Adding Time

1. T/K ) T ( S H 0 = H h S d a Q da Q H ) T ( d H 1 = H Adding Time a e i b Q t L g k Ignoring Time Q c bc c T T T T L H j （ b ） b f （ a ） Study on the Magnetocaloric Materials and Room Temperature Magnetic Refrigerator Yuhua Hou, Zhigang Zheng, Xichun Zhong, Dechang Zeng, Hongya Yu, Zhongwu Liu Department of Metallic Materials Science and Engineering, School of Material Science and Engineering, South China University of Technology, Guangzhou, 610640, China Research Group for Magnetic Materials and Functional Thin Filmshttp://www.mmff-scut.com Introduction Magneto-caloric Materials Magnetic refrigeration technology based on magnetocaloric materials has shown great advantages in providing green, environmentally friendly and energy efficient thermal management solutions. The various types of magnetocaloric materials were systematically investigated in SCUT, China. RE-TM based alloys with large Sm and high transition temperature have shown potential in room temperature applications. A practical time-dependent model for predicting the performance and efficiency of active magnetic regenerative refrigerator is also developed. This improved model has used to evaluate the cycle performance of the self-designed facility using spherical gadolinium particles as the magnetic material and water as the heat transfer fluid. The results show that the AMR is able to obtain a temperature span of 5 K in a 1 T magnetic field after 30 cycles. Room Temperature Magnetic Refrigerator Fig.2 The (–ΔSM)-T curves for Pr2Fe17-xCox compounds (H=5.0 T) Fig. 1 The (-ΔSM)-T curves for Pr2Fe17-xAlx compounds (H = 5. 0 T) Table.1 Curie temperature Tc and –∆SM for various RE-TM based alloys (H= 5T) The system (Fig.3) consists of pumps, magnetic refrigerant, precision linear slide module slipway, cold end, hot end, electromagnetic valves, stepping motors, control unit PLC, temperature control device flow meters, etc. Magnetic refrigerant is sealed in the refrigeration box which reciprocates in the work clearance of magnetic field. A complete AMR cycle includes four processes (Fig.4). Various series of Ce2Fe17-xCox, Pr2Fe17-xAlx, Er2-xPrxFe17 , Pr2Fe17-xCox , Er2-xCexFe17 and Gd1-xNix alloys with Th2Ni17-type hexagonal crystal structure were prepared (Table 1). The Curie temperature of those alloys can be shifted to around the room temperature by compositional modification with a small amount of addition. A relatively large magnetic entropy changes (-∆SM) near Curie temperature in a comparatively wide temperature range were obtained in these alloys. Theory Simulation Fig.6 The temperature dependence of the magnetic specific heat Fig.5. Improving the magnetic Ericsson refrigeration-cycle model Blue line is hot hydraulic circle Red line is cold hydraulic circle The improved model with an added time axis (Fig.5) provides a more accurate simulation to the real situation. Using Gd as the magntocaloric material, the temperature dependence of the magnetic specific heat under various applied magnetic field is shown in Fig.6. After 250s cycles, a temperature span △T of 5K can be obtained using a 1 T field (Fig.7). The time consumed from start to the cyclic steady-state decreases with the decreasing cycle periodicity from 60s to 2s (Fig.8). Fig.3 The schematic of the reciprocating magnetic refrigerator prototype Fig. 8 The cold end temperature vs time at H=1T Fig.7 The hot end and cold end temperatures as the function of time Conclusions 1. Compositionally modified RE-TM compounds are the potential working media for room temperature magnetic refrigeration with their large magnetic entropy changes, stable chemical properties, wide transition temperature range and especially low price. 2. A time-dependent Ericsson model is established based on the analysis of magnetic refrigeration cycle, which has reduced the errors of the conventional Ericsson model. The single cycle and multi-cycle were analyzed using this improved Ericsson model. The results show that the temperature drops 5K after running for a period of time. Fig.4 Four processes of the AMR cycle