层叠流道中天然高分子挤压流动过程的数值模拟

为探究层叠流道中天然高分子材料挤压流动过程与混合特性，建立层叠流道的三维物理模型和有限元网格模型，利用POLYFLOW软件计算了食品熔体在不同的入口流量，挤压过程中的压力、速度、剪切速率分布。结果表明，压力沿着挤出方向呈梯度递减，随着入口流量增大中间位置压力差增大；剪切速率在流道中变化明显，剪切速率从流道中间位置向四周递减，从壁面到流道内部递减；速度在流道内沿着挤出方向先增大后减小，靠近壁面速度小；层叠扭转流道的结构和尺寸设计，有助于提高天然高分子物料的混合效果，并且第1、4层流道混合效果优于第2、3层流道，提高入口流量也有利于提高物料的混合效果。     

微纳层叠天然橡胶/聚丙烯两相挤出的数值模拟研究

为了确保天然橡胶/聚丙烯（NR/PP）通过微纳层叠挤出的厚度均匀，建立了三维模型层叠流道，根据流变测试结果拟合材料黏度，并对NR/PP三维等温黏弹性流动进行了数值模拟。结果表明，当2种物料的入口流动速率相同时，流道出口处两相速度有突变，不同流道之间速度差较大，两相黏度分界不明晰，界面出现一定程度的相互渗入；调整两相的入口流动速率后，速度过渡平稳，不同流道间速度差减小，黏度分界规整，界面无偏移现象。     

数值模拟层叠流道结构参数对熔体压力损失的影响

利用POLYFLOW软件对聚丙烯熔体在层叠流道中的三维等温流场进行了数值模拟,研究了层叠流道结构参数对流道熔体压力损失的影响,并结合分析结果对层叠流道结构尺寸进行了优化。结果表明:熔体在层叠流道中的压力损失随流道水平流程长以及流道进、出口中心的高度差和横向偏距的增大而增大,并随着流道入口长和入口宽的增大而减小;与优化前相比,优化后的层叠流道的熔体压力损失显著降低。     

环形微纳层叠挤出模具的结构设计与流场分析

微纳层叠挤出技术通过对高聚物材料微观形态进行调控来提高多方面的性能,例如力学、阻隔性能等。针对目前微纳层叠挤出技术中层叠模具单位体积内层叠单元较少,流量较低的情况,提出了一种将层叠单元进行环向布置的创新设计思想。设计了用于环向布置的层叠单元流道结构,并提出了模具内单组层叠单元环向布置与多组层叠单元环向布置的具体方案。设计表明,在相同体积下该结构可以布置更多的层叠单元,流量是传统设计的4倍。同时,流道长度为传统设计的60%。利用Polyflow软件对层叠单元的流道进行了数值模拟,结果表明流道压力和速度分布均匀,整体压力降较低。     

层叠单元流道对纤维取向作用的数值模拟

基于广义非牛顿流体本构方程,建立了纤维增强聚合物三维层叠单元流道注塑成型充填阶段数学模型,采用Moldex3D对短纤维增强复合材料在层叠单元流道中的注塑流动过程进行模拟,研究了层叠单元流道对纤维流动取向的影响。结果表明:入口处的纤维从开放领域进入较窄领域,取向呈随机分布状态;进入流道后,表层纤维取向度迅速提高;在接近流道出口处,纤维取向度降低,在出口截面的两侧和中间部分均出现了随机取向纤维。     

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。     

模内扭转层叠器单元结构中的压力损失分析

针对塑料熔体通过自制的模内扭转层叠器时压力损失大的问题,采用Moldex3D模流分析软件对扭转层叠器单元中塑料熔体的流动情况进行模拟,研究了层叠器的流道沿挤出方向的长度、流道出口与入口垂直挤出方向的距离、层叠器分流数等结构参数对层叠器压力损失的影响.结果发现,层叠器压力损失均随上述3种结构参数的增加而增加,其中层叠器分流数对压力损失的影响最为明显.该研究结果为微纳层叠器的结构优化提供了参考.     

基于棉线的微流体燃料电池阳极传质特性LB模拟

基于棉线的微流体燃料电池采用棉线作为流道，无须外部泵、易于微型化，是便携式微流体设备非常有前景的电源，但其性能受阳极燃料传质的限制。本文采用格子Boltzmann方法研究基于棉线的微流体燃料电池阳极耦合电化学反应的传质特性，通过构建三维的棉线流道数值模型，计算得到该流道内燃料的速度及浓度分布，并讨论燃料的进口浓度及流量对该电池阳极性能及传质特性的影响。计算结果表明：阳极极化曲线与实验结果吻合较好；燃料在棉线内部的流速较低，在不同阳极过电位下，燃料浓度沿流动方向均降低，且过电位越大降低得越多；进口燃料浓度越高时，平均电流密度越高，阳极性能升高；随着进口燃料流量的增加，棉线与反应界面接触部位的浓度与其他区域浓度之间的差异增大，而进口流量较低时，该浓度的差异较小且流道后段的浓度较低。     

