Improving MD flux prediction in Janus membranes: The critical role of membrane-specific evaporation enthalpy in CFD modeling

Although Janus membranes have shown excellent anti-wetting and fouling-resistant properties in membrane distillation (MD), the associated heat and mass transfer mechanisms remain insufficiently understood, particularly concerning the trade-off between fouling resistance and permeate flux. In this study, a Janus membrane was fabricated by depositing a polyamide (PA) layer onto a polyvinylidene fluoride (PVDF) substrate to form a PA/PVDF composite. To elucidate the mass transfer behavior, an enhanced computational fluid dynamics (CFD) model, considering the effects of membrane material and surface temperature on evaporation enthalpy, was developed to simulate MD performance using both PA/PVDF and pristine PVDF membranes. When assuming a constant evaporation enthalpy of free water (FW) (2.44 MJ·kg −1 ), the modeled and experimental fluxes matched closely for the PVDF membrane, while a flux deviation exceeding 10 % was observed for the PA/PVDF membrane. Accounting for the membrane-specific evaporation enthalpy reduced the deviation to 0.59 %, emphasizing its critical role in flux prediction. These results highlight the importance of incorporating membrane-dependent thermodynamic properties to improve MD modeling accuracy and guide the rational design of Janus membranes.