Towards a CFD model for boiling flows: validation of QMOM predictions with TOPFLOW experiments

Boiling flows are very complex systems, usually confined in vertical pipes, where the liquid water moving upwards and the steam gas bubbles generated at the walls. The fluid dynamics of such systems is determined by the interplay of many different phenomena, including bubble nucleation, growth, condensation, coalescence, and breakage. For this reason, the development of a fully predictive computational fluid dynamics (CFD) model is very challenging, therefore we focus here only on some of the phenomena mentioned above (i.e. coalescence and breakage) by using population balance models (PBM). In this work, a coupled CFD-PBM model based on the two-fluid model and the quadrature method of moments (QMOM) was implemented in the open-source CFD code openFOAM. Simulation predictions are validated against the so-called TOPFLOW experiments, where simpler air-water cold systems that mimic the complexity of real boiling flows were investigated. Comparison between the available experimental data and the results show that great care must be paid on some modeling details, such as the inlet bubble size distribution (BSD) at the sparger and the coalescence and breakage rates modeling