Modelling transport mechanism through a porous partition

The physical nature of water flow, in vapour phase, through the pores of a microporous partition has been studied according to the possibilities suggested by the Kinetic Theory of Gases. A method is proposed that permits to decide which is the most reasonable possibility for the transport mechanism. In order to check the proposed model, the phenomenon of membrane distillation has been studied with four commercial membranes, in different experimental conditions. The influence of some relevant parameters, such as mean temperature and stirring rate, has been considered. Tile quantitative influence of the unstirred boundary layers, adjoining both faces of the membrane, has been taken into account. The calculations show that, apparently, the water flux is composed of two contributions: a Knudsen type flux plus a diffusive one.