2,451 research outputs found
Electrocaloric coolers and pyroelectric energy harvesters based on multilayer capacitors of Pb(Sc0.5Ta0.5)O3
No full textThe 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
NONLINEAR PYROELECTRIC MATERIALS FOR ELECTRO-THERMAL ENERGY HARVESTING
No full textNearly two-thirds of the global energy derived from primary resources is dissipated as low-grade waste heat, which remains a largely untapped source of recoverable energy. As global energy demand continues to increase, it is imperative to adopt alternative and sustainable energy conversion technologies that focus on reducing energy losses. One such technology is pyroelectric energy harvesting, which converts the heat directly into electrical energy by utilizing the intrinsic pyroelectric effect in certain polar dielectric materials. Moreover, this technology serves niche application areas where thermoelectric energy harvesting becomes ineffective, especially in harnessing low-grade heat. Unlike thermoelectric materials, which require a steady-state temperature difference, pyroelectric devices operate under temperature fluctuations, making them especially suitable for applications involving temperature variations over time. Although the concept of pyroelectric energy harvesting has been known for several decades, there is limited understanding of how nonlinear behaviour of pyroelectric materials, as a function of temperature and electric field, influences energy conversion performance. This work investigates the nonlinear pyroelectric conversion potential of a prototypical pyroelectric material, lead scandium tantalate (PST) in different device geometries, from thin films to bulk samples. Despite its excellent electrocaloric and pyroelectric properties, PST thin films were not widely studied due to the challenges associated with high processing temperatures. In this work, the processing conditions were carefully optimized to yield high quality PST thin films. Indeed, thin films can withstand high electric fields which directly enhance the pyroelectric energy output and are also suitable for integration in microelectronic devices. High-quality PST thin films developed in this work achieved a pyroelectric energy density of up to 9 J∙cm−3 under optimized thermal and electrical conditions. Furthermore, to expand the operating temperature range, the transition temperature of PST thin films was shifted to higher temperatures by systematically doping with Ti4+ ions. While thin films offer numerous advantages, their limited active volume restricts their applicability in macroscopic energy harvesting systems. To overcome this challenge, the study expanded to include both PST bulk ceramics and PST multilayer capacitors (MLCs). These geometries benefit from high B-site cation ordering, resulting in a first-order phase transition and high pyroelectric coefficient. In addition to the detailed electrical characterizations, direct pyroelectric energy conversion cycles were implemented on PST MLCs using a dedicated experimental setup. The results indicate that PST MLCs can achieve a maximum of 50% Carnot efficiency for a 5 K temperature span near their phase transition temperature, compared to 22% achieved by PST bulk ceramics for a ΔT of 10 K at their transition. These results were obtained under the Olsen pyroelectric conversion cycle without any heat regeneration. Based on these results, PST MLCs were selected to demonstrate two proofs of concept to highlight the practical feasibility of non-linear pyroelectric energy harvesting devices. First, a standalone autonomous pyroelectric energy harvester was developed using only two PST MLCs. The device automatically initiates the Stirling pyroelectric conversion cycle based on the temperature profile of the material obtained from a thermocouple and the energy harvested by the materials is reused to initiate successive cycles without drawing energy from external power sources. Following the same device concept, a macroscopic self-powered pyroelectric energy harvester consisting of 60 PST MLCs was developed. To successfully implement this system, a closed-loop fluidic control system was introduced for the first time, enabling nonlinear pyroelectric energy harvesting in a macroscopic device without relying on heat regeneration or large volumes of heat transfer fluid. The energy extracted from the device was used not only to sustain the autonomous operation of the device but also to continuously power an external Bluetooth communication module for more than 30 minutes, thereby demonstrating a fully self-sustaining pyroelectric energy harvesting device. The results presented in this dissertation highlight the practical feasibility of nonlinear pyroelectric energy conversion, showing that high electrical output and efficiency can be achieved by carefully tuning both the material properties and the device architecture. Furthermore, the macroscopic self-powered pyroelectric energy harvester indicate that this technology can be used to develop autonomous devices or serve as a supplementary energy source to extend device lifetime by harnessing energy from ambient sources such as the ubiquitous waste heat. These outcomes not only open new avenues for real-world applications but also suggest that future efforts in nonlinear pyroelectric energy harvesting should shift from purely material-focused improvements toward system-level design and integration.THERMODIMAT7. Affordable and clean energ
Scale law on energy efficiency of electrocaloric materials
No full textCaloric materials are suggested as energy-efficient refrigerants for future cooling devices.
They could replace the greenhouse gases used for decades in our air conditioners, fridges,
and heat pumps. Among the four types of caloric materials (electro, baro, elasto, magneto caloric), electrocaloric materials are more promising as applying large electric fields is
much simpler and cheaper than the other fields. The research in the last years has been
focused on looking for electrocaloric materials with high thermal responses. However, the
energy efficiency crucial for future replacement of the vapor compression technology has
been overlooked. The intrinsic efficiency of electrocaloric has been barely studied. In the
present dissertation, we will study the efficiency of EC materials defined as materials efficiency. It is the ratio of the reversible electrocaloric heat to the reversible electrical work
required to drive this heat. In this work, we will study the materials efficiency of the benchmark lead scandium tantalate in different shapes (bulk ceramic and multilayer capacitors).
