Argon Gas Injection Research Articles

Simulation Analysis of Influence of Argon Gas Injection Hole Position on Flow Field in Steel Ladle

Simulation Analysis of Influence of Argon Gas Injection Hole Position on Flow Field in Steel Ladle

Suppression of runaway electrons by injection of argon gas in the low-density discharges in the STOR-M tokamak

Behaviors of runaway electrons have been investigated by injection of argon impurity gas during the low-density hydrogen discharges in the STOR-M tokamak. Argon gas is puffed using a fast electromagnetic gas puffing valve with various amounts of gas puffed at different injection times. It has been found that puffing of an appropriate amount of gas can suppress the already generated runaway electrons evidenced by the intensity reduction of the hard X-ray (HXR) radiation caused by the impact of runaway electrons on the STOR-M chamber wall. On the other hand, excessive argon gas puffing causes earlier termination of the discharge.

CFD Predictions for Mixing Times in an Elliptical Ladle Using Single- and Dual-Plug Configurations

Argon bottom stirring is commonly practiced in secondary steelmaking processes due to its positive effects on achieving uniform temperatures and chemical compositions throughout a steel melt. It can also be used to facilitate slag metal refining reactions. The inter-mixing phenomena associated with argon gas injection through porous plugs set in the bottom and its stirring efficiency can be summarized by evaluations of 95% mixing times. This study focuses on investigating the impact of different plug positions and ratios of argon flow rates from two plugs on mixing behavior within a 110-tonne, elliptical-shaped industrial ladle. A quasi-single-phase modeling technique was employed for this purpose. The CFD findings revealed that the optimal position of the second plug is to be placed diametrically opposite the existing one at an equal mid-radius distance (R/2). An equal distribution of argon flow rates yielded the best results in terms of refractory erosion. A comparative study was conducted between single- and dual-plug-configured ladles based on flow behavior and wall shear stresses using this method. Furthermore, a transient multiphase model was developed to examine the formation of slag open eyes (SOE) for both single- and dual-plug configurations using a volume of fluid (VOF) model. The results indicated that the dual-plug configuration outperformed the current single-plug configuration.

Model of multiphase flow, superheat transport, and particle capture in a steel continuous caster

A model of turbulent multiphase flow, heat transfer, and particle entrapment during continuous casting of steel is presented. The model includes the top 7m of the vertical and curved strand, and considers the effects of argon gas injection and thermal buoyancy. RANS model flow results are compared with LES. Lagrangian particle transport through the Eulerian-Eulerian multiphase flow field from the k-ɛ RANS model is based on random walk and features advanced particle capture criteria, improved from previous work by including anisotropic turbulent velocity fluctuations near the walls. Particle capture via 3 mechanisms is included: capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by surrounding large particles. The fluid flow and bubble/inclusion capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests of particle locations, and good agreement is seen. The superheat has negligible effect on flow in the mold region but causes complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy. With high (30 K) superheat, this leads to less penetration, and slightly fewer and shallower capture of particles. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, and more surface capture. Capture bands occur near the transition from vertical to curved, where downward liquid flow velocity balances the particle terminal velocity.

Modeling of Multiphase Flow, Superheat Dissipation, Particle Transport, and Capture in a Vertical and Bending Continuous Caster

A new model of particle entrapment during continuous casting of steel is presented, which includes the effects of multiphase flow from argon gas injection and thermal buoyancy from superheat in the strand. The model simulates three different capture mechanisms, including capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by the surrounding of large particles. The fluid flow and bubble capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests, respectively, and good agreement is seen. Results suggest that the superheat has a negligible effect on the flow in the mold region. However, higher (30 K) superheat causes a more complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy effects. This causes less penetration deep into the strand, which leads to fewer and shallower particle captures. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, which sometimes (0.003%) capture large (1 mm) bubbles. Capture bands occur near the transition line from vertical to curved, due to the downward fluid velocity balancing the particle terminal velocity, enabling capture in the relative stagnation region beneath the longitudinal recirculation zone. These findings agree with plant observations.

