An experimental review on coupling of solar pond with membrane distillation

•The permeate mass flux across the membrane is at the high rate of 6l/m2/hr.•The coupled system delivers 1.2×10−3m3 of fresh water per m2 of membrane and m2 SGSP.•The trans-membrane coefficient of the used PTFE membrane is about 0.001l/m2/Pa/hr.•Experimental data corresponded well with 15% accuracy of the flux of Knudsen diffusion. The interest of using solar powered membrane distillation systems for desalination is growing worldwide due to the membrane distillation (MD) attractive features. This study experimentally investigates the utilization of direct contact membrane distillation (DCMD) coupled to a salinity-gradient solar pond (SGSP) for sustainable freshwater production and reduction of brine footprint on the environment. A mathematical model for heat and mass flux in the DCMD module and thermal model for SGSP are developed and coupled to evaluate the feasibility of freshwater production. The experiment results on RMIT University SGSP coupled with DCMD are presented. The feed stream of 1.3% salinity is heated up by the SGSP and circulated through DCMD module then injected to an evaporation pond. Also, a thermal energy system is used to recover heat from the outlet brine stream of DCMD and use it as preheating for inlet feed water stream. Results are compared and showed that if the flow is laminar, the connecting DCMD module to the SGSP could induce a marked concentration and temperature polarisation phenomenon that reduces fluxes. Therefor turbulence has to be created in the feed stream to reduce polarisation. Also, to reduce the environmental footprint, the brine is recirculated after passing through the heat exchanger.