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Research Containing: Fluid physics

Effect of ambient fluid flow upon onset of oscillatory thermocapillary convection in half-zone liquid bridge

by on 9 June 2015in Physical Sciences No comment

Onset of the oscillatory thermocapillary convection in a half-zone liquid bridge is known to be sensitive to heat transfer at free surface of the liquid bridge and the ambient air motion. The effect of the heat transfer through the free surface upon the onset of the transition mechanism and three-dimensional nature of the oscillatory flow, however, is not yet fully understood. In the present study, the thermal fluid behavior of the ambient gas and its effect upon the criticality were investigated experimentally and numerically. In the experiment, flows in the liquid bridge and the ambient air were visualized by suspending tracer particles in both fluids. Volume of the ambient air region was adjusted by placing two partition disks perpendicular to the liquid bridge. The onset of oscillation depended on the distance between the partition disks; the critical Marangoni number increased with the decreasing distance. Three-dimensional simulation of the liquid bridge and the ambient air has been performed by the finite difference method in order to determine the onset of the oscillation. The present calculations demonstrate significant influence of the heat transfer at the free surface on the onset of oscillation. The results of calculations yield a good agreement with the experimental critical values.

Related URLs:
http://dx.doi.org/10.1007/BF02945971

Results From the Physics of Colloids Experiment on ISS

by on 9 June 2015in Physical Sciences No comment

The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab ‘Destiny’ Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or sub-micron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

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Physics of colloids in space – Flight hardware operations on ISS

by on 9 June 2015in Physical Sciences No comment

The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab 'Destiny' Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or submicron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

Related URLs:
http://dx.doi.org/10.2514/6.2002-762

Preliminary Results of the Fluid Merging Viscosity Measurement Space Station Experiment

by on 9 June 2015in Physical Sciences No comment

During the Space Shuttle “down period” a call was put out for low upmass payloads. One of these “low up mass” International Space Station science experiments is the “Fluid merging Viscosity Measurement”, FMVM investigation. The purpose of FMVM is to measure the rate of coalescence of two highly viscous liquid drops and correlate the results with the liquid viscosity and surface tension. The experiment take advantage of the low gravitational free floating conditions in space to permit the unconstrained coalescence of two nearly spherical drops. The merging of the drops is accomplished by deploying them from a syringe and suspending them on 2 Nomex threads followed by the astronaut’s manipulation of one of the drops towards a stationary droplet till contact is achieved. Coalescence and merging occurs due to shape relaxation and reduction of surface energy, being resisted by the viscous drag within the liquid. The coalescence was recorded on video (ISS VTR) and some of the data was downlinked near real-time. A range of drop diameters, different liquids with differing viscosity and surface tensions should yield a large range of experiment parameters used to correlate with theory and to compare with numerical experiments. The results are important for a better understanding of the coalescence process. The experiment is also relevant to liquid phase sintering and is a potential new method for measuring viscosity of viscous glass formers at low shear rates.

Related URLs:
http://dx.doi.org/10.2514/6.2006-1142

Free surfaces in open capillary channels—Parallel plates

by on 9 June 2015in Physical Sciences No comment

This paper is concerned with forced flow through partially open capillary channels under microgravity conditions. The investigated channel consists of two parallel plates and is bounded by free liquid surfaces along the open sides. The curvature of the channel’s gas-liquid interface, which is exposed to the ambient pressure, adjusts to the pressure difference across the interface in accordance with the Young-Laplace equation. Flow within the channel becomes unstable when the free surface collapses and gas ingestion into the flow path occurs—a process that is also referred to as the “choking” phenomenon. During stable flow, the behavior of the free surface is influenced by flow conditions, geometric properties of the channel, and the pre-defined system pressure. In this work, a previously published stability theory is verified for a wide range of model parameters. A detailed study is provided for stable flow in capillary channels, including static and dynamic solutions. The results of the Capillary Channel Flow (CCF) experiment are evaluated and are found to agree well with numerical predictions. A clear limit is determined between stable and unstable flows. It is shown that the model can predict the shape of the free surface under various flow conditions. A numerical tool is employed to exploit the mathematical model, and the general behavior of free surfaces in said capillary channels is studied. Studies are conducted in both viscous and convective flow regimes and in the transition area between the two. The validity of the model is confirmed for a wide range of geometrical configurations and parameters.

