Computational fluid dynamics simulations of solar-assisted, spacer-filled direct contact membrane distillation: Seeking performance improvement

Significant downstream performance reduction and concentration polarisation reduce direct contact membrane distillation (DCMD) efficiency. These challenges are not well researched since they are difficult to implement experimentally and numerically. Hence, this study examined the impact of solar absorbers and different spacer filaments upon DCMD performance. A 2D computational fluid dynamics model that considered simultaneous mass and heat transfer across the membrane and throughout the channels was developed to simulate water flux in DCMD modules under the use of solar absorbers and spacer filaments of various designs. The simulation outcomes were in excellent agreement with experimental results provided by two different studies, with the assisted solar absorber module and the spacer-filled module deviating <5 % and 3 % from the experimental results, respectively. A module equipped with the solar absorber membrane enhanced the DCMD performance better than a module with a solar absorber plate. The results also illustrated that a module with cylindrical detached spacer filaments improved DCMD performance more than a module with rectangular and semicircular attached spacers. Finally, it was shown that a module equipped with an integrated developed spacer and solar absorber membrane significantly enhanced water flux and both concentration and temperature polarisations, specifically when the inlet velocity was increased. Water flux and the temperature polarisation coefficient increased by 220 % in the integrated module, and the concentration polarisation coefficient decreased by 10 %. Moreover, the developed module resulted in a substantial increase in downstream performance.