averaging of the transmission probability results, are found to be practically independent of the orientational distribution of the pores, that is, of whether the pores are randomly distributed or grouped into one, two or three bundles of parallel capillaries, in the major part of the porosity range.