Experiments on the Splashing Limit During Drop Impact Onto a Thin Liquid Film

The phenomenon of secondary droplet production during single drop impingement onto a liquid film is encountered in many industrial situations. Typical examples in the field of nuclear engineering are the spray cooling of hot surface and the atomization of radioactive liquids in severe accident. Therefore, the prediction of the onset of secondary droplet production is very important. It is known that the two types of droplet splashing mechanisms are present: the prompt splash and the late splash. The main purpose of this research is to determine the splashing limit separately for the prompt splash and the late splash. It is expected that the splashing limits are expressed using the three dimensionless numbers: the Weber number, the Ohnesorge number, and the dimensionless film thickness. Experiments were hence carried out using pure water and silicone oil as the working liquid. The experimental ranges were 129–606 for the Weber number, 0.00183–0.00300 for the Ohnesorge number, and 0.13–3.0 for the dimensionless film thickness. It was found that the occurrence of splashing can be predicted more accurately if the splashing limit is evaluated separately for the prompt splash and the late splash.