| 1. |
- Alevanau, Aliaksandr, 1965-, et al.
(författare)
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Mechanically assisted low temperature pyrolysis of hydrocarbons
- 2014
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Ingår i: Proceedings of the XVII International Conference Foundations & Advances in Nonlinear Science, September 29 - October 3, Minsk 2014.
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Konferensbidrag (refereegranskat)abstract
- We report experimental setups and conditions leading to pyrolysis (cracking) of such gaseous hydrocarbons as methane, mixed propane and butane, at the temper-atures of the heater below 200oC. The process was mechanically assisted by putting the substances being decomposed into a dynamic interaction with the tin and bismuth alloy. The alloy had periodically changing phase state thus creating fractal interfaces between its surface and the gases. Interaction of the gases with mechanically produced fractal surfaces of the alloy made possible gas decomposition even at lower temperatures of the heater (150oC). At this temperature the heater couldn't melt the alloy in the heated volume with the gas.
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| 2. |
- Alevanau, Aliaksandr, 1965-
(författare)
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Study of pyrolysis and gasification of biomass from the self-organization perspective
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the analysis of kinetics of i) low-temperature pyrolysis of gaseous hydrocarbons, ii) high-temperature steam gasification of char of wood pellets (>700oC), iii) high temperature pyrolysis of straw pellets in an atmosphere of argon and steam, and iv) high temperature pyrolysis of slices of transversally cut wooden sticks. The results of the kinetic measurements in the high-temperature cases are approximated using a least-square based optimization software, which was specially developed to analyse kinetics prone for deviation from the Arrhenius law.In the thesis a general analysis of the researched materials and kinetics of their pyrolysis and gasification is presented from the self-organization perspective. The energy transfer phenomena in both the pyrolysis and gasification processes of biomass are discussed with an emphasis on an analysis of basic phenomena involving the self-organized dynamics on fractal structures in the chosen biomass samples.
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| 3. |
- Arzpeyma, Niloofar, et al.
(författare)
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Mathematical Modeling of Postcombustion in an Electric Arc Furnace (EAF)
- 2019
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Numerical modeling was used to study the capability of postcombustion in an electric arc furnace (EAF) equipped with virtual lance burners. The CO flow rate at the molten bath surface was estimated using the off-gas data obtained close to the outlet of an EAF. Then, the effect of the secondary oxygen flow rate on postcombustion was studied. The results show a CO flow rate of 0.6 kgs(-1) and 0.8 kgs(-1) for operation modes of burner and burner + lancing. Increase of the secondary oxygen flow rates of 60% and 70% result in 17% and 7% increase in the postcombustion ratio (PCR) for the burner and burner lancing modes, respectively.
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| 4. |
- Arzpeyma, Niloofar, et al.
(författare)
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Mathematical Modeling of Scrap Melting in an EAF Using Electromagnetic Stirring
- 2013
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:1, s. 48-55
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Tidskriftsartikel (refereegranskat)abstract
- Numerical modeling has been used to investigate the influence of electromagnetic stirring on melting of a single piece of scrap in an eccentric bottom tapping (EBT) electric arc furnace (EAF). The heat transfer and fluid flow in the melt for both conditions with and without electromagnetic stirring were studied. The buoyancy and electromagnetic forces were considered as the source terms for momentum transfer in the studied conditions. The enthalpy-porosity technique was applied to track the phase change of a scrap piece defined in the EBT region of the furnace. Different scrap sizes, preheating temperatures, stirring directions and force magnitudes were considered, and the heat transfer coefficient was estimated from the heat transfer rate at the melt-scrap interface. The results showed that electromagnetic stirring led to a reduced melting time and an increased heat transfer coefficient by a factor of four. The results for Nusselt number versus Grashof number for natural convection and Reynolds number for electromagnetic stirring were compared with those obtained through correlations from previous studies.
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| 5. |
- Arzpeyma, Niloofar, 1985-
(författare)
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Model Developments to Study Some Aspects of Improving Efficiencies in EAF Plants
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to investigate some aspects of improvements with respect to the energy consumption and raw material selection as well as the understanding of the influence of uncertainties on the performance in electric arc furnace (EAF) plants. The effect of electromagnetic stirring on the scrap melting and post combustion capacity are investigated in two EAFs by using computation fluid dynamic (CFD) models. The results showed that electromagnetic stirring can contribute to a better heat transfer rate at the melt – scrap interface. The Grashof and Nusselt numbers for both electromagnetic stirring and natural convection were estimated, as well as compared to the data from previous studies. Also, the results of the post-combustion in the duct system were used to predict the concentration of uncombusted CO at the possible position to install an off – gas analysis equipment. Also, modeling of the post-combustion in the whole furnace showed that the post-combustion can be improved by increasing the flow rate of the secondary oxygen in a virtual lance burner (VLB) under the meltdown and refining periods of the process. In order to investigate the influence of additions of raw materials on energy, melt composition and slag properties, a static mass and energy balance model is developed. The distribution ratios for metallic elements and dust parameters are calibrated by using process data from an EAF. The model is then applied to investigate the effect of hot briquetted iron (HBI) additions in that particular EAF. The results showed that these additions resulted in an increased electricity consumption and slag amount. The model is then applied to predict how it is possible to adjust the amount of slag formers to reach a desired MgO saturation level. In addition, a statistical model is developed which simulate the melt composition by applying uncertainties in scrap composition, scrap weighing and element distribution factors. The model can estimate the mean and standard deviations in the element concentration of scraps. The results of the model application in an EAF showed that the simulated melt chemical composition is in good agreement with the measured one, when the estimated values for scraps are applied as data in the model.
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| 6. |
- Arzpeyma, Niloofar, et al.
(författare)
-
Modeling of post combustion inside the off-gas duct system of the Ovako electric arc furnace
- 2014
-
Ingår i: CDF 2014.
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Konferensbidrag (refereegranskat)abstract
- In order to study the post combustion (PC) inside the duct system of an electric arc furnace (EAF), a three-dimensional computational fluid-dynamics (CFD) model was developed. The reactions between the off gas species (oxygen and hydrogen) and oxygen which leaked into the duct, through the air gap, was considered. The off-gas composition, the off –gas velocity and the outlet pressure were considered as parameters affecting the PC. The results showed that there was a considerable amount of the uncombusted CO to be captured. The highest CO concentration was found at the central part of the duct. The results also showed that a higher off-gas mass flow rate and a higher power of the outlet fan led to a higher combustion of CO and H2. An off-gas analysis probe was then installed after the air gap, where the tip of the probe was placed according to the predicted high CO concentration area found in the simulations. Thereafter, the measured off-gas composition was used to predict the off-gas composition at the outlet of the EAF.
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| 7. |
- Bai, Haitong, 1986-
(författare)
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A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.
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| 8. |
- Bai, Haitong, et al.
(författare)
-
An Experimental and Numerical Study of Swirling Flow Generated by TurboSwirl in an Uphill Teeming Ingot Casting Process
- 2016
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 56:8, s. 1404-1412
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Tidskriftsartikel (refereegranskat)abstract
- A swirling flow has been demonstrated to be beneficial for making the flow pattern even and to reduce turbulence during filling in ingot casting. A new swirling flow generation device, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mold so that a more stable flow could be obtained. A water model was built including the TurboSwirl with different flaring angles of the divergent nozzle, according to a former numerical study indicating that a much more beneficial flow pattern could be obtained by reducing the flaring angle. To validate the mathematical model, the air-core vortex formed in the water model experiment was used, and the length of the vortex was measured and compared to the numerical predictions. Different turbulence models including the standard k-epsilon, realizable k-epsilon and Reynolds stress model were tested. It was found that only the Reynolds stress model could most accurately simulate the high swirling flow including a vortex. In addition, the radial velocity of the water around the vortex was measured by an ultrasonic velocity profiler (UVP). The experimental results revealed a high turbulence of the swirling flow and strong fluctuations of the vortex. The radial velocity of the water around the upper part of the vortex could be predicted well compared to the experimental results by the UVP measurements.
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| 9. |
- Bai, Haitong, 1986-, et al.
(författare)
-
Effect of swirling flow tundish submerged entry nozzle outlet design on multiphase flow and heat transfer in mould
- 2019
-
Ingår i: Ironmaking & steelmaking. - : TAYLOR & FRANCIS LTD. - 0301-9233 .- 1743-2812.
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Tidskriftsartikel (refereegranskat)abstract
- Effect of a swirling flow SEN (submerged entry nozzle) outlet design on the multiphase flow and heat transfer in a mould was investigated by using numerical simulation. It was found that different SEN outlet designs could form different flow patterns and temperature distributions on the upper of the mould. The enlarged outlet SEN design had an effect to decrease the horizontal velocity of liquid steel flowing out the SEN outlet, reducing the steel flow velocity towards the solidification front. Although a higher velocity was found near the slag/steel interface with the enlarged outlet SEN, but the turbulent kinetic energy was lower. The reason was that less circulation flows were formed in the region of the mould top. The weak horizontal flow towards the solidification front with the enlarged outlet SEN induced lower wall shear stresses, at the same time it also formed a lower temperature distribution near the solidified shell.
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| 10. |
- Bai, Haitong, et al.
