Argon Injection Research Articles

Improved Electrical Control of Ladle–Furnace Units by Means of Arc-Current Harmonics

Abstract—The influence of the intensity of argon injection in a two-position ladle–furnace unit on its electrical parameters is considered. Waves and surges formed at the surface of the liquid metal under the action of intense injection lead to periodic short-circuiting in the phases closest to the nonsteady zone. In addition, the deterioration in slag conditions lowers the thermal efficiency of the arc closest to the phase meniscus. To minimize these effects, improved electrical control is proposed, with adaptation to the changing arc-combustion conditions. To that end, the harmonic composition of the arc currents is analyzed. The new control algorithm decreases the power consumption of existing ladle–furnace units, with no loss in heating rate of the liquid steel.

Numerical simulation of turbulent boundary layers with foreign gas transpiration using OpenFOAM

Transpiration cooling in combination with porous high-temperature materials is a promising technique for thermal protection of highly-loaded aerospace applications. In this study, we present a modified OpenFOAM solver which is applied to the simulation of a turbulent channel flow with boundary layer blowing. Different models for porous wall injection of air, argon, and helium into a main flow of air are proposed and evaluated. Subsequently, same and foreign gas transpiration is simulated for cold and heated main flow conditions and the results are compared to experimental data and correlations from literature. A very good overall agreement is found for velocity and temperature boundary layer profiles as well as the dimensionless parameters for wall shear stress and heat transfer.

Laboratory Simulations of the Radial Distribution of the Toroidal Magnetic Field in an Axial Jet from a Young Stellar Object

Results from experiments on the radial distribution of the magnetic fields in axial plasma flows formed during the compression of a plasma–current sheath carried out at the KPF-4-PHOENIX plasmafocus installation are presented. The plasma flows were generated in a discharge with stationary filling of the chamber with a working gas of argon or hydrogen, and also with a pulsed injection of argon. Analysis of the radial profiles of the magnetic field distribution and their time variations are used to localize regions of trappedmagnetic field, as well as regions where a return current flows at the periphery of the plasma flow. It is shown that the transverse (radial) size of the plasma flow depends on the density of the ambient medium (background gas) through which it propagates. These experiments were carried out in the framework of a project on laboratory simulations of non-relativistic jets from young stars.

Analysis of Temperature Losses of the Liquid Steel in a Ladle Furnace During Desulfurization Stage

In this research, a multiphase numerical simulation (steel–slag–argon) was carried out by coupling the VOF model with the transitory heat losses of the liquid steel during the injection of argon in the secondary refining process. To model the radiation in the free surface of the ladle, three models, P-1, discrete ordinates, and Rosseland, were considered. The thermal behavior of magnesia-carbon (MgO-C) and high alumina (Al2O3), which are commonly used in the industry, as a work wall was compared. Likewise, the behavior of two slag of different chemical composition was analyzed with two layer thicknesses. The results of the fluid dynamics agreed with those obtained in a physical scale model with the PIV technique. In addition, it was found that the Rosseland model allowed to quantify the radiative heat losses with a good approximation according to the results obtained in the industry. It was observed that the more viscous slag with greater thickness reduced the opening of the slag layer. Finally, the heat losses in the liquid steel could be controlled by manipulating the variables of thickness and viscosity of the slag and also the type of refractory of the ladle.

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.

The role of kinetic instabilities in formation of the runaway electron current after argon injection in DIII-D

Kinetic instabilities in the MHz range driven by runaway electrons (REs) have been observed for the first time during the current quench (CQ) in disruptions triggered by massive injection of argon in DIII-D. These instabilities are well-correlated with intermittent RE losses in the beginning of RE current formation. The runaway current phase is not observed when the power of instabilities exceeds a threshold. Novel measurements of the RE distribution function during the CQ indicate that the instabilities appear when RE energy (ERE) exceeds 2.5–3 MeV, the number of modes grows linearly with ERE, and their frequencies lie in the range 0.1–3 MHz, below the ion cyclotron frequency. Possible plasma waves exciting by REs in this region are proposed. Increase of the amount of injected argon decreases the ERE and increases the success rate of the runaway current formation, while increase of the pre-disruption plasma current acts in the opposite direction. No dependence on the pre-disruption core electron temperature is found.

