scholarly journals Experimental study on two consecutive droplets impacting onto an inclined solid surface

2021 ◽  
Vol 37 ◽  
pp. 432-445
Author(s):  
Chun-Kuei Chen ◽  
Sheng-Qi Chen ◽  
Wei-Mon Yan ◽  
Wen-Ken Li ◽  
Ta-Hui Lin
Keyword(s):  
Solid Surface ◽  
Contact Angles ◽  
Maximum Height ◽  
Droplet Spreading ◽  
Droplet Impingement ◽  
Impact Phenomena ◽  
The Moment ◽  
The Impact ◽  
Inclined Surface ◽  
Surface Angle

Abstract The present study is concerned with the experimental impingement of two consecutive droplets on an inclined solid surface. Attention is mainly paid to the effects of impingement timing with various oblique angles (Φ) of the surface on the impact phenomena, which mainly affect the maximum droplet spreading diameter. The investigation considers four impingement scenarios differentiated by impingement timing, namely Case 1: single-droplet impingement; Case 2 of Δt1: the moment when the leading droplet starts spreading along the oblique surface; Case 3 of Δt2: the moment when the leading droplet reaches its maximum spreading; and Case 4 of Δt3: the moment when the leading droplet starts retracting. It is observed that deformation behavior of two successive droplets impacting on the inclined surface experiences a complex asymmetric morphology evolution due to the enhancement of gravity effect and various conditions of the impingement timing. The merged droplet becomes slender with increasing oblique surface angle in the final steady shape, causing the decrease in the value of front and back contact angles. The impingement timing has a significant influence on the change of the maximum height of the merged droplet. The coalesced droplet spreads to the maximum dimensionless width diameter at Δt = Δt2 and the oblique angle of Φ = 45°, but reaches the maximum dimensionless height for Δt = Δt2 at Φ = 30°. The front contact angles converge to a fixed value eventually for all conditions of impingement timing, and the values become lower with the increasing surface inclination.

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.

scholarly journals The effects of surface tension on the spreading ratio during the impact of multiple droplets onto a hot solid surface

2018 ◽  
Vol 197 ◽  
pp. 08016
Author(s):  
Rafil Arizona ◽  
Teguh Wibowo ◽  
Indarto Indarto ◽  
Deendarlianto Deendarlianto
Keyword(s):  
Surface Tension ◽  
Ethylene Glycol ◽  
Solid Surface ◽  
High Speed ◽  
Frame Rate ◽  
Stainless Steel Surface ◽  
Droplet Spreading ◽  
Secondary Droplets ◽  
The Impact ◽  
Maximum Spreading

The impact between multiple droplets onto hot surface is an important process in a spray cooling. The present study was conducted to investigate the dynamics of multiple droplet impact under various surface tensions. Here, the ethylene glycol with compositions of 0%, 5%, and 15% was injected through a nozzle onto stainless steel surface as the multiple droplet. The solid surface was heated at the temperatures of 100 °C, 150 °C, and 200 °C. To observe the dynamics of multiple droplets, a high speed camera with the frame rate of 2000 fps was used. A technique of image processing was developed to determine the maximum droplet spreading ratio. As the result, the surface tension contributes significantly to maximum spreading ratio. As the droplet surface tension decreases, the maximum spreading ratio increases. The maximum spreading ratio appears when the percentage of the ethylene glycol is 15% at the temperature of 150°C. From the visual observation, it is shown that a slower emergence of secondary droplets (droplet splashing) is carried out under a lower surface tension. Hence, surface tension plays an important role on the behavior of emerging secondary droplets. Furthermore, results of the experiments are useful for the validation of available previous CFD models.

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.

Computational Simulation of the Impact and Freezing of Micron-Size Water Droplets on Super-Hydrophobic Surfaces

2013 ◽  
Author(s):  
Mehdi Raessi ◽  
Miranda Thiele ◽  
Behrooz Amirzadeh
Keyword(s):  
Surface Temperature ◽  
Freezing Point ◽  
Computational Study ◽  
Computational Simulation ◽  
Contact Angles ◽  
Water Droplets ◽  
Hydrophobic Surfaces ◽  
Droplet Spreading ◽  
Micron Size ◽  
The Impact

We present a computational study on the dynamics and freezing of micron-size water droplets impinging onto super-hydrophobic surfaces, the temperatures of which are below the freezing point of water. Icing poses a great challenge for many industries. It is well known that increasing hydrophobicity can make a surface ice-phobic. Experiments show that millimeter size water drops landing on super-hydrophobic surfaces bounce off even when the surface temperature is well below the freezing point. However, it has been reported that the ice-phobicity feature of such surfaces can vanish due to frost formation on the surface, or when small micro-droplets begin to freeze and stick to the surface. Using an in-house, 3D, GPU-accelerated computational tool, we investigated the impact dynamics and freezing of a 40 μm water droplet impinging at 1.4 m/s onto two different super-hydrophobic surfaces chosen from [1]. The advancing and receding contact angles are 165° and 133°, respectively, on one surface, and 157° and 118°, respectively, on the other. The surface and initial droplet temperatures were varied from −25 to 25°C and from 0 to 25°C, respectively. On each surface a “transition” surface temperature was found, at which the drop behavior transitions from bouncing off the surface to sticking. The time between drop landing and bounce-off as well as the contact diameter between the stuck drop and the surface both increase with decreasing the surface temperature. The simulations also show that at some surface temperatures a thin ice layer forms during droplet spreading and then remelts as the droplet recoils.

