Electrohydrodynamic Thermal Oscillators for Waste Heat Harvesting Applications

There is a great need for a high efficiency, scalable thermal oscillator for applications such as pyroelectric waste heat harvesting. This work attempts to design and test the efficiency of a novel liquid-based thermal oscillator, which utilizes periodic electrohydrodynamic (EHD) capillary bridging and debridging between two coaxial droplets in a parallel plate capacitor under an electric field. In preliminary testing of liquids, five modes of liquid motion were observed and found to be dependent on liquid properties, as well as the applied voltage and gap width of the capacitor. Through droplet profile extraction from test videos of the thermal oscillator, electrical, surface, and gravitational energies were calculated using finite element method simulations in COMSOL. Each liquid behavior exhibited unique energy configurations, and optimal behavior was found when bridge free energy was lowered, but surface energy was raised compared to the debridged (droplet) state. Finally, thermal tests were conducted by placing a pyroelectric material in contact with the liquid droplet EHD switches. This resulted in efficient thermal cycling and power produced through the Olsen cycle, demonstrating the device's ability to effectively generate temperature oscillations.