Evaporative Characteristics of Al2O3 Nanofluid Droplet on Heated Surface

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Dae Yun Kim ◽  
Jae Bin Lee ◽  
Seong Hyuk Lee ◽  
Jung-Yeul Jung
Keyword(s):  
Contact Angle ◽  
Heated Surface ◽  
Dynamic Contact Angle ◽  
Average Diameter ◽  
Contact Angles ◽  
Textured Surface ◽  
Al2o3 Nanoparticles ◽  
Cnc Machine ◽  
Data Logger ◽  
Temperature Detector

The present study experimentally investigates the evaporative characteristics for a nanofluid droplet on heated surface. For experiments, the alumina (Al2O3) nanoparticles having a 50 nm average diameter were distributed in deionized (DI)water. The equilibrium contact angles (ECA) of DI-water on bare (without texturing) and hole-patterned textured (by µ-CNC machine) copper surfaces were 60o and 82o. Also, advancing and receding contact angles were 73.3o and 25.8o for bare surface, and 101.3o and 55.2o for textured surface. Surface temperature was fixed as 100±0.2oC, measured by resistance temperature detector (RTD) sensors with data logger. During the experiments, the ambient temperature was 22oC with the relative humidity of 32%. At the initial stage, the dynamic contact angle (DCA) of 0.01 vol.% nanofluid droplet on the textured surface drastically increased over its own ECA due to the generation of large bubbles inside the droplet. However, the contact angle of 0.1vol.% nanofluid droplet at t = 5 s was smaller than that of 0.01vol.% case because the increase in nanofluid concentration caused the reduction of surface tension. After that, DCA gradually decreased until dried out, and total evaporation time was significantly delayed in the case of textured surface. Moreover,the heat transfer characteristics during evaporation phenomenon was affected by the nanofluid concentration and the contact area with the heated surface.

scholarly journals Numerical Bifurcation Analysis of a Film Flowing over a Patterned Surface through Enhanced Lubrication Theory

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 405
Author(s):  
Nicola Suzzi ◽  
Giulio Croce
Keyword(s):  
Contact Angle ◽  
Bifurcation Analysis ◽  
Dynamic Contact Angle ◽  
Flow Characteristics ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Inclined Plate ◽  
Lubrication Equation ◽  
Static Contact ◽  
Numerical Bifurcation

The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to 75∘ are investigated due to the full implementation of the free surface curvature, which replaces the small slope approximation, accurate for film slope lower than 30∘. The dynamic contact angle is first verified with the Hoffman–Voinov–Tanner law in case of a stable film down an inclined plate with uniform surface wettability. Then, contamination spots, characterized by an increased value of the static contact angle, are considered in order to induce film instability and several parametric computations are run, with different film patterns observed. The effects of the flow characteristics and of the hybrid pattern geometry are investigated and the corresponding bifurcation diagram with the number of observed rivulets is built. The long term evolution of induced film instabilities shows a complex behavior: different flow regimes can be observed at the same flow characteristics under slightly different hybrid configurations. This suggest the possibility of controlling the rivulet/film transition via a proper design of the surfaces, thus opening the way for relevant practical application.

Spreading-Droplet Simulation With Surface Tension Model Using Inter-Particle Force in Particle Method

2013 ◽  
Author(s):  
Eiji Ishii ◽  
Taisuke Sugii
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Particle Method ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Particle Methods ◽  
Static Contact ◽  
Particle Force ◽  
Surface Tension Model

Predicting the spreading behavior of droplets on a wall is important for designing micro/nano devices used for reagent dispensation in micro-electro-mechanical systems, printing processes of ink-jet printers, and condensation of droplets on a wall during spray forming in atomizers. Particle methods are useful for simulating the behavior of many droplets generated by micro/nano devices in practical computational time; the motion of each droplet is simulated using a group of particles, and no particles are assigned in the gas region if interactions between the droplets and gas are weak. Furthermore, liquid-gas interfaces obtained from the particle method remain sharp by using the Lagrangian description. However, conventional surface tension models used in the particle methods are used for predicting the static contact angle at a three-phase interface, not for predicting the dynamic contact angle. The dynamic contact angle defines the shape of a spreading droplet on a wall. We previously developed a surface tension model using inter-particle force in the particle method; the static contact angle of droplets on the wall was verified at various contact angles, and the heights of droplets agreed well with those obtained theoretically. In this study, we applied our surface tension model to the simulation of a spreading droplet on a wall. The simulated dynamic contact angles for some Weber numbers were compared with those measured by Šikalo et al, and they agreed well. Our surface tension model was useful for simulating droplet motion under static and dynamic conditions.

