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 G08: Surface Tension II |
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Chair: Claudia Falcon, UCLA Room: 212 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G08.00001: Ultrasonic extraction and trapping of a droplet from fluid-fluid interfaces. Robert Lirette, Likun Zhang, Joel Mobley Ultrasonic waves provide a powerful means to exert forces on fluid objects (droplets and fluid interfaces) for the development of non-contact manipulation techniques or acoustic tweezers. Under the proper conditions, a propagating sound beam illuminating the interface of two immiscible fluids can exert a pulling force to deforming it against the incident direction of the sound beam. The direction of this force depends on the relative sound speeds and densities of the two fluids. We demonstrate the extreme case where a properly designed ultrasonic beam is used to break the interface and extract a single droplet from an interface of water to CCl\textunderscore 4. Remarkably, the extracted droplet is automatically and firmly trapped in the sound field which acts as an acoustic tweezer. High speed video was taken to display the dynamics of the interface during the procedure when the interface was broken and the droplet is extracted. This work can stimulate the development of techniques for the production and manipulation of fluid droplets. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G08.00002: Capillary surfers: Self-propelling particles at an oscillating fluid interface Giuseppe Pucci, Daniel Harris In the present work, we explore the dynamics of millimetric bodies trapped at the air-water interface of an oscillating bath. The relative vertical motion of the body and the free surface leads to the generation of propagating capillary waves. We demonstrate that when the rotational symmetry of an individual particle is broken, the particle can steadily self-propel along the interface. Such self-propelled particles interact with one another through their mutual capillary wavefield and resultant fluid flows, and exhibit a rich set of collective modes characterized by a discrete number of equilibrium spacings for a given set of experimental parameters. Our results open the door to further investigations of this novel active system at the fluid interface. Ongoing work and future directions will be discussed. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G08.00003: Collective dynamics of dense particles at a liquid interface Antoine Lagarde, Christophe Josserand, Suzie Protiere When two millimeter-sized identical objects are deposited at a liquid interface, the individual deformations they create may overlap, leading to an attractive capillary force. This everyday phenomenon that one can observe at the surface of water is central in many applications, from industrial processes where it is used to manufacture objects with a specific microstructure to Nature where fire ants gather into a raft to survive floods. The interaction between two identical spherical particles is now rather well understood, but the many-body interaction of non-identical aggregates still lacks a convincing description. Here, we experimentally study the aggregation of randomly distributed dense millimeter-sized beads placed at an oil-water interface. The particles are attracted by their neighbors and form an axisymmetric monolayer called a granular raft. The interfacial deformation created by such an object exceeds by at least one order of magnitude the deformation of a single bead, leading to high capillary forces that strongly depend on the number of particles in each raft. Thanks to a precise understanding of the interaction between two rafts, we undertake a statistical description of the aggregation process of a n-body system into a single giant granular raft. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G08.00004: Low-G inertial-capillary meniscus motions in a channel Josh McCraney, Paul Steen, Joshua Bostwick In low-g environments, residual accelerations can induce fluid reservoir reconfiguration, resulting in dynamic instabilities. Since channel geometries are prevalent aboard critical spacecraft fluid systems, such as propellents, cryogens, and wastes, understanding flow stability is crucial to ensure fluid is positioned and available when needed. In this work we analyze the normal oscillations of a low-g fluid in a rectangular channel, reporting fundamental frequencies for pinned, natural, and mobile contact line conditions. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G08.00005: Capillary Soring of Particles by Dip Coating Brian Dincau, Martin Bazant, Emilie Dressaire, Alban Sauret High-throughput sorting or filtration of suspensions is a critical step in many industrial, geophysical, and biomedical processes. Here, we present a new scalable size-based separation technique which utilizes a dip coating meniscus as a tunable filter. When a plate is withdrawn from a liquid bath, a thin layer of liquid coats its surface. Below a given film thickness on the plate, the meniscus generates a strong capillary force at the stagnation point and prevents large particles from being entrained in the liquid film. We leverage the capillary filtration effect induced by the meniscus to sort particles by size. Indeed, the size threshold depends on the withdraw speed and fluid properties, so smaller particles are entrained while larger particles remain in the bath. We demonstrate this technique with bidisperse suspensions and explain how it could be applied to polydisperse suspensions or extended to biological suspensions. We rationalize our results in terms of dimensionless numbers (capillary and Bond numbers) and estimate the range of capillary number to separate particles of given sizes. This technique is well-suited for high-throughput operation due to the demonstrated scalability of industrial dip coating, combined with the clog-free nature of this meniscus-based filter. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G08.00006: Steady Buckling of Viscous Capillary Jets Neil Ribe, Jingxuan Tian, Xiaoxiao Wu, Anderson Shum Steady buckling (coiling) of thin falling liquid jets plays an important role in instability-assisted high-resolution printing and ultra-fine liquid dispensing, situations in which the effects of surface tension are likely to be significant. To understand better these capillary effects, we have performed experiments with sub-millimetric jets and ultra-low flow rates ($\approx 10$ ml/h) together with numerical simulations and linear stability analysis to study a hitherto unexplored coiling regime dominated by capillarity with negligible inertia. We find that the critical fall height $H_c$ for coiling onset decreases with increasing flow rate, a tendency that is opposite to the zero surface-tension case and that has been previously documented only for inertia-dominated coiling. The enhanced resistance to buckling afforded by surface tension increases $H_c$ by up to a factor of 10 relative to the surface tension-free case. A regime diagram in the space of capillary number and jet slenderness agrees closely with the prediction of the linear stability analysis, but differs significantly from the analogous diagram for unsteady buckling of a compressed liquid bridge constructed previously by other workers. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G08.00007: The Dynamics of Curved Thin Films Under Soluto-Capillary Forces Xingyi Shi, Mariana RodrÃguez-Hakim, Gerald Fuller, Eric Shaqfeh Interfacial film dynamics is ubiquitous and is interesting in the presence of bulk and/or interfacial heterogeneity. To control the stability of thin films over different substrates, we need a fundamental understanding of the physical forces that affect the film, particularly when the film is heterogeneous. In the present study, we examine the thin film dynamics of a binary mixture subject to evaporation and drainage atop both a glass dome and an air bubble. Experimentally, we observe the film thickness profiles via a custom-made dynamic fluid-film interferometer. In the parallel computer simulations, we develop a lubrication theory to compute the film thickness evolution under the effects of capillarity, gravity, Marangoni forces, and van der Waals interactions with the substrate. We find the dynamics are quite complex and subject to long-lived time dependent states -- thus soluto-capillary forces stabilize the film. Moreover, we find that stabilizing van der Waals forces are crucial to create the conditions forMarangoni regeneration for drainage over a solid substrate. For a draining, heterogeneous thin film over a bubble surface, we find sustained, nonlinear thickness oscillations are rather easily accessible. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G08.00008: Dynamics of Capillary Flow in Curvy V-Grooves Nicholas White, Sandra Troian Capillary flows, also known as wicking flows, in straight open V-groove channels are widely used as a passive and reliable method of fluid delivery and flow control in applications such as point-of-care biomedical devices, heat micropipes for electronics cooling and spacecraft propellant management systems, to name a few. Advances in lithographic techniques and 3D printing now allow simple fabrication of curvy microscale V-groove channels which can be used to facilitate fluid transport in 3D using compact microgeometries. Romero and Yost (1996) and Weislogel (1996) first elucidated how the streamwise gradient in capillary pressure due to the change in curvature of the air/liquid interface from local variations in film thickness induces ultra rapid wicking of slender films into straight V-grooves of constant cross-section. Here we present an analytic model which extends their original formulation to systems with arbitrary channel curvature. Despite the complex flow trajectories which can ensue, a first order perturbation analysis yields an extended thin film equation which reveals the dynamics arising from the interaction between fluid interface and channel curvature. The resulting equation will be useful to the design of next generation 3D microfluidic systems. [Preview Abstract] |
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