A new coupled two-phase model for condensate film and steam condensation in the presence of air

•A coupled two-phase model for liquid film and steam-air condensation is proposed.•The film effect is proposed and the influence of the film effect is evaluated.•The various mechanisms of film thermal resistance and film flow are considered.•The distribution of the condensate film flow regime is obtained. Steam condensation containing air is a vital thermal-hydraulic phenomenon in containment under nuclear power plant severe accident sequences. This phenomenon has been extensively analyzed numerically. Due to the existence of air, the condensate film has been neglected in most studies and a single-phase model has been used for the numerical analysis. However, whether the condensate film can be ignored is still unknown under high pressure and high steam concentration. Due to the influence of condensate film is mostly ignored in the recent analysis of steam condensation containing air. To evaluate the influence of condensate film, the present work proposed a new coupled two-phase model for condensate film and steam condensation containing air based on diffusion boundary layer theory. In addition, the coupled two-phase model was validated with the COAST, Dehbi, Su, and Fan experimental results. The results indicated that the coupled two-phase model could predict the steam condensation heat transfer coefficient well within a wide range of parameters (tube diameter from 19 to 38 mm, tube length from 1 to 3.5 m, pressure from 0.15 to 1.6 MPa, air concentration from 10% to 80%, subcooling from 10 to 117 ℃), and the deviation is mostly within 20%. Moreover, the condensate film effect was proposed in this study and evaluated in detail based on the coupled two-phase model. The mechanism of the condensate film effect was considered, and the distribution of the film flow regime was obtained.