Water model experiment on the liquid flow behavior in a bottom blown bath with top layer

Water model experiments were performed to study the effect of top slag on the mean flow and turbulence characteristics in a steel bath agitated by bottom gas injection. The slag was modeled by silicone oil with a density of 0.968 g/cm³ and a kinematic viscosity 100 times larger than that of water at 25 °C. Velocity measurements were made using a two-dimensional (2-D) laser Doppler velocimeter (LDV) in the absence of swirl motions. The output signals of the LDV system were processed on a personal computer to obtain the axial and radial mean velocity components, the root-mean-square (rms) values of the axial and radial turbulence fluctuations, the Reynolds shear stress, and the turbulence production for two cases with and without top slag. The bubbling jet (or the bubble dispersion) region was localized near the centerline of the bath by the presence of the top oil layer. The mean flow and turbulence motions in the recirculation region located outside the bubbling jet region were also suppressed significantly by the top layer. This result could be attributed to the entrainment of top slag into steel in a real system.     

Bubble and liquid flow characteristics in a wood’s metal bath stirred by bottom helium gas injection

A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood’s metal with a melting temperature of 70 °C was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a two-needle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.     

Velocity and turbulence measurements in a cylindrical bath subject to centric bottom gas injection

Laser Doppler velocimeter (LDV) measurements were made to clarify the fluid flow behavior in a bath subject to centric bottom gas injection. Correlations of the axial mean velocity and turbulence components in the gas-liquid two-phase flow region,i.e., in the bubbling jet region, were proposed as functions of the inner diameter of nozzle, gas flow rate, and densities of gas and liquid. Measured values of the flow rate, momentum, and kinetic energy of water rising upward were approximated satisfactorily by these empirical correlations. In addition, the Reynolds shear stress was calculated and compared with measured values. Formerly Graduate Student, Osaka University,     

100 kg中频感应炉底吹氧搅拌的水模拟研究

采用几何相似比1:1的水模型对100 kg中频感应炉底吹氧的工艺参数(底吹流量0.2~0.56 m³/h,熔池高度120~330 mm)和流场进行模拟试验。结果表明,底吹熔池内形成的气相流速度在竖直方向上变化不明显,而在水平方向上存在较大梯度;随熔池高度和底吹流量的增加,气相流速度梯度变大,竖直气-液两相流变为倾斜向上运动;在熔池高度H小于240 mm、气体流量Q小于0.56 m³/h时,混匀时间分别随熔池高度和底吹流量的增加而减小,超过这一范围后混匀时间变化不明显。     

复吹转炉底吹氧气和石灰粉水模拟

 为了考察复吹转炉底吹氧气和石灰粉过程中的熔池特性,建立复吹转炉底吹喷石灰粉的水模型,用水模拟铁水,用空心玻璃微珠模拟石灰粉。利用图像处理法研究了底吹氧气和石灰粉时粉剂分布情况及熔池搅拌情况。采用熔池电导率法考察了相同条件下底吹喷粉与不喷粉时的混匀时间。研究结果表明,喷粉能够促进熔池搅拌,且粉剂扩散速度随底吹载气流量增大而增大;未喷粉时,混匀时间随载气流量增大而减小;在相同底吹载气流量条件下,喷粉时熔池的混匀时间明显低于未喷粉时的混匀时间,且在试验范围内,混匀时间在底吹载气流量为2 m3/h(标准态)时出现极小值。     

Turbulence characteristics of a gas-stirred steel bath outside the bubble plume

In order to understand the turbulence characteristic in melts stirred with injected gas, the relations for effective diffusion coefficient, turbulent kinetic energy and mean size of energy containing eddies were derived from the energy equation with an extended flow field for the steel bath, where strong bubble plume and surface currents are present. 67 or 23% of the energy is dissipated in the bubble plume or surface flow zone. An increasing entrainment coefficient leads to higher values of energy dissipation factor, effective diffusion coefficient and mean size of energy containing eddies, but to low degrees of turbulence. With increasing bath aspect ratio the energy dissipation factor increases, but the degree of turbulence decreases. With increasing gas flow rate and bath height the effective diffusion coefficient enlarges. Increasing bath size leads to large mean size of energy containing eddies, which reaches 17% of the bath diameter at high gas flow rates.     

