啮合型异向旋转双螺杆挤出机熔体输送流场及特性的近似解析解

从简化的物理模型和数学模型出发,参照流速分布数值计算结果所反映出的规律性,求出了C形小室内熔体流速分布的近似解析解,并由此导出了熔体输送段中产生的轴向力、扭矩、功耗和比功耗的计算公式。与数值计算得出的结果相比,这些公式由于具有解析形式,不但能直观地反映上述熔体输送特性参数与其他参数的关系,而且更便于运用。     

啮合型异向旋转双螺杆挤出机溶体输送流场及特性的近似解析解

从简化的物理模型和数学模型出发，参照流速分布数值计算结果所反映出的规律性，求出了C形小室内熔体流速分布的近似解析解，并由此导出了溶体输送段中产生的轴向力、扭矩、功耗和比功耗的计算公式。与数值计算得出的结果相比，这些公式由于具有解析形式，不但能直观地反映上述熔体输送特性参数与其他参数的关系，而且更便于运用。     

异向旋转啮合型双螺杆挤出机熔体输送机理的研究

迄今国外的研究者们在平行平板模型和压延理论的基础上已建立起某种理论模型来计算异向旋转啮合型双螺杆挤出机熔体输送段中 C 形小室的产量和压力降。本文作者描述了一种关于 C 形小室的新的物理模型,该模型把螺槽区和四个间隙联系起来,反映了异向旋转啮合型双螺杆挤出机螺杆几何参数的变化以及主要流动和漏流之间的关系。作者提出了根据 C 形小室和口模产量—压力特性来决定完全充满的C 形小室数和熔体输送工作点的方法,该方法使得计算熔体输送区的总压力降、总扭矩和总功耗成为可能。将实验结果和理论计算进行比较证明:该模型在决定压力降,扭矩,功耗和 C形小室充满数方面,对现有模型来说是一大改进。     

啮合型同向旋转双螺杆挤塑机熔体输送机理研究

本文提出了描述啮合型同向旋转双螺杆挤塑机中非等温三维熔体输送流场的理论模型。借助罚函数有限无及边界无法对该流场进行了求解。此后计算和分析了熔体输送段的重要工作特性参数。计算结果和实验结果的良好吻合证明所采用的模型合理、计算方法可行、计算结果可靠。     

计算流体动力学（CFD）及其软件包在双螺杆挤出中的应用

从数学模型、软件包的应用和数值模拟对象（即整根螺杆、熔体输送段、混合以及反应挤出等）三个方面介绍了计算流体动力学（CFD）及其软件包在双螺杆挤出中的应用,并讨论了双螺杆挤出加工数值模拟中尚特解决的问题。     

同向双螺杆不同螺纹元件混炼效果的数值研究

采用Polyflow软件数值模拟了啮合同向双螺杆挤出机流道内聚丙烯(PP)熔体的流动,数值计算了常规螺纹元件和开槽螺纹元件流道内PP熔体的三维等温流场,采用粒子示踪分析法(PTA)分析了不同螺纹元件流道内粒子的拉伸度自然对数、分离尺度和停留时间,比较了常规螺纹元件和开槽螺纹元件的混炼效果。研究表明,与常规螺纹元件相比,由于熔体在沟槽内产生漏流,开槽螺纹元件的建压输送能力较低,分散混合性能较弱;开槽螺纹元件流道内因粒子的停留时间较长,其分布混合性能优于常规螺纹元件。     

啮合型同向旋转双螺杆熔体输送段相似设计

本文根据熔体输送段流场相似理论,提出了一系列该段螺杆结构参数及工艺参数的相似设计和选择的准则。     

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。     

单螺杆挤出机熔体输送区螺棱间隙对熔体停留时间分布的影响

计算了螺棱间隙与熔体在熔体输送区停留时间分布的关系。分析表明：螺棱间隙不仅影响停留时间的量值而且影响其分布，并且这些影响可反映到一个由螺棱间隙几何参数和螺杆几何参数构成的无量纲数的影响中。     

PP-R双螺杆挤出熔体输送和降解行为的研究

对无规共聚聚丙烯(PP-R)在ZSK-300型双螺杆挤出机中熔体输送特性和热降解行为进行了研究,计算了ZSK-300的最大挤出量．分析了熔体输送流场;并对加料量、熔体流动指数、助剂量、熔体温度等工艺操作条件对熔体输送和降解行为的影响进行了讨论。结果表明,加料量的改变需要适当调整加热温度：粉料熔体流动指数的微小波动,对挤出物的质量和挤出过程的稳定性没有影响;降低熔体挤出温度,可明显降低PP-R的热氧降解。     

Isothermal effectiveness factor—I: Analytical expression for single reaction with arbitrary kinetics. Slab geometry

An analytical simple algebraic expression for isothermal effectiveness factor (η) in a porous pellet is presented. Arbitrary kinetic expressions are investigated and the external mass transfer effect is also considered. The resulting analytical expression is found after matching asymptotic expressions of η valid for large and small values of Thiele modulus.The agreement between approximated and numerical results is surprisingly good. For most cases analyzed maximum deviation are below 3% for power law type kinetic expressions provided the reaction order is greater than 0.5. More severe limitation arises for Langmuir-Hinshelwood kinetic expressions. In actual facts the proposed analytical expressions is unable to predict effectiveness factor greater than one.Nevertheless, as will be shown in future works, this very simple procedure can be safely used to predict the effectiveness in more complex situations such as those where activity distribution must be considered or where the kinetic parameters will be function of composition and/or spatial coordinates.     

