Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session BD: Bubble Breakup and Pinch-off |
Hide Abstracts |
Chair: Jose Gordillo, University of Seville Room: Hilton Chicago Continental A |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BD.00001: On the mechanisms of generation and pinch-off of bubbles and drops in high Reynolds number flows J.M. Gordillo, A. Sevilla, J. Rodriguez-Rodriguez, C. Martinez-Bazan It is well known that the formation of drops and bubbles in high Reynolds number flows can be described at early times in terms of Rayleigh (capillary) or Kelvin-Helmholtz (shear) instabilities. Our stability analyses and potential flow simulations have been employed to properly scale a large number of experimental measurements of the break-up frequency of drops and bubbles. The physics underlying above results, valid for the initial stages of the development of the instability, are also applicable near pinch-off and permit to clarify the different ways the minimum radius of drops and bubbles (hereafter denoted as r$_{n})$ approaches the finite time singularity. Thus, we recover the well known r$_{n}\propto \tau ^{2/3}$, being $\tau $ the time to singularity, valid for drops, and show that in the case of bubbles, r$_{n}\propto \tau ^{1/2}$ if the bubble break up is symmetric. However, we also show that if the break-up of bubbles is asymmetric the radius of the neck follows a r$_{n}\propto \tau ^{1/3}$power law. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BD.00002: The pinch-off of a bubble S.T. Thoroddsen, T.G. Etoh, K. Takehara We report ultra-high-speed imaging of the pinch-off of a bubble, using frame-rates up to 1,000,000 frames/s, with an exposure time as short as 0.5 $\mu $s and spatial resolution as small as 5 $\mu $m. The bubbles are grown attached to a circular needle at a very slow rate, until they become unstable to buoyancy forces and pinch off from the needle. Our focus is on measuring the power-law describing the reduction in the neck-radius vs time, for a bubble in a low-viscosity liquid, such as water. Our measurements will be compared to theory which suggests the radius should decrease as time to the power $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $. Results will be presented for three different gases as well as different bubble sizes, generated by using different sized needles from 2 to 5 mm. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BD.00003: Bubble breakup phenomena in a venturi tube Akiko Fujiwara, Shu Takagi, Yoichiro Matsumoto Microbubble has distinguished characteristics of large surface area to unit volume and small buoyancy, and it has advantages in many engineering fields. Recently microbubble generators with low energy and high performance are required to wide applications. In the present study, we propose one new effective technique to generate tiny bubbles with less than 200 $\mu $m diameter utilizing venturi tube under high void fraction condition. The objective of the present study is to elucidate the mechanism of bubble breakup phenomena in the venturi tube and to clarify the effects of parameters which are necessary to realize an optimum system experimentally. Experiment was conducted with void fraction of 4{\%} and variation of liquid velocity from 9 to 26 m/s at the throat. Under low velocity condition, bubbles which were observed with a high speed camera parted gradually in a wide region. On the contrary under high velocity condition, bubbles expanded after passing through the throat and shrank rapidly. Since the speed of sound in gas-liquid system is extremely lower than that of single-phase flow, the bubble breakup phenomenon in the venturi tube is explained as the supersonic flow in a Laval nozzle. By rapid pressure recovery in diverging area, expanding bubbles collapse violently. The tiny bubbles are generated due to the surface instability of shrinking bubbles. [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BD.00004: Break-up of a gas bubble in a uniaxial straining flow (USF) at finite $Re$ Antonio Revuelta, Javier Rodriguez-Rodriguez, Carlos Martinez-Bazan It has been shown in a recent work that a gas bubble immersed in a USF can be understood as a simplified model to describe some important aspects of the more complex problem of the turbulent break-up, provided that the Reynolds, $Re$, and Weber, $We$, numbers of the flow around the bubble are sufficiently high. Despite of its simplicity, the break-up time given by the model reproduces with reasonable accuracy experimental measurements performed in a real turbulent flow. The present investigation completes that work, exploring the effect of $Re$ on the break-up process. Besides, to clarify the bubble break-up at $We \approx We_c$ (the critical one), we have studied the effect of various mechanisms proposed in the literature, including bubble oscillations, resonance and compressibility effects. The USF model allows us to compare the efficiency of the different breaking mechanisms helping us to determine the most important ones. On the other hand, a systematic study of the effect of viscosity (Reynolds number) on the break-up process has been performed.The dependence of $We_{\rm c}$ on $Re$ has been observed to differ from the one previously reported in the literature for similar flows. Furthermore, when $We \gg We_{\rm c}$, an analytical expression for the break-up time that includes the effect of $Re$ is also proposed. [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BD.00005: Bubble Formation in a Quiescent Liquid Ronald Suryo, Osman Basaran Bubble formation is important in diverse applications such as distillation, blood oxygenation, gas absorption, and glass manufacturing. Dynamics of growth and breakup of a bubble from a tube (orifice) immersed in a container filled with a quiescent incompressible, Newtonian liquid are determined computationally by finite element analysis. Simulations are carried out over a wide range of Reynolds numbers \textit{Re} (inertial/viscous force), gravitational Bond numbers $G$ (gravitational/surface tension force), capillary numbers \textit{Ca} (viscous/surface tension force), and ratios of container to tube radii $a$. Variation of primary bubble volume and bubble length at breakup with the governing parameters are determined and rationalized to shed physical insights into the underlying physics governing bubble growth and breakup. Scaling behavior near pinch-off is also examined. The minimum radius of a necking bubble is found to scale linearly with time to breakup. As pinch-off nears, pressures in both phases remain bounded but the diverging surface tension pressure is shown to be balanced by the viscous stress exerted by the outer liquid. [Preview Abstract] |
Sunday, November 20, 2005 12:01PM - 12:14PM |
BD.00006: Capillary pinch-off of inviscid fluids at varying density ratios: the bubble limit David Leppinen, John Lister, Jens Eggers The axisymmetric pinch-off of an inviscid blob of fluid of density $\rho_{1}$ in an ambient fluid of density $\rho_{2}$ is examined in the limit as the density ratio $D = \rho_{1}/\rho_ {2} \rightarrow 0$ using a boundary integral formulation. It has previously been shown (Leppinen \& Lister, {\em Phys. Fluids}, {\bf 15(2)}, 568-578, 2003) that pinch-off is a self-similar process in the droplet limit as $D \rightarrow$ with the radial and the axial length scales decreasing as $\tau^{2/3}$ where $\tau$ is the time to pinch-off. In the droplet limit, the similarity form is independent of the initial conditions. In the bubble limit, as $D \rightarrow 0$, it is seen that pinch-off is also a self-similar process, however, in this case the similarity form is dependent on initial conditions. In the bubble limit the radial length scale decreases as $\tau^{c_{1}}$ and the axial length scale descreases as $\tau^{c_{2}}$ with both $c_{1}$ and $c_{2}$ (and the associated prefactors) depending on the value of the density ratio $D$ and on the initial conditions. In the limit of $D=0$, $c_{1} \approx 0.55 \pm 0.01$ and $c_{2} \approx 0.48 \pm 0.05$ dependent on initial conditions. [Preview Abstract] |
Sunday, November 20, 2005 12:14PM - 12:27PM |
BD.00007: Gas Bubble Pinch-off in Viscous and Inviscid Liquids P. Taborek, J.C. Burton, R. Waldrep We have used high-speed video to analyze pinch-off of nitrogen gas bubbles in fluids with a wide range of viscosity. If the external fluid is highly viscous ($\eta_{ext}>$100 cP), the radius is proportional to the time before break, $\tau$, and decreases smoothly to zero. If the external fluid has low viscosity ($\eta_{ext}<$10 cP), the neck radius scales as $\tau^{1/2}$ until an instability develops in the gas bubble which causes the neck to rupture and tear apart. Finally, if the viscosity of the external fluid is in an intermediate range, an elongated thread is formed which breaks apart into micron-sized bubbles. 100,000 frame-per-second videos will be presented which illustrate each of these flow regimes. [Preview Abstract] |
Sunday, November 20, 2005 12:27PM - 12:40PM |
BD.00008: Bubble Pinch-Off by Inertial Collapse: Loss of Radial Symmetry N.C. Keim, P. Moller, W.W. Zhang, S.R. Nagel Using high-speed video (120\,000 frames/s), we have studied the inertially driven pinch-off of air bubbles from an underwater nozzle. Our work is both consistent with earlier findings concerning the interfacial collapse rate\footnote{M.S.~Longuet-Higgins, B.R.~Kerman, K.~Lunde, J.~Fluid Mech.\ 230, 365--390 (1991)} and with data showing collapse that appears to end in sudden rupture instead of by smooth progression to zero radius\footnote{J.C.~Burton, R.~Waldrep, and P.~Taborek, Phys.\ Rev.\ Lett.\ 94, 184502 (2005)}. In addition, we find that changing the shape and orientation of the nozzle strongly modifies the outcome of pinch-off. A deviation of the nozzle axis by as little as $0.1^\circ$ from the vertical breaks the cylindrical symmetry of the drop neck. This, in turn, affects the form and orientation of rupture, and the number and sizes of satellite bubbles. Finally, we note the unusual observation of satellite drop formation {\it within} the cavity of the main bubble. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700