Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session L4: Drops VII: Impact and Interactions |
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Chair: Jun Sakakibara, University of Tsukuba Room: 307 |
Monday, November 21, 2011 3:35PM - 3:48PM |
L4.00001: Particle-drop Impact in Midair Alidad Amirfazli, Stefan Strzebin, Oliver Peise, David Chevrollier For the first time the impact of a drop and particle in the mid-air is studied, which is a fundamental physical phenomenon relevant to many applications involving a fluidized bed and a liquid jet, e.g. drug particle coating, and upgrading of heavy oil. To date it has not been clear what happens when a particle and drop collide in midair. An apparatus was build to allow deterministic impact of a particle and drop to occur in midair. Using high speed imaging the impact of three different particles with water drops is studied at different relative velocities. Possible collision outcomes are elucidated in terms of particle-drop diameter ratio, Weber number, and particle wettability. Three distinct regimes of bonding, ripping and coating, and shattering are identified and discussed in this novel study. The differences between on-axis versus off-axis impact is also briefly discussed. [Preview Abstract] |
Monday, November 21, 2011 3:48PM - 4:01PM |
L4.00002: Gravitational Collisions of Spherical Drops at Finite Stokes Numbers and Low Reynolds Numbers Michael Rother, Robert H. Davis Collision efficiencies are calculated by a trajectory analysis for two sedimenting spherical drops with exact methods for determining the hydrodynamic forces at finite Stokes number and low Reynolds number. When the Reynolds number is small, fluid inertia is negligible, and the hydrodynamic forces are linear functions of the translational velocities of the drops. However, at nonzero Stokes numbers, drop inertia must be taken into account, and the hydrodynamic forces do not balance the applied forces. For drops in close approach, lubrication forces and attractive molecular forces are considered. Comparison is made between the effects of unretarded and retarded van der Waals forces and Maxwell slip on collision efficiencies. An important application is to raindrop growth for drop radii between 10 and 30 $\mu$m. The collision efficiency goes through a minimum and then approaches the Smoluchowski limit of no hydrodynamic interactions as the drop size and Stokes number become increasingly large. Theoretical predictions are required in this range of drop sizes because experiments are difficult. [Preview Abstract] |
Monday, November 21, 2011 4:01PM - 4:14PM |
L4.00003: Bouncing Jets Navish Wadhwa, Pavlos Vlachos, Sunghwan Jung Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. We have developed a simple experimental setup to stably demonstrate and study the non-coalescence of jets on collision. We present the results of an experimental investigation of oblique collision between two silicone oil jets, supported by a simple analytical explanation. Our focus is on elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertia. A parametric study conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. We observed a transition from bouncing to coalescence with an increase in jet velocity and inclination angle. We propose that a balance between the contact time of jets and the time required for drainage of the trapped air film can provide a criterion for transition from non-coalescence to coalescence. [Preview Abstract] |
Monday, November 21, 2011 4:14PM - 4:27PM |
L4.00004: Bubble entrapment by droplet-meniscus collision Koen G. Winkels, Diederik L. Keij, Jacco H. Snoeijer The impact of a sessile droplet with a meniscus, close to a moving contact line, is studied experimentally with high-speed imaging. Above a certain velocity and impacting droplet size, bubbles are entrained into the liquid during the process of coalescence. By looking through the liquid we can resolve the formation of an air sheet that is trapped between the drop and the meniscus. This sheet breaks up into a single or multiple bubbles, depending on the experimental conditions. We characterize the various mechanisms for entrainment and identify scaling relations for the size of the entrained bubbles in terms of impacting droplet size and velocity. [Preview Abstract] |
Monday, November 21, 2011 4:27PM - 4:40PM |
L4.00005: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 4:40PM - 4:53PM |
L4.00006: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 4:53PM - 5:06PM |
L4.00007: The Effect of Gas Properties on Mesler Bubble Entrainment R.K. Sundberg, J.R. Saylor Mesler entrainment involves the generation of hundreds of micron size bubbles, frequently distributed in a chandelier- like pattern following the impact of a liquid drop with a bulk surface of the same fluid. To date, research on Mesler entrainment has taken place in air at atmospheric pressure and has therefore neglected to test the influence of gas properties. The results of drop impact studies are presented where a controlled environment was employed consisting of air- helium and air-carbon dioxide mixtures. The dynamic viscosity of pure air at STP is $1.85 \times 10^{-5}$ Pa.s and the kinematic viscosity is $1.6 \times 10^{-5}$ $m^2/s$. By using air-helium and air-carbon dioxide mixtures, kinematic viscosities ranging from 0.5 to 7 times that of air were attained, with dynamic viscosities ranging 0.8 to 1.0 times that of air. The frequency of occurrence of Mesler entrainment is noted for methanol in these environments and is compared with results gathered in air. The effect of the gas phase viscosities and the Capillary number are discussed. [Preview Abstract] |
Monday, November 21, 2011 5:06PM - 5:19PM |
L4.00008: Jetting from impact of a spherical drop with a deep layer Li Zhang, Jameson Toole, Kamel Fazzaa, Robert Deegan We performed an experimental study of jets during the impact of a spherical drop with a deep layer of same liquid. Using high speed optical and X-ray imaging, we observe two types of jets: the so-called ejecta sheet which emerges almost immediately after impact and the lamella which emerges later. For high Reynolds number the two jets are distinct, while for low Reynolds number the two jets combine into a single continuous jet. We also measured the emergence time, speed, and position of the ejecta sheet and found simple scaling relations for these quantities. [Preview Abstract] |
Monday, November 21, 2011 5:19PM - 5:32PM |
L4.00009: ``Effervescent'' Atomization in two dimensions Henri Lhuissier, Emmanuel Villermaux A planar \emph{Savart} water sheet uniformly seeded with small air bubbles in large surface concentration is studied as a model experiment of the so-called ``effervescent'' atomization process. This two-dimensional setup allows for a quantitative observation of all the steps of the sheet disintegration into a collection of disjointed droplets. The bubbles are heterogeneous nucleation sites which puncture the sheet forming growing holes. The dynamics of the holes opening competes with the simultaneous nucleation rate of new holes in a statistically stationary fashion. The liquid constitutive of the sheet is then transitorily concentrated into a web of ligaments of various lengths and diameters, at the junction between adjacent holes. Their break-up produces the final spray. We provide a complete description of the ligaments web statistics in the case where nucleation is synchronous, and show that the drop size dispersion from the breakup of a single ligament is responsible for the shape of the resulting overall spray drop size distribution. [Preview Abstract] |
Monday, November 21, 2011 5:32PM - 5:45PM |
L4.00010: Dynamics of a drop trapped inside a circular hydraulic jump Luc Lebon, Alexis Duschene, Laurent Limat We investigate the dynamics of a drop trapped inside a circular hydraulic jump : in our experiment, a circular hydraulic jump is formed by a viscous jet impacting a horizontal glass disk. A drop of the same liquid, deposited in the jump does not coalesce, and remains trapped at its periphery, because of the air entrainment linked to the high drop rotation speed. Depending on the flow rate, the drop can exhibit complex dynamics, from regular rotation along the jump to ``chaotic'' behaviour. We also studied in detail hydrodynamics of the liquid drop and its interaction with the jump. Our investigations show that hydrodynamics of the jump is still not fixed. [Preview Abstract] |
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