Application of Cooling Water in Controlled Runout Table Cooling on Hot Strip Mill

The controlled runout table cooling is essential in determining the final mechanical properties and flatness of steel strip. The heat of a hot steel strip is mainly extracted by cooling water during runout. In order to study the heat transfer by water jet impingement boiling during runout, a pilot facility was constructed at the University of British Columbia. On this pilotfacility, the water jet impingement tests were carried out under various cooling conditions to investigate the effect of processing parameters, such as cooling water temperature, water jet impingement velocity, initial strip temperature, water flow rate, water nozzle diameter and array of water nozzles, on the heat transfer of heated strip. The results obtained contribute to the optimization of cooling water during runout.     

钢板轧后冷却过程的数值模拟及变形分析

 针对钢板冷却发生翘曲变形的问题，利用热弹塑性有限元法对中厚板冷却过程的温度场及应力应变场进行数值模拟。采用分步循环加载的方法精确模拟不同换热边界条件，温度场模拟结果与实测值吻合较好。将热分析得到的温度场作为载荷进行钢板冷却过程应力应变的模拟，模拟结果表明塑性应变差出现在水冷的开始阶段。因此为了获得平直的板形，必须调整上下集管水量比，尽量减小水冷开始时上下表面的应力和塑性应变差。     

A Water Model Study of Impinging Gas Jets on Liquid Surfaces

Water modeling experiments were designed to observe the deformation of a liquid surface by impinging the gas jet. Video images were taken and processed in a systematic way. The important surface cavity parameters, such as depth, width, and their frequency of oscillation, were obtained. The relation between surface depression depth and the supplied gas momentum were consistent with previous findings and were extended to higher flow rates. The surface instability and the onset of splashing were observed and interpreted with the Blowing number. The wave behaviors were described qualitatively with a combination of photographic evidence and power spectral density analysis to extract the characteristic wave numbers for each gas flow rate. The analysis of the time series of the surface variables showed a connection to the attenuation of turbulence gas pressure fluctuation and the surface deformation by the gas impingement. Bath velocities were measured with a particle image velocimetry (PIV) technique. To quantify the transfer of kinetic energy from the gas to the liquid, an energy transfer index was defined and calculated with the PIV data. The index was insensitive to gas flow rate but increased with cavity width. The momentum transfer across the interface was also analyzed, and a similar cavity width dependence was found. A correlation between the cavity shape and momentum transfer was proposed.     

Flapping Instability of Vertically Impinging Turbulent Plane Jets in Shallow Water

A submerged, vertical, turbulent plane jet impinging onto a free water surface will be self-excited into a flapping oscillation when the jet velocity, exiting the jet orifice, exceeds a critical value. The dependence of the critical velocity W0c and the flapping frequency f0 on the water depth H and the jet orifice width d was investigated in detail in this study. The jet flapping motion was visualized by a laser induced fluorescence technique and measured with a laser Doppler velocimeter; a supplemental measurement of the displacement of water surface by a surface wave gauge was made. The jet flapping characteristics are interpreted in terms of the effective water depth given by He = H-z0, where z0 is the virtual origin of the jet. The critical jet exit velocity was found to increase linearly with the effective water depth and to decrease with the square root of the jet orifice width. The flapping frequency decreased with the root square of the effective water depth and independent of the jet orifice width. These results led to a critical condition for the onset of instability as St = 0.929[(H ? z0)/d]?3∕2, where St is the critical Strouhal number defined by St = f0d∕W0c.     

Erosion of Sand by Circular Impinging Water Jets with Small Tailwater

This technical note presents the results of an experimental study of the erosion of loose cohesionless sand beds by impinging circular water jets with a minimum depth of tailwater. Measurements were made of both the maximum dynamic and static scour depths and the radius of the scour hole. It was found that the dynamic scour depth is about three times that of static scour at the asymptotic state. Dimensional arguments and experimental results are used to show that the main dimensions of the scour hole at the asymptotic state are a function of the densimetric Froude number F0′ = U0′/, where U0′ = velocity of the jet at the original level of the sand bed; g = acceleration due to gravity; D = mean diameter of the sand particles; ρ = density of the eroding fluid; and Δρ = difference between particle and fluid densities. Useful correlations have been developed to estimate the size of the scour holes. Also included is a comparison between the erosion caused by submerged and unsubmerged impinging circular jets.     

