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The hydrodynamic behavior of a turbulent flow and the mixing characteristics generated by a V-grooved axial impeller inside an agitated tank reactor were investigated both experimentally and numerically. Angle resolved Particle Image Velocimetry (PIV) techniques with an angular displacement Δθ=5° have been applied and two aerodynamic planes along the blades were considered. PIV-based results were compared to those obtained by Large Eddy Simulation (LES), used with the dynamic Smagorinsky-Lilly sub-grid scale (SGS) model. Results showed the existence of distinctive recirculation zones in the aerodynamic planes, and new additional frequencies in the impeller stream, induced by the grooves. A decrease of mixing time of about 11 % was obtained experimentally, consequence of the better suction induced by the grooved blades in the early stages of mixing. Mean velocities, vorticity, TKE obtained from LES showed a good agreement with the PIV-based results. The distributions of turbulence dissipation rate ε were similar to those obtained from PIV, however showing high under-predicted magnitudes.

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The effects of axially symmetric control rods added to the archetypal four-blade pitched blade turbine (PBT) have been evaluated. The convectional PBT and two control rod configurations were tested (P2 and P3). Modifications resulted in a significant improvement in the hydrodynamic performance of the PBT impeller. Experimental measurements of torque and mixing time have been obtained, as well as flow measurement through particle image velocimetry (PIV) techniques to validate and compare the results obtained through numerical simulation using computational fluid dynamics. All these experimental tests and simulations have been used to evaluate the hydrodynamic behavior of these rod-controlled impellers. It was found that the modified PBT with control rods shows reduced power consumption compared to the conventional PBT. The use of control rods has achieved a reduction of up to 12.18% in the power number. It was found that the control rods reduce the fluid separation, reducing the pressure drag and the suction pressure zones on the rear of the blade, thus reducing the power consumption. Despite the reduction in the pumping number for the two configurations proposed, pumping efficiency is not greatly affected. For configuration P3, the efficiency is similar to that of the PBT. It is worth highlighting that all the control rods evaluated showed a reduction in the energy dissipation rate, and for the best case, P3, a maximum of 17.02% reduction was achieved. The reduction in the energy dissipation rate may be useful in applications that require low shearing stresses during processing. Also, the same impeller design may decrease the energy consumption during long-term processing tasks.