EAGER: Experimental Study of Condensation Enhancement on Durable Slippery Surfaces

增强冷凝可以提高电厂效率、集水、脱盐和制冷。一个理想的表面冷凝增强必须提供大的传热面积和快速液滴去除在持久的操作。到目前为止，由于液滴去除和表面耐久性方面的科学挑战，这一目标无法实现。首先，在不依赖空气的粗糙表面上，由于在粗糙表面上有很大的钉住力，所以没有实现被动的液体排斥。其次，在液滴持续脱落的蒸汽环境中，表面耐久性无法维持。现有的大多数防液表面依赖于空气润滑剂的存在，空气润滑剂可能在蒸汽环境中被置换，或与低表面张力流体接触，导致冷凝水去除失败。这个EAGER项目的目标是通过开发以前未实现的亲水性和光滑粗糙表面来解决这些挑战。研究成果与外联和教育相结合，招募和培训代表性不足的学生。PI还积极接触德克萨斯州的工业公司，以获得研究的广泛影响。不依赖空气的光滑粗糙表面上的凝结增强实验研究导致了一种概念上不同于超疏水表面上依赖空气的凝结策略。这种亲水光滑的粗糙表面为冷凝提供了大的表面积，同时保持了小的接触角滞后，有利于冷凝水的去除。研究目标包括：(1)实验证明光滑粗糙表面与现有冷凝表面相比可以显著提高冷凝换热系数；(2)了解光滑粗糙表面在连续液滴脱落的蒸汽环境下的破坏机制。为了提高表面耐久性，将聚合物链接枝到粗糙的基板上，同时增加传热面积和去除液滴。该项目旨在开发耐用的不依赖空气的光滑粗糙表面，以实现卓越的冷凝增强。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。

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.