HDPE/PP共混物注射冷却过程中二维温度场的研究

采用数值模拟结合实验验证的方法,先建立高密度聚乙烯(HDPE)/聚丙烯(PP)共混物注射冷却过程中二维温度场的数学模型,根据改进焓法用Mathematica软件对模型进行求解计算得到共混物二维温度分布的模拟值;通过数据采集器对不同比例的HDPE/PP共混物注射冷却过程中的温度变化进行了数据采集,并将采集所得温度的实验值与模拟值进行了比较分析。结果表明:共混物在液相冷却段和结晶段温度分布的实验值与模拟值吻合良好,在固相冷却段实验值略高于模拟值。     

PE-HD/PP共混物注射成型冷却过程中温度分布的研究

依据傅里叶定律和能量守恒力一程的基本原理,对聚合物注射成型冷却过程进行了合理假设和必要简化,采用数学模拟结合实验验证的方法,对高密度聚乙烯(PE-HD)和聚丙烯(PP)共混物注射成型冷却过程进行了实验和数值模拟研究。采用数据采集器对不同比例共混物注射冷却过程中的温度变化进行了数据采集。结果表明,在冷却第一阶段纯PE-HD的冷却速率最快,在固相冷却段共混物的冷却速率较纯净物慢。将采集所得温度的实验值与根据改进熔法用Matlab软件对共棍物冷却过程中温度分布数值模拟计算所得的值进行了比较分析,结果表明,共混物在冷却第一和第二阶段的温度分布实验值与模拟值几乎完全吻合,在固相冷却段共混物的冷却受热导率和聚合物的形态结钩的共同影响,此阶段实验值略高于模拟值。     

聚丙烯气体辅助注射成型冷却过程中温度分布的研究

通过对聚合物气体辅助注射成型冷却过程进行合理的假设与简化,对聚丙烯（PP）气体辅助注射成型冷却过程进行了实验与数值模拟研究。结果表明,注射氮气后,PP的冷却速度显著加快,并在气-熔界面处出现小范围的结晶平台。采用MATLAB软件对氮气辅助注射成型PP冷却过程中的温度分布进行了数值模拟,将计算所得模拟值与温度采集的实验值进行比较,发现在熔体降温阶段温度分布的模拟值与实验值吻合程度很高;在固相冷却阶段由于聚合物本身复杂特性以及气体的渗透效应,PP的模拟值略高于实验值,而氮气的模拟值低于实验值。     

洗衣机面板注射成型CAE分析

应用Moldfolw Plastics Insight(MPI)软件的流动、冷却、翘曲变形模块对洗衣机用聚丙烯面板进行注射成型数值模拟,并对注射成型工艺条件进行了优化.优化后的聚丙烯注射成型工艺参数:熔体温度为240℃,模具温度为70℃,注射压力为32 MPa,保压压力为26 MPa,注射时间为5s,保压时间为30 s...     

注射成型薄壁制品收缩与翘曲因素

介绍了薄壁注射成型的充填、保压、冷却和残余应力的数值模型,并将集成的模拟程序对收缩翘曲问题进行定量地模拟分析.采用Taguchi 实验优化设计理论,用L₂₇（3¹³）正交表设计实验并进行了统计分析.研究了因素如熔体温度、模具温度、保压时间、保压压力、浇口尺寸和注射速率对收缩与翘曲的影响的显著性.得出优化工艺参数如熔体温度、模具温度、保压时间和压力能减少残余热应力;保压压力和熔体温度是影响收缩与翘曲的最显著因素.     

PMMA/PC复合平板叠层注射压缩成型翘曲变形计算模拟

建立了一种基于注射成型模拟软件Moldflow和有限元软件ABAQUS联合计算模拟的方法,以用于分析聚甲基丙烯酸甲酯/聚碳酸酯（PMMA/PC）复合平板叠层注射压缩成型的翘曲变形。通过两步法完成翘曲变形的数值模拟：首先采用Moldflow软件对叠层注射压缩成型进行充填、保压和模具内冷却分析;然后将Moldflow获得的制件脱模时温度场和网格文件导入ABAQUS进行分析,计算脱模后制件完全冷却至室温的翘曲量,将应力释放的翘曲值与完全冷却的翘曲值线性相加得到平板的最终翘曲。同时通过注射成型实验实测PMMA/PC复合平板的翘曲变形。结果表明,联合计算模拟结果与实验结果的匹配性较好。     

