Environmental Engineering Reference
In-Depth Information
processed in the form of a multilayer capacitor in order to enhance their mechanical
properties and increase the total thermal mass of one electrocaloric element.
In conclusion, it would be hard to say which electrocaloric material is the best
choice for future applications. This will probably depend strongly on the desired
operating parameters, such as temperature span, cooling (or heating) power and the
ef
ciency of the device. Moreover, a lot of information is still missing for individual
materials. Many authors do not report on the entropy change of the materials, which
is, together with the adiabatic temperature change, a very important parameter.
Furthermore, the in
uence of some other effects, for example, the effect of the
number of polarization/depolarization cycles on the electrocaloric and mechanical
properties of the materials, are not well known.
fl
10.1.3 Review of Device Concepts and First Prototypes
In the past 8 years, since the discovery of the giant electrocaloric effect in PZT
ceramics in 2006, research in the area of electrocaloric refrigeration and heat pumping
has mainly been focused on searching for new materials and investigating their
properties. In order to transfer these new discoveries to an application, e.g. an
electrocaloric cooling device, it is important that the ideas about how to design an
electrocaloric cooling system are investigated and realized. So far, several different
concepts have been presented and are discussed in this chapter. However, just a few of
these presented concepts have been realized and experimentally veri
ed. This chapter
is divided into two parts. The
rst part is focused on the different concepts associated
with electrocaloric cooling devices and a theoretical evaluation of their performance.
In the second part, the
rst electrocaloric prototypes devices are presented.
10.1.3.1 Electrocaloric Cooling Devices: Concepts and a Theoretical
Evaluation of the Performance
Electrocaloric cooling devices should be designed in such a way that during or after
the polarization, the heat generated due to the electrocaloric effect is effectively
transferred from the electrocaloric material to the heat sink. In contrast, during or
after the depolarization, the electrocaloric material should absorb the heat from the
heat source. Furthermore, no heat should be transferred from the heat source to the
heat sink at any time, to avoid unnecessary heat losses (or gains).
For a better understanding, let us consider the simple case illustrated in Fig.
10.3
.
The electrocaloric material with dimensions w and h is put into direct thermal contact
(contact thermal resistance is neglected) with the heat sink and the heat source. If the
thickness of the electrocaloric material h is much smaller than the width w, then the
ratio between the heat-transfer area and the volume of the electrocaloric material is
large. In this case, the electrocaloric material can ef
ciently exchange heat with the
heat sink/source. However, during the polarization (when the material heats up) and
Search WWH ::
Custom Search