共查询到19条相似文献,搜索用时 187 毫秒
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为了了解勾形磁场下相关参数对CdZnTe晶体生长的影响,利用有限元法对坩埚内的热量和动量传递过程进行了全局数值模拟。分析了不同的磁场强度下重力水平、壁面温度梯度对CdZnTe晶体生长过程的影响。结果表明:重力水平存在1个临界值,此时CdZnTe熔体内最大流函数最小,流动最弱。随着温度梯度逐渐增大,熔体内最大流函数也逐渐增大,熔体的流动越来越强,不利于晶体稳定生长。通过施加勾形磁场,能有效抑制熔体内的流动,有利于晶体的稳定生长,为地面条件下制备大尺寸CdZnTe晶体创造了条件。 相似文献
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将撞击流结晶器应用于吡唑酮晶体的连续化生产过程,考虑到此晶体形成与原料液混合效果的关联性,选用丁酮酰胺水溶液和水作为液液流体介质。利用CFD模拟得到一种撞击流连续化结晶器内的流场分布并对流场进行分析,讨论撞击流结晶器内原料流速对混合性能的影响,研究撞击流连续化结晶器轴向速度、切向速度和近壁面流速随水的进口流速的变化规律,以及结晶器内沿轴向和径向的速度分布情况,根据混合均匀度指数评判结晶器中水在不同进口速度下的混合效果。计算结果表明:在丁酮酰胺水溶液进口速度为2 m/s及其他条件不变的情况下,水的进口流速增加会导致撞击流结晶器内混合均匀度指数降低,流场中流速分布更加不均匀,并且撞击混合区流体的切向速度随之升高,因此水的进口流速适度减小有利于晶体的生长。 相似文献
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应用基于边界保角变换技术的Galerkin有限元方法,研究熔体生长中动力学效应和自然对流的耦合作用探究了对流对生长系统中的温场分布、相界面2以及界面过冷度的影响。研究结果表明:自然对不充可使相界面的弯曲度减小,界面的相对位置降低,同时,对流使得小面端点处的夹角变得圆滑,小面域和粗糙面域的界线变得不明显,相应地,小面尺寸有所减小。 相似文献
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The effects of crystal growth rate and heat and mass transfer on solute distribution during solidification of binary melt have been theoretically investigated on the basis of a new theory of solute distribution proposed by the present authors. The solute distribution factor f at the solid-liquid (SL) interface is in inverse proportion to the one-half power of the dimensionless growth rate U. The growth rate U is in proportion to the second power of the normalized concentration difference between the SL interface and bulk melt. A new transport factor K, which describes heat and mass transfer in melt, gives an important contribution to the crystal growth and the solute distribution at the SL interface. The transport factor is used successfully to control the solidification of melt. The flow structure in melt exerts essential influence on the solid purity. 相似文献
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应用熔体流动速率仪考察了口模半径、载荷及温度对聚全氟乙丙烯(FEP)流动性能的影响。结果表明:FEP熔体的表观黏度随着剪切速率、温度、载荷和口模半径的增加而降低,表现出假塑性流体行为。应用差示扫描量热法测定FEP的熔融和结晶温度及热焓,发现:与聚四氟乙烯(PTFE)相比,FEP熔点较低,熔融热较低,结晶度较小,而且熔融峰较宽。 相似文献
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为有效控制晶体尺寸、金属杂质含量、掺杂元素及氧分布的均匀性,提出在非均匀轴对称勾形磁场中利用磁控提拉法生长硅单晶。用有限差分法对非均匀轴对称勾形磁场中直拉硅单晶体系中的浓度场进行数值模拟研究,基于直拉硅单晶生长系统的物理及数学模型,进行无量纲化处理,借助于相应的边界条件进行求解,并针对不同工艺条件下熔体中及界面处氧浓度分布情况进行模拟研究。结果表明:在勾形磁场作用下,通过改变磁场强度、晶体和坩埚转速及晶体半径可有效控制固一液界面处氧浓度及分布均匀性,从而在晶体中获得径向均匀的氧浓度。 相似文献
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注塑成型过程中,熔体在型腔中的流动和传热对制品质量性能有重要的影响.为了预测注塑制品的收缩、翘曲和力学性能,精确预测充填过程的流动及传热历史是十分必要的.本文考虑熔体的可压缩性及相变的影响,将充填过程中熔体的流动视为非牛顿可压流体在非等温状态下的广义Hele-Shaw流动.采用有限元/有限差分混合方法求解压力场和温度场,采用控制体积法跟踪熔体流动前沿,并应用Visual C++实现了注塑充填过程的可压缩流动分析.为了保证能量方程各项在单元内边界的连续性,结点能量方程各项由单元形心处的离散值加权平均获得,因而,能量方程在计算区域内整体求解.对两个算例进行了分析,模拟结果与实验结果的对比,验证了本文数值算法及程序. 相似文献
