Technical Note Design and modeling of a fluid-based micro-scale electrocaloric refrigeration system Dongzhi Guo a , Jinsheng Gao b , Ying-Ju Yu a , Suresh Santhanam b , Andrew Slippey c , Gary K. Fedder b , Alan J.H. McGaughey a , Shi-Chune Yao a,⇑ a Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213-3890, USA b Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA 15213-3890, USA c Advanced Cooling Technologies, Lancaster, PA 17601-5688, USA article info Article history: Received 21 October 2013 Received in revised form 7 December 2013 Accepted 17 January 2014 Keywords: MEMS P(VDF–TrFE–CFE) terpolymer Moving mesh COP abstract A refrigeration system composed of silicon MEMS cooling elements is designed based on the electroca- loric (EC) effect in a P(VDF–TrFE–CFE) terpolymer, poly(vinylidene fluoride–trifluoroethylene–chlorofluo- roethylene) 59.2/33.6/7.2 mol%. Each cooling element includes two diaphragm actuators fabricated in the plane of a silicon wafer, which drive a heat transfer fluid back and forth across terpolymer layers that are placed between them. In the EC effect, reversible temperature and entropy changes related to polariza- tion changes appear in a material under the application and removal of an electric field. Finite element simulations are performed to explore the system performance. The effect of the applied electric field is studied, and the time lag between the electric field and the diaphragm motion is found to significantly affect the cooling power. A parametric study of the operating frequency, externally-applied temperature span, and the electric field amplitude are conducted. The results indicate that when the system is oper- ated at a temperature span of 15 K, a cooling power density of 3 W/cm 2 and a percent of Carnot COP of 31% are achieved for one element. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Micro-scale coolers have a wide range of potential applications, such as cooling chip- and board-level electronics, sensors, and radio-frequency systems [1]. In recent years, new cooling technol- ogies that take advantage of the thermoelectric [2–5], magnetoca- loric [6] and electrocaloric (EC) [7] effects have attracted interest as traditional cooling methods cannot satisfy emerging requirements on energy efficiency and environmental impacts [8]. While ther- moelectric coolers are gaining traction in applications, significant challenges exist to increase the figure of merit beyond unity due to the difficulty of reducing the thermal conductivity while main- taining good electrical properties [5]. The EC effect is a phenome- non in which reversible temperature and entropy changes appear in certain materials under the application and removal of an elec- tric field. Applying the electric field orients the dipoles and reduces the entropy associated with the polarization. This process happens so fast (on the order of milliseconds [9]) that it can be considered to be adiabatic. The temperature of the material therefore in- creases, as required by the entropy decrease. Reversely, removing the electric field disorders the dipoles, increases the entropy, and cools the material. The main advantage of EC cooling over magnet- ocaloric cooling (which operates on an analogous principle) is that the high electric field required for the process is much easier and less expensive to generate than the high magnetic field required for magnetocaloric cooling [8]. Although the EC effect was first reported by Kobeco and Kurts- chatov in 1930 [10], potential applications have been limited by the relatively low entropy and temperature changes for most ferro- electric materials (the highest value reported before 2006 was 2.6 K at an electric field of 3 V/lm and a temperature of 707 K for bulk Pb 0.99 Nb 0.02 (Zr 0.75 Sn 0.20 Ti 0.05 ) 0.98 O 3 [11]). Recently, materi- als with a large EC effect have been discovered [12,13], suggesting practical applications in cooling devices. Among these materials, a P(VDF–TrFE–CFE) terpolymer, poly(vinylidene fluoride–trifluoro- ethylene–chlorofluoroethylene) 59.2/33.6/7.2 mol%, demonstrates an adiabatic temperature change of 16 K under an electric field of 150 V/lm over temperatures between 270 K and 320 K [14]. In this paper, we designed a refrigeration system based on the EC ef- fect of this terpolymer. In 2010, Ju proposed the design of a solid-state refrigeration system based on the EC effect where an EC material is dynamically http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.01.043 0017-9310/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: Scaife Hall 311, 5000 Forbes Ave, Pittsburgh, PA 15213-3890, USA. Tel.: +1 412 268 2508; fax: +1 412 268 3348. E-mail address: scyao@cmu.edu (S.-C. Yao). International Journal of Heat and Mass Transfer 72 (2014) 559–564 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt