Electrowetting-assisted Dropwise Condensation on Hybrid Superhydrophobic-Hydrophilic Surfaces

Cuny College Of Staten Island, Staten Island NY

Investigators

Abstract

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.