Comparative analysis of different static mixers performance by CFD technique: An innovative mixer

The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD,with Reynolds numbers ranging from 20 to 160. The performance of the new mixer is compared with those of Kenics, SMX, and Komax static mixers. The pressure drop ratio(Z-factor), coefficient of variation(CoV), and extensional efficiency(α) features have been used to evaluate power consumption, distributive mixing, and dispersive mixing performances, respectively, in all mixers. The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation. CFD results are consistent with measured data and those obtained by available correlations in the literature. The new mixer shows a superior mixing performance compared to the other mixers.     

Design and characterization of a Low-pressure-drop static mixer

Four-blade static mixer was designed for inline mixing of Newtonian fluids at Reynolds numbers from 700 to 6800. The mixer consists of four equally spaced blades mounted on cylindrical housing with 45° rotation relative to the circumference. It was tested in three different compartments of 6, 8, and 10 mixing elements; each element rotated 45° relative to the adjacent one. Multipoint sampling was used to measure concentration downstream the mixer. The mixing quality was measured by the coefficient of variance (CoV). The CoV decreases as the energy input per unit mass increases. This effect is more pronounced when the number of mixing elements increases. For the case of 10 mixing elements, a good mixing performance (typically more than 95% mixedness or CoV < 0.05) achieved, although a marginally good mixing performance could also be achieved by eight mixing elements. The friction factors were correlated as f = C₁/Re + C₂/Reⁿ with an average deviation of ±10% from experimental data. Furthermore, experimental friction factors were compared with existing models. For a wide range of Reynolds numbers, the friction factors are apparently smaller than those from SMV, KMX, and baffle-type static mixers. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1126–1133, 2019     

Development of a novel microcompounder for polymer blends and nanocomposite

In this article, we introduce a new type of small scale compounder. The compounder developed is for mixing of polymeric samples of 0.5–10 g. It consists of a heated cylindrical metal having two cylindrical cavities connected through a narrow channel and two cylindrical pistons, which squeeze molten polymers from one cavity to the other cavity through the narrow channel. During mixing procedure, the molten polymers flow from one cavity to the other cavity, repeatedly, and this operation generates the extensional flow in the converging and the diverging geometry. Because the compounder has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. We evaluated the mixing efficiency of the compounder by comparing with the commercialized small‐scale mixers including a cup and rotor batch mixer, an internal batch mixer, and a recirculating conical twin‐screw extruder. It was found that the compounder developed has many advantages over the existing small‐scale mixers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Design and assessment of a novel static mixer

This paper examines the performance of a novel static mixer comprising a circular tube fitted with eight alternating equi‐spaced semicircular rigid insert (baffles) as the mixer elements. Experiments were carried out to obtain the coefficient of variance (CoV) for the mixing of two streams of water and brine for Reynolds number between 60 and 700. Decreasing the baffles clearance ratio significantly reduces the CoV but at a cost of an increase in the pressure drop across the static mixer. The presence of the mixing elements (baffles) promotes a non‐laminar, turbulent‐like flow which considerably enhances the mixing. The static mixer described here represents a cost effective, easy to manufacture, low maintenance, and flexible alternative to the more sophisticated static mixers currently in use.     

Improving mixing performance by curved-blade static mixer

This article addresses design modification to a flat-blade static mixer to enhance mixing performance. The static mixer elements used in this work consist of four blades with curvature made to intensify turbulent-like flow, while reducing the pressure drop. The blades were mounted on a cylindrical housing with 45° rotation relative to the axial direction. The mixer assembly was used in three different arrangements of 8, 10, and 14 elements for a range of Reynolds number between 600 and 7,000. The coefficient of variance (COV) of samples was used to measure the mixing quality. The curved-blade mixer provides considerable improvement in mixing quality compared with the flat-blade mixer and comparable to the SMX mixer. Compared with the flat-blade static mixer, the new design reduces the COV by up to about 50%. This effect is more pronounced when the number of mixing elements increases. Furthermore, the friction factors for the modified mixer, obtained at a wide range of Reynolds number, were apparently smaller than those for the flat-blade, SMX, and SMV mixers. The correlation presented for the friction factor, when all mixer arrangements and aspect ratios were considered, supports the experimental data with ±15% deviation.     

