Two-dimensional shear rate field and flow structures of a pseudoplastic fluid in a stirred tank using particle image velocimetry

For non-Newtonian fluids, an accurate determination of the shear rate is essential to optimize process parameters, which can lead to the improvement of the process efficiency. This work proposes the evaluation of an aqueous solution of carboxymethylcellulose (CMC) analyzing two azimuthal planes, AZ 0 degrees and 45 degrees, and four blade positions, AR 0 degrees, 22.5 degrees,45 degrees and 67.5 degrees, by ensemble-averaged and angle-resolved PIV measurements, respectively, in a stirred tank equipped with a pitched-turbine impeller. Results are shown in terms of time-averaged velocity, shear rate, apparent viscosity and Reynolds number fields. Differences between both PIV measurements approaches were significant in terms of velocity magnitude and characteristics of trailing vortices. The results demonstrate that the shear rate is strongly influenced by spatial resolution. The highest shear rates were obtained in the impeller region. The presence of a vortex above the blade resulted in high values of local Reynolds number, reflecting the presence of turbulence in that region. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study evaluates the fluid characteristics of CMC aqueous solution using PIV measurements, demonstrating a strong influence of spatial resolution on shear rate, with the highest shear rates obtained in the impeller region.