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.

Honeycomb porous films of pentablock copolymer on liquid substrates via breath figure method and their hydrophobic properties with static and dynamic behaviour

RSC Advances ◽  
2015 ◽  
Vol 5 (27) ◽  
pp. 21084-21089 ◽  
Author(s):  
Zhiguang Li ◽  
Xiaoyan Ma ◽  
Duyang Zang ◽  
Qing Hong ◽  
Xinghua Guan
Keyword(s):  
Water Droplet ◽  
Dynamic Behaviour ◽  
Droplet Impact ◽  
Impact Behavior ◽  
Porous Films ◽  
Hydrophobic Properties ◽  
Breath Figure ◽  
Breath Figure Method ◽  
Pentablock Copolymer ◽  
Maximum Spreading

The peeled film obtained on the isopropanol substrate through breath figure method exhibits the best hydrophobic properties, and the water droplet impact behavior shows an obvious rebound tendency and a weak maximum spreading diameter.

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.

SUMMARY OF STUDIES OF COREXIT DISPERSANT DROPLET IMPACT BEHAVIOR INTO OIL SLICKS AND DISPERSANT DROPLET EVAPORATION1,2

2008 ◽  
Vol 2008 (1) ◽  
pp. 797-800 ◽  
Author(s):  
Timothy A. Ebert ◽  
Roger Downer ◽  
James Clark ◽  
Charles A. Huber
Keyword(s):  
High Speed ◽  
Impact Analysis ◽  
Droplet Impact ◽  
Impact Behavior ◽  
Oil Slick ◽  
Corexit 9500 ◽  
Droplet Sizes ◽  
Evaporative Loss ◽  
Pass Through ◽  
Oil Films

ABSTRACT This paper presents the results of two related studies concerning the aerial application of dispersants. The first study characterized the interactions of various sized Corexit 9500 and 9527 dispersant droplets with oil films of from 0.1 mm to 3.0 mm thickness. A film thickness of 0.1 mm was selected as the end point since this is the thinnest oil film recommended for the application of dispersants. The results of the high speed video droplet impact analysis showed that droplet diameters of 1,000 microns will not pass through an oil slick of 0.1 mm and mix with the underlying water column and that slick thickness of 0.2 mm or more will prevent even 2,000 micron diameter droplets from passing through the slick. These droplet sizes are considerably larger than the current ASTM Standard recommended droplet size of 300–500 microns for dispersant application. Additionally, it was shown that droplets that do pass through an oil slick will in whole or in part rise back up to the oil water interface. The second study characterized and compared the evaporation rates of Corexit 9500 and 9527 droplets with water over a 20 minute period under varying conditions of humidity and temperature. Under high evaporative conditions of high temperature (90° F) and low humidity (40%), droplets ranging from 0.25 to 1 uL showed 2–10% evaporative loss for Corexit 9500, 28–35% evaporative loss for Corexit 9527, and complete evaporative loss for water. When tested at low evaporative conditions of low temperature (40° F) and high humidity (95%), no evaporative loss was recorded for droplets of either 9500 or 9527, and water lost 18%.

scholarly journals Formation and rupture of gas film of antibubble

2020 ◽  
Vol 23 (1) ◽  
pp. 91-104
Author(s):  
Lichun Bai ◽  
Jinguang Sun ◽  
Zhijie Zeng ◽  
Yuhang Ma ◽  
Lixin Bai
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Liquid Surface ◽  
Single Layer ◽  
Liquid Films ◽  
Droplet Impact ◽  
Liquid Interface ◽  
High Speed Photography ◽  
Merging Process ◽  
The Impact

The formation and rupture of gas film in the process of formation, rupture and coalescence of antibubbles were investigated by high-speed photography. It was found that a gas film will appear and wrap a droplet when the droplet hit a layer of liquid film or foam before impacting the gas-liquid interface. The gas film may survive the impact on the gas-liquid interface and act as the gas film of an antibubble. A multilayer droplet will be formed when the droplet hits through several layer of liquid films, and a multilayer antibubble will be formed when the multilayer droplet impact a gas-liquid interface or a single layer of foam on the liquid surface. The way to generate antibubbles by liquid films will undergo the formation and rupture of gas films. The coalescence of two antibubbles, which shows a similar merging process of soap bubbles, also undergo the rupture and formation of gas films. The rupture of gas film of antibubble caused by aging and impact is also discussed.

