Special Heat Transfer Mechanisms: Active and Passive Thermal Diodes - Magnetocaloric Energy Conversion: From Theory to Applications - page 231

Fig. 6.15 Examples of electrowetting manipulation of uid,

a electrowetting on insulator-coated electrodes (EICEs), b electrowetting on a dielectric (EWOD)

the surface tension of the fl

to the heat-sink and heat-source heat exchangers, respectively. During the mag-
netization cycle, the thermal diode mechanism is in the OFF-position on both sides
of the magnetocaloric material. The magnetocaloric material heats during the
magnetization. During the process of the iso

eld cooling, the upper series of
thermal diodes is switched ON, thus providing the contact between the heat sink
and the magnetocaloric material. The thermal diodes are then switched OFF and the
process of demagnetization is performed. Therefore, the magnetocaloric material
cools down. The lower series of thermal diodes is switched ON, providing a contact
for the heat fl ux from the heat source.

Electrowetting as the Manipulation the Electrocapillary Flow of the
Thermal Diode Mechanism

ow (Fig. 6.17 ), the surface tension is based on
the electric potential that acts across an interface. Here, the velocity of the

In the electrocapillary-induced fl

uid can
reach up to 10 cms − 1 , or even higher in some applications. This is very high if we
take into account the microscale in which the thermal diode acts. The electro-
capillary

fl

fl ow is many times referred to as one of the basic mechanisms for digital

micro uidics [ 91 , 92 ].

In Fig. 6.17 a, planar parallel line electrodes (ELE) provide the spontaneous
electrowetting flow of the liquid lm [ 93 ]. A lm with a thickness of several
microns

fl

ows due to the elongated drop when the electric potential is applied over
the electrodes. The

fl

lm velocity is higher than the macroscopic spreading of the
drop itself [ 94 ]. The reason for this is the bulk electric pressure gradient in the