**3.8 Cooltech systems**

The company Cooltech Applications in France built a rotary magnetic refrigerator composed of eight pieces of supporting discs positioned in synthetic material (see Fig. 10), which were mechanically stable and thermally isolated (Vasile and Muller, 2005, 2006).. These inserts were interchangeable for the test of different magnetocaloric materials, different sensors for temperature, pressure, air velocity, hydrometry and electrical power. Each insert was packed with 165 g Gd. The rotating axes were made of stainless steel, where four pieces of NdFeB permanent magnets were rotating to provide a magnetic field of 1 T. However, the authors reported on a new type (open Halbach) magnetic assembly, which yielded a magnetic field between 1 to 2.4 T. The flow of fluid was controlled to improve the cooling capacity, which was obtained in the range of 100W to 360 W (Yu, 2010).

Magnetic Refrigeration Technology at Room Temperature 239

Fig. 12. The reciprocating prototype built at Cooltech Application in France (Bour et al.,

Magnetic Regenerative Refrigeration (AMRR) cycles and exploit different materials.

A second prototype was developed at G2Elab (Allab, 2008), (Bouchekara, 2008), (Dupuis, 2009). This structure is quite similar to a rotating machine. It is also similar to some existing prototypes (Okamura, 2005, 2007). It consists of a permanent magnet which forms the rotor

The yoke is composed of four poles which are aimed to better conduct the magnetic flux within the refrigerant bed. The magnetization and demagnetization phases are obtained by a simple rotation of the permanent magnet. The beds undergo an active magnetic

regenerative refrigeration AMRR cycle and operate two by two in the opposite way.

and of a stator made of magnetic yoke and four refrigerant beds (see Fig. 14).

The first device constructed at G2Elab (Grenoble Electrical Engineering Laboratory) is an alternating device type as shown in Fig. 13. The regenerator is composed of parallel plates of gadolinium with 1 mm in thickness and 50 mm in length. The magnetic field is produced by a permanent magnet (Halbach cylinder) creating a magnetic field of 0.8 T. The fluid used is water. Its circulation is ensured by a peristaltic pump operating in both directions (Clot, 2002). The pneumatic actuator produces the movement of the refrigerant blocs and provides magnetization / demagnetization phases. The controller is programmed to manage the Halbach cylinder and the flow of fluid to perform the four phases of the cycle. The system is closed and there is no exchange with the outside. It was designed to study the Active

2009).

**3.9 The G2Elab prototypes** 

Fig. 13. The G2Elab first device (Clot, 2002).

Fig. 10. 3D structure form of the Cooltech magnetic refrigerator, some details in further pictures, photography of the assembly and the open Halbach type of magnet (Vasile and Muller, 2005, 2006).

A rotary magnetic refrigerator prototype was developed in collaboration between the National Institute of Applied Sciences INSA of Strasbourg and the company Cooltech Applications in France (Muller et al., 2007). The system was composed by a rotary magnet assembly and of four static blocks of magnetocaloric material performed by gadolinium. The maximum magnetic field was 1.3 T and water was the working fluid. Unfortunately, there is no more information available. However, from Fig. 11, one may easily verify the manner how the magnetic field is produced in the magnetocaloric material (Yu, 2010).

Fig. 11. A rotary magnetic refrigerator of the joint collaboration action between Cooltech Applications and INSA in France (Muller et al., 2007).

In France at Cooltech Applications, Bour et al. built a reciprocating prototype as it is shown in Fig. 12. The AMR bed was composed of 37 parallel plates of Gadolinium of 0.6 mm thickness, showing a spacing of the heat transfer fluid channels of 0.1 mm and 0.2 mm, respectively. The Halbach arrays, which produced a magnetic field intensity between 0.8 T and 1.1 T in the air gap, consisted of an assembly of three sets of NdFeB magnets of 50 mm thickness. The French experts obtained experimentally the evolutions of the average temperatures at the hot end and the cold end reservoirs for different initial temperatures and operation frequencies. The device led to a maximum temperature span of 16.1 K (Yu, 2010).

Fig. 12. The reciprocating prototype built at Cooltech Application in France (Bour et al., 2009).
