Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L46: Drops and Bubbles I |
Hide Abstracts |
Sponsoring Units: DFD Chair: Thomas Brennan, Ferris State Univ Room: LACC 506 |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L46.00001: Modeling of droplet generation at shallow microfluidic T-junction Indrajit Chakraborty, Joshua Ricouvier, Pavel Yazhgur, Patrick Tabeling, Alexander Leshansky Generation of droplets at the T-junction is one of the unit operations of droplet-based microfluidics. As was previously demonstrated in [1] the droplet generation at the T-junction formed from square cross-section microchannels is a purely geometric process controlled by the single dimensionless parameter – the flow rate ratio of the continuous and disperse phases. However, when the microfluidic T-junction and the channels are made shallow, the droplet generation is no longer geometrically mediated and it exhibits various (squeezing, tearing and jetting) regimes depending on the capillary number, Ca. In this talk, we present a robust numerical approach for modelling this process. Quasi-2D Hele-Shaw hydrodynamics is employed using single-fluid formulation combined with interface capturing scheme based on Coupled level-set and Volume-of-Fluid methods. The numerical results show excellent agreement with in-house experiments on droplet generation at the microfluidic Hele-Shaw T-junction, confirming the Ca-1/3 dependence of the droplet volume in “tearing” regime. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L46.00002: Exit Conditions in Capillary Jets: A Two-Mode Spatial Approach Josefa Guerrero Millan, Heliodoro Gonzalez, Pedro Vazquez, Francisco Garcia Simple recipes are provided for predicting the breakup length of harmonically stimulated axisymmetric capillary jets as a function of the exit deformation and/or mean axial velocity perturbation.They are valid for arbitrary jet velocities thanks to the adoption of a spatial analysis. Among the spatial modes, only the two downstream capillary modes, dominant and subdominant, are sufficient to have good estimates of the linear evolution of the jet. Comparison with numerical determination of the breakup length shows a good agreement, provided that the exit perturbation is not too strong or its wavenumber not far from the one corresponding to the maximum of the Rayleigh curve. Including the subdominant mode extends the range of amplitudes for which the linear model gives accurate predictions. It has been generally assumed that the shortest intact length corresponds to highest growth rate. However, we show that the correlation is not strict because the amplitude of the dominant mode has a role in the breakup process and it depends on the stimulation frequency. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L46.00003: Droplet dynamics above the Faraday threshold Lucas Tambasco, Nilgun Sungar, Giuseppe Pucci, Pedro Saenz, John Bush We present the results of an experimental exploration of walking droplets above the Faraday threshold. First, we describe a hydrodynamic analog of the optical Talbot effect and illustrate the manner in which this effect can be used to trap bouncing and walking droplets. Then, we explore the behavior of a bouncing droplet above the Faraday threshold, where the Faraday wave field may contribute a stochastic element to the drop’s dynamics. In this chaotic bouncing regime, we deduce effective diffusivity coefficients for the bouncing drops. Finally, we investigate numerically the dependence of the system behavior as the relative magnitudes of drop-generated pilot-wave and the background field are varied continuously. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L46.00004: Simulation of the atomization of a droplet by a high-speed flow Kevin Schmidmayer, Fabien Petitpas, Éric Daniel This study deals with the modelling and the simulation of the atomization of an isolated droplet by a high-speed flow. During this phenomenon, two main stages are observed: the aerobreakup of the droplet starting with its flattening to the formation of filaments. The second stage concern the formation of a multitude of reduced sizes droplets. Direct numerical simulations are performed to study the breakup and to provide inaccessible information from experimental process. A multiphase compressible flow is necessary to model this liquid/gas interface problem. While the first stage is mainly due to hydrodynamics forces, the capillary effects have to be included in the model to well predict the fragmentation phenomena during the second stage. The model also insures the mass, momentum and energy conservation and the second law of thermodynamics is respected. An appropriate and specific numerical method involving a new adaptive mesh refinement structure with dual cell-boundary trees has been developed. Results on the atomization of an isolated water column and droplet are presented. Comparison with experiment gives good agreement. For the different atomization steps, essential information on the breakup mechanisms are described. Finally, a cloud of reduced sizes droplets is obtained. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L46.00005: Lattice Boltzmann simulations of immiscible drop collisions Ciro Semprebon, Neeru Srangal, Ilya karlin, Halim Kusumaatmaja Systems containing two or more fluid phases and one gas phase are of special practical interest. For example, in engines, compound droplets of oil and water can increase the effective burning rate. Despite the advancing of experimental techniques for managing ternary systems, accurate and flexible models that can predict complex interface dynamics with large density ratio are still lacking. Here I will introduce a versatile multiphase-multicomponent lattice Boltzmann scheme that allows density ratio of order 1000 between the gas and liquid phases. It combines the free energy approach, which ensures thermodynamic consistency and the entropic lattice Boltzmann algorithm, which strongly improves the simulation stability at high density ratios, and for high Weber and Reynold numbers. The novel ternary model can be exploited to study binary droplet collisions and wetting dynamics of droplets on liquid infused surfaces |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L46.00006: Particle Effect and Force