Effect of surface subcooling on the droplet impacting dynamics

Abstract:

To study the dynamic characteristics of a droplet impact on a supercooled surface and the influence of different parameters on the spreading process of the droplet, the spreading behavior of a single water droplet impacting on a silicon surface has been experimentally investigated. Various impact velocities and droplet sizes are employed to enlarge the Weber number range. Results show that under the subcooling condition of the surface, the droplet spreading dynamics with the increasing of surface temperature exhibits a complex dependence on the Weber number. For a small Weber number (We<190), the maximum spreading factor shows a monotonic increase with the decreasing of surface subcooling due to a smaller liquid viscosity and surface tension. In the high Weber number region (We>190), the maximum spreading factor first decreases and then increases with the decreasing of surface subcooling. The non-monotonic relationship is ascribed to the competition between the decreased non-dimensional maximum fingering length and the increased maximum interior spreading factor with the increasing of surface temperature. In the case of We=209, the surface temperature increases from -36.6 ℃ to -27.6 ℃, resulting in 5.9% decrease of the maximum spreading factor. A relatively high Weber number leads to the formation of a fingering pattern, and a low surface temperature strengthens the phenomenon attributed to the enhanced deceleration of the liquid film. The moment at the maximum spreading diameter weakly increases with the surface temperature and strongly increases with the droplet size, while it barely increases with the impact velocity.