STUDY OF NON-FICKIAN DIFFUSION ANOMALIES THROUGH TIME LAGS .3. SIMPLE DISTANCE-DEPENDENT ANOMALIES IN MICROPOROUS MEDIA

The time-lag treatment developed in Paper II is here applied to a microporous medium with porosity varying with position in the direction of flow. It is assumed that diffusion in such a medium can occur in both pore and adsorbed phases without sensible disturbance of the adsorption equilibrium and that the relevant diffusion and distribution coefficients are constant. The case of gaseous Knudsen diffusion through microporous powder compacts formed by uniaxial compression is then considered in some detail. It is found that the time-lag anomalies, which characterize many experimental systems of this kind, can plausibly be ascribed hi large part to distance-dependent non-Fickian" diffusion behavior and interpreted qualitatively or semiquantitatively in terms of the present treatment."