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

Li, Shaokang; Chu, Fuqiang; Zhang, Jun; Brutin, David; Wen, Dongsheng

doi:10.1016/j.ces.2019.115252

Cited by 35 publications

(34 citation statements)

References 51 publications

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“…7(a). Similar to the sliding droplet jumping discussed in our another work, 37 the horizontal departure velocity (Vx,depar) and the center velocity is directly proportional. The proportionality coefficients change from 0.37 to 0.47 when the droplet radius increases from 40 μm to 300 μm.…”

Section: Horizontal Departure Velocity and Departure Anglesupporting

confidence: 63%

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Departure Velocity of Rolling Droplet Jumping

Chu

et al. 2020

Langmuir

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Droplet jumping phenomenon widely exists in the fields of self-cleaning, anti-frosting and heat transfer enhancement. Numerous studies have been reported on the static droplet jumping while the rolling droplet jumping still remains unnoticed although it is very common in practice. Here, we used the volume of fluid (VOF) method to simulate the droplet jumping induced by coalescence of a rolling droplet and a stationary one with corresponding experiments conducted to validate the correctness of the simulation model. The departure velocity of the jumping droplet was mainly concerned here. The results show that when the center velocity of the rolling droplet (V0 =ωR, where ω is the angular velocity of the rolling droplet and R is the droplet radius) is fixed, the vertical departure velocity satisfies a power law which can be expressed as Vz, depar = aR b . When the droplet radius is fixed, the vertical departure velocity first decreases, and then increases if the center velocity exceeds a critical value. Interestingly, the critical center velocity is demonstrated to be approximately 0.76 times of the capillary-inertial velocity, corresponding to a constant Weber number of 0.58. Different from the vertical departure velocity, the horizontal departure velocity is basically proportional to the center velocity of the rolling droplet. These results deepen the understanding of the droplet jumping physics, which shall further promote related applications in engineering fields.

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Section: Horizontal Departure Velocity and Departure Anglesupporting

confidence: 63%

“…Please refer to our recent work for the detailed equations in the numerical model. 37 Figure 1(a) shows the schematic of rolling droplet jumping. The left droplet has a clockwise angular velocity and moves towards the stationary droplet, and then the merged droplet jumps up because of coalescence.…”

Section: Numerical Modelmentioning

confidence: 99%

Departure Velocity of Rolling Droplet Jumping

Chu

et al. 2020

Langmuir

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“…In the present work, the dynamic contact angle model proposed by Kistler is utilized to relate the contact velocity and dynamic contact angle on the triple line, which has been validated in numerous researches. [48][49][50] During the simulation, the value of advancing contact angle and receding contact angle are set according to the wettability of the experimental surface.…”

Section: B Numerical Methodsmentioning

confidence: 99%

Dynamics of droplet impacting on a cone

Luo

Chu

et al. 2021

Physics of Fluids

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Droplet rebound dynamics on superhydrophobic surfaces has attracted much attention due to its importance in numerous technical applications, such as anti-icing and fluid transportation. It has been demonstrated that changing the macro-structure of the superhydrophobic surface could result in significant change in droplet morphology and hydrodynamics. Here we conduct both experimental and numerical studies of droplet impacting on a cone, and identify three different dynamic phases by changing the impacting conditions, i.e., the Weber number and the cone angle. The spreading and retracting dynamics are studied for each phase. Particularly, it is found that in Phase 3, where the droplet leaves the surface as a ring, the contact time is reduced by 54% compared with that of a flat surface. A theoretical model based on energy analysis is developed to get the rebound point in Phase 3, which agrees well with the simulation result. Besides, the effect of Weber number and cone angle on the contact time is explored.Finally, the phase diagram of the three phases distribution with We and cone angle is given, which can provide guidance to related applications.

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“…Because the simulation is just Proof of Principle, we will not introduce more about the simulation method here, and please see more details about the simulation method in our previous work. 45 As shown in Fig. 3, according to the droplet morphology evolution, six stages are divided during the droplet impacting on the wettability-controlled surface, including spreading, retracting, departure, throwing, breaking up, and flight.…”

Section: Impacting Droplet Morphology and Directional Transportation Mechanismmentioning

confidence: 99%

Directional Transportation of Impacting Droplets on Wettability-Controlled Surfaces

et al. 2020

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Although a superhydrophobic surface could realize rapid rebounding (i.e., short contact time) of an orthogonal impacting droplet, the rebounding along the original impacting route may limit its engineering application; in contrast, the directional transportation seems to be more promising. Here, we achieve directional transportation of a droplet impacting on a wettability-controlled surface. When the droplet eccentrically impacts on the boundary between the superhydrophobic part and the hydrophilic part, it undergoes spreading, retracting, departure, throwing and breaking up stages, and finally bounces off directionally. The directional transportation distance could even reach more than ten times of the droplet size, considered the adhesion length (i.e., covering length on the hydrophilic part by the droplet at the maximum spreading) is optimized. However, there is a critical adhesion length, above which the directional transportation does not occur. To be more generalized, the adhesion length is de-dimensionalized by the maximum spreading radius, and the results show that as the dimensionless adhesion length increases, the transportation distance first increases and then decreases to zero. Under the present impacting conditions, the optimal dimensionless adhesion length corresponding to the maximum transportation distance is near 0.4, and the critical dimensionless adhesion length is about 0.7. These results provide fundamental understanding of droplet directional transportation, and could be useful for related engineering applications.

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

Cited by 35 publications

References 51 publications

Departure Velocity of Rolling Droplet Jumping

Departure Velocity of Rolling Droplet Jumping

Dynamics of droplet impacting on a cone

Directional Transportation of Impacting Droplets on Wettability-Controlled Surfaces

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