The effect of turbulence promoters on vacuum membrane distillation module performance

Computational fluid dynamic simulations are conducted to compare the performance of three proposed VMD module designs. Key parameters, including concentration polarization coefficient (CPC), temperature polarization coefficient (TPC), mass flux, and module pressure drop, are evaluated to analyze flux performance and membrane wetting implications. The CFD simulations are conducted on a three-dimensional domain for each design with representative membrane properties. The Reynolds numbers evaluated are 500 and 1500. Contour plots are provided to gain insight into the flow-field characteristics. Stream-wise profiles and average values are provided as a means to compare the design performance. The results indicate that adding either net-type spacers or membrane corrugation to the feed channel provides performance enhancement over an empty channel design. It is found that both the net-type spacer concept and the corrugated membrane offer better flux performance over the baseline design (49% - 60% for the net-type spacers and 62% - 67% flux enhancement for the corrugated membrane), reduced concentration polarization coefficient (51% for the Re = 500 case and 45% for the Re = 1500 case for spacers and 58% for the Re = 500 case and 49% for the Re = 1500 case for corrugation), increased TPC (2% - 3% higher), and increased wall shear stress over the baseline design. The most significant finding is that the corrugated membrane design accomplishes the listed performance improvement while yielding five times less pressure drop increase than the net-type spacer design.