ANOMALOUS HEAT-TRANSPORT BY THE PISTON EFFECT IN SUPERCRITICAL FLUIDS UNDER ZERO GRAVITY

The response to a boundary heating of a very compressible, low-diffusivity, supercritical fluid (CO2) under zero-gravity is studied by solving numerically the full non-linear one-dimensional Navier-Stokes equations. Both short (acoustic) and long (diffusion) time scales are investigated. A new mechanism of heat transport is seen, where the thermal energy is transformed into kinetic energy in a hot expanding boundary layer (the piston), which in turn is transformed in the bulk into internal energy. Steeply profiled waves are observed. In contrast to the critical slowing down behavior, the enhancement of heat transport is so important that it is nearly completed after 1% of the diffusion time. © 1990 The American Physical Society.