Electrowetting-assisted Dropwise Condensation on Hybrid Superhydrophobic-Hydrophilic Surfaces

火力发电厂消耗的水占美国淡水总取水量的40%。这是不可持续的；因此，电力公司需要更节水的冷却方法。供暖、通风和空调（HVAC）系统也受到低效冷却技术的影响，导致能源需求过高。在这些应用中，当水蒸气在金属表面凝结形成连续的液体膜时，废热被除去。与金属相比，这层水导热性差，因此降低了系统效率。然而，如果金属表面被修改为排斥水，蒸汽将以液滴的形式凝结，在形成连续的液体膜之前从表面滚下。轧制后，金属表面重新暴露。这提高了性能，减少了冷却水的消耗；提高电气效率；并减少了生产过程对环境的影响。这些优点导致了更小的冷凝器，减少了资本和运营支出。在这个NSF项目中，我们制造了一种新型的冷凝器表面，通过超疏水性和电润湿的结合来促进液滴冷凝，从而提高火力发电和暖通空调的能源效率。采用模拟与实验相结合的方法，研究了电润湿性、气体扩散、热输运和Marangoni对流等现象对Cassie态稳定性的影响。这需要捕捉变形半月板的影响，一旦液相达到前进的接触角，移动三重接触线。研究了超疏水织构表面上ew诱导的泵浦现象。分析了新型泵送结构，其中交流电场在液滴上诱导体力和扭矩以启动其滚动。在超疏水表面上。与开发耐用、可扩展、用于水滴冷凝的聚合物涂层相关的材料/制造问题也进行了研究，并将通过与当地高中学生的联系进行分享。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Water consumed by thermal power generation stations accounts for 40% of total US freshwater withdrawal. This is non-sustainable; hence, electric utilities need more water-efficient methods for cooling. Heating, ventilation and air conditioning (HVAC) systems also suffer from inefficient cooling technologies, resulting in excessive energy demands. In these applications, waste heat is removed when water vapor condenses on a metal surface forming a continuous liquid film. This layer of water conducts heat poorly, compared to the metal, and so decreases system efficiency. However, if the metal surface is modified to repel water, the vapor will condense in the form of droplets that roll-off the surface before forming a continuous liquid film. After rolling off, the metal surface is re-exposed. This results in enhanced performance that reduces cooling water consumption; increases electrical efficiency; and lessens the environmental impact of the process. These benefits result in smaller condensers and reduced capital and operational expenditures.In this NSF project, we fabricate novel condenser surfaces that increase energy efficiency in thermal power generation and HVAC by promoting dropwise condensation through a combination of superhydrophobicity and electro-wetting. The influence of phenomena like electrowettability, gas diffusion, thermal transport and Marangoni convection on the stability of the Cassie state are studied using a combination of modeling and experiments. This requires capturing the effects of deforming menisci and, once the liquid phase reaches the advancing contact angle, moving triple contact lines. EW-induced pumping on textured superhydrophobic surfaces is studied. Novel pumping configurations are analyzed, wherein AC electric fields induce a body force and a torque on the droplet to initiate its ?rolling? on superhydrophobic surfaces. Materials/manufacturing issues associated with the development of durable, scalable, polymer coatings for dropwise condensation are also investigated and will be shared through outreach to local high school students.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.