Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 99

The difference between Fig. 4.3 a, b corresponds to different utilization factors of

the fl uid fl ow. The utilization factor, which gives us information about the displaced

fl uid through the AMR and gives us the ratio between the heat capacity of the fl uid

and the magnetocaloric material during a single ned in

Eq. ( 4.26 ) later in the text. Figure 4.3 a corresponds to a low utilization factor and
Fig. 4.3 b corresponds to a high utilization factor. As can be seen from both

fl uid fl ow period, is de

gures,
there is a relatively smaller overlapping of the thermodynamic cycles between the
neighbouring particles at a low utilization factor, compared to the case with a higher
utilization of the

uid. The impact of operational conditions such as the utilization
factor and the operating frequency on the AMR

fl

' s performance is discussed further

in Sect. 4.4 .
In Fig. 4.3 c, d, magnet assembly is shown together with the corresponding
variation of the magnetic

le through the AMR. The
magnet assembly is an example of a rotary type of magnetic refrigerator. This kind
of magnet assembly (see also [ 13

eld and the fl uid fl ow pro

- 15 ]) provides the magnetic fl ux variation, which

can be applied for the Brayton, Ericsson or Hybrid (Brayton - Ericsson) thermo-

dynamic cycles.
In order to understand in detail the operation of the AMR, Figs. 4.4 and 4.5 show
how the temperature span is established between the hot and cold sides of the AMR
from the initial state with constant temperatures along the AMR to the periodic,
steady state (for the Brayton-like AMR cycle). Figure 4.6 shows a temperature
pro

uid (grey
line) along the AMR during all four operational phases in the periodic steady state.
Figure 4.4 shows the initial temperature response of the magnetocaloric material
at the hot and cold sides of the AMR based on the magnetic

le of the magnetocaloric material (black line) and the heat-transfer fl

eld and the fl uid fl ow

pro le shown in Fig. 4.3 d. It should be noted that in this case, the hot side of the

AMR is assumed to be maintained at a constant (i.e. room) temperature.
It is evident from Fig. 4.4 that after just two complete cycles, there is a slight
temperature difference between the magnetocaloric material at the hot and cold
sides.

Fig. 4.4 The initial
temperature response of the
magnetocaloric material at the
hot and cold sides of the
AMR, a Magnetization,
b Fluid ow,

c Demagnetization,
d Fluid

fl

fl ow