Turbulence Inhibitor Research Articles

Numerical Investigation on Transient Flow and Inclusion Removal Behavior in Tundish During Ladle Change Process

The removal of inclusion particles is an important function of tundish metallurgy. During ladle change, the liquid level fluctuation around the ladle shroud is severe, which may affect the effectiveness of inclusion removal. In the present study, the fluid flow characteristics and inclusion‐removal behavior in the tundish during ladle change are investigated by numerical simulation method. And the effectiveness of flow control devices on the flow characteristics of molten steel is evaluated. It is found that the escape rate of inclusion particles during ladle change is ordered as emptying process < steady process < filling process. The proper combination of weir, dam, and turbulence inhibitor can optimize the conditions for the floating and removal of inclusion particles to the greatest extent. In the tundish with weir and dam, the escape rates of inclusion particles with sizes of 10, 50, and 100 μm throughout the entire ladle change period are respectively reduced by 9.8%, 1.6%, and 1.4%, compared to not using flow control devices. With a combination of weir, dam, and turbulence inhibitor, the escape rates of the three types of inclusion particles are reduced by 24.7%, 9.9%, and 1.2%, respectively.

Physical Experiments and Numerical Simulations of the Influence of Turbulence Inhibitors and the Position of Ladle Shroud on the Steel Flow in an Asymmetric Five-Strand Tundish

The submitted article deals with the use of physical and numerical modelling to study the process of the steel flow in an asymmetric five-strand tundish that continuously casts steel. For the purposes of physical modelling, a 1:4-scale plexiglass model was used as the operating tundish, and for numerical modelling, the geometry of the operating tundish was created on a 1:1 scale. A model liquid (water) was used in the physical modelling of the melt flow process, while liquid steel was used as the standard flowing medium in the numerical modelling. We assessed the relevant operating parameters influencing the characteristics of the flow of the bath in the tundish—the shape of the turbulence inhibitor, the position of the ladle shroud in relation to the turbulence inhibitor and the distance between the ladle shroud orifice and the bottom of the turbulence inhibitor. The preliminary results show that optimal steel flow characteristic results are achieved by using the TI3-C configuration. The results from both modelling methods achieved the same characteristics, therefore verifying the results of each other and demonstrating that when taken together, the results of physical and numerical modelling can be considered sufficiently informative.

Digital Twin Design of a Turbulence Inhibitor in a Tundish Based on the Production Cluster Mining Algorithm

The lack of a direct and linear relation between inclusion removal from tundishes and the design of their turbulence inhibitors is a difficult challenge. In contrast to the traditional method of optimizing flow control devices based on the residence time distribution curve, this study used the inclusion/flow field database production clustering mining algorithm to conduct step-by-step data mining on the tundish flow field; to produce relevant facts of the flow field characteristics in the inclusion aggregation zone; and to extract the data mining results from the fact database to screen a digital twin algorithm that forecasts the inclusion aggregation area in a tundish to optimize the flow control device. The results showed that the inclusion aggregation area in the tundish impact zone is above the turbulence inhibitor and that the inclusion aggregation area outside the tundish impact zone is at the vortex center of the flow field. According to the mining results, a pseudo-code for screening the inclusion aggregation area was developed, and the turbulence inhibitor was optimized with the help of the digital convergence of the digital and physical models. Finally, in a tundish, the inclusion removal rate in molten steel was increased by 14.4%. The turbulence inhibitor designed by the digital twin method is currently being used in a Chinese steel mill.

