RH真空精炼吹氩参数对循环流动影响的数值分析

为研究RH真空脱气过程中的流动行为,建立了描述气泡驱动下的RH循环气-液两相流动的数学模型.基于欧拉-欧拉两流体模型,利用计算流体力学(CFD)商业软件FLUENT6.0,对不同充气量条件下的循环流量进行了预测.计算结果与实验数据的比较表明两者具有较好的一致性.应用该模型对充气压强与循环流量、充气量与上升管内气相及液相速度分布关系进行了数值模拟,用以理解其中的流动规律,为工程技术改进提供参考.     

新结构RH真空脱气装置水模型实验观察

为了延长RH真空脱气装置的寿命,同时增加RH系统的精炼效率,本文设计了一种RH真空循环脱气装置的新结构。使用水模型实验分析了新结构装置的环流特性,并同传统结构的RH真空脱气装置的环流特性进行了比较分析。利用碳黑墨水染色法分析系统内钢包的混合能力。结果表明：（1）当吹入相同的气体量（Q＝1．5）时,新装置中的水模型中碳黑墨水的扩散速度比传统装置中水的扩散速度快约1／3。（2）传统装置有一个上升管,而新装置中有三个上升管,当传统装置和新装置吹入相同的气体流量时,传统装置中的上升管管内体积被气体占据的多,影响水的循环运动。（3）当吹入相同的气体量时,新装置的液体循环流量比传统装置中的循环流量大,并随着喷入气体量的增加,新装置的循环流量增加也比传统装置增加的大。     

铝熔体旋转喷吹除气过程的数值研究

为了揭示铝熔体净化工艺中除气箱内净化气体的分布特性,利用欧拉模型和多参考坐标系法对铝熔体旋转喷吹除气过程中的气液两相流场进行了数值模拟,考察了离底间隙、气泡直径、除气箱形式等不同因素对流场产生的影响.结果表明,气体易从除气箱中心区域上浮至自由液面逃逸,边壁区的铝熔体不能与足够数量的氩气进行有效接触,不利于边壁区铝熔体的除氢,且在45°相位角位置处更加严重.减小离底间隙、减小气泡尺寸、采用方形除气箱可改善除气箱内气相的分布状况,有利于铝熔体的除氢.     

Heating sequence and hydrogen evolution in alloyed aluminium powders

The results reported here, showing the effect of a non-continuous degassing sequence on the Al-20Si-3Cu-1 Mg powder, are a complement of previous work concerning the continuous degassing of the same powder. The degassing experiments were carried out, under high vacuum, in the temperature range 20 to 550 °C in a horizontal furnace heated at a uniform heating rate of 2.5 °C min^–1. The partial pressures of the released gases were monitored and analysed during the heating phase by a computerized Edwards EQ80F residual gas analyser (RGA). RGA measurements indicate that water and hydrogen are the main degassing products. A complete degassing can only be achieved if the sample is heated up to a temperature where the chemical reactions are finished in the applied time. Thermodynamical equations alone are not enough to explain the kinetics of degassing of aluminium powders. The diffusion of aluminium through its surface oxide layer (Al₂O₃), described by the self-diffusion of aluminium, can explain to a large extent the kinetics of degassing aluminium powders.     

Sublimation Purification of Crude Arsenic Recovered from Nonferrous Waste

The degassing kinetics of crude arsenic recovered from nonferrous waste was studied in air, vacuum, and flowing inert gas, and the degassing conditions were optimized. The sublimation of crude arsenic was carried out in vacuum and flowing hydrogen. A metallic arsenic compact was obtained, which is suitable for the synthesis of ultrapure arsenic compounds.     

Gas entrapment and evolution in prealloyed aluminium powders

Part of a comprehensive research programme involving different aspects of degassing of powder metallurgy (P/M) aluminium alloys carried out in the P/M Group of the Delft University of Technology, is reported. The fundamental aspects of moisture and gas evolution during degassing of a porous billet are described in a semi-quantitative manner using a kinetic approach. During degassing of Al-20Si-X P/M alloys, at temperatures up to 550 °C, the partial pressures of moisture and hydrogen were within the range 10^–4 to 10^–7 mbar. The thermodynamics of gas desorption is mainly influenced by temperature which is the critical degassing parameter. It appears that the diffusion of aluminium through the oxide layer can explain, to a large extent, the kinetics of degassing of aluminium powders. A shift in the release of moisture and hydrogen towards higher temperatures is due to the presence of MgO in the surface layer, compared to the situation when only Al₂O₃ builds the oxide film. Thermodynamical data indicate that the reaction of magnesium with water vapour proceeds more intensely than that between aluminium and water vapour.     

