Freezing of a spreading droplet: A theoretical and experimental study

Here, we study the simultaneous spreading and freezing of sessile droplets. The droplets are generated by a jetting or a liquid needle system. The drop is deposited on a subcooled surface, triggering the droplet's solidification. Only a few studies have elucidated such a complex mechanism where the dynamics of droplet freezing is studied while the mass and volume of the sessile drop are increasing. The theoretical model presented here is inspired by the well-established overall energy balance approach. We modified the initial boundary condition considering the jetting paraments and coupled it with the heat transfer from the impinging cold substrate. Further non-dimensionalization of the governing equations suggests the Bond, Reynolds, and Weber numbers are decisive factors to comment on the outcome. This model predicts the temporal evolution of the droplet growth and solidification rate while the drop is spreading. We validated our model for earth gravity and extended the utilization of this analysis for micro and Martian gravity. The jetting parameters dictate the freezing dynamics in all three gravity conditions (earth, micro and Martian). We corroborated our theoretical analysis with the experimental results obtained in Martian and microgravity conditions simulated by parabolic flight maneuvers.