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 B23: Drops: Electric Field Effects I |
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Chair: Petia Vlahovska, Northwestern University Room: 605 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B23.00001: Electrohydrodynamic Equatorial Streaming Brayden Wagoner, Christopher Anthony, Petia Vlahovska, Michael Harris, Osman Basaran When subjected to electric fields, spherical liquid drops can deform, and disintegrate by fissioning, cone-jetting, and in a variety of other ways. The strength of the electric field as well as the electrical and other physical properties of the drop and surrounding medium determine both the extent and type of deformation (prolate/oblate) that the drops can undergo prior to disintegration. At large electric field strengths, prolate drops emit thin jets from conical structures (Taylor cones) that form at their poles. Oblate drops, on the other hand, may burst at their centers (dimpling) or emit a thin sheet from their equators (equatorial-streaming) [Brosseau and Vlahovska, Phys. Rev. Lett., vol. 119, 2017]. We probe the physics behind these two oblate instabilities through direct numerical simulation. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B23.00002: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B23.00003: ABSTRACT WITHDRAWN |
(Author Not Attending)
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B23.00004: Electrohydrodynamics of falling drops in inertial regime Nalinikanta Behera, Shubhadeep Mandal, Suman Chakraborty Buoyancy-driven motion of a Newtonian drop suspended in another Newtonian medium in the presence of uniform electric field is studied numerically. The inertial effects are considered to be strong enough to affect the drop dynamics, contrary to the case of Stokes flow. Irrespective of the flow regime, perfectly-dielectric drop always moves faster. However, in inertial regime the steady-state drop shape displays oblate to prolate shape transition and the transient deformation of drop is found to be non-monotonic, which is in sharp contrast to the similar case of Stokes flow. For certain electrical property ratios, the leaky-dielectric drop shows features similar to perfectly-dielectric drop. For leaky-dielectric drops, along with drop deformation, interfacial charge convection is found to be a vital controlling parameter. Charge convection can increase or decrease the net drag acting on the drop depending upon the electrical properties of fluids. For some fluids charge convection have significant effect on drop speed and its morphology. The present study finds its useful applications in oil-water separation process as well as in microfluidic devices. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B23.00005: Ambient Air Humidity Affects the Charge Acquired by Water Drops in Oil Kristen Fawole, William Ristenpart A water drop in an insulating fluid acquires charge when it contacts an electrode, but experimental measurements of the charge acquired by the drop have been hindered by irreproducibility, charge asymmetry $(q_+ \neq q_-)$, and time-dependence. Previous work, dating back to Maxwell in 1892, has implicitly assumed that the effect of external environmental conditions is negligible during the charging process of water droplets. Contrary to that assumption, we report that charge accumulation on the experimental apparatus itself increases with increasing ambient humidity in the presence of applied high voltages ($>3$ kV). Additionally, using dissimilar metals for connecting the high voltage source to the electrode magnifies charging effects in high humidities. A scaling analysis indicates the surface charge of the apparatus is much larger than the ostensible surface charge on the electrode due to the applied field. The humidity-dependent charge accumulation provides a possible explanation for the difficulties in quantitatively corroborating Maxwell's prediction for the charging dynamics of droplets contacting a planar electrode. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B23.00006: Dynamics of electrowetting-driven spreading and receding of a droplet Anne Juel, Pallav Kant, Pawin Iamprasertkun, Abd-Almalik Halfaoui, Bruno Etcheverry, Robert Dryfe Electrowetting is a powerful method to achieve external wetting control, by exploiting the potential-dependence of the liquid contact angle with respect to a solid substrate. We study the effect of electrolyte concentration $c_0$ on electrowetting-induced spreading and receding of a droplet on the basal plane of graphite, a very smooth conducting substrate. We find that for positive applied potentials, the static electrowetting contact angle is independent of $c_0$ over three decades of concentration but that the spreading time to reach this final state varies as $c_0^{-1}$. In contrast, for negative potentials, the electrowetting angle varies as $c_0^{1/2}$ and the spreading time varies as $c_0^{-1/2}$. We show that both spreading and receding times are governed by the formation of the electrical double layer (EDL) on the substrate, and that electrowetting can be used as a macroscopic probe into the structure of the EDL. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B23.00007: Drop Manipulation by Electrowetting for 3D Printing Jevon Plog, Jens Lowe, Yizjou Jiang, Yayue Pan, Alexander Yarin The experiments in the present work employ electrowetting for the controlled motion on a substrate of drops of different liquid inks used in 3D printing. The electrodes are embedded in dielectric substrates, on which droplet motion is triggered. It is demonstrated that drops of many aqueous polymer solutions and carbon fiber suspensions can be moved on horizontal surfaces. For example, several aqueous polymer solutions, like those of polyethylene oxide and polyacrylamide result in drop motions similar to that of water drops. Also drops of commercial hydrogel, agar-agar, alginate, xanthan gum, and gum Arabic can be moved by electrowetting. Drops of sizes of 200 \textmu m and 3 mm can be manipulated and moved by the electric field on different dielectric substrates accurately and repeatedly. This includes horizontal motions, motions on vertical wall, and upside down. Theoretical aspects are discussed as well. [Preview Abstract] |
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