Overview of Electromagnetic Forces to Control Flow During Continuous Casting of Steel

During continuous casting of steel slabs, electromagnetic forces can be applied to help control the flow pattern in the mold, augmenting the effects of nozzle and strand geometry, casting speed, and argon injection. Specific configurations include: local, single-ruler, and double-ruler electromagnetic braking, traveling magnetic fields which actively drive flow in the upper mold, (speeding up, slowing, or stirring), and recently combinations of both systems together. Electromagnetic forces have the advantage of being changeable with casting conditions, and naturally adjust with flow variations. This gives this important flow-control tool the potential to stabilize flow in the mold, and to control molten steel velocities to lessen defects. To achieve these benefits in practice, however, requires good understanding of how the defects form, and the details of how the electromagnetic field(s) affect the transient flow. The best way to gain this understanding is by combining validated computational models with plant measurements. This paper shows recent advances using these tools to understand how different configurations affect both steady and transient flow behaviour, the formation of defects from level fluctuations, meniscus freezing, inclusion entrapment, and other mechanisms. These findings suggest promising ways to implement electromagnetic forces to lower defects to improve the process.

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.

Effect of Argon Injection in Meniscus Flow and Turbulence Intensity Distribution in Continuous Slab Casting Mold Under the Influence of Double Ruler Magnetic Field

Effect of Argon Injection in Meniscus Flow and Turbulence Intensity Distribution in Continuous Slab Casting Mold Under the Influence of Double Ruler Magnetic Field

Physical and mathematical modeling of bubbles plume behaviour in one strand tundish

Moving through the liquid steel, argon bubbles intensify the chemical and thermal homogenisation processes and liquid metal refining. The present study reports the physical and mathematical modeling of bubbles behaviour in the tundish with argon injection system. The 210 litre–capacity one strand slab tundish model was made on a scale of 2:5. The laboratory water model experiments have demonstrated that the identical porous material used in gas-permeable barrier may generate gas bubbles varying in size and shape. This fact will also affect both vertical and horizontal velocities attained by the bubbles. From numerical simulations influence of argon flow rate on liquid steel velocity for free surface in the tundish was obtained. The results from numerical simulations indicate that argon create increasing of liquid steel velocity and vortex structures.

Numerical simulation of detached plasma in the end-cell of GAMMA 10/PDX for divertor simulation study

This research investigates the effect of Argon (Ar) and Neon (Ne) injection on the plasma parameters in the end-cell of GAMMA 10/PDX numerically by using a multi-fluid code. Reduction in the temperature of the electrons and ions is observed according to the increment of impurity injection. The electron density and the particle flux show tendency of roll-over phenomena for Ar injection. Temperature reduction in the electrons and ions during Ar injection is higher than those of the Ne injection. It is also observed that the charge-exchange (CX) loss and radiative power loss for Ar injection is higher than that of the Ne injection. These outcomes indicate that Ar is more effective radiative gas for generating detached plasma.

Overview of recent HL-2A experiments

Since the last Fusion Energy Conference, significant progress has been made in the following areas. The first high coupling efficiency low-hybrid current drive (LHCD) with a passive–active multi-junction (PAM) antenna was successfully demonstrated in the H-mode on the HL-2A tokamak. Double critical impurity gradients of electromagnetic turbulence were observed in H-mode plasmas. Various ELM mitigation techniques have been investigated, including supersonic molecular beam injection (SMBI), impurity seeding, resonant magnetic perturbation (RMP) and low-hybrid wave (LHW). The ion internal transport barrier was observed in neutral beam injection (NBI) heated plasmas. Neoclassical tearing modes (NTMs) driven by the transient perturbation of local electron temperature during non-local thermal transport events have been observed, and a new type of non-local transport triggered by the ion fishbone was found. A long-lasting runaway electron plateau was achieved after argon injection and the runaway current was successfully suppressed by SMBI. It was found that low-n Alfvénic ion temperature gradient (AITG) modes can be destabilized in ohmic plasmas, even with weak magnetic shear and low-pressure gradients. For the first time, the synchronization of geodesic acoustic mode (GAM) and magnetic fluctuations was observed in edge plasmas, revealing frequency entrainment and phase lock. The spatiotemporal features of zonal flows were also studied using multi-channel correlation Doppler reflectometers.

