Antonio Morandi

Experimental and Numerical Analysis of DC Induction Heating of Aluminum Billets

We have analyzed the characteristics of dc-induction heating of aluminium billets both numerically and experimentally and developed a numerical model for the calculation of the power and temperature distributions inside the billet during the heating. We validated the model by comparison with the experimental results from a laboratory-scale prototype using permanent magnets. We studied the heating process of a real scale system by means of the model, taking into account the weakening of the mechanical properties during the heating. We provide an example of design of an industrial scale dc induction heater.

DC induction heating of aluminum billets using superconducting magnets

Purpose – To analyse the heating process of an aluminum billet rotating in a static magnetic field produced by superconducting coils.Design/methodology/approach – The idea is to force the billet to rotate in a static magnetic field produced by a DC superconducting magnet. Since, a static superconducting magnet has no losses, the efficiency of the system is the efficiency of the motor used. In order to evaluate the temperature distribution arising from the field profile produced by a given coil configuration, a numerical model, based on an equivalent electric network with temperature‐dependent parameters, is used.Findings – The main heating parameters, i.e. heating time, total power injected and temperature difference, are evaluated for different values of angular velocity and magnetic field. The field profile suitable to meet the specifics of an industrial heating process in terms of temperature homogeneity and heating time is determined. Starting form this profile the layout of the magnet is arrived at a...

Design of a Superconducting Saddle Magnet for DC Induction Heating of Aluminum Billets

In this paper the design of a superconducting magnet for DC induction heating of aluminum billets is discussed. A split saddle geometry is considered in order to allow a good accessibility of the field area. The layout is obtained by first calculating the field profile needed to produce as uniform a temperature distribution as possible inside the billet at the end of the heating and then by determining the optimum current distribution suitable to produce the required field profile. The operating condition and the final design of the saddle coil are discussed based on present state of the art superconducting wires.

Electromagnetic and thermal analysis of the induction heating of aluminum billets rotating in DC magnetic field

Purpose – The paper aims to deal with the induction heating of metal billets rotating in a DC magnetic field.Design/methodology/approach – The induced power distributions are analysed and the main heating parameters are estimated with reference to an infinitely long Al billet 200 mm diameter. The paper refers to the activity developed in the frame of a National Italian Project carried out by research groups of the Universities of Bologna, Padua and Roma “La Sapienza.”Findings – The main process parameters have been evaluated for the heating up to 500°C of an Al billet 200 mm diameter.Practical implications – This innovative technology appears to be very promising for improving the efficiency of the through heating of high‐conductivity metals (e.g. copper, aluminum) before hot working, by using superconducting magnets.Originality/value – The paper analyses the induction heating of a infinitely long billet rotating in a uniform DC magnetic field.

A Modified Formulation of the Volume Integral Equations Method for 3-D Magnetostatics

A magnetization-based formulation of the volume integral equations method for 3-D magnetostatics is discussed. The magnetization of each element is related, via the constitutive law of the material, to the average magnetic flux density within the element rather than to the value at the center as is usually done. This assumption leads to more accurate distribution of magnetization and allows a faster convergence of the solution. Moreover, it leads to more symmetric matrix of the coefficients and reduces the numerical instability due to looping patterns of magnetization, which is inherent to integral methods. The formulation is made effective by the use of a hybrid numerical and analytical approach, which allows for the fast and accurate calculation of the coefficients. The proposed model is validated and compared with the usual model both for saturable and linear material with high susceptibility.

Experimental and Numerical Investigation of the Levitation Force Between Bulk Permanent Magnet and

The experimental investigation of the levitation force between a Permanent magnet (PM) and MgB2 disk prepared by means of the Reactive Mg Liquid Infiltration is presented. Both FC and ZFC levitation in the temperature range from 21 K to 37 K are considered. The long term behavior of the levitation force is also investigated. A numerical model is developed in order to investigate the electrodynamics of levitation. The hysteretic behavior of the levitation force is related to the dynamic of current penetration inside the MgB2 disk by means of the numerical model.

{\rm MgB}_{2}

A DC resistive SFCL consists of an inductance and a quenching superconducting resistance embedded in diode bridge. The superconductor operates in nearly DC current conditions. This regime of operation drastically reduces the AC losses and makes it possible to implement the device by means of present state of the art superconductors. In this paper the AC losses of a laboratory scale prototype of DC resistive SFCL (a 200 V/60 A) are experimentally investigated. The prototype consists of a non inductive Bi2223 winding series connected with a conventional iron core inductor and embedded in a diode rectifier which is connected to the protected circuit. The AC losses are measured and compared with those occurring in pure AC operation at the same current.

Disk

In order to investigate how a superconducting fault current limiter (SFCL) can enhance the performance of a power system, an accurate circuit model of the device needs to be introduced in power system simulators. In this paper, we present a finite-element numerical model to calculate the time evolution of the voltage across a magnetic-shield-type SFCL, when it is connected to an external circuit. The calculation of the voltage is carried out by using the energy conservation law, and requires the calculation, at any instant, of the current density distribution inside the superconducting tube and magnetization distribution inside the ferromagnetic core of the device. These distributions are determined by means of two coupled equivalent electric and magnetic circuits, whose topology and components are obtained through the spatial integration of quasi-static form of Maxwell equations. Comparisons between numerical and experimental results are shown.

Experimental Evaluation of AC Losses of a DC Restive SFCL Prototype

The levitation performance of a magnetic bearing, based on 48 mm inner diameter, 3 mm thickness and 80 mm height, MgB2 tube is experimentally investigated. A numerical model is developed and validated against the experimental results in order to compare different rotor geometries and to investigate the temperature behavior of the system. Investigation of the effect of the hysteresis on practical superconducting bearings is also carried out by means of the model.

Magnetic-shield-type fault current limiter equivalent circuit

Purpose – To investigate the feasibility of a novel scheme of high‐efficiency induction heater for nonmagnetic metal billets which use superconducting coils.Design/methodology/approach – The idea is to force the billet to rotate in a static magnetic field produced by a DC superconducting magnet. Since a static superconducting magnet has no losses, the efficiency of the system is the efficiency of the motor used. In order to evaluate the temperature distribution arising from the field profile produced by a given SC coil configuration, a numerical model, based on an equivalent electric network with temperature‐dependent parameters, is developed.Findings – A substantial independence of the shape of the temperature profile on the angular velocity and the value of the uniform magnetic field applied, is observed. A strong temperature gradient is observed in the radial direction in the proximity of the penetration front and in the axial direction at the top and bottom surface of the billet. Small temperature gra...