Computation on Nanosuspension Droplet Spreading: MD Simulations Baiou Shi, Weizhou Zhou, Edmund Webb III The behavior of nano-fluids, or fluid suspensions containing nanoparticles, has garnered tremendous attention recently in advanced optoelectronic applications. One concern is how to control the ordering of nano-particle arrays and to fabricate those functional semiconductor devices. Nano-suspension provides us a path to synthesize and disperse nanoparticles in fluids, however, the fundamental mechanisms about interfaces and wetting kinetics is still unknown when a nanosuspension drop spreads on a solid surface. Herein, we present results from molecular dynamics simulations with emphasis on revealing forces on suspended particles. Pinning of the advancing three phase contact line occurs for low contact angle while de-pinning occurs at higher angles; forces associated with such behaviors are presented. For increasing particle size, a transition from de-pinning to pinning is observed and interpreted in terms of the increasing capillary force between suspended nanoparticles and the solid/liquid/vapor interfaces. At higher nanoparticle concentrations, particle/particle interactions become relevant and particle pile up occurs, leading to pinning and non-equilibrium droplet morphology. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L46.00007: Capillary Imbibition Damped by Adsorption in Wood Cell Walls Meng ZHOU, Sabine Caré, Denis Courtier-Murias, Stéphane Rodts, Andrew King, Philippe Coussot Wood is a highly hygroscopic porous material in which water can exist in three forms: bound water adsorbed within cell walls, liquid water and water vapor in pores. The physical understanding of water transfers in wood remains poor. Imbibition tests with hardwood samples and interpreted with the Lucas-Washburn’s law show a strong contradiction: the very slow dynamics of water imbibition in wood implies a poor wetting, but the final height reached by water over long terms corresponds to an excellent wetting between water and wood cell walls. To clarify this phenomenon, we observed the imbibition process with high-resolution 3D synchrotron images and we found that, although the liquid-air interfaces in wood channels show a planar shape implying a negligible Laplace pressure, they still progress, erratically, throughout the sample. Besides, we carried out new MRI observations allowing to distinguish bound and free water distribution in time, and which show that bound water is absorbed beyond these interfaces. We finally explain these results through a model showing that the adsorption and diffusion of bound water in cell walls modify the liquid-air meniscus and finally damp the capillary imbibition. |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L46.00008: Droplet Migration on Conical Glass Fibers Clementine Fournier, Rafael Schulman, Kari Dalnoki-Veress Cacti have developed an efficient system to harvest water: needle-like conical spines on which fog condenses into droplets which then proceed to migrate towards the base. The mechanism responsible for this phenomenon is the spines’ conical shape. Motivated to understand this at a fundamental level, we explore self-driven motion of droplets on fibers by designing a simple experiment using conical glass fibers. The main goal is to understand precisely how the geometry of the conical structure affects the motion of the droplets. Using a simple theoretical model, we determine the droplet velocity as a function of geometrical parameters and find this to be in good agreement with our experimental data. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L46.00009: Dynamics of chaotic Rayleigh-Taylor bubble fronts Yousheng Zhang Mechanisms governing the general evolution of chaotic Rayleigh-Taylor bubble fronts are explored, including merger, competition and their interaction. Evolutions of characteristic quantities, i.e., the diameter of dominant bubble D and the height of bubble mixing zone h, are formulated and validated. The D expands self-similarly with universal aspect ratio D/h ≈ (1+A)/4. In contrast, the h grows quadratically with growth coefficient α≡ h/(Agt2) depending on mechanism:α=αm ≈1/36 for pure merger, α=αc ≈[2Φ/ln(2η0)]2 for pure competition, and α=max{αm,αc} when two mechanisms co-work, where A,η0 and Φ denote dimensionless density ratio, initial perturbation amplitude, and linear-growth-rate ratio of actual fluid to ideal fluid, respectively. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L46.00010: Drop solidification experiments on static and moving substrates, for varying feeding rates. Remy Herbaut, Philippe Brunet, Laurent Royon, Laurent Limat Inspired by problems of 3D printing that are currently motivating a large number of works, we consider two situations of liquid drops on a cold substrate, below the melting temperature : |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L46.00011: Understanding Sonoluminescence Thomas Brennan Sonoluminescence is the transformation of sound into light. In practice this phenomenon usually occurs as a result of the expansion and collapse of gas filled bubbles in a fluid driven with a powerful sound field. The most commonly accepted causal model is that the emission of light occurs after the heating of the contents of the bubble up to temperatures exceeding 10000K at the end of the collapse phase. We present data showing that, in the case of a sonoluminescing bubble driven at 23.4 kHz, the emission of light occurs during the bubble collapse, but typically 50 to 100 ns before the minimum bubble radius -- a time period when the conditions in the bubble are expected to be moderate and near room temperature and when the velocity of the collapsing bubble wall is below the speed of sound. These results imply that the cause of light emission during sonoluminescence may not be a violent heating like when a hammer strikes an anvil. Rather, we consider that the path of irreversible phase transformations occuring through the course of expansion and collapse might mediate a transfer of latent heat into an excited condensate. As the condensate discharges, high temperatures arise and a continuous bremsstrahlung spectrum results. We also discuss related phenomena. |
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