Experimental study on the performance of a room temperature magnetic refrigerator using permanent magnets

An investigation of a room temperature active magnetic refrigerator was carried out in this work. An experimental rig was built, in which two reciprocating regenerative beds packed with 1167.4 g of gadolinium were used, helium gas was used as a heat transfer fluid, and an average 1.5 T magnetic field was supplied by permanent magnets. With this apparatus, the influence of the gas pressure, the operating frequency and the temperature range were studied systematically. The lowest no heat load temperature of −2.79 °C at the cold end heat exchanger and a maximum no heat load temperature span of 42.28 °C were obtained. A maximum cooling power of 51.3 W was achieved over a temperature span of 18.16 °C. The results in this study provide useful data for future design and development of room temperature magnetic refrigerators.     

Magnetizing of permanent magnets using HTS bulk magnets

A demagnetized Nd–Fe–B permanent magnet was scanned just above the magnetic pole which contains the HTS bulk magnet generating a magnetic field of 3.27 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. We examined the magnetic field distributions when the magnetic poles were scanned twice to activate the magnet plate inversely with various overlap distances between the tracks of the bulk magnet. The magnetic field of the “rewritten” magnet reached the values of the magnetically saturated region of the material, showing steep gradients at the border of each magnetic pole. As a replacement for conventional pulse field magnetizing methods, this technique is proposed to expand the degree of freedom in the design of electromagnetic devices, and is proposed as a novel practical method for magnetizing rare-earth magnets, which have excellent magnetic performance and require intense fields of more than 3 T to be activated.     

室温磁制冷高场强永磁磁路

在中空圆柱型磁场源(hollow cylindrical flux source)的基础上,设计并制作出用于室温磁制冷机(往复式和旋转式)的高场强永磁磁路,在磁路工作气隙为20mm时,工作气隙中心的场强的计算值及实测值均高于1.5T.     

Quantitative considerations to self-centering magnetic suspensions with permanent magnets

Center containment and simultaneous support of rotating bodies by forces between two permanent magnets has become a technical reality due to high-coercive force magnets. The Self-Centering principle is described and experimental results are reported as examples for the advantages of the new arrangement over conventional magnetic bearings. Performance tests of prototype units are described concerning the damping conditions and the centering functions. Centering forces and supporting forces can be adjusted independently to meet changing requirements by positioning of the axle by an end bearing or by ac-forces. The actual forces measured for barium ferrite units are compared with the forces measured for samarium cobalt units. Typical values show the samarium cobalt units to be up to 25 times stronger (by weight) and up to 40 times better (per unit volume) than barium ferrite bearings, forces were measured in excess of 100 times the weight of the magnets. Analytical, computerized studies for the basic forces have been made for optimization and the design for combinations of many units for high stiffness requirements.     

Measurement of magnetic properties of cobalt-rare earth permanent magnets

Co-rare earth permanent magnets generally display a high intrinsic coercive force. In order to make magnetic measurements with such materials fully saturated, we have found it necessary to use magnetizing fields in excess of 50 kOe. The superconducting solenoid is ideally suited for generating such fields. In this study, we have used a 100 kOe Nb3-Sn superconducting solenoid for magnetizing samples and for measuring saturation magnetization. Demagnetization properties of long cylindrical samples have been measured in the superconducting solenoid, and also with a conventional hysteresigraph after the samples have been saturated with the superconducting solenoid or in some cases with a pulsed field solenoid. Short disk samples or ring magnets such as are used in traveling wave tube (TWT) designs are difficult to measure by these techniques. We have found torque magnetometry to be useful for such shapes. Open circuit magnetization is measured in this case. Results for ring magnets will be compared with peak axial field measurements for a periodic TWT structure. Reversible and irreversible changes in magnetization with temperature are also of interest. Techniques for measuring these changes are discussed.     

利用永磁体的室温磁制冷机性能研究

介绍了利用1.5 T永磁体驱动,氦气作为换热流体,采用主动式磁回热器的室温磁制冷机的实验研究情况.在现有实验装置下,通过调节气体压力与循环频率,高低温端最大达到了10.7K的温差,研究结果为室温磁制冷机的设计以及进一步发展提供了参考.     

The energy performances of a rotary permanent magnet magnetic refrigerator

The interest of the scientific community regarding magnetic refrigeration at room temperature is constantly growing. In recent years, there has been an increase in the experimental work relating to both new prototypes and new magnetocaloric materials. The magnetic refrigerators built to date still have some limitations that make them uncompetitive when compared with conventional vapour compression systems. However, among the different configurations realized, one can recognize that rotary devices, having rotating magnets and static regenerators, are of particular interest because of their good energy performances. In this paper, we report an experimental investigation on the identification of the energy performances of a Rotary Permanent Magnet Magnetic Refrigerator. Employing 1.20 kg of gadolinium and operating at a temperature of heat rejection equal to 296 K, the system was subjected to different operating conditions obtained by varying the thermal load, volumetric flow rate of the regenerating fluid and cycle frequency.     

