Design Issues and Future Perspectives for Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 334

8.2 Rotary AMR Magnetocaloric Devices

Rotary magnetocaloric devices present more complex and advanced systems
compared to linear ones. Also, the ef ciency of such devices can be expected to be

higher for devices that operate continuously, since one can avoid the losses asso-
ciated with the inertia and discontinuous operation. However, in a discontinuously
rotating device no substantial advantage in ef ciency can be expected over the

linear type of device. This holds true, especially for devices, where the magnet-
ocaloric material rotates, since these devices are in most cases related to losses in
the valve distribution system and its friction or leakage. However, in most rotary
devices, we can certainly expect the advantage of compactness or higher power
density for such a device, compared to a linear device.
In this section we provide some brief information about the different arrange-
ments of magnetic

eld sources and AMRs, which also depend on the rotation of
these two main parts of the magnetocaloric device. We will therefore generally
divide these devices into: rotary devices with static magnetic eld sources and a

rotating AMR, and rotary devices with a static AMR and with rotating magnetic

eld sources.

8.2.1 Rotary Magnetocaloric Devices with Rotating AMRs

These devices can be further divided according to the fl uid fl ow through the AMR

as follows:

￿ Axial fl uid- fl ow devices,

￿ Radial fl uid- fl ow devices,

Azimuth fl uid- fl ow devices.

￿

8.2.1.1 Axial Rotary Magnetocaloric Devices with Rotating AMRs

Figure 8.7 shows an example of a two-pole rotary magnetic device in which the
working ows through the AMRs in the axial direction (direction of the

observer in Fig. 8.7 , parallel to the axis of rotation). The principle of the operation is
also explained in Fig. 8.7 (right). In this particular case we do not show the

fl uid fl

uid
switching-valve system, but the reader should note that this, in the case of the uni-
directional pump, will not differ much from the one presented in Fig. 8.3 .
According to Fig. 8.7 (right), the coaxial cylinder consisting of four AMRs is
rotating through the two high and two lowmagnetic

fl

eld regions. We consider in this
case a continuously rotating and operating device. This means that not only is the
continuous rotation provided, but also that the continuous ow is provided to the

magnetocaloric material, so in any of time periods such a device produces cold.

fl uid fl