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Research Containing: Liquids

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

Modeling of the Fluid Merging Viscosity Measurement (FMVM) International Space Station experiment with COMSOL MultiPhysics

by on 9 June 2015in Physical Sciences No comment

The purpose of FMVM was 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 takes advantage of the low gravitational force free floating conditions in space allowing the unconstrained coalescence of two nearly spherical drops. The merging of the drops is accomplished by deploying them from a syringe and suspension on Nomex threads. An astronaut’s slow manipulation of one of the drops toward a stationary droplet till there is contact initiates the droplet coalescence. Coalescence and merging occurs due to shape relaxation and reduction of surface energy, being resisted by the viscous drag within the liquid. Experiments were conducted onboard the International Space Station in July of 2004 and subsequently in May of 2005. The coalescence was recorded on video and down-linked near real-time. When the coefficient of surface tension for the liquid is known, the increase in contact radius can be used to determine the coefficient of viscosity for that liquid. The viscosity is determined by fitting the time to achieve contact neck diameter equal to half of the initial droplet diameter. This time is compared with a relaxation time scaling coefficient to arrive at the liquid viscosity. Recent fluid dynamical numerical simulations with COMSOL MultiPhysics of the coalescence process will be presented. The results are important for a better understanding of the coalescence process. The experiment is also relevant to liquid phase sintering, free form in-situ fabrication, and as a potential new method for measuring the viscosity of viscous glass formers at low shear rates.

Related URLs:
http://dx.doi.org/10.2514/6.2009-1151

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

Fluid Merging Viscosity Measurement (FMVM) Experiment on the International Space Station

by on 9 June 2015in Physical Sciences No comment

The concept of using low gravity experimental data together with fluid dynamical numerical simulations for measuring the viscosity of highly viscous liquids was recently validated on the International Space Station (ISS). After testing the proof of concept for this method with parabolic flight experiments, an ISS experiment was proposed and later conducted onboard the ISS in July, 2004 and subsequently in May of 2005. In that experiment a series of two liquid drops were brought manually together until they touched and then were allowed to merge under the action of capillary forces alone. The merging process was recorded visually in order to measure the contact radius speed as the merging proceeded. Several liquids were tested and for each liquid several drop diameters were used. It has been shown that when the coefficient of surface tension for the liquid is known, the contact radius speed can then determine the coefficient of viscosity for that liquid. The viscosity is determined by fitting the experimental speed to theoretically calculated contact radius speed for the same experimental parameters. Experimental and numerical results will be presented in which the viscosity of different highly viscous liquids were determined, to a high degree of accuracy, using this technique.

Related URLs:
http://dx.doi.org/10.2514/6.2007-1151