Numerical Simulation of Two-Phase Boiling Flows and Prediction of DNB under PWR Conditions with a Multidimensional Two-Fluid Model

The present paper reports numerical modeling of multi-dimensional two-phase boiling flows with a multi-dimensional two-fluid model and prediction of the Departure from Nucleate Boiling (DNB) under PWR accidental conditions. The conventional two-fluid model is adopted and various constitutive equations are incorporated to develop a computer code capable of predicting multi-dimensional void fraction distribution in a flow-boiling channel. The numerical results are compared with the data in literature of the measured profile of void fraction, with the agreement being satisfactory. To predict the occurrence of DNB, the Weisman-Pei model is adopted, which predicts the occurrence of DNB when the local void fraction exceeds a predetermined value in the near-wall buble layer. The predicted DNB power is compared with the results from an experiment of DNB power in an annular channel under PWR flow and pressure conditions, and the agreement is encouraging.