Aluminium scrap melting under different liquid aluminium flow conditions: part-II: two phase flow

This experimental research work deals with aluminium (Al) alloy melting in an Al bath. In this liquid metal, nitrogen gas was introduced at specific locations and at different gas flow rates. The samples employed, along with their position in the liquid Al, and the procedure for melting detection, were identical with the ones utilised in Part I. The introduction of gas into liquid Al has different effects on the melting time of the immersed Al 6061 alloy cylinder. For the range of gas flow rates examined, the addition of gas into a stagnant Al bath (i.e. natural convection conditions) produces insignificant changes in melting time. However, when the liquid Al is moving (i.e. forced convection conditions), the gas addition leads to a sizeable reduction in melting time. The melting time reduction ratio is introduced as a way to compare the melting under single and two phase flow liquid Al conditions. It is found that this ratio is affected by the nozzle position and also by the gas flow rate. The concept of an equivalent single phase velocity is also introduced, and defines the single phase velocity of liquid Al which results in the same melting time of the cylinder as under two phase flow conditions. It is found that the equivalent single phase velocity is influenced by both the gas flow rate and the nozzle position. The parameter which most likely contributes to the acceleration of the melting rate in two phase flow is the turbulence intensity, which is expected to increase due to the nitrogen gas injection.     

EBT区域底吹流量变化对电弧炉炼钢的影响

 电弧炉底吹是加速熔池流动、减少EBT区域死区、改善炼钢反应的重要手段，底吹流量变化会影响电弧炉熔池流动和冶金效果。利用Fluent软件研究了100 t电弧炉EBT区域附近不同底吹流量的熔池流动特性，发现当EBT区域底吹流量从100增加至150 L/min时，熔池平均流速提高18.03%，死区面积减少22.06%；当进一步增加至200 L/min时，熔池流速和死区面积变化幅度降低。在此基础上，通过100 t电弧炉炼钢试验研究了不同底吹条件下的冶金效果，发现底吹可显著降低电弧炉钢铁料消耗和石灰消耗，缩短冶炼周期，降低炉渣FeO质量分数和钢液碳氧浓度积；随着EBT区域底吹气体流量从100增加至150 L/min，冶金效果进一步得到改善。     

Apparent Roughness in Wave–Current Flow: Implication for Coastal Studies

High turbulence intensities generated by waves in the wave bottom boundary layer affect the mean current velocity and should be taken into account for calculation of currents in the presence of waves. This influence of the wave-induced turbulence on the mean current can be schematized by introducing an “apparent” bed roughness, which is larger than the physical bottom roughness. Apparent bed roughness is defined here as roughness that provides the same depth-mean velocity for current alone configuration as for the wave–current flow. A one-dimensional vertical “k–l” turbulence closure model that allows detailed time dependent flow modeling has been applied for apparent roughness computations. The domain of variable parameters is chosen according to the Israeli near-shore conditions. An approximate expression for apparent bed roughness calculations as a function of wave and current parameters based on this turbulence closure model is derived. Simulation of flow patterns on the Tel Aviv coast using the three-dimensional Costal and Marine Engineering Research Institute flow model and implementing apparent roughness maps, calculated by the approximate expression, has been performed.     

Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model

Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm³/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm³/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.     

复吹转炉底吹非均匀供气对熔池搅拌混匀的影响

摘要：为了强化转炉熔池的搅拌,在200t复吹转炉1∶12的模型进行物理模拟试验,研究了底吹非均匀供气对转炉复吹和纯底吹熔池的搅拌混匀效果;采用数学模拟的方法计算了纯底吹条件下,转炉采用底吹非均匀供气时的熔池流体流动。研究结果表明,在所研究的不同的底吹非均匀供气方案中,与底吹均匀供气方案相比,线性底吹非均匀供气方案有利于改善转炉熔池搅拌效果,最佳的底吹非均匀供气方案的混匀时间比均匀供气降低了19%～25%。复吹时底吹非均匀供气的混匀时间降低程度要比纯底吹的非均匀供气大,即复吹条件下,底吹采用非均匀供气更有利于熔池搅拌混匀。采用线性底吹非均匀供气方案时,在熔池内形成了明显的大循环非对称流动,有利于整个熔池内的对流传质,从而缩短了混匀时间。     

