Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 105

heat transfer losses to the working uid, the heat gains and losses to the sur-

roundings, the heat generation (friction of the

fl

uid, eddy currents, valve friction,
pump losses) and the viscous losses have to be taken into account as well. Addi-
tionally, one should estimate the losses related to valve systems,

fl

ttings and the

pump ciency of the heat source heat exchanger

(CHEX) and the heat sink heat exchanger (HHEX). These losses can be included in
the dynamic numerical model of the AMR (see Sect. 4.3 ). However, a theoretical
investigation with thermodynamic diagrams (steady-state models) can give us basic
information, which is still very important for the understanding and the design of a
potential prototype device. With the optimization of thermodynamic cycles, we can
substantially improve the ef

' s operation, as well as the ef

ciency or the cooling power of a potential device, the
compactness and the corresponding cost. A direct numerical and experimental
comparison of the different, above presented, AMR thermodynamic cycles is shown
in Sect. 4.5 .

4.1.4 Maximum Speci c Cooling Power in the AMR Cycle

It is important to know the maximum cooling power of a particular magnetocaloric
material. If regeneration is performed, the cooling power corresponds only to a part
of the whole cooling energy, which is available within a particular thermodynamic
cycle. Namely, a large part of this power is transferred in the processes of regen-
eration, and therefore it does not contribute to the cooling power. Figure 4.10 shows
an example of a maximum temperature span that is restricted by the adiabatic
temperature changes of the magnetization and demagnetization process without
regeneration. Usually,

cient for a real application. Therefore,
regeneration should be applied. Figure 4.10 also shows the maximum speci

this is not suf

c

Fig. 4.10 a The maximum temperature span and the maximum specic cooling and heating
energy in a magnetic refrigeration cycle. b The ideally regenerated heat q Rreg = q Hreg , which
corresponds to the surfaces ABCD = abcd