Enhancing condensation improves power plant efficiency, water harvesting, desalination, and refrigeration. An ideal surface for condensation enhancement must provide large heat transfer areas and rapid droplet removal in durable operations. Until now, this could not be achieved because of scientific challenges in both droplet removal and surface durability. First, the passive liquid repellency on air-independent rough surfaces has not been achieved due to the large pinning forces on rough surfaces. Second, the surface durability in a steam environment with continuous droplet shedding cannot be sustained. Most of existing liquid-repellent surfaces rely on the existence of air lubricant, which can be displaced in a steam environment or in contact with low surface tension fluids, leading to the failure of condensate removal. The goal of this EAGER project is to address those challenges by developing previously unachieved hydrophilic and slippery rough surfaces. The research outcomes are integrated with outreach and education, with under-represented students recruited and trained. The PI also actively approaches the industrial companies in Texas for broad impact of the research .
The experimental study of condensation enhancement on air-independent slippery rough surfaces leads to a conceptually different strategy from the air-dependent condensation on superhydrophobic surfaces. This hydrophilic slippery rough surface gives a large surface area for condensation and in the meantime keeps a small contact angle hysteresis for condensate removal. The research objectives include: (1) experimentally demonstrate that the slippery rough surfaces can significantly increase the condensation heat transfer coefficient compared with the state-of-the-art condensing surfaces, and (2) understand the failure mechanism of this surface in a steam environment with continuous droplet shedding. To improve surface durability, polymer chains are grafted on the rough substrate to simultaneously enhance heat transfer areas and droplet removal. This project leads to the development of durable air-independent slippery rough surfaces for exceptional condensation enhancement.
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.