Effect of swirling addition on the liquid mixing performance in a T-jets mixer

Swirling addition to the stream is beneficial for the fluid mixing. This work aims to study the mixing process intensification in a conventional T-jets mixer by the swirling addition. After experimental verification by the planar laser-induced fluorescence technique, large eddy simulation with the dynamic kinetic energy sub-grid stress model is used to predict how the swirling strength (in terms of swirling number, S_w) and swirling directions affect the mixing performance, e.g. the tracer concentration distribution, mixing time, and turbulent characteristics in the T-jets mixers. Predictions show that the swirling strength is the key factor affecting the mixing efficiency of the process. The overall mixing time, τ₉₀, can be significantly reduced by increasing S_w. Vortex analysis shows that more turbulent eddies appear in the collision zone and the turbulent kinetic energy dissipation rate increases obviously with the swirling addition. When S_w is kept constant, the mixing process can be accelerated and intensified by adding swirling to only one stream, to both streams with the opposite swirling directions, or to both streams with the same swirling directions. Amplification of the mixing process by enlarging the mixer size or increasing the flow rates is also optimized. Thus, this work provides a new strategy to improve the mixing performance of the traditional T-jets mixers by the swirling addition.     

液-液快速混合设备研究进展

在分析了液-液混合机理的基础上,对几类常用的液一液快速混合设备及其混合过程机理方面的研究进行了全面的综述。在结合大量专利所涉及的工业混合设备分析的基础上,总结了射流喷射混合器、撞击流混合器、静态混合器、动态混合器等4类液-液快速混合设备的混合机理及各类混合设备的优缺点,并展望了工业液-液快速混合设备的研究前景。     

微混合器内流体混合的研究进展

Microreaction technology is one of the most innovative and rapid developing fields in chemical engineering, synthesis and process technology. Many expectations toward enhanced product selectivity, yield and purity, improved safety, and access to new products and processes are directed to the microreaction technology. Microfluidic mixer is the most important component in microfluidic devices. Based on various principles, active and passive micromixers have been designed and investigated. This review is focused on the recent developments in microfluidic mixers. An overview of the flow phenomena and mixing characteristics in active and passive micromixers is presented, including the types of physical phenomena and their utilization in micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, T-micromixer is highlighted as an example to illustrate the effect of design and operating parameters on mixing efficiency and fuid flow inside microfluidic mixers.     

Morphological study of two‐phase polymer blends during compounding in a novel compounder on the basis of elongational flows

A new laboratory‐scale mixing device based on an original concept was built and tested. This device has important technical features such as tightness to liquids and gases, the possibility of direct specimen molding after mixing, and easy handling of reactive systems. In comparison with existing laboratory mixers, the flow in this mixer is characterized by a high contribution from elongational flow. Morphological data on model polystyrene/poly(methyl methacrylate) blend systems have proved the high distributive and dispersive mixing efficiency in comparison with a classical rotational batch mixer. The influence of different experimental parameters such as the flow rate, mixing time, mixing element geometry, and viscosity ratio of blends is characterized and discussed. Much finer dispersions have been obtained with this new device versus those obtained with a conventional mixer with equivalent specific energy input. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Pressure drop and mixing behaviour of non‐Newtonian fluids in a static mixing unit

Static or motionless mixers have received wide application in chemical and allied industries due to their low cost and high efficiency. The pressure drop and mixing behaviour of such mixers have been widely studied. However, the available information for non‐Newtonian fluids is scanty. The results of pressure drop and mixing studies conducted with a locally made motionless mixer (MALAVIYA mixer) and four non‐Newtonian fluids—aq. CMC, PVA, and PEG solutions are reported in this article. The new mixer causes less pressure drop compared to some of the commercial mixers. Mixing behaviour of the unit is more closer to plug flow and a two‐parameter model correlates the dispersion data.     