(författare)
-
Effect of TurboSwirl Structure on an Uphill Teeming Ingot Casting Process
- 2015
-
Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 46:6, s. 2652-2665
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Tidskriftsartikel (refereegranskat)abstract
- To produce high-quality ingot cast steel with a better surface quality, it would be beneficial for the uphill teeming process if a much more stable flow pattern could be achieved in the runners. Several techniques have been utilized in the industry to try to obtain a stable flow of liquid steel, such as a swirling flow. Some research has indicated that a swirl blade inserted in the horizontal and vertical runners, or some other additional devices and physics could generate a swirling flow in order to give a lower hump height, avoid mold flux entrapment, and improve the quality of the ingot products, and a new swirling flow generation component, TurboSwirl, was introduced to improve the flow pattern. It has recently been demonstrated that the TurboSwirl method can effectively reduce the risk of mold flux entrapment, lower the maximum wall shear stress, and decrease velocity fluctuations. The TurboSwirl is built at the elbow of the runners as a connection between the horizontal and vertical runners. It is located near the mold and it generates a tangential flow that can be used with a divergent nozzle in order to decrease the axial velocity of the vertical flow into the mold. This stabilizes flow before the fluid enters the mold. However, high wall shear stresses develop at the walls due to the fierce rotation in the TurboSwirl. In order to achieve a calmer flow and to protect the refractory wall, some structural improvements have been made. It was found that by changing the flaring angle of the divergent nozzle, it was possible to lower the axial velocity and wall shear stress. Moreover, when the vertical runner and the divergent nozzle were not placed at the center of the TurboSwirl, quite different flow patterns could be obtained to meet to different requirements. In addition, the swirl numbers of all the cases mentioned above were calculated to ensure that the swirling flow was strong enough to generate a swirling flow of the liquid steel in the TurboSwirl.
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| 11. |
- Bai, Haitong, et al.
(författare)
-
Experimental Validation and Numerical Analysis of the Swirling Flow in a Submerged Entry Nozzle and Mold by using a Reverse TurboSwirl in a Billet Continuous Casting Process
- 2016
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- As an alternative to some traditional methods to generate a swirling flow in the continuous casting process, the use of a new swirling flow generator, TurboSwirl, was studied. Specifically, a reversed TurboSwirl device was designed as part of a submerged entry nozzle (SEN) for a round billet continuous casting process. Mathematical modelling was used to investigate this new design and a water model experiment was carried out to validate the mathematical model. The predicted velocities by the turbulence models: realizable k-ε model, Reynold stress model (RSM) and detached eddy simulation (DES) were compared to the measured results from an ultrasound velocity profile (UVP) method. The DES model could give the best prediction inside the SEN and had a deviation less than 3.1% compared to the measured results. Moreover, based on the validated mathematical model and the new design of the SEN, the effect of the swirling flow generated by the reverse TurboSwirl on the flow field of the SEN and mold was compared to the design of the electromagnetic swirl flow generator (EMSFG). A very strong swirling flow in the SEN and a stable flow pattern in the mold could be obtained by the reverse TurboSwirl compared to the EMSFG.
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| 12. |
- Bai, Haitong, 1986-, et al.
(författare)
-
Numerical study of an application of a divergent reverse TurboSwirl nozzle in the billet continuous casting process
- 2019
-
Ingår i: Ironmaking & steelmaking. - : TAYLOR & FRANCIS LTD. - 0301-9233 .- 1743-2812. ; 46:2, s. 148-158
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Tidskriftsartikel (refereegranskat)abstract
- The swirling flow has widely been investigated for liquid steel flowing in the continuous casting process. In this paper, a new design of the submerged entry nozzle (SEN) is applied by using a reverse TurboSwirl device with a divergent nozzle. This divergent reverse TurboSwirl nozzle (DRTSN) is shown to gain a more beneficial flow pattern compared to the straight nozzle. A stronger swirling flow can be obtained at the SEN outlet, which leads to a calmer flow field and an appropriately active meniscus flow that could improve the heat and mass transfer near the meniscus. The swirl number in the SEN is independent of the casting speed, while a lower casting speed yields a lower maximum wall shear stress. The DRTSN is connected to the tundish by an elbow and a horizontal runner. A longer horizontal runner supplies a more uniform velocity profile and a more symmetrical flow pattern.
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| 13. |
- Bai, Haitong, et al.
(författare)
-
Numerical Study of the Application for the Divergent Reverse TurboSwirl Nozzle in the Billet Continuous Casting Process
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The swirling flow is demanded from the submerged entry nozzle (SEN) to the mold for the continuous casting process. A new design of the SEN is applied by using the reverse TurboSwirl. The TurboSwirl has been proved that it can provide a more stable flow pattern of the liquid steel in the mold. It also can supply a strong enough swirling flow compared to other swirling flow generation methods. Furthermore, a divergent nozzle is added to replace the bottom part of the straight SEN. This new divergent reverse TurboSwirl nozzle (DRTSN) could gain a more beneficial flow pattern in the mold compared to the straight nozzle. The numerical results reveals that a stronger swirling flow can be gained at the SEN outlet with a calmer flow field and active meniscus flow. It is also found that the swirl intensity in the SEN is independent of the casting speed. Lower casting speed is more desired due to a lower maximum wall shear stress. The DRTSN is connected to the tundish by an elbow and a horizontal runner. Longer horizontal runner can supply a more uniform velocity profile and symmetrical flow pattern in the mold.
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| 14. |
- Bai, Haitong, et al.
(författare)
-
The physical and mathematical modelling of swirling flow by turboswirl in an uphill teeming ingot casting process
- 2015
-
Ingår i: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015. - : Chinese Society for Metals. ; , s. 473-476
-
Konferensbidrag (refereegranskat)abstract
- Ingot casting is widely used to produce some certain specialty steel grades. During the process of teeming the liquid steel from the ladle to the mould for a final solidification, the high velocity of the liquid steel can result in an uneven flow pattern either in the vertical and horizontal runners or in the mould. This can cause some serious problems, such as a high erosion of refractory walls or a mould flux entrapment. Here, some research indicate that a swirling flow is beneficial for making the flow pattern even and for reducing turbulence in the runners. Recently, a new swirling flow generation component, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mould so that a more stable flow could be obtained. The TurboSwirl is located on the intersection of the horizontal and vertical runners near the mould. It generates a tangential flow that can be used with an expanding nozzle with a flaring angle in order to decrease the vertical flow velocity. Moreover, a mathematical model has been developed to optimize the geometry of the physical model. The results shows that a much more beneficial flow pattern can be obtained by reducing the flaring angle or moving the vertical runner to an off-center position of the TurboSwirl, according to the numerical models. Therefore, a water modelling experiment was built, including the TurboSwirl, one mould and the runners. Tracers will be mixed into the water to detect the flow pattern and the velocity of the fluid would be recorded by a digital motion analysis recorder for later analysis. Firstly, different flaring angles of the expanding nozzle were simulated and compared. The results could supply a good support to the following water modelling experiments and to prove that the TurboSwirl setup produces a much calmer initial filling of the mould, compared to a conventional setup.
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| 15. |
- Bölke, Kristofer, et al.
(författare)
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Experimental Determinations of Mixing Times in the IronArc Pilot Plant Process
- 2019
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- IronArc is a newly developed technology and an emerging future process for pig iron production. The long-term goal with this technology is to reduce the CO2 emissions and energy consumption compared to existing technologies. The production rate of this process is dependent on the stirring, which was investigated in the pilot plant process by measuring the mixing time in the slag bath. Moreover, slag investigations were done both based on light optical microscope studies as well as by Thermo-Calc calculations in order to determine the phases of the slag during operation. This was done because the viscosity (which is another important parameter) is dependent on the liquid and solid fractions of the slag. The overall results show that it was possible to determine the mixing time by means of the addition of a tracer (MnO2 powder) to the slag. The mixing time for the trials showed that the slag was homogenized after seconds. For two of the trials, homogenization had already been reached in the second sample after tracer addition, which means <= 8 s. The phase analysis from the slag indicated that the slag is in a liquid state during the operation of the process.
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| 16. |
- Bölke, Kristofer, et al.
(författare)
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Importance of the Penetration Depth and Mixing in the IRONARC Process
- 2018
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 58:7, s. 1210-1217
-
Tidskriftsartikel (refereegranskat)abstract
- One of the most important parameters for gas injection into liquid baths is the penetration depth of the gas into the bath. This is due to that it strongly influences the flow structure and hence the stirring and plume behavior in metallurgical processes. The IRONARC process is a new energy efficient process for reduction of iron oxide to produce pig iron. The future goal is to continuously scale up the process to an industrial scale from the current pilot scale. In this process, gas is injected horizontally through a submerged nozzle into a slag bath. Hence, the penetration depth is of great importance since it greatly affect several parameters in this process. Moreover, this information is essential when scaling up the reactor from a pilot scale to an industrial scale. In this work, the penetration depth of gas injection into water in a small scale side blown converter was studied numerically. Two different approaches with different multiphase models were tested, namely the Volume of Fluid (VOF) model and Eulerian multiphase model (EE). The penetration depth could be accurately determined for both numerical models, with a small expected deviation of 13.9% from the physical experiment results. Also, the simulation time was shorter for the Eulerian multiphase model. The penetration depth was then determined for the IRONARC pilot plant process. The results show that the plume is detached from the nozzle wall, which in turn results in a better energy usage of the gas along with a small refractory wear.
