Recoil and solidification of a paraffin droplet impacted on a metal substrate: Numerical study and experimental verification

Drop impact is an important phenomenon in many industrial processes, such as ink-jet printing, plasma spraying, and spraying cooling. This study focused on numerical prediction of the whole drop-impact process, including impact, flattening, recoil, and solidification of the droplet, based on the finite difference method. A volume-of-fluid method was used to track the free surface. Drop impacts under both isothermal and non-isothermal conditions were investigated with consideration of the effects of the droplet temperature and impact velocity. Drop-impact videos were recorded with a high-speed camera to verify the simulation results. The simulation results agreed well with the experimental results of the spreading factor, recoil height, and geometry of the solidified splat. The numerical and experimental results showed that cooling and solidification of the droplet due to simultaneous heat transfer from the droplet to the substrate significantly reduced the spreading factor and facilitated recoil of the impacted droplet. In addition, a smaller spreading factor, a larger recoil height, and a thicker solidified splat occurred for lower droplet temperature and lower impact velocity.