Effect of module design and flow patterns on performance of membrane distillation process

•Effect of fiber configurations and flow patterns on MD performance has been studied.•Undulating fibers show best performance in terms of flux at low feed flow rates.•Helical modules and intermittent flows exhibit better energy efficiency.•Intermittent and pulsatile flows are the best optimum. The present study highlights the effect of different hollow fiber membrane configurations and flow patterns on performance of membrane distillation (MD) process. The modules with helical and wavy conformations have been tested under various hydrodynamic conditions and their performance has been compared with conventional straight fiber modules. The effect of flow patterns has been studied by applying the intermittent and pulsating flows to straight hollow fiber membranes. A flux enhancement of 47% and 52% with respect to the straight fibers has been observed for helical and wavy configurations, respectively, though packing density of such modules is significantly less than their straight counterparts. For intermittent flow, an improvement of ∼30% has been recorded. The difference is more prominent at low flow rates and approaches to the straight fiber performance under steady flow at high Reynolds numbers (Re) for all hollow fiber configurations and flow patterns studied. The intermittent flow and wavy fibers exhibit an energy efficiency enhancement of ∼180% and ∼90% over their conventional counter parts, respectively. In terms of surface and volume based enhancement factor and packing density, intermittent and pulsating flow exhibited the most optimal performance.