Multidimensional multicomponent model of condensation in presence of non-condensable gases

Full text of publication follows: Non-condensable gases, even in small quantities, are known to significantly influence the heat transfer and the condensation rate. Near the condensate interface, which typically forms liquid films on walls, the non-condensable gases will accumulate and create a mass transfer resistance. Thus, a proper prediction of the heat and mass transfer rates require an accurate estimation of the concentration of non-condensable gases in the boundary layer in the direct proximity of the condensate. This phenomenon plays an important role in many industrial applications, e.g. inside the steam-generation tubes during a small-break loss of coolant accident (SB-LOCA) in pressurized water reactors (PWRs). It can also take place during the course of a hypothetical sever accident in PWRs, when hydrogen can be produced and distributed in the containment due to convective and diffusive processes. High local hydrogen concentration can lead to detonations and the structural integrity of the containment may be in danger. In the present paper a new model for the condensation of vapor in presence of non-condensable gases is presented. The model has been implemented into a commercial CFD code CFX and has a full multidimensional capability. Both convective and diffusive terms responsible for the transport of the non-condensable gases are taken into account in the model. In that way the mass transfer rate at the condensate interface is modeled in a mechanistic way. The liquid films which are formed in the course of condensation on walls are modeled in detail. The film model predicts the local parameters which influence the local heat transfer intensity. This includes liquid film thickness and the temperature distribution in the liquid film. The current model has been validated against separate-effect experiments performed by Choi et al. (2002) and Malet et al. (2003) and promising results have been obtained. In the full paper a detailed description of the model will be given and a thorough validation will be presented. References: (1). K.Y. Choi et al. (2002), Direct-contact condensation heat transfer model in RELAP5/MOD3.2 with/without non-condensable gases for horizontally stratified flow, Nucl. Eng. Des. 211, pp. 139-151; (2). J.Karl et al.(1999), Effect of spontaneous condensation on condensation heat transfer in presence of non condensable gases, 5. ASME/JSME Joint Thermal Engineering Conference, San Diego, USA, March 15-19; (3). J. Malet et al. (2003), Film-wise steam condensation in the highly instrumented containment thermal-hydraulic facility TOSQAN, Proc. 10. Int. Top. Meeting on Nucl. Reactor Thermal- Hydraulics NURETH-10, Seoul, Korea, October 5-9. (authors)