Improved model structure of direct contact membrane distillation for saline water purification

Abstract

A pilot plant comprising membrane distillation is tested for coordinated inlet temperature for the feed and cold streams with a fixed difference. Selected inlet temperature differences of 30, 40, and 50 °C were examined. It is found that water production increases with both temperature difference and inlet feed temperature. Specifically, the water production at a temperature difference of 50 °C can be 13%, and 30% higher than that at a temperature difference of 40, and 30 °C, respectively. The measurements of the mass flux were used to validate the internal mass and heat transfer equations which proved to provide an excellent prediction of the water production with up to 3.7% average error. The measurements of the exit temperature of the brine and permeate streams were used to confirm the macroscale heat balance equations. They revealed a considerable discrepancy between the heat supplied by the feed stream and the heat transferred between the two channels as well as between the heat gained by the cold stream and the heat supplied. The first discrepancy is ascribed to the existence of environmental heat loss at the feed side. The second discrepancy is attributed to the existence of environmental heat loss and the contribution of the heat of condensation to additionally warm up the cold stream.