啮合异向双螺杆挤出过程轴向循环流道三维流场分析——轴向循环流场分析(Ⅲ)

介绍了作者在啮合异向双螺杆某一轴向位置设置一非啮合段 (且该段其中一根螺杆是反向输送元件 ) ,从而将轴向循环流动的概念引入到啮合异向双螺杆挤出过程中 ,并利用ANSYS有限元分析软件对啮合异向双螺杆挤出过程轴向循环流道中的非牛顿流体等温流动进行的三维模拟分析 ;在得出速度场和压力场的基础上 ,对剪切速率、剪切应力及剪切粘度进行了模拟 ,并将各模拟结果与未引入轴向循环段的啮合异向双螺杆挤出过程常规螺纹元件流道的模拟结果进行了比较。     

啮合同向双螺杆挤出过程轴向循环流道三维流场分析—轴向循环流场分析（Ⅱ）

介绍了作者在啮合同向双螺杆某一轴向位置设置一非啮合段（且该段其中一根螺杆是反向螺纹元件）,从而将轴向循环流动的概念引入到啮合同向双螺杆挤出过程中,并利用ANSYS有限元分析软件对啮合同向双螺杆挤出过程轴向循环流道中的非牛顿流体等温流动进行了三维模拟分析。在得出速度场和压力场的基础上,还对剪切速率、剪切应力及剪切粘度进行了模拟,并将各模拟结果与未引入轴向循环流的啮合同双螺杆挤出过程常规螺纹元件流道的模拟结果进行了比较。     

Numerical simulation of fluid flow and heat transfer in twin-screw extruders for non-Newtonian materials

A new simplified approach has been proposed for the numerical simulation of the thermal transport in corotating, tangential, and self-wiping twin-screw extruders. It is assumed that the flow domain in a twin-screw extruder can be divided into (i) the translation region (T-region), which represents a flow similar to that in a single-screw channel and (ii) the intermeshing region (I-region), which is located between the two screws. The two regions are simulated separately and then coupled for each screw section to model the overall transport in tangential and self-wiping twin-screw extruders. A finite difference method is employed for the developing flow and temperature fields in the T-region, in order to minimize the computing effort, while a finite element method is employed for determining the interchannel flow mixing and the thermal transport in the I-region. Results are obtained in terms of temperature, velocity, and pressure variations along the screw channels and mixing between the two screws.     

双螺杆挤出机螺杆组合对聚丙烯/纳米CaCO3复合材料在线流变性能的影响

采用啮合型同向旋转双螺杆挤出机制备聚丙烯(PP)/纳米碳酸钙(nano-CaCO3)复合材料,制备过程中在双螺杆挤出机末端连接Haake在线流变仪进行在线流变性能测试。研究了两种螺杆组合结构、纳米CaCO3含量对PP/纳米CaCO3复合材料在线剪切黏度的影响,比较了在不同聚合物加工流场下PP/纳米CaCO3复合材料的在线流变性能。结果表明,引入分布混炼有利于降低复合材料的剪切黏度,复合材料剪切黏度随纳米粒子的加入先呈下降趋势,当达到某一含量后,再提高纳米粒子含量会使黏度提高。     

同向啮合双螺杆挤出机捏合块流道三维流场分析

利用ANSYS有限元分析软件对啮合同向双螺杆挤出机的捏合块流场部分进行了三维模拟分析。通过速度场求出流量 ,并求出拉伸速率、剪切速率及剪切应力来衡量混合效果。得到了机筒表面和啮合区的压力分布 ,找出了捏合盘几何条件 (间隙、错列角 )及操作条件 (转速、压差等 )对挤出机混合效果的影响。     

Transport processes and feasible operating domain in a twin‐screw polymer extruder

The flow of a polymer and the associated heat transfer in a fully intermeshing, co‐rotating twin screw extruder are investigated numerically. The control volume technique is used for numerical modeling and simulation, considering both Newtonian and non‐Newtonian fluids. The velocity distributions in the screw channel are compared with experimental resultlsf and good agreement is obtained. Owing to limitations arising from the physical aspects of the problem, the numerical results show that not all operating conditions are feasible. A feasible domain, in terms of screw speed and mass flow rate, in which the extruder operation is satisfactroy, is obtained for pure starch. To improve the applicable range of this model, an axial formulation is adopted for the translation region that characterizes the domain away from the intermeshing zone of the extruder. This model yields results consistent with the earlier down‐channel model while the feasibility region is extended towards lower mass flow rates. For the upper limit, a physicdal restriction arises in terms of the maximum flow rate for a pressure rise in the extruder. Thus, the model can be used for simulating a wide range of operating conditions while retaining the appropriate physical behavior of the process.     