Analysis and simulation of calendering process of non-newtonian polymeric fluids

Maxwellian fluid flow between asymmetric calenders was analyzed by the numerical solution to the simplified equations of motion and energy equation. The solution techniques combined the power-law weighted upwind difference method for the energy equation with the analytical solution of the momentum equations. The calculated results provided not only pressure and temperature distributions of the flow field, but also the power consumption and the roll separating force of the calendering processes. The decrease in the elastic shear modulus led to the reduction in the temperature profile as well as in the power requirement. The asymmetry in the roll speeds generated higher temperature field throughout the whole flow region due to the higher viscous heating, compared with the case of the symmetry in the roll speeds.     

Velocity profiles and frictional pressure drop for shear thinning materials in lid-driven cavities with fully developed axial flow

A finite element numerical study has been carried out on the isothermal flow of power law fluids in lid-driven cavities with axial throughflow. The effects of the tangential flow Reynolds number (Re_U), axial flow Reynolds number (Re_W), cavity aspect ratio and shear thinning property of the fluids on tangential and axial velocity distributions and the frictional pressure drop are studied. Where comparison is possible, very good agreement is found between current numerical results and published asymptotic and numerical results. For shear thinning materials in long thin cavities in the tangential flow dominated flow regime, the numerical results show that the frictional pressure drop lies between two extreme conditions, namely the results for duct flow and analytical results from lubrication theory. For shear thinning materials in a lid-driven cavity, the interaction between the tangential flow and axial flow is very complex because the flow is dependent on the flow Reynolds numbers and the ratio of the average axial velocity and the lid velocity. For both Newtonian and shear thinning fluids, the axial velocity peak is shifted and the frictional pressure drop is increased with increasing tangential flow Reynolds number. The results are highly relevant to industrial devices such as screw extruders and scraped surface heat exchangers.     

Effect of sample size on microwave power absorption within dielectric materials: 2D numerical results vs. closed‐form expressions

This study deals with the analytical and numerical solutions of the heat source term because of microwave heating for high and low dielectric materials in 1D and 2D configurations. The authors compare closed‐form expressions dedicated to microwave power calculation to numerical simulations. A comprehensive and accurate analysis of the microwave power reflected from the surface of the sample is also carried out during microwave heating. The influence of sample length is studied using an original numerical procedure. The study highlights that 1D closed‐form expressions can be extended to 2D configurations in the case of sufficiently high dielectric properties. Examples of heating rate during 2D microwave heating in TE₁₀ mode are finally presented. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

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.     

A COMPARISON OF APPROXIMATE AND EXACT SOLUTIONS FOR HOMOGENEOUS IRREVERSIBLE CHEMICAL REACTION IN THE LAMINAR BOUNDARY LAYER

A comparison of approximate and exact solutions for homogeneous irreversible chemical reaction in the laminar boundary layer flow has been made. By using the Method of Weighted Residuals, approximate analytical expressions for the velocity and concentration profiles were developed for the case of a laminar boundary layer flow over a flat plate at zero incidence angle, where isothermal, homogeneous, nth order chemical reaction takes place. Both the Subdomain and Galerkin methods were employed to examine the influence of the choice of the weighting function on the predictions, and to provide a means for improving the solutions systematically. The problem was also solved numerically for the case of first order reaction by using a similarity solution for the hydrodynamic flow and a power series expansion method for the mass transfer. The analytical results were compared with the exact solutions in order to evaluate the accuracy of the approximate analytical solutions. The Method of Weighted Residuals provided approximate solutions that are qualitatively correct and, within limits, quantitatively accurate. The resulting approximate expressions can be used to give quick estimates for reactions investigated herein and to predict the results for higher order reactions when there are no exact solutions.     

Estimation of overall effectiveness factors for parallel catalytic reactions

Approximate analytical expressions of overall effectiveness factors for parallel catalytic reac-tions occurring in a spherical catalyst pellet with both internal and external mass transfer resistancesare obtained after taking the information given by asymptotic solutions valid for small and largevalues of Thiele moduli.This approximate procedure is feasible for power law as well asLangmuir-Hinshelwood kinetics and the agreement between the approximation and the numerical re-sults is good enough for practical purposes.Moreover,the method does not require any iterative ortrial-and-error computation,and can be conveniently applied in most practical calculations for reac-tors giving reliable results.     

多孔催化剂有效因子的近似分析解(Ⅱ)近似分析解与数值解的比较

根据本文第Ⅰ部分所提出的多孔催化剂有效因子近似计算式,针对不同形式的幂函数型动力学方程和双曲型动力学方程,计算了等温下Thiele模数不同时非一级反应的有效因子,并且用数值方法求出相应条件下的有效因子以作比较.大量的计算结果证明所提出的近似计算式较之文献上已有的近似式,不但精度高,而且适用范围广.同时近似式中参数估值简便,克服了以往研究者所提出的式子中这方面所存在的困难.