Rectifying Directional Liquid Transport for the Thermal Diode Application Using the Bio-inspired Approach

Description

Achieving the directional and long-range mass, momentum and energy transport on solidhydrophobic surfaces is highly desired for practical applications, but has proven to bechallenging. Particularly, directionality and long-range droplet transport on hydrophobicsurfaces are mutually exclusive. Such a tradeoff is further complicated at harsh environments,where the notorious liquid flooding is induced by the collapse of hydrophobicity. Recently weobserved a peculiar ballistic droplet transport phenomenon on a ubiquitous insect which canmaintain non-wetting property even in very high humidity. The drain fly serves as a flexiblefluid rectifier to allow a directional and long-range droplet propagation as well as self-removalwithout the need of the driving forces dictated on natural hydrophilic surfaces such as gradientsin surface energy or Laplace pressure. Moreover, the directional and long-range droplettransport is against gravity, and does not require any additional energy input.The objectives of the proposed project are to probe the fundamental mechanism underlying theunique ballistic droplet transport manifested on the drain fly, and to translate the directionalliquid transport to thermal diode application. We will first experimentally investigate how thelocalized droplet nucleation on the surface of drain fly is rectified to a directional and globalmigration, and analytically elucidate the effect of structural topography, in particular thenanoscale ratchet arrays, on the droplet transport dynamics. We will also explore the feasibilityof achieving such a preferential liquid transport on micro-patterned ratchets to demonstrate thegenerality of this peculiar transport. As an extension of the fundamental understanding, we willfurther design a bio-inspired liquid rectifier that promotes the droplet nucleation, growth anddirectional droplet movement and collection. By integrating with the wicking structure recentlydeveloped in our lab which allows for the directional liquid spreading for efficient thin filmevaporation, we will translate the directional liquid motion into a novel thermal diode with highrectification coefficient. We believe that this new liquid transport mechanism to be identifiedin this project will dramatically advance our fundamental understanding of the dropletdynamics as well as open up a new avenue for the design of liquid rectifiers for a wide rangeof applications.?