复合工质室温磁制冷机参数优化设计研究

Room-temperature magnetic refrigeration with environmental safety and saving energy is one of the research hotspots of novel technologies. Breaking through the bottleneck of small cooling power or small refrigeration temperature span, high manufacture cost of the existing room-temperature magnetic refrigerator (RTMR) is the necessary way to its commercial application. For this reason, to explore some new refrigeration materials with large temperature span, large refrigeration capacity and low cost is an important work for improving the cyclic performance of RTMR. In the present project, we are to study some new composites of RTMR, whose components include first-order transition magnetocaloric materials as MnFe based ones. Based on the molecular field theory, de Gennes factor model，the experimental characteristics of the iso-field heat capacity changing with temperature for the related materials as well as the target of keeping magnetic entropy changes of composite materials as an approximate constant within the large temperature span, the optimal mass ratio between components and composite material is obtained with theoretical analysis and numerical calculation. Furthermore, the regenerative Ericsson refrigeration cycle using the composite as the working substance is to be established and the influences of non-perfect regeneration, the temperatures of the cold and hot sources, application magnetic field,thermal hysteresis on the performance of the refrigeration cycle will be revealed. Then, AMR refrigerator using the composite as the working substance is to be built. Combining with theoretical research and experimental test results, we would obtain some new design parameters of the refrigerator with large temperature span, high COP and cooling power. The research results can provide theoretical and technology instructions for the optimal selection of the working substances and optimal parametric design of RTMR.

环保节能的室温磁制冷是高新技术的研究热点，突破制冷功率或温跨小、制造成本较高等瓶颈是其走向商业化的必经之路，进而探索大温跨、大制冷容量且廉价的工质材料是提高室温制冷机循环性能的重要部分。本项目研究组元包含一级相变磁热材料(如MnFe基系列磁热材料等）的若干新复合室温磁制冷材料，基于平均场理论和德金因子模型、相关组元材料等场热容随温度变化实验特性以及复合材料的总磁熵变在大温度范围内接近常数的目标，通过理论分析和数值计算，获得复合材料中各组元材料的优化质量比；进一步建立以这些复合材料为工质的回热Ericsson制冷循环，揭示非平衡回热、冷热源温度、应用磁场、材料热滞等对循环性能的影响；构建复合工质主动式室温磁制冷机实验台，理论研究与实验测试相结合，获得大温跨、高性能系数和较大制冷功率的室温磁制冷机新设计参数，为室温磁制冷机的工质优选和参数优化设计提供理论和技术指导。

环保节能的室温磁制冷是高新技术的研究热点，突破制冷功率、温跨小、制造成本高等瓶颈是其走向商业化的必经之路，而探索大温跨、大制冷容量且廉价的工质材料是提高室温制冷机性能的重要途径。本项目探索组分包含MnFePSi，MnFePGe等磁热材料的若干新复合室温磁制冷材料，基于复合材料总磁熵变在较大温区接近常数的目标，通过优化理论和数值计算，获得复合材料中各组分材料的优化质量比。如Mn1.24Fe0.76P0.75Ge0.25, Mn1.2Fe0.8 P0.75Ge0.25 和 Mn1.1Fe0.9P0.78Ge0.22组成的复合材料（简称F1）优化质量比为0.44, 0.11和0.45；Mn1.32Fe0.67P0.52Si0.49, Mn1.37Fe0.63P0.5Si0.5和Mn1.35Fe0.66P0.5Si0.5组成的复合材料(简称F2)优化质量比为0.22, 0.33, 0.45。进一步建立以这些复合材料为工质的回热Ericsson、Brayton制冷循环，揭示非平衡回热、热源温度、应用磁场、材料热滞等对净制冷量和COP的定量影响。结果表明：1）当Ericsson制冷循环工作在275-290K及0~2T场变时，F1对应的净制冷量最大值达2870 J/kg, 分别是对应组分材料的18.6, 10.43, 5.49倍，而对应的COP达16.4。2）当F2运行在回热Brayton制冷循环且材料热滞被考虑时，制冷循环的净制冷量、最优工作温度范围及COP分别减少14.6%, 18.8% 和16.1%。3）以复合材料F1为工质的回热Ericsson制冷循环的净制冷量和COP均比回热Brayton制冷循环的大些。4）制备了La0.8Ce0.2Fe11.495Mn0.205Si1.3, La0.8Ce0.2Fe11.515 Mn0.185Si1.3, La0.8Ce0.2 Fe11.535Mn0.165Si1.3，并设计了复合磁制冷材料（简称F3），按0.56,0.32,0.12质量比复合，在285K～296 K温跨内磁熵变保持较大。进一步搭建以F3为工质的主动式回热室温磁制冷机试验台，在应用磁场1.5T，运行周期4.6s或5.6s等参数下, 测试了制冷机的制冷功率、COP和制冷温差。5）申报了F2的发明专利。研究结果能为室温磁制冷机的工质优选和参数优化设计提供指导。