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Circuit for the demonstration of energy recovery. Electrical energy was passed via inductor L between EC capacitors C1 and C2, which are poled ferroelectric MLCs with a variable polarization P of finite magnitude and fixed direction. Switches S1 and S2, and diodes D1 and D2, prevented resonance so that heat could flow between each charge-transfer event (see Methods). For simplicity, we do not show the Sourcemeter used to inject the initial charge into C1 and subsequently measure its voltage, or the Sourcemeter used to measure voltage across C2
Source publication
Materials that show large and reversible electrically driven thermal changes near phase transitions have been proposed for cooling applications, but energy efficiency has barely been explored. Here we reveal that most of the work done to drive representative electrocaloric cycles does not pump heat and may therefore be recovered. Initially, we reco...
Citations
... The empty symbols refer to all prototype, which use fluids for the heat transport, the filled symbols refer to all prototype which use solid state contact for heat transfer. This work, which uses evaporation and condensation as a heat transfer mechanism is shown as a star [22][23][24][25][26][27][28][29][30][31] . The environment was kept at a temperature of 31°C to make sure the fluid condenses in the condenser and not elsewhere. ...
Electrocalorics (EC) is potentially more efficient than refrigeration and heat pumps based on compressors and does not need detrimental fluids. Current EC-prototypes use solid-state contact or forced convection with liquids to transfer the heat generated from the EC-material, which inhibits high cycle frequencies and thus limits power density. Here we present a heatpipe system solution, where the heat transfer is realized through condensation and evaporation of ethanol as a heat transfer fluid. Our prototype with lead scandium tantalate (PST) EC-material working at 5 Hz shows a specific cooling power of 1.5 W g ⁻¹ . This is one order of magnitude more than previously reported for ceramic EC-prototypes. Overcoming the limits of slow heat transfer is essential to reach high specific cooling powers enabling a future commercial success of the technology.
... While analogous magnetocaloric effects have been exploited for almost a century to achieve ultra-low temperatures in scientific laboratories 2 , the current push for environmentally friendly cooling and heating has led to a proliferation of prototypes based on EC, magnetocaloric and mechanocaloric materials near phase transitions close to room temperature 1,3-9 . Many of the EC prototypes [10][11][12][13][14][15][16] are based on EC effects that arise in BaTiO 3 and PbSc 0.5 Ta 0.5 O 3 near ferroelectric transitions that can be modified via grain size 17 , doping 18 , strain 19 and pressure 20 . Here we experimentally explore EC effects that arise in epitaxial films of SrTiO 3 (STO) near a ferroelectric transition that is created, rather than modified, by strain. ...
... In 2018, E. Defay et al. [18] proposed the charge recovery by a resonant circuit for electrocalorics, demonstrating up to 86% efficiency, charging ceramic capacitors in a system demonstrator. In 2020, Meng et al. [19] used a resonant circuit for a polymer-based system, reporting efficiencies of 70% and a measured COP R,SYS = 12% , the highest measured electrocaloric system COP known to the authors, which, however, is still significantly below the material limit. ...
... In [6] an electrocaloric PMN ceramic fabricated as in [23] by the authors from Fraunhofer IKTS, was measured, and driven with offset voltages. Offsets avoid the high permittivity at low voltages, as observed in [18], resulting in a calculated FOM = 28.6 , low DF TR = 0.06% and high COP R,MAT ≈ 87.7% for Carnot-like cycles [6]. ...
... Demonstrators (reviews: [24,25]) typically use Braytoncycles, less efficient [7] than the previously analyzed Carnotlike cycles. Initial resonant circuits [18,19] allowed energy recovery, but only square-like voltage waveforms (with sinusoidal-like transitions), resulting in Brayton-cycles. ...
Electrocaloric heat pumps for cooling or heating are an emerging emission-free technology, which could replace vapor-compression systems, harmful refrigerants, and mechanical compressors by a solid-state solution with theoretically even higher coefficient of performance. Existing electrocaloric ceramics could reach around 85% of the Carnot-limit, and existing electrocaloric polymers could enable a compact and high power density system. However, the performance of published system demonstrators stays significantly below this performance, partly because of the external electronic charging loss (cyclic charging/discharging of electrocaloric capacitors). This work analyzes how the latest 99.74% ultra-efficient power electronics enables to maintain a high performance even at the system level. A first-principle analysis on material and system parameters also shows the effect of significantly different material properties of ceramics (PMN, PST) and PVDF-based polymers on system parameters. A system benchmark provides insight into system characteristics not covered by material analysis.
