Electroslag remelting (ESR) is a well‐known process widely used in the production chain of high‐q... more Electroslag remelting (ESR) is a well‐known process widely used in the production chain of high‐quality alloys. Herein, numerical investigations of the implementation of a rotating‐electrode (low rotation speed) modification to the flow behavior inside the slag area of a lab‐sized ESR process are shown. Therefore, a coupled simulation approach between a commercial CFD (FVM) and electromagnetics (FEM) software is used. Comparative results for the simulated droplet formation between a stationary and a rotating electrode are shown. The results show a strong effect on the local shaping of the liquid metal film below the electrode and consequently a radial shift of the droplet incidence into the metal pool under electrode rotation. There are no observable positive effects on mean metal film thickness, droplet trajectory, or droplet size, which are suspected as possible explanations for observed material improvements in small‐scale rotating electrode ESR processes. In addition, an overview of current bottlenecks, restrictions, and possible strategies for improved ESR process simulations is given.
Abstract Detailed knowledge about gas-liquid multiphase flows is important to optimize industrial... more Abstract Detailed knowledge about gas-liquid multiphase flows is important to optimize industrial systems. Imaging with image processing is the most commonly used measurement technique. However, the workflow and parameters strongly depend on the experimental conditions and no generally applicable process has been developed yet. Here, a workflow based on convolutional neural networks (CNN) is proposed that can be used with a wider range of experimental conditions. The method, named BubCNN, employs a Faster region-based CNN (RCNN) detector to locate bubbles and a shape regression CNN to predict bubble shape parameters. Hyperparameters and network architectures for both modules were systematically analyzed. BubCNN achieved accurate results for different experimental conditions. A pretrained program was made publicly available on GitHub. Since the whole variety of bubble images was not yet captured in the training data set, an additional semi-automatic transfer learning module is provided that allows to customize BubCNN for different images.
In numerical computation of ladle metallurgy, multiphase models are essential. Still, these model... more In numerical computation of ladle metallurgy, multiphase models are essential. Still, these models are afflicted with great uncertainty, making a validation with experimental data mandatory. Validation experiments distinguish fundamentally from deterministic experiments because emphasis is on a complete documentation of all boundary conditions and a detailed uncertainty assessment. For this work, the experimental design for a comprehensive accuracy assessment of numerical models and reported quantities were jointly determined with international numerical experts. The framework comprises a plume analysis and flow measurements in the single- and multiphase region in a water model with defined conditions. All influencing factors are extensively documented and their contribution to the overall data uncertainty is quantified. Detailed data is made publicly available in a validation benchmark database for the isothermal multiphase flow in the ladle. A first draft of a standardized validat...
To account for increasing economic and ecological pressure, the steel industry is obligated to co... more To account for increasing economic and ecological pressure, the steel industry is obligated to continuously optimize all processes. An important optimization approach is numerical modeling although its potential is limited by the accuracy of the mathematical models. In a previous work, a validation database was created and a validation score was derived from this data which allows a comprehensive qualitative accuracy assessment for those models. Here, this system is employed for a systematic optimization of the isothermal flow in the casting ladle. For that, different submodels, namely the turbulence models, subgrid turbulence models, bubble-induced turbulence and interfacial closure models as well as influencing factors, such as the grid resolution or the initial bubble size, are analyzed. It is shown that the large eddy turbulence model is more accurate than the Reynolds-average approach because it is able to reproduce the anisotropy of turbulence in the bubble region. In accordan...
The meaning of numerical simulations of metallurgical reactors has increased during the last year... more The meaning of numerical simulations of metallurgical reactors has increased during the last years. The simulations offer detailed information about the process and new insights into regions, which are typical difficult to examine. For the simulated remelting processes, the growth direction of the dendrites is most important. The correlation between liquidus isothermal and growth direction allows the comparison to metallurgical samples produced in the real process. The validation of numerical simulations concerning measurable target values is indispensable for the expressiveness of the model. For the comparison of the dendrite growth direction, it is necessary to investigate the microstructure of the whole ingot diameter. An in-house development, the “macroscopic texture examination”, allows scanning huge metallurgical samples including the evaluation up to secondary dendrite arm spacings. The technic is based on a high-resolution reflex camera with a macro lens mounted on a travers...
The modelling of solidification processes in combination with fluid flow is one main application ... more The modelling of solidification processes in combination with fluid flow is one main application of ANSYS Fluent. The solidification is modelled with the enthalpy porosity technique. Therefor the fluid flow is damped like a flow through a porous media of dendrites. In case of materials with large solidification ranges, like the nickel based superalloy 718, the adjustment possibilities of ANSYS Fluent are often not adequate. The program postulates a linear dependency between liquid fraction and temperature. To improve the simulation, the solidification was implemented by a user defined function (UDF). The principal modelling of fluid flow is based on the theory of ANSYS Fluent, but it is now possible to adjust the liquid fraction in fine temperature steps.
In numerical computation of ladle metallurgy, multiphase models are essential. Still, these model... more In numerical computation of ladle metallurgy, multiphase models are essential. Still, these models are afflicted with great uncertainty, making a validation with experimental data mandatory. Validation experiments fundamentally differ from physical modeling experiments because emphasis is on a complete documentation of all boundary conditions and a detailed uncertainty assessment. For this work, the experimental design for a comprehensive accuracy assessment of numerical models and reported quantities were jointly determined with international numerical experts. The framework comprises a plume analysis and flow measurements in the single- and multiphase regions of a water model with defined conditions. All influencing factors are documented extensively and their contribution to the overall data uncertainty is quantified. Detailed data are made publicly available within a validation benchmark database for isothermal multiphase flow in metallurgical ladles. A first draft of a standard...
