Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session FF: Surface Tension II |
Hide Abstracts |
Chair: Enrique Rame, National Center for Space Exploration Research (NASA-Glenn) Room: Hilton Chicago Continental C |
Monday, November 21, 2005 8:00AM - 8:13AM |
FF.00001: Marangoni Convection and Deviations from Maxwells' Evaporation Model Phil Segre, Eddie Snell, Dan Adamek We investigate evaporation and natural convection from thin pools of volatile liquids. We find that evaporation rates can deviate from the classical Maxwell evaporation model, and that deviations become larger with increasing liquid volatility. High resolution thermal IR imaging is used to characterize the Marangoni convective patterns that can arise during evaporation. We develop a heat balance model to connect the evaporation rates to the convective dynamics, and show that the convective flows are the source of the deviations from Maxwells' evaporation model. [Preview Abstract] |
Monday, November 21, 2005 8:13AM - 8:26AM |
FF.00002: Evaporation of thin liquid droplets on heated surfaces: theory versus experiment Christof Sodtke, Vladimir Ajaev, Peter Stephan We carry out combined experimental and theoretical studies of liquid droplets on heated surfaces in a closed container filled with saturated vapor. The droplets are deposited on an electrically heated stainless steel foil. Evolution of droplet shapes is studied by optical methods simultaneously with high resolution temperature measurements using thermochromic liquid crystals (TLCs). A mathematical model is developed based on the assumption of liquid droplet thickness being much smaller than its radius. Both the dynamics of liquid-vapor interface and the temperature profiles in the foil are shown to be in good agreement with the experimental data. [Preview Abstract] |
Monday, November 21, 2005 8:26AM - 8:39AM |
FF.00003: Steady 3D thermocapillary flow and dryout inside a V-shaped wedge Li Yang, G.M. Homsy We consider a liquid meniscus inside a wedge of included angle $2\beta$ that wets the solid walls with a contact angle $\theta$. Under an imposed axial temperature gradient, the Marangoni stress moves fluid toward colder regions while capillary pressure gradients drive a reverse flow, leading to a steady state. Two curvatures contribute to the capillary forces: the axial curvature along the flow direction z and the transverse curvature of the circular arc inside the cross section perpendicular to the flow axis. Lubrication theory is used to derive a thin film equation for the shape of the interface. Solutions are governed by two parameters: D, a geometric parameter giving the relative importance of the two curvatures and M, a modified Marangoni number. Numerical solutions indicate that for sufficiently large M, the Marangoni stress creates a virtual dry region. The value of M at dryout is found to depend linearly on D. A simplified analytical model is developed which agrees very well with the exact solution for large values of D. It is found that dryout occurs more easily for larger wedge angle and/or contact angle. [Preview Abstract] |
Monday, November 21, 2005 8:39AM - 8:52AM |
FF.00004: Heat transfer and Marangoni convection in droplets on super-hydrophobic surfaces Daniel Tam, Volkmar von Arnim, Gareth McKinley, Anette Hosoi We study heat transfer properties of a small droplet of water sitting on top of a heated super-hydrophobic surface. Water is observed to be driven upwards on the surface of the spherical droplet and to accelerate downwards inside the droplet towards the contact point with the surface. The internal dynamics of the droplet is due to a temperature gradient which results in a gradient of surface tension. The surface tension gradient, in turn, drives water on the free surface away from the contact point. A solution to this thermocapillary driven Marangoni convection problem has been fully developed analytically in terms of streamfunctions. Analytical and experimental results are in excellent agreement. [Preview Abstract] |
Monday, November 21, 2005 8:52AM - 9:05AM |
FF.00005: Free-surface deformation of a liquid bridge Brent Houchens, John Walker Several groups have predicted free-surface deformations in thermocapillary driven liquid-bridge flows. In problems such as the half-zone, the temperature dependent surface tension confines the fluid, forming a liquid bridge between two solid cylinders, held at different temperatures. The shape of the free-surface influences the flow, and vice-versa. In even the simplest case, where buoyancy is neglected and the flow is axisymmetric, there is disagreement between predictions with respect to the free-surface shape. Furthermore, few models include the effect of dynamic pressure, which is non-negligible under microgravity conditions. To classify the discrepancies in the models, we investigate a half-zone in which the reference surface tension is large compared to the thermocapillary induced variations. Combined with a microgravity environment, these conditions produce a nearly cylindrical liquid bridge. Therefore, we calculate the flow corresponding to a cylindrical free-surface, and then allow for small surface-shape perturbations. Applying asymptotic expansions, we predict the leading order corrections to the free-surface velocity and deformation. This solution is very efficient and stable as compared to numerical schemes which iterate between the flow field and free-surface shape. It also offers insight into the relevance of each term, including the dynamic pressure variation. [Preview Abstract] |
Monday, November 21, 2005 9:05AM - 9:18AM |
