Numerical study on effects of tube bundle geometry and arrangement on external steam-air condensation

Condensation of steam mixed with non-condensable gases (NCGs) is a key physical process governing containment depressurization and thermal removal during severe nuclear reactor accidents. Previous studies on steam condensation with NCGs outside tube bundles have mostly focused on bundle structures with a single length and pitch. This paper examines the effects of bundle length, pitch, inclination angle, arrangement, and tube rows number on steam-air condensation outside tube bundles via numerical simulation. The coupling effects between tube length and arrangement, as well as between tube pitch and inclination angle, are also analyzed. Calculations indicate that for tubes of different lengths and arrangements, the overall heat transfer coefficient (CHTC) first decreases and then stabilizes as the tube length increases. Furthermore, the CHTC of different tubes within the bundle enhanced with larger tube pitch. At tube pitch of 1.5d, tube innermost tube exhibits the poorest heat transfer performance. At tube pitch of 3d, its heat transfer capacity becomes 2.55 times that under the 1.5d condition. Inclination induces more obvious overlap effect with narrow tube pitch, at a pitch of 2d, and the overall CHTC of the bundle increases with a larger inclination angle. Additionally, the overall CHTC for a 1m tube bundle gradually increases with increased tube rows, the CHTC surpasses that of a single tube when the number of rows exceeds 10. For 3m and 5m tube bundles, it initially decreases and then tends to stabilize as the number of rows increases.