Electrowetting-assisted Dropwise Condensation on Hybrid Superhydrophobic-Hydrophilic Surfaces

火力发电站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，导致能源需求过多。在这些应用中，当水蒸气在金属表面上冷凝形成连续的液膜时，废热被移除。 与金属相比，这层水的导热性很差，因此降低了系统效率。 然而，如果金属表面被改性以排斥水，则蒸汽将以液滴的形式冷凝，这些液滴在形成连续的液膜之前从表面滚落。在滚下之后，金属表面重新暴露。这将提高性能，减少冷却水消耗;提高电气效率;并减少工艺对环境的影响。 这些优点使得冷凝器体积更小，并降低了资本和运营支出。在这个NSF项目中，我们制造了新型冷凝器表面，通过超疏水性和电润湿相结合促进滴状冷凝，从而提高火力发电和HVAC的能源效率。使用建模和实验相结合的现象，如电润湿性，气体扩散，热传输和Marangoni对流的Cassie状态的稳定性的影响进行了研究。这需要捕获变形的接触角的影响，并且一旦液相达到前进接触角，移动三重接触线。研究了织构超疏水表面的电子束泵浦效应。新颖的泵送配置进行了分析，其中AC电场诱导的体积力和扭矩的液滴启动其？滚动？在超疏水表面上。材料/制造与持久的，可扩展的，滴状冷凝的聚合物涂层的发展相关的问题也进行了调查，并将通过推广到当地的高中生分享。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.