PA6/EPDM复合材料共挤过程的三维非等温数值模拟

建立橡胶和塑料2种熔体在矩形流道中共挤流动的三维非等温有限元模型,采用有限元法数值模拟了PA6/EPDM的共挤流动过程,研究了橡塑共挤的流动规律以及入口体积流量比与复合材料层厚比的关系。结果表明:在共挤过程中,共挤界面会倾于向熔体入口体积流量相对小、熔体黏度低的一侧偏移,同时黏度低的熔体流动速度快;入口体积流量比的减小有利于减小界面偏移和界面波动。将模拟计算得到的层厚比与实验结果进行了对比,结果表明数值模拟与实验基本一致。     

液力透平内气液两相流动的数值模拟

为进一步揭示气液两相条件下泵反转作液力透平的流动特性,考虑相间拖曳力和虚拟质量力,以空气和水作为能量回收工质,基于Euler-Euler非均相流模型,在泡状流型入流的假定条件下,对入口含气率分别为5%、15%、25%、40%的液力透平内流场进行了定常数值计算。结果表明:随着入口含气率的增加,相同流量下液力透平的水力效率和输出功率降低而压头升高,最高效率时对应的流量发生偏移;相同入口含气率下,沿蜗壳流道截面气相浓度和气相分布均匀度均降低,气相聚集于蜗壳截面中下方;不同入口含气率和流量下,各过流部件中蜗壳内气相分布相对最均匀;随入口含气率和流量的升高,各过流部件的气相浓度和分布的不均匀度均增加,存在明显的分界;叶轮流道内气相聚向叶片吸力面,随着入口含气率和流量的增加气相聚集程度增强、范围扩大,气相聚并成气团而滞留于叶轮流道,产生相态分离,气团上游存在对应漩涡;入口含气率较低时叶片压力面气相主要聚集在高压边侧,随着入口含气率增加,气相在叶片表面扩散,叶片压力面高压边附近靠近前盖板侧区域的气相浓度较高,叶片吸力面低压边附近区域的气相浓度较高;透平内气相速度总体上大于液相速度。     

振动力场作用下聚合物熔体单螺杆挤出过程数值模拟

根据塑料电磁动态塑化挤出过程中熔体输送的实际情况，对三维模型进行简化，利用大型有限元软件ANSYS模拟了叠加轴向振动力场作用下聚合物熔体在螺槽中的流动情况，求解出周期性变化的速度，压力场分布，结果表明，与稳态挤出过程相比，振动力场的引入在进出口压力差恒定的情况下，可以提高熔全输送流率。采用有限元模拟方法可以为确定和优化工艺参数，产品质量控制提供指导。     

Influence of Geometry Structures on the Transfer and Flow Characteristics of Membrane Modules

The effects of different inlet/outlet features and helical structures on the flow pattern and transfer performance of membrane modules were investigated with both three‐dimensional computational fluid dynamics and experimental methods. In a circular flat membrane module, two types of inlet/outlet with single‐port or three‐port configuration were used to evaluate the influence of small differences in the opening area structure of the inlet/outlet on the flow patterns. Although the transfer regions differ, large flow swirls appear in both systems, leading to stagnation regions and causing significant back‐mixing. To alleviate the swirls and improve the flow pattern, a helix clapboard was used to separate the membrane feed channel as spiral channel. Both the numerical and experimental results indicate that the helical structure can greatly enhance the transfer performance and increase the permeation rate while the increment in energy consumption is very small.     

细小槽道换热器内相变微胶囊悬浮液对流传热DPM模拟

基于离散相模型,采用颗粒比热容随温度变化分段函数描述颗粒的相变过程,模拟了相变微胶囊悬浮液在细小槽道换热器内的对流传热特性,考察了不同入口流量时换热器进出口压差及温差的变化规律,并与纯水进行比较,分析了换热器内部及加热面温度分布,研究了换热器典型通道修正的局部努赛尔数Nux*沿流动方向的变化规律. 结果表明,相变微胶囊悬浮液在换热器内的压损随流量变化规律与纯水一致,较纯水有所增大;引入相变微胶囊颗粒减缓了加热面和流体温度升高的速率,使换热器出口及加热面的温度比纯水低;受进出口位置影响,换热器内温度呈现中间通道低、向两侧逐渐升高的分布规律. 不同通道的Nux*沿流动方向的变化规律存在一定差异,部分通道内相变材料完全融化,而部分通道内相变材料尚未完全融化就流出换热器. 需改进换热器进出口位置或对换热器内部结构进行优化设计以获得较好的流量分配特性,从而改善换热效果.     

