Abstract
The isothermal and isobaric flow of pure gases and vapors through microporous Vycor glass was investigated under such conditions that the gasβphase flow occurred by Knudsen diffusion. The isothermal flows and the isobaric flow of nonadsorbed gases are correlated by existing relationships.
On the assumption that surface flow is a diffusive process and that equilibrium exists between the vapor and solid throughout the porous media, a correlation for the nonisothermal surface flow is developed. The factors determining the rate of surface flow are the physical properties of the solid, the temperature level and gradient, the enthalpy of adsorption, the surface concentration and spreading pressure of the adsorbed phase, and the activation energy and coefficient of resistance for surface diffusion. The latter two factors can be evaluated from isothermal surface flow measurements; hence no new arbitrary constants are required in the correlation. Agreement between predicted and measured surface flows is good for ethylene and propylene at a mean temperature of 25Β°C. Both the gasβphase and surface flows are from the cold to hot end of the porous solid.
It is suggested that the use of temperature gradients in porous solids and plastic films for separating mixtures of vapors be investigated.