Argon Bubbles Research Articles

Mathematical Modeling on the Multiphase Flow during Top–Bottom Combined Blowing Basic Oxygen Furnace Steelmaking Process

A 3D mathematical model on the multiphase flow and splashing phenomenon in a 210 t Basic oxygen furnace converter is established. The turbulent multiphase flow of the molten steel, slag, and oxygen is simulated by the combined realizable k−ε model and volume of fluid model. The trajectory of argon bubbles and the interaction between the molten steel and argon is simulated by the two‐way coupled Lagrangian discrete phase model. Effects of the lance height and bottom‐blowing gas flow rate on the multiphase flow and splashing phenomenon are investigated. The results indicated that the cavity depth is decreased from 0.45 to 0.36 m when the lance height increases from 1700 to 2300 mm. The cavity depth is not significantly affected by the bottom‐blowing argon flow rate with the 44 000 m3 h−1 top‐blowing oxygen flow rate and 1700 mm lance height. The increased lance height resulted in a decrease in splashing. When the oxygen lance height increases from 1700 to 2300 mm, the amount of the splashed molten steel decreases from 3774.3 to 1953.0 kg.

Thermodynamic and Kinetic Behavior Study of Gas Bubbles in High‐Temperature Steel Melts

This study provides an exhaustive exploration of the thermal expansion of low‐temperature argon bubbles in high‐temperature molten steel and the resulting dynamic effects. The energy equation of compressible fluid simultaneously with the volume of fluid model under the Euler framework is solved. The generation and rising behavior of bubbles are validated through rigorous physical water model experiments. Findings reveal that, within a heating time of 0.2–0.45 ms, gas bubbles already complete 65–90% of their internal energy increase. The total heat transfer time and heat transfer coefficient of bubbles exhibit distinctive patterns influenced by the initial diameter and temperature of the bubbles. Specifically, under the conditions studied, bubbles exhibit a total heat transfer time of ≈20–60 ms, accompanied by a heat transfer coefficient ranging from 500 to 2600 W (m2 * K)−1. During the thermal expansion process, gas bubbles experience energy transfer and conversion within the two‐phase flow. This article establishes a dynamic model describing bubble thermal expansion in steel melts based on underwater bubble dynamics’ first principles. The model provides a quantitative depiction of instantaneous changes in bubble size, velocity, and kinetic energy under specific conditions.

Influence of bubble size on perfluorooctanesulfonic acid degradation in a pilot scale non-thermal plasma treatment reactor

A 25L working volume non-thermal plasma-based treatment reactor was trialled to destroy per- and polyfluoroalkyl substances (PFAS) utilising argon bubbles to transport PFAS to the surface to be destroyed with plasma interaction at the argon-liquid interface. The breakdown rate of PFAS and the system's overall energy efficiency could be improved while minimising gas usage by utilising small bubbles (0.6–0.7 mm d32) to maximise the transport of PFAS to the plasma discharge for destruction. Vertically scaling the treatment reactor dimensions increases the overall liquid height and dwell time for bubbles to contact and transport PFAS molecules to the surface. The removal rate of perfluorooctane sulfonate (PFOS) correlated with the total surface area of the gas. Significant concentration gradients of PFOS could be observed when sampling from different liquid heights within the 25 L reactor. A one-dimensional model of mass transfer to the surface of rising bubbles was developed and gave good predictions of the overall rates of PFOS breakdown with modelled time constants of 0.14–0.18 min−1 versus 0.16 ± 0.01 min−1 for the fine bubble diffuser, and 0.048–0.053 min−1 versus 0.06 min−1 for the medium bubble diffuser. The time constant compared favourably with similar experiments at the 2 L scale of 0.11 min−1.

