偏心射流-刚柔组合桨搅拌器内混沌混合行为研究

Chaotic mixing performance in rigid-flexible impeller stirred tank with eccentric air jet

搅拌反应器内普遍存在混合隔离区,是实现高效混合的一大障碍。流场耦合诱发流体的混沌现象,可减少混合隔离区,提高流体混合效率。结合Matlab软件,探究偏心空气射流-单层刚柔组合桨体系的混合行为演变规律,对比分析了不同偏心率下桨叶类型、桨叶离底高度、空气射流量以及转速对流体混沌混合的影响。结果表明,刚柔组合桨通过其自身刚-柔-流的多体运动与偏心空气射流的流场耦合,破坏了流体混合过程中出现的对称性流场,使更多的流体进入混沌状态。刚-柔组合桨(RF-RDT、RF-IRDT)比刚性桨(RDT、IRDT)的LLE值大,其中RF-RDT相比于其他3种类型的搅拌桨(IRDT、RDT、RF-IRDT),其LLE值分别提高了约42.8%,27.0%、6.9%;空气射流的偏心率等于0.6时,其最大LLE值相比于其他偏心率(0.8、0.4、0.2、0),依次提高了6.5%、2.4%、17.6%、25.1%。该研究结果可为刚柔组合桨的优化设计提供理论依据。

Isolated mixing regions exist widely in the stirred tank, which is a major obstacle for efficient mixing. In order to increase the mixing efficiency, the method of multiple flow fields coupling, which can bring out fluid chaos, is used to increase fluid mixing efficiency by reducing the isolated mixing regions. The largest Lyapunov exponent and multi-scale entropy are investigated with the aid of Matlab in the coupling of eccentric air jet and rigid-flexible combined impeller system. Meanwhile, the effects of impeller types, impeller off-bottom clearances, air jet flow rates, and the impeller speeds on the mixing performance are analyzed at different eccentricities. The results show that the flow field coupling of the rigid-soft-flow of multi-body motion of rigid-flexible combined impeller and eccentric air jet destroy the symmetry flow in the process of fluid mixing and made more fluid into the chaotic state. The LLE of rigid-flexible combined impeller is larger than that of rigid impeller. The LLE of rigid-flexible combined impeller compared with the other three types agitators（IRDT, RDT, RF-IRDT） increases 42.8%, 27.0%, and 6.9%. When the eccentricity of the air jet is equal to 0.6, the maximum LLE value is 6.5%, 2.4%, 17.6% and 25.1% which is higher than the other eccentricity（0.8, 0.4, 0.2, 0）. The results of this study can provide the theoretical basis for the optimal design of rigid-flexible agitator.