Conjugate heat and mass transfer in vacuum membrane distillation for solution regeneration using hollow fiber membranes

To avoid problems such as low efficiency of liquid desiccant processes in high humidity environments, vacuum membrane distillation (VMD) solution regenerators are proposed. This study investigates the conjugate heat and mass transfer mechanism in the vacuum membrane distillation solution regeneration. The study reveals that the solution temperature and concentration in the hollow fiber membrane tube exhibit a tower -shaped distribution, with the lowest temperature near the membrane surface and the highest concentration at the outlet. The membrane flux decreases along the direction of the solution flow, ranging from 0.62 to 0.36 g/(m2 & sdot;s). Increasing the solution flow rate and vacuum degree enhances the heat and mass transfer, while increasing the solution concentration reduces the heat and mass transfer. The Nusselt and Sherwood number formulas applicable to the VMD solution regeneration process were fitted, which is more accurate than the empirical formulas at atmospheric pressure. The resistance distribution during the solution regeneration process in VMD shows that the membrane -side resistance has a significant impact on the heat and mass transfer during solution regeneration, with the membrane -side thermal resistance accounting for 91 % of the total resistance in the heat transfer process and 67 % in the mass transfer process. The findings in this paper can more accurately guide the design of vacuum membrane distillation solution regenerators.