Spontaneous Capillarity-Driven Droplet Ejection

AbstractThe rst large length-scale capillary rise experiments were con-ducted by R. Siegel using a drop tower at NASA LeRC shortly after the1957 launch of Sputnik I. Siegel was curious if the wetting uid wouldexpel from the end of short capillary tubes in a low-gravity environ-ment. He observed that although the uid partially left the tubes, itwas always pulled back by surface tension, which caused the uid to re-main pinned to the tubes’ end. By exploiting tube geometry and uidproperties, we demonstrate that such capillary ows can in fact eject avariety of jets and drops. This uid dynamics video provides a histor-ical overview of such spontaneous capillarity-driven droplet ejection.Footage of terrestrial and low earth orbit experiments are also shown.Droplets generated in a microgravity environment are 10 6 times largerthan those ejected in a terrestrial environment. The accompanying ar-ticle provides a summary of the critical parameters and experimentalprocedures. Scaling the governing equations reveals the dimension-less groups that identify topological regimes of droplet behavior whichprovides a novel perspective from which to further investigate jets,droplets, and other capillary phenomena over large length scales.