磁制冷工质材料的研究进展

本文简要叙述了磁制冷的基本原理和历史发展,详细地总结了国内外不同温区的磁制冷工质材料的研究成果,并展望了磁制冷工质材料的研究前景。     

磁制冷工质材料的研究进展

本文简要叙述了磁制冷的基本原理和历史发展,详细地总结了国内外不同温区的磁制冷工质材料的研究成果,并展望了磁制冷工质材料的研究前景。     

一种耦合斯特林制冷效应的复合式磁制冷循环的数值模拟

介绍了一种斯特林回热式制冷效应和主动式磁制冷效应耦合的新型制冷循环。循环采用的回热填料钆既是磁制冷循环的磁热材料又是斯特林制冷的回热材料。通过斯特林回热式制冷循环和磁制冷效应的正面耦合叠加获得更优良的制冷效果。同时介绍了一种磁制冷回热器的数值计算模型,本模型是基于控制容积法计算的一维交变流动模型,并对常规回热器内填料能量控制方程进行了修正,考虑了磁性材料磁热效应的影响,添加内热源项。论文计算分析了系统相位角、压力和频率的变化对制冷性能的影响。文中给出的部分模拟结果对后续实验台的改造有一定的借鉴指导作用。     

耦合高压斯特林制冷效应的复合磁制冷循环的数值模拟

本文借助计算流体力学软件, 对复合磁制冷机进行整机数值模拟分析. 以复合磁制冷机为建模原形, 分别计算了主动式磁制冷循环以及复合磁制冷循环. 利用模型计算分析了利用系数, 工作频率对主动式磁制冷的制冷效果影响, 同时模拟计算了不同相位角、不同频率下的复合磁制冷机的制冷效果, 计算得到适合复合磁制冷循环的最佳匹配相位角. 模拟计算结果对后续实验台的设计搭建有很好的指导作用.     

磁热效应材料的研究进展

磁制冷技术的发展取决于具有大磁热效应磁制冷材料的研发进展.经过长期的工作积累,特别是近20年来的努力,许多新型磁制冷材料的探索和研究极大地促进了磁制冷技术的进步.本文介绍了磁热效应的基本原理和磁制冷研究的发展历史,系统综述了低温区和室温区具有大磁热效应的磁制冷材料的研究进展,重点介绍了一些受到较为关注的磁热效应材料的最新研究成果.低温区磁制冷材料主要包括具有低温相变的二元稀土基金属间化合物(RGa,RNi,RZn,RSi,R_3Co以及R_(12)Co_7)、稀土-过渡金属-主族金属三元化合物(RTSi,RTAl,RT_2Si_2,RCo_2B_2,RCo_3B_2)以及四元化合物RT_2B_2C等,其中R代表稀土元素,T代表过渡金属.这些材料一般都具有二级相变,具有良好的热、磁可逆性,也因其合金属性具有良好的导热性.室温区磁制冷材料主要包括Gd-Si-Ge,La-Fe-Si,Mn As基,Mn基Husler合金,Mn基反钙钛矿,Mn-Co-Ge,Fe-Rh以及钙钛矿氧化物等系列.这些材料一般都具有一级相变,多数在室温具有巨大的磁热效应而受到国内外的极大关注.其中,La-Fe-Si系列是国际上普遍认为具有重要应用前景的磁制冷工质之一,也是我国具有自主知识产权的材料.本文还对磁制冷材料的发展方向进行了展望.     

在室温磁制冷中铁磁体作为工作物质的可能性

在室温磁制冷中铁磁体是合适的工作物质．铁磁体内部存在的交换相互作用，使我们能够以较低的外场达到排出磁熵的目的．同时，铁磁体磁热过程本身的可逆性，使我们有可能用它构成高效的磁制冷机．本文从铁磁体磁热效应的基本实验事实出发，讨论磁制冷机工作物质选择的判据，强调真实磁化过程在制冷应用中的意义，利用分子场近似给出对材料选取有用的公式，通过对比指出，Ｆｅ基合金具有很好的应用前景．     

二级不可逆磁Brayton制冷循环性能分析及参数优化

建立受有限速率热传导和绝热过程不可逆性影响的二级磁Brayton制冷循环模型,导出循环的性能系数和制冷率表达式,分析等磁场过程的磁场比、绝热不可逆因子、等磁中冷过程等对二级不可逆磁Brayton制冷循环最大制冷率及相关参数的影响,所得结论能为提高磁制冷机的循环性能提供参数设计参考.     

平板磁制冷和热电磁复合制冷微元循环数值研究

本文借助COMSOL多物理场耦合软件,构建了二维瞬态平板磁制冷微元模型和热电磁复合制冷微元模型,考察了热电臂厚度、电流、运行频率、外界对流换热系数对复合制冷性能的影响。模拟结果显示,在大多数工况下热电磁复合模型的比制冷功均大于磁制冷模型的比制冷功率;改变不同几何和运行参数对复合制冷性能有不同的影响。在研究工况范围内,改变热电臂厚度(0.05～0.5 mm)、电流(0.4～0.8 A)、运行频率(0.5～4 Hz)和对流换热系数(500～2000 W·m^-2·K^-1),热电磁复合制冷微元模型相比于平板磁制冷微元模型,制冷功率密度最大提高分别为2.05倍、2.12倍、2.68倍、1.87倍。本研究对后续开展热电磁复合制冷系统机理研究提供重要指导。     

