Harnessing buoyancy-driven instabilities for enhanced membrane desalination

美国的工业活动产生了大量复杂的废水，这些废水的处理具有挑战性，因为它们含有高浓度的溶解盐类。这些废水通常排放到当地地表水、下水道、水井和地表，在那里它们污染资源和生态系统。该项目使用计算机模拟和实验室实验相结合的方法来开发一种名为膜蒸馏的高级水处理工艺，该工艺可以淡化和回收复杂的废水。具体地说，我们证明了可以利用重力来改善膜蒸馏中的混合，并使可再生太阳能的使用能够减少能源消耗。综合教育活动包括高中生暑期实习、本科生研究活动、编写免费教科书和组织学生研究研讨会。膜蒸馏是一种热脱盐过程，在膜蒸馏过程中，水蒸发并通过多孔膜去除盐分。这项拟议的工作解决了膜蒸馏两个长期存在的技术挑战。首先是膜附近的水冷却，这会减缓蒸发和淡水的回收。第二种是溶解的盐类在膜附近堆积，在那里沉淀并堵塞膜。我们解决这些问题的方法是调整膜的方向，使重力使富含盐分的凉水从膜上沉淀下来，在废水中产生浮力混合。我们还表明，通过与膜相对的表面主动加热废水，可以加强这种混合。为此，拟议的工作使用计算流体力学和小规模实验来(1)阐明浮力混合的物理原理；(2)探索利用电力或可再生太阳能主动加热废水的最佳方法；以及(3)针对日益受到关注的真实世界的市政和工业废水来验证该过程。我们预计这项工作将通过缓解水资源短缺和改善海水淡化过程的环境可持续性来广泛影响社会，并将关键应用于能源-水-气候关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Industrial activities in the United States generate large volumes of complex wastewaters that are challenging to treat, because they have a high concentration of dissolved salts. These wastewaters are often discharged to local surface waters, sewers, wells, and land surfaces, where they contaminate resources and ecosystems. This project uses a combination of computer simulations and laboratory experiments to develop an advanced water treatment process called membrane distillation, which can desalinate and recycle complex wastewaters. Specifically, we show that gravity can be harnessed to improve mixing within membrane distillation, and enable the use of renewable solar energy to reduce energy consumption. Integrated educational activities include summer internships for high-school students, undergraduate research activities, the development of free textbooks, and the organization of student research symposia.Membrane distillation is a thermal desalination process in which water evaporates and travels through a porous membrane that removes salts. The proposed work solves two long-standing technical challenges of membrane distillation. The first is cooling of the water near the membrane, which slows evaporation and the recovery of freshwater. The second is the accumulation of dissolved salts near the membrane, where they precipitate and clog the membrane. We address these issues by orienting the membrane so that gravity causes cool, salt-rich, water to sink away from the membrane, generating buoyant mixing within the wastewater. We also show that this mixing can be strengthened by actively heating the wastewater through a surface opposite the membrane. To that end, the proposed work uses computational fluid dynamics and bench-scale experiments to (1) elucidate the physics of the buoyant mixing; (2) explore optimal methods of actively heating the wastewater using electricity or renewable solar energy; and (3) validate the process against real-world municipal and industrial wastewaters of growing concern. We expect the work to broadly impact society by mitigating water scarcity and improving the environmental sustainability of desalination processes with critical applications to the energy-water-climate nexus.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.