Two-component droplet wall-film interaction: Crown morphology as a function of liquids viscosity and surface tension

The study of single droplet impact onto thin films of a different liquid (two-component droplet wall-film interaction) has a great number of industrial applications like combustion processes, spray freeze drying or extinguishing film fuelled fires. In order to improve these applications the prediction of the number and size of the secondary droplets is essential. In this work special emphasis is given to the formation process of secondary droplets during crown-type splashing. In this process liquid jets (or fingers) develop along the upper rim, which later on break-up into secondary droplets. Hence, the first step for the prediction of secondary droplets is to predict the number of jets. Therefore, a systematic experimental study is carried out, employing low surface tension liquids (~28 mN/m like n-Hexadecane and Hyspin. First, the splashing morphologies are linked to the characteristic crown parameters. Second, it is shown that the maximum number of liquid fingers from the liquid crown Nmax is not a linear function of the crown rim radius. Instead, we present the dependency of Nmax on experimental parameters like the non-dimensional film thickness (0.1 < δ < 0.5) and the Weber number (400 <We < 1700). The dimensionless film thickness δ has the strongest influence. An increase in δ results in a decrease of the maximum number of liquid fingers Nmax.