Dynamics of drop coalescence at fluid interfaces

2009 ◽  
Vol 620 ◽  
pp. 333-352 ◽  
Author(s):  
FRANÇOIS BLANCHETTE ◽  
TERRY P. BIGIONI
Keyword(s):  
Bond Number ◽  
Capillary Waves ◽  
Fluid Interfaces ◽  
Ohnesorge Number ◽  
Liquid Drops ◽  
Drop Coalescence ◽  
Partial Coalescence ◽  
Flat Interface ◽  
Low Viscosity ◽  
Set Up

Drop coalescence was studied using numerical simulations. Liquid drops were made to coalesce with a body of the same liquid, either a reservoir or a drop of different size, each with negligible impact velocity. We considered either gas or liquid as a surrounding fluid, and experimental results are discussed for the gas–liquid set-up. Under certain conditions, a drop will not fully coalesce with the liquid reservoir, leaving behind a daughter drop. Partial coalescence is observed for systems of low viscosity, characterized by a small Ohnesorge number, where capillary waves remain sufficiently vigourous to distort the drop significantly. For drops coalescing with a flat interface, we determine the critical Ohnesorge number as a function of Bond number, as well as density and viscosity ratios of the fluids. Studying the coalescence of two drops of different sizes reveals that partial coalescence may occur in low-viscosity systems provided the size ratio of the drops exceeds a certain threshold. We also determine the extent to which the process of partial coalescence is self-similar and find that the viscosity of the drop has a large effect on the droplet's vertical velocity after pinch off. Finally, we report on the formation of satellite droplets generated after a first pinch off and on the ejection of a jet of tiny droplets during coalescence of a parent drop significantly deformed by gravity.

Generation of secondary droplets in coalescence of a drop at a liquid–liquid interface

2010 ◽  
Vol 655 ◽  
pp. 72-104 ◽  
Author(s):  
B. RAY ◽  
G. BISWAS ◽  
A. SHARMA
Keyword(s):  
Critical Value ◽  
Bond Number ◽  
Viscous Force ◽  
Time Range ◽  
Main Body ◽  
Ohnesorge Number ◽  
Partial Coalescence ◽  
Daughter Droplets ◽  
Secondary Droplets ◽  
Secondary Drop

When a droplet of liquid 1 falls through liquid 2 to eventually hit the liquid 2–liquid 1 interface, its initial impact on the interface can produce daughter droplets of liquid 1. In some cases, a partial coalescence cascade governed by self-similar capillary-inertial dynamics is observed, where the fall of the secondary droplets in turn continues to produce further daughter droplets. Results show that inertia and interfacial surface tension forces largely govern the process of partial coalescence. The partial coalescence is suppressed by the viscous force when Ohnesorge number is below a critical value and also by gravity force when Bond number exceeds a critical value. Generation of secondary drop is observed for systems of lower Ohnesorge number for liquid 1, lower and intermediate Ohnesorge number for liquid 2 and for low and intermediate values of Bond number. Whenever the horizontal momentum in the liquid column is more than the vertical momentum, secondary drop is formed. A transition regime from partial to complete coalescence is obtained when the neck radius oscillates twice. In this regime, the main body of the column can be fitted to power-law scaling model within a specific time range. We investigated the conditions and the outcome of these coalescence events based on numerical simulations using a coupled level set and volume of fluid method (CLSVOF).

scholarly journals Capillary waves control the ejection of bubble bursting jets

2019 ◽  
Vol 867 ◽  
pp. 556-571 ◽  
Author(s):  
J. M. Gordillo ◽  
J. Rodríguez-Rodríguez
Keyword(s):  
Capillary Wave ◽  
Bubble Radius ◽  
Bond Number ◽  
Capillary Waves ◽  
Liquid Density ◽  
Ohnesorge Number ◽  
Capillary Suction ◽  
Lower Base ◽  
Capillary Pressures ◽  
The Moment

