An electrocaloric refrigerator without external regenerator

Gu, Hui; Qian, Xiao Shi; Ye, Hui Jian; Zhang, Qiming

doi:10.1063/1.4898812

Cited by 62 publications

(53 citation statements)

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“…C The discovery one decade ago of giant electrocaloric (EC) effects near ferroelectric phase transitions in ceramic thin films, 1 and then in thicker films of polymers, 2 triggered intense research into ferroelectric materials for environmentally friendly EC cooling. [3][4][5][6] Although there have been significant advances in materials developments, [7][8][9] measuring techniques, [10][11][12][13][14][15][16] and heat-pump prototypes, [17][18][19][20][21] the commercial application of EC materials remains elusive. The main obstacle is that EC performance is limited by breakdown field, while another major obstacle is that electric-fieldinduced strain produces mechanical fatigue and ultimately failure.…”

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confidence: 99%

Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

et al. 2016

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We use calorimetry to identify pressure-driven isothermal entropy changes in ceramic samples of the prototypical ferroelectric BaTiO3. Near the structural phase transitions at ∼400 K (cubic-tetragonal) and ∼280 K (tetragonal-orthorhombic), the inverse barocaloric response differs in sign and magnitude from the corresponding conventional electrocaloric response. The differences in sign arise due to the decrease in unit-cell volume on heating through the transitions, whereas the differences in magnitude arise due to the large volumetric thermal expansion on either side of the transitions.

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Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

et al. 2016

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“…Furthermore, ECE refrigeration can prove to be more economical and environmentally friendly than commercial refrigerating systems. [16,17] The first instance of reported ECE can be dated back to 1930, when the observations were first made. [18] However, it was only upon the discovery of highly polar ferroelectric materials that interest in ECE was renewed.…”

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confidence: 99%

Enhanced Electrocaloric Effect in Pre‐stressed Ferroelectric Materials

2015

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The effect of mechanical uniaxial stress on the electrocaloric behavior of ferroelectric materials has been analyzed. The magnitude of the electrocaloric effect was enhanced using controlled uniaxial stress. This study was performed for two classes of ferroelectric materials: 94(Bi1/2Na1/2)TiO3–6BaTiO3 (BNT–BT) bulk ceramics and Pb(Mn1/3Nb2/3)O3–32PbTiO3 (PMN–32PT) single crystals. Indirect measurements were made for pre‐stressed materials by using ferroelectric hysteresis loops and Maxwell’s relations. Peak adiabatic temperature changes of approximately 3 K and 0.65 K were obtained for BNT–BT and PMN–32PT materials, respectively. These values represent significant improvements (73 % and 200 %) over those obtained under unstressed conditions. The electrocaloric effect (ECE) could be harnessed in these materials for environmentally friendly refrigeration systems.

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“…A corresponding rotary EC refrigerator is described in Ref. [47]. two neighbouring EC rings are directly contacted to facilitate the heat exchange with each other.…”

Section: Device Prototypesmentioning

confidence: 99%

“…With regard to losses, Φ is limited to a value of approximately 10-15%, which is comparable to thermoelectric energy converters. Efficiencies of Φ ≥ 0:5 have been reported in literature for a micro-EC cooling module comprising a micro-electromechanical heat switch [46], a chip scale EC oscillatory refrigerator (ECOR) [28] and a EC refrigerator with intrinsic regenerator [47]. It seems that such a Φ value originates from unreasonably large values of COP > 8.…”

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Electrocaloric Cooling

Suchaneck¹,

Pakhomov²,

Gerlach³

2017

Refrigeration

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The electrocaloric effect describes a reversible temperature change in dielectric materials submitted to an applied electric field. Adiabatic polarization raises their temperature, and adiabatic depolarization lowers it, analogous to temperature changes that occur when a gas is compressed or expanded. For refrigerator application, the reverse Brayton cycle is currently the most promising for practical implementation. The electrocaloric effect provides a large material efficiency. However, existing refrigerator prototypes lack from the absence of efficient heat switches for thermal linkage to the load and the heat sink. Cooling power densities of a few W/cm 2 and temperature spans in the order of 20 K (in regeneration systems) are achievable at a cycle time of 100 ms.Keywords: electrocaloric effect, thermodynamic cycles, coefficient of performance, refrigeration devices IntroductionFor almost 150 years, refrigeration applications were solved by means of vapour compression. While the most efficient fluids for this approach are based on chlorofluorocarbons, hydrochlorofluorocarbons and hydrofluorocarbons, they come with the severe drawback of contributing to global warming and ozone depletion. Therefore, in 1987, the Montreal Protocol issued a ban on these chemicals providing regulations for phasing them out. Promising natural alternative substances are impractical due to their toxicity (ammonia) or-in particular-their flammability (propane) [1].Vapour compression refrigerators (VCRs) are operated as reverse Rankine cycles. They use a circulating liquid refrigerant as a medium. The refrigerant is: (i) adiabatically compressed, (ii) condensed at constant pressure undergoing a phase transition (thereby rejecting heat to the heat sink), (iii) adiabatically throttled in an expansion valve and (iv) evaporated at constant © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.pressure undergoing the reverse phase transition (thereby absorbing heat from the load). The amount of transferred heat is determined by the latent heat of the first-order phase transition. Similarly, in solid-state electrocaloric (EC) cooling, the adiabatic compression/expansion of the refrigerant is analogous to adiabatic polarization/depolarization, while the isobaric processes are replaced by isofield ones. Contrary to VCR, where the adiabatic expansion of the vapour is thermodynamically irreversible, the EC and the magnetocaloric (MC) effects are thermodynamically reversible processes that could reach the limit of the Carnot efficiency. This is another aspect making them promising for future application.Electric fields required for the EC refrigeration cycle can be supplied much easier and less expensively than the high magnetic fields required for the MC refrigeration [2]. Other advantages in compar...

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An electrocaloric refrigerator without external regenerator

Cited by 62 publications

References 18 publications

Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

Enhanced Electrocaloric Effect in Pre‐stressed Ferroelectric Materials

Electrocaloric Cooling

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