ID 241

Content of secondary droplets formed by drop impact onto a solid wall wetted by another liquid

 

Abstract:

Drop impact onto a wetted substrate is of importance in many engineering applications, for example in a combustion chamber, during spray coating or airframe icing. In some applications the liquids of the impacting drops and of the wall films are different, as in the case of internal combustion engines, where fuel spray impacts onto walls of a cylinder, lubricated by a thin oil film. The composition of secondary drops generated by the splashing of impacting drops significantly influence the transport processes in the resulting spray, like evaporation, mixture preparation and combustion. The impact outcome is determined by the inertial, viscous and capillary forces. If the drop and wall film are of different fluids, the miscibility and the interfacial forces also influence the outcome. The main focus of this experimental work is on the characterization of the secondary spray produced by an impact of a single drop onto a thin, horizontal wall film of a different fluid. The liquids of drop and wall film are non-miscible. A dye is added to the liquid of the drop in order to distinguish both liquids during and after the drop impact. Using an optical measurement technique consisting of a color highspeed camera, the fluid motion of both liquids after the impact is visualized and analyzed. The number and the size of the secondary drops are measured and their composition is characterized for a wide range of impact parameters and for different viscosity ratios of the drop and film liquids. Finally, a theoretical model describing the liquid composition of the secondary droplets is developed on the basis of the experimental data.