Effect of total pressure gradient on unsteady-state diffusion rates of gases in porous media.

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Abstract
In the unsteady-state or dynamic methods of determining transfer properties of gases in porous media, a simplified isobaric diffusion rate equation of the Fick''s type has been used even for some cases with a pulse of pure gas. By measuring the pressure response at one end of a single porous pellet accompanied by a stepwise change in gas concentration at the other end, however, it is shown that a relatively large and rapid pressure gradient appears in the porous pellet. The pressure response curves are analyzed theoretically by using non-isobaric rate equations to obtain good accord between the theoretical and observed results. The effects of the appearance of the total pressure gradient on the concentration change at the pellet end and on the diffusion rate are discussed in detail.

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