Numerical investigation of blade shape in static mixing

The mixing performance of the KMX and SMX static mixers have been compared using 3D high-resolution computational fluid dynamics (CFD) simulations. Although these mixers have a similar design composed of layers of blades, their blade shape is different: curved for the KMX and flat for the SMX. The flow of a Newtonian fluid in steady laminar regime has been considered as the benchmark of the study. The simulation was first validated by assessing the pressure drop vs. the number of mixer elements and the results were found to be in good agreement with experimental data. To evaluate the mixing quality, cross-section stream function, extensional efficiency, mean shear rate, residence time, intensity of segregation, stretching, and Lyapunov exponent have been selected. Analysis of the flow pattern and mixing parameters shows differences between the mixers and it appears that the curved blade is more efficient than the flat blade design at the expense of a slightly higher pressure drop. In practice, the KMX mixer should provide a higher mixing rate at high viscosity ratio than the SMX mixer. © 2004 American Institute of Chemical Engineers AIChE J, 51: 44–58, 2005     

Effects of geometry and flow rate on secondary flow and the mixing process in static mixers—a numerical study

A method based on computational fluid dynamics (CFD) for the characterization of static mixers using the Z factor, helicity and the rate of striation thinning is presented. These measures were found to be well-suited for the characterization of static mixers as they reflect the pressure drop, the formation of secondary flow, i.e. vortices, and their effect on the mixing process. Two commercial static mixers, the Kenics KM and Lightnin Series 45, have been characterized. In the mixers investigated, secondary flow is formed in the flow at the element intersections and due to the curvature of the mixer elements. The intensity of the vortices is higher in the Lightnin than the Kenics mixer due to edges in the middle of the Lightnin mixer elements. The formation of vortices affects the Z factor by an increase in the power requirement, and the rate of striation thinning by an increase in the stretching of the striations. The formation of vortices was observed at a Reynolds number of 10 in both mixers with aspect ratios of 1.5. However, the intensity of the vortices was greater in the Lightnin than the Kenics mixer, which was observed in not only the magnitude of the helicity, but also the Z factor, rate of striation thinning and the distribution of striation thickness.The distribution in striation thickness is shifted towards thin striations as the flow rate is increased from below to above the Reynolds numbers of which vortices were first observed, but some striations still pass the mixer elements almost unaffected, which can be seen in the skewness of the distribution of the striation thickness, which shifts from being negative to positive.     

The design and performance of a vane mixer based on extensional flow for polymer blends

A new laboratory‐scale mixing device called the “Vane Mixer” was designed, built, and tested. The vane mixer consists of three vane plasticizing and conveying unit. In comparison with the existing laboratory mixers, material flow in this vane mixer is characterized by a high contribution from extensional flow. As the mixer has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. The influences of mixing time and rotor speed on dispersed phase size were characterized and discussed. Morphology data on model immiscible polystyrene/high density polyethylene (PS/HDPE) blend have proved the high distributive and dispersive mixing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41551.     

Mechanisms of mixing in single and co-rotating twin screw extruders

Previous experimental studies have revealed that the mixing efficiencies of widely used continuous processors such as the single and twin screw extruders depend on the types of screw elements, which are utilized. It is generally recognized that the basic single screw extruder and the fully-fighted sections of the fully-intermeshing co-rotating twin screw extruders are not efficient mixers, in contrast to the specialized mixing elements such as the kneading discs used in co-rotating twin screw extruders. However, no simulation techniques were available to characterize quantitatively and rigorously the mixing efficiencies of continuous processors. In this study, we have solved the three-dimensional equations of conservation of mass and momentum, and utilized various tools of dynamics to analyze the mixing occurring in single and co-rotating twin screw extruders. It is shown that simulation methods can indeed capture the relative differences in the mixing mechanisms of continuous processors like the single and twin screw extruders. The ability to distinguish quantitatively between the distributive mixing capabilities of various continuous processors should facilitate numerical testing of new continuous mixer designs, optimization of operating conditions and geometries of existing mixers and the material-specific design of new mixers.     

宽粘度域搅拌器的开发及其研究进展

考虑到过程工业中诸多混合体系的变粘特性以及传统搅拌器应用范围的局限性,研究开发宽粘度域搅拌器很有必要。在介绍单一叶片式和双轴组合式宽粘度域搅拌器类型、结构特点和应用范围的基础上,概述了其性能研究的国内外进展,分析了各宽粘度域搅拌器的优、缺点。最后对单一叶片式和双轴组合式宽粘度域搅拌器进行了比较,明确了发展趋势,并指明宽粘度域搅拌器的选用应兼顾体系物性的变化、设备结构的复杂程度、功率及混合特性等因素。     

Experimental characterization and multi-scale modeling of mixing in static mixers

