连铸板坯滑动水口三维流场湍流计算模型比较

分别采用标准k-e模型、雷诺应力模型(RSM)和超声波多普勒测速(UDV)方法对滑板控制浇注流量浸入式水口内部和出口流动特征进行对比分析,并探讨湍流模型对滑板浇注系统数值模拟的适用性. 结果表明,由于滑板的节流作用,在滑板下方的水口内出现高度约为80 mm的二次流,在滑板下方100 mm处出现高度为50 mm的分离流,并在水口出口出现旋转出流,其方向由滑板堵塞侧、经水口底部向滑板开启侧旋转. 标准k-e模型计算的水口出流的旋转方向与UDV测量的旋转方向相反,RSM计算结果与实验测量结果比较吻合,具有更好的适用性. 并从分子动力理论角度、各向同性假设和历史效应等方面,分析了标准k-e模型存在的理论缺陷.     

Experimental verification of interstage sluice gate design equations

An attempt was carried out earlier to obtain design equations for a new setup of sluice gate to stabilize interstage brine flow in a multiple-stage flash desalination system, based on a two-phase momentum equation. These theoretically developed equations indicated that the sluice gate opening height could be easily obtained, which could maximize and stabilize the interstage brine flow and in turn increase availability and thermal efficiency of desalination plants.In the present work an experimental verification for the above mentioned design equations which governs the stability of interstage brine flow was carried out. A test rig was designed and constructed, which accommodates two adjustable sluice gates. The brine flow in the test section varied from 1.28 to 2.91 kg/s at a 5°C temperature drop per stage. The experimental results obtained indicated good agreement with the theoretical predictions based on earlier work.     

A semi-empirical algorithm for flow balancing in multi-cavity transfer molding

Multi-cavity transfer molding is an important process step in several electronic and photonic technologies. In some applications, uniform filling of the cavities of the mold, or mold balancing, is required. A semi-empirical flow model to predict mold filling patterns was developed. The algorithm is a one-dimensional network flow simulation that uses experimental pressure drop data to determine the volumetric flow rate through the gates and runners. A comprehensive experimental program was undertaken to determine these hydraulic resistances for different flow rates and mold geometries. A theoretical treatment is also described to compute hydraulic resistance from gate geometry. Uniform gate resistances provide unbalanced filling and higher velocities in the cavities. Balanced filling can significantly reduce the molding compound velocity and the flow induced stresses, but imperfect balancing compromises the benefits. Experimental filling patterns were obtained for two sets of gates. The agreement between the model and the experiments was satisfactory, and the discrepancies were attributed to correctable phenomena.     

Optimization of injection molding design. Part I: Gate location optimization

The placement of a gate in an injection mold is one of the most important variables of the total mold design. The quality of the molded part is greatly affected by the gate location, because it influences the manner in which the plastic flows into the mold cavity. Some defects, such as weldline and overpack, can be effectively controlled only by the gate location. Therefore, the product quality can be greatly improved by determining the optimum gate location. In this paper, we develop a general methodology for gate location optimization. We first quantify quality in terms of flow simulation outputs. We can thus assess detrimental effects such as warpage and dimensional instability as a function of the independent variable, which is in this case the gate location. Next we develop methods to search for the optimum gate location. The search method introduced in this paper is a method that combines a deterministic hill climbing search with a stochastic annealing search method. The method is appropriately called simulated annealing and hill climbing (SANHIL). The criteria used for evaluation during the search process are a function of the flow simulation outputs. We demonstrate the success of the method for a complex industrial mold. The approach is applicable to any complex mold geometry and any plastic.     

