Special Heat Transfer Mechanisms: Active and Passive Thermal Diodes - Magnetocaloric Energy Conversion: From Theory to Applications - page 241

Fig. 6.23 a Manipulation of
the ferrofluid drop by a
uniform magnetic eld,
b Manipulation of the
ferrofluid drop by a
nonuniform magnetic eld

6.4.3 Magnetohydrodynamics

Magnetohydrodynamics (MHD) represents the interaction of an electric and a
magnetic

uids (e.g. plasma, electrolytes, liquid
metals, etc.). This results in a Lorentz force on the

eld with electrically conducting fl

fl uid, and as a consequence, the

fl ow (Fig. 6.24 ). With respect to magnetic refrigeration, the most interesting

applications represent the use of liquid metals, such as Hg, NaK and liquid metal
alloys based on Ga and In. The MHD principle can be also applied for the liquid
metal bi-directional

uid fl

ow, which is common in active magnetic regenerators
(AMRs). Therefore, it could also serve for the principle shown in Fig. 6.22 .
In this case we place the electrodes over the two regions of the AMRs
(Fig. 6.25 ). Instead of a ferro

fl

uid, a liquid metal will be applied as the working
fluid. In the case of Fig. 6.25 a, one pair of AMRs is being magnetized. Since the
magnetic

fl

eld is applied to this region, the electrodes are switched ON and
therefore propel the liquid metal from the magnetized AMR to the HHEX. Since the

Fig. 6.24 Example of the MHD fl uid fl ow induced by an electric and magnetic eld