Environmental Engineering Reference
In-Depth Information
Fig. 8.9 Axial rotary magnetocaloric device principle with the closed magnet assembly, a two-
pole magnet assembly, classication no: R20(3)0(5)(6)01111(12), b four-pole magnet assembly,
classication no: R20(3)0(5)(6)01111(12)
to other permanent motor drives, stepper motors are usually not very energy ef
-
cient; therefore, we need to take important care about this issue.
Closed magnet assemblies generally provide better
ef
ciency
of the magnets,
as well as offer better shielding of the magnetic
fl
ux to the environment. Two such
examples are shown in Fig. 8.9 .
As can be seen from Figs. 8.9 and 8.10 , different number of poles can be applied
in the system. Furthermore, the coaxial rotating ring may consist fully of mag-
netocaloric material (one rotating AMR), or may consist of separated AMRs. In the
latter case, especially if the magnetic
eld is
not homogeneous, it makes sense to apply the stepper motor and the fast rotation of
the coaxial ring. This issue however depends also on the type of the thermodynamic
cycle. The difference between applying the full coaxial ring of AMRs or separated
AMRs is mostly in the rotation principle (continuous or discontinuous) or in the
valve distribution system. The latter needs to provide or prevent certain
eld distribution in the high and low
fl
uid
fl
ows
for the AMRs, which are in transition from the high to low magnetic
eld region or
vice versa. Other issues relate to the costs of the construction of the AMR.
Axial rotary devices may also apply multiple magnet assemblies, as shown in
Fig. 8.10 . However, as noted before, the closed magnet assembly will provide better
usage of the magnetic energy by reducing the leakage of the magnetic
ux.
Another arrangement of magnet assemblies is shown in Fig. 8.11 . Both solutions
a and b, respectively, show two-pole arrangements. However, Fig. 8.11 a shows
another, alternative solution for the guidance of the magnetic
fl
ux.
In Fig. 8.11 a, the whole magnet assembly contributes to the guidance and
concentration of the magnetic
fl
ux, whereas in the case of Fig. 8.11 b, only a portion
of the magnet assembly is actually active. Other parts (where AMRs in the
demagnetized state are positioned) serve mostly for shielding. In a comparison of
both cases, Fig. 8.11 a provides a more ef
fl
cient solution (with regard to the intensity
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