Abstract:

Rigid impeller is widely used in stirring mixer. Two mixing regions are usually generated easily: chaotic mixing region and isolated mixing region. Reasonable design of impeller is an effective way to enhance fluid mixing, so that the behavior of chaotic mixing can be regulated. In this study, the signal of pressure fluctuation in the fluid and the chaotic characteristic parameter of Kolmogorov entropy are managed by Labview and Matlab software, and the variation of Kolmogorov entropy with revolving speed in punched impeller system is investigated. The results indicate that the punched impeller system has a negligible influence on Kolmogorov entropy comparing to the traditional rigid impeller system. With punched-flexible impeller, the flow field structure can be regulated efficiently by the co-effect between punch hole and flexible impeller, resulting in excellent chaotic mixing in fluid field with the best effect at 180 r·min^-1. Simultaneously, the Kolmogorov entropy of punched-flexible impeller system achieves 0.285, while the value is 0.125 for the traditional rigid impeller system. Obviously, the mixing time in punched-flexible impeller system is superior to that in traditional rigid impeller system, which is decreased by about 17% at revolving speed of 120 r·min^-1.

Key words: stirred vessel, chaos, mixing, punched-flexible impeller, Kolmogorov entropy, mixing time

摘要：

刚性搅拌桨在搅拌混合过程中得到广泛的应用,在搅拌容器内容易形成两种不同的混合区域:混沌混合区和混合隔离区。强化流体混合的有效途径是合理设计搅拌桨,从而调控流体混沌混合行为。实验运用Labview和Matlab软件采集和处理流体内部压力脉动信号,并获取流体混沌特性参数Kolmogorov熵,对穿流-柔性组合桨体系的Kolmogorov熵随转速的变化规律进行了研究。结果表明,相比传统刚性桨,穿流桨对Kolmogorov熵影响不大。穿流-柔性组合桨通过穿流孔与柔性部分的共同作用调控流场结构,使流体混沌混合的效果最好,在转速为180 r·min^-1时流体的混沌混合达到最佳状态,穿流-柔性组合桨体系的Kolmogorov熵为0.285,而传统刚性桨体系的Kolmogorov熵只为0.125;穿流-柔性组合桨体系的混合时间明显低于传统刚性桨体系,当转速为120 r·min^-1时穿流-柔性组合桨体系的混合时间比传统刚性桨体系缩短了17%。

关键词: 搅拌容器, 混沌, 混合, 穿流-柔性组合桨, Kolmogorov熵, 混合时间