Liquid Droplet Impact Over Hydrophobic Mesh Surfaces and Assessment of Weber Number Dependent Characteristics

2022 ◽  
Author(s):  
Abba Abdulhamid Abubakar ◽  
Bekir Sami Yilbas ◽  
Hussain Al-Qahtani ◽  
Anwaruddin Siddiqui Mohammed
Keyword(s):  
Weber Number ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Mesh Size ◽  
Vertical Axis ◽  
Capillary Length ◽  
Flat Surfaces ◽  
Mesh Surface ◽  
Droplet Behavior ◽  
Fluid Penetration

Abstract Impacting droplets and droplet ejection from hydrophobic mesh surfaces have interest in biomedicine, heat transfer engineering, and self-cleaning of surfaces. The rate and the size of newborn droplets can vary depending on, the droplet fluid properties, Weber number, mesh geometry, and surface wetting states. In the present study, impacting water droplets onto hydrophobic mesh surface is investigated and impact properties including, spreading, rebounding, and droplet fluid penetration and ejection rates are examined. Droplet behavior is assessed using high recording facilities and predicted in line with the experiments. The findings reveal that the critical Weber number for droplet fluid penetrating/ejecting from mesh screen mainly depends on the droplet fluid capillary length, and hydrophobic mesh size. The contact time of impacting droplet over mesh surface reduces with increasing droplet Weber number, which opposes the case observed for impacting droplets over flat hydrophobic surfaces. The restitution coefficient attains lower values for impacting droplets over mesh surfaces than that of flat surfaces. The rate and diameter of the ejected droplet from the mesh increases as droplet Weber increases. At the onset of impact, streamline curvature is formed inside droplet fluid, which creates a stagnation zone with radially varying pressure at the droplet fluid mesh interface. This reduces the ejected droplet diameter from mesh cells as mesh cells are located away from the impacting vertical axis.

Numerical Simulation of Liquid Droplet Coalescence and Breakup

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Shuxia Yuan ◽  
Ramin Dabirian ◽  
Ovadia Shoham ◽  
Ram S. Mohan
Keyword(s):  
Weber Number ◽  
Recovery Time ◽  
Relative Velocity ◽  
Shape Recovery ◽  
Liquid Droplet ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Continuous Phase ◽  
Collision Time ◽  
Coalescence Time

Abstract This paper studied the evolution of binary droplet collision in liquid and also a mathematical calculation method of coalescence time. Binary droplet collisions occur in many engineering applications; however, the accurate models to predict the collision of droplets in the liquid are still lacking. In this work, the binary collision processes of droplets were simulated through computational fluid dynamic (CFD) method, where the interfaces between the two phases were tracked by the volume of fluid (VOF) approach. The results reveal that Weber number determines the results of the head-on collisions, and the cases with the same Weber number present similar evolution processes. If coalescence happens, the collision time decreases with increase in relative velocity, whereas the shape recovery time is independent with the relative velocity, but depends on droplet diameter. It is derived from this research that the collision time is proportional to the droplet diameter, and the shape recovery time is proportional to the 3/2 power of droplet diameter. The droplet moving directions play an important role in the collision results, and the case of two droplets moving toward each other with equal velocity is the easiest way to coalesce. When two droplets with different sizes collide, besides relative velocity, the coalescence and breakup are determined by the absolute velocities, the size, and size ratio of the two droplets. The increase in viscosity of continuous phase results an increase in collision time, but decrease in coalescence time.

Dynamics of thin precursor film in wetting of nanopatterned surfaces

2021 ◽  
Vol 118 (38) ◽  
pp. e2108074118
Author(s):  
Utkarsh Anand ◽  
Tanmay Ghosh ◽  
Zainul Aabdin ◽  
Siddardha Koneti ◽  
XiuMei Xu ◽  
...  
Keyword(s):  
High Speed ◽  
Liquid Droplet ◽  
Water Film ◽  
Precursor Film ◽  
Intermediate Step ◽  
Dense Array ◽  
Flat Surfaces ◽  
Transmission Electron ◽  
Phase Transmission ◽  
Two Stages

The spreading of a liquid droplet on flat surfaces is a well-understood phenomenon, but little is known about how liquids spread on a rough surface. When the surface roughness is of the nanoscopic length scale, the capillary forces dominate and the liquid droplet spreads by wetting the nanoscale textures that act as capillaries. Here, using a combination of advanced nanofabrication and liquid-phase transmission electron microscopy, we image the wetting of a surface patterned with a dense array of nanopillars of varying heights. Our real-time, high-speed observations reveal that water wets the surface in two stages: 1) an ultrathin precursor water film forms on the surface, and then 2) the capillary action by nanopillars pulls the water, increasing the overall thickness of water film. These direct nanoscale observations capture the previously elusive precursor film, which is a critical intermediate step in wetting of rough surfaces.

