An electro-thermal braid-reinforced PVDF hollow fiber membrane for vacuum membrane distillation

In membrane distillation (MD) process, the unfavorable effect due to latent heat of vaporization is the creation of a temperature difference between the feed bulk and the membrane surface, which is called temperature polarization (TP). This phenomenon causes a decrease of membrane surface temperature, and ultimately, induces a loss in driving force for mass transportation. In this study, a kind of electrical heating wire (nichrome resistance wire, NRW) was introduced into braid-reinforced polyvinylidene fluoride (PVDF) hollow fiber membrane (HFM), aiming to suppress the TP in MD process by localized heating the membrane surface. Results showed that the PVDF/NRW HFM surface temperature increased from room temperature to 70 degrees C by applying a pretty low direct current (0.15 A). In comparison to the membrane without electricity applied, the electro-thermal membrane (a current of 0.15 A) showed up not only about 2.5 times enhancement in permeate flux, but also the lowest specific energy consumption (SEC), while the salt rejection maintained above 99.0%. Meanwhile, owing to the electro-thermal effect, the value of temperature polarization factor (TPF) was higher than 100%, which demonstrated the effective suppression of temperature polarization.