THE FLOW OF FLUIDS THROUGH ACTIVATED CARBON RODS: III. THE FLOW OF ADSORBED FLUIDS

Abstract

Total flow rates of gases through activated charcoal rods are regarded as consisting of the sums of comparatively independent flows through macropores and micropores. The flow rate through the macropore system is related to the relevant adsorption isotherm by means of an empirical equation having three arbitrary constants. The empirical equations can be fitted to all of our observed results within the experimental error. Assuming that the adsorbate behaves as a one-component fluid such as a gas in a gravitational field, it is shown that compressive surface forces give rise to large fluid pressures within micropores. A very simple flow equation is derived which is qualitatively in agreement with observed results and which indicates a mean micropore diameter, of the order of 10−7 cm. The derived equation illustrates the nature of the physical factors involved and shows that surface forces may increase flow rates of adsorbable gases by very large factors. The increased flow rates are due mainly to the greatly increased densities and to the increased pressure gradients resulting from the action of surface forces. A model porous adsorbent is presented which exhibits many properties of real adsorbent systems and illustrates especially the relations between adsorbate densities and the various tensions and pressures existing within micropore systems.