Experiment and numerical simulation of chaotic mixing performance enhanced by perturbed rigid-flexible impeller in stirred tank

doi:10.11949/0438-1157.20200313

Abstract

Abstract:

To eliminate the isolated mixing regions in the stirred tank, factors associated with chaotic mixing performance were studied, including flow field structure and fluid velocity of rigid RT impeller (R-RT), perturbed rigid RT impeller (PR-RT) and perturbed rigid-flexible RT impeller (PRF-RT). The maximum Lyapunov exponent (LLE) and multi-scale entropy (MSE) were calculated by using Matlab software programming, and the differences in flow field structure and fluid velocity of the three blade systems were studied through computational fluid mechanics. The experimental and computational results showed that perturbed rigid-flexible RT impeller could destroy the boundary of the mesostatic flow field in the isolated mixing regions and the symmetry flow in the process of fluid mixing through the random disturbance of the flexible blade, eliminating the isolated mixing regions. At 90 r/min, the LLE of the perturbed rigid-flexible RT impeller is larger than that of rigid RT impeller and perturbed rigid RT impeller. The LLE of the rigid-flexible RT impeller compared with the rigid RT impeller and perturbed rigid RT impeller increases 13.29% and 7.25% respectively and the MSE of the perturbed rigid-flexible RT impeller is also larger than that of rigid RT impeller and perturbed rigid RT impeller. The perturbed rigid-flexible RT impeller enhances the flow field instability, forms an asymmetric flow field structure, and reduces the distribution range of isolated mixing regions. The perturbed rigid-flexible RT impeller enhances the energy dissipation of the blade, improves the fluid velocity at the bottom and top of the tank and the wall of the tank, and reduces the mixing time.

Key words: perturbed rigid-flexible impeller, largest Lyapunov exponents, multi-scale entropy, numerical simulation

摘要：

为消除搅拌反应器中混合隔离区，对标准刚性桨（R-RT）、错位刚性桨（PR-RT）和错位刚柔桨（PRF-RT）三种桨叶体系的流体混沌特性参数、流场结构以及流体运动速度进行了探讨。采用Matlab软件编程计算最大Lyapunov指数（LLE）和多尺度熵（MSE），通过计算流体力学研究了三种桨叶体系流场结构和流体运动速度的差异。实验及计算结果表明，错位刚柔桨通过柔性桨叶的随机扰动破坏了隔离区介稳态流场边界，较大程度地消除了混合隔离区。PRF-RT的LLE相比于R-RT和PR-RT分别提高了13.29%和7.25%，MSE也较PR-RT和R-RT大；PRF-RT增强了流场不稳定性，形成了不对称性流场结构，减少了隔离区分布范围；PRF-RT强化桨叶能量耗散，提高了搅拌槽底部、顶部液面以及搅拌槽壁区域流体运动速度，减小了流体混合时间。

关键词: 错位刚柔桨, 最大Lyapunov指数, 多尺度熵, 数值模拟

CLC Number:

TQ 027.2

Zuohua LIU,Hongjun WEI,Xia XIONG,Changyuan TAO,Yundong WANG,Fangqin CHENG. Experiment and numerical simulation of chaotic mixing performance enhanced by perturbed rigid-flexible impeller in stirred tank[J]. CIESC Journal, 2020, 71(10): 4621-4631.

刘作华,魏红军,熊黠,陶长元,王运东,程芳琴. 错位刚柔桨强化搅拌槽内流体混合实验及数值模拟[J]. 化工学报, 2020, 71(10): 4621-4631.

Figures/Tables 14

Fig.1 Mixing experimental apparatus and mesh model

Fig.2 Impellers used in experiment and impeller size

Fig.3 Grid independence (R-RT)

Fig.4 Effect of impeller types on θm

Fig.5 Effect of impeller types on LLE

Fig.6 Flexible pieces shape in experiment

Fig.7 Effect of flexible piece shape on LLE

Fig.8 Effect of impeller types on MSE

Fig.9 Effect of flexible piece shape on MSE

Fig.10 Effect of impeller types on P

Fig.11 Effect of impeller types on contour plots of velocity magnitude

Fig.12 Effect of impeller types on the area size of fluid moving speed (V≤0.20 m/s)

Fig.13 Effect of impeller types on velocity magnitude of axial direction

Fig.14 Effect of impeller types on velocity magnitude of radial direction

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