Heat and mass transport analysis of membrane distillation using thermal network method

In this study, we investigate membrane distillation (MD), which is a promising desalination technology. Conventional evaporation methods require seawater to be heated to its boiling point, and reverse osmosis (RO) methods require the liquid to be pressurized to a high pressure. MD is a technology that enables freshwater production without imposing high temperature and pressure conditions. This technology uses the phase transition of water in seawater to separate the generated water vapour from seawater using separation membranes with nanoscale pores. The driving force of the water vapour is the difference in water vapour pressure before and after passing through the separation membranes, which depends on the temperatures near both ends of the separation membrane surfaces. We analysed heat and mass transport by using a thermal network method assuming a 1D steady state. The network models were applied to a direct contact membrane distillation (DCMD) and a permeate gap membrane distillation (PGMD) and compared with experimental values for distillation simply using pure water. The results show that, for the temperatures, the experimental and calculated values agreed about the membrane surface temperatures within approximately 7.5 % to 15 % of the temperature difference between the hot water and cooling water temperatures, and for the permeate fluxes, the experimental and calculated values were consistent within 25 % of the calculated values.