矿用空气幕数值模拟研究

矿用空气幕作为一种新型的矿井风流调控技术,具有广泛的应用前景。建立了矿用空气幕的数学模型和有限元模型,并应用ANSYS软件对风流特性进行数值模拟,结果表明:(1)矿用空气幕供风器的结构影响其供风风压及风流速度,在供风器出口面积一定时,供风器出口宽度小能量损失也小,空气幕的作用效果好;(2)当矿用空气幕风机风量为14m3/s、风压为480Pa、供风器异面矩形管的进出口面积分别为1.0m2和0.54m2时,其进出口最佳宽度分别为333mm和180mm;(3)解决了以往矿用空气幕的研究和设计主要依靠经验所带来的不足,对矿用空气幕调控风流技术的推广应用具有重要意义。     

Aeration Characteristics of Ski Jump Jets

Scour downstream of ski jumps may be avoided by jet deflection to an area where the energy dissipation is accomplished. The main purpose of this experimental study was the analysis of the jet air entrainment downstream of a ski jump, both for pure water and preaerated approach flow conditions. A systematic variation of the Froude number and the flow depth in the approach flow channel resulted in a range of discharge characteristics, whereas the geometry of the ski jump was maintained for all tests. The air concentration profile was measured at different locations downstream from the ski jump to evaluate the: (1) jet air concentration distribution; (2) location of minimum air concentration along the mixture flow jet and development of the minimum and the cross-sectional average air concentrations; (3) jet trajectories; and (4) process of air entrainment characteristics and jet disintegration. The results demonstrate the significant effect of the approach flow Froude number, the approach flow depth, and of preaeration on jet disintegration.     

聚合射流流场的仿真模拟

 为研究有低密度伴随的聚合射流氧枪射流流场,利用氧枪射流检测系统,对常温下(冷态)以空气模拟的射流进行了物理模拟。结合数值模拟结果,分析了传统无伴随流射流以及带有副孔氦气低密度伴随情况下射流流场的流动状态,讨论了在不同的滞止压力和环境温度时有、无伴随射流流场特性。结果表明,修正的k ε双方程模型能较好地预测实验结果,伴随流的存在减缓了中心射流的沿程衰减,环境温度的变化影响射流在径向和轴向的流动状态。     

Experimental Study on Selective Withdrawal in a Two-Layer Reservoir Using a Temperature-Control Curtain

An experimental study was conducted to investigate the use of a temperature-control curtain in selective withdrawal from a two-layer stratified reservoir. This study focused on the case where cool water at a depth was forced to flow under the curtain. The evolution of the mean flow, the withdrawal water quality, and the mean velocity field were studied using particle image velocimetry and laser-induced fluorescence. Practical relationships were developed for predicting the withdrawal water quality and the interface height as a function of time. The structures of the flow field in both the upper and lower layers are discussed in detail. The flow in the lower layer was dominated by the recirculation eddy induced by the jet flow under the curtain and a relation between the eddy length and the interface height was obtained. Close to the intake, within about 3d (where d = intake diameter), the velocity field can be well described by the potential flow theory. Beyond 3d, however, the flow field considerably deviated from the potential flow theory due to the jet expansion and stratification. A general discussion of the results and engineering applications are also provided.     

Effect of an Electromagnetic Brake on the Turbulent Melt Flow in a Continuous-Casting Mold

This article presents numerical and experimental investigations with respect to the fluid flow in the continuous-casting process under the influence of an external direct current (DC) magnetic field. Numerical calculations were performed by means of the software package CFX (Ansys, Inc., Canonsburg, PA) with an implemented Reynolds-averaged Navier–Stokes (RANS)-SST turbulence model. The nonisotropic nature of the magnetohydrodynamic (MHD) turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements carried out in a small-scale mockup using the eutectic alloy GaInSn. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mold. The comparison between our numerical calculations and the experimental results displays a good agreement; in particular, we reconstructed the peculiar phenomenon of an excitation of nonsteady, nonisotropic, large-scale flow perturbations caused by the application of the DC magnetic field. Another important result of our study is the feature that the electrical boundary conditions, namely the wall conductivity ratio, have a serious influence on the mold flow while it is exposed to an external magnetic field.     

Experimental and mathematical investigation of the fluid flow inside and below a 1/4 scale air model of a flash smelting burner

Single-phase turbulent fluid flow inside and below a burner model was studied to better understand the fluid flow processes occurring inside and below flash smelting burners. The effect of Reynolds number and temperature on the axial velocity profiles in a 1/4 scale experimental air model of a jet flow burner and shaft were investigated. Laser Doppler anemometry (LDA) was used to determine the mean and fluctuating axial velocity components within and below this burner. Also experimentally determined were the pressure profiles along the length of the burner and shaft and the inlet air and wall temperature profiles. In the experiments, the Reynolds number range was approximately 60,600 to 76,100, which was in the turbulent flow regime. A mathematical model was used to simulate axisymmetric two-dimensional air flow through a jet flow burner and shaft for Reynolds numbers of 60,000 to 304,000. The axial velocity predictions of the high axial velocity region and surrounding region in the shaft were in reasonable agreement with the axial velocity experimental results. Recommendations are made for the improvement of the design of flash smelting burners.     

