聚合物流体入口收敛流动的数值模拟

聚合物流体从大截面流道进入小截面流道时产生的入口收敛流动,是工业中常见的流型之一。基于聚合物流体入口收敛边界流线方程,应用MATLAB对入口收敛流动进行了数值模拟,讨论了Bagley校正因子(e)、非牛顿指数(n)、流道收缩比(λ)等因素对入口收敛流线和入口自然收敛半角(α0)的影响。结果表明:在一定的条件下,入口收敛边界流线的半径r随着e的增加而增大,但随着n的增加而减小,而λ对入口流型的影响不明显;另外α0随着e的增加而减小,但随着n的增加而增大,α0与λ之间呈非线性关系。模拟结果与实验观测较为接近。     

炭黑填充NR／SBR毛细管挤出流动中进口自然收敛角的估算

当聚合物流体（熔体或液体）从容器进入挤出机的小机筒后，流体不会成平行状态，由于流体的粘弹性作用和机筒断面的收缩，会在机筒前端形成圆锥形界面。这是一种进口收敛流动。机简进口的收敛流动是聚合物加工（例如挤出、注射等）时常见的流动形状。界面流线的切线和机筒的中心轴线之间的角度（α）称为流体自然收敛半角（θ）。当α〈θ时，会形成一个“环流区”。而且，流体成环流形式运动，如图1所示。     

混炼胶入口压力降和入口自然收敛半角的数值模拟

基于非牛顿流体人口收敛压力降和人口自然收敛半角方程,应用Matlab软件对NR/SBR混炼胶挤出过程中入口收敛流动进行数值模拟,并讨论非牛顿指数、流道收缩比、表观剪切速率、流体粘附特性系数和BagIey校正因子等因素对人口压力降和人口自然收敛半角的影响.结果表明,在一定条件下,人口压力降随着非牛顿指数、流道收缩比、表现剪切速率和流体粘附特性系数等增大而增大;人口自然收敛半角随着Bagley校正因子增大而减小等.模拟结果与文献报道有较好的一致性.     

PIV技术测试聚合物流体拉伸流动的实验研究

针对低相对分子质量、低黏度的牛顿流体（如聚异丁烯）和非牛顿流体（如3 %苯甲酸钠溶液）,采用粒子成像速度仪（PIV）系统测试了2种流体在同一流率下流经渐变收缩流道时的速度分布,并研究比较了壁面处的纯剪切流动与流道中心轴线上的拉伸流动。通过实验测试与有限元模拟比较发现,牛顿流体和非牛顿流体的速度分布形态具有一定的差异。在确定速度分布的情况下,根据渐变收缩流动的特点,可以得到流体流动时中心轴线上的拉伸速率和边界处的剪切速率。     

聚合物流体入口自然收敛半角和涡流长度比方程的建立和初步验证

入口收敛流动是聚合物流体黏弹特性的重要表现,流体入口自然收敛半角和涡流长度比是表征入口收敛流动的重要参数。对已提出的基于等效思想和最小能原理推导的在圆形流道的入口收敛流动方程进一步分析,引入黏度因子,提出了流体的入口自然收敛半角和涡流长度比的方程。结果表明,基于推导的方程对流体入口自然收敛半角和涡流长度比的预测与实验数据相符。随着Bagley校正因子的增加,流体入口自然收敛半角减小,涡流长度比增加。随着流道收缩比的增加,流体入口自然收敛半角先增大,然后几乎保持不变,而涡流长度比随着流道收缩比的增加而减小。     

有限元方法在圆形收敛流道设计中的应用

本文使用有限元软件模拟了聚合物熔体在圆形收敛流道内的流动，得到了收敛流道内熔体速度的分布，特别关注了收敛流道内、垂直于流动方向上的流动速度的大小和分布同时，还对流道有倒圆角和没有倒圆角的两种情况的流动进行了模拟，分析了倒角对流体两个方向上的速度大小和速度分布的影响。     

聚合反应工程——第5章 非牛顿流体的传递过程(一)

