Droplet Oscillation After Impact on a Solid Surface

2016 ◽  
Author(s):  
Yina Yao ◽  
Shuai Meng ◽  
Cong Li ◽  
Xiantao Chen ◽  
Rui Yang
Keyword(s):  
Contact Angle ◽  
Spray Deposition ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Oscillation Period ◽  
Droplet Spreading ◽  
Oscillation Phenomenon ◽  
The Impact

Droplet spreading and oscillation occur when a liquid droplet impacts on the solid surfaces. This process is vital in many industrial applications, such as ink-jet printing technologies, spray coating and agricultural spray deposition. However, the researches that have been done mainly focused on the spreading process, and less attention has been paid to the droplet oscillation phenomenon, which has influence on the solidification and evaporation process. Therefore, the study on droplet oscillation phenomenon after the impact is necessary and valuable. This paper aims at analyzing the droplet oscillation phenomenon using VOF method. Since the contact angle varies dramatically in the dynamic process, a dynamic contact angle model is introduced to improve the simulation accuracy. The dynamic contact angle model has been verified by comparing the numerical results with experimental and theoretical results. In order to study the factors that may influence the droplet oscillation period, different droplet diameters and impact velocities are utilized in this simulation. The results show that the oscillation period presents a positive relationship with droplet diameter. However, the impact velocity has no apparent influence on the oscillation period, which agrees well with the theoretical analysis.

Simulation of Spreading Dynamics of a EWOD Droplet With Dynamic Contact Angle and Contact Angle Hysteresis

2009 ◽  
Author(s):  
Fangjun Hong ◽  
Ping Cheng ◽  
Zhen Sun ◽  
Huiying Wu
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Low Voltage ◽  
Contact Angle Hysteresis ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Dielectric Surface ◽  
Contact Radius ◽  
Droplet Spreading ◽  
Spreading Dynamics

In this paper, the electrowetting dynamics of a droplet on a dielectric surface was investigated numerically by a mathematical model including dynamic contact angle and contact angle hysteresis. The fluid flow is described by laminar N-S equation, the free surface of the droplet is modeled by the Volume of Fluid (VOF) method, and the electrowetting force is incorporated by exerting an electrical force on the cells at the contact line. The Kilster’s model that can deal with both receding and advancing contact angle is adopted. Numerical results indicate that there is overshooting and oscillation of contact radius in droplet spreading process before it ceases the movement when the excitation voltage is high; while the overshooting is not observed for low voltage. The explanation for the contact line overshooting and some special characteristics of variation of contact radius with time were also conducted.

A METHOD TO CHARACTERIZE MATERIALS TO BE USED ON OLEOPHILIC SKIMMERS1

2005 ◽  
Vol 2005 (1) ◽  
pp. 837-840 ◽  
Author(s):  
Victoria A. Broje ◽  
Arturo A. Keller
Keyword(s):  
Contact Angle ◽  
Oil Spill ◽  
Oil Spills ◽  
Dynamic Contact Angle ◽  
Polymeric Materials ◽  
Dynamic Contact ◽  
Test Surface ◽  
Oil Composition ◽  
Scientific Equipment ◽  
The Impact

ABSTRACT A significant amount of effort is being devoted by scientists and industry in order to increase the efficiency of oil spill recovery equipment as it determines the impact of oil spills on coastal ecosystems as well as the time and cost of cleanup operations. One way to increase the efficiency of adhesion skimmers is to replace traditional recovery materials with polymeric materials that have the highest affinity for oil. The research conducted at the University of California Santa Barbara has shown that modern scientific equipment such as a Dynamic Contact Angle Analyzer can be used for evaluation of candidate materials and selection of materials that can be most efficiently used for oil spill cleanup. The study found that the contact angle formed between oil and test surface can be used to characterize the affinity of material to oil. The contact angle correlates well with the mass of recovered oil. For a given oil, the lower the contact angle the higher the recovered mass. The study also showed that surface roughness and oil composition have a significant effect on the results of the adhesion tests. Higher roughness results in lower contact angle and larger recovered mass, for the same oil-polymer pair.

