Degassing Research Articles

Hydrogel impeller formation via vacuum degassing photopolymerization for micromixers

For effective mixing within microfluidic devices through the application of obstacle-based structures, a straightforward approach involves in-situ fabrication, such as the free-radical photopolymerization of hydrogel structures. However, oxygen inhibition presents a challenge for polydimethylsiloxane (PDMS)-based microfluidic chips. In this paper, we present a solution to the problem of hydrogel-structure formation hindered by oxygen inhibition at low light intensities and the photoinitiator concentration achieved using vacuum degassing. Furthermore, a kinetic model for photopolymerization under vacuum conditions was established and converted into an equation of light intensity and exposure time while keeping the other parameters constant. The exposure time range was successfully predicted by comparing the experimental data and analyzing scenarios. This method was used to fabricate an impeller for a passive micromixer. The impeller rotation was then analyzed. The results demonstrated that with an increased flow rate exceeding 6 mL/min, the mixing efficiency is significantly higher owing to the rotation of the impeller. The mixing efficiency was quantitatively assessed through experiments involving the mixing of three dyes, showing a three-fold increase compared to the chip without the impeller. Our research provides valuable insights into the fabrication of hydrogel structures in PDMS-based microfluidic chips under vacuum conditions.

Microstructure and properties of a HIP manufactured B4Cp reinforced highly alloyed Al-Zn-Mg-Cu-Zr aluminum matrix composite

In this study, an aluminum matrix composite with good mechanical property and excellent corrosion resistance, B4C particles (B4Cp) reinforced highly alloyed Al-Zn-Mg-Cu-Zr matrix composite, was successfully fabricated through ball-milling, cold isostatic pressing, vacuum degassing, hot isostatic pressing (HIP), homogenization, hot extrusion, solution treatment, and aging treatment. It was found that the B4C/MgAl2O4/Al was the dominant interface structure, which was coherent and enhanced the bonding between the particles and the matrix considerably, while the B4C/Al2O3/Al was the minor interface structure. The grain boundary was very clean in both T4 and T6 aging states, without aging precipitates and O element segregation. In T4 aging state, the composite exhibited superior properties, with the mass density of 2.84 g cm−3, the elastic modulus of 119.18 GPa, the yield strength of 576.08 MPa, the ultimate tensile strength of 655.27 MPa, the tensile elongation of 1.48 %, and the very low electrochemical corrosion current density of 4.4581 × 10−8 A cm−2 in 3.5 wt% NaCl water solution. The MgAl2O4 and BO3-rich interface phases, the strengthening mechanisms and the anti-corrosion mechanisms of the composite were discussed in detail.

Analysis of Thermophysical Properties of Electro Slag Remelting and Evaluation of Metallographic Cleanliness of Steel.

Improving the competitiveness of steel companies is linked to sustainable, quality-compliant steel production. Therefore, new steel production technologies contributing to increased cleanliness of steel are continuously being developed and optimized. One way to achieve a high steel quality is to use electro slag remelting (ESR) technology. In this paper, the principle of ESR technology and the importance of fused slags for optimizing the process are outlined. The aim of this work was to analyze the main thermophysical properties of steel and fused slags used in the ESR process. Determination of the properties of steel and slags was performed using the FactSage calculation software, which involved the calculation of the liquid and solid temperature of steel and slags, the calculation and construction of quaternary diagrams, and the calculation of viscosity. The resulting quaternary diagrams revealed the substantial influence of chemical composition on melting temperatures of slags. In order to validate the acquired results, a CrNiMoV-type steel was subjected to investigation of its metallographic cleanliness and evaluation of its mechanical properties; the ESR process was shown to significantly improve the cleanliness of the steel and improve the mechanical properties of the steel compared to its cleanliness and quality when produced via vacuum degassing (VD) technology. During the ESR process, the average size of non-metallic inclusions was reduced from 20 μm to 10 μm, and the maximum size of non-metallic inclusions was reduced from 50 μm to 28 μm. The mechanical properties of the steel produced using ESR technology were impacted as follows: the ductility increased by 10%, contraction increased by 18%, notched toughness at 20 °C increased by 46%, and at -40 °C (respectively -50 °C) it increased by 30%.

A filling rig for liquid and gas working fluids for two-phase thermal management systems

Two-phase cooling devices are used to remove and dissipate heat from high power-density electronic systems to maintain them within their operating temperature limits. The manufacture of these devices, such as heat pipes, thermosyphons or vapour chambers, involves firstly removing any internal air or non-condensable gases before charging with the required volume of working fluid. This paper presents detailed designs and operating instructions for a single bench-top station for use in a laboratory environment for the vacuum evacuation, degassing and charging of these devices. Two configurations allow for the filling of fluids which are either liquids or gases at standard temperature and pressure conditions. For liquids, the dispensed volume can be measured directly on an integrated burette, while the method of vapour transfer is used for gases.The hardware was demonstrated by filling multiple thermosyphon devices with a number of common working fluids used in two-phase systems, including water, acetone and ammonia. It was shown to deliver precise and repeatable filling volumes with average differences compared to target volumes of 1.7% and 10.5% for liquids and gases respectively. The design is intended to be highly customisable where its size can be modified to accommodate filling volume requirements for different applications.

The Trincheras Tradition from the Valleys to the Coast: Mortuary Practices in Puerto Libertad, Sonora

This paper presents archaeological findings from excavations within the Salvamento Arqueológico Planta de Licuefacción de Gas Natural in winter 2022. The project area is located 2 kilometers southeast from the town of Puerto Libertad, Sonora and 800 meters inland from the coastline. A pre-Hispanic cemetery was recorded and excavated, with secondary pit cremations, secondary cremations placed inside locally produced plain ware and decorated vessels, and an articulated primary burial of a female, between 18 and 20 years old and with evidence of scalping. A possible crematorium 1.8 km away with cremations was also identified. The study area borders the precolonial cultural limits of the Costa Central and Trincheras Traditions and the documentation of cremations from the site were compared against previously excavated mortuary features across both cultural traditions. In addition to funerary practices, ceramic analysis demonstrated that the ancient inhabitants of Puerto Libertad belonged to the Trincheras Tradition and suggests they may have migrated from the valleys.

Formation and removal mechanism of SiO2-MnO-Al2O3 inclusions in Al-killed 42CrMo4 wind turbine bearing steel forgings

SiO2-MnO-Al2O3 (SMA) inclusions were identified in the defective areas during the ultrasonic inspection of Al-killed 42CrMo4 wind turbine bearing steel forgings. To explore their formation mechanism, we systematically sampled 42CrMo4 steel through industrial experiments, analysing SMA inclusions’ morphology and composition at various stages. Thermodynamic calculations were also employed to assess the origin and formation of these inclusions. It was observed that these inclusions primarily formed during electric arc furnace tapping, where the mass ratio of SiO2 to MnO was close to 1, while the Al2O3 content varied. Despite undergoing the ladle furnace and vacuum degassing (VD) refining processes, these inclusions persisted in the molten steel. Following the conclusion of electric furnace smelting, the dissolved oxygen content in the molten steel could reach 193 ppm. During the tapping process, high oxidising steel comes into direct contact with silicon-manganese alloy. During this phase, the uneven distribution of Al content around the alloy results in the formation of SMA inclusions with varying Al2O3 content. Dynamic calculations suggest that in subsequent smelting processes, SMA inclusions with high Al2O3 content and large size are relatively easier to eliminate, while those with low Al2O3 content and small size are more likely to persist in the molten steel. During solidification, residual SMA inclusions agglomerate, forming larger sizes, consequently resulting in the ultrasonic inspection failure of 42CrMo4 steel forgings. After the process improvement, the SMA inclusions are greatly reduced and the effect is obvious.

