A new modified diffusion boundary layer steam condensation model in the presence of air under natural convection conditions

Steam condensation in the presence of non-condensable gases is a dominating phenomenon inside a containment under LOCA scenarios. In numerical simulations, the basic diffusion boundary layer condensation model (BDBLM) has been proposed for containment thermal-hydraulics analysis. However, there are still some incompleteness such as the under prediction of heat transfer coefficient when the steam mass fraction is high. Besides, the effect of thermal diffusion (Sorer effect) on condensation heat transfer has not been specified quantitatively. In order to compensate these shortcomings, a modified diffusion boundary layer model (MDBLM) was proposed and assessed in detail. In the modified condensation model, the under prediction of condensation heat transfer at high steam mass fraction conditions was modified by adding a suction effect parameter. The Sorel effect was assessed by adding a new term including the temperature gradient, thermal diffusion coefficient, and steam mass fraction. The results indicate that the MDBLM could give a good prediction of heat transfer coefficient (HTC) at low air mass fraction conditions with deviations within 20%. The Sorel effect takes less than 7% in the total mass transfer when the mainstream temperature is saturated and could be more than 80% when the mainstream temperature is superheated.