Applications of Computational Fluid Dynamics (CFD) in iron- and steelmaking: Part 2

Abstract

After presenting a review of some applications of computational fluid mechanics (CFD) to ironmaking processes in Part 1, the authors now explore the use and extent of CFD in steelmaking and steel casting processes. Steelmaking processes generally include the basic oxygen furnace, electric arc furnace or equivalent, the ladle and continuous casting and incorporating a tundish and moulds. All these steelmaking processing steps involve highly coupled complex transport phenomena. The use of CFD to model such processes has been an active area of research for the last three decades. Many models have been developed to predict mixing behaviour, slag foaming, gas–liquid interactions, multiphase flows, as well as heat and mass transfer aspects. In the present review, the role of CFD in modelling steelmaking operations is reviewed, discussed and critiqued.     

Cold model studies of mixing and mass transfer in steelmaking vessels

Abstract

Room temperature model studies using water to simulate 'metal' and paraffin oil (when required) as 'slag' were conducted to study the extent of mixing and the rate of mass transfer between metal and slag in the 130 t basic oxygen furnaces (BOFs) in operation in Tata Steel. Several systems of gas injection including top blowing, combined blowing and exclusive bottom purging were investigated. Similar work was undertaken in a room temperature model of an 80 t energy optimising furnace (EOF), in operation for a brief period earlier in Tata Steel. Details of the optimum blowing conditions, including the number/distribution of bottom tuyeres for the BOFs, are elaborated in the present paper. How mixing/mass transfer in an EOF compares with the BOF case(s) is also highlighted.     

Numerical study of dc arc plasma and molten bath in dc electric arc furnace

Abstract

A numerical study of the arc plasma and molten bath in a dc electric arc furnace (EAF) is useful for understanding and improving the production process of the dc EAF. In the present paper, a mathematical model based on conservation equations of mass, momentum and energy along with Maxwell's equations is developed to describe the flow field and heat transfer in the arc and molten bath regions of a dc EAF simultaneously. The governing equations are solved using the PHOENICS software package. The calculated results show good agreement with those of previous studies, giving a useful insight into the factors of arc heat transfer and bath circulation.     

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.     

Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace

A thin-slice computational fluid dynamics (CFD) model of a conventional tuyere blown slag-fuming furnace has been developed in Eulerian multiphase flow approach by employing a three-dimensional (3-D) hybrid unstructured orthographic grid system. The model considers a thin slice of the conventional tuyere blown slag-fuming furnace to investigate details of fluid flow, submerged coal combustion dynamics, coal use behavior, jet penetration behavior, bath interaction conditions, and generation of turbulence in the bath. The model was developed by coupling the CFD with the kinetics equations developed by Richards et al. for a zinc-fuming furnace. The model integrates submerged coal combustion at the tuyere tip 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 several user-defined subroutines in FORTRAN programming language were used to develop the model. The model predicted the velocity, temperature field of the molten slag bath, generated turbulence and vortex, and coal use behavior from the slag bath. The tuyere jet penetration length (l _P) was compared with the equation provided by Hoefele and Brimacombe from isothermal experimental work $ \left( {\frac{{l_{\text{P}} }}{{d_{o} }} = 10.7\left( {N^{\prime }_{Fr} } \right)^{0.46} \left( {\rho_{\text{g}} /\rho_{l} } \right)^{0.35} } \right) $ and found 2.26?times higher, which can be attributed to coal combustion and gas expansion at a high temperature. The jet expansion angle measured for the slag system studied is 85?deg for the specific inlet conditions during the simulation time studied. The highest coal penetration distance was found to be l/L?=?0.2, where l is the distance from the tuyere tip along the center line and L is the total length (2.44?m) of the modeled furnace. The model also predicted that 10?pct of the injected coal bypasses the tuyere gas stream uncombusted and carried to the free surface by the tuyere gas stream, which contributes to zinc oxide reduction near the free surface.     

