Hydrodynamics and mass transfer in multiscale multiphase flows : a novel CFD modelling approach

Multiphase flows are ubiquitous in both nature and man-made applications. In most cases these flows exhibit a broad range of interfacial scales, ranging from small droplets or bubbles embedded in a continuous phase to large-scale interfaces observed in segregated flows. In this context, Computational Fluid Dynamics (CFD) represents a valuable predictive tool; however, standard off-the-shelf multiphase flow modelling approaches are not applicable to multiphase flows encompassing a broad range of interfacial scales. Recently, a GEneralized Multifluid Modelling Approach (GEMMA) has been developed to address this issue and allow for the simulation of multiscale multiphase flows. In this work, a mass transfer modelling methodology is coupled with the hydrodynamic results obtained with GEMMA, thus allowing for the evaluation of the mass transfer rate within the computational domain. The resulting modelling framework can be used to predict hydrodynamics and mass transfer in complex multiphase flows; in the context of nuclear engineering, flows that are of interest range from pressurized thermal shocks to liquid-liquid extraction processes relevant to the nuclear fuel cycle. In this work, the methodology is applied to the simulation of liquid-liquid extraction in a Rotating Disc Column (RDC) and in an Annular Centrifugal Contractor (ACC). It is shown that the numerical results for both hydrodynamics and mass transfer are in a good agreement with the experimental observations. It is concluded that the proposed modelling framework provides an accurate predictive tool for complex multiphase flows, such as those observed in intensified liquid-liquid extraction and encountered in numerous thermal hydraulic applications.