Refractory metals based on niobium are progressively attracting interest in the industrial world for the production of components used in high-temperature environments. With superior thermal and mechanical properties compared to those of nickel-based superalloys, NbSi composites represent a promising alterative for the fabrication of turbine components, and they open a way to the further increase of their efficiency. But the melting process of such refractories still faces relevant technical limitations related to their high melting point, chemical reactivity and poor homogenization of the alloy. For these reasons, numerical simulations play a fundamental role in detailed analysis of their melting process. With the help of multiphysical simulations and the particle tracing method, the addition of targeted metals into the NbSi base is investigated and optimized.

Controlling the melt flow and free surface motion is crucial to maintain stability of many metallurgical processes. In the direct strip casting process, a known problem is the back-flow of liquid metal into the small gap between the moving belt and the refractory. Apart from geometrical and feeding modifications reported in the literature to reduce the back-flow, electromagnetic technologies could potentially solve this issue. We investigate numerically the application of AC magnetic field to deflect the melt from the back-flow area. Simulations show that it is possible to completely prevent the back-flow but at the expense of introducing oscillations in the shape of the cast solid sheet downstream. Combination of AC field for back-flow prevention with static (DC) magnetic field for free surface stabilization downstream can provide a fully stable casting process.

The necessity to process chemically reactive metals makes the cold wall crucible an attractive alternative to conventional furnaces, even for materials with a melting point of 2500oC and higher. A significant research work in this field is though missing. In this paper, steps conducing to melting high-melting temperature metals (niobium, in this case) by electromagnetic induction are described. Multiphysical numerical simulations were successfully validated for aluminium and titanium-aluminium alloy. In the case of niobium, authors evidence some differences between numerical and experimental results, and limits of the induction melting setup are examined for future improvements. Tables 1, Figs 7, Refs 11.

The article describes a numerical model of solidification of the SnPb alloy with electromagnetic stirring. The model is based on two open access computational codes. Comparison of the results of the calculation of directional horizontal solidification with natural and electromagnetically forced convection forces is presented. It is shown that the electromagnetic driven flow can affect the final segregation map only at the first stage of the solidification process.

Dynamics of the liquid metal free surface is an important aspect in many different metallurgical processes, such as cold crucible melting and continuous casting. An AC magnetic field can be used to change the shape of the liquid metal volume. Here, we study experimentally and numerically a rectangular liquid metal layer exposed to a transverse AC magnetic field. Depending on different parameters, such as the layer thickness and the surface oxidation, different free surface shapes and their dynamics are observed experimentally. We have simulated this fundamentally three-dimensional process using the coupled open-source software. Based on experimental observations, surface oxidation in the numerical model is approximated as a modified contact angle between the liquid metal and the vessel's walls. The numerical results agree well with experiments.

In this paper, the authors present the results of software verification for solving magnetohydrodynamic problem in duct exposed to constant magnetic fields. The proposed approach uses the following open source software: OpenFOAM for solving problems of continuum mechanics using the finite volume method, Elmer for solving magnetic field distribution based on the finite element method, and EOF-library for data exchange between these two programs. The verification results were demonstrated by fluid flow in a square duct exposed to constant uniform spanwise magnetic field. The research was carried out with a laminar fluid flow, which makes it similar to the Hartmann's problem. The existing experience of calculating such problems, their verification and application were discussed. The paper provides a brief mathematical description of the proposed solution and basic procedures for implementing the code proposed by the authors. At the first stage of verification, the comparison of fluid velocity distribution results at Hartmann’s numbers equal to 1, 10, 20 and 50 was demonstrated. These results were obtained by means of proposed software, an analytical solution, and a test problem provided by OpenFOAM developers for two-dimensional case. At the second stage of software verification, sufficient convergence of the results was shown for fluid velocity distribution in the three-dimensional case of the Hartmann’s problem compared with the OpenFOAM test problem data and the results obtained by Comsol Multiphisics and ANSYS. As a result, distributions of the fluid flow velocity between Hartmann’s walls were obtained for various study cases: a two-dimensional problem, a three-dimensional problem with electrically insulated walls, and a three-dimensional problem with walls having infinite electrical conductivity. The last stage of the study corresponds to assessing of software performance in comparison with the built-in OpenFOAM solver and commercial software Comsol Multiphysics and ANSYS. It was found that the proposed approach takes more time to calculate these problems than the built-in OpenFOAM solver, but less than Comsol. However, the problem formulation in EOF-library allows solving problems with complex geometry, which is not available in the built-in OpenFOAM solver. In conclusion, analysis of computation performance with parallelization was carried out. It showed significant reducing of computation time with the help of EOF-library in comparison with the commercial software Comsol and ANSYS .

