Gaseous Diffusion in Porous Media. II. Effect of Pressure Gradients
A previously proposed model for the diffusion of gases in porous media at uniform pressure is extended to allow for pressure gradients. The effect of pressure gradients is to introduce into the fundamental kinetic theory equations both a pressure diffusion term and an external force term, which is needed to keep the porous medium from being pushed along by the pressure gradient, There is a considerable cancellation of terms, and the final diffusion equation has the same form as in the uniform pressure case. No additional parameters beyond those necessary to define a diffusing system at uniform pressure are thus required to compute the diffusion rates when pressure gradients are present. The coefficienis of the diffusion equation, however, now depend on position through their dependence on pressure, and the net flux J of all molecules is an undetermined quantity. A complete solution requires also a forced flow equation giving J as a function of the pressure gradient. Two forced flow equations, which were derived, are shown to be not inconsistent in viscous flow regimes, and to complement rather than contradict each other. Agreement of the calculations with available experimental data is good. As in the uniform pressure case, the Poiseuille flow equation does not give an a priori characterization of any porous medium, but rather permits prediction of the behavior of different gas mixtures under a variety of conditions on the basis of three parameters which can be obtained from only a few experimental measurements.
- Research Organization:
- Oak Ridge National Lab., Tenn.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-16-017660
- OSTI ID:
- 4784463
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 7 Vol. 36; ISSN JCPSA6; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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