Numerical simulations of multi-hop jumping on superhydrophobic surfaces

Yuan, Zhiping; Wu, Renzhi; Wu, Xiaomin

doi:10.1016/j.ijheatmasstransfer.2019.01.147

Cited by 32 publications

(23 citation statements)

References 45 publications

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“…When condensation occurs on the superhydrophobic surface, merged droplet can jump from the surface, which called the droplet jumping phenomenon. This phenomenon was first reported by Boreyko and Chen in 2009, 1 and following that, many experimental observations [2][3][4][5][6][7] and numerical simulations [8][9][10][11][12][13][14] have been reported. Since the occurrence of droplet jumping is spontaneous which means no external energy is required, it could be applied to many applications, such as hotspot cooling, self-cleaning, heat transfer enhancement, anti-icing and defrosting.…”

Section: Introductionmentioning

confidence: 56%

“…1(b), the size of computation domain is 1.5 mm × 1.5 mm × 1.5 mm, and the radius of droplet is 150 m. The bottom surface is set as a no-slip wall with the other boundaries as pressure outlet boundaries. 8,11,34 The distance between droplets and the surrounding boundary is large enough which ensures the pressure boundaries have a minimal effect for the process. The equilibrium contact angle of the bottom surface, , is 160° with a dynamic contact angle of ±5°, which means the advancing contact angle, A, is 165° and receding contact angle, R, is 155°.…”

Section: σUmerical Modelmentioning

confidence: 99%

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Droplet jumping induced by coalescence of a moving droplet and a static one: Effect of initial velocity

Chu

Zhang

et al. 2020

Chemical Engineering Science

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The phenomenon of coalescence-induced droplet jumping on superhydrophobic surfaces has a wide range of applications such as hotspot cooling, surface self-cleaning, anti-icing, and defrosting. Previous experimental and numerical studies mainly focused on the coalescence of static droplets with varying droplet properties and substrate structures. However, in practice, it is more common to see a moving droplet hit a stationary one, which leads to a coalesced droplet jumping from the surface. To explore the effect of initial velocity on the jumping behavior of coalesced droplet, we performed simulations using the volume of fluid method with a dynamic contact angle model, and validated the simulation results against our experiments. We analyzed the morphology evolutions, velocity variations and energy conversion rates during the jumping process. The results show that the initial velocity of the moving droplet accelerates the droplet deformation during jumping, resulting in a unique departure feature. Droplet departs at different stages under different initial velocities, and the departure velocity is approximately constant at the first stage and then increases with increasing initial velocity. The variation in energy conversion rate is consistent with the departure velocity which suggests the conversion rate has a slight change in low initial velocity range. This work shall bring new insights into the droplet jumping regulation and promote the application of droplet jumping in related fields.

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Section: Introductionmentioning

confidence: 56%

Section: σUmerical Modelmentioning

confidence: 99%

Droplet jumping induced by coalescence of a moving droplet and a static one: Effect of initial velocity

Chu

Zhang

et al. 2020

Chemical Engineering Science

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“…The VOF method was introduced to simulate the hydrophobic properties, which could reduce the arbitrary geometric morphology of the design and save many sample preparation costs, by solving the continuity equation of volume fraction to capture the gas–liquid surface and simulate the droplet dynamics in the solid surface accurately. The fluid flowed under the dominance of surface tension under laminar flow, and the governing equations of fluid flow were mainly described by mass conservation equations and momentum conservation equations. − The mass conservation equation is given by eq . where ρ is the fluid density, v ⃗ is the fluid velocity vector, t refers to the time, and S m is the mass of the source term by a user-defined function attached to the continuous phase where α k is the volume fraction of k phase fluid, and the sum of the volume fraction of all phases is 1.…”

Section: Methodsmentioning

confidence: 99%

Prediction of Droplet Sliding on the Continuity of the Three-Phase Contact Line

Qiu

Chen

Di³

et al. 2021

Langmuir

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Many animals and plants have evolved wonderful hydrophobic abilities to adapt to the complex climate environment. The microstructure design of a superhydrophobic surface focuses on bionics and will be restricted by processing technology. Although certain functions can be achieved, there is a lack of unified conclusion on the wetting mechanism and a few quantitative analyses of the continuity of the three-phase contact line. Therefore, the relationship between the surface microstructure of the lattice pattern and the critical sliding angle of the water droplet in the Cassie state was investigated in this paper, and we proposed a method to quantitatively analyze the continuity of the three-phase contact line by a dimensionless length f. The results showed that the three-phase contact line was an important factor to determine the sliding performance of the droplet. The upward traction force generated by the surface tension through the force analysis on the three-phase contact line can enhance the sliding ability of the droplet on the solid surface. There was a good negative linear correlation between the critical sliding angle and dimensionless length, which provided a guiding basis for the optimal design of superhydrophobic surfaces.

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“…u is the velocity field, p is the pressure, Re is the Reynolds number and Ca is the Capillary number. We usually assume the density ρ and viscosity η have the following linear relations (Yuan et al, 2019),…”

Section: Governing Equationmentioning

confidence: 99%

Interfacial dynamics with soluble surfactants: A phase-field two-phase flow model with variable densities

Zhu

2020

Adv. Geo-Energ. Res.

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In this work, we present a hydrodynamics coupled phase-field surfactant model with variable densities. Two scalar auxiliary variables are introduced to transform the original free energy functional into an equivalent form, and then a new thermodynamically consistent model can be obtained. In this model, evolutions of two phase-field variables are described by two Cahn-Hilliard-type equations, and the fluid flow is dominated by incompressible Navier-Stokes equation. The finite difference method on staggered grid is used to solve the above model. Then a classical droplet rising case and a droplet merging case are used to validate our model. Finally, we study the effect of surfactants on droplet deformation and merging. A more prolate profile of droplet is observed under a higher surfactant bulk concentration, which verifies the effect of surfactant in reducing the interfacial tension. Increases in surface Péclet number and initial surfactant bulk concentration can enhance the non-uniformity of surfactant distribution around the interface, which will arise the Marangoni force. The Marangoni force acts as an additional repulsive force to delay the droplet merging.

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Numerical simulations of multi-hop jumping on superhydrophobic surfaces

Cited by 32 publications

References 45 publications

Droplet jumping induced by coalescence of a moving droplet and a static one: Effect of initial velocity

Droplet jumping induced by coalescence of a moving droplet and a static one: Effect of initial velocity

Prediction of Droplet Sliding on the Continuity of the Three-Phase Contact Line

Interfacial dynamics with soluble surfactants: A phase-field two-phase flow model with variable densities

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