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| 17. |
- Bölke, Kristofer
(författare)
-
IronArc a New Process for Pig Iron Production : A Numerical and Experimental Investigation Focusing on Mixing
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I den här studien så var syftet att undersöka omrörningen och relaterade fenomen i den nyutvecklade IronArc processen. Processen använder sig av gasinjektion genom plasmageneratorer för att smälta och reducera en slagg bestående av järnoxid. Både penetrationsdjupet hos gasen och omrörningstiden undersöktes under olika förhållanden för att de är viktiga parametrar för processen. Undersökningen har gjorts både genom experiment och Computational Fluid Dynamics (CFD).Först utvecklades en nerskalad modell i akrylplast av IronArc pilot reaktorn i skala 1:3, där både penetrationsdjupet och omrörningstiden bestämdes för ett system med luft och vatten genom fysiska experiment. Sedan så skapades en matematisk modell för att beskriva penetrationen av luft injicerat i vatten. Den validerade modellen användes sedan för att beskriva penetrationsdjupet av den injicerade gasen i slaggen för pilotreaktorn. Vidare så utvecklades en ny metod för att bestämma omrörningstiden i pilotreaktorn med slagg som flytande medium. Slaggen undersöktes också både med hjälp av ljusoptiskt mikroskop (LOM) och även genom beräkningar i Thermo-Calc. Detta gjordes för att undersöka huruvida slaggen är i smält tillstånd då processen körs. Ytterligare en matematisk modell utvecklades sedan för att beskriva omrörningen i den nedskalade modellen av akrylplast med luft och vatten. Samma CFD modell användes för att beskriva omrörningen i pilotreaktorn, där modellen validerades mot de tidigare resultaten från de fysiska experimenten med slagg i pilotreaktorn. Slutligen så utfördes ytterligare försök i pilotreaktorn för att bestämma omrörningstiden, men med vatten istället för slagg. Det bör även nämnas att det enbart var luft som injicerades utan att gasen värmdes upp i plasmageneratorn, då vattnet skulle evaporerat om man värmt gasen.Den genomsnittliga omrörningstiden för den nerskalade modellen där luft injicerades i vatten bestämdes till 7,6 s och 10,2 sekunder för respektive homogeniseringsgrad på 95% och 99%. Detta gjorde då ett inlopp användes med ett gasflöde på 282 NLmin-1 användes. Det visade sig att den genomsnittliga omrörningstiden ökade med 15,8% för 95% homogenisering och 17,6% för 99% homogeniseringsgrad då 3 inlopp användes för samma gasflöde. Penetrationsdjupet visade på ett pulserande beteende med ett maximum och minimum värde för respektive undersökt gasflöde.Penetrationsdjupet för experimentet med gas injicerat i vatten kunde beskrivas korrekt med CFD modellen, där Euler-Euler metoden bestämde penetrationsdjupet av experimentet inom en noggrannhet på 86%. Det visade sig också att denna metod reducerade beräkningstiden jämfört med den andra testade Volume of Fluid (VOF) modellen. Penetrationsdjupet av gas i slagg predikterades till 0.3 m, vilket motsvarar radiens läng i reaktorn.Resultaten visade att möjligt att experimentellt bestämma omrörningstiden i pilotreaktorn genom att addera ett spårämne (MnO2 pulver) till slaggen och ta kontinuerliga prover. Mer specifikt så var tiden för att homogenisera badet under 10 sekunder efter att spårämnet tillsatts. Både LOM (Ljusoptiskt Mikroskop) observationerna och Thermo-Calc beräkningarna indikerade att det var rimligt att anta att slaggen är i smält tillstånd under körning.Den predikterade omrörningstiden för den numeriska modellen för luft-vatten systemet var 7,5 sekunder och överensstämmer med experimentresultaten med 1,3%. omrörningstiden bestämdes till 6.5 sekunder för simuleringen av pilotreaktorn och det stämmer överens med resultaten från experimenten i pilotskalan som visade att omrörningstiden var under 10 sekunder. Även resultaten från experimenten då omörningstiden bestämdes 8,5 och 14 sekunder för 95 % och 99% homogeniseringsgrad, då reaktorn var vattenfylld.Denna undersökning av den nya IronArc-processen har gett värdefull information om omrörningen som kan användas i designbeslut för en framtida storskalig järnframställningsprocess.
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| 18. |
- Bölke, Kristofer, et al.
(författare)
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Physical Modeling Study on the Mixing in the New IronArc Process
- 2018
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Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 89:7
-
Tidskriftsartikel (refereegranskat)abstract
- IronArc is a newly developed technology for pig iron production with the aim to reduce the CO2 emission and energy consumption, compared to a conventional blast furnace route. In order to understand the fluid flow and stirring in the IronArc reactor, water modeling experiments are performed. Specifically, a down scaled acrylic plastic model of the IronArc pilot plant reactor is used to investigate the mixing phenomena and gas penetration depth in the liquid bath. The mixing time is determined by measuring the conductivity in the bath, after a sodium chloride solution is added. Moreover, the penetration depth is determined by analyzing the pictures obtained during the experimental process by using both a video camera and a high speed camera. The results show that the bath movements are strong and that a circular movement of the surface is present. The mixing in the model for the flow rate of 282 NLmin(-1) is fast. Specifically, the average mixing times are 7.6 and 10.2s for a 95% and a 99% homogenization degree, respectively. This is 15% and 18% (per degree of homogenization) faster compared to the case when using 3 gas inlets and the same flow rate.
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| 19. |
- Chanouian, Serg, et al.
(författare)
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A Fundamental Investigation of Decarburization Reactions in the Argon–Oxygen Decarburization Converter Using Coupled Computational Fluid Dynamics and Thermodynamics Databases
- 2022
-
Ingår i: Steel Research International. - : John Wiley and Sons Inc. - 1611-3683 .- 1869-344X. ; 93:12
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Tidskriftsartikel (refereegranskat)abstract
- Metallurgical converters such as the argon–oxygen decarburization (AOD) converter generally utilize gas blowing for the mixing and refinement of liquid steel. Due to the harsh environment of the complex and opaque system, it is common practice to study the stirring of the process through physical and numerical models. Effective mixing in the bath has an important role in refinement such as decarburization and has been vividly studied before. However, high-temperature chemical reactions that also play a major role are sparsely investigated. With the help of modeling, a computational fluid dynamics model coupled with chemical reactions is developed, allowing the study of both dynamic fluid transport and chemical reactions. Herein, the chemical reactions for a single gas bubble in the AOD are investigated. The study shows that a 60 mm oxygen gas bubble rapidly reacts with the melt and is saturated with carbon in 0.2–0.25 s at low-pressure levels. The saturation time is affected by the pressure and the composition of the injected gas bubble. The impact of ferrostatic pressure on the reactions is more significant at larger depth differences.
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| 20. |
- Chanouian, Serg, et al.
(författare)
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Inclination Effect on Mixing Time in a Gas–Stirred Side–Blown Converter
- 2021
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 92:10, s. 2100044-
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Tidskriftsartikel (refereegranskat)abstract
- Small-scale physical models are commonly used to investigate gas-stirred processes in steelmaking practice. The argon oxygen decarburization (AOD) converter is among various processes widely used in the metallurgy field and utilizes side blowing of oxygen and inert gas for mixing in the bath. Herein, the effect of the converter inclination on mixing time and jet-penetration length with a side-blown physical model is investigated. Scaling with the modified Froude number is applied on data from a real industrial AOD converter to achieve a system with reasonable gas flow rates. During the experiments, water is used to simulate liquid steel and air is blown through side-mounted nozzles for stirring. A NaCl tracer is added and subsequent conductivity measurements are used to measure mixing time. Overall, the penetration length is shown to be independent of inclination angle. The mixing time is found to be influenced by the change of bath height to diameter ratio, change of geometry in the bath volume, gas flow rate, and the intensified wave motion at the interface caused by the inclination of the vessel. The mixing time increase with 14% when 14° angle is applied.
