Environmental Engineering Reference
In-Depth Information
There have been a number of studies performed for the different magnetic
refrigeration cycles. For instance, analyses of the Ericsson magnetic refrigeration
cycles have been reported in the following references: Hakuraku [ 56 ], who con-
sidered Ericsson cycle without regeneration; He et al. [ 57 ], Lucia [ 58 ], Wei et al.
[ 59 ], Xia et al. [ 60 ] and Ye et al. [ 61 ], who considered a magnetic Ericsson cycle
with passive regeneration. Magnetocaloric Carnot cycles without regeneration, i.e.
basic Carnot cycles, were evaluated by, e.g. Sasso et al. [ 33 ], Steyert (for cryo-
cooling without regeneration) [ 62 ]. Analyses of the Stirling magnetic refrigeration
cycles (two isothermal processes and two iso-magnetization processes) have been
performed by Steyert, who analysed the Stirling AMR cycle [ 24 ]; and by Chen
[ 28 ], who carried out analyses for passive regeneration.
In most cases, the magnetocaloric material represents an active refrigerant, and
also acts as the regenerator. This kind of regeneration is called an active magnetic
regeneration (AMR). Therefore, it should be distinguished from the passive
regenerators that are common in, e.g. conventional Stirling devices. The AMR
cycle usually performs a kind of regenerative Brayton-like cycle (see, for example
[ 63
69 ]).
None of the studies systematically focused on the evaluation of different AMR
thermodynamic cycles. However, this was done recently by Kitanovski et al. [ 66 ]
and Plaznik et al. [ 67 ].
As described in Chap. 4 for AMR thermodynamic cycles, the main difference
between a cascade and an AMR cycle is that in the latter all the parts of the AMR
simultaneously accept or reject heat to the heat transfer
-
uid, which further transfers
heat between the neighbouring parts of the AMR (Tishin and Spichkin [ 32 ]). The
regenerative process is established due to the oscillatory (counter current)
fl
fl
uid
fl
nitesimally small part of the magnetocaloric material
performs its own thermodynamic cycle.
Figure 1.4 shows a simple schematic of the Brayton-type cycle based on the
AMR (or so-called AMR cycle). The Brayton-like AMR cycle is the most com-
monly applied thermodynamic cycle in magnetic refrigeration at room temperature.
Its basic operation can be described with the following processes. First, during the
magnetization process, the magnetocaloric effect leads to an increase in the tem-
perature of the magnetocaloric material. The working
ow. In the AMR each in
uid, which leaves the heat
source heat exchanger (CHEX), enters the voids of the porous magnetocaloric
material in the AMR, when this is subjected to a magnetic
fl
eld. Passing through the
porous structure of the magnetocaloric material, the working
uid is heated and
leaves the material. Then it enters the heat sink heat exchanger (HHEX), where it
rejects the heat to the ambient. The same
fl
uid, cooled by the ambient, again enters
the magnetocaloric material, which is not subjected to the magnetic
fl
eld (and thus
cooled down due to the magnetocaloric effect), in the counter-
fl
ow direction. The
working
uid cools, exits the magnetocaloric material structure (AMR), and enters
the CHEX.
From Fig. 1.4 it is clear that the maximum temperature span at the side of the
chilled
fl
uid (cooling), which leaves the AMR and enters the heat source heat
exchanger (CHEX), cannot exceed the adiabatic temperature change during the
fl
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