Drop Impact on Heated Nanostructures

Drop
impact on a heated surface not only displays intriguing flow
motion but also plays a crucial role in various applications and processes.
We examine the impact dynamics of a water drop on both heated flat
and nanostructured surfaces, with a wide range of impact velocity
(V) and surface temperature (Ts) values. Via high-speed imaging and temperature measurements,
we construct phase diagrams of different impact outcomes on these
heated surfaces. Like those on the heated flat surface, water drops
can deposit, spread, rebound, or break-up with atomizing on the heated
nanostructures as V and Ts are increased. We find a significant influence of nanostructures
on the impact dynamics by generating particular events in specific
parameter ranges. For example, events of splashing, gentle central
jetting, and violent central jetting are observed on and thus triggered
by the heated nanostructures. The heated nanotextures with high roughness
can easily trigger the splashing and the central jetting. Our data
of the normalized maximum spreading diameter for the heated surfaces
display distinct trends at low and high Weber number (We) ranges, where We compares the kinetic to surface
energy of the impacting droplet. Finally, compared with the flat surface,
the dynamic Leidenfrost temperature (TLD) for We ≈ 10 is decreased (by ≈60 °C) by the high-roughness
nanotextures. In addition, our experimental data of TLD is consistent
with a model prediction proposed by balancing the droplet dynamic
and vapor pressure.

对加热表面上的水滴冲击不仅展现了引人入胜的流动现象，而且在诸多应用与工艺中扮演着至关重要的角色。本研究探究了水滴在加热平板及纳米结构表面上的冲击动力学，涵盖了广泛的冲击速度（V）和表面温度（Ts）数值。通过高速摄影和温度测量，我们构建了不同冲击结果在加热表面上的相图。与加热平板表面类似，水滴在加热纳米结构上随着冲击速度（V）和表面温度（Ts）的提升，可以发生沉积、扩散、弹跳或破碎成雾状。我们发现纳米结构对冲击动力学具有显著影响，能够在特定参数范围内产生特定的现象。例如，在加热纳米结构上观测到溅射、温和的中心喷射以及剧烈的中心喷射等现象，这些现象均由加热纳米结构触发。具有高粗糙度的加热纳米纹理能够轻易触发溅射和中心喷射。我们的实验数据表明，在低和高韦伯数（We）范围内，加热表面的标准化最大扩散直径呈现出显著的趋势，其中韦伯数（We）比较了冲击液滴的动能与表面能量。最终，与平板表面相比，由于高粗糙度的纳米纹理，动态莱登弗罗斯特温度（TLD）在韦伯数（We）约为10时降低了（约60°C）。此外，我们的动态莱登弗罗斯特温度（TLD）实验数据与平衡液滴动力学和蒸汽压所提出的模型预测相一致。