Here we provide a theoretical framework describing the generation of the fast jet ejected vertically out of a liquid when a bubble, resting on a liquid–gas interface, bursts. The self-consistent physical mechanism presented here explains the emergence of the liquid jet as a consequence of the collapse of the gas cavity driven by the low capillary pressures that appear suddenly around its base when the cap, the thin film separating the bubble from the ambient gas, pinches. The resulting pressure gradient deforms the bubble which, at the moment of jet ejection, adopts the shape of a truncated cone. The dynamics near the lower base of the cone, and thus the jet ejection process, is determined by the wavelength $\unicode[STIX]{x1D706}^{\ast }$ of the smallest capillary wave created during the coalescence of the bubble with the atmosphere which is not attenuated by viscosity. The minimum radius at the lower base of the cone decreases, and hence the capillary suction and the associated radial velocities increase, with the wavelength $\unicode[STIX]{x1D706}^{\ast }$. We show that $\unicode[STIX]{x1D706}^{\ast }$ increases with viscosity as $\unicode[STIX]{x1D706}^{\ast }\propto Oh^{1/2}$ for $Oh\lesssim O(0.01)$, with $Oh=\unicode[STIX]{x1D707}/\sqrt{\unicode[STIX]{x1D70C}R\unicode[STIX]{x1D70E}}$ the Ohnesorge number, $R$ the bubble radius and $\unicode[STIX]{x1D70C}$, $\unicode[STIX]{x1D707}$ and $\unicode[STIX]{x1D70E}$ indicating respectively the liquid density, viscosity and interfacial tension coefficient. The velocity of the extremely fast and thin jet can be calculated as the flow generated by a continuous line of sinks extending along the axis of symmetry a distance proportional to $\unicode[STIX]{x1D706}^{\ast }$. We find that the jet velocity increases with the Ohnesorge number and reaches a maximum for $Oh=Oh_{c}$, the value for which the crest of the capillary wave reaches the vertex of the cone, and which depends on the Bond number $Bo=\unicode[STIX]{x1D70C}gR^{2}/\unicode[STIX]{x1D70E}$. For $Oh>Oh_{c}$, the jet is ejected after a bubble is pinched off; in this regime, viscosity delays the formation of the jet, which is thereafter emitted at a velocity which is inversely proportional to the liquid viscosity.

scholarly journals Pseudo-Planar Organic Heterojunctions by Sequential Printing of Quasi-Miscible Inks

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 586
Author(s):  
Ana-Gianina Gereanu ◽  
Camillo Sartorio ◽  
Aurelio Bonasera ◽  
Giuliana Giuliano ◽  
Sebastiano Cataldo ◽  
...  
Keyword(s):  
Inkjet Printing ◽  
Organic Solar Cells ◽  
Bulk Heterojunction ◽  
Acid Methyl Ester ◽  
Bond Number ◽  
Molecular Organization ◽  
Low Viscosity ◽  
Donor Acceptor ◽  
Interfacial Mixing ◽  
Planar Heterojunction

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~101). Differently from solution dispensing processes at a high Bond number such as spin coating, the deposition by inkjet printing is strictly controlled by droplet velocity, ink viscosity, and surface tension. In particular, this study considers the interfacial mixing of droplets containing the most investigated donor/acceptor couple for organic solar cells, i.e., poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), showing how low-viscosity and low-surface energy inks can be leveraged for the fabrication of an interface suitable for a pseudo-planar heterojunction (pseudo-PHJ) organic solar cell (OSC) that is a convenient alternative to a bulk heterojunction (BHJ) OSC. The resulting thin-film morphology and molecular organization at the P3HT/PCBM interface are investigated, highlighting the roles of dissolution-driven molecular recirculation. This report represents a first step toward the sequential inkjet printing fabrication of pseudo-PHJ OSCs at low consumption of solvents/chemicals.

