液滴接触变形对融合过程影响的实验研究

采用一种产生大尺寸液滴和顶视视角观测的新方法，借助高速阴影系统，捕捉到液滴融合过程中液桥截面形态的变化。从光学观测的角度验证了以前电测法所得到的初期融合过程描述。利用顶视方法所特有的辨别液桥几何形状、中心位置等优势，观测了不同液滴靠近速度（v_a）下2种融合模式。根据液桥中心演变特征分别判定为中心融合和边缘融合模式，并发现两者之间存在一临界液滴靠近速度（v_cross），当v_a < v_cross时，融合过程始于接触中心，而当v_a >v_cross时，融合自液滴挤压形成的液膜边缘开始，与融合前液滴接触变形密切相关。

Experimental study of the effects of contact deformation on drop coalescence scenario

The evolution of cross section of the liquid bridge during drop coalescence is captured with a new type of experimental setup which contains the generation of large drops, top-view observation and high-speed shadowgraph. The optical results support the previous findings obtained with electrical measurements in the initial stage of the coalescence. Thanks to the unique advantages of the top-view observation, the shape and position of the liquid bridge connecting the drops is clearly demonstrated in this paper. Two coalescence scenarios with different approaching speed of the drops, v_a, are distinguished as the center scenario and the off-center scenario based on the location of the starting point of coalescence. The critical speed, v_cross, which divides the scenarios, is noticed and measured with the present device. It is found that the approaching speed has little influence on the coalescence process in the center scenario when v cross. On the contrary, the onset of coalescence switches to the edge of the contacting film formed by the approaching drops and the off-center scenario appears consequently when v> v_cross.