Mirko Javurek | Johannes Kepler University Linz (original) (raw)

Papers by Mirko Javurek

Materials Today: Proceedings

steel research international, 2010

In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in t... more In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in the tundish outlet where the submerged entry nozzle (SEN) tube begins. The flow pattern inside the SEN plays an important role for the bubble formation at the argon injection nozzle at the stopper rod tip. High flow velocities are reached in the small gap between stopper rod and the surrounding SEN walls, and a flow separation has to be expected after the gap due to the fast expansion of the cross section. According to theoretical considerations and to the simulations, the absolute pressure in the gap becomes very low for liquid steel, which can cause cavitation-like effects. PIV-flow measurements in a 1:1 scaled water model of the caster show a highly oscillating and asymmetric flow pattern with rapidly changing separation regions. The low pressure effects expected in liquid steel cannot be investigated on the water-model due to the lower density of water. In numerical simulations of the water-model, the choice of the turbulence model and the usage or the non-usage of geometrical symmetries for the bound of the computational domain have a great impact on the resulting flow pattern and the accuracy of the predicted pressure drop. The results of various turbulence models are compared with results from measurements on a water-model. It turns out that only a 3D model using advanced turbulence models (SST k-v or Large Eddy) produce acceptable results, while 2D simulations completely fail and the standard turbulence models (e.g. k-e) significantly underestimate the pressure drop even in a 3D simulation.

International Journal of Cast Metals Research, 2009

ABSTRACT In continuous casting of steel, the slow solidification results in a flat increase of th... more ABSTRACT In continuous casting of steel, the slow solidification results in a flat increase of the solidified shell thickness. Thus, the liquid core reaches up to 20 m into the strand. In most of the numerical flow simulations of continuous steel casting, the solidification process and its influence on the flow are completely neglected. Furthermore, only the upper part of the liquid core is simulated, which requires the introduction of an unphysical boundary condition at the lower bound of the simulated domain. On the other hand, the flow of the liquid steel in numerical solidification simulations is often not considered because of the complexity of solidification models. In this paper, a model that considers the shape of the solidification front in the flow simulation as well as the loss of material through the solidification front is presented. Therefore, the shell thickness has to be known a priori from theoretical or empirical results. Thus it is possible to model a great part of the liquid core inside the strand with respect to inclusion behaviour and variations of the solidified shell thickness due to the flow. Applications to intermediate, thick and thin slab casters as well as round bloom casters will be described.

BHM Berg- und Hüttenmännische Monatshefte, 2008

... Ing. Klaus Forstner, Dr. Mirko Javurek, Dr. Stefan Pirker, alle: Institut für Strömungsleh-re... more ... Ing. Klaus Forstner, Dr. Mirko Javurek, Dr. Stefan Pirker, alle: Institut für Strömungsleh-re und Wärmeübertragung, JKU Linz, Altenberger Straße 69, 4040 Linz / Österreich. ... In dieser Studie wird κ so gewählt, dass der globale Reaktionsumsatz mit Mes-sungen übereinstimmt. ...

steel research international, 2014

ABSTRACT In the continuous casting of steel, the control of the flow to the mould is a critical i... more ABSTRACT In the continuous casting of steel, the control of the flow to the mould is a critical issue as a constant mould level is essential for a good quality of the cast product. A stopper rod is a commonly used device to control the flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (clogging). The mechanisms involved in clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross-section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the refractory material. In this paper the criteria for degassing of liquid steel at low pressures are analyzed and compared with water. A mathematical model for a two phase flow situation (liquid steel/gas) in the SEN that links the pressure distribution and the throughput with the geometrical parameters, the amount of gas in the SEN and the pressure loss coefficient at the stopper rod is presented. An explanation theory for the diminishing influence of the gas injection on clogging is outlined.

CFD simulations of ventilation and dedusting systems in melting shops with an electric arc furnac... more CFD simulations of ventilation and dedusting systems in melting shops with an electric arc furnace are presented. The models include free and forced convection, multiphase flow and complex geometry. Special emphasize is given to the modelling of the dust phase: An Euler-Lagrangian discrete random walk approach, the stochastic transport of particles (STP) model and an algebraic drift flux model are briefly reviewed and applied in simulation. While application of the STP-model was unsuccessful, both the Euler-Lagrange approach and the drift flux model perform well, with the drift flux model being more computationally efficient. Studies on the influence of blower (ID fan) power and the effect of turbulence modelling (standard and RNG k-ε model) on dust dispersion are included. The numerical studies resulted in the optimization of blower power together with the crane/trolley arrangement and the canopy hood design. NOMENCLATURE cp specific heat capacity Dp particle diameter Gr Grashof nu...

