Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session GW: Mini-Symposium: Tip-Streaming and Flow/EHD Flow Focusing |
Hide Abstracts |
Chair: Osman Basaran, Purdue University Room: 004 |
Monday, November 24, 2008 8:00AM - 8:22AM |
GW.00001: Tip-Streaming in simple viscous co-flows Invited Speaker: The formation of hydrodynamic structures able to yield micron-sized drops -smaller than 1.5 microns- through a simple coflowing device (R. Suryo and O. A. Basaran, \textit{PoF} \textbf{18}, 082102, 2006) will be experimentally demostrated. The so-called tip-streaming structures appearing when a deformed drop emits fine jets from its tip, have been occasionally found with the aid of surfactants and with electrohydrodynamic-driven flows. Here, we report tip-streaming by simply making two liquid streams co-flow coaxially under creeping flow conditions, avoiding the use of either surfactants or electric fields. In our experimental parametric range, liquid micrometric jets are generated with diameters over two orders of magnitude smaller than the diameter of the capillary from which the inner stream is injected. Moreover, a system consisting of multiple injectors has been constructed and tested with optimal results: the tip streaming regime is perfectly reproduced for all the injectors, which are arranged in an hexagonal pattern. In the case when the inner fluid is a gas instead of a liquid we find that, up to our optical resolution, conical tips are visualized if no gas is injected. For small values of the gas flow rate, and no matter how large the outer capillary number is, no stable long gas jets are formed. Instead, we observe the periodic formation of bubbles from an unsteady conical tip. In collaboration with Jose M. Gordillo, Universidad de Sevilla. [Preview Abstract] |
Monday, November 24, 2008 8:22AM - 8:44AM |
GW.00002: Electrohydrodynamic Liquid Disintegration in Micro-, Meso- and Nanoscopic Dimensions Invited Speaker: The electrohydrodynamic dispersion of liquids spans length scales from 1 mm to 1 nm and involves temporal variations from 1 s to 10 ps. The disintegration mechanisms are diverse and, due to the differences in the dominating forces, vary on the micro-, meso- and nanoscale extending to lower boundaries of 1 $\mu $m, 10 nm and 1 nm, respectively. Using fast imaging, spray current measurements, phase Doppler anemometry and molecular dynamics calculations, we followed the behavior of electrified liquids in the three most common geometries, spherical, pendant drop and slender jet, with dimensions ranging from 100 $\mu $m to 1 nm. Microscale disintegration involves jet ejection from conical surface deformations, jet breakup due to varicose, kink and ramified jet instabilities, and asymmetric droplet fission resulting in side jets. As the liquid dimensions shift from the microscopic dimensions where the processes are governed by the surface tension and the Maxwell stress, to the meso- and nanoscale, thermal fluctuations become increasingly important. The presence of charges in nanodroplets leads to enhanced surface fluctuations, the formation of extreme protrusions and eventually solvated ion evaporation. Charging of slender nanojets results in longer shape relaxation times along with the fission of systems charged below the Rayleigh limit. In collaboration with Jelena Lusic and Peter Nemes, George Washington University. [Preview Abstract] |
Monday, November 24, 2008 8:44AM - 9:06AM |
GW.00003: Electrohydrodynamic and flow induced tip-streaming Invited Speaker: A liquid subjected to a strong electric field emits thin fluid jets from conical structures (Taylor cones) that form at its surface. Such behavior has both practical and fundamental implications, e.g. for raindrops in thunderclouds and in electrospray mass spectrometry. Theoretical analysis of the temporal development of such electrohydrodynamic (EHD) tip- streaming phenomena has been elusive given the large disparity in length scales between the macroscopic drops/films and the microscopic (nanoscopic) jets. Here, simulation and experiment are used to investigate the mechanisms of EHD tip-streaming from a film of finite conductivity. In the simulations, the full Taylor-Melcher leaky-dielectric model, which accounts for charge relaxation, is solved. Simulations show that tip- streaming does not occur for perfectly conducting or perfectly insulating liquids. Scaling laws for sizes of drops produced from the breakup of the thin jets is developed. Further, simulations demonstrate the critical role played by electrically induced surface shear stresses in the inception of tip-streaming. This invites a comparison to flow focusing, i.e. tip-streaming induced by co-flowing two fluids. The latter phenomenon is also investigated by simulation. In collaboration with Ronald Suryo, Exxon-Mobil; and Jeremy Jones, Michael Harris, and Osman Basaran, Purdue University. [Preview Abstract] |
