CFD prediction of critical heat flux in vertical heated tubes with uniform and non-uniform heat flux

In this paper, Eulerian Two-fluid model coupled with extended wall boiling model was used to simulate the departure from nucleate boiling (DNB) in vertical heated tubes under high pressures by using STAR-CCM+ 10.04. Based on CFD approach, new methods were developed to predict the critical heat flux (CHF) in both uniform and non-uniform heated tubes. The results showed some differences between the uniform and non-uniform heated cases. The transition in boiling curves was used as the criterion of DNB for uniform heat flux while the peaks of wall temperature and near wall void fraction were used for non-uniform cases. Good agreement was obtained between the predictions and experimental data, including both the values of critical heat flux and their locations. For uniform heat flux, sensitivity analysis for pressure, local quality and mass flow rate were performed, and the results showed that the new prediction method could work well under a wide range of conditions except under the high local quality and low mass flow rate conditions. The mechanism of this prediction method was discussed as well.