两液层体系传质引发的Marangoni效应的数值模拟

The Marangoni effect induced by mass transfer at the interface between two immiscible liquids displays important influence on laboratory and industrial operation of solvent extraction. A systematic numerical study of the two-dimensional Marangoni effect in a two liquid layer system was conducted. The linear relationship of the inter- facial tension versus the solute concentration was incorporated into a mathematical model accounting for liquid flow and mass transfer in both phases. The typical cases analyzed by Sternling ＆ Scriven （AIChE J., 1959） using the linear instability theory were simulated bv the finite difference method and good agreement between the theory and the numerical simulation was observed. The simulation suggests that the Marangoni convection needs certain time to develop sufficiently in strength and scale to enhance the interphase mass transfer, the Marangoni effect is dynamic and transient, and remains at some stabilized level as long as the mass transfer driving force is kept con- stant. When certain level of shear is imposed at the interface as in most cases of practical significance, the Maran- goni effect is suppressed slightly but progressively as the shear is increased gradually. The present two-dimensional simulation of the Marangoni effect provides some insight into the underlying mechanism and also the basis for further theoretical study of the three-dimensional Marangoni effect in the real world and in chemical engineering applications.     

影响化学气相沉积多晶硅致密料比例的因素

改良西门子法生产多晶硅还原工艺是高纯的三氯氢硅和氢气在还原炉内发生化学气相沉积反应,得到固态多晶硅,多晶硅根据表观质量,分为致密料、玉米料、珊瑚料。目前,国内多晶硅生产以大型还原炉为主,对成本控制具有明显优势,但存在的问题是多晶硅致密料比例较低。本文通过对还原炉反应温度控制、进料喷嘴布置、反应配比等因素的分析研究,得出了提高还原炉化学气相沉积多晶硅致密料比例的方法、思路。     

化学气相沉积法多晶硅生产工艺的研究

对化学气相沉积法生产多晶硅的工艺进行了研究。多晶硅生产过程中的温度、流量、压力、物料摩尔比、进料气体分布以及操作安全性是影响多晶硅生产的重要因素,通过生产过程的研究和总结,实现了相关参数控制和安全性的优化,为企业带来了可观效益。     

多晶硅化学气相沉积数值模拟的研究进展

介绍了多晶硅气相沉积反应的几何模型和数学模型。回顾了。重点综述了近几年国内外还原炉内SHC13-H系统三维过程数值模拟的研究进展,并对其评述。讨论了化学气相沉积数值模拟的研究现状和存在的问题,展望了今后的发展方向。     

气相温度脉动对碳黑生成反应的影响(英文)

The effects of gas temperature fluctuations on soot formation and oxidation reactions are investigated numerically in a reacting flow. The instantaneous variations of soot mass fraction with time are obtained under the time-averaged gas temperature of 1500-1700 K. The simulation results show that the gas temperature fluctuation has obvious influence on the instantaneous processes of soot formation and oxidation. Within the present range of gas temperature, the gas temperature fluctuation results in generally lower soot mass fraction comparing to that without gas temperature fluctuation. The increase in the fluctuation amplitude of gas temperature leads to decrease in time-averaged soot mass fraction and increase in time-averaged soot particle number density.     

流化床化学气相沉积多晶硅的技术进步与挑战

Various methods for production of polysilicon have been proposed for lowering the production cost and energy consumption, and enhancing productivity, which are critical for industrial applications. The fluidized bed chemical vapor deposition (FBCVD) method is a most promising alternative to conventional ones, but the homogeneous reaction of silane in FBCVD results in unwanted formation of fines, which will affect the product quality and output. There are some other problems, such as heating degeneration due to undesired polysilicon deposition on the walls of the reactor and the heater. This article mainly reviews the technological develop-ment on FBCVD of polycrystalline silicon and the research status for solving the above problems. It also identifies a number of chal-lenges to tackle and principles should be followed in the design of a FBCVD reactor.     

甲烷/空气射流燃烧中氮氧化物生成模型的研究

With the development of reaction kinetics and transfer science, the modeling of NOx formation plays more and more important roles in the protection of environment and the design of combustion reactors; in this case, turbu-lence-chemistry model and NOx formation model are the two most important aspects. For thermal NOx mechanism, this article studied the CH4/air system and applied a set of latest NO formation rate constants published at the Leed University which replaced the original model code in FLUENT to increase its precision on prediction of NO concentration. The realizable k-ε model, Reynold Stress model and standard k-ε model were also investigated to predict the turbulent combustion reaction, which indicated that the simulation results of velocities, temperatures and concentrations of combustion productions by the standard k-ε model were in good accordance with the experimental data. With the application of the simulation results to the experimental data to fit some important kinetic parameters in the equation of O atom model and revision of the equation later, this article obtained a new NO formation rate model. It has been proved that the prediction of the developed model coincides well with the measurements.     

物理气相沉积对化学钢化玻璃抗冲击强度的影响

用真空热蒸发沉积、离子束辅助沉积和磁控溅射三种方法在化学钢化玻璃上分别镀制铬薄膜和硫化锌薄膜,并对镀膜的化学钢化玻璃进行落球冲击实验,结果表明:镀膜的化学钢化玻璃的抗冲击强度变弱,不同的物理气相沉积方法对化学钢化玻璃的抗冲击强度影响不同.本文主要分析了薄膜应力和粒子束能量对化学钢化玻璃表面压应力的影响,并探讨化学钢化玻璃抗冲击强度变弱的原因,提出了解决的方法.     

