Flow characteristics of xanthan gum solutions agitated by a perturbed six-bent-bladed turbine

Pseudoplastic fluids are non-Newtonian fluids and are widely used in chemical production processes. During agitation, a well-mixed cavern will form around the impeller. By contrast, the fluid outside this region is nearly stagnant, which severely limits mixing efficiency. In this study, the standard k-ε model is used to simulate the flow field in a xanthan gum solution agitated by a perturbed six-bent-bladed turbine, with the results validated against a particle image velocimetry experiment. The effects of rotational speed and rheological properties on the flow field are examined. The impeller performance is also studied. The results indicate that under laminar flow conditions, the power number is inversely proportional to the Reynolds number, while the pumping capacity and pumping efficiency increase with increasing Reynolds number and decrease with increasing viscosity. The fluid velocity peaks near the agitator blades. The shear rate displays distinct A-type and M-type distributions across different horizontal planes. Furthermore, when the rotational speed and the xanthan gum mass fraction in the solution reach 540 rpm and 1.25%, respectively, the flow field structure stabilizes with no significant change. Key findings indicate that increasing the rotational speed is more effective than increasing the xanthan gum mass fraction in enhancing global fluid motion and improving mixing efficiency. Under turbulent flow conditions, the formation of two distinct vortices near the top of the tank could reduce stagnant regions in that area. Turbulent kinetic energy is concentrated in the vicinity of the impeller, reaching its peak around the blade tips.