Superhydrophobic Si nanowires for enhanced condensation heat transfer

Lu, Ming-Chang; Lin, Chien Chang; Lo, Ching‐Wen; Huang, Cheng; Wang, Chi-Chuan

doi:10.1016/j.ijheatmasstransfer.2017.04.021

Cited by 69 publications

(36 citation statements)

References 38 publications

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“…Super-hydrophobic surfaces have promising prospects in the areas including selfcleaning [1], drag reduction [2], anti-corrosion [3] and enhanced heat transfer [4]. When a droplet beads up with water contact angle (WCA) over 150°, the solid surface is defined as super-hydrophobic with the lotus effect (i.e., rolling angle (RA) less than 10°) or the pinning effect (i.e., no RA or RA greater than 10°) [5].…”

Section: Introductionmentioning

confidence: 99%

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Yang

Liu

Tian

2019

Journal of Colloid and Interface Science

233

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Super-hydrophobic surfaces are attractive due to self-cleaning and anti-corrosive behaviors in harsh environments. Laser texturing offers a facile method to produce super-hydrophobic surfaces. However, the results indicated that the fresh laser ablated surface was generally super-hydrophilic and then gradually reached super-hydrophobic state when exposed to ambient air for certain time. Investigating wettability changing mechanism could contribute to reducing wettability transition period and improving industrial productivity. To solve this problem, we have studied the bare aluminum surface, fresh laser ablated super-hydrophilic surface, 15-day air exposed surface, and the aged super-hydrophobic surface by time-dependent water contact angle (WCA) and rolling angle (RA), scanning electron microscopy (SEM), 3D profile and X-ray photoelectron spectroscopy (XPS). The origins of super-hydrophilicity of the fresh laser ablated surface are identified as (1) the formation of hierarchical rough structures and (2) the surface chemical modifications (the decrease of nonpolar carbon, the formation of hydrophilic alumina and residual unsaturated atoms). The chemisorbed nonpolar airborne hydrocarbons from air moisture contributed to the gradual super-hydrophobic transition, which can be proved by the thermal annealing experiment. Particularly, to clearly explore the wettability transition mechanism, we extensively discussed why the laser-induced freshly outer layer was super-hydrophilic and how the airborne hydrocarbons were chemisorbed. This work not only provides useful insights into the formation mechanism of laser ablated super-hydrophobic surfaces, but also further guides industry to effectively modify surface chemistry to reduce wettability transition period and rapidly produce stable and durable super-hydrophobic surfaces.

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Section: Introductionmentioning

confidence: 99%

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Yang

Liu

Tian

2019

Journal of Colloid and Interface Science

233

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“…The newest research showed that Si nanowire (SiNW) array‐coated surface could simultaneously provide a large number of nucleation sites and prevent condensate from penetrating into the nanostructure . The obtained highest heat transfer on the superhydrophobic (SHB) SiNW surface was investigated, showing 155% and 87% higher than those on the plain hydrophilic and hydrophobic surfaces, respectively.…”

Section: Applicationmentioning

confidence: 99%

Wetting Models and Working Mechanisms of Typical Surfaces Existing in Nature and Their Application on Superhydrophobic Surfaces: A Review

Jiaqiang

Deng

et al. 2017

Adv Materials Inter

115

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decades, researchers have shown great interests in bionics, which was a new multidisciplinary subject inspired by biological characteristics and features to imitate it to build technology devices. [1] With the rise of biomimetic biomaterial researches, a lot of attention was paid on the observation of living organism, especially on plant leaves, such as lotus, rice, taro leaves, etc. [2] As the development of scanning electron microscope (SEM), a wealth of data dealing with SEM of plant surface has been published since 1960s. [3] The cuticular structure was investigated with regard to function, and substances that were secreted onto the cuticle had great effects on the surface properties, while intracuticular waxes were the main barrier to wettability. [4] Some kinds of special wettability like superhydrophobicity and superhydrophilicity were also found in other surfaces, such as self-cleaning lotus leaf, [5] hydrophilicity of red rose petals, [6,7] the anisotropic dewetting behavior on rice leaf, [8,9] hydrophobicity of shark skin, [10] gecko toe, [11] insect wings, [12] etc., and striking superhydrophobic force provided by a water strider's legs, [13] and they were all related to the unique microstructures on their surface. In fact, the special wettability of surfaces is attributed to the interaction of both the surface microstructures and surface covers. As the development and progress of the observation device, smaller nanosized structures were found on the microstructure, and better properties of multiscale hierarchical structure was shown then. [14] Wetting is a phenomenon that solid interface was transferred from solid-gas interface to solid-liquid interface, wettability was a kind of ability that a liquid could be unfolded on one solid surface. The wettability of surface could be characterized by contact angle (CA) of interface. Sliding angle (SA) and contact angle hysteresis were introduced to evaluate the highly valued superhydrophobicity and superhydrophilicity of surfaces. Superhydrophilicity was defied as that of CA was smaller than 5°, superhydrophobicity was defied as that of CA was greater than 150°, as well as a really small sliding angle. It is worth noting that many researchers applied themselves to excavate the theories under the phenomena. Young's equation, Wenzel equation, and Cassie-Baxter equation [15,16] were the representations of hundreds years of research results. Improving and developing Surfaces of plants and animals are evolved to optimal states to accommodate environments better after billions of years of natural selection. As the development of further study on bionics, surfaces with special wetting properties in nature are discovered, extremely related to the micro-/nanostructures on surface. The wetting models and wetting mechanism of several surfaces in nature are investigated, followed by lifting the veil of superhydrophobic field. Various facile, effective, and convenient methods for fabricating superhydrophobic surfaces are obtained and optimized in scientific research and ...

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“…Even though it has been a challenge to realize sustained CDC on engineered surfaces in real applications, there have recently been reported experimental works demonstrating jumpingdroplet-enhanced condensation on nanostructured surfaces in carefully-designed vapor chambers. 8,24,[44][45][46] Instead of using conventional wicks, Boreyko and Chen developed a novel vapor chamber with jumping-drop liquid return, 44 in which superhydrophobic condenser is composed of 150-300 nm clusters of 50-100 nm silver nanoparticles on copper, and the overall lumped heat transfer coefficient has reached as high as 55 kW m À2 K À1 . Both tiers of silver nanoparticles structures on the condenser are in nanoscale, which is in excellent agreement with our analysis of structural optimization.…”

Section: Discussionmentioning

confidence: 99%

“…Both tiers of silver nanoparticles structures on the condenser are in nanoscale, which is in excellent agreement with our analysis of structural optimization. Two other recent works, which used superhydrophobic Si nanowires 45 and hydrophobic Cu nanowires 46 respectively on their condensers, have conrmed enhanced condensation heat transfer due to droplet jumping behaviour. It is noteworthy that these nominal single layer nanostructures actually consist of bundles of nanowires with microscale gaps, indicative of essentially twotier hierarchical structures.…”

Section: Discussionmentioning

confidence: 99%

Resistant energy analysis of self-pulling process during dropwise condensation on superhydrophobic surfaces

2019

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Superhydrophobic Si nanowires for enhanced condensation heat transfer

Cited by 69 publications

References 38 publications

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Wetting Models and Working Mechanisms of Typical Surfaces Existing in Nature and Their Application on Superhydrophobic Surfaces: A Review

Resistant energy analysis of self-pulling process during dropwise condensation on superhydrophobic surfaces

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