Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P04: Focus Session: Leidenfrost Drops and the Physics of the Vapor Layer |
Hide Abstracts |
Chair: Justin Burton, Emory University Room: 203 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P04.00001: The vibrating life of Leidenfrost drops Invited Speaker: Ambre Bouillant A volatile liquid is deposited on a hot solid can survive for minutes, which is known since Leidenfrost to rely on the presence of an insulating vapor layer beneath the liquid. In this levitating state, vapor prevents liquid adhesion leading to thriving dynamics, either spontaneous or forced. Among those spectacular features is the liquid ability to undergo a shape transition from axisymmetric to self-organized oscillations. Such liquid stars are not only encountered with Leidenfrost drops, but with weakly adhering liquids subjected to external periodic forcing. Brunet et al. reported stars are observed provided excitation exceeds a threshold. For Leidenfrost drops, however, the mechanism remains a mystery since there is no prescribed forcing - stars spontaneously appear and sustain. Various mechanisms were proposed invoking thermal convection. Yet, drops supported by steady air flow perform such oscillations. Our plan is to discuss the origin of Leidenfrost stars. We report that vapor self-vibrates, and explain the ensuing coupling that leads to those spectacular oscillations. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P04.00002: Characterizing the final moments of the Leidenfrost vapor layer Dana Harvey, Joshua Mendez, Justin Burton The vapor layer generated between a very hot surface and an evaporating liquid thins as the surface cools down. Eventually, hydrodynamic fluctuations of the liquid will cause the vapor layer to fail, leading to liquid/solid contact and explosive boiling. Using a new electrical technique we can characterize the failure of the vapor layer on sub-microsecond time scales. The vapor layer is treated as a complex circuit component with measurable impedance. A heated titanium electrode is lowered into a bath of salt water. A 10 MHz carrier signal passes through the vapor layer and the liquid so that the capacitive reactance of the system is low. The amplitude of the carrier wave is monitored in time. Using a model circuit for the vapor layer, physical properties of the layer can be determined. Within the first millisecond, a touchdown event occurs where the liquid rapidly wets the solid surface, characterized by a precipitous drop in the resistive part of the impedance. Then, the heat transfer to the liquid causes vaporization and boiling spreads from the point of contact. We expect this technique will also shed light on the sensitive role that salt plays in the Leidenfrost effect, as well as surface properties such as roughness. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P04.00003: The nanoscale instability driving Leidenfrost film collapse Tom Y. Zhao, Neelesh A. Patankar Above a critical temperature known as the Leidenfrost point (LFP), a heated surface can suspend a liquid droplet above a film of its own vapor. Here, we identify the vapor film instability for small length scales that ultimately sets the collapse condition at the LFP. From a linear stability analysis, it is shown that the main film stabilizing mechanisms are the liquid-vapor surface tension, viscous transport of vapor mass, and evaporation at the liquid-vapor interface. Meanwhile, van der Waals interaction between the bulk liquid and the solid substrate across the vapor phase drives film collapse. This physical insight into vapor film dynamics allows us to derive an ab-initio, mathematical expression for the Leidenfrost point of a fluid. The expression captures the experimental data on the LFP for different fluids under various surface wettabilities and ambient pressures. For fluids that wet the surface (small intrinsic contact angle), the expression can be simplified to a single, dimensionless number that encapsulates the nanoscale instability governing the LFP. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P04.00004: Explosive Events in Bicomponent Droplet Impact on Superheated Substrates Tamal Roy, Uddalok Sen, Ranjan Ganguly, Louis A. Angeloni, W. Andreas Schroeder, Constantine M. Megaridis Droplet impact on superheated smooth solids has attracted enormous attention since Leidenfrost reported the eponymous phenomenon more than 250 years ago. The related literature is almost exclusively focused on single component liquids, which maintain their identity even under disruptive boiling conditions. In this work, we provide evidence for the existence of a new regime - termed explosive boiling - for the impact of bicomponent (ethanol and water) droplets on superheated substrates at temperatures between the respective Leidenfrost temperatures of the two liquid constituents. This regime is characterized by a violent shattering of the main droplet upon impact, and is observed only for a certain range of alcohol concentrations of the binary mixture. We explore this behavior experimentally through high-speed imaging at different substrate temperatures, droplet concentrations, and impact velocities. Furthermore, we provide interferometric evidence for the cause of occurence of this unprecedented regime. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P04.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 6:21PM - 6:34PM |
