Secondary Atomization of Liquid Metal Droplets at Moderate Weber Numbers

Abstract

Atomization of liquid metal is an essential process in a variety of production methods such as spray forming or laser sintering. A critical part of all atomization processes is the breakup of single droplets, also termed secondary atomization. While it has been widely analyzed for conventional liquids, studies focusing on the influence of the specific properties of liquid metals remain rare. To identify differences, this work investigates single liquid metal Galinstan droplets exposed to a shock-induced crossflow by recording the breakup with a high-speed camera. The experimental test series covers a Weber number range of 11-104, and results show that the breakup morphology of Galinstan droplets follows the known sequence of bag, bag-and-stamen, multimode, and shear stripping breakup. We identify transition Weber numbers of ~15, ~35, and ~80, respectively, but also show that transition between modes is a continuous process with gradual changes. Compared to conventional liquids, the initial deformation of Galinstan droplets is very similar with respect to the shape, the initial deformation time, and the maximum cross-stream diameter. In contrast, later stages of the breakup process show clear differences. We observe that the onset of breakup appears significantly earlier in non-dimensional time, that Galinstan bags inflate much less, and that the bag breakup does not exhibit the same phenomenology as that of a water droplet. Further differences in the droplet shape and fragmentation suggest that the elastic oxide layer forming on Galinstan plays an essential role.