Bubble Formation at Impingement of a Liquid Droplet on a Solid Surface

2000 ◽  
Author(s):  
Hitoshi Fujimoto ◽  
Tomoyuki Ogino ◽  
Osamu Takahashi ◽  
Hirohiko Takuda ◽  
Natsuo Hatta
Keyword(s):  
Solid Surface ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Bubble Formation ◽  
Liquid Droplets ◽  
Vapor Bubbles ◽  
Experimental Conditions ◽  
Video Cameras ◽  
The Moment ◽  
The Impact

Abstract The collision of liquid droplets with a solid has been studied experimentally. The time evolution of the liquid/solid contact area as well as the shape of droplets has been observed by means of a flash-photographic method using two video cameras. It has been found that some air between the solid surface and the incoming droplet is entrapped at the moment of impact. In the case where the solid temperature is high (= 450 °C), numerous vapor bubbles appear at the liquid/solid interface after the collision. The bubble formation due to the entrapment of air has been examined for various experimental conditions. Water, and ethanol are used as test liquid. The droplet diameter is 2.4 mm for water and 1.9 mm for ethanol. The impact velocity varies from 0.8 to 3.1 m/s. The entrapment of air has been observed for both liquids under all conditions in the present study.

Shape Characterization for Droplet Impingement Dynamics in Ink-Jet Deposition

2012 ◽  
Author(s):  
Wenchao Zhou ◽  
Drew Loney ◽  
Andrei G. Fedorov ◽  
F. Levent Degertekin ◽  
David W. Rosen
Keyword(s):  
Deposition Process ◽  
Shape Evolution ◽  
Droplet Deposition ◽  
Droplet Spreading ◽  
Droplet Impingement ◽  
Droplet Shape ◽  
Part Quality ◽  
Ink Jet ◽  
Jet Printing ◽  
The Impact

The impact of droplets onto a substrate in ink-jet printing is critical for control and optimization of the droplet deposition process to improve part quality and accuracy and to reduce the manufacturing time. However, most previous research on droplet impingement dynamics mainly utilized one metric — the droplet spreading radius, which does not provide enough information for manufacturing purposes. This paper presents a new metric that is relevant to manufacturing by characterizing the droplet shape by measuring the similarity between the droplet shape and a desired shape over time. This enables a model of droplet shape evolution and optimization of the droplet deposition process to build desired geometries. Meanwhile, analyses with this shape metric aids understanding the physics of droplet shape evolution during impingement. A 2-D shape metric is first proposed and test cases are given to validate the effectiveness of the shape metric. Then the definition is extended to characterize 3-D droplet shape. Results also show the 3-D shape metric is effective and robust.

Diffuse-interface modelling of droplet impact

2007 ◽  
Vol 581 ◽  
pp. 97-127 ◽  
Author(s):  
V. V. KHATAVKAR ◽  
P. D. ANDERSON ◽  
P. C. DUINEVELD ◽  
H. E. H. MEIJER
Keyword(s):  
Solid Surface ◽  
Droplet Diameter ◽  
Spectral Element ◽  
Contact Angles ◽  
Diffuse Interface ◽  
Diffuse Interface Model ◽  
Impact Behaviour ◽  
A Value ◽  
Micron Size ◽  
The Impact

The impact of micron-size drops on a smooth, flat, chemically homogeneous solid surface is studied using a diffuse-interface model (DIM). The model is based on the Cahn–Hilliard theory that couples thermodynamics with hydrodynamics, and is extended to include non-90° contact angles. The (axisymmetric) equations are numerically solved using a combination of finite- and spectral-element methods. The influence of various process and material parameters such as impact velocity, droplet diameter, viscosity, surface tension and wettability on the impact behaviour of drops is investigated. Relevant dimensionless parameters are defined and, depending on the values of the Reynolds number, the Weber number and the contact angle, which for the cases considered here range from 1.3 to 130, 0.43 to 150 and 45° to 135°, respectively, the model predicts the spreading of a droplet with or without recoil or even rebound of the droplet, totally or partially, from the solid surface. The wettability significantly affects the impact behaviour and this is particularly demonstrated with an impact at Re = 130 and We = 1.5, where for θ < 60° the droplet oscillates a few times before attaining equilibrium while for θ ≥ 60° partial rebound of the droplet occurs, i.e. the droplet breaks into two unequal sized drops. The size of the part that remains in contact with the solid surface progressively decreases with increasing θ until at a value θ ≈ 120° a transition to total rebound happens. When the droplet rebounds totally, it has a top-heavy shape.

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.

Contact time of impacting droplets on a superhydrophobic surface with tunable curvature and groove orientation

2021 ◽  
Author(s):  
Chunfang Guo ◽  
Lei Liu ◽  
Changwan Liu
Keyword(s):  
Weber Number ◽  
Contact Time ◽  
Superhydrophobic Surface ◽  
The Other ◽  
Impact Dynamics ◽  
Azimuthal Direction ◽  
Droplet Spreading ◽  
Droplet Impingement ◽  
Practical Applications ◽  
The Impact

Abstract Regulating the impact dynamics of water droplets on a solid surface is of great significance for some practical applications. In this study, the droplet impingement on a flexible superhydrophobic surface arrayed with micro-scale grooves is investigated experimentally. The surface was curved into cylindrical shapes with certain curvatures from two orthogonal directions, where axial and circumferential grooves were formed, respectively. The effects of curvature diameter and Weber number, as well as the orientation of grooves on droplet spreading and retracting dynamics were discussed and explained. Results show that the circumferential grooves promote the spreading of droplet in the azimuthal direction, where the droplet rebounds from the surface with a stretched shape. This mechanism further reduces the contact time of impacting droplets on the superhydrophobic surface compared to the other curving mode.

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.

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