On the Impact of Liquid Drops on Immiscible Liquids

2016 ◽  
Author(s):  
Eduardo Castillo-Orozco ◽  
Ashkan Davanlou ◽  
Pretam K. Choudhury ◽  
Ranganathan Kumar
Keyword(s):  
Oil Spills ◽  
Silicone Oil ◽  
Density Ratio ◽  
High Viscosity ◽  
Impact Behavior ◽  
Immiscible Fluid ◽  
Liquid Droplets ◽  
Liquid Drops ◽  
Low Viscosity ◽  
The Impact

The release of liquid hydrocarbons into the water is one of the environmental issues that have attracted more attention after deepwater horizon oil spill in Gulf of Mexico. The understanding of the interaction between liquid droplets impacting on an immiscible fluid is important for cleaning up oil spills as well as the demulsification process. Here we study the impact of low-viscosity liquid drops on high-viscosity liquid pools, e.g. water and ethanol droplets on a silicone oil 10cSt bath. We use an ultrafast camera and image processing to provide a detailed description of the impact phenomenon. Our observations suggest that viscosity and density ratio of the two media play a major role in the post-impact behavior. When the droplet density is larger than that of the pool, additional cavity is generated inside the pool. However, if the density of the droplet is lower than the pool, droplet momentary penetration may be facilitated by high impact velocities. In crown splash regime, the pool properties as well as drop properties play an important role. In addition, the appearance of the central jet is highly affected by the properties of the impacting droplet. In general, the size of generated daughter droplets as well as the thickness of the jet is reduced compared to the impact of droplets with the pool of an identical fluid.

The Effects of Vibration and Pulsation on Metal Removal by a Plasma Torch

1973 ◽  
Vol 95 (2) ◽  
pp. 240-245 ◽  
Author(s):  
G. T. Dyos ◽  
J. Lawton
Keyword(s):  
Molten Metal ◽  
Gas Flow ◽  
Metal Removal ◽  
Capillary Waves ◽  
Plasma Jets ◽  
Removal Rates ◽  
Workpiece Vibration ◽  
Arc Current ◽  
Set Up ◽  
Gas Pulsations

An experimental study has been carried out on the effects of workpiece vibration and gas pulsations on metal removal rates using plasma jets. In the case of workpiece vibration, increases in removal rates of up to 30 percent were found, which can be accounted for in terms of capillary waves set up in the melt. The influence of pulsation of gas flow velocity and arc current at modulation levels of 10 percent was found to be negligible. A theoretical model has been developed which explains the results in terms of the development of resonance capillary waves in the molten metal and predicts the average depth of the layer of molten metal.

scholarly journals Tribological properties of surface microtexture friction pairs under different lubrication conditions

2019 ◽  
Vol 11 (10) ◽  
pp. 168781401988156
Author(s):  
Lili Wang ◽  
Xingtang Zhao ◽  
Shaohui Guo ◽  
Min Wang
Keyword(s):  
Friction Pair ◽  
Element Model ◽  
High Viscosity ◽  
Navier Stokes ◽  
Solid Mixture ◽  
Low Viscosity ◽  
Frictional Performance ◽  
Friction Performance ◽  
Set Up ◽  
Lubrication Conditions

In the field of journal bearings, the microtexture processing technology of the bush inner surface has become an effective way to improve the performance of journal bearing. The two-dimensional finite element model of microtexture surface with different shapes of friction pairs is established based on the Navier–Stokes (N-S) equation, and the effect of lubrication conditions on the frictional performance of friction pairs is analyzed. Four microtextures that are radial grooves, circular pits, local reticulation, and circumferential grooved microtexture are processed by laser microcarving on the surface of specimen, and three different lubricating medium conditions are set up with high-viscosity oil, low-viscosity oil, and oil–solid mixture, and the effect of lubrication condition and texture shape on the wear reduction of the microtexture friction pair is studied. Results show that the concave microtexture and the radial groove can improve effectively the friction performance of the friction pair. The microtexture can effectively store the lubricating medium and wear abrasive particles in the mixed lubrication, and avoid effectively the second wear, and its average friction coefficient of radial groove microtexture is 22%, 30% lower than that of high- and low-viscosity lubricating media, respectively. Both theory and experiment have proved that the effect of microtexture on high-viscosity lubricant is better than that of low-viscosity lubricant.

