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

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 (cavg) 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. (c) 2021 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.

Automated summary

This study presents the main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers using particle image velocimetry (PIV) experiments. The average shear rate in the whole tank and the local value near the impeller both increase linearly with impeller speed. The shear coefficient at the impeller outlet is linearly related to the impeller flow number and decreases with the increase of impeller flow number at constant power consumption per unit volume. Computational fluid dynamics (CFD) results show that the volume-averaged shear rate decreases faster for a Reactor Design for Tolerance (RDT) impeller compared to other impellers with the same impeller tip velocity during scale-up based on constant power consumption per unit volume and geometric similarity. The novel multi-blade combined (MBC) impeller with an increased height-to-diameter ratio improves the distribution uniformity of shear rate at the same power consumption per unit volume after scale-up. These studies provide a data basis for selecting impeller types and improving the shear rate environment in large-scale stirred tanks.