Nx1 MUSIG model -- implementation and application to gas-liquid flows in a vertical pipe

A multiple velocity multiple size group (NxM MUSIG) model was developed for inhomogeneous poly-dispersed multiphase flows in cooperation with ANSYS CFX. The model is constructed by incorporating the population balance equation into the multi-fluid modeling framework. The dispersed phase is allowed to be classified into $N$ continuum fields (velocity groups) according to their hydrodynamic behaviors; each group allowing an arbitrary number of sub-size classes. This model has generalized all possible class model variants and is applicable to large-scale computations. As a pre-investigation for the CFX5.8 development, the Nx1 variant was implemented based on CFX5.7 and applied to investigate as-liquid flows in a vertical pipe. The results confirm that this model is capable of predicting the separation of bubbles of different sizes and the development of the gas volume fraction along the pipe.