Computational Fluid Dynamic (CFD) Simulations of Liquid Steel Infiltration in Ceramic Foam Structures. Part II: Application to Laboratory‐Scale Experiments

The infiltration of liquid TRIP steel into a porous zirconium dioxide foam ceramics is a possible production line for a new composite material. This composite is currently under investigation and development in the Collaborative Research Center 799. Coupled numerical simulations of the hot infiltration process at the pore scale are presented in the paper. The results of the simulations are analysed in order to study similarities and differences between heat and fluid flow phenomena during the infiltration of the foam ceramics. Among others, temperature distributions in the liquid steel and the ceramics are evaluated for typical casting conditions in a laboratory‐scale experiment.     

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier–Stokes equations, closed with the k–ω turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, “quiescent,” region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract coherent eddies from the chaotic turbulent flow. Application of this technique to several abutment configurations yielded results that support the numerical findings.     

Hot-Metal Desulfurization Using Calcium Carbide and Calcium Oxide in Transfer Ladle: A Computational Fluid Dynamics Investigation

In this study, a 3D transient computational fluid dynamics (CFDs) model that simulates hot-metal desulfurization (HMD) using calcium carbide and calcium oxide in an experimental-scale ladle with a 70 kg capacity is presented. The model takes into account the efficiency of reagent-particles-penetrating carrier gas bubbles and is validated through experimental work, with an average difference of 7.06%. In this research, the effects of varying reagent particle sizes, hot-metal temperatures, gas flow rates, and ladle design on desulfurization rates are discussed. The results indicate that when particle diameter decreases from 30 to 20.9 and 11.8 μm, desulfurization rates rise from 50.92% to 66.02% and 89.99%, respectively. Regarding hot-metal temperature, a 100° range results in a final desulfurization rate difference of less than 3%. This study also reveals that increasing the carrier gas flow rate from 13 to 15 SLPM reduces the removal rate by 6.10%. As particle gas flow rate increases from 200 to 300 g min⁻¹, the removal rate increases by 9.02%. In the lance arrangement analysis, the duo lance system demonstrates nearly identical desulfurization performance to the single-center lance system, which outperforms the off-center lance system.     

Transient liquid phase sintering of high density Fe3Al using Fe and Fe2Al5/FeAl2 powders Part 1: Experimentation and results

Abstract

High density Fe₃Al was produced through transient liquid phase sintering, using rapid heating rates of greater than 150 K min^-1 and a mixture of prealloyed and elemental powders. Prealloyed Fe₂Al₅/FeAl₂ (50Fe/50Al, wt-%) powder was added to elemental iron powder in a ratio appropriate for producing an overall Fe₃Al (13·87 wt-%) ratio. The heating rate, sintering time, sintering temperature, green density and powder particle size were controlled during the study. Heating rate, sintering time and powder particle size had the most significant influence upon the sintered density of the compacts. The highest sintered density of 6·12 Mg m^-3 (92% of the theoretical density for Fe3Al) was achieved after 15 minutes of sintering at 1350°C, using a 250 K min^{- 1} heating rate, 1-6 μm Fe powders and 5·66 μm alloy powders.

SEM microscopy suggests that agglomerated Fe₂Al₅/ FeAl₂ particles, which form a liquid during sintering, are responsible for a significant portion of the remaining porosity in high sintered density compacts, creating stable pores, larger than 100 μm diameter, after melting. High density was achieved by minimising the Kirkendall porosity formed during heating by unbalanced diffusion and solubility between the iron and Fe₂Al₅/FeAl₂ components. The lower diffusion rate of aluminium in the prealloyed powder into the iron compared with elemental aluminium in iron, coupled with a fast heating rate, is expected to permit minimal iron-aluminium interdiffusion during heating so that when a liquid forms the aluminium dissolves in the iron to promote solidification at a lower aluminium content. This leads to a further reduction in porosity.     

Fluid flow in pachuca (Air-Agitated) tanks: Part II. Mathematical modeling of flow in pachuca tanks

A generalized mathematical model that combines Bernoulli’s equation and thek-ε model of turbulence, using only the gas flow rate and tank geometry as inputs, has been formulated to predict the fluid flow pattern in industrial-scale full-center-column Pachuca tanks. Predictions from this model reproduce reasonably well the trends that were observed in experiments when design and operating parameters, such as superficial air velocity and tank height/tank diameter ratio, were varied. Results from these calculations indicate that design parameters, such as tank height/tank diameter and draft tube/tank diameter ratios, have a significant effect on the flow pattern in full-center-column Pachuca tanks at large tank diameters or small tank height/tank diameter ratios.     

