Analysis of room temperature magnetic regenerative refrigeration

Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 °C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed.     

Thermal investigations of an experimental active magnetic regenerative refrigerator operating near room temperature

In this paper, numerical and experimental investigations on a magnetic refrigeration device based upon the active magnetic regeneration (AMR) cycle operating near room temperature are presented. A numerical 1D model based on the transient energy equations is proposed for modelling the heat exchange between the magnetocaloric material and the carrier fluid in the regenerator bed. The validity of 1D AMR-numerical model is investigated through the recently developed magnetic cooling demonstrator by Clean Cooling Systems SA (CCS) at the University of Applied Sciences of western Switzerland (HES−SO). The obtained results including the temperature span, the coefficient of performance and the cooling power are presented and discussed. In general, good agreements have been noted between the experimental and numerical results.     

A magnetic field source system for magnetic refrigeration and its interaction with magnetocaloric material

The magnetic field source system constitutes an important component of magnetic refrigeration. A specific methodology for its' dimensioning is proposed in this paper. It is based on analytical calculation models and takes into account the geometry of the system, the magnetic properties of the magnetocaloric material and the magnetothermal cycle (direct or active magnetic regenerative refrigeration). The analytical calculation of the field is first developed and applied to usual permanent magnet-based field sources with and without soft magnetic materials. Then the forces generated by the interaction between the field and the magnetocaloric effect material are analytically evaluated considering the real field distribution. All calculations are validated thanks to two- or three-dimensional finite element method simulations.     

Experimental investigation of a three-material layered active magnetic regenerator

This work reports on experimental studies using an active magnetic regenerative test apparatus (AMRTA) in near room-temperature refrigeration cycles. Experiments using regenerator beds composed of three different magnetocaloric materials combined in a layered configuration with applied fields of 2 T have produced no-load temperature spans in excess of 50 K. The test apparatus uses two active magnetic regenerators each containing approximately 135 g of refrigerant. An overview of the test apparatus, operating parameters, and performance is described. The impacts of operation at varying heat rejection temperatures, applied fields of 1.5 T and frequencies between 0.65 and 1.0 Hz are presented. In addition, the impacts of operating pressure and applied load on temperature spans are discussed.     

Experimental results for a magnetic refrigerator using three different types of magnetocaloric material regenerators

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.     

回热损失对磁斯特林制冷循环制冷率的影响

从铁磁质的磁化强度一般表示式出发，探讨热阻和回热损失对磁斯特林制冷循环性能的影响，导出最大制冷率及其它性能参数。得到了结果适用于以顺磁质为工质的磁斯特林制冷循环。并指出在理想回热条件下的结论也适用于磁卡诺制冷循环。     

(La0.6Dy0.1)Sr0.3MnO3的磁热效应研究

对庞磁电阻材料(La0.6Dy0．1)Sr0.3MnO3的磁热效应进行了研究．通过不同温度下的等温磁化(M-H)曲线的测量和计算，发现伴随铁磁-顺磁(PM—FM)相变出现大的磁热效应，额外的磁性交换作用将导致额外的磁熵变化．结果表明，(La0.6Dy0．1)Sr0.3MnO3可以作为室温下使用的磁制冷工质候选材料．     

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.     

Magnetic and Magnetocaloric Properties of Er2TiMnO7 Compound

Magnetic properties and magnetocaloric effects of the Er₂TiMnO₇ compound have been evaluated by magnetization and heat capacity measurements. The reversible magnetic-entropy change is found to be just above the boiling point of helium and hydrogen liquefaction temperature range of 2 to 50 K. The magnetocaloric behavior estimated from specific heat data is confirmed by adiabatic magnetization above 2 K, and indicates that Er₂TiMnO₇ is a potential candidate for application in magnetic refrigeration in the low-temperature range.     

Simulation of solid-state magnetocaloric refrigeration systems with Peltier elements as thermal diodes

Magnetic refrigeration as an alternative for vapor-compression technology has been the subject of many recent studies. Most of the studies focus on systems with limited cycle frequency in which a fluid transfers heat to and from the magnetocaloric material. A suggested solution for increasing the frequency is use of solid-state magnetic refrigeration in which thermal diodes guide the heat from the cold end to the warm end. In this work a solid-state refrigeration system with Peltier elements as thermal diodes is modeled in details unprecedented. The performance of Peltier elements and magnetocaloric materials under their transient working conditions after reaching cyclic steady state are simulated by two separate computer models using finite element method and finite volume method. The models, in parts and as a whole, are verified. The verified finite element model is used for a parametric study and the results are analyzed.     

Design and performance of a room-temperature hybrid magnetic refrigerator combined with Stirling gas refrigeration effect

The experimental prototype described in this work is a hybrid refrigerator that combines the active magnetic refrigeration effect with the Stirling gas regenerative refrigeration effect. In this prototype, gadolinium sheets are packed in the regenerator matrix for both Stirling and active magnetic regenerative refrigeration. Experimental tests were carried out to measure the cooling performance of this hybrid prototype. The influence of the phase angle on the cooling performance was investigated, and a reasonable phase angle of 90° was determined to obtain optimal cooling performance. By combining the two refrigeration effects, a minimum cooling temperature without heat load of 3.5 °C was reached, which is lower than that of 6.5 °C for the pure Stirling refrigeration effect without the magnetic cooling effect. The results of this study show that the cooling performance is improved by 24% for the hybrid effects compared with that exploiting only the Stirling gas refrigeration effect.     