Graphical abstract
... The advantages of the interface-regulative EC polymer on the temperature span of the EC device could be more prominent in an AER cycle. The refrigeration devices employ the AER cycles that pump heat from a low temperature to a high temperature, using a solid 24,34,35 or liquid 16,[36][37][38] heat-transfer medium. The AER refrigerator is featured to expand the temperature span of the device, exceeding the adiabatic temperature change of the EC working body, which should exhibit a temperature-independent ECE. ...
This work demonstrates that there exists a conflict between the structural ordering required by high thermal conductivity and the polar disordering required by the large ECE. By designing a molecular interface-regulated nanocomposite, we opened up the space between the BNNS and the polymer chains and concurrently achieved large ECE and high thermal conductivity, i.e., a facile order-disorder synergy. The interface-regulative polymers doubled the cooling power density of a film EC device, compared with that using BNNS/terpolymer blends. SUMMARY High thermal conductivities are highly desired for electrocaloric (EC) materials to improve the key performances of EC devices, including cooling power density (CPD) and coefficient of performance (COP). However, despite the large EC effect (ECE), the state-of-the-art EC polymer exhibits low thermal conductivity. The simple mixture of the EC polymer and two-dimensional (2D) high-thermal-conductivity nanofillers would dramatically reduce ECE by increasing long-range ordering. To free dipole orientations, we introduced 3-sulfurouspropyltrimethox-ysilane (SPTMS) to covalently graft boron-nitride nanosheets on the EC polymer. The interface-regulated nanocomposite exhibited the EC en-tropy change of 30.94 Jkg À1 K À1 under 100 MVm À1 and thermal conductivity of 0.72 Wm À1 K À1 , and utilizing which, the standard model of EC refrigerator achieved a 5.23 Wg À1 CPD, 6.8-fold higher than the one operating a simple mixture. A figure of merit of electrocaloric nano-composites was proposed to assess their overall capability in the heat-pumping applications.
... Also, the capacitive nature of electrocaloric elements requires only a dynamic charging and discharging current, but no static current such as the Peltier element. Most of the stored energy in the electrocaloric capacitance can furthermore be recovered [8]. All together, it is thus predicted that the electrocaloric effect might enable a competitive high heat pump system COP [9] in future. ...
... A two-stage prototype using commercial electrocaloric capacitors and a simple linear servo actuator was presented in [20] to demonstrate Carnot-like thermodynamic cycles. Also many one-stage systems were published, where the temperature span of the system is below the adiabatic temperature change, for example in [8] where electrical energy recovery was demonstrated in addition to the heat pump prototype. Cascading with the need for thermal control devices is also known from magnetocalorics [15,21,22] and elastocalorics [23]. ...
... Figure 3 shows an all-solid-state arrangement, which consists of one electrocaloric capacitor (forming the second part of the one EC element, C EC,2 in figure 2(c)) on top of twelve electrocaloric capacitors (forming the first part of the one EC element, C EC,1 in figure 2(c)). This work uses commercial Y5V SMD capacitors (as in [8,35], Multicomp MC1210F476Z6R3CT) which show a small electrocaloric effect at room temperature (≈23 • C), since they are based on a modified BaTiO 3 dielectric which is known to have an electrocaloric effect [36,37]. The setup was built by first soldering 12 EC MLCCs together at both electrodes. ...
In an all-solid-state electrocaloric arrangement, an absolute temperature change which exceeds twice the electrocaloric adiabatic temperature change is locally realized, using just the distributed thermal capacitances and resistances and spatio-temporal distributed electric field control. First, simulations demonstrate surface temperature changes up to four times (400%) the electrocaloric adiabatic temperature change for several implementations of all-solid state distributed element configurations. Then, experimentally, an all-solid-state assembly is built from commercial electrocaloric capacitors with two independently-controlled parts, and the measured surface temperature change was 223% of the adiabatic electrocaloric temperature change, which clearly exceeds twice the adiabatic temperature change and verifies the practical feasibility of the approach. This allows a significant increase of the maximum temperature difference per stage in cascaded and thermal switch-based electrocaloric heat pumps, which was previously limited by the adiabatic electrocaloric temperature change (100%) under no-load conditions. Distributed thermal element simulations provide insight in the spatio-temporal temperatures within the all-solid-state electrocaloric element. Since only the distributed thermal capacitance and resistance is used to boost the temperature change, the maximum absolute temperature change occurs only in parts of the all-solid-state element, for example close to the surfaces. A trade-off of the approach is that the required electrocaloric capacitance increases more than the gained boost of the absolute temperature change, reducing the power density and electrical efficiency in heat pump systems. Nevertheless, the proposed approach enables to simplify electrocaloric heat pumps or to increasing the achievable temperature span, and might also improve other electrocaloric applications.
