共查询到20条相似文献,搜索用时 109 毫秒
1.
2.
3.
磁制冷技术是一种高效节能、绿色环保、可靠性强的先进制冷技术,其核心原理是磁性材料的磁热效应,即磁制冷工质等温磁化时向外界放出热量,绝热退磁时从外界吸收热量.理论上所有的磁性材料都具有磁热效应,但只有极少数具有显著磁热效应的磁性材料可用于磁制冷.因此,研发具有较大磁热效应的磁制冷工质是决定磁致冷技术能否得到应用和推广的关键因素.经过几十年的发展,人们陆续发现了许多性能优异的磁制冷材料,推动和促进了磁制冷技术的发展.目前,磁制冷技术在20 K以下的低温区已经得到了较为广泛的应用,如液氦的制备、低温物理研究以及航空航天等领域都采用了磁制冷技术.低温区的磁制冷材料通常为顺磁状态,其构型熵可以忽略不计,但随着温度的升高,用于低温区磁制冷的顺磁材料的晶格振动变大,构型熵对磁制冷系统的影响不可忽略,即传统的顺磁态磁制冷工质在近室温区已不再适用,因此研发近室温区的磁制冷材料具有重要意义.近20年间,国内外研究者对近室温区磁制冷材料进行了大量研究并取得了许多重要成果,如以Gd(SiGe)4、La(FeSi)13、MnAs合金和NiMn基Heusler合金等为代表的具有优异磁热效应的一级相变磁制冷材料,这些合金的磁热效应通常是由结构相变与磁相变的叠加引起的,但常常伴有较大的热滞与磁滞损耗,进而会大幅度降低磁制冷的效率.除了一级相变磁制冷材料外,还有稀土Gd及其化合物、Gd基非晶态合金等具有二级磁相变的近室温磁制冷材料.其中,Gd基非晶态合金具有制冷温区宽、涡流损耗低、磁滞低、成分范围宽、耐腐蚀和易于加工等优点,其较宽的制冷温区特别适合室温埃里克森磁制冷循环,具有广阔的应用前景.本文简要介绍了磁热效应的原理以及磁制冷技术的发展,重点介绍了近室温磁制冷材料的磁热性能和最新研究进展,包括Gd(SiGe)4、La(FeSi)13、MnAs合金、NiMn基Heusler合金等一级相变磁制冷材料和具有二级磁相变的Gd基非晶态合金,并分析了它们作为磁制冷材料的优点和存在不足,讨论了各系材料未来的发展方向和趋势. 相似文献
4.
介绍了一种历史悠久但又极具发展潜力的制冷方式-磁制冷技术.从磁制冷的基本原理-磁热效应(MCE)出发,分别从熵和热力学的角度分析了MCE,给出了MCE的表征参数及常用测试方法,列举了常见的磁制冷循环及几种典型的磁制冷机,总结了磁制冷技术的研究历史,并对其进行了展望. 相似文献
5.
6.
磁制冷材料中一级磁相变的研究进展 总被引:1,自引:0,他引:1
磁制冷技术作为21世纪的新一代制冷技术已经受到了关注。因此近年来具有一级磁相变的磁制冷材料成为全球学术界的一个研究热点,并越来越受到工业界的重视。主要介绍了磁制冷材料中的一级磁相变特点,综述了具有一级磁相变的磁制冷材料的研究进展和应用现状。最后展望了具有一级磁相变的磁制冷材料的发展趋势。 相似文献
7.
8.
9.
10.
室温磁制冷作为一种高能效、环境友好和运行可靠的制冷技术,具有广阔的应用前景。室温磁制冷技术利用磁工质的磁热效应以及AMR循环实现制冷。在过去数十年的探索中,室温磁制冷的研究主要集中于磁工质的研发和磁制冷机的设计。本文综述了目前已开发的几种典型的室温磁工质以及研制的磁制冷样机。目前研究较丰富的室温磁工质主要包括稀土金属Gd及其合金、NaZn13型La(Fe, Si)13系合金以及Fe2P型MnFePAs系合金,本文对它们的磁热性能进行对比并分析存在的实际应用问题。基于运行方式的不同,目前研制的磁制冷样机主要分为往复式和旋转式,介绍了不同研究机构研发的磁制冷样机的实验参数与制冷性能。回顾了室温磁制冷技术在不同领域已取得的实际应用,并对该技术未来的发展趋势进行展望。 相似文献
11.
