Impact of emulsion drops on a solid surface: The effect of viscosity

Abstract

This paper presents a study of the impact of various water in Jatropha biodiesel emulsion drops on a stainless steel surface. The composition of the emulsion is varied by changing the volume percentage of water. The effect of the change in the composition and the Weber number (We) is reported. With the increase in the percentage of water, the domination of the viscous force is observed to increase. The emulsions having lower percentages of water (less than 20%) are found to be inertia dominated, while the others (equal or greater than 20%) are viscous dominated. The maximum spreading diameter normalized by the preimpact diameter, βmax, decreases with an increase in the percentage of water due to the increased viscous losses. Consequently, the minimum splat thickness factor and the equilibrium splat thickness factors increase with the percentage of water. Higher viscous losses affect the shape of the drop during spreading as well. Emulsification delays the splashing due to the higher viscous losses. No splashing is observed for the emulsions containing 20 or higher percentage of water, since viscosity dominantly affects the impact. To confirm the effect of the viscosity, βmax obtained from the experiments are compared with that obtained from various existing models. Another purpose of the comparison is to check the suitability of the models for the emulsion drop impact. Only one model among all studied is found to compare well because the model assumes that the characteristic length for viscous dissipation is of the order of splat thickness.