Mixing processes in the cavity transfer mixer: A thorough study

In many industrial applications, the quality of mixing between different materials is fundamental to guarantee the desired properties of products. However, properly modeling and understanding polymer mixing presents noticeable difficulties, because of the variety and complexity of the phenomena involved. This is also the case with the Cavity Transfer Mixer (CTM), an add‐on to be mounted downstream of existing extruders, to improve distributive mixing. The present work proposes a fully three‐dimensional model of the CTM: a finite element solver provides the transient velocity field, which is used in the mapping method implementation to compute the concentration field evolution and quantify mixing. Several simulations are run assessing the impact on mixing of geometrical and functioning parameters. In general, the number of cavities per row should be limited and the cavity size rather big to guarantee good mixing quality. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1034–1048, 2018     

密炼机的三维流场模拟

建立同步转子和异步转子密炼机物理、数学和有限元模型，同步转子密炼机流场沿圆周取6个位置，异步转子密炼机流场沿圆周取3个位置，对密炼机流场进行有限元模拟。分析结果表明，同步转子密炼机流场在转子旋转一周内可分为两个循环，并有较多的漩涡，有利于提高胶料的分散和分布效果；异步转子密炼机流场的啮合部分有较多漩涡，在转子转过1／3周时，出现类似紊流的流动，有利于提高胶料局部分散。     

二维平面内密炼机温度场分析

利用有限元法对混炼过程中密炼室，胶料的温度分布以及变化情况进行了分析。分析结果对于研究如何避免温升过高、优化混炼条件、改进转子和密炼室的结构和提高混炼胶的质量，以及根据配方不同，探讨时间都有着重要的指导意义。     

密炼机同步转子流场和异步转子流场的分析

本文建立了密炼机同步转子和异步转子的物理、数学和有限元模型,对同步转子和异步转子的密炼机内的胶料进行了流场分析。分析表明,同步转子和异步转子的压力最大值点均在转子剪切面一侧的棱顶处;同步转子对胶料的剪切作用更强,分散混合作用也更好。     

370密炼机密炼室温度场分析

通过有限元分析方法，对密炼机炼胶过程中的温度场温度分布做了分析和模拟，介绍了各种基本计算方法和计算公式，如传热、瞬态传热、对流换热系数等。模拟了胶料在密炼机室中的升温过程。该方法可预测密炼机排胶温度、排胶时间等。     

Hydrodynamic analysis of a Banbury mixer

A fluid dynamics analysis package—FIDAP—using a finite element method was employed to simulate the flow patterns in a Banbury mixer. The flow simulations were carried out only for the intensive mixing region, and they were limited to a two-dimensional analysis. A Lagrangean point of view was adopted and 18 different geometries were selected to represent one revolution of the rotor. A power-law model with time and temperature dependent parameters was used to characterize the rheological behavior of the mixture. Steady-state, isothermal flow simulations as well as a transient, non-isothermal flow analysis were performed for a Banbury B mixer. The results of the analysis show good agreement with experimental observations regarding the development of vortices, the pressure, and the temperature profiles.     

Flow analysis of rubber transfer molding

An experimental study has been carried out on rubber I transfer molding. It reveals that the filling is frequently limited more by the resistance of flow across the transfer pot than by resistance of flow through the sprue holes into the cavities. A mathematical model has been derived, which predicts semi-quantitatively the molding behavior observed. The mode1 predicts that fill time is proportional to the ratio of compound viscosity divided by molding pressure raised to about the fourth power. For the common cases where most of the fill time is from the resistance to the transverse flow on the top of the sprue plate, the fill time is proportional to about the fifth power of the ratio of transverse distance divided by the charge thickness. Experimental results showed that preheating and mastication of the compound reduced transfer time substantially. The charge pattern did not seem to have a major influence on transfer time.     

Mixing analysis in a coaxial mixer

The performance of a coaxial mixer in the laminar-transitional flow regime was numerically investigated with Newtonian and non-Newtonian fluids. These mixers comprised two shafts: a central fast speed shaft mounted with an open turbine, and a slow speed shaft fitted with a wall scraping anchor arm. To model the complex hydrodynamics inside the vessel, the virtual finite element method (POLY3D^TM software) coupled with a Lagrange multiplier approach to cope with the non-linearity coming from the rheological model was employed. Co-rotation and counter-rotation mode were compared, based on several numerical criteria, namely, mixing time, power consumption and pumping rate. It was found that co-rotating mode is more efficient than counter-rotating mode in terms of energy, pumping rate and homogenization time.     

Heat transfer coefficients for viscous fluids in a static mixer

An experimental study has been done on heat transfer at constant heat flux as well as at constant wall temperature of a pipe filled with Sulzer mixing elements. A semi-empirical model is developed with which the experimental results agree. The influence on heat transfer of free sections between mixing sections has been studied.     

密炼机四棱同步转子三维温度场分析

采用有限元分析软件ADINA对密炼机混炼过程中四棱同步转子的温度场进行分析.结果表明,转子棱顶端处温度较高,主要是由于该处离冷却水道较远、换热面积较小;转子棱两侧为强换热区,而转子内孔水道的热交换较少.为改善转子冷却效果,结构设计时其冷却水道的过渡应尽量圆滑,以减少紊流,提高换热效率.     

密炼机二棱同步转子的三维温度场分析

建立密炼机二棱同步转子的物理和数学模型,并对其工作时的三维温度场进行有限元分析.结果表明,二棱同步转子在炼胶过程中,转子凸棱和密炼室壁间产生的热量最多,转子冷却和散热效果对排胶温度影响很大,转子强制冷却的效果非常明显.     

一种多翼离心风机流场模拟与性能分析

综合多叶片离心风机噪音低以及长短叶离心风机气流稳定的优点,设计了一种具有大小叶片交错组合结构的多翼离心风机.采用计算流体力学方法,分别模拟了前向式和后向式2种不同叶轮形式的风机流场.通过对比发现,在相同转速和流量下,后向式风机进出口压差比前向式叶轮风机小11.8％,但功率消耗降低了24.5％,综合效率较前向式高;后向式...     

An evaluation of the cavity transfer mixer for the extrusion of rigid PVC on both single and twin screw extruders

PVC powder compound fed into single- and twin-screw extruders retrofitted with cavity transfer mixers improved PVC grain fusion. Consequent improvements in appearance and properties ought to reduce current tight comprises that must be made between materials costs, output rate, and quality.     

小型密炼机压力场有限元分析

对小型密炼机压力场进行有限元分析.结果表明,转子棱顶部存在高压区,转子的剪切面一侧的压力值较大,而另一侧则急剧减小.压力等值分布云图显示,转子的剪切棱和压砣建立了高压区,而4条啮合短棱也建立了一定的压力区,整个混炼室内流场压力呈左右和前后对称分布,胶料流动性较好.     

CFD analysis of a rotor-stator mixer with viscous fluids

The characterization of the hydrodynamics of a rotor-stator mixing head has been carried out in the laminar regime with viscous Newtonian fluids. The rotor-stator considered is a very common design composed of a flat blade rotating in a fixed slotted cage. A numerical methodology has been used based on the virtual finite element method to model the velocity patterns, estimate the distribution of shear stress and the flow rate through the head. We have found that the numerical prediction of the power consumption and flow profiles compare well with experimental data. The generation of a pseudo-cavern around the mixing head and how it scales with the Reynolds number have also been investigated, showing that there is a minimum speed limit below which the rotor-stator cannot be used.     

Infrared temperature measurements and DEM simulations of heat transfer in a bladed mixer

An understanding of heat transfer in a bladed mixer is important for drying of pharmaceutical drug crystals. This study presents thermal imaging experiments of the particle bed surface in a bladed mixer to investigate how the impeller speed influences the rate and the uniformity of heat transfer. Next, the process is simulated using the discrete element method. The bed thermal properties are lumped into an effective thermal conductivity, that is calibrated for one impeller speed. The experiments and the simulations show the same trends and generally agree well for all agitated beds. However, to obtain good agreement of the rate of heat transfer between the simulations and experiments in a static bed, we need to adopt a higher thermal conductivity than for the agitated beds. Finally, we discuss the implications of these results for the design of operating protocols.     

Power consumption and flow field characteristics of a coaxial mixer with a double inner impeller

A coaxial mixer meeting the actual demand of a system with high and variable viscosity is investigated. It has an outer wal-scraping frame and a double inner impeller consisting of a four-pitched-blade turbine and Rushton turbine. The power consumption and flow field characteristics of the coaxial mixer in laminar and transitional flow are simulated numerically, and then the distribution of velocity field, shear rate and mass flow rate are analyzed. The simulation results indicate that the outer frame has little effect on the power consumption of the double inner impeller whether in laminar or transitional flow, whereas the inner combined impeller has a great effect on the power consumption of the outer frame. Compared with the single rotation mode, the power consumption of the outer frame will decrease in co-rotation mode and increase in counter-rotation mode. The velocity, shear rate and mass flow rate are relatively high near the inner impeller in all operating modes, and only under double-shaft agitation wil the mixing performance near the free surface be improved. In addition, these distributions in the co-rotation and counter-rotation modes show little difference, but the co-rotation mode is recommended for the advantage of low power consumption.     

仿柳叶形静态混合器的流动及混合特性

对仿柳叶形静态混合器内混合气流进行了速度场与浓度场的试验研究,结果表明该混合器内速度场与浓度场偏差均达到了非常理想的效果（优于国家标准偏差值）。同时采用CFD软件对该静态混合器内的流场进行了数值模拟,试验与模拟的数值结果以及两者的浓度云图分布都有着较好的一致性。随后的研究结果表明：在混合元件尾迹区域出现了纵向涡和发卡涡来促进混合;在经过混合元件区域时因为湍流动能耗散率增加形成的高湍流动能耗散率区能够使物质交换更加频繁;整个静态混合器的流动阻力也主要发生在该区域,随之出现的返混现象也在一定程度上加强了混合效果。