Study on the heat and mass transfer in air-bubbling enhanced vacuum membrane distillation

Air-bubbling vacuum membrane distillation (AVMD) process was designed to boost the heat and mass transfer in membrane distillation (MD). Both effect of flow pattern on the performance of AVMD process and the heat and mass transfer mechanism in this process were studied in this paper. The results showed that the performance of VMD was improved obviously by air-bubbling method. The flux was doubled at certain feed velocity and gas/liquid proportion. The study showed that flow pattern was the key factor affecting the mass and heat transfer efficiencies. The heat transfer coefficients, corresponding to the two main flow patterns in AVMD process, bubbly flow hfbub=1.7527Retp0.4215Pr13μb/μw0.14λ/d and slug flow hfslu=0.0632Retp1.0420Pr13μb/μw0.14λ/d, were obtained and employed in the modeling of AVMD process. The modeling results showed that the theoretical prediction of flux aligned with experimental results well, in which the error was within ± 5%. Both variations of Temperature Polarization Coefficient (TPC) and Concentration Polarization Coefficient (CPC) in AVMD process were studied based on the obtained correlations. And the result showed that both TPC and CPC were significantly influenced by the flow patterns.