Chaotic mixing and droplet dispersion characteristics of liquid - liquid with elastic combined impeller

doi:10.11949/0438-1157.20200675

Abstract

Abstract:

Traditional mixing and clarification tanks generally use rigid stirring blades to achieve liquid-liquid two-phase mixed extraction, which generally suffers from low efficiency and high energy consumption. A kind of elastic combined impeller was used in the mixing clarifier in this work to enhance the liquid-liquid biphase mixing behavior. Lyapunov exponent (LLE) and multiscale entropy (MSE) were used to characterize the chaotic state of the system, the particle size distribution and D₃₂ were used to characterize the dispersion effect. The influence of impeller type (elastic combined impeller, rigid-flexible combined impeller and rigid impeller), spring length, wire diameter and outer diameter on mixing effect was studied. The results indicated that compared with the rigid impeller and the rigid-flexible combined impeller, the elastic combined impeller strengthens the energy dissipation mode of the flow field through the deformation and energy storage of the spring, improves the dispersion effect of the dispersed phase, and was conducive to the chaotic mixing of the liquid-liquid biphase. When stirring speed N = 200 r/min, the spring wire diameter was 0.6 mm, the relative length of the spring was 1.2, and the external diameter of the spring was 7 mm, the LLE value and the amplitude of MSE were the largest and the MSE values fluctuate most strongly. At the same time, there was a log-linear relationship between the D₃₂ of dispersed phase and the stirring speed in each stirring system, and the droplet size of dispersed phase in the elastic combined impeller system was smaller and more.

Key words: elastic combined impeller, mixing, mixer-settler, Lyapunov exponent, multiscale entropy, particle size distribution, D₃₂

摘要：

传统的混合澄清槽一般采用刚性搅拌桨来实现液-液两相的混合萃取，普遍存在效率低、能耗高等问题。将一种弹性搅拌桨应用在混合澄清槽中，以强化液-液两相混沌混合及分散特性。以最大Lyapunov指数（LLE）和多尺度熵（MSE）表征体系混沌状态，以分散相液滴粒径分布、Sauter平均粒径（D₃₂）等表征分散效果，分别研究了桨叶类型（弹性搅拌桨、刚柔组合桨及刚性桨）、弹簧长度、线径、外径等因素对混沌混合效果和分散特性的影响。结果表明，相比较刚性搅拌桨和刚柔组合搅拌桨，弹性搅拌桨通过弹簧的形变和储能作用，强化了搅拌能量的传递方式，提高了分散相的分散效果，有利于液液两相的混沌混合，在搅拌转速N=200 r/min、弹簧线径为0.6 mm、弹簧相对长度为1.2、弹簧外径为7 mm时，弹性搅拌桨体系的LLE和MSE更大，且MSE值波动最强；同时，各搅拌体系内分散相平均粒径D₃₂与转速呈对数线性关系，弹性搅拌桨体系内分散相液滴尺寸更小且数量更多。

关键词: 弹性搅拌桨, 混合, 混合澄清槽, Lyapunov指数, 多尺度熵, 粒径分布, D₃₂

CLC Number:

TQ 027.2

Zuohua LIU, Chuang WANG, Wei SUN, Changyuan TAO, Yundong WANG. Chaotic mixing and droplet dispersion characteristics of liquid - liquid with elastic combined impeller[J]. CIESC Journal, 2020, 71(10): 4611-4620.

刘作华, 王闯, 孙伟, 陶长元, 王运东. 弹性搅拌桨强化液-液两相混沌混合及液滴分散特性的研究[J]. 化工学报, 2020, 71(10): 4611-4620.

Figures/Tables 16

Fig.1 Schematic diagram of elastic combined impeller enhancing mixing

Table1 Physical property of mediums

Material	Density/(kg/m³)	Viscosity/(Pa?s)
water	998.2	0.0010
kerosene	780.0	0.0024

Fig.2 SOPAT measurement system

Fig.3 Structure of mixer-settler

Fig.4 Impellers used in experiment

Fig.5 Effect of impeller type on LLE

Fig.6 Effect of outer diameter of spring on LLE

Fig.7 Effect of length of spring on LLE

Fig.8 Effect of wire diameter of spring on LLE

Fig.9 Effect of impeller type on MSE

Fig.10 Effect of outer diameter of spring on MSE

Fig.11 Effect of length of spring on MSE

Fig.12 Effect of wire diameter of spring on MSE

Fig.13 The distribution of dispersed phase droplets in different impeller systems at different stirring speeds

Fig.14 Effect of stirring speed on droplet distribution

Fig.15 The effect of stirring speed on D32

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