室温磁制冷最新研究进展

室温磁制冷作为一种高效环保的新制冷技术,具备十分广阔的应用前景。文章阐述了室温磁制冷中磁性材料的最新发展情况,分析了磁Brayton与磁Ericsson制冷循环的热力特性,讨论了基于非Darcy效应的活性蓄冷器的多孔介质模型,介绍了新型室温磁制冷样机,并指出了室温磁制冷研究的方向。     

室温磁制冷研究进展

室温磁制冷技术是一项新的制冷技术,具有高效环保的特点,应用前景十分广阔,有望取代传统的蒸气压缩式制冷方法。阐述了磁热效应的原理,系统介绍了室温磁制冷中磁性材料、磁制冷循环、蓄冷器以及典型制冷机的发展情况,并对室温磁制冷的发展进行了展望。     

普适定常流内可逆制冷机循环模型的(火用)经济性能优化

用有限时间热力学方法分析工作在恒温热源TH、TL之间内可逆普适制冷机循环模型的(火用)经济性能,导出循环利润率与工质温比、制冷系数与工质温比的关系式,和利润率与制冷系数的特性关系.所得结果包含了内可逆Carnot、Diesel、Otto、Atkinson和Brayton制冷循环的有限时间(火用)经济性能.     

三热源制冷机的制冷系数的分析

推导出 q 正比于△1/T 传热情况下最大制冷率时,内可逆三热源制冷循环的制冷系数ε_m可表示为ε_m=T_L(T_H-T_0)/[TH(2T_0-T_L)-T_LT_0],而相应的最大制冷率为 R_(max)=(α/16)T_L(T_H-T_0)~2/[T_HT_0~2(T_H-T_L)]。其中,T_H,T_L 和 T_0分别为高温热源、制冷物体和环境温度,α为传热系数。所得结果不同于线性传热 q 正比于△T 情况下所得结果。     

室温磁制冷研究新动态及应用

室温磁制冷是磁制冷技术发展的必然趋势.本文介绍了近10年室温磁制冷研究的最新动态,分析了磁制冷循环理论研究的结果,详细说明了室温磁制冷材料和样机的新近成果,并对室温磁制冷的商业化应用前景进行了展望.     

磁埃里克森制冷循环

对磁埃里克森制冷循环作了简要的讨论和介绍.指出磁埃里克森制冷循环不具有理想(完全)的热,其制冷系数低于同样温度的卡诺制冷循环的制冷系数.但磁埃里克森制冷循环仍是磁制冷机研制中值得重视的一种循环方式.可存磁制冷技术劈展中起重要作用.     

普适定常流内可逆制冷机循环模型的炯经济性能优化

用有限时间热力学方法分析工作在恒温热源TH、TL之间内可逆普适制冷机循环模型的炯经济性能，导出循环利润率与工质温比、制冷系数与工质温比的关系式，和利润率与制冷系数的特性关系。所得结果包含了内可逆Carnot、Diesel、Otto、Atkinson和Brayton制冷循环的有限时间炯经济性能。     

磁制冷循环分析

磁制冷循环是磁制冷技术中的重要环节,为磁制冷机的高效运行提供了理论基础.本文结合磁制冷循环的理论研究,详细介绍了磁制冷基本循环和活性蓄冷器(Active Magnetic Regenerator,AMR)循环,重点分析了影响循环的不可逆因素,并对磁制冷循环的发展进行了展望.     

磁制冷发展现状及趋势：Ⅱ磁制冷技术

简要介绍了磁制冷实现的原理,概括了磁制冷与气体压缩制冷的差异,比较了4种磁制冷循环的优缺点及适用场合,重点评述了室温温区磁制冷样机的研究进展,分析了磁制冷的关键技术,最后给出了磁制冷的潜在市场并展望了发展趋势。     

Er2-xCexFe17金属间化合物的磁熵变特性研究

在氩气气氛中用熔炼法制备了Er2-xCexFe17(x=0,0.05,0.08,0.1,0.15,0.2,0.3,0.4)化合物,通过粉末X射线衍射和SQUID磁强计研究了样品的结构、磁性和磁熵变.结果表明,Er2-xCexFe17化合物具有Th2Ni17型六方结构,通过成分微调使其居里温度处在室温附近.Er2-xCexFe17化合物的λ形(-△SM)-T曲线表明其在居里点附近发生的相变属于二级相变,它使化合物可在较宽温区范围内保持较大的磁熵变.当x=0.05～0.15时,Er2-xCexFe17化合物在2.0和5.0 T外场作用下的最大磁熵变达到金属Gd的40～50%,且其化学性质稳定、制冷温区宽、价格低廉,是一类性价比较高、应用潜力较大的新型低场室温磁制冷工质材料.     

