Validation of Cfd Models for Mono- and Polydisperse Air-water Two-phase Flows in Pipes

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is continuous and the other phase consists of gas or vapor of the liquid phase. The validation of the CFD multiphase flow models against detailed experimental data for simplified flow configurations is a basic requirement for the accurate prediction of more complex flows, like e.g. multiphase flow in fuel rod assemblies with spacer grids under the conditions from ONB to DNB including bulk and wall boiling in a pressurized polydisperse liquid-vapor flow. This paper is therefore aimed on validation of the underlying multiphase flow modeling concepts for gas-liquid monodisperse and polydisperse bubbly flows. CFD predictions using ANSYS CFX and taking into account interphase momentum transfer (drag and non-drag forces) as well as bubble break-up and coalescence are compared to experiments of MT-Loop and TOPFLOW test facilities (FZ Rossendorf, Germany). Best Practice Guidelines [8] have been applied in order to allow for a systematic error quantification and thoroughly assessment of model formulations. 1 Corresponding author