Measurements of the Contact Angles for Various Fluids Which Are Widely Used in the Oilfields to Improve Oil Recovery

2018 ◽  
Author(s):  
M. Elsharafi ◽  
K. Vidal ◽  
R. Thomas
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Interfacial Tension ◽  
Oil Recovery ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Rock Face ◽  
Angle Measurements ◽  
Contact Angle Measurements

Contact angle measurements are important to determine surface and interfacial tension between solids and fluids. A ‘water-wet’ condition on the rock face is necessary in order to extract oil. In this research, the objectives are to determine the wettability (water-wet or oil-wet), analyze how different brine concentrations will affect the wettability, and study the effect of the temperature on the dynamic contact angle measurements. This will be carried out by using the Cahn Dynamic Contact Angle. Analyzer DCA 315 to measure the contact angle between different fluids such as surfactant, alkaline, and mineral oil. This instrument is also used to measure the surface properties such as surface tension, contact angle, and interfacial tension of solid and liquid samples by using the Wilhelmy technique. The work used different surfactant and oil mixed with different alkaline concentrations. Varying alkaline concentrations from 20ml to 1ml were used, whilst keeping the surfactant concentration constant at 50ml.. It was observed that contact angle measurements and surface tension increase with increased alkaline concentrations. Therefore, we can deduce that they are directly proportional. We noticed that changing certain values on the software affected our results. It was found that after calculating the density and inputting it into the CAHN software, more accurate readings for the surface tension were obtained. We anticipate that the surfactant and alkaline can change the surface tension of the solid surface. In our research, surfactant is desirable as it maintains a high surface tension even when alkaline percentage is increased.

Hydrosilation-Cured Poly(dimethylsiloxane) Networks:  Intrinsic Contact Angles via Dynamic Contact Angle Analysis

2003 ◽  
Vol 36 (10) ◽  
pp. 3689-3694 ◽  
Author(s):  
Janelle M. Uilk ◽  
Ann E. Mera ◽  
Robert B. Fox ◽  
Kenneth J. Wynne
Keyword(s):  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Contact Angle Analysis

Effect of Contact Angle on the Heat Transfer to an Evaporating Meniscus on a Moving Heated Surface

2005 ◽  
Author(s):  
A. Mukherjee ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Stokes Equations ◽  
Contact Region ◽  
Heated Surface ◽  
Contact Angles ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Moving Wall ◽  
Liquid Circulation

Numerical simulation is carried out to study a 2D evaporating meniscus formed on a moving wall. The complete Navier-Stokes equations along with continuity and energy equations are solved. The liquid vapor interface is captured using the level set technique. The meniscus is fed with saturated water from the top whereas the bottom wall is maintained at a higher temperature and is also imparted with a velocity. The meniscus attains a steady shape when all the incoming liquid gets evaporated due to heat transfer from the wall. The advancing and receding contact region of the meniscus are provided with different contact angles. Results indicate that the average heat flux at the meniscus base increases with increase in contact angle. The primary reason for heat transfer from the wall is attributed to the liquid circulation inside the meniscus and the corresponding transient conduction from the wall. As the meniscus contact angle increases the liquid circulation is found to disturb the thermal boundary layer more effectively thereby resulting in increased wall heat transfer. The effect of contact angle on wall heat transfer to the moving and evaporating meniscus is compared to partial nucleate pool boiling.

scholarly journals The Effect of Water Droplet Size, Temperature, and Impingement Velocity on Gold Wettability at the Nanoscale

2017 ◽  
Vol 5 (3) ◽  
Author(s):  
Jhonatam Cordeiro ◽  
Salil Desai
Keyword(s):  
Contact Angle ◽  
Droplet Size ◽  
Water Droplet ◽  
Molecular Diffusion ◽  
Dynamic Contact Angle ◽  
Contact Angles ◽  
Gold Substrate ◽  
Stabilization Time ◽  
Lower Contact ◽  
Impingement Velocity

Molecular dynamics (MD) simulations are performed to investigate the wettability of gold substrate interacting with nanosized droplets of water. The effects of droplet size, temperature variation, and impingement velocity are evaluated using molecular trajectories, dynamic contact angle, spread ratios, radial distribution function (RDF), and molecular diffusion graphs. Droplets of 4 nm and 10 nm were simulated at 293 K and 373 K, respectively. Stationary droplets were compared to droplets impinging the substrate at 100 m/s. The simulations were executed on high-end workstations equipped with NVIDIA® Tesla graphical processing units (GPUs). Results show that smaller droplets have a faster stabilization time and lower contact angles than larger droplets. With an increase in temperature, stabilization time gets faster, and the molecular diffusion from the water droplet increases. Higher temperatures also increase the wettability of the gold substrate, wherein droplets present a lower contact angle and a higher spread ratio. Droplets that impact the substrate at a higher impingement velocity converge to the same contact angle as stationary droplets. At higher temperatures, the impingement velocities accelerate the diffusion of water molecules into vapor. It was revealed that impingement velocities do not influence stabilization times. This research establishes relationships among different process parameters to control the wettability of water on gold substrates which can be explored to study several nanomanufacturing processes.

