Experimental Study And Simulation Of High Viscous Fluid Mixing In A Stirred Tank

In some industrial applications, the viscosity of fluids change in a wide range during different reaction stages, possibly covering low, middle and high viscous fluid mixing.Ribbon, anchor and Maxblend impeller are several traditional impellers applied in high viscosity fluid with low mixing efficiency in transitional or turbulent mixing.On the other hand, PBT, Rushton turbine and some other traditional impellers usually used in the mixing of turbulent area cannot provide satisfied mixing of highly viscous fluid. Recently, multiple impellers with relatively large diameter was proposed to solve the mixing problem in above industrial application. Take the FCC catalyst production as application background, we study the power consumption and mixing performance of different geometric parameters multiple impellers agitator consisting of Pfaudler and CBY, both with relatively large diameter based on both the experimental research and numerical simulation.In the experiments, syrup solutions with different concentrations were used as fluids. The diameter of stirred tank (T) is 476 mm, same as the liquid level (H). Effects of the geometric parameters of Pfaudler, such as diameter (D), curvature radius (r), blade width (b), angle of the blade root (θ) on the power consumption and mixing performance were studied. CFX software was used to numerically simulate the flow pattern, velocity distribution and the mixing area.The experimental results show that in the laminar region, D/T of Pfaudler should be as large as 0.7 in order to cause the radial mixing in the stirred tank. The axial well-mixed height of fluid in laminar region is 0.58H. The power number of Pfaudler increases with increasing D, r and b; but decreases with increasing θ. Moreover, Pfaudler with θ=20°has the best mixing efficiency among all impellers in this research. Recommended agitator applied in the production of FCC catalysts is Pfaudler (D/T=0.7, r/D=0.333,θ=20°) as below and CBY was upper one.The CFD simulation results show that in the laminar region, the radial well-mixed region of Pfaudler is about 1 AD. The stagnant area exists near the wall when D/T<0.7. Moreover, the increase of r has little effect on the flow pattern and the increase of θ contributes to the circulation ability in axial direction, the height of the relatively high speed fluid region increases 10% when θ increases from 10° to 20°.