Chaotic mixing in a barrier‐embedded partitioned pipe mixer

Inspired by the partitioned pipe mixer (PPM), a barrier‐embedded partitioned pipe mixer (BPPM) is designed and analyzed using a numerical simulation scheme. The BPPM is a static mixer, composed of orthogonally connected rectangular plates with a pair of barriers, which divide, stretch, and fold fluid elements, leading to chaotic mixing via the baker's transformation. The aspect ratio of the plate (α) and the dimensionless height of the barrier (β) are chosen as design parameters to conduct a parameter study on the mixing performance. The flow characteristics and mixing performance are analyzed using the cross‐sectional velocity vectors, Poincaré section, interface tracking, and the intensity of segregation. The results indicate that several designs of the BPPM significantly enhance the PPM's mixing performance. The best BPPMs are identified with regard to compactness and energy consumption. © 2017 American Institute of Chemical Engineers AIChE J, 64: 717–729, 2018     

Effects of geometry and operating conditions on the mixing behavior of an in-line impinging stream mixer

The present study investigated experimentally the effects of various geometric and operating parameters on the mixing characteristics of model liquids undergoing mixing in a novel in-line mixer, viz. an in-line impinging stream (IS) mixer. First, the mixer with one set of three inlet jets was used. Later two sets of inlet jets were used in order to increase the number of impingement zones and hence the mixing capability of the mixer. A statistical analysis was performed to indicate the best geometry of the mixer based on the data of both the mixing effectiveness and the pressure loss due to impingement of liquid streams.     

Study of mixing efficiency in roll-mills

A fluid dynamics analysis package (FIDAP) based on the finite element method was used to simulate the 2-D, isothermal flow of a power law model fluid in the bank and nip area of a two roll-mill geometry, including the determination of the free surface. Dispersive mixing efficiency was analyzed in terms of the shear stresses generated and the elongational flow characteristics. The latter were quantified using a frame invariant flow strength parameter. We found that the converging region rather than the nip region provides better mixing flow characteristics. We also found that the presence of vortices in the bank region is not beneficial for dispersive mixing.     

Experimental evaluation of gas mixing with a static microstructure mixer

Mixing plays an important role in chemical reaction engineering. In the last years several types of static microstructure mixers have been developed. The characterization of microstructure mixing is difficult to perform as the dimensions are too small for conventional methods. Therefore, we report a method to characterize the mixing of two gases directly by measuring the concentration of the gases at the outlet of the mixer. The experiments have been carried out up to gas flows of 5000 ml/min STP per passage. The mixing degree and mixing length were determined as well as the mixing time was calculated. These values depend on the properties of the gases and other parameters as temperature and gas velocity. Thus complete mixing is achieved after a mixing length, i.e., the distance to the microchannel outlet, of only 300-800 μm. Corresponding mixing times are just 100-600 μs. Furthermore, discontinuities in the mixing characteristic can be explained with the results obtained. Also design parameters for a further improvement of the mixer geometry individually for various applications could be set up.     

Effects of blade rake angle and gap on particle mixing in a cylindrical mixer

Performance optimization of a mixer is an issue of great significance in many industrial technologies dealing with particulate materials. By means of Discrete Element Method (DEM), this work examines how the mixing performance of a cylindrical mixer is affected by the two design parameters: blade rake angle and blade gap at the vessel bottom, extending our previous work on particulate mixing. The flow and mixing performance are quantified using the following: velocity fields in vertical cylindrical sections, Lacey’s mixing index, inter-particle forces in vertical cylindrical sections through the particle bed and the applied torque on the blade. Simulation results show that the mixing rate is the fastest for a blade of 90° rake angle, but inter-particle forces are large. Conversely, the inter-particle forces are small for a blade of 135° rake angle, but the mixing rate is slow. The simulation results also indicate that the force applied on particles, velocity field and mixing are interrelated in that order.     

Production of commercial dyes via impingement-sheet mixing: Part I. Testing of a device suitable for industrial application

Impingement-sheet mixing is a proven technique for the rapid mixing of liquids on the laboratory scale. In this paper a practical mixer design for use on the industrial scale is presented. The industrial impingement-sheet mixer was tested at flow rate ratios typical of commercial applications and, compared with earlier laboratory results, only a slight loss in mixing speed was noted. At flow rates of the order of liters/minute and pressure drops up to 1.5 bar, the micromixing times of the industrial impingement-sheet mixer are of the order of tens of milliseconds for reactant stoichiometric ratios near 1.00. If one of the reactants is present in at least a 10% excess, then the micromixing time of the limiting reagent is reduced to several milliseconds.     

