Chaotic mixing behavior of non-Newtonian fluid intensified by multilayer rigid-flexible impeller induced flow field interface instability

doi:10.11949/0438-1157.20200315

Abstract

Abstract:

The traditional multilayer rigid impeller has large dead zone for the mixing of pseudoplastic non-Newtonian fluid, stable flow field interface and low mixing efficiency. A method for enhancing the chaotic mixing of non-Newtonian fluid by multilayer rigid-flexible impeller induced flow field interface instability was proposed. In the experiment, sodium carboxymethylcellulose was used as the non-Newtonian fluid system. The power characteristics were measured by the torque sensor. The mixing time was determined by the acid-base neutralization and decolorization method. The largest Lyapunov exponents were calculated by using Matlab software programming. The chaotic characteristics and mixing performance in the mixing process are analyzed. The results show that when the combination mode was RF-(PBTD+PBTD+DT), the impeller arrangement mode θ=60°, and the flexible sheet length installation ratio r=0.8, 1.2, the degree of chaos was higher and the mixing performance was better. Multilayer rigid-flexible impeller can generate multiple spiral flows, and realize the flow field interface instability under the disturbance frequency difference of the flexible sheet between the layers, the stirring dead zone was reduced, and the system enters a chaotic state at a lower speed (when the multilayer rigid-flexible impeller system N>88 r/min, LLE>0; when the multilayer rigid impeller system N>125 r/min, LLE>0). At the same speed, the mixing rate and power per unit volume of the multilayer rigid-flexible combined impeller are higher than that of the multilayer rigid impeller, but the mixing energy per unit volume is approximately the same.

Key words: chaos, multilayer rigid-flexible impeller, non-Newtonian fluid, mixing, mixing rate, largest Lyapunov exponents

摘要：

传统多层刚性桨用于假塑性非牛顿流体混合搅拌死区较大，流场界面稳定，混合效率低。提出多层刚柔组合桨诱发流场界面失稳强化非牛顿流体混沌混合的方法。实验以羧甲基纤维素钠为非牛顿流体体系，通过扭矩传感器测量功率特性，酸碱中和脱色法测定混合时间，并利用Matlab 软件编程计算最大Lyapunov 指数，分析了非牛顿流体混合过程中的混沌特性及其混合性能。结果表明，组合方式为RF-（PBTD+PBTD+DT）、桨叶排列方式θ=60°、柔性片长度安装比例r=0.8、1.2时，混沌程度较高，混合性能较好。多层刚柔组合桨可以产生多股螺旋流，并在层间柔性片扰动频率差下实现流场界面失稳，搅拌死区减小，在较低转速下使体系进入混沌状态（多层刚柔组合桨体系N>88 r/min时LLE>0，多层刚性桨体系N>125 r/min时LLE>0）；在相同转速下，多层刚柔组合桨混合速率、单位体积功率高于多层刚性桨，而单位体积混合能大致相同。

关键词: 混沌, 多层刚柔组合桨, 非牛顿流体, 混合, 混合速率, 最大Lyapunov 指数

CLC Number:

TQ 027.2

LIU Zuohua,YANG Linrong,XIONG Xia,TAO Changyuan,WANG Yundong,CHENG Fangqin. Chaotic mixing behavior of non-Newtonian fluid intensified by multilayer rigid-flexible impeller induced flow field interface instability[J]. CIESC Journal, 2020, 71(12): 5470-5478.

刘作华,杨林荣,熊黠,陶长元,王运东,程芳琴. 多层刚柔组合桨诱发流场界面失稳强化非牛顿流体混沌混合行为[J]. 化工学报, 2020, 71(12): 5470-5478.

Figures/Tables 13

Fig.1 Experimental device

Fig.2 Schematic diagram of impellers

Fig.3 Impact of mixing impeller type on LLE

Fig.4 Effect of the mixing impeller combination method on LLE

Fig.5 Effect of arrangement of stirring impeller on LLE

Fig.6 Effect of flexible sheet length installation proportion on LLE

Fig.7 Effect of stirring impeller type on π1

Fig.8 Effect of the mixing impeller combination mode on π1

Fig.9 Effect of the arrangement of stirring impeller on π1

Fig.10 Effect of the length of the flexible sheet installation ratio on π1

Fig.11 Comparison of Wvand Pv in different types of impeller systems

Fig.12 Relationship between mixing energy per unit volume and mixing time

Fig.13 Mechanism of flow field interface instability induced by multilayer rigid-flexible impeller

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