A polyvinylidene fluoride (PVDF)–silica aerogel (SiAG) insulating membrane for improvement of thermal efficiency during membrane distillation

Abstract

Membranes with low thermal conductivity for membrane distillation (MD) can decrease heat conduction and improve thermal efficiency, which is important for MD applications. Silica aerogel (SiAG) was employed for blending with polyvinylidene fluoride (PVDF) to fabricate PVDF-SiAG insulating membranes in this study. The effects of SiAG addition on membrane characteristics and heat transfer during MD testing were investigated. The addition of SiAG resulted in an increase in mean pore size and thickness. Total thermal conductivity of the membrane decreased from 0.111 to 0.083 W/(m·K). Theoretical calculation and modeling illustrated that the thermal conductivity of the membrane material (mixture of PVDF and SiAG) decreased from 0.190 to 0.135 W/(m·K) because of low thermal conductivity of SiAG. For MD testing, permeate flux increased by 50% as did latent heat, and the conduction of heat decreased from 19.68 to 10.90 kW/m2. The thermal efficiency increased from 22.01% to 42.81%. Permeate flux kept stable and salt rejection was higher than 99.99% during 24-h-MD test. The PVDF-SiAG insulating membranes improved thermal efficiency remarkably and have a great potential for industrial applications of MD.