Collision Behavior of Heterogeneous Liquid Droplets

Abstract

Processes involved in the collision of liquid droplets enhance their atomization. If droplets contain more than one component, these processes become especially strong and intense. In this paper, we describe experiments for heterogeneous droplets of water solutions, emulsions, and slurries typical of fuel, firefighting, and heat and mass transfer technologies. We determine the conditions for a stable occurrence of the four droplet collision regimes: bounce, coalescence, separation, and disruption. We go on to establish how droplet dimensions, velocities, impact angles, component concentrations, as well as liquid viscosity, surface tension, and density affect collision parameters. The experimental results are generalized using collision regime maps produced in the coordinate systems controlling for the variations of Weber, Reynolds, Ohnesorge, and capillary numbers, as well as angular and linear interaction parameters. The results are compared with the scarce data by other authors. The Weber number variation range is not the only factor influencing the droplet collision behavior the form of four interaction regimes. Viscosity and surface tension of the liquid have a significant impact as well. An increase in the viscous forces can provide conditions for droplet breakup into a maximum number of small fragments. Coalescence is the dominating mode at low viscosity and high surface tension. Droplet bounce occurrence does not only depend on the Weber number range but also on phase transformations and thermophysical properties of the liquid. Finally, we determine the droplets interaction parameters for group of liquids that can provide intense droplet atomization through collisions.