An integrated module with synergistic heating and turbulence promotion for enhanced vacuum membrane distillation

Abstract

Conventional membrane distillation (MD) experiences 50–80 % flux reduction due to temperature polarization (TP), while metallic heat exchangers are susceptible to corrosion when treating high-salinity feeds. To address these limitations, an integrated heat-exchange vacuum membrane distillation (IHEVMD) module was developed by incorporating polymer-based heat-exchange tubes within the MD process, enabling simultaneous in-situ feed heating and distillation. Heat transfer performance and MD flux were thoroughly examined in relation to heat-exchange temperature, heat-exchange area, feed, and heat-exchange fluid flow rates. Results demonstrate that the total heat transfer rate (Q) and overall heat transfer coefficient (K) are governed by the heat-exchange temperature and feed flow rate. The flux in MD was favorably influenced by the temperature and membrane area. The IHEVMD module D achieved an 83 % flux enhancement at 56 °C compared to conventional MD, along with a 90 % improvement in gained output ratio (GOR) and a 50 % reduction in specific thermal energy consumption (STEC). Notably, the module exhibited superior performance with high-salinity feeds (e.g., 3.5 and 5 wt% NaCl), leveraging brine's lower specific heat capacity for higher feed temperatures and fluxes. Long-term stability tests confirmed effective TP mitigation and anti-fouling properties. This work provides an energy-efficient, corrosion-resistant strategy for high-salinity water treatment utilizing low-grade heat sources.