Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D08: Bubbles: General |
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Chair: Badarinath Karri, Indian Institute of Technology, Hyderabad Room: Georgia World Congress Center B213 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D08.00001: Dynamics of bubble formation by the star-nosed mole Alexander B Lee, Lana Hanlon, Benjamin Seleb, Alexander Sun, David L Hu The star-nosed mole can sniff underwater by rapidly blowing and inhaling bubbles. Does the speed of blowing influence the largest bubble that can be formed underwater? We fabricate a plastic star analogous to the star-nosed mole's fleshy nose, and use a weighted syringe to create bubbles using constant pressure. We present scalings of the time for the bubble to expand, elongate, deform, and pinch-off. We show that higher flow rates lead to larger bubbles with shorter lifetimes, which may be advantageous to the mole which would like to sniff often and intake as much odor as possible. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D08.00002: Scaling Laws for Freezing Bubbles Farzad Ahmadi, Christian Kingett, Saurabh Nath, Pengtao Yue, Jonathan Boreyko We deposit bubbles on an icy substrate and model the dynamics of the resulting freeze front using scaling analysis. First, the substrate temperature was ranged from -10 °C to -40 °C using a Peltier stage in a room temperature environment. The freeze front was modeled as a one-dimensional Stefan problem; the latent heat of fusion was balanced by the net difference in thermal conduction across the frozen and unfrozen portions of the bubble. For most bubbles, the freeze front stopped progressing entirely at a critical height where conduction across the ice and liquid were balanced. Second, freezing bubbles were observed under isothermal conditions in a walk-in freezer set to -20 °C. With the bubble initially exhibiting a uniform temperature, the latent heat of fusion now induces a Marangoni flow going up the bubble that detaches and entrains ice particles. These flowing ice particles continue to grow, resulting in multiple freeze fronts that interlock together like hexagons on a soccer ball. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D08.00003: Bubbles at contaminated water interfaces S. Poulain, L. Bourouiba Upon burst, surface bubbles emit droplets that disperse chemicals and pathogens in the air. Water properties affect the physics governing such bubbles, thus affecting the droplets they emit. Yet, the effect of water composition on bubble physics remains little understood. From natural bacterial contamination to controlled contamination, we present the results of a combined experimental and theoretical study of the life of bubbles at contaminated interfaces, with a focus on the physics governing their thinning. We show that the presence of bacteria at the water-air interface has an important effect on the lifetime and thinning of bubbles. We quantify this effect and validate a model that allows to elucidate the observed dynamics. We discuss how bacteria interestingly alter the bubble physics in a manner that can ultimately enhance their own water-to-air dispersal. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D08.00004: Bubble entrainment from acoustically driven meniscus shape deformations in a piezo-acoustic drop-on-demand inkjet nozzle Maaike Rump, Tim Segers, Arjan Fraters, Roger Jeurissen, Marc van den Berg, Hans Reinten, Youri de Loore, Herman Wijshoff, Detlef Lohse, Michel Versluis In piezo acoustic Drop-On-Demand (DOD) inkjet printing a single droplet is produced for each piezo driving pulse. A phenomenon that disturbs the droplet formation process is the entrainment of bubbles in the ink channel. Here, we study bubble entrainment during DOD inkjet printing as a result of meniscus deformations. We show that the fundamental low-frequency acoustic resonance mode of the ink channel (7 kHz) drives the high-amplitude meniscus motion and the corresponding concave meniscus shape. The higher frequency traveling acoustic waves (110 kHz) focus the flow at the concave meniscus which drives the meniscus shape deformations resulting in bubble entrainment. Depending on the piezo driving pulse length, we observe alternating windows of bubble entrainment and no bubble entrainment resulting from the interference of the high frequency acoustic waves that are mainly generated at the rising and falling edges of the piezo driving pulse. |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D08.00005: Pumpless, directional transport of gas bubbles on wettability-patterned diverging tracks Mohamad Jafari Gukeh, Uddalok Sen, Ranjan Ganguly, Constantine Megaridis The manipulation of gas bubbles in an aqueous medium is useful for a variety of applications. Motion of bubbles on a submerged solid substrate is dominated by buoyancy, which renders bubble manipulation tasks difficult. A wettability-patterning technique that allows for continuous directional transport of gas bubbles on submerged flat surfaces, without any external source of energy, is presented. The design consists of a diverging superaerophilic track laid on a superaerophobic background. Gas bubbles are dispensed using a submerged nozzle at the narrow end of the superaerophilic track on the submerged substrate. The diverging nature of the track results in a Laplace pressure difference due to curvature variation of the bubble, which then propels it from the narrow to the wide end of the track. Spontaneous motion of gas bubbles on such tracks is demonstrated, and the forces responsible for such transport are identified. Scaling arguments for the nature of said forces are presented. The transport rates of gas bubbles are compared with a similar mode of droplet transport on superhydrophilic, diverging tracks laid on an open-air surface, and the salient differences are highlighted. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D08.00006: Abstract Withdrawn
