scholarly journals Electrically charged droplet: case study of a simple generator

2014 ◽  
Vol 92 (10) ◽  
pp. 1203-1207 ◽  
Author(s):  
Martin Brandenbourger ◽  
Stéphane Dorbolo
Keyword(s):  
Surface Tension ◽  
Silicone Oil ◽  
Perfect Conductor ◽  
Charged Droplet ◽  
Ejection Time ◽  
Capillary Length ◽  
Droplet Ejection ◽  
Planar Capacitor ◽  
Electrically Charged

We studied the behavior of a simple apparatus that allows charging droplets by induction. We imposed the following constraints: (i) any liquid should be charged (more precisely whatever its surface tension and therefore whatever its wettability, capillary length, etc.); and (ii) the system is to remain as simple as possible. The design of the device results of a compromise regarding both constraints. The device developed is based on a planar capacitor in which the droplets are generated. The influence of the nature of the liquid (i.e., presence of ions in solution, polarity, surface tension, and conductivity) on the charge induced was measured and was found to be independent of the liquid properties (except for the silicone oil). We deduced that, in the considered configuration, fluids behave like a “perfect conductor” as soon as conductive relaxation time is smaller than the droplet ejection time. Under this condition, the charge has the time to move in the droplet to reach the electrostatic regime.

Investigation of Droplet-Ejection Characteristics for a Piezoelectric Inkjet Printhead

2006 ◽  
Vol 220 (4) ◽  
pp. 435-445 ◽  
Author(s):  
A-S Yang ◽  
C-H Cheng ◽  
C-T Lin
Keyword(s):  
Surface Tension ◽  
Piecewise Linear ◽  
Time Interval ◽  
Force Model ◽  
Ejection Time ◽  
Theoretical Formulation ◽  
Construction Technique ◽  
Droplet Ejection ◽  
Ejection Process ◽  
Inkjet Printhead

Numerical simulations are performed to explore the droplet-ejection process for a piezoelectric inkjet printhead. In the analysis, the theoretical model takes account of a set of three-dimensional, time-dependent conservation equations of mass and momentum, with the incorporation of the continuous surface force model for treating the interfacial surface tension effect. The resultant governing equations are solved using an iterative semi-implicit method for pressure-linked equations consistent algorithm for resolving flow properties. The volume-of-fluid method along with the piecewise linear-interface construction technique is implemented to characterize the behaviour of liquid surface movement. With a typical piezodiaphragm printhead as an illustration case, the time evolution of the gas-liquid interface is calculated for an entire ejection cycle of 164 μs. The predicted droplet shapes throughout the ejection process are compared with microphotographed images for the verification of the present theoretical formulation. The flow and transport phenomena in the stages of the ink ejection and the droplet formation are further examined in detail. In response to design needs, the study is extended to determine the variations of ejection characteristics at different settings of nozzle exit diameter, ejection time interval, surface tension, and viscosity of fluid.

Numerical Simulation of Droplet Ejection Based on VOF Method

2014 ◽  
Vol 548-549 ◽  
pp. 1257-1264 ◽  
Author(s):  
Xiao Yong Suo
Keyword(s):  
Numerical Simulation ◽  
Surface Tension ◽  
Numerical Model ◽  
Physical Properties ◽  
Vof Method ◽  
Numerical Results ◽  
Droplet Ejection ◽  
Ejection Process ◽  
Ink Jet ◽  
Jet Nozzle

Taking ejection process of the ink droplets from ink-jet nozzle as the prototype, a similar numerical model of droplet ejection was established. The VOF method was applied to track the interface of droplet ejection process and it is shown that the numerical results simulated by the VOF method were accurate and reliable. Six kinds of liquid with different physical properties were chosen as the research object. The numerical results were analyzed and compared. Finally, the effect of the surface tension, viscosity and density on the droplet ejection process was discussed.

Numerical Simulation of Jetting Instability in Flow Focusing Microfluidics

2014 ◽  
Vol 609-610 ◽  
pp. 630-636
Author(s):  
Hong Bo Zhang ◽  
Jian Pu Liu ◽  
Huan Xin Lai
Keyword(s):  
Numerical Simulation ◽  
Surface Tension ◽  
Rate Ratio ◽  
Silicone Oil ◽  
Flow Rate Ratio ◽  
Absolute Instability ◽  
Flow Ratio ◽  
Flow Focusing ◽  
Immiscible Liquids ◽  
Main Factor

In this paper, jetting behavior of two immiscible liquids, water as the outer liquid and silicone oil as the inner liquid in typical flow focusing microchannels were numerically studied using VOF method. At low capillary number, uniform microdroplets were obtained by the absolute instability. With the increasing of fluid flow ratio, the jet is thinner and tends to break up further away the cross junction. The results showed that the flow rate ratio is the main factor that influences the microdroplet sizes, while the frequency of microdroplets formation can be controlled mainly by the surface tension when it is in the jetting regime.

