Abstract

2D Large Eddy Simulations (LES) were conducted to study the effect of channel geometry on the Vacuum Membrane Distillation process. The geometry was altered by imposing a sinusoidal (“wiggly”) wall profile. The results of the study show at a critical Reynolds number between 750 and 1,000, transient vortices appear in the channel. As the Reynolds number is increased from 1,000 to 1,500, the origin of the vortices moves further upstream, and the frequency and intensity of the vortex activity increase. Areas, where vortex shedding provides mixing, serve to enhance the performance of membrane distillation profoundly. The mixing reduces temperature and concentration polarization along the membrane surface. With better mixing provide at Reynolds number 1,500 versus 1,000, the difference in performance versus the corresponding flat sheet membrane case is increased. The vapor flux in the wiggly channel module increases 6% at Reynolds number 1,000 and 22% at Reynolds number 1,500 compared to the flat channel module. The change in flux is from 61.6 to 65.7 kg/m2/h at Reynolds number 1,000 and 66.5 to 81.4 kg/m2/h at Reynolds number 1,500. Temperature polarization was also mitigated at Reynolds number 1,500 even though the flux was increased.

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