Numerical study of convective heat transfer to supercritical CO2 in vertical heated tubes

Supercritical heat transfer is important to design and operate advanced power generation system. Non-uniform heating is frequently encountered such as for sCO(2) boiler and solar receiver applications. Here, 3D numerical simulations are performed in turbulent regime, coupling solid wall and sCO(2) in tubes. Non-uniform heating is simulated by applying heat via a thin metal layer at the outer tube wall, covering half circumference of tube wall. Calculation results matched experimental data well. Heat transfer is compared between uniform heating and non-uniform heating. Numerical results are re-processed by the pseudo-phase transition theory, including a liquid-like region in tube core and a gas-like layer near the tube wall. The two layers of structure are interfaced by a terminating temperature T+ which is determined by thermodynamics. Hence, supercritical heat transfer is evaluated based on the relative importance of thermal resistances induced by the liquid-like region and the gas -like film region. It is found that wall temperatures for uniform heating are higher than those for non-uniform heating, which is explained by larger thermal resistance of the gas-like film for uniform heating than that for non-uniform heating. This difference ensures better heat transfer for non-uniform heating than uniform heating. We conclude that in turbulent regime, the gas-like film dominates the magnitudes of wall temperature and the occurrence of heat transfer deterioration for both uniform and non-uniform heating. Our work is important for heat transfer facilities in supercritical domain, especially under non-uniform heating condition.