Environmental Engineering Reference
In-Depth Information
operating frequency was increased to 4 Hz, the device showed similar performance
as at 2 Hz. Operating at frequency of 6 Hz led to a decrease in the zero-temperature
span speci
c cooling power of 187.5 W kg
−
1
. When the speci
c cooling load was
set to 35.7 W kg
−
1
the temperature span increased to 17 K. Operating at a frequency
of 10 Hz further decreased the speci
c cooling power to 134 W kg
−
1
at a tem-
perature span of 1 K. When 35.7 W kg
−
1
of speci
c cooling load was applied the
temperature span was 14.5 K. The decrease in the device performance with a higher
operating frequency was mostly related to the heat generation in valves caused by
friction between the seals and the
ow-head.
In the same year another study on the performance of the Danish prototype was
presented by Bahl et al. [
66
]. Tests on two different AMR con
fl
gurations were
carried out. In the
rst
tests,
the AMR beds were
lled with Gd spheres of
0.35
0.85 mm in diameter. The length of the AMRs was 50 mm, which corre-
sponded to a total mass of 1,400 g for all 24 beds. This Gd material had a peak
entropy change of 3.5 J kg
−
1
K
−
1
at 290.5 K and a magnetic
-
eld of 1 T. The hot-
side temperature was set to 297 K. At an operating frequency of 1.5 Hz, the no-load
temperature span was 13.9 K, while at 10.5 K the speci
c cooling power was
71.4 W kg
−
1
and at 1.5 K the device could produce 142.8 W kg
−
1
of speci
c
cooling power. When the operating frequency was increased to only 1.75 Hz, the
device performance also increased. At a speci
c cooling load of 142.8 W kg
−
1
the
temperature span increased to 10 K, while at 71.4 W kg
−
1
to 13.9 K. In the second
tests, the AMR beds were
lled with 2,800 g of Gd spheres, which corresponded to
the
lled bed length of 100 mm. The diameter of the spheres was 0.25
0.8 mm. The
-
peak entropy change of this Gd was slightly lower than in the
rst example. It
peaked at 3.2 J kg
−
1
K
−
1
at a temperature of 288 K and a magnetic
eld of 1 T. The
hot-side temperature in the tests was set to 298 K. When the device was operating at
a frequency of 2.25 Hz and a speci
c cooling load of 71.4 W kg
−
1
was applied, the
temperature span was 18.9 K. However, when the speci
c cooling load was
increased to 142.8 W kg
−
1
, the maximum temperature span was 13.8 K and was
achieved at a lower operating frequency of 1.5 Hz.
A photograph of the prototype and some additional characteristics are also
presented in Table
7.35
.
7.2.11 Italian Prototypes
The Italian rotary prototype was built in a collaboration between the University of
Salerno, University of Naples Federico II and the Canadian University of Victoria. It
was presented in 2014 by Aprea et al. [
67
]. The device consisted of eight static AMR
beds and a rotating magnet assembly. The magnet assembly was a Nd
-
Fe
-
B Halbach
array structure with two high-
eld and two low-
eld areas. The high-
eld areas
peaked with 1.25 T and had an average magnetic
eld of 1.1 T. Eight AMR beds were
lled with 1,200 g of Gd spheres with a diameter of 0.4
0.5 mm. The heat-transfer
-
fl
uid was demineralized water with anti-corrosion inhibitors. The temperature of the
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