Laser Induced Nano-Droplet Ejection for the Construction of Nano-Inkjets

2012 ◽  
Author(s):  
Yu Yang ◽  
Vijay M. Sundaram ◽  
Alok Soni ◽  
Sy-Bor Wen
Keyword(s):  
Surface Tension ◽  
Pulse Energy ◽  
Nanosecond Laser ◽  
Continuous Laser ◽  
Fluidic Channel ◽  
Robust Approach ◽  
Power Intensity ◽  
On Demand ◽  
Drop On Demand ◽  
Droplet Ejection

To achieve precise nano-droplet ejection, the existing microscale inkjet module could be scaled down to nanoscale, including both the fluidic channel and the pressure driver. While 2D/3D nanoscale fluidic channels are currently available, a nanoscale pressure driver providing high enough power intensity to overcome surface tension for nano-droplet ejection is still lacking. In this study, laser induced nanoscale confined heating with nano-nozzles are constructed and demonstrated as a simple and robust approach to achieve the required pressure driver. For the heating with continuous laser, micro spray composed with nano-droplets can be induced from the nano-nozzles. For the heating with nanosecond laser of adequate pulse energy, drop-on-demand ejection of droplets with similar diameter as the apertures of the nano-nozzle can be achieved.

scholarly journals Steep capillary-gravity waves in oscillatory shear-driven flows

2009 ◽  
Vol 640 ◽  
pp. 131-150 ◽  
Author(s):  
SHREYAS V. JALIKOP ◽  
ANNE JUEL
Keyword(s):  
Surface Tension ◽  
Gravity Waves ◽  
Pitchfork Bifurcation ◽  
Nonlinear Regime ◽  
Radius Of Curvature ◽  
Square Root ◽  
Capillary Length ◽  
Weakly Nonlinear ◽  
Gravitational Forces ◽  
Steep Waves

We study steep capillary-gravity waves that form at the interface between two stably stratified layers of immiscible liquids in a horizontally oscillating vessel. The oscillatory nature of the external forcing prevents the waves from overturning, and thus enables the development of steep waves at large forcing. They arise through a supercritical pitchfork bifurcation, characterized by the square root dependence of the height of the wave on the excess vibrational Froude number (W, square root of the ratio of vibrational to gravitational forces). At a critical valueWc, a transition to a linear variation inWis observed. It is accompanied by sharp qualitative changes in the harmonic content of the wave shape, so that trochoidal waves characterize the weakly nonlinear regime, but ‘finger’-like waves form forW≥Wc. In this strongly nonlinear regime, the wavelength is a function of the product of amplitude and frequency of forcing, whereas forW<Wc, the wavelength exhibits an explicit dependence on the frequency of forcing that is due to the effect of viscosity. Most significantly, the radius of curvature of the wave crests decreases monotonically withWto reach the capillary length forW=Wc, i.e. the lengthscale for which surface tension forces balance gravitational forces. ForW<Wc, gravitational restoring forces dominate, but forW≥Wc, the wave development is increasingly defined by localized surface tension effects.

Stability of an Electrically Charged Droplet

1962 ◽  
Vol 5 (5) ◽  
pp. 575 ◽  
Author(s):  
Gedalia Ailam (Volinez) ◽  
Isaiah Gallily
Keyword(s):  
Charged Droplet ◽  
Electrically Charged

Long-wavelength surface-tension-driven Bénard convection: experiment and theory

1997 ◽  
Vol 345 ◽  
pp. 45-78 ◽  
Author(s):  
STEPHEN J. VANHOOK ◽  
MICHAEL F. SCHATZ ◽  
J. B. SWIFT ◽  
W. D. MCCORMICK ◽  
HARRY L. SWINNEY
Keyword(s):  
Surface Tension ◽  
Steady State ◽  
Temperature Difference ◽  
Silicone Oil ◽  
Interface Temperature ◽  
Layer Model ◽  
Long Wavelength ◽  
Two Layer Model ◽  
Gas Layer ◽  
Dry Spot

