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     

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.     

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.     

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.     

高黏度流体在SK型静态混合器内的流动特性

根据流体动力学、非线性动力学及Ottino理论,建立了高黏度流体在SK型静态混合器内的流体流动改进模型,分析二维Navier-Stokes方程基于双极坐标系下流函数形式的边值问题并建立了相应的流体微分运动方程。用Poincare映射方法对静态混合器内的蠕动流的动力学行为进行了数值仿真研究。给出了系统响应随管壁转动角频率变化的分岔图、最大Lyapunov指数曲线图、典型的Poincare截面图和相图。结论表明:高黏度流体在SK型静态混合器内轴截面的径向流动存在混沌特性。     

Nonisothermal modeling of heat transfer inside an internal batch mixer

A nonisothermal transient process of temperature increase due to viscous heating was simulated for a 69 cm³ internal batch mixer (BM) using a computational fluid dynamics (CFD) software, Polyflow 3.9 form ANSYS, Inc., to obtain the temporal temperature distribution and characterize the heat transfer between polymer melt and mixer wall. The melt temperature obtained from simulation was verified with experiments. Starting from a uniform temperature of 463 K, when a rotation speed of 5.24 rad/s is imposed, viscous heating caused a maximum temperature rise of 3 K for a polyethylene (PE) resin, and 6 K for a polystyrene (PS) resin. The transient flow fields inside the batch mixer were characterized with velocity profiles and a mixing index parameter, which show that laminar flow dominates inside the mixer while a small percentage of elongational flow, converging flow, and recirculation flow is also present. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Flow field analysis of an intermeshing counterrotating twin screw extruder

The intermeshing counterrotating twin screw extruder is widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package-FIDAP, using the finite element method, was implemented to simulate the 3-D flow patterns in the region of conveying elements and shearing discs of a Leistritz LSM30.34 twin screw extruder. The rheological behavior of the fluid was described by a power law model. The flow fields were characterized in terms of velocity profiles, pressure distributions, shear stresses generated, and a parameter λ quantifying the elongational flow components. The influence of screw rotational speed and axial pressure difference on the flow characteristics was also analyzed. A comparison between the flow characteristics in the shearing discs operated in a corotating or counterrotating mode was also presented.     

ADINA对新型剪切啮合复合型转子流场的分析

新型剪切啮合复合型转子具有复杂的构型,在混炼过程中胶料的流动状态也十分复杂。利用ADINA对新型剪切啮合复合型转子在混炼过程中的流场进行了有限元分析,能够得到该流场的压力、速度、黏度等参数的变化情况,为对胶料混炼状态进行分析提供了直观的依据。     

Flow field analysis of the kneading disc region in a co-rotating twin screw extruder

Co-rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co-rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time-dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package—FIDAP—using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-30 co-rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristics was analyzed.     

全方位旋转射流搅拌器流场数值模拟分析

在自行研发并制造的立体全方位旋转射流搅拌器的基础上,介绍了其结构组成和工作原理。为了考察该搅拌器的防沉降搅拌效果,采用SIMPLE算法和标准k-ε双方程湍流模型,运用Fluent软件对其三维稳态流场进行了数值模拟。通过对不同出射速度下全方位旋转射流搅拌器的3种不同偏转角度下的喷嘴与水平喷嘴喷射时在罐底产生的冲击压力、流速和湍动能进行分析并对比,结果表明:偏角喷嘴能够对罐底沉积物起到冲刷搅拌作用,但随着偏转角度的增大,冲刷搅拌效果相应减弱;相同出射速度下3种偏角喷嘴的相应参数均比水平喷嘴的数值更大,影响范围更广,防沉降效果更好;结合全方位旋转射流搅拌器立体旋转的结构特点进一步说明了全方位旋转射流搅拌器具有三维立体的搅拌作用。     

密炼机同步转子的三维温度场分析

在传统的密炼机或转子的设计中,许多参数的选择都是凭经验和一些理论确定,所设计部件的合理性要通过实验才能知道,而现在我们可以利用CAD软件设计和造型出装有新型转子的密炼机,然后利用有限元分析软件ADINA等对其进行性能分析,从而缩短了新产品的开发时间,提高了效率。