scholarly journals Liquid Droplet Impact on a Sonically Excited Thin Membrane

2021 ◽  
Author(s):  
Abba Abubakar ◽  
Bekir Yilbas ◽  
Hussain Al-Qahtani ◽  
Ammar Alzaydi
Keyword(s):  
High Speed ◽  
Liquid Droplet ◽  
Excitation Frequency ◽  
Membrane Dynamics ◽  
Contact Period ◽  
Restitution Coefficient ◽  
Time Duration ◽  
Hydrophobic Membrane ◽  
Droplet Spreading ◽  
Low Frequencies

Abstract Impacting droplet characteristics on hydrophobic surfaces can be altered by introducing surface oscillations. Impacting water droplet contact duration, spreading, retraction, and rebounding behaviors are examined at various sonic excitation frequencies of the hydrophobic membrane. Membrane oscillation and droplet behavior are analyzed by utilizing a high-speed camera. The restitution coefficient and membrane dynamics are formulated and the findings are compared with those of the experiments. It is found that the mode of membrane oscillation changes as the sonic excitation frequency is changed. The droplet spreading and retraction rates reduce while rebound height and restitution coefficient increase at a sonic excitation frequency of 75 Hz. However, further increase of the excitation frequency results in reduced rebound height because of increased energy dissipation on the impacted surface. The droplet contact (transition time) duration reduces as the excitation frequency increases. Increasing droplet Weber number enhances the droplet contact period on the membrane, which becomes more apparent at low frequencies of sonic excitation.

Impact Characteristics of a Carbonated Water Droplet On Hydrophobic Surface

2021 ◽  
Author(s):  
Abba Abdulhamid Abubakar ◽  
Bekir Sami Yilbas ◽  
Hussain Al-Qahtani
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Gas Bubbles ◽  
Hydrophobic Surface ◽  
Restitution Coefficient ◽  
Droplet Spreading ◽  
Co2 Gas ◽  
Carbonated Water ◽  
Bubble Sizes ◽  
Spreading Rates

Abstract Carbonated water drops impact on a hydrophobic surface is examined. The influence of CO2 gas bubbles in droplet fluid on impacting droplet characteristics, such as spreading rates and restitution coefficient, are explored. The predictions of droplet wetting diameter and spreading rates are validated through the experimental data obtained from high-speed recording. The findings reveal that predictions agree well with the experimental data. CO2 gas bubbles in the droplet are compressed by the total impact pressure of the droplet liquid while slightly reducing the gas bubble sizes. The small size of close by bubbles at high pressure can merge forming large size bubbles, which occur towards the end of droplet spreading and retraction periods. The pressure increase in the fluid gives rise to increased vertical height of the droplet and slightly reduces the droplet contact diameter on the impacted surface. The work done during the compression of CO2 gas in bubbles lowers the restitution coefficient of the droplet after the retraction period.

Gas-Assisted Droplet Impact on a Solid Surface

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Andres J. Diaz ◽  
Alfonso Ortega
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Liquid Droplet ◽  
High Speed Photography ◽  
Droplet Deformation ◽  
Droplet Spreading ◽  
Carrier Gas ◽  
Air Jet ◽  
Vof Model ◽  
Theoretical Predictions

An experimental, numerical, and theoretical investigation of the behavior of a gas-assisted liquid droplet impacting on a solid surface is presented with the aim of determining the effects of a carrier gas on the droplet deformation dynamics. Experimentally, droplets were generated within a circular air jet for gas Reynolds numbers Reg = 0–2547. High-speed photography was used to capture the droplet deformation process, whereas the numerical analysis was conducted using the volume of fluid (VOF) model. The numerical and theoretical predictions showed that the contribution of a carrier gas to the droplet spreading becomes significant only at high Weo and when the work done by pressure forces is greater than 10% of the kinetic energy. Theoretical predictions of the maximum spreading diameter agree reasonably well with the experimental and numerical observations.

Capillary Force-Driven Fluid Flow of a Wetting Liquid on a Surface With Multiple Parallel Open Microchannels

2012 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Fluid Flow ◽  
Capillary Force ◽  
High Speed ◽  
Liquid Droplet ◽  
Rectangular Cross Section ◽  
Liquid Penetration ◽  
Droplet Spreading ◽  
Penetration Length ◽  
Initial Stage ◽  
Wetting Liquid

Fluid flow driven by the capillary force is omnipresent in nature and important in many engineering technologies. The focus of this work is capillary force-driven fluid flow of a wetting liquid in open microchannels when a liquid droplet is gently introduced to a metal surface on which multiple parallel microchannels with an open rectangular cross section are formed. It is found that, aided with a high-speed camera, the capillary-force driven fluid behavior consists of uni-directional spreading of the bulk droplet on the microchannel fins and liquid penetration into the microchannels. The kinetics of fluid flow due to the liquid penetration into the microchannels can be divided into three distinct stages: initial stage, transition stage, and Washburn stage; only in the Washburn stage, the flow has a penetration length-time dependence in proportion to square root of time as described by the Washburn’s equation. Comparison with liquid spreading on a plain surface having only one microchannel (the same geometry and size) revealed that the bulk droplet spreading on the microchannel fins, after elapse of the initial stage, has little effect on the fluid flow kinetics in the multiple microchannels. Some analytical results shed more insights into the capillary force-driven fluid flow in open microchannels.

