scholarly journals Pinned Droplet Size on a Superhydrophobic Surface in Shear Flow

Aerospace ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 34
Author(s):  
Mitsugu Hasegawa ◽  
Katsuaki Morita ◽  
Hirotaka Sakaue ◽  
Shigeo Kimura
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Droplet Size ◽  
Water Droplet ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
High Speed Camera ◽  
Sessile Droplet ◽  
Air Velocity

The recent development of a superhydrophobic surface enhances the droplet shedding under a shear flow. The present study gives insights into the effects of shear flow on a pinned droplet over a superhydrophobic surface. To experimentally simulate the change in the size of a sessile droplet on an aerodynamic surface, the volume of the pinned droplet is expanded by water supplied through a pore. Under a continuous airflow that provides a shear flow over the superhydrophobic surface, the size of a pinned water droplet shed from the surface is experimentally characterized. The air velocity ranges from 8 to 61 m/s, and the size of pinned droplets shed at a given air velocity is measured using an instantaneous snapshot captured with a high-speed camera. It is found that the size of the shedding pinned droplet decreases as air velocity increases. At higher air velocities, shedding pinned droplets are fully immersed in the boundary layer. The present findings give a correlation between critical air velocity and the size of pinned droplets shed from the pore over the superhydrophobic surface.

Experimental Investigation on Flow Field in a Rotating Channel With a New TR-PIV System

2018 ◽  
Author(s):  
Shengjun Zhou ◽  
Haiwang Li ◽  
Zhi Tao ◽  
Ruquan You ◽  
Haoyu Duan
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Laser Diode ◽  
High Speed ◽  
Flow Behavior ◽  
Particle Image Velocimetry System ◽  
Main Stream ◽  
High Speed Camera ◽  
Time Resolved ◽  
Rotating Channel

In the current study, the influence of different rotation conditions on the flow behavior is experimentally investigated by a new system which is designed for time-resolved PIV measurements of the smooth channels at rotation conditions. The Reynolds number equals 15000 and the rotation number ranges from 0 to 0.392 with an interval of 0.098. This new time-resolved Particle Image Velocimetry system consists of a 10 Watts continuous laser diode and a high-speed camera. The laser diode can provide a less than 1mm thickness sheet light. 6400 frames can be captured in one second by the high-speed camera. These two parts of the system are fixed on a rotating disk. In this case, the relative velocity of flows in the rotating smooth square channel can be measured directly to reduce the measurement error. This system makes high-speed camera close to the rotating channel, which allows a high resolution for the measurements of main stream. In addition, high accuracy and temporal resolution realize a detailed analysis of boundary layer characteristics in rotation conditions. Based on this system, experimental investigation has been undertaken. Results are presented of the evolution of velocity and boundary layer thickness at various rotation numbers and different circumferential positions.

Pulsating and Bouncing off of Dropwise Condensate on Superhydrophobic Surface

2011 ◽  
Author(s):  
Xuehu Ma ◽  
Sifang Wang ◽  
Zhong Lan ◽  
Benli Peng ◽  
Tao Bai ◽  
...  
Keyword(s):  
Superhydrophobic Surface ◽  
High Speed ◽  
High Speed Camera ◽  
Dropwise Condensation ◽  
High Concentration ◽  
Long Distance ◽  
Noncondensable Gas ◽  
Pinning Effect

The steam dropwise condensation (DWC) characteristics on superhydrophobic plates were investigated experimentally in the presence of a high concentration noncondensable gas (NCG, >80mol%). The behaviors of condensate droplets on the roughness-induced superhydrophobic surface were observed with a photron high speed camera attached to a microscope. Pulsating features are found during droplets coalescence movement. Bouncing off of coalesced droplet was also observed induced by the strong effect of pulsating motion to overcome the pinning effect of the surface micro-nanostructures. Induced by the pulsating effect of droplets coalescence, the droplet can move at a long distance to join a coalesced droplet.

scholarly journals Performance of a Monofiber Optical Probe in Determining the Droplet Size and Velocity in Spray Systems Compared with a High-Speed Camera

