Analysis of coupled heat transfer and flow behaviors of supercritical CO2 in horizontal circular tube

In the field for pre-cooler of the Brayton cycle, research on the physical mechanisms of coupled thermal transfer processes involving supercritical CO₂ in horizontally arranged tube remains insufficient. Therefore, this research established a three-dimensional computational model that accounts for tube wall thickness to explore the heat exchange process of supercritical CO₂ at various working conditions. The research results indicate that using a one-dimensional radial method with the outer surface temperature to determine local wall temperature can provide more precise description of the convective heat transfer. The fluctuation in the heat transfer performance exhibits a direct correlation with the peak Prandtl number, whereas the kinetic energy acts as a gauge for heat transfer efficiency. Since the fluid temperature is greater than the pseudo-critical temperature in a certain region, an increase in the heat flux in this region results in an enhanced heat transfer. The point to be emphasized is that dimensionless heat flux primarily reflects heat transfer changes caused by fluctuations in fluid temperature, while ignoring the impact of local wall temperature changes on the heat exchange process. By respectively incorporating the parameters associated with non-dimensional heat flux and buoyancy parameter into the correlation, it may be found that the proportions of prediction errors falling within the range of ±15 % are 95 % and 93.4 %.