Colloquium
Properties
and Convection of Supercritical Fluids
Prof. Horst Meyer
Department of Physics
Duke University
Thursday, April 17,
2008, 1:40
p.m.,
SCIC 126
This talk starts with a tutorial on supercritical fluids
(SCF) – fluids above the liquid-vapor critical point. The anomalous
behavior of several properties is described as the critical point is
approached from above and from below; also the "Piston Effect", and how it influences both temperature
equilibration and heat transfer. Experiments under microgravity conditions
to avoid the effect of stratification and the application of supercritical
fluids in industrial purification processes are briefly discussed. Fluid convection
studies of a supercritical fluid - He3 - in a Rayleigh-Bénard
cell will be described. They consist in observing the temperature
difference across the layer versus time after start of the heat flow. The
diverging compressibility of the fluid as the critical point is approached
strongly influences its mechanical stability in a vertical heat flow. The
combination of the Rayleigh - and Schwarzschild criteria
to determine the stability limit is described, and the predictions are
compared with experiments. The investigation of a SCF fluid over a large
range of compressibilities permits presentation
of scaled plots for both convection heat currents and for transient characteristic
times. Such scaling plots as functions of certain dimensionless parameters
are to be expected from general theoretical arguments.
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