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 <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.