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.

scholarly journals Pressure generated at the instant of impact between a liquid droplet and solid surface

2018 ◽  
Vol 5 (12) ◽  
pp. 181101 ◽  
Author(s):  
Y. Tatekura ◽  
M. Watanabe ◽  
K. Kobayashi ◽  
T. Sanada
Keyword(s):  
Solid Surface ◽  
Shape Factor ◽  
Liquid Droplet ◽  
Pressure Rise ◽  
Propagation Speed ◽  
Spherical Shape ◽  
Water Hammer ◽  
Droplet Impact ◽  
Maximum Pressure ◽  
The Impact

The prime objective of this study is to answer the question: How large is the pressure developed at the instant of a spherical liquid droplet impact on a solid surface? Engel first proposed that the maximum pressure rise generated by a spherical liquid droplet impact on a solid surface is different from the one-dimensional water-hammer pressure by a spherical shape factor (Engel 1955 J. Res. Natl Bur. Stand. 55 (5), 281–298). Many researchers have since proposed various factors to accurately predict the maximum pressure rise. We numerically found that the maximum pressure rise can be predicted by the combination of water-hammer theory and the shock relation; then, we analytically extended Engel’s elastic impact model, by realizing that the progression speed of the contact between the gas–liquid interface and the solid surface is much faster than the compression wavefront propagation speed at the instant of the impact. We successfully correct Engel’s theory so that it can accurately provide the maximum pressure rise at the instant of impact between a spherical liquid droplet and solid surface, that is, no shape factor appears in the theory.

Acoustic Cloud Condensation Nuclei Counter

2005 ◽  
Author(s):  
Abhijit Deshpande ◽  
Marcellin Zahui
Keyword(s):  
Water Surface ◽  
Cloud Condensation Nuclei ◽  
Droplet Diameter ◽  
Bubble Formation ◽  
Maximum Velocity ◽  
Acoustic Energy ◽  
Water Droplets ◽  
Condensation Nuclei ◽  
Micro Scale ◽  
The Impact

Analysis and simulation of an acoustic cloud condensation nuclei counter is presented. The instrument is capable of accurately counting the number of micro scale water droplets impacting a water surface. The sound produced underwater by the water droplets is determined when the droplets strike the water surface with an impact velocity equal to either their terminal or maximum velocity. First, the terminal velocities of the droplets are calculated using Stoke’s law and compared to measured velocities from Gunn and Kinzer. Then the maximum velocities that these droplets can sustain without breaking are calculated as a function of droplet diameter. Second, the sound due to droplet impact is estimated. Due to their size and water surface tension, there is no bubble formation at impact when the droplets are falling with terminal velocities. However conditions for regular bubble entrainments are established and limit velocities are calculated. Assuming that the micro water droplets can be accelerated, the maximum velocities for no bubble entrainments are calculated. The results show that the level of the sound produced by individual micro scale droplet falling with terminal velocity is so small that experimental verification is not possible. However, reasonable level of acoustic energy can be obtained by increasing the impact velocities of the droplets or by measuring the sound radiated by a group of impacting droplets. Finally, the droplets counting process is simulated using a water surface of one centimeter squared and a vertical growth chamber.

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.

The mechanism of a splash on a dry solid surface

2011 ◽  
Vol 690 ◽  
pp. 148-172 ◽  
Author(s):  
Shreyas Mandre ◽  
Michael P. Brenner
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Liquid Droplet ◽  
Contact Point ◽  
Quantitative Agreement ◽  
Gas Pressure ◽  
Liquid Viscosity ◽  
Ink Jet ◽  
Jet Printing ◽  
The Impact

AbstractFrom rain storms to ink jet printing, it is ubiquitous that a high-speed liquid droplet creates a splash when it impacts on a dry solid surface. Yet, the fluid mechanical mechanism causing this splash is unknown. About fifty years ago it was discovered that corona splashes are preceded by the ejection of a thin fluid sheet very near the vicinity of the contact point. Here we present a first-principles description of the mechanism for sheet formation, the initial stages of which occur before the droplet physically contacts the surface. We predict precisely when sheet formation occurs on a smooth surface as a function of experimental parameters, along with conditions on the roughness and other parameters for the validity of the predictions. The process of sheet formation provides a semi-quantitative framework for studying the subsequent events and the influence of liquid viscosity, gas pressure and surface roughness. The conclusions derived from this framework are in quantitative agreement with previous measurements of the splash threshold as a function of impact parameters (the size and velocity of the droplet) and in qualitative agreement with the dependence on physical properties (liquid viscosity, surface tension, ambient gas pressure, etc.) Our analysis predicts an as yet unobserved series of events within micrometres of the impact point and microseconds of the splash.

scholarly journals Optical Technique to Measure Transient Interface Temperature During Droplet Impingement on a Cooled Surface

2000 ◽  
Author(s):  
Y. Li ◽  
J. P. Longtin
Keyword(s):  
Laser Beam ◽  
Temperature Change ◽  
Temporal Resolution ◽  
Solid Surface ◽  
Liquid Droplet ◽  
Liquid Interface ◽  
Temperature History ◽  
Interface Temperature ◽  
Measured Temperature ◽  
Liquid Droplets

Abstract Liquid droplets impinging upon a solid surface are present in many diverse and important engineering and scientific applications. Examples include impingement cooling of surfaces, condensation phenomena in which liquid droplets fall and strike a surface, vigorous mixing of gas-liquid systems, and in manufacturing, e.g., pouring a liquid material onto a cooled surface or mold to form objects. The accurate measurement of the solid-liquid interface temperature of a liquid droplet impinging on a solid surface is extremely difficult to do using traditional, contact-based techniques, however. This work presents a laser-based technique that is capable of resolving the transient interface temperature change as a liquid droplet strikes a surface. The measurement records changes in reflected light from the liquid-solid interface, which is correlated to temperature change. In this work, the substrate is BK7 glass or quartz. The liquid falls from a height of several centimeters, while the laser beam is sent through the transparent solid material from the underside for the measurement. Results are presented for water and glycerin, with good agreement found between predicted and measured temperature histories. Additional features of the technique include extremely fast temporal resolution, which is limited only by the speed of the light-capturing electronics. A temporal resolution of 1 microsecond is readily obtainable with inexpensive electronics. Also, the use of a high-quality Gaussian laser beam from, e.g., a HeNe laser or a single-mode fiber can be focused to a spot size ranging from several millimeters to 10 microns in diameter at the liquid interface, thus providing a wide variety of spatial resolutions, including those in the microscale. Finally, an array of interrogation beams can be employed simultaneously to monitor the spatial temperature history of a droplet as it spreads and cools once striking the surface. Both present and future applications of the technique will be discussed in the talk.

Numerical study for the impact of liquid droplets on solid surfaces

2007 ◽  
Vol 221 (3) ◽  
pp. 293-301 ◽  
Author(s):  
A-S Yang ◽  
M-T Yang ◽  
M-C Hong
Keyword(s):  
Indium Tin Oxide ◽  
Numerical Study ◽  
Liquid Droplet ◽  
Solid Surfaces ◽  
Stainless Steel Surface ◽  
Force Model ◽  
Liquid Droplets ◽  
Construction Technique ◽  
Practical Applications ◽  
The Impact

The impinging behaviour of liquid droplets on solid surfaces is studied using a computational approach. The analysis comprises the unsteady three-dimensional conservation equations of mass and momentum, with the surface tension effect treated by the continuous surface force model. Gas-liquid interfacial motions are simulated by the volume-of-fluid method in conjunction with the piecewise linear interface construction technique. In the computer code validation for a water droplet impacting on a polished stainless steel surface, computer-generated images of the time evolution of the droplet impingement dispersal shape are compared with magnified photographs by Pasandideh-Fard et al. The flow and transport phenomena in the impingement flowfield are further examined in detail. In order to respond to the need for its use in practical applications, the study is extended to explore the spreading progression to achieve a better understanding of the interaction of a 30 μm diameter polyethylenedioxy thiophene liquid droplet with a 50 × 50 μm indium tin oxide-coating square cavity at an impact velocity of 6 m/s.

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.

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.

Events before droplet splashing on a solid surface

2010 ◽  
Vol 647 ◽  
pp. 163-185 ◽  
Author(s):  
MADHAV MANI ◽  
SHREYAS MANDRE ◽  
MICHAEL P. BRENNER
Keyword(s):  
Surface Tension ◽  
Solid Surface ◽  
Liquid Droplet ◽  
Thin Sheet ◽  
Initial Contact ◽  
Viscous Forces ◽  
Self Similar Solution ◽  
Self Similar ◽  
Physical Effects ◽  
The Impact

A high-velocity (≈1 ms−1) impact between a liquid droplet (≈1 mm) and a solid surface produces a splash. Classical observations traced the origin of this splash to a thin sheet of fluid ejected near the impact point, though the fluid mechanical mechanism leading to the sheet is not known. Mechanisms of sheet formation have heretofore relied on initial contact of the droplet and the surface. In this paper, we theoretically and numerically study the events within the time scale of about 1 μs over which the coupled dynamics between the gas and the droplet becomes important. The droplet initially tries to contact the substrate by either draining gas out of a thin layer or compressing it, with the local behaviour described by a self-similar solution of the governing equations. This similarity solution is not asymptotically consistent: forces that were initially negligible become relevant and dramatically change the behaviour. Depending on the radius and impact velocity of the droplet, we show that the solution is overtaken by initially subdominant physical effects such as the surface tension of the liquid–gas interface or viscous forces in the liquid. At low impact velocities surface tension stops the droplet from impacting the surface, whereas at higher velocities viscous forces become important before surface tension. The ultimate dynamics of the interface once droplet viscosity cannot be neglected is not yet known.

scholarly journals Algorithms for Particle Detection in Complex Plasmas

2019 ◽  
Vol 5 (2) ◽  
pp. 30
Author(s):  
Daniel Mohr ◽  
Christina Knapek ◽  
Peter Huber ◽  
Erich Zaehringer
Keyword(s):  
Moment Method ◽  
Granular Matter ◽  
Synthetic Data ◽  
Single Particles ◽  
Particle Detection ◽  
Threshold Detection ◽  
Video Cameras ◽  
The Moment ◽  
Complex Plasmas ◽  
The Impact

In complex plasmas, the behavior of freely floating micrometer sized particles is studied. The particles can be directly visualized and recorded by digital video cameras. To analyze the dynamics of single particles, reliable algorithms are required to accurately determine their positions to sub-pixel accuracy from the recorded images. Typically, a straightforward algorithm such as the moment method is used for this task. Here, we combine different variations of the moment method with common techniques for image pre- and post-processing (e.g., noise reduction and fitting), and we investigate the impact of the choice of threshold parameters, including an automatic threshold detection, on synthetic data with known attributes. The results quantitatively show that each algorithm and method has its own advantage, often depending on the problem at hand. This knowledge is applicable not only to complex plasmas, but useful for any kind of comparable image-based particle tracking, e.g., in the field of colloids or granular matter.

Sign in / Sign up

Export Citation Format

Share Document