Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is a continuous liquid and the other phase consists of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase has to be characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model, where the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and where each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 testcase data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow.