Investigation of Sessile Droplet Wetting, Dynamics and Evaporation on Micro-Structured Substrates

2016 ◽  
Author(s):  
Gui-Ping Zhu ◽  
Kian-Soo Ong ◽  
Karen Siew-Ling Chong ◽  
Hu-Lin Huang ◽  
Fei Duan
Keyword(s):  
Droplet Size ◽  
Contact Line ◽  
Pure Water ◽  
Volume Ratio ◽  
Size Ratio ◽  
Pure Liquid ◽  
Nickel Surface ◽  
Evaporation Process ◽  
Sessile Droplet ◽  
Evaporation Coefficient

The wetting, spreading and drying of pure liquid and nanofluid sessile droplets on a patterned solid surface were investigated systematically in terms of liquid and surface property. The patterned nickel surface was characterized with diamond, circular, hexagon and rectangular pillars. The size ratio between interval and pillars varies from 1.0 to 5.0. The study was firstly carried out for the effect of pure water droplet size on liquid spreading and droplet evaporation process on diamond-shape micro structured substrate with LInterval/LPillar=1.0. Larger amount of liquid leads to a larger wetting area. With fixed substrate (diamond, LInterval/LPillar=1.0) and droplet size (1 μm), mixture of DI water and Ethanol (volume ratio varies from 0.5 to 2.0) was used for generating droplets with different surface tension and evaporation coefficient. Fingering shape would generate on the contact line. With higher concentration of ethanol, the fingering effect is stronger and appeared in a shorter time. The contact area shrinks when increase the size ratio of interval and pillar. This would reduce the length of the contact line, and thus slow down the liquid evaporation. The role of pillar shape was examined based on time for complete evaporation. The effect of surface material on evaporation process was conducted on nickel and PMMA substrate fabricated with the same design. Additionally, investigations were conducted with solutions consisted with nanoparticles and DI water. The mixture were made at different weight ration to achieve concentration of nanoparticles varies from 0.02% to 0.18% with an interval at 0.04%.

Forces Acting on Sessile Droplet on Inclined Surfaces

2009 ◽  
Author(s):  
S. Ravi Annapragada ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Contact Angle ◽  
Droplet Size ◽  
Contact Line ◽  
Contact Area ◽  
Contact Angles ◽  
Force Model ◽  
Sessile Droplet ◽  
Droplet Motion ◽  
Droplet Shape ◽  
Receding Contact

Although many analytical, experimental and numerical studies have focused on droplet motion, the mechanics of the droplet while still in its static state, and just before motion starts, are not well understood. A study of static droplets would shed light on the threshold voltage (or critical inclination) for initiating electrically (or gravitationally) induced droplet motion. Before the droplet starts to move, the droplet shape changes such that the forces acting at the triple contact line balance the actuation forces. These contact line forces are governed by the contact angles along the contact line. The contact angle varies from an advancing angle at the leading edge to a receding angle at the trailing edge of the droplet. The present study seeks to understand and predict these forces at the triple contact line. The droplet shape, as well as the advancing and receding contact angles, is experimentally measured as a function of droplet size under the action of a gravitational force at different inclination angles. The advancing and receding contact angles are correlated with static contact angle and Bond number. A Volume of Fluid - Continuous Surface Force model with varying contact angles along the triple contact line is developed to predict the same. The model is first verified against a two-dimensional analytical solution. It is then used to simulate the shape of a sessile droplet on an incline at various angles of inclination and to determine the critical angle of inclination as a function of droplet size. Good agreement is found between experimental measurements and predictions. The contact line profile and contact area are also predicted. The contact area predictions based on a spherical-cap assumption are also compared against the numerical predictions.

scholarly journals Fluid flow structures in an evaporating sessile droplet depending on the droplet size and properties of liquid and substrate

2021 ◽  
Vol 1730 (1) ◽  
pp. 012029
Author(s):  
M.N. Turchaninova ◽  
E.S. Melnikova ◽  
A.A. Gavrilina ◽  
L.Yu. Barash
Keyword(s):  
Fluid Flow ◽  
Droplet Size ◽  
Flow Structures ◽  
Sessile Droplet

scholarly journals Self-Sorting of Bidispersed Colloidal Particles Near Contact Line of an Evaporating Sessile Droplet

Langmuir ◽  
2018 ◽  
Vol 34 (40) ◽  
pp. 12058-12070 ◽  
Author(s):  
Nagesh D. Patil ◽  
Rajneesh Bhardwaj ◽  
Atul Sharma
Keyword(s):  
Contact Line ◽  
Colloidal Particles ◽  
Sessile Droplet

