黏弹性聚合物熔体多相成型界面不稳定的机理分析

基于动网格法和EVSS/SU等混合有限元技术,建立了黏弹性聚合物多相成型界面不稳定的数值模拟系统,模拟结果与Matsunaga的理论研究和Yamaguchi的实验研究结论相符合。通过研究流率、黏度和松弛时间（弹性）对界面不稳定的影响规律,发现在相应条件下流率、黏度和松弛时间都能使界面变得不稳定,而界面两侧第一法向应力差的阶跃是导致黏弹性界面不稳定的根本原因,进而揭示了黏弹性界面不稳定的机理,并对生产实践提出了若干指导原则。     

弹性体挤出流动中第一法向应力差的预测

本文探讨了如何通过聚合物熔体流变特性参数的测量来估算挤出流动中第一法向应力差Ｎ１的问题。简要评述了这方面研究的进展。提出了两个描述Ｎ１与其他流变参数如挤出胀大比的关系式，并进行了比较和分析。     

内胎胶挤出流动中第一法向应力差的预测

用毛细管流变仪考察了内胎胶挤出口型膨胀行为。基于实测的挤出胀大比数据,借助相关的公式估算了试样的第一法向应力差（Ｎ１）,并与几个熟知公式的预测结果进行了比较。结果表明,预测的Ｎ１与用Ｂａｇｌｅｙ等和Ｇｒａｅｓｓｌｅｙ等提出的公式的计算值较为接近。     

聚合物多相分层充模流动成型的界面不稳定形成的数值分析

基于聚合物多组分成型技术的工程背景建立了全三维非稳态非等温多相分层充模流动的理论模型,提出了求解理论模型的稳定高效的数值算法,通过数值模拟给出了不同流变性能参数、过程条件下聚合物多相分层充模流动成型过程的界面不稳定形成过程和不稳定界面形貌的定量对比,在此基础上通过理论分析,揭示了界面不稳定的产生机理,并研究了流变性能参数和过程条件对分层界面形貌和界面不稳定影响的规律.模拟研究表明,模拟结果与Mohammad等的实验研究结论相吻合.     

聚合物多相分层充模流动成型的粘性包围形成机理数值分析

基于聚合物多组分成型技术的工程背景，建立了全三维非稳态非等温多相分层充模流动的理论模型，提出了求解理论模型的稳定高效的数值算法。通过数值模拟，给出了不同流变性能参数、过程条件下多相分层充模流动成型时的粘性包围形成过程和其形貌的定量对比。在此基础上，通过理论分析，揭示了粘性包围的产生机理，并研究了流变性能参数和过程条件对分层界面形貌和粘性包围影响的规律性关系。模拟研究表明，模拟结果与Bamin Khomani等的实验研究结论相吻合。     

黏弹性复杂流动的微观-宏观确定性模拟

Deterministic simulation approach was applied to simulating viscoelastic complex flows,in which,the SIMPLE algorithm based on collocated grid was used to solve the conservation equations on the macroscopic level and the spectral method was used to solve the Fokker-Planck equation on the mesoscopic level.Here,the transient 4∶1 planar contraction flow for dilute polymer solution was computed by using the coupled technique and the calculated polymeric stress distributions at steady state were identical with the results of continuum approach as well as the corresponding references.Therefore,the presented results indicated that the SIMPLE algorithm based on collocated grid coupled with the spectral method can be used to simulate viscoelastic complex flows effectively.Moreover,the influence of Deborah number and viscosity ratio on polymeric stress was also investigated.     

聚合物热黏弹塑性变形微热压成型机理的数值模拟研究

研究了聚甲基丙烯酸甲酯（PMMA）超疏性阵列圆柱微结构特征功能表面的微热压成型技术,通过模拟研究了成型工艺参数对成型过程的影响规律,揭示了其热黏弹塑性变形充填流动机理,明晰了关键调控参数。结果表明,基片材料的弹性模量、成型温度和压力是影响充填成型的关键调控参数,成型压力和变形应力与成型温度呈负关联关系,而充填高度与成型温度呈正关联关系;提高成型温度至高于基片材料的玻璃化转变温度（Tg）,使基片处于黏弹性高弹态,易使基片快速产生明显的热黏弹塑性变形,且可使成型压力和变形应力趋于最小值,这有利于基片避免断裂损伤并加速充模流动。     

