Diagnosis of solid distribution in vessels stirred with multiple PBTs and comparison of two modelling approaches

The features of solids concentration distribution were investigated in two baffled vessels of different scale. The vessels were of high aspect ratio and were stirred with multiple PBTs. Both steady- and unsteady-state experiments were performed. The experimental data were compared with the previsions of the one-dimensional sedimentation-dispersion model and of CFD tools. The former approach provides good estimates only of the average, steady-state vertical profiles, while the latter describes the local variations much more accurately. Both approaches give fairly good estimates of the transient solids concentration distribution. The dynamic CFD simulations allowed us also to tune the value of the turbulent Schmidt number as a relevant parameter. Finally, both simulation approaches have confirmed that the particle settling velocity in a stirred liquid is a correct parameter to be used instead of the terminal settling velocity.