University of Cambridge
Electrocaloric applications based on multilayer capacitors of PbSc₀.₅Ta₀.₅O₃
Abstract
dc:description.abstractSolid-state refrigerants that exhibit electrically driven reversible thermal changes, known as electrocaloric (EC) effects, represent a potentially eco-friendly alternative to the greenhouse gases currently used as refrigerants in refrigerators and heat pumps. The phenomenology of EC effects is first briefly discussed, and EC materials and prototypes are then reviewed. Methods for parameterizing EC effects are summarized and critically analyzed with the goal of guiding experimental design and cautioning against potential pitfalls. Multilayer capacitors (MLCs) of PbSc₀.₅Ta₀.₅O₃ (PST) are demonstrated to be well-suited for cooling applications. The embodiment of highly ordered PST in the MLC geometry yielded a very high breakdown strength in this macroscopic EC working body, allowing the first-order ferroelectric transition to be driven supercritically via fields of up to E = 29.0 V μm‾¹. The resultant EC effects in the large central area of the capacitor were found to peak at 5.5 K near room temperature, and exceed 3 K for starting temperatures that span 176 K. These EC effects compare favourably to magnetocaloric (MC) effects in gadolinium working bodies, suggesting that MC heat-pump design could be repurposed to achieve better performance. Efficiency values for cooling cycles based on MLCs of PST are computed and analyzed by assuming a hypothetical fluid regenerator that is ideal. The refrigerant efficiency γ is defined as the factor by which the coefficient of performance (COP) for any given cycle is reduced due to losses in the working body. For balanced regenerative cycles with large temperature spans near room temperature (e.g. Th − Tc = 50 K), the MLCs of PST are found to attain refrigerant efficiencies of up to γ ~ 97%. MLCs of PST are exploited as the EC working body in a device where Peltier elements that separate it from a load and sink are synchronously driven at constant current and voltage. This protocol is found to increase the efficiency of Peltier cooling, but device optimization is required to evaluate meaningful improvements in efficiency.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2020
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Nair, Bhaskaran
- Advisor dc:contributor.advisor
-
- Mathur, Neil
Subjects
dc:subject × 6Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.59904
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/312805