Inkjet droplets in the very first issue of Physical Review Applied
Inkjet printers fire droplets that travel a thousand times their own radius every second. The dynamics of this process involve a delicate interplay between surface tension and hydrodynamics that have now been experimentally measured in unprecedented detail. Experimental data are compared with analytic predictions to reveal internal velocities within a droplet that likewise vary by many meters per second within a droplet only tens of microns across.
Inkjet printing deposits droplets with a well-controlled narrow size distribution. This paper aims at improving experimental and numerical methods for the optimization of drop formation. We introduce a method to extract the one-dimensional velocity profile inside a single droplet during drop formation. We use a novel experimental approach to capture two detailed images of the very same droplet with a small time delay. The one-dimensional velocity within the droplet is resolved by accurately determining the volume distribution of the droplet. We compare the obtained velocity profiles to a numerical simulation based on the slender jet approximation of the Navier-Stokes equation and we find very good agreement.