... The recoverable part of the stored energy in the electrocaloric capacitor can be recycled by an external charge recovery circuit [14], [15], [19]- [21], such that almost all stored energy is reused for cyclic charging and discharging operation. High electrocaloric materials energy efficient has also been demonstrated in lead scandium tantalate (PST) [22], and achieved already a 13 K high temperature span using an electrocaloric regenerator [23]. ...
... To provide the alternating voltage, an external power conversion circuit is required, which adds additional electrical system losses. State-of-the-art charging circuits for electrocaloric capacitive loads were previously demonstrated with up to 80% efficiency using resonant circuits [19], [20], and recently significantly improved by the authors to around 99.2% by a switched mode power converter approach [15], [28], which then was also applied to an electrocaloric heatpump prototype [29]. However, the associated 0.8% loss still dominated the material dissipation factor which is below 0.1% for the PMN material. ...
... This optional offset voltage was not shown in the simplified Fig. 1 for more clarity. The operation with non-zero positive offset is useful to improve the coefficient of performance of electrocaloric materials, as described in [15], [19], to avoid the high permittivity region around low capacitor voltages. By changing the polarity of the offset voltage, it is also possible to realize bipolar load voltage operation, for example between ± ∆VMAX 2 , which might be useful for other capacitive load applications. ...
This work combines a 99.2% efficient GaN-based low-voltage fast-switching half-bridge converter with a Si-based high-voltage slow-switching and almost lossless switched capacitor multiplexer using a partial power processing approach to a six-level prototype with 99.74% efficiency. A loss breakdown shows how the ideal partial power processing efficiency is theoretically increased to 99.84% by using four additional voltage levels, but then reduced to the measured efficiency by the additional static and dynamic losses of the multiplexer. For electrocaloric heat pumps, an emerging technology for cooling and heating applications with zero global warming potential, such high charging efficiencies enable a high heat pump system coefficient of performance (COP). Based on available data of electrocaloric lead magnesium niobate (PMN)-based samples, and based on a first-principle and best-case analysis for Carnot-like cycles, it is predicted that the 99.74% electrical charging efficiency in combination with the electrocaloric material data enables to surpass 50% of the thermal Carnot limit (for cooling with a heat pump). Ultra-high efficiency of power converters thus pave the way towards future electrocaloric heat pumps of competitive system performance.
... In the last two decades, intensive studies have been conducted on different types of macroscopic, mechanical and micro-electromechanical (MEMS) thermal switches [1][2][3][4], which also includes their integration in caloric (ferroic) technologies [5]. By focusing on the last 5 years, and considering (micro)mechanical thermal switches and their applications in cooling, heating or thermal energy harvesting using ferroic materials, the majority of research activities were performed in the field of electrocalorics [6,7,[16][17][18][19][8][9][10][11][12][13][14][15] or pyroelectrics [20][21][22][23][24]. A much smaller number of publications can be found for the domains of magnetocalorics [13,[25][26][27] and ...
The quest for better performance from magnetocaloric devices has led to the development of thermal control devices, such as thermal switches, thermal diodes, and thermal capacitors. These devices are capable of controlling the intensity and direction of the heat flowing between the magnetocaloric material and the heat source or heat sink, and therefore have the potential to simultaneously improve the power density and energy efficiency of magnetocaloric systems. We have developed a new type of thermal control device, i.e., a silicon mechanical thermal switch capacitor (
TSC). In this paper we first review recently developed thermal switches based on micro-electromechanical systems and present the operation and structure of our new TSC. Then, the results of the parametric experimental study on the thermal contact resistance, as one of the most important parameters affecting the thermal performance of the device, are presented. These experimental data were later used in a numerical model for a magnetocaloric device with a thermal switch-capacitor. The results of the study show that for a single embodiment, a maximum cooling power density of 970 W m ^−2 (510 W kg _mcm ^−1 ) could be achieved for a zero-temperature span and an operating frequency of 5 Hz. However, a larger temperature span could be achieved by cascading multiple magnetocaloric elements with TSCs. We have shown that the compact TSC can be used in caloric devices, even with small temperature variations, and can be used in a variety of practical applications requiring thermal regulation.
... To realize thermal management applications based on ECE, intense efforts have been devoted to both materials research and engineering aspects. [5][6][7][8][9] To search for materials suitable for ECE, it is necessary to know how a large temperature change is generated for the simplest action of applying and removing an electric field E. There are two known approaches to do this: indirect and direct methods. [10][11][12] The indirect method is based on Maxwell's relation: the temperature T dependence of the electric polarization P at various values of E is converted into the adiabatic temperature change DT ad ECE induced by ECE through ...
