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General Quantitative Description of Pore Diffusion

In an actual solid, with its complicated pore structure, the concept of an effective diffusivity is defined by the equation  [Pg.167]

The definition of tortuosity factor in Eq. 3.5.b-2 includes both the effect of altered diffusion path length as well as changing cross-sectional areas in constrictions for some applications, especially with two-phase fluids in porous media, it may be better to keep the two separate (e.g., Van Brakel and Heertjes [39]). This tortuosity factor should have a value of approximately 3 for loose random pore structures, but measured values of 1.5 up to 10 or more have been reported. Satterfield [40] states that many common catalyst materials have a t 2 3 to 4 he also gives further data. [Pg.167]

the effective diffusivity would have the form [Pg.167]

Turning to a general description of pore diffusion, the dusty gas theory of Mason et al. [41,42] utilizes the results from the formal kinetic theory of gases, with one species, the dust, having a very large molecular wei t. Their final results can be clearly visualized in the form utilized by Feng and Stewart [43]. [Pg.168]

Equations 3.S.b-4 to 6 can also be combined to give a single equation containing only the total flux resulting from both diffusive and viscous flow mechanisms  [Pg.168]


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