Interdiffusion of Gases in a Low Permeability Graphite at Uniform Pressure

Abstract

An experimental investigation of the interdiffusion behavior of gases in a low permeability graphite was performed by sweeping the opposite faces of a graphite septum with helium and argon at uniform pressure and measuring the diffusive flux of both gases. The objectives were to ascertain the diffusion mechanism, to verify the applicable equations and associated theories, and to determine the parameters required to use these equations. At all experimental pressures, contributions of both normal and Knudsen diffusion effects were detectable via the pressure dependence of the diffusion fluxes. It was found that a previously proposed dusty-gas model formed an excellent basis for correlating the results. The dusty-gas model yields flux equations which predict the diffusion behavior over a wide range of pressures for particular gas concentrations at the boundaries. Only two experimentally determined parameters (characteristic of the gases and graphite) are required. These are: an effective normal-diffusion coefficient obtained through interdiffusion experiments and a Knudsen coefficient obtained through single-gas (permeability) experiments. The procedures used to evaluate these parameters in terms of the experimental data are described in detail.

Tortuosity in electrochemical devices: a review of calculation approaches

“…In the absence of this information, effective transport properties of porous structures have been derived experimentally by means of diffusion cell experiments 16,17,[64][65][66][67][68][69][70] and electrochemical measurements. 15,19,46,71 …”

New Light on Some Old Problems: Revisiting the Stefan Tube, Graham's Law, and the Bosanquet Equation

“…For the Knudsen region this follows directly, but the data for the system He-Ar of Evans et al (1962), which are more in the slip-flow region, show the same behavior at constant pressure diffusion. Although not convinced of the exact nature of the dusty gas model (Jackson, 1977, p 16), Jackson derives from these equations that Graham's law should hold also at low Knudsen numbers, as for the isobaric case the viscous flow term vanishes and only the terms with the Knudsen coefficients remain, and subsequently derives a multicomponent version of Graham's law (Jackson, 1977, pp 53 and 54).…”

“…The model gives remarkably good coverage of both ultrafiltration of aqueous poly(ethylene glycol) solutions and several gas diffusion phenomena such as the counterdiffusion of He and Ar across porous graphite plugs (Evans et al, 1962(Evans et al, , 1963 and counterdiffusion of various gases in capillaries (Waldmann and Schmitt, 1961). In the process I discovered errors in the basic derivations of the dusty gas model of Mason et al (1967Mason et al ( , 1978Mason et al ( , 1983Mason et al ( , 1985Mason et al ( , 1990, which had been used to explain counterdiffusion phenomena and still finds widespread application, and also in heterogeneous catalysis (Jackson, 1977;Froment and Bischoff, 1979;Veldsink et al, 1995;Keil, 1996) and adsorption (Kä rger and Ruthven, 1992).…”

Modification of TOUGH2 to Include the Dusty Gas Model for Gas Diffusion

“…The DGM is discussed in great detail by Mason and Malinauskas (1983) and Cunningham and Williams (1980). Webb (1998) compared Fick's law and the DGM to comprehensive gas diffusion data in low-permeability graphite (k=2.13 x 10 -18 m 2 ) obtained by Evans et al (1962Evans et al ( , 1963. The DGM predictions compared very well with the experimental data and to Graham's laws, which are fundamental gas diffusion relationships for porous media.…”

“…The DGM has been compared to the experimental data of Evans et al (1962Evans et al ( , 1963 for a low permeability (2.13 x 10 -18 m 2 ) graphite by Webb (1998), which showed that the DGM compares well to the data while Fick's law does not. Some of these same data have been used in the present verification exercise.…”