Analysis of droplet jumping phenomenon with lattice Boltzmann simulation of droplet coalescence

Peng, Benli; Wang, Sifang; Lan, Zhong; Xu, Wei; Wen, Rongfu; Ma, Xuehu

doi:10.1063/1.4799650

Cited by 110 publications

(98 citation statements)

References 16 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 the shape and the wettability property of the textured surface are designed properly, the coalesced droplet can not only jump from the textured surface easily but also enhance the heat transfer performance, which is widely used in the applications of self-cleaning, microfluidics, and lab-on-chip devices. Recently, more and more studies have been focusing on the spontaneous jumping of coalesced droplet on superhydrophobic surfaces during dropwise condensation [2,3]. Peng et al [3] experimentally observed the properties of the coalesced droplet induced by the coalescence of two droplets with the same volume and used the two-dimensional free energy lattice Boltzmann model to simulate the droplet coalescence process.…”

Section: Introductionmentioning

confidence: 99%

Investigation of coalescence-induced droplet jumping on superhydrophobic surfaces and liquid condensate adhesion on slit and plain fins

Shi

Tang

Xia

2015

International Journal of Heat and Mass Transfer

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“…Coalescence-induced jumping phenomena occur on superhydrophobic surfaces but within a small range of initial droplet radii. Recent interest in these phenomena has led to the influence of the droplets radii on the resulting jumping velocity to be explored [3,[8][9][10][11][12]. However, previous analysis on coalescence-induced jumping droplets focused only a limited range of contact angles and droplet radius [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multi-disciplinary approach

Khatir

Kubiak

Jimack

et al. 2016

Applied Thermal Engineering

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Dropwise condensation has superior heat transfer efficiency than filmwise condensation; however condensate evacuation from the surface still remains a significant technological challenge. The process of droplets jumping, against adhesive forces, from a solid surface upon coalescence has been studied using both experimental and Computational Fluid Dynamics (CFD) analysis. Both Lattice Boltzmann (LBM) and Volume of Fluid (VOF) methods have been used to evaluate different kinematic conditions of coalescence inducing a jump velocity. In this paper, an optimisation framework for superhydrophobic surface designs is presented which uses experimentally verified high fidelity CFD analyses to identify optimal combinations of design features which maximise desirable characteristics such as the vertical velocity of the merged jumping droplet from the surface and energy efficiency. A Radial Basis Function (RBF)-based surrogate modelling approach using design of experiment (DOE) technique was used to establish near-optimal initial process parameters around which to focus the study. This multidisciplinary approach allows us to evaluate the jumping phenomenon for superhydrophobic surfaces for which several input parameters may be varied, so as to improve the heat transfer exchange rate on the surface during condensation. Reliable conditions were found to occur for droplets within initial radius range of r=20-40 m and static contact angle s~160º. Moreover, the jumping phenomenon was observed for droplets with initial radius of up to 500 m. Lastly, our study also reveals that a critical contact angle for droplets to jump upon coalescence is c~1 40º. KeywordsCondensation heat transfer, Super-hydrophobic surface, Jumping droplets velocity, Multi-disciplinary optimisation. IntroductionDrop-wise condensation processes, where condensation occurs through small droplets on a solid surface, has been demonstrated to significantly improve heat transfer rates in comparison to filmwise condensation (where a whole surface is covered by a thin film of liquid) [1,2]. Drop-wise condensation usually takes place on hydrophobic or super-hydrophobic surfaces as demonstrated by Boreyko and Chen [3]. One of the main technological challenges is to create such a surface, so as to allow condensation and evacuation of the droplets to take place in a continuous manner. Droplet coalescence is a complex physical phenomenon and optimisation of kinematic conditions leading to surface dewetting and jumping of droplets is of paramount importance for processes like heat transfer, de-icing, atmospheric water harvesting or dehumidification [4][5][6]. Dropwise condensation heat transfer performance can be enhanced by allowing condensed droplets to be removed rapidly from the surface to minimize the thermal barrier [7]. Recently, researchers showed that superhydrophobic surfaces provide a higher mobility of condensates, which may enhance the heat transfer performance [1][2][3][4][5][6][7]. Coalescence-induced jumping phenomena occur on superhydrophobic surfa...

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Analysis of droplet jumping phenomenon with lattice Boltzmann simulation of droplet coalescence

Cited by 110 publications

References 16 publications

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Investigation of coalescence-induced droplet jumping on superhydrophobic surfaces and liquid condensate adhesion on slit and plain fins

Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multi-disciplinary approach

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