Power Demand and Mixing Performance of Coaxial Mixers in Newtonian Liquids

All experiments were carried out in a transparent dished bottom stirred tank with the diameter T of 0.48 m and liquid level of 0.6T. The power consumption and mixing performance of a coaxial mixer consisting of a wall-scraping anchor and different dispersion impellers (CBY, 45o pitched blade turbine and Rushton turbine) operating in co-and counter-rotating modes were experimentally characterized in viscous Newtonian fluids with different viscosities. The results show that for the co-rotating dispersion modes, the power consumption of the anchor could decrease up to 10% of that for anchor rotating only, whereas for the counter-rotating dispersion ones, it could increase 2 times of that for anchor rotating only. The power consumption of the dispersion impellers is almost independent of the anchor rotation. The new correlations based on the impeller geometry and speed ratios for the generalized Reynolds number and the power number are proposed, and a reasonable power curve can be generated for different experimental speed ratios of each system. Impellers in co-rotating mode are more efficient than the counter-rotating ones in the mixing of the Newtonian fluids. Among above three dispersion impellers, the power consumption of the CBY impeller-anchor combination is about 20% to 30% of that for other two combinations given the similar mixing performance.