Laboratory of Thermodynamics in Emerging Technologies (LTNT), ETH Zurich, Sonneggstrasse 3, Zurich 8092, Switzerland.
Institute of Nanoscience and Nanotechnology, NCSR Demokritos, Agia Paraskevi 15341, Greece.
Langmuir. 2023 Jan 31;39(4):1585-1592. doi: 10.1021/acs.langmuir.2c03029. Epub 2023 Jan 16.
Rapid and sustained condensate droplet departure from a surface is key toward achieving high heat-transfer rates in condensation, a physical process critical to a broad range of industrial and societal applications. Despite the progress in enhancing condensation heat transfer through inducing its dropwise mode with hydrophobic materials, sophisticated surface engineering methods that can lead to further enhancement of heat transfer are still highly desirable. Here, by employing a three-dimensional, multiphase computational approach, we present an effective out-of-plane biphilic surface topography, which reveals an unexplored capillarity-driven departure mechanism of condensate droplets. This texture consists of biphilic diverging microcavities wherein a matrix of small hydrophilic spots is placed at their bottom, that is, among the pyramid-shaped, superhydrophobic microtextures forming the cavities. We show that an optimal combination of the hydrophilic spots and the angles of the pyramidal structures can achieve high deformational stretching of the droplets, eventually realizing an impressive "slingshot-like" droplet ejection process from the texture. Such a droplet departure mechanism has the potential to reduce the droplet ejection volume and thus enhance the overall condensation efficiency, compared to coalescence-initiated droplet jumping from other state-of-the-art surfaces. Simulations have shown that optimal pyramid-shaped biphilic microstructures can provoke droplet self-ejection at low volumes, up to 56% lower than superhydrophobic straight pillars, revealing a promising new surface microtexture design strategy toward enhancing the condensation heat-transfer efficiency and water harvesting capabilities.
从表面迅速且持续地脱离冷凝液滴是实现冷凝高传热速率的关键，这是一个对广泛的工业和社会应用至关重要的物理过程。尽管通过使用疏水性材料来诱导滴状模式从而在增强冷凝传热方面取得了进展，但仍然非常需要能够进一步提高传热效率的复杂表面工程方法。在这里，我们通过采用三维多相计算方法，提出了一种有效的非平面双亲和表面形貌，揭示了一种以前未被探索的冷凝液滴的毛细驱动脱离机制。这种纹理由双亲和发散微腔组成，其中在其底部（即在形成腔体的金字塔形超疏水微纹理之间）放置有小亲水斑点的基质。我们表明，亲水斑点和金字塔结构的角度的最佳组合可以实现液滴的高变形拉伸，最终实现从纹理中令人印象深刻的“弹弓状”液滴喷射过程。与其他最先进的表面从合并引发的液滴跳跃相比，这种液滴脱离机制有可能减少液滴喷射量，从而提高整体冷凝效率。模拟表明，最佳的金字塔形双亲和微结构可以在低体积下引发液滴自喷射，比超疏水直柱低 56%，这揭示了一种有前途的新表面微观结构设计策略，可提高冷凝传热效率和集水能力。