Suppression of runaway current generation by supersonic molecular beam injection during disruptions on J-TEXT

The suppression of disruption-generated runaway electrons (REs) by supersonic molecular beam injection (SMBI) has been investigated on the J-TEXT tokamak. Experimental results demonstrate that the hydrogen injected by SMBI during plasma current flattop phase can provoke magnetic perturbations, which increase RE losses rapidly. The effective radial diffusion coefficient of REs due to SMBI is estimated as Dr ≈ 16 m2 s−1. Based on this benefit, the SMBI has been used to explore the suppression of disruption-generated REs. In J-TEXT, RE current is created with rapid argon injection by a massive gas injection valve. It is found that hydrogen SMBI before disruption efficiently suppresses the generation of RE current.

The impacts of effective stress and CO2 sorption on the matrix permeability of shale reservoir rocks

We assess the impacts of effective stress and CO2 sorption on the bedding-parallel matrix permeability of the Utica shale through pressure pulse-decay experiments. We first measure permeability using argon at relatively high (14.6MPa) and low (2.8MPa) effective stresses to assess both pressure dependence and recoverability. We subsequently measure permeability using supercritical CO2 and again using argon to assess changes due to CO2 sorption. We find that injection of both argon and supercritical CO2 reduces matrix permeability in distinct fashion. Samples with permeability higher than 10−20m2 experience a large permeability reduction after treatment with argon, but a minor change after treatment with supercritical CO2. However, samples with permeability lower than this threshold undergo a slight change after treatment with argon, but a dramatic reduction after treatment with supercritical CO2. These results indicate that effective stress plays an important role in the evolution of relatively permeable facies, while CO2 sorption dominates the change of ultra-low permeability facies. The permeability reduction due to CO2 sorption varies inversely with initial permeability, which suggests that increased surface area from hydraulic stimulation with CO2 may be counteracted by sorption effects in ultra-low permeability facies. We develop a conceptual model to explain how CO2 sorption induces porosity reduction and volumetric expansion to constrict fluid flow pathways in shale reservoir rocks.

Numerical and Physical Modeling of Liquid Steel Flow Structure for One Strand Tundish with Modern System of Argon Injection

In the continuous steel casting process, argon, as a gas neutral to liquid steel, is used as a protective gas or medium developing the pattern of liquid steel and non‐metallic inclusions motion. With the appropriate argon flow rate, the hydrodynamic structure of liquid steel motion can be effectively modified in the tundish. The facility under investigation is a single‐nozzle slab tundish. Two unique argon injection barrier have been designed, whose purpose is to stimulate the motion of liquid steel within the working space of the tundish. Computer simulations of the liquid steel flow and argon behavior were done using the Ansys‐Fluent computer program. For the validation of the numerical model and verification of the correctness of the computer simulation results, a glass water model was used. It has been found that the use of the gas‐permeable barrier with two porous plugs in the tundish effectively influences the pattern of liquid steel flow.

Hydrodynamic effects created by argon stirring liquid steel in a one-strand tundish

ABSTRACTContinuous casting of steel ensures the flexible production of different grades of slabs intended for the Rolling Mill departments. Therefore, it seems justifiable to search new solutions for tundish metallurgy. This study puts forward a new gas-permeable barrier’s design solution with two circular porous plugs, whose purpose is to punctually agitate the liquid steel in tundish. Two argon injection system locations were tested. The results for the hydrodynamic pattern of liquid steel and bubbles’ behaviour in the tundish were obtained from laboratory experiments with water glass model and computer simulations. Within the framework of the investigation, three argon flow rates, i.e. 5, 10 and 15 NL min−1, were considered. The designed gas-permeable barriers effectively stimulate active flow in the tundish for isothermal and non-isothermal conditions, while reducing the stagnant flow share and the transient zone extent.

