The Effect of a Pulsed Flow Inlet on Vacuum Membrane Distillation Performance

Abstract

Abstract 2D Large Eddy Simulations (LES) were run to determine the effect of multiple hydrodynamic optimizations on a vacuum membrane distillation module (VMD). The first optimization considered is a morphology change from a straight channel wall to a sinusoidal one. The second change is a pulsed mass flow at the inlet — similar to adding turbulent energy to the incoming flow. Two different Reynolds/Strouhal numbers were considered, 1,500 (0.24) and 750 (0.48). Three pulsation amplitudes were considered 15%, 25%, and 50% of the base inlet velocity. Simulation results show that by only having one performance increase, going from flat to wiggly, the flux increased by 23% of the baseline value, while both the wiggly channel with pulsations showed a flux increase of 31% of the baseline value. The increase is because the vortex shedding in the wiggly channel reduces temperature polarization near the membrane surface. As pulsations are introduced into the wiggly channel, the flow separates earlier, and more of the channel experiences mixing vortices. In the flat sheet case with no geometric alterations, there is no flow separation regardless of a pulsed inlet.