聚合物熔体与CO2气泡在螺旋流场中的动态特性研究

利用自行设计的长方形可视化流道进行了大量的试验，观察CO2气泡在聚合物熔体中的动态特性，分析了CO2气泡与聚合物熔体在螺旋流场及组合流场中的形态及变化。通过改变加工条件及控制参数，利用可视化流道和机头，观察并摄取了熔融聚合物中气泡的形态、变形、破裂等动力学现象，从实验观察角度出发，总结出CO2气泡在螺旋流场中的形态、分布，大小及变形等的影响因素。     

气体进入聚合物熔体时界面运动状态的研究

研究了气体进入聚合物熔体时界面的运动状态。结果表明，4气体经喷嘴进入聚合物熔体时所形成的气－熔界面的运动情况随进气压力、螺杆转速和熔体温度等的不同而发生变化，且气体在界面上各点的速度不同。气泡在熔体中的上升速度很小，可以忽略。在同一流场中，气－熔界面有一定的运动规律，而流场突变时，界面运动发生剧变。界面运动的变化直接影响界面形态和最终发泡制品的质量。     

聚丙烯非织造布熔喷过程的计算流体力学模拟研究进展

聚丙烯非织造布采用熔喷工艺制成,在过滤、阻菌、吸附、防水等方面性能优异,有着非常广阔的市场前景。熔喷工艺中的聚合物拉伸过程复杂且迅速,难以用实验观察。因此,为降低熔喷布生产成本,提高成品质量,计算流体力学（computational fluid dynamics, CFD）方法被广泛应用于该工艺过程分析之中,包括模头中的流道分析、喷射流场分析等。其中,喷射流场分析是主要应用方向,可为喷丝板结构优化、喷射流场优化等问题提供解决方案。本文简要介绍了聚丙烯非织造布熔喷工艺原理及其特点,主要对该领域中应用CFD模拟的相关研究进展进行了综述。文中指出,目前熔喷过程的CFD模拟一般基于喷射流场中的气流,没有考虑黏性聚合物纤维对其影响。然而,黏性聚合物纤维在高速高温气流条件下会发生振动,对射流流场的影响不容忽视。熔喷非织造布的关键问题是减小聚合物纤维的直径,提高熔喷非织造布的质量。因此,研究的重点应逐渐由气流场转变为纤维流场。虽然CFD已被广泛应用于熔喷过程模拟,但熔融状态下聚合物纤维流场模拟研究仍需要在未来的工作中进行展开。     

多相聚合物在正交剪切流场中相形态的模拟

借鉴多组分聚合物相分离的动力学方程，对共混过程的外界流场进行简化并推导了动力学方程。应用形态模拟的CDS算法，对推导的动力学方程进行了数值模拟。模拟结果给出了两相聚合物在简化的流场(正交剪切场)的作用下的相形态的演化过程，在一定程度上反映了共混过程的主要形态演化特征，同时指出了提高模拟精度的途径。本文为多相聚合物共混过程的形态模拟提供了一种新方法。     

偏光显微镜观察聚合物结晶形态的实验教学改革

"偏光显微镜观察聚合物结晶形态"实验项目是高分子物理实验中一个重要的实验项目,本文通过对实验内容的设计扩展,将传统的验证性实验项目转化为综合性实验项目,使学生能更加形象生动地理解各种聚合物结晶形态的形成机理,激发了学生的实验热情,教学效果良好。     

三螺杆挤出机与双螺杆挤出机混合性能的比较

利用聚合物流体分析软件Polyflow,对倒三角形排列的三螺杆挤出机和等规格的双螺杆挤出机的混合性能进行了深入分析。通过计算不同角度的拟稳态流场,采用示踪粒子法对聚合物熔体在流场中的动态混合情况进行三维等温数值模拟,在此基础上对粒子轨迹进行统计后处理,并分别采用混合指数、面积伸展率和停留时间分布表征流场的分散混合能力、分布混合能力和轴向混合能力,进而比较两种挤出机的混合性能。另外,在实验条件与模拟条件相同的情况下,进行了实验验证。模拟结果表明,三螺杆挤出机各方面的混合性能均优于双螺杆挤出机。实验结果表明,实验数据与模拟结果基本一致。     

