RH真空精炼吹氩喷嘴结构参数对循环流量影响的数值模拟

循环流量是判断RH真空脱气装置精炼效率的重要指标之一.本文针对某钢厂180t RH真空精炼装置,基于计算流体动力学(CFD)方法,建立了RH真空精炼过程中气泡驱动的气-液两相流动理论模型,并利用CFD商业软件FLUENT进行数值模拟,探讨了相同真空度下吹氩喷嘴分布形式、喷嘴排间距等参数对循环流量的影响.结果表明:相同真空度和吹氩流量条件下,相比于单排圆周均布形式,喷嘴双排圆周交错分布时的循环流量更大、精炼效率更高,并存在最优的排间距,可作为RH真空精炼操作参数优化及工程结构改进的参考.     

RH精炼过程循环流场模拟研究

RH真空循环是以真空室钢液与钢包钢液循环流动来实现,由于RH循环流量不足和生产工艺不完善等问题,这些问题制约了RH的效率提高。应用N-S方程和双方程模型对RH炉外精炼真空室钢液和钢包内钢液进行数值模拟,ANSYS模拟分析循环流量及气体流量和RH混均情况。基于180t RH的参数分析钢液流动的三维数学模型模拟,并且分析影响循环流量的因素。掌握RH流动规律为工程技术改进提供参考。     

自然循环在新型低温传热元件中的性能

针对自然循环与低温热管耦合的新型传热元件稳态特性进行了数值计算.基于一些合理假设,利用一维均相流模型对液氮在自然循环管路中的流动与传热过程进行计算,得到了两相流动中干度沿管程方向的分布,循环流量、干度等参数随外加热负荷变化的规律,以及不同管径对循环流量、干度分布、冷头稳定温度的影响,并与实验结果进行了比较与分析,为优化实验装置提供了理论依据.     

新型侧底复吹真空精炼装置循环特性研究

对某钢厂180 t RH真空精炼装置浸渍管结构改造并增加底吹氩气功能,通过数值方法对新型侧底复吹真空精炼装置内气液两相循环流动进行了模拟,并与实验数据进行了比较。结果表明:数值模拟所得到循环流量值与物理模拟所得到的实验数据有较好的一致性;侧吹0.8 m~3/h、底吹0.6 m~3/h时,循环流量达到最大数值0.227 m~3/h,新型结构用较小的吹氩流量即可达到传统RH的循环精炼效率,具有重要的应用前景。     

循环流化床底部区域流动特性的数值模拟

基于欧拉两相流模型计算循环流化床底部区域的流动特性。在低气速(1.0～2.5m/s)、低循环量下(5.2～34.5kg/(m2·s)),模拟时黏性采用层流模型取得了较好的效果。实验采用光导纤维探头测量仪测量流化床底部区域3个截面的局部颗粒浓度,模拟计算了循环流化床底部3个截面的颗粒浓度的径向分布,并同循环流化床装置的实验数据进行了对比。结果表明,数值模拟计算与实验结果相吻合。     

泡沫金属湍流射流发泡过程数值模拟研究

应用欧拉-欧拉双流体模型,并采用分别描述气泡和液相湍流的k-ε两相湍流模型,描述制备泡沫金属过程中气体射流发泡过程的两相流动.通过对气泡和液体在流场中的受力分析,详细讨论了阻力、升力等相间作用力对气泡分布和流体流动的影响.预测结果和文献中的实验结果进行的对比表明,在给出合理的相间作用力模型时,该模型预测值和实验结果符合较好.但由于目前尚缺乏气体射流破碎模型,喷嘴附近还存在较明显差异.     

水平管内四氟甲烷流动沸腾传热实验研究

实验测定了四氟甲烷(R14)在内径为6 mm的水平管内两相流动沸腾传热特性.实验测试的压力范围为0.22-0.60 MPa,热流密度范围19.9-73.6 kW/m2,质量流量范围370-862 kg/m2s.实验结果表明,传热系数随质量流量的增大而有一定程度的上升,而热流密度及饱和压力与传热系数呈明显的正相关关系.将实验数据与已有文献模型的计算结果进行比较发现,Kandlikar模型、Gungor-Winterton模型以及Shah模型与实验数据的关联性较好,平均偏差均在15％以内.     