Analysis of the performance of cooling extruders in thermoplastic foam extrusion

The performance of cooling extruders widely used in thermoplastic foam extrusion was analyzed, by numerically solving the equations of motion and heat transfer. Analysis of cooling extruders does not require a consideration of the melting behavior of polymers, thus simplifying the system equations considerably. The flow geometry analyzed was an unwound screw channel of a single-screw extruder, i.e., a rectangular channel of uniform height followed by diverging and converging sections. Due to the cooling of both the extruder barrel and the screw, the heat transfer equation considered includes the terms describing the convective heat transfer in the down-channel direction and the conductive heat transfer in the cross-channel direction, in addition to the terms describing the viscous shear heating. For the analysis, a power-law model was used as the constitutive rheologlcal equation, describing the viscosities of a mixture of a fluorocarbon blowing agent and a low-density polyethylene melt (or polystyrene melt). The parameters in the Theological model were determined using the data of Han and Ma (13). In obtaining numerical solutions of the equations of motion, an integration method was employed to overcome the problem of numerical instabilities. The present analysis predicts the profiles of developing temperature and velocity in the down-channel direction, and the profiles of temperature, velocity, shear rate, and viscosity in the cross-channel direction. In presenting the results of computer simulation, emphasis is placed on the effects of cooling the extruder barrel and screw on the performance of cooling extruders, in terms of the pressure drops along the extruder axis and the mechanical power consumption. This study provides a rational basis for the design of cooling extruders widely used in thermoplastic foam extrusion and for the selection of optimum extrusion conditions in producing thermoplastic foams.     

啮合同向双螺杆挤出机中组合螺杆性能的数值研究（Ⅰ）瞬态流场分析

采用聚合物流动分析软件POLYFLOW,数值模拟了聚合物熔体在组合式啮合同向双螺杆挤出机ZSK60的组合螺杆中的三维等温流动。在计算所得速度场和压力场的基础上,全面分析并讨论了由不同厚度和不同错列角的捏合块元件组成的组合螺杆的流场分布规律;研究了组合螺杆的输送性能和挤出稳定性;并分别采用平均剪切速率、平均特征剪切应力以及平均拉伸流动指数等瞬态混合指数表征了组合螺杆的瞬态混合特性。此外还考察了两种不同流变性质的聚合物熔体在组合螺杆中的瞬态流场分布规律。所得结论可为双螺杆挤出的数值模拟研究提供一定的方法指导,并为其工程实践提供一定的理论指导。     

三螺杆挤出机螺纹元件流场分析

基于三角形排列的三螺杆挤出机的研究开发实践,对螺纹元件所形成的流场,特有的三个啮合区和中心区流场进行了模拟研究。通过对流速、流向、剪切速率、剪切黏度等挤出特性的剖析,说明这种三螺杆挤出机具有较强的输送能力;三个啮合区较其他区域有高的速度梯度、剪切速率;中心区存在瞬态环流和回流。在计算条件下,中心区的物料中的95％会在5 s内流出中心区,其余物料在中心区的停留时间不会超过100 s。     

非啮合双螺杆挤出过程轴向循环流道三维流场分析——轴向循环流场分析（Ⅰ）

引入了轴向循环流动的概念,且利用ANSYS有限元分析软件对非啮合双螺杆挤出机轴向循环流道中的非牛顿流体等温流动进行了三维模拟分析。在得出速度场和压力场的基础上,分析了螺杆转速及轴向循环长度对输送特性及混合能力的影响,同时还对剪切粘度、剪切速率及剪切应力进行了模拟。     

非啮合双螺杆挤出过程常规螺纹元件流道三维流场分析

利用ANSYS有限元分析软件对并列型和错列型非啮合双螺杆挤出过程常规螺纹元件流道非牛顿流体等温流动进行了三维模拟分析。在得出速度场和压力场的基础上，对剪切速率，剪切应力及剪切粘度进行了模拟。同时将并列型和错列型的模拟结果进行了比较，对其输送能力和混合能力进行了分析。     

Three-dimensional flow modeling of a self-wiping corotating twin-screw extruder. Part II: The kneading section

Three-dimensional flow simulations of kneading elements in an intermeshing corotating twin-screw extruder are performed by solving the Navier Stokes equations with a finite element package, Sepran. Instead of using the whole geometry of the 8-shaped barrel a simplified geometry is used, representing a large part of the geometry during the rotating action of the kneading paddle. The goal of these calculations is to study the dependence of several factors that influence mixing, such as shear rate, elongation rate, pressure, and the flow profile in the extruder on various extruder parameters, such as fluid viscosity, rotation speed, and throughput. The shear and elongation rate and the pressure drop are calculated for varying viscosities. The various stagger angles possible for disc configurations in the corotating twin-screw extruder are modeled. The axial backflow volume is calculated for varying values of rotation speed and throughput.     

