Downward jetting of a dynamic Leidenfrost drop

Abstract

Jetting is a universal phenomenon frequently observed in nature and industries, for instance, in rain drop impact, inkjet printing, spray cooling, fuel atomization, etc. In drop impact on a superheated surface, we observe the formation of a vapor cavity beneath the dynamic Leidenfrost drop and a consecutive downward ejection of a jet into the cavity using ultrafast x-ray phase contrast imaging. We reveal that the cavity is induced mostly by the retraction of the drop and the jetting is caused by the convergence of capillary waves along the liquid-cavity interface. We find a jetting criterion based on the viscous damping of capillary waves: [OhWe(2)] <= 66 +/- 10. These results can provide important insight that leads to understanding and modeling of jets in nature.