Fluid flow and bath temperature destratification in gas-stirred ladles

The transient fluid flow and temperature distributions in argon-stirred ladles have been investigated. The governing equations of unsteady fluid flow and energy were solved numeri-cally with a control-volume technique, while the turbulence was modeled by the two-equationk- ∃ model. The two-phase zone was described by novel experimental equations, which char-acterize the gas-fraction distribution in the bath for a wide range of variables in both aqueous and liquid metal systems. Fully transient computational results are presented and compared against transient temperature computations based on a steady-state velocity field. The resulting mixing times compare closely with industrial experience. A.H. Castillejos E., formerly Postdoctoral Fellow, The University of British Columbia,.     

Mass transfer between solid and liquid in a gas-stirred vessel

Mass transfer between solid and bulk liquid in an axisymmetric gas-stirred water model of a metallurgical reactor has been investigated both experimentally and theoretically. To this end, mass transfer rates from benzoic acid compacts submerged in an aqueous gas bubble driven system were measured via a weight loss technique. In conjunction with the weight loss measurements, liquid velocity and turbulence kinetic energy distributions in the bath were also mapped via laser doppler velocimetry (LDV). From the detailed LDV measurements, relevant dimensionless groups such as $\operatorname{Re} _{loc,r} \left( { = \frac{{d\rho \sqrt {u^2 + v^2 } }}{\mu }} \right)$ and $\operatorname{Re} _t \left( { = \frac{{d\rho \hat u}}{\mu }} \right)$ were estimated. Experimental measurements indicated that flow parameters varied from one location to another within the system. The corresponding variation in dissolution rates was, however, less pronounced. Such a trend was observed for all three gas flow rates studied. It was found that experimentally measured dissolution rates can be correlated with the measured flow and turbulence parameters (viz., √u ²+v ² and û) in terms of a previously reported dimensionless correlation, viz., Sh=0.73 (Re_loc,r )^0.25 (Re _t )^0.32 (Sc)^0.33. Parallel to flow measurements, a two-phase turbulent flow model was also applied to numerically compute the distributions of mean and fluctuating velocity components in the vessel. Embodying the predicted velocity components in the aforementioned correlation, mass transfer rates were recalculated. A comparison between the two sets of Sherwood numbers (estimated on the basis of the experimentally measured and theoretically predicted flow fields) suggests that solid-liquid mass transfer rates in a gas-stirred vessel can be predicted reasonably well via an axisymmetric, steady-state, two-dimensional turbulent flow model.     

板翅式换热器流道中流体流动与传热的数值模拟研究

对板翅式换热器平直翅片流道中流体流动与传热的性能进行了数值计算,得出了七种不同高度、厚度和翅片间距大小的翅片流道中流体平均Nu数和压力降随Re数变化的曲线.     

幂律流体在旋转盘上的流动与传热数值分析

针对非牛顿幂律流体在无限大旋转圆盘上层流边界层内三维流动与传热问题,在普朗特数为常数的条件下,利用广义Karman相似变换,将连续方程、动量方程及能量方程形成的偏微分方程组化成常微分方程组,再采用多重打靶法数值求解非线性两点边值问题.分别针对剪薄型流体、牛顿流体和剪厚型流体,得到不同幂律指标下的速度和温度分布及不同普朗特数下温度场的结果.结果表明径向速度分量的峰值随幂律指标的增大而增大,轴向速度受边界层厚度的影响较突出,盘表面的传热随幂律指标和普朗特数都呈现递增趋势.最后将本文流场结果与Andersson等在不考虑传热情况下的结果进行比较表明吻合性较好.     

缩放管流体流动与传热性能数值研究

基于无源强化传热理论,提出一种新型缩放强化传热管.采用数值模拟方法研究了不同扩张段跨度时管内流体的传热及阻力降性能,并与光管进行了对比.结果表明,强化管可促进核心流体与边界层流体的混合,减薄层流底层,强化对流传热,同时增大换热面积,流体的阻力降显著增加,较光管的综合性能有所提高.数值结果为强化管的理论分析提供依据.     

