Experimental study on mixing characteristics of flexible-blade Rushton impeller

doi:10.11949/0438-1157.20190961

Abstract

Abstract:

Rapid mixing is the key factor to efficient operation of many industrial devices involving fluid flow. During the past several decades, extensive contributions have been made to improve the mixing effect and efficiency either by modifying and developing new types of impellers, or by employing and developing new fluid mixing techniques. In this paper, the turbulent mixing characteristics of the flexible-blade Rushton impeller developed by ourselves were experimentally studied by the planar laser induced fluorescence (PLIF) technique. Roddinmin 6G was used as fluorescer. The agitated fluid was water. Result of the calibration experiment shows that the fluorescer luminosities are linear with their concentration, which can be used as a benchmark to measure the mixing time under the same experimental conditions. Diffusion processes of fluorescer show that flexible-blade Rushton impeller has better mixing performance than the standard Rushton impeller. It can improve the mixing uniformity and increase the mixing speed, especially at the initial stage of the mixing process. By comparison with standard Rushton impeller, it was found that mixing time of flexible-blade Rushton impeller is shorter, which is helpful to improve the fluid mixing efficiency. Results of this work lay a solid foundation for the industrial application of this impeller.

Key words: stirred vessel, flexible-blade Rushton impeller, mixing, experimental measurement, planar laser induced fluorescence

摘要：

提高混合效率是流体搅拌混合领域的重点研究内容之一。几十年来，人们在开发新型搅拌桨及研发流体混合新技术方面做了大量工作。基于刚性Rushton桨，开发了一种柔性叶片Rushton搅拌桨，并以罗丹明6G为荧光剂，采用平面激光诱导荧光法对介质为水时该桨在湍流状态下的混合性能进行了实验测试研究。结果发现，标定实验结果表明，荧光剂强度与浓度呈线性关系，可以此为基准衡量同等实验条件下的宏观混合时间。荧光剂的扩散情况表明，与刚性桨相比，柔性桨具有更好的混合性能，尤其在混合的初始阶段，混合均匀程度及混合速度均有一定的优势。与刚性桨混合时间的对比表明，柔性桨的宏观混合时间较短，有助于提高流体混合效率。研究结果为该桨的工业应用奠定了基础。

关键词: 搅拌容器, 柔性Rushton搅拌桨, 混合, 实验测量, 平面激光诱导荧光

CLC Number:

TQ 027

Fengling YANG, Cuixun ZHANG, Meiting LI. Experimental study on mixing characteristics of flexible-blade Rushton impeller[J]. CIESC Journal, 2020, 71(2): 626-632.

杨锋苓, 张翠勋, 李美婷. 柔性Rushton搅拌桨混合性能的实验研究[J]. 化工学报, 2020, 71(2): 626-632.

Figures/Tables 8

Fig.1 Impellers and stirred vessel

Fig.2 Diagram of PLIF experimental set-up

Fig.3 Calibration of fluorescer concentration

Fig.4 Fluorescence adding and monitoring positions

Fig.5 Dispersion of fluorescence at speed N=0.5 r·s -1

Fig.6 Dispersion of fluorescence at speed N=2 r·s -1

Fig.7 Dispersion of fluorescence at speed N=3.5 r·s -1

Table 1 Experimentally determined mixing time

转速 N/(r·s ^-1)	桨型	宏观混合时间 t/s				平均混合时间/s
转速 N/(r·s ^-1)	桨型	P ₁	P ₂	P ₃	P ₄	平均混合时间/s
0.5	刚性桨	12.5	6.5	7.0	10.0	9.0
0.5	柔性桨	11.0	6.0	7.0	9.0	8.3
2	刚性桨	9.0	4.5	5.5	8.0	6.8
2	柔性桨	7.0	3.0	3.5	5.5	4.8
3.5	刚性桨	6.5	2.0	3.3	5.3	4.3
3.5	柔性桨	5.0	1.5	2.5	4.3	3.3

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