Self-propelled sweeping removal of dropwise condensate

Qu, Xiaoyan; Boreyko, Jonathan B.; Liu, Fangjie; Agapov, Rebecca L.; Lavrik, Nickolay V.; Retterer, Scott T.; Feng, James J.; Collier, C. Patrick; Chen, Chuan‐Hua

doi:10.1063/1.4921923

Cited by 101 publications

(83 citation statements)

References 31 publications

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“…The subsequent re-clearing of the surface and re-nucleation makes dropwise condensation up to ten times more efficient than filmwise condensation. 14 Furthermore, the recent combination of surface micro/nanostructure with hydrophobic promoter coatings has enabled ever-smaller length scales (≈10 µm) of droplet shedding 7,[16][17][18][19][20] providing further increases in heat transfer rates via coalescence-induced droplet jumping. 7,19 Promoting lasting dropwise condensation is still an unsolved problem despite considerable effort spanning the 20 th century.…”

Section: Take Down Policymentioning

confidence: 99%

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

et al. 2019

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Superhydrophobicity has received significant attention over the past three decades owing to its significant potential in self-cleaning and anti-icing surfaces, drag reduction, energy harvesting devices, anti-bacterial coatings, and enhanced heat transfer applications. Superhydrophobicity can be obtained via the roughening of an intrinsically hydrophobic surface, the creation of a re-entrant geometry, or by the roughening of a hydrophilic surface followed by a conformal coating of a hydrophobic material. Intrinsically hydrophobic surfaces have poor thermophysical properties such as thermal conductivity, and thus are not suitable for heat transfer applications. Re-entrant geometries, although versatile in applications where droplets are deposited, break down during spatially random nucleation and flood the surface. Chemical functionalization of rough metallic substrates, although promising, is not utilized due to the poor durability of conformal hydrophobic coatings. Here we develop a radically different approach to achieve stable superhydrophobicity. By utilizing laser processing and thermal oxidation of copper (Cu) to create a high surface energy hierarchical copper oxide (CuO), followed by repeatable and passive atmospheric adsorption of hydrophobic volatile organic compounds (VOCs), we show that stable superhydrophobicity with apparent advancing contact angles ≈ 160° and contact angle hysteresis as low as ≈ 20° can be achieved. We exploit the structure length scale and structure geometry dependent VOC adsorption dynamics to rationally design CuO nanowires with enhanced superhydrophobicity. To gain an understanding of the VOC adsorption physics, we utilized X-Ray Photoelectron and Ion Mass Spectroscopy to identify the chemical species deposited on our surfaces in two distinct locations: Urbana, IL, USA and Beijing, China. To test the stability of the atmosphere-mediated superhydrophobic surfaces during heterogeneous nucleation, we used high-speed optical microscopy to demonstrate the occurrence of dropwise condensation and stable coalescenceinduced droplet jumping. Our work not only provides rational design guidelines for developing passively-durable superhydrophobic surfaces with excellent flooding-resistance and self-healing capability, but also sheds light on the key role played by the atmosphere in governing wetting.

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Section: Take Down Policymentioning

confidence: 99%

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

et al. 2019

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“…To our knowledge, gravitational shedding enabled by coalescence-induced droplet detachment has not been previously reported. Past studies have instead focused on the ability of coalescence to trigger out-of-plane jumping 11,24,25 or in-plane sweeping 36,50 for micrometric droplets where gravity was not playing a role. Other works have characterized the chain reactions triggered by jumping droplets returning to the surface for subsequent coalescence-induced jumping events.…”

Section: Model Of Gravity-assisted Droplet Departurementioning

confidence: 99%

How Surface Orientation Affects Jumping-Droplet Condensation

Mukherjee

Berrier

Murphy

et al. 2019

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Because of its smaller condensate departure size, jumping-droplet condensation on superhydrophobic surfaces provides better heat transfer performance than does regular dropwise condensation. As the jumping mechanism is gravity independent, the effects of surface orientation on jumping-droplet condensation were previously ignored. Here, with the help of long-term condensation experiments on different surface orientations, it is shown that jumping-droplet condensers are dramatically enhanced when gravitational shedding complements the jumping. The analysis presented here can be useful in designing more efficient condensers.

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“…To obtain a more exact comparison, we estimated the preferential leaping probability ( p ) by calculating the ratio of leaping events along the positive direction versus the total jumping events on the MATS and NASS surfaces. Variations of the preferential leaping probability ( p ) with the diameters of the coalesced microdroplets on both NASS and MATS surfaces are given in Figure c. As confirmed by the curves, the jumping direction on the NASS surface is indeed non‐biased, while the jumping direction on the MATS surface exhibits a clear orientation and this preference is more pronounced when the size of the coalesced water droplet is larger. For example, Figure c reveals that 54 % of the coalesced microdroplets leaped along the positive direction when their size was around 14±2 μm, but the ratio increased to 86 % when the droplet size was around 63±11 μm.…”

Section: Figurementioning

confidence: 65%

Guided Self‐Propelled Leaping of Droplets on a Micro‐Anisotropic Superhydrophobic Surface

et al. 2016

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By introducing anisotropic micropatterns on a superhydrophobic surface, we demonstrate that water microdroplets can coalesce and leap over the surface spontaneously along a prescribed direction. This controlled behavior is attributed to anisotropic liquid–solid adhesion. An analysis relating the preferential leaping probability to the geometrical parameters of the system is presented with consistent experimental results. Surfaces with this rare quality demonstrate many unique characteristics, such as self‐powered, and relatively long‐distance transport of microdroplets by “relay” coalescence‐induced leaping.

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Self-propelled sweeping removal of dropwise condensate

Cited by 101 publications

References 31 publications

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

How Surface Orientation Affects Jumping-Droplet Condensation

Guided Self‐Propelled Leaping of Droplets on a Micro‐Anisotropic Superhydrophobic Surface

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