Numerical computation of flow phenomena in gas-stirred ladle systems

Quasi-single-phase mathematical models as applied to the ladle hydrodynamics have been analysed rigorously. It is shown that choice of convergence criteria, nodal configuration and differencing schemes all influence the computed results significantly and consequently, results independent of these numerical parameters must first be established to draw any useful conclusion. Several quasi-single-phase computational procedures reported in the literature to study the gas-injection-induced flow phenomena have been critically examined. To this end, experimentally measured bulk flow-fields, plume-rise velocity and gas voidages have been compared with those predicted numerically. Such comparisons indicate that the bottom injection phenomena (viz., bulk flow, plume-rise velocity, and gas volume fraction within the plume etc.) can be adequately represented by assuming bubble slippage and considering a constant rise velocity in the two-phase region in the numerical solution scheme.     

Numerical analysis of fluid flow and heat transfer in pool of twin roll strip caster

Abstract

Twin roll strip casting is regarded as a prospective technology offering many economic benefits. The control of fluid flow in the pool is, however, particularly difficult due to the high casting speed and small pool volume. In the present study, a three-dimensional mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in the pool using the finite difference method. The characteristics of transport phenomena in the pool of a twin roll strip caster using a wedge type melt delivery system were analysed by numerical simulation. The results show that it is desirable for the wedge melt delivery system to provide the uniformity of flow and temperature in the pool to maintain the casting process and improve the strip quality.     

Numerical investigation on the fluid flow and heat transfer in electroslag remelting furnace with triple-electrode

Electroslag remelting (ESR) furnace with triple-electrode is always used to produce large ingots and the process complexity makes the application not widely spread. Thus, a transient three-dimensional coupled model in industrial scale has been developed to investigate the coupled magneto-hydrodynamics two-phase flow and heat transfer in system. Different from the previous studies with multi-electrode, the current work reveals the triple-electrode ESR with the formation of metal droplets and the solidification of liquid metal. Compared with single-electrode system with the same fill ratio, the heat source in the slag pool with triple-electrode is much more dispersive, and the U-shape metal pool in the ESR furnace with triple-electrode is much shallower and flatter than the V-shaped one in the single-electrode system. A shorter distance from each electrode to the center of system brings a higher heat efficiency, as well as a deeper and narrower metal pool.     

步进式加热炉内流动与传热过程的数值模拟

建立了步进式加热炉内流动、燃烧和传热的数学模型.湍流模型采用k-ε双方程模型,辐射换热计算采用六通量法,气相燃烧采用修正EBU模型,流场计算采用Simpler算法.采用上述模型与算法得到了炉内详细合理的温度、速度和浓度分布.     

散堆拉西环蓄热室三维非稳态传热与流动的数值模拟

基于散堆拉西环床层特性,应用多孔介质模型,对散堆拉西环蓄热室进行建模,研究其动态传热及气体流动特性。对蓄热室不同渐变段角度时的温度场、流场进行了对比分析,得到的模拟结果可以在一定程度上反应实际,其反应温度场及流场诸多现象的可视化结果对实际工程应用有一定借鉴作用。     

圆形喷口紊流冲击射流流动与传热过程数值模拟

中厚板无约束淬火主要采用上下集管圆形射流冲击冷却方式，使淬火钢板在向前行进的过程中得到冷却。本文通过建立单股圆形喷口紊流冲击射流流动与传热过程数学模型，对单股射流冲击热钢板的射流流场、温度场、压力场和自由液面进行了数值模拟，得到了冲击射流各物理场的变化规律及钢板表面的换热特性。数值计算结果不仅为钢板淬火过程的温度场模拟、热应力应变场模拟提供了较为准确的换热边界条件，也为优化钢板淬火控冷工艺、保证钢板淬火质量提供了坚实的理论基础。     

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.     

