Impact and Spreading of a Microdroplet on a Solid Wall

2009 ◽  
Author(s):  
Metin Muradoglu ◽  
Savas Tasoglu
Keyword(s):  
Contact Angle ◽  
Single Cell ◽  
Numerical Method ◽  
Solid Wall ◽  
Spreading Rate ◽  
Solid Substrate ◽  
Droplet Spreading ◽  
Front Tracking Method ◽  
Static Contact ◽  
The Impact

Impact and spreading of a viscous micro droplet on dry solid surfaces are studied computationally using a finite-difference/front-tracking method. The problem is motivated by single cell epitaxy developed for printing biological cells on a solid substrate using ink-jet printer technology. In this study, we consider impact and spreading of a simple droplet on a partially wetting substrate as a first step in developing a complete compound droplet model for the single cell epitaxi. The numerical method is general and can treat non-wetting, partially wetting and fully wetting cases but the focus here is placed on partially wetting substrates. The contact angle is specified dynamically using the empirical correlation given by Kistler (1993). In addition, a precursive film model is also used especially for the highly wettable cases, i.e., the static contact angle is smaller than 30° due to numerical difficulty of resolving thin liquid later penetrating into surrounding gas near the solid surface. The numerical method is first applied to simple droplet spreading and the results are compared with experimental data of Sikalo et al. (2005). Then the effects of governing non-dimensional numbers on the spreading rate, apparent contact angle and deformation of the droplet are investigated. Finally a few preliminary results are presented for the impact and spreading of a compound microdroplet on a partially wetting surface.

Modeling of Transport During Droplet Deposition and Spreading on Smooth and Microstructured Superhydrophilic Surfaces

2016 ◽  
Author(s):  
Jordan P. Mizerak ◽  
Van P. Carey
Keyword(s):  
Contact Angle ◽  
Contact Angles ◽  
Ansys Fluent ◽  
Effective Contact ◽  
Microstructured Surfaces ◽  
Static Contact ◽  
Droplet Behavior ◽  
Contact Line Pinning ◽  
The Impact ◽  
Superhydrophilic Surfaces

The dynamic behavior of impinging water droplets is studied in the context of varying surface morphologies on smooth and microstructured superhydrophilic surfaces. The goal of this study is to evaluate the capability of contact angle wall adhesion models to accurately produce spreading phenomena seen on a variety of surface types. We analyze macroscale droplet behavior, specifically spreading extent and impinging regime, in situations of varying microscale wetting character and surface morphology. Axisymmetric, volume of fluid (VOF) simulations with static contact angle wall adhesion are conducted in ANSYS Fluent. Simulations are performed on water for low Weber numbers (We<20) on surfaces with features of length scale 5–10μm. Advanced microstructured surfaces consisting of unique wetting characteristics and lengths on each face are also tested. Results show that while the contact angle wall adhesion model shows fair agreement for conventional surfaces, the model underestimates spreading by over 60% for surfaces exhibiting estimated contact angles below approximately 0.5°. Microstructured surfaces adapt the wetting behavior of smooth surfaces with higher effective contact angles based on contact line pinning on morphology features. The propensity of the model to produce Wenzel and Cassie-Baxter states is linked to the spreading radius, introducing an interdependency of microscale wetting and macroscale spreading behavior. Conclusions describing the impact of results on evaporative cooling are also discussed.

scholarly journals Numerical Simulations of the Impact and Spreading of a Particulate Drop on a Solid Substrate

2012 ◽  
Vol 2012 ◽  
pp. 1-10
Author(s):  
Hyun Jun Jeong ◽  
Wook Ryol Hwang ◽  
Chongyoup Kim
Keyword(s):  
Numerical Simulations ◽  
Solid Surface ◽  
Reynolds Numbers ◽  
Suspended Particles ◽  
Solid Substrate ◽  
Oscillatory Behavior ◽  
Navier Stokes ◽  
Droplet Spreading ◽  
Navier Stokes Equation ◽  
The Impact

We present two-dimensional numerical simulations of the impact and spreading of a droplet containing a number of small particles on a flat solid surface, just after hitting the solid surface, to understand particle effects on spreading dynamics of a particle-laden droplet for the application to the industrial inkjet printing process. The Navier-Stokes equation is solved by a finite-element-based computational scheme that employs the level-set method for the accurate interface description between the drop fluid and air and a fictitious domain method for suspended particles to account for full hydrodynamic interaction. Focusing on the particle effect on droplet spreading and recoil behaviors, we report that suspended particles suppress the droplet oscillation and deformation, by investigating the drop deformations for various Reynolds numbers. This suppressed oscillatory behavior of the particulate droplet has been interpreted with the enhanced energy dissipation due to the presence of particles.

