Model Tundish Research Articles

Synthesis of a CFD Benchmark Exercise: Examining Fluid Flow and Residence-Time Distribution in a Water Model of Tundish.

Computational Fluid Dynamics (CFD) has become an indispensable tool that can potentially predict many phenomena of practical interest in the tundish. Model verification and validation (V&V) are essential parts of a CFD model development process if the models are to be used with sufficient confidence in real industrial tundish applications. The crucial aspects of CFD simulations in the tundish are addressed in this study, such as the selection of the turbulence models, meshing, boundary conditions, and selection of discretization schemes. A series of CFD benchmarking exercises are presented serving as selected examples of appropriate modelling strategies. A tundish database, initiated by German Steel Institute VDEH working group “Fluid Mechanics and Fluid Simulation”, was revisited with the aim of establishing a comprehensive set of best practice guidelines (BPG) in CFD simulations for tundish applications. These CFD benchmark exercises yield important results for the sensible application of CFD models and contribute to further improving the reliability of CFD applications in metallurgical reactors.

Numerical study of influence of casting speed on fluid flow characteristics in the four strand tundish

Steel maker companies attempt to achieve high production quality and decrease production costs due to high competition of the global steel industry. Steel cleanliness plays a significant role in the steel quality which is the key success factor for the steelmaker. In order to optimize the steel cleanliness in the continuous casting process, flow characteristics were studied to enhance the inclusion removal efficiency in four strand tundish. The purpose of this research is to study the effect of casting speed on the flow characteristics of molten steel inside a four-strand tundish. The investigation was carried out by using the commercial computational fluid dynamic (CFD) software ANSYS 18.2. A 1:3 water model tundish based on process parameters from Millcon Steel PLC were employed in this study. The simulation results were validated with the physical water model. The residence time distribution (RTD) curves were applied to analyze the flow characteristics of the tundish. The results of this study show the different casting speeds have an effect on the flow characteristics inside the tundish. The start point of RTD curve of the flow in the tundish with casting speed of 3.0 m/min is the shortest amongst all casting speeds used (1.7, 2.0, 2.3 and 3.0 m/min). A short time period of the start point of RTD curve increases the chance of inclusion contamination in the casting mould and leads to low quality products. Furthermore, the outlet positions affect the minimum residence time of RTD curves and the tracer concentration directly. The RTD start point of the middle outlet located close to the inlet position is faster than that of the far outlet located far from the inlet. The results obtained from the study contributes to the optimization of productivity and quality of the example plant.

Experimental investigation of flow control devices effect on inclusion separation in a four strand tundish

ABSTRACTIn continuous casting, molten steel often contains non-metallic inclusions that have a very high melting temperature and thus remain suspended in the molten flow. Given the lower density of these substances compared to the melt, they can be filtered in the form of top slag by proper use of buoyancy forces. Thus, providing a desirable flow pattern, reduced flow turbulence, and adequate residence time for inclusions in the tundish will improve the inclusion separation performance and therefore the product quality. In this study, a reduced-scale water model of a tundish was used to evaluate the effect of melt level in the tundish on the flow pattern and inclusion separation performance. Then, the flow control devices are added to this simple tundish model to examine the effect of them on the flow behaviour and inclusion separation. Experimental investigation showed that raising the water level in the model tundish has desirable effects on inclusion separation and the use of the dam at the inlet with tall dam improves the flow pattern and inclusion separation almost 20% in the form of top slag.

A Water Experiment Benchmark to Evaluate Numerical Models for the Motion of Particles in Continuous Casting Tundish

This paper presents a water experiment benchmark for evaluation of the numerical models for the particle motion in a continuous casting tundish. The particles are optically tracked in the model tundish and additionally are captured by instrumented wooden frames at the water surface. In the meantime, an attempt is made to simulate the water flow and motion of the particles by using the Eulerian–Lagrangian approach. It is shown that for the experiment with large particles (ϕ3.5 mm) the experimentally determined distribution of the particles as captured by the wooden frames can be numerically simulated, but for the small particles (with a diameter distribution between 50 and 600 μm) there is still relative large mismatch between the simulation and the experiment. Some modeling options and parameters must be tuned carefully. This raises concern for the future application of the models in real engineering process where experimental calibration and evaluation are not possible. Therefore, the goal of this paper is to (i) call contributions from researchers to propose their models and evaluate them against the same benchmark; (ii) verify the agreement of the numerical solutions obtained by different contributors, and (iii) comment on further improvements and modifications to the existing models.