Optimized Fluid Flow Control System for a Tundish Used in Frequent Steel Grade Change Operations

A slab caster with a wide casting mix carries high‐frequency steel grade changes using a small, 14 ton capacity tundish and needs to decrease the intermixed steel tonnage. Testing different tundish arrangements, through a water one‐third scale model, permits a flow control design to decrease the amount of mixed steel. A computer fluid dynamics approach, based on the Realizable k–ε model, replicates the experimental results. It helps to elucidate the role of the tundish filling rate, finding that increasing it increases the dissipation rate of kinetic energy coming out from the turbulence inhibitor. At high filling rates, the degraded kinetic energy of the downstream flow drives the residues of the “old” steel, prolonging the intermixing phenomena. In its later stages, the intermixing phenomena imply diffusion and transport on small scales, and both are governed by the Schmidt number given by the ratio of the Batchelor and Kolmogorov length scales, according to . The Schmidt, Sc, numbers in steel are in the range of 28–440. These large Sc numbers mean that the diffusion process must reach the dissipative scales of turbulence, that is, beyond Kolmogorov´s scale, to achieve a complete mixing at microscale levels.

Inclusion Removal Studies in a Two-Strand Tundish: Effect of Substitution of Turbulence Inhibitor with Dams and Effect of Teeming Ladle and Ladle Shroud Set Asymmetry Employing Physical and Mathematical Modeling

Inclusion Removal Studies in a Two-Strand Tundish: Effect of Substitution of Turbulence Inhibitor with Dams and Effect of Teeming Ladle and Ladle Shroud Set Asymmetry Employing Physical and Mathematical Modeling

Three-Phase Flow in a Single-Strand Tundish During Start-Up Operation Using Top-Swirling Turbulence Inhibitor

Three-Phase Flow in a Single-Strand Tundish During Start-Up Operation Using Top-Swirling Turbulence Inhibitor

Experimental investigation of turbulent flow in a rectangular bonneted slide gate and eliminating random fluctuating loads

Bonneted slide gates are widely used in dam bottom outlets for flow regulation. High kinetic energy flow generates turbulence, which induces vibrations in bonneted slide gates under partially open conditions. Significant vibrations can indicate problems and cause damage or expedited deterioration of the gate if left unchecked. This experimental study focuses on two aspects: turbulent flow formation due to rectangular bonneted slide gates and elimination of random fluctuating loads on the gate using a turbulence inhibitor. Five reservoir heads were combined with nine gate openings (10%–90%) to produce 45 different discharges of 12–182 l/s. The different types of the gate flow create different turbulence and random loads based on the water–air mixture and the kinetic energy of the flow. Flow analysis indicates considerable random static pressure fluctuations under the slide gate. The results show the formation of swirling secondary flows in the gate's side guide slots, and their movement and collision with the gate are the leading cause of the turbulent multiphase flow and random fluctuations in static pressure. Also, the use of turbulence inhibitors on the gate can prevent the formation of secondary flows, which results in a 98.92% reduction in the amplitude of random static pressure fluctuations and the elimination of the random fluctuating loads on the slide gate. After removing the swirling secondary flows, a stable air boundary layer was formed under the gate. Finally, the gate flow changed from a turbulent two-phase flow to a steady single-phase jet of water.

Study of the Impact of Opening Streams on Turbulence Inhibitors in Tundishes

Study of the Impact of Opening Streams on Turbulence Inhibitors in Tundishes

Removal of Inclusions using Swirling Flow in a Single-Strand Tundish

Swirling flow tundish was developed to enhance the coalescence of inclusions, so as to deeply clean the liquid steel. Inclusions would gather to the center of the swirling flow by centripetal force, due to the density difference between inclusions and liquid steel. Thus, small inclusions can coalesce into larger ones, and then float to the free surface by their self-buoyance. Physical experiments were carried out in a 1/2.5 scale single strand tundish to study the flow characteristics of tundish with swirling chamber. Numerical modeling was developed to simulate the movements of small inclusions in swirling flow. Discrete phase model was employed together with the O’Rourke algorithm to characterize the coalescence of the inclusions in the swirling flow. The removal of inclusions was investigated, considering the absorption by upper slag and trapping by outside wall of ladle shroud. Compared with a turbulence inhibitor, a swirling chamber shows a similar effect on flow improvement, while performs better in inclusion removal, owing to the inclusion coalescence caused by centripetal force. The results revealed that swirling chamber in diameter of 450 mm is an optimized scheme for deep cleaning of liquid steel, with only 1.66% of the inclusions flowing out of the tundish nozzle.