Detection of Advancing Edge and Existing Length of Precursor Film Ahead Macroscopic Contact Line of Droplet Spreading on Solid Substrate

2008 ◽  
Author(s):  
Ichiro Ueno
Keyword(s):  
Contact Line ◽  
High Speed ◽  
Thin Liquid Film ◽  
Experimental Studies ◽  
Laser Interferometry ◽  
Spreading Rate ◽  
Solid Substrate ◽  
Precursor Film ◽  
Boundary Line ◽  
Droplet Spreading

The author introduces a series of experimental studies on a simple but complex wetting process; a droplet spreads on a solid substrate. The spreading droplet on the solid substrate is accompanied with the movement of a visible boundary line so-called ‘macroscopic contact line.’ Existing studies have indicated there exits a thin liquid film known as ‘precursor film’ ahead the macroscopic contact line of the droplet. The present author’s group has dedicated their special effort to detect the advancing edge of the precursor film by applying a convectional laser interferometry and a high-speed camera, and to evaluate the spreading rate of the precursor film.

On the Boundary Condition for the Level Set Function in the Numerical Simulation of Moving Contact Lines

2020 ◽  
Author(s):  
Pablo Gómez ◽  
Adolfo Esteban ◽  
Claudio Zanzi ◽  
Joaquín López ◽  
Julio Hernández
Keyword(s):  
Boundary Condition ◽  
Contact Angle ◽  
Level Set ◽  
Contact Line ◽  
Solid Wall ◽  
Interfacial Flows ◽  
Moving Contact ◽  
Level Set Function ◽  
Static Contact ◽  
Set Function

Abstract We present a method based on a level set formulation to reproduce the behavior of the contact line on solid walls in the simulation of 3D unsteady interfacial flows characterized by large density ratios. The level set method poses a particular difficulty, related to the reinitialization procedure, when used in the simulation of interfacial flows in which the interface intersects a solid wall, due to the appearance of a blind zone where standard reinitialization procedures produce inconsistent results. The proposed method overcomes this difficulty by introducing a boundary condition for the level set function on the solid surface based on the normal extension of the contact angle from the interface along the solid wall. In order to reproduce the dynamics of the contact line we use a simplified model that imposes a boundary condition on the interface curvature based on the static contact angle, and define a thin slip zone at the solid wall around the contact line. To assess the accuracy and robustness of the proposed method, we conducted several preliminary numerical tests in three dimensions, whose results are compared with analytical solutions and other results available in the literature.

Numerical study of the melting and resolidification of the substrate during the impact of a ceramic droplet in a plasma spraying process

2019 ◽  
Vol 88 (2) ◽  
pp. 20901 ◽  
Author(s):  
Mouloud Driouche ◽  
Tahar Rezoug ◽  
Mohammed El Ganaoui
Keyword(s):  
Numerical Model ◽  
Phase Change ◽  
Solid Phase ◽  
Numerical Study ◽  
Solid Substrate ◽  
Navier Stokes ◽  
Droplet Spreading ◽  
Substrate Melting ◽  
Volume Method ◽  
The Impact

The substrate melting can significantly improve the properties of plasma spray coatings. Indeed the adhesion of the projected particles to the substrate can be ameliorated by the substrate melting. In this article, a numerical model is developed to study the dynamics of fluids and heat transfer with liquid/solid phase change during impact of a fully melted alumina particle on an aluminum solid substrate, taking into account of the substrate melting. The model is based on solving the Navier-Stokes and energy equations with liquid / solid phase change. These equations are coupled with the fluid of volume method (VOF), to follow the free surface of the particle during its spreading and solidification. The finite volume method is used to discretize the equations in a 2D axisymmetric domain. A comparison with the published experimental results was carried out to validate this numerical model. Simulations were performed for different initial droplet diameters to study its effect on droplet spreading as well as on substrate melting. It has been observed that the substrate melting begins before the droplet spreads completely; the substrate melting reaches its maximum when the droplet is close to its total solidification. Droplet spreading and substrate melting are more important for large sizes droplets.