Microbubble Swarms in a Full-Scale Water Model Tundish

Water modeling, using microbubble swarms, was performed in a full-scale, four-strand, delta-shaped tundish, located at the McGill Metals Processing Centre (MMPC). The objective of the study was to investigate the effectiveness of microbubbles in removing inclusions smaller than 50 μm, applying the principles and conditions previously researched using a smaller scale arrangement. Air was injected into a full-scale model of a ladle shroud (the connecting tube through which liquid steel flows into the tundish below). The model ladle shroud was fitted with twelve, laser-drilled orifices, so as to create microbubbles. The bubbles generated using different gas injection protocols were recorded using a high-speed camera, and the bubble images were postprocessed using the commercial software, ImageJ. With this newly designed ladle shroud, bubble sizes could be reduced dramatically, to as small as a 675 µm average diameter. A three-dimensional, CFD model simulation was developed, using parameters obtained from the corresponding water model experiments, in order to predict the behavior of these microbubbles within the tundish and their potential influence on flow patterns and inclusion float-out capability.

Removal of Inclusions Using Micro-bubble Swarms in a Four-strand, Full-scale, Water Model Tundish

Removal of Inclusions Using Micro-bubble Swarms in a Four-strand, Full-scale, Water Model Tundish

Effect of Inflow Rate Variation on Intermixing in a Steelmaking Tundish during Ladle Change‐Over

The intermixing of dissimilar grades of steel in tundish during the ladle change‐over is a problem of growing interest. During sequential casting of different grades, it is important that the intermixing of the grades is kept to a minimum. Present work deals with computational and water model studies of the three‐dimensional turbulent fluid flow in a multi‐strand tundish during ladle change‐over process. The physical investigation has been carried out by conducting experiment on a 1:4 scale model of tundish. The numerical simulations have been carried out with the help of educational version of ANSYS Fluent, using the Volume of Fluid (VOF) method and incorporating standard k–ɛ turbulence model. The numerical model has been validated with the results of physical investigation and is found to be in good agreement. Further, the numerical model is used to study the ladle change‐over process considering effect of inflow rate on grade mixing and interface positions, i.e., different bath height positions in tundish with and without advance pouring box (APB). It has been observed that the use of APB is not helpful in reducing the intermixed time while increase in flow rate of new grade steel decreases the intermixed amount.

Physical Modeling of Different Configurations of a Tundish for Casting Grades of Steel that Must Satisfy Stringent Requirements on Quality

Residence time in a tundish equipped with the Turbostop system and dams is compared to the same parameter in a Turbostop-equipped tundish with dams and weirs. The symmetrical dual-strand tundishes are tested at two different casting speeds. The tundish design with Turbostop, dams, and weirs is currently being used at U.S. Steel Kosice, s.r.o. to cast steel that must satisfy stringent requirements on quality. The main objective of the comparison testing was to substantiate the use of the weirs. The tests were performed in the Steel-Flow Simulation Laboratory at the Technical University of Kosice with the participation of specialists from U. S. Steel Kosice. A water model of a continuous caster was built on a scale of 1:3. The rate of flow of the test solution was measured by adding calcium chloride to the inlet of the model tundish and visually evaluating its flow with the use of KMnO4 as an indicator.

Effects of Salt Tracer Amount, Concentration and Kind on the Fluid Flow Behavior in a Hydrodynamic Model of Continuous Casting Tundish

AbstractThe hydrodynamic modeling method that widely used to simulate the fluid flow was reconsidered and discussed in this paper. The effects of injected salt tracer amount, concentration and kind on the fluid flow behavior in a hydrodynamic model tundish were investigated. The results were compared with the mathematical modeling calculation results, that the tracer density effect was eliminated. The residence time distribution (RTD) curve of tracer introduced deviated to the left side of the calculated curve, besides the deviation was increased as dimensionless tracer amount (the ratio of tracer amount to hydrodynamic model tundish volume) increased from 0.202 × 10−3 to 1.008 × 10−3. The results of tracer concentration study were similar, namely the deviation was increased with concentration increased; on the other hand, the deformation of a “stair‐shape” RTD curve occurred when tracer concentration was much lower (at dimensionless tracer amount of 0.168 × 10−3 with converting to saturated solution). Besides, the effect of tracer kind on the accuracy of hydrodynamic modeling was also studied; the measurements of KCl solution with lower density than that of NaCl solution exhibited more of accuracy. Finally, the optimized tracer in hydrodynamic model tundish of present work is saturated KCl solution with dimensionless tracer amount of 0.202 × 10−3.

