Afef Kedous-Lebouc

A magnet-based device for active magnetic regenerative refrigeration

To study magnetic refrigeration an experimental device is developed. It uses gadolinium as a giant magnetocaloric effect material and a Halbach magnet cylinder as the magnetization source. A specific thermodynamic cycle, active magnetic regenerative refrigeration, is required to enhance the temperature span. The system is simple and compact. The first results obtained (/spl Delta/T=4/spl deg/C or 7/spl deg/C, COP=2) are promising and confirm the model developed. It can be used already to evaluate the potential of different magnetocaloric effect materials and the efficiency of different active magnetic regenerative refrigeration cycles.

Influence of Magnetic Materials on Claw Pole Machines Behavior

This paper presents a study on magnetic materials for claw pole machines which are widely used nowadays in the automobile industry for their simple manufacturing and cost reasons. The finite element analysis with the loss surface model is used to evaluate the iron losses for three categories of material: M800-50A, M330-35A, and AFK502. Comparisons are made in terms of output current, efficiency, as well as iron loss as main characteristics of the machine. On the other hand, the experimental method of loss separation provides a clear idea of the loss distribution in the machines, from which the iron loss can be deduced. A qualitative comparison is made between the two methods, which proves to be coherent.

Magnetic flux and losses computation in electrical laminations

This paper deals with the numerical computation of the average induction over sheet laminations by solving the magnetic diffusion equation. Different models are used to describe the magnetization law: an anhysteretic law and the static and dynamic hysteresis Preisach models. The computed flux and associated losses are then compared to experimental results for wide frequency range and different magnetization levels.

Giant magnetocaloric effect in Mn1−x(Ti0.5V0.5)xAs: Experiments and calculations

In this paper, we present the giant magnetocaloric effect exhibited by the Mn1−x(Ti0.5V0.5)xAs compound with x=0.1. The ordering temperature decreases from 318K in the case of MnAs (x=0) to 266K in the case of Mn0.9Ti0.05V0.05As (x=0.1). A large magnetic entropy change −ΔSm attributed to a first order magnetic transition has been observed. For Mn0.9Ti0.05V0.05As, the maximum of −ΔSm occurs near TC=266K and is about 30J∕kgK for an applied field change of 2T, a value very close to that (∼31J∕kgK) measured in MnAs. For materials with a first order transition at TC, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to structural changes. A model based on the phenomenological approach of Bean and Rodbell [Phys. Rev. 126, 104 (1962)] has been developed in order to describe such a behavior. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by Mn1−x(Ti0.5V0.5)xAs (x=0, 0.1) materials.

Application of Preisach model to grain oriented steels: comparison of different characterizations for the Preisach function p(/spl alpha/, /spl beta/)

To take into account scalar hysteresis in magnetic calculations, accurate models are required to correctly describe soft magnetic material behavior. The Preisach model makes it possible to do so if its distribution function p(/spl alpha/, /spl beta/) is well determined. This paper presents a comparison of four methods of characterization of the function that uses different peak magnetization level loops of grain oriented sheets. The choice of a lorentzian function with a term of interaction field shows interesting results.

Numerical computation of the dynamic behavior of magnetic material considering magnetic diffusion and hysteresis

The numerical solution of the diffusion equation in an electrical steel sheet cross section is studied with a time-dependent surface applied field. The study implements a local hysteresis magnetic law. The solutions are compared to both the classical nonlinear anhysteretic resolution and the experiment. The effect of taking into account an hysteretic magnetic law in numerical simulation is studied with different excitation frequencies.

Macroscopic anisotropy characterization of SiFe using a rotational single sheet tester

Macroscopic magnetic anisotropy of two electrical steel samples of GO and NO SiFe materials are characterized thanks to a rotational single sheet tester. This nonstandard set up allows us to perform magnetic measurements under both a rotating excitation field and an alternating one applied along any direction of the sheet plane. The anisotropy of the magnetic losses and of the exciting field of each material quality is discussed. As expected, the GOSS texture of the GO SiFe is well pointed out with its very easy magnetization rolling direction. The hard magnetization axis at 55/spl deg/ emerges as the induction increases and replaces the transverse direction. The NO SiFe shows closely similar magnetic characteristics but remains anisotropic. The vectorial aspect of B(H) law is also highlighted. Such characteristics will be useful in many fields, e.g. material elaboration, magnetic law behaviour modelling and construction of electrical machines.

2D analysis of rotational loss tester

In this study a rotational single sheet tester is simulated using a 2D finite element software Flux2D. Its main goal is to find the best geometrical structure of the device which reaches the largest homogeneity of the magnetic field in the sheet plane. This imposes the size of the sheet area in which the measurements have to be achieved. The simulations have been performed using the magnetic vector potential A formulation and have been limited to a magnetostatic case. The results point out that the square shaped specimen is the best one. The influence of the yokes width is also shown and discussed.

A chemical reaction hysteresis model for magnetic materials

The authors present a new static hysteresis model for magnetic materials based on physical meaning. The idea is original: electronic transformation of the material is compared to a chemical reaction. Then a simple analytic formulation of the B(H) law for GO iron sheet in the rolling direction is obtained. Results are compared with measurements. The model is as simple as the Potter one, its parameters can be easily determined and its accuracy could compete with the Preisach model. Finally an easy computation by finite element software is gained.

Numerical and Experimental Investigations of the Thermal Management of Power Electronics With Liquid Metal Mini-Channel Coolers

Thermal management became a limiting factor in the development of high-power electronic devices, and new methods of cooling are required. Therefore, the use of liquid gallium alloys, whose thermal conductivity (approximately 28 W/m/K) is 40 times greater than thermal conductivity of water, is introduced. In the first part of this paper, we present a numerical modeling and an experimental study of a mini-channel liquid metal cooler. In these experiments, the working fluid is moved via an electromagnetic pump. Numerical and experimental results are compared. Then, a numerical study dealing with the influence of the thermal conductivity of the cooler material is conducted, and a discussion on the use of classical convective heat transfer correlations is presented. In the last part, a numerical study of the cooling of a silicon chip is carried out. The cooling capacity of the liquid metal is compared with that of the water cooling, and very attractive results are obtained. The concept discussed in this paper is expected to provide a powerful cooling strategy for high-power-density electronic devices.