Thermocapillary migration of droplets under molecular and gravitational forces

2018 ◽  
Vol 847 ◽  
pp. 1-27 ◽  
Author(s):  
J. R. Mac Intyre ◽  
J. M. Gomba ◽  
Carlos Alberto Perazzo ◽  
P. G. Correa ◽  
M. Sellier
Keyword(s):  
Contact Angle ◽  
Power Law ◽  
Molecular Interactions ◽  
Heated Surface ◽  
Contact Angles ◽  
Numerical Results ◽  
Constant Thickness ◽  
Polar Liquids ◽  
Time Dynamics ◽  
Thermocapillary Migration

We study the thermocapillary migration of two-dimensional droplets of partially wetting liquids on a non-uniformly heated surface. The effect of a non-zero contact angle is imposed through a disjoining–conjoining pressure term. The numerical results for two different molecular interactions are compared: on the one hand, London–van der Waals and ionic–electrostatics molecular interactions that account for polar liquids; on the other hand, long- and short-range molecular forces that model molecular interactions of non-polar fluids. In addition, the effect of gravity on the velocity of the drop is analysed. We find that for small contact angles, the long-time dynamics is independent of the molecular potential, and the footprint of the droplet increases with the square root of time. For intermediate contact angles we observe that polar droplets are more likely to break up into smaller volumes than non-polar ones. A linear stability analysis allows us to predict the number of droplets after breakup occurs. In this regime, the effect of gravity is stabilizing: it reduces the growth rates of the unstable modes and increases the shortest unstable wavelength. When breakup is not observed, the droplet moves steadily with a profile that consists in a capillary ridge followed by a film of constant thickness, for which we find power law dependencies with the cross-sectional area of the droplet, the contact angle and the temperature gradients. For large contact angles, non-polar liquids move faster than polar ones, and the velocity is proportional to the Marangoni stress. We find power law dependencies for the velocity for the different regimes of flow. The numerical results allow us to shed light on experimental facts such as the origin of the elongation of droplets and the existence of saturation velocity.

CHARACTERIZATION OF DYNAMIC WETTING OF PLASMA-TREATED PTFE FILM

2007 ◽  
Vol 14 (04) ◽  
pp. 821-825 ◽  
Author(s):  
Q. F. WEI ◽  
Y. LIU ◽  
F. L. HUANG ◽  
S. H. HONG
Keyword(s):  
Contact Angle ◽  
Plasma Treatment ◽  
Surface Properties ◽  
Contact Angle Hysteresis ◽  
Frictional Coefficient ◽  
Dynamic Contact Angle ◽  
Contact Angles ◽  
Dynamic Wetting ◽  
Ptfe Film ◽  
Receding Contact

Polytetrafluoroethylene (PTFE) has been increasingly used in many industries due to its low frictional coefficient and excellent chemical inertness. The surface properties of PTFE are of importance in various applications. The surface properties of PTFE can be modified by different techniques. In this study, PTFE film was treated in oxygen plasma for improving surface wettability. The effects of plasma treatment on dynamic wetting behavior were characterized using Scanning Probe Microscopy (SPM), Fourier transform infrared spectroscopy (FTIR), and dynamic contact angle (DCA) measurements. SPM observations revealed the etching effect of the plasma treatment on the film. The introduction of hydrophilic groups by plasma treatment was detected by FTIR. The roughened and functionalized surface resulted in the change in both advancing and receding contact angles. Advancing and receding contact angles were significantly reduced, but the contact angle hysteresis was obviously increased after plasma treatment.

scholarly journals Preparation of Superhydrophobic Teflon® AF 1600 Sub-Micron Fibers and Yarns Using the Forcespinningtm Technique

2013 ◽  
Vol 8 (4) ◽  
pp. 155892501300800 ◽  
Author(s):  
Yatinkumar Rane ◽  
Aleksey Altecor ◽  
Nelson S. Bell ◽  
Karen Lozano
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Average Diameter ◽  
Contact Angle Measurement ◽  
Contact Angles ◽  
Angle Measurement ◽  
Sem Analysis ◽  
Fiber Formation ◽  
Excellent Thermal Stability ◽  
Wetting Properties

Superhydrophobic materials combined with manufacturing processes that can increase surface roughness of the material, offer an opportunity to effectively control wetting properties. Rapid formation of Teflon® AF (TAF) fibrous mats with sub-micron fiber diameter using the Forcespinning™ technique is presented. The fiber formation technique is based on the use of centrifugal forces. SEM analysis shows uniform formation of TAF 1600 fibers with average diameter of 362±58nm. Contact angle measurement confirms the superhydrophobic nature of the mats with contact angles as high as 169° ± 3° and rolling angles of 2°. TAF 1600 mats were forcespun at a rate of 1gr/min. The relationship between the contact angle and hierarchical surface roughness of the TAF mat is also discussed. TAF yarns were also manufactured and characterized. Yarns with diameters of 156 microns withstood 17.5 MPa of engineering stress with a Young's modulus of 348 MPa in the elastic region and excellent thermal stability.

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