2019 ◽  
Vol 58 (51) ◽  
pp. 23366-23379 ◽  
Author(s):  
Kritchart Wongwailikhit ◽  
Nicolas Dietrich ◽  
Gilles Hébrard ◽  
Pisut Painmanakul
Keyword(s):  
Droplet Size ◽  
High Speed ◽  
Optical Probe ◽  
High Speed Camera

Dynamic of Water Droplet Impacting on a Hydrophilic Surface Accompanied With Stagnation Flow

2014 ◽  
Author(s):  
Morteza Mohammadi ◽  
Mohammadreza Attarzadeh ◽  
Moussa Tembely ◽  
Ali Dolatabadi
Keyword(s):  
Shear Flow ◽  
Water Droplet ◽  
High Speed ◽  
Air Flow ◽  
Droplet Impact ◽  
Impact Behavior ◽  
Aluminum Surface ◽  
High Speed Photography ◽  
Stagnation Flow ◽  
Maximum Spreading

Droplet impact on solid surfaces has been extensively reported in the literature, however the effect of accompanying air flow on the outcome of impacting droplet has yet to be addressed and analyzed which is similar to real scenario of impacting water droplet on aircraft’s leading edge at in-flight icing conditions. This study addresses the net effect of airflow (i.e. stagnation and the resultant shear flow) on the impacting water droplet with the same droplet impact velocity which is exposed to different airspeeds. In order to provide stagnation flow, a droplet accelerator was built which can generate different airspeeds up to 20 m/s. Droplet impact behavior accompanied with stagnation flow on a polished aluminum surface with a contact angle of 70° was investigated by high speed photography. 2.5 mm water droplet size with impact velocities of 2, 2.5 and 3 m/s which correspond to non-splashing regime of impacts are exposed to three different regimes of air speeds namely 0 (i.e. still air case), 10, and 20 m/s. It was observed that when droplet reaches to its maximum spreading diameter, some fingered shape at the end of spreading lamella (i.e. Rayleigh-Taylor instability) is appeared. When stagnation flow is present these fingered shape droplets are exposed to the generated shear flow close to the substrate (i.e. Homann flow approach) causes a droplet break up while complete non-splashing regime is observed in still air case. In spite of the fact that maximum spreading diameter is not largely affected by air flow compare to still air case, droplet height variation is significantly reduced by about 70 percent for strong stagnation flow (i.e. 20 m/s) which generates non-recoiling condition resulting in the thin film formation.

Concurrent Droplet Coalescence and Solidification on Surfaces With Various Wettabilities

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Sara Moghtadernejad ◽  
Mehdi Jadidi ◽  
Moussa Tembely ◽  
Nabil Esmail ◽  
Ali Dolatabadi
Keyword(s):  
Experimental Study ◽  
Shear Flow ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
Experimental Setup ◽  
High Shear ◽  
Cold Plate ◽  
Droplet Coalescence ◽  
Cold Surface ◽  
Rivulet Formation

An experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different airflow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence, and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario, the experimental setup is designed to generate shear flow as high as 90 m/s. The droplet shedding at high-speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet, which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.

Concurrent Droplet Coalescence and Solidification on Surfaces With Various Wettabilities

2014 ◽  
Author(s):  
Sara Moghtadernejad ◽  
Mehdi Jadidi ◽  
Moussa Tembely ◽  
Nabil Esmail ◽  
Ali Dolatabadi
Keyword(s):  
Experimental Study ◽  
Shear Flow ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
High Shear ◽  
Cold Plate ◽  
Cold Surface ◽  
Flow Speeds ◽  
Set Up ◽  
Rivulet Formation

Experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different shear flow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario experimental set up is designed to generate shear flow as high as 90 m/s. The droplet shedding at high speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.

