High Rayleigh number turbulent convection in a gas near the gas-liquid critical point

SF6 in the vicinity of its critical point was used to study turbulent conve ction up to exceptionally high Rayleigh numbers, Ra (up to 5 x 10(14)) and to verify for the first time the generalized scaling laws for the heat tran sport and the large scale circulation velocity as a function of Ra and the Prandtl number, Pr, in a very wide range of these parameters. Both scaling laws obtained are consistent with theoretical predictions by Shraiman and S iggia [Phys. Rev. A 42, 3650 (1900)].