5.1 化工流变学基础 5.1.1 非牛顿流体概述 在聚合物生产中,往往要处理聚合物溶液、聚合物熔体或高固物含量浓悬浮液等非牛顿流体,其流动、传热、传质等特性,均与牛顿流体有很大的差别。因此,非牛顿流体的传递过程,是聚合反应工程研究的一个重要领域,而弄清聚合物系的流变行为,即     

聚合物熔体收敛流动的可视化实验与理论研究

采用可视化实验技术,获和了流过楔形收敛流道的高密度聚乙烯（ＨＤＰＥ）熔体内着色条料的流迹图像。实验结果表明,收敛流道内ＨＤＰＥ熔体的流速与由于文推导的幂律流体较接近,在此基础上,采用该幂律流体模型,揭示了楔形收敛流道内流速与延伸应变速率随径向位置和偏心角度的变化规律,并利用该规律对聚合物熔体的连续挤出自增强作了分析。     

聚合物流体平入口收敛流型的理论分析

对前文发表的非牛顿流体平入口收敛流动的边界流线微分方程进行了分析，求出了当非牛顿指数n=1／3时的入口收敛边界流线方程，及其与n≠1／3时边界流线微分方程的关系。在此基础上，建立了n=1／3时的聚合物流体自然收敛半角方程和收敛区长度方程，并讨论了影响入口流型的主要因素。     

微层共挤出过程层叠单元流道三维流场分析

采用Cross-WLF本构方程,建立了层叠单元流道短纤维填充聚合物注塑成型充填阶段三维黏弹数值模型,运用有限元法,对聚合物熔体在层叠单元流道中注塑流动过程进行数值模拟。研究了层叠单元流道中聚合物熔体的流动过程、剪切场分布以及微层剪切流场对短纤维填料的取向作用。结果表明:分流道结构的微小差异会引起聚合物熔体流动波前的不一致,但最终趋于平稳流动状态;聚合物熔体进入扭转、展宽、变薄的区域时,由于流道结构和尺寸突变,剪切速率急剧增大,影响了流动的稳定性;层叠单元流道的结构设计有利于聚合物熔体中短纤维的取向。     

聚苯乙烯熔体挤出流动特性的研究

应用毛细管流变仪,考察了两种聚苯乙烯-Styron498(PS498)和Styron492J(PS492J)熔体挤出过程中的流动行为及其影响因素。实验发现,两试样熔体的流动均不严格地服从幂律;在相同条件下,PS492J的非牛顿性较PS498明显;两试样熔体的粘度对温度的依赖关系符合Arrhenius方程。本文还就熔体流变行为与分子结构参数的关系进行了初步定量分析。     

Planar Entry Converging Flow During Extrusion of Polymer Melts

In this article, a planar entry converging flow during die extrusion of polymeric melts was analyzed and a differential equation of entry converging boundary streamline equation with rheological parameters and channel geometry is established. By applying limit theory, the entry converging boundary streamline equation in the case with different non-Newtonian index (n) was discussed, and the corresponding expressions of entry natural convergent half angle and convergent region length were derived. The entrant flow pattern might be described with the half angle of entry natural convergence (α₀) and the convergent region length (L _e ) of the melts, and α₀ and L _e were mainly a function of the entry elastic storage deformation energy (e) and n. The values of α₀ and L _e were calculated by means of these simplified expressions. It was found that the estimations of α₀ decrease nonlinearly white L _e increases linearly with an addition of e. Finally, a preliminary verification of the natural converging half angle equation was made. The results showed that the estimations of 2α₀ based on the experiments of a low-density-polyethylene (LDPE) and a high-density-polyethylene (HDPE) were close to the data reported in reference.     

