Numerical simulation on electrolyte flow field in 156 kA drained aluminum reduction cells

Based on the commercial CFD software CFX-4.3, two-phase flow of electrolyte in 156 kA drained aluminum reduction cells with a new structure was numerically simulated by multi-fluid model and k-ε turbulence model. The results show that the electrolyte flow in the drained cells is more even than in the conventional cells. Corresponding to center point feeding, the electrolyte flow in the drained cells is more advantageous to the release of anode gas, the dissolution and diffusion of alumina, and the gradient reduction of the electrolyte density and temperature. The average velocity of the electrolyte is 8.3 cm/s, and the maximum velocity is 59.5 cm/s. The average and maximum velocities of the gas are 23.2 cm/s and 61.1 cm/s, respectively. The cathode drained slope and anode cathode distance have certain effects on the electrolyte flow.     

Computational study on fumace process in a multi-burner boiler of pulverized coal fired tangentially at four corners

Aiming at the optimization of the operation condition, a general numerical method for calculating pulverized coal combustion in a full-scale furnace fired tangentially at four corners is adopted. “κ-ɛ” turbulence model is used for the gas phases and a stochastic approach based on the Lagrangian technique is used for particle phases. Two-competing reactions model for the coal devolatilization and PDF (the probability density function) method for the combustion of the gas phases are employed. In the numerical simulations, assuming the air distribution of second port level is of pagoda, waist drum and uniform type. The results show that pagoda type air distribution is advantageous to ignition and smooth combustion of pulverized coal, and suitable to inferior coal combustion in practice. In the present furnace, the igniting distance at 1st and 3rd corner is longer than that at 2nd and 4th corner. The results from numerical calculations are in good agreement with those of observed in practice. Biography of the first author: ZHOU Ping, associate professor, born in 1965, majoring in simulation and optimization of pyro-installations.     

用数值模拟方法进行脱硫塔的优化设计

基于多相流数值模拟,进行了湿法脱硫喷淋塔的优化设计研究,气相湍流由标准模型描述,喷淋液滴由确定颗粒轨道模型描述,通过对流场和温度场模拟计算得到优化设计结果是烟气入口向下倾斜15°,喷嘴采用高低位布置,在喷雾区加装环形导流分布器,可使脱硫塔流场右侧湍流强度明显增加,左侧烟气贴壁流动有所改善,脱硫塔内流场分布更加合理,塔出口温度低于优化前温度,增加气液传质、传热,提高脱硫效率。     

CFB-FGD布袋除尘器内气固流动特性的数值模拟研究

采用k-ε双方程湍流模型和离散相模型对循环流化床烟气脱硫(CFB-FGD)布袋除尘器内气固两相流动进行了数值模拟,分析了进口烟道结构形式、气流均布板和锅炉负荷等对改进前后布袋除尘器的流场分布、阻力特性及颗粒相流动状况的影响规律.模拟结果表明,渐扩型进口烟道和具有一定开孔率的气流均布板可很好地改善除尘器内流场分布的均匀性.与布袋除尘器原型相比,改进型除尘器内的颗粒流动更加均匀,同时灰斗积灰对颗粒相均匀分散有一定的改善作用.不考虑粉尘堆积情况下,改进型布袋除尘器总阻力损失与锅炉负荷满足二次函数关系.     

电除尘区低温省煤器烟道导流优化的数值模拟

为实现电除尘区低温省煤器的节能改造,利用FLUENT 6.3对电除尘区低温省煤器烟道的流场均化和导流优化设计进行了数值模拟研究.研究结果表明:电除尘区加装低温省煤器后烟道流场严重不均,存在回流和漩涡,局部速度高达26 m/s,最大速度偏差系数达90%,电除尘入口速度分布不均;导流板可有效改善烟道流场,削减回流与漩涡,换热管屏处速度偏差减小30%;电除尘入口烟气向下的平均速度分量由3 m/s削减至0.6 m/s,入口烟气分布趋向均匀;通过变工况数值分析,不同运行工况下的导流板作用变化不大,均具有良好的均流效果.此结果可为工程技术改造提供参考.     

水泥线窑头余热锅炉对流烟道流动特性研究

锅炉烟道流场设计是决定水泥线低温余热锅炉性能的重要因子.针对每年5000 t水泥线余热锅炉的烟道流动,采用标准κ-ε模型对锅炉烟道烟气流动特性、不同受热面布置方式的流场分布不均匀性进行了数值模拟研究.结果表明:锅炉废气引入弯管外侧聚集流动,而其内侧出现负压区;受热面管束可降低锅炉引入弯管所致的流动不均匀性.研究结果对水泥线余热锅炉烟道和受热面设计分析和锅炉运行安全性有重要意义.     

