Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S48: Drops IIFocus
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Sponsoring Units: DFD GSOFT GSNP Chair: Irmgard Bischofberger, Massachusetts Institute of Technology Room: BCEC 251 |
Thursday, March 7, 2019 11:15AM - 11:27AM |
S48.00001: Drying of colloidal droplets on hydrophobic surfaces Paul Lilin, Philippe Bourrianne, Guillaume Sintes, Irmgard Bischofberger The evaporation of drops of colloidal suspensions on hydrophilic substrates leads to a variety of patterns, from the well-known coffee stain effect to radial crack formation. Here, we investigate the drying of aqueous solutions of silica nanoparticles on hydrophobic substrates for a large range of particle volume fractions. As the water evaporates, the particle volume fraction increases leading to a transition from a moving to a pinned contact line. This pinned contact line induces a large stress buildup within the material during the further evaporation process, which eventually gets released through the formation of fractures that shatter the dried drop into a multitude of pieces. |
Thursday, March 7, 2019 11:27AM - 11:39AM |
S48.00002: Analyzing the Effect of Collision of Droplets on Evaporation Rate Siavash Zamani, Aaron B Morris Spray drying is a process used by many industries such as food, agricultural and pharmaceutical to convert a liquid feed into powder. Many studies have used CFD to model fluid and powder flow. However, continuum approaches track bulk powder properties resulting in loss of data for individual particles. To improve the accuracy of these models, fundamental research on drying behavior is critical. This work focuses on simulating the initial phase of the process where an atomized droplet behaves as a liquid due to excess moisture content. At this stage, the droplets collide frequently, and particle size distribution changes rapidly. Accurate calculation of the moisture content of the droplet is essential for further analysis on drying kinetics and morphology of particulate form. A computational framework has been developed where the gas phase is modeled as a continuum and individual droplets are tracked in the Lagrangian frame. Using this approach, individual droplets and their characteristic properties are captured, while evaporation effects are accurately accounted for. This works provides high-fidelity data for particle size distribution and moisture content which paves the path toward modeling of the second phase of drying, when liquid droplet has transformed into a wet-particle. |
Thursday, March 7, 2019 11:39AM - 11:51AM |
S48.00003: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 11:51AM - 12:03PM |
S48.00004: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 12:03PM - 12:15PM |
S48.00005: Dynamics and structure in the deposition profile of the coffee-ring effect Nicholas Schade, Jerome Seebeck, Sidney Robert Nagel We investigate the growth dynamics and three dimensional structure of ring stains in evaporating drops of solutions and colloidal suspensions. Drying solutions generally leave behind ring stains. While this “coffee-ring effect” has been widely studied, the microscopic details of how the deposition patterns form have not been completely characterized experimentally. Using fluorescence and laser-confocal microscopy, we measure the growth rate and height profile of the deposit as functions of time, initial particle concentration, and particle size. Starting at the contact line, the particle deposition grows into the interior of the drop. The deposition front accelerates as the drop dries and the front steadily becomes sharper until the thickest part of the deposit has formed. Our experiments with fluorescent microspheres reveal the growth of a film of particles over the entire fluid-air interface. This film contracts and detaches from the contact line during the later stages of evaporation. The final deposits often contain patterns of particles in the interior of the rings resembling fractals. Prior theoretical work does not adequately describe many of the phenomena that we observe. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S48.00006: The underside of a Leidenfrost drop on a bath Laurent Maquet, Benjamin Sobac, Alexis Duchesne, Hatim Macrafi, Alexey Rednikov, Pierre Dauby, Pierre Colinet, Stephane Dorbolo The Leidenfrost effect can also be observed on a liquid substrate, i.e volatile drops may levitate on their own vapor when placed on a hot bath of non-volatile liquid. Compared to the classical Leidenfrost effect on solid substrates, the liquid bath presents three major differences: the substrate is atomically smooth, deformable, and fluid. As a consequence of such fluidity, heat transfer through the bath to the drops is most certainly dominated by convection and not by just conduction as in the solids. Here, we examine experimentally and numerically the flow motion in the bath of silicone oil V20 under the action of a Leidenfrost drop. We highlight the development of a toroidal vortex under the drop. Interestingly, the sense of circulation in this vortex is found to depend on the nature of the liquid that makes the drop. We show that this is due to a shift in a complex and delicate interplay between three mechanisms pulling in different directions: the local cooling of the bath by the drop gives rise to both (i) a buoyancy action and (ii) Marangoni stresses, whereas the vapor escaping from the gap between the drop and the bath exerts (iii) a shear action on the bath surface. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S48.00007: Droplet moving on frosted glass Stephane Dorbolo The surface of the frosted glass is very rough. This roughness offers numerous pinning sites for any sessile droplet. In the present case, the angle of contact of a water droplet is about 50°. The advancing angle is rather large (about 70°) and contrasts with the receding angle that is quite zero. This strong hysteresis has a direct consequence on the motion of a droplet when the plate is inclined. The droplet leaves a trace after its passage. The dynamic of the droplet going down the plane is studied and the microflows in the trace are described. Finally, the behavior of oil droplets is compared. As the oil wets the glass, the motion of the sliding droplet superposes to the diffusion process of the oil in the crevices of the frosted surface. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S48.00008: Experimental and analytical studies on colliding merging of two immiscible drops Chu-Po Huang, Kuo-Long Pan Two types of merging between two immiscible drops have been found in their collisions. Depending on the interfacial tensions among the three media of different components, including air and immiscible liquids, at an equilibrium state with negligible impact energy, partial engulfing and complete engulfing between the drops can be identified. With sufficient inertia of relative motion between the drops, it would yield adhesive merging, whereby two drops adhere to each other, or encapsulation, whereby the softer drop totally encapsulates the harder one which has higher surface tension. Based on two dimensionless numbers, a Weber number and an impact parameter, we have identified a regime diagram that indicates the parametric conditions of different regimes, including other types of consequences specifically those show separation following temporary coalescence. While the outcome of interaction between two drops at rest can be analyzed by an approach of free energy, those with significant relative motions need to account for the impact inertia. Via an analysis based on conservation of energy, a model has been established to predict the critical Weber number of transition between two different regimes of merging. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S48.00009: Oscillations of a hydrodynamic crystal lattice Stuart Thomson, Miles Couchman, John WM Bush When brought into close proximity, two or more droplets bouncing on a vertically vibrating fluid bath exhibit a rich spectrum of dynamical behaviour. In particular, pairs of droplets have been shown to destabilize into oscillatory, orbiting, and promenading modes, while a collection of multiple droplets can form crystal-like lattices with highly regular structure. In this talk, we present the results of a combined experimental and theoretical study in which we characterize and rationalize the behaviour of a circular chain of bouncing drops, reminiscent of a one-dimensional crystal lattice. As the vibrational forcing is increased, the stationary chain first destabilizes into an oscillatory mode and then into a striking soliton-like disturbance, before ``melting'' at sufficiently high acceleration of the bath. Similarities with models such as the Toda lattice, used to model crystal vibrations in solid-state physics, are discussed. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S48.00010: A hydrodynamic analog of the quantum potential John Bush, Matthew Durey, Paul Milewski A droplet may walk on a vibrating fluid bath through a resonant interaction with its own wave field. This walking droplet system has become the subject of research in the nascent field of hydrodynamic quantum analogs. We here consider the motion of droplets walking in closed systems, and demonstrate the relation between the histogram of the particle and its mean pilot-wave field. Furthermore, we demonstrate that as the Faraday threshold is approached, the instantaneous wave field converges to its mean. The resulting mean pilot-wave potential thus plays the role of the quantum potential in Bohmian mechanics. Our study highlights the differences between Bohmian mechanics and de Broglie's relatively rich double-solution theory of quantum dynamics. |
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