Abstract: The laminar model, the multiple reference frame(MRF) and the tracer concentration method are employed to simulate the laminar flow field and the mixing time of highly viscous non-Newtonian fluid in stirred tank with double layer straight impeller. The flow field characteristics, the spreading process of tracer, the responding curves of tracer concentration and the mixing time are analyzed. The tracer particles and the acid-base indicator method are used to measure the flow field and the mixing process in a transparent plexiglass stirred tank in experiment. The results show that the tracer is flowing and diffusing with main medium first in the feeding half of stirred tank because of the intermediate surface between double paddle, then diffusing to the other half when the concentration difference has increased. The shorter mixing time is obtained when feeding tracer at the blade-closed-area which stirred vigorously or at the intermediate surface. Different time are used to complete mixing at different points, so choosing reasonable monitor points with mixing require could avoid resource wasting or insufficient stirring. The mixing process of the medium in stirred tank is faster and the mixing time is shorter when increasing stirring speed. The accuracy of the numerical simulation results is verified by the experimental results. The research provides the theory basis for the design and engineering application of the laminar flow stirred tank with non-Newtonian fluid.

Key words: computational fluid dynamics(CFD), laminar model, mixing time, stirred tank, tracer