Numerical Simulation of the Density Effect on the Macroscopic Transport Process of Tracer in the Ruhrstahl–Heraeus (RH) Vacuum Degasser

Silicon steel (electrical steel) has been used in electric motors that are important components in sustainable new energy Electrical Vehicles (EVs). The Ruhrstahl–Heraeus process is commonly used in the refining process of silicon steel. The refining effect inside the RH degasser is closely related to the flow and mixing of molten steel. In this study, a 260 t RH was used as the prototype, and the transport process of the passive scalar tracer (virtual tracer) and salt tracer (considering density effect) was studied using numerical simulation and water model research methods. The results indicate that the tracer transports from the up snorkel of the down snorkel to the bottom of the ladle, and then upwards from the bottom of the ladle to the top of the ladle. Density and gravity, respectively, play a promoting and hindering role in these two stages. In different areas of the ladle, density and gravity play a different degree of promotion and obstruction. Moreover, in different regions of the ladle, the different circulation strength leads to the different promotion degrees and obstruction degrees of the density. This results in the difference between the concentration growth rate of the salt tracer and the passive scalar in different regions of the ladle top. From the perspective of mixing time, density and gravity have no effect on the mixing time at the bottom of the ladle, and the difference between the passive scalar and NaCl solution tracer is within the range of 1–5%. For a larger dosage of tracer case, the difference range is reduced. However, at the top of the ladle, the average mixing time for the NaCl solution case is significantly longer than that of the passive scalar case, within the range of 3–14.7%. For a larger dosage of tracer case, the difference range is increased to 17.4–41.1%. It indicates that density and gravity delay the mixing of substances at the top area of the ladle, and this should be paid more attention when adding denser alloys in RH degasser.

A closer look at high-energy X-ray-induced bubble formation during soft tissue imaging.

Improving the scalability of tissue imaging throughput with bright, coherent X-rays requires identifying and mitigating artifacts resulting from the interactions between X-rays and matter. At synchrotron sources, long-term imaging of soft tissues in solution can result in gas bubble formation or cavitation, which dramatically compromises image quality and integrity of the samples. By combining in-line phase-contrast imaging with gas chromatography in real time, we were able to track the onset and evolution of high-energy X-ray-induced gas bubbles in ethanol-embedded soft tissue samples for tens of minutes (two to three times the typical scan times). We demonstrate quantitatively that vacuum degassing of the sample during preparation can significantly delay bubble formation, offering up to a twofold improvement in dose tolerance, depending on the tissue type. However, once nucleated, bubble growth is faster in degassed than undegassed samples, indicating their distinct metastable states at bubble onset. Gas chromatography analysis shows increased solvent vaporization concurrent with bubble formation, yet the quantities of dissolved gasses remain unchanged. By coupling features extracted from the radiographs with computational analysis of bubble characteristics, we uncover dose-controlled kinetics and nucleation site-specific growth. These hallmark signatures provide quantitative constraints on the driving mechanisms of bubble formation and growth. Overall, the observations highlight bubble formation as a critical yet often overlooked hurdle in upscaling X-ray imaging for biological tissues and soft materials and we offer an empirical foundation for their understanding and imaging protocol optimization. More importantly, our approaches establish a top-down scheme to decipher the complex, multiscale radiation-matter interactions in these applications.

Enhanced selective adsorption of H2S from CO2 by incorporating methylated polyethyleneimine into a porous carbon matrix

In this study, a series of hybrid adsorbent materials (AC@mPEI) with superior selective separation properties of H2S and CO2 are prepared by taking advantage of the differences in reaction mechanisms between H2S and CO2, as well as tertiary amines. Using a straightforward impregnation method, the methylated polyethyleneimine (mPEI) is successfully introduced into the pores of the porous carbon to create the desired hybrid adsorbents. The strong interaction between the tertiary amine groups and H2S facilitates the selective separation of H2S and CO2 gases. Remarkably, the adsorbent (1:1)AC@mPEI exhibits a substantial H2S adsorption capacity of 5.83 mmol·g−1 at 298 K and 1.0 bar and a high separation selectivity of H2S to CO2 (133), which is approximately 16.6 times higher than that of the porous carbon supporter. Further investigations, involving adsorption thermodynamics, breakthrough experiments, and spectroscopy, confirm that the strong interaction between the hybrid materials and H2S plays a pivotal role in enhancing the separation selectivity of H2S. Additionally, the adsorbed H2S can be well desorbed through vacuum degassing, allowing for multiple cycles of the adsorbent. This strategy, which leverages differences in gas adsorption mechanisms to fabricate hybrid adsorbents, presents novel concepts for the development of functional adsorbent materials for selective separation of gases.

