Effect of impeller type and scale-up on spatial distribution of shear rate in a stirred tank

With the assistance of particle image velocimetry (PIV) experiments, the spatial distribution features of shear rate in a stirred tank operated with different impellers are displayed. Both the average and local shear rates are correlated with the impeller speed or the flow number. Furthermore, the trends of change in volume-averaged shear rate and shear rate distribution in a stirred tank are investigated by means of CFD simulation based on the scale-up rule of the constant Pv and/or geometric similarity. It is found that the novel MBC impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate after scale-up. [Display omitted] The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry (PIV) experiments. Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed. Furthermore, the shear coefficient (Ks,imp) at the impeller outlet is linearly related to the impeller flow number (Nq) and decreases with the increase of Nq in general at the constant power consumption per unit volume (Pv). During scale-up based on the constant Pv and geometric similarity, CFD results show that the volume-averaged shear rate (γavg) for RDT decreases faster than that of other impellers with the impeller tip velocity (Utip). The novel multi-blade combined (MBC) impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up. These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.