Effect of Modified Impellers with Added Leading Edges Flanges on Pumping Efficiency in Agitated Tanks

In this work, a modification in the blade profile of the classic PBT turbine has been proposed by adding flanges on the leading edges with the purpose of analyzing the hydrodynamic performance and its effects on the reduction of energy consumption. The hydrodynamic characteristics and mixing performance of the modified PBT were evaluated in a standard baffled tank. Experimental measurements by PIV and CFD simulations were used to assess the effect of flanges added to the blade profile on power consumption, pumping efficiency, and their correlation with the pressure drag form. The hydrodynamic effect of the flanges was analyzed using pressure coefficients and local pressure gradient, both evaluated on the leading and trailing faces of the blades. Mixing parameters such as power number, pumping number, pumping efficiency, and mixing time were assessed. The proposed flanges have a substantial effect on the delay of the flow separation and reduction of the recirculating region in the rear edge of the blade. These effects are related to pressurization in the rear blade surfaces, which in turn reduces the energy needed to overcome drag as the impeller rotates, and, therefore, power consumption. In addition, as the flow energy is redirected by the flanges, the pumping is improved and the mixing time is shortened. The highest power reduction reached with the flange models was 12.5%, and the highest increase in the pumping was 6.4%. Moreover, the maximum increase in pumping efficiency achieved with these modified profiles was 31.3%, and a maximum decrease in mixing time of 11.2% was observed.