Numerical and Experimental Analysis of the Vacuum Corn Seed Degassing System

Vacuum degassing of seeds is a basic preliminary stage of the treatment process to improve the viability of seeds of various crops. In this work, the degassing process of corn seeds was experimentally and numerically analyzed by removing air or other gases from around the seeds, specifically from the seed coating, in a rough vacuum chamber. Two complementary variants were employed to understand and optimize this process to improve the quality and germination rate of the seeds. The average germination percentage on the first day was about 98%, and the germination speed of 5.0 days. Several experiments were conducted with well-established durations of 10 min and masses of 5 kg and masses of corn seeds at different temperatures to observe and record the behavior of the system, facilitating the modeling of the degasification process in the vacuum compartment. Modeling the degasification operation in the vacuum chamber allowed for determining the pressure profiles on the vacuum chamber and its lid. Numerical simulations were either conducted using a simulation program developed in the Visual Basic Applications (VBA) language for Microsoft Excel to model the degassing process in the vacuum chamber or with the assistance of specialized software (transient structural analysis and simulation program in the ANSYS Workbench environment). Statistical analysis of the correlation between experimental and estimated pressure values revealed that both the proposed mathematical model and the solution method are well-chosen, with differences expressed through the absolute error (EA) being very small, only 1.425 mbar. Structural dynamic analysis carried through the Finite Element Method (FEM) highlights that the chosen materials for manufacturing the vacuum chamber vessel (316 stainless steel—yield strength 225 MPa and tangent modulus 2091 MPa) or the chamber lid (transparent acrylic plastic—yield strength 62.35 MPa and shear modulus 1445.3 MPa) are durable and capable of withstanding the desired pressure and temperature demands in the seed treatment process. Additionally, through structural dynamic analysis, it was possible to study the deformation of system components, providing a detailed perspective on their structural distribution. Thus, the paper aims to improve the quality and survival/germination rate of corn seeds as an important step to improve corn yield through simulations and analyses (numerical and experimental) of the vacuum corn seed degassing system. The degassing process of the vacuum chamber was simulated with a simulation program developed for Microsoft Excel for Microsoft 365 MSO (Version 2401 Build 16.0.17231.20236) 64-bit in the VBA language and software (transient structural dynamic analysis in the ANSYS environment through FEM). Vacuum degassing of corn seeds involves the removal of air or other gases around the seeds or products, which is crucial in various fields such as the food, pharmaceutical, or space technology industries.

Analyzing changes in volatile flavor compounds of soy protein isolate during ultrasonic-thermal synergistic treatments using electronic nose and HS-SPME-GC-MS combined with chemometrics

The beany flavor of soy protein isolate (SPI) creates barriers to their application in food processing. This study investigated the effect of ultrasonic-thermal synergistic treatments, combined with vacuum degassing, on the removal of volatile compounds from SPI. The results revealed that ultrasonic-thermal synergistic treatments altered protein secondary structure and increased fluorescence intensity and surface hydrophobicity, which affected the flavor-binding ability of protein, resulting in reduced electronic nose sensor response values. At synergistic treatment (350 W, 120 ℃ and 150 s), the content of hexanal, (E)-2-hexenal, and 1-octen-3-ol reduced by 70.60 %, 95.60 % and 61.23 %. (E)-2-nonenal and 2-pentylfuran were not detected. Chemometric analysis indicated significant flavor differences between control and treated SPI. Furthermore, α-helix, β-sheet, β-turn, and surface hydrophobicity highly correlated with volatile compounds through correlation analysis, indicating that altered protein structure affected interactions with volatile compounds. The study reduced beany flavor and further expanded the range of applications of plant protein in food industry.