烟羽消白冷凝器的设计与实验研究

湿法脱硫燃煤电厂烟气中含有大量的水蒸气,形成具有视觉污染的白色烟羽。在脱硫塔后加装烟气冷凝器,可以消除白色烟羽、回收大量水资源,同时还可以进一步降低烟气中的污染物含量。针对Colburn-Hougen方法传质方程中j因子需要通过查表来获得的繁琐性,基于菲克定律和传热传质类比定律,推导出了一个传质系数Kv。利用获得的Kv,采取逐段计算的方法设计了烟气冷凝器,并进行了实验验证。结果表明:设计计算结果与实验结果非常接近,可以采用Kv计算水蒸气的冷凝速率,采用逐段计算方法设计烟气冷凝器。     

烟气再循环对生物质炉排炉燃烧影响的数值模拟

针对生物质锅炉实际运行过程中常出现水冷壁腐蚀严重、屏式过热器积灰多和NO_x排放量高等问题,以一台某电厂额定蒸发量为130 t/h的生物质往复式水冷炉排炉为研究对象,提出二次风掺混再循环烟气燃烧的方法,采用计算流体力学（CFD）数值模拟技术对炉内燃烧过程进行热态模拟,旨在为锅炉的实际运行操作提供理论指导. 计算结果表明,采用烟气再循环可以增强炉膛上部气流扰动,改善炉内温度分布的均匀性,提高燃尽率,同时降低屏区火焰温度,减轻大屏积灰结渣风险;后墙下二次风掺混再循环烟气后,主燃区形成还原性气氛,温度下降,有效抑制热力型NO_x的生成.后墙下二次风掺混30%再循环烟气的工况炉内气流均匀饱满,高温烟气分布从炉膛深度中心向前、后墙两侧稳定下降,NO_x排放质量浓度相对于无再循环烟气时减少了32.1%.     

烟气再循环对炉内氮氧化物生成影响的数值模拟

利用Fluent软件对某电站四角切圆燃烧锅炉有、无烟气再循环时的燃烧过程和NOx排放特性进行数值模拟。计算结果表明:有烟气再循环时,炉内平均温度分布和最大温度分布整体明显降低;炉膛出口CO2浓度有一定幅度的上升,O2浓度有了较大幅度的下降;同时NOx生成量有较大幅度降低,其数值模拟结果与试验结果基本相符。还对烟气再循环倍率和烟温等对氮氧化物生成量的影响进行了研究,并对烟气再循环倍率进行了优化数值模拟。其研究结果为烟气再循环锅炉的设计、运行提供了参考依据。     

舰用增压锅炉烟风阻力计算方法研究

增压锅炉是适合于大型水面舰艇的主动力装置.通过对增压锅炉烟气通道、配风器和对流管束内烟气的流动特性分析,借助对部分烟气流动情况复杂区段的流场数值模拟,根据流体力学基本理论,结合在现有非增压锅炉设计运行中广泛采用的烟风阻力相关参数、计算公式和线算图表,探讨了适合增压锅炉的烟气通道、配风器和对流管束的烟风阻力计算方法.并以现役某型增压锅炉为实体,利用选定的公式进行烟气通道、配风器和对流管束的阻力校核计算,验证了公式的可行性.     

Physical simulation of hot deformation of TiAI based alloy

In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti-49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1 100 ℃ with strain rates of 10^-3-10^-1 s^-1. Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n, has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ = K1 drex^-0.56. The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lgdrex= -0.281 1gZ 3.908 1.     

Numerical simulation and analysis of water flow over stepped spillways

Numerical simulation of water flow over the stepped spillway is conducted using Mixture multiphase flow model. Different turbulence models are chosen to enclose the controlling equations. The turbulence models investigated are realizable k-ε model, SST k-ω model, v2-f model and LES model. The computational results by the four turbulence models are compared with experimental ones in the following aspects: mean velocity, the spanwise vorticity and the growth of the turbulent boundary layer thickness in the st...     

Flow stress behavior of Cu13Zn alloy deformed at elevated temperature

Ｃｏｎｓｔｉｔｕｔｉｖｅｍｏｄｅｌｉｓａｍａｔｈｅｍａｔｉｃａｌｒｅｐｒｅｓｅｎｔａｔｉｏｎｏｆｔｈｅｄｅｆｏｒｍａｔｉｏｎｒｅｓｐｏｎｓｅｏｆａｍａｔｅｒｉａｌｔｏｅｘｔｅｒｎａｌｌｙａｐ ｐｌｉｅｄｌｏａｄｉｎｇ ,ｉｎｃｌｕｄｉｎｇｅｎｖｉｒｏｎｍｅｎｔａｌｆａｃｔｏｒｓ .Ｔｈｅｐｒｅ ｃｉｓｅｋｎｏｗｌｅｄｇｅｏｆｔｈｅｃｏｎｓｔｉｔｕｔｉｖｅｂｅｈａｖｉｏｒｏｆｔｈｅｍａｔｅｒｉａｌｉｓｔｈｅｆｏｕｎｄａｔｉｏｎｏｆｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｔｅｃｈｎｏｌｏｇｙｏｆｍａｔｅｒｉ…     

余热锅炉通流结构数值分析

采用标准κ-ε湍流模型对水泥窑余热锅炉通流结构流场进行了计算机仿真模拟,得出烟气速度在烟道内的分布情况.通过对3种均流装置的对比分析表明:加装倒V型角钢均流装置可以均匀过渡段出口的流场,提高受热面的传热有效性.     

