Girard Henri-Louis, Soto Dan, Varanasi Kripa K
Department of Mechanical Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
ACS Nano. 2019 Jul 23;13(7):7729-7735. doi: 10.1021/acsnano.9b01301. Epub 2019 Jun 27.
Superhydrophobic surfaces can dramatically reduce the transport of mass or energy from impacting droplets by making them bounce off. Such transport processes are dependent on both the contact time and the contact area between the drop and the surface. To reduce transport, recent studies have focused on reducing the contact time. However, the contact area, which is dictated by the conformal spreading of the droplet, remains large, thereby limiting the reduction in the overall transport. Here, we show how surfaces can be designed to redirect the momentum of the spreading lamella causing it to lift off into 3-dimensional shapes, thereby dramatically reducing the contact area. We design superhydrophobic surfaces with an in-plane discontinuity leading to the accumulation of vertical momentum resulting in the out-of-plane ejection of the lamella into water bowls. We demonstrate a 2-fold reduction in the heat transfer between a cold rain and a warm surface. These insights can be broadly applied to other transport phenomena involving mass and energy exchange to limit heat loss under precipitation, icing of surfaces, reduce salt deposition on a surface exposed to ocean spray, or inhibit the formation of a water film on wings or wind turbine blades.
超疏水表面可以通过使撞击的液滴反弹，显著减少质量或能量的传递。这种传递过程取决于液滴与表面之间的接触时间和接触面积。为了减少传递，最近的研究集中在减少接触时间上。然而，由液滴的共形铺展决定的接触面积仍然很大，从而限制了整体传递的减少。在这里，我们展示了如何设计表面来重新引导铺展薄片的动量，使其升华为三维形状，从而显著减少接触面积。我们设计了具有面内不连续性的超疏水表面，导致垂直动量的积累，从而使薄片向水碗中进行面外喷射。我们证明了冷雨与温暖表面之间的热传递减少了两倍。这些见解可以广泛应用于涉及质量和能量交换的其他传输现象，以限制降水条件下的热损失、表面结冰、减少暴露于海浪飞沫的表面上的盐沉积，或抑制机翼或风力涡轮机叶片上形成水膜。