A comparison to other caloric materials is presented in this dissertation. Our work gives
more insights on the figure merit of materials efficiency to further improve the efficiency of
our devices.CAMELHEAT C17/MS/11703691/Defa
Emmanuel Kutik
No full textabstract: Emmanuel Kutik was almost eight years old when he left his home. He walked for three months and traveled with fifty people.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 23Region: BentiuThis picture and bio was donated to the Lost Boys Found project from The Arizona Lost Boys Cente
Honorable Emmanuel Okocha Oral History Interview
No full textThis is an oral history interview with the Honorable Emmanuel Okocha, author of Blood on the Niger, the only book about the Asaba Massacre, a mass killing of civilians which occurred in 1967 during the Nigerian Civil War. Okocha, a survivor of the massacre, was a small child at the time; his father was killed at Asaba, and two older brothers also died during the war. Okocha began researching the massacre after finishing his university studies, and has interviewed hundreds of survivors and relatives of those who were killed. He describes some of his research, the publication of his book, and his efforts to document the massacre
Emmanuel Cooper OBE 1938–2012 A Retrospective Exhibition
No full textDr Emmanuel Cooper OBE (HonDFA) 1938–2012 was a distinguished craftsman, writer, teacher and broadcaster. A potter of international standing, his work is represented in many public collections. The author of nearly thirty books, he was editor of Ceramic Review, visiting Professor at London’s Royal College of Art, and a regular broadcaster on television and radio. He was awarded an OBE in 2002 for services to art. Emmanuel’s contribution to the world of ceramics was hugely significant. This will be celebrated with a touring exhibition of his ceramics and a publication looking at his life in pots – produced by Ruthin Craft Centre in collaboration with the University of Derby
Immobile History: An Interview with Emmanuel Le Roy Ladurie
No full textThe author spoke with renowned French historian Emmanuel Le Roy Ladurie about Computers, Geography and History. Le Roy Ladurie was the "standard bearer" of the third generation of the French Annales school, a group of French intellectuals that combined different disciplines such as history, geography, anthropology, and more to delve into social history
Emmanuel B. Dongala
No full textA chapter on Congolese writer Emmanuel B. Dongala in the Dictionary of Literary Biography. (Vol. 360: Contemporary Arican Writers). --author-supplied descriptio
High cooling performance in a double-loop electrocaloric heat pump
No full textCooling through solid-state electrocaloric materials is an attractive replacement for vapor compression. Despite recent efforts, devices that are potentially commercially competitive have not been developed. We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 4.2 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown. Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 64% of Carnot’s efficiency as long as energy is properly recovered. We believe that this demonstration shows electrocaloric cooling to be a very promising alternative to vapor compression cooling.J.L., A.T., T. G., U.P., V.K., and E.D. acknowledge the Fonds National de la Recherche (FNR) of Luxembourg for supporting this work through the projects BRIDGES2021/MS/16282302/CEC0HA/Defay, THERMODIMAT C20/MS/14718071/Defay and RIDGES2020/MS/15410586/CALPOL/DefayPeer ReviewedPostprint (author's final draft
Can reforming global institutions help developing countries share more in the benefits from globalization?
No full textGlobalization could significantly expand trade, international investment, and technological advances, but the gains from global integration have been unevenly distributed across and within nations. Greater global interdependence has also brought greater macroeconomic volatility, resulting in several serious financial crises in the second half of the 1990s. The global matrix of Bretton Woods and United Nations institutions that developed starting in the 1940s, formed under a different balance of power, in a world of fixed exchange rates and limited capital mobility. Since the 1960s regional financial institutions have emerged because of the greater autonomy of different regions and the greater financial needs of development. The author reviews different proposals for reform of the international financial institutions and changes in the roles of the International Monetary Fund (IMF) and the World Bank. He highlights the implications for developing countries of (1) Policy conditionality. (2) The countercyclical role of multilaterals'lending. (3) Greater lending to middle-income than to low-income developing countries. (3) Access to liquidity at times of crisis. (4) Mechanisms for giving low-income countries a greater voice in IMF and World Bank decisionmaking. The author streses the overlapping responsibilities of the Bretton Woods and regional financial institutions and the need to reassess the allocation of responsibilities and to develop better coordination mechanisms between these institutions. Those designing institutional reform must consider the corporate capabilities of each type of institution. The corporate cultures of global and regional institutions differ. So does the kind of knowledge they generate and disseminate, and so do patterns of interactions with, and mechanisms for representation of, client countries.Finally, the author calls attention to the need to harmonize national and global growth-oriented policies in a way that reduces volatility and promotes social equity.Environmental Economics&Policies,Governance Indicators,Financial Intermediation,Economic Theory&Research,Banks&Banking Reform
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