The Effects of Asymmetric Micro Ratchets on Dynamic Contact Angle and Pool Boiling Performance

2012 ◽  
Author(s):  
Lance Austin Brumfield ◽  
Sunggook Park
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Pool Boiling ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Equilibrium Contact Angle ◽  
Droplet Impingement ◽  
Receding Contact ◽  
Receding Contact Angle

The dynamic advancing and receding contact angles of 5μl water droplets were experimentally measured via the droplet impingement technique on a polished brass surface, one brass symmetric micro ratchet, and five brass asymmetric micro ratchet samples of varying dimensions. Droplets were released from varying heights (Weber number) and the impacts studied via high speed camera. Equilibrium advancing and receding contact angles were measured by placing a water droplet on the surfaces and tilting it. Contact angle values were then compared to an existing pool boiling model which incorporates the dynamic receding contact angle, surface roughness ratio, and equilibrium contact angle.

Motion of drops on inclined surfaces in the inertial regime

2013 ◽  
Vol 726 ◽  
pp. 26-61 ◽  
Author(s):  
Baburaj A. Puthenveettil ◽  
Vijaya K. Senthilkumar ◽  
E. J. Hopfinger
Keyword(s):  
Contact Angle ◽  
Slip Length ◽  
Water Drop ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Drop Diameter ◽  
Angle Variation ◽  
Hydrodynamic Description ◽  
Receding Contact ◽  
Receding Contact Angle

AbstractWe present experimental results on high-Reynolds-number motion of partially non-wetting liquid drops on inclined plane surfaces using: (i) water on fluoro-alkyl silane (FAS)-coated glass; and (ii) mercury on glass. The former is a high-hysteresis ($3{5}^{\circ } $) surface while the latter is a low-hysteresis one (${6}^{\circ } $). The water drop experiments have been conducted for capillary numbers $0. 0003\lt Ca\lt 0. 0075$ and for Reynolds numbers based on drop diameter $137\lt Re\lt 3142$. The ranges for mercury on glass experiments are $0. 0002\lt Ca\lt 0. 0023$ and $3037\lt Re\lt 20\hspace{0.167em} 069$. It is shown that when $Re\gg 1{0}^{3} $ for water and $Re\gg 10$ for mercury, a boundary layer flow model accounts for the observed velocities. A general expression for the dimensionless velocity of the drop, covering the whole $Re$ range, is derived, which scales with the modified Bond number ($B{o}_{m} $). This expression shows that at low $Re$, $Ca\sim B{o}_{m} $ and at large $Re$, $Ca \sqrt{Re} \sim B{o}_{m} $. The dynamic contact angle (${\theta }_{d} $) variation scales, at least to first-order, with $Ca$; the contact angle variation in water, corrected for the hysteresis, collapses onto the low-$Re$ data of LeGrand, Daerr & Limat (J. Fluid Mech., vol. 541, 2005, pp. 293–315). The receding contact angle variation of mercury has a slope very different from that in water, but the variation is practically linear with $Ca$. We compare our dynamic contact angle data to several models available in the literature. Most models can describe the data of LeGrand et al. (2005) for high-viscosity silicon oil, but often need unexpected values of parameters to describe our water and mercury data. In particular, a purely hydrodynamic description requires unphysically small values of slip length, while the molecular-kinetic model shows asymmetry between the wetting and dewetting, which is quite strong for mercury. The model by Shikhmurzaev (Intl J. Multiphase Flow, vol. 19, 1993, pp. 589–610) is able to group the data for the three fluids around a single curve, thereby restoring a certain symmetry, by using two adjustable parameters that have reasonable values. At larger velocities, the mercury drops undergo a change at the rear from an oval to a corner shape when viewed from above; the corner transition occurs at a finite receding contact angle. Water drops do not show such a clear transition from oval to corner shape. Instead, a direct transition from an oval shape to a rivulet appears to occur.