热滞对以LaFe_(11.6)Si_(1.4)为工质的回热Ericsson制冷循环性能的影响

一级相变材料LaFe_(11.6)Si_(1.4)是磁制冷应用中的重要磁热材料,其固有的磁滞和热滞对实际制冷循环性能有较大影响,然而现有文献对此尚未研究。本文基于考虑热滞影响的材料LaFe_(11.6)Si_(1.4)的等场热容实验数据,建立考虑热滞效应的回热Ericsson制冷循环,揭示热滞、非平衡回热和冷热源温度等对制冷循环主要热力学性能参量的影响,应用数值计算方法,比较了考虑热滞与否时制冷循环的净制冷量、性能系数等性能参量。研究结果能为磁制冷机循环的优化参数设计提供有益的参考。     

不同换热时间对旋转式磁制冷性能影响

为分析不同换热时间对旋转式室温磁制冷系统制冷性能的影响,设计了一套以Gd颗粒钆(粒径：0.3-0.5 mm)为磁工质的双永磁旋转式室温磁制冷系统。通过对该系统制冷性能的试验研究,绘制出了不同工况下系统冷端温度的变化曲线,计算出其理想COP和实际COP。试验得出：在换热时间为2 s时冷端保温箱与环境温差最大为10℃,系统制冷系数最高,性能最好。     

Properties of magnetocaloric La(Fe,Co,Si)13 produced by powder metallurgy

We present a comprehensive study of the magnetocaloric materials series La(Fe_1−xCo_x)_11.9Si_1.1 with 0.055<x<0.122. The ferromagnetic samples were manufactured using a novel powder metallurgy process by which industrial scale production is feasible. This new production method makes the materials more attractive as magnetic refrigerants for room temperature magnetic refrigeration. The Curie temperature of the compounds can be easily tuned by altering the Co content and all samples have little magnetic anisotropy and present a second-order magnetic transition so that thermal and magnetic hysteresis is absent. For all seven samples, we have calculated the magnetic entropy change, ΔS_M, from initial curve measurements and measured the adiabatic temperature change, ΔT_ad, directly. In addition, for two of the samples, we determined the heat capacity as a function of applied magnetic field and the thermal conductivity. Where relevant, the results are compared with those of Gd, the benchmark material for room temperature magnetic refrigeration.     

An optimized magnet for magnetic refrigeration

A magnet designed for use in a magnetic refrigeration device is presented. The magnet is designed by applying two general schemes for improving a magnet design to a concentric Halbach cylinder magnet design and dimensioning and segmenting this design in an optimum way followed by the construction of the actual magnet. The final design generates a peak value of 1.24 T, an average flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an average low flux density of 0.08 T also in a 2 L volume. The working point of all the permanent magnet blocks in the design is very close to the maximum energy density. The final design is characterized in terms of a performance parameter, and it is shown that it is one of the best performing magnet designs published for magnetic refrigeration.     

Enhancement of magnetocaloric effects in La0.8R0.2(Fe0.919Co0.081)11.7 Al1.3 (R=Pr, Nd) compounds

The magnetic properties and magnetocaloric effects (MCEs) in La_0.8R_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La_0.8Nd_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 compound are −4.56 and −9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.     

Magnetocaloric effect in La0.67Sr0.33MnO3 manganite above room temperature

The La_0.67Sr_0.33MnO₃ composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La_0.67Sr_0.33MnO₃ could be considered as a potential candidate for magnetic refrigeration applications above room temperature.     

Einstein制冷循环研究新进展

文中介绍了单压吸收式制冷的主要类型,对两种单压吸收式制冷循环进行了对比阐述。就Einstein制冷循环的研究进展进行了归纳总结,对目前研究Einstein制冷循环所面临的部分问题进行了分析,并对进一步研究提出展望。     

采用非单一吸附式制冷方式的研究现状与展望

固体吸附式制冷是一种可直接利用余热作为驱动热源和使用天然制冷剂的制冷方式,它对环境保护与节约能源具有重要意义,吸附式制冷技术目前已成为国际上普遍关注的一个学术方向。其中,采用其他以热能为动力的制冷循环方式与固体吸附式联合制冷在制冷领域已成为一个重要方向。首先介绍非单一吸附式制冷方式的总体研究进展,随后对其未来研究和应用发展方向作了展望。     

Theoretical study of the magnetic and magnetocaloric properties of the ZnFe3N antiperovskite

The antiperovskite ZnFe₃N is studied by using density functional theory calculations and Monte Carlo simulation. Based on the electronic and magnetic properties, it is found that ZnFe₃N behaves as a ferromagnetic metallic material. The exchange interactions and the magnetic anisotropy, defined as the Hamiltonian parameters of the studied system, are calculated and used in the Monte Carlo study. The second order transition at a Curie temperature T_c = 760K, reviled experimentally in a previous work, has been confirmed. The magnetic entropy change and the relative cooling power, under various applied magnetic fields are analyzed in order to evaluate the magnetocaloric effect of ZnFe₃N. The results suggest that ZnFe₃N is a good candidate for the magnetic refrigeration applications.     

低温制冷技术在光电器件中的应用及发展

】重点论述了与光电子技术的密切相关的低温制冷技术应用及发展 ,叙述了光电器件常用的几种制冷机的主要特点。根据我国光电器件对低温制冷机的需求概况 ,对我国今后制冷机的发展做了初步展望