AbstractA priori derivation for the extra free energy caused by the passing electric current in metal is presented. The analytical expression and its discrete format in support of the numerical calculation of thermodynamics in electric current metallurgy have been developed. This enables the calculation of electric current distribution, current induced temperature distribution and free energy sequence of various phase transitions in multiphase materials. The work is particularly suitable for the study of magnetic materials that contain various magnetic phases. The latter has not been considered in literature. The method has been validated against the analytical solution of current distribution and experimental observation of microstructure evolution. It provides a basis for the design, prediction and implementation of the electric current metallurgy. The applicability of the theory is discussed in the derivations. 相似文献
12.
The differential thermal analysis (DTA) apparatus has been designed in order to investigate the effect of magnetic fields on solid-melt phase transformation in pure bismuth. The endothermic peaks of DTA curves show that melting is insensitive to magnetic fields, which can be verified from thermodynamics. However, the exothermic peak obviously shifts to higher temperature as the magnetic field strength increases, from which the magnetic field does not affect the crystal growth but nucleation. On the basis of the assumption that there is an intermediate state between a crystal nucleus and a liquid atom, one possible reason for the shift of exothermic peaks is that kinetic barrier of nucleation is lowered and nucleation is activated by magnetic fields. 相似文献
13.
《Current Opinion in Solid State & Materials Science》2013,17(4):193-201
Static magnetic field processing of non-ferromagnetic materials has been of broad interest and been applied in such fields as drug delivery, colloid chemistry and engineering of materials containing particles. A ‘strong’ magnetic field refers to a ‘strong’ response from the manipulated material and can vary in definitions. The response is corresponding to a local interaction between the material and the local magnetic field, being influenced by the magnetic susceptibilities of the material and the surrounding/coated medium. By carefully designing the medium, a significantly ‘strong’ response from a weakly magnetic material can even be generated by a traditional magnet, i.e. magnetic flux density ∼0.01 T. Therefore, the ability to manipulate materials by using a magnetic field depends critically on the understanding of the principles of the magnetic properties of materials and their magnetic responses. This paper provides a critical discussion on the principles including magnetic field effect thermodynamics, magnetic energy, magnetic anisotropy and different magnetic forces during ’strong’ magnetic field processing of weakly magnetic materials (focusing on metallic materials). A series of case studies and the related magnetic field effect are subsequently integrated and discussed. Overall this review aims to provide a better understanding and efficient overview on the phenomenon principles in the field of magnetic field processing. 相似文献
14.
H.R.E.H. Bouchekara A. Kedous-LeboucJ.P. Yonnet 《International Journal of Refrigeration》2012,35(1):115-121
Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a prime candidate for the next generation of cooling systems. The essential components of magnetic refrigeration are the magnetic field generator and the magnetocaloric material. Although, several permanent magnet systems (magnetic field sources) for MR have been developed, recent development in magnetic refrigeration technology has encouraged researchers all over the world to think about new and original systems. This paper aims to describe a new and original magnetic refrigeration system based on a simple principle of magnetism called the Halbach effect. The proposed system is running with rotating bar-shaped magnets. This structure provides the desired varying magnetic field to the magnetocaloric material. Several configurations for the proposed systems have been investigated and presented in this paper. The design and modeling have been accomplished by using the finite elements method. 相似文献
15.
A. Pérez Galván B. PlasterJ. Boissevain R. CarrB.W. Filippone M.P. MendenhallR. Schmid R. AlarconS. Balascuta 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,660(1):147-153
We present in this article a prototype magnetic coil that has been developed for a new search for the electric dipole moment of the neutron at the Spallation Neutron Source at Oak Ridge National Laboratory. The gradients of the magnetic field generated by the coil have been optimized to reduce known systematic effects and to yield long polarization lifetimes of the trapped particles sampling the highly uniform magnetic field. Measurements of the field uniformity of this prototype magnetic coil are also presented. 相似文献
16.
