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Research Containing: Fluid physics

IVIDIL: on-board g-jitters and diffusion controlled phenomena

by on 9 June 2015in Physical Sciences No comment

The experiment IVIDIL (Influence of Vibrations on Diffusion in Liquids) has been performed in 2009-2010 onboard the ISS, inside the SODI instrument mounted in the Glovebox at the ESA Columbus module. 55 experimental runs were carried out and each of them lasted 18 hours. The objectives of the experiment were multi-fold and here we report results for one of them. After each space experiment there is a discussion about the role of onboard g–jitters. The attention is focused on reproducibility of the results, their accuracy and comparison with numerical simulations conducted in exact geometry and using the physical properties of the system. We shortly report on the results of six experiments which were performed in natural environment of the ISS without forced vibrations. Thermodiffusion process in the cells filled with binary mixtures was monitored by means of optical digital interferometry. Perturbations of the diffusion control processes by on-board g-jitters is not observed in nominal regime of the ISS. Perturbations of thermodiffusion process were observed in non-nominal regime of the ISS, e.g. attitude control maneuvers.

Related URLs:
http://stacks.iop.org/1742-6596/327/i=1/a=012031

3D PTV measurement of oscillatory thermocapillary convection in half-zone liquid bridge

by on 9 June 2015in Physical Sciences No comment

Three-dimensional (3D) reconstruction of a unique particle motion in oscillatory thermocapillary convections in a small-sized half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3D particle tracking velocimetry (PTV). By placing a small cubic beam splitter above a transparent top rod, simultaneous observation of the particles in the bridge by use of two CCD cameras was realized. Reconstruction of the 3D trajectories and the particle velocity fields in several types of oscillatory flow regimes was conducted successfully for a sufficiently long period without losing particle tracking.

Related URLs:
http://dx.doi.org/10.1007/s00348-004-0885-0

Instability of thermocapillary convection in long liquid bridges of high Prandtl number fluids in microgravity

by on 9 June 2015in Physical Sciences No comment

This paper reports experimental results on the instability of thermocapillary convection in long half-zone liquid bridges of high Prandtl number fluids (Pr=67, 112 and 207 for 5, 10 and 20 cSt silicone oils, respectively). The experiments were carried out in microgravity on the International Space Station, which allowed sufficiently long waiting period for the development of instability. Critical temperature differences were measured for liquid bridges of 30 and 50 mm diameters and up to 62.5 mm length. The resultant critical Marangoni numbers (Mac) were obtained for a wide range of aspect ratio (=height/diameter), AR, up to AR=2.0. Linear stability analyses for Pr=67 were also carried out to obtain numerical data for comparison. The present experimental results for Pr=67 indicate 5.0×103<Mac<2.0×104 for large AR (AR>1.25) and they are in good agreement with the present linear stability analysis result. In contrast, the present results are considerably smaller than the previous data (Pr=74) taken in the Space Shuttle experiments. It is shown that this difference is due to the effect of heating rate of the liquid bridge. The data for oscillation frequency and azimuthal mode number are also presented. The non-dimensional oscillation frequencies as well as Mac for Pr=67 have shown a sudden decrease at around AR=1.25, suggesting the bifurcation of neutral stability curves.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0022024815002353

Bubble Formation and Transport During Directional Solidification in Microgravity: Model Experiments on the Space Station

by on 9 June 2015in Physical Sciences No comment

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Related URLs:
http://dx.doi.org/10.2514/6.2004-627

Interim Results from the Capillary Flow Experiment Aboard ISS: The Moving Contact Line Boundary Condition

by on 9 June 2015in Physical Sciences No comment

This paper highlight the in-flight operations of the Capillary Flow Experiment Contact Line experiments (2 each) performed aboard the International Space Station (ISS) during the period between Increment 9 ad 13 (8/2004-9/2006). The CFE-CL vessels are simple fluid interface experiments that probe the uncertain impact of the boundary condition at the contact line – the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluid management systems aboard spacecraft. Difference in fluid behavior of nearly identical statics interfaces to nearly identical disturbances are attributed to differences in fluid physics in the vicinity of the contact line. The CFE-CL experiments are conducted on five occasions by ISS Astronauts M. Fincke, W. McArthur, and J. Williams. The number of tests performed including additional science experiments is made possible by various centrifuge techniques employed by the astronauts permitting the re-use of the once-wetted container. Several of these ‘extra science’ experiments are briefly described herein. Intermittent real-time video and audio downlink, continuous communication with the ground crews at NASA JSC, MSGFC and GRC, and the clear and entreating commentary of the crew made the conduct of the tests on ISS an enjoyable, laboratory-like experience for the science on the ground. The flight tapes from the onboard cameras have been results to Earth (name flight) and are expected to be digitized, reduced and made publically available in the near future. A concurrent blind numerical analysis is underway to predict the experiments result using a generally accepted CFD-tool with specific contact line boundary conditions.

Related URLs:
http://dx.doi.org/10.2514/6.2007-747

The Capillary Flow Experiments Aboard ISS: Moving Contact Line Experiments and Numerical Analysis

by on 9 June 2015in Physical Sciences No comment

This paper serves as a first presentation of quantitative data reduced from the Capillary Flow Contact Line Experiments recently completed aboard the International Space Station during Expeditions 9-16, 8/2004-11/2007. The simple fluid interface experiments probe the uncertain impact of the boundary condition at the contact line—the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluids management systems aboard spacecraft. Differences in fluid behavior of nearly identical static interfaces to nearly identical perturbations are attributed primarily to differences in fluid physics in the vicinity of the contact line. Free and pinned contact lines, large and small contact angles, and linear and nonlinear perturbations are tested for a variety of perturba- tion types (i.e. axial, slosh, and other modes) to right circular cylinders. The video and digi- tized datasets are to be made publicly available for model benchmarking. In parallel with the experimental effort, blind numerical predictions of the dynamic interface response to the experimentally applied input perturbations are offered as a demonstration of current capa- bilities to predict such phenomena. The agreement and lack of agreement between the experiments and numerics is our best guide to improve and/or verify current analytical methods to predict such phenomena critical to spacecraft fluid systems design.

