Effective suppression of concentration polarization by nanofiltration membrane surface pattern manipulation: Numerical modeling based on LIF visualization

This study attempts to advance the understanding of concentration polarization (CP) suppression by patterned membranes during nanofiltration. A validated Computational Fluid Dynamics (CFD) model was established to study the suppression effect and its mechanisms by evaluating CP development over time. Triangular and cambered membrane surface patterns were designed to investigate the real-time evolution of CP and suppression effect during nanofiltration in comparison with the control flat membrane, while the model was firstly experimentally validated by in-situ Micro Laser-Induced Fluorescence (Micro-LIF). Preliminary simulation results confirmed a significant effect microstructured membranes had on the control of CP evolution by disturbing the flow field near the microstructures. An investigation of the concentration distribution revealed that the maximum concentration accumulation on the patterned surface was reduced by 10–12% compared to that on the flat membrane surface, while the cambered membrane performed better than the triangular membrane. By comparison with the flat membrane, the minimum mass transfer coefficient increased by 3.3 times, and the CP factor reduced by 50% on the cambered surface. Moreover, the dynamic velocity distribution showed the existence of the disturbed flow and vortex around the patterned membrane surface, and shear stresses were further qualified to explain the suppression mechanism. This detailed numerical study is of practical significance to improve understanding of CP suppression by the optimized morphologies.