Environmental Engineering Reference
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were given about how to improve the more ef
cient AMR operation at higher
frequencies, i.e. from improving the AMR geometry, layering different magnet-
ocaloric materials, using different working
uids, to using different design concepts
for the magnetic device (reciprocating or rotary) as well as to apply different
thermodynamic cycles. However, all these potential improvements still revolve
around one more fundamental issue, which is the conventional concept of the active
magnetic regenerator itself. This concept remains the focus of research and it most
de
fl
nitely has some more room for improvement. However, it is becoming
increasingly clear that this course of magnetic refrigeration research will most
probably not give us the desired results (high operating frequency, large tempera-
ture span, high cooling power and simultaneously high ef
ciency). The problem is
that even very advanced active magnetic regenerator has its limitations with regard
to ef
cient heat transfer at higher operating frequencies, which is clear from the
presented state-of-the-art devices in previous years (Chap.
7
) as well as some
theoretical studies [
157
].
Hence, it is important to try some other potential research directions, especially
in terms of new magnetocaloric device concepts as a whole: different approaches to
AMR research or even completely new concept ideas should be welcomed and
encouraged.
In the previous chapters we provided comprehensive information about the
different mechanisms that can be applied as thermal diodes. The following sub-
sections give certain theoretical aspects and suggestions about how to approach the
design con
guration of such systems. Note again that the research of magnetoca-
loric energy conversion with the application of thermal diodes is still a very fresh
and new
eld of research and therefore still needs a lot more work and attention.
The aim of this subsection is to describe and show how thermal diodes should be
implemented regarding magnetocaloric material and what operation is to be
expected. Different design concepts are presented, each with an explanation of the
operation.
Note that these are strictly theoretical suggestions, the sole purpose of which is
to give the reader an idea behind the technology and especially to try to encourage
her/his creative thinking towards different approaches to magnetocaloric energy
conversion.
6.6.1 Single-Stage Magnetocaloric Device
with Thermal Diodes
A single-stage device incorporating thermal diodes is presented in Fig.
6.28
.Itisa
thin layer of magnetocaloric (MC) material stacked between two thermal diodes
1 and 2. Each thermal diode faces one heat exchanger, cold and hot, respectively.
Similar concepts were already presented in some works in the
eld of electrocaloric
energy conversion [
158
-
160
]. The notion of
“
single stage
”
means that only the
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