Abstract In the present study, the impact and spreading dynamics of a single droplet on a heated surface are experimentally investigated. Ethanol-water droplets with ethanol concentrations of 0–8 vol% are adopted as the working fluid with a wide range of surface temperature from 75 °C to 450 °C and the Weber number ranges from 7 to 63. The instantaneous droplet evolution after impact is studied via visualization. All the observed phenomena implied that ethanol additive has a significant influence on both impact dynamics and spreading characteristics. A new phenomenon is observed that the addition of ethanol can compensate for the negative influence of small Weber numbers, i.e., some ethanol–water droplets with smaller Weber numbers show better spreading dynamics, higher breakup and atomization possibility but weaker rebound compared with water droplets with higher Weber numbers. It is speculated that droplet impact is no longer solely dependent on the Weber number for ethanol–water droplet, and lower surface tension caused by ethanol additive and Marangoni effect due to concentration gradient along the interface are mainly responsible for this difference. The result also shows that impact behavior exhibits complex dependence on the surface temperature and Weber number, including deposition, rebound, rebound with atomization, breakup with atomization and breakup, while the regime map is significantly affected by ethanol additive.

中文翻译：

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单个乙醇-水滴在加热表面上的冲击和扩散动力学的实验研究

摘要 在本研究中，实验研究了单个液滴在加热表面上的冲击和扩散动力学。采用乙醇浓度为 0-8 vol% 的乙醇-水滴作为工作流体，表面温度范围为 75°C 至 450°C，韦伯数范围为 7 至 63。 撞击后的瞬时液滴演变通过可视化进行研究。所有观察到的现象都表明乙醇添加剂对冲击动力学和扩散特性都有显着影响。观察到一个新现象，乙醇的加入可以补偿小韦伯数的负面影响，即一些韦伯数较小的乙醇-水滴表现出更好的扩散动力学，与韦伯数较高的水滴相比，破碎和雾化的可能性较高，但回弹较弱。据推测，液滴的影响不再仅仅取决于乙醇-水滴的韦伯数，乙醇添加剂引起的较低表面张力和沿界面的浓度梯度引起的马兰戈尼效应是造成这种差异的主要原因。结果还表明，冲击行为表现出对表面温度和韦伯数的复杂依赖性，包括沉积、回弹、雾化回弹、雾化破裂和破裂，而乙醇添加剂对状态图有显着影响。乙醇添加剂引起的较低表面张力和界面浓度梯度引起的马兰戈尼效应是造成这种差异的主要原因。结果还表明，冲击行为表现出对表面温度和韦伯数的复杂依赖性，包括沉积、回弹、雾化回弹、雾化破裂和破裂，而乙醇添加剂对状态图有显着影响。乙醇添加剂引起的较低表面张力和界面浓度梯度引起的马兰戈尼效应是造成这种差异的主要原因。结果还表明，冲击行为表现出对表面温度和韦伯数的复杂依赖性，包括沉积、回弹、雾化回弹、雾化破裂和破裂，而乙醇添加剂对状态图有显着影响。