Drug-loaded vegan gummies for personalized dosing of simethicone: A feasibility study of semi-solid extrusion-based 3D printing of pectin-based low-calorie drug gummies

Chewable gummies are an attractive dosage form for all age groups because of their appearance and texture. Although, this dosage form has been highly preferred administering nutraceuticals, its application in the pharmaceutical sector is worth exploring. In this study, simethicone (SMT), an OTC drug prescribed for anti-flatulence was incorporated in pectin- based, low-calorie, 3D printed gummies. Semi-solid extrusion (SSE)-based 3D printing was used to dispense personalized dose of SMT i.e 40 mg for children and 125 mg for adults. Formulation optimization was carried out based on the texture profile of the gummies, using a texture analyzer. The inks were thoroughly characterized for their rheological behavior since it is a critical attribute for SSE-based 3D printing. Printing parameters like the printing speed, layer height and the type of the nozzle were optimized based on the printing accuracy achieved. The printed gummies were further evaluated for their disintegration time, drug content, weight variation, water activity and total microbial count. SSE-based 3D printing was found to be an effective tool to print pectin-based shear thinning gels for accurate drug dispensing. The texture profile of the printed gummies was comparable to the gummies prepared by conventional method as well as the marketed samples.

Determination of cytotoxic, antioxidant activities and LC/MS-MS profiles of three endemic Verbascum L. species

The Verbascum genus includes many species used in folk medicine or the treatment of various diseases. In this study, the cytotoxic, antioxidant activity, and LC/MS-MS profiles of three Verbascum species, which are endemic in Eskişehir and its surroundings, were investigated. The cytotoxic effects of methanol extract of V.detersile, V. eskisehirensis, and V.gypsicola species on the cervical (HeLa) and ovarian cancer (SKOV-3) cells were investigated using a colorimetric assay. The results indicated that cytotoxic effect was not observed after treatment of SKOV-3 cells with Verbascum. On the other hand, the cytotoxic activity of V. detersile was found to be 0.1910 mg/dL and 1.057 mg/dL for HeLa cells after 24 or 48 hours incubation with V.detersile, respectively. The antioxidant activity was determined as 1,1-diphenyl-2-picrylhydrazyl (DPPH•) radical scavenging activity, trolox equivalent antioxidant capacity (TEAC assay), and also the total phenolic content of the samples was found. Total phenols were estimated as Gallic acid equivalents (GAE), expressed as mg Gallic acid/in 1g extract previously described by Singletton. LC/MS profiles separation and detection of phytochemicals of the extract were performed on a Shimadzu UPLC system consisting of a vacuum degasser, an autosampler (SIL20A Shimadzu Autosampler), a binary pump (LC20AD Shimadzu), an oven (CTO20A Shimadzu Column Oven) and DAD dedector (SPD M20A Shimadzu DAD Detector). In terms of antioxidant activity, V. gypsicola was found to have the least antioxidant activity among the three extracts, which is also correlated with the total amount of phenolic content in its content. In this way, it differs from other species. V. detersile exhibits a different chemical profile from the other two species with the iridoid catalpol derivatives it contains. Apigenin pentoside is the only flavonoid molecule detected in V. detersille.

Efficient and precise fabrication of Wolter type-I x-ray mirrors via nickel electroforming replication using quartz glass mandrels

This study presents an approach for fabricating Wolter type-I mirrors for x-ray telescopes using a nickel electroforming replication process with quartz glass mandrels. The proposed method addresses the challenges encountered in conventional fabrication techniques, which involve using electroless nickel-coated aluminum mandrels that are susceptible to corrosion and thermal deformation. Quartz glass mandrels offer excellent chemical, thermal, and mechanical stability, enabling the efficient production of high-performance mirrors. Wolter type-I mirrors for telescopes possess a large aperture that collects x-ray photons from the universe. However, previous nickel electroforming replication processes using quartz glass mandrels have challenges in fabricating large mirrors, particularly due to bubble pit formation during nickel shell development. In this study, we introduced an efficient pitting inhibition technique via vacuum degassing. This technique facilitates the precise replication of pit-free Wolter type-I mirrors for telescopes using quartz glass mandrels. We demonstrated the fabrication process on a Wolter type-I mirror proposed for FOXSI-4 [(FOXSI) Focusing Optics X-ray Solar Imager], resulting in three mirrors obtained from the same mandrel without repolishing or repairing. The figure error of the mirror was within 1 µm over most areas in both longitudinal and circumferential directions. The ray-tracing simulation indicated that the performance of the mirror was ∼12 arcsec in half-power diameter, comparable to the performance achieved by previous high-resolution x-ray missions.

