Coalescence-induced droplet jumping on surfaces with hydrophobic thin-walled-lattice microstructures

Coalescence-induced droplet jumping (CIDJ) has significant applications in heat transfer, anti-frosting, and corrosion prevention. The thin-walled-lattice (TWL) microstructure design enhances CIDJ by continuously sieving condensing droplets on solid surfaces. However, the simultaneous appearance of many droplets has the risk of film formation, which can degrade surface performance. This study addresses this challenge by proposing symmetric four-TWL units to improve CIDJ efficiency. Using three-dimensional conservative phase-field lattice Boltzmann simulations with large density ratios, we demonstrate that these units achieve superior CIDJ performance compared to existing designs, with droplet jumping velocities reaching up to 10.15 m/s under certain conditions. The height of the TWL structure, the radius of the superhydrophilic spots (Rspot), and the wall contact angle (θw) were found to affect the jumping performance of the droplets significantly. Our results indicate that the strict requirements for θw (160 ± 10 deg) commonly seen in current CIDJ research could be relaxed to θw>120 deg on the proposed surface. A phase diagram for droplet jumping with the radius of the spot Rspot and the contact angle θw as independent variables was generated to provide essential guidance for the design of similar lattice structures. Finally, after reviewing the numerical results, we proposed two innovative surface designs, which could provide new design paradigms for future CIDJ research and applications.