Theoretical Study on Effective Diffusivities of Bi-disperse Porous Solids at Constant Pressure
Munekazu OHMI, Tateo USUI, Keiji NAKAJIMA
For predicting effective diffusivities of bi-disperse porous media, an improved model in which tortuosity factors of the macro- and micro-pore are taken into account is proposed on the basis of the WAKAO and SMITH random pore model. The diffusion rates of binary gases at constant pressure and the effective diffusivities are derived according to the model.
By the use of the experimental data of WAKAO and SMITH and HENRY et al, tortuosity factors of their porous solids are determined approximately on the basis of the model. The theoretical effective-diffusivities calculated by using the tortuosity factors agree rather well with the experimental ones than those calculated on the basis of the random pore model over the pressure range 0.0006 to 12 atm.
In order to examine the influence of an inert gas on the diffusion process, solutions to the Stefan-Maxwell diffusion equations for equimolar counter diffusion in a ternary gas mixture through bidisperse porous media are derived on the basis of the model: The diffusion rates and the effective diffusivities in this system are given.
The expressions for the simple one-dimensional diffusion mentioned above are extended to those for the radial diffusion in a spherical shell.