We report on a direct measurement method for electrocaloric effects, the heating/cooling upon application/removal of an electric field in dielectric materials, based on a lock-in thermography technique. By use of sinusoidal excitation and multi-harmonic detection, the actual temperature change can be measured by a single measurement in the frequency domain even when the electrocaloric effect shows a nonlinear response to the excitation field. We demonstrated the method by measuring the temperature dependence of the electric-field-induced temperature change in two Sr-doped BaTiO 3 systems with different ferroelectric-paraelectric phase transition temperatures, where we introduce the procedure for extracting the pure electrocaloric contribution free from heat losses and Joule heating due to leakage currents. This method can be used irrespective of the type of dielectric material and enables simultaneous estimation of the polarization change and power dissipation during the application of an electric field, making it a convenient imaging measurement method for the electrocaloric effect.
... Wide bandgap semiconductors in converters enable at the same time a compact and highlyefficient system. To the best of the author's knowledge, for efficient charging of electrocaloric components so far only two approaches by E. Defay [3] (LIST, 80% efficient) and Y. Meng [5] (UCLA, 70% efficient) using resonant circuits were applied to prototypes. A Marx modulator adapted for electroactive polymers in [6] (88% efficient) could also be applied. ...
... This arrangement does not require an additional large (dc-link) buffer capacitor at the input of the converter, in contrast to a setup where only one EC-C is connected to the converter (as in [2]), since the energy from one EC-C is directly transferred to the other instead of to an external buffer capacitor. This strategy, using two capacitors, was also used with LC resonant circuits for electrocalorics in [3], [5] and is also known from efficient drivers for piezoelectric actuators [8]. From this arrangement it also follows that one capacitor is charged while the other is discharged (resulting in reversible temperature increase or decrease under adiabatic conditions), and vice versa. ...
... Two different optimal dead times were selected to achieve optimal zerovoltage switching at the peak and valley. Fig. 4 shows the EC-HP prototype built by this work, which is similar to [3] but with two series-connected thermal stages (instead of one) consisting of EC elements between the heat sink and source, and using a higher number of EC-Cs. Since the capacitors in the two thermal stages are oppositely charged and discharged, the thermal series connection allows to double the temperature span of the HP. ...
A 99% efficient power converter is applied to an electrocaloric heat pump prototype for the first time, enabling cyclic electrical field variation in electrocaloric capacitors and high heat pump performance. The electrocaloric effect is an almost fully reversible temperature change in special dielectrics caused by changed electrical field. The GaN power converter achieves high efficiency by zero-voltage switching hysteretic current control. Blocks of commercial multi-layer ceramic capacitors which exhibit an electrocaloric effect are efficiently charged and discharged, synchronized to contacting to a heat sink and source by actuators, which forms a heat pump prototype. Brayton cycles are caused by trapezoidal voltage. Then, arbitrary voltage (E-field) variation for Carnot-like cycles with quasi-isothermal heat transfer is demonstrated and verified by the measured almost constant heat flux during contact to the heat sink. The performance of electrocaloric heat pump prototypes in literature was limited by losses of LC resonant circuits, and is improved by an up to 15.5-fold decrease by this work. The work demonstrates electrocalorics as an emerging power electronics application and contributes to realize future efficient and emission-free, solid state, and electrocaloric heat pump systems.
... Electrocaloric cooling is an active and solid-state refrigeration technology with zero-global warming potential, high efficiency, environmentally benign, and easy miniaturization [7][8][9][10][11][12][13] . It exploits the reversible thermal change of ferroelectric materials with the Check for updates A full list of affiliations appears at the end of the paper. ...
With speeding up development of 5 G chips, high-efficient thermal structure and precise management of tremendous heat becomes a substantial challenge to the power-hungry electronics. Here, we demonstrate an interpenetrating architecture of electrocaloric polymer with highly thermally conductive pathways that achieves a 240% increase in the electrocaloric performance and a 300% enhancement in the thermal conductivity of the polymer. A scaled-up version of the device prototype for a single heat spot cooling of 5 G chip is fabricated utilizing this electrocaloric composite and electromagnetic actuation. The continuous three-dimensional (3-D) thermal conductive network embedded in the polymer acts as nucleation sites of the ordered dipoles under applied electric field, efficiently collects thermal energy at the hot-spots arising from field-driven dipolar entropy change, and opens up the high-speed conduction path of phonons. The synergy of two components, thus, tackles the challenge of sluggish heat dissipation of the electroactive polymers and their contact interfaces with low thermal conductivity, and more importantly, significantly reduces the electric energy for switching the dipolar states during the electrocaloric cycles, and increases the manipulable entropy at the low fields. Such a feasible solution is inevitable to the precisely fixed-point thermal management of next-generation smart microelectronic devices.
