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Key Questions We Want to Answer:
Molasses
flows slower than water because is has a greater viscosity-a
property resulting from the interactions between a fluid's
molecules. These interactions are so complicated that the
viscosity of few fluids can be accurately calculated from
theory. Experiments must be conducted to measure viscosity.
What We Already Know:
Although
the critical temperature and viscosity can differ greatly
among fluids, there is a remarkable regularity in the relative
size of viscosity increase for all pure fluids. Current
theories predict this increase in viscosity at the critical
point to be universal behavior, and relate the increase
in viscosity to spontaneous fluctuations in density near
the critical point of the phase transition between liquid
and gas states.
The
Critical Viscosity of Xenon (CVX) experiment will test these
theories with great precision. Xenon was chosen because
it is a simple fluid, its other critical properties have
been thoroughly explored and its critical temperature is
near room temperature. Having this information would also
aid the analysis of the data from the previously-flown ZENO
mission, which is designed to better understand the light
scattering aspect of the same phase transition.
What We Hope to Find Out:
To
measure the viscosity, liquid xenon is placed in a container
with a small paddle that vibrates. By measuring the drag
force on the moving paddle, the viscosity of the material
can be measured. Measuring the viscosity in this manner
as the sample of xenon is caused to approach the phase transition
allows the experimenter to study the properties of the material
near the critical phase transition. The experiment is about
1 inch by 2 inches in size.
How
We'll Conduct Our Experiment:
To achieve the most accurate results, it is best to measure
the viscosity of xenon closer to the transition from fluid
to superfluid state, in a microgravity environment. The
absence of gravity allows for creation of a more uniform
sample than is possible on the ground. The larger, more
uniform sample improves accuracy of the measurement results
by at least 100 times.
Additional information:
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