Design of a permanent magnetic circuit with air gap in a magnetic refrigerator

We calculate the magnetic field distribution of a permanent magnetic circuit with an air gap in a magnetic refrigerator by a finite-element method, and compare the field strengths of different structural parameters of the magnetic circuit. We show how the structure of the magnetic circuit can be optimized and present some approaches to improve the structure for a specific magnetic circuit. The main purpose is to provide basic parameters for the design of a practical magnetic refrigerator.     

Selection of parameters for testing magnetic properties of permanent magnets

Conclusions The testing of the parameters B_r, H_c, B_d, and H_d does not always provide an unambiguous estimation of whether the PM whose working point lies on the regression line is suitable for utilization in a magnetic system.The evaluation of the PM efficiency by means of the induction at the working regressionline departure point and the induction at the intersection point of the working regression line with the conductance line corresponding to the condition of the magnet in an assembled product is more efficient and universal, since it is virtually independent of the working regression-line departure-point position and it serves to halve the number of tested parameters.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 49–50, February, 1979.     

Materials for permanent magnets

Until the middle 50's, both magnetically soft and hard materials were produced mostly by melting, casting and hot manipulation. Powder techniques were being applied on a pilot plant scale only, but during the last two decades these have become predominant and in the future almost all permanent magnets will be produced by this route. The development of new compositions and processes is traced, with examples of applications, with emphasis on the impact which the latest rare earth cobalt or iron super energy magnets are having in this field. They are penetrating into existing markets and expanding into new ones not possible hitherto.     

Quasi-sheet multipole permanent magnets

A Rare-Earth Permanent Magnet design system with which a desired pure multipole field can be achieved by accurately deploying REPM blocks around a working region so as to generate magnetic sheet currents which follow the profile of a magnetically soft yoke is presented here. In addition to the general Quasi-Sheet Multipole model, examples of two small operating QSM quadrupoles together with a large QSM dipole are also described.     

Modulating thickness multipole permanent magnets

The magnetic field distributions of modulating thickness permanent magnets [1,2] are discussed in this paper. The field distributions are calculated by using the program POISCR and the actual demagnetization curve of the REC permanent magnet material. The results show that the performance of the MT type magnets is about the same as or even better than that of the modulating magnetization direction type (MMD) [3] and that the MT type magnet with soft iron shield requires less REC material than MMD type magnets.     

New thin film permanent magnets

Abstract

An overview is provided of research on coupled hardsoft magnetic multilayers as model exchange-spring systems, with an emphasis on uncovering the fundamental magnetic reversal processes and the correlation between microstructure and magnetic properties. The goal is to illustrate the rich opportunities to understand and hopefully improve permanent magnets by utilising the principles of nanotechnology and the microscopic tools of the modern materials science.     

SEM investigation of the magnetic domain structure of sintered SmCo5 permanent magnets

The paper presents scanning electron microscopy (SEM) study of the magnetic microstructure of anisotropic sintered SmCo₅ permanent magnets. Observations were made in the thermally demagnetized state of the magnets at the surfaces both perpendicular and parallel to the alignment axis. Magnetic domains were revealed using the technique of type-I magnetic contrast (for the first time) and the colloid-SEM method. The domain structure consists of main domains (which extend through the whole grain thickness) and surface domains of reverse magnetization (reverse spikes). The main domains form a maze pattern near the surface perpendicular to the alignment axis. The reason for the presence of the maze domain structure and reverse spikes at the surface perpendicular to the alignment axis is the reduction in the magnetostatic energy at the cost of a larger total Bloch wall area. Investigations carried out on the surface parallel to the alignment axis allowed to obtain much better insight into the orientation of grains.     

各向异性热压稀土永磁体的热变形机制及微磁结构研究

重点研究制备工艺对各向异性热压稀土永磁体性能的影响,探讨了热压永磁体的热变形机理和数学描述模型,并尝试从微磁结构的角度研究各向异性纳米晶Nd-Fe-B磁体,揭示纳米晶粒之间的静磁和交换耦合相互作用、磁化和反磁化、热退磁等微观机制。获得了最佳磁性能为:Hcj=1 157 kA/m,Br=1.465 T,(BH)max=426 kJ/m3纳米晶Nd-Fe-B磁体。     

Calculating the external magnetic field from permanent magnets in permanent-magnet motors-an alternative method

We present an alternative method for calculating the magnetic field from a set of permanent magnets in a permanent-magnet motor. The method uses a cylindrical coordinate system to model the geometry of the structure enclosing the magnets. A Fourier series expansion yields an alternative to the more familiar multipole expansion given in spherical coordinates. The expansion is developed by using Green's function in cylindrical coordinates. A technique called charge simulation allows computation of an equivalent point charge distribution. Finally, Coulomb's law is applied to express the magnetic scalar potential in a mathematically tractable form.     

First-principles determination of intergranular atomic arrangements and magnetic properties in rare-earth permanent magnets

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