Effects of Submerged Entry Nozzle Bottom Shape on the Size Distribution of Argon Bubbles in a Steel Continuous Casting Slab Strand Using Multiple‐Size‐Group Approach

Herein, the effects of the bottom shape of the submerged entry nozzle (SEN) on the molten steel flow and size distribution of argon bubbles are analyzed in a steel continuous casting slab strand using multiple‐size‐group approach. The type of nozzle bottom includes the well bottom, flat bottom, and mountain bottom. Most of argon bubbles are larger than 4.5 mm inside the SEN and the mold at the three types of nozzles. The frequency distribution of bubbles inside the SEN increases from 28.29% to 32.65% and 35.74% for 5.0–5.5 mm bubbles and decreases from 53.71–50.49% and 47.38% for 5.5–6.0 mm bubbles with the nozzle bottom varied from the flat to mountain and well shape, respectively. The number density of argon bubbles with 4.0–5.5 mm diameter in the mold decreases and increases for 5.5–6.0 mm bubbles with the nozzle bottom varying from the well to flat and mountain shape, respectively. In addition, the results of the industrial trials show that inclusions adhesion and aggregation at the bottom of the nozzle are eliminated using the flat bottom SEN casting. Meanwhile, the mechanism of SEN clogging under the different types of nozzle bottoms is analyzed.

Flow visualization experiments of argon injection in a molten salt natural circulation loop

Off-gas systems are implemented in molten salt reactor designs to control the release of gaseous fission products. Two-phase flow in molten salt must be studied to understand how the system will behave in comparison to traditional working fluids like water. Flow visualization experiments and particle image velocimetry measurements were performed for three argon bubble sizes injected into a co-current stream of molten salt in a natural circulation loop facility. Similar bubble sizes were injected in experiments with water to compare the bubble shape, trajectory, and wake flow behavior of the fluids. The bubble region of interest was used to calculate the equivalent diameter and terminal velocity. Results for water showed a wobbling bubble surface and less stable bubble trajectory due to lower surface tension and viscosity compared with molten salt. Particle image velocimetry results demonstrated the increased viscosity of salt dampens turbulent fluctuations for the smaller bubble size. For a cap bubble, turbulent fluctuations were larger and longer lasting than in results for the wake flow of an argon cap bubble in water.

Numerical Investigation on Coalescence Behavior of Liquid Inclusion Particles in Argon Bubble Wake Flow

Microinclusions in steel will significantly affect mechanical performance of final products and therefore require serious concern during metallurgical process. Herein, the collision, coalescence as well as floatation of bubble–inclusion coexisting system is fully studied through a new mathematical model. It comes to the following conclusions: as bubbles rise, they induce a flow of liquid steel from their upper surface to their lower surface, and inclusion droplets rise and collide in the wake of the bubble. The velocity of the bubbles is affected by their deformation, with deformation rates being linked to the Weber number. The coalescence time of these inclusions is primarily influenced by viscosity and surface tension. Coalescence accelerates with higher surface tension or reduced viscosity, and this phenomenon can be described by a formula, which is developed by simulation results. According to this formula, coalescence time of 3CaO·Al2O3 is 20% longer than that of 12CaO7·Al2O3. Consequently, 12CaO7·Al2O3 is more prone to coalescence. The movement of inclusions can be controlled by adjusting gas volume and flow rate. Moreover, promoting coalescence can be achieved by altering the viscosity of inclusions and the surface tension coefficient, making it easier to remove these unwanted inclusions.

Volume of fluid simulation of single argon bubble dynamics in liquid steel under RH vacuum conditions

Volume of fluid simulation of single argon bubble dynamics in liquid steel under RH vacuum conditions

Mathematical modeling of the effect of SEN outport shape on the bubble size distribution in a wide slab caster mold

Herein, the effects of outport shapes of the submerged entry nozzle (SEN) on the size distribution of argon bubbles were studied in a wide slab caster mold by the mathematical modeling. The Eulerian–Eulerian model coupled with Multiple-Size-Group (MUSIG) approach were used to solve equations of the two phase flow and polydispersed bubbly flow in the mold, respectively. The effect of the SEN outport angle and shape on the distribution of the molten steel flow, argon gas volume fraction, and argon bubble size were investigated. The outport shapes of the SEN included large rectangular, small rectangular, square, trapezoid, and runway. Results showed that the speed of molten steel increased within the range of 260 mm from the SEN, and decreased within the range of 550 mm from the narrow face with the outport angle of SEN increased from 20° to 45°. The bubble diameter was 5.7 mm at 255 mm distance from the SEN along the mold width at different outport angles. The average speed of molten steel at the outport of SEN decreased from 0.91 to 0.72 m/s with the outport shape changed from small rectangular to runway, trapezoid, square and large rectangular. The average diameter of bubbles was approximate 5.2 mm at the outport for the five types of nozzles, and increased from 3.2 to 3.45 mm inside the mold with the outport shape changed from the runway to square, trapezoid, large rectangular and small rectangular, indicating the rate of bubble breakup was larger with the runway and square SEN casting.

