Environmental Engineering Reference
In-Depth Information
6.4.4.1 MR or ER Thermal Diode that Applies a Magnetically
Induced Fluid Flow
The application of the MR or ER
ow, due to very large pressure gradients, is
not a mechanism that could be used for thermal diodes. Therefore, especially under
an electric
fl
uid
fl
eld or magnetic
eld gradients, this kind of
fl
uid should not be con-
sidered as a heat transfer
fl
uid.
6.4.4.2 MR or ER Thermal Diode that Acts as a Thermal
Contact Switch
The time response in MR or ER
fl
uids is in the time period of milliseconds [ 130 ,
131 , 138 , 139 ]. This is suf
ciently applied as a
thermal contact switch. However, one should combine the phenomena of the liquid
to solid state of MR or ER
cient for such a
fl
uid to be ef
uids into smart solutions, especially because some
thermodynamic processes will require the simultaneous demagnetization and the
operation of the contact thermal switch.
fl
6.4.4.3 MR or ER Thermal Diode that Applies the Anisotropy
of Thermal Conductivity
The anisotropy of the thermal conductivity is more obvious in MR and ER suspen-
sions with a smaller volume fraction [ 140 ]. The recti
cation factor is rather low for
these
fl
uids to be ef
ciently applied as thermal recti
cators with an anisotropic,
electric
eld [ 141 ], or magnetic
eld [ 140 , 142
144 ] dependent thermal conductivity.
-
6.5 Review of the Research on Thermal Diodes in Magnetic
Refrigeration
The idea on application of a thermal diode mechanism in magnetic refrigeration at
room temperature was
rst introduced by Kitanovski and Egolf in 2010 [ 4 ]. They
realized that the application of an AMR with convective heat transfer and all the
corresponding losses will strongly restrict the realization of magnetic refrigeration
technology in cost-and energy-ef
cient market applications. As the thermal diode
mechanisms, Kitanovski and Egolf proposed two domains: the solid state and the
micro
uidic thermal diodes [ 4 ].
As the reader of this topic will realize, magnetocaloric energy conversion faces
some major obstacles. Namely, the best prototypes can ef
fl
ciently work at a fre-
quency of operation of less than 5 Hz (the number of thermodynamic cycles per
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