Agitation of Herschel–Bulkley fluids with the Scaba–anchor coaxial mixers

The design of the coaxial mixers depends on many interrelated parameters including the geometry and dimensions of the mixing vessel, the location and type of the impellers, speed ratio, impeller diameter, rotation mode, and fluid rheology. No study has been reported in the literature regarding the mixing performance of the coaxial mixers in the agitation of yield-pseudoplastic fluids. Thus, the main objective of this study was to evaluate the performance of a Scaba–anchor coaxial mixer (a novel configuration) in the mixing of xanthan gum solutions (yield-pseudoplastic fluids). The Herschel–Bulkley model was used to describe the rheological behavior of the xanthan gum solutions. To develop new correlations for the generalized Reynolds and power numbers of the coaxial mixers employed in the agitation of this class of non-Newtonian fluids, we utilized numerous experimental and computational fluid dynamics (CFD) data. The new correlations were tested successfully at different operating conditions (e.g. speed ratio, fluid rheology, and operation mode).

► Mixing of yield-pseudoplastic fluids with coaxial mixers was investigated using CFD and experiments.
► The effects of the speed ratio, operation mode, and fluid rheology were characterized.
► Interactions of the Scaba and anchor impellers in co- and counter-rotating modes were quantified.
► The rheological parameters of the Herschel–Bulkley model were incorporated into the correlations.
► New correlations captured successfully the effect of the operating conditions on the power number.