Enhancing the thermal efficiency of a broad range of condenser devices requires means of achieving sustainable dropwise condensation on metallic surfaces, where heat transfer can be further enhanced, by harvesting the advantage of the sweeping action of vapor flow over the surface, facilitating a reduction in the droplet departure diameter. Here, we present a rationally driven, hierarchical texturing process of copper surfaces, guided by fundamental principles of wettability and coalescence, which achieves controlled droplet departure under vapor flow conditions and thus significantly enhances phase change thermal transport. The desired texture is attained by fabricating an array of 3D laser-structured truncated microcones on the surface, covered with papillae-like nanostructures and a hydrolytically stable, low surface energy self-assembled-monolayer coating. Passive droplet departure on this surface is achieved through progressive coalescence of droplets arising from microcavities formed by the microcone array, resulting in depinning and subsequent departure of the depinned condensate drops through vapor shear. The synergistic combination of vapor shear and the sustained dropwise condensation on the hierarchical copper surface results in a nearly 700% increase in heat transfer coefficients as compared to filmwise condensation from identical, standard unstructured surfaces.
Keywords: copper; dropwise; flow condensation; hierarchical; nanostructure; superhydrophobic.