A PHYSICAL MODELLING STUDY OF INCLUSION REMOVAL IN TUNDISH USING INERT GAS CURTAIN

The control and minimization of non-metallic inclusions content in the tundish and in the mold of a continuous casting unit is crucial for ensuring the final quality of the steel cast product. Nonmetallic inclusions of sizes smaller than 15 µm are hard to remove, as they are difficult to float. They are easily carried by the flow of steel melt into the mold and adversely affect the steel cleanliness. It is suggested that a gas curtain made of small bubbles of argon can be used to capture and remove these inclusions in the tundish, thus avoiding their transport into the mold. A 1:3 scale physical model of tundish of the continuous casting unit of ArcelorMittal plant, in Vitoria, Brazil, was built to investigate the effects of gas flow, shape and positioning of the gas curtain inside the tundish, on the efficiency of removal of inclusions. The results suggest that the gas bubbling inside the tundish can be effective in inclusion removal. The efficiency is dependent upon the location of argon bubbling.

Effect of submergence depth of the ladle shroud on liquid steel quality output from a delta shaped four strand tundish

Physical and mathematical modelling was performed in a full-scale water model tundish to study the effect of the submergence depth of the shroud on melt flow and liquid metal quality. In the full-scale water model tundish, slag entrainment tests were performed at various immersion depths of the shroud. Polyethylene beads (920 kg m−3) were used to simulate the slag phase and the number of beads collected in each submerged entry nozzle during a ladle change, indicated relative performances in terms of slag entrainment. A three-dimensional mathematical model was developed and contours of turbulence (turbulent kinetic energy (TKE) contours) were examined at different depths of submergence of the ladle shroud. At low depths of submergence there is high turbulence within the tundish and this causes more slag entrainment. On the contrary, at high submergence depths there is very low turbulence and hence amount of slag entrained is less. Tundish operations with higher submergence depth of the shroud may eliminate the use of turbulence inhibitors and thereby reduce refractory consumption and cost.

Investigation of effect of dam on intermixing during ladle changeover in six strand billet caster tundish

A study has been carried out to find the effect of placing a dam at different positions in a six strand billet caster tundish on the intermixed amount of liquid steel during ladle changeover in the continuous casting process. The experiment was conducted on a one-fourth scale model tundish fabricated with Perspex sheet. Water was used to represent the old grade steel and salted water was used to represent the new grade of steel. Step input tracer concentration study was carried out after attainment of a steady state velocity field and the intermixed amount was calculated from different outlets. Maximum intermixed amount was obtained from the outlet nearest the ladle stream inlet and the minimum was observed from the outlet furthest from the ladle stream. A numerical study was carried out on full scale tundish and it was seen that the numerical and physical experimental results were very close to each other. The numerical investigation was further extended for investigating the effect of a dam placed at different positions on the intermixed amount from the different outlets. It was found that the placement of dams decreased the intermixed amount in most of the cases. Minimum intermixed amount was found at the position when the dam was placed at a dimensionless distance of 0·083 from the inlet to the tundish.

Investigation of Flow Characteristics in a Six‐Strand CC Tundish Combining Plant Measurements, Physical and Mathematical Modeling

AbstractThe tundish plays a major role in the continuous casting process. The flow in a tundish has a very substantial effect on the quality of the final product and on efficient casting conditions. Efforts are being made worldwide to obtain the most favourable shape of tundish interior by using dams, weirs and gas curtains. The aim of these flow control devices is to reduce the dead zone areas and improve the conditions for the separation of non‐metallic inclusions. Numerous model studies are being carried out to explain the effect of the tundish working space shape and steel flow conditions on the inclusions floating processes. The presented article shows the results of investigations performed to obtain the mass exchange characteristics in the investigated tundish. The measurements were done directly at the steel plant during normal working conditions. By controlling the changing content of manganese in steel, the residence time distribution (RTD) characteristics were acquired. The RTD characteristics are also obtained with a water model of the tundish with dimensional scale of 1:3. Parallel to the water model, numerical simulation based on mathematical modelling of fluid flow, relying on the system of differential equations, is employed in the research work. Numerical simulations were carried out with the finite‐volume commercial code FLUENT using the standard k‐ε turbulence model. The primary purpose of the investigations carried out is to present the characteristics describing the transitory zone in a six‐strand tundish. It is shown that the F‐curve, describing the transitory zone, can be obtained by using different measurement techniques. Tracer concentration characteristics for the model of tundish obtained from both modelling techniques ‐ physical as well as numerical ‐ are very similar.

