Influence of the oxygen concentration on the aerodynamic breakup of oxidizing liquid metals

This study investigates the effect of varying oxygen concentration on the secondary atomization of Galinstan. The concentration was varied between 0.0021 % and atmospheric concentration (21 %) and compared to water experiments in air where oxidation is not present. Independent of the oxygen concentration, we observe the known breakup morphologies of bag, bag-and-stamen, multimode breakup and shear stripping with similar transition Weber numbers. The results show that early stages during breakup remain unaffected by the oxygen concentration, given that droplets are initially fully oxidized. However, low oxygen environments in the bag, bag-and-stamen, and multimode breakup regimes lead to a later onset of breakup, larger droplet sizes at burst, and more pronounced deformation. In these conditions, Galinstan bags, rims, and, if present, stamens disintegrate more similarly to water. A key finding is the reduced particle size and more spherical particle shape of Galinstan at lower oxygen concentrations. In the shear stripping regime, oxygen concentration affects fragmentation only after the initial oxide layer of the droplet has been shed. Comparisons with water experiments reveal that decreasing the rate of oxidation results in Galinstan atomizing more similarly to common liquids such as water.