P04.00006: Self-propulsion and capillary orbits of inverse Leidenfrost droplets. Anais Gauthier, Guillaume Lajoinie, Christian Diddens, Detlef Lohse, Jacco Snoeijer, Devaraj Van Der Meer Ambient temperature drops deposited on a liquid nitrogen bath can be maintained in the inverse Leidenfrost state, a levitating state that is enabled by a continuous vapor flow produced by the cryogenic bath. In such freezing conditions, the droplets (which do not evaporate) can levitate for a dozen of minutes. We show here how the deformability of the liquid substrate dramatically impacts the Leidenfrost dynamics. First, we show that a micrometer-sized instability grows within the film sustaining the drop, which causes a partial redirection the vapor flow and generates spontaneous self-propulsion. The drops then behave as active particles, which hover in straight lines above the bath and form a remarkably regular pattern. In addition, the bath surface is deformed at the millimeter scale by the droplets weight. Due to this non-wetting meniscus, the particles are repelled at large distance by objects dipped into the bath: this can be used as a contactless method to finely control the particles trajectories. Conversely, we show that the attraction between identical menisci impacts the motion of approaching droplets which spontaneously orbit around each other -- mirroring a miniature celestial system. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P04.00007: Explosive behavior of binary drops upon impact on a hot solid Pierre Chantelot, Pallav Kant, Juliette Colin, Andrea Prosperetti, Detlef Lohse The vapor layer generated during the impact of a drop on a hot plate can prevent contact between the liquid and solid. The minimum temperature, $T_L$, needed to observe this dynamic Leidenfrost effect depends on the impact speed, and the thermal properties of the solid and liquid. Here, we perform impacts of binary drops of miscible liquids with different boiling points while monitoring the existence of contact using Total Internal Reflection (TIR) imaging. We report the occurrence of explosions, associated with a sudden failure of the vapor film, at the transition from levitation to contact. We study the destabilization of the vapor layer by measuring its dynamics for different liquid combinations and mixing ratios. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P04.00008: Low-g Demonstrations of Leidenfrost Droplet Impacts with Applications to Non-Contact Fluidics Processing in Space Rawand Rasheed, Mark Weislogel Leidenfrost phenomenon has been studied extensively for its role in applications ranging from nuclear reactor cooling, to metals manufacturing, combustion, and other fields. Herein, Leidenfrost phenomenon is exploited as a potential solution to spacecraft water processing challenges by providing a method for non-contact fluid distillation. Leidenfrost investigations have been almost exclusively conducted in terrestrial environments and are in turn largely defined by the ever-presence of gravity. In this work we demonstrate a variety of dynamic Leidenfrost effects for large liquid droplets in the microgravity environment of a 2.1 second drop tower. A scaling model for the impact reveals the ease with which `non-contact' impacts are achieved at low Weber numbers and low gravity levels. We find the vapor film thicknesses at impact can be millimetric as estimated analytically and confirmed qualitatively via experiments. Dynamic drop impact experiments are extended to a variety of heated substrates including macro-pillar arrays, confined passageways, and others. Leidenfrost droplet evaporation rates and lifetimes are estimated analytically and confirmed qualitatively via experiments for sliding/rolling drops at varying velocities in a terrestrial gravity environment. The empirical and analytical results serve as key design tools for sizing a prototypical non-contact distillation system for terrestrial desalinization or spacecraft water recycling. The potential for contamination-free processing aboard spacecraft is obvious, with further proofs of concept under pursuit. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P04.00009: Unexpected Suppression of Leidenfrost Phenomenon on Superhydrophobic Surfaces Meng Shi, Ratul Das, Sankara Arunachalam, Himanshu Mishra The Leidenfrost phenomenon ascribes to a non-equilibrium situation, wherein a liquid droplet levitates above a superheated surface. Superhydrophobic surfaces are believed to dramatically reduce water's Leidenfrost point (LFP - the temperature when the Leidenfrost phenomenon occurs), even approaching its boiling point in some cases. The causation is that superhydrophobic surfaces robustly entrap air when brought in contact with water, which reduce the contact area and adhesion between the droplet and the surface, and thus promote the formation of the vapor layer on heating. Here, we report on a curious exception. Using high-speed imaging, we investigated water droplets placed on hot superhydrophobic SiO2/Si surfaces adorned with arrays of doubly reentrant pillars (DRPs). We found the LFP for water droplets on SiO2/Si DRPs could be significantly higher than that smooth SiO2/Si surfaces, even though the former exhibits superhydrophobicity and the latter is hydrophilic. Thus, we advance the notion that superhydrophobic surfaces may not always lower the LFP of water. We will present deeper insights into our observations based on complementary experiments and theory. [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