Gas permeation and direct contact membrane distillation experiments and their analysis using different models

Gas permeation experiments using helium, air and argon and direct contact membrane distillation (DCMD) experiments using distilled water are reported. From gas permeation experiments the characteristic parameters of the Knudsen and Poiseuille transport mechanisms were determined. Such parameters were extrapolated in order to obtain the values corresponding to water vapour and these were used to estimate theoretical fluxes in DCMD processes employing two different models, one proposed by Schofield et al. (with some improvements) and another one according to the "Dusty-Gas" literature. In both models, the different transport mechanisms: ordinary diffusion, Knudsen flow and Poiseuille flow were taken into account. A good agreement between the experimental fluxes and their theoretical predictions was found. A comparison between both models was also carried out. It was proved that in both models the viscous flow could be neglected under our experimental conditions. (C) 2002 Elsevier Science B.V. All rights reserved.