Kenics型静态混合器和GK型静态混合器流场的数值模拟及比较

采用计算流体动力学(CFD)的方法,分别计算了Kenics型静态混合器和GK型静态混合器内的流场。数值模拟的结果表明,Kenics型静态混合器内流场的湍动强度大于GK型静态混合器的,导致了Kenics型静态混合器的流体阻力和传热系数大于GK型静态混合器的。GK型静态混合器的压力降大约只是Kenics型静态混合器压力降的0.554~0.579倍,但两者的传热膜系数相差不大。GK型静态混合器具有较强的综合性能。     

Polymerisation of methyl methacrylate in a pilot-scale tubular reactor: modelling and experimental studies

A pilot-scale tubular reactor fitted with in-line static mixers is experimentally and theoretically evaluated for the polymerisation of methyl methacrylate (MMA). A non-isothermal and non-adiabatic axially dispersed plug-flow model is used to describe the flow characteristics of the reactor. The model is applied to the polymerisation of a concentrated MMA solution (up to 72% (v/v)). Key model parameters were attained through independent bench and pilot-scale experiments. Measured monomer conversions and polymer molecular weight were accurately predicted by model simulation. The presence of static mixers is shown to give near-ideal plug-flow operation for the experimental conditions of this study. Furthermore, an approximately four-fold increase in overall heat transfer coefficient is indicated due to the radial mixing incited by the mixers. Studies also demonstrated the importance of inhibitor kinetics on the dynamic and steady-state performance of the reactor.     

Static mixers: Mechanisms,applications, and characterization methods – A review

Static mixers and multifunctional heat exchangers/reactors (MHE/R) are qualified as efficient receptacles for processes including physical or chemical transformations accompanied by heat transfer due to their high productivity and reduced energy expenditures. The present work reviews recent conceptual and technological innovations in passive static mixers and continuous in-line reactors. Current industrial applications are discussed from a process intensification perspective, focusing on mixing and mass transfer performance. Typical experimental techniques employed to characterize and quantify the mixing process are explored. The work is complemented by a review of mixing fundamentals, knowledge of which allows the development of theoretical models crucial for the analysis of experimental data, like the chemical probe mixing assessment method. Considering the development of continuous flow equipment in numerous processes, advances in this field will certainly be of increasing interest to the scientific and industrial communities.     

Three‐dimensional flow measurements in a static mixer

Laminar heat and mass transfer are central to a wide range of industrial processes, encompassing (thermal) processing of viscous fluids, compact equipment for process intensification, and emerging microfluidic devices. Many of these applications incorporate the “static‐mixing principle” (stirring of a throughflow by internal elements) for mixing and heat‐transfer enhancement. Investigations on static mixers primarily concern numerical simulations. Experimental studies, on the other hand, are relatively rare and to date restricted to visualization of mixing patterns or integral quantities as for example, pressure drop and heat‐transfer coefficients. The present study expands on this by quantitative experimental analysis of three‐dimensional (3‐D) flow fields and streamline patterns in a representative static mixer using 3‐D particle‐tracking velocimetry. This necessitates tackling of (internal) refractions and reflections caused by the complex mixer geometry. Comparison of experimental results with numerical predictions reveals a good agreement. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1746–1761, 2013     

Transposition from a batch to a continuous process for microencapsulation by interfacial polycondensation

A novel continuous process is proposed and investigated to produce microcapsules by interfacial polycondensation. Polymeric microcapsules are obtained via a two-step process including an initial emulsification of two immiscible fluids in static mixers and a subsequent interfacial polycondensation reaction performed in two different continuous reactors, the Deanhex heat exchanger/reactor or a classical coiled-tube. This study is carried out through a step by step approach. A model system involving polyurea as the polymeric membrane and cyclohexane as the encapsulated species is chosen. A semi-batch reaction kinetic study is first performed in order to obtain kinetics data of the polycondensation reaction and to highlight hydrodynamic issues that can happen when running the encapsulation reaction in classical stirred tank. Parameters influencing droplets size obtained when carrying out emulsification in static mixers are then investigated. The hydrodynamic of the Deanhex reactor used is also characterized in terms of mixing time and residence time distribution. To validate the innovative continuous process, the emulsion droplets obtained at the static mixer outlet are encapsulated firstly in the Deanhex reactor and secondly in the coiled-tube. The apparent reaction kinetics and microcapsules characteristics corresponding to different operating conditions are discussed.     

