Abstract In order to understand the evaporation dynamic of sessile droplet in pure vapor environment, this paper presented a series of experimental observations on the evolution of thermal patterns and the variation of evaporation rate during water and ethanol droplet evaporation at low pressures. The contact radius of droplet is fixed at 2.5 mm and the height varies from 0.4 to 1.6 mm. Results show that the surface temperature distributions for both water and ethanol are uniform at a high pressure ratio. When the pressure is reduced, a ring-like thermal pattern appears on the water droplet surface, while the gear-like pattern and the cellular flow happen on the ethanol droplet surface. Interestingly, the gear-like pattern is static when the substrate temperature is low, while it will oscillate at a high substrate temperature. Meanwhile, the cellular flow is affected by the droplet height. The evaporation is promoted by reducing the pressure. Moreover, due to the decrease of the evaporation surface area and the increase of surface temperature, the evaporation rate decreases first and then increases with the decrease of the droplet height.

中文翻译：

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低压纯蒸汽环境中固着液滴蒸发动力学的实验研究

摘要 为了解纯蒸气环境下固着液滴的蒸发动态，本文对水和乙醇液滴在低压下蒸发过程中热模式的演变和蒸发速率的变化进行了一系列实验观察。液滴的接触半径固定为 2.5 毫米，高度从 0.4 到 1.6 毫米不等。结果表明，在高压比下，水和乙醇的表面温度分布是均匀的。当压力降低时，水滴表面出现环状热模式，而乙醇液滴表面出现齿轮状模式和细胞流动。有趣的是，齿轮状图案在基板温度低时是静态的，而在基板温度高时会振荡。同时，细胞流动受液滴高度的影响。通过降低压力促进蒸发。此外，由于蒸发表面积的减小和表面温度的升高，蒸发速率随着液滴高度的降低先降低后升高。