It is important to control magnetic anisotropy of ferromagnetic materials. In this work, magnetic anisotropy of amorphous FeCoSiB films is controlled by stress annealing. FeCoSiB films are deposited on glass substrate and annealed with stress in vacuum. When the annealed films are released from clamp, permanent tensile or compressive strain can be introduced in the films. Influences of both tensile and compressive strain on the magnetic properties of FeCoSiB films have been studied. The results show that FeCoSiB films by stress annealing exhibit strong magnetic anisotropy while the samples by normal annealing exhibit magnetic isotropy. Easy axis along the stress is induced in the films with tensile stress, while easy axis perpendicular to the stress is induced in the samples with compressive stress. It has also been found that the magnetic anisotropy increases with the increase of the strain. The effects of strain on the magnetic properties of FeCoSiB films have been interpreted by stress induced anisotropy via magnetoelastic coupling. 相似文献
17.
18.
The boundary element method (BEM) has been established as an effective means for magnetostatic analysis. Direct BEM formulations for the magnetic vector potential have been developed over the past 20 years. There is a less well-known direct boundary integral equation (BIE) for the magnetic flux density which can be derived by taking the curl of the BIE for the magnetic vector potential and applying properties of the scalar triple product. On first inspection, the ancillary boundary integral equation for the magnetic flux density appears to be homogeneous, but it can be shown that the equation is well-posed and non-homogeneous using appropriate boundary conditions. In the current research, the use of the ancillary boundary integral equation for the magnetic flux density is investigated as a stand-alone equation and in tandem with the direct formulation for the magnetic vector potential. 相似文献
19.
Magnetic refrigeration is a potentially environmentally-friendly alternative to vapor compression technology because it has a potentially higher coefficient of performance and does not use a gaseous refrigerant. The active magnetic regenerator refrigerator is currently the most common magnetic refrigeration device for near room temperature applications, and it is driven by the magnetocaloric effect in the regenerator material. Several magnetocaloric materials with potential magnetic refrigeration applications have recently been developed and characterized; however, few of them have been tested in an experimental device. This paper compares the performance of three magnetocaloric material candidates for AMRs, La(Fe,Co,Si)13, (La,Ca,Sr)MnO3 and Gd, in an experimental active magnetic regenerator with a parallel plate geometry. The performance of single-material regenerators of each magnetocaloric material family were compared. In an attempt to improve system performance, graded two-material regenerators were made from two different combinations of La(Fe,Co,Si)13 compounds having different magnetic transition temperatures. One combination of the La(Fe,Co,Si)13 materials yielded a higher performance, while the performance of the other combination was lower than the single-material regenerator. The highest no-load temperature span was achieved by the Gd regenerator. 相似文献
20.
A. Fleischmann C. Enss G. M. Seidel 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):48-51
The properties and performance of magnetic calorimeters based on Au containing a few hundred ppm of Er can be fully described by equilibrium thermodynamics. As a consequence, the magnitude of the change of magnetization of the sensor, resulting from the absorption of a particle, can be calculated with confidence. The magnetization change depends upon a number of parameters such as the external magnetic field, the temperature and the concentration of the Er ions. This theoretical understanding of the calorimeter also allows us to calculate the flux signal detected by a SQUID and how that signal depends on the detector geometry and other relevant parameters. To date we have measured only cylindrically shaped sensors, which are located directly in a circular SQUID loop. However, a sensor having the shape of a thin strip, possibly in form of a meander pattern, enclosed by a loop of the same geometry, has the potential of providing enhanced flux coupling to the SQUID. We discuss the relation of sensor geometry to other parameters such as the dimensions and heat capacity of an attached particle absorber. The values of the adjustable parameters that optimize the performance of a magnetic calorimeter are investigated under a number of different experimental constraints. 相似文献