Modeling Air Entrapment in the Impact-Freezing of YSZ Drops Using a Cahn–Hilliard Phase Field Model.

Air entrapment in drop impact onto solid surfaces has riveted the attention of the scientific community since it could drastically influence heat rate and splat porosity in additive manufacturing or thermal spraying processes. Due to the limitations of experimental methods, numerical methods have been gaining popularity in probing into air entrapment dynamics. To that end, this paper developed a paralleled phase field model. The model couples the Navier–Stokes equations with the Cahn–Hilliard equation to capture the liquid–gas interface, and adopts the liquid fraction, defined all over the computational domain, to distinguish between solid and liquid. The model is discretized using a finite difference method on a half-staggered grid. The model was first compared with experimental data, achieving reasonable agreement. Afterward, it was applied to a couple of cases. The air entrapment process was captured entirely and the interaction between solidification and air entrapment was also given. It shows that under the parameters studied here air entrapment may occur twice, one in the impacting center in the form of a bubble and the other in the form of a bubble ring. Besides, the effect of phase field mobility on air entrapment was examined as well. [ABSTRACT FROM AUTHOR]