基于动态接触角对固着液滴蒸发过程影响因素的模拟分析

Simulation of influencing factors of evaporation progress of sessile droplets based on dynamic contact angle

在综合了动态接触角模型、液滴蒸发冷却效应、空气域的水蒸气扩散及Marangoni效应影响的情况下,使用二维轴对称模型对水平基板上固着液滴的蒸发过程进行了研究,分析了环境因素、基板性质及液滴的热物理性质对液滴蒸发的影响。结果表明:Marangoni流动在液滴蒸发过程中占据主导作用;随着液滴蒸发,液滴内部流速逐渐减小,温度逐渐升高,液滴表面蒸发通量逐渐增大;由于楔形效应,液滴蒸发初期接触线处蒸发通量较小,后期楔形效应消失,该处蒸发通量达到最大值;环境因素也会对液滴蒸发产生影响,相对湿度增大会抑制液滴蒸发,温度升高会促进液滴蒸发;基板过热度增大能显著提高液滴的蒸发速率,而液滴的初始接触角和后退接触角的减小均会提高液滴蒸发速率;通过改变液滴导热系数判断普朗特数(Pr)对液滴蒸发的影响,发现Pr增大会略微降低液滴的蒸发速率。

In the case of integrating the dynamic contact angle model,droplet evaporative cooling effect,vapor diffusion in the air domain and Marangoni effect,the two-dimensional axisymmetric model is used to study the evaporation process of sessile droplets on the horizontal substrate,and the effects of environmental factors,substrate properties and droplet thermophysical properties on droplet evaporation are analysed.The results show that the Marangoni flow plays a dominant role in the droplet evaporation process.As the droplet evaporates,the velocity inside the droplet decreases,the temperature increases,and the evaporation flux on the surface of the droplet increases.Due to the wedge effect,the evaporation flux at the contact line is small at the initial stage of droplet evaporation,and the evaporation flux reaches the maximum at the point where the wedge effect disappears in the later stage.Environmental factors will also affect droplet evaporation.The increase in relative humidity will inhibit the droplet evaporation,and the increase in ambient temperature will promote the droplet evaporation.The increase of substrate superheat can significantly increase the droplet evaporation rate.The decrease of the initial contact angle and receding contact angle of the droplet will increase the droplet evaporation rate.The effect of Prandtl number on the droplet evaporation is judged by changing the thermal conductivity of the droplet,and it is found that the increase of Prandtl number will slightly reduce the droplet evaporation rate.