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| 21. |
- Chanouian, Serg, 1995-
(författare)
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Mixing Time and Decarburization Reactions in Side-blown Metallurgical Converters : A Practical Approach using CFD and Thermodynamics
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The side-blowing Argon Oxygen converter (AOD), known for its intense gas stirring and turbulentnature, poses complex fluid dynamics and thermodynamic challenges. Modeling has played asubstantial role in the development of metallurgical converters, particularly in understanding jetbehavior, mixing, flow patterns, and chemical reactions. Flow characteristics and mixing time arerecognized as crucial factors that enhance the efficiency and decarburization rate in metallurgicalreactors. However, to the best of the author's knowledge, no prior study has investigated the impactof mixing time on the decarburization reaction. While most studies suggest that reducing mixing timeis beneficial, it is reasonable to assume that there might be a point at which further reduction inmixing time does not lead to an increase in reaction rates. Adjustments like tilting the converter orrepositioning the nozzles could improve decarburization efficiency by altering pressure conditions andmixing. This study aims to explore how these factors affect the decarburization reaction in side-blownconverters through modeling. The work has been done in a few steps resulting in differentsupplements.Side-blowing water model experiments were carried out to investigate how a vessel inclination wouldaffect the mixing time. The results showed a clear increase in mixing time when higher inclinationangles (14°) were applied. However, studying the non-reacting water models could only give insightto mixing efficiency and not provide information about decarburization efficiency.A numerical model capable of integrating mass and heat transfer with high temperature chemicalreactions was developed to aid in this investigation. First, the model was applied to an ascending gasbubble in liquid steel. The effect of pressure was investigated by injecting the bubble in different bathdepths. It was shown that a mere oxygen bubble injected at the nozzle position under industrialconditions did not decarburize efficiently, rather dissolved into the steel. Only pressure levels at thebath surface could maintain gas as a stable phase and decarburize efficiently.With high grid resolutions the model consumed a lot of computational time calculating equilibriumlocally in each cell with gas and liquid present. Therefore, a more practical approach was taken tostudy the AOD converter that showed high agreement to the first decarburization step whencomparing against two industrial heats. It was shown that with a coarse Computational Fluid Dynamic(CFD) solution the model could be practical, yet fundamental. In the study it was also found that nochromium oxidation was found in one of the heats at the beginning of the process when the initialcarbon content was high. The trends were compared against an industrial online process model andshowed similar behavior.With further developments, the model was tested with different treatments of the thermodynamiccoupling, including reactions limited by turbulence in an intensely stirred side-blown reactor. Themixing time was shown to have an insignificant effect on the decarburization rate. The system wasgoverned by thermodynamics and gas supply rate.Overall, this work developed a general model capable of coupling chemical reactions with CFD. Theuse of this model led to the conclusion that an inclination of the vessel within practical operationalangles would not benefit the decarburization rate in the early stages of decarburization. Withincreased mixing times and small pressure variations from the lowered bath height, the benefits todecarburization might not be worth compared to the engineering challenges posed by such changes.Even relocating the nozzle would require large and unpractical height differences to acquire thepressure decrease needed to benefit thermodynamically.
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| 22. |
- Chanouian, Serg, et al.
(författare)
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Modelling Decarburization in the AOD Converter : A Practical CFD-Based Approach with Chemical Reactions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Gas blowing technology is widely used in converter steelmaking to homogenize liquid steel and accelerate chemical reactions, with Argon oxygen decarburization (AOD) being the dominant process for stainless steelmaking. Due to the harsh environment, it is advisable to study the phenomenon using small-scale physical models and numerical simulations before conducting industrial-scale trials. This paper presents a practical computational fluid dynamics (CFD) approach for simulating the AOD process, with chemical reactions considered. This approach can simulate the entire process in a reasonable time using a standard workstation. The simulation employs a Finite Volume Method CFD approach to handle mass, momentum and energy transfer, and a local equilibrium assumption is utilized. The study shows that a practical approach can be used to model the initial stage of decarburization in the AOD process with a reduced accuracy in mass transport calculations. The accuracy of the simulation is validated using industrial data, and good agreement is found.
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| 23. |
- Chanouian, Serg, et al.
(författare)
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The Importance of Mixing Time in Intensely Stirred Metallurgical Reactors : Applied on Decarburization Reactions
- 2023
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 13:10
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Tidskriftsartikel (refereegranskat)abstract
- In metallurgical converter processes, numerical modeling is a useful tool for understanding the complexity of the systems. In this paper, we present a practical model that couples fluid dynamics and chemical reactions to explore the impact of mixing time on decarburization. Using computational fluid dynamics (CFD), in this study, we investigate an arbitrary metallurgical reactor with continuous oxygen supply, focusing on the Fe–C–O system. The model employs local equilibrium, a turbulence limiter, and finite volume method for mass, momentum, and energy transfer. Tracer injection points in the gas plume’s rising region exhibit faster mixing, and a comparison of reaction cases reveals distinct decarburization rates based on oxygen injection distribution and the influence of turbulence on reactions. Overall, while mixing time matters, the results show that this system is primarily governed by thermodynamics and oxygen supply, and a 270% increase in mixing time increase had a small impact on the end carbon content.
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| 24. |
- Engskog, Mikael K. R., et al.
(författare)
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β-N-Methylamino-L-alanine (BMAA) perturbs alanine, aspartate and glutamate metabolism pathways in human neuroblastoma cells as determined by metabolic profiling
- 2017
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Ingår i: Amino Acids. - : Springer Science and Business Media LLC. - 0939-4451 .- 1438-2199. ; 49:5, s. 905-919
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Tidskriftsartikel (refereegranskat)abstract
- β-Methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid that induces long-term cognitive deficits, as well as an increased neurodegeneration and intracellular fibril formation in the hippocampus of adult rodents following short-time neonatal exposure and in vervet monkey brain following long-term exposure. It has also been proposed to be involved in the etiology of neurodegenerative disease in humans. The aim of this study was to identify metabolic effects not related to excitotoxicity or oxidative stress in human neuroblastoma SH-SY5Y cells. The effects of BMAA (50, 250, 1000 µM) for 24 h on cells differentiated with retinoic acid were studied. Samples were analyzed using LC-MS and NMR spectroscopy to detect altered intracellular polar metabolites. The analysis performed, followed by multivariate pattern recognition techniques, revealed significant perturbations in protein biosynthesis, amino acid metabolism pathways and citrate cycle. Of specific interest were the BMAA-induced alterations in alanine, aspartate and glutamate metabolism and as well as alterations in various neurotransmitters/neuromodulators such as GABA and taurine. The results indicate that BMAA can interfere with metabolic pathways involved in neurotransmission in human neuroblastoma cells.
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| 25. |
- Ersson, Carolina
(författare)
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Conditions for resource-efficient production of biofuels for transport in Sweden
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transportation has continued to increase worldwide and fossil-fuel dependency is strong which leads to a number of problems, e.g. increased emissions of green-house gases (GHG) and risks related to energy security. Biofuels have until now been one of the few renewable alternatives which have been able to replace fossil fuels on a large scale. The biofuel share in relation to the total use of fuel in the transportation sector is still small, but in many places in the world political targets are set to increase the share of renewable fuels, of which biofuels are supposed to be an important part. Within the European Union targets for renewable energy have been set, including within the transportation sector, where 10% shall come from renewable sources by 2020 according to the EU Renewable Energy Directive (EU RES). Biofuels also need to fulfill the sustainability criteria in the EU RES, to be regarded as renewable. Depending on how biofuels are produced their resource efficiency varies, and the differences in environmental and economic performance can for instance be significant.The aim of this thesis is to describe and analyze conditions for a development towards increased and more resource-efficient production of biofuels in Sweden. The conditions have been studied from a regional resource perspective and from a biofuel producer perspective since it has been assumed that the producers are in possession of important knowledge, and potentially will play an important role in future biofuel development. The concept of resource efficiency used in this thesis includes an environmental and economic perspective as well as an overall societal dimension to some extent. The region of Östergötland in Sweden was used for the assessment of the resourcefocused biofuel potential for the year 2030, where two scenarios based on assessments regarding socio-technical development in relation to regional resources were used. The scenarios were based on semi-structured interviews with biofuel actors, literature studies and information from experts in the field. In the EXPAN (Expansion) scenario a continued development in line with the current one was assumed, but also an increased availability of feedstock primarily within the agricultural and waste sectors (also including byproducts from industry) for biofuel production. In the INNTEK (Innovation and Technology development) scenario greater technological progress was assumed to also enable the use of some unconventional feedstock besides increased available arable land and improved collection/availability of certain feedstock. Biomass feedstock from four categories was included in the potential: waste, agriculture, forestry and aquatic environments. One important feedstock which was not included in this study, but which is often included in studies of potential, is lignocellulosic material from the forest. This choice was also supported by the regional actors who judged it as less probable that there will be any large-scale use of such feedstock for biofuels in this region within the given timeframe. Regarding arable land available for biofuel production a share of 30% was assumed at maximum in the region, of which 15% is already used for cereal production for ethanol fuel. On these additional 15% assumed to be available for biofuel production year 2030, ley cropping for production of biogas was assumed in this study. Aquatic biomass is often not included in biofuel potentials. Here, algae were assumed to be a potentially interesting substrate for biogas production since harvesting algae in for instance the Baltic Sea could be seen as a multifunctional measure, i.e., contributing additional environmental benefits such as reducing eutrophication. Based on the assumption that the energy need in the transportation sector will be the same in 2030 as in 2010, up to 30% could be substituted with biofuels in the EXPAN scenario and up to 50% in the INNTEK scenario, without seriously conflicting with other interests such as food or feed production. In the study of potential, production systems for biogas production were prioritized since such systems were judged to have a large potential for resource efficiency. This is because they have a big capacity to utilize by-products and waste as feedstock, and also because they can contribute to closing the loops of plant nutrients, seen as an important goal in society, if the digestate is returned to arable land.The utilization of by-products and waste however in many cases requires cooperation between different actors in society. Within the research field of industrial symbiosis, cooperation regarding material and energy flows is studied from different perspectives, e.g. how such cooperation between actors evolves and to what extent such cooperation can contribute to improving the environmental and economic performance of systems. Both these perspectives are interesting in relation to biofuels since production often involves a large number of energy- and material flows at the same time as resource efficiency is important. How the producers organize the production when it comes to feedstock, energy, by-products and products and what influences this is therefore interesting to study. In this thesis four biofuel producers of three different biofuels (ethanol, biodiesel and biogas) on the Swedish market were studied, focusing on how they organize their biofuel production in terms of e.g. their material and energy flows, and how they intend to organize it in the future. The study is based on semi-structured interviews with the biofuel producers as well as literature studies. In all the cases, a number of areas of material and energy flow cooperation were identified and it could also be concluded that there had been some change regarding these patterns over time. Looking into the future a clear change of strategy was identified in the ethanol case and partly also in the biodiesel case where a development towards improved valorisation and differentiation of by-product flows was foreseen. If such a “biorefinery” strategy is realized, it can potentially improve the economic viability and resource efficiency in these biofuel producers. In the biogas cases, instead a strategy to lower the costs for feedstock through the use of lower quality feedstock was identified. This strategy also has a potential to increase economic viability and improve the resource efficiency. However, the success of this strategy is to a large extent dependent on how the off-set of the biofertilizer can be arranged regarding the economic challenges that the biogas producers’ experience, and yet no strategy for implementation regarding this was identified. The EU Renewable Energy Directive was mentioned in relation to most cooperation projects and therefore regarded as an important critical factor. All of the studied companies also struggle to be competitive, for which reason the importance of the direct economic aspects of cooperation seems to increase.
