Abstract: Convection heat transfer of CO 2 at supercritical pressure in a vertical circular tube (d in=2 mm) at high inlet Re (about 9 000) was investigated numerically to analyze the effects of the variation of the physical properties and buoyancy on the wall temperature and the turbulent energy. The results show that in the case of high heat fluxes the local heat transfer deterioration and enhancement during the upward flow due to the strong influence of buoyancy result in change of the turbulent energy distribution. Simulations using the LB turbulence model correspond well with the experimental data in upward flow. In the case of low heat fluxes the phenomenon of heat transfer deterioration or enhancement was not observed.