**3.2 The magnetic system of Steyert**

An alternative system with a rotating refrigerant, implementing a Brayton's cycle has been designed by Steyert (Yu, 2003). In this system, the porous magnetocaloric material has a form of rings. This wheel (the regenerator with a ring form) rotates through a first area of

Magnetic Refrigeration Technology at Room Temperature 235

Okamura et al. have constructed a magnetic refrigeration system, as shown in Fig. 7-a (Okamura, 2006). The yoke has an outer diameter of 27 cm and a length of 40 cm. The magnetic field is produced by rotating permanent magnets, producing a maximum field of 0.77 T. The bed regenerator is composed of 4 blocks. Each block is composed of a different alloy GdDy (sphere shaped) to enhance the range of variation of temperature. The fluid circulation is ensured by a pump and a rotary valve. The power obtained is about 60 W. The initial system has been improved as shown in Fig. 7-b (Okamura, 2007). The stator used was a laminated yoke and the magnetic field source was improved (the maximum field is 0.9 T).

(a)

Fig. 6. The Magnetic device made in Spain (Bohigas, 2000).

This helped to obtain a power of 100 W (using Gd as MCE material).

**3.5 Japanese system** 

low magnetic field and a second area of high magnetic field as shown in Fig. 5. The exchange fluid enters the wheel (regenerator) at the temperature *Thot* and exits at the temperature*Tcold* , having transferred its heat to the coolant located in the area of weak field. After receiving the heat of the load to cool *Qcold* the fluid enters the wheel again at a temperature *Tcold* + Δ due to heat exchange with the wheel which is at this instant at the temperature *Thot* + Δ . The temperature of the fluid increases to *Thot* + Δ . Finally, the fluid transfers heat *Qhot* to the reservoir of the hot source completing one cycle at the same time. Fig. 5 describes schematically the magnetic system of Steyert.

Fig. 5. Schematic representation of the Steyert's magnetic system.
