Physics Colloquium, April 12, 2005

Convection in a supercritical fluid

Horst Meyer

Duke University

This talk starts with a tutorial on supercritical fluids (SCF) - fluids above the liquid-vapor critical point. Fluid convection in a Rayleigh-Benard cell, and the difference in behavior between "ordinary" and "supercritical" fluids will be described. The interest of SCF's in science and industry is also briefly described. 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 with a pure fluid, Helium-3. After a heat flow has been started across the fluid layer, an oscillatory behavior of the temperature difference across the layer is observed versus time in the convective regime. This phenomenon is the signature of the "piston effect", which will be described. Scaled plots of both convection heat currents and of transient characteristic times at various compressibilities are presented. Simulations and calculations by groups in Japan and France are compared with the experimental data.

Dr. Meyer's Web Site

3.30 p.m., Robert Smith Seminar Room, PRB

Refreshments served at 3:00 p.m., Atrium PRB