SBC-SNOLAB scintillation system and SiPM implementation for dark matter searches

The Scintillating Bubble Chamber (SBC) collaboration is constructing a 10 kg liquid argon (LAr) bubble chamber at SNOLAB called SBC-SNOLAB having the main objective of detecting dark matter. One of the most novel aspects of SBC-SNOLAB is the scintillation system, consisting of LAr doped with on the order of 10 ppm Xe, 48 FBK VUV silicon photomultipliers (SiPMs), the SiPM electronics, two quartz jars, and liquid CF4 used as an hydraulic fluid and additional source of scintillation photons. In contrast with traditional single or dual phase scintillation experiments, the collected LAr scitillation light is used to veto signals which involve the detection of at least a single photoelectron. These proceedings will describe in detail the current SBC-SNOLAB scintillation system which includes the unique design considerations for SBC-SNOLAB that limit the light collection efficiency and the electronics.

Numerical Simulation of Flow and Argon Bubble Distribution in a Continuous Casting Slab Mold under Different Argon Injection Modes

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases.

Optimization of Port Angle for Narrow‐Width Mold Flow Field under High Casting Speed Based on Large Eddy Simulation and High‐Temperature Measurement of Velocity

Herein, the flow field of the mold through numerical simulation and high‐temperature measurement is studied, and discussed the effects of casting speed and port angle on the flow field of the 880 mm wide mold. The velocities near the mold surface of the numerical simulation are in good agreement with those of the high‐temperature measurement. As the casting speed continues to increase, the surface flow velocity of the mold also increases. When the casting speed increases to 1.8 m min−1, the flow pattern of the mold exhibits a strong double‐roll flow, the strong jet increases the risk of argon bubbles being captured by the solidification front inside the mold. As the port angle of the submerged entry nozzle (SEN) gradually increases, the surface flow velocity of the mold gradually decreases. By appropriately increasing the port angle of the SEN to 20°, the surface flow velocity of the mold decreases, and the stability of the molten steel–slag interface improves. At the same time, there is no significant change in the distribution of argon bubbles, and the removal rate of inclusions is the highest.

Theory of Movement Behavior of Argon Bubbles in Upper Nozzle of Tundish During Argon Blowing Process

Theory of Movement Behavior of Argon Bubbles in Upper Nozzle of Tundish During Argon Blowing Process

Sustainable recycling of aerospace-grade ultra-clean 7050 aluminum alloy melts through argon refining without secondary aluminum dross generation

The refining of aluminum scraps commonly employs nitrogen-fluxes to eliminate impurities. However, the aluminum nitride (AlN) generated by the reaction between nitrogen and the aluminum melt, along with residual fluxes, contribute to low cleanliness of the recycled aluminum melt and pose difficulties for the disposal of secondary aluminum dross (SAD). Our innovative research has resulted in the recycling of aerospace-grade clean aluminum alloy melts. The results indicate that the argon bubble floating process adsorbs inclusions and hydrogen, achieving an aerospace-grade ultra-clean melt. The solid-liquid interface between the tube wall and the melt provides a diffusion channel for hydrogen atoms, and the bubbles rising up along the wall lead to a higher hydrogen content in the melt. The argon refining dross is primarily composed of Al and Al2O3, which can be recycled as a raw material for aluminum electrolysis. Argon refining can decrease the hydrogen content and the number of inclusions with particle size ≥40 μm in the recycled aluminum melt to the level of aerospace aluminum alloy melt. Nonetheless, the particle size ≥20 μm remains 1.5–2.5 times that of primary aluminum.

