Oscillations and Short Waves on a Free Falling Drop Surface (Experiment and Theory)

Chashechkin, Yu. D.

doi:10.14311/tpfm.2019.007

Cited by 4 publications

(4 citation statements)

References 8 publications

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“…However, for the cases shown in figures 6(a) and 6(b), the fluid viscosities are always low (3.9-12.2 mPa s). Considering surface tension is the main cause for the oscillation in droplet coalescence dynamics where it is free of external forces (Chashechkin 2019), and the liquids used in figures 6(a) and 6(b) have rather different oil-water interfacial tensions and also different surface tensions, we thus speculate that both the interfacial tension and the surface tension should have a marked influence on the droplet oscillation dynamics, and the influence of interfacial tension on the droplet oscillation dynamics should be further investigated. To avoid the damping effect of high viscosity, low-viscosity oil droplets are then used to analyse the oscillation behaviour.…”

Section: Oscillation Of the Coalescing Dropletmentioning

confidence: 99%

Coalescence of immiscible sessile droplets on a partial wetting surface

Xu,

Ge,

Wang

et al. 2023

J. Fluid Mech.

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Droplet coalescence is a common phenomenon and plays an important role in multidisciplinary applications. Previous studies mainly consider the coalescence of miscible liquids, even though the coalescence of immiscible droplets on a solid surface is a common process. In this study, we explore the coalescence of two immiscible droplets on a partial wetting surface experimentally and theoretically. We find that the coalescence process can be divided into three stages based on the time scales and force interactions involved, namely (I) the growth of a liquid bridge, (II) the oscillation of the coalescing sessile droplet and (III) the formation of a partially engulfed compound sessile droplet and the subsequent retraction. In stage I, the immiscible interface is found not to affect the scaling of the temporal evolution of the liquid bridge, which follows the same 2/3 power law as that of miscible droplets. In stage II, by developing a new capillary time scale considering both surface and interfacial tensions, we show that the interfacial tension between the two immiscible liquids functions as a non-negligible resistance to the oscillation which decreases the oscillation periods. In stage III, a modified Ohnesorge number is developed to characterize the visco-capillary and inertia-capillary time scales involved during the displacement of water by oil; a new model based on energy balance is proposed to analyse the maximum retraction velocity, highlighting that the viscous resistance is concentrated in a region close to the contact line.

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Section: Oscillation Of the Coalescing Dropletmentioning

confidence: 99%

Coalescence of immiscible sessile droplets on a partial wetting surface

Xu,

Ge,

Wang

et al. 2023

J. Fluid Mech.

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“…The general asymmetry of the flow pattern is because of the difference in the shape of the incoming drop and the spherical one due to Rayleigh oscillations and capillary waves traveling along its surface [85]. The general gray background of the veil and darker lines, which are traces of the thrown liquid layer and single ligaments (thin jets that arise at the contact line of the drop with the target liquid), indicate the complexity of the emerging flow pattern.…”

Section: Drop Spreading Of Alizarin Ink Solution In Watermentioning

confidence: 99%

“…The presence of "colored tongues" is explained by the difference in the drop shape from the spherical one at the time of the initial contact. The droplet surface is distorted by Rayleigh oscillations and traveling capillary waves [85], and it is also deformed by a radially spreading air jet [48].…”

Section: Drop Spreading Of Saturated Potassium Permanganate Solution ...mentioning

confidence: 99%

“…The droplets from their tops fall on the surface of the merging drop and form short capillary waves (in Figure 12b-in sectors for "6" and "8" o'clock [85]). The complex structure of the fluids' contact domain boundary (colored fibers visualizing thin trickles flowing along the cavity bottom, the crown walls and reaching the spikes on its edge) is preserved throughout the process of droplet coalescence (Figure 12c,d).…”

Section: Drop Spreading Of Copper Sulphate Solution In Watermentioning

confidence: 99%

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Fine Flow Structure at the Miscible Fluids Contact Domain Boundary in the Impact Mode of Free-Falling Drop Coalescence

Chashechkin,

Ilinykh

2023

Fluids

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Registration of the flow pattern and the matter distribution of a free falling liquid drop in a target fluid at rest in the impact mode of coalescence when the kinetic energy (KEn) of the drop exceeds its available surface potential energy (ASPe) was carried out by photo and video recording. We studied the evolution of the fine flow structure at the initial stage of the cavity formation. To carry out color registration, the observation field was illuminated by several matrix LED and fiber-optic sources of constant light. The planning of experiments and interpretation of the results were based on the properties of the complete solutions of the fundamental equations of a fluid mechanics system, including the transfer and conversion of energy processes. Complete solutions of the system of equations describe large-scale flow components that are waves or vortices as well as thin jets (ligaments, filaments, fibers, trickles). In experiments, the jets are accelerated by the converted available surface potential energy (ASPe) when the free surfaces of merging fluids were eliminated. The experiments were performed with the coalescence of water, solutions of alizarin ink, potassium permanganate, and copper sulfate or iron sulfate drops in deep water. In all cases, at the initial contact, the drop begins to lose its continuity and breaks up into a thin veil and jets, the velocity of which exceeds the drop contact velocity. Small droplets, the size of which grows with time, are thrown into the air from spikes at the jet tops. On the surface of the liquid, the fine jets leave colored traces that form linear and reticular structures. Part of the jets penetrating through the bottom and wall of the cavity forms an intermediate covering layer. The jets forming the inside layer are separated by interfaces of the target fluid. The processes of molecular diffusion equalize the density differences and form an intermediate layer with sharp boundaries in the target fluid. All noted structural features of the flow are also visualized when a fresh water drop isothermally spreads in the same tap water. Molecular diffusion processes gradually smooth out the fast-changing boundary of merging fluids, which at the initial stage has a complex and irregular shape. Similar flow patterns were observed in all performed experiments; however, the geometric features of the flow depend on the individual thermodynamic and kinetic parameters of the contacting fluids.

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Hydrodynamics of detachment, free falling and impact of drops

Chashechkin

2021

J. Phys.: Conf. Ser.

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The results of optical measurements of drop dynamics are presented. Oscillations and waves on its surface were traced. The pattern of the secondary droplets falls onto an immersed drop and the discrete distribution of the substance of a uniformly colored drop in the targeted liquid was visualized. The important role of energy transport processes, both fast – local atomic-molecular – and slow that are translational and dissipative, in the formation of flow patterns is highlighted. A system of fundamental equations of fluid mechanics with equations of state for the Gibbs potential and density is applied. Ligaments – thin trickles with scales from atomic-molecular and macroscopic sizes – are investigated. Their images in the family of intrinsic solutions of the fundamental system and drop impact phenomena are shown.

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Oscillations and Short Waves on a Free Falling Drop Surface (Experiment and Theory)

Cited by 4 publications

References 8 publications

Coalescence of immiscible sessile droplets on a partial wetting surface

Coalescence of immiscible sessile droplets on a partial wetting surface

Fine Flow Structure at the Miscible Fluids Contact Domain Boundary in the Impact Mode of Free-Falling Drop Coalescence

Hydrodynamics of detachment, free falling and impact of drops

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