Safety assessment of the process Silver Plastics, based on the Reifenhäuser technology, used to recycle post-consumer PET into food contact materials.

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids (CEP) assessed the safety of the recycling process Silver Plastics (EU register number RECYC299), which uses the Reifenhäuser technology. The input material consists of hot caustic washed and dried poly(ethylene terephthalate) (PET) flakes mainly originating from collected post-consumer PET containers, including no more than 5% PET from non-food consumer applications. The flakes are extruded under vacuum into sheets. Having examined the challenge test provided, the Panel concluded that the decontamination in the extruder under vacuum degassing (step 2), for which a challenge test was provided, is critical in determining the decontamination efficiency of the process. The operating parameters to control the performance are temperature, pressure and throughput. The Panel concluded that this recycling process is able to ensure a level of exposure to potential unknown contaminants from food below 0.0025 μg/kg bw per day, when such recycled PET is used from 15% to 100% in mixtures with virgin PET, depending on the specific intended application. Therefore, the Panel concluded that the recycled PET obtained from this process is not considered to be of safety concern when used from 15% to 100% in mixtures with virgin PET for the manufacture of materials and articles depending on the specific intended application. Articles made of this recycled PET are not intended to be used in microwave and conventional ovens and such uses are not covered by this evaluation.

Greenhouse gas emissions from Brazilian agriculture and convergence clubs

ABSTRACT This work aims to assess whether there is a convergence in the emission of Greenhouse Gases (GHG) in the states of Brazil. To achieve this objective, the Phillips and Sul (2007) time series methodology was employed, testing the hypothesis of global (or common) convergence, using data from the Greenhouse Gas Emissions and Removal Estimation System (Sistema de Estimativas de Emissões e Remoções de Gases do Efeito Estufa - SEEG), for the period of 1989–2018, which provides the emission, in tons, of Carbon Monoxide (CO) in agriculture and livestock, as well as of Carbon Dioxide (CO2), for changes in land and forest use. Among the main results, the formation of different convergence clubs is suggested, rejecting the hypothesis of global convergence, and thus presenting four convergence clubs for the CO pollutant and three clubs for the CO2, with two divergent states. When analysing the convergence clubs, it was found that there was a significant reduction in CO emissions in all clubs, and while analysing the CO2, only two of the clubs, which were clubs 3 and 4, managed to reduce their emissions.

Efficiently Removing Hydrogen of H-Supersaturated Liquid Steel in the Vacuum Degasser with Various Gas Injection Modes

Hydrogen removal of H-supersaturated liquid steel produced in a hydrogen-rich environment in an industrial vacuum degasser (VD) is simulated here using a two-phase (argon–steel) Eulerian model. The dehydrogenation efficiency is evaluated for a series of ladle plug layouts and argon-purging modes. Increasing the plug number from the prototype double-plug of the ladle to four or slightly prolonging the degassing time of a triple-plug ladle enables to obtain the specified dehydrogenation efficiency and the end-point hydrogen level. Varying the plug position of the triple-plug ladle makes no significant difference in the dehydrogenation efficiency, which, however, is improved by adjusting the plug angle. For the triple-plug ladle, the non-uniform argon-purging mode improves the melt hydrodynamic conditions, but the optimal dehydrogenation performance is achieved in the uniform mode. The plug number has the greatest impact on the dehydrogenation efficiency compared to the other ladle designs considered. The high-efficiency dehydrogenation of H-supersaturated liquid steel in the VD can be achieved through using the quadruple plugs, or by using the triple plugs positioned at 0.57R, 0.57R, and 0.41R and the angles of 108.6° and 71.4°, with the uniform argon-purging flow rate.

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.

A Numerical Study on Dehydrogenation of Liquid Steel Supersaturated With Hydrogen in a Vacuum Degasser (VD)

A Numerical Study on Dehydrogenation of Liquid Steel Supersaturated With Hydrogen in a Vacuum Degasser (VD)