Modeling of Fluid Flow and Residence Time Distribution in a Four-strand Tundish for Enhancing Inclusion Removal

The introduction of the appropriate size and precise location of flow control devices such as dam, turbulence inhibitor, etc., helps to modify the flow pattern and minimizing short circuiting and dead zone. Beside this, these also create the surface directed flow and maximize the residence time available for the flotation of inclusions and assimilation of the reaction products from the molten steel into the slag phase. These can be products of deoxidation, reoxidation, precipitation, emulsification and/or entrainment of refractory components into the melt and thus encompass both indigenous and exogenous inclusions. To this end, both the numerical and physical simulations were carried out mainly for three cases: a) in absence of flow control devices (i.e., bare tundish), b) in the presence of a dam, and c) with the application of turbulence inhibiting device (TID) and dam combination in the existing tundish configuration. The commercial CFD (computational fluid dynamics) package FLUENT® was used to predict the flow field prevalent in the water model tundish at steady state, whereas in the experimental program, both Particle Image Velocimetry (PIV) techniques for flow measurements and tracer dispersion experiments for concentration measurements were applied in the present study. Among all types of configurations applied in the present study, a combination of TID with holes+a dam work reasonably found to be an optimum configuration of the four-strand tundish regarding inclusion floatation. A superior strand similarity is also achieved in this configuration. Also the predicted time averaged horizontal and vertical components agreed within ±10% with the experimentally derived ones.

Concentration Measurements in a Water Model Tundish using the Combined DPIV/PLIF Technique

The mixing process in a 1:3 scaled water model of a single‐strand tundish for the production of stainless steel is investigated using the combined DPIV/PLIF (Digital Particle Image Velocimetry/Planar Laser Induced Fluorescence) technique. The velocities in the water model are measured in different light sheet planes up to a size of 300 mm · 1100 mm by the conventional DPIV method. The variation of the time‐dependent concentration field is measured in the same plane by the PLIF method. The tracers are polyamide particles for DPIV and a rhodamine 6G solution as fluorescent dye for PLIF. Due to the special calibration procedure of the DPIV/PLIF system, the optical, geometrical and physical parameters do not have to be determined analytically, thus leading to reliable results. The experiments are carried out with a turbulent Reynolds number of Re = 5000 and show that the mixing process correlates with the quasi steady‐state flow pattern. The residence time of some water region in the tundish model is significantly longer than the mean residence time (θ < 5). Such information is important for the steel production because the number of mixed slabs produced during sequence casting with a grade change is closely related to the mixing of the tundish melt. The presented laser‐optical investigations have been used to establish the combination of DPIV and PLIF technique. The results of combined DPIV/PLIF measurements will be used to validate numerical simulations of the mixing processes in water models of metallurgical reactors.

Basis for Systematic Hydrodynamic Analysis of a Multi-strand Tundish

Despite significant work done till date on single/dual strand tundish (those applied to slab casting) not much information on an equivalent multi-strand tundish (which are of significance to billet casting) is available regarding residence time distribution (RTD) measurements and its analysis. The proportions of various flow volumes estimation (e.g., dead, plug, well mixed, etc.) on the basis of a single/dual strand tundish cannot be directly extrapolated to a multi-strand tundish from its individual strand data only. In the present study, therefore, the principle and the methodology underlying the derivation for concentration vs. time curves (C curves) of a multi-strand tundish is addressed to provide a basis for the evaluation of RTD parameters. To this end, several experiments in a four-strand water model tundish were carried out for RTD measurements and estimation of associated flow volumes. The tracer dispersion experiments were performed by injecting potassium chloride (20 mL solution) as a pulse into the submerged inlet stream and the variation of conductivity of water caused by the differential mixing of the injected tracer into the bath were recorded continuously at the exits of the water model tundish with a 75 L volume. These conductivity values of individual strands were converted into corresponding concentrations, and the dimensionless concentrations were plotted against dimensionless time to derive the characteristic C curves. The individual C curves effect the strand to strand variations whereas the overall C curve (average of individual C curves) is used to determine the flow volumes in a multi-strand tundish system.