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Single crystal of butyl branched polyethylene with various molecular weight formed from the melt in the presence of electric field was studied. It was found that electric field influenced morphology and structure of the butyl branched polyethylene single crystals formed. The lateral habits of the single crystals were circular shape, which was different from truncated lozenge or lenticular shape single crystals formed from the melt in the absence of electric field. The stems in the single crystals formed in the presence of electric field were perpendicular to the basal plane of the single crystals, which was different from chain tilting in single crystals formed from the melt in the absence of electric field. The electron diffraction patterns showed that the structure of the circular single crystals was a quasi-hexagonal with looser chain packing. This looser chain packing was favorable to thickening growth of single crystals through chain sliding diffusion. The thickness of the single crystals was much larger and depended on molecular weight. It indicated that the single crystal in the presence of electric field should be an extended chain type single crystal. 相似文献
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Summary We have synthesized a paramagnetic organometallic liquid crystal polymer containing a tetradentate Schiff base complex of copper II. The main chain liquid crystal polymer forms when the functionalized complex is combined at 220°C with the melt of a low molecular weight terpolymer. The terpolymer is a nematic liquid crystal at this temperature and contains oxybenzoate, dioxyphenyl, and pimeloate structural units. The organometallic material melts reversibly into a liquid crystalline fluid at a slightly lower temperature than the terpolymer. In external magnetic fields the tendency is for the backbone axis of the organometallic fluid to rotate away from the field direction. This observation suggests that strong interactions between the field and the paramagnetic units dictate the orientation of diamagnetic chemical sequences which normally align parallel to the magnetic field. 相似文献
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Microchannel reactors are commonly used in micro-chemical technology. The performance of microreactors is greatly affected by the velocity field in the microchannel. The flow field is disturbed by the cylindrical etch holes caused by air dust on the microchannel surface during its processing procedure. In this approach, a two-dimensional computational fluid dynamics (CFD) model is put forward to study the effect of etch holes on flow field. The influenced area of single or two concave etch holes is studied for the case of laminar flow. The hole diameter, the Reynolds number and the distance between the center of holes are found to have influences on the flow field. Numerical results indicate that the effects of etch hole on the flow field should be evaluated and the way of choosing the economic class of cleanroom for microreactor manufacture is presented. 相似文献
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建立了同向旋转三螺杆挤出机计量段实际流道真实尺寸的三维非牛顿模型,利用ANSYS软件中的FLOTRAN CFD分析功能对该流场进行数值模拟,分析了振动力场作用下挤出机计量段内的黏度分布、压力分布、速度分布以及振幅对流量的影响,同时与无振动状态的挤出特性进行了比较。研究结果表明:振动力场的引入使熔体黏度和流量呈周期性变化,熔体黏度降低,螺棱两侧压差随振幅增大而增大,剪切作用增强,分散性混合能力和分布性混合能力提高。 相似文献
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在290℃下经熔融共聚制得60PHB/PET热致液晶共聚酯。用毛细管流变仪测定流动性能,表明此共聚酯为切力变稀流体;其非牛顿指数、屈服应力在260℃均有突变。结合DSC,DLI,TOT等研究,共聚酯在255~258℃为PHB微晶向向列型液晶转变点。流变特征与相态有关。经高温处理(>260℃)的共聚酯熔体在较低温度下呈保持高温流动特征。而经不同温度热处理后冷却样品,其相转变热焓、相转变温度均随热处理温度的增加而增加,尤其是在260℃以上热处理后冷却样品,其相转变热焓增加较大,而280℃以上热处理后冷却样品的相转变热焓达到最大值。 相似文献