Onset of heat transfer deterioration caused by the gas-like layer formation in horizontal tubes using supercritical CO2

Accurately predicting the onset of heat transfer deterioration (HTD) is crucial for the safe operation of advanced power systems, such as supercritical carbon dioxide (sCO 2 ) power cycles. A key factor influencing supercritical HTD is the formation of a gas-like layer near heated surfaces, which prevents convective heat transfer and degrades thermal performance. Due to the challenges of experimentally observing this layer, a comprehensive numerical investigation was conducted on sCO 2 flow in heated horizontal tubes to predict the onset of HTD, considering the gas-like layer. The simulations covered a wide range of operating conditions, including operating pressures that varied from 7.5 MPa to 30 MPa, heat fluxes that ranged from 25 kW/m 2 to 500 kW/m 2 , and mass fluxes that ranged from 200 kg/(m 2 s) to 1000 kg/(m 2 s). The model employed the Eulerian approach and the Shear Stress Transport ( S S T ) k − ω turbulence model, validated against experimental data. Seven existing correlations for HTD onset in sCO 2 were evaluated, revealing that most correlations developed for other fluids cannot be directly applied to sCO 2 , as all correlations fail to account for the gas-like layer. To address this limitation, a new correlation incorporating the pseudo-mass quality was developed, demonstrating 93.75% accuracy in the HTD dataset, 94.74% accuracy in the non-HTD dataset, and an overall accuracy of 94.21%.