The use of hydrogen as an alternative energy offers many applications, they can be found in vehicle technology for fuel cells or as a reducing agent. Classical production methods like steam reforming generate carbon dioxide as a byproduct. In the proposed method, hydrogen is produced CO2 free by thermal decomposition of methane. To realize the production, methane is injected into a reactor that is filled with liquid tin. Inside the melt, methane bubbles react with carbon and hydrogen. To optimize the reaction, different parameters for influencing the bubble flow are discussed. The focus is set on the electromagnetic stirring of bubbles. A solving method is developed to simulate this effect and will be demonstrated in parameter studies. To get a detailed view on the produced hydrogen, also a chemical calculation method is developed that can be coupled with the electromagnetic solver and allows a validation of the model considered in this article.

We study liquid metal free surface deformation in an electrically induced vortical flow system, both numerically and experimentally. A 50 Hz current is applied between a small bottom electrode at the center and a conducting cylindrical side wall, and consequently an upward fluid jet is driven causing a notable free surface deformation. The surface jet height measurements at relatively low currents are in good agreement with the axisymmetric numerical model. Increasing injected current leads to melt swirling and free surface sloshing, which cannot be modelled in an axisymmetric approximation. 3D simulations have revealed the melt rotation and surface instabilities.

This article is dealing with a research on high frequency longitudinal induction welding of cladded pipes with use of simultaneous double frequency. Solutions are proposed to reach the required temperature distribution at the welding edge for the cladding composite of S355 and Alloy 625 with single and simultaneous double frequency. An advanced consideration of magnetic and other material properties was performed to simulate the dominating physical effects of high frequency (HF) welding. The background of use and advantages of simultaneous double frequency are presented. In the context of the research, a correlation for welding speed, frequency and temperature distribution with industrial relevance was found for the cladded pipe welding.

In this paper, a dripand leakage-free approach for electromagnetic (EM) levitation melting of metallic samples in horizontal and orthogonal two-frequency fields is studied further. The developed numerical model is used to investigate instabilities of liquid metal shape excited by the interaction of two-frequency EM fields and to design a scaled-up experimental setup for a stable levitation melting of 500 g of aluminum for further validation of the method.

In this work, we study electrically induced flows numerically using open-source software and experimentally. Two systems are considered - single and multiphase (free surface) flows driven by axisymmetric DC and AC current injection. We investigate characteristic velocity and free surface deformation dependence on the injected current and validate it with experimental data. Results show that maximum axial velocity is a linear function of injected current, but free surface deformations are approximately proportional to current squared.

The paper describes the results of an experimental research, demonstrating and explaining the effect of grain fragmentation, caused by pulsed resonant electromagnetic stirring. In the experiments, 6082 aluminium alloy melt was directionally solidified under the influence of continuous (AMF) and pulsed application (PMF) of an alternating magnetic field. The frequency of applied PMF was in accordance to the low-frequency circulation of the melt, causing the resonant increase of a pulsed component of the melt velocity. The structure of electromagnetically stirred specimens was compared to those, solidified without a magnetic field. A strong fragmentation effect (decrease of an average grain size on 51%, comparing with the solidification in natural conditions) for the case of resonant EM stirring was stated. Further, to analyse the influence of the flow, appearing due to the resonant stirring, we observed the formation of solid/liquid interface and a macro-crystalloid structure during solidification of continuously and pulsed stirred melt by applying the novel method of neutron radiography. The results confirmed the strong influence of the pulsed component of velocity on thermal conditions during solidification and, consequently, the metal structure.

This article contains findings of simulation research on longitudinal induction welding of cladded pipes with use of simultaneous double frequency. Solutions are proposed to reach the required temperature distribution at the welding edge for the cladding composite of S355 and Alloy 625 with single and simultaneous double frequency. An advanced consideration of magnetic and other material properties was performed to simulate the dominating physical effects of high frequency (HF) welding. The background of use and advantages of simultaneous double frequency are presented. In the context of the research, a correlation for welding speed, frequency and temperature distribution with industrial relevance was found for the cladded pipe welding.

