Abstract:
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.
