Robust jumping-droplet condensation

Maximizing jumping frequency and growth rate of condensed droplets on superhydrophobic surfaces has been considered as a promising approach to enhance heat transfer in many energy systems. For pure steam condensation, achieving efficient self-droplet jumping remains a significant challenge, requiring the simultaneous creation of a stable cushion layer for fast droplet removal and its associated low additional thermal resistance for rapid droplet growth. Here, we report a hierarchical superhydrophobic surface with nanowire-bunch arrays and rational V-shaped microgrooves that exhibit preferential nucleation sites for site-specific droplet formation, highly dynamic droplets in Cassie-state driven by self-upward Laplace pressure, and a superior heat transfer pathway across the growing droplets. Robust jumping-droplet condensation of pure steam is demonstrated for high-performance heat transfer on the hierarchical nanowire-bunch arrays with an optimal microgroove angle of 27°. The exponent factor of droplet growth rate on the microgroove is increased by 56% compared with that on the superhydrophobic nanowired surface without microgrooves. A record-high average heat transfer coefficient of 332 kW m^-2 K^-1 and maximum heat flux of 1063 kW m^-2 are achieved for pure steam jumping-droplet condensation.