Rupture of thin films formed during droplet impact

2009 ◽  
Vol 466 (2116) ◽  
pp. 1229-1245 ◽  
Author(s):  
Rajeev Dhiman ◽  
Sanjeev Chandra
Keyword(s):  
Impact Velocity ◽  
Liquid Films ◽  
Solid Substrate ◽  
Contact Angles ◽  
Droplet Impact ◽  
Film Rupture ◽  
Droplet Spreading ◽  
Spreading Model ◽  
Wide Range ◽  
The Impact

Rupture of liquid films formed during droplet impact on a dry solid surface was studied experimentally. Water droplets (580±70 μm) were photographed as they hit a solid substrate at high velocities (10–30 m s −1 ). Droplet–substrate wettability was varied over a wide range, from hydrophilic to superhydrophobic, by changing the material of the substrate (glass, Plexiglas, wax and alkylketene dimer). Both smooth and rough wax surfaces were tested. Photographs of impact showed that as the impact velocity increased and the film thickness decreased, films became unstable and ruptured internally through the formation of holes. However, the impact velocity at which rupture occurred was found to first decrease and then increase with the liquid–solid contact angle, with wax showing rupture at all impact velocities tested. A thermodynamic stability analysis combined with a droplet spreading model predicted the rupture behaviour by showing that films would be stable at very small or at very large contact angles, but unstable in between. Film rupture was found to be greatly promoted by surface roughness.

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.

scholarly journals Observation of contact angle hysteresis due to inhomogeneous electric fields

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wei Wang ◽  
Qi Wang ◽  
Jia Zhou ◽  
Antoine Riaud
Keyword(s):  
Contact Angle ◽  
Free Energy ◽  
Electric Fields ◽  
Contact Angle Hysteresis ◽  
Dynamic Control ◽  
Static Contact Angle ◽  
Chemical Contamination ◽  
Sample Collection ◽  
Droplet Spreading ◽  
Static Contact

AbstractStatic contact angle hysteresis determines droplet stickiness on surfaces, and is widely attributed to surface roughness and chemical contamination. In the latter case, chemical defects create free-energy barriers that prevent the contact line motion. Electrowetting studies have demonstrated the similar ability of electric fields to alter the surface free-energy landscape. Yet, the increase of apparent static contact angle hysteresis by electric fields remains unseen. Here, we report the observation of electrowetting hysteresis on micro-striped electrodes. Unlike most experiments with stripes, the droplet spreading on the substrate is experimentally found to be isotropic, which allows deriving a simple theoretical model of the contact angle hysteresis depending the applied voltage. This electrowetting hysteresis enables the continuous and dynamic control of contact angle hysteresis, not only for fundamental studies but also to manufacture sticky-on-demand surfaces for sample collection.

scholarly journals Effect of Chemical Modification on Mechanical Properties of Wood-Plastic Composite Injection-Molded Parts

Polymers ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1391 ◽  
Author(s):  
Joo Sohn ◽  
Sung Cha
Keyword(s):  
Contact Angle ◽  
Chemical Modification ◽  
Wood Flour ◽  
Flexural Modulus ◽  
Wood Plastic Composite ◽  
Plastic Composite ◽  
Furniture Manufacturing ◽  
Static Contact ◽  
Injection Molded ◽  
The Impact

Wood chips from furniture-manufacturing byproducts, which do not include adhesive or paint in the waste wood, were used for the flouring process and chemical modification of wood flour (WF). After chemical modification, the WF was mixed with polypropylene through extrusion compounding and injection-molding to prepare wood-plastic composite (WPC) injection-molded specimens for the American Society for Testing and Materials. Static contact angle measurements and stereomicroscope observations were performed. In this study, it was confirmed that the impact strength was improved by up to 55.8% and the tensile strength by up to 33.8%. The flexural modulus decreased marginally. As a result of WF chemical modification, the measured contact angle of WPC increased, which means that the wettability of the WPC specimen surface decreased. In addition, it was observed through stereomicroscopy that the whitening of the surface of the WPC specimen improved.

Numerical Simulation of Droplet Impact on an Isothermal Micro-Grooved Solid Surface

2010 ◽  
Author(s):  
Yujia Tao ◽  
Xiulan Huai ◽  
Zhigang Li
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Solid Surface ◽  
Initial Velocity ◽  
Surface Tension Coefficient ◽  
Liquid Region ◽  
Spreading Factor ◽  
Droplet Spreading ◽  
Droplet Dynamics ◽  
The Impact

The process of a micro droplet of distilled water impact on an isothermal micro-grooved solid surface is numerical simulated in this paper. To accurately represent the droplet dynamics, special attention is given to the variation of the droplet pressure and velocity, the movement of the free surface between two fluids and the deforming of the droplet after impact. The Volume Of Fluid method is used to track the position and the shape of the liquid region. The PISO algorithm is selected to solve the pressure-velocity coupling. The influences of the droplet initial velocity, the contact angle for water on the surface perpendicular to the groove direction and the surface tension coefficient on the impact process are discussed in detail. The results show that the droplet spreading factor improves notably with the increase of the initial velocity, and reduces with the increase of the contact angle. When the surface tension coefficient increases, the spreading factor reduces greatly. The spreading factor is the largest and the time elapsing is the longest in the case of σ = 0.038 N/m.

Sign in / Sign up

Export Citation Format

Share Document