Modeling and Optimization of Photothermal Membrane Distillation Incorporating Reverse Temperature Polarization

This study explores photothermal membrane distillation (PMD) to enhance the energy efficiency of solar-driven desalination. A carbon black embedded nanophotonic membrane is used that enables direct solar energy absorption at the membrane surface. Three commercial membranes, PE (Polyethylene), PVDF (Polyvinylidene fluoride), and PTFE (Polytetrafluoroethylene), each coated with a 5.5 wt % carbon black photothermal layer, are examined. A comprehensive analytical model incorporating fluid flow, heat transfer, and mass transfer was developed and experimentally validated to evaluate the optimized distillate production and gain output ratio (GOR). The results show that the PMD outperformed both distillate production and GOR compared to conventional membrane distillation (MD). Production of water increased with membrane length, solar power, and temperature, while higher feed Reynolds numbers reduced performance due to convective losses. Pore sizes greater than 0.15 μm improved flux up to the continuum region. Higher porosity enhanced permeability, whereas increased thickness decreased flux. Minimizing the flow gap below 2 mm optimized localized heating and vapor pressure gradients. The optimal configuration identified was a pore size of 0.15 μm, 90% porosity, 50 μm thickness, laminar feed flow (Re = 500), and module dimensions of 200 x (10–16) cm.