Numerical simulation study on heat transfer characteristics of steam condensation in the presence of multi-component non-condensable gas outside the tube bundle.

Under severe accident conditions, in addition to steam and air, there may also be hydrogen produced by the reaction of zirconium alloys and steam, CO 2 produced by the molten corium concrete interaction (MCCI) and other gases in the containment. These gases, whose properties are quite different from air, can significantly affect the steam condensation process outside the tube bundle. This paper aims to investigate the effects of non-condensable gas mixtures with varying component concentrations on the steam condensation process outside a 3 × 5 tube bundle using computational fluid dynamics (CFD) methods. The thermal conditions studied are set to a pressure of 0.4 MPa, a subcooling of 40 K, and a molar concentration of steam of 0.66. The results show that CO 2 has an acceleration effect on the flow field outside the tube bundle, which promotes the diffusion of steam to the inside of the bundle, thus increasing the condensation heat transfer coefficient (CHTC) of the bundle and decreasing the difference in CHTC between different heat transfer tubes inside the bundle. Hydrogen, on the other hand, inhibits the downward flow of the gas mixture, causing a decrease in CHTC. However, at high hydrogen concentration (X H2 >0.1), the gas mixture will form a buoyant flow upward, and then the CHTC of the tube bundle will be significantly increased by up to 177%. When the two gases act together, they will weaken each other's influence on the flow field, thus reducing the CHTC of the tube bundle. [ABSTRACT FROM AUTHOR]