Environmental Engineering Reference
In-Depth Information
10.3.3 Review of Design Concepts
Even though the EsCE is the oldest-known ferroic (caloric) effect, its usage in
prototypes for cooling (or heat pumping) devices is in the earliest stage of devel-
opment. However,
rst and still the only up-to-date presented prototype
exploiting the EsCE was developed by DeGregoria [
115
] in 1994. It is based on a
shape-memory polymer (natural rubber) in the form of thin layers (foils) con-
structed into a regenerator with a thin spacing for the counter-flow heat-transfer
fl
the
uid (analogous to the AMR in magnetic refrigeration). In order to balance and
recover the force, four such regenerators were applied into the acentric rotary
system, where two of them were loaded (stretched) and two unloaded (unstretched)
at the particular time. Air was used as the heat-transfer
uid. The authors published
19 K of temperature span (with the hot-side temperature of 298 K). Unfortunately,
other more detailed results are not available, most probably due to the technical
problem associated with the fatigue life of the rubber, especially at the parts con-
nected to the supporting structures, where the stresses are the largest [
116
].
In 2012, a group from the University of Maryland [
117
] patented various dif-
ferent design ideas exploiting the EsCE, from a single-stage device with a single
elastocaloric material to more sophisticated concepts with elastocaloric porous
structures using a heat-transfer
fl
uid. Some of them are already in the prototyping
phase, but more detailed information is not yet available.
More detailed experimental or theoretical (numerical) analyses of the perfor-
mance characteristics of the elastocaloric device in order to estimate the available
cooling power, temperature span and ef
fl
ciency, were not yet performed. Since the
EsCE is signi
cantly larger compared to the MCE and in the most cases also the
ECE, its potential for application in a cooling (or heat pumping) device is therefore
very large. According to a report by the US Department of Energy on alternative
cooling technologies from 2014, it has the largest potential among all the alternative
non-vapour-compression HVAC technologies [
118
]. Currently, the major limitation
of this technology is in the limited fatigue life of the elastocaloric (superelastic)
materials. It is currently not possible to apply up to 108 loading cycles, which
would be required for 10 years of operating lifetime for such a device, without
causing cracks and failure of the material. However, some recent results on the
elastocaloric Ni
Co alloy are very promising and show no fatigue, even
after 106 cycles, which is an important step towards the application [
119
]. Fur-
thermore, in order to increase the ef
Ti
Cu
-
-
-
ciency, the mechanical hysteresis should be
reduced as much as possible. This would further reduce the required stress for the
transformation and therefore allow the simpler application of this technology on the
micro as well as larger scales.
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