Numerical Analysis on Heat Transfer Characteristics of Supercritical CO2 Cooled in a Horizontal Tube

The turbulent heat transfer characteristics of supercritical CO2(S-CO2) cooled in horizontal tubes were studied numerically. The abilities of five turbulence models including AB, YS, LS, AKN and SST k-ω to predict heat transfer coefficients of supercritical CO2 were verified against experimental data, and it was determined that the SST k-ω low-Reynolds number turbulence model had the best prediction ability. Based on the hypothesis that S-CO2 undergoes a pseudo-phase change at the pseudo-critical temperature Tpc, the heat transfer mechanism of S-CO2 cooled in a horizontal tube was studied and the reasons for difference in heat transfer coefficient distribution between the top generatrix and the bottom generatrix were explained by obtaining physical properties and turbulence distribution of fluid in the cross section. The effects of heat flux qw and mass flux G on heat transfer performance were analyzed. The calculation results show that the cooling heat transfer characteristics of S-CO2 are closely related to the thickness of liquid-like film near the wall, thermal conductivity and radial turbulent kinetic energy distribution. The conclusions of this paper have certain guiding significance for the cooler design and economic operation of S-CO2 Brayton cycle system. © 2021 Chin. Soc. for Elec. Eng.