A novel solar-driven air gap membrane distillation system

Membrane distillation (MD) is a thermal-based membrane technology that is capable of treating highly concentrated or contaminated brines, including use as part of a zero liquid discharge desalination system. The low temperatures of operation of MD make it ideal to be used with solar energy as a heat source. However, current solar powered MD systems show poor performance and operate at low temperature compared to other thermal desalination systems. This paper describes a novel configuration of air gap MD which employs direct heating of the MD membrane by solar energy. The configuration provides a more uniform temperature profile over the membrane in the flow direction thereby enhancing vapor production. Heat transfer process modeling of the system shows that it can achieve a thermal efficiency that is nearly twice that of current solar powered MD systems.