Get Preliminary Results of the CVX experiment.
Viscosity originates in the interactions between fluid molecules. These
interactions are so complicated that, except for low density gases, no
fluid's viscosity can be calculated accurately from theory. Progress in
understanding viscosity has been made by studying moderately dense gase
and, more recently, fluids near the critical point. A pure fluid's critical
point occurs at the highest temperature (Tc) where liquid and vapor can
coexist in the same container. One of the unusual behaviors near this
unique temperature and pressure is an increase in viscosity. Although the
critical temperature and viscosity can differ greatly among fluids, the
relative size of the viscosity increase is the same for all pure fluids.
Modern theories predict this universal behavior and relate the increase in
viscosity to the spontaneous fluctuations in density that occur near the
critical point. By measuring the viscosity of a small sample of xenon, the
CVX experiment will test these theories with great precision.
Xenon was chosen because it is a simple fluid, its other critical
properties have been well measured, and it has a critical temperature which
is conveniently just below room temperature. CVX will measure the predicted
40% viscosity increase as the sample is cooled to within 0.0006 degrees of
Tc. Measurements this close to Tc cannot be made on Earth because normal
gravity causes the xenon's density to vary with height. Near Tc, the
density at the bottom of a 1-millimeter-high sample is 8% higher than the
density at the top of the sample. This so-called "stratification" is
greatest exactly at Tc, the temperature of most significance. In contrast,
CVX's microgravity sample will be uniform to within 0.3%.
In addition to advancing fundamental science, CVX's development fostered
several technical innovations. For example, CVX's viscometer is the first
to be calibrated by exploiting a hydrodynamic similarity which relates
viscosity to frequency. Also, CVX's programmable voltage divider is an
innovative circuit which fits on a single electronic card while maintaining
voltage stability to within one part per million.
Data provided by Irene Bibyk
This Page Last Updated 2/4/97 by Ted Fabian Submit Feedback!!