Modeling the impingement deformation and solidification of a hollow zirconia droplet onto a dry substrate and solidified layer

Despite the numerous research studies involving the solidification of continuous molten metal droplet impingement on dry substrates during the process of plasma spraying, the impingement between a hollow molten metal droplet and a solidified layer has, to date, not yet been thoroughly explored. A liquid shell enclosing the air cavity forms a hollow droplet. The coupled level set and volume of fluid method is used to track the air–liquid interface, and the enthalpy–porosity method is used to track the liquid–solid interface. A two-dimensional axis symmetric model is adopted to describe the impingement and solidification process. This study includes a detailed investigation of transient impact deformation and solidification. The heat transfer characteristics of the solidification of a continuous dense and hollow molten droplet impacting on a dry substrate and solidified layer are studied and compared. A thin solidified layer appears and develops between the droplet and the substrate, and the impacting droplet finally pins to the surface with mainly the liquid solidified. For a hollow droplet impact on the solidified layer, a splashed crown liquid sheet forms from the drop-solidified layer neck area. Various temperatures of the solidified layer induce a different development of the crown, spreading, and rebound counter-jet. The deterioration of local heat transfer is attributed to a strong fluctuation of the rebound counter-jet and the existence of an annular cavity (formed by the crown sheet falling back). Attention should be paid to this phenomenon in industrial applications involving droplet impact.