Related URLs:
http://dx.doi.org/10.2514/6.2008-816

Vibrating liquids in space

by on 9 June 2015in Physical Sciences No comment

Everybody is familiar with the action of gravity on a fluid where density gradients are present due to heating or compositional difference. Due to buoyancy, the denser portions sink to the bottom of the container, pushing away the lighter ones. As a result, convection sets in, transporting heat and mass. In weightlessness conditions, this driving force is absent but inertia exists as the tendency of a body to resist acceleration. When a container filled with liquid is subjected to high frequency vibrations, the fluid is not able to react due to inertia and this may create a flow. If the density is uniform, then the fluid moves as a solid body. However, when density gradient is present, also inertia will not be uniform, resulting in convective motion. Obviously, there is analogy between gravity-induced and inertia-driven convection, as a result of the Einstein equivalence principle, although the second one is almost unknown. What would be the impact of vibration on dispersion by molecular diffusion and heat transfer without buoyancy?

Related URLs:
http://dx.doi.org/10.1051/epn/2010601

Postflight summary of the Capillary Flow Experiments aboard the International Space Station

by on 9 June 2015in Physical Sciences No comment

This paper provides a summary of the experimental, analytical, and numerical results of the Capillary Flow Experiment (CFE) performed onboard the International Space Station (ISS) from Increment 9 (beginning August, 2004) through Increment 16 (ending December, 2007), with 19 operations by 7 astronauts; M. Fincke, W. McGarthur, J. Williams, S. Williams, M. Lopez-Alegria, C. Anderson, and P. Whitson. CFE consists of 6 approximately 1 to 2kg experiment units designed to probe certain capillary phenomena of fundamental and applied importance, such as capillary flow in complex containers, critical wetting in discontinuous structures, and large length scale contact line dynamics. Highly quantitative video images from the simply performed flight experiments provide immediate confirmation of the usefulness of current analytical design tools as well as provide guidance to the development of new ones. A brief review of the experiments and procedures is provided before reporting the status of the data collection, reduction, and comparisons with both analytic and numerical predictions. The products of the work include design tools for modeling capillary interface dynamics relevant to spacecraft engineering systems. The CFE experimental program was initiated in February 2003 as part of a fast-paced unscheduled payloads/experiments program. All six of the units were performed on standby or at times as part of NASA Saturday Science and all units have been returned to Earth for post flight analysis. The experiments were conducted in stand-alone mode by a single crewmember on the Maintenance Work Area of the ISS.

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Initial transient behavior in directional solidification of a bulk transparent model alloy in a cylinder

by on 9 June 2015in Physical Sciences No comment

To characterize the dynamical formation of three-dimensional (3-D) arrays of cells and dendrites under diffusive growth conditions, in situ monitoring of a series of experiments on a transparent succinonitrile–0.24 wt.% camphor model alloy was carried out under low gravity in the Device for the Study of Critical Liquids and Crystallization (DECLIC) Directional Solidification Insert on board the International Space Station (ISS). The present paper focuses on the study of the transient solid–liquid interface recoil. Numerical thermal modeling led us to identify two thermal contributions to the interface recoil that increase with the pulling rate and add to the classical recoil associated with the solute boundary layer formation. As a consequence of those additional contributions, the characteristic front recoil is characterized by a fast initial transient followed by stabilization to a plateau whose location depends on pulling rate. The analysis of comparative experiments carried out on the ground shows the absence of stabilization of the interface position, attributed to longitudinal macrosegregation of the solute induced by convection. This behavior is surprisingly also observed in space experiments for low pulling rates. An order of magnitude analysis of the mode of solute transport reveals that for these conditions, the effective level of reduced gravity on board the ISS is not sufficiently low to suppress convection so that the interface recoils with longitudinal macrosegregation in a similar way as in ground experiments.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S1359645414008775

Thermocapillary Phenomena and Performance Limitations of a Wickless Heat Pipe in Microgravity

by on 9 June 2015in Physical Sciences No comment

A counterintuitive, thermocapillary-induced limit to heat- pipe performance was observed that is not predicted by current thermal-fluid models. Heat pipes operate under a number of physical constraints including the capillary, boiling, sonic, and entrainment limits that fundamentally affect their performance. Temperature gradients near the heated end may be high enough to generate significant Marangoni forces that oppose the return flow of liquid from the cold end. These forces are believed to exacerbate dry out conditions and force the capillary limit to be reached prematurely. Using a combination of image and thermal data from experiments conducted on the International Space Station with a transparent heat pipe, we show that in the presence of significant Marangoni forces, dry out is not the initial mechanism limiting performance, but that the physical cause is exactly the opposite behavior: flooding of the hot end with liquid. The observed effect is a consequence of the competition between capillary and Marangoni-induced forces. The temperature signature of flooding is virtually identical to dry out, making diagnosis difficult without direct visual observation of the vapor-liquid interface.

Related URLs:
http://link.aps.org/doi/10.1103/PhysRevLett.114.146105