Numerical simulation of heat transfer characteristics of steam condensation in the presence of air under rolling conditions

Floating nuclear power plants (FNPPs) operating in ocean environments are continuously subjected to wave-induced rolling motions, which can strongly modify the condensation performance of the PCCS, particularly when non-condensable gases (NCGs) accumulate in the containment. In this work, a numerical framework is established to analyze film-wise condensation of steam–air mixtures on subcooled walls under rolling motion. The model couples an Eulerian description of the condensate film with diffusion-boundary-layer treatment of the gas phase, enabling detailed resolution of coupled momentum, heat, and mass transfer near the interface. Parametric simulations are carried out to examine the influence of roll amplitude and period, bulk gas-mixture velocity, and air mass fraction on the local and overall heat transfer behaviour. The results demonstrate that the rolling motion can substantially intensify condensation relative to stationary conditions. Under representative operating parameters, the CHTC increases from 447 W/(m²·K) in the static case to more than 778 W/(m²·K) with rolling, and the enhancement becomes stronger for larger rolling amplitudes and shorter periods. A non-monotonic dependence on gas-mixture velocity is identified, with maximum enhancement occurring at intermediate flow rates. Increasing air mass fraction, however, markedly attenuates this benefit. These findings offer quantitative guidance for the design and safety evaluation of PCCSs on FNPPs under realistic marine motions.