Effects of millimetric geometric features on dropwise condensation under different vapor conditions

Zhao, Yajing; Preston, Daniel J.; Lu, Zhengmao; Zhang, Lenan; Queeney, John; Wang, Evelyn N.

doi:10.1016/j.ijheatmasstransfer.2017.11.139

Cited by 62 publications

(37 citation statements)

References 46 publications

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“…The predicted frost coverages are slightly lower than the experimental values, indicating that the boundary layer thickness of 1 cm used for simulations could be larger than that in reality (see SI Appendix, Fig. S9 for the simulated results by using a range of ξ values) (38,40,41). It is worth noticing that, in the limiting case, f → 0 as α → 0°, while f → 1 as α → 180°.…”

Section: Resultsmentioning

confidence: 87%

“…A steady-state diffusion model is employed such that the Laplace equation is satisfied. The thickness of the diffusion boundary layer ξ is assumed to be 1 cm according to previous reports (28,38). The c w is set to be the equilibrium vapor pressure of supercooled water at the surface temperature (−12°C), that is, p sat,w = 223 Pa, or, equivalently, 0.091 mol/m 3 at ambient temperature (23.5°C), and c 0 is set to be the water vapor concentration in the ambient air, which is 0.29 mol/m 3 (or, equivalently, P = 707 Pa) if RH = 25% at 23.5°C (34,39).…”

Section: Resultsmentioning

confidence: 99%

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Frost-free zone on macrotextured surfaces

Yao

Zhao

Machado

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Numerous studies have focused on designing functional surfaces that delay frost formation or reduce ice adhesion. However, solutions to the scientific challenges of developing antiicing surfaces remain elusive because of degradation such as mechanical wearing. Inspired by the discontinuous frost pattern on natural leaves, here we report findings on the condensation frosting process on surfaces with serrated structures on the millimeter scale, which is distinct from that on a conventional planar surface with microscale/nanoscale textures. Dropwise condensation, during the first stage of frosting, is enhanced on the peaks and suppressed in the valleys, causing frost to initiate from the peaks, regardless of surface chemistry. The condensed droplets in the valley are then evaporated due to the lower vapor pressure of ice compared with water, resulting in a frost-free zone in the valley, which resists frost propagation even on superhydrophilic surfaces. The dependence of the frost-free areal fraction on the geometric parameters and the ambient conditions is elucidated by both numerical simulations based on steady-state diffusion and an analytical method with an understanding of boundary conditions independent of surface chemistry. We envision that this study would provide a unified framework to design surfaces that can spatially control frost formation, crystal growth, diffusion-controlled growth of biominerals, and material deposition over a broad range of applications.

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Section: Resultsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Frost-free zone on macrotextured surfaces

Yao

Zhao

Machado

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…When NCGs are present, as in the case of our experiments, they act as a diffusive barrier to the water vapor. [58][59][60] This slows the growth rate of condensate and decreases the heat transfer coefficient but is not expected to affect the orientationdependent droplet dynamics captured here, which govern the maximum droplet sizes. The droplet size distribution is also a function of the coalescence length scale, which is related to the nucleation density and depends on both the supersaturation and the concentration of NCGs.…”

Section: Heat Transfer Analysismentioning

confidence: 92%

How Surface Orientation Affects Jumping-Droplet Condensation

Mukherjee

Berrier

Murphy

et al. 2019

Joule

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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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“…[1][2][3][4][5] Extensive research efforts have been devoted to promote dropwise condensation of water by employing various surface chemistries and micro-/nano-textures. [2][3][4][5][6][7][8][9][10] While recent studies have shown that droplet growth on millimetric convex surfaces by condensation is facilitated, [11][12][13] a more detailed study on droplet growth on textured surfaces is required to systematically understand the impact of the sign and the magnitude of the radius of curvature of surface features. Here, we provide a quantitative analysis of droplet growth dynamics on hydrophobic surfaces with a wide range of millimeter-scale surface topographies ranging from convex textures (e.g., bumps) to concave textures (e.g., dimples).…”

Section: Main Textmentioning

confidence: 99%

Dropwise condensation on hydrophobic bumps and dimples

Yao

Aizenberg

Park

2018

Applied Physics Letters

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Surface topography plays an important role in promoting or suppressing localized condensation. In this work, we study the growth of water droplets on hydrophobic convex surface textures such as bumps and concave surface textures such as dimples with a millimeter scale radius of curvature. We analyze the spatio-temporal droplet size distribution under a supersaturation condition created by keeping the uniform surface temperature below the dew point and show its relationship with the sign and magnitude of the surface curvature. In particular, in contrast to the well-known capillary condensation effect, we report an unexpectedly less favorable condensation on smaller, millimeter-scale dimples where the capillary condensation effect is negligible. To explain these experimental results, we numerically calculated the diffusion flux of water vapor around the surface textures, showing that its magnitude is higher on bumps and lower on dimples compared to a flat surface. We envision that our understanding of millimetric surface topography can be applied to improve the energy efficiency of condensation in applications such as water harvesting, heating, ventilation, and air conditioning systems for buildings and transportation, heat exchangers, thermal desalination plants, and fuel processing systems.

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Effects of millimetric geometric features on dropwise condensation under different vapor conditions

Cited by 62 publications

References 46 publications

Frost-free zone on macrotextured surfaces

Frost-free zone on macrotextured surfaces

How Surface Orientation Affects Jumping-Droplet Condensation

Dropwise condensation on hydrophobic bumps and dimples

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