DEFORMATION PROCESS OF A DROPLET IMPINGING ON A HOT OXIDE-SCALED SURFACE ABOVE THE LEIDENFROST TEMPERATURE

This paper is concerned with the collision dynamics of a water droplet impinging on a hot surface heated to above the Leidenfrost temperatur e, focusing upon the case where the impingement side is rough (oxide-s caled) with an oxide film. The rough surface has been artificially mad e by rapidly quenching as-rolled stainless steel by water spraying, af ter it has been heated to 1000 degrees C in a furnace. A sequence of p hotographs showing the progressive stages of droplet deformation have been taken on several Weber number conditions. It has been found that the droplet configuration is not axially symmetric around the initial impact point even at an early Stage immediately after collision and th at the irregularity of the droplet configuration is amplified as the d roplet deformation proceeds. With increasing Weber number, the irregul arity has been seen to be more remarkable in the later stage and final ly the droplet breaks up into some parts. Therefore, the critical Webe r number to specify whether or not the droplet is disintegrated on the rough surface has been found to become small compared with the smooth surface case.