In this paper, the influence of the liquid droplet temperature on thermo–hydrodynamics of a single droplet impinging on surfaces having different hydrophobicities is experimentally investigated. Variation in the liquid temperature typically results in alteration of properties such as the density, the viscosity, the surface tension, and the enthalpy, consequently, the droplet dynamics gets to be modified. Employing high-speed imaging technique, the morphology and spreading pattern are investigated for water droplet collision on hydrophilic, hydrophobic and super-hydrophobic surfaces. The droplet deformation is monitored qualitatively and quantitatively for drops in the temperature range from 5 to 85°C and the Weber number between 14.5 and 160. It is observed that with an increase in the liquid temperature the spreading factor increases owing to the combined effect of reduction in the density, the surface tension, the viscosity and the contact angle of the solid surface. The differences in extension of droplets under the extreme temperatures for hydrophilic, hydrophobic and super-hydrophobic surfaces are noted to be 62.7, 27.76, and 20.52%, respectively. At the low temperature, the surface tension force dominates and the Cassie–Baxter state prevails on a textured super-hydrophobic surface and the droplets bounce off. In contrast at elevated temperatures, the liquid–solid interface ruptures and liquid penetrates into the cavities and results in the Wenzel state. Furthermore, the drop which exhibits multiple bounces in the low temperature regime is found sticking on a super-hydrophobic substrate at the high droplet temperature irrespective of the Weber number.

中文翻译：

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液滴温度和表面润湿性对单液滴冲击动力学的同时影响

在本文中，液滴温度对撞击具有不同疏水性的表面的单个液滴的热流体力学的影响进行了实验研究。液体温度的变化通常会导致诸如密度、粘度、表面张力和焓等特性的改变，因此，液滴动力学会发生变化。采用高速成像技术，研究了水滴在亲水、疏水和超疏水表面上碰撞的形态和扩散模式。对于 5 至 85°C 温度范围内的液滴和 14.5 至 160 之间的韦伯数，对液滴变形进行定性和定量监测。据观察，随着液体温度的增加，由于密度、表面张力、粘度和固体表面接触角的降低的综合影响，扩展因子增加。在极端温度下，亲水、疏水和超疏水表面的液滴延伸差异分别为 62.7、27.76 和 20.52%。在低温下，表面张力占主导地位，Cassie-Baxter 状态在有纹理的超疏水表面上占主导地位，液滴反弹。相比之下，在升高的温度下，液固界面破裂，液体渗入空腔并导致温泽尔态。此外，