Abstract:

In this paper, through the droplet visualization experiment, the dynamic surface wetting characteristics of the freezing droplets on the surface of the aluminum plate at different substrate temperatures were summarized. Based on mechanical analysis, the article summarizes the changing laws of wetting parameters such as droplet wetting area, volume, contact angle and phase transition time. Experimental results showed that the wettability of droplets is mainly affected by gravity, surface tension and thermal capillary force. Gravity promoted the lateral spread of droplets. The surface tension and thermal capillary force were affected by the temperature of the bottom plate, and have the effect of inhibiting the diffusion process of the droplets. Under the two different conditions, the change of the height of the frozen droplets was the same. As the melting progresses, the height of the droplets dropped sharply and then slowly decreases. Under different freezing conditions, the infiltration of frozen droplets in the initial stage of melting was very obvious. At this stage, gravity promotes the wettability of the droplets, and the contact angle of the droplets was between 65° and 85°. In the later stage, the decrease of contact angle led to the weakening of gravity and the increase of surface tension, which hindered the spread of droplets and slows down the trend of volume reduction. Under different heating conditions, the droplets hardly undergo diffusion movement. Thermal capillary force and surface tension dominated the wetting process. As the substrate temperature increases, the temperature difference between the inside of the droplet and the three-phase line gradually increased, and the number of Ma increased from 1802 to 22876. The capillary force always restrained the movement of the droplet.

Key words: droplet, melting process, wettability, contact angle, thermal capillary force

摘要：

通过液滴可视化实验，发现并归纳了冻结液滴在不同基底温度下于铝板表面融化过程的动态表面润湿特性，结合力学分析，总结了液滴润湿面积、体积、接触角等润湿参数与相变时间之间的变化规律。实验结果表明：液滴的润湿性主要受重力、表面张力、热毛细力的影响，重力对液滴的横向扩散促进作用、表面张力与热毛细力受底板温度影响具有抑制液滴润湿过程的作用；两种不同条件下，冻结液滴高度变化规律相同，随着融化的进行，液滴高度骤降，然后缓慢降低；不同冻结条件下，冻结液滴的润湿过程主要发生在融化初始阶段，重力促进液滴的润湿过程，液滴接触角处于65°~85°之间，而在润湿后阶段，接触角减小，重力的作用减弱，表面张力的作用增强，液滴的扩散进程受阻，体积下降的趋势也变缓；不同升温条件下，冻结液滴的润湿过程几乎没有发生，热毛细力与表面张力在润湿过程中占据主导性，随着基底温度的升高，液滴内部与三相线温差逐渐增大，Ma数呈增加的趋势，数值由1802增至22876，热毛细力始终抑制液滴的运动。

关键词: 液滴, 熔化过程, 润湿性, 接触角, 热毛细力