Chapter 1: Introduction

1.1 Motivation 1.1.1 Droplet collision dynamics The droplet dynamics plays an important role in industrial applications such as a raindrop splashing on the ground, the impact of a fuel droplet on the walls of a combustion chamber, pesticide sprays, ink-jet printing, even more a comet impacts a planet, etc. The collision dynamics can be divided into two categories, including the droplet collision and the droplet collision on a liquid or solid surface. In the collision process, it is found that qualitatively different behaviors and phenomena can occur under different condition: the drop coalescence with the liquid surface, splashing by creating a crown, a so-called Worthington jet or a vortex, droplet rebound, etc. 1.1.2 Continuum scale The normal impact of a single drop onto a liquid film is a complicated fluid mechanics phenomenon. The major physical processes include mass, momentum and energy conservation due to spray drop impingement, splashing effects, various shear forces, piston acceleration, dynamic pressure effects, gravity driven flow, conduction, and convective heat and mass transfer. In process of collisions, the droplet will lose kinetic energy as the droplet strains and deforms. The strains will lead to viscous