Fast microdroplet impact: a high-detail investigation using novel experimental methods

Optimization of everyday applications (e.g. diesel engines and spray cleaning) requires full control of high-speed microdroplet impact. However, experimental data in this regime is scant. We present a novel method to visualize impact of droplets with a diameter of 50 micometers on hydrophillic and -phobic surfaces, at frame rates beyond 10Mfps. This allowed us to study in high detail the impact dynamics for velocities up to 50 m/s. In addition, the exact droplet shape during spreading was determined by a bottom-view interferometry technique. The study was complemented with numerical simulations, providing a complete and detailed picture of the 3D-flow field during impact. The physics of microdroplet spreading are scale-independent (they are governed by the Weber- and Reynolds numbers alone). This allows to describe and optimize the impact of droplets in a range of industrial applications.