A phase-change thermal diode using electrostatic-induced coalescing-jumping droplets

Abstract

Analogous to the electronic diode, a thermal diode is a device which allows heat to flow to a preferential direction. Compared with other thermal diodes, phase-change thermal diodes yield greater thermal rectification performance due to high latent heat. With coalescing-jumping droplets as a result of dropwise condensation and water evaporation through a vapor space in the forward mode and thermal conduction through a high thermal resistance material in the reverse mode, the thermal rectification of this phase-change thermal diode can be higher than 100. However, due to the limited jumping height of coalescing-jumping droplets, progressive flooding occurs on a non-wetting surface causing a degraded heat transfer performance. Nevertheless, an applied electric field has proved to be one of the effective methods to enhance heat transfer in water evaporation and dropwise condensation. Thus, this study aims to investigate the effects of applied electrical fields on the effective thermal conductivity and thermal rectification of a phase-change thermal diode using electrostatic-induced coalescing-jumping droplets. The thermal diode is designed, assembled and investigated experimentally. The results show that the applied electric field potentially enhances the effective thermal conductivity and thermal rectification of the phase-change thermal diode. At the applied electrical voltage of 50 V, the maximum average thermal rectification of 325 is reported. This number shows a 90% greater improvement over thermal rectification in the no-electric-field condition and is considered to be one of the highest performances of all experimental thermal diode studies.