More investigations in capillary fluidics using a drop tower

Abstract

A variety of contemplative demonstrations concerning intermediate-to-large length scale capillary fluidic phenomena were made possible by the brief weightless environment of a drop tower (Wollman and Weislogel in Exp Fluids 54(4):1, 2013). In that work, capillarity-driven flows leading to unique spontaneous droplet ejections, bubble ingestions, and multiphase flows were introduced and discussed. Such efforts are continued herein. The spontaneous droplet ejection phenomena (auto-ejection) is reviewed and demonstrated on earth as well as aboard the International Space Station. This technique is then applied to novel low-g droplet combustion where soot tube structures are created in the wakes of burning drops. A variety of new tests are presented that routinely demonstrate ‘puddle jumping,’ a process defined as the spontaneous recoil and ejection of large liquid drops from hydrophobic surfaces following the step reduction in ‘gravity’ characteristic of most drop towers. The inverse problem of ‘bubble jumping’ is also demonstrated for the case of hydrophilic surfaces. A variety of puddle jump demonstrations are presented in summary as a means of suggesting the further exploitation of drop towers to study such large length scale capillary phenomena.