Liquid jet breakup regimes in lava fountains

Primary magma fragmentation in “fluid-dominated” (as opposed to “ash-dominated”) lava fountains involves the hydrodynamic breakup of a jet of magma. Lava fountains partly resemble industrial liquid jets issued from a nozzle into a quiescent atmosphere, on which there is a vast literature. Depending on the internal liquid properties, nozzle diameter and ejection velocity, liquid jet breakup in industrial applications occurs in four regimes: (I) coarse laminar breakup (Rayleigh regime); (II) transition region between laminar and turbulent breakup (first wind-induced regime); (III) turbulent breakup at the jet surface and unstable but intact liquid core (second wind-induced regime); (IV) fully turbulent fine spray (atomization regime).Ductile magma breakup associated with regimes II, III and IV have been reproduced during the initial expansion of experimental magma fragmentation pulses as part of this study. In each experiment, volcanic rocks were re-melted at 1200 °C, then fragmented through the injection of compressed argon gas within a few tens of milliseconds. Three compositions were used: olivine-melilitite, alkali basalt, and basaltic trachy-andesite. Each composition was ejected at 3 and 10 MPa gas driving pressure, yielding exit velocities between 11–13 and 33–44 m/s, respectively. The ultramafic magma ejected at high speed developed quickly into a fully developed spray (regime IV), whereas the basaltic trachy-andesite ejected at low-speed initially expanded as a coherent magma mass before breaking into coarse domains (regime II). The observed variability among the experiments is linked to the relative balance among surface tension, viscosity, density, jet diameter and ejection velocity of the magma versus external aerodynamic effects acting on the jet surface. These factors, particularly viscosity and exit velocity, are also likely to control jet breakup regimes in natural lava fountains and some Strombolian pulses.

Numerical Simulation for Two‐Phase Flow, Heat Transfer, and Inclusion Transport in Bloom Mold Considering the Effects of Argon Gas Injection and Mold Electromagnetic Stirring

A mathematical model based on the Eulerian–Eulerian–Lagrangian method is developed to investigate the two‐phase flow, temperature distribution, and inclusion transport, considering the effect of argon gas injection (AGI) and mold electromagnetic stirring (M‐EMS) in the bloom mold. The magnetic resistance force is adopted to account for the effect of the magnetic field on bubbles. It is demonstrated in the results that when AGI is applied, plumes form near the submerged entry nozzle (SEN) and increase the velocity in the upper part of the mold. While M‐EMS is applied, the swirl flow significantly increases the overall flow velocity and superheat dissipation. In addition, AGI and M‐EMS increase the fluctuation and temperature of the free surface, lower the peak heat flow, and promote inclusions removal. When AGI is applied with M‐EMS, the swirl flow and plumes in the upper part of the mold are weakened due to the interaction between them, and the level fluctuation is lower than that of applying AGI or M‐EMS separately. The heat flow and free surface temperature are more uniform, and the inclusion removal rate further increases. Meanwhile, M‐EMS drives bubble columns to the location between the two ports of SEN and gathers bubbles around the SEN.

Bubble Characterization in a Continuous Casting Mold: Comparison and Identification of Image Processing Techniques

Gas injection is a common practice in numerous metallurgical vessels, and continuous casting mold is one of the examples of such vessels. Argon gas injection into the submerged entry nozzle contributes to increasing the sequence length. However, in some unfavorable conditions, these bubbles become responsible for the occurrence of steel defects such as blister, sliver, and mold slag exposure, etc. Bubbles size distribution in the mold is one of the indicators of cast steel slab quality. Previous studies on estimating the bubble size distribution in mold lack in providing the challenges of automatic image processing (IP) techniques employed to measure the size of the bubbles. On the other hand, bubble size measurement studies performed on other reactors such as bubble columns, etc., are programming intensive and need in-depth knowledge of coding. Some automatic IP techniques also exist which facilitate a user-friendly environment and quick estimation of bubble characteristics. Even though these IP techniques are easy to use, an assessment of their applicability with respect to experiments performed in a particular study is required. Therefore, in this study, details of imaging and automatic IP techniques are discussed through a comprehensive comparative analysis. Three different IP techniques were examined for measuring the bubble sizes, and the performances of these techniques were compared with respect to a newly developed manual benchmark technique. One of the identified techniques, Ellipse Split, was applied to estimate the bubble size distribution at different gas fractions for validation.

