Liquid impingement dynamics on superheated superhydrophobic surfaces

在需要冷却、冷凝或清洁性能的多种应用中，表征从固体板到液体的热传递非常重要。超疏水表面可以是自清洁的，因此在与液体接触时对其使用具有直接优势。水将位于微/纳米结构的顶部，在结构之间留下空气间隙，并允许水在表面上几乎完全成球。水会从表面滚动，因此它会自我清洁。虽然在超疏水表面上的冲击的液体动力学是相当公知的，从这些表面与微尺度的空气间隙的冲击液体的热传递的理解没有很好地表征。撞击液体能够通过不断补充新的、较冷的液体来带走热量。这项研究将探索撞击水滴或撞击水射流从超疏水表面去除热量的能力，同时仍然有效地进行自清洁。超疏水表面是通过将微尺度结构化和疏水涂层相结合来产生的，使得液体通常仅与固体表面的一部分接触。撞击过程中的基本流体流动和热传输物理丰富，并代表了一个很好的测试床，考虑与超疏水表面，因为超疏水性施加巨大的影响，液体-固体表面张力，这是占主导地位的撞击过程。预计超疏水表面上的液体冲击的热传输物理将经历比流体动力学观察到的更大的偏离经典行为。这项工作的目的是表征运输：1）碰撞液滴（正常和倾斜的冲击角），和2）液体射流冲击（正常和倾斜冲击）。拟议的研究计划包括耦合实验和分析方法。将探索的过程在下一代高效冷凝器、脱盐过程、自清洁表面和易于维护的喷雾冷却系统中具有重要意义。

Characterizing heat transfer from a solid plate to a liquid is important in multiple applications where cooling, condensation, or cleaning properties are necessary. Superhydrophobic surfaces can be self-cleaning and thus present an immediate advantage for their use when in contact with liquids. Water will sit atop the micro/nano structures, leaving an air gap in between the structures and allowing for water to bead up almost completely into a ball on the surface. The water will then roll from the surface and thus it becomes self-cleaning. Although the liquid dynamics of impingement on a superhydrophobic surface are fairly well known, the understanding of heat transfer from these surfaces with micro-scale air gaps to an impinging liquid is not well characterized. Impinging liquids are able to remove heat by the constant replenishing of new, cooler liquid. This study will explore the capability of impinging water droplets or impinging water jets to remove heat from a superhydrophobic surface while still effectively being self cleaning. Superhydrophobic surfaces are generated by combining microscale structuring and a hydrophobic coating such that liquids are often only in contact with a fraction of the solid surface. Impinging processes are rich in fundamental fluid flow and thermal transport physics and represent an excellent test bed to consider with superhydrophobic surfaces since superhydrophobicity exerts enormous influence on the liquid-solid surface tension, which is dominant in impinging processes. It is expected that thermal transport physics of liquid impingement on superhydrophobic surfaces will experience greater departure from classical behavior than has been observed hydrodynamically. The objectives of this work are to characterize the transport for: 1) impinging droplets (normal and oblique impingement angles), and 2) liquid jet impingement (normal and oblique impingement). The proposed research plan includes coupled experimental and analytical approaches. The processes that will be explored have significance in next generation high efficiency condensers, desalinization processes, self-cleaning surfaces, and easily maintained spray cooling systems.