A new perspective in the evaluation of the mixing of biopolymer solutions with different coaxial mixers comprising of two dispersing impellers and a wall scraping anchor

Abstract The hydrodynamic performances of coaxial mixers consisting of a close clearance impeller and dual central impellers in the agitation of the xanthan gum solution, a yield-pseudoplastic biopolymer solution, were explored in the laminar-transitional regimes in the co-rotating mode. The different coaxial mixers utilized in this study were dual Scaba impellers, dual Rushton turbines, or dual pitched blade turbines in combination with an anchor impeller. Considering both numerical and experimental approaches, three techniques were employed: computational fluid dynamics (CFD) to simulate the flow domain of the fluid, electrical resistance tomography (ERT) to measure mixing time and visualize flow behavior inside the stirred vessel, and design of experiments (DOE) combined with the response surface methodology (RSM) to analyze the data. The experimental and numerical data were collected to assess the performances of the coaxial mixers in the mixing of the complex fluids with respect to the power consumption, mixing time, velocity vector plots, streamline plots, axial, radial and tangential velocity profiles, axial shear strain rate profiles, and flow number. It was found that among the three coaxial mixers considered in this research work, the mixing time achieved by the double Scaba-anchor coaxial (DSAC) mixer was the lowest. Furthermore, the DSAC coaxial mixer created a more uniform velocity profile throughout the tank compared to the other two coaxial mixers. The results also demonstrated that the DSAC mixer was the most efficient mixing system for the mixing of the highly viscous non-Newtonian fluids.

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