Mean Age Theory in Continuous Casting Tundish

Mean age theory is introduced to characterize the mixing performance of tundish based on the spatial distribution of tracer’s mean age. Conventional residence time distribution theory was widely used in the tundish analysis; however, it contains no information of the local mixing states. Based on mean age distribution, melt change efficiency is defined as a performance index to evaluate how quickly the old melt in the tundish can be replaced by the young melt from the ladle. Case studies, divided into three groups, were carried out to test the applicability of the new theory in a single-strand tundish with flow control devices of weir, dam and turbulence inhibitor. The developed mean age model was well validated by comparison with measurement in water model and computational fluid dynamics (CFD) results using residence time distribution (RTD) model. Mean age model can reduce the computing time to two orders of magnitude less in comparison with conventional transient RTD model, which improves the feasibility of CFD modelling in parameter studies to a broader extent.

Combined models with tanks in series for characterization of tundish flows in continuous casting of steel

Abstract The traditional combined model of a mixed flow reactor and a plug flow reactor in series with a dead zone has been commonly used to characterize tundish flows in continuous casting of steel. However, there are noticeable differences in residence time distribution curve profile between model predictions and the corresponding experimental measurements. In order to pursue a better characterization of typical tundish flows, two new combined models are outlined in the current work: One involves uniform tanks and a plug flow reactor in series with a dead zone, while the other features two non-uniform tanks and a plug flow reactor in series with a dead zone. The application of the models to a tundish with a turbulence inhibitor in the pouring compartment reveals that both of the two new models can provide a much better representation of the experimental measurements in comparison with the traditional model. Regarding the two new models, the one with two non-uniform tanks is seen to perform better than that with uniform tanks.

Effect of flow control devices on grade change process in a five-strand Tundish

A mathematical model was developed to investigate turbulent flows in steady-state casting and steel intermixing during grade change process in a five-strand tundish under different flow control devices (FCDs). The results showed that the baffle had significant influence on flow state of molten steel during steady-state casting, while the dam and turbulence inhibitor (TI) showed smaller effect. When the tundish was equipped with baffle, the mean residence time and the overall mean standard deviation of each strand decreased by nearly 100.3 s and 46%, the volume of the piston region and dead zone decreased by 13.5% and 6.4%, respectively, compared to without baffle. For grade change process, the baffle had great influence on the steel mixing, while the dam and TI showed less influence. The mass fraction of new grade reached 0.9 at 333 s near the third strand, and remained around 0.8 near the fifth strand at the later stage when the baffle was removed, which seriously deteriorated the steel mixing and the consistency among strands. The tundish equipped with baffle and square TI, but without dam, shows better performances both on flow consistency and new grade diffusion.

Effect of Top‐Swirling Turbulence Inhibitor on Multiphase Flow in a Single‐Strand Tundish During Transient Casting

The turbulence and multiphase flows in a single‐strand slab casting tundish during the start‐up operation, steady‐state casting, and the ladle changeover process without a turbulence inhibitor (TI), with an ordinary TI, and with a top‐swirling TI are numerically investigated and compared to assess the metallurgical advantages of a top‐swirling TI. The results show that the designed top‐swirling TI has no negative effect on the turbulence flow of molten steel during steady‐state casting, as the swirling flow may enhance the inclusion removal rate, and erosion of the guide vanes is relatively weak. During start‐up operation, the use of a top‐swirling TI effectively alleviated level fluctuations in the impact zone, which decreased from 38.75 mm at 90 s to 12.5 mm at the start‐up tonnage, then decreased to zero within 180 s. During ladle changeover, the second stage of steel exposure could be eliminated by the top‐swirling TI, while the areas of steel exposure remaine around 1550 and 750 cm2 without a TI and with an ordinary TI after 60 s of refilling time. The top‐swirling TI could effectively improve the turbulence flow of molten steel, avoiding secondary oxidation and slag entrapment, making it suitable for widespread application and popularization.

