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A Heat-switch-based Electrocaloric Heat Pump
Keywords: Electrocaloric , Heat pump, Heat switch
The electrocaloric effect (ECE) refers to the change in the temperature of a polar dielectric material with a changing electric field. Recently discovered materials with large ECE, including relaxor ferroelectric ceramics [1] and polymers[2][3] have the potential to enable heat pump systems that are compact, efficient, reliable, and environmentally benign [4]. Several approaches to exploiting the ECE to make heat pumping systems have been suggested, including regenerative and heat-switch-based designs. In a heat-switch-based system, the heat flux to and from capacitors with EC dielectrics is controlled with heat switches, devices whose thermal conductance can be actively switched between a high and a low value. Such a system has been shown theoretically to have the potential for high efficiency in comparison with thermoelectric heat pump, if heat switches with high thermal conductance ratios between the closed (or "on") and open (or "off") states are utilized [5]. Recently, several studies and simple demonstrations of EC cooling devices have been reported [6][7]. While these have successfully achieved positive temperature lifts, none has also reported concurrent non-zero heat flux. Moreover, none of the demonstrations has been operated continuously for extended periods. In this presentation we report a heat-switch-based EC cooling system that achieves simultaneous temperature lift and cooling power, enabled by high-thermal-contrast heat switches. The system core comprises two micromachined silicon heat switches modulating heat flux to and from an EC module formed from BaTO3 multilayer capacitors (MLCs), which have a small measureable ECE and are commercially available. To operate the heat pump, the heat switches are actuated synchronously with the application of electric fields across the MLCs. Heat flux versus temperature lift is fully characterized. With an electric field strength of 277 kV/cm, the system achieves a maximum heat flux of 36 mW and maximum temperature lift of greater than 0.3C, which 60% of the expected MLC adiabatic temperature change of 0.5C. The device has been operated reliably for several tens of thousands of switching cycles and a total operating time of >10 h without failure. The device design is readily adaptable to MLCs with higher ECE, and is scalable both to higher temperature lifts and heat fluxes by combining multiple sections thermally in series or parallel, respectively.
Yunda Wang, Member of Research Staff
PARC, a Xerox Company
Palo Alto,, CA
USA


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