注塑冷却分析模内复膜数学模型建模

由于模内复膜工艺是在模具内将塑件表面增加一层薄膜,本文利用注塑冷却分析将模具型腔表面离散为平面三角单元的特点,将薄膜和塑件视为两层具有良好接触的平板,对于每一层平板,建立第一类边界条件下一维非稳态导热模型,并将该导热模型应用到冷却分析中,完成了模内复膜冷却分析的建模.     

注塑冷却分析BEM模型中积分项的计算

注塑冷却分析最终归结为求解模具表面温度场BEM方程组,方程组中存在大量的积分项,这些积分项很难用解析式表示,因此无法求得它们的精确解析解,多采用高斯数值积分获得近似数值解,计算精度较低。本文采用近似解析解和半解析解代替原来的数值解,使得关键部位积分计算的精度提高了10％以上,不仅有利于提高冷却分析的精度,也有效地改善了边界元方程组的性态。     

注塑结晶性塑料平板冷却时间的讨论

对注塑结晶性塑料平板的冷却问题进行了分析。注塑结晶性塑料平板的冷却模型实质是伴有相变的不稳定一维导热。通过Neumann方法求得了这一模型冷却时间的数值解，并与其他方法进行了比较。     

带嵌件的注塑模具温度场数值模拟

冷却分析（模具温度场计算）是注塑成型计算机辅助工程的关键技术之一,在优化模具设计、提高制品质量方面具有重要作用,本研究提出了采用边界元法建立带嵌件的注塑模具温度场数值模拟的方法,并针对嵌件与模具接触面上的边界条件给定的关键问题,采用耦合边界元法对其转化,将嵌件与模具接触面上的边界条件转移到嵌件与塑件制品的接触面上,使得它的计算可以采用解析法替代原来的差分法,有效提高了分析计算的精度。     

注塑模温度场的计算机模拟

本文运用有限元法，采用二次等参单元，对注塑模二维非稳态温度场进行了数值分析，推导了有限元数值求解方程并研制了有限元求解程序软件。实例所得温度场等温线与实验所得结果基本相符，验证了计算机求解的可靠性。通过计算机模拟分析，可了解各瞬时模具温度场的分布状态，观察模具体能否使塑件均匀冷却，如不合理，可通过改变冷却管道参数，达到温度场均匀一致，从而提高塑件质量。通过程序运转，根据塑件的热定型温度，可以预知最短冷却时间，从而缩短冷却周期，提高塑件生产率     

模流分析在汽车后视镜外壳模具设计中的应用

以后视镜外壳为例,研究了模流分析软件在注塑模具设计中的应用。基于后视镜外壳工艺性分析,建立了塑件的双层面网格模型,根据塑件浇口位置分析结果和外观要求确定了浇口位置在塑件表面凹槽内,结合该模具设计创建了一模两件的热流道浇注系统模型;对塑件进行了冷却-填充-保压-翘曲整个注塑成型过程的模拟分析,两个塑件能实现平衡浇注,冷却回路液进出口温差在允许范围内,通过翘曲分析发现影响塑件翘曲变形的主因是收缩变形,该变形可通过调整保压曲线进行优化。本模流分析应用可对壳体类模具设计提供借鉴。     

斜扣手深腔抽屉的注射模设计

分析了斜扣手深腔抽屉的工艺特点,阐述了该塑件注射模的结构设计和工作过程。结合模流分析结果确定了浇口位置;采用斜顶内抽芯机构和液压外抽芯机构实现扣手位的成型和顺利脱模;设计了多股循环冷却水路,塑件得到均匀冷却。实践证明,模具结构设计合理,工作稳定。     

平板手机后盖注塑成型CAE模拟与正交优化

以平板手机后盖为例,基于CAE软件Moldflow对该手机后盖塑件浇口数量与位置、充填和冷却进行分析;为减小塑件的翘曲变形,采用正交试验方法进行成型工艺参数模拟;通过极差与方差法对试验数据进行分析,得到了四个工艺参数对翘曲变形的影响程度及最佳组合工艺条件。结果表明:CAE的应用可以改善塑件的翘曲变形,得到模具合理的结构设计方案,缩短模具开发周期,提高企业核心竞争力。     

斜滑块侧抽芯水壶注塑模设计

分析了水壶塑件的结构特点,介绍了水壶注塑模的结构与工作过程。采用斜滑块进行外侧抽芯,利用开模力驱动推板脱出塑件,在斜滑块和动模型芯中开设冷却水道加强对塑件的冷却,保证了塑件的质量。     

注射塑料制品冷却时间分析

塑料制品在注射生产过程中,塑件冷却时间占整个注射生产周期的80％左右~(1),因此,冷却时间的长短决定了生产率的高低。合理地安排注射、保压和冷却时间,可大大提高注射生产的效率。本文从传热学出发,导出了平板,柱体和球体塑件冷却计算公式,并运用计算公式对塑料制品的冷却时间加以分析。     

用于超结构换热器网络热计算和网络综合的显式解

For the optimal design of a heat exchanger network, the inlet and outlet stream temperatures of each heat exchanger in the network should be known. An explicit analytical solution of stream temperatures of an arbitrary connected heat exchanger network was introduced, which is suitable for the thermal calculation of heat exchanger networks. For the heat exchanger network synthesis, this solution was further developed and coupled with the stage-wise superstructure heat exchanger networks. The new calculation procedure reduced the computer memory requirement dramatically. On the basis of this solution, a mathematical model for synthesis of heat exchanger networks with genetic algorithm was formulated, which is always feasible and no iteration is needed. Two examples were calculated with the proposed approach and better results were obtained.     