Surface-tension-driven Bénard (Marangoni) convection in liquid layers heated from below can exhibit a long-wavelength primary instability that differs from the more familiar hexagonal instability associated with Bénard. This long-wavelength instability is predicted to be significant in microgravity and for thin liquid layers. The instability is studied experimentally in terrestrial gravity for silicone oil layers 0.007 to 0.027 cm thick on a conducting plate. For shallow liquid depths (<.017 cm for 0.102 cm2 s−1 viscosity liquid), the system evolves to a strongly deformed long-wavelength state which can take the form of a localized depression (‘dry spot’) or a localized elevation (‘high spot’), depending on the thickness and thermal conductivity of the gas layer above the liquid. For slightly thicker liquid depths (0.017–0.024 cm), the formation of a dry spot induces the formation of hexagons. For even thicker liquid depths (>0.024 cm), the system forms only the hexagonal convection cells. A two-layer nonlinear theory is developed to account properly for the effect of deformation on the interface temperature profile. Experimental results for the long-wavelength instability are compared to our two-layer theory and to a one-layer theory that accounts for the upper gas layer solely with a heat transfer coefficient. The two-layer model better describes the onset of instability and also predicts the formation of localized elevations, which the one-layer model does not predict. A weakly nonlinear analysis shows that the bifurcation is subcritical. Solving for steady states of the system shows that the subcritical pitchfork bifurcation curve never turns over to a stable branch. Numerical simulations also predict a subcritical instability and yield long-wavelength states that qualitatively agree with the experiments. The observations agree with the onset prediction of the two-layer model, except for very thin liquid layers; this deviation from theory may arise from small non-uniformities in the experiment. Theoretical analysis shows that a small non-uniformity in heating produces a large steady-state deformation (seen in the experiment) that becomes more pronounced with increasing temperature difference across the liquid. This steady-state deformation becomes unstable to the long-wavelength instability at a smaller temperature difference than that at which the undeformed state becomes unstable in the absence of non-uniformity.

scholarly journals The wetting properties of frosted glass

2021 ◽  
Vol 13 ◽  
pp. 130006
Author(s):  
Stéphane Dorbolo
Keyword(s):  
Contact Angle ◽  
Optical Properties ◽  
Silicone Oil ◽  
Low Cost ◽  
Contact Angle Hysteresis ◽  
Water Droplets ◽  
Capillary Length ◽  
Wetting Properties ◽  
Travel Distances ◽  
Frosted Glass

Frosted glass is a common, low cost material. Its roughness can be used to control how it is wet by water. In this paper, the wetting properties of silicone oil and water are investigated. For the oil, wetting is total since the oleophilic character of the glass is enhanced by its roughness. Due to the remarkable optical properties of frosted glass, the spreading of oil droplets on its surface was recorded over three months. Frosted glass is a parahydrophilic surface because of its large contact angle hysteresis (up to 80° ). The behaviour of oil and water droplets was compared on a long piece of inclined frosted glass. The trajectories (and the spreading) of the droplets were studied and phenomenological laws were deduced to describe the dependence of the droplet speed on the initial volume of the droplet and the angle of inclination. Such dependences of speed at long travel distances (100 times the capillary length) were deduced and rationalised with a simple model that takes into account the thickness of the wake. Moreover, we analysed the flow inside the wake of water droplets sliding on inclined frosted glass. Suggestions are given on how to exploit drainage of the water droplet wake and the high hysteresis of water within the framework of open microfluidics.

Electrostatic Preclusion of Droplet Adhesion in a Microchannel

2015 ◽  
Author(s):  
Jonathan C. Hui ◽  
Peter Huang
Keyword(s):  
Thin Film ◽  
Surface Tension ◽  
Charged Droplet ◽  
Thin Film Lubrication ◽  
Threshold Pressure Gradient ◽  
Film Drainage ◽  
Lubrication Layer ◽  
Conduit Wall ◽  
Flow Blockage ◽  
Film Lubrication

In many multiphase fluidic processes, such as in petroleum extraction and biochemical analysis involving microscale conduits, the lodging of immiscible droplets often leads to disastrous flow blockage. Without a thin-film lubrication layer surrounding the adhered droplets, a significantly higher threshold pressure gradient is required to reinitiate bulk flows. In this work, we investigate the surface tension-driven thin-film drainage process that leads to droplet adhesion and study how electrostatic repulsion between a charged droplet interface and a charged conduit wall can prevent direct contact between the two. We report on our multiphysics computational results of an oversized gas droplet in a water-filled flow microchannel under the influence of surface tension and interfacial electrostatic forces.

Density and surface tension of dioctylphthalate, silicone oil and their solutions

1986 ◽  
Vol 28 (2) ◽  
pp. 215-223 ◽  
Author(s):  
E. Ricci ◽  
R. Sangiorgi ◽  
A. Passerone
Keyword(s):  
Surface Tension ◽  
Silicone Oil
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