Study on the flow characteristics and mixing performance of multi-blade combined agitator

Developing an agitator suitable for wide viscosity range is of great significance to the energy saving and efficiency improvement by the intensification of fluid flow and mixing process. The power characteristics, flow field distribution, turbulence characteristics and mixing performance of multi-blade combined (MBC) agitator under laminar to turbulent flow state were studied experimentally and numerically at the level of large eddy simulation. The predicted power curve is consistent with the experimental results. Tangential flow is the main flow in laminar flow. With the increase of Reynolds number (Re), axial and radial flows in the vessel gradually increase. When Re reaches 486, the velocity field distribution is basically the same as that in the turbulent flow. At the same energy consumption level, MBC agitator is superior to the commercial Maxblend agitator in mixing high viscosity fluid. The intensification of axial and radial flows is due to the dispersed arrangement of the blades, enabling the MBC agitator to achieve larger axial and radial flows from the transitional flow to the turbulence state. Moreover, the turbulent kinetic energy is evenly distributed and the mixing process is significantly accelerated.     

宽黏度域轴流桨及在非牛顿流体中功率特性的实验研究

根据某反应的特定工艺过程要求,提出了一种适合宽黏度域的高效轴流式搅拌桨--SP304型轴流式搅拌桨,该桨叶片呈空间扭转状,且具有曲率,可减少流体阻力,提高排出性能.并设计了一套实验装置对这种高效轴流桨在非牛顿流体中的功率特性进行研究,得到了功率常数K_p、Metzner常数k_s和功率特性曲线,为工业化装置的设计提供实验数据.通过观察实验中不同浓度、不同转速下的流体流动细节,可以获得整个流动场的概念,对搅拌桨离低高度、桨间距等参数设计具有重要的指导意义.根据实验结果对此高效轴流搅拌桨成功地进行了工业应用.     

多叶片组合式搅拌桨釜内流动特性和混合性能研究

开发可适用于较宽黏度范围的搅拌桨,强化釜内的流体流动和混合过程对于搅拌釜的节能增效具有重要的意义。实验与数值模拟相结合,在大涡模拟层面研究了多叶片组合式搅拌桨（MBC桨）从层流到湍流状态下,釜内的功率特性、流场分布、湍流特性和混合性能。结果表明：预测的功率曲线与实验结果一致;层流状态下釜内以切向流动为主,随着Reynolds数（Re）的增大,釜内轴向和径向流动逐渐增强,当Re达到486时,速度场分布与湍流状态下基本一致;在相同的能耗水平下,MBC桨对高黏度流体的混合性能优于商业Maxblend桨。桨叶的分散组合布置,强化了釜内的轴向和径向流动,使得MBC搅拌桨在从过渡流到湍流状态下均可实现较大的轴径向流动,湍动能分布较为均匀,混合过程显著加快。     

内外单螺带式搅拌器的Metzner常数

对１１种不同向何尺寸的内外单累带搅拌器（ＩＯ－ＨＲ），在６６中不同流动行为指数（ｎ＝０．３７－１）的幂律流体中的剪切特性进行了实验研究。发现内外单螺带 的Ｍｅｔｚｎｅｒ常数，Ｋｓ与流动行为指数ｎ、桨的几何尺寸均相关。提出改进的数据处理方法来求算Ｋｓ，并详细分析了桨的几何尺寸和流体剪切稀化特性对Ｋｓ的影响。最后的对包括经典的Ｍｅｔｚｎｅｒ方法在内的不同求解Ｋｓ的方法做了分析比较。     

An analytical model for the prediction of power consumption for shear-thinning fluids with helical ribbon and helical screw ribbon impellers

An approximate analytical model has been developed to predict power consumption for the mixing of shear-thinning fluids with helical ribbon and helical screw ribbon impellers in the laminar flow regime. Extensive data on power input measurements embracing a wide range of flow behaviour index, with strong (n<0.4) and weak (0.4<n<1) shear-thinning fluid characteristics, available in the literature have been used to demonstrate the applicability of the present model for a wide range of helical ribbon mixer configurations. The model is able to explain the differences in the data reported in the existing literature and to successfully predict the complex dependence of power consumption on the fluid properties and the system geometry. Finally, the proposed correlation only requires a knowledge of the flow behaviour index of the fluid and of the geometrical parameters of the mixing systems (wall clearance, number of ribbons, pitch and width of the ribbons) and one characteristic parameter K_p of the mixing system which can be obtained from a single measurement of power for Newtonian liquids in the laminar regime.     

