Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 143

Fig. 4.28 The speci c
maximum cooling power per
mass of magnetocaloric
material and the maximum
COP as a function of the
magnetic eld prole
( ʔʼ 0 H =1T, ʔ T =15K)

As can be seen from Fig. 4.28 , the Brayton-like AMR cycle, regardless of the
˄ mag : ˄ const ratio, can exhibit greater cooling powers than the Hybrid and Ericsson-

like AMR cycles. However, both the Hybrid and the Ericsson-like AMR cycles can
operate with a higher COP than the Brayton-like AMR cycle.

4.5.2 Experimental Investigation and Comparison
of Different AMR Thermodynamic Cycles

Tests were carried on an experimental device that was presented in detail in [ 101 ].
This experimental device is also presented in the Chap. 7 .
The gadolinium parallel-plate AMR was applied in experiments (see Fig. 4.24
for the photographs and the geometry). The heat-transfer fluid (solution of water
(70 %) and ethylene glycol (30 %)) is pumped through the AMR by means of two
connected pistons that are driven by an electric actuator. Different mass

fl ow rates

can be achieved by varying the piston ' s offset distance and its velocity. The average

magnetic eld provided by the permanent magnet assembly was measured to be

1.15 T (magnetization area).
In the experiment, three different working regimes (AMR thermodynamic
cycles) were investigated (Fig. 4.29 ). They represent

the real measured time

dependence between the magnetic eld pro le and the fl uid fl ow pro le to which

the AMR was exposed.
Because of the technical characteristics of the experimental device, the (de)
magnetization time was relatively long (

˄ mag = 0.75 s) and therefore the frequencies
of the test device and consequentially the cooling powers were relatively low.