Experimental study on heat transfer of supercritical CO2 flowing in a mini tube under heating conditions

•Heat transfer of supercritical CO2 (S-CO2) was experimentally studied under high ratio of heat flux to mass flux (q/G) conditions.•Heat transfer deterioration of S-CO2 and the buoyancy effect under high q/G conditions were analyzed.•A number of heat transfer correlations for S-CO2 were compared with the experimental data.•A new correlation was proposed to predict the heat transfer of S-CO2 under high q/G conditions.