基于DEM研究分形结构对剪切流场中团聚体分散行为的影响

应用于聚合物基和金属基纳米复合材料中的纳米颗粒易形成团聚体,极大降低了颗粒的比表面积和其优异性能,因此提高纳米颗粒在加工流场中的分散程度和均匀性具有十分重要的研究意义。使用自主开发的三维颗粒离散元软件DEMix3D,模拟了DLA和DLCA两种不同形态的团聚体在剪切流场作用下的形态演变过程,并通过碎片数、碎片加权颗粒数和可视化图像等结果分析了团聚体在分散过程中形态和结构变化及差异。研究表明:在剪切流场中,分形结构团聚体会发生剥蚀、破裂和重组行为;相比于DLA团聚体,DLCA团聚体在剪切流场中有更少的剥蚀和重组行为,且分散效率高,分散效果好。     

微注塑制品微观形态及性能最新研究进展

微注塑(μIM)被认为是最具灵活性、可靠性以及成本优势的聚合物微/纳器件制造技术之一。因尺寸效应影响,μIM过程中熔体流场明显不同于普通注塑过程,进而产生特殊的制品微观形态及其性能。本文分别从纯聚合物材料与聚合物复合材料两方面综述了μIM制品微观形态及其性能的最新研究进展。最后,对该领域未来的发展方向进行了预测。     

固体输送中聚合物形态的层析测量与分析

基于聚合物自由体积理论和应力应变关系，提出了对固体输送中聚合物形态进行计算机层析图像测量和形态特性撮与分析的新方法，实验表明，该方法不仅能对处于密闭空间的挤出聚合物形态进行动态、在线、非破坏性地测量，而且可以推导出固体输送中聚合物的形态与其性能之间的关系。     

超声速气体浸没射流的数值计算和实验

从实验和数值计算两方面研究了超声速气体射流在水中的喷射过程.用高速摄影机拍摄了三维水下超声速气体射流的流场.针对实验工况,基于VOF方法,建立水下超声速气体射流的二维轴对称数值计算模型,并开展了相关数值模拟.成功模拟了射流初期气泡运动演化的复杂过程;分析了水下超声速气体欠膨胀射流的流场结构,包括流场的压力和速度等参数分布以及变化规律.数值结果与实验结果对比得知数值计算结果不仅与实验数据吻合较好,而且给出了实验中没有发现的激波、膨胀波等流场结构.     

Behavior of Multicomponent Gas Bubbles in Glass Melts

A mathematical model is proposed to study the behavior of multicomponent gas bubbles in glass melts. The effects of the melt temperature on bubble radius, trajectory, and composition were studied as a function of time, both accounting for and disregarding bubble boundary motion. It is shown that accounting for the boundary motion results in shorter refining times, smaller bubbles, and larger concentrations of the gaseous species than if this motion is disregarded. It is also shown that the bubble trajectory is almost a linear function of time and that mass transfer has a very small effect on bubble trajectory and refining times; however, it has a strong influence on the bubble radius, which, in the absence of mass transfeir, increases linearly with the temperature.     

Bubble growth in the microcellular foaming of CO2/polypropylene solutions

This article is concerned with bubble growth dynamics in the CO₂/polypropylene microcellular foaming process. The effect of the melt strength on the bubble growth was thoroughly investigated in theory for the first time. The theoretical results indicate that enhanced melt strength effectively restrains the bubble growth and stabilizes the bubble oscillation. Higher melt strength leads to lower bubble growth rate, shorter growth time, and smaller ultimate bubble size. Compared to the melt strength, the viscoelasticity and the gas pressure have less effect on the microcellular foaming process. The bubble growth varies a little as the viscoelasticity is varied. The bubble oscillation and growth rate are enhanced with increasing gas pressure, which leads to the augmentation of the bubble size. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

对塑料发泡膨胀过程气泡振动的研究

研究了塑料发泡过程的气泡振动行为 ,通过对塑料熔体和气相气体同时进行研究 ,列出了气泡振动的控制方程 ,并进行了离散化处理和数值模拟 ,获得气泡振动的规律 ,讨论了气相气体和塑料熔体的粘弹性对气泡振动的影响 ,为有效控制塑料发泡过程提供理论依据     

Behavior of Bubbles in Glassmelts: II, Dissolution of a Stationary Bubble Containing a Diffusing and a Nondiffusing Gas

The effect of a foreign nondiffusing gas on the rate of shrinkage of an oxygen bubble in a soda-lime-silica melt was studied. The rate of change of bubble radius with time was computed using the quasi-stationary approximation. The effects of melt under saturation and initial fraction of foreign gas in the bubble are considered and compared with those calculated using previously derived expressions.     

