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effect in the electrocaloric material). The electric signal consisted of rectangular
pulses with a constant amplitude of 12 kVcm
−
1
; however, different pulse repetition
rates (the time between two neighbouring electrical pulses) were considered. The
results showed that in the second experiment, at a pulse repetition rate of 2.4 s, the
sandwiched-like structure cooled down to ambient temperature in approximately
600 s, which was almost twice as fast as in the
rst experiment.
A team of researchers (also the authors of this topic) from the Faculty of
Mechanical Engineering, University of Ljubljana and scientists from the Institute
“
(IJS) developed a small-scale electrocaloric cooling device with an
AER [
56
]. As the electrocaloric material, 0.2-mm-thick (PbMg
1/3
Nb
2/3
O
3
)
0.90
-
(PbTiO
3
)
0.10
bulk ceramic plates, characterized and processed by the team at the IJS
were used. The maximum adiabatic temperature change of the ceramic material was
measured for an electric
Jo
ž
ef Stefan
”
eld change of 160 MVm
−
1
and accounted for 3.5 K
(which is one of the highest ECE values ever measured in bulk ceramics). However,
the electrocaloric cooling device operated at much lower electric
eld changes, the
maximum being 50 MVm
−
1
(which corresponded to 0.89 K of adiabatic temper-
ature change). A total of 30 ceramic plates were used, constructing a 60-mm-long
AER with a total mass of approximately 9 g. To create a void for the
ow, a
conductive distance holder with a thickness of 0.1 mm was inserted between the
individual ceramic plates. The distance holders were also used to connect the
electrodes of the ceramic plates to the electric eld generator. The device is
schematically presented in Fig.
10.14
. The AER was inserted into a housing and a
peristaltic pump was used to pump the
fl
uid
fl
fl
uid through the AER. Silicon oil was used
as the working
uid. A detailed description of the working principle of an elect-
rocaloric cooling device with an AER was already described in this chapter. The
authors reported that a maximum temperature span of 3.3 K (the temperature dif-
ference between the heat source and the heat sink) was measured at a frequency of
0.75 Hz and an electric
fl
eld change of 50 MVm
−
1
. This means that a regeneration
factor (the temperature span of the device over the adiabatic temperature change of
the electrocaloric material) of 3.7 was achieved. The photograph of the device and
its main characteristics are presented in Table
10.6
.
Additionally, the teams from the University of Ljubljana and the IJS proposed
numerous ideas and solutions about how to improve the performance of such a
device and gathered them in a patent application [
46
].
Table
10.7
shows the main characteristics of the
ve presented prototypes. It can
be concluded that these
rst prototypes are far from being competitive with mag-
netocaloric or compressor-vapour cooling devices. Nevertheless, these prototypes
serve more as proof-of-concept devices. However, the domain of electrocaloric
refrigeration and heat pumping was only recently given more attention by the
research community. In Fig.
10.15
, the total number of publications related to the
topic of electrocaloric refrigeration and heat pumping since 1990 is presented.
The data from Fig.
10.15
were obtained from the online database Web of Science. It
is clear that the number of publications is increasing exponentially and has more
than doubled in the past 3 years. Therefore, an increase in the number and the
performance of electrocaloric cooling devices is expected in the future.
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