Practical Models for Isothermal Diffusion and Flow of Gases in Porous Solids

Abstract

The mass flux model of Mason and Evans (1969) is extended to cross-linked pore networks with wide pore size distributions and surface diffusion. Three simplified forms of the new model are tested. The use of two lumped pore radii gives good agreement with experiments on a wide variety of solids. The optimal lumped radii can be estimated from measured pore size-distributions.

Diffusion in pore networks: Effective medium theory and smooth field approximation

“…As expected, this is the expression for the effective diffusivity given by the flux models of Stewart and coworkers (Johnson and Stewart, 1965;Feng and Stewart, 1973) for small concentrations of the diffusing species in a binary mixture. If the pore length is distributed independently of the pore size, i.e.,…”

Diffusion in pore networks: Effective medium theory and smooth field approximation

“…As expected, this is the expression for the effective diffusivity given by the flux models of Stewart and coworkers (Johnson and Stewart, 1965;Feng and Stewart, 1973) for small concentrations of the diffusing species in a binary mixture. If the pore length is distributed independently of the pore size, i.e.,…”

Controlled Release

“…The tortuosity value predicted by this model for an isotropic system is identical to that calculated by and Feng and Stewart (1973) employing the mass-flux model.…”

Study of Transport Phenomena in Chromatographic Columns by Pulsed Field Gradient NMR

“…43 On the other hand, a tortuosity factor of 3 was predicted for isotropic pore systems made of straight, nonintersecting, cylindrical pores, with no dead-end branches. 44 On the basis of the examination of microphotographs, Gibbs et al 37 concluded that the typical "popcorn ball" geometry of the porous particles used in their studies accounts well for the value that they obtained for the tortuosity factor, around 2.2 and close to the isotropic porous medium value of 2. 42 The values of the tortuosity factors obtained in our experiments (T ) 1.9-2.3), the spherical shape of the porous silica particles, and what is known of their pore structure 14 combine strongly to favor the isotropic porous medium model, also.…”

Diffusion in pore networks: Effective medium theory and smooth field approximation

“…As expected, this is the expression for the effective diffusivity given by the flux models of Stewart and coworkers (Johnson and Stewart, 1965;Feng and Stewart, 1973) for small concentrations of the diffusing species in a binary mixture. If the pore length is distributed independently of the pore size, i.e.,…”

Controlled Release

“…The tortuosity value predicted by this model for an isotropic system is identical to that calculated by and Feng and Stewart (1973) employing the mass-flux model.…”

Study of Transport Phenomena in Chromatographic Columns by Pulsed Field Gradient NMR

“…43 On the other hand, a tortuosity factor of 3 was predicted for isotropic pore systems made of straight, nonintersecting, cylindrical pores, with no dead-end branches. 44 On the basis of the examination of microphotographs, Gibbs et al 37 concluded that the typical "popcorn ball" geometry of the porous particles used in their studies accounts well for the value that they obtained for the tortuosity factor, around 2.2 and close to the isotropic porous medium value of 2. 42 The values of the tortuosity factors obtained in our experiments (T ) 1.9-2.3), the spherical shape of the porous silica particles, and what is known of their pore structure 14 combine strongly to favor the isotropic porous medium model, also.…”

Diffusion in pore networks: Effective medium theory and smooth field approximation

“…As expected, this is the expression for the effective diffusivity given by the flux models of Stewart and coworkers (Johnson and Stewart, 1965;Feng and Stewart, 1973) for small concentrations of the diffusing species in a binary mixture. If the pore length is distributed independently of the pore size, i.e.,…”

Controlled Release

“…The tortuosity value predicted by this model for an isotropic system is identical to that calculated by and Feng and Stewart (1973) employing the mass-flux model.…”

Study of Transport Phenomena in Chromatographic Columns by Pulsed Field Gradient NMR

“…43 On the other hand, a tortuosity factor of 3 was predicted for isotropic pore systems made of straight, nonintersecting, cylindrical pores, with no dead-end branches. 44 On the basis of the examination of microphotographs, Gibbs et al 37 concluded that the typical "popcorn ball" geometry of the porous particles used in their studies accounts well for the value that they obtained for the tortuosity factor, around 2.2 and close to the isotropic porous medium value of 2. 42 The values of the tortuosity factors obtained in our experiments (T ) 1.9-2.3), the spherical shape of the porous silica particles, and what is known of their pore structure 14 combine strongly to favor the isotropic porous medium model, also.…”