Dental procedures and infective endocarditis: current approaches of cardio-vascular surgery departments from different centres (Part 1)

For centuries mankind has benefited from yeast for its survival as well as for joy and even solace in moments of pain. Today the yeast cell is considered a universal model yielding answers to important and intriguing questions about cell division, differentiation, transduction of signals and cell disorders. Classical and molecular genetic methods have been successfully applied to understand the association of genes with proteins and functions-a knowledge which has also led to the development of new biotechnologies.     

Human cervico-facial morphogenesis. Evaluation of acquired data and current outlook. (Part 1: facial morphogenesis)

The embryonic development of the face has been studied in many reviews, this work purposes only to clear up some points which remain obscure concerning cervico-facial morphogenesis. In the first part of this study only the facial development, properly speaking, is considered, although it cannot be separate of cervical development to which a second study will be reserved. In the present study we recall the particular aspects of the neurulation in the cephalic area, then the establishment of the facial processes. Then we approach among other things the way to consider the maxillary process with regard to the other facial processes. After is considered constitution and natured of the prechordal plate which has been diversely explained. Finally, the modelling of the face is evocated, in which the dissociation between the olfactive and buccal spheres is pointed out, with the disparition of the muzzle, as it is established in the haplorhinae, a class of primates in which the human being is involved. This phenomenon raises different questions, in particular about the relation of this disposition with the nasoseptal center, the medial part of the nasodorsal center.     

Control of rubella and congenital rubella syndrome (CRS) in developing countries, Part 1: Burden of disease from CRS

A pool of sera from individuals classified as putatively immune (PI) to Onchocerca volvulus infection was employed in the screening of a fourth-stage larval cDNA expression library. A highly immunogenic clone, encoding the Ov 53/80 protein, was identified. The full length cDNA of clone 4.21 contained 2527 nucleotides encoding 769 amino acids of which 100 are glutamine residues (13%). Antibodies raised against recombinant protein encoded by a partial cDNA sequence (clone 73-k) recognized a 53 and 80 kDa protein in O. volvulus larval and adult parasite extracts, respectively. The antibodies localized the native protein in the cuticle, hypodermis, secretory vesicles and in granules of the glandular esophagus of larvae and in the hypodermis and the cuticle of adult worms. The recombinant 73-k polypeptide (r73) was recognized by 90-100% of sera from PI and infected individuals from Liberia, but only by 67% of similar groups from Ecuador. r73 specific IgG2 and IgG3 levels in the PI from Liberia and Ecuador, respectively, were significantly lower than in the infected, whereas the r73 specific IgG1/IgG3 or IgG1/IgG2 in the PI and the infected individuals from Liberia or Ecuador, respectively, were similar. The IgG4 specific antibody response in the PI from Liberia and Ecuador were lower than in the infected. The T-cell proliferative responses to r73 in infected individuals from Cameroon were found to be inversely correlated with their levels of microfilariae.     

全尾砂膏体流变学研究现状与展望（上）:概念、特性与模型

膏体充填为矿产资源的深部开采及可持续发展提供了安全、绿色、高效的技术保障,已成为矿业领域的研究热点和发展趋势之一。全尾砂膏体流变学是膏体充填全套工艺流程的重要理论基础,深刻影响着膏体充填技术的发展。本文从膏体的内涵出发,系统性地论述了膏体流变学研究的必要性、特殊性及复杂性。并以膏体流变实验结果为基础,分析了全尾砂膏体的典型流变特性及最新研究成果。总结了常用的屈服型非牛顿流体流变模型,并探讨了常用流变本构方程对膏体料浆的适用性,对其实际应用提出合理建议。同时对膏体流变特性的关键影响因素进行了概述。根据膏体流变学的研究现状,归纳总结并提出了膏体流变学研究的重点与难点,指出现阶段膏体流变学须从测试标准、本构方程、微观机理及工程应用等方面深入研究。