Wetting indicators, modes, and trade-offs in membrane distillation
Wetting indicators, modes, and trade-offs in membrane distillation
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DOI：
10.1016/j.memsci.2021.119947
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发表时间：
2021-10
影响因子：
9.5
通讯作者：
Allyson L. McGaughey;Amy E. Childress
中科院分区：
文献类型：
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作者：
Allyson L. McGaughey;Amy E. Childress
在这项研究中，我们提出并演示了一种简单的溶质质量平衡，以确定几种膜材料在基线和润湿条件下膜蒸馏中的蒸气通量和液体通量。我们观察到，由于实验人为因素，馏出液盐度会增加，但液体通量可用于最终诊断润湿、量化润湿率并指示润湿孔隙的相对数量。我们确定了两种润湿模式：“恒定润湿”，其特征是增加馏出液盐度和恒定液体通量；以及“增加润湿”，其特征是增加馏出液盐度和增加液体通量。持续润湿表明孤立的孔隙在整个操作过程中保持润湿，而增加润湿表明随着时间的推移，更多的孔隙被润湿。在低液体通量下可以容忍持续润湿，无需干预并且不会导致润湿阻力和产水量之间的权衡。相反，增加润湿需要干预。减小膜孔径或增加厚度可以增加润湿阻力并延迟液体通量，但也可以减少蒸汽通量，从而导致润湿阻力和蒸汽通量之间的权衡。这些结果为膜蒸馏中的润湿模式和权衡提供了新的理解，并可以指导传统和具有挑战性的应用的膜设计和操作。
In this study, we propose and demonstrate a simple solute mass balance to determine vapor flux and liquid flux in membrane distillation for several membrane materials under baseline and wetting conditions. We observe that distillate salinity can increase due to an experimental artefact, but that liquid flux can be used to conclusively diagnose wetting, quantify wetting rates, and indicate the relative number of wetted pores. We identify two wetting modes: “constant wetting”, characterized by increasing distillate salinity and constant liquid flux, and “increasing wetting”, characterized by increasing distillate salinity and increasing liquid flux. Constant wetting indicates that isolated pores remain wetted throughout operation, while increasing wetting indicates that more pores wet over time. Constant wetting may be tolerable at low liquid flux, requiring no intervention and resulting in no trade-off between wetting resistance and water production. In contrast, increasing wetting requires intervention. Reducing membrane pore size or increasing thickness can increase wetting resistance and delay liquid flux – but can also reduce vapor flux, resulting in trade-offs between wetting resistance and vapor flux. These results provide new understanding of wetting modes and trade-offs in membrane distillation and can guide membrane design and operation, for conventional and challenging applications.