Experimental and Simulation Analysis of Physical Water Model through Tracer Injection under Various Baffles and Turbulence Inhibitor Conditions for Developing the Fluid Flow Parameters and Inclusion Removal Rates in Tundish

Tundish is a critical part involved in the continuous casting process, which ensures the constant flow of liquid metal and with performing different functions. In odd-numbered multistrand tundish, the confirmation consistency of the fluid flow among all the strands is one of major concerns. In this study, five-strand tundish with a set of weirs and a baffle is utilized for investigation concerning fluid flow parameters and inclusion removal analysis. The simulation is carried out in ANSYS FLUENT 19.2 software through the defined numerical model, and the experimental analysis is performed on a scaled physical water model through tracer injection. Four different baffles are designed along with two different types of turbulence inhibiter for the tundish to enhance the fluid flow parameters and inclusion removal rates. The inclusion sizes were varied from 10 to 100 µm with a difference of 20 µm respectively for studying the inclusion removal rate concerning inclusion sizes. From the outcomes obtained like the residence time distribution (RTD) curves and others, it was concluded that the fourth baffle version with the first turbulence inhibiter, which are equipped in tundish version TV8 is the most beneficial tundish version for the enhancement in fluid flow and inclusion removal rates as compared to other tundish versions in this study.

Comparison of Fluid Flow and Temperature Distribution in a Single-Strand Tundish with Different Flow Control Devices

The effects of flow control devices (FCD) in a single-strand tundish, including weir, dam, turbulence inhibitor and gas curtain, have been investigated using water model experiments and CFD simulations. A scaled-down water model was built up to visualize flow pattern and measure the residence-time distribution (RTD) of different tundish configurations. A CFD model was applied to calculate the fluid flow, heat transfer and RTD curves in the prototype tundish under the nonisothermal conditions. The Eulerian–Lagrangian approach was applied to investigate the bubble flow in the system. The results show that each FCD has its own unique function to control the flow. It is important to evaluate the combined effects of FCD based on their installations. The molten steel flow in the tundish could be improved if these flow control devices were arranged properly.

Effect of Thermal Buoyancy on Fluid Flow and Residence-Time Distribution in a Single-Strand Tundish.

Natural convection of molten steel flow in a tundish occurs due to the temperature variation of the inlet stream and heat losses through top surface and refractory walls. A computational fluid dynamics (CFD) model was applied to study the effect of thermal buoyancy on fluid flow and residence-time distribution in a single-strand tundish. The CFD model was first validated with the experimental data from a non-isothermal water model and then applied to both scale-down model and prototype. The effects of flow control devices, including weir, dam and turbulence inhibitor, were compared and analyzed. Parameter studies of different heat losses through the top surface were performed. The results show that thermal buoyancy has a significant impact on the flow pattern and temperature distributions of molten steel in the tundish. The increase of heat loss through the top surface shortens the mean residence time of molten steel in the tundish, leading to an increase in dead volume fraction and a decrease in plug flow volume fraction.

Effect of Turbulence Inhibitors on Molten Steel Flow in 66-Ton T-Type Tundish with Large Impact Area

A multiphase numerical simulation of the steel-slag flow was established by using the volume of fluid (VOF) model to study the effect of different turbulence inhibitors on the improvement of the steel-slag flow in the tundish. The steel-slag interface fluctuation was studied by vorticity magnitude and transient fluctuation change. A prediction model of residence time distribution (RTD) curve was established based on mathematical simulation and the error of prediction model can be controlled below 6% by comparing with the hydraulic results. The results show that jet flow into the tundish generated very different flow patterns. Case 1 produced a double-roll flow pattern and case 2 produced a four-roll flow pattern in the impact area. The ratio of vorticity magnitude above 1.00 s−1 near the ladle shroud was 2.60% in case 1 and the ratio of vorticity magnitude above 1.00 s−1 near the ladle shroud was 13.15% in case 2, which indicates case 2 increased the possibility of slag entrainment via the upward flow mechanism and shear layer instability. Surface velocity fluctuations in case 2 were much more severe near the ladle shroud. The thickness of the slag layer was 60 mm, the interface fluctuation towards surface in case 2 was close to 20 mm. Meanwhile, case 1 involved very small volume-fraction contours near interface. The turbulence inhibitor with internal ripples (case 1) showed a better optimization effect and the results could provide a theoretical basis for the selection of a suitable turbulence inhibitor for the 66-ton T-type tundish.