Neutron activation of impurity seeding gases within a DEMO environment

In preparation for the design of a future tritium-handling plant for the DEMO fusion reactor, a study was undertaken to consider the activation of gases, in addition to those used as fuel, which are to be injected into DEMO for the purpose of reducing damage to the divertor. Likely impurity gases were identified as nitrogen, neon, argon, krypton and xenon, with no clear consensus as to which were preferred, and in what quantities these would be injected. Modelling with the FISPACT-II code, using the TENDL-2014 libraries as input, was performed to determine the products arising from their activation by the neutron flux expected at the DEMO first wall. The subsequent evolution of the progeny was investigated, along with a variation in the activation time.Results indicate a variety of progeny are produced, most of which are short lived. However, the gamma emission from some progeny such as argon-41 from argon injection, from some metastable states and other isotopes of krypton and bromine following krypton injection, and from some metastable states of xenon following injection of xenon, could potentially cause concern.

Runaway electron generation during disruptions in the J-TEXT tokamak

A systematic study of disruption-generated runaway electrons has been performed in the J-TEXT tokamak. During the intended disruption by the argon injection in J-TEXT, the runaway electron plateau is more easily obtained with a higher loop voltage and shorter onset time of high loop voltage. Magnetic fluctuations are observed at the beginning of the current quench during the disruptions. The generated runaway electron (RE) current is larger at a lower level of magnetic fluctuation. Experimental evidence supporting that the theory of hot tail RE generation might be playing a role has also been found. With higher temperature before the disruption, more REs are generated via the hot tail mechanism during the thermal quench. By increasing the hot tail RE generation by increasing the temperature, an obvious RE plateau is observed even with a low toroidal magnetic field (1.2 T).

Sequential PLD in oxygen/argon gas mixture of Al-doped ZnO thin films with improved electrical and optical properties

Highly conductive transparent Al-doped ZnO (AZO) thin films were obtained at room temperature through sequential PLD (SPLD) from Zn and Al metallic targets in an oxygen/argon gas mixture. We have investigated the structural, electrical and optical properties as a function of the oxygen/argon pressure ratio in the chamber. The measured Hall carrier concentration was found to increase with argon injection from 1.3×1020 to 6.7×1020cm−3, while the laser shots ratio for Al/Zn targets ablation was kept constant. This increase was attributed to an enhancement of the substitution doping into the ZnO lattice. The argon injection also leads to an increase of the Hall mobility up to 20cm2V−1s−1, attributed to a reduction of interstitial-type defects. Thus, the approach of using an oxygen/argon gas mixture during SPLD from metallic targets allows obtaining at room temperature AZO samples with high optical transmittance (about 90%) and low electrical resistivity (down to 5.1×10−4Ωcm).

Evaluation of the efficacy of therapeutic endoscopy in gastrointestinal bleeding secondary to angiodysplasias.

Gastrointestinal angiodysplasias are defined as vascular dilations that communicate capillaries and veins in the walls of the digestive tract. The clinical presentation of these lesions varies from chronic occult bleeding to severe gastrointestinal hemorrhage. The primary aim of our study was to analyze lesion location, the efficacy of therapeutic endoscopy with argon plasma coagulation, and the factors associated with rebleeding in patients with gastrointestinal angiodysplasias. A retrospective study of 32,042 endoscopies was carried out within the time frame of January 2012 and December 2013 at our hospital center. Gastrointestinal angiodysplasia was the diagnosis in 331 of the endoscopies. The procedures included upper gastrointestinal endoscopy, colonoscopy, sigmoidoscopy, and enteroscopy. The most frequent location of the angiodysplasias was the cecum (49%), followed by the ascending colon (17%) and the sigmoid colon (16%). They were most frequently found in the duodenum (60%) and gastric body (49%) at upper gastrointestinal endoscopy. Therapeutic endoscopy was performed in 163 cases (49.8%) and the most predominant methods were fulguration with argon (90%) and combination treatment (argon plasma coagulation and injection sclerotherapy) (6.7%). The macroscopic rebleeding rate after therapeutic endoscopy was 7.4%. Patients that had rebleeding presented with a lower hemoglobin concentration, higher mean age, and the presence of multiple angiodysplasias at endoscopy (P<.05). Therapeutic endoscopy was performed in 49.8% of the patients with angiodysplasias. The macroscopic rebleeding rate after treatment was 7.4%. There were statistically significant differences in the patients with rebleeding in relation to mean age, hemoglobin values, and the presence of multiple angiodysplasias.