NIST experiment’s data acquired before space shuttle tragedy

NIST scientists used an experiment aboard the STS-107 mission of the space shuttle Columbia to look for a particular type of flow behavior, never before seen in a pure liquid, that may have practical applications in products ranging from paints and plastics to foods and pharmaceuticals. Almost all of the data from the experiment-sent by telemetry to the ground during the mission-were acquired before the tragic loss of the shuttle orbiter and its seven- member crew on Feb. 1, 2003.

The “Critical Viscosity of Xenon-2″ (CVX2) experiment measured the changes in viscosity (resistance to flow) of a xenon sample as it was stirred rapidly and approached the “critical point.” Xenon, an inert gas, exhibits unusual behavior near its critical point, at which it turns into a milky fluid with properties between those of a liquid and a gas. The experiment was conducted in the microgravity of orbit because the changes in viscosity that take place in the critical state cannot be measured accurately in Earth’s gravity.

The experimental data should reveal whether xenon exhibits “shear thinning,” meaning its usual resistance to flow is weakened by a large shear rate. Although predicted for decades, shear thinning has never been observed near the critical point of any pure fluid. Xenon, a pure fluid with a very simple structure and a critical temperature just below room temperature, is convenient for such experiments. The data may help scientists better understand shear thinning in complex fluids such as paints and foods (e.g., whipped cream), which need to flow easily during application and stand firm afterwards.

The latest results will expand on those gathered during a 1997 NIST space shuttle experiment, which accurately measured the viscosity of xenon and revealed a viscosity increase of 37 %-double the best measurements on Earth. That experiment also showed that xenon, when close to the critical point, is partly elastic; that is, it can “stretch” as well as flow.

CONTACT: Robert Berg, (301) 975-2466; robert.berg@nist.gov or Michael Moldover, (301) 975-2459; michael.moldover@nist.gov.

Copyright Superintendent of Documents Mar/Apr 2003