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0.5 mm and the spacing between the plates was 0.25 mm. The total mass of both
AMRs together was 180 g. The heat-transfer
fl
uid was distilled water. At no-load,
the temperature span was 3.5 K and the speci
c cooling power at zero temperature
span was 16.7 W kg 1 .
7.1.14 Conclusion
In this section, we have presented all the reciprocating magnetocaloric devices, as
experimental prototypes, which have been built to date. Altogether, 29 devices were
built and tested. It is clear that the operating frequencies are limited to 1 Hz and
below, which also affects the speci
c cooling powers. At certain signi
cant tem-
perature spans, e.g., 20 K, the maximum speci
c cooling powers are in the range of
approximately 50 W kg 1 . Such speci
cient to be
commercially viable. From this perspective it is clear that reciprocating magnet-
ocaloric devices are not suitable for real refrigeration/heat-pump applications.
However, reciprocating magnetocaloric devices are mostly useful as the AMR
testing devices. Reciprocating devices are usually designed in such a manner that
different AMRs may be easily interchangeable. This allows for a fast experimental
testing of different AMR congurations. Different geometries and magnetocaloric
materials can be tested, as well as different thermodynamic AMR cycles (e.g.,
Brayton, Ericsson, Stirling). Also, a combination of different ferroic technologies
can be investigated as, for example, in a magneto-baro caloric device. All these
aspects are extremely important for the further design of rotary magnetic refriger-
ators or heat pumps.
At the end of this section, all the reciprocating devices are collected in
Table 7.13 with their general geometric as well as operating characteristics.
c cooling powers are not suf
7.2 Rotary Prototypes
7.2.1 USA Prototypes
According to Kirol and Dacus [ 42 ] the
rst-ever rotary magnetic refrigeration
prototype was built in Idaho National Engineering Laboratory in 1987. However,
the authors stated that the device was being built at that time, thus no photography
of the prototype was available as the proof. The prototype consisted of a rotating
AMR and a stationary magnet assembly. The rotating AMR was in the form of a
disc and consisted of parallel Gd plates. The circular plates were 0.076 mm thick
with a spacing of 0.126 mm. The total mass of the whole AMR was 270 g. The
heat-transfer
fl
uid used in the device was water. The stationary Nd
-
Fe
-
B magnet
assembly consisted of four high-
eld (0.9 T) areas. In this manner, the rotating
AMR made four thermodynamic cycles per revolution. The thermodynamic cycles
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