Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
The modelling of condensation in presence of non-condensable gases is of relevance for the design of passive containment cooling condenser of the third generation of Passive Nuclear Power Plants. Fast and accurate methods of predictions for condensation in presence of non-condensable gases are necessary in order to be implemented in the thermal-hydraulic codes without slowing down the computational speed of these codes. In this paper we present a mechanistic model for condensation in presence of non-condensable gases inside vertical tubes. In this model we take into account the influence of the non-condensable gases over the liquid side heat transfer without any iteration to calculate the liquid-steam interfacial temperature. The trick is to perform a set of Taylor expansions for the main physical magnitudes as viscosity, steam mass fraction and so on. We also consider the interfacial shear stress exerted by the steam-non-condensable mixture flow over the condensate layer thickness. The calculation of the condensate layer thickness can be performed with the help of the mass, energy and momentum conservation equations and can be achieved without any iteration following the method of Munoz-Cobo et al [1,2]. The new proposed mechanistic model solves explicitly the real interfacial temperature by means of a cubic or a quartic equation depending on the degree of approximation that has been chosen. Moreover, as the main non-condensable effects can be accounted for in the heat and mass transfer processes, the new model will be more realistic. The model has been validated with the Vierow experimental data, obtaining a total average relative error, for the fourth order equation method model, of 21% with 268 experimental points at different conditions