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| 26. |
- Ersson, Mikael, 1977-, et al.
(författare)
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A Mathematical Model of an Impinging Air Jet on a Water Surface
- 2008
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 48:4, s. 377-384
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental mathematical model of the flow field and surface deformation caused by an impinging jet in a top blown reactor has been developed. The results have been validated against water model experiments. More specifically, the predicted penetration depth has been found to agree well with surface deformation measurements and predictions using analytical equations. Furthermore, the predictions of the location of a vortex have been found to agree fairly well with PIV measurements. Calculations were also done to compare the widely used standard k-ε model against the realizable extension of the standard k-ε model to calculate the turbulent conditions of the flow. It was found that the penetration depth caused by the impinging jet on the liquid surface is relatively unaffected by the choice of turbulence model employed. However, when the main re-circulation loop in the bath was investigated there was a clear distinction in the flow fields produced when the two different turbulence models were used.
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| 27. |
- Ersson, Mikael
(författare)
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Colocated pressure-velocity coupling in finite difference methods
- 2019
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Ingår i: Progress in Computational Fluid Dynamics, An International Journal. - : INDERSCIENCE ENTERPRISES LTD. - 1468-4349 .- 1741-5233. ; 19:5, s. 273-281
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Tidskriftsartikel (refereegranskat)abstract
- A simple method to be used for colocated pressure-velocity coupling in incompressible flows is presented with a full derivation. A number of standard test cases are shown that demonstrate the ability of the method to produce accurate results. The method avoids spurious pressure oscillations while keeping the pressure Poisson equation stencil compact. This is obtained by discretising the continuity and pressure derivatives with first order differences with opposite directions, i.e., backward difference for continuity and forward difference for pressure (BCFP). The equations are also approximated using a forward difference for continuity and a backward difference for pressure (FCBP). In order to obtain a second order approximation the mean between BCFP and FCBP is used, i.e., a central difference. The paper gives a useful alternative to existing methods for pressure-velocity coupling in finite difference methods in which a staggered arrangement is not desirable.
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| 28. |
- Ersson, Mikael, et al.
(författare)
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Coupled thermodynamic and kinetic modeling of a top-blown bath
- 2006
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Ingår i: Sohn International Symposium Advanced Processing of Metals and Materials, Vol 2. - 0873396359 ; , s. 271-281
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Konferensbidrag (refereegranskat)abstract
- A fundamental mathematical model of lance blowing on a bath surface has been developed with a purpose to increase the understanding of various phenomena in top blown oxygen converters. The model is based on the Navier-Stokes equations and turbulence is predicted using the k-epsilon model. In the present model the deformation of the liquid surface, caused by the impinging gas jet, is described using a VOF formulation. The mathematical model results have been verified by comparing predicted penetration-depth data with experimental results from physical model trials. The fluid dynamic modeling has also been coupled with the thermodynamic modeling to predict the reaction rate/distribution occurring in the vessel. The focus has been on carbon and a qualitative comparison of the predicted carbon content in the hot spot area and in droplets with experimental data from laboratory trials has been done.
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| 29. |
- Ersson, Mikael, 1977-, et al.
(författare)
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Dynamic Coupling of Computational Fluid Dynamics and Thermodynamics Software : Applied on a Top Blown Converter
- 2008
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 48:2, s. 147-153
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Tidskriftsartikel (refereegranskat)abstract
- A novel modeling approach is presented where a computational fluid dynamics software is coupled to thermodynamic databases to obtain dynamic simulations of metallurgical process phenomena. The modeling approach has been used on a fundamental model of a top-blown converter. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag have been considered. The results show that the mass transport in the surface area is totally controlled by convection. Also, that a large amount of CO produced during the decarburization might slow down the rate of decarburization in droplets ejected from the bath. For the present simulation conditions reflecting laboratory experiments, it was also seen that the amount of slag (FeO and/or SiO2) created is close to zero, i.e. only gas (CO+CO2) is created as the oxygen jet hits the steel bath. It was also illustrated how an extrapolation of the decarburization rate, sampled from a few seconds of simulation, could be done to get a rough estimate of the carbon content at a later stage in the process as long as the carbon content is relatively high. The overall conclusion is that it is possible to make a dynamic coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.
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| 30. |
- Ersson, Mikael, 1977-, et al.
(författare)
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Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter
- 2008
-
Ingår i: ISIJ International. - 0915-1559 .- 1347-5460.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A dynamic modeling approach is presented where a computational fluid dynamics software is coupled to a thermodynamics software to obtain simulations of reactions between steel, slag and gas in a top-blown converter. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. The overall conclusion is that the present calculation procedure is successful for dynamic simulations of interaction between an oxygen gas jet with a melt and a slag. The predicted rate of decarburization was found to agree well with experimental data from laboratory trials. In addition, four cases where simulated for which the temperature, the dissolved carbon content and the dissolved oxygen content were varied. The most important findings from these comparisons were that: i) a higher initial oxygen concentration in the melt yields a larger decarburization rate, ii) carbon content also plays a big role for the desiliconization where a low carbon content is required for desiliconization to take place, iii) decarburization and desiliconization is largely influenced by the temperature at which reactions take place, where low temperature favors desiliconization and iv) the region affected by a lower carbon/silicon concentration (hot-spot region) directly below the jet was approximately 10 mm for the current setup.
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| 31. |
- Ersson, Mikael, et al.
(författare)
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Dynamic modelling of steel, slag and gas during initial blowing in a top-blown converter
- 2011
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Ingår i: Steel Grips - Journal of Steel and Related Materials. - 1611-4442 .- 1866-8453. ; :9, s. 41-47
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Tidskriftsartikel (refereegranskat)abstract
- A coupling between computational fluid dynamics (CFD) and thermodynamics has recently been done. In the current model improvement, a more realistic model was developed, where the numbers of gas species and slag phases were increased. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. Read how this calculation procedure can handle dynamic simulations of interaction between an oxygen gas jet, a melt and a slag. How is the agreement between the predicted rate of decarburization and experimental data? Which findings were achieved from the simulation of four cases varying the temperature, the dissolved carbon content and the dissolved oxygen content?
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| 32. |
- Ersson, Mikael, 1977-, et al.
(författare)
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Fluid Flow in a Combined Top and Bottom Blown Reactor
- 2006
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 46:8, s. 1137-1142
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Tidskriftsartikel (refereegranskat)abstract
- Physical modeling was done to study the flow field in a cylindrical bath agitated by bottom purging, top lance blowing and a combination of both injection types. A particle image velocimetry (PIV) system has been used to capture the velocity field of all three cases mentioned above. Special attention was paid to the recirculation loop. Top blowing creates a re-circulation loop in a relatively small volume close to the surface, compared to bottom- and combined-blowing. Increasing bottom flow rate moves the center of the re-circulation loop downwards into the liquid. When top blowing is combined with bottom blowing the center of the re-circulation loop is moved downwards into the liquid with increasing top lance flow rate.
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| 33. |
- Ersson, Mikael, 1977-
(författare)
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Fundamental Experimental and Numerical Investigation Focusing on the Initial Stage of a Top-Blown Converter Process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work is to increase the knowledge of phenomena taking place during the initial stage in a top blown converter. The work has been done in a few steps resulting in four different supplements. Water model experiments have been carried out using particle image velocimetry (PIV) technology. The system investigated was a fundamental top blown converter where an air jet was set to impinge on a water surface. The flow field of the combined blown case, where an air jet was introduced through a bottom nozzle, was also captured by the PIV. The work clearly showed that the flow field caused by an impinging top blown jet alone could not match that of the bottom blown case. The main re-circulation loop (or vortex) was investigated with respect to position and it was found that an increased flow rate pushes the center of the re-circulation loop downwards into the bath. However, for the top-blown case there is a point when the flow rate is too large to cause a distinguishable re-circulation loop since the jet becomes more plunging (i.e. penetrates deep into the bath) than impinging, with large surface agitation and splashing as a result.A numerical model with the same dimensions as the experimental system was then created. Three different turbulence models from the same family were tested: standard-, realizable- and a modified-(slight modification of one of the coefficients in order to produce less spreading of the air jet) k-ε turbulence model. It could be shown that for the family of k-ε turbulence models the difference in penetration depth was small and that the values corresponded well to literature data. However, when it comes to the position of the re-circulation loop it was shown that the realizable k-ε model produced better results when comparing the results to the experimental data produced from the PIV measurements, mentioned earlier.It was then shown how the computational fluid dynamics (CFD) model could be coupled to thermodynamics databases in order to solve for both reactions and transport in the system. Instead of an air-water system, a gas-steel-slag system was created using the knowledge obtained in the previous simulation step described above. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag were considered. Extrapolation of data from a few seconds of simulation was used for comparison to experimental data from the literature and showed reasonable agreement. The overall conclusion was that it is possible to make a coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.A parametric study was then undertaken where two different steel grades were tested; one with high initial carbon content (3.85 mass-%) and one with lower carbon content (0.5 mass-%). The initial silicon content was held constant at 0.84 mass-%. Different initial temperatures were tested and also some variation in initial dissolved oxygen content was tried. It was found that the rate of decarburization/desiliconization was influenced by the temperature and carbon concentration in the melt, where a high temperature as well as a high carbon concentration favors decarburization over desiliconization. It was also seen that the region affected by a lower concentration of alloys (or impurities) was quite small close to the axis where the impinging jet hits the bath. Add the oscillating nature of the cavity and it was realized that sampling from this region during an experiment might be quite difficult.