磁力搅拌器的故障分析和解决措施

介绍了聚酯装置中酯化反应釜磁力搅拌器的内部结构和工作原理,对磁力搅拌器运行中多次出现的轴承卡死等故障进行了分析并提出了解决措施。主要故障是物料在反应时产生的小颗粒堵塞轴承润滑孔及磨损轴承,导致轴承失效。通过增加过滤系统,在轴承内表面开设导流槽,保证冷却水流量,并加强在线监控,可减少设备故障。     

Optimization of filling process in RTM using a genetic algorithm and experimental design method

In the resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important issue in RTM processing is minimizing the cycle time without sacrificing part quality or increasing the cost. In this study, a numerical simulation and optimization process for the filling stage was conducted in order to determine the optimum gate locations. The control volume finite element method (CVFEM), modeled as a 2‐dimensional flow, was used in this numerical analysis along with the coordinate transformation method to analyze a complex 3‐dimensional structure. Experiments were performed to monitor the flow front to validate the simulation results. The results of the numerical simulation corresponded with that of the experimental quite well for every single, simultaneous, and sequential injection procedure. The optimization analysis of the sequential injection procedure was performed to minimize fill time. The complex geometry of an automobile bumper core was chosen. A genetic algorithm was used to determine the optimum gate locations in the 3‐step sequential injection case. Taguchi's experimental design method was also used for determining the pressure contribution of each gate. These results could provide the information on the optimum gate locations and injection pressure in each injection step and predict the filling time and flow front.     

Some relationships between injection molding conditions and the characteristics of vitrified molded parts

The various mold filling phenomena influencing the characteristics of fabricated parts are surveyed. The phenomena leading to jetting in injection mold filling are considered. These are associated with the magnitude of swell by the melt as it exits the gate into the mold. Special attention is given to the influence of non-isothermal runner flow. A theory of extrudate swell of polymer melts with temperature profiles is developed using Tanner's unconstrained recovery theory. In the. absence of jetting, mold filling by a simple advancing front takes place. The hydrodynamics of the advancing front and the stress fields in the flowing melt are determined. Analysis and modeling are presented based on the use of hydrodynamic lubrication theory involving a solid layer along the mold wall and a hot isothermal melt core. This theory is compared with experimental measurements of pressure losses in mold filling. The development of birefringence in injection molding processes is analyzed. Birefringence distributions are due to frozen-in flow birefringence. A new experimental study is presented and its results compared with theoretical predictions. The problem of thermal stresses in injection molded parts is considered.     

Experimental investigation on two-phase air/high-viscosity-oil flow in a horizontal pipe

The flow of very-viscous-oil and air through a horizontal pipe (inner diameter 22 mm) is experimentally studied. We first build and analyze the flow pattern map; a comparison between the air–water and the air–oil flow pattern maps shows a strong influence of the fluid properties. The experimental flow maps are compared with empirical and theoretical ones – Baker (1954), Mandhane et al. (1974), and Petalas and Aziz (1998) – showing a poor agreement. Experimental pressure gradients are also reported and compared with theoretical model, but also in this case the agreement is not very satisfactory. Finally, the elongated bubble velocity and length are measured and compared to model present in the literature. We conclude that the high viscosity of the liquid phase has a strong influence on the results and that the current models are not able to predict the flow features satisfactorily.     

The effect of interstitial air pressure gradients on the discharge from bins

This paper presents theoretical and experimental work on the effect of interstitial air pressure on the flow of granular materials from hoppers. In the first part of the paper, a theory is developed for the case of low Reynolds number flow in a conical hopper. In subsequent sections, the theory is extended to cylindrical bunkers, to higher Reynolds numbers, (where inertia effects cannot be neglected) and to cases where the compressibility of the gas is important. In all cases, the theory agrees well with experiment.     

Analysis of gate freeze‐off time in injection molding

Gate solidification time is an important topic in injection molding technology, as it determines cycle time, which itself is an important issue in the balance of the production process. In this work, a study of the effect of both gate and cavity geometries on gate solidification time was conducted, using a commercial polymer, injection molded with constant holding pressure into a rectangular cavity. Three cavity lengths were used, and for each, two cavity thicknesses were adopted. Special dies containing different gates were assembled in the mold. Gate thickness was found to be the most important factor determining gate sealing time. However the cavity geometry is also quite important. A clear indication on gate solidification could be drawn by analyzing time evolution of pressure distribution inside the mold. The solidification phenomenon leading to gate sealing was analyzed by a simple model, which also takes into account the effect of cavity geometry, by comparing the heat flow through the gate walls and the energy required to solidify the packing flow rate. Model results satisfactorily describe the main features of the experimental data.     