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。     

Mathematical Modeling of Impinging Gas Jets on Liquid Surfaces

In top-blowing operations, the gas jet is a major source of momentum, so to model the momentum exchange properly with the liquid, the full-stress boundary conditions must be applied. A new mathematical method for better representation of the surface boundary condition was developed by combining the Cartesian cut cell method and volume of fluid method. The computational code was validated with the broken dam problem and reported critical phenomena in wave generation. The model was applied to impinging jets on liquid surfaces in two dimensions. The cavity depth was in good agreement with experimental measurements. The process of ligament and droplet formation was reproduced. The extent of momentum transfer to the liquid was investigated, and the trends with lance height and gas flow rate were similar to experimental evidence. The following important aspects of momentum transfer were identified: surface roughness as well as the development of local pressure gradients around wave crests. Kelvin–Helmholtz instability theory was used to interpret the results with respect to critical velocity for the onset of droplet formation. These principles were extended to conditions relevant to basic oxygen furnace (BOF) steelmaking. The critical velocities for droplets were calculated as functions of the physical properties for the gas–steel, gas–slag, slag–steel interfaces. The implications for BOF steelmaking were discussed. The mathematical model was applied to a simplified configuration of full-scale BOF steelmaking, and the local force balance was well described.     

圆形冲击射流对水层的穿透深度研究

要使中厚板淬火控冷装置获得最佳的冷却能力,必须要保证冲击射流可以穿透钢板表面的滞留水层。通过实验和数值模拟的方法,研究了圆形冲击射流对水层的穿透深度与射流速度、射流直径和射流高度的关系,并给出了穿透深度与射流出口弗鲁德数Fr的拟合曲线关联式。     

Scour of Cohesive Soil by Submerged Circular Turbulent Impinging Jets

This paper introduces a method for estimating the scour in cohesive soils produced by a submerged vertical circular turbulent impinging jet. Determining scour in cohesive soils is a complex problem, partly because the clay particles within the soil are held together by electrochemical forces that are not easily quantifiable. As well, erosion occurs in many forms, such as the removal of individual particles or as large chunks of soil. Results of a laboratory study of scour by a circular impinging jet of a cohesive soil, consisting of 40% clay, 53% silt, and 7% fine sand, are presented. Analysis based on the mechanics of the impinging jets shows that the dimensions of the scour hole at an equilibrium state of scour are a function of the momentum flux from the jet, the impingement height (for “large” impingement heights), the viscosity and density of the eroding fluid, and the critical shear stress of the soil. Mass erosion was the predominant type of erosion observed.     

Experimental Investigation of Three-Dimensional Nonbuoyant Rectangular Jets

The behavior of a nonbuoyant three-dimensional rectangular water jet with aspect ratios of 5, 10, and 20 were investigated based on experimental results of the mean velocity field obtained by particle image velocimetry. The theoretical centerline velocity equation derived from the point source concept using the spreading rate for the axisymmetric jet gave velocity results that agreed well with the measured centerline velocity, and provided the potential core region, two-dimensional region, and axisymmetric region. The similarities of the measured cross-sectional velocity profiles along both major and minor axes were verified. In the two-dimensional region, the Gaussian constant and Strouhal number tended to be preserved, and the spreading rate decreased at the end of the two-dimensional region. In the transition zone between the two-dimensional and the axisymmetric regions, the centerline velocity decay rate and the spreading rate were observed to drop, whereas the Gaussian constant and Strouhal number were found to increase with axial distance. The range of the two-dimensional region demarcated by the criterion of the theoretical centerline velocity decay was very similar to those based on the conservations of the Gaussian constant and Strouhal number, and that based on the change in the spreading rate along the minor axis.     