Electroslag remelting (ESR) is a well‐known process widely used in the production chain of high‐q... more Electroslag remelting (ESR) is a well‐known process widely used in the production chain of high‐quality alloys. Herein, numerical investigations of the implementation of a rotating‐electrode (low rotation speed) modification to the flow behavior inside the slag area of a lab‐sized ESR process are shown. Therefore, a coupled simulation approach between a commercial CFD (FVM) and electromagnetics (FEM) software is used. Comparative results for the simulated droplet formation between a stationary and a rotating electrode are shown. The results show a strong effect on the local shaping of the liquid metal film below the electrode and consequently a radial shift of the droplet incidence into the metal pool under electrode rotation. There are no observable positive effects on mean metal film thickness, droplet trajectory, or droplet size, which are suspected as possible explanations for observed material improvements in small‐scale rotating electrode ESR processes. In addition, an overview of current bottlenecks, restrictions, and possible strategies for improved ESR process simulations is given.
Abstract Detailed knowledge about gas-liquid multiphase flows is important to optimize industrial... more Abstract Detailed knowledge about gas-liquid multiphase flows is important to optimize industrial systems. Imaging with image processing is the most commonly used measurement technique. However, the workflow and parameters strongly depend on the experimental conditions and no generally applicable process has been developed yet. Here, a workflow based on convolutional neural networks (CNN) is proposed that can be used with a wider range of experimental conditions. The method, named BubCNN, employs a Faster region-based CNN (RCNN) detector to locate bubbles and a shape regression CNN to predict bubble shape parameters. Hyperparameters and network architectures for both modules were systematically analyzed. BubCNN achieved accurate results for different experimental conditions. A pretrained program was made publicly available on GitHub. Since the whole variety of bubble images was not yet captured in the training data set, an additional semi-automatic transfer learning module is provided that allows to customize BubCNN for different images.
In numerical computation of ladle metallurgy, multiphase models are essential. Still, these model... more In numerical computation of ladle metallurgy, multiphase models are essential. Still, these models are afflicted with great uncertainty, making a validation with experimental data mandatory. Validation experiments distinguish fundamentally from deterministic experiments because emphasis is on a complete documentation of all boundary conditions and a detailed uncertainty assessment. For this work, the experimental design for a comprehensive accuracy assessment of numerical models and reported quantities were jointly determined with international numerical experts. The framework comprises a plume analysis and flow measurements in the single- and multiphase region in a water model with defined conditions. All influencing factors are extensively documented and their contribution to the overall data uncertainty is quantified. Detailed data is made publicly available in a validation benchmark database for the isothermal multiphase flow in the ladle. A first draft of a standardized validat...
To account for increasing economic and ecological pressure, the steel industry is obligated to co... more To account for increasing economic and ecological pressure, the steel industry is obligated to continuously optimize all processes. An important optimization approach is numerical modeling although its potential is limited by the accuracy of the mathematical models. In a previous work, a validation database was created and a validation score was derived from this data which allows a comprehensive qualitative accuracy assessment for those models. Here, this system is employed for a systematic optimization of the isothermal flow in the casting ladle. For that, different submodels, namely the turbulence models, subgrid turbulence models, bubble-induced turbulence and interfacial closure models as well as influencing factors, such as the grid resolution or the initial bubble size, are analyzed. It is shown that the large eddy turbulence model is more accurate than the Reynolds-average approach because it is able to reproduce the anisotropy of turbulence in the bubble region. In accordan...
The meaning of numerical simulations of metallurgical reactors has increased during the last year... more The meaning of numerical simulations of metallurgical reactors has increased during the last years. The simulations offer detailed information about the process and new insights into regions, which are typical difficult to examine. For the simulated remelting processes, the growth direction of the dendrites is most important. The correlation between liquidus isothermal and growth direction allows the comparison to metallurgical samples produced in the real process. The validation of numerical simulations concerning measurable target values is indispensable for the expressiveness of the model. For the comparison of the dendrite growth direction, it is necessary to investigate the microstructure of the whole ingot diameter. An in-house development, the “macroscopic texture examination”, allows scanning huge metallurgical samples including the evaluation up to secondary dendrite arm spacings. The technic is based on a high-resolution reflex camera with a macro lens mounted on a travers...
The modelling of solidification processes in combination with fluid flow is one main application ... more The modelling of solidification processes in combination with fluid flow is one main application of ANSYS Fluent. The solidification is modelled with the enthalpy porosity technique. Therefor the fluid flow is damped like a flow through a porous media of dendrites. In case of materials with large solidification ranges, like the nickel based superalloy 718, the adjustment possibilities of ANSYS Fluent are often not adequate. The program postulates a linear dependency between liquid fraction and temperature. To improve the simulation, the solidification was implemented by a user defined function (UDF). The principal modelling of fluid flow is based on the theory of ANSYS Fluent, but it is now possible to adjust the liquid fraction in fine temperature steps.
In numerical computation of ladle metallurgy, multiphase models are essential. Still, these model... more In numerical computation of ladle metallurgy, multiphase models are essential. Still, these models are afflicted with great uncertainty, making a validation with experimental data mandatory. Validation experiments fundamentally differ from physical modeling experiments because emphasis is on a complete documentation of all boundary conditions and a detailed uncertainty assessment. For this work, the experimental design for a comprehensive accuracy assessment of numerical models and reported quantities were jointly determined with international numerical experts. The framework comprises a plume analysis and flow measurements in the single- and multiphase regions of a water model with defined conditions. All influencing factors are documented extensively and their contribution to the overall data uncertainty is quantified. Detailed data are made publicly available within a validation benchmark database for isothermal multiphase flow in metallurgical ladles. A first draft of a standard...
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