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Sunday, November 18, 2018 3:48PM - 4:01PM |
D08.00007: Investigation of Neighboring Laser-Induced Cavitation Bubbles near Orifices Vicente Robles, Ariana Sabzeghabae, Luis Felipe Devia-Cruz, Guillermo Aguilar The antiphase generation of two neighboring cavitation bubbles results in the formation of a slow jet countered in the opposite direction by high-speed jet. The direction of the focused jet can be predetermined from the axis of the two bubbles whereas the speed of the jet can be controlled by modifying the relative bubble sizes, positions, and initiation times. In this study we explore the dynamics of neighboring same millimeter-sized bubbles generated in deionized water using two Nd:YAG 1064 nm wavelength, 6ns pulsed lasers. The two bubbles were modified antiphase to study the resulting jet through different orifice sizes and imaged with high speed shadowgraph at 105 fps. Further, the resulting pressure waves are measured and compared to those released by an isolated cavitation bubble. The dynamics are observed and discussed with regards to natural diffusion and as potential application to micro-pumping. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D08.00008: Capturing Bubbles using Aerophilic Surfaces Leonid Rapoport, Theo Emmerich, Kripa Varanasi When a rising bubble approaches a surface the thin film separating the bubble and the surface drains. If the surface is sufficiently non-wetting, this film will break at a critical thickness and the surface will capture the bubble. In this presentation, we explore the dependency between the ability of a hydrophobic surface to catch bubbles and its texture parameters. We focus on aerophilic surfaces that can entrap a gaseous layer between their textures when submerged, and show how texture parameters affect the dynamics of film drainage. We show how this process can be driven by either bubble deceleration or buoyancy and propose simple guidelines, based on the surface slip length and liquid properties, to determine when the film would drain. We use these findings to design a hierarchical surface with three levels of textures that enable a reduction of two order of magnitude in capture time relative to a flat hydrophobic surface. Finally, we leverage these principles to create an easily scalable device that prevents foam in a passive, and additive-free manner by capturing bubbles as they rise through the bulk of a foaming solution. |
(Author Not Attending)
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D08.00009: On the biggest bubble formed in quasi-static conditions from a submerged orifice Mariano Rubio-Rubio, Rocio Bolanos-Jimenez, Carlos Martínez-Bazán We present an experimental study on quasi-static bubble formation from a submerged orifice on a super-hydrophobic substrate. When injecting air in a quiescent liquid, bubbles grow until the surface tension forces cannot longer balance the buoyancy, and the detachment occurs. If the contact line is pinned to the injector, the maximum diameter, and therefore the volume of the bubble, is limited by the Rayleigh-Taylor instability. However, this limitation can be overcome if the contact line movement allows the bubble base expansion. The properties of the surface, in particular the contact angle θ, affect crucially this contact line dynamics. Thus, to determine how the surface wettability affects the dynamics of the bubble formation, we have performed experiments using a substrate whose contact angle is modified with a super-hydrophobic coating, reaching values of θ≈165o, significantly higher than those previously studied. Our results show that the expansion of the base diameter in the early times, in addition to its retraction to the orifice scale prior to the detachment, results in the generation of bubbles with volumes substantially larger than those reported up to date.
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Sunday, November 18, 2018 4:27PM - 4:40PM |
D08.00010: Experimental study on a rising air bubble in liquid medium through confinement Badarinath Karri, Y Veera Prasad Reddy, Kirti Sahu The effect of confining an air bubble in a fluid between two parallel plates is experimentally studied by analyzing the path and shape oscillations of an air bubble rising in Millipore water. The confinement parameter ‘h’ was defined as the ratio of the distance between the two parallel plates (H) to the bubble radius (R). High speed imaging was used to obtain both front and side views of the bubble. This study is representative of a bubble that moves at a high Reynolds number and has a small Weber number. Results show that the bubble velocity fluctuations due to the interaction with the plates are greater for the confined bubble as compared to a bubble with no confinement. The trajectory of the rising bubble changes from zig-zag (for h = 2.1) to nearly spiral trajectory (for 2.1<h<6). Because of the plates, the bubble is attracted towards one of the plate and repelled continuously and bubble is raised towards one of the plate. The effect of confinement becomes negligible if the distance between the plates is greater than 6.0 times of the radius of the bubble (h>6.0). |
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