Mechanism and Modeling of Micro-Droplet Impact, Fragmentation, and Solidification

New applications have been identified for thermal spraying using micro-droplets. Mechanisms of impact, fragmentation, and solidification developed for millimeter size droplets are no longer applicable for micro-droplets due to the significance of the surface tension and wall interaction. New fragmentation mechanisms and advanced numerical modeling are required to develop a better understanding of the transport phenomena for droplet spreading and solidification. In this paper, the existing fragmentation mechanisms have been reviewed, and a new mechanism is proposed. The proposed mechanism considers the effects of flow instability, wettability, surface roughness, surface chemistry, and moisture absorption. This mechanism has been incorporated into an advanced numerical model that consists of a multizone adaptive grid generation used for tracking the movement of the solidification interface and a curvilinear level-set method for capturing the movement of free surface. Impact, fragmentation, and solidification of a molybdenum micro-droplet has been simulated, and the fragmentation morphology has been predicted.