The Physics PhD Seminar Series is held over Zoom. One PhD student gives a 15-minute presentation on their work, followed by questions. The presentations are aimed at a general physics audience.
Collision rate of micron-sized water droplets in clouds crucially affects the rate of rain formation. In thunderclouds, the droplets carry electrical charges which must affect their collision rates. How charges affect droplet collisions is not well understood, even in still air. The state-of-the-art employs numerical integration of trajectories, an approach which obscures a general understanding of the effect of droplets' inertia, fluid inertia, and other physical effects.
In this talk, I discuss the effect of electrical charge on collisions of hydrodynamically interacting, micron-sized water droplets settling in still air. Analysis of experimental data, and numerical simulations suggest that the relative dynamics of charged droplets contains a non-trivial fixed point. The relative dynamics of water droplets may be analysed using a dynamical systems approach, where the dynamics is controlled by the non-trivial fixed point and its associated separatrix. This approach allows, for the first time, to advance beyond numerical trajectory integration and develop a general picture of charged droplet collisions. I detail how this approach could be used to describe collisions of charged droplets.