Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 409

consisted of an electrocaloric BaTiO 3 multilayer capacitor and a mechanical drive
that was used to move the multilayer capacitor and create an alternating thermal
contact with the heat sink and the heat source. The contact surfaces of the heat sink
and the heat source were coated with liquid-based thermal interfaces to enhance the
heat transfer from the multilayer capacitor to the heat sink/source. The operation of
the device can be divided into four main steps. In the rst step, the electrocaloric

material is polarized and heats up. Next, the multilayer capacitor is moved into
physical contact with the heat sink. Therefore, the heat is transferred from the
multilayer capacitor to the heat sink by thermal conduction (Fig. 10.11 a). In the
third step, the material is depolarized and, due to the electrocaloric effect, it cools
down. Then the capacitor is moved into contact with the heat source and can absorb
the heat (Fig. 10.11 b). In this study, a constant Joule heating of 15 mW was induced
in a thin-

lm heater (heat source). The authors reported that at a frequency of 3 Hz
(the number of thermodynamic cycles per unit of time) the heat source was cooled
down by 1 K with respect to a reference point. To set the reference point, the device
was rst operated only by applying mechanical motion. The electrocaloric element

was not subjected to an electric eld change and no electrocaloric effect was

induced. In this case, the heat was passively transferred from the heat source to the
heat sink.
An interesting prototype device was presented by Gu et al. [ 54 ] in 2013. In their
paper, they describe a chip-sized electrocaloric cooling device. The concept of the
device was already described earlier in this chapter and it is based on an active heat
regenerator with a solid-state matrix to transfer the heat from the electrocaloric
material to a heat source/sink. As a basic unit of the active electrocaloric heat
regenerator, a multilayer module made out of 24 layers of 8- µ m-thick high-energy-

electron-irradiated poly(vinylidene fl uoride-tri fl uoroethylene) 68/32 % (copolymer)

lm was covered with Au electrodes. The layers
were then glued together to form a 0.25-mm-thick multilayer module. It was shown
that the polymer used to construct the multilayer module can achieve an adiabatic
temperature change that is even higher than 20 K in a 160-MVm − 1 electric

lms was used. Each layer of the

eld
change [ 31 ]. However, the adiabatic temperature change of the constructed multi-
layer module was reported to be much smaller. It was measured to be 2.25 K under
80 MVm − 1 of electric

eld change. Two multilayer modules were used in the
device, a schematic presentation of which can be seen in Fig. 10.12 . The photo-
graph of the device and its main characteristics are presented in Table 10.5 . The
solid matrix was constructed from stainless-steel plates with a thickness of 0.5 mm.
Thin slits were cut in the stainless-steel plates in the direction perpendicular to the
mechanical motion. The slits were lled with low-thermal-conductivity epoxy to

decrease the rate of heat ux from the heat sink to the heat source. A step-motor

drive was used to move the steel plates. At a frequency of 1 Hz and under an
electric

fl

eld change of 100 MVm − 1 , the maximum temperature span between the
heat sink and heat source was measured to be 6.6 K at room temperature.