基于黏弹性模型的PMMA微流控芯片模内键合微通道变形研究

针对聚合物微流控芯片模内键合过程中微通道变形的问题,采用黏弹性材料模型对聚甲基丙烯酸甲酯(PMMA)微流控芯片模内键合过程中具有梯形截面的微通道变形进行了仿真分析;研究了在105℃下,芯片微通道在不同键合压力和键合时间下微通道的变形。结果表明:微通道不能保持键合前的尺寸,温升对微通道变形影响很小;微通道顶部与两侧的黏合使得微通道顶部宽度和微通道高度变形远大于底部宽度变形,并随着键合压力的增大而增大;当键合时间超过50 s后,键合时间对微通道变形影响很小,可以采用较长的键合时间来保证键合强度而不影响微通道形貌。     

基于激光后向散射法的湍动流化床颗粒流动参数测量

提出一种基于激光后向散射法的集成测量系统,用于湍动流化床上升管内颗粒速度和浓度的空间分布测量。在湍动流化床上升管上,使用双激光光纤探头获得各测点速度、浓度的光信号,经过信号转换和数据采集后最终在计算机上显示。实验结果表明:该系统能够准确测量湍动流化床颗粒流动参数;上升管内,颗粒分布呈中心稀而壁面浓的现象;随着流化风量的增加,床内颗粒速度增加,但浓度降低;上升管中心区域,颗粒速度随轴向高度的增加呈先增加后减小的趋势。     

ELM法提取磷酸中La3+的相界面反应-传质机理研究

在以(D2EHPA+TOPO)/ROSO3H/液体石蜡/煤油为膜相,HCl为内相,磷酸中La3+为外相的乳化液膜(ELM)体系中研究了不同相比A/O、膜相D2EHPA(H2A2)、TOPO、ROSO3H浓度、料液相H3PO4、H2PO4和H+浓度和内相HCl浓度对总分配比DT的影响。实验结果表明:随A/O的增加,DT显著下降;随膜相H2A2、TOPO、ROSO3H浓度的增加,DT先增加后基本不变;但料液相H3PO4和H+浓度的增加使DT降低,DT随H2PO4浓度增加而升高;DT随內相HCl浓度的增加而升高。通过斜率法对ELM各组分H2A2、TOPO、ROSO3H、H2PO4、H3PO4、H+的logc-logDT的线性拟合直线的斜率确定了其参与的摩尔数,得到了该ELM体系的相界面反应-传质机理,并计算出萃取、反萃反应平衡常数k1、k2分别为107.7237、104.8025。     

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimented data are presented for the void fraction aud the shear stresses of stratified gas-liquid flow in a pipe, A new technique was used to measure the interface shear strew. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress prone at the gas-liquld interface. A new formula ,relatiog to the interfacial friction factor with the void fraction and superficiol gas Rcynold number, was dewloped to predict the interface shear stress. The predicted values are in good agreement with experimental data.     

Numerical Simulation of Oil‐water Hydrocyclone Using Reynolds‐Stress Model for Eulerian Multiphase Flows

A three‐dimensional oil‐water turbulent flow and oil separation process in a double‐cone liquid‐liquid hydrocyclone (LLHC) is numerically simulated using FLUENT software. The Euler‐Euler approach and Reynolds‐stress model are combined and adopted in this simulation to handle the challenging situation of anisotropic turbulent two‐phase flow with a higher volumetric ratio (over 10%) in the dispersed phase. It is visualized well in the simulation how separation, aggregation and shift of oil and water proceed in the LLHC. The oil separation efficiency is determined based on flow field and phase concentration distribution. The simulation is verified by comparing predicted and measured separation efficiency in the LLHC.     

Robust Direct Numerical Simulation of Viscoelastic Flows

Many technical processes involve viscoelastic flows, which makes the subject interesting for CFD. Despite the complex fluid rheology and related numerical problems in solving the constitutive equations, recent stabilization approaches allow for a robust simulation of viscoelastic flows in the technical relevant range at high degrees of fluid elasticity. A recent general‐purpose numerical stabilization framework, based on the finite‐volume method of OpenFOAM is presented and its capability for the robust simulation of viscoelastic single‐, as well as two‐phase flows is shown.     