Computational Fluid Dynamic Modeling of Zinc Slag Fuming Process in Top-Submerged Lance Smelting Furnace

Slag fuming is a reductive treatment process for molten zinciferous slags for extracting zinc in the form of metal vapor by injecting or adding a reductant source such as pulverized coal or lump coal and natural gas. A computational fluid dynamic (CFD) model was developed to study the zinc slag fuming process from imperial smelting furnace (ISF) slag in a top-submerged lance furnace and to investigate the details of fluid flow, reaction kinetics, and heat transfer in the furnace. The model integrates combustion phenomena and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with a number of user-defined subroutines in FORTRAN programming language were used to develop the model. The model is based on three-dimensional (3-D) Eulerian multiphase flow approach, and it predicts the velocity and temperature field of the molten slag bath, generated turbulence, and vortex and plume shape at the lance tip. The model also predicts the mass fractions of slag and gaseous components inside the furnace. The model predicted that the percent of ZnO in the slag bath decreases linearly with time and is consistent broadly with the experimental data. The zinc fuming rate from the slag bath predicted by the model was validated through macrostep validation process against the experimental study of Waladan et al. The model results predicted that the rate of ZnO reduction is controlled by the mass transfer of ZnO from the bulk slag to slag–gas interface and rate of gas-carbon reaction for the specified simulation time studied. Although the model is based on zinc slag fuming, the basic approach could be expanded or applied for the CFD analysis of analogous systems.     

Effects of surface flow control on fluid flow phenomena and mixing time in a bottom blown bath

The intensity of mixing in a molten metal bath stirred by bottom gas injection can be represented by the mixing time. According to previous water model experiments, the mixing time is known to be dependent on the operational variables such as the bath diameter, bath depth, location of a bottom nozzle, and gas flow rate. It is not easy to control the former three variables during processing, and the dependence of the mixing time on the gas flow rate is weak. In this study, the possibility of changing the mixing time drastically due to the control of the surface flow in the bath is examined. Three kinds of boundary conditions were imposed on the bath surface, and the relation between the fluid flow phenomena resulting from the surface flow control and the mixing time was investigated. The mixing time was found to be significantly influenced by the surface flow control. In particular, when the surface flow was suppressed by bringing a circular cylinder into contact with the bath surface, the mixing time became very long.     

Physical and mathematical models of gas‐liquid fluid dynamics in LD converters

Fluid dynamics of gas‐liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing‐bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring.     

On the numerical calculation and non-dimensional representation of velocity fields in bubble-stirred ladle systems

The numerical simulation of axisymmetric gas stirred ladle systems has been considered and a mathematical model based on the dimensionless form of the turbulent Navier-Stokes equations developed. Embodying a simplified turbulence model in the calculation procedure, it is demonstrated from the first principles that non-dimensional velocity components at relatively low gas flow rates, follow identical distribution patterns at equivalent dimensionless bath depths and radii, provided values of the parameters L/R and Q/R^2.5 are similar for the various gas stirred systems being considered. The theoretical analysis has been substantiated through numerical experimentations and by considering a set of five independant experimental studies on liquid velocity measurements reported in the literature.     

Water model study of horizontal molten steel-Ar two-phase jet in a continuous casting mold

A water model study was carried out to understand the behavior of a molten steel and Ar gas two-phase jet issuing out of a submerged entrance nozzle in continuous casting modls. A mixture of water and air was injected horizontally from a circular pipe settled flush with the narrow face of a mold having a rectangular cross section. The water-air two-phase jet thus generated was pulled upward through the effect of buoyancy force acting on air bubbles. The deflection of the jet in the upward direction was correlated by introducing a velocity scale, which could characterize the upward moving velocity of the jet. The mean velocity and turbulence components of water flow were measured with a laser Doppler velocimeter. Empirical equations were proposed for predicting the two velocity components.     