Einsatz und Auslegung statischer Mischer

Application and design of static mixers . Static mixers are units without, or only with fixed, internal fittings which effect the mixing of flowing materials with the aid of their kinetic energy. They are used for continuous homogenization and dispersion, for limitation of the residence time spectrum, and for raising heat and mass transfer in all areas of chemical engineering. Over 20 static mixers are presented, and compared with regard to pressure drop, mixing quality, energy consumption, and residence time and heat transfer behaviour. Important selection criteria are reported. Static mixers have the following advantages over dynamic mixers: use for a wide range of viscosities, narrow residence time spectrum, readily adaptable to existing pipe systems, frequently require no extra space (in-line mixers), negligible maintainance and wear, low investment and operating costs.     

Evaluation of static mixers as convection promoters in the ultrafiltration of dairy liquids

An investigation was made to determine the efficiency of various types of static mixer (variants of the Kenics type) for enhancing the permeate flux in ultrafiltration plants. A theoretical analysis of the transport phenomena that occur in the laminar-flow region in a tube divided into two half-cylindrical channels, showed that the mass transfer coefficient increased by a factor 1.95 as compared with the mass transfer coefficient in a cylindrical tube. The increase in permeate flux obtained in the experiments, however, amounted to a factor 2.9. This extra effect should be attributed to rotation of the liquid and changes in the direction of rotation, caused by the static mixers. It was also found that the effect was intensified at increasing Sc-number and decreasing Re-number.From energy considerations it appeared that, at equal energy input levels, approximately equal permeate fluxes were achieved in both the laminar flow and the turbulent-flow region, whether static mixers were used or not. So it has to be concluded that the types of static mixer tested did hardly improve the energy efficiency in ultrafiltration plants under the prevailing conditions.     

有无静态混合器时的机械搅拌气升式环流反应器传递特性研究

The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation or static mixers on gas hold-up, mixing time, liquid circulating velocity and volumetric mass transfer coefficient have been investigated with tap water and carboxymethyl cellulose (CMC) aqueous solution. The experimental results indicate that mechanical agitation is more efficacious than static mixer in highly viscous media for improving mass transfer in airlift reactors. The empirical correlation of volumetric mass transfer coefficient with apparent viscosity, and energy consumption for mechanical agitation and aeration is developed.     

Gas holdup in homogeneous and heterogeneous gas—liquid bubble column reactors

The velocity‐holdup relationship is the most important design parameter for gas—liquid bubble column reactors, providing the basis for the prediction of heat and mass transfer coefficients and information on hydrodynamic conditions. A summary of the literature on gas holdup in bubble columns is supplemented by new experimental results which extend the data range. A criterion for the gas velocity leading to the transition between homogeneous and heterogeneous regimes for perforated plate gas distributors has been developed. Correlations for gas holdup in both regimes are developed and verified against both new and existing data.     

水平液固循环流化床换热器传热性能评价

对管内插入Kenics静态混合器的水平液固循环流化床换热器进行实验研究,实验考察了静态混合器扭率、静态混合器安装方式、液体流速、颗粒体积分数对传热性能和流阻性能的影响,并运用综合强化传热性能评价指标（PEC）对其进行分析。实验发现,传热性能和阻力系数均随扭率增加而减小。当雷诺数在10000~45000之间时,扭率为1.5、2、2.5、3.5的Kenics静态混合器的PEC指标均大于1,说明了水平流化床换热器插入Kenics静态混合器能够改善传热。在雷诺数达到25000左右、Kenics静态混合器扭率为2.5、颗粒体积分数为4%时,水平流化床换热器的PEC指标最高达到1.18。当两个扭率均为2.5的Kenics静态混合器安装间距为200mm时,水平流化床换热器的PEC指标最高。     

