International Journal of Applied Electromagnetics and Mechanics

Preface to the Selected papers from the Heating by Electromagnetic Sources Conference 2013 (HES-2013) special issue.

Dual frequency induction hardening can be a low distortion alternative to case hardening for gearings. However, profound process understanding is still lacking, which is reflected by the absence of appropriate models allowing the prediction of final component properties in terms of residual stresses and distortion. In order to close this gap, a 2-D numerical model has been developed, considering short time austenitization kinetics of quenched and tempered AISI 4140. The induction heating model considering the nonlinear magnetic material behaviour is realized with MSC.Marc®, whereas the mechanical response is implemented in Abaqus/Standard®. The comparison of residual stresses and distortion with experimental results shows that the developed model is in good agreement. Numerical investigations have shown that the core temperature and the TRIP strain during the martensitic transformation will determine the quantitative distribution of the residual stresses.

In the present paper, a new numerical model for calculating martensite microstructure in induction surface hardening processes is introduced. The model was developed with the help of the Department of Electrotechnology and Converter Engineering (LETI). It takes into account the heating as well as the quenching process and uses the temperature history of a work piece to calculate martensite formation. The calculation is based on an empirical equation found by Koistinen and Marburger [1]. A comparison between the heat distribution within a work piece at the end of the heating process and the distribution of martensite after quenching is performed for different process parameters. Thus, it is determined, in which case the temperature distribution is sufficient to predict the hardened layer and in which case the microstructure has to be calculated to receive accurate results. The model is verified by comparing simulation results with different experiments.

Dual frequency AC magnetic field effects are analyzed in the case of levitated samples heated, melted and confined. The time dependent numerical models based on accurate spectral approximation give an insight to oscillation patterns and stability conditions for a copper sample both in solid and liquid state after the melting stage. Application to microgravity experiments planned at International Space Station and the full gravity magnetic levitation for the similar sample are presented.

The paper studies specific pumping characteristics of the Annular Linear Induction Pumps (ALIP) with travelling field for liquid sodium. The present work is focused on the analysis of very large electromagnetic pumps able to provide high flow rates. The magnetic Reynolds number is quite large, therefore, it is necessary to take into account the full magnetohydrodynamic interaction between the electromagnetic field and the liquid metal flow inside pump channel. We couple the electromagnetic aspects with the hydrodynamic ones by means of two commercial softwares. The geometry considered here is 2D axisymmetric. It is found that in such induction pumps the effect of convection is very important. Two main effects have been put forth. Firstly, due to the magnetic entrainment significant end effects are observed for large velocities. This leads to the existence of regions where the axial force is negative. Secondly, a Hartmann effect occurs near the walls. The electric current and the corresponding forces are confined near the wall in Hartmann layers. Global stability of e.m. pump is also analysed.

A great deal of work with respect to both physical and numerical modelling of Czochralski crystal growth has been conducted in the generic Rayleigh-Bénard system. In order to come closer to the conditions in a real Czochralski puller, specific effects such as the influence of a rounded crucible bottom, deviations of the thermal boundary conditions from the generic case, crucible and/or crystal rotation, and the influence of magnetic fields are often studied separately. Within this paper we present a model experiment focusing on investigations of the impact of magnetic fields on the flow in a Czochralski puller. To achieve similar thermal boundary conditions as in an industrial growth facility, a double-walled rounded bottom glass crucible was chosen to hold the fluid. Similarity of the heat transfer conditions was guaranteed by selecting the ternary alloy GaInSn as the model fluid. Measurements of the fluid flow have been conducted by means of the ultrasound Doppler velocimetry. The results reveal the complex flow structure of natural convection in a Czochralski crucible. Because the growth of high quality mono-crystalline crystals is impeded by such a non-axisymmetric flow, rotating magnetic fields (RMF) are often proposed to render the flow more axisymmetric. To study the effect of an RMF on the natural convection in a Czochralski system the experimental apparatus was mounted inside the home-made MULTIpurpose MAGnetic field facility (MULTIMAG). In the present contribution the three-dimensional convective patterns as well as the resulting temperature fluctuations will be discussed both for the pure buoyant case and for the application of an RMF.

On account of ANSYS Classic, ANSYS Fluent and ANSYS CFX-Post external coupling a new approach for joined simulation of liquid metal flow, free surface dynamics and electromagnetic (EM) field in induction furnaces is developed. The model is adjusted for the case of EM levitation and extended on 3D consideration with application of standard k-ω Shear Stress Transport (SST) or précised Large Eddy Simulation (LES) turbulence description.

Calculated steady state free surface shapes of molten metal are compared to other models and experimental measurements in traditional and EM levitation induction furnaces. Calculated free surface dynamics of melt is compared to analytical estimation of free surface oscillation period.

Parameter studies performed in ICF and conventional EM levitation setup briefly illustrate capabilities of the model and demonstrate the influence of current, frequency, surface tension and viscosity on free surface dynamics and steady shape of the melt in 2D approximation. Finally, full 3D calculation of free surface dynamics in ICF using k-ω SST and LES turbulence models is performed and the impact of turbulence model on meniscus is discussed.

