Condensation heat transfer enhancement through durable, self-propelling fluorine-free silane-treated anodized surfaces

Abstract

When two or more adjacent droplets coalesce, excess surface energy is generated, which can be converted into the kinetic energy of the merged droplet through a suitable nanostructure and the superhydrophobicity of the surface. This causes a self-propelled behavior on the condenser surface and, consequently, a much higher condensation heat transfer coefficient. Despite these advantages, developing a durable self-propelled condenser surface that is easy to fabricate and employs non-toxic and fluorine-free materials for its superhydrophobicity remains a challenge. Addressing this gap in knowledge, we introduce a durable yet versatile fluorine-free superhydrophobic surface through the modification of anodized aluminum, which can enhance the condensation heat transfer coefficient by up to 676.7% compared to a pristine aluminum surface at a subcooling temperature of 2.77 K. Furthermore, this surface can retain its superhydrophobic properties even after 320 hours of continuous condensation. Moreover, after undergoing 10 meters of abrasion, the superhydrophobicity of the surface remains unaffected. Additionally, a superhydrophilic surface obtained through anodizing aluminum has also proven to be effective only at low subcooling temperatures, improving the condensation heat transfer coefficient up to 16.15% compared with pristine aluminum at a subcooling temperature of 3.96 K. Both the superhydrophilic and superhydrophobic surfaces presented in this study show anti-corrosive behavior as well, reducing the corrosion current density by 2 and 4 orders of magnitude, respectively.