微槽道内流动沸腾的流阻特性研究

研究了去离子水在3种规格矩形微槽内竖直向上流动沸腾的流阻特性,着重考察了出口干度、质量流速、进口过冷度和微槽尺寸对沸腾流动压降的影响.试验结果表明,两相摩擦压降随出口干度增大而增大,在相同出口干度下,入口质量流速越大摩擦压降越大,摩擦压降与入口过冷度无关;随着微槽道尺寸减小,摩擦压降增大.     

A CFD model for gas uniform distribution in turbulent flow for the production of titanium pigment in chloride process☆

The fluid dynamic behavior of feeding gas (TiCl4) in an annular channel affects the combination of O2 and TiCl4 in an oxidation reactor, a key piece of equipment in titanium pigment production. The numerical procedure was validated by a 3-dimensional gas flow in the annular channel. Applying the validated model, the flow character-istics of TiCl4 in the oxidation reactor with a tangential inlet were simulated and characterized. The flow distribu-tion with five rectifying rings of different structure was simulated and analyzed. The results showed that the rectifying ring improved the distribution uniformity of the pressure and outlet velocity. Compared to the original case without a rectifying ring, the non-uniformity of the pressure and outlet velocity could be reduced by up to 91%and 69%respectively. The rectifying ring #5, which can be instal ed and adjusted easily, is more effective in realizing even distribution. In addition, instal ation of the rectifying ring effectively reduced the circulating flow in an annular channel as well as the total energy loss.     

The flow of polymer melts through the clearance over a barrier flight in extruders

The flow of polymer melts through the clearance over a barrier flight in extruders involves high, rapidly changing shear rates. Polymer melts, being viscoelastic, are expected to exhibit a high elasticity when they flow through the clearance, so the flow through the clearance may not be predictable or stable. The flow through the clearance over a barrier flight was investigated using a shear refining (SR) module connected to an extruder. Three polymers with different melt properties were tested: branched low density polyethylene (BLDPE), high‐density polyethylene (HDPE), and polystyrene (PS). The measured drag flow rate through the clearance was found to be equal to the prediction for a purely viscous fluid, which gives a linear velocity profile in the clearance. At the threshold rotor speed of the SR module whereupon the predicted drag flow rate through the clearance is the same as the extruder output rate, the melt pressures at the inlet and the outlet of the SR module were nearly equal and stable. Below the threshold rotor speed, the inlet pressure was higher than the outlet pressure. Above the threshold rotor speed, the inlet pressure was nearly zero and the outlet pressure fluctuated. The magnitude of the pressure fluctuation increased with increasing rotor speed and decreased with increasing melt temperature. HDPE, which had a higher melt elasticity, showed more pressure fluctuation than BLDPE and PS. The pressure fluctuation probably results from the flow instability through the clearance caused by the melt elasticity.     

基于Fluent软件的恒温出水混水阀模拟

在设计恒温出水混水阀阀体模型的基础上,采用k-e双方程湍流模型,应用计算流体力学软件Fluent对恒温阀流场进行了数值模拟,得到默认边界条件下恒温阀压力、温度及速度场的分布情况,分析了冷热水入口压强、水力直径和温度对温水出口参数的影响,用恒温阀样机进行实验测试. 结果显示,入口压强增加100倍,出口流量随之增加10倍;热水入口温度增加5℃,温水出口温度随之增加1.3℃. 模拟与实验结果基本吻合,证明了理论研究的正确性,同时为改进对恒温阀的设计奠定了基础.     

The Flow Simulation and Experimental Study of Low-Specific-Speed High-Speed Complex Centrifugal Impellers

1 INTRODUCTION Low-specific-speed high-speed centrifugal pumps are widely used in petrochemical, aerospace and chemical industries to deliver low flow rate and high-head liquids, but there exist many problems to be solved, such as low efficiency due to disc loss and low flow rate instability due to positive slope of head-capacity characteristic curve. Through the ex- perimental study on the low-specific-speed high-speed centrifugal pumps, it is found that complex impeller with long, mid an…     

低比转速高速复合离心叶轮的流动模拟和试验研究

Based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model, three-dimensional turbulent flow in four low-specific-speed centrifugal impellers are simulated numerically and analyzed. The relative velocity distribution, pressure distribution and static pressure rise at the design point are obtained for the regular impeller with only long blades and three complex impellers with long, mid or short blades. It is found that the back flow region between long-blade pressure side and mid-blade suction side is diminished and is pushed to pressure side of short blades near the outlet of impeller at suction side by the introduction of mid, short blades, and the size of back flow becomes smaller in a multi-blade complex impeller. And the pressure rises uniformly from inlet to outlet in all the impellers. The simulated results show that the complex impeller with long, mid and short blades can improve the velocity distribution and reduce the back flow in the impeller channel. The experimental results show that the back flow in the impeller has an important influence on the performance of pump and a more-blade complex impeller with long, mid and short blades can effectively solve low flow rate instability of the low-specific-speed centrifugal pump.