Experimental study of supercritical carbon dioxide heat transfer deterioration in a vertical tube under high heat flux

Supercritical carbon dioxide (S-CO2) energy conversion devices have been widely studied because of their high thermal efficiency, compactness and flexibility. However, S-CO2 may experience heat transfer deterioration during the heat transfer process. At present, the study of S-CO2 for heat transfer deterioration is mainly carried out at low heat flux (<500 kW·m−2). The heat transfer characteristics of S-CO2 in a vertical circular tube with an inner diameter of 10 mm were investigated by constructing an S-CO2 experimental rig with a heat flux ranging from 37.75 kW·m−2 ∼ 782.48 kW·m−2. The results show that the S-CO2 deteriorates heat transfer in the entrance section of the experimental section as the heat flux increases. When the heat flux increases from 194.82 kW·m−2 ∼ 358.38 kW·m−2, the heat transfer deterioration in the inlet section is aggravated by the increase in heat flux; when the heat flux increases from 436.98 kW·m−2 to 778.03 kW·m−2, the heat transfer deterioration in the inlet section is gradually slowed down with the increase in heat flux, but a second heat transfer deterioration region occurs at high heat flux. Among them, the buoyancy force is the main cause of heat transfer deterioration in the inlet section, while the thermal acceleration effect affects the generation of the second heat transfer deterioration region. The results of the experimental study are of great significance for the engineering application of S-CO2.