啮合同向双螺杆挤出机普通螺纹元件末端共混物的混合形态Ⅰ.物料三维流动路径的计算

用有限元方法对啮合同向双螺杆挤出机的螺纹元件流场进行了三维等温非牛顿模拟分析,根据流场分析所得到的速度场,通过编程计算得到了物料在啮合同向双螺杆挤出机螺纹元件中的三维流动路径。结果表明,由于存在着轴向回流,部分物料不能流出元件出口,而是从元件入口返流;物料在元件中的运动轨迹不尽相同,有的物料微元在整个流动过程中都围绕着2根螺杆以螺旋“∞”形向前运动,有的物料微元在流动过程中时而围绕1根螺杆连续旋转,时而围绕2根螺杆以螺旋“∞”形向前运动;在螺槽区,物料在螺槽的横截面内上下流动;回流物料微元数随着螺杆转速的增大、双螺杆挤出机产量的减小而增大。     

啮合盘元件中粉体聚集体分散混合的数值模拟

采用有限元方法对啮合同向双螺杆挤出机的啮合盘元件流场进行了三维等温模拟计算，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啮合盘元件中的三维流动路径,结合粉体聚集体的分散模型和三维流动路径，计算得到了粉体聚集体在啮合盘元件出口的平均直径及其分布。     

往复式单螺杆销钉挤出机新型混合元件的开发及其混合性能研究

结合Φ45往复式单螺杆销钉挤出机(Buss Kneader)新型四头螺纹混合元件NKE的开发研究,利用有限元方法对物料在NKE元件内的流动情况进行了三维动态模拟.并与常规三头螺纹混合元件(KE)从动态混合过程、停留时间分布、分布混合及分散混合性能4个方面进行了对比;分析了加工条件对NKE元件停留时间分布、分布混合及分散混合性能的影响.     

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。     

啮合同向双螺杆挤出机普通螺纹元件末端共混物的混合形态Ⅱ.混合形态的计算

用物料三维流动路径结合分散模型计算了螺纹元件出口处分散相液滴的直径。分析了螺杆转速、挤出机产量和液滴初始直径对末端分散相液滴直径的影响。结果表明。当液滴初始直径较大时,其集聚变化率随着初始直径的变化而变化较小;提高螺杆转速和降低挤出机产量可以提高螺纹元件的分散效果。当液滴初始直径较小时。其集聚变化率随着初始直径的变化而急剧变化;提高螺杆转速和降低挤出机产量有利于集聚的发生。分散效果较差。螺杆转速和挤出机产量的变化对末端分散相液滴直径的分布范围影响不大。     

三螺杆挤出机常规螺纹元件挤出过程的CAE研究

利用ANSYS软件分析了三螺杆挤出机常规螺纹元件中等温非牛顿流体的压力场、速度场和粘度场，并和双螺杆挤出机常规螺纹元件进行了比较，尤其对流道中心区进行了重点研究。结果表明，三螺杆挤出机的混合性能好于双螺杆挤出机；中心区的物料压力梯度和速度梯度都较小，物料在中心区流动缓慢，中心区的物料粘度值较大；对反应时间不宜过长的聚合物，应避免使用三螺杆挤出机。     

往复式单螺杆销钉挤出机典型螺纹元件混合性能研究

使用Polyflow有限元软件对往复式单螺杆销钉挤出机（简称Buss机）的三类典型螺纹元件内物料流动和混合过程进行了数值模拟。流场分析中使用了网格重叠技术。在得到流场速度分布后,基于粒子轨迹跟踪技术计算了物料微元在螺纹元件内的流动轨迹,并分析了Buss机螺纹元件内物料的动态混合过程。以分布混合指数和分隔比例为指标定量地对比了螺纹元件的分布和分散混合性能,在此基础上分析了加工条件、物料特性及销钉布置对Buss机混合性能的影响。数值模拟结果与前人研究有较好的吻合性。     

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。     

组合式同向旋转双螺杆特性曲线分析

应用有限元分析软件ANSYS对同向旋转双螺杆挤出机螺纹输送元件中的三维非牛顿流动进行了模拟，计算出在一定转速和挤出量等工艺条件下螺纹元件的建压能力，确立了一定导程螺纹元件的特性曲线。在此基础上，对组合式同向旋转双螺杆挤出机工作特性进行了分析，并对双螺杆计量段充满长度和排气段脱挥长度的确定作了初步探讨。     

往复式单螺杆销钉挤出机停留时间分布研究

使用Polyflow软件对往复式单螺杆销钉挤出机(Buss机)三类典型螺纹元件的停留时间分布(RTD)进行了三维动态模拟,分析了工艺条件和物料特性对RTD的影响。根据Buss机的螺杆组合构型,应用卷积技术求得了物料沿整根螺杆的RTD曲线,探讨了物料在Buss机内的RTD规律与工艺条件变化的相关性。     

啮合同向双螺杆挤出机中组合螺杆性能的数值研究（Ⅱ）混合特性分析

采用有限元软件POLYFLOW,对组合式啮合同向双螺杆挤出机ZSK60中不同构型的组合螺杆进行了混合分析。通过计算螺杆转过不同角度时的拟稳态流场,采用粒子示踪分析(PTA)方法,对组合螺杆中聚合物熔体的动态混合过程进行了可视化模拟;在此基础上通过对大量粒子运动轨迹的统计处理,分别采用停留时间分布、分布混合指数、分离尺度等累积混合指数表征了组合螺杆的轴向混合性能、分布混合性能以及分散混合性能。此外还研究了不同工艺条件下组合螺杆的混合特性。并将部分数值模拟结果与前人实验研究进行了对比。     

