Prediction of Critical Heat Flux and dryout is crucial for BWRs. Today 1-D models based on empirical correlations are used in order to model these phenomena. However, in order to get a better physical understanding and be able to model more complex geometries CFD modeling of annular flow is developed. The complexity of annular flows makes modeling of the different interactions involved challenging.

In the present study a three-field approach is used in order to model annular flow; steam, liquid droplets and liquid film represent the different fields which are coupled to each other, i.e. both mass and momentum are exchanged between the modeled fields. The steam and droplets are modeled using Euler-Lagrangian multiphase CFD model and the liquid film is modeled through empirical models implemented at the wall boundary.

The implemented model is validated against experimental data with good agreement. In order to enlarge the model validity range further improvements are needed especially concerning the entrainment modeling.

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