Dynamics of a Water Droplet on the Heated Surface of Nano- and Micro-Structures

2012 ◽  
Author(s):  
Seol Ha Kim ◽  
Ho Seon Ahn ◽  
Joonwon Kim ◽  
Moo Hwan Kim
Keyword(s):  
Water Droplet ◽  
High Speed ◽  
Zirconium Alloy ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Complete Wetting ◽  
Structured Surfaces ◽  
Bare Surface

In this study, we investigated the dynamic behavior of a water droplet near the Leidenfrost point (LFP) of bare and modified zirconium alloy surfaces with bundles of nanotubes (∼10–100 nm) or micro mountain-like structures using high-speed photography. A deionized water droplet (6 μL) was dropped onto the sample surfaces (20 × 25 × 0.7 mm) that were heated to temperatures ranging from 250°C to the LFP. The modified zirconium alloy surfaces showed complete wetting and well-spread features at room temperature due to strong liquid spreading by the structure. The meniscus of the liquid droplet on the structured surface experienced more vigorous dynamics with intensive nucleate boiling, compared with the clean, bare surface. The cutback phenomenon was observed on the bare surface; however, the structured surfaces showed a water droplet “burst”. We observed that the LFPs were 449°C, 522°C, and 570°C, corresponding to the bare, micro-, and nano-structures, respectively.

Dynamic Impact Behavior of Water Droplet on a Superhydrophobic Surface in the Presence of Stagnation Flow

2012 ◽  
Vol 232 ◽  
pp. 267-272 ◽  
Author(s):  
Morteza Mohammadi ◽  
Sara Moghtadernejad ◽  
Percival J. Graham ◽  
Ali Dolatabadi
Keyword(s):  
Water Droplet ◽  
Weber Number ◽  
Contact Time ◽  
Superhydrophobic Surface ◽  
Superhydrophobic Surfaces ◽  
Impact Behavior ◽  
Stagnation Flow ◽  
Dynamic Impact ◽  
Air Flow Velocity ◽  
Impact Experiments

The following study investigates splashing of impinging water droplets on superhydrophobic surfaces with and without the presence of a stagnation flow. Droplets were accelerated by either gravity or gravity and co-flow. By changing the height and the air flow velocity different combinations of stagnation flow and droplet velocity were created. The spreading diameter, spreading velocity and contact time were studied for different air and droplet speeds. It was clearly observed that for a fixed impact velocity (i.e. constant Weber number), the presence of the stagnation flow promotes splashing and formation of satellite droplets. Consequently, for the co-flow droplet impact experiments, the mass of the recoiled droplet is significantly smaller than that of the impinging droplet in still air.

Phase-Doppler Anemometry Measurements in Water-Air Impinging Jet Flows

2016 ◽  
Author(s):  
Yakang Xia ◽  
Lyes Khezzar ◽  
Mohamed Alshehhi
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Liquid Droplet ◽  
Air Flow ◽  
Turbulent Jets ◽  
Spray Angle ◽  
Jet Flows ◽  
High Speed Photography ◽  
Phase Doppler Anemometry ◽  
Radial Profiles

Flow visualization using high speed photography is used to study the structure of two liquid and one air impinging turbulent jets. The break up structure is discussed and the resulting spray angle at large air flow rates is obtained. The spray angle increases with the air flow rate except for the case when the water jet velocity is so small that the flow rate of air does not have significant effects on the spray angle. Phase Doppler Anemometry measurements of liquid droplet sizes and velocities are also given in terms of radial profiles at several axial locations from the point of impingement.

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