Environmental Engineering Reference
In-Depth Information
Table 3.2 Characteristics of some designs of permanent-magnet assemblies in magnetic
refrigeration (reproduced from Bj
ø
rk [
65
])
Name
V
magnets
(dm
3
)
V
eld
(dm
3
)
B
high
(T)
B
low
(T)
P
eld
Λ
cool
/
P
eld
Λ
cool
0
a
Bohigas et al. [
40
]
(Fig.
3.29
)
0.38
0.02
0.9
1
0.05
0.05
0
a
0.9
a
Zheng et al. [
38
]
(Fig.
3.29
)
0.5
0.09
0.93
0.17
0.15
A.
Š
arlah (reported by
0.11
0.65
0.97
0.1
1
0.13
0.13
Tu
ek et al. [
41
]
Fig.
3.3
0)
š
0.9
a
Okamura et al. [
54
]
(Fig.
3.36
)
3.38
0.8
1
0
0.24
0.21
Tura and Rowe [
49
,
50
]
(Fig.
3.34
)
1.03
0.05
1.4
0.1
0.5
0.05
0.03
0.1
a
0.9
a
Chell and Zimm [
61
]
(Fig.
3.46
)
4.7
0.15
1.5
0.04
0.03
a
estimation
cycles). Furthermore, the
ʛ
cool
does not give information about torque issues, eddy
currents and
nally, the cost of the device, which strongly depends on the costs of
the elements of the magnet assembly as well as the costs related to different shapes
of permanent magnets. Moreover, the
ʛ
cool
parameter strongly depends on the type
of operation of the AMR, for which as could be seen, different operating regimes
can be taken into account, which strongly depend on the AMR
s effectiveness
(which also denes the time required for the fluid flow) as well as the method or
mechanism that is used for the motion of the magnet or the AMRs. Table
3.2
shows
some of the results from the analysis that was performed by Bj
'
ø
rk et al. [
66
].
ne the effectiveness of the magnet assembly is
simply through the economics of a device in terms of investment or total costs
(investment, maintenance and operation costs) versus the cooling power of the
device. Note that the permanent-magnet assembly in almost all cases represents the
highest costs among all the elements of a device (see also the Chap.
9
on economics
of magnetic refrigeration). On the other hand, a full economic analysis requires a
full knowledge of the geometry, the operation and other characteristics of a device.
Since there was no general standardisation method implemented, we are left with
more simple
The most important way to de
gures of merit, such as the one from Bj
ø
rk [
63
]. This can serve for a
rst and very fast evaluation of the different magnet designs.
In the article of Bj
rk et al. [
66
], the authors evaluated different designs and
operation characteristics of permanent-magnet assemblies used in prototypes of
magnetic refrigerators. Besides the
ø
ʛ
cool
parameter, the authors also de
ned the
parameter
ʛ
cool
/P
eld
, since this takes into account only the magnet design and not
the ratio of the time period during which the magnet assembly is actively used.
Detailed information about the calculation of particular parameters and some other
designs can be found in Bj
ø
ø
rk [
65
] and Bj
rk et al. [
66
].
Search WWH ::
Custom Search