Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 146

Ericsson-like AMR cycle exhibits a signi cantly lower cooling power for all the

temperature spans. However, it is predicted that the Ericsson-like AMR cycle can
operate with much higher ef

ciency, especially when the thermodynamic cycles are

compared at higher speci c cooling power. Note again, that the frequency in this

particular case as well as the utilization U = 0.3 were kept constant.
A direct comparison of the numerical results and the experimental ones under the
same operating conditions is beyond the scope of this analysis. This is due to the fact
that there are some factors (the demagnetization effect and

fl ow maldistribution — see

Sect. 4.3.4 for details) that have a strong in uence on the performance of the AMR

(see [ 92 ] for details), and have not been included in the particular numerical model.
However, it can be concluded that both, the numerical and experimental analysis
showed the same trend of dependency for all the analysed cycles.

fl

4.5.3 Guidelines for Future Research on AMR
Thermodynamic Cycles

Future magnetic refrigeration devices will have to ef ciently operate at high tem-

perature spans between the heat source and the heat sink. Furthermore, high fre-
quencies are required, since these are related to high power densities (compactness
and related cost). In order to perform an ef cient operation, the thermodynamic

cycles have to be carefully studied. We have proven that at present the mostly
applied Brayton-like AMR thermodynamic cycle should be replaced by other types
of thermodynamic cycles.
It has been shown in this chapter that the performance of the Carnot-like AMR
cycle was signi cantly poorer compared to other analysed AMR cycles. Among all

the evaluated thermodynamic cycles, the Ericsson-like AMR cycle is the most
ef s diagram. It is evident that the

thermodynamic cycles based on isothermal (de)magnetization require less magnetic
work, e.g. compared to the Brayton-like AMR thermodynamic cycle. On the other
hand, isothermal magnetization is related to higher heat transfer irreversibility
losses due to a smaller average temperature difference between the

cient, which can also be seen from the T

-

uid and the
magnetocaloric material and therefore a less intense heat transfer. This directly
results in a smaller cooling power (and the temperature span), which is the main
disadvantage of an Ericsson-like AMR cycle, and most probably also the Stirling-
like AMR cycle, although the latter was not the subject of an analysis.
With regard to high ef

fl

ciency and the cooling power, the Hybrid Brayton

- Ericsson-like AMR cycle represents a serious alternative to the Brayton cycle. The

introduction of this kind of thermodynamic cycle will not only affect the ef

ciency
and the power density of a device, but will also have an important impact on the
design features of the magnet assembly. It has been shown by Kitanovski et al. [ 10 ],
that the homogenization of the magnetic eld, such is required for instance for the

Brayton type of magnetic refrigeration cycle, may lead to a higher required mass of