Research on performance of regenerative room temperature magnetic refrigeration cycle

On the basis of classical Langevin theory along with statistical mechanics, thermodynamics and magnetism, a new expression of magnetocaloric parameters used for room temperature magnetic refrigeration is proposed, which is briefer and more accurate than the existing one, providing a new way for studying performance of regenerative room temperature magnetic Ericsson refrigeration cycle. Influences of temperature of heat reservoirs and magnetic intensity on cycle refrigeration capacity and coefficient of performance are analyzed. The results show that the maximal temperature span of the cycle increases but its increasing rate decreases with the increase of magnetic field strength. In addition, there exists only one maximum value of effective refrigerating capacity. Two cycles with the same COP can reach a same temperature span under a certain magnetic field strength. A large magnetic field strength can improve COP but the increase rate of COP decreases.     

多种不可逆性对磁埃里克森制冷循环性能的影响

建立以顺磁盐为工质的不可逆埃里克森制冷循环新模型,探讨热阻、热漏、回热损失及工质内部不可逆性等对循环性能的影响,分析和讨论制冷循环的重要性能参数及优化工作区域,所得结论比现有文献的相关结论更普遍,可为磁制冷机的优化设计和性能评价提供新理论参考.     

一种新型吸收-压缩复合制冷循环模拟

为了对一种新型吸收-压缩复合制冷循环的性能进行模拟,使用Visual Basic语言自行编制了一个程序.该程序模拟了发生温度、蒸发温度、冷凝温度、加热量、制冷量对系统性能的影响,并将其性能与传统蒸气压缩式制冷循环作了对比.模拟结果表明:当发生温度升高时,新循环的制冷系数先增大后减小;当蒸发温度升高或加热量增大时,新循环...     

R404A直接接触凝结制冷循环的性能分析

提出R404A直接接触凝结换热的制冷循环,分析R404A直接接触凝结制冷循环的热力性能,并与常规双级压缩制冷循环的性能进行对比。得出结论:在一定的冷凝温度、蒸发温度和过冷液体的过冷度下,直接接触凝结制冷循环存在最佳的饱和液体温度,并在此最佳的饱和液体温度下,获得最优的性能和最小的冷凝热负荷,随着过冷液体的过冷度增大和蒸发温度升高,直接接触凝结制冷循环的性能系数增加、冷凝热负荷减少,获得最优性能的最佳饱和液体温度值提高。过冷液体的过冷度为25℃时,直接接触凝结制冷循环的最佳性能系数较双级压缩制冷循环的最佳性能系数提高6.2%。直接接触凝结制冷循环的最小冷凝热负荷较双级压缩制冷循环的最小冷凝热负荷减小1.8%。     

Magnetic stirling cycles--A new application for magnetic materials

There is the prospect of a fundamental new application for magnetic materials as the working substance in thermodynamic cycles. Recuperative cycles which use a rare-earth ferromagnetic material near its Curie point in the field of a superconducting magnet appear feasible for applications from below 20K to above room temperature. The elements of the cycle, advanced in an earlier paper, are summarized. The basic advantages include high entropy density in the magnetic material, completely reversible processes, convenient control of the entropy by the applied field, the feature that heat transfer is possible during all processes, and the ability of the ideal cycle to attain Carnot efficiency. The mean field theory is used to predict the entropy of a ferromagnet in an applied field and also the isothermal entropy change and isentropic temperature change caused by applying a field. Results are presented for J=7/2 and g=2. The results for isentropic temperature change are compared with experimental data on Gd. Coarse mixtures of ferromagnetic materials with different Curie points are proposed to modify the path of the cycle in the T-S diagram in order to improve the efficiency or to increase the specific power.     