公路隧道空气幕与射流风机通风方法对比及优化

针对隧道射流通风存在功率利用率低，大浓度尾气调控不理想等问题，运用FLUENT软件，以模拟优化瓮福磷矿隧道的通风系统问题为实例，将射流风机和空气幕引射风流进行风流对比，提出引射风流空气幕替代射流风机加强隧道通风的全新命题。研究结果表明:两种优化风机组合都能达到隧道所需的通风标准，在进行对比过程中，如果总功率一样，引射风流空气幕组合产风量大于射流风机组合，而总功率145.5 kW空气幕组合可产生与总功率180 kW射流风机组合类似的通风效果，且总功率可节约34.5 kW。在风机组合优化过程中，各风机功率分配越平均对风机组合通风效率提升越大，同种功率的风机两两并联，通风效果要优于不同功率风机两两并联。      

Effect of Jet Air Content on Plunge Pool Scour

The effect of air discharge on plunge pool scour was investigated by using a simplified experimental configuration. Instead of considering the complete arrangement involving chute and deflector resulting in an air-water jet impinging on a sediment surface, the mixture flow was produced with a circular pipe for which the air concentration and the jet diameter close to impact on the free water surface are known. The results of this study were primarily directed to the definition of a three-phase Froude number that accounts for the combined effects of an air-water mixture jet on scour. The analysis of data allows simple estimates of the scour geometry including a generalized scour profile, the width of scour, and the temporal advance of the extreme scour depths. It was pointed out that for a certain water velocity and selected grain characteristics, the addition of air to the jet results in an increase of scour depth. However, if the reference would be the air-water mixture velocity, scour depth decreases significantly by the addition of air to the jet.     

平面射流连续反应器三角区内压力分布的研究

在冷态模拟的条件下,对平面射流连续反应器内由两相交平面射流界定的不同结构的三角区内的压力分析进行了实验测量,结果表明,在三角区只有 中空通道与大气相连而其他连都处于密闭的条件下,三角区内存在负压分布,尽管很小,却有利于保护粉剂通畅地加入到反应器内,这为平面射流连续反应器的结构设计提供了重要的实验依据。     

空气幕研究进展

阐述了国内外大门空气幕和矿用空气幕的研究进展,列出了不同时期矿用空气幕的理论公式,介绍了矿用空气幕的结构和功能,归纳了矿用空气幕的布置形式和取风方式.可以看出,在大门空气幕研究的基础上,矿用空气幕的研究与应用进展良好,可替代风门隔断风流、替代辅扇或风机机站引射风流和替代风窗增阻减少风流,这对解决矿井运输巷道或易变形巷道上风流短路、污风停滞、风流反向、污风循环等风流调控的技术难题具有重要作用,其研究成果将得到进一步的推广应用.     

Strongly Advected Jet in a Coflow

We present the results of an experimental investigation into the behavior of a strongly advected jet (weak jet) in a coflowing ambient fluid. Laser-induced-fluorescence and image processing techniques are employed to provide quantitative information about the mean properties of the flow. Data are obtained at previously inaccessible distances from the flow source, enabling the mean and fluctuating behavior of the flow in the strongly advected region to be more clearly defined. The spread relationship, traditionally employed to model the mean behavior of these flows, is redefined based on this experimental information. Both the spread constant and the ratio of the tracer to the velocity spread are shown to change in the strongly advected region. The results presented are discussed in the context of recent observations about the importance of large-scale eddy motions in defining the mean behavior of weakly advected jets and plumes. In addition the experiments provide information on the contrasts between the mixing processes in the weakly advected and strongly advected coflowing jet regions, and their influence on the mean behavior of these flows. Concentration fluctuation statistics from both regions are presented and implications for the application of the entrainment assumption in the strongly advected region are also discussed.     

Influence of Design and Operation Parameters on Bag-Cleaning Performance of Pulse-Jet Baghouse

In this study, a filter test system with clean new fabric bags was used to measure the pulse pressure and acceleration of the filter bag. Fabric acceleration and pulse pressure were used as an index of bag-cleaning intensity. The jet pump curves, which relate the flow rate through the venturi to the average developed pressure by the venturi, were determined by the similar system. The intersection of the jet pump curve and the bag operating line, which relates the pressure drop to flow rate across the bag during pulse-jet cleaning, is the system operating point that was used to predict the average pulse pressure in the bag during pulse-jet cleaning. Experimental results of this study show that a higher pulse pressure can be achieved without the venturi at the top of the bag for bag materials with low resistance coefficient. For bags with higher resistance coefficients, higher pulse pressure is obtained with a venturi installed at the top of the bag. The predicted pressure values are in good agreement with experimental data. Dimensional analysis for jet pump performance was developed to reduce the experimental data. The results show that the jet pump curves obtained under different operating conditions can be reduced to the same nondimensional curve, which can be used to facilitate the design and operation of a pulse-jet cleaning system.     

