An experimental investigation on the collision outcomes of binary liquid metal droplets

Droplet collisions are widely observed either in industrial engineering or in natural phenomena. However, unlike the fully investigated interaction behaviors between water or alkanes droplets, it is still unclear what happens when the droplets are produced of liquid metal, which has larger density and surface tension compared to the common liquids, and hence the collision regimes are expected to be remarkably different from the well-known transition phase maps. In the present study, a series of experiments have been conducted to investigate different collision regimes between binary liquid metal droplets, which are typically of liquid GalnSn, and a wide range of parameter spaces is investigated by covering the Weber number (We) from 5 to 400 and the impact parameter (X) from 0 to 1, respectively. It turns out that six different collision types are observed, respectively of coalescence, stretching separation, coalescence after finger, separation of finger, breakup after finger and stretching separation with finger pinching, and the transitional borders between them are identified experimentally. Moreover, a theoretical correlation is derived as the upper limit of the transitional curve between stretching separations and other collisions, and by using Ashgriz & Poo's correlation as the lower limit, a transitional region is produced to distinguish stretching separations and other regimes. Particularly, for head-on collision of GalnSn droplets, we also present an empirical and a theoretical correlation for the prediction of dimensionless maximum spreading diameter (0 in variance with Weber number (We > 30) within the framework of energy conversion principle. After that, new empirical correlations for the onset of breakup after finger are presented, and the collision outcomes could be divided into surface tension dominated, viscosity dominated, inertia dominated and inertia & viscosity dominated regimes in different regions of the We/48 - Ca map. (C) 2019 Elsevier Ltd. All rights reserved.