Bubble detection in liquid metal by perturbation of eddy currents: Model and experiments

A model has been developed to predict the response of an eddy current flow meter (ECFM) to the passage of a non-conductive inclusion moving in a cylindrical tube filled with a liquid metal. The model can be solved analytically for small inclusion diameters and moderate AC frequencies of the excitation signal. This condition is expressed as vbSω≪1, where vb is the dimensionless inclusion volume and Sω is a function of the ratio between the characteristic length of the system and the penetration depth of the magnetic field. The magnetic induction equation for this problem has also been solved numerically. A very good agreement between the analytical model and numerical solutions has been found for vbSω≪1. Two experimental setups have been designed. First, the ECFM model has been validated by comparing the response due to the passage of traveling beads of known diameters in a low melting point alloy. In a second experiment, the diameters of ascending argon bubbles have been estimated with the ECFM model. The numerical model predicts the gas volume with very good accuracy in the range of bubble diameters studied, between 1.5 and 6 mm, while the analytical model only deviates significantly from the experimental data when vbSω≳0.1. Moreover, we establish that the ECFM can also measure the radial deviation of the bubble trajectory, and the results are consistent with the theoretical limit for isolated bubbles between the regimes of oscillating/zigzag motion of ellipsoidal bubbles and non-oscillating motion of spherical bubbles. Another observation is that the dependence of the ECFM response on the shape of the bubble is negligible; indeed, the ECFM response is well approximated by a linear relation with the bubble volume as is assumed in the analytical model. Finally, an estimation of the terminal rising velocity of bubbles was also carried out.

Electrical breakdown dynamics in an argon bubble submerged in conductive liquid for nanosecond pulsed discharges

This study delves into the dynamics of cold atmospheric plasma and their interaction within conductive solutions under the unique conditions of nanosecond pulsed discharges (22 kV peak voltage, 10 ns FWHM, 4.5 kV ns−1 rate-of-rise). The research focuses on the electrical response, breakdown, and discharge propagation in an argon bubble, submerged in a NaCl solution of varying conductivity. Full or partial discharges were observed at conductivities of 1.5 µS cm−1 (deionized water) to 1.6 mS cm−1, but no breakdown was observed at 11.0 mS cm−1 when reducing the electrode gap. It is demonstrated that at higher conductivity electric breakdown is observed only when the gas bubble comes into direct contact with the electrode and multiple emission nodes were observed at different timescales. These nodes expanded in the central region of the bubble over timescales longer than the initial high-voltage pulse. This work offers a temporal resolution of 2 ns exposure times over the first 30 ns of the initial voltage pulse, and insight into plasma formation over decaying reflected voltage oscillations over 200 ns.

Alumina Nucleation, Growth Kinetics, and Morphology: A Review

The reaction between aluminum and the dissolved oxygen in liquid steel yields the precipitation of alumina crystals with characteristic morphologies and size distributions. Alumina precipitation and growth involve a wide spectrum of time, length, velocity, and thermodynamic supersaturation scales throughout the refining processes. The smallest length and time scales are those quantifying the nucleation kinetics and the initial growth at the highest supersaturation. Further growth and crystal morphology depend on the concentration of surface tension elements which inhibit the crystal's faces suffering further modifications due to washing effects provided by turbulent flows. This step involves longer time, velocity, length, and moderate supersaturations. The final step involves the growth of alumina inclusions through collision–agglomeration–sintering, and capillary processes on the surfaces of argon bubbles under low supersaturations. Jumps of supersaturation, due to late aluminum additions or steel reoxidation, lead to alumina crystals changing their morphology to dendritic‐type growth. The present contribution reviews each one of these kinetic phenomena closing with the consequences that alumina precipitation has on the continuous casting process. The content of this review is useful to practitioners and theorists alike.

Morphological and microstructural evolutions of chemical vapor reaction-fabricated SiC under argon ion irradiation

Chemical vapor reaction (CVR) fabricated-SiC samples were irradiated with 300 keV Ar2+ ions in the fluence range of 5 × 1015 –1 × 1017 ions·cm−2. Raman spectrum and grazing incidence X-ray diffraction analysis display amorphization and lattice expansion of the irradiated CVR-SiC. Transmission electron microscope observations show that small black spots with an average diameter of 1.5 nm are formed at a low fluence of 5 × 1015 ions·cm−2. Moreover, large argon bubbles with an average diameter of 15.1 nm are formed at a high fluence of 1 × 1017 ions·cm−2, and the Ar concentration threshold for bubble formation is 8.83 at.%. The influence of implantation amorphization and Ar atom migration in CVR-SiC on the formation of Ar bubbles is discussed. The results provide a basis for understanding the noble-gas-induced irradiation behavior of CVR-SiC for preventing irradiation damages in future nuclear applications.

