Application of an Eulerian-Eulerian CFD approach to simulate the thermohydraulics of rod bundles

The Eulerian-Eulerian computational fluid dynamics (CFD) approach is widely applied in the simulation of industrial scale thermal fluid dynamics problems, such as flow and heat transfer in fuel elements. However, the case dependency of sub models in the Eulerian-Eulerian CFD approach currently hampers its applicability. In order to reduce this dependency, a sub model to predict the bubble departure in both pool and flow boiling was developed in our group, which includes the impact of microlayer, thermal diffusion, condensation, mutual effect and force balance. Moreover, we also raised a new CHF- concept. It is currently based on correlations but we are continuously working on a transition to a fully physics-based model, which e.g. considers the dependency of boiling on the microlayer thickness, bubble base expansion speed and local shear stress. In order to implement the bubble dynamics model and CHF model into the Eulerian-Eulerian CFD framework, a new cavity activation and heat partitioning model was developed, which is not only used for bubble nucleation but also connects the nucleation boiling and CHF- in one CFD approach. However nucleation site density is strongly dependent on the surface properties, which is difficult to model without correlations.