CFD Simulation Of Mixing In Pseudoplastic Fluid With Wide Viscosity Impellers

Mixing equipments are widely used in many industry processes such as chemicalindustry, pharmaceutical industry and biology fermentation process. Mixing fluids includeNewtonian and Non-Newtonian. Xanthan gum is a natural biological glue which can beenwidely used in many fields, broth will shift from low viscosity Newtonian fluid to highviscosity pseudo-plastic fluid in the process of fermentation. This seriously influences thequality and production of xanthan gum. To solve this problem, it is urgent to research anddevelop high efficient mixing equipments which can adapt to a wide viscosity range.Mixing characteristics of six kinds of agitator were simulated by computational fluiddynamics method in xanthan gum solution, including five types wide viscosity blender:Maxblend (MB1, MB2and MB3), Fullzone (FZ1, FZ2), and a classical stirrer—dualRushton turbine (DT). In the paper, researches were focused on agitator hydrodynamicperformances and mixing process.It was found from experiments of hydrodynamic performances of six kindsof agitator that the power consumption of FZ2blender is maximum and MB3blender isminimum in turbulent region. The flow pattern of Maxblend blender is doublecirculations, that of Fullzone impeller is three circulations in upper, middle and lower partof tank, and that of dual turbines is parallel flow. The shear amount and pumping numberof Fullzone impeller is highest and those of dual Rushton turbines are lowest in turbulentregion.The mixing processes of six kinds of agitator were investigated under same powerconsumption and found that Mixing time was calculated by minimum value of tracerconcentration: In the whole power range of study, MB1<FZ1<FZ2<DT; with high powerconsumption, MB3<MB2<MB1.By analyzing mixed volume curves to describe macro mixing process, it is found thatthe structure and installation of MB1and FZ1impeller is reasonable. Bad mixed zoneexists at low speeds with MB2and MB3impeller. The large area of FZ2impellerobstructs flow. The interaction between two layers blades of DT impeller is small at low speeds.The micro mixing process was studied by mixed coefficients and found thatconvective diffusion plays a main role when the mixed coefficients>1, molecular diffusionwhen the mixed coefficients<1. The tracer concentration distribution is uniform andmixing time is short of MB2and MB3impeller in achieving mixed requirement.