Role of CFD techniques in discriminating experimental solids concentration data in stirred suspensions and modelling of the solids concentration profiles in a pilot reactor

In this work, the suitability of an optical probe for studying local solid particle distribution in agitated systems and of Computational Fluid Dynamics (CFD) as a means to discriminate among the experimental data is investigated. Solids concentrations are determined in a high-aspect-ratio baffled tank stirred with three Rushton turbines by means of a fibre-optical probe and by CFD simulations. The local analysis of the simulated liquid flow field allows to better understand the source of differences in the measured solid concentrations that are obtained by changing the angular orientation of the probe in a few specific positions and, therefore, to identify the best operating mode for the measurements. The predicted radial and axial solid concentration profiles are then compared with the experimental data obtained with the most reliable probe orientation and very good agreement is found. This study allows to point out that, once proper computational strategies are selected, the usefulness of CFD simulations is twofold: they can be adopted for obtaining reliable predictions of various parameters in solid-liquid systems and used for gaining a better understanding of the complex fluid flow features of turbulent multiphase flows.