Condensation and jumping relay of droplets on lotus leaf

Lv, Cunjing; Hao, Pengfei; Yao, Zhaohui; Song, Yu Dong; Zhang, Xiwen; He, Feng

doi:10.1063/1.4812976

Cited by 142 publications

(147 citation statements)

References 36 publications

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“…However, the experimental velocities of the self-jumped microdrops are apparently smaller than their theoretical values. Later, researchers noted that the energy dissipation caused by viscous flow (E vis ) and interface adhesion (E int ) must be considered, [31,[56][57][58][59][60] while gravi tational potential energy may be neglected due to microdrop sizes that are far smaller than the capillary length. Very recently, our group further found that, besides the solid-liquid van der Waals attraction, nanoscale line tension at three-phase contact lines cannot be neglected in calculating adhesioninduced dissipation.…”

Section: Cmdsp Mechanismmentioning

confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

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interest has focused on utilizing the lowadhesivity nature of superhydrophobic surfaces for the rapid removal of condensate microdrops, as this has significance in fundamental research and technological innovation. Example applications are the enhancement of condensation heat transfer for high-efficiency thermal management and energy utilization, [20][21][22][23][24][25] energy-effective antifreezing for airconditioner heat exchangers and aircraft wings, [26][27][28] and electrostatic energy harvesting. [29] In general, condensate drops on typical flat hydrophobic surfaces are only shed off under gravity when their sizes are comparable to the capillary length (≈2.7 mm for water), [30] which creates undesirable effects such as large thermal resistance [20][21][22][23][24][25] and the freezing of subcooled drops. [26][27][28] Clearly, a great challenge is the timely removal of condensate drops at the microscale where the gravitational effect does not work. The latest research has indicated that these small-scale condensate microdrops may self-remove via mutual coalescence as long as the coalescence-released excess surface energy is larger than the interface adhesion-induced energy dissipation. [31] Much effort has been devoted to exploring the utilization of knowledge of bionic low-adhesivity superhydrophobicity to develop innovative condensate microdrop self-propelling (CMDSP) surfaces. Different from traditional superhydrophobic surfaces, which are characterized by the bouncing or rolling off of deposited millimeter-size large drops, [32,33] CMDSP surfaces support the self-removal capability of smallscale condensate microdrops. It has been reported that classical superhydrophobic lotus leaves (Figure 1a), [34][35][36][37] as well as artificial surfaces consisting of hierarchical micro-and nanostructures, [38] one-tier microstructures, [39][40][41][42][43] or nanostructures [44,45] with larger characteristic interspaces, present a low-adhesivity property to the deposited water macrodrops, but become highly adhesive to condensed microdrops (Figure 1b). This is because moisture easily penetrates the microscale valleys or cavities. Clearly, superhydrophobic surfaces with irrationally designed surface structures can enhance the solid-liquid interfacial adhesion instead of promoting the rapid removal of condensed drops. Accordingly, it is still a challenge to design and fabricate very effective low-adhesivity superhydrophobic surfaces with the self-removal ability of condensate microdrops. Recently, there has been a large breakthrough in understanding the mechanism and construction rules of bionic CMDSP surfaces, leading to the exploration of fabrication methods for the surface functionalization of widely used metal materials and the Bionic condensate microdrop self-propelling (CMDSP) surfaces are attracting increased attention as novel, low-adhesivity superhydrophobic surfaces due to their value in fundamental research and technological innovation, e.g., for enhancing heat transfer, energy-effective antifreezing, and...

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Section: Cmdsp Mechanismmentioning

confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

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“…If droplet jumping does not occur again upon droplet return, progressive flooding may initiate at the top surface. This risk is mitigated by the fact that the probability of having an upward trajectory at the top surface tends to zero since most droplets jump at some angle away from the surface 12,21 and the area having a surface normal in the upward direction is infinitesimally small for a radial geometry.…”

Section: Condensate Removalmentioning

confidence: 99%

“…38,55 Upon return, droplets can coalesce again, become larger in size, and impede heat transfer until they either jump again or finally shed due to gravity. [21][22]53 This poses the problem of removing the droplets from the condensing surface at the microscale in order to enhance heat transfer. Naturally, jumping droplets cannot be removed if the condensing surface is oriented upwards (jumping against gravity).…”

