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 Q25: Drops: General II |
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Chair: Anne Juel, University of Manchester Room: 607 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q25.00001: Experiments in oil-water ring-sheared drop Shannon Griffin, Patrick McMackin, Frank Riley, Shreyash Gulati, Amir Hirsa, Juan Lopez Launched to the International Space Station (ISS) in late July 2019, the ring-sheared drop (RSD) is a containerless reactor where surface tension provides fluid containment, and shear is conveyed primarily through surface shear viscosity. The RSD is a 2.5 cm diameter drop constrained by two thin rings. A stationary ring contacts the drop in one hemisphere, and a rotating ring contacts in the opposite hemisphere. The RSD allows the study of sheared fluid interfaces and how they affect amyloid fibril formation. Amyloid fibrils of certain brain proteins play central roles in some neurodegenerative diseases, such as Alzheimer's or Parkinson's. The RSD was studied in the lab using a density-matched silicone oil-water system. Through these experiments, previous computational work on the RSD was verified. Drop deformation was found to be a balance between viscous, inertial, and capillary forces. These laboratory experiments provided some evidence for the robustness of the RSD. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q25.00002: Formation and evolution of thin water films encapsulating oil droplets crossing an oil-water interface. Joseph Katz, Omri Ram This study examines phenomena occurring as mm-scale oil droplets rise through water, cross an oil-water interface, and then coalesce with a layer of the same oil. Inline holography and planar laser induced fluorescence are used for examining interfaces involving layers of silicone oil of different viscosity and hexadecane above both purified and nearly refractive index-matched sugar water. They show that for all cases, after crossing the interface, thin water films remain around these droplets, preventing them from mixing with the bulk oil. Subsequently, in a slow process, film segments located close to the contact point with the interface are attracted to the bulk water, presumably by electrostatic forces, causing the droplet to flatten, and creating a kink, where the film begins to break up into submicron droplets. The region of submicron droplets propagates from the peripheral kinks inward to the center of the droplet, and they begin to diffuse. These processes occur in less than one minute for a 4 cst oil, and about one hour for a 50 cst oil, preventing the merging of the droplet with the surrounding oil for much longer than previously presumed. These phenomena do not occur when water droplet descends across the oil-water interface, namely oil films do not form. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q25.00003: Nonlinear Phenomena in Trajectories of Spherical Drops with Incompressible Surfactant in Combined Buoyant and Marangoni-induced Motion Michael Rother We consider the interactions of two sedimenting, spherical drops in a temperature gradient with negligible thermal convection. The drops are covered with a nearly uniform surfactant film. When drop and surrounding fluid inertia are insignificant, as indicated by small Stokes and Reynolds numbers, respectively, the governing equations are linear, and the trajectories are symmetric. In the linear case, it is possible for two drops to fall as a pair with constant horizontal separation, but the drops must have the tandem arrangement initially. Moreover, a saddle point can occur in the trajectory phase plane. When drop inertia is considered, as measured by a finite Stokes number, with surrounding fluid inertia still unimportant, the governing equations become non-linear, and the trajectories lose symmetry. Asymmetric limit cycles can be observed. In addition, trajectories with a constant, finite horizontal gap become stable, with the drops oscillating into the final steady state arrangement. Retrograde motion is also possible. For small water drops in air, at a fixed drop radius and size ratio, the collision efficiency vanishes, depending on the relative strength and orientation of the gravitational and thermocapillary driving forces. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q25.00004: ABSTRACT WITHDRAWN |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q25.00005: Role of Laplace pressure in the equilibrium of a pendent drop highlighted by a particle loading L. Lecacheux, A. Sadoudi, D. Cassan, A. Duri, T. Ruiz A pendent drop at the end of a capillary needle remains in near equilibrium just before breaking: the action of the capillary force must oppose the weight of the drop, to which should be added the force due to Laplace pressure (LP). Thus, for a given fluid and a fixed wet perimeter, its maximum mass should be constant. We modulated the LP by modifying the main curvatures of the drop and we observed the impact on its mass. Drops were loaded with glass beads of increasing mass and induce a stretching of the drops that modulates their main curvatures. Volumes and curvature radii are measured by image analysis. These loading experiments highlight the increase of LP with the loading and the non-linear decrease of the drop mass. However, we observe that the liquid mass in the loaded drop decreases linearly with the increase of the bead mass without verifying the mass balance. Such a result is included in a master curve which highlights the role of the LP in the equilibrium of a pendent drop just before its rupture. It challenges the validity of the well-known Tate's law and allows the setting of functional ranges for capillary micromanipulators. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q25.00006: Drop formation following bursting of molten steel thick liquid films in a steel plate illuminated by a high energy laser Mary Lanzerotti, K. Brakke, K. Allen, J. Hartke, A. Hirsa This talk presents preliminary observations of the formation of a single liquid drop of molten steel following bursting of a thick liquid film formed by illumination of a thin vertical steel plate by a 1075-nm continuous-wave 1000W Ytterbium fiber laser. Images of the initial hole captured by a high-speed digital camera at room temperature conditions show a rapidly expanding hole. Liquid then gathers at the lower part of the hole, forming a liquid lump where the pre-burst bulge was located. The liquid lump vibrates twice as it settles into a sphere. Gravity pulls the liquid drop down, to form a neck between the rim of the hoop and the drop. The neck pinches off, detaching a drop. The neck retracts slightly before it freezes with a small droplet that appears to form at the bottom of the neck before the neck freezes. The falling drop oscillates as it falls until it hits the mount surrounding the steel plate. The high-speed images also show an ejected droplet that is launched and then falls, apparently in front of the plate. No satellite drops are observed. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q25.00007: Onset time of fog collection using a single wire. Youhua Jiang, Christian Machado, Shaan Savarirayan, Neelesh Patankar, Kyoo-Chul Park Fog collection is a promising solution to water scarcity while also being of vital importance in industrial processes. To date, many studies have investigated the fog collection rate, a parameter that denotes the average performance over a period of time. However, the initial period (referred to as onset time) between the start of the fog flow and the collection of the captured liquid (a delay in time caused by droplet growth to a critical weight) has not been understood. A longer onset time results in a more serious clogging issue that deteriorates the collection rate and, therefore, understanding this phenomenon is important. Here, we study how the onset time is determined by the capture and transport of fog droplets using single, vertical wires with various surface wettabilities and diameters, under different wind speeds. We derive a scaling law that correlates the onset time with the fog capture process and droplet-surface retention force, governed by aerodynamics and interfacial phenomena, respectively. In particular, the onset time decreases with an increasing rate of fog capture or a decreasing droplet-surface retention. This study introduces a new aspect in the evaluation of fog collection and provides insights for the design of fog collectors. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q25.00008: Clogging-enhanced fog harvesting on the hole pattern Jihye Park, Changje Lee, Hyesung Cho, Myoung-Woon Moon, Sangyoup Lee, Seong Jin Kim Clogging has been considered as a drawback in fog-harvesting as it hinders local airflow around a hole. However, in this study, it is demonstrated that the clogging effect on the fog-harvesting performance differs between the stable clogging and the unstable clogging. Unlike the stable clogging that is stably stuck in the hole, the unstable clogging is observed to form and break up repeatedly during the fog-harvesting process. Due to this break-up, fog flow through the unstably-clogged mesh experiences much less pressure drop than that across the stably-clogged mesh even though those meshes have the same shade coefficient. Moreover, it is found that the clogging can be used even for enhancing the fog-capturing efficiency than the clogging-free mesh with the same shade coefficient by increasing the effective shade coefficient to collide with more fog drops, which suggests that the clogging could be not a simple drawback. Rather, especially for the unstable clogging, it can be used to optimize the fog-harvesting performance with maintaining low pressure drop. Moreover, the particle image velocimetry is performed to quantify the increase in the effective shade coefficient of the clogged mesh by measuring the turbulent kinetic energy of the fog flow to the mesh. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q25.00009: Droplets sliding on fiber arrays Floriane Weyer, Alexis Duchesne, Nicolas Vandewalle At a time when water becomes a scarce commodity in the most arid regions, fog harvesting has stood out as a sustainable alternative way to supply drinkable water. The small droplets from the fog impact the mesh net and, as more and more water hits the mesh fibers, the droplets fuse together and slide along the fibers due to gravity. Even though the collection process has been widely studied, the motion of the droplets on the fibers remains an open question. Here, we focus on the motion of droplets on an entanglement of fibers. We use a model system made of silicone oil droplets, to insure total wetting, sliding on nylon fibers. The movement of the droplet depends mostly on the volume of the drop, the fiber inclination and the fiber diameter. The results allow us to better understand the path chosen by the droplets once collected. These results could be used to improve the collection rate of the fog collection devices. [Preview Abstract] |
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