Gas absorption and outgassing of metals

The solution of the diffusion equation is taken as a foundation of the theory of gas-metal interaction in high vacuum. The boundary conditions are formulated from the analysis of the gas balance equations on a metal surface and in a gas volume. The boundary conditions are generally non-linear but in some important cases linearization is permissible. In this way it is possible to obtain analytical expressions for the instantaneous gas flow on electron- and photon-induced desorption, low temperature thermal desorption and gettering at a constant pressure. By means of these formulae one can generalize the experimental data of various authors and calculate the kinetics of such processes as the outgassing of an electron collector, the gas desorption by synchrotron radiation in a vacuum chamber of electron or positron colliding-beam storage-rings, the degassing of an ultra-high vacuum system, the gas sorption by barium and titanium, etc.     

Ultrasonic degassing of aluminium alloys: basic studies and practical implementation

Ultrasonic processing is known to be an efficient means of aluminium melt degassing and structure modification with additional benefits of being economical and environment friendly. The present paper reports on the kinetics of ultrasonic degassing and regassing of foundry aluminium alloys and on pilot scale degassing trials. Efficiency of ultrasonic degassing is compared with conventional Ar rotary degassing. Direct measurements of hydrogen concentration in the melt by Foseco Alspek-H probe are used along with reduced pressure test. The effects of ultrasonic processing on porosity are studied using three-dimensional X-ray tomography.     

Numerical Simulation of Fluid Flow and Mixing in Gas-Stirred Ladles

In this work air injection into a water physical model of an industrial steel ladle was simulated. Calculations were developed based on a multiphase Eulerian fluid flow model involving principles of conservation of mass, momentum, and chemical species for both phases to predict turbulent flow patterns and mixing times for centric and eccentric injections. Effects of gas flow rate, injector position, number of injectors, and geometry of ladle on mixing time were analyzed. Optimum injection conditions are: single injector at 2/3 of radius and high gas flow rates. Quantitative correlation of mixing time as a function of main process variables was obtained.     

Degassing of magnesium alloy by rotating impeller degasser: Part 1 – Mathematical modelling

Abstract

A mathematical model was used to simulate the removal of hydrogen from magnesium alloy by a rotary impeller. It has been shown that the degassing efficiency is mainly dependent on the total surface area of the inert gas bubbles that is related to the rotation speed and the gas flowrate as well as the design of the impeller. An oxygen/water system was used to determine the total surface area of the inert gas bubbles experimentally. Finally, degassing experiments were carried out on magnesium melt to verify the mathematical model. Excellent agreement was obtained between the model predicted and the measured degassing efficiency. It was concluded that this model and the oxygen/water system are suitable to predicate the removal of hydrogen from magnesium alloy by the rotary impeller, and are also useful to the design of the impeller and the research of the effect of the processing parameters.     

Volatilization Rate of SnS from Sn-Fe Mattes

The kinetics of volatilization of SnS from Sn-Fe mattes was investigatd by using a unique experimental method. A water model test was also carried out for the proper interpretation of the experimental results. It has been demonstrated that the volatilization process displays the first order kinetics with respect to the concentration of SnS in the matte. The process is controlled by the mass transport of SnS in gas phase. The apparent activation energy for the process is found to be 127.4 kJ/mol. The effect of temperature and carrier gas flow rate on the reaction rate is discussed in accordance with the mathematical model developed.     

1750℃高温钽片真空炉的研制

本文介绍了一种用于高压电容器钽粉高温脱气处理的新型金属热处理炉，这种炉子是针对钽粉高温脱气的特点开发研制的，即使在工作温度，真空度较高，除气量，温度梯度较大的情况下，仍能保证高温脱气的合理性和延长加热器的使用寿命，并能广泛适用于高温脱气，真空钎焊等场合。     

快递末端配送体系的问题分析及优化研究

目的 针对粉体螺旋输送时物料含气导致的物料密实度不足、包装机工作效率低等问题,设计一种变螺距螺旋来达到密实粉体、提高螺旋输送效率的目的。方法 首先通过气体容积法,测定粉体物料的压实密度,由粉体螺旋输送过程中密度流量关系式,计算得出在转速、螺旋叶片直径一定时,达到压实密度的最小螺距。然后在输送长度确定的情况下,运用等差设计原则,计算出密实段变螺距螺旋的设计参数。最后进行三维建模及仿真分析,对所设计的螺旋进行优化。结果 设计出了三段式变距螺旋,相较于等螺距螺旋,输送过程中物料密度增加了6.541%,螺旋输送质量流量提高了2.475%。结论 验证了通过变螺距螺旋来达到密实粉体的可行性,提高了螺旋输送效率,为螺旋输送过程中粉体脱气方法提供了参考。     

