Electrostatically actuated thermal switch device for caloric film

Abstract

An innovative thermal switch device using a thin metallic film electrostatically actuated by an electrode mainly conceived for caloric cooling is studied. Our study focuses on the characterization of the thermal conductance at the interface for the “on” and “off” states. Our setup uses the current passing through the metallization of the film as a heater, while the temperature is deduced from the measurement of its electrical resistivity. Using a thermal diffusion model and our measurements, we deduce the on and off state thermal conductances, and we achieve an on/off conductance ratio of 103. Lastly, we use a simple finite-time thermodynamic model to estimate the efficiency at maximum power, and we would obtain by integrating a standard electrocaloric film in our thermal switch. The result is a micro-refrigerator working at 85% of Carnot efficiency with a power density of 228 W g−1 which is far more than what it has been currently demonstrated.

Fluidic and Mechanical Thermal Control Devices

“…The switching ratio of electrically actuated mechanical thermal switches varied from a minimum of SR = 1.8 (characteristic time of the order of seconds) for aluminum film [ 229 ] to a maximum of SR = 1000 (characteristic time of the order of seconds) for polypropylene film. [ 222 ] However, theoretical models show that the switching ratio can potentially be increased up to SR = 1 000 000 using a gold film, as reported by Keum et al. [ 227 ] The characteristic times varied from τ = 1 ms for a gold film [ 228 ] to the order of several seconds for an aluminum film (SR = 1.8).…”

“…Electrically actuated mechanical thermal switches exploit electromechanical effects. [ 221–223 ] This effect produces a change in shape or size when a material is subjected to an external voltage or electric field. In a thermal switch, this effect is used to control the thermal contact between the heat source and the heat sink.…”

“…[ 221 ] considered bending a ceramic cantilever upward at up to 40 µm cm −1 under an external bias of U = 18 V. Similarly, Almanza et al. [ 222 ] observed a deflection of d = 1000 µm in a polypropylene film under a bias of U = 300 V. Further, Kim et al. [ 223 ] deflected gold beams by d = 30 µm under U = 140 V, and Driesen et al.…”

“…Thermal management is a common issue in several applications including cryogenics, [ 10–12 ] energy conversion, [ 13–15 ] caloric refrigeration, [ 16–18 ] microfluidics, [ 19–21 ] biology, chemistry, and pharmacy, [ 22–24 ] buildings, [ 25–28 ] outer space, [ 11,29,30 ] and sensor technologies. [ 31,32 ] Therefore, TCDs for these application areas are being studied theoretically and experimentally.…”

Thermal energy harvesting system based on magnetocaloric materials★

“…Since, we are focusing on the Steps 1 and 3, parameters related to the whole thermodynamic cycle as the frequency [7] the electrical power, the thermal transfer [8] will not be treated. Our main point here is to study the ratio between the electrical energy harvested and the mechanical energy available.…”