Drop Towers provide brief terrestrial access to microgravity environments. When used for capillary fluidics research, a drop tower allows for unique control over an experiment's initial conditions, which enables, enhances, or otherwise improves the study of capillary phenomena at significantly larger length scales than can normally be achieved on the ground. This thesis provides a historical context for the introduction of a new, highly accessible, 2.1s tower design used for capillary research and presents a variety of demonstrative experimental results for purely capillarity-driven flows leading to bubble ingestion, sinking flows, multiphase flows, and droplet ejections. The focus of this thesis is paid to capillarity-driven droplet ejection including historical significance, mathematical models, criteria for ejection and experimental validation. A scale analysis provides a single parameter Su+ which is used to predict the flow velocity at the base of the nozzle. By simplifying the flow in the nozzle we identify two criteria for auto-ejection, the nozzle must be `short' and the velocity of the flow must be sufficient to invert the liquid meniscus and overpower surface tension at the nozzle tip such that We⁺ > 12. Drop tower experiments are conducted and compared to analytical predictions using a regimemap. This thesis also includes results from experiments experiments conducted in a stationary ground-based laboratory and aboard the International Space Station which clearly demonstrate droplet ejection in regimes from transient liquid jets to large isolated drops. Droplets generated in a microgravity environment are 106 times larger than 1g₀ counter-parts.

Capillary flows continue to be important in numerous spacecraft systems where the effective magnitude of the gravity vector is approximately one millionth that of normal Earth gravity. Due to the free fall state of orbiting spacecraft, the effects of capillarity on the fluid systems onboard can dominate the fluid behavior over large length scales. In this research three investigations are pursued where the unique interplay between surface tension forces, wetting characteristics, and system geometry control the fluid behavior, whether in large systems aboard spacecraft, or micro-scale systems on Earth. First, efforts in support of two International Space Station (ISS) experiments are reported. A description of the development of a new NASA ground station at Portland State University is provided along with descriptions of astronaut training activities for the proper operation of four handheld experiments currently in orbit as part of the second iteration of the Capillary Flow Experiments (CFE-2). Concerning the latter, seven more vessels are expected to be launched to the ISS shortly. Analysis of the data alongside numerical simulations shows excellent agreement with theory, and a new intuitive method of viewing critical wetting angles and fluid bulk shift phenomena is offered. Secondly, during the CFE-2 space experiments, unplanned peripheral observations revealed that, on occasion, rapidly compressed air bubbles migrate along paths with vector components common to the residual acceleration onboard the ISS. Unexpectedly however, the migration velocities could be shown to be up to three orders of magnitude greater than the appropriate Stokes flow limit! Likely mechanisms are explored analytically and experimentally while citing prior theoretical works that may have anticipated such phenomena. Once properly understood, compressed bubble migration may be used as an elegant method for phase separation in spacecraft systems or microgravity-based materials manufacturing. Lastly, the stability of drops on surfaces is important in a variety of natural and industrial processes. So called 'wall-edge-vertex bound drops' (a.k.a. drops on blade tips or drops on leaf tips which they resemble) are explored using a numerical approach which applies the Surface Evolver algorithm through implementation of a new file layer and a multi-parameter sweep function. As part of a recently open sourced SE-FIT software, thousands of critical drop configurations are efficiently computed as functions of contact angle, blade edge vertex half-angle, and g-orientation. With the support of other graduate students, simple experiments are performed to benchmark the computations which are then correlated for ease of application. It is shown that sessile, pendant, and wall-edge bound drops are only limiting cases of the more generalized blade-bound drops, and that a ubiquitous 'dry leaf tip' is observed for a range of the critical geometric and wetting parameters.