Environmental Engineering Reference
In-Depth Information
AMR on its performance is presented in Sect.
4.4
, while the review of the different
applied fabrication techniques for the AMRs is given in Sect.
4.7
.
2.1.7 High Electrical Resistivity
The high electrical resistivity of the MCM prevents the generation of eddy currents
(which results in energy dissipation and heating of the material) under the in
fl
uence
of the changing of the external magnetic
eld. However, in a typical AMR,
operating with frequencies up to 10 Hz, the impact of the eddy currents are, in
general, negligible, but for applications at higher operating frequencies this might
play an important role. For details of the energy dissipation due to the eddy currents
in magnetic materials see, e.g. [
37
].
2.1.8 Good Corrosion Properties
It is preferable that the MCM does not corrode when in contact with water (or other
heat-transfer fluids). From this point of view the ceramic manganite MCMs (e.g.
La
MnO
3
) have a certain advantage as they are non-corrosive. However, as
explained in Sect.
4.6
the corrosion of other MCMs can be prevented by adding the
proper inhibitors to the heat-transfer
Ca
Sr
-
-
-
fl
uid.
2.2 Most Common Magnetocaloric Materials
with a Near-Room-Temperature MCE
The subsequent subsections are intended to present groups of different MCMs that
are currently the most promising in the
eld of magnetic refrigeration near room
temperature. Only a brief description of the different materials are given to show the
design engineer of the magnetocaloric prototypes basic idea of how to approach
MCMs so as to apply them in the AMR. Detailed descriptions, reviews and studies
of MCMs are already well covered in the known literature and are also more of the
domain of material scientists.
Note that the majority of studies on different MCMs report their MCEs in the
form of magnetic entropy change. This is, of course, a fundamental physical
property for de
ning the MCE; however, in terms of system design and heat
transfer it would be more useful to also have the data for the adiabatic temperature
change and the speci
c heat for given MCMs. In this way, one could quickly
consider the different MCMs to be suitable for the AMR design, at least during the
initial design stages.
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