Numerical Simulation of Interfacial Closures for 3D Bubble Column Flows

Numerical investigation of flow hydrodynamics in a square cross‐sectioned bubble column was conducted in a transient Euler‐Euler environment by applying the simulation tool Ansys CFX 14.0. The influence of the drag coefficient (C_D) was investigated and the results were also compared with drag force models. Furthermore, three different lift force models and a defined lift coefficient were studied. All results were compared with the available experimental data. All simulations were carried out for a single‐hole sparger with given aspect ratio (H/D) and superficial gas velocity.     

气固并流向上流动中颗粒聚集的机理

Two-dimensional unsteady cocurrent upward gas-solid flows in the vertical channel are simulated and the mechanisms of particles accumulation are analyzed according to the simulation results. The gaseous turbulent flow is simulated using the large eddy simulation （LES） method and the solid phase is treated using the Lagrangian approach, and the motion of the gas and particles are coupled. The formation of clusters and the accumulation of particles near the wall in dense gas-solid flows are demonstrated even if the particle-particle collisions were ignored. It is found that a cluster grows up by capturing the particles in the dilute phase due to its lower vertical velocity. By this way the small size clusters can evolve to large-scale clusters. Due to the interaction of gas and particles, the large-scale vortices appear in the channel and the boundary layer separates from the wall, which results in very high particle concentration in the near wall region and a very large-scale cluster formed near the separation point.     

气固并流向上流动中颗粒聚集的机理

1 INTRODUCTION Cocurrent upward gas-solid flows are widely used in industrial situations such as circulating fluid- ized bed, fluid catalytic cracking and pneumatic transport. Due to its industrial relevance, many quan- titative experimental and numerical investigations have been carried out[1―4]. Investigations show that upward gas-solid flow always appears heterogenously structured and the distribution of particles is always non-uniform unless the solid phase is very dense or very dilut…     

Tomographic Measurement Techniques – Visualization of Multiphase Flows

Tomographic measurement techniques have become increasingly popular for the application in the field of chemical and process engineering. With this techniques, the fields of density, concentration, temperature, velocity or local void fraction can be measured without interfering with the multiphase flow. These fields are often either instationary or even have transient character. Therefore, the used tomographic measurement techniques have to have a high spatial and temporal resolution. In this paper known tomographic measurement systems are described and compared to each other. The sensor systems and reconstruction methods are explained. As an example, the applications of electrical and x-ray tomography are described for the imaging the flow inside random and structured packings. With the electrical tomographic measurement technique a temporal resolution of up to 100 frames per second is achieved, whereas with the x-ray tomography spatial resolutions of 0.4mm are possible.     

A Model for Primary Normal Stress Difference of Dynamic Extrusion of a Polymer Melt through a Capillary

The dynamic extrusion process of a polymer melt through a capillary under a superimposed vibration has been was researched deeply, and a mathematical model for the primary normal stress difference of a polymer melt under the vibration force field was set up. Accordingly, the calculation steps of above primary normal stress difference were established based on a rheological measuring equipment which was disigned by the authors. The primary normal stress difference of polymer melt under a vibration force field can be calculated by measuring the instantaneous data of capillary die swell, capillary entry pressure, capillary volume flux, and their phase difference under vibration with different frequencies and amplitudes.     

颗粒群研究：多相流多尺度数值模拟的基础

用两流体模型及颗粒轨道模型数值模拟过程工程设备中的多相流,都需要表达浓度较高的分散相和连续相间的作用力的本构方程. 本工作综述了多相流中颗粒受力研究的现状和尚待解决的问题. 对单个颗粒(包括流体颗粒)在静止和运动流体中的受力情况的研究结果比较丰富,但对颗粒群的研究则很不充分. 对颗粒受的曳力研究较多,但还缺乏可信的计算升力、非稳态力等的公式. 因此颗粒群的研究成为多相流准确多尺度数值模拟的关键. 开发能处理整体和局部均存在非均匀性的多相流的高效算法也是有待克服的困难.     

多相混输管道弯管流动腐蚀数值计算

凝析气田管道中含有气液两相,在弯头处经常发生腐蚀穿孔现象。针对这一现象,利用计算流体力学方法,根据流体流动的规律,建立了弯管流动腐蚀的数学模型,运用有限元法来解方程。研究发现弯管的流动腐蚀与流体的运动息息相关,多相流经过弯管后流速、液相分布、湍动能、压力的大小和分布都发生了变化,引起管壁处某些部位剪切应力、含液率、湍动能、压力发生变化,加速了弯管的腐蚀。研究结果可以为弯管流动腐蚀的理论研究和多相混输管道安全管理提供指导。