Impact and boiling characteristics of an impinging ethanol drop on a heated Al alloy surface

摘要

When a liquid drop impacts onto a heated surface, it can be levitated by an evaporating vapor layer if the surface temperature exceeds a certain threshold. Therefore, impact outcomes and heat transfer between a drop and surface are largely affected by the existence of the vapor layer. Recent researches directly measured the vapor layer using state of the art measurement techniques, but these methods were restricted to transparent surface materials. This study reinvestigates the metallic surface A6061 and compares the impact and boiling characteristics with those obtained in recent studies. With clear visual evidence, we directly visualized and quantitatively analyzed a momentary contact phenomenon in which the vapor layer recovered from temporary collapse. The transient impact force and great heat transport properties of a metallic material are considered to be the main factors that lead to this phenomenon. The time required to recover the vapor layer is well matched with the current understanding that the rate of heat transfer is dependent on the temperature difference between the surface and saturation point of a drop. We also completely differentiate boiling regimes and verify that the surface temperature for a stable vapor layer depends on the impact momentum. Occurrence patterns of disintegrating and splashing drops are similar to those observed for nonmetallic surfaces. In addition, distinct spreading characteristics according to the existence of the vapor layer are quantitatively investigated and compared to those of nonmetallic surfaces.