Environmental Engineering Reference
In-Depth Information
Motor cores are, for instance, made of stacks of thin, coated steel sheets, where
steel comprises additives such as silicon for a higher electrical resistance. Note that
due to the relatively high electrical conductivity of Nd
Fe
B magnets, the eddy-
-
-
current losses can be signi
cant, especially in devices with a high pole number or a
high rotational speed. This can also lead to heating of the magnet, which causes
additional problems of lower magnetization (see, e.g. Zhu et al. [
34
]).
Depending on the operation of a device, the rotating magnet device can apply a
continuous permanent magnet motor or a stepper motor where in the latter a dis-
crete number of steps is used (e.g. 200 per revolution, see e.g. Hughes [
35
]). This
kind of motor will precisely shift the positions from the magnetized to the
demagnetized zone and vice versa. A note in this chapter was also given for the
combination of the motor drive and the magnet assembly. This kind of system has
not been yet developed, but it makes sense to enter such developments as well.
8.7.4 Pumping and Valve System
Two types of pumping systems can be applied in future magnetocaloric devices,
uni-directional and bi-directional pumps. For the
rst there is no need for some
deeper explanation, except for the fact that heating from the pump motor should not
be transferred to the working
uid. One solution is also to place such a pump in the
vicinity of the HHEX and therefore to reject heat from the pump to the environ-
ment. Note also that the pump losses are not negligible so the selection of a pump
with good ef
fl
ciency is very important. A larger problem is with the bi-directional
pump. An electric drive of the two pistons in order to provide the oscillating
movement of
uid is one solution. However, our tendency is to drive such a system
by, e.g. 20 Hz (for 10 Hz operation frequency of the magnetocaloric device). A gear
pump is another solution, but it is rather expensive. The peristaltic pump also
represents a solution, but it is inef
fl
ow. Another way
is to apply membrane pumps. The issue of the cost and energy ef
cient and causes pulsations of
fl
cient bi-direc-
tional pumping system was not fully solved so far. Note that in the case of high
frequency and very ef
ow particle will in some cases make
only about 25 % of the full length of the AMR. If the AMR is short, e.g. 50 mm,
this will mean that the
cient AMR, the
fl
uid
fl
12.5 mm.
Since we propose a static AMR for future applications, we also consider a static
valve system for the application of the uni-directional pump. In this case, one
should pay attention of the dead volume in which the working
fl
uid particle will oscillate in the path of
±
uid is captured
between the valve system and the AMR. The same holds true also for the heat-sink
(HHEX) and the heat source (CHEX) heat exchangers, which should be positioned
as close as possible to the AMR.
All the dynamic valves to date were developed for the purpose of being used in
magnetic refrigeration technology. However, in static valve systems, besides
applying some traditional valves, these can be newly developed for the application.
fl
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