Overview of Existing Magnetocaloric Prototype Devices - Magnetocaloric Energy Conversion: From Theory to Applications - page 293

were hybrid ones (Brayton eld was

applied parallel to the plates in order to minimize the demagnetization effect of the
magnetocaloric material. Unfortunately, no performance regarding device

Ericsson cycles). Furthermore, the magnetic

-

s tem-
perature spans or cooling powers was reported. The researchers mainly focused on
certain design issues, such as problems with dynamic seals and the corresponding
frictional heat generation, taking care to obtain acceptable magnetic

'

eld pro les

and reducing the complexity of the overall system design.
The second US rotary magnetic prototype was built by Astronautics Corporation
of America in collaboration with Tohoku University from Japan and was presented
by Zimm et al. [ 43 , 44 ] at the First International Conference on Magnetic Refrig-
eration at Room Temperature in Montreaux, Switzerland in 2005. The prototype
consisted of a rotating disc with AMRs called “ the Wheel ” and a stationary

Nd had three separated sectors. Each sector

had one inlet/outlet to/from the hot heat exchanger at each end of the sector. The
inlet/outlet to/from the cold heat exchanger was the only one common in the middle
of the sector. In this manner,

Fe B magnet assembly. “ The Wheel ”

- -

actually comprised six AMRs. The
AMRs were rotating through one stationary 1.5 T magnetic

“ the Wheel ”

eld area. The heat-

transfer fl uid was water. Two experiments employing two different AMR con g-

urations were carried out. In the lled with Gd

spherical particles with diameters from 0.425 to 0.5 mm. The mass of the mag-
netocaloric material was not reported. Such an AMR conguration could produce
18 K of no-load temperature span at an operating frequency of 4 Hz. When a
cooling load of 15 W was applied, the temperature span decreased to 14 K. At 0.5 K
of temperature span the device could produce 44 W of cooling power. The second
experiment was carried out with a changed con

rst experiment the AMR beds were

guration of the AMRs. The AMR

beds were lled with a layer of Gd Er spherical particles (0.25 0.355 mm in

- -

diameter) and a layer of Gd spherical particles (0.425 0.5 mm in diameter). Also, in

this case the mass of the magnetocaloric material was not reported. The experiments
were again carried out at the operating frequency of 4 Hz. The no-load temperature
span achieved was in this case 25 K, whereas at 14 and 0.5 K the device could
produce 27 and 41 W of cooling power, respectively.
The second rotary magnetic prototype built by Astronautics Corporation of
America was presented in 2007 by Zimm et al. [ 45 ]. This device consisted of 12
stationary AMR beds positioned in a ring arrangement and a rotating, modi

-

ed,

Halbach Nd Fe B permanent-magnet assembly. The magnet assembly consisted of

- -

two high- lled with Gd

plates. The geometry, regarding the thickness and spacing of the plates, was not
reported; however, the total mass of all the beds was 916 g. The experiments were
carried out at an operating frequency of 2 Hz with the hot-side temperature

eld (1.5 T) and two low- eld areas. The AMR beds were

xed at
298 K. In this manner, the no-load temperature span was 11.5 K. At temperature
spans of 8 and 4 K, the device could produce 76.4 and 158.3 W kg − 1 of speci

c

cooling power, respectively. The zero-temperature span speci c cooling power was

240.2 W kg − 1 .
The third prototype built by Astronautics Corporation of America was presented
in 2014 by Jacobs et al. [ 46 ] (Table 7.14 ).