Experimental Investigation of Supercritical Carbon Dioxide Horizontal Heated Flow with Buoyancy Effect

For the supercritical carbon dioxide (S-CO₂) with heated flow in a horizontal tube, to research the influence of the buoyancy effect on flow and heat transfer characteristics, experiments were conducted on flowing and heating in optical and inner coiled wire tubes under the same condition. Investigations were carried out for the influence of the wall heat flux density and mass velocity on the buoyancy effect, while discussions were given for the influence of the inserted coiled wires on the wall temperature distribution, heat transfer mode, etc. Results show that the temperature stratification caused by the buoyancy effect occurs along the gravity direction during SO₂ horizontal flowing with heating, which leads to the severe wall temperature divergence at the top and bottom, with a maximum wall temperature difference of up to 48 K. The inserted coiled wires in tube can effectively inhibit the temperature stratification caused by the buoyancy effect, while the heat transfer coefficients at the bottom and top are increased by more than 60% and more than 140%, respectively. Based on the validation of experimental results with four heat transfer correlations, it is found that Bishop correlation has the best comprehensive performance.