Foam generation in a rotor—stator mixer: schaumerzeugung in einem rotor—stator mischer

The foaming process of an aqueous liquid system with surface active agents and thickeners in a rotor-stator mixer has been studied.The foaming capacity of a rotor—stator mixer may be represented by a so-called mixing characteristic. The foamabilities of several liquid systems have been measured as a function of the mixer geometry and the rotational speed.The hydrodynamics in a rotor-stator mixer is characterized by a Newton—Reynolds relationship. The mechanism of foaming and the dependence of several mixing parameters are different for the turbulent and laminar flow regions. The mixing process is evaluated in both regimes. In the transition region from turbulent to laminar the foaming is very poor in comparison with that in the turbulent and laminar flow regimes.     

A SIMULATION OF A MOTIONLESS MIXER

Continuous laminar mixing in segmented twisted-tape motionless mixers is considered. A solution to the steady isothermal creeping flow of a Newtonian fluid in a twisted-tape mixer has been obtained via two-dimensional numerical procedures. The developed flow within a section of the mixer has been solved in a helical coordinate system by an iterative scheme. The resulting solution is rigorously correct in the absence of entrance and exit flows at the junction between sections. An algorithm is presented for the modelling of these junction flows via two-dimensional procedures. Simulated cross-sectional mixing patterns have been generated for comparison with experimental results

The performance of twisted-tape mixers is simulated for various designs, beginning with the particular geometry of the Kcnics Static Mixer, and for different operating conditions Results suggest that the rate of mixing as a function of the total twist per section is optimized with respect to pressure drop when sections contain 80 degrees of twist. The capability for rational improvement in other design and operating parameters is illustrated. The mechanisms of laminar mixing are discussed and quantified; of primary importance is the tendency for interfacial area to assume an orientation within each section which is favorable to mixing in subsequent sections.     

螺带式混凝土搅拌机混合特性及DEM模拟

采用离散单元法模拟新拌混凝土于搅拌机中的混合过程,研究了双筒螺带式混凝土搅拌机的混合效率。 用Hertz-Mindlin with JKR接触方法建立新拌混凝土离散元模型,模拟了坍落度实验、L箱实验和流变仪实验,将模拟结果与实验结果进行对比,校准模型参数,采用混合系数定量研究了不同初始装填方式下搅拌机的混合效率。结果表明,采用上下装填方式时搅拌机混合效率较高;对任一初始装填方式,左部区域与右部区域、前部区域与后部区域间混合效率无明显差别,而上部区域混合效率比底部区域高,底部出料口处存在搅拌盲区,采用舍弃初始出料的方法可提高新拌混凝土性能。转速较高时混合效率较高,相同旋转圈数时,混合效率基本相同。     

Influence of design on dispersive mixing performance in an axial discharge continuous mixer—LCMAX 40

The axial discharge continuous mixer combines the features of a continuous mixer and a twin screw extruder, expanding the flexibility of this compounding machine. In this work we analyzed the influence of rotor design on the dispersive mixing performance of a LCMAX 40 unit. Specifically we looked at various arrangements for the pushing and counter pushing units in the design of the LCMAX 40. A fluid dynamics analysis package—FIDAP, based on the finite element method, was used to model the flow behavior of a power law model fluid under different pressurization conditions. Dispersive mixing efficiency was quantified in terms of shear stresses and elongational flow components generated in the flow field. We found that the counter-pushing unit generally contributes more in building up high shear stresses. However, the generation of elongational flow components, which is beneficial for dispersive mixing, is not solely dependent upon the pushing–counter pushing configuration but rather on the overall rotor geometry. We found that the maximum number of counter-pushing units in the rotor design of the LCMAX 40 should not exceed two in order to provide adequate material pumping. Rotor designs with alternating arrangements of pushing and counter-pushing units provide overall better dispersive mixing conditions.     

SV型静态混合器湍流阻力的初步研究

为了获得流体在SV型静态混合器中湍流流动时的流动阻力规律,提出一种新的含有SV型静态混合器重要几何结构参数的流体阻力计算模型。对于不可压缩流体,将其在SV型静态混合器中的运动分解成沿管壁与轴线方向平行和沿混合元件凹槽方向的直线运动。运用流体力学理论,分别求解出流体作2种运动时所产生的湍流流体阻力的计算式,并计入相邻混合元件交接部分的局部阻力,然后进行叠加得到流体阻力理论计算式。以水为实验介质,对SV型静态混合器流体湍流阻力进行了实验测量,与理论结论进行比较分析,得出摩擦因子λ与Re-0.2呈线性关系的结论。     

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.     

Mixing dynamics in the SMX static mixer as a function of injection location and flow ratio

A detailed Lagrangian analysis of partially mixed structures in an SMX static mixer is presented, with emphasis on laminar flows with Reynolds numbers between 1 and 100. The distribution of a small amount of equal‐viscosity additive is examined based on computing the trajectories of passive tracer particles through the mixer. Three radial positions (one centerline and two off‐center) are chosen for injection and the mixing patterns are compared in order to investigate the effect of injection location on mixing. Mixing measures, such as the decrease in the variation coefficient with axial distance, and the increase in the average rate of stretching, are discussed in order to quantify mixing performance. It is found that mixing rates for the centerline injections are larger than for the off‐center injection positions investigated. The presence of self‐similarity in the stretching field and the mixing patterns, and the exponential decrease in variation coefficient with increasing axial distance provides evidence for chaotic mixing behavior in this device.     

