Dropwise condensation heat transfer on vertical superhydrophobic surfaces with fractal microgrooves in steam

• Published in: International journal of heat and mass transfer 2023-12, Vol.217, p.124641, Article 124641
• Main Authors: Gao, Shangwen, Wu, Suchen, Gulfam, Raza, Deng, Zilong, Chen, Yongping
• Format: Article
• Language: English
• Subjects: Dropwise condensation; Fractal groove; Heat transfer; Superhydrophobic surface
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2023.124641

•A fractal groove functional hydrophobic surface has self-similar multi-level grooves designed by Cantor set fractal principle.•The multi-level grooves on the fractal groove surface not only facilitate the merging, bouncing, and removal of droplets at low subcooling degrees but also enable effective droplet removal at high subcooling, thereby enhancing the condensation heat transfer performance.•The heat flux on the fractal groove surface would increase by about 110% compared to that on the plane superhydrophobic surface at surface subcooling of 3 ℃, and by 74% at surface subcooling of 12 ℃. Despite dropwise condensation witnesses the superior heat transfer performance with in-time removal of condensate, pinning and flooding phenomena significantly limit its application at high subcooling. In this study, we design and fabricate a self-similar fractal groove superhydrophobic surface inspired by the self-similar fractal spines of cactus thorns. A visualization and condensation heat transfer measurement experimental platform is established to investigate droplet dynamics and heat transfer performance on the vertical self-similar fractal groove superhydrophobic surface. Dropwise condensation is analyzed and compared with that on plane and groove superhydrophobic surfaces. The fractal grooves promote spontaneous coalescence-induced jumping of mismatched condensate droplets at low subcooling, resulting in a higher probability and frequency of droplet jumping. Furthermore, second-level grooves constrain the shape of large droplets more effectively and facilitate condensate removal after the failure of first-level grooves at high subcooling. In agreement with droplet dynamics, the heat transfer measurements demonstrate that the fractal groove superhydrophobic surface achieves the highest condensation heat flux and heat transfer coefficient among the three investigated superhydrophobic surfaces as subcooling increases.