Monday, November 24, 2008 9:06AM - 9:28AM |
GW.00004: Transitions in viscous withdrawal Invited Speaker: A process analogous to flow-focusing occurs in extended and stably stratified layers of immiscible, viscous liquids. In viscous withdrawal, an axisymmetric converging flow is imposed in the upper layer. When the upper layer flow is weak, the interface forms a hump. No liquid from the lower layer is entrained. When the upper layer flow is strong, liquid from the lower layer is entrained and the interface becomes a spout. Here I summarize recent results on the fundamental mechanisms controlling these regimes. For selective withdrawal, a clear picture has emerged, with good agreement between theory, simulation and experiment. The regime ends when the viscous stress exerted by the upper layer flow overcomes surface tension, creating a saddle-node bifurcation in the hump solution. Less is understood about viscous entrainment. A long-wavelength model including only local information is degenerate, possessing many solutions for the same withdrawal condition. Including information about the global geometry removes this degeneracy but also makes the surprising prediction that global geometry can change the nature of the transition. First-order, weakly first-order or continuous transitions are all possible. How these results relate to the variety of experimental phenomena, such as stable, micron-sized spouts, intricate patterns of hysteresis and multiple stable spout states under the same condition, is at present unclear. (Includes material from joint works with Blanchette, Cohen, Kleine Berkenbusch, and Schmidt.) [Preview Abstract] |
Monday, November 24, 2008 9:28AM - 9:50AM |
GW.00005: On the physics of hydrodynamic and electrohydrodynamic tip-streaming revealed from published experimental literature Invited Speaker: Thousands of published experimental measurements on electrospray and flow focusing are analyzed in this work. The scaling analysis shows two cases of uniformly valid incomplete similarity for the emitted jet diameter for electrospray and flow focusing within the parametrical space of steady capillary jetting from experiments. These cases, reducible to a single formulation, compellingly points to a single underlying and remarkably simple physics for both phenomena. In electrospray, however, the scaling analysis of the emitted current does not show the degree of uniformity exhibited by the jet diameter, reflecting the dominance of different charge transport mechanisms based on different hydrodynamic regimes. The existence of analytical conical tip solutions is also discussed, and the events of ``unconditional jetting'' delimited; under these findings, the smallest attainable droplet sizes from experiments are analyzed. These minimum sizes exhibit two interesting additional cases of incomplete similarity for electrospray and flow focusing, uniformly valid in the corresponding spaces of hydrodynamic and electrohydrodynamic Weber and Capillary numbers. [Preview Abstract] |
Monday, November 24, 2008 9:50AM - 10:12AM |
GW.00006: The Role of Surfactant Dynamics on Tipstreaming in Planar Flow Focusing Invited Speaker: We have previously shown that tipstreaming occurs in microfluidic flow focusing experiments when soluble surfactants are present in the internal liquid phase. While we have characterized the conditions under which the process occurs in terms of the capillary number, flow rate ratio, viscosity ratio, and other geometric parameters for the device, the role of the surfactant molecular properties in the process is not clear. In this talk, we vary the characteristic timescales for transport of surfactant to and along the interface by considering ionic and nonionic surfactants with varying charge, tail length, and critical micelle concentration. We find that the process is robust in that many different surfactants will promote tipstreaming. We organize our observations of the thread length and diameter as well as the range of flow conditions in which tipstreaming occurs in terms of dimensionless parameters including the capillary number, Peclet number, and Biot numbers. [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