Energy exchange during the early phase of droplet impact onto a dry surface

Abstract

This study investigates droplet impact dynamics on a rigid substrate using droplets of water and water–glycerol mixtures. Experiments are conducted in the Weber number range of 179–929, and the corresponding Reynolds numbers are in the range of 5253–12 090. The profile of the droplet interface is studied. Assuming self-similarity in the internal flow at the interface of the droplet, the profiles are scaled using appropriate scales. It is observed that the profiles of the droplet interface (at different points of time) collapse close to each other when plotted in this manner. This observation serves as an experimental evidence to the self-similarity of the internal flow in this phase. Based on this fact, we make an estimate of kinetic energy at early stages of droplet impact. The surface energy is also estimated by assuming axisymmetry in the droplet profile obtained through back-light imaging. We observe that a considerable amount of the kinetic energy is lost during the early stages of droplet impact. We believe that an accurate estimation of this deficit in kinetic energy at an early stage of impact will be necessary to account in the energy based models for droplet impact.