Environmental Engineering Reference
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Fig. 4.8 The AMR hybrid Brayton - Ericsson-like AMR cycle and its characteristics
system, separately; however, better performances are to be expected if the AMR is
magnetized adiabatically, at least to the middle value of the magnetic
eld or more
[ 18 , 19 ].
The combination of the (de)magnetization and the
fl
uid
fl
ow (heat transfer)
process is especially interesting in the case where the magnetic
eld is generated by
permanent magnets. There is always a volume with a gradient of the magnetic
ux
density close to the magnetized air gap, which is due to the unavoidable leakage of
the magnetic
fl
ux out of the desired magnetized volume in such systems. It is
therefore not possible to ensure a steep Dirac function of the magnetic
fl
eld vari-
ation, as would be ideal for the Brayton thermodynamic cycle. This makes the
Ericsson-like and the Hybrid Brayton
Ericsson-like AMR cycles very interesting
solutions where permanent magnets are used to magnetize the AMR (which is the
case for all prototypes of magnetic refrigerators built in the past 10 years).
-
4.1.3 Characteristics of a Carnot-like AMR Cycle
In the case that the AMR cycle performs adiabatic magnetization with no
ow
(a - b), followed by isothermal magnetization with a fluid flow (b - c), adiabatic
demagnetization with no
fl
uid
fl
fl
uid
fl
ow (c
d) and
nally isothermal demagnetization
-
with a
a), this will lead to a Carnot-like AMR cycle. It is schematically
shown in Fig. 4.9 a in the periodic steady state, together with the required magnetic
fl
uid
fl
ow (d
-
eld pro
le and the
fl
uid
fl
ow regime (Fig. 4.9 c).
ow direction
(v f < 0) compared to the magnetization process (v f > 0), as noted in Fig. 4.9 c.
Again, the
fl
uid
fl
ow during the demagnetization is in the counter-
fl
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