Laminar mixing of shear thinning fluids in a SMX static mixer

Flow and mixing of power-law fluids in a standard SMX static mixer were simulated using computational fluid dynamics (CFD). Results showed that shear thinning reduces the ratio of pressure drop in the static mixer to pressure drop in empty tube as compared to Newtonian fluids. The correlations for pressure drop and friction factor were obtained at Re_MR?100. The friction factor is a function of both Reynolds number and power-law index. A proper apparent strain rate, area-weighted average strain rate on the solid surface in mixing section, was proposed to calculate pressure drop for a non-Newtonian fluid. Particle tracking showed that shear thinning fluids exhibit better mixing quality, lower pressure drop and higher mixing efficiency as compared to a Newtonian fluid in the SMX static mixer.     

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     

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     

The Influence of Viscosity Ratio on Mixing Effectiveness in a Two‐fluid Laminar Motionless Mixer

An investigation of dependence of laminar mixing efficiency of a motionless mixer upon viscosity ratio at low Reynolds number (?3) was performed. Viscosity ratios up to 340 were investigated. The liquids were aqueous solutions of carboxymethylcellulose (CMC). Two transparent liquid streams, one marked with a fluorescing dye, were injected into a pipe housing five elements of an SMX mixer. The degree of mixing was evaluated by imaging a downstream cross‐section of pipe using laser induced fluorescence (LIF). Highly resolved spatial variations of fluorescence intensity were recorded using a CCD camera. Mathematical evaluations using correlograms, scale of segregation, COV, and intensity histograms are presented.     

FRICTION FACTOR IN STATIC MIXER AND DETERMINATION OF GEOMETRIC PARAMETERS OF SMX SULZER MIXERS

Pressure drops were determined in fluid flow through SMX Suizer static mixer of different sizes. In order to investigate a large range of Reynolds number, the experiments were performed with fluids of different viscosities. Pressure drops measurements in static mixer considered as a porous medium, are analysed with a capillary model for the determination of the geometric parameters of static mixers: pore diameter and tortuosity. These parameters allow the expression of pressure drops in terms of friction factor,f_c as a function of pore Reynolds number, Re_pA universal equation is obtained for the friction factor:f_c=16/Re_p+,0.194 which covers both viscous and inertial flow regimes.     

RESIDENCE TIME DISTRIBUTION OF RHEOLOGICALLY COMPLEX FLUIDS PASSING THROUGH A SULZER SMX STATIC MIXER

Static mixers are widely used in continuous mixing, heat and mass transfer processes and chemical reactions. However, a proper understanding of the flow pattern is still missing when rheologically complex fluids are involved. This paper presents a study of the Residence Time Distribution (RTD) determination in a Sulzer SMX static mixer. A two-parameter RTD model, based on each mixing element, was proposed to describe the flow pattern of rheologically complex fluids in a such mixer. It was shown that in this model the flowrate fraction across the plug flow component increases with the generalized Reynolds number. However, the volumetric fraction of the plug flow component depends not only on the generalized Reynolds number, but also on the number of mixing elements, apparently due to memory effects of viscoelastic fluids.     

数值模拟静态混合器结构对PS/CO_2熔体温度的影响

利用专用CFD软件Polyflow对SMX型和Kenics型静态混合器中PS/CO_2发泡溶液进行数值模拟计算,分析比较不同板厚在不同元件个数条件下两种静态混合器消耗的压力损失,以及不同CO_2浓度对静态混合器压力损失的影响;并引入"离散系数"分析比较两种静态混合器出口温度均匀性的变化.数值模拟的结果表明:SMX型静态混合器冷却效果优于Kenics型静态混合器,并且SMX型静态混合器出口温度均匀性高于Kenics型静态混合器.     

SD型静态混合器压力降的特性分析

借助计算流体力学软件FLUENT5/6,对含有3个流道的螺旋式静态混合器在不同的长宽比和雷诺数下的流动特性进行了数值模拟。模拟结果表明,当螺旋片长宽比为4∶1时该混合器压力降与雷诺数的1.715次方成正比;当雷诺数一定时,压力降与混合元件单元数在双对数坐标下成线性分布规律;压力降随着螺旋叶片长宽比的减小而增大;该混合器的压力降与对应结构的SK型静态混合器基本相同,大约是相同直径和管长的光滑空管压力降的10倍。     

The numerical simulation of a new double swirl static mixer for gas reactants mixing

For the nitrogen oxide removal processes, high performance gas mixer is deeply needed for the injection of NH₃ or O₃. In this study, a new type of double swirl static mixer in gas mixing was investigated using computational fluid dynamics (CFD). The results obtained using Particle Image Velocimetry (PIV) correlated well with the results obtained from simulation. The comparisons in pressure loss between the experimental results and the simulation results showed that the model was suitable and accurate for the simulation of the static mixer. Optimal process conditions and design were investigated. When L/D equaled 4, coefficient of variation (COV) was <5%. The inlet velocity did not affect the distributions of turbulent kinetic energy. In terms of both COV and pressure loss, the inner connector is important in the design of the static mixer. The nozzle length should be set at 4 cm. Taking both COV and pressure loss into consideration, the optimal oblique degree is 45°. The averaged kinetic energy changed according to process conditions and design. The new static mixer resulted in improved mixing performance in a more compact design. The new static mixer is more energy efficient compared with other SV static mixers. Therefore, the double swirl static mixer is promising in gas mixing.     