Mathematical Modeling of a Continuous Vibrating Fluidized Bed Dryer for Grain

A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine the heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results.     

Heat Transfer Phenomena of Power Law Fluids in Double‐Pass Heat Exchangers with Isoflux Conditions

A new design of conjugated heat transfer in double‐pass parallel‐plate laminar countercurrent operations of power law fluids under wall isoflux was investigated experimentally and theoretically. The analytical solutions were obtained with a superposition model by introducing an eigenfunction expansion in terms of a power series for the homogeneous part and an asymptotic solution for the inhomogeneous part. The influence of the power law index on the average Nusselt numbers with the various design and operating parameters is also delineated. The theoretical predictions of the experimental results are represented graphically. The heat transfer performance was considerably improved when compared with a single‐pass parallel‐plate heat exchanger (without inserting a solid separator sheet). Suitable adjustments of the solid separator sheet position can effectively enhance the heat transfer efficiencies for such a recycling double‐pass device, as compared with the efficiencies of single‐ and double‐pass devices.     

滚塑工艺加热阶段的传热模型的解析解

对从滚塑模具开始受热到其内部粉料开始熔融之间的加热阶段建立一个传热理论模型。在该模型中,忽略模具、内部空气和粉料的温度梯度,即各自只有一个随时间变化的平均温度。将模具的内部分成内部空气区域和粉料区域。内部空气和粉料在与模具发生对流换热的同时,这两者之间通过掺混也在发生对流换热。根据能量守恒原理,对模具、内部空气和粉料分别列出热能平衡方程式,然后通过简化和求解常微分方程组得到了它们平均温度的解析表达式。由此计算所得的内部空气温度与其实验结果吻合的较好,从而证明了此传热模型及其解析解的准确性。     

第一类边界条件下板状多孔物质中分子扩散型传质时升华问题的摄动解

本文用摄动方法分析了板状多孔介质在第一类边界条件下Fick分子扩散传质时的升华干燥问题.基于对问题本质特征的分析,提出了运动界面处边界条件的处理的新方法,得到了无量纲形式的温度、浓度及运动界面位置的解析表达式.理论与实验结果的比较表明,摄动解比准稳态解更接近于实验结果.     

A monogenetic algorithm for optimal design of large-scale heat exchanger networks

The optimal design of large-scale heat exchanger networks is a quite difficult task not only due to its non-linear characteristics but also due to a great number of local optima in its solution space. An explicit analytical solution of stream temperatures for the superstructure heat exchanger networks was developed, which reduces number of decision variables significantly. Based on this solution, a mathematical model for synthesis of heat exchanger networks was formulated for searching the optimal configuration of a heat recovery system by a hybrid genetic algorithm. For large-scale heat exchanger networks, a monogenetic algorithm based on the optimization of sub-networks is proposed. In the first step of the optimization, the hybrid genetic algorithm is applied to the synthesis of the whole heat exchanger network for finding the functional groups (sub-networks) rather than the chromosomes (positions of the heat exchangers and splits of the streams) and genes (areas and heat capacity flow rates). Then the monogenetic algorithm for evolution of the functional groups is carried out to improve the HEN. This procedure was applied to examples taken from literature and better results were obtained.     

Condensational Growth and Evaporation in the Transition Regime

The condensational growth and evaporation of liquid droplets in the transition regime and in the continuum regime are considered. An analytical solution that includes both transition regime corrections for mass and heat transfer and the Kelvin effect is derived. The solution represents an improvement over earlier analytical solutions, which are valid only in the continuum regime. The growth (evaporation) times predicted by the analytical solution are compared with the times obtained by a numerical solution. In the transition regime the new analytical expression estimates the growth time within 20%. The closer the saturation ratio is to unity, and the smaller the latent heat of vaporization of the substance in question, the better is the accuracy of the new expression     

Fractional thermoelectric viscoelastic materials

A new mathematical model of thermoelectro viscoelasticity theory was constructed in the context of a new consideration of heat conduction with fractional order. The state space approach developed earlier by Ezzat was adopted for the solution of a one‐dimensional problem in the presence of heat sources. The Laplace‐transform technique was used. A numerical method was employed for the inversion of the Laplace transforms. According to the numerical results and their graphs, a conclusion about the new theory was constructed. Some comparisons are shown in figures to estimate the effect of the fractional order parameter on all of the studied fields. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Numerical and experimental analysis of resin flow and cure in resin injection pultrusion (RIP)

This work presents the results of modeling, numerical simulation, and experimental study of resin flow and heat transfer in the resin injection pultrusion (RIP) process. A control volume/finite element method (CV/FEM) was used to solve the flow governing equations, together with heat transfer and chemical reaction models. Resin viscosity, degree of cure, and fiber stack compressibility and permeability were measured in order to understand their influences on the process. An analytical flow model has also been develped based on the one‐dimensional flow approximation for the resin flow in the injection die. A high‐pressure small‐taper injection die was tested with different line speeds. Experimental data were used to verify the simulation results and the analytical solutions.     

考虑结壳现象的液滴干燥过程数值模拟

为更清楚地了解液滴的干燥过程,文中综合考虑溶剂扩散系数与溶液质量分数,溶液质量分数与液滴表面蒸汽压和滴径变化与传热传质之间的耦合关系,建立了包含液滴内部径向热传导方程,液滴内部的传质方程及液滴质量变化方程的液滴蒸发的完整模型。用所建模型对不同操作工况下液滴的挥发过程进行了模拟,描述了干燥过程中液滴质量损失,滴径的变化及液滴表面到中心的溶液组分变化,并对影响液滴干燥速度的重要因素进行了分析。模型模拟结果跟实验结论比较一致。