Use of Tracer Particles for Tracking Fluid Interfaces in Primary Cementing

2019 ◽  
Author(s):  
Amir Taheri ◽  
Jan David Ytrehus ◽  
Ali Taghipour ◽  
Bjørnar Lund ◽  
Alexandre Lavrov ◽  
...  
Keyword(s):  
Numerical Models ◽  
Secondary Flows ◽  
Equivalent Model ◽  
Fluid Interfaces ◽  
Element Analysis ◽  
Two Fluids ◽  
Tracer Particles ◽  
Narrow Side ◽  
Primary Cementing ◽  
Set Up

Abstract In this study, a new approach for detailed tracking of the interface between well fluid and cement by using particles is investigated. This can improve the quality of annular cementing of CO2 wells and thus the storage safety. For this purpose, the displacement mechanisms of Newtonian and non-Newtonian fluids in the annulus of vertical and inclined wells is investigated by using an experimental set-up with an eccentric annular geometry and by finite element analysis of an equivalent model with COMSOL Multiphysics solver. For more efficient displacement, the displacing fluid has a higher density than the displaced fluid, and the intermediate-buoyancy particles that reside at the interface between successive fluids are introduced into the models. Such particles must overcome strong secondary flows in order to travel with the interface. Particle motions are investigated in different experimental and numerical models, and their effectiveness is investigated. The experimental results confirm that while the particles with a size of 425–500 um are unable to overcome the secondary flows in eccentric vertical models and track the interface, they can be useful for tracking the interface between two fluids in an eccentric model with a small inclination to the narrow side. CFD analysis investigates this behavior with more details and shows the effects of some parameters on the particle motions.

Coalescence, Partial Coalescence, and Noncoalescence of Two Free Droplets Suspended in Low-Viscosity Oil under a DC Electric Field

2020 ◽  
Vol 124 (34) ◽  
pp. 7508-7517
Author(s):  
Xin Huang ◽  
Limin He ◽  
Xiaoming Luo ◽  
Ke Xu ◽  
Yuling Lü ◽  
...  
Keyword(s):  
Electric Field ◽  
Partial Coalescence ◽  
Low Viscosity ◽  
Dc Electric Field

scholarly journals Faraday instability on a sphere: numerical simulation

2019 ◽  
Vol 870 ◽  
pp. 433-459 ◽  
Author(s):  
A. Ebo-Adou ◽  
L. S. Tuckerman ◽  
S. Shin ◽  
J. Chergui ◽  
D. Juric
Keyword(s):  
Body Force ◽  
Three Dimensional ◽  
Capillary Waves ◽  
Platonic Solids ◽  
Interface Motion ◽  
Spherical Drop ◽  
Low Viscosity ◽  
Faraday Instability ◽  
Viscous Drop ◽  
Time Periodic

We consider a spherical variant of the Faraday problem, in which a spherical drop is subjected to a time-periodic body force, as well as surface tension. We use a full three-dimensional parallel front-tracking code to calculate the interface motion of the parametrically forced oscillating viscous drop, as well as the velocity field inside and outside the drop. Forcing frequencies are chosen so as to excite spherical harmonic wavenumbers ranging from 1 to 6. We excite gravity waves for wavenumbers 1 and 2 and observe translational and oblate–prolate oscillation, respectively. For wavenumbers 3 to 6, we excite capillary waves and observe patterns analogous to the Platonic solids. For low viscosity, both subharmonic and harmonic responses are accessible. The patterns arising in each case are interpreted in the context of the theory of pattern formation with spherical symmetry.

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