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| 34. |
- Ersson, Mikael, et al.
(författare)
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Review on CFD Simulation and Modeling of Decarburization Processes
- 2018
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Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 89:1
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Forskningsöversikt (refereegranskat)abstract
- Over the last few decades, a number of CFD models have been dedicated to increasing the understanding of the decarburization processes in steelmaking. However, these processes are highly complex with large variations in time and length, and this makes the systems extremely demanding to simulate. Several reports have been published where parts of the processes have been investigated numerically, but to date no models have been presented that can handle the entire complexity of the processes. Here, a review of the research performed on the subject from 1998 to 2016 is given. A table summarizing the models used and the key focus of the studies is given, and it can be concluded that the effort put in so far to investigate the decarburization in steelmaking is substantial, but not complete. The currently available numerical models give an insight into process parameters such as reactions, mixing time, temperature distribution and thermal losses, off-gas post combustion and de-dusting, and also nozzle configuration. With the recent developments in numerical modeling and the increase in hardware capability, the future of simulation and modeling of the decarburization processes in steelmaking seems bright.
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| 35. |
- Hoseini-Athar, Mohammad Mehdi, et al.
(författare)
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Towards implementation of alloy-specific thermo-fluid modelling for laser powder-bed fusion of Mg alloys
- 2024
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Ingår i: JOURNAL OF MAGNESIUM AND ALLOYS. - : Elsevier BV. - 2213-9567. ; 12:6, s. 2327-2344
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Tidskriftsartikel (refereegranskat)abstract
- Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion (L-PBF). However, its capabilities for being implemented as a reliable tool for material design, where minor changes in material-related parameters must be accurately captured, is still in question. In the present research, first, a thermo-fluid computational fluid dynamics (CFD) model is developed and validated against experimental data. Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys, parametric studies are done attempting to elucidate how the difference in some of the material properties, i.e., saturated vapor pressure, viscosity, and solidification range, can influence the melt pool dynamics. It is found that a higher saturated vapor pressure, associated with the ZK60 alloy, leads to a deeper unstable keyhole, increasing the keyhole-induced porosity and evaporation mass loss. Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls, resulting in increased keyhole instability and formation of defects. Finally, the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss, providing theoretical support to the extensive use of this alloy in L-PBF. In summary, this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification, which can be extremely helpful for future design of new alloys suitable for L-PBF.
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| 36. |
- Khodabandeh, E., et al.
(författare)
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CFD study of non-premixed swirling burners : Effect of turbulence models
- 2020
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier BV. - 1004-9541 .- 2210-321X. ; 28:4, s. 1029-1038
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Tidskriftsartikel (refereegranskat)abstract
- This research investigates a numerical simulation of swirling turbulent non-premixed combustion. The effects on the combustion characteristics are examined with three turbulence models: namely as the Reynolds stress model, spectral turbulence analysis and Re-Normalization Group. In addition, the P-1 and discrete ordinate (DO) models are used to simulate the radiative heat transfer in this model. The governing equations associated with the required boundary conditions are solved using the numerical model. The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities. Among different models proposed in this research, the Reynolds stress model with the Probability Density Function (PDF) approach is more accurate (nearly up to 50%) than other turbulent models for a swirling flow field. Regarding the effect of radiative heat transfer model, it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior. This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion.
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| 37. |
- Khodabandeh, Erfan, et al.
(författare)
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Numerical investigation of thermal performance augmentation of nanofluid flow in microchannel heat sinks by using of novel nozzle structure : sinusoidal cavities and rectangular ribs
- 2019
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Ingår i: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : SPRINGER HEIDELBERG. - 1678-5878 .- 1806-3691. ; 41:10
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a numerical simulation of a laminar, steady and Newtonian flow of f-graphene nanoplatelet/water nanofluid in a new microchannel design with factors for increasing heat transfer such as presence of ribs, curves to enable satisfactory fluid mixing and changing fluid course at the inlet and exit sections. The results of this study show that Nusselt number is dependent on nanoparticles concentration, inlet geometry and Reynolds number. As the nanofluid concentration increases from 0 to 0.1% and Reynolds number from 50 to 1000, the Nusselt number enhances nearly up to 3% for increase in fluid concentration and averagely from 15.45 to 54.1 and from 14.5 to 55.9 for geometry with and without rectangular rib, respectively. The presence of ribs in the middle section of microchannel and curves close to hot walls causes a complete mixing of the fluid in different zones. When the nanoparticles concentration is increased, the pressure drop and velocity gradient will become higher. An increased concentration of nanoparticles in contribution with higher Reynolds numbers only increases the fraction factor slightly. (The fraction factor increases nearly 37% and 35% for Re = 50 and 1000, respectively.) The highest uniform temperature distribution can be found in the first zones of fluid in the microchannel and by further movement of fluid toward exit section, because of decreasing difference between surface and fluid temperature, the growth of temperature boundary layer increases and results in non-uniformity in temperature distribution in microchannel and cooling fluid. With decrease in the concentration from 0 to 0.1%, the average outlet temperature and FOM decrease nearby 0.62% and 6.15, respectively.
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| 38. |
- Khodabandeh, E., et al.
(författare)
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The effects of oil/MWCNT nanofluids and geometries on the solid oxide fuel cell cooling systems : a CFD study
- 2020
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer Netherlands. - 1388-6150 .- 1588-2926.
-
Tidskriftsartikel (refereegranskat)abstract
- In this numerical study, the variations in the surface area of the cooling channels in a solid oxide fuel cell with different cross sections and multi-walled carbon nanotubes oil/MWCNT nanofluid volume fractions are considered. Rectangular, trapezoidal and elliptical cross sections, and nanofluid volume fractions of 0–6% for the fluid are chosen as the studied parameters as well as the mass flow rates. In this research, a 3D model is developed by the finite volume method using the computational fluid dynamics (CFD). Then, the flow field and the heat transfer rate are predicted. The results show that the dissipated heat in the fuel cell is dependent on the mass flow rate of the fluid. That increased heat increases the heat transfer rate. The presence of the solid particles can also reinforce the heat conduction of the coolant fluid and consequently improve the heat transfer performance. The pumping power is maximum for the highest mass flow rate and the highest solid nanoparticle volume fractions. Additionally, the pumping power is dependent on the route in which the sections with lowest momentum changes and lowest pressure drops have the least amount of the pumping power. The ratio of the dissipated heat by the nanofluid over the base fluid is compared to a pressure drop. The movement of flow with the lower mass flow rates will result in penetrations of the thermal boundary layers into different flow regions, which can increase the optimum temperature in the solid part of the fuel cell. By increasing the mass flow rate of the fluid passing through the channels from 0.002 to 0.004 kg s−1, the maximum temperature is decreased by 6.13, 3.34 and 6.35% for rectangular, trapezoidal and elliptical channels, respectively.
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| 39. |
- Liu, Yu, et al.
(författare)
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A Review of Physical and Numerical Approaches for the Study of Gas Stirring in Ladle Metallurgy
- 2019
-
Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : SPRINGER. - 1073-5615 .- 1543-1916. ; 50:1, s. 555-577
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Forskningsöversikt (refereegranskat)abstract
- This article presents a review of the research into gas stirring in ladle metallurgy carried out over the past few decades. Herein, the physical modeling experiments are divided into four major areas: (1) mixing and homogenization in the ladle; (2) gas bubble formation, transformation, and interactions in the plume zone; (3) inclusion behavior at the steel-slag interface and in the molten steel; and (4) open eye formation. Several industrial trials have also been carried out to optimize gas stirring and open eye formation. Approaches for selecting criteria for scaling to guarantee flow similarity between industrial trials and physical modeling experiments are discussed. To describe the bubble behavior and two-phase plume structure, four main mathematical models have been used in different research fields: (1) the quasi-single-phase model, (2) the volume of fluid (VOF) model, (3) the Eulerian multiphase (E-E) model, and (4) the Eulerian-Lagrangian (E-L) model. In recent years, the E-E model has been used to predict gas stirring conditions in the ladle, and specific models in commercial packages, as well as research codes, have been developed gradually to describe the complex physical and chemical phenomena. Furthermore, the coupling of turbulence models with multiphase models is also discussed. For physical modeling, some general empirical rules have not been analyzed sufficiently. Based on a comparison with the available experimental results, it is found that the mathematical models focusing on the mass transfer phenomenon and inclusion behaviors at the steel-slag interface, vacuum degassing at the gas-liquid interface, dissolution rate of the solid alloy at the liquid-solid interface, and the combination of fluid dynamics and thermodynamics need to be improved further. To describe industrial conditions using mathematical methods and improve numerical modeling, the results of physical modeling experiments and industrial trials must offer satisfactory validations for the improvement of numerical modeling.