Stability of the PEG Fatty Acid Glycerides Based O/W Emulsions

2021 ◽  
Vol 58 (4) ◽  
pp. 271-277
Author(s):  
Zihan Wang ◽  
Liangliang Lin ◽  
Hujun Xu
Keyword(s):  
Droplet Size ◽  
Lauric Acid ◽  
Volume Ratio ◽  
Water Volume ◽  
Optimal Conditions ◽  
Rotational Rheometer ◽  
Emulsion Systems ◽  
Oil Water ◽  
The Stability ◽  
Emulsifier Concentration

Abstract In the present work, oil-in-water (O/W) emulsion systems were prepared by using the PEG-7 lauric acid glycerides as the emulsifiers and the liquid paraffin as the oil phase. The influence of processing parameters such as emulsification temperature, stirring speed, emulsifier concentration, oil-water volume ratio and polymer addition on the stability of the emulsion systems was investigated. In order to determine the optimal conditions for the preparation of the emulsion systems based on PEG-7 lauric acid glycerides, a laser drop size analyser and a rotational rheometer were used. As the stability of the O/W emulsion systems increased, the average droplet size of the O/W emulsions measured by the laser droplet size analyser became smaller and the viscosity, storage modulus and loss modulus of the O/W emulsions measured by the rotational rheometer became larger. The following optimal conditions were determined in this study: emulsification temperature 80°C, stirring speed 500 r/min, emulsifier concentration 5 wt%, oil-water volume ratio 1:1 and added amount of xanthan gum 0.2 wt%. The droplet morphology of the O/W emulsion prepared under the optimal conditions, which was characterised by a super high magnification microscope, is small. Furthermore, the long-term stability of the emulsion system prepared under the optimal conditions was investigated over a period of time (4 weeks). The O/W emulsion proves to be well stable even after 4 weeks, with a water separation rate of 0%.

scholarly journals Effect of Solid Particles on Droplet Size Applying the Time-Shift Method for Spray Investigation

2020 ◽  
Vol 10 (21) ◽  
pp. 7615
Author(s):  
Simon Wachter ◽  
Tobias Jakobs ◽  
Thomas Kolb
Keyword(s):  
Droplet Size ◽  
High Speed ◽  
Solid Particles ◽  
Time Shift ◽  
Pure Liquid ◽  
Sauter Mean Diameter ◽  
Shift Method ◽  
Spray Formation ◽  
Primary Breakup ◽  
Shift Effect

This study investigated the influence of solid particles on primary breakup and resulting droplet size for different process parameters. Two sets of Newtonian fluids (each consisting of one pure liquid and one suspension at the same respective viscosity) were used, for isolated investigation of solid particles on spray formation independent of liquid viscosity. The spray was recorded by a high-speed camera and a SpraySpy® system based on the time-shift effect, while a commonly used Spraytec® laser diffraction analyzer was employed for validation. An external-mixing twin-fluid atomizer was operated at different gas velocities and corresponding GLR at constant liquid mass flow. For the investigated suspensions an increased Sauter mean diameter was detected, compared to the pure liquids with identical dynamic viscosity. This effect was explained by the tensile strength stabilizing the suspension droplets.

Uniform and Gaussian Ultraviolet Light Intensity Distribution on Droplet for Selective Area Deposition of Particles

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Tianyi Li ◽  
Aravinda Kar ◽  
Ranganathan Kumar
Keyword(s):  
Contact Line ◽  
Sessile Drop ◽  
Uv Light ◽  
Incident Light ◽  
Droplet Surface ◽  
Light Distribution ◽  
Surface Tension Gradient ◽  
Sessile Droplet ◽  
Selective Area ◽  
Light Profiles

Abstract Particle transport through Marangoni convection inside a sessile droplet can be controlled by the ultraviolet (UV) light distribution on the surface. The photosensitive solution changes the surface tension gradient on the droplet surface and can induce clockwise and counterclockwise circulations depending on the incident light distribution. In this paper, the stream function in the sessile drop has been evaluated in toroidal coordinates by solving the biharmonic equation. Multiple primary clockwise and counterclockwise circulations are observed in the droplet under various concentric UV light profiles. The downward dividing streamlines are expected to deposit the particles on the substrate, thus matching the number of deposited rings on the substrate with the number of UV light rings. Moffatt eddies appear near the contact line or centerline of the droplet depending on the UV light profile and its distance from the contact line.

