Enhancing Vacuum Membrane Distillation Performance via Asymmetric NACA 2412 Airfoil-Based Mixing Promoters

Even though vacuum membrane distillation (VMD) for low-temperature desalination is an innovative technology, industrial applications remain limited by the concentration and thermal polarization, and conventional passive spacers mitigate these issues at the cost of high hydraulic energy consumption. This article aims to reduce boundary-layer limitations using an asymmetric NACA 2412 cambered airfoil that acts as a passive mixer. The effect of the airfoil's angle of attack (AoA) was assessed in both upward and downward orientations, with airflow modeled at Reynolds numbers of Re = 1000 and 1500. The results show that the airfoil in the upward orientation was highly effective at directing airflow inducing flow separation and coherent wake structures within the boundary layer, while maintaining low form drag and a correspondingly small hydraulic penalty. The upward design at AoA = 12° improved the permeate flux by 14.6% compared to the zero-incidence baseline (AoA = 0°) at Re = 1500, reaching a permeate flux of 66.03 kg/m²h. This gain came at a modest hydraulic cost, with the channel pressure drop rising by only ≈10 Pa (from 13.33 to 23.52 Pa). These results indicate that the airfoil-based mixing promoter offers a favorable balance between flux enhancement and the hydraulic penalty, making it a promising passive design strategy for VMD channels.