Portal de Periódicos da CAPES

A mean free path theory of void diffusion in a porous medium with surface diffusion. II. Numerical evaluation of the effective diffusivity for arbitrary Knudsen number

1982; American Institute of Physics; Volume: 76; Issue: 1 Linguagem: Inglês

10.1063/1.442720

1520-9032

Fun Gau Ho, William Strieder,

Gas Dynamics and Kinetic Theory

A mean free path kinetic theory of gaseous void transport with simultaneous surface diffusion on the pore walls has been developed for diffusion through a porous medium. A variational upper bound expression for the effective diffusivity is applied to a model porous medium, a bed of randomly placed, freely overlapping solid spheres all of the same radius. The effects of tortuosity are rigorously considered by explicitly including the flux of diffusing material around obstructions in its path in the trial functions. Numerical calculations of the variational integrals are performed for porosities from 0.01 to 0.90 and the full range of Knudsen numbers and surface diffusivities. From asymptotic values at large Knudsen numbers, a table of effective diffusivities versus the surface diffusion coefficient is presented for pure Knudsen diffusion in the voids.