An experimental study on the contact angle dynamic during the impact of single water droplet onto a hot flat practical stainless steel surface under medium weber number was performed. The tested solid material was practical stainless steel of SUS 304. The surface roughness of the hot surface, the static contact angle at ambient pressure, and the diameter of the solid materials were respectively Ra = 0.2 µm, 85.7^o, and 30 mm. The surface temperatures were varied from (60–200) ^oC. The liquid droplet diameter was 2.4 mm. The Weber numbers were 52.1, 57.6, and 63.1. The dynamic contact angles of single droplet during the impact were determined by implementing the developed image processing technique of the obtained video images from experiments. As a result, it was found that (1) the time needed to reach a maximum diameter of single droplet on a flat hot solid surface decreases with the increase of surface temperature, (2) the increase of the Weber number will postpone the spreading of the droplet from its receding, (3) there are three regions of the dynamic contact angle during the liquid evaporation, those are transient spreading region (region 1), a quasi-mechanical equilibrium region (region 2), and transient evaporation region (region 3), and (4) The contact angle in quasi-mechanical equilibrium region the under the nucleate boiling is insensitive to the surface temperature.

在中等韦伯数下，对单个水滴撞击热的实用不锈钢表面时的接触角动态进行了实验研究。所测试的固体材料是SUS 304的实用不锈钢。热表面的表面粗糙度，环境压力下的静态接触角以及固体材料的直径分别为Ra = 0.2 µm，85.7 ^o和30 mm。表面温度在（60–200）^{o之间变化}液滴直径为2.4mm。韦伯数为52.1、57.6和63.1。通过实施从实验中获得的视频图像的改进的图像处理技术，可以确定冲击过程中单个液滴的动态接触角。结果发现，（1）随着表面温度的升高，在平坦的热固体表面上达到最大液滴直径所需的时间减少；（2）Weber数的增加将延缓表面活性剂的扩散。从液滴的后退开始，（3）液体蒸发过程中存在三个动态接触角区域，分别是瞬态扩散区域（区域1），准机械平衡区域（区域2）和瞬态蒸发区域（区域） 3），