Section: Jumping Droplet Condensation Critical Heat Fluxmentioning

confidence: 99%

“…[11][12][13][14][15][16] This phenomenon has been termed jumping-droplet condensation and has been shown to further enhance heat transfer by up to 30% when compared to classical dropwise condensation due to a larger population of microdroplets which more efficiently transfer heat to the surface. 17 A number of works have since fabricated superhydrophobic nanostructured surfaces to achieve spontaneous droplet removal [18][19][20][21][22][23][24][25][26][27][28] for a variety of applications including self-cleaning, [29][30][31] thermal diodes, 30,32 anti-icing, [33][34][35][36] vapor chambers, 37 electrostatic energy harvesting, [38][39][40] and condensation heat transfer enhancement. [41][42][43][44][45][46][47][48][49][50][51][52] However, heat transfer enhancement can be limited by droplet return to the surface due to…”

Section: Jumping Droplet Condensation and External Electric Fieldsmentioning

confidence: 99%

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A Comprehensive Model of Electric-Field-Enhanced Jumping-Droplet Condensation on Superhydrophobic Surfaces

Birbarah

Pauls

et al. 2015

Langmuir

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Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding positively charged water droplets via coalescence-induced droplet jumping at length scales below the capillary length, and allowing the use of external electric fields to enhance droplet removal and heat transfer, in what has been termed electric-field-enhanced (EFE) jumping-droplet condensation. However, achieving optimal EFE conditions for enhanced heat transfer requires capturing the details of transport processes that is currently lacking. While a comprehensive model has been developed for condensation on micro/nanostructured surfaces, it cannot be applied for EFE condensation due to the dynamic droplet-vapor-electric field interactions. In this work, I developed a comprehensive physical model for EFE condensation on Furthermore, the results suggest that EFE electrodes can be optimized such that the work input is minimized depending on the condensation heat flux. To analyze overall efficiency, I defined an incremental coefficient-of-performance and showed that it is very high (~10 6 ) for EFE iii condensation. I finally proposed mechanisms for condensate collection which would ensure continuous operation of the EFE system, and which can scalably be applied to industrial condensers. This work provides a comprehensive physical model of the EFE condensation process, and offers guidelines for the design of EFE systems to maximize heat transfer.iv ACKNOWLEDGMENTS

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“…When adjacent metastable droplets coalesce, sufficient surface energy is released to overcome the adhesion of the droplet to the surface, resulting in droplet departure from the surface. [24,33,34] This departure can result either in the jumping or random sweeping of mobile droplets off the surface (see the droplets enclosed by the dashed lines in Figure 3b). As a result, many fresh areas on the substrate are exposed and can contribute to the cyclical process of nucleation, coalescence, and departure; a high frequency of surface refreshing, which shifts the distribution of droplets on the surface to smaller sizes, will lead to high heat transfer coefficients in dropwise condensation.…”

mentioning

confidence: 99%

Exploiting Microscale Roughness on Hierarchical Superhydrophobic Copper Surfaces for Enhanced Dropwise Condensation

Chen

Weibel

Garimella

2015

Adv Materials Inter

112

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Condensation of water vapor is of great interest in thermal management [1] and power generation [2] owing to the improved heat transfer by phase change, and in desalination [3] and dew/fog harvesting [4,5] systems for its ability to extract vapor from carrier gases. Enhancement of the condensation heat and mass transfer processes in these systems could lead to considerable performance gains, economic return, and energy savings. Heterogeneous condensation is dramatically influenced by the physical structure and chemical properties of a surface. Depending on the surface wettability, water vapor can condense on a surface either as a continuous liquid film (filmwise) or as individual droplets (dropwise). It is reported that dropwise condensation can produce heat transfer coefficients that are an order of magnitude higher than in filmwise condensation. [6] To attain this performance, condensed droplets must be rapidly removed from the surface and fresh spaces on the substrate exposed for nucleation; otherwise, accumulated large droplets will act as a thermal barrier and inhibit the heat/mass transfer rate. [7] To promote removal of condensate droplets, the droplet adhesion to the substrate must be minimized. Structured superhydrophobic surfaces [8][9][10][11][12] could offer an ideal

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Condensation and jumping relay of droplets on lotus leaf

Cited by 142 publications

References 36 publications

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

A Comprehensive Model of Electric-Field-Enhanced Jumping-Droplet Condensation on Superhydrophobic Surfaces

Exploiting Microscale Roughness on Hierarchical Superhydrophobic Copper Surfaces for Enhanced Dropwise Condensation

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