Effect of Dynamic Contact Angle on Single Bubbles During Nucleate Pool Boiling

2004 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Contact Angle ◽  
Numerical Study ◽  
Removal Rate ◽  
Pool Boiling ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Heated Wall ◽  
Nucleate Pool Boiling ◽  
Static Contact

Nucleate pool boiling at low heat flux is typically characterized by cyclic growth and departure of single vapor bubbles from the heated wall. It has been experimentally observed that the contact angle at the bubble base varies during the ebullition cycle. In the present numerical study, dynamic advancing and receding contact angles obtained from experimental observations are specified at the base of a vapor bubble growing on a wall. The complete Navier-Stokes equations are solved and the liquid-vapor interface is captured using the level-set technique. The effect of dynamic contact angle on the bubble dynamics and vapor removal rate are compared to results obtained with static contact angle. The results show that bubble base exhibits a slip/stick behavior with dynamic contact angle though the overall effect on the vapor removal rate is small. Higher advancing contact angle is found to increase the vapor removal rate.

Visualization of Dynamic Contact Angle

2013 ◽  
Author(s):  
Brandon S. Field
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
High Speed ◽  
Solid Phase ◽  
Capillary Rise ◽  
Dynamic Contact Angle ◽  
Fluid Phase ◽  
Dynamic Contact ◽  
Force Balance ◽  
Receding Contact

Capillary rise of air-water-solid systems have been recorded with high-speed video. Glass and metal have been used as the solid phase, and the dynamic shape of the meniscus and contact angle have been characterized. The advancing and receding contact angle is of interest in computational simulations of boiling flow, and the present visualizations attempt to quantify the dynamic aspects of contact line motion. The centroid of the capillary meniscus has been tracked in order to determine the force at the contact line based on a force balance of the elevated fluid phase. The solid phase is raised and lowered in the fluid at different rates to observe advancing and receding contact lines.

The Surface Modification with Fluorocarbon Thin Films for the Prevention of Stiction in Mems

1998 ◽  
Vol 518 ◽  
Author(s):  
Sang-Ho Lee ◽  
Myong-Jong Kwon ◽  
Jin-Goo Park ◽  
Yong-Kweon Kim ◽  
Hyung-Jae Shin
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Fluorocarbon Films ◽  
Perfluorodecanoic Acid ◽  
Large Hysteresis ◽  
Static Contact ◽  
Receding Contact ◽  
Highly Hydrophobic ◽  
Receding Contact Angle

AbstractHighly hydrophobic fluorocarbon films were prepared by the vapor phase (VP) deposition method in a vacuum chamber using both liquid (3M's FC40, FC722) and solid sources (perfluorodecanoic acid (CF3(CF2)8COOH), perfluorododecane (C12F26)) on Al, Si and oxide coated wafers. The highest static contact angles of water were measured on films deposited on aluminum substrate. But relatively lower contact angles were obtained on the films on Si and oxide wafers. The advancing and receding contact angle analysis using a captive drop method showed a large contact angle hysteresis (ΔH) on the VP deposited fluorocarbon films. AFM study showed poor film coverage on the surface with large hysteresis. FTIR-ATR analysis positively revealed the stretching band of CF2 groups on the VP deposited substrates. The thermal stability of films was measured at 150°C in air and nitrogen atmospheres as a function of time. The rapid decrease of contact angles was observed on VP deposited FC and PFDA films in air. However, no decrease of contact angle on them was observed in N2.

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.

Dynamics of Droplet Motion Induced by Electrowetting

2016 ◽  
Author(s):  
Yi Lu ◽  
Aritra Sur ◽  
Dong Liu ◽  
Carmen Pascente ◽  
Paul Ruchhoeft
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Numerical Models ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
High Speed Photography ◽  
Droplet Dynamics ◽  
Droplet Shape ◽  
Moving Contact Line ◽  
Moving Contact

Electrowetting has drawn significant interests due to the potential applications in electronic displays, lab-on-a-chip devices and electro-optical switches, etc. Current understanding of electrowetting-induced droplet dynamics is hindered by the inadequacy of available numerical and theoretical models in properly handling the dynamic contact angle at the moving contact line. A combined numerical and experimental approach was employed in this work to study the spatiotemporal responses of a droplet subject to EW with both direct current and alternating current actuating signals. The time evolution of the droplet shape was measured using high-speed photography. Computational fluid dynamics models were developed by using the Volume of Fluid-Continuous Surface Force method in conjunction with a selected dynamic contact angle model. It was found that the numerical models were able to accurately predict the key parameters of the electrowetting-induced droplet dynamics.

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