The Reducing Agents in Sonochemical Reactions without Any Additives.

It has been experimentally reported that not only oxidation reactions but also reduction reactions occur in aqueous solutions under ultrasound without any additives. According to the numerical simulations of chemical reactions inside an air or argon bubble in water without any additives under ultrasound, reducing agents produced from the bubbles are H, H2, HO2 (which becomes superoxide anion (O2-) in liquid water), NO, and HNO2 (which becomes NO2- in liquid water). In addition, H2O2 sometimes works as a reducing agent. As the reduction potentials of H and H2 (in strongly alkaline solutions for H2) are higher than those of RCHOH radicals, which are usually used to reduce metal ions, H and H2 generated from cavitation bubbles are expected to reduce metal ions to produce metal nanoparticles (in strongly alkaline solutions for H2 to work). It is possible that the superoxide anion (O2-) also plays some role in the sonochemical reduction of some solutes. In strongly alkaline solutions, hydrated electrons (e-aq) formed from H atoms in liquid water may play an important role in the sonochemical reduction of solutes because the reduction potential is extremely high. The influence of ultrasonic frequency on the amount of H atoms produced from a cavitation bubble is also discussed.

Investigations on Vibrational Interpretations of Bubbles in Metal-Making Processes

Vibration measurements were carried out using highly sensitive accelerometers in an experimental ladle integrated into the LIMMCAST (Liquid Metal Model for Steel Casting) facility at HZDR. The model is operated with liquid Sn–40 wt pctBi alloy at 200 °C, whose physical properties are close to those of molten steel. Three accelerometers were attached to the outer wall of the LIMMCAST vessel to record the vibrations caused by the argon bubble flow in the liquid metal at different process parameters. The results obtained at the liquid metal experiments differ from those reported for water models where the relationship between root mean square (RMS) value of the vibration amplitude and the gas flow rate follows different curve shapes. Furthermore, the results of vibration measurements in the LIMMCAST model are compared with vibration measurements in a steel plant during vacuum degassing. The comparison of the RMS data shows a fairly good agreement. This indicates that the vibrations in both the industrial process and the laboratory model are caused by the same physical mechanisms, and thus, the vibration behavior in an industrial steelmaking ladle can be reproduced quite well by suitable liquid metal models. These studies on bubble flows can help to improve the understanding of industrial stirring processes and thus contribute to a better process control.

A mathematical model for dehydrogenation of molten steel in the Vacuum degasser

This paper presents a mathematical model of VD dehydrogenation aimed at predicting hydrogen removal during the VD vacuum refining process and investigating the effect of controllable parameters on the dehydrogenation process. Taking into account the behavior of argon bubbles during their uplifting, the model considers that the dehydrogenation reaction occurs at three sites, the surface of the Ar bubbles, the bath surface of the molten steel, and the bulk steel. The calculated results are in good agreement with the industrial production data. The hydrogen content of the molten steel during VD dehydrogenation is observed to vary as an inversely proportional function with the vacuum holding time, decreasing rapidly in the early stage and slowing down in the later stage. Using the model, the contribution of different reaction sites to the dehydrogenation process was investigated. It was found that the internal spontaneous nucleation of the molten steel dominated the dehydrogenation process at the beginning. Then, the internal spontaneous nucleation gradually weakened to disappear as the hydrogen content of the molten steel decreased, followed by the dominance of dehydrogenation on the surface of the Ar bubble. The model also investigated the effect of vacuum pressure and argon flow rate on the VD dehydrogenation process. It was found that the vacuum pressure significantly influenced the dehydrogenation rate on the Ar bubble surface and the bath surface mainly by affecting the equilibrium hydrogen concentration in the gas phase and by influencing the critical nucleation depth, which affected the internal spontaneous dehydrogenation. Moreover, the increase of the argon flow rate not only increases the reaction area of the Ar bubble but also the reaction area at the activation zone on the bath surface. Additionally, the increase of the initial hydrogen content in the molten steel significantly promotes the spontaneous dehydrogenation of the internal nucleation in the bulk steel.