空气幕研究进展

阐述了国内外大门空气幕和矿用空气幕的研究进展,列出了不同时期矿用空气幕的理论公式,介绍了矿用空气幕的结构和功能,归纳了矿用空气幕的布置形式和取风方式.可以看出,在大门空气幕研究的基础上,矿用空气幕的研究与应用进展良好,可替代风门隔断风流、替代辅扇或风机机站引射风流和替代风窗增阻减少风流,这对解决矿井运输巷道或易变形巷道上风流短路、污风停滞、风流反向、污风循环等风流调控的技术难题具有重要作用,其研究成果将得到进一步的推广应用.      

Experimental Simulation of a Vertical Round Jet Issuing into an Unsteady Cross-Flow

This paper investigates the discharge of a vertical round jet into an unsteady cross-flow that consists of a mean flow and a sinusoidally oscillating component. An experimental technique is devised to simulate the unsteady cross-flow situation in the laboratory. A vertical jet-pipe-nozzle assembly is physically oscillated backward and forward in the steady flow stream of a laboratory flume, and the flow patterns are viewed by an observer moving with the jet. Dispersion patterns of the dye-marked jet fluid are studied with a phase-locked analysis of digitized flow images. Oscillations in cross-flow velocity are found to organize the jet fluid into regular large-scale fluid patches, which, after time averaging, lead to a widened jet width and enhanced dilution. Experiments are also carried out on a vertical jet discharging into a current with surface waves, a situation that approximates to a genuine oscillating cross-flow with a nonzero mean velocity. The two sets of experimental observations are found to match with each other. The validity of the experimental simulation technique is further supported by a computational fluid dynamics study of the flow problem, in which it is possible to produce an idealized oscillating cross-flow situation. The numerical results agree well with the experimental observations.     

多孔喷流冲击换热实验结果及分析

喷流冲击换热是一种高效换热形式，用在冷流体侧可以降低换热壁面温度。本文针对影响喷流冲击的几个主要因素进行了实验研究，其中包括喷流速度、喷流高度、喷孔板的开孔率等，并针对交叉流对换热的影响进行了分析;用90多组实验数据拟合了准则公式，此公式已被用在某化工厂燃油焦炉实验台的设计中。     

气流粉碎机在高压高比容钽粉中的应用研究

介绍了用气流粉碎机制备高压高比容钽粉的方法。采用DOE试验设计的方法对气流粉碎机制备高压高比容钽粉过程中的关键参数进气压力和分级轮频率进行全因子试验设计、实施、结果分析,确定了最佳的工艺参数,成功实现了气流粉碎机在高压高比容钽粉制备中的应用。     

气刀对热镀锌锅流场影响的数值模拟

气刀喷吹是带钢连续热镀锌生产的重要工序,理解气刀喷吹过程对锌锅内部流场和表面流场规律的影响对提高带钢质量具有重要意义.建立了带钢连续热镀锌过程中气刀喷吹三维流场数学模型及锌锅流场三维数学模型,将气刀喷吹在锌锅表面的压力作为动量源项加载到锌锅流场数学模型的动量方程中,分析气刀喷吹压力及带钢速度对锌锅内部及表面流场的影响,...     

狭缝射流冲击柱状凸形表面流动换热特性

采用数值方法研究了狭缝射流冲击柱状凸形表面的流动换热特性,通过四种湍流模型计算结果与实验数据对比,确定了湍流模型适用性.以压力梯度分布为依据,重点分析了狭缝射流沿柱状凸形表面的流动结构和边界层分离特点及柱状凸形表面的强化换热特性.结果表明:RNG k-ε和Realizable k-ε模型具有预测适应性;狭缝射流冲击至柱状凸形表面,气体沿表面运动,速度降低,并在流动下游发生边界层分离;量纲一的逆压梯度随量纲一的曲率半径(D/B)的减小而增大,使得边界层分离更早出现;驻点区域换热Nu随量纲一的曲率半径(D/B)的减小而获得增强,但流动进入下游后,D/B对换热基本无影响;压力梯度是影响狭缝射流冲击柱状凸形表面换热分布的重要因素.      

冷、热风幕气幕式空调伞的实验研究和对比分析

介绍了一种营造局域舒适性环境的新型空调设备--气幕式空调伞,借助实验手段比较了两种空调伞的流场、温度场以及最佳高径比,并对有效空调区和舒适性进行了分析和比较.