Related URLs:
http://scitation.aip.org/content/aip/journal/pof2/27/1/10.1063/1.4906154

The capillary channel flow experiments on the International Space Station: experiment set-up and first results

by on 9 June 2015in Physical Sciences No comment

This paper describes the experiments on flow rate limitation in open capillary channel flow that were performed on board the International Space Station in 2011. Free surfaces (gas–liquid interfaces) of open capillary channels balance the pressure difference between the flow of the liquid in the channel and the ambient gas by changing their curvature in accordance with the Young-Laplace equation. A critical flow rate of the liquid in the channel is exceeded when the curvature of the free surface is no longer able to balance the pressure difference and, consequently, the free surface collapses and gas is ingested into the liquid. This phenomenon was observed using the set-up described herein and critical flow rates are presented for steady flow over a range of channel lengths in three different cross-sectional geometries (parallel plates, groove, and wedge). All channel shapes displayed decreasing critical flow rates for increasing channel lengths. Bubble ingestion frequencies and bubble volumes are presented for gas ingestion at supercritical flow rates in the groove channel and in the wedge channel. At flow rates above the critical flow rate, bubble ingestion frequency appears to depend on the flow rate in a linear fashion, while bubble volume remains more or less constant. The performed experiments yield vast data sets on flow rate limitation in capillary channel flow in microgravity and can be utilised to validate numerical and analytical methods.

Related URLs:
http://dx.doi.org/10.1007/s00348-013-1519-1

Does water foam exist in microgravity?

by on 9 June 2015in Physical Sciences No comment

Liquid foams are omnipresent in everyday life, but little is understood about their properties. On Earth, the liquid rapidly drains out of the foam because of gravity, leading to rupture of the thin liquid films between bubbles. Several questions arise: are liquid foams more stable in microgravity environments? Can pure liquids, such as water, form stable foams in microgravity whereas they do not on Earth? In order to answer these questions, we performed experiments both in parabolic flights and in the International Space Station.

Related URLs:
http://dx.doi.org/10.1051/epn/2014303

How foams unstable on Earth behave in microgravity?

by on 9 June 2015in Physical Sciences No comment

Foams made of gas bubbles dispersed in a liquid have limited stability and disappear rapidly unless surface active species are used. Foams can be a nuisance or very much sought after, however the control over the foaming and stability is still hampered because of the limited understanding of foam properties. On Earth, liquid rapidly drains out of the foam because of gravity, the liquid films formed between bubbles thin and break. In microgravity conditions, gravity drainage is suppressed and stability is expected to be greatly enhanced. We describe investigations of foams that are very unstable on Earth, including foams made with liquids containing antifoaming agents. Experiments performed in the International Space Station (ISS) show that foam generation can still be limited, however once created these foams are very stable.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0927775714005238

Effect of shape of HZ liquid bridge on particle accumulation structure (PAS)

by on 9 June 2015in Physical Sciences No comment

We focus on the dynamic particle accumulation structure (PAS) due to thermocapillary effect in a half-zone liquid bridge. Effects of shape of liquid bridge upon shape of the PAS itself and motion of particle on the PAS are discussed in the present study by tracking particles in the liquid bridge and by measuring temperature over the free surface. It is found that the variation of the shape of the liquid bridge leads to a significant variation of the temperature gradient on the free surface, which results in difference of the shape of the PAS. The variation of the PAS shape is mainly explained by drastic change of the axial velocity of the particle and less change of its azimuthal velocity near the free surface.

Related URLs:
http://dx.doi.org/10.1007/BF02915760

Dynamic Particle Accumulation Structure due to Thermocapillary Effect in Noncylindrical Half-Zone Liquid Bridge

by on 9 June 2015in Physical Sciences No comment

We focus on the dynamic particle accumulation structure (PAS) due to the thermocapillary effect in a half-zone liquid bridge. In this study, by tracking particles in the liquid bridge and by measuring temperature on the free surface, we discuss the effects of a liquid bridge shape described by its volume ratio upon the shape of the PAS itself and motion of particle on the PAS. The variation of the liquid bridge volume ratio leads to a significant variation of the temperature gradient on the free surface, which results in difference of the shape of the PAS, especially width of the PAS blade. By considering the simply modeled particle motion, we explain that the width of the PAS blade is determined by several parameters, and we find that its variation is explained mainly by a drastic change of the axial velocity of the particle on the surface.

Related URLs:
http://dx.doi.org/10.1111/j.1749-6632.2008.04073.x