A theoretical and experimental investigation of the simultaneous spreading and freezing of droplets

This research explores the freezing process of water droplets on solid surfaces through a validated theoretical model with experimental observations. Understanding the dynamics of frozen droplets is essential in advancing manufacturing research, such as 3D printing and freeze casting, as well as bioengineering. A very few studies have delved into the intricacies of this process, specifically the freezing dynamics while the droplet's mass and volume are increasing. To study this, a liquid needle technique was used to deposit droplets on a subcooled surface and trigger solidification. The theoretical model considers the overall energy balance, including incoming jet kinetic energy, surface energy, gravitational energy, viscous dissipation, and heat transfer on a subcooled substrate. A jet impact model, combined with heat transfer between the drop and substrate, is used for the initial condition. The current model simultaneously predicts the temporal evolution of droplet growth and solidification rate while the droplet is spreading. Non-dimensionalization of the governing equations indicates that the Bond, Reynolds, Weber, and Stefan numbers significantly influence the outcome and help us better understand the different stages of droplet freezing.