CFD Simulation and PIV Measurement of Local Fluid Velocity Distribution of Newtonian and Highly Shear-Thinning Fluid in an Impeller Rotational Region

Multistage impellers are widely used in the chemical industry to enhance the mixing of shear-thinning fluids. However, the local velocity around multistage impellers has not been sufficiently investigated. This study investigated the mixing behavior of Newtonian and shear-thinning fluids in the laminar regime using a three-stage impeller with four blades pitched at 45°. The local fluid velocity distribution was analyzed using particle image velocimetry (PIV) in order to validate the computational fluid dynamics (CFD) simulations. PIV experiments showed that, for Newtonian fluids, the radial and circumferential velocities at the front and back of the blade were the same. For non-Newtonian fluids, the lower edge of the impeller blade exhibited greater positive radial velocities than the upper edge. Moving from the middle height of the blade to the upper edge caused the circumferential velocities to decrease at the front of the blade, whereas moving from the middle height of the blade to the lower edge caused them to increase. Additionally, the conventional and fine validation methods were used to validate the CFD simulations. When comparing CFD results to PIV measurements, the power values and local velocity distributions for Newtonian and non-Newtonian fluids nearly matched with the experimental results. However, slight discrepancies were observed in the local fluid velocity distribution for highly shear-thinning fluids.