Numerical simulation of fluid flow and solidification in continuous slab casting mould based on inverse heat transfer calculation

Abstract

A mathematical model based on an inverse heat transfer calculation was built to determine the heat flux between the mould and slab based on the measured mould temperatures. With K–? turbulence model, a mathematical model of three-dimensional heat transfer and solidification of molten steel in continuous slab casting mould is developed. Solidification has been taken into consideration, and flow in the mushy zone is modelled according to Darcy’s law as is the case of flow in the porous media. The heat flux prescribed on the boundaries is obtained in the inverse heat conduction calculation; thus, the effect of heat transfer in the mould has been taken into consideration. Results show that the calculated values of mould temperature coincide with the measured ones. Results also reveal that the temperature distribution and shell thickness are affected by the fluid flow and heat transfer of slab which is governed by the heat flux on the mould/slab interface.     

Numerical modelling of iron flow and heat transfer in blast furnace hearth

Abstract

The erosion of hearth refractories is widely recognised as the main limitation for a long campaign blast furnace life. Distributions of liquid iron flow and refractory temperatures have a significant influence on hearth wear. In this investigation, a comprehensive computational fluid dynamics model is described which predicts the fluid flow and heat transfer in the hearth; specifically, the flow and temperature distributions in the liquid iron melt, and temperature distributions in the refractories. The accuracy and representativeness of the model was evaluated using plant data from BHP Steel's Port Kembla no. 5 blast furnace and OneSteel's Whyalla no. 2 blast furnace. Generally, there is good agreement between measured and calculated refractory temperature profiles. A series of sensitivity tests provided cause-effect relationships between operational and fluid flow parameters (floating deadman, different extent of refractory erosion, presence of embrittled layer).     

蓄热式钢包烘烤流动与传热过程数值模拟

采用ANSYS CFX10.0商业软件对蓄热式钢包烘烤燃烧、流动、传热耦合过程进行模拟计算,给出钢包内部的气流和温度分布情况,分析了不同空气预热温度对钢包烘烤温度、火焰辐射强度的影响,计算结果表明蓄热式钢包烘烤更有利于提高钢包温度及其均匀性。     

Mathematical and physical modelling of fluid flow and heat transfer in electric smelting

Heat and momentum transfer in a submerged electric smelting furnace were investigated in a physical model, using oil and an aqueous calcium chloride solution to simulate the slag and matte phases, respectively. Gas evolution at the electrode was simulated by the injection of gas through the electrode in the model. A mathematical model for fluid flow and heat transfer in the model was also developed. The measured temperature distributions near the oil⧹solution interface could only be reproduced in the mathematical model by the imposition of a no-slip boundary condition at the interface. This condition impedes the transfer of heat and momentum into the lower phase; the implications for smelting are discussed.     

偏心M-EMS作用下连铸圆坯流动-传热模拟

 为探究偏心结晶器电磁搅拌(M-EMS)对圆坯钢液流动和传热的作用,减轻偏心M-EMS对圆坯的不利影响,通过建立三维耦合模型研究了偏心M-EMS作用下Φ380 mm连铸圆坯钢液流动和传热特点及M-EMS参数的影响。结果表明,在偏心M-EMS(300 A/2 Hz)作用下,由水口进入结晶器钢液流向外弧侧,碰壁后会形成较大回流;外弧侧钢液温度比内弧侧温度高;随着距弯月面距离增加,外弧侧钢液温度先增加后降低,温度最大处在M-EMS中心,为1 779 K;内弧侧钢液温度则一直降低。随着电流强度由100增加到500 A,圆坯下方回流区由1个变为2个;内、外弧侧钢液温差先减小后增加,在300 A时最小,为8.4 K。随着电流频率由1增加5 Hz,外弧侧回流区变小直至消失。当电流频率小于3 Hz时,内、外弧侧钢液温差小于10 K;而当频率大于3 Hz时,温差则大于16 K。Φ380 mm圆坯推荐M-EMS参数为300 A/2 Hz。     

Numerical modeling of multiphase flow,heat transfer and titanium flow behavior in blast furnace hearth

Understanding the complex phenomena in BF hearth is essential to increase furnace productivity and to extend furnace campaign.We have developed several continuum-based mathematical/numerical models to simulate the multi-phase flow,heat transfer and chemical reactions in the BF hearth.These models have generated an improved insight on the mechanisms for liquid drainage efficiency,lining erosion and wall protection in BF hearth under operational conditions.The current paper gives an overview of these studi...     

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.