RH真空度和真空室钢水液位高度对精炼效率影响的实验研究

本实验以某厂210 tRH-TOP真空精炼装置和钢包为原型,以模型与原型比为1∶4的比例,建立了RH真空精炼的物理模型。研究了真空度、真空室液位高度和浸渍管浸入深度对钢包循环流量及混匀时间的影响规律。实验结果表明:在本实验范围内,真空度为11.2 kPa~16.8 kpa和实际液位高度为320 mm~400 mm时对循环流量和混匀时间最有利。     

基于FLUENT的不同喷嘴轮廓线形对流出系数影响分析

利用Fluent软件对5种内轮廓曲线喷嘴进行了三维流动仿真,采用标准的k-ε两方程湍流模型,计算了管道与喷嘴上的压力值.数值模拟结果表明,当在相同的工作状态下,且流量相同的情况下,喷嘴的曲线形状影响差压值,从而影响喷嘴的流出系数.数值模拟方法能够反映喷嘴内部的复杂流动,为喷嘴的设计和改进提供了理论依据.     

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。     

Effect of Process Variables on Kinetics and Gas Consumption in Rotor-Degassing Assisted by Physical and Mathematical Modeling

Mathematical and physical models of water deoxidation in a batch aluminum degassing reactor using the rotor-injector technique were developed. The mathematical model was successfully validated against measured degassing kinetics. The physical model was employed to perform a process analysis using a two-level factorial experimental design to determine the influence of gas flow rate, impeller angular velocity, and gas injection points on gas consumption efficiency and degassing kinetics. A combination of higher rotor speeds and gas flow rates results in fast degassing kinetics. However, moderate gas flow rates are recommended to save gas.     

Effect of hydrodynamics on solids internal circulation characteristics in an annular catalyst cooler

Annular catalyst cooler (ACC) can intensify the bed-to-wall heat transfer compared with traditional base catalyst cooler (BCC). Although the intensified mechanism has been investigated, it is necessary to clearly understand information on hydrodynamics and internal circulation characteristics in the whole cooler. Euler-Euler model with modified Gidaspow drag model is employed to simulate the hydrodynamics and internal circulation characteristics. The results show that the hydrodynamics difference between two coolers is positioned at their downer region, where the solids volume fraction in the ACC is bigger than those in the upper region of dense bed and in the whole BCC. The internal circulation of particles in the ACC is also located in the downer region of dense bed, which is verified by profiles of axial and radial velocities at different positions. In order to quantify this internal circulation flow, both internal circulation height and flux are proposed and determined respectively by radial velocity of particles and by their flux below heat tube. The height increases and the flux decreases with increasing gas velocity from center distributor. Those results indicate that the heat transfer intensified effect is mainly influenced by internal circulation height, which is agreement with the effect of gas velocity on heat transfer intensified height.     

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.     

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.     

Multiple failures of API 5L X42 natural gas pipe: Experimental and computational analysis

Multiple failures of API 5L X42 (X42) coal–tar coated natural gas feeder line due to vertical jetting of high pressure erosive slurry was studied experimentally and computationally. Computational Fluid Dynamic (CFD) was used as the simulation tools to study the flow pattern, velocity distribution and strain rates on pipe surface. Experimental work was performed to determine the erosion pattern. Three different diameters of jetting sources produced three distinct impact patterns were clearly identified. These patterns were frequently referred in the experimental study. A CFD simulation result shows that the highest shear strain rate area coincides with the leakage point. These results thus support the hypothesis that it is very likely that the failure of the gas pipeline was caused by the high pressure water jet gusting from the failed welded joint of the water pipeline.     

