Synergistic enhancement of droplet self-transport efficiency and condensation performance utilizing downward microstructures and wettability

The condensate behaviors and heat transfer performance during steam condensation on downward-facing microstructured surfaces are numerically investigated using a hybrid thermal lattice Boltzmann method. The effects of surface wettability, micropillar dimensions, and non-condensable gas (NCG) are systematically evaluated. The results reveal that hydrophobic surfaces promote droplet detachment and accelerate surface renewal by enhancing droplet mobility. The superhydrophobic surface with a contact angle of 150.18° exhibits the highest heat flux, attributed to the intensified coalescence-induced droplet jumping. Micropillar height produces competing effects on droplet nucleation and departure, whereas micropillar width regulates substrate temperature distribution and available nucleation sites, thereby influencing condensation characteristics. An optimized combination of micropillar dimensions further enhances heat transfer performance. The optimal micropillar height and width are determined to be 10 and 15 lattice units, respectively. The presence of NCG significantly deteriorates condensation heat transfer, with the average heat flux decreasing by 48.84%, 58.93%, and 66.03% at NCG concentrations of 1%, 3%, and 5%, respectively, compared with pure steam. This study further elucidates the relationships among microstructural parameters, droplet dynamics, and condensation heat transfer performance.