Droplet generation during spray impact onto a downward-facing solid surface

Experiments were conducted to explore the droplet generation process when an ascending liquid spray impacts on a downward-facing solid surface. The droplets generated in the present experiments were classified into the two types: one is the splashing droplets generated by the impacts of droplets in spray and the other is the falling droplets produced from a liquid film formed on the solid surface. The falling droplets were further classified to the first falling droplets and the satellite droplets. It was found that the ratio of the splashing droplets increases with an increase in the impact Weber number. As for the droplet size, the splashing droplets were much smaller than the falling droplets. Hence, the oil immersion method and the image analysis were used to measure the sizes of the splashing droplets and the falling droplets, respectively. The size of the splashing droplets was in the same order with the impacting droplets in spray. On the other hand, the size of the falling droplets was proportional to the wavelength of the most unstable wave in the Rayleigh-Taylor instability. Interestingly, the diameters of the falling droplets (first falling and satellite droplets) were inversely proportional to their order. Using the experimental data accumulated in this work, dimensionless correlations were developed for the rates and sizes of the splashing and falling droplets. © 2021 Elsevier Inc.