Design Issues and Future Perspectives for Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 329

Fig. 8.1 A magnetocaloric device with a linear movement of the magnet assembly over two static
AMRs with the application of a bi-directional pump (a left AMR demagnetized, right AMR
magnetized; b left AMR magnetized, right AMR demagnetized), classi cation no: R20(3)1(5)(6)
001000

pump. This will enable the fl ow of the fl uid from the HHEX through the demag-

netized AMR. There, the fl uid will cool down and it will continue to fl ow to the

CHEX. In the case of Fig. 8.1 b, the rst cycle (shown in Fig. 8.1 a) will actually be

repeated, and this will be provided by the movement of the magnetic eld source

from the rst to the second AMR. The previously warm AMR will thus cool down

due to demagnetization and the previously cold AMR will heat up due to mag-
netization. In this particular case the bi-directional pump will switch the fl ow

direction and thus the ow for the case in Fig. 8.1 b will be provided in the

opposite direction with respect to the case of Fig. 8.1 a. This kind of system may be
considered as simple since it does not necessarily need switching valves. Switching
is provided by the bi-directional pump. Since the oscillating

fl uid fl

ow is also provided
through the CHEX and HHEX heat exchangers we have to keep in mind that in this
particular case they somehow also act as the passive regenerators, which can
slightly in

fl

uence their design.
It is simple to show the case in Fig. 8.1 for the rotating magnet assembly. In this
particular case the reader has to observe Fig. 8.1 as she (he) would look at it from
the rotating centre, thus in the radial direction. Figure 8.2 shows such an example.
In the particular case of Fig. 8.2 we show four AMRs to be put together in a device.
Therefore, changing the position of the magnets from a magnetized AMR to a
demagnetized AMR will require switching of the bi-directional pump. Note that the
example in Fig. 8.2 is only illustrative. More information about rotary devices is
given in the subsequent text.
Note that in any case, the bi-directional pump should be as close as possible to
both heat exchangers, CHEX and HHEX, respectively. This also holds for the
AMR. The reason to reduce such a distance to the minimum possible is in order to
avoid a too large dead volume. In the worst case, the

fl

uid particle from the AMR
will actually not enter the heat exchanger or vice versa. This, of course, means that
the system will not operate.

fl