In this work, we study liquid gallium stirring by rotating permanent magnets. We demonstrate possibility of easily creating different flow patterns by rotating permanent magnets, which can be industrially important for controlling heat and mass transfer processes in the system. Unlike the typical approach of simulating magnet rotation as a transient problem and time-averaging the Lorentz forces, we solve the magnet rotation as a harmonic (frequency domain) problem, which leads to forces equal to time-averaged ones and decreases the simulation time considerably. Numerical results are validated using qualitative flow structure results from the neutron radiography visualization of tracer particles and quantitative data from Ultrasound Doppler velocimetry.

The presented paper describes an innovative self-adaptive multi-objective optimization code. Investigation goals concern proving the superiority of this code compared to NGSA-II and applying it to an inductor's design case study addressed to a "tailored" heating forging application. The choice of the frequency and the heating time are followed by the determination of the turns number and their positions. Finally, a straightforward optimization is performed in order to minimize energy consumption using "optimal control".

The present paper is dedicated to the investigation of Marangoni and Lorentz forces in a rapid heating process. During the melting of aluminum-silicon (AlSi) layer on the bormanganese steel 22MnB5, the liquid AlSi is shifting from the middle to the side and leaves dry spots on the steel due to a combination of both forces. In order to solve this process design issue, the impact of each force in the process will be evaluated. Evaluation is carried out using experimental data and numerical simulation.

In this work, a method to increase the residence time of bubbles in tubes or pipes filled with liquid metal is investigated. Imposing a horizontal electric current and a perpendicular horizontal magnetic field generates an upward-directed Lorentz force. This force can counteract gravity and cause floating of bubbles. Even with homogeneous electric fields these float in the mean but fluctuate randomly within the swarm due to mutual interactions. In the present case the cylindrical shape of the container furthermore creates inhomogeneous electric currents and an inhomogeneous force distribution resulting in a macroscopic convection pattern stirring the bubbles and further homogenising the spatial distribution of the bubbles.

Visual information about the influence of electromagnetic stirring on solidifying metal is essential for the optimization of material processing methods. It has recently been shown that the method of neutron radiography can be extended for the investigation of complex metallurgical processes in opaque media. The paper discusses the results of successful neutron imaging technique application to observe in real time the formation of the solid/liquid interface of a solidifying gallium melt stirred by a travelling magnetic field. Continuous and pulsed at low frequency application of the field was investigated to analyze the influence of the EM driven flow on the formation of ingots. The shape of the interface between the solid and liquid phases and the structural irregularity of the solid/liquid surface were analyzed. The results were compared with those for crystal growth without electromagnetic stirring. Comparing to other regimes has shown that the pulsed stirring at frequencies close to the characteristic frequency of melt circulation leads to the formation of a flatter solidification front with a more regular solid/liquid interface, which evidences of more uniform heat transfer conditions in the melt, and the method of neutron radiography makes it possible to obtain such information.

The present report summarizes the theoretical modelling and experimental investigation results of the study on the direct thermal methane cracking. This work is a part of the LIMTECH-Project (Liquid Metal Technologies) funded of Helmholtz Alliance and was carried out from 2012 to 2017. The Project-part B5 "CO2-free production of hydrogen" focused on experimental testing and particularly on modelling the novel methane cracking method based on liquid metal technology. The new method uses a bubble column reactor, filled with liquid metal, where both the chemical reaction of methane decomposition and the separation of gas fraction from solid carbon occur. Such reactor system was designed and built in the liquid metal laboratory (KALLA) at KIT. The influences of liquid metal temperature distribution in reactor and feed gas flow rate on methane conversion ratio were investigated experimentally at the temperature range from 930°C to 1175 °C and methane flow rate at the reactor inlet from 50 to 200 mLn/min. In parallel with experimental investigations, a thermochemical model, giving insight in the influence of the above mentioned parameters has been developed at KIT and a CFD model was developed at LUH to get an overview about the bubble dynamics in the reaction system. The influence of different bubble sizes and shapes, multi-inlet coalescence effects as well as the potential of electromagnetic stirring have been investigated.

The paper discusses transient distributions of physical fields computed with LES for a turbulent bubbles flow through an electrically conducting liquid in a cylindrical bubble reactor which is placed in an external uniform transversal or a longitudinal magnetic field. The experimentally verified (without magnetic field) Euler-Euler approach, realized with the ANSYS Fluent MHD module is used for multiphase flow when the continuous phase is Wood metal and the dispersed phase is nitrogen bubbles.