Numerical investigation of buoyancy effect on forced convective heat transfer to supercritical carbon dioxide flowing in a vertical tube was carried out. When the mass flux is low and wall heat flux high, it shows that the buoyancy effect is obvious, which might redistribute the radial and axial velocity, even M shaped distribution in the radial direction. When the zero-velocity-gradient region corresponding to the M shaped velocity distribution appears in the edge of viscous layer, the production and diffusion of eddy will be weakened, resulting in heat transfer deterioration. According to the extended simulations based on experimental data, reducing the wall heat flux, adding the mass flux or raising the inlet temperature can relieve the deterioration of heat transfer caused by buoyancy effect.

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