Flow physics of upward cocurrent gas-liquid annular flow in a vertical small diameter tube

In this paper, a steady RNG k-ε model, in conjunction with enhanced wall treatment method, was applied to the gas core in order to simulate the flow physics of annular two-phase flow. The model incorporated a physical model of wave characteristics and included the liquid entrainment influence on the flow. Based on the simulation results, flow features in the gas core were quantitatively presented and a model of the liquid entrainment mechanism was proposed. In addition, a parametric study was conducted to determine the impact of changing wave velocity, pressure, and gravitational force on the liquid film flow. The results were validated using a large set of experimental data at normal and microgravity conditions. Also, the law of the wall was applied to previously-collected experimental data. Analysis yielded different flow features of the liquid film at microgravity and normal gravity conditions.     

真空炉高温除气工艺对降低不锈钢出气率的作用

真空炉高温除气工艺可以大大降低不锈钢出气率。通过应用实例,给出了真空炉高温除气和现场烘烤除气及二者结合除气的结果,分析了真空炉高温除气的有利因素,证明采用该工艺对于降低不锈钢出气率,从而获得超高真空具有显著的效果。     

Factors limiting the attainment of ultra-high vacuum below 10 torr

The present capabilities of ultra high vacuum pumping systems are such that the major limitation on the attainment of ultra high vacuum is the gas loas presented by degassing and permeation of walls and of internal components. Considerable work has been undertaken, theoretically, and experimentally, to illustrate the effects of high temperature bake-out on minimizing outgassing rates but these usually refer to effects at ambient or constant elevated temperature. The present communication analyzes the rate of degassing of components when subjected to time varying heating cycles, in terms of diffusion from the bulk of the solids. It is shown that measurements of degassing rate as a function of increasing temperature can lead to detailed knowledge of the diffusion process which is important in determining the degree of bake-out necessary for individual systems.     

Etching characteristics and mechanism of Ga-doped ZnO thin films in inductively-coupled HBr/X (X = Ar, He, N2, O2) plasmas

We investigated the etch characteristics and mechanisms of Ga-doped ZnO (Ga-ZnO) thin films in HBr/X (X = Ar, He, N₂, O₂) inductively-coupled plasmas. The etch rates of Ga-ZnO thin films were measured as a function of the additive gas fraction in the range of 0-100% for Ar, He, N₂, and O₂ at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using a combination of the global (zero-dimensional) plasma model and Langmuir probe diagnostics. By comparing the behavior of the etch rate and fluxes of plasma active species, we found that the Ga-ZnO etch process was not limited by ion-surface interaction kinetics and appeared in the reaction rate-limited etch regime. In the HBr/O₂ plasma, the etch kinetics were probably influenced by oxidation of the etched surface.     

空炉冷态和满装炉量下真空高压气淬过程流场与温度场数值模拟和实验研究

本文采用标准的k-ε三维紊流模型,利用FLUENT软件对喷嘴型真空高压气淬炉中空炉冷态流场和工件满装炉量下气固耦合流动传热过程进行了数值模拟计算.建立了符合实际的控制方程和简化物理模型,对空炉冷态下炉内的气体流动特征点进行流速测量,通过实测值与计算机模拟结果进行对比,验证了流场模拟计算的准确性和适用性;预测了满炉状态下炉区内的气体流动和工件温度分布,实测了指定工件的冷却曲线,比模拟冷却时间慢,误差在10％以内.     

Effect of Degassing Temperature on the Specific Surface Area and Other Physical Properties of Magnesium Stearate

Abstract

The effect of degassing temperature on the magnitude of the BET specific surface area and other physical properties of magnesium stearate was investigated. Magnesium stearate samples from two manufacturers were degassed using helium at 23°, 30°, 40°, 50° and 60°C. The specific surface area of the degassed samples was measured using both single- and multi-point BET methods. The moisture content and thermal properties of the degassed magnesium stearate samples were also examined. The specific surface area values decreased with an increase in the degassing temperature. The Karl Fischer and thermogravimetric analysis results also showed a decrease in the moisture content with an increase in the degassing temperature. The differential scanning calorimetry thermograms of the degassed samples showed changes in the endotherm characteristics along with changes in the melting point and heat of fusion values. It is hypothesized that the lower specific surface area values obtained after degassing at higher temperatures may be due to a partial conversion of the magnesium stearate dihydrate crystals into a monohydrate, an anhydrate or a mixture of the two forms. These results suggest that magnesium stearate samples should be degassed only at room temperature prior to the BET surface area analysis. The results of this study also show that it is important to consider the degassing conditions used when comparing specific surface area data from different sources.