scholarly journals Not spreading in reverse: The dewetting of a liquid film into a single drop

2016 ◽  
Vol 2 (9) ◽  
pp. e1600183 ◽  
Author(s):  
Andrew M. J. Edwards ◽  
Rodrigo Ledesma-Aguilar ◽  
Michael I. Newton ◽  
Carl V. Brown ◽  
Glen McHale
Keyword(s):  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Equilibrium Contact Angle ◽  
Droplet Spreading ◽  
Spherical Cap ◽  
Liquid Marbles ◽  
Exponential Relaxation ◽  
Wetting Process ◽  
Fluid Manipulation

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet—a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.

Effect of Dynamic Contact Angle on Single/Successive Droplet Impingement

2007 ◽  
Author(s):  
S. Sangplung ◽  
J. A. Liburdy
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Solid Surface ◽  
Contact Line ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Droplet Impingement ◽  
Spreading Velocity ◽  
Fluid Properties ◽  
The Impact

Successive droplet impingement onto a solid surface is numerically investigated using a CFD multiphase flow model (VOF method). The main focus of this study is to better understand the hydrodynamics of the non-splash impingement process, particularly the effect of a dynamic contact angle and fluid properties along with the interaction between successive droplets while they are impinging onto a solid surface. The pre-impact droplet conditions are prescribed based on a spherical droplet diameter, velocity, and inter-droplet spacing. The molecular kinetic theory is used to model the dynamic contact angle as a function of a contact line velocity. The numerical scheme is validated against experiment results. In the impact spreading and receding processes, results are analyzed to determine the nondimensional deformation characteristics of both single and successive droplet impingements with the variation of fluid properties such as surface tension and dynamic viscosity. These characteristics include spreading ratio, spreading velocity, and a dynamic contact angle. The inclusion of a dynamic contact angle is shown to have a major effect on droplet spreading. In successive droplet impingement, the second drop causes a surge of spreading velocity and contact angle with an associate complex recirculating flow near the contact line after it initially impacts the preceding droplet when it is in an advancing condition. This interaction is less dramatic when the first drop is receding or stationary. The surface tension has the most effect on the maximum spreading radius in both single and successive droplet impingements. In contrast to this, the viscosity directly affects the damping of the spreading-receding process.

Fuel Drop Spreading on a Flat Smooth Surface: Numerical Simulations With a VOF Method

2010 ◽  
Author(s):  
Yan Zhang ◽  
Albert Ratner
Keyword(s):  
Contact Angle ◽  
Smooth Surface ◽  
Variable Viscosity ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Static Contact Angle ◽  
Drop Spreading ◽  
Static Contact ◽  
Commercial Solver ◽  
The Impact

With the current interest in bio-derived and blended transportation fuels, the impact of the variable viscosity in these fuels on spray and splash properties has become an area of concern. In this work, the dynamics of a liquid drop impacting and spreading on a flat, smooth surface was computationally investigated by employing the volume of fluid (VOF) approach with the commercial solver Fluent 12.0.16, and the results were base-lined with experimental measurements. Of particular interest was the degree of fidelity required of the contact angle model, with the present work proposing and testing a combined static contact angle-dynamic contact angle (SCA-DCA) model to describe drop spreading. This model was shown to reduce the behavior information required as compared with full dynamic contact angle (DCA) models while significantly improving over the accuracy of a pure static contact angle (SCA) model. Two different computational domains were tested and compared for the proposed SCA-DCA model, a quarter-drop versus a full-drop domain, with the results showing that the error was reduced when the full domain was employed.

Investigation of behavior of the dynamic contact angle in a problem of convective flows

2017 ◽  
Vol 5 (4) ◽  
pp. 27-42
Author(s):  
O.N Goncharova ◽  
◽  
I.V. Marchuk ◽  
A.V. Zakurdaeva ◽  
◽  
...  
Keyword(s):  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Convective Flows
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