Modeling of Fluid Flow and Residence-Time Distribution in a Five-Strand Tundish

Quantified residence-time distribution (RTD) provides a numerical characterization of mixing in the continuous casting tundish-thus allowing the engineer to better understand the metallurgical performance of the reactor. This study describes a computational fluid dynamic (CFD) modeling study for analyzing the flow pattern and the residence-time distribution in a five-strand tundish. Two passive scalar-transport equations were applied to separately calculate the E-curve and F-curve in the tundish. The numeric modeling result were compared to water-modeling results to validate the mathematical model. The volume fraction of different flow regions (plug, mixed and dead) and the intermixing time during the ladle changeover were calculated to study the effects of the flow control device (FCD) on the tundish performance. From the results of CFD calculations, it can be stated that a combination of the U-baffle with deflector holes and the turbulence inhibitor had three major effects on the flow characteristics in the tundish: (i) to reduce the extent of the dead volume; (ii) to evenly distribute the liquid streams to each strand and (iii) to shorten the intermixing time during the ladle changeover operation.

Investigation on the control of multiphase flow behavior in a continuous casting tundish during ladle change

The transient multiphase flow behavior in a single-strand tundish during ladle change was studied using physical modeling. The water and silicon oil were employed to simulate the liquid steel and slag. The effect of the turbulence inhibitor on the slag entrainment and the steel exposure during ladle change were evaluated and discussed. The effect of the slag carry-over on the water-oil-air flow was also analyzed. For the original tundish, the top oil phase in the impact zone was continuously dragged into the tundish bath and opened during ladle change, forming an emulsification phenomenon. By decreasing the liquid velocities in the upper part of the impact zone, the turbulence inhibitor decreased considerably the amount of entrained slag and the steel exposure during ladle change, thereby eliminating the emulsification phenomenon. Furthermore, the use of the TI-2 effectively lowered the effect of the slag carry-over on the steel cleanliness by controlling the movement of slag droplets. The results from industrial trials indicated that the application of the TI-2 reduced considerably the number of linear inclusions caused by ladle change in hot-rolled strip coils.

Optimization of flow, heat transfer and inclusion removal behaviors in an odd multistrand bloom casting tundish

The steel flow, heat transfer, and inclusion removal behaviors in a five-strand bloom tundish for five baffles and two types of turbulence inhibitors (TIs) were investigated by a multiphysical model to enhance the consistency among the strands and the purity of molten steel. Water model experiments were conducted to verify the simulated results of flow and residence time distribution (RTD). The results showed that the simulated steel flow and RTD curves were basically consistent with those of the experiments. Compared to original conditions, the total residence time reaches 595.0 s, and the volume of the plug region increases by 4.8%, while the volume of dead zone decreases by 0.2% when applying the optimized baffle and TI. In addition, the response and residence times at the 3rd strand increase by 42.5 s and 264.6 s, the total average standard deviation decreases to 0.0057. Meanwhile, the maximum temperature drop decreases from 28.6 K to 22.8 K, and the temperature difference among strands decreases from 3.7 K to 1.4 K. The inclusions removal rate increases by 0.9% to 8.3% with diameters ranging from 10 μm to 100 μm and reaches 94.4% at 100 μm. Furthermore, the qualification rates of flaw detection and nonmetallic inclusions in high rails after optimization increase from 97.94% to 98.73% and from 97.3% to 99.1%, respectively, and the consistency among the strands is apparently enhanced.