An experimental method to evaluate global pumping in a mixing system: Application to the Maxblend™ for Newtonian and non-Newtonian fluids

Abstract

This work introduces an experimental method to determine the global pumping capacity of an impeller in a transparent vessel using a decolorization method. Contrary to commonly used experimental methods such as Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV), this new inexpensive and easy-to-use method can be employed to quickly fill the lack of data in the literature about the impact of impeller geometry on the pumping efficiency. The new method was first applied to three well-known mixing systems and a Newtonian fluid to assess its reliability and accuracy: a six-blade Rushton turbine (RT), a pitched blade turbine (PBT) with four 45° blades, and a three-blade hydrofoil propeller (HP). It was then applied to evaluate the global pumping capacity of the Maxblend™ impeller in the case of Newtonian and non-Newtonian fluids. The results obtained show that, for the Newtonian fluid, the Maxblend™ impeller performs better than the other three impellers in the transitional regime, and it has a similar pumping capacity than that of the PBT and the RT in the complete turbulent regime. In this case, it was also noticed that the HP is outperformed by the other tested impellers over the entire range of Reynolds numbers. Moreover, it was observed that the extreme shear-thinning behavior of the non-Newtonian fluid used does not significantly affect the pumping generated by the Maxblend™ impeller in the transitional regime, that is for Reynolds number larger than 80. A global flow number, normalized by the power draw, is also introduced. Based on this criterion, the HP is shown to perform the best in the fully turbulent regime. Mixing times evaluated by means of the decolorization method also reveal that the Maxblend™ impeller is the most efficient for all regimes.