Steel Research International, 2020

The injection of gas at the stopper rod tip in continuous casting of steel slabs is a common prac... more The injection of gas at the stopper rod tip in continuous casting of steel slabs is a common practice to prevent clogging and to control the produced steel quality. The injected gas forms bubbles and is transported by the liquid steel through the submerged entry nozzle in the mould region of the strand (Figure 1). Most of the gas bubbles rise to the mold surface and leave the liquid steel there. In a resting liquid, single gas bubbles start rising due to their buoyancy and reach quickly the terminal rising velocity where the buoyancy force and drag force are in equilibrium. Basically, the terminal rising velocity is higher for larger bubbles. Drag forces and resulting terminal rising velocities for bubbles in liquid have been intensively investigated for air bubbles in water, but also for bubbles in liquid metals, as shown in Figure 2a. The unstable shape of bubbles in contrast to rigid spheres causes a saturation-like effect as the terminal rising velocity is only slightly increasi...

steel research international, 2010

In a comparative benchmark, nine participants of the German Steel Institute VDEh working group ''... more In a comparative benchmark, nine participants of the German Steel Institute VDEh working group ''Fluid Mechanics and Fluid Simulation'' studied the melt flow in a 16-t single-strand tundish. Starting with a steady-state simulation of the melt flow, the transient flow behaviour was simulated for an idealized ladle change involving a sudden jump in temperature and concentration. In addition, the separation of non-metallic particles to the melt surface was examined. No guidelines and limitations were made regarding the simulation strategy. The predicted flow profiles, temperature and concentration distributions coincide with each other within a good approximation. Systematic differences in the transient temperature and turbulence fields are explained by the selection of the boundary condition at the free surface. All CFD programs reproduce the fundamental flow structure with a good degree of accuracy. The separation rate for non-metallic particles calculated on the basis of the Lagrange Method are greater than would be expected according to theory and measurement results obtained on the water model.

steel research international, Mar 24, 2020

IOP Conference Series: Materials Science and Engineering

View the article online for updates and enhancements. Related content Harmonic mode-locking and s... more View the article online for updates and enhancements. Related content Harmonic mode-locking and sub-round-trip time nonlinear dynamics of electrooptically controlled solid state laser M V Gorbunkov, Yu Ya Maslova, V A Petukhov et al.

steel research international

steel research international

steel research international

IOP Conference Series: Materials Science and Engineering, 2016

ABSTRACT In the continuous casting of steel controlling the flow rate to the mould is a critical ... more ABSTRACT In the continuous casting of steel controlling the flow rate to the mould is a critical issue as a constant mould level is essential for a good quality of the cast product. A stopper rod is a commonly used device to control this flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (“clogging”). The mechanisms involved in clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the refractory material. In the first part of this paper the criteria for degassing of liquid steel at low pressures are analysed and compared to water. It can be shown that the degassing process in liquid steel is mainly taking place directly at the stopper rod and its surrounding. The steel flow past the stopper is highly turbulent. In addition refractory material in general is non wetting to liquid steel. So the first step to understand the flow situation near the stopper is to understand the behaviour of this two phase flow. Accordingly water experiments are conducted using a convergent divergent nozzle. These experiments show the strong impact of the wettability of the wall material on the actual flow structure.

tm - Technisches Messen, 2016

A transient surface heating or cooling process of a solid is considered. A procedure for the dete... more A transient surface heating or cooling process of a solid is considered. A procedure for the determination of surface temperature and surface heat flux density during such a process is presented using a submersed temperature sensor in the solid. From this measured temperature the surface temperature and surface heat flux density are calculated by inverse process modelling. This method is prone to errors since measurement errors are amplified in the inverse process modelling and can thus easily become unacceptably large. The LSQR regularisation algorithm is optimised for fast performance as well as less memory requirement and applied to the inverse problem solution. The proposed method allows to simulate an experimental setup and to determine the accuracy of the results gained from the simulated experiment. This is essential for the determination of the accuracy of a planned or existing test facility. The influence of process parameters like sensor depth, sensor noise level, sampling...

tm - Technisches Messen, 2016

ZusammenfassungBei hohen Temperaturgradienten in einem Festkörper ist die exakte Kenntnis der Mes... more ZusammenfassungBei hohen Temperaturgradienten in einem Festkörper ist die exakte Kenntnis der Messposition selbst innerhalb der Perle eines Thermoelements wichtig. Anhand einer numerischen thermoelektrischen Simulation wird gezeigt, wie die thermoelektrischen Effekte im Thermoelement im Detail zusammenwirken, und wo sich die daraus resultierende Messposition innerhalb des Thermoelements befindet.

