LES and PIV investigation of turbulent characteristics in a vessel stirred by a novel long-short blades agitator

Abstract

This study focuses on the macroscopic characteristics of the turbulent flow in a vessel equipped with a newly developed long-short blades (LSB) agitator. After validation by PIV experiments, the LES method using dynamic kinetic energy sub-grid scale model, coupled with sliding mesh approach, was used to investigate the flow patterns, the axial and radial flow rates, turbulent dynamic energy distribution, and the power number in the vessel with the LSB agitator at the liquid height, H/T = 1.0 and 1.5, respectively. It is found that the turbulent characteristics are substantially different from those of the conventional agitators. The short blades of the LSB agitator generate a strong axial up-flow in the center, which interacts with the dominant radial motion of the long blades, leading to formation of multiple vortexes along the axis. The direction of the flow in the vortex above the short blades is opposite to that below the short blades, which is completely different from the classical Rushton turbine. Effective mass exchange between the axial and radial flows occurs nearly in the entire vessel. Compared with the conventional agitators, the LSB agitator can achieve high mixing performance and much better homogeneity in the distribution of the turbulent kinetic energy. The effect of the liquid height on the power number and the specific power consumption was also discussed.