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| 40. |
- Liu, Yu, et al.
(författare)
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An Experimental and Mathematical Work on Single Bubble Behavior under Reduced Pressure
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- During secondary steelmaking, argon bubbles are often passed through molten steel to ensure a clean and homogeneous product. The behavior of the bubbles and the capacity of the bubbles to stir the melt and remove impurities depends on their size, shape, and velocity. These factors depend on the ambient pressure of the melt, the temperature and flow rate of the gas and the geometry of the gas nozzles. There have been many studies that investigate the behavior of bubbles when the melt is under atmospheric pressure, but few when the melt is held under vacuum. This makes it difficult to optimize the argon blowing process. The current study addresses this lack of knowledge by studying bubble behavior when the melt is under vacuum. Physical modeling was used to analyze the effects of the reduced pressure and nozzle diameter on the bubbles’ initial diameter and ascent behavior in a molten steel. Moreover, a multiphase fluid dynamics solver for compressible fluids called ‘compressibleInterFoam’ was validated and used. Increasing the flow rate leads to larger initial bubble diameters and more frequent bubble formation, and increasing the nozzle diameter leads to larger initial bubble diameters and less frequent bubble formation. Decreasing the subjected pressure causes the bubble diameter to increase substantially but bubbles to form less frequently. For flow rates in the range of 5.0(mL·min-1)STP to 2000(mL·min-1)STP, the bubble diameter ranges from 6.0mm to 20.0mm. The frequency of bubble generation initially increases with flow rate before reaching a constant value. During the ascent, a bubble will shed several small bubbles at the bottom to reach a constant shape. In the steel-argon system, under laminar flow conditions, the maximum bubble width under a pressure of 0.2bar is 65mm and is 58mm under a pressure of 2.0bar. As the surrounding pressure increases, the maximum size of the bubble under the steady condition will decrease. These findings can be used to determine the bubble behaviors and to optimize the conditions of argon blowing to produce steel that is sufficiently clean, while minimizing argon usage.
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| 41. |
- Liu, Yu, et al.
(författare)
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Comparison of Euler-Euler Approach and Euler–Lagrange Approach to Model Gas Injection in a Ladle
- 2019
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 90:5
-
Tidskriftsartikel (refereegranskat)abstract
- The gas injection in a ladle using a porous plug is simulated using both the Euler-Euler and Euler-Lagrange approaches. The effects of various forces, bubble sizes, and bubble injection frequencies on the flow pattern are modeled. For predicting axial velocity and turbulent kinetic energy, the Euler-Lagrange approach fits better than Euler-Euler approach with the measured data. In the Euler-Euler approach, differences in axial velocities and turbulent kinetic energies for various bubble sizes mainly appears in the plume zone. In the Euler-Lagrange approach, different bubble sizes with the same injection frequency have a small impact on the turbulence dissipation. Furthermore, the turbulent dispersion from the gas phase to the liquid phase has an important effect on the plume structure and spout eye formation. For both modeling, the smaller the bubble diameter is, the larger the axial velocity and turbulent kinetic dissipation are in the central zone. For the bubble coalescence and breakup, according to the comparison of two modeling approaches, the Euler-Lagrange approach is more accurate in predicting the flow pattern for gas injection with a porous plug in the ladle.
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| 42. |
- Liu, Yu, et al.
(författare)
-
Decarburization in an Electric Arc Furnace using Coupled Fluid dynamics and Thermodynamics
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A coupled method of Fluid dynamics and Thermodynamics, named as Multi-zone Reaction Model, was established to simulate the flow pattern with bottom oxygen injection in a 145t electric arc furnace. The simulated maximum hot spot temperature and decarburization rate in the refining phase were compared against the data measured in the industrial operation. Moreover, the physical modeling was carried out to study the effect of nozzle size on the flow characteristics in the reaction zone. The results show, under high flow rates, the effect of nozzle size on the flow field in the reaction zone of the plume area can be neglected. The decarburization rate and hot spot temperature predicted by the modeling are consistent with the industrial measurements. The maximum hot spot temperature gradually decreases during the refining phase. The oxygen flow rate has a significant influence on the decarburization rate, hot spot temperature and average steel temperature. In terms of combined injection of O2 and inert argon gas, for a certain O2 flow rate, the decarburization rate increases due to the efficient mass transfer of carbon in the molten steel. Furthermore, for the replacement of argon using CO2, it is demonstrated that as the ratio of CO2 mass fraction increases from 0% to 40%, the maximum hot spot temperature decrease with the value of 570K, and the increment rate of average steel temperature, and the decarburization rate in the molten steel decrease with the ratio of 68%, and 81%, respectively. The endothermic reaction of CO2 with the molten steel results in a temperature drop in the plume above the hot spot zone.
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| 43. |
- Liu, Yu, et al.
(författare)
-
Influence of Plug Design on Bubble Injection Characteristics in Ladle Metallurgy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The bubble characteristic created during bottom injection in a ladle has been studied using physical modeling and mathematical modeling. The width of central plume, statistical number of bubbles, and the periodic behavior of bubble injection have been compared using a slot plug and three porous plugs with various porosities. Furthermore, the effect of the plug’s permeability on the plume structure and bubble size distribution has been predicted using the Eulerian Multiphase Model and Population Balance Model. The results show that, for the bottom blowing using a slot plug, an increased flow rate will not change the gas-liquid plume width significantly, but lead to an increased periodic behavior of bubble’s statistic amount. For the bottom blowing using porous plug, an increased flow rate results in a wider central plume, but no obvious change of the periodic characteristic of bubbles. The effect of porosity on the bubble behavior was also studied. As the porosity increases, the volume fraction of gas and the average size of bubbles at the central plume zone increases, and the width of two-phase plume decreases. Moreover, the results predicted by the mathematical modeling are consistent with those from the physical modeling. The difference between a slot plug and a porous plug in industrial applications has been analyzed theoretically. The results show that it is more beneficial to use the slot plug to create strong stirring and to reach beneficial desulfurization condition nearby the open eye, and to use the porous plug for the inclusion removal.
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| 44. |
- Liu, Yu, et al.
(författare)
-
Physical and Numerical Modelling on the Mixing Condition in a 50 t Ladle
- 2019
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 9:11
-
Tidskriftsartikel (refereegranskat)abstract
- The bubbly flow and mixing conditions for gas stirring in a 50t ladle were investigated by using physical modelling and mathematical modelling. In the physical modelling, the effect of the porous plugs' configurations on the tracer homogenization was studied by using a saturated NaCl solution to predict the mixing time and a color dye to show the mixing pattern. In the mathematical modelling, the Euler-Lagrange model and species transport model were used to predict the flow pattern and tracer homogenization, respectively. The results show that, for a +/- 5% homogenization degree, the mixing time with dual plugs using a radial angle of 180 degrees is shortest. In addition, the mixing time using a radial angle of 135 degrees decreases the most with an increased flow rate. The flow pattern and mixing conditions predicted by mathematical modelling agree well with the result of the physical modelling. For a +/- 1% homogenization degree, the influence of the tracer's natural convection on its homogenization pattern cannot be neglected. This is especially true for a 'soft bubbling' case using a low gas flow rate. Overall, it is recommended that large radial angles in the range of 135 degrees 180 degrees are chosen for gas stirring in the present study when using dual porous plugs.
