How can dropwise condensation be achieved on superhydrophobic nanocones?

Abstract

The condensation of jumping droplets on superhydrophobic surfaces has garnered significant interest because of its potential to enhance heat transfer efficiency. Among the various nano- and micro-structures, nanocone arrays have emerged as particularly effective in promoting dropwise condensation. However, the critical role of nanoconical structures and the material properties required to achieve robust dropwise condensation, essential for enhancing heat transfer, remain to be understood. Moreover, the contradiction that hydrophobicity can maintain a stable wetting state but inhibit nucleation is yet to be resolved. In this work, we experimentally investigated the droplet condensation process and the resulting wetting state of droplets on superhydrophobic nanocone arrays. Furthermore, we performed systematic simulations, exploring the impact of material parameters, including contact angle and nanocone geometry, on the condensation process. Based on these analyses, we constructed a parametric phase diagram to address the question of when robust dropwise condensation coupled with high efficiency can be achieved. Our findings revealed that surfaces with high-density nanocones and small-scale structures are essential for achieving this goal, and we identified the corresponding contact angles necessary for this outcome. We also developed simple models that predict both experimental and simulation results very well. This study provides novel insights into optimizing nanotextured surfaces for superior heat transfer performance.