CFD-PBM simulation of bubble columns based on fixed pivot method: Influence of the moment closure

The fixed pivot method can conserve two moments while other moments suffer from inherent errors caused by internal inconsistency. The influence of moment closure in the CFD-PBM simulation is studied on population balance and hydrodynamics of bubble columns. The CFD-PBM model, which conserves the surface area and volume (second and third moment, i.e. CFD-PBM-SV model), and the number and volume (zeroth and third moment, i.e. CFD-PBM-NV model), is developed based on a two-fluid model. A rectangular bubble column is simulated by the CFD-PBM-SV and CFD-PBM-NV model, respectively. It is found that both models can capture the oscillating plume of the gas-liquid flow inside the reactor. The flow features predicted by the CFD-PBM-SV model show better agreement with experimental data, in terms of the time-averaged vertical liquid velocity, gas hold-up and plume oscillation period, than the CFD-PBM-NV model. It is speculated that the better performance of the CFD-PBM-SV model is ascribed to more accurate predictions of interfacial forces and momentum transfer between two phases due to internal consistency of the local Sauter Mean Diameter compared to the CFD-PBM-NV model.