Numerical study on a semi-mechanistic wall boiling model based on dry-patch mechanism for CHF prediction in vertical tube and fuel assembly

Abstract

With the development of observations on micro bubble behaviors, a wall boiling model based on dry-patch mechanism was proposed by Demarly (2020). To qualify its performance in CFD simulations, the model was implemented into Fluent by User Defined Function in this paper and coupled with the multi-scale interface model. The model prediction accuracy was tested by the data collected from the 2006 CHF look-up-table and the Large Water Loop experiments. The predicting deviations were less than ±30% in both vertical tube and fuel assembly simulations, which showed the models could perform well under the selected conditions. Different boundary conditions were discussed to analyze the effects on CHF prediction. In addition, the most sensitive parameters of Demarly’s model were identified. It was shown that the diameter ratio, bubble departure diameter and departure frequency had a significant impact on the predicted results, which may could support a further model development in CFD.