Central liquid jet emanating from an impacting drop on superheated laser-ablated surfaces

Abstract

Drop impacts on superheated textured surfaces have been studied extensively due to the unique characteristics arising from the roughness, which can be controlled through texturing features. The characteristics include novel modifications of the wettability and boiling regimes. The increased roughness of a textured surface also results in an unusual phenomenon where a central liquid jet emanates from an impinging drop. The central jet can interfere with the designated objective of textures or can be used in other applications, but it has rarely been reported and analyzed. Therefore, this study provides detailed and quantitative information on the central jet. With sufficient spatial and temporal resolutions, the impact and boiling behaviors including the central jet are clearly acquired and explained. The time-resolved height and speed of the jets are correlated to varying impact conditions such as the impact momentum of droplets, roughness and temperature of the surfaces. To understand and estimate the origin of the central jet, we also analyze several key findings, such as the motion of a cluster of vapor bubbles and the rim pattern of contact boiling. In addition, a hypothetical mechanism of the jet formation is proposed based on experimental evidence and a simplified heat transfer situation.