Experimental investigations on Joule effect enhanced air gap membrane distillation for water desalination

For desalination by membrane distillation, direct current was applied to self-made conductive carbon membrane to produce Joule effect which can enhance the air gap membrane distillation process. Experimental results showed that the prepared coal-based carbon membrane has good structural stability within 100℃. In the experimental range, the rejection rate of carbon membrane for sodium chloride was over 99.96%, and the introduction of Joule effect during membrane distillation process would not produce additional membrane fouling. The Joule effect could increase the permeate flux up to 60%, and it gave better enhancement on the membrane distillation and higher electric conversion efficiency at low temperature. The introduced Joule heat can not only evaporate water but also increase the temperature of material and liquid, improving temperature polarization and increasing the driving force of mass transfer. The Joule effect also affects the mass transfer coefficient in the process of membrane distillation. When the feed temperature was 50-80℃, affected by Knudsen diffusion and molecular diffusion, the mass transfer coefficient would reduce at 1A current, and increase at 3A and 5A current. Meanwhile, the introduction of current into the carbon membrane will not damage the structure of the carbon membrane and the PDMS layer on its surface, and there is no synergistic effect such as REDOX in the carbon membrane. The research content of this paper enriches the methods of membrane distillation seawater desalination process and also provides a basis for simulation research and industrial application of the Joule effect affecting the membrane distillation process. © 2022, Editorial Board of CIESC Journal. All right reserved.