In a previous study, column experiments were carried out with Toyoura sand (permeability 2.05 × 10− 11 m2) and Toyoura sand mixed with bentonite (permeability 9.96 × 10− 13 m2) to obtain the molecular diffusion coefficient, the Knudsen diffusion coefficient, the tortuosity for the molecular diffusion coefficient, and the mechanical dispersion coefficient of soil gas systems.
The equation of the dusty gas model already includes obstruction factors for Knudsen diffusion and molecular diffusion, which relate to medium heterogeneity and tortuosity and depend only on the structure of the porous medium.
Based on visualization and quantitation of the three-dimensional (3D) morphological features (i.e., appearance, size, volume, shape, and distribution) of pores, the porosity, tortuosity-connectivity, permeability, and molecular diffusion of cement mortar were computed and simulated.
Thus, molecular diffusion considers only the obstruction factor related to tortuosity.
[1, 28] He proposes the following equation: where D i is the molecular diffusion coefficient of the i-th species corrected for tortuosity, r1 the radius of the vertical, cylindrical burrows, r2 the half-distance between burrows, and (∂C/∂r) the concentration gradient of solute i extending from the burrow wall into the bulk sediment.
The effective diffusion coefficient can be calculated by the following equation: D_{text{eff}} = frac{{Dvarepsilon_{p} }}{{tau_{p} }} (20 where D is the molecular diffusion coefficient, ( varepsilon_{p} ) porosity of catalyst particle, ( tau_{p} ) is the catalyst particle tortuosity.
In nature, sediment may account for the persistence of hydrate in otherwise methane-depleted environments by increasing the diffusive boundary layer and slowing the rate of molecular diffusion via porosity/tortuosity effects.
Molecular diffusion coefficient.
Molecular diffusion coefficient (L2 T−1).
Three diffusion types are in porous materials: molecular diffusion, Knudsen diffusion, and single-file diffusion.