Numerical Analysis of Influence of Roughness of Material Surface on High-Speed Liquid Droplet Impingement

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Hirotoshi Sasaki ◽  
Yuka Iga
Keyword(s):  
Numerical Analysis ◽  
High Speed ◽  
Erosion Rate ◽  
Liquid Droplet ◽  
Material Surface ◽  
Liquid Droplets ◽  
Fluid Machinery ◽  
Droplet Impingement ◽  
Surface Liquid ◽  
Droplet Impingement Erosion

This study explains why the deep erosion pits are formed in liquid droplet impingement erosion even though the droplets uniformly impinge on the entire material surface. Liquid droplet impingement erosion occurs in fluid machinery on which droplets impinge at high speed. In the process of erosion, the material surface becomes completely roughened by erosion pits. In addition, most material surface is not completely smooth and has some degree of initial roughness from manufacturing and processing and so on. In this study, to consider the influence of the roughness on the material surface under droplet impingement, a numerical analysis of droplets impinging on the material surface with a single wedge and a single bump was conducted with changing offsets between the droplet impingement centers and the roughness centers on each a wedge bottom and a bump top. As results, two mechanisms are predicted from the present numerical results: the erosion rate accelerates and transitions from the incubation stage to the acceleration stage once roughness occurs on the material surface; the other is that deep erosion pits are formed even in the case of liquid droplets impinging uniformly on the entire material surface.

Measurement of Dynamic Strain

1943 ◽  
Vol 10 (2) ◽  
pp. A85-A92
Author(s):  
C. O. Dohrenwend ◽  
W. R. Mehaffey
Keyword(s):  
High Speed ◽  
Shock Loading ◽  
Low Frequency ◽  
Dynamic Strain ◽  
Time Axis ◽  
Low Frequencies ◽  
Strain Measurements ◽  
Moving Vehicles ◽  
Machine Parts ◽  
Dynamic Strains

Abstract The measurement of dynamic strains of both high and low frequency give rise to a variety of problems in instrumentation. Two types of equipment and circuits designed and used by the authors are discussed in detail. The first type based on the amplitude-modulated method is for low frequencies from zero to about 15 per cent of the carrier frequency of 1025 cycles per sec. The equipment has application to strain measurements varying from static values to those produced in moving vehicles, various machine parts, structures such as crane bridges, in fact all strain measurements where the frequency is 150 cycles per sec or less. The second type of equipment discussed is a potentiometer type and is for high-frequency strain measurements from 100 cycles per sec to 8000 cycles per sec. This high-speed equipment is conveniently used for impact strain, such as produced in hammer blows, shock loading, forging equipment, and impact-factor determination. Both units are designed to be used with a cathode-ray oscillograph which lends itself to a variety of recording methods. The methods discussed include both the type where the time axis is obtained by sweeping the oscilloscope beam on a stationary film and where the time axis is obtained mechanically.

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.

scholarly journals Superluminal Motion in CTA 102

1989 ◽  
Vol 134 ◽  
pp. 529-530
Author(s):  
Ann E. Wehrle
Keyword(s):  
Flux Density ◽  
High Speed ◽  
Low Frequency ◽  
Precise Determination ◽  
Flux Variation ◽  
Low Frequencies ◽  
Superluminal Motion ◽  
Low Frequency Variability ◽  
Expansion Speed

Sholomitskii (1965) discovered that the flux density of the quasar CTA 102 varies at low frequencies on a timescale of a few months. Low-frequency variability can be explained by “superluminal flux variation” (Romney et al. 1984): If the intrinsic brightness of a component moving in a relativistically beamed source varies by only a few percent, the observer sees its flux density change by a much larger factor δ3-α when the optically thin blob moves almost directly toward the observer. Such a relativistically beamed source is likely to exhibit superluminal motion if studied with sufficient resolution and sensitivity. Superluminal motion in CTA 102 was discovered by Bååth (1987) who concluded on the basis of maps made at three epochs at a frequency of 932 MHz that two components were separating at a rate of 0.65 milliarcseconds (mas) per year. Using a redshift z = 1.037 and H0 = 100 km s−1 Mpc−1, q0 = 0.5, this expansion speed corresponds to (18 ± 4)h−1c. The extraordinarily high speed led us to make VLBI images of the source at a higher frequency in order to increase the resolution and make a more precise determination of the speed.

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