Investigation of different hollow fiber module designs for flux enhancement in the membrane distillation process

In this paper, the flux enhancement effects of different hollow fiber membrane module designs with baffles, spacers and modified hollow fiber geometries were investigated through the direct contact membrane distillation process applied for desalination. By modeling the transport phenomena involved in the process, feed-side heat-transfer coefficient for modules with different baffles were estimated. It was found that the application of baffles can increase the feed-side heat-transfer coefficient from 2600 W/(m2 K) for the unbaffled module to 3150 and 3750 W/(m2 K) for the window and helical baffles, which correspond to 20% and 28% flux enhancements, respectively. In addition, it was observed that using spacers among the fibers may increase the effective membrane area 18–33%. Lastly, the application of different hollow fiber configurations with wavy geometries (twisted and braided) led to flux enhancements as high as 36% without inserting any external turbulent promoter. In overall, greater flux enhancements with modified hollow fiber membranes modules were achieved at higher feed temperatures. The proposed approaches in this study may be efficiently and easily applied to enhance the flux in industrial applications involving membrane distillation with hollow fiber membranes.