Environmental Engineering Reference
In-Depth Information
Increasing the number of beds from 4 to 6, strongly decreased the magnetic
torque. This was observed for the magnet assembly (e) versus magnet assembly
(a), where the torque was reduced by a factor of 5. In the case when the magnet
assemblies without the iron poles are compared, and with a different number of
AMRs (i.e. magnet assembly (f) versus magnet assembly (c), the torque was
reduced by a factor of 4. However, the magnetic
fl
ux density was also reduced
in both cases. The distribution of the magnetic
fl
ux density was not trapezoidal
any more.
The embodied AMRs in the soft iron ring do not represent a good solution. The
torque is reduced, and the magnetic
ux density also substantially decreases.
Moreover, the force along the magnet bar is substantially increased, compared to
the reference magnet assembly.
fl
The results of the simulations showed that the soft magnetic parts attached to the
AMRs in the magnet assembly (d) can signi
cantly overtake the force applied
on the AMR, by cancelling the force in the direction X (perpendicular to the
magnet bar) and by reducing the force in the Y direction by 40 %. This solution,
however, substantially decrease the magnetic
fl
ux density.
In the magnet assembly, denoted by (h), the torque, compared to the reference
magnet assembly (a), was substantially reduced. However, the magnetic
fl
ux
density was decreased as well.
The special cascade arrangement of magnet assembly (i) substantially decreased
the magnetic torque compared to the reference magnet (a). Also, the magnetic
fl
ux density remained almost the same. According to Bouchekara et al. [
56
] such
a system with several shifted blocks could be used for the higher cooling power
or the cascade use of different magnetocaloric materials in order to increase the
temperature span (similar to the layering of magnetocaloric materials
—
see also
the chapter on AMRs).
As can be seen from solutions presented in this section, we can learn much about
the design of rotating magnet structures by studying another domain, which regard
permanent magnet motors (see also Hanselman [
57
], Gieras [
58
]). For instance, the
cogging torque (or the reluctance torque) between the permanent magnets in a rotor
and the slot openings in a stators occurs in such motors.
When each magnet in the rotor of such a motor rotates, the reluctance is
experienced by magnets of the rotor passing the sloth opening between the stator
teeth, which are elongated into so-called shoes (Fig.
3.44
a).
The slot openings create a varying reluctance for the magnet
fl
ux, and therefore,
the cogging torque. Without the
and only with stator teeth, the reluctance
variance and the consequent cogging torque are much larger. Therefore, the shoes
can drastically reduce the cogging torque. Also, the smaller the slot opening is,
smaller will be the cogging torque, so without slot openings, the cogging torque
should become zero. One should not misinterpret this situation with the magnet
assembly (g) in the Fig.
3.42
; however, in both cases, the magnetic
“
shoes
”
fl
ux density
(induction) will be smaller, as will the torque.
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