Experimental Study of Sand and Slurry Jets in Water

This paper presents the results of an experimental study of turbulent sand jets and sand-water slurry jets impinging vertically into a stagnant water body. The jets contained silica sand with a median diameter D50 of 206?μm, and with an initial concentration 0.60 by volume for the sand jets, and 0.055–0.124 by volume for the slurry jets. The jets had densimetric Froude numbers between 2.0 and 5.94. The sand concentration and velocity profiles were measured simultaneously using a novel fiber optical probe, up to a distance of 130do for sand jets, and 65do for slurry jets, where do is the jet diameter at the water surface. The jets were found to have self-similar Gaussian profiles. The centerline sand concentration within the jets was found to decrease rapidly, following trends similar to single phase plumes. The centerline sand velocity profile decreased significantly before reaching a plateau region. The “terminal” centerline sand velocity within this region varies somewhat depending upon sand mass flux, and is between 0.32 and 0.43 m/s. The spreading rates of the jets were found to vary with the particle Froude number. Within the sand jets and the higher Froude number slurry jet, the sand concentration had a smaller spreading rate than the velocity. The other slurry jets had equal concentration/velocity spreading rates. The momentum flux of the sand within the jets was found to decrease sharply, followed by a constant flux below a depth of 25 to 30 jet diameters.     

连铸二冷气雾射流特性研究

通过对钢厂连铸二冷区使用的某喷嘴进行流动特性试验,探讨喷射角度、水量分布、雾滴粒径分布等对其的影响,为进一步研究二次冷却的传热机理、二次冷却的配水制度以及二次冷却喷嘴的最佳排布方式等奠定了基础.     

Three-Dimensional Numerical Study of Flows in Open-Channel Junctions

An open-channel junction flow is encountered in many hydraulic structures ranging from wastewater treatment facilities to fish passage conveyance structures. An extensive number of experimental studies have been conducted but a comprehensive three-dimensional numerical study of junction flow characteristics has not been performed and reported. In this paper, a three-dimensional numerical model is developed to investigate the open-channel junction flow. The main objective is to present the validation of a three-dimensional numerical model with high-quality experimental data and compare additional simulations with classical one-dimensional water surface calculations. The three-dimensional model is first validated using the experimental data of a 90° junction flow under two flow conditions. Good agreement is obtained between the model simulation and the experimental measurements. The model is then applied to investigate the effect of the junction angle on the flow characteristics and a discussion of the results is presented.     

层流冷却条件下碳钢相变过程的数值模拟

 采用数值模拟的方法,结合宝钢2050热连轧层流冷却生产线,模拟研究了不同碳当量钢种在层流冷却条件下的奥氏体转变过程,计算了前段主冷、稀疏冷却、后段主冷3种冷却模式对奥氏体转变过程的影响,定量分析了带钢厚度方向不同部位处奥氏体转变的差别。结果表明:在所选定的工艺条件下,随着碳当量的增加,铁素体开始转变时间明显推迟,铁素体开始转变温度明显降低,而珠光体开始转变时间和温度变化不大;不同冷却模式下铁素体、珠光体各相开始转变时间及演变过程差别较大,但最终各相的体积分数接近一致;带钢厚度方向各部位由于冷却速度的不同而存在明显的组织不均匀性。     

雾化冲击射流冷却热轧钢板的研究

利用有限元耦合场数值模拟计算方法对热轧钢板雾化冲击射流冷却进行模拟计算,结果表明,在其它条件相同的情况下,单喷嘴喷射时,在上喷和下喷的喷嘴附近冷却能力相同;多喷嘴喷射时,横向存在二次冷却,钢板表面横向温度分布总体上呈现逐渐降低的趋势。     

关于中间降温流程的差异

通过对氧化铝种子分解中间降温不同流程的简要测算,对相关流程的优劣进行了比较,并给出了该部分工艺流程的推荐意见。     

高炉冷却壁冷却水管管形研究

利用数值模拟的方法分析了冷却水管的截面形状与布置方式对冷却壁散热的影响;辅之以水力学试验,分析水管结构的阻力特性.分析结果表明:圆形水管内接方式是适用铸钢冷却壁的最佳方案;铜冷却壁可采用椭圆形水管,水管的长短轴比为0.8的结构能够同时达到提高冷却壁的冷却性能和节约冷却水的目的.研究结果表明:此研究可以为高炉冷却壁及冷却水管的优化提供技术支持.