Design of a High-Efficiency Dual-Helical Antenna for Microwave Plasma Sources

Achieving a sustainable dense plasma source has always been of broad interest. Notably, in microwave discharges, gaining dense uniform plasma has held numerous efforts. In this article, a high-efficiency dual-helical antenna for microwave plasma source to improve the performance of the Alborz Tokamak neutral beam injection (NBI) system is presented. For evaluation and analysis of the designed antenna and a conventional rod antenna, COMSOL Multiphysics software is used. Besides, by feeding the antenna using a 2.45-GHz magnetron in the 20-Pa vacuum steel enclosure and the Argon gas injection, a practical experiment has been conducted. Finally, the plasma with a density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.5\times 10^{17}\,\,1/\text{m}^{3}$ </tex-math></inline-formula> and the electric field intensity results show that the designed antenna is an optimal alternative in microwave plasma sources.

Thermal quench and current profile relaxation dynamics in massive-material-injection-triggered tokamak disruptions

3D non-linear magnetohydrodynamic simulations of a disruption triggered by a massive injection of argon gas in JET are performed with the JOREK code. The key role of the thermal drive of the m = 2, n = 1 tearing mode (i.e. the drive from helical cooling inside the island) in the disruption process is highlighted by varying the amplitude and position of the argon source across simulations, and also during a simulation. In cases where this drive persists in spite of the development of magnetic stochasticity, which is favoured by moving the argon source in an ad hoc way from the plasma edge into the 2/1 island at some point in the simulation, a relaxation in the region (roughly) takes place. This relaxation generates a plasma current spike comparable to the experimental one. Simulations are compared in detail to measurements via synthetic diagnostics, validating the model to some degree.

Design and performance of shattered pellet injection systems for JET and KSTAR disruption mitigation research in support of ITER *

Shattered pellet injection (SPI) systems that form cryogenic pellets in a pipe-gun for injection of material to mitigate disruptions have been fabricated and installed for use in thermal mitigation and runaway electron (RE) dissipation experiments on JET and KSTAR. These systems are to support disruption mitigation research for ITER and are based on an ORNL three-barrel design for flexibility in pellet size selection and variable pellet composition studies. The SPI systems for JET and KSTAR have a common feature of the barrels being collimated into a single injection line that enters the vacuum vessel. The pellets are shattered in bent stainless steel tubes that are mounted inside the vacuum vessel of the tokamak, vertically on JET and horizontally on KSTAR. The JET installation has the unique feature of vertical SPI mounting and injection with the shatter plume aimed toward the inner wall to intercept known RE beam locations generated from argon gas injection induced disruptions. The KSTAR SPI installation has two identical SPIs that are mounted on the midplane 180 degrees apart with identical injection lines and shatter tubes aimed at the plasma magnetic axis. Installation and operation of these SPI systems has provided useful lessons learned in the implementation of this SPI technology and valuable experience in optimizing the formation and firing of the pellets to optimize the physics performance.

Modeling Air Aspiration in Steel Continuous Casting Slide-Gate Nozzles

Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to occur when the flow control system (slide-gate or stopper rod) causes the pressure inside the nozzle to drop below atmospheric pressure, drawing gas into the system through possible cracks or gaps in the refractory walls. In this work, a 1-D pressure-energy model of the complete metal delivery system from the tundish to the mold is developed to predict the pressure distribution and throughput under dynamic operating conditions and varying clogging conditions. The energy balance approach includes pressure losses in the slide-gate, wall friction, and nozzle geometry variations, including the effects of multiphase flow due to argon gas injection. The model also predicts air aspiration, oxide inclusion formation, and the time for clogging shutdown. The predicted pressure distribution is verified with a three-dimensional numerical simulation of multiphase turbulent flow, and is validated with plant measurements. Parametric studies with different submerged entry nozzle (SEN) designs revealed that a smaller SEN diameter may lessen negative pressure by redistributing the pressure loss from the slide-gate to the entire nozzle through increased friction losses. Under negative pressure, a submillimeter-thin gap was shown to cause considerable air aspiration. Clogging shutdown times were evaluated for several scenarios under static and dynamic operating conditions.