COLLECTION OF INERTIALESS PARTICLES ON SPHEROIDS AND SPHERES WITH ELECTRICAL FORCES AND GRAVITATIO

Collection efficiencies are predicted for the capture of fine, incrtialess, charged particles on a single spheroidal collector in a gaseous flow field by the action of coulombic and external electric field forces and gravity. With the flow and external fields parallel to the axis of symmetry, collection efficiencies for spheroidal collectors are found by determining particle trajectories. For three-dimensional nonsymmetric systems resulting from the flow being at an arbitrary angle to both the axis of symmetry and the external fields, collection efficiencies are found by determining particle fluxes to the collector. For single force cases, particle deposition is independent of collector geometry and, for point panicles, is the same for all stationary incompressible flows. Using a cellular model of flow around a sphere, droplet density in wet scrubbers is shown to have little hydrodynamic effect on single droplet collection efficiencies.     

COLLECTION OF INERTIALESS PARTICLES ON SPHEROIDS AND SPHERES WITH ELECTRICAL FORCES AND GRAVITATIO

Collection efficiencies are predicted for the capture of fine, incrtialess, charged particles on a single spheroidal collector in a gaseous flow field by the action of coulombic and external electric field forces and gravity. With the flow and external fields parallel to the axis of symmetry, collection efficiencies for spheroidal collectors are found by determining particle trajectories. For three-dimensional nonsymmetric systems resulting from the flow being at an arbitrary angle to both the axis of symmetry and the external fields, collection efficiencies are found by determining particle fluxes to the collector. For single force cases, particle deposition is independent of collector geometry and, for point panicles, is the same for all stationary incompressible flows. Using a cellular model of flow around a sphere, droplet density in wet scrubbers is shown to have little hydrodynamic effect on single droplet collection efficiencies.     

The Relationship between Secondary Flows and Particle Deposition Patterns in Airway Bifurcations

The relationship between localized fluid dynamics and localized particle deposition patterns within bronchial airway bifurcations upon inspiration and expiration was analyzed for different bifurcation geometries, flow conditions, and particle sizes. For the simulation of three-dimensional airflow patterns in airway bifurcation models, the Navier-Stokes and continuity equations were solved numerically by the finite volume Computational Fluid Dynamics (CFD) program package FIRE. Spatial particle deposition patterns were determined by the intersection of randomly selected particle trajectories with the surrounding wall surfaces. While three-dimensional flow patterns were characterized by their corresponding two-dimensional secondary flow fields, three-dimensional deposition patterns were represented by their related two-dimensional deposition density plots. Two particle sizes were selected to explore the relationship between secondary flows and localized particle deposition patterns: 0.01 w m, to illustrate the effects of Brownian motion, and 10 w m, to display the effects of impaction and sedimentation. Changes in bifurcation geometry (shape of bifurcation zone, branching angle) and flow conditions (flow rate, inlet flow profile, direction of flow) lead to variations in resulting secondary flow patterns, which were reflected by corresponding differences in related particle deposition patterns. In conclusion, a distinct relationship could be observed between secondary flow patterns and deposition density plots, demonstrating that particle deposition patterns in airway bifurcations are not only determined by physical forces acting upon individual particles, but also by convective transport processes of the carrier fluid.     

Numerical investigation of coarse powder and air flow in an electrostatic powder coating process

The work presented here reports on the numerical simulation of an electrostatic powder coating process that uses a commercial computational fluid dynamic code, FLUENT v6.1. The purpose of this study was to understand the gas and particle flow fields inside a coating booth under given operating conditions and the effect of particle sizes on its trajectories and the final coating quality. The air and powder particle flows in a coating booth were modeled as a three-dimensional turbulent continuous gas flow with solid particles as a discrete phase. The continuous gas flow was calculated by solving Navier-Stokes equations including the standard k − ε turbulence model with non-equilibrium wall function and the discrete phase was modeled based on the Langrangian approach. Since the solid phase volumetric fraction was less than 0.1%, the effect of particle-particle interaction on particle trajectories was not taken into account. In addition to drag force and gravity, the electrostatic force including the effect of space charge due to the free ions was considered in the equation of motion and implemented using user defined scalars and functions. The governing equations were solved using the second order upwind scheme. Information was provided on the particle trajectories with respect to the particle diameters that could be used to develop suitable operating conditions for the use of fine powders in a powder coating process.     

固体推进剂同向双螺杆元件混合性能模拟

首先设计了4种固体推进剂用螺杆元件,并进行了固体推进剂药浆的流变性能测试,通过使用Polyflow软件对4种螺杆元件的流场进行数值模拟。对各螺杆元件流场的剪切速率、加权平均剪切应力、平均回流系数、累积停留时间分布等表征螺杆元件混合性能以及流场特性的指标进行分析,对比4种螺杆元件的分散和分布混合性能,并建立了螺杆元件混合性能的评价体系。结果表明,KB元件和S型元件对药浆有较好的综合混合性能,有利于固体推进剂的混合。     

啮合同向双螺杆挤出机中S型元件不同螺杆构型下的流场模拟

应用FEM模拟计算了啮合同向双螺杆挤出机新型螺杆元件——S型元件的正反向螺纹部分不同长度构型下的流场。考察了三种不同螺杆构型流场的特性，对比了流场的挤出特性、分散和分布混合能力。在相同操作条件下，三种构型具有相似的分散混合能力，不同之处主要在于分布性混合和输送能力，反向输送部分较长的构型具有良好的轴向分布混合能力、正反向输送部分等长的构型具有最好的周向分布混合，正向输送部分较长的构型具有最优异的输送能力。