Pressure drop and mixing in single phase microreactors: Simplified designs of micromixers

Continuous flow microreactors can greatly improve the safety and product yields of processes in the pharmaceutical and fine chemical industry by overcoming many of the drawbacks of traditional batch and semi-batch stirred reactors. This study compares on a common scale the pressure drop and mixing performance of different size commercial microreactor plates composed of a tangential, SZ-shaped or caterpillar mixer followed by a rectangular serpentine main channel. The pressure drop was fitted to a friction factor model, which suggests that the mixing zone had significant chaotic secondary flow patterns, whereas the main channel did not. Moreover, the mixing zone was the main contributor to the overall pressure drop. Mixing performance was then characterized using competitive parallel reactions. Upon the formation of chaotic secondary flows, typically due to the interactions of artificially induced vortices, the mixer performance was found to be independent of geometry for a given energy dissipation rate. However, the mixer geometry will affect the critical Reynolds number that induces chaotic advection and changes the mixing time scale.     

Estimation of roll press design parameters based on the assessment of a particular nip region

Granular solids are compacted in roll presses to obtain dust free products from fine powders. This mainly takes place through the increase of the bulk density due to the pressure applied by the press. The well known theory by Johanson [J.R. Johanson, A rolling theory for granular solids, Transactions of the ASME, Journal of Applied Mechanics, December 1965, 842-848.] was based on defining the nip angle which identifies a nip region where the material is trapped and pressed to higher bulk density. The nip region was introduced in terms of sets of parameters which needed a lot of experimental work to be obtained. In this study it is shown that these parameters are not needed to be determined. The output of the machine as described by the ratio of bulk density can give the design parameters of the roll press; mainly described by the roll dimensions and roll force. This is mainly obtained using one single test, where a particular nip region can be defined, which accounts implicitly for the parameters which represent the flow properties and the material-machine interaction parameters.     

A novel microfluidic mixer using aperiodic perturbation flows

A novel technique is proposed for enhancing the mixing performance of a ‘crisscross’ microfluidic mixer by means of aperiodically-varying perturbation flows. The effects of the perturbation and geometry parameters on the fluid flow characteristics and mixing performance are analyzed numerically. In performing the simulations, the flow field and species concentration field are obtained by solving the two-dimensional time-dependent Navier–Stokes equations and the convection–diffusion equation, respectively. In addition, the oscillating source used to modulate the perturbation flows is modeled using the Sprott system. The results show that the irregularly-alternating flow perturbations cause a repeated stretching and folding of the species streams and enhance the mixing performance as a result. It is shown that an effective improvement in the mixing performance can be obtained through a suitable choice of the Sprott system scaling factor. Moreover, it is shown that having assigned an appropriate scaling factor, the mixing performance can be further improved by specifying suitable values of the geometry and perturbation parameters.     

Analysis and optimization of low-pressure drop static mixers

Various designs of the so called Low-Pressure Drop (LPD) static mixer are analyzed for their mixing performance using the mapping method. The two types of LPD designs, the RR and RL type, show essentially different mixing patterns. The RL design provides globally chaotic mixing, whereas the RR design always yields unmixed regions separated by KAM boundaries from mixed regions. The crossing angle between the elliptical plates of the LPD is the key design parameter to decide the performance of various designs. Four different crossing angles from 90° to 160° are used for both the RR and RL designs. Mixing performance is computed as a function of the energy to mix, reflected in overall pressure drop for all designs. Optimization using the flux-weighted intensity of segregation versus pressure drop proves the existence of the best mixer with an optimized crossing angle. The optimized angle proves to be indeed the LLPD design used in practice: the RL-120 with θ = 120°, although RL-140 θ = 140° performs as good. Shear thinning shows minor effects on the mixing profiles, and the main optimization conclusions remain unaltered. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

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.     

旋转流化床粉体混合机混合效果数值模拟和实验验证

为了对旋转流化床粉体混合机进行优化设计,采用CFD-DEM联合仿真的方法,对旋转流化床粉体混合机内球形颗粒的混合过程进行数值模拟,通过Lacey指数具体评价颗粒的混合效果,研究了进气管倾斜角度、进气管布置方式、进气方式对球形颗粒混合效果的影响,并进行球形颗粒混合实验验证。结果表明,进气管最合适的倾斜角度应保证气流作用区域面积恰好为底部颗粒物料区域面积的一半。进气管水平布置时能够保证很好的混合质量及较快的混合速率。脉冲及连续方式进气均能实现均匀混合,脉冲进气方式比连续进气方式耗气量更低。颗粒混合实验有很好的混合效果,与数值模拟的结果具有较高的一致性,从而获得了一种混合效果优越的结构形式,进气管倾斜角度α=35°,水平布置。