Collision dynamics of two droplets impinging successively onto a hot solid

Abstract

The collision of two successive water droplets with a hot solid was investigated. Experiments were carried out on water droplets with a diameter of approximately 0.6 mm and an impact velocity of 3.5 m/s at various droplet spacing and time intervals. The temperature of the solid surface was set at 120, 300, and 500°°C. The Weber number, based on the pre-impact diameter of droplet and the impact velocity, is approximately 100. At low surface temperature (120°°C), the coalesced liquid is deformed into the shape of a crown with its height increasing with droplet spacing. The hydrodynamics of the formation process of the crown is also studied in detail by numerical simulations under isothermal conditions. For the cases of 300 and 500°°C, the coalesced liquid breaks up into small droplets as boiling occurs at the liquid-solid interface. The time evolution of droplet shape is dependent on the surface temperature as well as the spacing between two droplets.