Extrusion of non-newtonian fluids in a single-screw extruder with pressure back flow

The transport phenomena underlying the extrusion of non-Newtonian fluids in single-screw extruders is investigated numerically and experimentally. The viscosity of the investigated fluids is a strong function of the temperature and, for the non-Newtonian case, of the shear rate. Therefore, the governing equations of motion are coupled to the energy equation through the viscosity. The velocity in the down channel direction of the screw extruder is a result of both shear and pressure driven transport. The pressure acts in a direction opposite to that of the drag flow, and comparatively high pressures arise at the die in typical extruders. When a narrow die is used in the screw extruder, the pressure gradient in the down-channel direction becomes so large that the down-channel velocity near the screw root becomes negative in terms of the coordinate system fixed to the screw. The conventional marching schemes fail to simulate the fluid flow when the down-channel velocity becomes negative, since the downstream conditions are not known. Two different numerical schemes used to simulate the fluid flow in a single-screw extruder for this circumstance, which often arises when dies with high flow resistance are used and which is termed as pressure back flow in the literature, have been discussed. One scheme is based on including the down-channel thermal diffusion, making the problem elliptic, and the other scheme uses a different coordinate system. Both formulations are found to yield results that are fairly close. Experiments were also carried out to measure the pressures at three different locations in a single-screw extruder. The computed results were found to be in good agreement with the experimental results. The pressures at the die obtained numerically by treating the flow as isothermal are found to be lower than those obtained when the flow is treated as nonisothermal, indicating the strong influence of thermal transport in this problem.     

四螺杆挤出机常规螺纹元件三维流场分析

利用大型有限元软件ANSYS对聚乙烯熔体在四螺杆挤出机常规螺纹元件中的流动情况进行了分析,求出了速度场、压力场、黏度场,对流道的中心区进行了重点分析。计算结果表明:四螺杆的四个啮合区具有较大的压力梯度、速度梯度,其混合性能明显好于双螺杆挤出机。中心区有明显的环流现象,物料在中心区的停留时间较长,中心区物料没有滞留现象。     

高分散混合元件设计及混合性能的研究

根据啮合同向双螺杆挤出机的啮合原理,设计了一种高分散混合双螺杆元件。运用Polyflow有限元分析软件对该双螺杆元件的3种螺杆构型的流场进行了模拟分析,并且对这3种螺杆构型进行了实验研究。研究表明,错列角为150°的元件的分散混合性能最好,其次是错列角为30°的元件,错列角为90°的元件的分散混合性能最差。     

LDPE熔体在双螺杆挤出机中流动的有限元分析

利用大型有限元分析软件包ANSYS分析了低密度聚乙烯(LDPE)在双螺杆挤出机三头常规螺纹元件中的流动情况,讨论了整个流道的速度分布、压力分布、粘度分布及螺杆挤出特性曲线。计算结果表明：LDPE熔体在双螺杆挤出机中得到了充分的混合。     

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.     

啮合同向双螺杆挤出机普通螺纹元件中物料停留时间计算

采用有限元方法对啮合同向双螺杆挤出机的普通螺纹元件流动进行了三维等温非牛顿模拟计算，根据流场计算所得到的速度场通过编程计算得到了物料在螺纹元件中的三维流动路径，利用物料的三维流动路径计算结果分析了普通螺纹元件中物料的停留时间分布和平均停留时间随螺杆转速和挤出机产量的变化规律。     

Solid transportation in the feeding zone of intermeshing co-rotating twin-screw extruders

A mathematical model was proposed for the characteristics of solid transportation in the feeding zone of an intermeshing co-rotating twin screw extruder. The model was based on the observations made from a “transparent” extruder. The analysis considered optimal solid conveyed with maximum throughput rate, i.e., when the upper and lower intermeshing zones, and the two sides of the screws were all partially filled with solid resin to an extent that a slight increase in the solid filling would immediately cause blocking of the solid transportation. Because of these starve-fed characteristics, the conventional approach for analysing solid feeding used in single-screw extruders was inadequate for twin-screw extruders. This paper also suggests a solution for the mathematical expressions describing the stress and velocity fields in the solid feeding zone of a twin-screw extruder. Finally, the predicted values are compared with our experimental findings.     

啮合型双螺杆挤出机非常规螺纹元件设计新方法

双螺杆挤出机发展的高速高效化使常规螺杆元件不能满足混合要求,因此需要设计输送、混合性能好的非常规螺杆元件。本文从齿轮啮合原理的角度出发,用齿形法法对非常规螺纹元件端面曲线几何学进行了分析,并给出了一套以CAD为工具来设计非常规螺纹元件的新方法。