Numerical study on flow and heat transfer of S - CO2 in inclined tubes under different flow conditions

In this paper, the numerical simulation of supercritical carbon dioxide (S - CO2) flowing in large diameter inclined circular tubes with different heat flux and inlet temperature is studied. According to the experimental results of S - CO2 flow in a horizontal tube, the SST k - omega model was found to be the most accurate predictor of heat transfer. Based on the phase transition temperature of the pseudo-boiling phenomenon under subcritical conditions, a gas-like film radius model was established. The results show that when heat flux is too large, the wall temperature rises quickly, which makes the density gradient in the cross-section, buoyancy and gas-like film radius increase constantly, resulting in the gathering of a large number of low-density and poor heat transfer performances at the top generatrix, causing a sudden increase in wall temperature and the heat transfer coefficient decrease significantly. As the inlet temperature increases, buoyancy and relative secondary flow energy decreases and the fluid temperature rises dramatically, eventually leading to a rapid decrease in thermal conductivity and heat transfer capacity.