变模温注塑模瞬态温度场数值模拟与工艺优化

应用Autodesk三维有限元瞬态传热分析方法对变模温模具传热过程和模具与熔体之间的耦合传热进行了瞬态求解和数值模拟,获得了模具温度场的变化过程及分布规律。应用三维瞬态注塑模拟,结合正交试验设计,对变模温成型工艺参数进行了优化。数值模拟后获得的最优结果:热水温度150℃,熔体温度250℃,冷却时间4s,注射时间0.3s,保压时间2s,保压压力为注射压力的110%。最后对最佳工艺参数进行了数值模拟验证,获得的结果是最大翘曲变形量为0.180 mm。     

注塑制品翘曲变形的最显著影响因素

采用Moldflow进行了塑料制品注塑过程模拟实验,分析了模具温度、熔体温度、保压时间、保压压力、冷却时间、注射时间和速度/压力控制转换（V/P转换）对注塑制品翘曲的影响,从中确定影响最显著的注塑过程参数。首先按一次因子法进行实验,根据因子效应,各因子影响权重顺序为：保压时间>冷却时间>熔体温度>注射时间> V/P转换>保压压力>模具温度,其中熔体温度、保压时间、冷却时间、注射时间对制品的翘曲有明显影响;再采用田口实验方法对这4个因素进行模拟实验,用L9（34）正交表设计实验,根据实验数据计算信噪比以评判影响因子的权重,由翘曲信噪比、体积收缩率信噪比和缩痕指数信噪比三方面分析,发现熔体温度对制品翘曲的影响最为显著。     

四斜叶桨搅拌下釜内盘管非稳态对流传热过程的模拟和实验研究

搅拌釜内的强放热反应过程常常需采用内置螺旋盘管来增加换热面积,对带盘管搅拌釜内传热过程的数值模拟与盘管外侧对流传热系数的实验测定有重要的应用价值。今使用流体力学软件FLUENT对四斜叶桨搅拌下釜内盘管非稳态对流传热过程进行模拟,得到了搅拌釜内温度场分布和盘管内外两侧平均对流传热系数。模拟采用标准k-ε湍流模型和强化壁面函数,考虑了釜内液体黏度、导热系数随温度的变化关系。在模拟搅拌釜的非稳态冷却过程中,将搅拌釜内温度的变化过程分成四段,模拟得到四个釜温下的拟稳态温度场和对流传热系数,在此基础上计算得到全冷却过程的平均对流传热系数。为了验证模拟的可靠性,对盘管外侧对流传热系数进行了实验测定。模拟获得的盘管外侧对流传热系数值与实验值相比误差为22.5%,盘管内侧对流传热系数模拟值与经验公式计算值相比误差为2.6%,不同釜温下盘管出口温度模拟值与实验测定值偏差在1.52 K以内,表明所用模拟方法在工程上是可行的。     

基于AMI与正交试验的餐盘翘曲变形优化

针对塑料餐盘在注射成型过程中由于翘曲变形造成的中间凸起引起使用性能的缺陷,结合AMI注射成型分析软件和正交试验设计对餐盘的注射成型过程进行数值模拟,通过对试验结果数据的定量分析,系统分析了模具温度、熔体温度、注射速率、保压压力、保压时间、冷却时间等工艺参数对餐盘翘曲变形的影响规律和影响贡献率,从而得到最优的工艺参数组合,并模拟分析出最优工艺参数组合下的翘曲变形量。用数值模拟结果指导餐盘注射成型模具设计,并通过实际注射成型验证其明显改善了塑料餐盘的翘曲变形缺陷。     

Optimal temperature profiles for heterogeneous catalytic parallel reactions

The problem of determination of the optimal temperature profiles in a fixed-bed catalytic reactor for the catalytic parallel reactions including transport phenomena (external or internal diffusion) has been worked out.Special attention was given to predict the shapes of the optimal temperature profiles. The general considerations are illustrated by some numerical examples. It has been found that for every studied case the optimal temperature profile need not to end by the isotherm T = T_max.     

Analysis of reaction injection molding process of polyurethane-unsaturated polyester blends. Part I: Computer simulation

A computer simulation model was developed to analyze the reaction injection molding (RIM) process of polyurethane and unsaturated polyester blends. The reaction kinetics and viscosity functions of each component were obtained through actual experiments, and a mathematical scheme for numerical calculation was set up in cylindrical coordinates to predict the temperature and conversion profiles within a disc-type mold. The temperature change calculated from the simulation was compared with the temperature rise measured in actual RIM experiments. The effects of the feed temperature, wall temperature, and catalyst levels on the maximum exothermic temperature and the demolding time were evaluated in a search for the optimum processing conditions.     

