Dropwise condensation heat transfer on vertical superhydrophobic surfaces with gradient microgrooves in humid air

Self-propelled droplet removal contributes vitally to the enhancement of condensation heat transfer performance. Here, inspired by the prickle tip of the cactus, we design and fabricate a gradient groove superhydrophobic surface. A visualization system in humid air has been established to investigate the droplet dynamic behaviors and heat transfer performance on the vertical gradient groove superhydrophobic surface. The dropwise condensation is also analyzed and compared to that on the plane and square groove superhydrophobic surfaces. The results indicate that the gradient groove superhydrophobic surface has the highest condensation heat flux among the three mentioned superhydrophobic surfaces with the increasing subcooling. The gradient grooves facilitate the condensed droplets departure under the synergistic effect of the dual-Laplace induced jumping and gravity-driven sliding removal even at higher subcooling. The dual-Laplace induced jumping possesses greater driving force, conducting the smaller droplet departure diameter and smaller angle between initial velocity and surface wall, which effectively improves the surface refreshment and further strengthens the surface heat transfer.& COPY; 2022 Elsevier Ltd. All rights reserved.