General analysis of magnetic refrigeration and its optimization using a new concept: maximization of refrigerant capacity

A general approach to the problem of refrigeration optimization is presented based on the concept that the most appropriate and meaningful measure of the level of refrigeration is the product of entropy absorbed by the refrigerant at the cycle cold temperature, ΔS_c, and the temperature span, ΔT, over which it is pumped. Results are presented of mean-field calculations of ΔS_cΔT, the refrigerant capacity, for ferromagnetic, paramagnetic, and antiferromagnetic refrigerants as a function of the various operating parameters and those values that lead to maximization of refrigerant capacity are shown. Good agreement is found with values of ΔS_cΔT obtained from experimentally determined magnetic entropies. Several prototype magnetic refrigerators have been analysed using this approach and alternatives are suggested. In addition it is proposed that useful measures of the performance of a refrigerant-cycle combination are given by two ratios. These ratios are of refrigerant capacity to the energy in the applied magnetic field over the volume of the refrigerant and of refrigerant capacity to the positive work done on the refrigerant in one cycle. For T < ≈ 20 K, maximum values of these ratios for optimized ferromagnetic refrigerant cycles typically occur for applied magnetic fields of < 1 T. This is achievable using permanent, rather than superconducting, magnets. It is concluded that two of the greatest needs for further development of low temperature magnetic refrigeration are finding and characterizing ferromagnetic refrigerants with appropriate Curie temperatures (compounds containing Eu²⁺ appear promising), and the analysis and development of regenerative magnetic cycles using He gas as a heat transfer medium that take full advantage of optimized ferromagnetic refrigerant cycles in fields < 1 T.     

Thermodynamics of magnetic refrigeration

A comprehensive treatment of the thermodynamics of cyclic magnetic refrigeration processes is presented. It starts with a review of the work, heat and internal energy of a magnetized specimen in a magnetic field, and a list of the thermodynamic potentials is given. These are based on the very recent discovery of an alternative Kelvin force. It is shown that this force is compatible with the internal energy proposed by Landau and Lifshitz. New formulas for the specific enthalpies are presented. Cyclic processes are discussed in detail, e.g. the Brayton, Ericsson and Carnot cycles. Magnetic refrigeration and magnetic heat pump cycles are preferably designed by applying the cascade or/and regeneration principle. Cascade systems allow wider temperature ranges to be obtained. The main objective of this article is to yield a theoretical basis for an optimal design of new magnetic refrigeration and heat pump devices.     

Impact of the initial field on the thermodynamic performance of room-temperature magnetic refrigeration cycle

The thermodynamic cycle performance of Gadolinium (Gd) and Gd_0.87Dy_0.13 used as the working substance in regeneration magnetic Brayton and Ericsson refrigeration cycles are investigated under different external magnetic field conditions. Based on the experimental iso-field heat capacities of Gd with different magnetic fields, the effects of magnetic field change on thermodynamic performances including the magnetic entropy change, cooling quantity, non-perfect regeneration, net cooling quantity, and coefficient of performance (COP) are analyzed and discussed. The present work shows the possibility of reducing the regenerative losses and thereby improving the net cooling quantity for a given field change by selecting optimal initial and final magnetic field values. The similar analysis and calculation of the related thermodynamic performances are further applied to the magnetic material Gd_0.87Dy_0.13 which exhibits better net cooling quantities when compared to Gd at low temperature.     

一个用太阳能驱动的新型吸收制冷循环

提出了一个由太阳能驱动的新型吸收制冷循环。论文将热变器原理用于吸收制冷,从而大大提高了吸收制冷的循环效率。详细介绍该新型循环的热力学模型,同时以一个典型的太阳日照为例,计算了新循环的性能系数（ＣＯＰ）、冷凝热、理论极限制冷温度和制冷量,并与传统循环进行了比较。结果表明,新循环不仅克服了传统循环在热源工况不稳定时将导致系统工况不稳定甚至不能工作的缺点,而且还具有更高ＣＯＰ值。     

Performance characteristics of an irreversible magnetic Brayton refrigeration cycle

Based on the thermodynamic properties of a paramagnetic salt, an irreversible model of the magnetic Brayton refrigeration cycle is established, in which the working substance is a special paramagnetic material. The expressions of the important performance parameters, such as the coefficient of performance, refrigeration load and work input, are derived. Moreover, the optimal performance parameters are obtained at the maximum coefficient of performance. The results obtained here may include the ones of the magnetic Brayton refrigeration cycle using the magnetic material obeyed the Curie law as the working substance, the magnetic Brayton refrigeration cycle without regeneration and the eversible magnetic Brayton refrigeration cycle. Therefore, the results obtained here have general significance and will be helpful to deeply understand the performance of a magnetic Brayton refrigeration cycle.