steel research international, 2005

Materials Today: Proceedings

steel research international, 2010

In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in t... more In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in the tundish outlet where the submerged entry nozzle (SEN) tube begins. The flow pattern inside the SEN plays an important role for the bubble formation at the argon injection nozzle at the stopper rod tip. High flow velocities are reached in the small gap between stopper rod and the surrounding SEN walls, and a flow separation has to be expected after the gap due to the fast expansion of the cross section. According to theoretical considerations and to the simulations, the absolute pressure in the gap becomes very low for liquid steel, which can cause cavitation-like effects. PIV-flow measurements in a 1:1 scaled water model of the caster show a highly oscillating and asymmetric flow pattern with rapidly changing separation regions. The low pressure effects expected in liquid steel cannot be investigated on the water-model due to the lower density of water. In numerical simulations of the water-model, the choice of the turbulence model and the usage or the non-usage of geometrical symmetries for the bound of the computational domain have a great impact on the resulting flow pattern and the accuracy of the predicted pressure drop. The results of various turbulence models are compared with results from measurements on a water-model. It turns out that only a 3D model using advanced turbulence models (SST k-v or Large Eddy) produce acceptable results, while 2D simulations completely fail and the standard turbulence models (e.g. k-e) significantly underestimate the pressure drop even in a 3D simulation.

International Journal of Cast Metals Research, 2009

ABSTRACT In continuous casting of steel, the slow solidification results in a flat increase of th... more ABSTRACT In continuous casting of steel, the slow solidification results in a flat increase of the solidified shell thickness. Thus, the liquid core reaches up to 20 m into the strand. In most of the numerical flow simulations of continuous steel casting, the solidification process and its influence on the flow are completely neglected. Furthermore, only the upper part of the liquid core is simulated, which requires the introduction of an unphysical boundary condition at the lower bound of the simulated domain. On the other hand, the flow of the liquid steel in numerical solidification simulations is often not considered because of the complexity of solidification models. In this paper, a model that considers the shape of the solidification front in the flow simulation as well as the loss of material through the solidification front is presented. Therefore, the shell thickness has to be known a priori from theoretical or empirical results. Thus it is possible to model a great part of the liquid core inside the strand with respect to inclusion behaviour and variations of the solidified shell thickness due to the flow. Applications to intermediate, thick and thin slab casters as well as round bloom casters will be described.

BHM Berg- und Hüttenmännische Monatshefte, 2008

... Ing. Klaus Forstner, Dr. Mirko Javurek, Dr. Stefan Pirker, alle: Institut für Strömungsleh-re... more ... Ing. Klaus Forstner, Dr. Mirko Javurek, Dr. Stefan Pirker, alle: Institut für Strömungsleh-re und Wärmeübertragung, JKU Linz, Altenberger Straße 69, 4040 Linz / Österreich. ... In dieser Studie wird κ so gewählt, dass der globale Reaktionsumsatz mit Mes-sungen übereinstimmt. ...

steel research international, 2014

ABSTRACT In the continuous casting of steel, the control of the flow to the mould is a critical i... more ABSTRACT In the continuous casting of steel, the control of the flow to the mould is a critical issue as a constant mould level is essential for a good quality of the cast product. A stopper rod is a commonly used device to control the flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (clogging). The mechanisms involved in clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross-section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the refractory material. In this paper the criteria for degassing of liquid steel at low pressures are analyzed and compared with water. A mathematical model for a two phase flow situation (liquid steel/gas) in the SEN that links the pressure distribution and the throughput with the geometrical parameters, the amount of gas in the SEN and the pressure loss coefficient at the stopper rod is presented. An explanation theory for the diminishing influence of the gas injection on clogging is outlined.

CFD simulations of ventilation and dedusting systems in melting shops with an electric arc furnac... more CFD simulations of ventilation and dedusting systems in melting shops with an electric arc furnace are presented. The models include free and forced convection, multiphase flow and complex geometry. Special emphasize is given to the modelling of the dust phase: An Euler-Lagrangian discrete random walk approach, the stochastic transport of particles (STP) model and an algebraic drift flux model are briefly reviewed and applied in simulation. While application of the STP-model was unsuccessful, both the Euler-Lagrange approach and the drift flux model perform well, with the drift flux model being more computationally efficient. Studies on the influence of blower (ID fan) power and the effect of turbulence modelling (standard and RNG k-ε model) on dust dispersion are included. The numerical studies resulted in the optimization of blower power together with the crane/trolley arrangement and the canopy hood design. NOMENCLATURE cp specific heat capacity Dp particle diameter Gr Grashof nu...