Evaluation of Mean Velocity and Turbulence Measurements with ADCPs

To test the ability of acoustic Doppler current profilers (ADCPs) to measure turbulence, profiles measured with two pulse-to-pulse coherent ADCPs in a laboratory flume were compared to profiles measured with an acoustic Doppler velocimeter, and time series measured in the acoustic beam of the ADCPs were examined. A four-beam ADCP was used at a downstream station, while a three-beam ADCP was used at a downstream station and an upstream station. At the downstream station, where the turbulence intensity was low, both ADCPs reproduced the mean velocity profile well away from the flume boundaries; errors near the boundaries were due to transducer ringing, flow disturbance, and sidelobe interference. At the upstream station, where the turbulence intensity was higher, errors in the mean velocity were large. The four-beam ADCP measured the Reynolds stress profile accurately away from the bottom boundary, and these measurements can be used to estimate shear velocity. Estimates of Reynolds stress with a three-beam ADCP and turbulent kinetic energy with both ADCPs cannot be computed without further assumptions, and they are affected by flow inhomogeneity. Neither ADCP measured integral time scales to within 60%.     

Mixing and solid-liquid mass-transfer rates in a creusot-loire uddeholm vessel: A water model case study

The process of mixing and solid-liquid mass transfer in a one-fifth scale water model of a 100-ton Creusot-Loire Uddeholm (CLU) converter was investigated. The modified Froude number was used to relate gas flow rates between the model and its protoype. The influences of gas flow rate between 0.010 and 0.018 m³/s and bath height from 0.50 to 0.70 m on mixing time were examined. The results indicated that mixing time decreased with increasing gas flow rate and increased with increasing bath height. The mixing time results were evaluated in terms of specific energy input and the following correlation was proposed for estimating mixing times in the model CLU converter: T _mix=1.08Q ^−1.05 W ^0.35, where Q (m³/s) is the gas flow rate and W (tons) is the model bath weight. Solid-liquid mass-transfer rates from benzoic acid specimens immersed in the gas-agitated liquid phase were assessed by a weight loss measurement technique. The calculated mass-transfer coefficients were highest at the bath surface reaching a value of 6.40 × 10⁻⁵ m/s in the sprout region. Mass-transfer coefficients and turbulence parameters decreased with depth, reaching minimum values at the bottom of the vessel.     

Turbulent Flow near Vertical Angled Fish Screen

Mean and turbulent flow characteristics on the upstream and downstream sides of the screen in a flow diversion channel have important implications for operation and maintenance (e.g., sedimentation) and for assessing fish behavior related to flow turbulence. This technical note extends an earlier study on mean flow near screens to turbulence characteristics. Acoustic Doppler velocimeter was used to explore three-dimensional mean and turbulent flow characteristics on the upstream and downstream sides of vertical angled fish screens. The present study confirms the two-dimensional mean velocity observations of the previous experimental work and shows that the vertical mean velocities are less than 10% of the local magnitudes of longitudinal velocity and hence can be ignored. Horizontal components of the mean velocity on the downstream side of the screen were relatively small, but the turbulent velocity fluctuations were two to three times as intense as those measured on the upstream side.     

Mixing time and fluid flow phenomena in liquids of varying kinematic viscosities agitated by bottom gas injection

A model experiment was carried out to investigate the mixing condition and related fluid flow phenomena in a slag layer of metal-refining processes agitated by bottom gas injection. Silicone oil was used as a model for the molten slag. Mixing time in a silicone oil bath was measured with a newly developed laser optical sensor. Measured mixing time values increased with an increase in the kinematic viscosity of the silicone oil. In order to explain the relation between mixing time and the kinematic viscosity of silicone oil, the rising velocity of bubbles and the vertical and horizontal velocities of silicone oil flow were measured with an electroresistivity probe and a laser Doppler velocimeter, respectively. The increase in the mixing time with the kinematic viscosity of silicone oil was caused mainly by the suppression of upward motion of bubbles and silicone oil in the bubbling jet region. An empirical correlation for the mixing time was derived as a function of the kinematic viscosity of silicone oil, in addition to conventionally used parameters such as the gas flow rate, bath diameter, and bath depth.