Experimental and CFD simulation studies on power consumption in mixing using energy saving turbine agitator

Experimental and simulation investigation on power consumption in new energy saving turbine agitator has been presented here. Modification was done by introducing single and double rectangular and V cuts in the conventional turbine agitator. The power consumption for new energy-saving turbine agitator has been found to be less than that of the conventional turbine agitator. Also, the power consumption for V cut has been found to be less than that of rectangular cut in turbine agitator. Power characteristics for different geometrical parameters of energy saving turbine agitators were obtained for both the transition and turbulent regimes of the flow in agitated vessel. CFD simulations have been used to predict power consumption. The simulation results have been compared with the experimental data obtained on a pilot-scale set up.     

Determination of operating characteristics of agitators in tubes

Operating characteristics of an agitator in a tube are necessary for the calculation of its pumping capacity and power consumption in a given configuration. General dimensionless equations for pumping and power characteristics are presented which were derived by inspection analysis of basic equations. Experimental procedure for the determination of these characteristics is put forward. This procedure is based on the measurement of flow rate or pressure rise and power consumption for an agitator in a draft tube, calandria or closed tube. The measurements and their evaluation are illustrated on the example of a three-blade screw agitator.     

气固搅拌流化床内压力脉动特性的数值模拟

在传统气固流化床中引入搅拌桨,可减轻聚合物颗粒的黏附并强化流态化过程。采用计算流体力学(CFD)方法对搅拌流化床内的压力脉动特性进行数值模拟,考察流态化过程中的气泡行为。模拟过程采用多重参考坐标系方法解决搅拌桨区域的运动问题,由欧拉双流体模型和颗粒动力学方法模拟气固两相流。床层压力脉动的统计分析和功率谱分析表明,随着搅拌桨转速的增加,流化床内的压力脉动标准偏差和功率谱幅值变小,床层内的平均气泡尺寸减小,床层可由鼓泡流态化向散式流态化转变。     

A collection of experimental data for aerosol monitoring cyclones

Cyclone behavior is complex and difficult to model. Recent years have seen the development of new and better predictive models for cyclone performance, which are providing new insights into how cyclone performance is affected by cyclone geometry. Experimental data are essential for verification of such models. In this article we present a dataset of more than 250 experimental determinations of cyclone penetration. The dataset includes cyclones with a wide range of sizes and geometries, tested at a wide range of flow rates. We illustrate some empirical, semi-empirical and mathematical approaches to modeling these cyclone data. For our data, we show that mathematical modeling approaches developed for large gas-cleaning cyclones can also be applied to small aerosol monitoring cyclones, to diverse cyclone geometries, and laminar flow operating conditions.

Copyright © Crown copyright     

Investigation of the temperature homogeneity of die melt flows in polymer extrusion

Polymer extrusion is fundamental to the processing of polymeric materials and melt flow temperature homogeneity is a major factor which influences product quality. Undesirable thermal conditions can cause problems such as melt degradation, dimensional instability, weaknesses in mechanical/optical/geometrical properties, and so forth. It has been revealed that melt temperature varies with time and with radial position across the die. However, the majority of polymer processes use only single‐point techniques whose thermal measurements are limited to the single point at which they are fixed. Therefore, it is impossible for such techniques to determine thermal homogeneity across the melt flow. In this work, an extensive investigation was carried out into melt flow thermal behavior of the output of a single extruder with different polymers and screw geometries over a wide range of processing conditions. Melt temperature profiles of the process output were observed using a thermocouple mesh placed in the flow and results confirmed that the melt flow thermal behavior is different at different radial positions. The uniformity of temperature across the melt flow deteriorated considerably with increase in screw rotational speed while it was also shown to be dependent on process settings, screw geometry, and material properties. Moreover, it appears that the effects of the material, machine, and process settings on the quantity and quality of the process output are heavily coupled with each other and this may cause the process to be difficult to predict and variable in nature. POLYM. ENG. SCI., 54:2430–2440, 2014. © 2013 Society of Plastics Engineers     