This paper attempts to present a novel development of an electromagnetic non-contact surface velocity measurement technique in electrically conducting liquids which could be applied in high-temperature metallurgical processes involving metal melts. The technique is based on Lorentz force velocimetry, i.e. on measuring the force which is generated by the interactions of the melt flow and an externally applied magnetic field that is spanned by permanent magnet system. The electromagnetically induced force pushes the magnet system into the direction of the flow and can be measured using a force sensor that is attached to the magnet system. As the measured force linearly depends on melt velocity, a non-contact evaluation of the velocity can be achieved. However, the recorded force also depends on the electrical conductivity of the melt. In application this material property is a priori unknown as it strongly depends on both temperature and composition of the melt. Hence, calibration of such a measuring device becomes a cumbersome task. Our development aims to circumvent this deficit by applying a time-of-flight technique. According to this principle we design and test a prototype of sensor for measuring free-surface velocity. In the model experiments we use both solid bodies and the liquid metal GaInSn as test liquids.

A comparison between a classical parametric NSGA (Non-dominated Sorting Genetic Algorithm) and a non-parametric NSKA (Non domination Sorting Kinetic Algorithm) optimization method is proposed on a benchmark problem of inverse induction heating characterized by two conflicting objectives.

Nowadays, the induction heating market is continuously growing due to its benefits including precise output power control, reduced heating times, and cleanness. The domestic induction heating application, based on the same principle, includes some extra features such as the controlled temperature profiles or over-temperature detection for an outstanding cooking process. Because of the high power density and the reduced cooling capabilities, efficiency becomes critical in this application. This paper introduces some techniques to improve the efficiency of the induction heating power converters. The proposed converters are analyzed, including the main losses sources, proving that the proposed solution improves the overall efficiency while the component count and cost are keep to reasonable values.

Induction cooktops are more and more used in the houses with increasing market in comparison with gas cooktops and resistance or halogen cooktops. The main reasons for this are the higher energy efficiency, the low heating times, the controllability of the power delivered to the pot, the safety with reference to the low temperature of the glass, the superior cleanability. The main core of the Induction Hob (IH) is constituted by the power electronics board and the inductor which are strictly correlated in the sense that the frequency converter (the frequency operating range is 20–100 kHz) must be designed in order to correctly resonate with the coil in order to achieve its optimum efficiency over the broadest possible operation range; this means that the inductor must be designed in order to fulfill the Zero Voltage switching condition of the frequency converter over the whole range of operation. These requirements are much more important in the quasi resonant converters for the limitations in the controllability of soft switch mode of solid state switching. In the paper a design procedure based on a fully 3D FEM model of the inductor coupled with the frequency converter circuit is presented. The simulation results will be discussed and compared with experimental data.

A laboratory implementation of a two-phase travelling wave induction heating setup is described. The focus is the development of a versatile power control system for multi-coil experiments and parameter studies. The drive system features high temporal accuracy, full real-time controllability, and integrated measurement technology, analyzed step wise. The performance was tested using a full pitch travelling wave inductor based on litz wire with a flux concentrator from a powder material. Thermographic images from the experiments are presented and the results are compared with simulations. The challenges related to multi-coil configurations are explained, many of which are difficult to predict from simulations.

Nano-sized superparamagnetic Y _{3} Fe _{5} O _{12} ferrite having a high heat generation ability in an AC magnetic field was prepared by physical bead milling. The highest heat ability in the AC magnetic field was for the fine Y _{3} Fe _{5} O _{12} powder with a 16-nm crystallite size (the samples were milled for 4 h using 0.1 mm� beads). The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. For the samples milled for 4 h using 0.1 mm� beads, the heat generation ability (W·g ^{-1} ) was estimated using a 3.58 × 10 ^{-4} · f· H ^{2} frequency (f/kHz) and the magnetic field(H/kA·m ^{-1} ), which is the highest reported value of superparamagnetic materials. Furthermore, Y _{3} Fe _{5} O _{12} microspheres having a 20–32 μm diameter range were prepared by a spray dryer using the bead-milled nano-sized particles.

A solid-state microwave generators system is considered as an alternative to the magnetron, in order to inject electromagnetic energy into the cavity of a microwave oven for domestic use. Over current devices, the use of solid state technology allows one to control the frequency and phase of the electromagnetic field generated.

Considering a simplified cavity with 2 solid state sources, the influence of the electrical parameters on maximum efficiency obtainable in the process of microwave heating is investigated. By varying the frequency, different values of optimal phases and different values of maximum efficiency are detected.

Moreover, the procedure is repeated with varying the position of one source port and the influence of geometry on the system performance is evaluated.

Our results demonstrate that the ability to control the electrical quantities of a microwave heating process makes it possible to obtain better results in terms of energy efficiency over the current poorly controllable systems.