Jet Breakup and Droplet Formation in Immiscible Liquid-Liquid System

2016 ◽  
Author(s):  
Shimpei Saito ◽  
Yuzuru Iwasawa ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Tetsuya Kanagawa ◽  
...  
Keyword(s):  
Weber Number ◽  
Droplet Diameter ◽  
Droplet Formation ◽  
Liquid System ◽  
Immiscible Liquid ◽  
Satellite Droplet ◽  
Breakup Length ◽  
Jet Breakup ◽  
Fundamental Process ◽  
Median Diameter

Mitigative measures against the event of a core disruptive accident (CDA) are of the importance from the viewpoint of safety of a sodium-cooled fast reactor (SFR). If the CDA occurs, the so-called post-accident heat removal must be surely achieved. The present study focuses on the scenario that the molten materials are injected into the lower plenum as jets. The jet breakup behavior during the CDA will be very complicated. Therefore, a specialized study on the fundamental process during the jet breakup is believed to be an effective approach. The aim of this paper is to understand the fundamental process of hydrodynamic interaction of jet breakup and droplet formation Using the immiscible liquid-liquid system, water and silicon oil as the test fluids, visualization via high-speed videography was performed. From the visualization results, the breakup length and droplet diameter were measured by image processing. The experimental data were scaled with ambient Weber number. When the Weber number was smaller than 1, the droplet diameter was close to the nozzle diameter, and distribution of droplet size was not observed. When the Weber number exceeded 1, the breakup length became longer and the generated droplet diameter possessed a distribution with two peaks due to satellite droplet formation. In both cases, the droplet formed at the leading edge of jet. In case that Weber number is around 100, the droplets were formed by entrainment of interfacial wave at jet side. From the mass median diameter data, we can see that the increase of the Weber number caused the decrease of median diameter and the increase of the width of the distribution.

Evaluation of Local Thinning Shape by LDI for Seismic Safety Evaluation of Piping System

2011 ◽  
Author(s):  
Ryo Morita ◽  
Fumio Inada ◽  
Michiya Sakai ◽  
Shin-ichi Matsuura ◽  
Shigenobu Onishi ◽  
...  
Keyword(s):  
Liquid Droplet ◽  
Safety Evaluation ◽  
Piping System ◽  
Flow Conditions ◽  
Droplet Impingement ◽  
Seismic Safety ◽  
Seismic Safety Evaluation ◽  
Droplet Behavior ◽  
Seismic Tests ◽  
The Relationship

For seismic safety evaluation of piping system with local thinning surface by liquid droplet impingement erosion (LDI), hybrid seismic tests were conducted to the piping with a locally-thinned elbow. In this paper, a method for predicting the thinning shape by LDI on the elbow is developed. To determine the thinning shape by LDI, droplet behavior at the elbow is calculated for various flow conditions and geometries. With the calculation of the collision point and velocity for each droplet, collision frequency and average collision velocity on the elbow are estimated. Then, the thinning shape on the elbow is determined with the relationship between the flow conditions and thinning rate. Finally, the evaluated thinning shape is compared with an actual LDI case for the validation of the method.

scholarly journals Designing bioinspired surfaces for water collection from fog

2018 ◽  
Vol 377 (2138) ◽  
pp. 20180269 ◽  
Author(s):  
Dev Gurera ◽  
Bharat Bhushan
Keyword(s):  
Flat Surface ◽  
Unit Area ◽  
Water Repellency ◽  
Vertical Axis ◽  
Collection Rate ◽  
Flat Surfaces ◽  
Single Cone ◽  
Water Collection ◽  
The Difference ◽  
Conical Surfaces

A systematic study is presented on various water collectors, bioinspired by desert beetles, desert grass and cacti. Three water collecting mechanisms including heterogeneous wettability, grooved surfaces, and Laplace pressure gradient, were investigated on flat, cylindrical, conical surfaces, and conical array. It is found that higher water repellency in flat surfaces results in higher water collection rate and inclination angle (with respect to the vertical axis) has little effect. Surfaces with heterogeneous wettability have higher water collection rate than surfaces with homogeneous wettability. Both cylindrical and conical surfaces resulted in comparable water collection rate. However, only the cone transported the water droplets to its base. Heterogeneity, higher inclination and grooves increased the water collection rate. A cone has a higher collection rate per unit area than a flat surface with the same wettability. An array of cones has higher collection rate per unit area than a single cone, because droplets in a conical array coalesce, leading to higher frequency of droplets falling. Adding heterogeneity further increases the difference. Based on the findings, scaled-up designs of beetle-, grass- and cactus-inspired surfaces and nets are presented. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

Research on the Process of Liquid Droplet Impinging on the Liquid Film

2014 ◽  
Vol 933 ◽  
pp. 295-299
Author(s):  
Z.H. Wang ◽  
X. Meng
Keyword(s):  
Liquid Film ◽  
Fusion Reactor ◽  
Liquid Droplet ◽  
Flow Behavior ◽  
Droplet Diameter ◽  
High Heat ◽  
High Heat Flux ◽  
Experiment Research ◽  
Fluid Properties ◽  
Secondary Drop

The impacting of liquid droplet on the liquid film appears in many engineering processes. In the fusion reactor, liquid metal is used as the heat transfer media, moderator and breeder in the condition of high heat flux. The paper analyzes the flow behavior of liquid droplet impinging on the liquid film from the aspects of experiment research. In the impinging, splashing means the production of secondary drop coming from the cusp of the crown flow or Worthington jet. Impinging velocity, liquid film thickness, droplet diameter, fluid properties and impinging angle have been analyzed separately.