Ion-induced nucleation rate measurement in SO2/H2O/N2 gas mixture by soft X-ray ionization at various pressures and temperatures

This paper reports the systematic investigation of ion-induced nucleation rate measurement in a SO₂/H₂O/N₂ gas mixture, employing soft X-ray at different pressure and temperature levels. Experiments were conducted using a modified continuous flow gas-generation system employing a soft X-ray ionizer and a particle counter, with an improved integrated online temperature, pressure and a relative humidity (RH) control system. Nucleation rates were measured as a function of SO₂ concentration at different levels of RH, pressure (600–970 hPa) and temperature (5–25 °C). The results show that the nucleation rate dependence on SO₂ concentration followed a power law, and the slope varied slightly in a range from 1 to 1.26 at different RH levels (15–60%). A positive pressure effect was generally found and a power law was followed with varied scaling for different SO₂ concentrations. The trend of an increase in nucleation rate with temperature was consistent with observations in homogenous nucleation experiments, and with the behavior predicted by classical binary nucleation theory. These experimental results will be useful to explain the contribution of ion-induced nucleation in different locations and atmospheric conditions.     

Experimental investigation of the auxiliary gas circuit of a diffusion absorption chiller with natural and forced circulation

The auxiliary gas circuit has a significant influence on the cooling capacity and the efficiency of a diffusion absorption chiller. Nevertheless, there are only a few theoretical studies and experimental investigations concerning this topic. The reason is the difficulty to gain measurement data of the volume flow rate and the partial pressures without affecting the natural circulation of the auxiliary gas circuit negatively.This paper presents a detailed experimental investigation of the auxiliary gas circuit. The gas mixture in the circuit mainly consists of the vapour of the refrigerant (ammonia) and the inert gas (helium). A clamp-on ultrasonic flowmeter measures the volume flow rate of the gas mixture and the mole fraction of helium and ammonia continuously. The influence of an increasing volume flow on the mass transfer in the auxiliary gas circuit is shown by using a propeller to force the circulation of the gas mixture.     

Numerical analysis of spontaneously condensing phenomena in nozzle of steam-jet vacuum pump

The primary fluid in a steam-jet vacuum pump is not assumed as a perfect gas as general research in the present study. A mathematic model based on the wet steam model for transonic flow is proposed to investigate the flow behaviours of primary fluid in the nozzle of a steam-jet vacuum pump. The simulation based on a wet steam model was carried out to predict the flow characteristics of primary fluid along the nozzle axis by a commercial computational fluid dynamics (CFD) code (FLUENT6.3). The simulation results showed that there was spontaneous condensation as the supersonic flow passing through the nozzle and the simulation results had a good agreement with the experimental data. It is found from the numerical simulation results that the steam flow characteristics in nozzle are quite different from a wet steam model and a perfect gas assumption: the outlet pressure of the nozzle predicted in the present study is higher than that as the primary fluid assumed as perfect gas, the outlet velocity is about 10% lower than that as the primary fluid assumed as a perfect gas, and the temperature at the outlet of the nozzle is much higher than that as the primary fluid assumed as a perfect gas. The simulation results demonstrate that the thermo-positive process due to steam condensation would hinder the supersonic expanding flow process in nozzle and depress the efficiency of the nozzle which would affect the pumping performance of steam-jet pump.     

Low Resistance Polycrystalline Diamond Thin Films Deposited by Hot Filament Chemical Vapour Deposition

Polycrystalline diamond thin films with outgrowing diamond (OGD) grains were deposited onto silicon wafers using a hydrocarbon gas (CH4) highly diluted with H2 at low pressure in a hot filament chemical vapour deposition (HFCVD) reactor with a range of gas flow rates. X-ray diffraction (XRD) and SEM showed polycrystalline diamond structure with a random orientation. Polycrystalline diamond films with various textures were grown and (111) facets were dominant with sharp grain boundaries. Outgrowth was observed in flowerish character at high gas flow rates. Isolated single crystals with little openings appeared at various stages at low gas flow rates. Thus, changing gas flow rates had a beneficial influence on the grain size, growth rate and electrical resistivity. CVD diamond films gave an excellent performance for medium film thickness with relatively low electrical resistivity and making them potentially useful in many industrial applications.