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.

Prolonged exposure to microgravity is known to invoke physiological changes which predispose individuals to orthostatic intolerance upon readaptation to the earth's gravitational field. Attenuated baroreflex responsiveness has been implicated in contributing to this inability to withstand orthostatic stress. To test this hypothesis, eight individuals were exposed to 15 days of simulated microgravity exposure using the 6° head-down bed rest model. Prior to, and after the simulated microgravity exposure, the following were assessed: a) aortic baroreflex function; b) carotid baroreflex function; c) cardiopulmonary baroreflex function; and d) the degree of interaction between the cardiopulmonary and carotid baroreflexes.

In orbit, finding the "bottom" of your coffee cup is a non-trivial task. Subtle forces often masked by gravity influence the containment and transport of fluids aboard spacecraft, often in surprising non-intuitive ways. Terrestrial experience with capillary forces is typically relegated to the micro-scale, but engineering community exposure to large length scale capillary fluidics critical to spacecraft fluid management design is low indeed. Low-cost drop towers and fast-to-flight International Space Station (ISS) experiments are increasing designer exposure to this fresh field of study. This work first provides a wide variety of drop tower tests that demonstrate fundamental and applied capillary fluidics phenomena related to liquid droplets and gas bubbles. New observations in droplet auto-ejection, droplet combustion, forced jet combustion, puddle jumping, bubble jumping, and passive phase separation are presented. We also present the Capillary Beverage Experiment on ISS as a fun and enlightening application of capillary fluidics where containment and passive control of poorly wetting aqueous capillary systems is observed. Astronauts are able to smell their coffee from the open stable container while still drinking in an Earth-like manner with the role of gravity replaced by the combined effects of surface tension, wetting, and special container geometry. The design, manufacture, low-g demonstrations, and quantitative performance of the Space Cups are highlighted. Comparisons of numerical simulations, drop tower experiments, and ISS experiments testify to the prospects of new no-moving-parts capillary solutions for certain water-based life support operations aboard spacecraft.

The design of fluid management systems requires accurate models for fluid transport. In the low gravity environment of space, gravity no longer dominates fluid displacement; instead capillary forces often govern flow. This thesis considers the redistribution of fluid along an interior corner. Following a rapid reduction of gravity, fluid advances along the corner measured by the column length z = L(t), which is governed by a nonlinear partial differential equation with dynamical boundary conditions. Three flow types are examined: capillary rise, spreading drop, and tapered corner. The spreading drop regime is shown to exhibit column length growth L ~ t2/5, where a closed form analytic solution exists. No analytic solution is available for the capillary rise problem. However, a perturbed power law similarity solution is pursued to approximate an analytic solution in the near neighborhood of the exact solution for the spreading drop. It is recovered that L ~ t1/2 for the capillary rise problem. The tapered corner problem is not analytically understood and hence its corresponding L is undocumented. Based on the slender corner geometry, it is natural to hypothesize the tapered corner column length initially behaves like the capillary rise regime, but after sufficient time has elapsed, it transitions into the spreading drop regime. This leads to a conjecture that its column length growth L is restricted to t2/5 < L < t1/2. To verify this conjecture an explicit finite difference numerical solution is developed for all three regimes. As will be shown, the finite difference scheme converges towards the analytic solutions for the spreading drop and capillary rise regimes. From this we assume the finite difference scheme is accurate for corner flows of similar geometries, and thus apply this scheme the more onerous criteria of the tapered corner. Numerical results support the conjectured L behavior for the tapered corner. Understanding the dynamics of such flows and responses to various geometries offers design advantages for spacecraft waste-management systems, fuel control, hydration containment, cryogenic flows, and a myriad of other fluid applications.

We study the formation and spreading of a turbulent jet of bubbles in microgravity. This has been analyzed from the recordings obtained in previous experimental campaigns of microgravity. Results have been compared with a simplified model of passive bubbles, in which bubbles are advected by the mean flow and dispersed due to the local degree of turbulence at each point of the jet. Thanks to the expertise obtained with this part of the thesis, we have designed and built a new experiment that has been used 36 times in the 4.7 s drop tower of ZARM (“Center of Applied Space Technology and Microgravity”) in Bremen. With this experiment we have obtained, for the first time in history, a monodisperse suspension of bubbles, within a turbulent flow, in microgravity. From the resulting measures we have characterized the relaxation time of pseudo-turbulence (previously generated due to the effect of buoyancy forces upon the injected bubbles in normal gravity conditions). We have also studied the interaction between bubbles and the turbulent medium. Results have been compared with Lattice-Boltzmann simulations of the flow. On the other hand, we have also studied the impact of residual gravitational vibrations (known as g-jitters) upon the quality of semiconductors solidified in microgravity. The quality of the resulting crystals has been studied from the analysis of the inhomogeneities in their dopant concentration. This study has been based entirely on simulations, but g-jitters have been modeled from acceleration signals measured in real space missions. / En la present tesi s’estudia, en primer lloc, la formació d’un doll turbulent de bombolles en condicions de microgravetat. Aquest ha sigut analitzat a partir del tractament de les gravacions obtingudes per altres investigadors en experiments de microgravetat. Els resultats s’han comparat amb un model simplificat de bombolles passives, en el que aquestes són arrossegades pel flux mitjà i, simultàniament, són dispersades degut al grau local de turbulència a cada punt. Gràcies a la experiència obtinguda en aquest anàlisi, s’ha dissenyat un nou experiment que ha sigut utilitzat en 36 llançaments de la torre de caiguda de 4.7 segons del ZARM (“Centre de Tecnologia Espacial Aplicada i Microgravetat”) a Bremen. Amb aquest experiment s’ha aconseguit, per primera vegada a la història, una suspensió monodispersa de bombolles, en el sí d’un flux turbulent, en condicions de microgravetat. A partir dels resultats obtinguts, s’ha caracteritzat per primera vegada el temps de relaxació de la pseudo-turulència (generada prèviament degut a l’efecte de les forces de flotació sobre les bombolles injectades en gravetat normal). També s’ha estudiat l’efecte causat per les bombolles en el medi turbulent. Els resultats han sigut comparats amb simulacions realitzades mitjançant el model de Lattice-Boltzmann. Per altra banda, s’ha estudiat també l’efecte que tenen les vibracions gravitatòries residuals sobre la qualitat de semiconductors solidificats en microgravetat. S’ha analitzat la qualitat dels cristalls resultants a partir de l’estudi de les inhomogeneïtats en la concentració de dopant. Aquest estudi ha sigut realitzat íntegrament a base de simulacions, però s’han establert els paràmetres dominants del soroll gravitatori a partir de valors mesurats en missions espacials reals.