Environmental Engineering Reference
In-Depth Information
Because of the varying magnetic
eld-actuated
valve system. One such example has been proposed by Eriksen et al. [
36
].
Another way is to apply a ferro
eld it makes sense to think about a
fl
uid or better, a magnetorheologic
fl
uid, which
activates/de-activates in the presence/absence of a magnetic
eld. Therefore, to
learn more about the potential design of such a system the reader is directed here to
the literature which we denote in the chapter on magnetocaloric
fl
uids, where a
large part of the chapter is dedicated to the rheology of magnetic
fl
uid and magnetic
particle suspensions.
Note again that in the application of thermal diode mechanisms a uni-directional
pump is required and actually no valve system is needed.
8.7.5 Working Fluid
Most of the applications apply water with freezing depressant, which in some cases
acts also as the inhibitor to prevent corrosion of the magnetocaloric material.
However, other corrosion inhibitors may serve as well. The most important char-
acteristics of the working
uid are the low viscosity and high thermal conductivity.
Note that application of nano
fl
uids will not lead to a better solution than that with
water, despite the slightly higher thermal conductivity. This is due to the fact that
they cause larger viscous losses, which result not only in increased power con-
sumption of the pump, but also heat generation in the
fl
uid due to higher viscosity
and related friction at the wall. Our experimental and theoretical work with the
liquid metal Galinstan, however, has shown that liquid metals possess excellent
properties, which may be successfully applied in AMRs and allow higher operating
frequencies than water-based systems (see also Sect.
4.6
for details). However, the
cost of liquid metals based on Ga, In, Sn is very high. Despite this our analyses
have shown that the high cost of the liquid metal will be compensated by the
substantially reduced cost of magnets. Other solutions that may apply toxic mercury
or NaK could be applied as well. In this case, however, there is a question about
their use in usual applications. So one can expect such applications will be applied
in special market niches as well as environments.
There is no evidence that (phase-change) refrigerants, with condensation and
evaporation, have been applied in magnetocaloric devices. This is possible, but not
in applications where such a
fl
fl
uid is oscillating with high frequency. Most probably
such
uid in the
case of the application of thermal diode mechanisms, where no oscillation of the
working
fl
uids can be applied as secondary refrigerants or as the working
fl
fl
uid is required.
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