An experimental investigation of water droplet impingement on a heated wax surface

The impact of a distilled water droplet upon a heated wax surface was investigated experimentally using a high-speed digital camera. The droplet impact Weber number (We) was varied and the collision dynamics were investigated with the temperature of the wax surface varied from 20 to 75 °C. For each impact We number, the evolution of the liquid film diameter was measured as a function of surface temperature. At We=27, the liquid film diameter was observed to recoil faster as the surface temperature of the wax was increased. At We=150, as the droplet recoiled, an unstable column of fluid was observed to rise above the wax surface. The instability of the fluid column at We=150 was explained using Rayleigh instability theory. At the melting point of the wax, 75 °C, the droplet impacted upon a liquid surface. Over the range of impact We numbers considered, the jet formed in the molten wax pool did not result in separation of droplets from the jet.