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC^3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength σ _c of rock sample decreases firstly and then increases; when β is in the range of 20°–30° and 80°–90°, σ _c has the largest sensitivity to β; while β falls in the range of 30°–70°, σ _c varies little. When ϕ _j <β<90° (β _j is friction angle of structure plane), the results obtained from numerical simulation and theoretical analysis are in almost the same values; while β⩽ ϕ _j or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations of β⩾ ϕ _j and β=90°, which is in more accordance with the real situation. Foundation item: Project (50099620) supported by the National Natural Science Foundation of China     

Study on the removal of MIBK from aqueous solution by vacuum membrane distillation

Ｖａｃｕｕｍｍｅｍｂｒａｎｅｄｉｓｔｉｌｌａｔｉｏｎ(ＶＭＤ)ｉｓａｐｒｏｍｉｓｉｎｇｓｅｐａｒａｔｉｏｎｔｅｃｈｎｉｑｕｅｆｏｒｔｈｅｐｕｒｉｆｉｃａｔｉｏｎｏｆｄｉｌｕｔｅａｑｕｅｏｕｓｓｏｌｕｔｉｏｎｓ,ｓｕｃｈａｓｓｅｐａｒａｔｉｏｎｏｆｇａｓｅｓｆｒｏｍａｑｕｅｏｕｓｓｏｌｕ ｔｉｏｎｓａｎｄｒｅｍｏｖａｌｏｆｖｏｌａｔｉｌｅｏｒｇａｎｉｃｃｏｍｐｏｎｅｎｔｓ(ＶＯＣ)ｆｒｏｍｄｉｌｕｔｅａｑｕｅｏｕｓｓｏｌｕｔｉｏｎｓ .Ｉｎｒｅｃｅｎｔｙｅａｒｓ ,ｔｈｅｒｅｍｏ ｖａｌｏｆＶＯＣｆｒｏｍｄ…     

Flow stress equation for multipass hot-rolling of aluminum alloys

Ｔｈｅｆｌｏｗｓｔｒｅｓｓｏｆａｍａｔｅｒｉａｌｒｅｌａｔｅｓｎｏｔｏｎｌｙｔｏｔｈｅｓｔｒａｉｎ ,ｓｔｒａｉｎｒａｔｅ ,ａｎｄｔｅｍｐｅｒａｔｕｒｅｏｆｄｅ ｆｏｒｍａｔｉｏｎ,ｂｕｔａｌｓｏｔｏｔｈｅｍｉｃｒｏｓｔｒｕｃｔｕｒｅ .Ａｓａｎｅｓｓｅｎｔｉａｌｉｎｐｕｔｆｏｒｃｏｍｐｕｔｅｒｍｏｄｅｌｉｎｇｔｈｅｒｍｏｍｅ ｃｈａｎｉｃａｌｐｒｏｃｅｓｓｉｎｇｏｐｅｒａｔｉｏｎｓｕｓｉｎｇｆｉｎｉｔｅｅｌｅｍｅｎｔｍｅｔｈｏｄｓ,ａｎａｃｃｕｒａｔｅｆｌｏｗｓｔｒｅｓｓｖａｌｕｅｏｒｆｌｏｗｓｔｒｅ…     

Deformation behavior and microstructural evolution of Al-Zn-Cu-Mg-Sc-Zr alloy during high temperature compression

The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of 380–470 °C and strain rate range of 0.001–10 s⁻¹ using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow softening at low strains (ɛ<0.05). The stress decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon exponential equation with the activation energy for deformation of 157.9 kJ/mol. The substructure in the deformed specimens consists of few fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations at the grain boundaries. The dynamic flow softening is attributed mainly to dynamic recovery and dynamic recrystallization. Foundation item: Project(2006AA03Z523) supported by the National High-Tech Research and Development Program of China     

直接接触式湿烟气余热回收热质传递数值研究

在Fluent软件中,基于欧拉-拉格朗日方法和自定义函数(UDF),构建了三维稳态模型,并在离散相模型(DPM)基础上,耦合欧拉壁膜模型(EWF)对冷凝室内湿烟气与喷淋液滴及周围壁面间的凝结传热进行数值模拟研究。研究结果表明,DPM与EWF耦合可以更精确地模拟湿烟气在冷凝室内的凝结换热;入口烟气流速越大,冷凝室高度越低,则出口烟气温度和出口烟气水蒸气体积分数越高,烟气换热效率越低,且变化幅度逐渐减缓;冷凝室高度越高,则壁面湿烟气凝结量越大,但随着入口烟气流速增大,冷凝室高度对凝结换热的影响逐渐减弱,换热效率提高幅度也明显减小。