Environmental Engineering Reference
In-Depth Information
In the following text we present some major design issues that need to be solved
in the future. We, however, will not address new permanent-magnet materials or
new magnetocaloric materials, because this would be too speculative.
8.7.1 Active Magnetic Regeneration AMR (Conventional
Principle)
The application of the principle of AMR will certainly be improved in the future by
using some new processes of manufacturing for magnetocaloric regenerators (very
ne, ordered structures with large heat-transfer surfaces and a layered magnetoc-
aloric material), or by applying some advanced working
uids with a higher
thermal conductivity than that of water and with low viscosity.
For instance, if the feature of the AMR (which strongly depends on the working
fl
fl
uid) is the following: porosity from 30 to 45 %; wall thickness of the struc-
ture 30
-
100 microns;
fl
uid voids from 30 to 100 microns (depends on the working
fl
ow maldistribution, then the magnetocaloric device will approach a
frequency of the operation of 5 Hz and simultaneously similar or better ef
uid) with no
fl
ciency as
the compressor refrigerator with a temperature span of about 40 K (see also Sect.
4.4
).
These features can be achieved because of the very high heat-transfer surface as
well as the ordered structure, by which high viscous losses will be avoided,
especially at higher frequencies of operation.
In order to perform this, better manufacturability and processing knowledge with
respect to magnetocaloric materials is required (see Sect.
4.7
). One should also not
forget the mechanical properties which will allow such tiny structures to sustain
mechanical stresses.
8.7.2 Active Magnetic Regeneration with Thermal Diodes
The upper limit of the frequency for operation of the AMR will also limit market
applications, whether because of the low ef
ciency at large temperature spans, or
low ef
ciency at higher power density. Therefore, in order to boost the frequency of
the operation from, e.g. 5
25, 50 Hz or even 100 Hz, the conventional AMR
principle certainly cannot be applied. The only at present known mechanism that
can solve this problem is the application of thermal diodes. Note that the principle
of thermal diodes also solves other existing problems for the magnetocaloric energy
conversion technology. Namely, the solution of thermal diode, with embodied
magnetocaloric material, enhances the heat-transfer rate and simultaneously also
provides a solution for
-
fl
uid connections and
fl
uid-
fl
ow dividers, and thus also
prevents internal
fl
uid leakage and avoids high viscous losses. Furthermore, it can
create a signi
cant impact of improvements for the technology by achieving the
following solutions:
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