Influences of surface nanotubes at high temperatures are investigated on droplet impact dynamics and Leidenfrost effect. Five distinct regimes of impact droplets are found on the nanotube surface, including contact boiling, film levitation, central jet levitation, central jet, and Leidenfrost phenomenon. The regimes of film levitation, central jet levitation, and central jet are characterized by either film levitation and/or liquid central jet. The regime of Leidenfrost phenomenon is characterized by droplet bounce-off behavior free of any liquid jets. Film levitation is driven by the vaporization of two parts of the droplet, with one as the droplet bottom layer over the contact area above the nanotube structure, and the other as the hemiwicking liquid in nanotubes. Both the vaporization is impaired by increasing the surface temperature, which is attributed to the reduced contact time and less extent of spread of the droplet at a higher surface temperature. The central jet phenomenon is driven by the vapor stream produced by hemiwicking liquid in the central area upon impact. It is enhanced and then suppressed by elevating the surface temperature, resulting from the collective effects of the vapor pressure in nanotubes which increases with the surface temperature, and the cross-sectional area of the vapor stream, which increases and then decreases with the surface temperature. At a high Weber number, the Leidenfrost temperature can be increased by ${125}^{\circ }\mathrm{C}$ on the nanotube surface, implying a great potential in heat transfer enhancement for droplet-based applications.

中文翻译：

---

在过热条件下，膜的悬浮和液滴的中心喷射冲击纳米管表面

研究了表面纳米管在高温下对液滴冲击动力学和莱顿弗罗斯特效应的影响。在纳米管表面上发现了五种不同的冲击滴形态，包括接触沸腾，薄膜悬浮，中心喷射悬浮，中心喷射和莱顿弗罗斯特现象。薄膜悬浮，中央喷射悬浮和中央喷射的状态以薄膜悬浮和/或液体中央喷射为特征。莱顿弗罗斯特现象的特征在于没有任何液体射流的液滴反弹行为。膜的悬浮是由两部分液滴的汽化驱动的，其中一部分是纳米管结构上方接触区域上方的液滴底层，另一部分是纳米管中的半芯吸液体。升高表面温度会损害两种蒸发，这归因于在较高的表面温度下减少的接触时间和较小的液滴散布程度。中心射流现象是由撞击时中心区域中的液体半芯吸产生的蒸气流驱动的。由于纳米管中蒸汽压的集体效应（随表面温度的升高而增加）和蒸汽流的横截面面积（随表面温度的升高而随后降低）的集体效应而导致表面温度升高，从而增强并抑制了它。 。在较高的韦伯数下，莱顿弗罗斯特温度可以提高 由于纳米管中蒸汽压的集体效应（随表面温度的升高而增加）和蒸汽流的横截面面积（随表面温度的升高而随后降低）的集体效应而导致表面温度升高，从而增强并抑制了它。 。在较高的韦伯数下，莱顿弗罗斯特温度可以提高 由于纳米管中蒸汽压的集体效应（随表面温度的升高而增加）和蒸汽流的横截面面积（随表面温度的升高而随后降低）的集体效应而导致表面温度升高，从而增强并抑制了它。 。在较高的韦伯数下，莱顿弗罗斯特温度可以提高${125}^{\circ }\mathrm{C}$ 在纳米管表面上，这意味着在基于液滴的应用中增强传热的巨大潜力。