Solids transport in mixed-flow dryers

Mixed-flow dryers are broadly used in worldwide agriculture for the drying of grain, corn and rice but are also applied in industry. Although this drying process is well established, there is still a need to optimize the dryer apparatus. Unfavorable design can cause uneven mass flow and air flow distributions, broad residence time distributions and, hence, inhomogeneous drying histories of the particles resulting in non-uniform drying. The transport of solids in mixed-flow dryers has not yet been sufficiently considered and investigated. Therefore, the objective of this study is to derive basic equations on particle flow in mixed-flow dryers which are practically operated in the interrupted flow regime and equipped with discharge gates. The function of the discharge gate, the discharge characteristic and the solids mass flow rate were studied by varying the discharge and standstill times, respectively. The experiments were conducted at a semi-technical dryer test station with a transparent acrylic glass front wall using wheat as bed material. The fundamentals developed serve as a basis for further theoretical and experimental investigations. The future goal is to improve apparatus design and process control so as to homogenize the drying process, to increase energy efficiency and to save product quality.     

循环硫化床上升管中动态行为的拟流体模拟

The kinetic theory of granular flow (KTGF) is modified to fit the Einstein′s equation for effective viscosity of dilute flow. A pseudo-fluid approach based on this modified KTGF is used to simulate the dynamic formation and dissipation of clusters in a circulating fluidized bed riser. The agglomeration of particles reduces slip velocity within particle clusters, and hence results in two reverse trends: discrete particles are lifted by air while particle clusters fall down along the wall. The dynamic equilibrium of these two types of motion leads to the characteristic sigmoid profile of solid concentration along the longitudinal direction. The predicted solid velocity, lateral and longitudinal profiles of solid volume fraction and annulus thickness are in reasonable agreement with experimental results.     

Waves in a rivulet falling down an inclined cylinder

In the long-wave approximation, a theoretical model is developed to describe waves in a rivulet flowing down the lower surface of an inclined cylinder. The model equations are derived by the weighted residual method by projecting the Navier–Stokes equations onto the constructed system of basic orthogonal polynomials. The simplest case of quasi-two-dimensional waves is studied in detail. The stability of the rivulet flow is analyzed and dispersion dependences for linear waves are obtained. The characteristics of nonlinear steady-state traveling waves have been obtained by numerical method for the first time, and the spatial development of forced waves has been studied. The results of calculations are in good agreement with the available experimental data for various liquids in a wide range of parameters.     

Review on morphology development of immiscible blends in confined shear flow

The bulk dynamics of immiscible polymer blends during flow is relatively well understood, especially when the system contains Newtonian components. Recently, a number of studies have focused on flow of immiscible blends in confined geometries. In that case, the morphology development is not only affected by the material characteristics and the type of flow, but also by the degree of confinement. Here, we present an overview on the morphology development in immiscible two-phase blends in confined shear flow. Firstly, we focus on the typical microstructures that are observed in confined dilute blends. Secondly, in order to understand those peculiar morphologies, the systematic studies on single droplets in confined shear flow are reviewed. In addition to the experimental work, theoretical, phenomenological, and numerical models that include the effects of confinement are discussed.     

Production of Well-Controlled Laminar Aerosol Jets and Their Application for Studying Aerosol Combustion Processes

Generation of steady-state solid aerosol jets with controllable parameters is often necessary in experimental studies and industrial processes. Most of the current approaches use a fluidized bed to produce an aerosol flow and always introduce initial turbulence into the jet. Toproduce a laminar aerosol jet, flow straighteners and long tubes are used that make the design cumbersome and inflexible. In addition, in a fluidized bed-type system, the aerosol number density and gas flow rate are inherently interdependent. In a new apparatus described in this paper, metal aerosol is produced using an electrostatic recharging of particles in a DC electric field of a parallel plate capacitor, a so-called electrostatic particulate method. The powder is aerosolized within the capacitor without using any gas flows and only a small velocity, a laminar gas jet is used to carry the aerosol away from the chamber through a small nozzle made in the top plate of the capacitor. It is shown that the aerosol number density is controlled by an electric field, independently of the gas flow rate. The usefulness and flexibility of the new technique for the aerosol combustion studies is demonstrated. Preliminary results on characterization of the produced small-scale, laminar, premixed, lifted aluminum-air flames are reported. The flame propagation velocities are measured and compared to the earlier results; overall flame dimensions and radiation profiles are determined. Individual particle flame zones are visualized in the aluminum-air aerosol flame for the first time.     

