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See detailElectrocaloric coolers and pyroelectric energy harvesters based on multilayer capacitors of Pb(Sc0.5Ta0.5)O3
Torelló Massana, Àlvar UL

Doctoral thesis (2022)

The following work investigates the development of heat pumps that exploit electrocaloric effects in Pb(Sc,Ta)03 (PST) multilayer capacitors (MLCs). The electrocaloric effect refers to reversible thermal ... [more ▼]

The following work investigates the development of heat pumps that exploit electrocaloric effects in Pb(Sc,Ta)03 (PST) multilayer capacitors (MLCs). The electrocaloric effect refers to reversible thermal changes in a material upon application (and removal) of an electric field. Electrocaloric cooling is interesting because 1) it has the potential to be more efficient than competing technologies, such as vapour-compression systems, and 2) it does not compel the use of greenhouse gases, which is crucial in order to slow down global warming and mitigate the effects of climate change. The continuous progress in the field of electrocalorics has promoted the creation of several electrocaloric based heat pump prototypes. Despite the different designs and working principles utilized, these prototypes have struggled to maintain temperature variations as large as 10 K, discouraging their industrial development. In this work, bespoke PST-MLCs exhibiting large electrocaloric effects near room temperature were embodied in a novel heat pump with the motivation to surpass the 10 K-barrier. The experimental design of the heat pump was based on the outcome of a numerical model. After implementing some of the modifications suggested by the latter, consistent temperature spans of 13 K at 30 °C were reported, with cooling powers of 12 W / kg. Additional simulations predicted temperature spans as large as 50 K and cooling powers in the order of 1000 W / kg, if a new set of plausible modifications were to be put in place. Similarly, these very same PST-MLCs samples were implemented into pyroelectric harvesters revisiting Olsen's pioneering work from 1980. The harvested energies were found to be as large as 11.2 J, with energy densities reaching up to 4.4 J / cm3 of active material, when undergoing temperature oscillations of 100 K under electric fields applied of 140-200 kV / cm. These findings are two and four times, respectively, larger than the best reported values in the literature. The results obtained in this dissertation are beyond the state-of-the-art and show that 1) electrocaloric heat pumps can indeed achieve temperature spans larger than 10 K, and 2) pyroelectric harvesters can generate electrical energy in the Joule-range. Moreover, numerical models indicated that there is still room for improvement, especially when it comes to the power of these devices. This should encourage the development of these kinds of electrocaloric- and pyroelectric-based applications in the near future. [less ▲]

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