Assessing the performance of solar thermal driven membrane distillation for seawater desalination by computer simulation

A computer model was developed to simulate the performance of an integrated solar thermal driven direct contact membrane distillation (DCMD) system for seawater desalination using recorded weather data. The results highlight the importance of simulating the DCMD process together with the energy source. Indeed, when considered in isolation from the thermal energy source, increasing water cross flow velocities in the feed and distillate channels results in an increase in water flux and thermal efficiency of the DCMD module. By contrast, when coupling the DCMD module with the solar thermal collector, increasing water cross flow velocities reduces both the process water flux and thermal efficiency. This is because of the limited supply of solar thermal at any given time, and hence the feed temperature decreases when cross flow velocities increase. Thus, any benefits in the reduction of temperature polarisation due to increasing cross flow velocities are overwhelmed by the effects of feed temperature decrease on water flux and thermal efficiency. Results from our simulation also demonstrate the viability of the solar thermal driven DCMD process for small-scale seawater desalination applications. Distillate production is dependent on the availability of solar radiation during the day; nevertheless, a small system with a 7.2 m2 spiral-wound DCMD module and a 22.6 m2 flat plate solar thermal collector can produce over 140 kg of distillate each day under real weather conditions. This is equivalent to a daily distillate production rate of 19.7 kg per m2 of membrane or 6.3 kg per m2 of solar thermal collector