泛能式搅拌桨搅拌特性研究

在直径为 2 4 0mm的搅拌釜内 ,考察了泛能式搅拌桨的功率、传热特性 ,混合实验在直径为 386mm的搅拌釜中进行。在层流域内 ,建立了功率准数Np 与桨几何尺寸及雷诺准数Re的关联式 ;得到了努塞尔准数Nu与桨几何尺寸、雷诺准数Re、普朗特准数Pr以及体系粘度的关系 ,并采用单位质量流体表示的雷诺准数εD4/ν3 取代雷诺准数关联 ,误差均在 10 %以内。在中低粘度区内相同功耗下 ,泛能式桨的传热系数明显高于螺带桨。当Re >3时 ,泛能式桨的混合效率比双螺带桨要高。     

搅拌槽内固液两相流的数值模拟及功率计算

使用计算流体动力学的方法对搅拌槽中的流场进行模拟,得到搅拌槽中液体的流动状况和体积分数分布。对流场分布规律、固体颗粒体积分数特点加以分析,进而利用模拟出的数据计算搅拌轴的功率,为搅拌器的设计提供参考。     

Optimization of flow in additively manufactured porous columns with graded permeability

Chemical engineering systems often involve a functional porous medium, such as in catalyzed reactive flows, fluid purifiers, and chromatographic separations. Ideally, the flow rates throughout the porous medium are uniform, and all portions of the medium contribute efficiently to its function. The permeability is a property of a porous medium that depends on pore geometry and relates flow rate to pressure drop. Additive manufacturing techniques raise the possibilities that permeability can be arbitrarily specified in three dimensions, and that a broader range of permeabilities can be achieved than by traditional manufacturing methods. Using numerical optimization methods, we show that designs with spatially varying permeability can achieve greater flow uniformity than designs with uniform permeability. We consider geometries involving hemispherical regions that distribute flow, as in many glass chromatography columns. By several measures, significant improvements in flow uniformity can be obtained by modifying permeability only near the inlet and outlet.     

Investigation on the flow characteristics of a novel multi-blade combined agitator by time-resolved particle image velocimetry and large eddy simulation

We investigated the flow characteristics in a tank of H/T = 1.5 stirred by a novel multi-blade combined agitator (MBC) by using time-resolved particle image velocimetry and large eddy simulation approach. The predictions were assessed by Y⁺ values, Taylor microscale and power spectrum analysis, as well as experimental validation of velocity distributions. Results demonstrate that the MBC agitator can load the energy into the system effectively with a power number of 12.5 in a turbulent regime, resulting in improved axial and radial mass exchange. The upper and lower short blades produce an axial down-flow in the top half and an axial up-flow in the bottom half, respectively. Part of axial flows change to radial flows by the radial pumping of the long blades, meanwhile, the impingement of two axial flows improves the axial mass exchange. These flow characteristics lead to an obvious improvement in the turbulent kinetic energy distribution uniformity with higher turbulent intensity.     

Axial pressure profiles in non-newtonian flow: Part I: Theoretical and experimental considerations

The flow behavior of polymeric fluids in tubes can be determined from measurements of the radial stress profile in the flow direction. This subject, the focus of our research, will be examined in Part II of this communication. Part I describes a research designed to test the accuracy of stress measurement with pressure transducers in a variety of recess mount geometries. No mount geometry errors were detected for the fluids used in this work over a shear rate range of 1 to 2000 sec^?1. Part I also contains a survey of the literature and theoretical considerations pertinent to the entire work.     

Pressure Drop Models for Gas/Non‐Newtonian Power‐Law Fluids Flow in Horizontal Pipes

Models commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry.     

