The thermal-hydraulic properties of supercritical pressure CO2 (SCO2) in vertical tubes under cooling and heating conditions were numerically investigated by using SST turbulent model with variable turbulent Prandtl number model. Under cooling condition, the peak of heat transfer coefficient appears near the pseudo-critical point, the buoyancy effect enhances local heat transfer for upward flow while deteriorates that for downward flow, and the criterion (Gr) over bar /Re-27 is more accurate than Bo* in the evaluation of buoyancy effect. Under heating condition, the buoyancy effect improves local heat transfer for downward flow while deteriorates that for upward flow. The local heat transfer deterioration only occurs in the case of T-b,T-in

Keywords:Supercritical pressure CO2 (SCO2);Buoyancy effect;Heat transfer deterioration;Heat exchanger;Heat transfer;Pressure drop