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.

scholarly journals Investigations on the Influence of Chemical Compounds on Fog Microphysical Parameters

Atmosphere ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 225
Author(s):  
Ognyan Ivanov ◽  
Petar Todorov ◽  
Ismail Gultepe
Keyword(s):  
Droplet Size ◽  
Pure Water ◽  
Potassium Dihydrogen Phosphate ◽  
Chemical Compounds ◽  
Water Volume ◽  
Dihydrogen Phosphate ◽  
Aerosol Composition ◽  
Size Spectra ◽  
The Impact ◽  
Generating System

Lab experiments related to artificial fog studies are limited due to instrument sensitivity to small fog and aerosol particles; therefore, the goal of this work is to evaluate aerosol solute effects on fog physical properties in a lab environment. To reach the goal, an automated fog-generating system was designed and that includes controlled chemical compounds dissolved in pure water. In the analysis, the impact of changing the mass concentration of potassium dihydrogen phosphate—KH2PO4, urea-CO(NH2)2, and potassium hexacyanoferrate trihydrate-K3(Fe(CN)6) on fog droplet size spectra is studied, because visibility is directly related to fog droplet spectra and aerosol composition. In the experiment, various microphysical conditions, including fog droplet size and volume concentration, were analyzed as a function of changing aerosol composition/spectra and fixed thermodynamic conditions. The results showed that fog droplet size spectra vary with the addition of chemical impurities to the pure water volume. For example, increasing KH2PO4 concentration compared to distilled water volume resulted in a higher mean particle size, which led to faster droplet settlement, and that resulted in cleaning air more efficiently compared to pure water fog. Overall, both issues and challenges of the experimental fog generating system with respect to water and aerosol solutions resembling CRBN (chemical, radiological, biological, and nuclear agents) characteristics are provided and evaluated.

Experimental Study on Instability Behavior of Thermosyphon and Grooved Heat Pipe with TiO2-Nanofluid

2013 ◽  
Vol 711 ◽  
pp. 285-290
Author(s):  
Dong Ryun Shin ◽  
Seok Ho Rhi ◽  
Kyung Il Cha
Keyword(s):  
Heat Pipe ◽  
Pure Water ◽  
Volume Ratio ◽  
Heat Pipes ◽  
Temperature Perturbation ◽  
Stable Operation ◽  
Stability Behavior ◽  
Inner Diameter ◽  
Cooling Media ◽  
The Stability

In the present study, TiO2-nanofluid with different volume ratio was used as working fluids of thermosyphon and grooved heat pipe to investigate working stability. The stability behavior of system was studied with various parameters such as volume concentration of nanoparticle, orientation, heat flux, and cooling media were investigated. Specially, the present experimental unstable working behaviors between TiO2-nanofluid and pure water were compared. In the present study, the TiO2-nanoparticles were dispersed into pure water with each of cross blended concentrations of 0.05%, 0.1%, 0.5%, and 1%. In the present study, the rate of growth of unstable disturbances is expressed in terms of temperature perturbation. The best stable operation was observed with thermosyphon of 0.5 % TiO2-nanofluid. The best operation state with nanofluidic TS was observed in the 90° inclination and α = 0.5. In the present study, the enhancement of heat pipe performance with TiO2-nanofluid is presented. The both heat pipes were fabricated from the straight stainless pipe with the inner diameter and length of 10, 500 mm, respectively.

Hydratation und hydrophobe Wechselwirkung der Ionen in Polyelektrolyten mit einer Folgerung bezüglich der biologischen Membranen

1969 ◽  
Vol 24 (4) ◽  
pp. 375-377 ◽  
Author(s):  
G. Zundel ◽  
A. Murr
Keyword(s):  
Sulfonic Acid ◽  
Pure Water ◽  
Water Structure ◽  
Water Molecules ◽  
Pure Liquid ◽  
Ammonium Ions ◽  
Alkali Ions ◽  
Stretching Vibration ◽  
Polystyrene Sulfonic Acid ◽  
Alkyl Ammonium

The OH stretching vibration of the water molecules in membranes of salts of polystyrene sulfonic acid is investigated by IR spectroscopy. In the series of the alkali ions anomalous behaviour of the position of this band is to be seen. If one compares the position of this band with the corresponding one in pure liquid water this anomality is to be understood like follows: From Li⊕ to Cs⊕ in a progressing degree the molecules of water are not still attached between cation and neighboring anions, but they are present as network of „pure“ water structure cross-linked by hydrogen bonds in the neighbourhood of the ions. A similar situation but to an even greater extend is found in the presence of alkyl ammonium ions. These ions are interacting more strongly with the - SO3⊝ ions. The reasons for this are given. By these results it is understandable that in biological membranes the alkyl ammonium group of the lecithins and sphingomyelines - as postulated by FINEAN - are turned away the surface inwardly in the membran. In the end the different hydration behaviour of the Na⊕ and K⊕ ions is discussed.

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