Numerical Simulation of a Small Bubble Impinging Onto an Inclined Wall

2006 ◽  
Author(s):  
Be´renge`re Podvin ◽  
Francisco Moraga ◽  
Daniel Attinger
Keyword(s):  
Weber Number ◽  
Classical Mechanics ◽  
Vertical Axis ◽  
Terminal Velocity ◽  
Excess Pressure ◽  
Small Bubble ◽  
Film Drainage ◽  
Bubble Deformation ◽  
Horizontal Wall ◽  
Comparison With Experiments

This paper presents a numerical modeling of the collision between a small bubble -of a few hundred microns, initially moving at terminal velocity, and an inclined wall, with relevance to drag reduction schemes. The theoretical model uses the lubrication theory to describe the film drainage as the bubble approaches the wall, and compute the force exerted by the wall as the integral of the excess pressure due to the bubble deformation. The model is solved using finite differences. The trajectory of the bubble is then determined using equations of classical mechanics. This study is an extension of previous work by Moraga, Cancelos and Lahey, [Multiphase Science and Technology, 18,(2),2006] where the simulation and comparison with experiments was carried out for a horizontal wall. In the present study where the wall is inclined, the bubble trajectory is no longer onedimensional and axisymmetry around the vertical axis is lost, allowing for more complex behavior. The influence of various parameters (Reynolds number, Weber number) is examined. Numerical results are compared with the experimental data from Tsao and Koch [Physics Fluids 9, 44, 1997]

Experiments on Liquid Droplet Impinging Erosion

2010 ◽  
Author(s):  
Takayuki Yamagata ◽  
Nobuyuki Fujisawa ◽  
Akiharu Ikarashi ◽  
Daichi Hama ◽  
Tsuyoshi Takano
Keyword(s):  
Erosion Rate ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Optical Measurements ◽  
Light Extinction ◽  
Number Density ◽  
Direct Imaging ◽  
Threshold Velocity ◽  
Type Apparatus ◽  
Aluminum Material

In the present paper, liquid droplet impinging erosion is studied using a newly developed spray-jet-type apparatus to evaluate the erosion rate of aluminum material due to the droplets having a diameter of tens of micrometers. In order to characterize the droplet properties, such as velocity, diameter and number density, optical measurements have been introduced using PIV, direct imaging and light extinction method, respectively. While, the erosion rate of aluminum material is evaluated using the spray-jet apparatus. The present measurements indicate that the non-dimensional erosion rate agrees closely with the previous result obtained at larger droplet diameters. However, the threshold velocity was estimated to be larger than that of the previous result, suggesting the influence of droplet diameter on the threshold velocity.

On the Breakup Process of Round Liquid Jets in Gaseous Crossflows at Low Weber Number

2013 ◽  
Author(s):  
Shao-lin Wang ◽  
Yong Huang ◽  
Fang Wang ◽  
Zhi-lin Liu ◽  
Lei Liu
Keyword(s):  
Weber Number ◽  
High Speed ◽  
Droplet Diameter ◽  
Liquid Jets ◽  
Breakup Process ◽  
Ohnesorge Number ◽  
Propulsion Systems ◽  
Momentum Ratio ◽  
Breakup Length ◽  
Primary Breakup

Liquid jets in cross air flows are widely used and play an important role in propulsion systems, such as ramjet combustors. In this paper, experiments were carried out to investigate the properties of the primary breakup of liquid jets in subsonic transverse airflows at low Weber number. The test ranges included crossflow Weber numbers of 0.5–6.7, liquid-to-gas momentum ratios of 3–120, and Ohnesorge number of 0.0086. Four different injectors with diameter 0.4mm, 0.5mm, 0.6mm and 1mm have been used. A high speed camera was used to observe the jet column breakup process. Results show that the surface wavelength decreases not only with the increase of the gas Weber number but also with the increase of the momentum ratio. The breakup length decreases with the increase of the gas Weber number, in addition to its increase with the increase of the momentum ratio. The droplet diameter decreases with the increase of both the gas Weber number and momentum ratio, although the gas Weber number will dominate the breakup process. The surface wavelength, breakup length, and droplet diameter were also analyzed with to obtain semi-theoretical correlations.

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