矩形薄腔中聚合物熔体非等温注气充填的数值模拟

采用五参数Cross粘度模型,利用有限元和控制体积法对矩形薄腔中聚合物熔体非等温注气充填过程中不同时刻的气泡边界、熔体前沿、熔体压力场、温度场和速度场等进行了数值模拟,结果表明:气泡主体边界平行于模壁方向生长,其前沿总是先向中心线附近移动,再向中心线两边移动;熔体压力在气泡周围某一区域内保持不变且等于气压;对于充模时间很短的情况,除气泡附近外,温度在各处相差不大。     

Numerical simulation of bubble growth in a limited amount of liquid

In this study, we examined the growth of a spherical bubble in a limited amount of liquid by using a finite‐element‐based numerical simulation method. The bubble growth was assumed to be controlled by both momentum and mass transfer. A truncated power‐law constitutive equation was used to describe the rheology of the melt. The gas inside the bubble followed the ideal gas law. The gas concentration at the bubble surface obeyed Henry's law. A computer code was programmed to solve the equations with the Galerkin method. A backward Euler scheme was used to discretize time. Grids were remeshed after each incremental time step to ensure the accuracy of the numerical results. The bubble growth process was simulated with the code. The numerical results, such as the instantaneous bubble size, gas pressure inside the bubble, and gas concentration profile in the liquid, were predicted. The influences of the liquid volume, initial gas pressure, temperature, and rheology of the melt on bubble growth were also studied. The results of the bubble growth simulation in this study were in satisfactory agreement with others' work. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

低电导率工质中气泡的极化运动实验研究

为探讨电场作用下气泡在低电导率工质中的极化运动特性,采用高速数码摄像技术对气泡在正庚烷溶液中的生长和分散过程进行了可视化研究,并结合无量纲数分析了不同气体流量和施加电压下的气泡演变特征以及极化力主导的气泡运动规律。结果表明,增大电场强度可导致气泡生长周期缩短,气泡尺寸显著减小,产生频率加快。在低电场强度下,气泡运动主要表现为流体动力学特性;而在强电场作用下,气泡首先受极化力主导而表现为电流体动力学特性,其直线轨迹高度随Bo_E增大而增大。但随着电场强度在竖直方向上的衰减以及液相阻力影响,气泡运动速度不断减小;当气泡脱离极化力主导区域后,其运动再次表现为流体动力学特性,受尾迹诱导和气泡间相互作用影响,气泡在竖直方向上沿毛细管轴向四周扩散。     

Plasticization effects on bubble growth during polymer foaming

During polymer foaming with physical blowing agents, plasticization affects the melt viscosity, gas diffusivity in the melt, and the gas–melt interfacial tension. In this paper, we propose a model for plasticization during bubble growth, and estimate its effects under typical foaming conditions. The theoretical model incorporates well‐established mixture theories into a recent model for diffusion‐induced bubble growth. These include the free‐volume theories for the viscosity and diffusivity in polymer‐blowing agent mixtures and the density gradient theory for the interfacial tension. The viscoelasticity of the melt is represented by an Oldroyd‐B constitutive equation. We study the radial growth of a single bubble in an infinite expanse of melt, using parameter values based on experiments on polystyrene–CO₂ systems. Our results show that even at relatively low gas concentrations, plasticization increases the blowing‐agent diffusivity markedly and thus boosts the rate of bubble growth. In contrast, the reduction in melt viscosity and interfacial tension has little effect on bubble growth. Though not intended as quantitative guidelines for process design, these results are expected to apply qualitatively to typical foaming conditions and common polymer‐blowing agent combinations. POLYM. ENG. SCI., 46:97–107, 2006. © 2005 Society of Plastics Engineers