The heat and mass transfer of vacuum membrane distillation: Effect of active layer morphology with and without support material

• Heat and mass transfer on vacuum membrane distillation (VMD) have been analyzed.
• Mass transfer coefficient and temperature polarization coefficient (TPC) were calculated.
• A dead-end feed VMD set-up was used for model validation.
• TPC is close to unity at low feed temperature and decreases with increase of evaporation flux.
• Membrane with or without support shows a large difference on tortuosity values, which greatly affect the mass transfer.

The aim of this research was the analysis of heat and mass transfer in vacuum membrane distillation (VMD), specifically for a dead-end feed set-up. The influence of support material on the supported membranes VMD performance was identified. A mathematical model was proposed to evaluate the membrane/feed interface temperature, membrane tortuosity, membrane mass transfer coefficient, and temperature polarization coefficient (TPC). The model was solved by an excel solver based on experimental results of feed temperature, system pressure and the evaporative fluxes. The SEM images showed that the thickness of unsupported membrane was reduced by 42% after the VMD test. Pore shrinkage and tortuosity increase were also expected during this pore collapsing process. On the other hand, the cross-sectional views of the supported membranes did not show significant changes. These results show that the support material can help prevent the membrane pore channel structure from collapsing during the VMD experiment. TPC is close to unity at low feed temperatures. However, it decreases with an increase in evaporation flux as the feed temperature increases, or when a high flux supported membrane is applied.

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