Nano-structured aluminum surfaces for dropwise condensation

Superhydrophobic surfaces represent a promising strategy to consistently promote dropwise condensation, which can lead to an important increase of the heat transfer coefficient as compared to filmwise condensation. To get superhydrophobicity, it is necessary to reduce the surface energy and to modify the surface structure by achieving superficial micro-roughness. In this work, aluminum surfaces were modified via chemical methods to promote dropwise condensation due to superhydrophobic behavior. The metal substrates were etched using three different strategies to impart nanoscale roughness; a fluorosilane film was subsequently deposited over them to decrease the surface energy in two different modes (spin coating and immersion). In the end, four different surfaces were investigated. Experimental tests of pure steam condensation on the resulting substrates showed that dropwise condensation was successfully achieved on the superhydrophobic surfaces, measuring heat transfer coefficients as high as 100 kW m−2 K−1. Although the dropwise condensation moves soon to hybrid and filmwise condensation, the performance during pure dropwise condensation appears to be clearly linked to the different chemical procedures used in the sample preparation.