The electrocaloric effect in thin films of a poly(vinylidene fluoride-trifluoroethylene chlorofluoroethylene) terpolymer (62.6/29.4/8 mol. %, 11-12 lm thick) is directly measured by infrared imaging at ambient conditions. The adiabatic temperature change is estimated to be 5.2 K for an applied electric field of 90 V/lm. The temperature change is independent of the operating frequency in the range of 0.03-0.3 Hz and is stable over a testing period of 30 min. Application of this terpolymer is promising for micro-scale refrigeration. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4890676] Micro-scale refrigeration systems are widely used for the cooling of integrated circuits, microelectromechanical sensors, and biomedical devices.1 Environment-friendly cooling technologies with a high efficiency are attractive due to growing energy demands and stringent environmental requirements.
2Although thermoelectric cooling is commonly applied and has been scaled to the micro-domain, 3-6 the low efficiency and challenges in material fabrication suggest that alternatives are needed. 6 While refrigeration based on the magnetocaloric effect 7 can be employed to achieve extremely low temperatures, miniaturization of devices is challenging while maintaining a high cooling performance due to the difficulty of realizing the large magnetic fields required.
2The electrocaloric (EC) effect is a phenomenon in which reversible, polarization-related temperature and entropy changes occur when an electric field is applied to certain materials. EC cooling, which operates on a refrigeration cycle analogous to magnetocaloric cooling, is an emerging technology. 8 The highest reported adiabatic temperature change in a bulk EC material is 2.5 K at an electric field of 3 V/lm and a temperature of 434 K 11 The P(VDF-TrFE-CFE) terpolymer demonstrates an adiabatic temperature change of 16 K at an electric field of 150 V/lm near room temperature 12 and is easily and economically fabricated, making it favorable for mass production.13 These findings point to the potential of applying EC cooling in micro-devices using polymer thin films.Direct and indirect techniques can be applied to measure the EC effect. In the indirect measurement, a differential scanning calorimeter is used to measure the heat flow under a high electric field and isothermal conditions. 14,15 This technique is best suited to bulk materials as the output heat flow signal for a thin film sample is very small. Jia and Ju 16 reported an approach for characterizing the EC effect in a thin film sitting on an insulating substrate. In this approach, the temperature response of a resistance thermometer deposited on the bottom of the EC film is monitored as an electric field is turned on and off. In the reported measurements, the temperature change is less than 10% of that expected because the heat loss from the EC film to the substrate is large. Lu et al.17 employed a specially designed calorimeter to measure the EC effect in a thin film. In this approach, the heat generated in the...
A new Stirling microrefrigeration system composed of arrays of silicon MEMS cooling elements has been designed and evaluated. The cooling elements are to he fabricated in a stacked array on a silicon wafer. A regenerator is placed between the compression (hot side) and expansion (cold side) diaphragms, which are driven electrostatically. Air at a pressure of 2 bar is the working fluid and is sealed in the system. Under operating conditions, the hot and cold diaphragms oscillate sinusoidally and out of phase such that heat is extracted to the expansion space and released from the compression space. Parametric study of the design shows the effects of phase lag between the hot space and cold space, swept volume ratio between the hot space and cold space, and dead volume ratio on the cooling power. Losses due to regenerator nonidealities are estimated and the effects of the operating frequency and the regenerator porosity on the cooler peiformance are explored. The optimal porosity for the best system coefficient of performance (COP) is identified.
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