Enhancement of liquid–liquid mixing in a mixer-settler by a double rigid-flexible combination impeller

Abstract Mixing is crucial in the dispersion of two immiscible fluids. The rational design of an impeller is necessary to form suitable flow conditions and improve fluid mixing efficiency. A double rigid-flexible combination impeller was designed by connecting the upper and lower rigid impeller blades with flexible pieces. Experimental measurements were performed in a laboratory-scale mixer-settler under different impeller types. The largest Lyapunov exponent (LLE) and multi-scale entropy (MSE) were investigated using Matlab. Results showed that the double rigid-flexible combination impeller enhanced liquid–liquid mixing in the mixer-settler through the multiple-body motion behavior triggered by the swings of flexible pieces. At the optimum mixing point of each impeller, the LLEs of the double impeller, double rigid combination impeller, and double rigid-flexible combination impeller were 0.018, 0.055, and 0.057, respectively. At 75 rpm, the MSE of the combination impellers was obviously greater than that of the double impeller, and the rigid-flexible combination impeller had larger MSE than the double rigid combination impeller. The mixing efficiency of the rigid-flexible combination impeller increased with increasing width and quantity of the flexible piece. The quantity of rigid blade slice also influenced the enhancement of mixing ability. The double rigid-flexible combination impeller intensified the chaotic mixing of the two-phase fluid by changing the flow field structure and energy dissipation mode, ultimately achieving an efficient-mixing operation.

[1]  Liu Zuohu.  Chaotic mixing enhanced by rigid-flexible impeller in stirred vessel , 2014 .

[2]  Eric G. Paterson,et al.  Fluid–structure interaction analysis of flexible turbomachinery , 2011 .

[3]  Tao Changyuan.  Fractal flow structure in eccentric air jet-stirred reactor with double impeller , 2011 .

[4]  Koji Takahashi,et al.  Mixing performance experiments in impeller stirred tanks subjected to unsteady rotational speeds , 1998 .

[5]  Wang Yundong.  Chaotic mixing performance of high-viscosity fluid synergistically intensified by flexible impeller and floating particles , 2013 .

[6]  Abdul Latif Ahmad,et al.  Minimum agitation speed for liquid–liquid–gas dispersion in mechanically agitated vessels , 2001 .

[7]  Xiangyang Li,et al.  Numerical simulation of liquid–liquid turbulent flow in a stirred tank with an explicit algebraic stress model , 2013 .

[8]  J. Richman,et al.  Physiological time-series analysis using approximate entropy and sample entropy. , 2000, American journal of physiology. Heart and circulatory physiology.

[9]  Haina Hu,et al.  The Judgment of Chaotic Detection System's State Based on the Lyapunov Exponent , 2012 .

[10]  Fernando J. Muzzio,et al.  Laminar mixing in eccentric stirred tank systems , 2008 .

[11]  Liu Zuohu.  Energy efficiency analysis for high-viscosity fluid mixing enhanced by flexible impeller , 2013 .

[12]  Zai-Sha Mao,et al.  Numerical and Experimental Investigation of Liquid-Liquid Two-Phase Flow in Stirred Tanks , 2005 .

[13]  Fouad Azizi,et al.  Turbulently flowing liquid-liquid dispersions. Part I: Drop breakage and coalescence , 2011 .

[14]  Philippe A. Tanguy,et al.  Time-periodic mixing of shear-thinning fluids , 2004 .

[15]  Suzanne M. Kresta,et al.  Evolution of drop size distribution in liquid–liquid dispersions for various impellers* , 1998 .

[16]  Takehiko Inaba,et al.  Chaotic analysis of mixing enhancement in steady laminar flows through multiple pipe bends , 2007 .

[17]  Madalena Costa,et al.  Multiscale entropy analysis of complex physiologic time series. , 2002, Physical review letters.

[18]  Rafał Rakoczy,et al.  Power consumption, mixing time, heat and mass transfer measurements for liquid vessels that are mixed using reciprocating multiplates agitators , 2007 .

[19]  M. S. Bakharev,et al.  Simulation of nonequilibrium extraction of rare-earth elements with liquid membranes: I. Generalized mathematical model , 2008 .

[20]  Liu Zuohu.  Enhancement of macro-instability in mixer-settler with rigid-flexible impeller , 2014 .

[21]  Franco Magelli,et al.  Experimental and computational analysis of immiscible liquid–liquid dispersions in stirred vessels , 2009 .

[22]  Zied Driss,et al.  Numerical simulation of fluid-structure interaction in a stirred vessel equipped with an anchor impeller , 2011 .

[23]  G. Papadakis,et al.  Determination of mixing time and degree of homogeneity in stirred vessels with large eddy simulation , 2005 .

[24]  Bin Sun,et al.  Multi-scale Chaotic Analysis of the Characteristics of Gas-Liquid Two-phase Flow Patterns , 2010 .

[25]  M. S. Bakharev,et al.  Simulation of nonequilibrium extraction of rare-earth elements with liquid membranes: II. Comparison of theoretical and experimental data , 2008 .

[26]  Jos Derksen,et al.  MULTI-SCALE SIMULATIONS OF STIRRED LIQUID -- LIQUID DISPERSIONS , 2007 .

[27]  Jing Li,et al.  Dynamics analysis and synchronization of a new chaotic attractor , 2014 .

[28]  S L Yeoh,et al.  Numerical Simulation of Turbulent Flow Characteristics in a Stirred Vessel Using the LES and RANS Approaches with the Sliding/Deforming Mesh Methodology , 2004 .

[29]  C. Peng,et al.  Analysis of complex time series using refined composite multiscale entropy , 2014 .

[30]  Sebastian Maaß,et al.  Prediction of drop sizes for liquid–liquid systems in stirred slim reactors—Part II: Multi stage impellers , 2010 .

[31]  R. Thuraisingham,et al.  On multiscale entropy analysis for physiological data , 2006 .