Thermal analysis of thermoplastic composites during processing

Unsteady two-dimensional thermal analysis has been performed on PEEK/AS-4 fiber thermoplastic composites. To calculate the crystallinity of the composite, a spherulite growth model was applied. A numerical analysis was carried out with variations in mold cooling rate, the prepreg lay-up, and the composite geometry. The effect of geometry and the cooling rate is significant in the temperature profiles. The degree of crystallinity varies with the cooling rate, but the gradient of crystallinity is small, with the exception of complex geometries at fast cooling rates. The results of numerical calculations are in excellent agreement with the experiments and offer validation of the numerical formulation.     

Process monitoring and kinetics of rigid poly(urethane–isocyanurate) foams

Process temperature profiles of a two‐component rigid poly(urethane–isocyanurate) foam system were studied and compared with the predictions of a one‐dimensional numerical simulation. This model is based on experimentally determined thermophysical properties including thermal diffusivity, enthalpy of reaction, and rate of reaction. Temperature profiles were measured at three positions within the foam and at the foam surface for mold temperatures of 25°C and 55°C. A high rate of reaction and heat of reaction, along with low thermal diffusivity, cause temperatures near the foam center to be insensitive to mold temperatures for thick samples. Thermal analysis was used for determination of thermophysical properties. Temperature‐dependent heat capacity, reaction kinetics, and heat of reaction were evaluated using temperature‐scanning DSC. Thermal conductivity was analyzed from steady‐state heat profiles. The system reaction kinetics indicated much faster kinetics than reflected by process cure temperature profiles made using thermocouples. The simulations accurately predict experimental results, allowing determination of demold time dependence on process conditions, including feed temperature, mold temperature programming, and sample thickness. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 374–380, 2000     

STUDIES OF ADIABATIC FIXED-BED REACTORS (Ⅱ) STEADY-STATE TEMPERATURE PROFILES

One-dimensional heterogeneous model has been used for studying steady-state temperature profiles in adiabatic fixed-bed reactors.Since high temperature zone is determined by the temperature profile in the reactor, it is obviously of primary importance to study the effects affecting the steady-state temperature profiles. This paper shows how heat conductance of the packed catalysts, gas mixture and the reactor wall affect the temperature profile, and, a numerical example is given for illustration. It is indicated that the heat conductance of the laboratoryscale reactor wall is considerable and its effect is not negligible during scaling-up.     

Real-time measurements of temperature,pressure and moisture profiles in High-Performance Concrete exposed to high temperatures during neutron radiography imaging

High-Performance Concrete (HPC) is particularly prone to explosive spalling when exposed to high temperature. Although the exact causes that lead to spalling are still being debated, moisture transport during heating plays an important role in all proposed mechanisms. In this study, slabs made of high-performance, low water-to-binder ratio mortars with addition of superabsorbent polymers (SAP) and polypropylene fibers (PP) were heated from one side on a temperature-controlled plate up to 550 °C. A combination of measurements was performed simultaneously on the same sample: moisture profiles via neutron radiography, temperature profiles with embedded thermocouples and pore pressure evolution with embedded pressure sensors. Spalling occurred in the sample with SAP, where sharp profiles of moisture and temperature were observed. No spalling occurred when PP-fibers were introduced in addition to SAP. The experimental procedure described here is essential for developing and verifying numerical models and studying measures against fire spalling risk in HPC.     

Experimental and Numerical Investigations of an Ice-slurry Generator

A new test facility equipped with refrigerant and brine circulation systems, and a rotating-scraper ice-slurry generator was constructed to analyze the ice-slurry flow and heat transfer accompanied by phase change in an industrial generator. The axial and transverse brine temperature and ice fraction concentration profiles in the ice generator were measured. The heat transfer efficiency lower than the average was identified in the upper half of the ice generator and its cause was determined by conducting three-dimensional numerical simulation using a commercial CFD code, FLUENT. Approaches of improving the brine-side heat transfer rates were investigated by incorporating extra mixing blades from numerical simulation.     

微波敏化剂传热模型

介绍了采用敏化剂为内加热源，利用微波加热塑化聚合物的原理。通过空间离散建立了敏化剂在聚合物基体中为内热源加热塑化聚合物过程中的传热模型，进行了详细的理论推导，并给出了求解此传热模型的数值解法。     

Numerical observations on symmetric and asymmetric profiles in catalyst slabs

A numerical procedure is described for generating either symmetric or asymmetric steady-state mass and temperature profiles in a catalyst slab. Observations on the dynamic behavior of these catalyst slabs and the stability of the steady-state profiles are quoted. The validity of the frequently used assumption of symmetry or isothermality of a catalyst particle is also discussed.