Electrocaloric refrigerator using electrohydrodynamic flows in dielectric fluids

摘要

Heat switches are a key enabling element of efficient refrigerators that are based on the electrocaloric effect. We demonstrate a new concept for a heat switch that is based on micro-scale electrohydrodynamic (EHD) flows in thin layers of dielectric fluids. In this device, convective flow of the fluid is controlled by applying an electric field across the fluid layer. This creates a heat switch that can be cycled between a "closed" state with efficient convective heat transport and an "open" state with less efficient conductive heat transport. Substantial switching of the thermal transport coefficient was achieved in 500 μm thick layers of commercial hydrofluoroethers and bias voltages of typically 390 V. The efficacy of the heat switch varied by almost four orders of magnitude for different biasing schemes. The highest efficacy was achieved by biasing a patterned strip electrode and using a planar ground electrode. A preliminary experiment found a thermal conductivity contrast of 4.7+1.1 for the switch in the closed vs. open state. We also characterize the electrocaloric response of commercial multilayer ceramic chip capacitors and show that they can serve as serve as a useful surrogate material for first-generation electrocaloric refrigerators until higher performing multilayer structures of ferroelectric polymers are available.