Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 421

Fig. 10.18 Schematic
presentation of the concept of
a pyroelectric device
employing a heat regeneration
process (see also Olsen et al.
[ 75 ])

However, in the cycle with the heat regeneration, considerably less heat is
transferred from the heat source to the material, thus increasing the ef ciency of the

cycle. Olsen and Brown [ 75 ] estimated the ef ned as the ratio between

the work performed by the pyroelectric material and heat transferred from the heat
source to the pyroelectric material) of an idealized device working under the
regenerative pyroelectric Ericsson cycle (neglecting the energy losses such as
the Joule heating of the pyroelectric material, the losses due to the hysteresis of the
pyroelectric material, the energy input needed to move the pyroelectric material
from the heat source to the heat sink, and the other way around, and the heat

ciency (de

ow
between the heat source and the heat sink by means of thermal conduction). They
showed that such a device could reach an ef

fl

ciency of a
Carnot engine operating between the same temperatures. However, in practical
cases, the devices working under the regenerative pyroelectric Ericsson cycle differ
from the concept presented in Fig. 10.18 . Furthermore, the ef

ciency equal to the ef

ciencies achieved are
considerably lower than those of an ideal Carnot engine working between the same
temperatures [ 62 , 67 ]. For example, Olsen et al. [ 67 ] reported that a pyroelectric
energy converter working under the Ericsson cycle and employing heat regenera-
tion reached an ef

ciency of 0.42 %, which was equal to 5.7 % of the Carnot

(Exergy) ef ciency.

10.1.6.2 Pyroelectric Energy Harvesting: First Prototypes

In this section, the rst generation of pyroelectric energy harvesting prototypes is

presented. These rst group

includes the so-called self-driven pyroelectric energy harvesting devices that need
no external power supply. The second group relates to the pyroelectric energy
harvesting devices based on the Ericsson thermodynamic cycles.

rst prototypes can be divided into two groups. The