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Fig. 4.9 The AMR Carnot thermodynamic cycle and its characteristics
It should be pointed out that the Carnot-like AMR cycle looking at the overall
surface in a T
s diagram (the entire AMR) does not look like a Carnot thermo-
dynamic cycle, but similar to a Hybrid Brayton
-
Ericsson-like AMR cycle (see
Fig. 4.8 a). We should therefore not expect such a cycle to be, a priori, the most
ef
-
cient. The well-known Carnot thermodynamic cycle from classic thermody-
namics is not even regenerative. However, if each in
nitesimally small particle of
magnetocaloric material is treated separately, it can be seen from Fig. 4.9 a that each
of them performs its own local Carnot thermodynamic cycle. It is based on adia-
batic and isothermal (de)magnetization, which for the same reason as described
above cannot be ideal, but rather quasi-adiabatic and quasi-isothermal.
Figure 4.9 b represents a simple schematic of a magnet assembly, which could be
applied to provide the magnetic
eld distribution that is required for the operation
of the Carnot-like AMR cycle.
It is evident that this kind of AMR cycle does not require a homogeneous
magnetic
eld can
be generated with a smaller input energy or a smaller mass of permanent magnets
compared to the homogenous magnetic
eld, but utilizes only its increase and decrease. Such a magnetic
eld required for the Brayton-like and the
Ericsson-like AMR cycles. This is one of the advantages of the Carnot-like AMR
cycle.
Note the application of thermodynamic diagrams, for instance a T - s diagram, is
not suf
cient to theoretically de
ne the performance of a particular AMR cycle. The
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