Comparison of the Effect of Air and Permeate Gap Regions on Highly Saline Water Desalination Using Hollow Fiber Membrane Distillation Modules

Abstract

The present research work discussed the impact of permeate gap region (PGR) on the high mass transfer resistance and low productivity resulted from the air gap region (AGR) sandwiched between the membrane and condensing surface in the air gap membrane distillation (AGMD). Two hollow fiber permeate gap (PGMD) and air gap membrane distillation (AGMD) modules were built, examined, and compared experimentally under several operating parameters such as feed salt concentration (Cf), feed temperature (Tf), coolant temperature (Tc), and flow rate (Mf). The performance comparison was done according to the values of energy consumption (STEC), water productivity (Pw), waste heat (QH.I), and gained output ratio (GOR). Results showed that the PGR was more effective than AGR on the membrane module performance at all investigated operating parameters. Under operating parameters of Cf = 7.5 g/L, Tc = 15 oC, Tf = 70 oC, Mf = 4 L/h, and compared with AGR, the PGR minimized STEC and QH.I by around 78.32% and 47.06%, and improved the Pw and GOR by about 95.93% and 90.33%, respectively. Thus, the negative gap region effect could vanish completely by filling it with the permeated water instead of air, promoting by which the performance of the membrane distillation module remarkably.