Steel Research International, 2020

The injection of gas at the stopper rod tip in continuous casting of steel slabs is a common prac... more The injection of gas at the stopper rod tip in continuous casting of steel slabs is a common practice to prevent clogging and to control the produced steel quality. The injected gas forms bubbles and is transported by the liquid steel through the submerged entry nozzle in the mould region of the strand (Figure 1). Most of the gas bubbles rise to the mold surface and leave the liquid steel there. In a resting liquid, single gas bubbles start rising due to their buoyancy and reach quickly the terminal rising velocity where the buoyancy force and drag force are in equilibrium. Basically, the terminal rising velocity is higher for larger bubbles. Drag forces and resulting terminal rising velocities for bubbles in liquid have been intensively investigated for air bubbles in water, but also for bubbles in liquid metals, as shown in Figure 2a. The unstable shape of bubbles in contrast to rigid spheres causes a saturation-like effect as the terminal rising velocity is only slightly increasi...

steel research international, 2010

In a comparative benchmark, nine participants of the German Steel Institute VDEh working group ''... more In a comparative benchmark, nine participants of the German Steel Institute VDEh working group ''Fluid Mechanics and Fluid Simulation'' studied the melt flow in a 16-t single-strand tundish. Starting with a steady-state simulation of the melt flow, the transient flow behaviour was simulated for an idealized ladle change involving a sudden jump in temperature and concentration. In addition, the separation of non-metallic particles to the melt surface was examined. No guidelines and limitations were made regarding the simulation strategy. The predicted flow profiles, temperature and concentration distributions coincide with each other within a good approximation. Systematic differences in the transient temperature and turbulence fields are explained by the selection of the boundary condition at the free surface. All CFD programs reproduce the fundamental flow structure with a good degree of accuracy. The separation rate for non-metallic particles calculated on the basis of the Lagrange Method are greater than would be expected according to theory and measurement results obtained on the water model.

steel research international, Mar 24, 2020

IOP Conference Series: Materials Science and Engineering

View the article online for updates and enhancements. Related content Harmonic mode-locking and s... more View the article online for updates and enhancements. Related content Harmonic mode-locking and sub-round-trip time nonlinear dynamics of electrooptically controlled solid state laser M V Gorbunkov, Yu Ya Maslova, V A Petukhov et al.

steel research international

steel research international

steel research international

IOP Conference Series: Materials Science and Engineering, 2016

ABSTRACT In the continuous casting of steel controlling the flow rate to the mould is a critical ... more ABSTRACT In the continuous casting of steel controlling the flow rate to the mould is a critical issue as a constant mould level is essential for a good quality of the cast product. A stopper rod is a commonly used device to control this flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (“clogging”). The mechanisms involved in clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the refractory material. In the first part of this paper the criteria for degassing of liquid steel at low pressures are analysed and compared to water. It can be shown that the degassing process in liquid steel is mainly taking place directly at the stopper rod and its surrounding. The steel flow past the stopper is highly turbulent. In addition refractory material in general is non wetting to liquid steel. So the first step to understand the flow situation near the stopper is to understand the behaviour of this two phase flow. Accordingly water experiments are conducted using a convergent divergent nozzle. These experiments show the strong impact of the wettability of the wall material on the actual flow structure.

tm - Technisches Messen, 2016

A transient surface heating or cooling process of a solid is considered. A procedure for the dete... more A transient surface heating or cooling process of a solid is considered. A procedure for the determination of surface temperature and surface heat flux density during such a process is presented using a submersed temperature sensor in the solid. From this measured temperature the surface temperature and surface heat flux density are calculated by inverse process modelling. This method is prone to errors since measurement errors are amplified in the inverse process modelling and can thus easily become unacceptably large. The LSQR regularisation algorithm is optimised for fast performance as well as less memory requirement and applied to the inverse problem solution. The proposed method allows to simulate an experimental setup and to determine the accuracy of the results gained from the simulated experiment. This is essential for the determination of the accuracy of a planned or existing test facility. The influence of process parameters like sensor depth, sensor noise level, sampling...

tm - Technisches Messen, 2016

ZusammenfassungBei hohen Temperaturgradienten in einem Festkörper ist die exakte Kenntnis der Mes... more ZusammenfassungBei hohen Temperaturgradienten in einem Festkörper ist die exakte Kenntnis der Messposition selbst innerhalb der Perle eines Thermoelements wichtig. Anhand einer numerischen thermoelektrischen Simulation wird gezeigt, wie die thermoelektrischen Effekte im Thermoelement im Detail zusammenwirken, und wo sich die daraus resultierende Messposition innerhalb des Thermoelements befindet.

steel research international, 2005