A novel and energy-efficient coaxial mixer for agitation of non-Newtonian fluids possessing yield stress

A novel impeller called ASI (a combination of the A200 and the Scaba impellers) has been introduced in this paper. By using electrical resistance tomography (ERT) and computational fluid dynamics (CFD), the performance of the ASI impeller in the agitation of the yield-pseudoplastic fluids was assessed and compared to the performances of the Rushton (a radial impeller), ARI (an axial-radial impeller), and A200 (an axial impeller) impellers in terms of power consumption and cavern sizes. The new ASI impeller exhibited superior performance in the mixing of the pseudoplastic fluid possessing yield stress. Agitation of such a non-Newtonian fluid in a vessel results in the formation of cavern around the impeller. An enlarged cavern can be achieved by increasing the impeller speed. However, this leads to increased power consumption as well as non-uniform mixing in the vessel, i.e. a high-shear region around the impeller and dead zones at the wall and the bottom. These issues can be resolved by using a coaxial mixer, a combination of a central impeller and an anchor. Our data revealed that the anchor-ASI impeller, the combination of the novel impeller and the anchor, was the most efficient mixer for the agitation of the yield-pseudoplastic fluids in term of mixing energy compared to the other coaxial mixers employed in this study.