Experiment on the dynamics of a compound drop impinging on a hot surface

A stable stream of compound drops which are composed of core fluid, water, encased by a layer of shell fluid, diesel, was utilized to investigate the dynamic behavior of a liquid-liquid compound drop impinging on a hot surface above the Leidenfrost temperature. The core-to-shell mass ratio and the modified normal Weber number, which takes into account the two interfaces involved, were taken to be the controlling parameters. The outcomes of a compound drop impacting on a hot surface consist largely of reflection with or without secondary drops. Based on energy conservation, the dissipated energy was estimated and a criterion for secondary drop formation was presented. The normal velocity after impact is reduced due to viscous dissipation while the tangential component remains almost unaffected. In addition, there is an interesting phenomenon of the core drop escaping from the compound drop. The experimental results show that an increasing core-to-shell mass ratio raises the momentum loss, reduces the number of secondary drops, and promotes core-drop escaping.