粘弹性聚合物熔体挤出胀大的三维计算机模拟

采用粘弹性PTT模型对聚合物熔体的挤出胀大进行了三维计算机模拟研究 ,其中用罚函数有限元方法以降低模拟对计算机内存的要求 ;在动量方程中引入参考粘度 ,并把动量方程转化成椭圆类方程的去藕算法 ,以增加计算收敛的稳定性。研究表明本文提出的算法是可行的     

压出过程中胎面胶流动特性的研究

应用Monsanto加工性能试验机(MPT)对胎面胶进行压出流变试验。在实验条件下,考察试样熔体的流动特性及其影响因素,并作初步的分析和讨论。实验发现,试样的流动曲线可近似用指数方程描述;而熔体粘度对温度的依赖性则大体上符合Arrhenius方程。     

Prediction of PVT behavior of polymer melts by the group-contribution lattice-fluid equation of state

The group-contribution lattice-fluid equation of state (GCLF-EOS), which is capable of predicting equilibrium behavior in polymer systems, was developed by establishing group contributions of the lattice-fluid EOS using the PVT properties of low molecular weight compounds only. This model was used to predict the PVT behavior of common polymers over a wide temperature range in the melt region and over a wide range of pressures up to about 2,000 bar. The GCLF-EOS predicted accurately the effect of pressure and temperature on the specific volumes of the polymer melts. Prediction results by the GCLF-EOS were compared with those by the group-contribution volume (GCVOL) method. The GCLF-EOS requires only the structure of the polymer repeat unit in terms of their functional groups as input information. No other polymer properties are needed. The GCLF-EOS is the only model that is capable of predicting the specific volumes of polymer melts as a function of temperature and pressure.     

Temperature dependence of the viscous flow of glass-forming melts in a broad temperature range

An equation which is able to describe the temperature dependence of the viscous flow of glassforming melts in a broad range, including the glass-transition range and elevated temperatures has been obtained. The equation contains three parameters; one of them is the preexponential multiplier, which is defined by the extension of the viscosity curve to elevated temperatures (using the Lagrange polynomial), and the other two, the delocalization energy of the atom and the transition potential of the particle, are adjustable parameters. The delocalization energy of the atom that is determined by adjustment is in sufficient accordance with the calculation according to the model of delocalized atoms. The nature of the viscous flow of glass and its melts is discussed.     

Simulation of the Relaxation Processes of Diffusion in Glasses

To consider the relaxation nature of a mass transfer in glass under its interaction with chemical reagents (solutions and melts), the hyperbolic equation, namely, the diffusion wave model was used. The adequacy of the model was confirmed by the calculations of the processes in different glass–reagent systems. The deviation of the calculated values of the mass transfer characteristics from the experimental ones did not exceed the experimental error and, at the initial phase, is by several orders smaller than that in the case of using the Fick equation.     

Prediction of elongation viscosity of polymer melts

Melt extension flow is a common flow pattern during polymer processing, such as entrance converging flow in die extrusion or runner injection of polymer melts from an extruder barrel, blow molding, blowing film and melt spinning. Extensional viscosity is one of the important characterizations of the flow characteristics for polymer fluids. A new extension viscosity equation was established based on White‐Metzner model, Vinogradov‐Malkin viscosity equation and a new relaxation time equation in the present paper. The melt elongation viscosities of metallocene linear low‐density polyethylene (mLLDPE) and polyvinyl butyral (PVB) resins at 130°C were estimated applying this viscosity equation, and the predictions were compared with the measured data of mLLDPE and PVB resins at 130°C reported from reference. The results showed that calculations were close to the experimental data. The parameters in this equation were easy to be determined and the equation was convenient to use for estimating the extension viscosity of polymer melts. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

振动剪切作用下聚合物熔体的非仿射网络结构模型 Ⅱ．非仿射网络结构模型

假设聚合物熔体的缠结网络形变是非仿射的，运用瞬态网络结构原理，采用在本课题第一部分^[1]中所建立的动态速率方程，并对上随体Maxwell本构方程加以修正来建立一个非仿射网络结构模型，利用这一模型来研究振动剪切作用下LDPE熔体的流变行为，研究表明，随着应变振幅和频率的增加，LDPE熔体的剪切应力也增加，同时指出了非仿射网络结构模型的精确变比仿射结构模型有较大提高，这表明在振动力场作用下，网络形变发生了非仿射形变，因此在建立振动力场作用下聚烯烃熔体本构方程时，不能假设其网络是仿射形变的。