Theoretical and experimental validation of water gap membrane distillation

Theoretical and experimental validation of a water gap membrane distillation (WGMD) process has been proposed and successfully tested for seawater desalination. It has been observed that, employing water in the air gap between the membrane and condensation plate of an air gap membrane distillation (AGMD) module, there is a significant enhancement of the water vapor flux, reaching 800 %. A detailed investigation on the influence of thickness of the water gap has been carried in this study. Water vapor flux enhancement in the WGMD process has been described with the help of a theoretical explanation of heat and mass transfer mechanisms through the membrane and water gap. Heat and mass transfer resistance in the air gap during an AGMD process is the major limiting factor for the lower water vapor flux. It was observed that employing water in the air gap of an AGMD module eliminates the heat and mass transfer resistance in the air gap and results in increased water vapor flux. Temperature polarization is another phenomenon which adversely affects all MD processes and causes a significant decrease in the water vapor flux. During the WGMD process, occurrence of natural convection in the water gap helps to decrease the temperature polarization and provide a synergistic effect along with the sensible heat transfer to enhance the water vapor flux. A theoretical explanation of the natural convection during the WGMD process will be described in this paper.