Internal Flow Effects in Prefilming Airblast Atomizers: Mechanisms of Atomization and Droplet Spectra

1986 ◽  
Vol 108 (3) ◽  
pp. 465-472 ◽  
Author(s):  
T. Sattelmayer ◽  
S. Wittig
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Mass Flow ◽  
High Speed ◽  
Internal Flow ◽  
Droplet Size Distribution ◽  
Drop Formation ◽  
Air Velocity ◽  
Liquid Separation ◽  
Liquid Mass

Fuel atomization with prefilming airblast nozzles has been investigated. The present analysis is directed toward a detailed investigation of the atomization processes and the clarification of the fundamental phenomena. Two-dimensional models were utilized. High-speed films, showing the deterioration of the liquid film close to the atomizing edge, reveal the dynamics of the liquid’s deterioration and show the motion of the film during the drop formation. The liquid separation is shown to be a periodic process with the drop formation caused by momentum transfer. The frequency spectrum of the liquid separation is determined by means of an optical technique. It is seen that the main frequencies depend only on the air velocity. They are always lower than the corresponding wave frequencies. The droplet size measurements obtained by a light scattering technique emphasize the dominant role of the air velocity at the atomizing edge. A decrease in the surface tension provides an improvement in atomization quality. Other parameters such as liquid flow rate, liquid viscosity, gap height, and length of the prefilming surface within the nozzle were found not to affect directly the droplet size distribution produced, if the air velocity in each of the two ducts of the nozzle is kept constant. The pressure drop of the air, however, rises. It is shown that the droplet size distribution can be easily determined, if the arithmetic mean value of the air velocity in both ducts is known, e.g., from a calculation of the internal flow. Due to the high liquid mass flow rates of airblast nozzles, the wavy film is partly atomized within the nozzle before the liquid separates at the atomizing edge. The measurements show that the portion of the liquid mass flow atomized remains relatively small and that the droplet sizes are equivalent to those produced at the atomizing edge.

The transitions of time-independent spreading diameter and splashing angle when a droplet train impinging onto a hot surface

RSC Advances ◽  
2016 ◽  
Vol 6 (17) ◽  
pp. 13644-13652 ◽  
Author(s):  
Lu Qiu ◽  
Swapnil Dubey ◽  
Fook Hoong Choo ◽  
Fei Duan
Keyword(s):  
High Temperature ◽  
Water Droplet ◽  
High Speed ◽  
High Speed Camera ◽  
Hot Surface

The hydrodynamic patterns of the impingement of a water droplet train on a high temperature substrate are captured with a high-speed camera, and then analyzed.

Flame Propagation Following the Autoignition of Axisymmetric Hydrogen, Acetylene, and Normal-Heptane Plumes in Turbulent Coflows of Hot Air

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Christos N. Markides ◽  
Epaminondas Mastorakos
Keyword(s):  
Flame Propagation ◽  
Air Temperature ◽  
High Speed ◽  
High Speed Camera ◽  
Stoichiometric Mixture ◽  
Air Velocity ◽  
Flame Propagation Velocity ◽  
Hot Air ◽  
Air Temperatures ◽  
Continuous Injection

Axisymmetric plumes of hydrogen, acetylene, or n-heptane were formed by the continuous injection of (pure or nitrogen-diluted) fuel into confined turbulent coflows of hot air. Autoignition and subsequent flame propagation was visualized with an intensified high-speed camera. The resulting phenomena that were observed include the statistically steady “random spots” regime and the “flashback” regime. It was found that with higher velocities and smaller injector diameters, the boundary between random spots and flashback shifted to higher air temperatures. In the random spots regime the autoignition regions moved closer to the injector with increasing air temperature and/or decreasing air velocity. After a localized explosive autoignition event, flames propagated into the unburnt mixture in all directions and eventually extinguished, giving rise to autoignition spots of mean radii of 2–5mm for hydrogen and 6–10mm for the hydrocarbons. The average flame propagation velocity in both the axial and radial directions varied between 0.5 and 1.2 times the laminar burning speed of the stoichiometric mixture, increasing as the autoigniting regions shifted upstream.

Sign in / Sign up

Export Citation Format

Share Document