Fuel Pressure Distribution as a Criterion for the Bipolar Plate Geometry Optimization in PEM Fuel Cells,Modeling and Experiment

In this study the pressure distribution homogeneity on the catalytic surface is found to provide a simple and reliable fuel flow parameter that can be used to optimize the bipolar plate geometry and the PEM fuel cell performance. Finite element commercial ANSYS software was used to determine the fuel velocity, pressure and mass distribution on eight different bipolar plate geometries. These geometries were also fabricated and characterized experimentally in order to establish a correlation between the power densities with the fuel flow parameters obtained from the simulations. The results show that a highly uniform pressure distribution of the fuel in the bipolar plate is necessary to obtain higher power densities. Inversely, non‐homogeneous pressure distributions lead to lower power densities. Additionally, the measured power density increases when the geometry dependent effective catalytic surface area increases. These results are interesting since they provide an optimization methodology for PEM fuel cells that simplifies and reduces computing requirements, experimentation and manufacturing time.     

新型行星式搅拌器开发及性能研究

介绍了新型行星式搅拌器的结构和设计原理。该新型搅拌器有一个传动轴和数个行星叶轮组成,行星轮自转的驱动力来自液体阻力,行星叶轮自转速度的大小与公转速度、公转半径和自转半径有关,而与行星叶轮高度无关;自转方向与公转方向相反。测试采用IKA EUROSTAR power control搅拌装置和Labword软件,试验介质为水和甘油。通过对搅拌器的搅拌性能试验研究发现,流体质点的轴向流线为高速螺旋线,主要流型为径向流和轴向流,因此,在主轴转速较低的情况下被搅拌液体亦可获得满意的混合效果。通过对试验数据分析处理,得到测试用行星式搅拌器的功率准数、混合时间数、排液量和循环量等搅拌性能曲线及经验公式。     

Tensorial navier‐slip boundary conditions for patterned surfaces for fluid mixing: Numerical simulations and experiments

Navier‐slip boundary condition has been investigated for patterned surfaces with various grooves for the application to fluid mixing by controlling flow patterns. Simple tensorial expression is applied for anisotropically patterned surfaces and effective slip lengths for various grooves have been evaluated for a wide range of Reynolds numbers and aspect ratios using a flow rate matching technique. By doing so, the applicability of the effective tensorial slip model has been presented that replaces physical surface patterns to reduce computational cost significantly. Using a simple model agitator with a rotating disk, modification of flow characteristics with various alignment angles of the patterned surface has been investigated. We report a critical Reynolds number of O(1) for flows in agitators, below which effective slip dominates over fluid inertia. Patterned poly(dimethylsiloxane) sheets are fabricated using a compression‐molding/soft‐lithography technique and flow visualization with laser‐induced fluorescence reveals controllability of flow patterns with the patterned surface. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4574–4585, 2016     

Design,simulation, and characterization of a radial opposed migration ion and aerosol classifier (ROMIAC)

We present the design, simulation, and characterization of the radial opposed migration ion and aerosol classifier (ROMIAC), a compact differential electrical mobility classifier. We evaluate the performance of the ROMIAC using a combination of finite element modeling and experimental validation of two nearly identical instruments using tetra-alkyl ammonium halide mass standards and sodium chloride particles. Mobility and efficiency calibrations were performed over a wide range of particle diameters and flow rates to characterize ROMIAC performance under the range of anticipated operating conditions. The ROMIAC performs as designed, though performance deviates from that predicted using simplistic models of the instrument. The underlying causes of this non-ideal behavior are found through finite element simulations that predict the performance of the ROMIAC with greater accuracy than the simplistic models. It is concluded that analytical performance models based on idealized geometries, flows, and fields should not be relied on to make accurate a priori predictions about instrumental behavior if the actual geometry or fields deviate from the ideal assumptions. However, if such deviations are accurately captured, finite element simulations have the potential to predict instrumental performance. The present prototype of the ROMIAC maintains its resolution over nearly three orders of magnitude in particle mobility, obtaining sub-20 nm particle size distributions in a compact package with relatively low flow rate operation requirements.

© 2017 American Association for Aerosol Research