Prediction of annular flows in vertical pipes with new correlations for the cathare-3 three-field model
Résumé
Prediction of the critical heat flux is crucial for boiling system such as water cooled reactors. In the case of high steam qualities in the core, occurrence of the critical heat flux, also called dryout, is usually associated with evaporation of thin liquid film from the heated rods, thus leaving their clad in direct contact with the vapor phase. Several phenomena annular flow transition with corresponding initial conditions as well as entrainment and deposition of the droplets from or onto the liquid film require appropriate modeling in order to accurately estimate the occurrence of the dryout and its location.This work re-evaluates the models of CATHARE-3 system code with the extended data base of adiabatic and diabatic tests in vertical pipes. At the same time, a comparative study is performed which aims at the validation of the alternative model for entrainment and deposition of the droplets for the three-field model of the CATHARE-3 code. On one hand, extended adiabatic database shows area where the new models improve the prediction as well as indicates what the common weaknesses of both models are. On the other hand, extended diabatic database shows that current models of boiling entrainment and deposition inhibition for high pressures overpredict measured values for experiments with high heat fluxes. Moreover, the inherent models of CATHARE-3 are extended by the implementation of the Initial Entrainment Fraction (IEF) phenomenon. The model for IEF is developed using KTH film flow experiment and validated with diabatic Wurtz experiments. New set of models improve the predictions of droplet field against this database.