This work was funded in part through NASA cooperative agreements NNX12AO47A and NNX16AC38G, and NIAC grant NNX15AR93G (PI John Graf, NASA JSC). L.T. would like to thank Dr. A. Wollman, K. Cardin, E. Schmidt, R. Rasheed, I. Rodriguez, C. Turner, and R. Mungin for their support.
Fluid dynamics, Microfluidics, Capillarity, Reduced gravity environments, Contact angle
When confined within containers or conduits, drops and bubbles migrate to regions of minimum energy by the combined effects of surface tension, surface wetting, system geometry, and initial conditions. Such capillary phenomena are exploited for passive phase separation operations in micro-fluidic devices on earth and macro-fluidic devices aboard spacecraft. Our study focuses on the migration and ejection of large inertial-capillary drops confined between tilted planar hydrophobic substrates (a.k.a., wedges). In our experiments, the brief nearly weightless environment of a 2.1 s drop tower allows for the study of such capillary dominated behavior for up to 10 mL water drops with migration velocities up to 12 cm/s. We control ejection velocities as a function of drop volume, substrate tilt angle, initial confinement, and fluid properties. We then demonstrate how such geometries may be employed as passive no-moving-parts droplet generators for very large drop dynamics investigations. The method is ideal for hand-held non-oscillatory ‘droplet’ generation in low-gravity environments.
Copyright (c) 2021 The Authors
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Torres, L.J., Weislogel, M.M. The ejection of large non-oscillating droplets from a hydrophobic wedge in microgravity. npj Microgravity 7, 52 (2021). https://doi.org/10.1038/s41526-021-00182-4