Nature of flow on sweeping gas membrane distillation

The process of sweeping gas membrane distillation (SGMD), with the liquid feed and the sweeping gas counterflowing in a plate and frame membrane module, has been studied. A theoretical model, which was presented in a previous paper and permitted to obtain the temperature profiles inside the fluid phases, has been developed in order to analyse the physical nature of the transmembrane water flux. Two porous hydrophobic membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as the inlet and outlet temperatures or the circulation velocities of the fluids, has been studied. The experimental results have been analysed according to the model and the conclusion is that the water transport takes place, apparently, via a combined Knudsen and molecular diffusive flow mechanism. From the temperature profiles, a local temperature polarisation coefficient may be defined. From this local value, an overall one for the whole system is then defined. The new theoretical predictions have been applied to the obtained results and the accordance may be considered good. (C) 2000 Elsevier Science B.V. All rights reserved.