变频空调用无稀土磁阻电机的退磁仿真及验证

在以往的变频空调中,压缩机电机常采用高效节能的稀土永磁同步电机,但稀土价格的上涨使其在空调中的继续应用受到限制。无稀土磁材的永磁辅助式同步磁阻电机（无稀土磁阻电机）成本低廉,性能可与稀土永磁同步电机相媲美,在空调上具有很好的应用前景,但因无稀土磁材磁性能较弱,电机抗退磁能力较差而难以系列化生产。本文借助Ansoft软件对无稀土磁阻电机的退磁情况进行仿真,并与等效磁路法计算结果及实测结果进行对比。结果表明,采用三维瞬态场的动态退磁仿真结果与实测值很接近,该仿真方法能够很好地反映电机实际的抗退磁能力,在缩短开发周期、降低开发成本方面效果显著。     

放电等离子烧结NdFeB磁体的磁化特征

利用放电等离子烧结技术(SPS)制备烧结钕铁硼磁体SPS NdFeB。为了更好地理解SPS Nd-FeB磁体的磁硬化机理,利用振动样品磁强计研究了SPS NdFeB磁体在室温下的磁化和反磁化过程。结果表明,在强度为800kA/m的较低外加磁场和强度为1760kA/m的较高外加磁场下的磁化特征明显不同,前者可称为形核控制模式,后者则为钉扎控制模式。比较样品的磁化过程和反磁化过程的曲线,发现样品的矫顽力大小等于样品磁化过程钉扎场的大小。     

Review on research of room temperature magnetic refrigeration

Room temperature magnetic refrigeration is a new highly efficient and environmentally protective technology. Although it has not been maturely developed, it shows great applicable prosperity and seems to be a substitute for the traditional vapor compression technology. In this paper, the concept of magnetocaloric effect is explained. The development of the magnetic material, magnetic refrigeration cycles, magnetic field and the regenerator of room temperature magnetic refrigeration is introduced. Finally some typical room temperature magnetic refrigeration prototypes are reviewed.     

The influence of the magnetic field on the performance of an active magnetic regenerator (AMR)

The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20-40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5-20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30-50% but the maximum temperature span by only 20-30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry.     

热容率对室温磁制冷机工质盘传热影响研究

在室温磁制冷机主动式磁回热器(AMR)工质盘强化传热研究中,引入了一个新的参数热容率TCR(Thermal Capacity rate Ratio)。TCR参数反映了工质盘内换热流体将磁体在励磁过程中产生的热量从回热器中置换出去的能力。计算磁制冷系统的TCR,通过和制冷功率、COP进行对比分析,提出了室温磁制冷机工质盘强化传热的思路。     

磁制冷材料研究进展

综述了磁制冷机理及几种磁制冷材料的研究进展,特别对具有热弹性马氏体相变的Heusler型铁磁性材料以及快速凝固技术在磁制冷材料制备中的应用予以关注,并指出该技术发展的关键在于寻找室温附近具有宽工作区间、易制备、低成本且在永久磁铁磁场下具有大磁熵变的材料。     

A review on Mn based materials for magnetic refrigeration: Structure and properties

Magnetic refrigeration employing magnetically ordered materials is a relatively novel technique, differing in some respects from magnetic cooling by means of adiabatic demagnetization of paramagnetic substances. Magnetic refrigeration has been known for more than a century and is based on the magnetocaloric effect. It has received new impetus recently because it has several advantages over vapor-compression refrigeration. In the last few years the magnetic and magnetocaloric properties of a large number of intermetallic compounds were investigated, in which the magnetic moments are carried by atoms of 3d transition elements. In the present paper we will focus on intermetallic compounds in which one of the components is Mn. The results obtained on several groups of such intermetallic compounds will be reviewed. By far the most promising materials of this group of intermetallics are compounds of the type MnFeP_1−xAs_x. Although it is understood that these compounds are probably nontoxic, the presence of As atoms in them might form a mental barrier to exploit these materials on a commercial basis. Special attention will therefore be paid to efforts attempting to substitute other elements for As in MnFeP_1−xAs_x with the proviso that the favorable magnetocaloric properties be retained.     

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。     

Theoretical study on stress-induced demagnetization in magnetic recording media

A simple and fundamental model of stress-induced demagnetization, which has scarcely been analyzed theoretically, is presented. Stress-induced demagnetization in a magnetic recording medium results from the magnetization reversal of individual magnetic particles dispersed in the magnetic layer. The magnetoelastic energy due to the application of three-dimensional stresses and the magnetostatic energy due to the demagnetizing field must be taken into account for an investigation of the magnetization reversal of each particle. It is found that the magnetization reversal can take place even during small stresses if a sufficient demagnetizing field exists. The sign of the magnetostrictive coefficient λ100has a significant relation to the susceptibility of magnetization reversal.