The petal effect of parahydrophobic surfaces offers low receding contact angles that promote effective boiling

Allred, Taylor P.; Weibel, Justin A.; Garimella, Suresh V.

doi:10.1016/j.ijheatmasstransfer.2019.02.002

Cited by 66 publications

(20 citation statements)

References 45 publications

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“…In particular, at the bottom of the sample where the "holes" density is higher, the receding contact angle is the lowest and the surface resulted to be flooded by the condensate. This is in agreement with several studies reported in literature [34,35] that demonstrated how the surface wettability is mostly influenced by the receding contact angle. Due to small dimension of the "holes", in loco analysis was not possible to be done, but correlating the results with a bare aluminum sample tested in the same experimental conditions, it is reasonable to suppose the formation of aluminum hydroxide at the bottom of the "holes" or the exposure of bare Aluminum due to coating's removal (See Figures S5 and S6).…”

Section: Dwc Evolutionsupporting

confidence: 94%

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Optimization of Hybrid Sol-Gel Coating for Dropwise Condensation of Pure Steam

et al. 2020

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We developed hybrid organic–inorganic sol–gel silica coatings with good durability in harsh environment (high temperatures, high vapor velocities) and with slightly hydrophobic behavior, sufficient to promote dropwise condensation (DWC) of pure steam. DWC is a very promising mechanism in new trends of thermal management and power generation systems to enhance the heat transfer during condensation as compared to film-wise condensation (FWC). The sol–gel coatings have been prepared from methyl triethoxy silane (MTES) and tetraethyl-orthosilicate (TEOS) and deposited on an aluminum substrate. The coatings were optimized in terms of precursor ratio and annealing temperature highlighting potentials and limits of such mixtures. A comprehensive surface characterization before and after saturated steam condensation tests has been performed and related to the thermal measurements for evaluating the heat transfer augmentation as compared to FWC obtained on untreated aluminum surfaces. The results showed that the developed hybrid organic-inorganic sol–gel silica coatings are promising DWC promoters.

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Section: Dwc Evolutionsupporting

confidence: 94%

“…Similar degradation trends with time have already been found for other coatings [34], meaning that coatings change over time due to the harsh environment of the condensation experiments. In particular, such high temperatures (around 100 • C) of saturated steam induce shrinkage of the sol-gel treatments, as reported in [31].…”

Section: Dwc Evolutionsupporting

confidence: 80%

Optimization of Hybrid Sol-Gel Coating for Dropwise Condensation of Pure Steam

et al. 2020

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“…Surfaces exhibiting the petal effect have been proposed for separation processes and collection of water via directional liquid transport . It has also been recently demonstrated that parahydrophobic surfaces are ideal for facilitating bubble nucleation and departure during boiling . Models of the wetting state are typically used to design surface topologies that provide the desired wetting characteristics .…”

Section: Introductionmentioning

confidence: 99%

The Wetting State of Water on a Rose Petal

Chakraborty

Weibel

Schaber

et al. 2019

Adv Materials Inter

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However, surfaces with a high contact angle (CA > 150°) can also exhibit "sticky" behavior characterized by high CAH; such surfaces are termed parahydrophobic. [7] A rose petal is a prime example exhibiting such parahydrophobic behavior; this socalled petal effect [8] has attracted significant research attention [7] in an attempt to understand this somewhat puzzling wetting state.Research over the last two decades has led to noteworthy progress in the synthesis of functional surfaces inspired by nature. [9] Self-cleaning surfaces inspired by the lotus leaf [10] have potential applications in enhancing the efficiency of solar cells, reducing surface drag, enhancing fluidic transport, and preventing water corrosion of batteries and fuel cells. [5] Surfaces exhibiting the petal effect have been proposed for separation processes [11] and collection of water via directional liquid transport. [12][13][14] It has also been recently demonstrated that parahydrophobic surfaces are ideal for facilitating bubble nucleation and departure during boiling. [15,16] Models of the wetting state are typically used to design surface topologies that provide the desired wetting characteristics. [17] Unlike the lotus leaf, for which the wetting state has been confirmed and is well accepted, [4] a recent review of the current understanding of parahydrophobic surfaces reveals a lack of experimental evidence to confirm the postulated wetting states on the rose petal. [7] As the surface morphology of natural surfaces is typically complex, and the features themselves delicate, it is difficult to obtain an accurate characterization of the microscopic wetting state. The existing explanation of the petal effect is based on a partially wetting "Cassie-impregnating" state. [7] The Cassieimpregnating wetting state is adapted to the dual-scale surface features of the rose petal, [18] namely, microscale papillae (bumps) with nanoscale striae (folds) [18] on top of each micropapilla. [19] Water droplets on the petal are thought to penetrate the gap between micro-papillae but not wet the nanoscale features. Although it was postulated that high apparent CA and high adhesion exhibited by surfaces could be explained by a mixed wetting state, [20] there has been no direct experimental evidence or visualization of these hypothesized wetting states on a rose petal. One recent study visualized the wetting state on a rose petal using top-down optical microscopy, [21] and postulated the trapping of air at the surface; however, it is difficult to view the liquid-air and liquid-solid interfaces underneath the droplet using this technique. Progress has been made on visualizing the liquid-air and liquid-solid interfaces between and below condensing droplets [22,23] and moving droplets [24] on microstructured surfaces using scanning electron microscopy (SEM).The rose petal features surface structures that offer unique wetting properties. A water droplet placed on a rose petal forms a high contact angle but exhibits significant contact angle hysteresis, such that re...

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“…The growth characteristics are also similar to those reported on hydrophilic surfaces (surfaces with low receding contact angles). 65 , 66 The bubble first experiences a fast growth process, e.g., 0–6, 0–3, and 0–2 ms on SS, CPF-1, and SPF-2, respectively. The bubble then shows a quick shrinking process of the gas–liquid–solid phase line because buoyancy begins to distort the bubble shape.…”

Section: Resultsmentioning

confidence: 99%

Nanoparticle-Assisted Pool Boiling Heat Transfer on Micro-Pin-Fin Surfaces

et al. 2021

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Boiling heat transfer intensification is of significant relevance to energy conversion and various cooling processes. This study aimed to enhance the saturated pool boiling of FC-72 (a dielectric liquid) by surface modifications and explore mechanisms of the enhancement. Specifically, circular and square micro pin fins were fabricated on silicon surfaces by dry etching and then copper nanoparticles were deposited on the micro-pin-fin surfaces by electrostatic deposition. Experimental results indicated that compared with a smooth surface, the micro pin fins increased the heat transfer coefficient and the critical heat flux by more than 200 and 65–83%, respectively, which were further enhanced by the nanoparticles up to 24% and more than 20%, respectively. Correspondingly, the enhancement mechanism was carefully explored by high-speed bubble visualizations, surface wickability measurements, and model analysis. It was quantitatively found that small bubble departure diameters with high bubble departure frequencies promoted high heat transfer coefficients. The wickability, which characterizes the ability of a liquid to rewet a surface, played an important role in determining the critical heat flux, but further analyses indicated that evaporation beneath bubbles was also essential and competition between the wicking and the evaporation finally triggered the critical heat flux.

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The petal effect of parahydrophobic surfaces offers low receding contact angles that promote effective boiling

Cited by 66 publications

References 45 publications

Optimization of Hybrid Sol-Gel Coating for Dropwise Condensation of Pure Steam

Optimization of Hybrid Sol-Gel Coating for Dropwise Condensation of Pure Steam

The Wetting State of Water on a Rose Petal

Nanoparticle-Assisted Pool Boiling Heat Transfer on Micro-Pin-Fin Surfaces

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