Experimental Study of Deformation Mechanism of a Water Droplet Impinging on Hot Metallic Surfaces Above the Leidenfrost Temperature

This paper is concerned with the collision dynamics of a water droplet impinging on three kinds of smooth surfaces (Inconel alloy 625, stainless-steel, and silicon) heated to above the Leidenfrost temperature (500°C). It has been found that the time histories of the droplet diameter, the height and the distance between the bottom of droplet and the hot surface after rebounding are almost unchangeable regardless of the kind of surface material, when the Weber number is kept so low that the droplet does not break up into some parts. However, the critical Weber number, whether or not the droplet is disintegrated into some pieces during deformation, has been confirmed to be changeable depending upon the kind of surface material. For relatively low Weber number cases, but above the critical one, the droplet breaks up into some parts after the droplet reaches a maximum diameter on the surface. As the Weber number is increased further, the droplet disintegration occurs during the spreading process. Also, the droplet disintegration mechanism has been discussed from an experimental point of view.