组合桨搅拌槽内部流场及混合时间数值模拟

Numerical simulation of internal flow field and mixing time in stirred tank with combined paddles

针对组合形式的搅拌桨在搅拌领域广泛应用的问题,采用计算流体力学分析方式,将双螺带搅拌桨和六斜叶圆盘涡轮搅拌桨在搅拌槽内部流场进行研究,采用多重参考系(MRF)方法建立基础模型,基于Navier-Stokes方程和标准k-ε湍流模型对搅拌槽内部流体产生的流场进行数值计算,分析搅拌桨在180,240,300 r/min的搅拌转速下产生的流场数据,并在槽内加入示踪剂,研究槽内搅拌过程中混合时间的测定.研究结果表明:搅拌槽内液相在双层浆区出现了典型的回旋涡流型,设定监测点,分析示踪剂在不同监测点的浓度变化曲线,得出混合时间为9.6 s,并对比得出240 r/min转速的搅拌效果和混合时间以及搅拌功率对于工业生产具有绝对优势的结论,通过工业放大的试验形式验证了模型的正确性,为非牛顿流体湍流层搅拌槽的设计和工程应用提供了理论依据.

Since combined stirring paddles have been used in many industrial fields,internal flow fields in a stirred tank generated by double helical ribbon stirring blades and six pitched blades disk turbine impellers at 180,240,300 r/min rotating speeds were studied by using CFD analysis. The Navier-Stokes equations in multiple reference frame( MRF) and standard k-ω turbulence model were used in numerical simulations. Tracers were put into in the tank to measure the mixing time in mixing processes. The results show that a typical vortex swirling flow appears in the stirred tank in liquid phase in the region between two paddles. The mixing time is determined to be 9.6 s based on analysis of tracer concentration curves at monitoring points. Stirring effect and mixing time and stirring power at 240 r/min rotating speed have an absolute advantage for industrial application. An industrial scale experiment has proven the correctness of the model mentioned above. The study in the paper can provide a theore-tical basis for design and engineering application of stirred tank with non-Newtonian fluid turbulent mixing layers.