Environmental Engineering Reference
In-Depth Information
research on magnetic refrigeration at University of Ljubljana, especially in the early
years before 2009. Furthermore, a special acknowledgement goes also to the Centre
for Element and Structure Modelling (CEMEK) from University of Ljubljana.
Researchers from LAMEK contributed greatly to the design of the prototypes built
at University of Ljubljana.
The prototype consisted of a rotating AMR drum and a stationary magnet
assembly. The magnet assembly consisted of four Nd
Fe
B magnets that could
-
-
induce a magnetic
eld of 0.98 T. The AMR drum was divided into 34 sectors that
were
lled with Gd plates. The plate thickness was 0.25 mm and the total mass was
600 g. The heat-transfer
uid was distilled water. The main goal of the prototype
design was to make the parts from low-cost materials with high quality standards
and under general tool-making principles, using standard machining methods.
However, the prototype faced some issues regarding its high weight and the sealing
of the dynamic valve system of the rotating AMR drum. Too-tight sealing caused
heat generation due to the friction of the AMR
fl
s drum rotation. On the other hand,
to loose sealing caused high leakage. Unfortunately, there is no performance data
available regarding this magnetic prototype. A photograph of the prototype and
some additional characteristics are also presented in Table
7.33
.
Based on the experience from the
'
rst prototype, a second device from the
University of Ljubljana in a collaboration with the Slovenian company SMM was
built in 2012. It was composed of a rotating AMR wheel and a Nd
-
Fe
-
B magnet
assembly. The magnet assembly consisted of four 0.8 T magnetic
eld areas.
A photograph and some general characteristics are presented in Table
7.34
.
7.2.10 Danish Prototypes
The Danish rotary magnetic refrigeration prototype was built at the Technical
University of Denmark and
rst presented in 2012 by Engelbrech et al. [
63
]
(Table
7.35
). The prototype consisted of an AMR ring rotating in the gap of two
concentric cylindrical Nd
Fe
B Halbach magnets. The magnet assembly had four
-
-
poles with four low-
eld areas separating them. Such a magnet assembly induced the
peak magnetic
eld of 0.9 T. The AMR
ring had 24 separated beds, which were 250 mm in length. The initial idea was to
eld of 1.24 T, with an average magnetic
ll
the beds with parallel plates, hence the long AMR beds. However, in reality the beds
were
lled with Gd spheres of 0.25
-
0.8 mm in diameter. To reduce the pressure drop
the beds were only
lled 100 mm in length, which corresponded to 2,800 g of
magnetocaloric material. The heat-transfer
uid was a mixture of 75 % deionized
water and 25 % commercial ethylene glycol with anti-corrosion inhibitors. The hot-
side temperature varied between 300.8 and 301.4 K. The maximum no-load tem-
perature span was 25.4 K, operating at a frequency of 2 Hz. At a temperature span of
21 K and an operating frequency of 2 Hz, the device could produce 35.7 W kg
−
1
of
speci
fl
c cooling power. At a temperature span of 0.3 K and a frequency of 1.8 Hz,
360.7 W kg
−
1
of speci
c cooling power was produced. When 142.8 W kg
−
1
of
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