Singular ratchet-valley structure inducing droplet directional transport crossing all boiling states

Abstract

Droplet directional transport on a heated surface is important for thermal management technologies. Current research is well on the droplet manipulation in the Leidenfrost state, but has yet to achieve droplet directional transport below the Leidenfrost temperature, especially nucleate boiling. We demonstrate that the proposed singular ratchet-valley structure (SRVs) exhibits the ability to transport droplets crossing all boiling states including nucleate, transition and film boiling. It is worth noting that the introduced deep-narrow valley on the traditional ratchet array is the key to realize the directional self-transport of boiling droplets. The array wall of the designed valley causes nucleate-boiling droplets to generate evaporative momentum along the ratchet direction, and it also blocks the sub-droplets that are splashing to the wall direction in the transition and spraying-film boiling, forcing the droplets to move along the ratchet direction. In certain scenarios, the SRVs surfaces can achieve droplet's anti-gravity transport, trajectory manipulation, fixed-point heat dissipation, and high-temperature self-cleaning.