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.     

The numerical simulation of a new double swirl static mixer for gas reactants mixing

For the nitrogen oxide removal processes, high performance gas mixer is deeply needed for the injection of NH₃ or O₃. In this study, a new type of double swirl static mixer in gas mixing was investigated using computational fluid dynamics (CFD). The results obtained using Particle Image Velocimetry (PIV) correlated well with the results obtained from simulation. The comparisons in pressure loss between the experimental results and the simulation results showed that the model was suitable and accurate for the simulation of the static mixer. Optimal process conditions and design were investigated. When L/D equaled 4, coefficient of variation (COV) was < 5%. The inlet velocity did not affect the distributions of turbulent kinetic energy. In terms of both COV and pressure loss, the inner connector is important in the design of the static mixer. The nozzle length should be set at 4 cm. Taking both COV and pressure loss into consideration, the optimal oblique degree is 45°. The averaged kinetic energy changed according to process conditions and design. The new static mixer resulted in improved mixing performance in a more compact design. The new static mixer is more energy efficient compared with other SV static mixers. Therefore, the double swirl static mixer is promising in gas mixing.     

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.     

Performance of Kenics static mixer over a wide range of Reynolds number

The present study deals with the numerical simulation of flow patterns and mixing behaviour in Kenics static mixer over a wide range of Reynolds number. Three different sets of Kenics mixer (aspect ratio = 1.5) comprised of 3, 9 and 25 elements each have been characterized. The Reynolds number was varied in the range of 1 to 25,000 (i.e., from laminar to turbulent flow regime). The numerical approach takes into account the aspects of the fluid flow at higher Reynolds number values including circumferential velocity profiles at different cross-sections within the Kenics mixer, which were neglected in previous studies. It was observed that cross-sectional mixing in the turbulent flow regime takes place up to 30% of each element length at element-to-element transition; beyond that velocity profiles were uniform. The experiments were also carried out to measure the circumferential and axial velocity profiles and pressure drop in three different Kenics Mixers using air as fluid. The pressure drop per unit element (ΔP/η) was found to be independent of the number of Kenics mixing elements used in the system. The total pressure drop across Kenics mixer obtained by CFD simulations were compared with the experimental pressure drop values and correlations available in the literature. The numerical results were found in good agreement with the experimental as well as the results reported in the literature. A new pressure drop correlation in the Kenics static mixer has been developed.     

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.     

SMX型静态混合器湍流特的数值模拟

以SMX型静态混合器为研究对象,运用计算流体力学软件Fluent对3种结构静态混合器管内湍流流场进行数值模拟.结果表明:SMX型静态混合器的混合元件对流体有切割和分散作用,可使径向速度与周向速度的最大值达到轴向平均表观流速的2～2.5倍;流体流经3、4个混合元件后流动基本达到稳定;混合器前3个混合元件对流体湍动强化作用...     

Homogeneity of multilayers produced with a static mixer

A multiflux static mixer can be used to produce multilayered structures. The flow is repeatedly cut, stretched and stacked by mixing elements in the channel of such a device. In the standard design, however, the obtained layer thicknesses are inhomogeneous. The causes for the multiflux static mixer's deviation from ideal behavior are identified by 3D numeical simulations as unequal pressure drops in the separating flows. Changes in the arrangements of the elements are proposed and their effects are verified by simulations and experiments. A significant improvement of the layer homogeneity is achieved by introducing additional elements with separatings walls at the inlets and at the outlets of the mixing elements.     

缩放螺旋混合器的实验评价与优化设计

为了增强普通螺旋管的混合效率,在普通的螺旋管结构中引入突放突缩结构,设计制造出缩放螺旋混合 器。以竞争串连反应的离集指数为指标,对缩放螺旋混合器的结构进行了优化设计,考察了缩放螺旋混合器的几何参数--混合单元数、粗细段长度比、螺距、曲率半径以及Reynolds数对混合器的混合效率的影响。结果表 明:缩放螺旋混合器的粗细段长度比为1/4,曲率半径为10.5 mm,混合单元数为40,Reynolds数在1000～1575时混合效率最佳;参数优化后的缩放螺旋混合器比普通螺旋管混合器以及具有缩放结构的直管混合器中的混合效率更高。     

脉冲式静态混合器压力降分析

测定了雷诺数Ｒｅ从６８变化到１６５１时混合器压力降与雷诺数，摩擦系数与雷诺数的关系曲线和相应的曲线拟合方程。Ｒｅ＜５５０时，摩擦系数ｆ＝１３９．６６Ｒｅ－０．７４２，当Ｒｅ＞５５０时，流动基本处于湍流状态，ｆ＝５．２Ｒｅ－０．２０３。当雷诺数增大时，混合器内元件数量的改变对摩擦系数影响不大。     

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.     

Drop Breakup in an SMX Static Mixer in Laminar Flow

The mechanism of drop breakup inside SMX static mixers in the laminar flow regime was studied using experimental observations and computational fluid dynamics (CFD). The deformation and breakup of a single drop was simulated using the volume of fluid (VOF) model. It was observed that drops break up after collision with the leading edges and cross‐points of the bars in the SMX static mixer. It was found that drop collision with the bar cross‐points of the SMX static mixer elements is most effective for drop breakup. Elongation and folding result in drop breakup at the cross‐points.