Visual study on the characteristics of liquid and droplet in a novel rotor-stator reactor

Rotor–stator reactor (RSR), an efficient mass transfer enhancer, has been applied in many fields. However, the hydrodynamic characteristics of liquid flow in RSR are still a mystery despite they are fundamental for the mass transfer performance and processing capacity. In view of the above, this paper studies the liquid–liquid flow and liquid holdup in RSR under various conditions with a high-speed camera. The paper firstly demonstrates two flow patterns and liquid holdup patterns that we obtained from our experiment and then presents in succession a flow pattern and a liquid holdup criterion for the transition of film flow to filament flow and complete filling to incomplete filling. It is found that experimental parameters, including rotor–stator distance, rotational speed and volume flow rate exert great influence on the average droplet diameter and size distribution. Besides, by comparison and contrast, we also find that the experimental values match well with our previous predicted calculations of the average diameter, and the relation between the average diameter and the mean energy dissipation rate.     

Statische Mischer und ihre Anwendung

Static mixers and their applications . Static mixers are generally made up of similar, fixed mixing units installed at right angles to each other in series along a tube or a channel. The energy of mixing is extracted from the flow. Twelve different units are presented. The mixing effect in static mixers under conditions of laminar flow is accomplished either by specially designed feed systems, by cutting and twisting, by displacement and distortion, or by separation and expansion. Depending upon the mixer, very different lengths are required to achieve the same degree of homogeneity. Compared with an empty tube, the pressure drop in static mixers is some 7-to 200-fold greater for laminar flow and 100- to 600-fold greater for turbulent flow. Static mixers are employed in all areas of chemical engineering for homogenization, for reduction of the resisdence-time spectrum, and for heat exchange. Since maintenance and wear are negligible, since incorporation frequently requires no extra space, and since they can be used over wide ranges of viscosity, static mixers are being increasingly employed in continuous processes.     

SMGK型换热器的应用

介绍了SMGK型换热器的开发和应用情况。该换热器采用了静态混合器、折流杆和带导流板传热夹套3项强化传热技术,提高了传热系数,并在合成氨厂作为变换热交换器试用成功。     

Pressure Drop and Mass Transfer Study in Static Mixers with Gas Continuous Phase

The aim of this work was to characterize both the influence of the gas and the liquid flow rates on the pressure drop generated by static mixers type Sülzer, and on the mass transfer performances of these gas‐liquid contactors. The originality of this work rests on the use of the static mixers with a gas continuous phase. Several configurations were studied: vertical upward flow, vertical downward flow, and horizontal positions, with one to five mixing elements. It was concluded that the pressure drop is mainly generated by the gas phase, whatever the configuration chosen. Moreover, the volumetric mass transfer coefficients k_La found were lower than those obtained with the same static mixers used in classic conditions (that is with a liquid continuous phase), but greater than values obtained with classic reactors like bubble columns or packed columns. The efficiency of these gas‐liquid reactors was found high, as well as the energy dissipated, unfortunately.     

螺带桨搅拌槽内给热系数和所需功率的研究

本文详细研讨了螺带桨搅拌槽内给热系数及其与所需功率的关系.研究中使用了4个不同几何尺寸的螺带装以及8种不同稠度的假塑性非牛顿流体和高粘度牛顿流体.结果表明:在雷诺数小于0.1时,试验流体在槽内的给热系数与浆叶几何尺寸有关.通过回归分析法得到了4个对应于各螺带桨的给热系数关联式;雷诺数大于10时,给热系数和搅拌浆几何尺寸无关,从而得出一个适用于不同螺带浆的共同关联式.实验还研究了给热系数和所需搅拌功率的关系,并用多项式回归法得到了整个实验雷诺数范围的传热-搅拌功率关联式.     

