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Stirring Up an Elastic Fluid: Critical Viscosity of Xenon-2 (CVX-2)Whipped cream stays in place even when turned upside down. Yet it readily flows through the nozzle of a spray can to reach the dessert plate. This demonstrates the phenomenon of shear thinning that is important to many industrial and physical processes. Paints, film emulsions, and other complex solutions that are highly viscous under normal conditions but become thin and flow easily under shear forces. A simple fluid, such as water, does not exhibit shear thinning under normal conditions. Very close to the liquid-vapor critical point, where the distinction between liquid and vapor disappears, the fluid becomes more complex and is predicted to display shear thinning. At the critical point, xenon atoms interact over long distances in a classical model of cooperative phenomena. Physicists rely on this system to learn how long-range order arises. The Critical Viscosity of Xenon Experiment (CVX-2) will measure the viscous behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. Although it does not easily combine with other chemicals, its viscosity at the critical point can be used as a model for a range of fluids. Viscosity originates from the interactions of individual molecules. It is so complicated that, except for the simplest gas, it cannot be calculated accurately from theory. Tests with critical fluids can provide key data, but are limited on Earth because critical fluids are highly compressed by gravity. CVX-2 employs a tiny metal screen vibrating between two electrodes in a bath of critical xenon. The vibrations and how they dampen are used to measure viscosity. CVX flew on STS-85 (1997), where it revealed that, close to the critical point, the xenon is partly elastic: it can 'stretch' as well as flow. For STS-107, the hardware has been enhanced to determine if critical xenon is a shear-thinning fluid.
Document ID
20030011402
Acquisition Source
Glenn Research Center
Document Type
Other
Authors
Berg, Robert F.
(National Inst. of Standards and Technology Gaithersburg, MD United States)
Moldover, Michael R.
(National Inst. of Standards and Technology Gaithersburg, MD United States)
Zimmerli, Gregory A.
(NASA Glenn Research Center Cleveland, OH United States)
Motil, Susan M.
Date Acquired
August 21, 2013
Publication Date
December 16, 2002
Publication Information
Publication: STS 107 Shuttle Press Kit: Providing 24/7 Space Science Research
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
NASA/FS-2002-06-069-MSFC
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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