Collision of a droplet with a hemispherical static droplet on a solid

The collision of a liquid droplet with a hemispherical droplet on a horizon tal smooth solid surface is studied experimentally as well as numerically. The hemispherical droplet is in the static state on the surface at room tem perature and its volume is the same as an incoming droplet. The incoming dr oplet impinges vertically on the top of the hemispherical droplet. Qualitat ive and quantitative observations of the collision behavior of the liquid d roplets are performed by means of a flash photographic method. The effect o f impact velocity of the incoming droplet is investigated. It is found that a circular thin liquid film like a crown is formed around the bottom of th e incoming droplet after the collision. The magnitude of the circular thin film becomes large with increasing the impact velocity. The collision behav ior of liquid droplets is also analyzed numerically. The Navier-Stokes equa tions for incompressible viscous fluid in the axisymmetric coordinate syste m are solved by a finite difference method. The effects of viscosity, surfa ce tension, and gravity are taken into account. The numerical results agree reasonably well with the experimental data. The hydrodynamics of the liqui d is investigated to understand the physics of phenomena. (C) 2001 Elsevier Science Ltd. All rights reserved.