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Growth Rates and Spontaneous Navigation of Condensate Droplets Through Randomly Structured Textures
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posted on 2017-02-07, 00:00 authored by Chander
Shekhar Sharma, Juliette Combe, Markus Giger, Theo Emmerich, Dimos PoulikakosDropwise
condensation is a phenomenon of common occurrence in everyday
life, the understanding and controlling of which is of great interest
to applications ranging from technology to nature. Scalable superhydrophobic
textures on metals are of direct relevance in improving phase change
heat transport in realistic industrial applications. Here we reveal
important facets of individual droplet growth rate and droplet departure
during dropwise condensation on randomly structured hierarchical superhydrophobic
aluminum textures, that is, surfaces with a microstructure consisting
of irregular re-entrant microcavities and an overlaying nanostructure.
We demonstrate that precoalescence droplet growth on such a surface
can span a broad range of rates even when the condensation conditions
are held constant. The fastest growth rates are observed to be more
than 4 times faster as compared to the slowest growing droplets. We
show that this variation in droplet growth on the hierarchical texture
is primarily controlled by droplet growth dynamics on the nanostructure
overlaying the microstructure and is caused by condensation-induced
localized wetting nonuniformity on the nanostructure. We also show
that the droplets nucleating and growing within the microcavities
are able to spontaneously navigate the irregular microcavity geometry,
climb the microtexture, and finally depart from the surface by coalescence-induced
jumping. This self-navigation is realized by a synergistic combination
of self-orienting Laplace pressure gradients induced within the droplet
as it dislodges itself and moves through the texture, as well as multidroplet
coalescence.
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4 timesRandomly Structured Textures Dropwise condensationgrowth ratesScalable superhydrophobic texturesself-orienting Laplace pressure gradientsmicrocavity geometrydroplet growth rateprecoalescence droplet growthCondensate Dropletscondensation conditionsmultidroplet coalescenceSpontaneous Navigationphase change heat transportnanostructure overlayingGrowth Ratesdroplet growthdroplet departuresuperhydrophobic aluminum texturesoverlaying nanostructuresurfacedroplet growth dynamicsdropwise condensationdroplets nucleatingre-entrant microcavities
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