Ross LPD型静态混合器内湍流传热与混合强化特性

在湍流状态Re=2640~17600下,采用恒热通量传热实验与数值模拟相结合的方法,系统研究Reynolds数Re和交错角对Ross LPD型静态混合器内湍流流动与传热性能影响,采用Nusselt数、Darcy摩擦系数、综合传热系数、速度场与温度梯度和压力梯度协同角等参数评价混合器内传热强化性能;基于CFD与LPT相耦合分析混合器内流体微元拉伸率。研究结果表明：SST k-ω模型预测Ross型静态混合器湍流阻力及传热结果与实验结果具有很好一致性;Ross混合器流场内形成与流场尺度较为接近的纵向涡,其涡心在圆形截面与半圆形截面中心间周期性迁移,横截面内湍流分散混合效率是Kenics的3.36~1.72倍;当Re>7040时,Ross LPD综合传热性能明显优于KSM;当叶片夹角为30°时,综合传热性能系数具有最大值;Ross LPD内插件具有高效低阻的技术优势和结构改进潜力。     

Ross LPD型静态混合器内湍流传热与混合强化特性

在湍流状态Re=2640~17600下,采用恒热通量传热实验与数值模拟相结合的方法,系统研究Reynolds数Re和交错角对Ross LPD型静态混合器内湍流流动与传热性能影响,采用Nusselt数、Darcy摩擦系数、综合传热系数、速度场与温度梯度和压力梯度协同角等参数评价混合器内传热强化性能;基于CFD与LPT相耦合分析混合器内流体微元拉伸率。研究结果表明：SST k-ω模型预测Ross型静态混合器湍流阻力及传热结果与实验结果具有很好一致性;Ross混合器流场内形成与流场尺度较为接近的纵向涡,其涡心在圆形截面与半圆形截面中心间周期性迁移,横截面内湍流分散混合效率是Kenics的3.36~1.72倍;当Re>7040时,Ross LPD综合传热性能明显优于KSM;当叶片夹角为30°时,综合传热性能系数具有最大值;Ross LPD内插件具有高效低阻的技术优势和结构改进潜力。     

Analysis of local heat transfer and hydrodynamics in a bubble column using fast response probes

A fast response probe is used to measure local heat transfer in a bubble column. It captured the variations in local heat transfer coefficients due to changes in local hydrodynamic conditions in radial and axial directions. These measurements have been used to identify flow regime transitions, variations in flow patterns and local hydrodynamic structure as obtained with different gas distributors and varying gas velocity. Standard deviations of pressure measurements obtained with a fast response probe have been compared with heat transfer coefficient fluctuations for the first time and the similarities and differences have been pointed out. Variations in average heat transfer coefficients and standard deviations in radial and axial directions point to different hydrodynamic conditions and are compared with literature studies. Relationships between local heat transfer measurements and hydrodynamic conditions are shown.     

Numerical investigation of the performance of several static mixers

The performance of six static mixer (Kenics, Inliner, LPD, Cleveland, SMX and ISG) are compared using 3D numerical simulations in laminar creeping flow regime. Numerical pressure drop results are tested against experimental ones, showing overall a good agreement. Besides pressure drop, four criteria (extensional efficiency, stretching, mean shear rate and intensity of segregation) are chosen to compare the static mixers. It appears that Kenics, Inliner, LPD and Cleveland mixers are rather similar. The ISG mixer seems better than this first group of mixers, but pressure drop is too high compared to other advantages. From our numerical results, SMX appears to be the most efficient of the six compared static mixers.     

Mischen und Wärmeaustausch in hochkonsistenten Medien

Mixing and heat transfer in high-consistency media. A creeping motion always has to be considered in the handling of high-consistency, i. e. high-viscosity media. Heat transfer and mixing processes differ considerably from those occurring in turbulent flow because of the absence of convective exchange perpendicular to the main flow. The mode of functioning of equipment and machines for high-consistency media is explained. A detailed consideration of mixing and heat transfer in static mixers and screw machines is also presented.