Mixing in static mixers is studied using a set of competitive-parallel chemical reactions and computational fluid dynamics (CFD) in a wide range of operating conditions. Two kinds of mixers, a wide angle Y-mixer and a two jet vortex mixer, referred to as Roughton mixer, are compared in terms of reaction yields and mixing times. It is found that the Roughton mixer achieves a better mixing performance compared to the Y-mixer. The effect of flow rate ratio on mixing in the Roughton mixer has been studied as well and it is shown that the mixing efficiency is not affected by the flow rate ratio. Moreover, experimental results and model predictions are in good agreement for all mixer geometries and operating conditions. CFD is used to calculate absolute mixing times based on the residence time in the segregated zone and it is shown that mixing times of less than 1 ms can be achieved in the Roughton mixer. In addition, CFD provides insight in local concentrations and reaction rates and serves as a valuable tool to improve or to scale-up mixers.     

Residence Time and Concentration Distribution in a Kenics Static Mixer

Static mixers, often referred to as motionless mixers, are in-line mixing devices that consist of mixing elements inserted into a length of pipe. Most of the experimental works in this field have concentrated on establishing design guidelines and pressure drop correlations. Due to experimental difficulties, few articles have been published on the investigation of the flow and mixing mechanisms. In this work, a Kenics KMX static mixer was utilized to study concentration and residence time distribution (RTD) and effect of Reynolds number on mixing. The static mixer had six mixing elements arranged in-line along the length of the tube, and the angle between two neighboring elements was 90°. The length of the mixer was 0.98 m with internal and external diameters of 5.0 cm and 6.0 cm, respectively. The main continuous fluid was water, and NaCl solution was used as a tracer. All experiments were conducted with three replications at three Reynolds numbers, Re = 1188.71, 1584.95, and 1981.19. A dispersion model was used to model the RTD data. The experimental results were compared with the model results and reasonable agreement was achieved.     

Strain mode of general flow: Characterization and implications for flow pattern structures

Understanding the mixing capability of mixing devices based on their geometric shape is an important issue both for predicting mixing processes and for designing new mixers. The flow patterns in mixers are directly connected with the modes of the local strain rate, which is generally a combination of elongational flow and planar shear flow. We develop a measure to characterize the modes of the strain rate for general flow occurring in mixers. The spatial distribution of the volumetric strain rate (or non‐planar strain rate) in connection with the flow pattern plays an essential role in understanding distributive mixing. With our measure, flows with different types of screw elements in a twin‐screw extruder are numerically analyzed. The difference in flow pattern structure between conveying screws and kneading disks is successfully characterized by the distribution of the volumetric strain rate. The results suggest that the distribution of the strain rate mode offers an essential and convenient way for characterization of the relation between flow pattern structure and the mixer geometry. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2563–2569, 2016     

Influence of agitator design on powder flow

Design influences the flow within a powder mixer but quantitative guidance is lacking. Here the performance of mixers of different geometry was compared using positron emission particle tracking. One mixer had six long flat blades; the other carried short paddles. With the former, blade angle and number of axial compartments had little effect on agitation in the transaxial plan but axial dispersion was enhanced by longer axial compartments. A loop of circulation was found below the shaft. For the short paddle device, the transaxial agitation was more uniform, with a lower mean angular velocity and narrower ranges of velocities. The mixing elements inhibited the formation of the loop of circulation. In both cases, the axial flow had a cellular structure created by the radial supports for the blades but the short paddles mixer showed more chaotic behaviour, the axial dispersion coefficient being typically five times higher and increasing with fill rather than decreasing as seen with the six-blade device. A rationale for the design of powder mixers is thus emerging.     

Method of analyzing and quantifying the performance of mixing sections

In this article, the performance of three different mixing elements on color dispersion in high‐density polyethylene and linear low‐density polyethylene polymer stream during extrusion is studied. Two similarly designed Maddock mixers and a Stratablend II mixer are used as the last part of a general purpose single screw. Moreover, an inline melt camera is used for the quantification of mixing quality by visualization of grayscale of the color dispersion and thus mixing. The Stratablend II mixer produces the lowest and most uniform standard deviation. Both the Maddock mixers showed the same trend but higher values of standard deviation. All results are then compared with a full 3D finite element method simulation. Simulations clearly indicate that the Stratablend II mixer has the best mixing abilities and that these are mainly given by its unique design with high average value of shear stress. The role of elongational stress does not appear to have a high influence on mixing for these mixers. The results also suggest that the key factor for achieving better mixing is the frequency by which a large fraction of the material passes through the high shear stress regions of the mixer. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers