Experiments and Heat Transfer Correlation Validations of Low-Parameter Region of sCO2 Flow in a Long Thin Vertical Loop

The focus of this study is to accurately predict the convective heat transfer of CO2 to ensure the safe and efficient design of supercritical and trans-critical CO2 energy systems. The heat transfer performance of CO2 is crucial for the stable operation of these systems. This research study explored the flow and heat transfer behavior of CO2 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 degrees C and 45 degrees C, the pressure ranged from 6.0 to 9.0 MPa, mass fluxes varied from 500 to 1500 kg/m2s, and the heat flux reached up to 300 kW/m2. Experiments were performed at Reynolds number 104. By adjusting these parameters, the experiments were able to simulate CO2 heat transfer performance under various real-world conditions. Additionally, numerical simulations were employed to further analyze CO2's flow and heat transfer behavior. Different turbulence models were tested, and the results showed that the SST k-omega model can best predict CO2 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.