Minor disruptions triggered by supersonic molecular beam injection on J-TEXT tokamak

Disruption mitigation experiments with supersonic molecular beam injection of argon gas on J-TEXT were conducted to explore the evolution process during multistage minor disruption. The corresponding numerical simulation was performed using a 3D magnetohydrodynamic (MHD) code, namely, NIMROD (Sovinec et al 2004 J. Comput. Phys. 195 355). The experimental and numerical simulation results are shown in the following. The central plasma temperature decreases to less than tens of electovolts after a relatively long period of multistage thermal collapse. Different MHD instability modes appear when the impurity cold front propagates toward the q = 2 surface. During the burst of MHD activity and central plasma thermal collapse, the heat flux is transferred from the core region to the plasma boundary. Further numerical simulation results show that the MHD process is accompanied by a significant increase in the core-oriented spread of impurities through the q = 2 surface. During the transition stage from the minor disruption to the major disruption, the high order modes play an important role and the magnitude of the n = 3 growth rate is even larger than that of the n = 1 or n = 2 mode. What seems to separate major from minor disruptions is that in a minor disruption, a single MHD crash is not sufficient to cause a full radiative collapse.

Evaluation of Argon-Gas-Injected Solvothermal Synthesis of Hydroxyapatite Crystals Followed by High-Frequency Induction Heat Sintering

In this study, the two-state solvothermal method (180 °C) was used for the synthesis of hydroxyapatite nanoparticles. The former is traditional (2, 4 h), and the latter, with argon gas injection (1...

Vibration‐Based Monitoring of Gas‐Stirring Intensity in Vacuum Tank Degassing

Liquid steel is typically stirred in a vacuum tank using argon gas injection to achieve a homogeneous composition and high‐purity steel. The aim of this work is to study the effect of vessel vibration on the operational state monitoring of the gas stirring in a vacuum tank degasser. Following an extensive analysis of vibration features, the root mean square (RMS) of vertical velocity is found to be the best feature for the measurement of the stirring intensity caused by the volumetric gas injection rate into the ladle. Smoothing is conducted using a centered median filter with a window length of 21 s. In this work, the operational state monitoring of gas stirring is described using a ladle responsiveness value (LRV). This describes the ability of a ladle to generate the maximum amount of vibration with the minimum amount of argon gas. The LRV summarized for each ladle reveals significant differences between them. Correspondingly, a rolling ladle responsiveness value (rLRV) is used for online monitoring of possible gas leakages. The rLRV can also be used for the online monitoring of the stirring efficiency and as its comparison with the overall efficiency of a specific ladle or all ladles.

Measurement of Molten Steel Velocity near the Surface and Modeling for Transient Fluid Flow in the Continuous Casting Mold

In the current work, a rod deflection method (RDM) is conducted to measure the velocity of molten steel near the surface in continuous casting (CC) mold. With the experimental measurement, the flow velocity and direction of molten steel can be obtained. In addition, a mathematical model combining the computational fluid dynamics (CFD) and discrete phase method (DPM) has been developed to calculate the transient flow field in a CC mold. The simulation results are compared and validated with the plant measurement results. Reasonable agreements between the measured and simulated results are obtained, both in the trends and magnitudes for the flow velocities of molten steel near the mold surface. Based on the measured and calculated results, the velocity of molten steel near the surface in the mold increases with increasing casting speed and the casting speed can change the flow pattern in the mold. Furthermore, three different types of flow patterns of molten steel in the mold can be obtained. The pattern A is the single-roll-flow (SRF) and the pattern C is the double-roll-flow (DRF). The pattern B is a transition state between DRF and SRF, which is neither cause the vortices nor excessive surface velocity on the meniscus, so the slag entrainment rarely occurs. Argon gas injection can slow down the molten steel velocity and uplift the jet zone, due to the buoyancy of bubbles. Combination of the measurement and numerical simulation is an effective tool to investigate the transient flow behavior in the CC mold and optimize the actual operation parameters of continuous casting to avoid the surface defects of the automobile outer panels.

Experimental modelling of continuous casting of steel in slab moulds using low melting liquid metals

