Intensification of power efficiency by grooves in flanged impellers

Abstract

The effect of grooved blade impellers and leading-edge flanged impellers on mixing in agitated tanks has been studied separately in an already published study. It was found that both configurations reduced impeller power consumption. The most significant reduction of power consumption, compared to the classical Pitched Blade Turbine (PBT), was achieved using flanges. Based on these results, in this work, the blades of the classical PBT were modified with the combination of both previous, flange and groove structures to evaluate their performance. It was found that such a combination produces a synergistic effect that reduces flow separation caused not only by flow impinging on the leading-edge of the blade but also by suction flow leaving the lateral edge of the blade tip. The combination of flanges with curved structures results in a reduction in power of 29.6 % compared to PBT, and more than twice that modified impeller with only leading-edge flanges. Also, the pumping efficiency is increased with the combination of both modifications as it resulted in 40.6 % higher than the PBT. Experimental and Computational Fluid Dynamics (CFD) measurements were performed with different patterns of grooves, modifying angles, and curvature. Different parameters such as power number, pumping number, and mixing efficiency, among other important parameters for bioreactors such as the Kolmogorov length scale (k), and hydrodynamic stresses were evaluated experimentally and by CFD.