Experimental evaluation of multistage direct contact membrane distillation system for water desalination

The performance of a multistage direct contact membrane distillation system (MS-DCMD) is experimentally investigated using a laboratory-scale three stages system. The effects of operating conditions on the system performance are studied for parallel, series, and mixed flow stages con-nections for the feed and coolant streams. Results showed that the productivity of the parallel flow arrangement is well-higher than the series and mixed flow arrangements due to fewer temperature changes from stage to another. The experimental investigation showed that maintaining the feed and permeate temperatures at the required values required high energy consumption for heater and chiller circulation baths due to the high conduction heat transfer between feed and permeate sides across the membrane of the DCMD stages. Energy analysis showed lower specific energy consumption and higher gain output ratio for the parallel flow arrangement of the MS-DCMD system operating at feed temperature around 60°C. Salt rejection factor of 99.7% had been achieved for feed salts concentration of 35 g/L.