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 (${\mathrm{CO}}_{2}$) 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.