Experiments and Heat Transfer Correlation Validations of Low-Parameter Region of sCO 2 Flow in a Long Thin Vertical Loop

The focus of this study is to accurately predict the convective heat transfer of CO 2 to ensure the safe and efficient design of supercritical and trans-critical CO 2 energy systems. The heat transfer performance of CO 2 is crucial for the stable operation of these systems. This research study explored the flow and heat transfer behavior of CO 2 in a long thin vertical loop through experiments. A range of key parameters were set in the experiments to ensure the broad coverage of operating conditions. The inlet temperature was set between 10 °C and 45 °C, the pressure ranged from 6.0 to 9.0 MPa, mass fluxes varied from 500 to 1500 kg/m 2 s, and the heat flux reached up to 300 kW/m 2 . Experiments were performed at Reynolds number 10 4 . By adjusting these parameters, the experiments were able to simulate CO 2 heat transfer performance under various real-world conditions. Additionally, numerical simulations were employed to further analyze CO 2 ’s flow and heat transfer behavior. Different turbulence models were tested, and the results showed that the SST k-ω model can best predict CO 2 convective heat transfer, effectively capturing the complex heat transfer characteristics under varying flow conditions. The research outcomes were compared with established correlations through the Nusselt number, and while a ±30% uncertainty was observed, the overall agreement was satisfactory. This indicates that the experimental and simulation results are within a reasonable range, confirming their reliability.