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| 45. |
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| 46. |
- Liu, Yu, 1990-
(författare)
-
Thermodynamics and Kinetics in Metallurgical Processes - with a Special Focus on Bubble Dynamics
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas stirring is commonly used in the steelmaking processes to reinforce chemical reactions, kinetic transfer, and inclusion removal, etc. This dissertation concentrates on multiphase flows with gas bubbling to study fluid dynamics and thermodynamics in metallurgical processes. A study of bubble behavior has been carried out using a multiscale approach as follows: Prototype scale (macro) → Plume scale → Single bubble scale → Reaction scale (micro).Initially, previous works on physical modeling and mathematical modeling in relation to the gas bubbling in the ladle have been reviewed. From that, several aspects that can be improved were found:For physical modeling, such as mixing and homogenization in ladles, the general empirical rules have not been analyzed sufficiently;The mathematical models focusing on inclusion behaviors at the steel-slag interface need to be improved;The phenomena governing the transfer of elements, vacuum degassing, and the combination of fluid dynamics and thermodynamics, such as in desulfurization, need to be investigated further.The kinetics transfer with regards to temperature and element homogenization is one of the most extensive research fields in steel metallurgy. For the analysis on prototype scale, the optimal plug configuration has been studied for a 50t ladle. For stirring using bottom-blowing, a separation angle between dual plugs of 160 degree is mostly recommended, and the optimal dual-plug radial position is around 0.65R. Moreover, the influence of the tracer’s natural convection on its homogenization pattern cannot be neglected, especially for ‘soft bubbling’ conditions using low gas flow rates.Subsequently, in studies of the statistical behavior of gas bubbling in the plume, mathematical modeling using an Euler-Euler approach and an Euler-Lagrange approach have been compared. With respect to the bubble coalescence and breakup, the Euler-Lagrange approach is more accurate in predicting the flow pattern for gas injection using a porous plug. With regards to the effect of plug design on the statistical behavior of gas bubbling, gas injection using a slot plug promotes kinetic reactions close to the open eye due to the concentrated plume structure, and gas bubbling using a porous plug promotes a good inclusion removal because of the increased amount of bubbles.Focusing on single bubble behavior, under the same flow rate, as the top gauge pressure is reduced, the bubble diameter increases and the bubble generation frequency decreases. During the bubble ascent, a large bubble gradually reaches stable conditions by means of shedding several small bubbles. In a steel-argon system, under a flow rate in the range of 5.0(mL‧min-1)STP to 2000(mL‧min-1)STP, the bubble diameter is in the range of 6.0mm to 20.0mm. Under laminar conditions, the maximum bubble width is 65mm when the surrounding pressure is 0.2bar, and the steady bubble width is around 58mm under a pressure of 2.0bar.Finally, a coupling method, named Multi-zone Reaction Model, has been developed to predict the conditions in the EAF refining process. Using a combined injection of O2 and argon, and the same injected mass of O2, the decarburization rate increases due to an efficient kinetic mass transfer of carbon in the molten steel. Furthermore, using CO2 to replace argon, as the ratio of the CO2 content in the injection increases, the maximum hot spot temperature, the increment rate of average temperature, and the decarburization rate decrease dramatically.The research step from multiphase fluid dynamics to its coupling with high temperature thermodynamics is a large advancement in this study. Moreover, the research process using open source software to replace the commercial software is also an important technical route. This can help the transparent development of future modules for reacting flow in metallurgical processes.
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| 47. |
- Lu, Yu-Chiao, et al.
(författare)
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Direct Reduction of Iron Ore Pellets by Using CO/CO2 and CO Gases
- 2023
-
Ingår i: Steel Research International. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 95:3
-
Tidskriftsartikel (refereegranskat)abstract
- Gas-based direct reduction in a shaft furnace is the dominant process in the world for production of direct reduced iron. As fresh reducing gas passes through the iron ore burden, it is diluted by the gas emitted from the reacted iron ores which decreases the reduction potential of the reducing gas. Previous reduction experiments mostly used single pellet which could not examine this phenomenon. In this study, hematite pellets arranged in multiple layers inside a molybdenum basket are reduced isothermally at 1173–1273 K using 50% CO + 50% CO2% and 100% CO gases under flow rates of 0.2–5.0 NL min−1 to simulate the dilution of CO by CO2 in the shaft. It is discovered that the reduction of pellets in the basket is highly uneven even in pure CO atmosphere. Pellets in the middle layer are reduced ≈2 times less than the pellets in the top and bottom layers. The top side of a pellet is also less reduced than the bottom side facing the gas inlet. During melting of incompletely reduced pellets at 1873 K, intensive interaction between the unreduced iron oxides and the alumina crucible was observed. Thus, smelting of incompletely reduced iron could potentially shorten the refractory lifetime.
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| 48. |
- Ni, Peiyuan
(författare)
-
A Study on Particle Motion and Deposition Rate : Application in Steel Flows
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-metallic inclusions in molten steel have received worldwide attention due to their serious influence on both the steel product quality and the steel production process. These inclusions may come from the de-oxidation process, the re-oxidation by air and/or slag due to an entrainment during steel transfer, and so on. The presence of some inclusion types can cause a termination of a casting process by clogging a nozzle. Thus, a good knowledge of the inclusion behavior and deposition rate in steel flows is really important to understand phenomena such as nozzle clogging. In this thesis, inclusion behaviors and deposition rates in steel flows were investigated by using mathematical simulations and validation by experiments.A ladle teeming process was simulated and Ce2O3 inclusion behavior during a teeming stage was studied. A Lagrangian method was used to track the inclusions in a steel flow and to compare the behaviors of inclusions of different sizes. In addition, a statistical analysis was conducted by the use of a stochastic turbulence model to investigate the behaviors of different-sized inclusions in different nozzle regions. The results show that inclusions with a diameter smaller than 20 μm were found to have similar trajectories and velocity distributions in the nozzle. The inertia force and buoyancy force were found to play an important role for the behavior of large-size inclusions or clusters. The statistical analysis results indicate that the region close to the connection region of the straight pipe and the expanding part of the nozzle seems to be very sensitive for an inclusion deposition.In order to know the deposition rate of non-metallic inclusions, an improved Eulerian particle deposition model was developed and subsequently used to predict the deposition rate of inclusions. It accounts for the differences in properties between air and liquid metals and considers Brownian and turbulent diffusion, turbophoresis and thermophoresis as transport mechanisms. A CFD model was firstly built up to obtain the friction velocity caused by a fluid flow. Then, the friction velocity was put into the deposition model to calculate the deposition rate.For the case of inclusion/particle deposition in vertical steel flows, effects on the deposition rate of parameters such as steel flow rate, particle diameter, particle density, wall roughness and temperature gradient near a wall were investigated. The results show that the steel flow rate/friction velocity has a very important influence on the rate of the deposition of large particles, for which turbophoresis is the main deposition mechanism. For small particles, both the wall roughness and thermophoresis have a significant influence on the particle deposition rate. The extended Eulerian model was thereafter used to predict the inclusion deposition rate in a submerged entry nozzle (SEN). Deposition rates of different-size inclusions in the SEN were obtained. The result shows that the steel flow is non-uniform in the SEN of the tundish. This leads to an uneven distribution of the inclusion deposition rates at different locations of the inner wall of the SEN. A large deposition rate was found to occur at the regions near the SEN inlet, the SEN bottom and the upper region of two SEN ports.For the case of an inclusion/particle deposition in horizontal straight channel flows, the deposition rates of particles at different locations of a horizontal straight pipe cross- section were found to be different due to the influence of gravity and buoyancy. For small particles with a small particle relaxation time, the gravity separation is important for their deposition behaviors at high and low parts of the horizontal pipe compared to the turbophoresis. For large particles with a large particle relaxation time, turbophoresis is the dominating deposition mechanism.
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| 49. |
- Ni, Peiyuan, 1987-, et al.
(författare)
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A study on the nonmetallic inclusion motions in a swirling flow submerged entry nozzle in a new cylindrical tundish design
- 2018
-
Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 49:2, s. 723-736
-
Tidskriftsartikel (refereegranskat)abstract
- Different sizes and shapes of nonmetallic inclusions in a swirling flow submerged entry nozzle (SEN) placed in a new tundish design were investigated by using a Lagrangian particle tracking scheme. The results show that inclusions in the current cylindrical tundish have difficulties remaining in the top tundish region, since a strong rotational steel flow exists in this region. This high rotational flow of 0.7 m/s provides the required momentum for the formation of a strong swirling flow inside the SEN. The results show that inclusions larger than 40 µm were found to deposit to a smaller extent on the SEN wall compared to smaller inclusions. The reason is that these large inclusions have Separation number values larger than 1. Thus, the swirling flow causes these large size inclusions to move toward the SEN center. For the nonspherical inclusions, large size inclusions were found to be deposited on the SEN wall to a larger extent, compared to spherical inclusions. More specifically, the difference of the deposited inclusion number is around 27 pct. Overall, it was found that the swirling flow contains three regions, namely, the isotropic core region, the anisotropic turbulence region and the near-wall region. Therefore, anisotropic turbulent fluctuations should be taken into account when the inclusion motion was tracked in this complex flow. In addition, many inclusions were found to deposit at the SEN inlet region. The plotted velocity distribution shows that the inlet flow is very chaotic. A high turbulent kinetic energy value of around 0.08 m2/s2 exists in this region, and a recirculating flow was also found here. These flow characteristics are harmful since they increase the inclusion transport toward the wall. Therefore, a new design of the SEN inlet should be developed in the future, with the aim to modify the inlet flow so that the inclusion deposition is reduced.
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| 50. |
- Ni, Peiyuan, et al.
(författare)
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Application of a swirling flow producer in a conventional tundish during continuous casting of steel
- 2017
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 57:12, s. 2175-2184
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Tidskriftsartikel (refereegranskat)abstract
- A swirling flow producer was designed for a conventional tundish in order to produce a swirling flow in the SEN driven by the steel flow potential. CFD simulations were carried out to investigate the flow phenomena in the new tundish system. The results show that a swirling flow in the tundish SEN was successfully obtained. The swirl number of the obtained steel flow inside the SEN can reach a value of 1.34, with a tangential velocity of around 2.8 m/s. The possibility of slag entrainment at the top of the tundish was estimated by analyzing the steel flow characteristics near the top surface. The calculated Weber Number is around 0.3 outside the cylinder, which indicates a low possibility of slag entrainment. A high value of shear stress was found on the SEN wall. This is due to the rotational steel flow in SEN. Also, non-metallic inclusions were tracked in the fully developed steel flow field. It was found that the number of inclusions that touch the top surface increases with an increased inclusion size. Small size inclusions mainly move into the cylinder from the left side of tangential inlet. Therefore, methods like installing a dam at the tundish bottom may be helpful to change the inclusion trajectories to move towards the top of the tundish.
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