Numerical study on the effect of CO2 on the heat transfer characteristics of steam condensation outside a vertical tube

Abstract

Under severe accident conditions of a pressurized water reactor nuclear power plant, the reactor core may melt, and the molten corium even reacts with concrete in the containment, producing a large amount of CO2 into the entire containment gas space. This may have an obvious impact on the heat transfer characteristics of steam condensation in the containment. However, there are few studies focused on this phenomenon. In this paper, a commercial CFD software, STAR-CCM+, is used to study the effect of CO2 on steam condensation heat transfer. The calculations are based on 0.4 MPa gas pressure, 40 K wall sub-cooling, 0.66 or 0.2 steam mole fraction, and the CO2 mole fraction varies from 0 to 0.34 or 0.8. The results show that the CO2 demonstrates different influence laws at high and low steam concentrations, respectively. When the steam mole fraction is 0.66, as the proportion of CO2 in the non-condensable gas increases, the condensation heat transfer coefficient (HTC) will increase, and the enhancement can reach 30%. When the steam mole fraction is 0.2, the condensation HTC will first decrease and then increase, as the proportion of CO2 in the non-condensable gas increases. The effects of gas pressure and wall sub-cooling on the condensation HTC are also analyzed. The results show that the condensation HTC increases with the increase of the gas pressure and decreases with the increase of wall sub-cooling.