FF.00006: A novel mechanism of Marangoni motion based on liquid-liquid phase transition Viatcheslav Berejnov Marangoni motion is caused by inhomogeneity of the temperature and concentration fields along the liquid interfaces. In the case of a drop immersed in another liquid, the interface produces a momentum that propels the drop. Most existing models assume the surface tension to be a linear function of temperature and concentration. However the universality of the linear approximation should be reconsidered. We propose a new view on the drop locomotion where the local inhomogeneity of surface tension plays a central role. We observed fast self-running oil ``lenses'' on the air/water interface. Measured velocities of these drops were two orders of magnitude higher than the corresponding velocities in the linear model. It was found that our water/oil system continuously evolves during its equilibration and eventually reaches the spinodal decomposition. The liquid-liquid transition across the interface randomly creates areas of spontaneous emulsification (very low surface tension). Competition between the low and high surface tension areas results on the average in highly nonlinear surface tension gradients that enormously propel the drop. [Preview Abstract] |
Monday, November 21, 2005 9:18AM - 9:31AM |
FF.00007: Breakup of threads and rupture of films: Singularity-free solutions in the framework of a unified approach Yulii Shikhmurzaev As is known, the standard approach of fluid mechanics applied to the thread breakup problem leads to a singular, and hence unphysical, solution whereas the film rupture problem appears to have no solution at all, unless one ``augments'' the continuum model with intermolecular forces. The present work gives a regular description of both flows as particular cases of the same physical phenomenon. As can be shown by analyzing the standard model, the developing instability of a thread or an external disturbance of a film lead to the creation of a fresh free-surface area. The rate of this process tends to infinity as the thickness of the thread/film goes down and, as it becomes comparable with the inverse surface tension relaxation time, one can no longer treat the surface tension as a material constant; it becomes a variable whose dynamics and distribution along the interface are coupled with the flow. Thus, both problems appear to be particular cases of the fluid motion with forming/disappearing interfaces and can be described using an earlier developed theory of such flows that has first been applied to the moving contact-line problem of dynamic wetting. [Preview Abstract] |
Monday, November 21, 2005 9:31AM - 9:44AM |
FF.00008: Spreading of thin films assisted by thermal fluctuations Benny Davidovitch, Esteban Moro, Howard Stone We derive a nonlinear stochastic lubrication equation that describes the dynamics of a thin film on a solid substrate in the presence of thermal fluctuations. Numerical simulations followed by self-similarity analysis indicate that, asymptotically, when thermal fluctuations become dominant the radii $r(t)$ of spreading drops grow in time as $t^{1/4},t^{1/6}$ in channel and radial flow geometries, respectively. These spreading rates are much faster than the classical Tanner's law, according to which $t^{1/7},t^{1/10}$ in these flow geometries, respectively. In many fluids, thermal effects might be attenuated by gravitational or van der Waals forces. We propose, however, that in certain complex fluids, such as colloidal liquids, such enhanced rate of spreading drop might be observed. [Preview Abstract] |
Monday, November 21, 2005 9:44AM - 9:57AM |
FF.00009: Chaotic Mixing in a Meandering Channel Segmented by Gas Bubbles Metin Muradoglu, Howard A. Stone Mixing in a meandering channel segmented by gas bubbles is studied computationally in a two dimensional setting using a finite-volume/front-tracking method. Molecular diffusion is neglected and only the stirring due to chaotic advection is considered. Passive tracer particles are used to visualize the mixing patterns and mixing is quantified using both an entropy measure and average stretching of fluid elements. It is found that the corrugation of the channel, the capillary number and the distance between the bubbles relative to the channel width are the most important parameters influencing the quality of mixing. The liquid film between the bubbles and the channel wall causes a leakage that significantly deteriorates the quality of mixing in the bulk fluid. It is verified that the film thickness $\delta$ normalized by the channel width $h$ increases with the capillary number as $\delta/h \sim Ca^{2/3}$ in straight portions of the channel but it increases rapidly as the bubble turns around a sharp corner. Therefore the leakage is much larger in a winding channel than that in a straight channel. It is also found that the bubble size does not have a significant influence on the mixing if it is equal or larger than the channel width but the mixing quality decreases rapidly as the bubble size gets smaller than the channel width due to increased leakage. The mixing is found to be weakly dependent on the Reynolds number and the viscosity ratio. [Preview Abstract] |
Monday, November 21, 2005 9:57AM - 10:10AM |
FF.00010: Controlled Patterning of Carbon Nanotube Arrays Using Liquids -- Toward ``Capillography''. Elijah Sansom, Lydia Trevino, Morteza Gharib, Flavio Noca We present results of controlled patterning experiments using dense, vertically aligned carbon nanotube arrays (``nanocarpets''). Small amounts of liquids placed on these surfaces result in various micro-scale patterns of rearranged nanotubes. Feature sizes produced range from a few microns for the semi-circular nest patterns to hundreds of microns or more for the trench patterns. Flow effects, evaporation rate dependence (from 8 x 10$^{-8}$ to 3 x 10$^{-5}$ g/cm$^{2}$/s), surface tension (from $\sim $20 dyn/cm to $\sim $70 dyn/cm), and properties of the nanocarpet substrates (packing density, nanotube length, adhesion to substrate) are considered along with the patterns they produce. Once made, the patterns are robust to further wetting and evaporation. Using SEM image analysis, the mean size, distribution, and character of the hole and trench patterns are used for comparison between these experiments and others reported in the literature. The typical spread of feature sizes within a sample is about half the mean. This method of patterning nanostructures using liquid-based self-assembly, here termed ``capillography,'' represents a useful nanotechnology and involves rich physical phenomena. Some potential applications are in surface drag reduction, field emission displays, thermal management, and cellular tissue growth substrates. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700