Condensation, re-evaporation and associated heat transfer in membrane evaporation and sweeping gas membrane distillation
Condensation, re-evaporation and associated heat transfer in membrane evaporation and sweeping gas membrane distillation
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DOI：
10.1016/j.memsci.2014.11.002
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发表时间：
2015-02
影响因子：
9.5
通讯作者：
Shuaifei Zhao;Leigh T. Wardhaugh;Jianhua Zhang;P. Feron
中科院分区：
文献类型：
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作者：
Shuaifei Zhao;Leigh T. Wardhaugh;Jianhua Zhang;P. Feron
在膜蒸馏、膜冷凝、烟气脱水等工业过程中，水蒸气在膜中的传递是非常重要的。在这项研究中，我们研究了在低气体流量下膜蒸发和扫气膜蒸馏中的冷凝、再蒸发和相关的换热。研究发现，膜的冷凝和再蒸发都与膜的性质密切相关。传质阻力越小的膜，凝结越严重。冷凝层发生在分离层和模块中的主体气体之间。二次蒸发速率取决于液滴的总表面积、气提速度和气相温度。总传质系数随气体流量的增加而显著增加，而液体流量对总传质系数的影响有限。总传质系数随蒸发温度的升高而减小。由于水蒸气的凝结，传统的温度偏振效应量化方法可能不适用于低流量的SGMD。提高气体流量或蒸发温度可以有效地提高SGMD的蒸发效率，而液体流量对蒸发效率的影响有限。
Vapor transport through membranes is very important in many industrial processes such as membrane distillation (MD), membrane condensation and flue gas dehydration. In this study, we explore the condensation, re-evaporation and associated heat transfer in membrane evaporation and sweeping gas membrane distillation (SGMD) at low gas flow rates. It is found that both condensation and re-evaporation are closely related to the membrane properties. Condensation is more severe for the membrane with lower mass transfer resistance. The condensation layer takes place between the separation layer and the bulk gas in the module. The re-evaporation rate is determined by the total surface area of the droplets, the gas stripping velocity and the gas temperature. The overall mass transfer coefficient increases significantly with the increases of the gas flow rate, while the liquid flow rate has limited effect on the overall mass transfer coefficient. The overall mass transfer coefficient decreases with the increase in the evaporation temperature. The traditional way to quantify temperature polarization effect may not be applicable for SGMD at low gas flow rates because of vapor condensation. The increase in the gas flow rate or evaporation temperature can effectively improve evaporation efficiency (EE) in SGMD, while the liquid flow rate has limited effect on EE.