Design Issues and Future Perspectives for Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 342

Fig. 8.15 An opened magnet assembly of a rotary magnetocaloric device with the azimuth fluid
flow through the AMRs, a the rotating disc with eight AMRs, classi cation no: R20(3)0(5)(6)0(8)
111(12), b the rotating AMR discs, classi cation no: R20(3)0(5)(6)0(8)111(12)

8.2.2 Rotary AMR Magnetocaloric Devices with Rotating
Magnetic Field Sources

The rotating magnetic eld source has advantages over static sources because of the

fact that one can avoid complex valve systems and related losses. These are still
required in the case of applications of uni-directional pumps. However, conventional
valves can be applied as well. Figure 8.16 shows an example of the application of a
rotary magnet system in which two rotating magnets are applied over two static
AMRs. This is done in order to provide a quasi-continuous production of cold. In the
case of Fig. 8.16 a, a bi-directional pump is used. The working ows to both

AMRs, one being magnetized and the other being demagnetized. Because of the
rotary magnet system, the magnets will provide a kind of ON-OFF operation for the
magnetization or demagnetization of the AMRs. Therefore, as shown in Fig. 8.16 b,
the previously magnetized AMR (from Fig. 8.16 a) will be demagnetized and the
previously demagnetized AMR will become magnetized. In order to provide the
regenerative process, the bi-directional pump should switch its operation from
the case shown in Fig. 8.16 a to the case shown in Fig. 8.16 b. As noted before, since
the oscillatory

fl uid fl

ow is provided also through the heat exchangers, we should
pay attention to the passive regeneration in those heat exchangers.
The application of the bi-directional pumping system provides an advantage over
the uni-directional pumping system because in the

fl uid fl

rst no valves are actually
required. However, the potential losses due to the dead volume should be as small as
possible. The

uid simply oscillates with the help of the bi-directional pump, which
is synchronized with the rotation of the magnetic

fl

eld source (synchronized with the
magnetization and demagnetization). The time period between the switching from
magnetized to demagnetized state and vice versa is not desired, since it restricts the
power density. In the case of the AMR Brayton-like refrigeration cycle, the pump
will not operate during the processes of magnetization and demagnetization.