Electromagnetic actuators are widely used in industry for contactless control of the steel flow in the continuous casting process. However, a real control of the flow structure by those actuators is a challenging task due to the lack of flow monitoring devices. Even a satisfying non real-time characterisation of the melt flow from plant measurements is missing. Beside numerical simulations, only a very few spatially and temporally limited measurements in liquid steel are available to investigate the actual action of the magnetic fields on the fluid.Therefore, model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in the mould of a continuous caster. Their advantage is the availability of a variety of measurement techniques for quantitative flow measurements. The application of the Ultrasonic-Doppler-Velocimetry (UDV) and the Contactless-Inductive-Flow-Tomography (CIFT) allows for a detailed characterization of the mould flow with a reasonable spatial and temporal resolution.In recent experiments at HZDR, the systematic study on the influence of an electromagnetic brake on the mould flow in a slab caster was continued. The measurements were carried out using a 1:2 scaled model operated with SnBi and a 1:8 scaled model operated with GaInSn, respectively. The melt surface was partly measured by a laser scanner system. In particular, the immersion depth of the submergence entry nozzle (SEN) was varied during the experiments. It became obvious that changes in the mould flow had a strong influence on the free surface of the melt, where strong perturbations can significantly impair the surface quality of the final steel strands. Moreover, effects from the “artificial” clogging of one SEN-port or the injection of Argon gas at the stopper rod were investigated.

Modeling Argon Gas Behavior in Continuous Casting of Steel

In the continuous casting of steel, argon gas injection through the upper tundish nozzle wall or stopper tip is known to decrease clogging and remove inclusions. In addition to this intended gas injection, gas may be passively aspirated into the flow system by negative pressure developed inside of the nozzle. The injected gas forms gas pockets and bubbles through complex redistribution processes that greatly affect flow in the mold, leading to defects in the final product. Estimating the number and size distribution of bubbles is crucial to optimize multiphase flow in this important manufacturing process. This article introduces an integrated methodology to investigate these phenomena and provides examples to validate the approach. The system features models to predict: gas leakage, pressure distribution in the entire system, gas pockets and the size distribution and trajectories of bubbles using a new hybrid method, and multiphase flow in the nozzle and mold.

Experimental investigation of gas lift pump in a lead-bismuth eutectic loop

The gas lift pump has been used in the development of an Accelerator Driven System (ADS) nuclear reactor instead of mechanical pumps due to its simple mechanical structure. The two phase flow of Lead Bismuth eutectic (LBE)-inert gas in rising pipe could remarkably increase natural circulation capacity. This study aims to evaluate the performance of the gas lift pump and to conduct the relevant parametric study. As a result, the Natural Circulation Capability Loop (NCCL) test facility was designed and constructed. The height of the experimental loop is 4.5 m and the rising height is 3.5 m. The maximum temperature of the loop is 500 °C. The experiments about the gas lift pump in LBE were performed with risers of three different heights. The results showed that the LBE mass flow rate increases rapidly with an increase of argon flow rate when it is less than 300 NL/h. When the argon flow rate is larger than 300 NL/h, the growth of the LBE mass flow rate is reduced. The LBE mass flow rate increased process is accompanied by the transformation of the flow pattern. The variation trend of the LBE flow rate is consistent with the trend of the void friction in the riser. Under the same amount of argon gas injection, the LBE circulation ability increases as the height of the riser increased. Based on the experimental data and drift-flow model of Zuber and Findlay, a new correlation of the void fraction is obtained and the relative error between the calculated and the experimental value is within 30%. The purpose of this study is to reveal the enhancement mechanism of the natural circulation capacity of gas lift pump and to provide experimental data and model support for the design of ADS in China.

Tomographic reconstruction of two-dimensional radiated power distribution during impurity injection in KSTAR plasmas using an infrared imaging video bolometer

Based on the two-dimensional radiation images obtained by an infrared imaging video bolometer (IRVB) with tangential view, the two dimensional radiation profiles of plasmas in KSTAR were reconstructed. The IRVB installed on KSTAR has a tangential view of the plasma, and thus tomographic reconstruction of the raw images of radiation profiles was performed to remove the chord-integration effect by using a tomographic reconstruction code based on the Phillips-Tikhonov algorithm. Phantom reconstruction tests with various synthetic images were carried out to validate the accuracy of the reconstruction results. It is found that hollow radiation phantoms with strong divertor radiation were reconstructed with high accuracy. Furthermore, the effects of the number of channels of the IR camera, and the number of pixels of the plasma and of the IRVB on reconstruction performance are studied with phantom tests. Two-dimensionally reconstructed images of KSTAR plasmas demonstrated that radiation loss at the plasma edge and near the divertor region increased significantly after gaseous impurity injection. The total radiated power was up to 1.2 MW at the disruption, which was 40% of the NBI power. After argon and krypton gas injection, total radiated power was increased by 325 kW and 180 kW, respectively.