Numerical and Physical Simulation of Flow Patterns in a Swirling Flow Tundish

Swirling flow tundish is a new kind of tundish which has shown good effects on flotation of inclusion and reduction of inclusion content. In this paper, studies have been carried out on the flow fields in a one‐strand slab tundish. A full scale model of the flow patterns in the water model tundish was developed using a self‐developed code. RTD curves under different experimental conditions were obtained from both physical and numerical simulations. The effects of the swirling flow chamber geometry and the flowrate on flow patters in the tundish were discussed and compared with results from the numerical simulation. Validation of the self‐developed codes was achieved by comparing the physical and numerical results of the RTD curves and the mean rotational velocities in swirling flow tundish. As a result, significant rotational flow in the swirling flow chamber and asymmetrical flow pattern in the whole tundish were confirmed and the effects of these parameters on dead zone and mean residence time were also obtained. Further and more comprehensive studies are needed to optimize the design and application of such tundishes.

An Assessment of Fluid Flow Modelling and Residence Time Distribution Phenomena in Steelmaking Tundish Systems

A summary of computational work reported in the literature on tundish hydrodynamics has been presented wherein, it is shown that a diverse range of both computational (e.g., nodal configurations, boundary conditions, inlet turbulence etc.) and physical parameters (e.g., size, number of strands, inlet mass flow rates etc.) were applied. Accordingly, the conclusions drawn were found to vary from one study to another. In the present work, an attempt has therefore been made to assess computationally the role of various mathematical model parameters. To this end, mathematical model results were validated against experimental measurements on Residence Time Distribution (RTD) parameters derived from water model tundish. Experimental measurements of RTD were carried out continuously by monitoring conductivity of water at the tundish exit port on a digital computer using a DAS interface. On the other hand, numerical calculations were carried out via the commercial CFD (Computational Fluid Dynamics) software FLUENT 6.0. The combined experimental and computational study indicated that a sufficiently small grid resolution (control volume of the order of 10 -6 m 3 ) is necessary to arrive at a practical grid independent solution. Furthermore, Reynolds stress model was found to simulate RTD in the system somewhat superior to the standard coefficient k-e model. Through comparison of the predicted results with experimental measurements, a set of optimal mathematical model configurations was deduced. It was demonstrated that mathematical model configured in this work is sufficiently reliable and robust as this leads to estimates of RTD parameters (e.g., t min , t max , t mean ) close to experimental measurements in a tundish with and without flow modifiers.

Fluid flow analysis in horizontal continuous casting tundish

Water model studies were carried out to analyze fluid flow characteristics in a horizontal continuous casting tundish. The effects of LSN (ladle submerged nozzle) and dams on the flow pattems in a tundish were investigated and casting speeds were also changed as experimental parameters. Dye injection experiments were made to observe qualitative flow patterns and mixing characteristics in a continuous flowing tundish. And quantitative analyses of RTD (residence time distribution) curves using tracer pulse injection were also made to calculate the dead volume fraction in the water model tundish under consideration. From the results it was found that flow modification devices with an open stream have little effect on the flow patterns in the tundish, whether the dam is installed or not. This was confirmed by the flow visualization method showing upward flow near falling stream driven by the buoyancy force caused by air entrapment during liquid falling. However when LSN was installed between a ladle and a tundish there was a great change in flow pattern and a bypassing flow that existed in bare tundish was decreased with the use of dams. Especially, dead volume fraction was decreased with the increase of dam height.

Fluid flow behaviour in a water model tundish under open, submerged and modified inlet conditions

A systematic study has been conducted on the fluid‐flow behaviour in in a two‐strand continuous casting model tundish under conditions of submerged entry nozzle (SEN) and open entry nozzle (OEN) with different levels of water in tundish. Flow has been characterised from the profiles of tracer responses at the tundish outlets. 2 configurations of entry nozzle, one the conventional straight tube (for SEN and OEN) and the other T‐shaped (for SEN only), were employed. Flow in the slag layer has been simulated by monitoring the tracer responses on the surface at 250, 500 and 750 mm away from the stream entry. It has been found that the lower the immersion depth of nozzle, the lower the inclusion level in the melt. Similarly a T‐shaped entry nozzle into the tundish also produces a cleaner melt and improves flow patterns in the vessel.