Anchor impellers are commonly used for the homogenization of non‐Newtonian fluids, often in association with a set of coaxial turbines. The optimal design of such mixers relies on the knowledge of power drawn by the individual impellers. In non‐Newtonian mixing, this can be readily obtained using the Metzner‐Otto (1957) concept. In this article, the Metzner‐Otto concept and the determination of the constant Ks for anchor impellers have been revisited using numerical and experimental techniques for the case of shear‐thinning and shear‐thickening fluids. Contrary to literature findings, it is shown that the constant Ks does not vary strongly with the power law index and that, for mixer design purposes, the use of a constant value of Ks for each of the rheological behaviors considered is adequate.

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The flow patterns produced by two dual mixing systems composed of independently driven impellers were studied. The dual impellers included a turbine rotating at high speed (Rushton or Smith) and a slowly rotating helical ribbon agitator (HR). Visualizations and power input were used to evaluate mixing performance. The influence of the rotational speed ratio on the flow patterns was evaluated. For high shear-thinning fluids, N T /N HR modifies the flow patterns considerably. Three typical behaviors were found with shear thinning fluids: segregation of two principal flow patterns (N T /N HR < 10), turbine dominance (N T /N HR > 10), and a well-distributed flow pattern throughout the tank (N T /N HR = 10). For low-viscosity fluids, the motionless HR reduced the vortex length and the T-HR systems eliminated vortex when the impellers rotated in opposite directions at N T /N HR = 10. Finally, a relationship between the dimensionless vortex length and the Froude number is proposed for individual turbines as well as for the turbine-motionless HR systems.

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