Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A12: Drops: Heat Transfer and Evaporation I |
Hide Abstracts |
Chair: Justin Burton, Emory University Room: 3018 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A12.00001: Apparent contact angles induced by evaporation into air: interferometric measurements and lubrication-type modeling Pierre Colinet, Yannis Tsoumpas, Sam Dehaeck, Alexey Rednikov For volatile liquids, finite contact angles on solid substrates can occur even in the case of perfect wetting, immobile contact lines and ideally smooth surfaces. This is a fluid-dynamic effect due to evaporation typically intensifying towards a small vicinity of the contact line. In the present talk, we first overview recent theoretical results on the subject, where we focus primarily on the case of diffusion-limited evaporation into air. The model is based upon the so-called de Gennes' paradigm, incorporating simultaneously the spreading coefficient and the disjoining pressure in the form of an inverse cubic law. Then we carry out comparison with experimental results for the contact angles of evaporating sessile drops of several perfectly-wetting HFE liquids of different volatility recently obtained by Mach-Zehnder interferometry. The scaling-type theoretical prediction for the apparent contact angle is found to be in good agreement with experimental measurements. Another model based upon the Kelvin effect (curvature dependence of the saturation conditions) is also briefly discussed, an important conceptual feature of which being that contact-line singularities (both evaporation- and motion-induced) can be fully regularized, in contrast with the first model. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A12.00002: Evaporation of a drop on a flat solid substrate with pinned \& perfect slip contact line Amirhossein Amini, G.M. Homsy We study the evolution of the profile of a 2D axisymmetric, incompressible, Newtonian droplet while evaporating on a flat solid substrate. The droplet has an initial circular cross section, the surface tension and the temperature of the solid-liquid interface are constant, and gravity and van der Waals effects are neglected. We deploy the one-sided model\footnote{Burelbach et al. Journal of Fluid Mechanics, \textbf{195} 463-494 (1988)} which, together with the lubrication approximation, results in an evolution equation for the local height of the droplet. The evolution equation is a nonlinear partial differential equation that is 4$^{\mathrm{th}}$ order in space and 1$^{\mathrm{st}}$ in time and which is solved numerically using the method of lines. The problem is governed by several parameters, the key being the contact line condition and the wall superheat. For the case in which the contact line is pinned, we predict the drop thickness and contact angle as a function of time over a wide range of parameters. Interestingly, we observe a new self-similar regime near the end of the droplet evaporation and derive scaling laws from the numerical solutions. These results are contrasted with those for the case of perfect slip. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A12.00003: Local analysis of the contact region of an evaporating sessile drop S.J.S. Morris In experiments by Gu\'ena et al. (2007), a drop of perfectly wetting pure liquid evaporates from a non--heated substrate at a rate controlled by vapour diffusion. The drop spreads until reaching a radius $a$ determined by initial drop volume; the apparent contact line then reverses direction. The apparent contact angle measured at reversal was found experimentally to vary as $a^{-1/6}$ for $a<1$ mm (about); for larger drops $\theta$ decreases more strongly. Local analysis (Morris {\it J. Fluid Mech.} 739: 308--337. 2014) predicts that $\theta\propto a^{-1/6}$; for the smaller drops obeying the 1/6th rule, predicted values agree with experiment to within 10--30\%. Though the behaviour of drops smaller than the capillary length thus appears to be understood, that of larger drops is not. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A12.00004: Atmospheric convective transport contribution to evaporative sessile droplets Florian Carle, Sergey Semenov, Marc Medale, David Brutin The scientific community struggles with the creation of an accurate quantitative description of sessile droplet evaporation flux rate. The classically used description considers evaporation as a quasi-steady process controlled by the diffusion of vapor into the air, and the whole system is assumed to be isothermal at the ambient temperature. However, when two types of fluids (alcohols and alkanes) are let to evaporate on heated substrates while a side view camera measures their evaporation flux rate, droplets tend to see their evaporation flux rate underestimated by this model mostly due to convection. This experimental study aims to understand how atmospheric convective transport in the vapor phase influences evaporation in order to developed an empirical model that describes with accuracy the evaporation flux rate. The Rayleigh number is used to analyze the contribution of natural convection and an empirical model is developed combining diffusive and convective transport for each type of fluid. The influence of the molecular chain length (and the increasing number of carbon atoms) is also being discussed. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A12.00005: Two-phase DNS of evaporating drops with 3D phenomena and contact-line dynamics Prashant Valluri, Pedro J. S\'{a}enz, Khellil Sefiane, Omar K. Matar A novel 3D two-phase model based on the diffuse-interface method is developed to investigate the fully-coupled two-phase dynamics of a sessile drop undergoing evaporation on a heated substrate. General transient advection-diffusion transport equations are implemented to address the conservation of energy and vapour in the gas phase, which also allows the more realistic modelling of interface mass and energy transport based on local conditions. The emphasis of this investigation is on addressing three-dimensional phenomena during evaporation of drops with non-circular contact area. Irregular drops lead to complex interface shapes with intricate contract-angle distributions along the triple line and with a three-dimensional flow which previous axisymmetric approaches cannot show. The versatility of this model also allows the simulation of the more complex case of drops evaporating with a moving contact line. Both constant-angle (CA) and constant-radius (CR) modes of pure evaporation are successfully simulated and validated against experiments. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A12.00006: On the emergence of vortices in irregular evaporating sessile droplets Pedro J. S\'{a}enz, Dimitrios Mamalis, Khellil Sefiane, Prashant Valluri, Omar K. Matar The spontaneous development of 3D azimuthal vortices parallel to the plane of substrate in an evaporating drop of water with irregular contact area is reported by means of experiments and direct numerical simulations (DNS). In spherical droplets, the non-uniform evaporation flux leads to a 2D axisymmetric flow with fluid being transported along the interface from the contact line (hotter) towards the apex (colder) due to the Marangoni effect. However, infrared recordings of a non-spherical drop show the break of symmetry and the consequent development of a preferential direction for thermocapillary convection. As a result, counter-rotating whirling currents emerge in the drop playing a critical role in regulating the interface thermal motion. This geometry-induced phenomenon is also investigated via simulations with a fully-coupled two-phase model. DNS show good agreement with experiments and reveal the intricate drop dynamics due to this geometry-induced phenomenon. The triggering mechanism is analysed along with the resulting bulk flow. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A12.00007: The effect of vapor diffusion and unsteady heating on the evolution of a sessile droplet on a substrate Mahnprit Jutley, Vladimir Ajaev The behavior of a sessile droplet on a heated substrate has been a topic of interest due to its subtle dependencies on the surrounding environmental conditions and its many applications, such as the coating of a solid substrate with another material, the spray cooling of electronics, and DNA microarray technology to name a few. Prediction of the height evolution of a sessile droplet on heated substrate is governed by the unsteady heating of the substrate, the vapor diffusion into the atmosphere above the droplet, and the effects of surface tension, gravity, thermocapillarity, and disjoining pressure. Using lubrication theory and developing coupling relationships between the heat equation in the substrate, height evolution equation of the droplet, and the vapor diffusion equation in the atmosphere, the system of coupled partial differential equations can be derived and solved. Connection of the numerical simulation to experimental studies is discussed. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A12.00008: How surfactants influence evaporation-driven flows Robert Liepelt, Alvaro Marin, Massimiliano Rossi, Christian J. K\"ahler Capillary flows appear spontaneously in sessile evaporating drops and give rise to particle accumulation around the contact lines, commonly known as \textit{coffee-stain effect} (Deegan \textit{et al.}, Nature, 1997). On the other hand, out-of-equilibrium thermal effects may induce Marangoni flows in the droplet's surface that play an important role in the flow patterns and in the deposits left on the substrate. Some authors have argued that contamination or the presence of surfactants might reduce or eventually totally annul the Marangoni flow (Hu \& Larson, J. Phys. Chem. B, 2006). On the contrary, others have shown an enhancement of the reverse surface flow (Sempels \textit{et al.}, Nat. Commun., 2012). In this work, we employ Astigmatic Particle Tracking Velocimetry (APTV) to obtain the 3D3C evaporation-driven flow in both bulk and droplet's surface, using surfactants of different ionic characters and solubility. Our conclusions lead to a complex scenario in which different surfactants and concentrations yield very different surface-flow patterns, which eventually might influence the colloidal deposition patterns. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A12.00009: Free surface profile of evaporative liquids at the vicinity of the contact line Sammy Houssainy, Pirouz Kavehpour Interfacial phenomenon, specifically those associated with evaporation from thin liquid films near the contact line of a liquid drop, play a major role in many current engineering applications which require high local heat fluxes, as evident in heat pipes, grooved evaporators, fuel cells and suction nucleate boiling devices. This study will prove useful in the improvement of such applications. Fluoresces microscopy was used as our main technique of investigating the free surface profiles of evaporative liquids, as it delivers sufficient range and resolution to address the challenge of capturing the microscopic and macroscopic aspects of this phenomenon. Subsequent to our experimental findings, the results are compared with non-volatile liquids for both contact angle and free surface structures. [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