Superhydrophobic aluminum with hierarchical micro-nano structured surface for high-efficiency condensation

Aluminum sheets are widely used as fins in condensers because of their high thermal conductivity, tractability and affordability. However, the heat transfer efficiency of the aluminum fins was encumbered by the hydrophilicity of the surface where filmwise condensation tends to occur. This work demonstrates the fabrication of a superhydrophobic aluminum surface based on a micro-nano structured hierarchical design using electrochemical wire machining and surface modification technique. By optimizing the applied voltage and the scanning speed of the tool electrode, a superhydrophobic aluminum surface was obtained with a maximum contact angle of 157.2° and a minimum sliding angle of 2.3°. The superhydrophobic aluminum surface demonstrates a dropwise condensation, exhibiting a heat transfer coefficient of 38.2 kW (m²· K)^-1, which is 2.7 times higher than that of the original aluminum sheet. Moreover, the superhydrophobic aluminum surface shows outstanding delayed icing performance, which delays the icing time by 1.9 times compared to the original aluminum sheet under identical conditions. In addition to its superior performance, the proposed electrochemical wire machining method offers significant advantages, including environmental friendliness, mild processing conditions, high efficiency and cost-effectiveness. This work provides a new option for the scalable fabrication of superhydrophobic aluminum fins for high efficiency condensation.