一模多腔注塑模流道的优化设计

在注塑模设计中,分流道和浇口的设计对塑料成型的质量影响较大,一直是人机交互式流道设计的难点。对一模多腔注塑模流道的优化设计进行了初步探索,并对流道尺寸的理论计算及人机交互设计时的参数优化设置作了公式推导,得出了可以节省设计时间的经验公式。     

PRESSURE DROPS OF NON-NEWTONIAN PURELY VISCOUS FLUID FLOW THROUGH SYNTHETIC FOAMS

This work aims at giving a first insight of non-Newtonian fluid flow through synthetic foams.

At first, a review of experimental pressure drops measured with Newtonian fluids through various foams is proposed as well as a recall of a capillary-type flow model used to determine structural parameters. In this particular case of Newtonian fluid flow, a single equation is shown to correlate experimental data whatever the grade of the foam. Results of an image analysis study are also given; they allow to give a physical sense to the value of the equivalent diameter of pore given by the flow model.

In a second part, results of pressure drops measured with a non-Newtonian fluid are reported. A model allowing the determination of the pressure drops for non-Newtonian purely viscous fluid flow through packed beds of particles, based on the same capillary representation of porous media, is tested in the case of fluid flow through synthetic foams. The model predictions are acceptable for foams of high grades, but a discrepancy is observed for foams of low grades. An attempt is made to explain the underevaluation of pressure drops with the aid of results of image analysis.     

Dynamics of flow macro-formation and its interference with liquid surface in mixing vessel with pitched blade impeller

The paper deals with the experimental and theoretical study of flow pattern dynamics and their manifestation on the liquid surface in a flat bottomed cylindrical stirred vessel with inner diameter T = 0.29 m, filled with water to the height H = T. The vessel was stirred by down pumping a six-pitched blade impeller with pitch angle 45°, pumping downwards. Based on flow visualization in a vertical, and three horizontal planes, parameters describing flow macro-formation behaviour during its generation by the primary circulation loop, including the total time of flow macro-formation existence, were obtained. These experimental results were compared with the results calculated from a proposed theoretical model of flow macro-formation dynamics.In the next part of the contribution, the theoretical solution of quantitative expression for liquid surface swell dimensions is presented. The liquid swell is supposed to be an effect resulting from an interaction between the surface level and the flow macro-formation. The data obtained from the theoretical solution are compared with swell dimensions determined from the visual analysis of the liquid surface behaviour. Finally, the comparison of experimental and theoretical results is statistically analyzed and corresponding summaries are concluded.     

Numerical analysis of injection molding of glass fiber reinforced thermoplastics. Part 2: Fiber orientation

Numerical predictions of fiber orientation during injection molding of fiber-filled thermoplastics are compared to measurements. The numerical work successfully describes the flow of fiber-filled plastic during injection molding, using finite-difference solutions for the transport equations and marker particles to track the flow front. The flow is modeled as a 2-D, non-isothermal, free-surface flow with a new viscosity model dependent upon temperature, pressure, and fiber concentration. The fiber orientation is based upon solution to the Fokker-Planke equation. The comparison demonstrates fair agreement between predicted fiber orientation and experimental results for slow and fast injection speeds. For the slow speed case at 10 and 20 wt% fibers, the numerical and experimental works show that the fibers are more random at the flow front than at the centerline, and that the fibers become more aligned as they flow from the gate to the midstream region. At fast injection speeds, the agreement between the numerical and experimental works is not as good as at slow injection speed. Possible explanations for the discrepancies are that the flow is assumed to be simple shear when injection molding is known to be a pressure-driven flow, the fibers have an initial orientation for the runner rather than the assumed random orientation, the fibers that were displayed from the camera were more oriented just behind the flow front (owing to the fast injection speed), and the orientation requires more than a 2-D video image to represent a 3-D fiber orientation.