Magnetocaloric Fluids - Magnetocaloric Energy Conversion: From Theory to Applications - page 194

Fig. 5.6 A regenerative magnetocaloric- fl uid-based refrigerator concept proposed by Rosensweig

[ 7 , 15 ]

Rosensweig was a suspension of 5.5-nm gadolinium particles suspended in NaK. As
pointed out by Rosensweig [ 15 ], highly concentrated suspensions of magnetic par-
ticles are necessary to achieve a reasonable power density for the device. However,
the disadvantages of this application are certainly the rheological in uences of yield

stress and viscosity that increase the energy dissipation and demand, therefore, an
increase in the pump power. The results of the study [ 15 ] reveal the exergy ef

fl

ciency

(denoted as Carnot ef ciency) of such a system, depending on different parameters,

could be between 24 and 50 %.
In 2009 a group from the University of Applied Sciences of Western Switzerland
[ 174 ] patented the concept of performing refrigeration or heat pumping with
magnetocaloric

uids.
In 2010, from the same group, Kitanovski and Egolf [ 170 ] described a new
system for magnetic refrigeration and heat pumping using magnetocaloric

fl

uids
(Fig. 5.7 ). This regenerative system would apply different magnetocaloric materials
in several magnetic

fl

uid would correspond to a certain temperature
range of operation, thus providing the

fl uids. Each fl

of magnetocaloric materials in the
direction of the temperature gradient. Figure 5.7 shows the conceptual principle of
operation for such a device.
According to Fig. 5.7 , a static quadruple permanent magnet assembly provides
the magnetic

“ layering ”

eld (note also the different number of poles and also other types of

magnetic eld sources could be applied). Different magnetocaloric fl uids with

magnetocaloric particles having different Curie temperatures fl ow in the azimuth

direction. The uids is provided by a pump system, which

may also be based on magnetohydrodynamic propulsion (note also that this kind of
application might also be used for the magnetization of the magnetocaloric parti-
cles). The system is fully static, except for the

fl ow of magnetocaloric fl

uids,
as well as the secondary refrigerant (secondary fluid). The fluid flow of the sec-
ondary

fl uid fl ow of magnetocaloric fl

fl uid and the magnetocaloric fl uids is performed through an internal cross-

fl ow heat exchanger.