Experimental and numerical investigation of vacuum membrane distillation: Effects of Reynolds number and feed temperature on mass transfer, polarization, and energy consumption

This study investigates vacuum membrane distillation through integrated experimental measurements and three-dimensional Computational Fluid Dynamics (CFD) simulations across Reynolds numbers of 200 to 2400 and feed temperatures of 40 °C and 50 °C using polytetrafluoroethylene membranes. The CFD model solves the momentum, heat, and mass transfer equations without empirical correlations. Mass flux ranged from 14.68 to 21.48 kg/m 2 h at 40 °C and from 17.9 to 32.7 kg/m 2 h at 50 °C, representing 22–52 % enhancement at elevated temperatures owing to the exponentially higher vapor pressure. Temperature polarization decreases from 0.4 to 0.6 at low Reynolds numbers to 0.8 – 0.9 at high Reynolds numbers. Concentration polarization coefficients decrease from 1.4 to 1.6 to 1.1 – 1.15, demonstrating that enhanced convective mixing mitigates boundary layer effects. Nusselt and Sherwood numbers exhibit inverse relationships with temperature due to Stefan flow effects, with values 10 – 15 % higher at 40 °C. Energy consumption ranges from 663 to 917 kWh/m 3 , stabilizing at 680 – 700 kWh/m 3 at high Reynolds numbers. Scanning electron microscopy reveals maximum salt deposition at the channel entrance due to highest local flux and vacuum-induced instantaneous evaporation under 4 kPa permeate pressure. The CFD predictions demonstrate good agreement with experimental measurements at 40 °C with typical deviations of 5 – 10 %. The results establish that Reynolds number enhancement and temperature elevation both increase productivity under laminar flow conditions relevant for energy-efficient vacuum membrane distillation systems. • Temperature polarization level enhanced from 0.6 to 0.95 with increasing Reynolds number. • Optimized VMD achieves 56 % higher flux at 50 °C compared to 40 °C. • 3D CFD model, free of empirical correlations, deviates <8 % from experimental data. • 50 °C vs. 40 °C: 56 % higher flux, lower energy (680 vs. 690 kWh/m 3 ).