Numerical Analysis on Heat Transfer Characteristics of Supercritical Pressure CO2 in Inclined Smooth Tube

Numerical simulation on upward flow and heat transfer of CO2 at supercritical pressure in inclined smooth circular tube with inner diameter of 10mm and heated length of 2000mm was carried out. The inclination angles of tube were α=0°, 30°, 45°, 60°, 90°, respectively. Based on the experimental data of supercritical pressure CO2 flowing upward in a vertical and smooth circular tube, the SST k-ω turbulence model and four low Reynolds number k-ε turbulence models that included AKN model, YS model, LS model and AB model were evaluated to predict heat transfer deterioration (HTD) and normal heat transfer (NHT) for CO2 at supercritical pressure. It was found that the SST k-ω turbulence model gave a satisfying predication for HTD and NHT. From the perspective of phase transition from liquid-like to vapor-like for supercritical fluid at pseudocritical point, the effect of inclination angles on the heat transfer of supercritical CO2 in circular tube was studied. By the detailed temperature distribution, thermophysical properties including specific heat capacity at constant pressure cp and thermal conductivity l distribution and velocity distribution in the inclined circular tube, the reasons for temperature difference between top generatrix and bottom generatrix were analyzed. And the mechanism of heat transfer deterioration and recovery at top generatrix under supercritical pressure was discussed. It can be determined that the thickness and property of vapor-like film, kinetic energy k and the thickness of viscosity sub-layer are the main factors affecting wall temperature distribution during heat transfer of supercritical CO2. © 2020 Chin. Soc. for Elec. Eng.