Magnetic Field Sources - Magnetocaloric Energy Conversion: From Theory to Applications - page 72

Fig. 3.29 A 5 T three-dimensional (3D) magnet assembly-note the air gap is not shown in the
proportion the dimensions of the magnet assembly (see also Kumada et al. [ 37 ])

of the best solutions, especially due to the fact that different friction losses and
fl uid leakages are associated with the sealing of the rotary magnetocaloric

material (usually in the form of a rotating disc). This, however, does not rep-
resent the same problem for solutions where the linear motion of the magnet-
ocaloric material is applied.

Halbach (3D) magnet assemblies
A three-dimensional guidance of the magnetic

￿

fl ux can lead to a high magnetic

fl ux density (Fig. 3.29 ). Of course, such a magnet assembly becomes rather

complicated and in most cases too expensive for any future application in
magnetic refrigeration near or at room temperature. Figure 3.29 shows an
example of a 5 T magnet assembly, which has not been developed for magnetic
refrigeration, but shows the possibility of reaching very high magnetic

elds.

3.4.1 Static or Moving Simple (2D) Magnet Assemblies

Such magnet assemblies, especially because of the simplicity of shapes, can rep-
resent an interesting solution, especially for experimental devices or demonstrators.
In all the cases represented below (Figs. 3.30 and 3.31 ), the magnet assembly is
static. However, there is no reason why such an approach could not also be used for
solutions where the magnet assembly or a part of it represents a rotating part (with
static magnetocaloric material).
Figure 3.30 a shows a magnet assembly that was presented by Zheng et al. in
2009 [ 38 ]. This magnet was designed using the Ansys multiphysics tool. After the
optimization the author reported the following features: gap size (20 × 40 mm),
Nd Fe B magnet size (120 × 80 mm), and magnet assembly outer dimensions

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(168 × 180 mm). No thickness of the magnet was reported. The magnetic fl ux