Mixing behavior of pseudoplastic fluid in a fractal perforated impeller stirred tank

doi:10.11949/0438-1157.20241257

Abstract

Abstract:

In order to increase the cave area, reduce the stagnant area, and improve the mixing efficiency of pseudoplastic fluid, the fractal theory is applied to the perforation design of the impeller, and a fractal perforated impeller is proposed to enhance the mixing behavior of pseudoplastic fluid. The mixing behavior of pseudoplastic fluid in a fractal perforated impeller stirred tank was investigated by combining experiment and computational fluid dynamics. The results showed that the power consumption and power number of FPT impeller system were lower than those of RT system, but the power consumption and power number increased with the increase of fractal iteration number of perforated holes at the same Reynolds number. Under the same power consumption, FPT impeller can enhance the shear effect on the fluid, increase the shear strain rate, increase the fluidity of the fluid, shorten the dimensionless mixing time, enlarge the cavern area, reduce the stagnation area and enhance the fluid chaotic mixing degree compared with RT impeller. Among them, the dimensionless mixing time of FPT-1 impeller system is shortened by 2.88%—5.65%, the cave area is increased by 6.58%, and the dimensionless mixing time of FPT-2 impeller system is shortened by 8.04%—11.00%, and the cave area is increased by 8.25%. Compared with conventional matrix perforation, fractal-arranged perforation was more advantageous in enhancing fluid mixing effect and improving fluid mixing efficiency.

Key words: fractal perforated impeller, mixing, pseudoplastic fluid, computational fluid dynamics

摘要：

为了增大洞穴区，减小停滞区，提高假塑性流体的混合效率，将分形理论应用于桨叶的穿孔设计，提出一种分形穿流搅拌桨来强化假塑性流体的混合行为。采用实验和计算流体力学探究了分形穿流桨搅拌槽内假塑性流体的混合行为。结果表明，在相同Reynolds数下，分形穿流桨（FPT）体系的搅拌功耗和功率准数均低于RT桨体系，但随着穿流孔分形迭代次数的递增，搅拌功耗和功率准数有所增加。在相同功耗下，相较于RT桨，FPT桨能够增强对流体的剪切作用，增大剪切应变率，增加流体的流动性，缩短流体的无量纲混合时间，增大洞穴区，减小停滞区，增大流体的混沌混合程度。其中，FPT-1桨体系的无量纲混合时间缩短了2.88%~5.65%，洞穴区域面积增加了6.58%；FPT-2桨体系的无量纲混合时间缩短了8.04%~11.00%，洞穴区域面积增加了8.25%。与普通矩阵排列的穿流孔相比，分形排布的穿流孔更有助于改善流体混合效果，提高流体混合效率。

关键词: 分形穿流搅拌桨, 混合, 假塑性流体, 计算流体力学

CLC Number:

TQ 027.2

Deyin GU, Hao YANG, Changshu LI, Zuohua LIU. Mixing behavior of pseudoplastic fluid in a fractal perforated impeller stirred tank[J]. CIESC Journal, 2025, 76(6): 2569-2579.

谷德银, 杨豪, 李昌树, 刘作华. 分形穿流桨搅拌槽内假塑性流体的混合行为[J]. 化工学报, 2025, 76(6): 2569-2579.

Figures/Tables 18

Fig.1 Schematic diagram of experimental set-up

Fig.2 Physical diagram of impeller

Fig.3 Schematic diagram of impeller blade

Fig.4 Extraction process of betti number

Fig.5 Grid independence verification

Fig.6 Numerical simulation predicted power consumption with experimental data

Fig.7 Changes in power consumption and power number with Reynolds number in different stirring blade systems

Fig.8 Viscosity distribution of longitudinal section of stirred tank (P = 33 W)

Fig.9 Viscosity distribution of longitudinal section of FPT-2 impeller stirred tank (P = 33 W)

Fig.10 Shear strain rate distribution of longitudinal section of stirred tank (P = 33 W)

Fig.11 Shear strain rate distribution at r/R = 0.6 in the stirred tank (P = 33 W)

Fig.12 Dimensionless mixing time under different power consumption per unit volume

Fig.13 Cavern structure during the coloring process (P = 33 W)

Fig.14 Cavern structure during the decolorization process (P = 33 W)

Fig.15 0-1 test result

Fig.16 Shear strain rate distribution on the planes of FPT-2 and MPT（P = 33 W）

Fig.17 Viscosity distribution of longitudinal section in the FPT-2 and MPT stirring systems (P = 33 W)

Fig.18 Comparison of dimensionless mixing time in FPT-2 and MPT stirring systems

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