载料气体对化学气相沉积合成石英玻璃沉积速率的影响

采用化学气相沉积工艺合成了石英玻璃,研究了沉积速率与载料气体之间的关系.利用扫描电子显微镜观察火焰中SiO2粒子微观形态和尺寸.通过对SiCl4水解、氧化反应速率的计算表明:在一定温度下,当同时存在充足的H2O和O2时,SiCl4氧化反应速率远高于水解反应速率.当载料气体为H2,Sicl4流量为25g/min时,观察火焰中SiO2粒子的微观形态发现存在大量非球状无定形聚集体,表明SiCl4未反应完全,沉积速率较低,约为220～240 g/h.同样SiCl4流量下.采用O2作为载料气体时火焰中颗粒均为球状,SiCl4全部反应,沉积速率较高,达到300～350 g/h.当SiCl4流量为15 g/min时,载料气体的改变对SiO2粒子形态和尺寸没有影响,SiCl4可以全部反应,沉积速率基本相同.当SiCl4流量较高(25 g/min)时,载料气体对反应机理和沉积速率有显著影响,若要SiCl4在极短时间内完全反应生成球状SiO2粒子,需选择O2作为载料气体,充足的O2保证SiCl4可以通过氧化反应全部反应完毕,沉积速率相应提高.     

气体流量对化学气相沉积法制备碳纳米管的影响

用化学气相沉积法裂解乙炔制备无序多壁碳纳米管,以Fe/S iO2粉状物作为催化剂,考察了气体流量等环境因素对碳纳米管生长的影响。通过TEM和SEM分析得出,当N2流量分别为200、500和800 mL/m in时,碳纳米管的平均直径分别为20、36和82 nm,即碳纳米管的直径随着N2流量的升高而增大。当N2流量增加到800mL/m in时,还生成了大量的直径约为20~30 nm的碳纳米球。不通H2制备不出碳纳米管。     

Chemical Vapor Deposition of Silicon Layers on Capillary and Pore Walls

An analytical model of silicon layer deposition on capillary (pore) walls is suggested for isothermal tetrachloride and hydride processes. The model enables one to assess the uniformity of the layer growth rate over the pore length and to calculate the healing time of capillary (pore) mouths.     

Low-Temperature Metal-Organic Chemical Vapor Deposition of Silicon Nitride

Amorphous silicon nitride films have been deposited on single-crystal silicon from the gas mixture of methylsilazane and ammonia at 873 to 1073 K. The films have been characterized by ellipsometry, Fourier transform infrared spectroscopy, and Auger electron spectroscopy. The Si-C, Si-H, and C-H bonds in methylsilazane can be effectively cleaved and the associated C and H species removed. The structure and composition of the films do not show any apparent dependence on the deposition temperature.     

Chemical Vapor Deposition for Silicon Cladding on Advanced Ceramics

Polycrystalline Si was used to clad several advanced ceramic materials such as SiC, Si₃N₄, sapphire, Al₂O₃, pyrolytic BN, and Si by a chemical vapor deposition (CVD) process. The thickness of Si cladding ranged from 0.025 to 3.0 mm. CVD Si adhered quite well to all the above materials except Al₂O₃, where the Si cladding was highly stressed and cracked or delaminated. A detailed material characterization of Si-clad SiC samples showed that Si adherence to SiC does not depend much on the substrate surface preparation; that the thermal cycling and polishing of the samples do not cause delamination; and that, in four-point bend tests, the Si–SiC bond remains intact, with the failure occurring in the Si.     

多晶硅产业现状及发展趋势

介绍多晶硅国内生产企业的现状、市场需求、技术水平以及未来的发展趋势。     

多晶硅产业现状及发展趋势

介绍多晶硅国内生产企业的现状、市场需求、技术水平以及未来的发展趋势.     

多晶硅还原炉内三氯氢硅氢还原过程的数值模拟

建立了多晶硅还原炉内SiHCl3氢还原过程的三维模型,利用CFD软件对炉内的流动、传热和化学反应过程进行了数值模拟,并分析了硅棒高度和硅棒直径对沉积特性的影响。结果表明:随着硅棒高度的增加,SiHCl3转化率、硅产率和硅表面沉积速率不断增大,单位能耗不断减小;从反应的角度来说,硅棒高度越高越好;随着硅棒直径不断增加,SiHCl3转化率和硅产率逐渐增大,硅表面沉积速率先减小、后增大,单位能耗先急剧减小、然后趋于平缓;理论上硅棒直径越大越好,且最好超过120mm。     

硅粉密相气力输送技术在多晶硅生产中的应用

介绍某多晶硅厂对硅粉加料采用密相气力输送技术的输送方式和工艺流程,分析了该气力输送系统中主要设备和管道、阀门选型及设计时的考虑因素。     

Modeling of Laser-Induced Chemical Vapor Deposition of Silicon Carbide Rods from Tetramethylsilane

Finite-difference fluid-dynamics modeling has been used to predict deposition rates, fractional amounts of phases, and deposition morphology for the codeposition of silicon carbide and pyrolitic carbon from tetramethylsilane via laser-induced chemical vapor deposition (LCVD). Calculated results agree fairly well with rod deposition experiments. The morphologic features of rods that have been grown using LCVD are examined and explained using the results of the finite-difference calculations.     

等离子体增强化学气相沉积法制备氢化硅膜的自晶化倾向性

为了探寻生长过程中硅膜的自晶化沉积,采用等离子体增强化学气相沉积(PECVD)法沉积了氢化硅薄膜,系统研究了不同沉积阶段所得硅膜微观结构的迁变规律。结果表明,硅膜的显微结构依赖于沉积时间,当沉积时间仅为30min时,所得硅膜的结构为非晶;而当沉积时间延至60min时,硅膜形成微晶颗粒;此后随着沉积时间的增加,晶化程度提高,且非晶区域面积相应减小。另外,硅膜的沉积速率也随沉积时间的增加而增加。在硅膜沉积过程中,随时间不断变化的界面状态可能为其自晶化的主要原因。