Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G34: Interfacial Fluid Mechanics I: Bubbles/Drops/Films |
Hide Abstracts |
Sponsoring Units: DFD Chair: Sunghwan Jung, Virginia Polytechnic Institute and State University Room: 210A |
Tuesday, March 3, 2015 11:15AM - 11:27AM |
G34.00001: Influence of Marangoni flows on extraction and reaction performance Radhakrishna T G, Anil Vir, Jason Picardo, Pushpavanam Subramaniam In this work, the effect of Marangoni flows on mass transfer is investigated for stratified flow of two immiscible liquids in a microchannel. Experiments involving reactive extraction of carboxylic acids from organic phase using aqueous sodium hydroxide are performed. Often in analysis, the liquid-liquid interface is assumed to be flat. However, a deforming interface was observed for certain flow rate ratios. The conditions under which the interface deforms are determined. The experiments are complemented with mathematical modeling and simulation. Navier-Stokes equation and transport equation are simplified using the lubrication approximation and an approximate solution is obtained. The interphase mass transfer and hydrodynamics are coupled through the shear stress boundary condition. In cases where the interface is flat, the transport equation is solved numerically using finite difference method. In cases where the interface deforms, the evolution of interface is captured using kinematic boundary condition and the transport equation is solved numerically. [Preview Abstract] |
Tuesday, March 3, 2015 11:27AM - 11:39AM |
G34.00002: Radiation Pressure Induced Nonlinear Optofluidics in Liquid Droplets Peng Zhang, Sunghwan Jung, Yong Xu, Aram Lee In the present study, we analyze a nonlinear optofluidic process associated with a high quality (Q) factor whispering gallery mode (WGM) in liquid droplets. Optical radiation pressure induced droplet deformation can produce a frequency shift proportional to the WGM power. Droplet deformation will be obtained both theoretically and numerically by boundary element method. We will show that the nonlinear optofluidic effect is stronger than temperature-induced nonlinearity. Using liquid properties that are experimentally attainable (e.g., oil drop in water), we find that measurable WGM resonance shift may be generated by only a few photons. This technique may also lead to the possibility of fluid viscosity and interfacial tension measurement by non-destructive optical forces. [Preview Abstract] |
Tuesday, March 3, 2015 11:39AM - 11:51AM |
G34.00003: From viscous to elastic sheets: Dynamics of smectic freely floating films Kirsten Harth, Kathrin May, Torsten Trittel, Ralf Stannarius Oscillations and rupture of bubbles, composed of an inner fluid separated from an outer fluid by a membrane, represent an old but still immensely active field of research. Membrane properties except surface tension are often neglected for simple fluid films (e.g. soap bubbles), whereas they govern the dynamics in systems with more complex membranes (e.g. vesicles). Due to their layered phase structure, smectic liquid crystals can form stable, uniform and easy-to handle fluid films of immense aspect ratios. Recently, freely floating bubbles detached from a support were prepared. We analyze the relaxation from strongly non-spherical shapes and the rupture dynamics of such bubbles using high-speed video recordings. Peculiar dynamics intermediate between those of simple viscous fluid films and an elastic response emerge: Oscillations, slowed relaxation and even the formation of wrinkles and extrusions. We characterize these phenomena and propose explanations. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:03PM |
G34.00004: Thin sheets achieve optimal wrapping of liquids Joseph Paulsen, Vincent D\'emery, Benny Davidovitch, Christian Santangelo, Thomas Russell, Narayanan Menon A liquid drop can wrap itself in a sheet using capillary forces [Py et al., PRL 98, 2007]. However, the efficiency of ``capillary origami'' at covering the surface of a drop is hampered by the mechanical cost of bending the sheet. Thinner sheets deform more readily by forming small-scale wrinkles and stress-focussing patterns, but it is unclear how coverage efficiency competes with mechanical cost as thickness is decreased, and what wrapping shapes will emerge. We place a thin ($\sim 100$ nm) polymer film on a drop whose volume is gradually decreased so that the sheet covers an increasing fraction of its surface. The sheet exhibits a complex sequence of axisymmetric and polygonal partially- and fully- wrapped shapes. Remarkably, the progression appears independent of mechanical properties. The gross shape, which neglects small-scale features, is correctly predicted by a simple geometric approach wherein the exposed area is minimized. Thus, simply using a thin enough sheet results in maximal coverage. [Preview Abstract] |
Tuesday, March 3, 2015 12:03PM - 12:15PM |
G34.00005: Pool Boiling of Ethanol-Water mixture on Nano-Textured Surfaces Alexander Yarin, Rakesh Sahu, Sumit Sinha-Ray, Suman Sinha-Ray An experimental and theoretical study of pool boiling of ethanol-water mixtures on nano-textured surfaces was studied. A comparison of pool boiling on bare copper surface with pool boiling on surfaces covered by copper-plated supersonically-blown nanofibers revealed a significant increase in the heat flux in the latter case. Namely, the heat flux on the nano-textured surfaces was about 3-8 times higher than that on the bare copper surfaces, while the surface temperature due to the nano-texture would be lower by about 10 $^{\circ}$C at the same heat flux. The significant positive effect of the nano-texture is due to the fact that it facilitates bubble nucleation. Some preliminary results of numerical modeling of boiling process in the framework of the Cahn-Hilliard approach are discussed and several examples of the predictions are given. [Preview Abstract] |
Tuesday, March 3, 2015 12:15PM - 12:27PM |
G34.00006: Simple analytical model of evapotranspiration in the presence of roots Cesare Cejas, Jean-Christophe Castaing, Larry Hough, Christian Fretigny, Remi Dreyfus Water is essential for plant growth. The loss of water via evaporation in soil remains to be an important limiting factor for root growth and consists of well-debated mechanisms. The presence of a plant also provides an additional pathway for water transport in the form of transpiration. Prediction of total evapotranspiration flux permits estimation of the remaining quantity of water in the soil. Using a controlled visual 2D model set-up, we perform evaporation experiments with real root systems under different relative humidity conditions. We use the results on mass loss and evaporation front positions to develop a simple model, based on basic principles of evaporation flux, which predicts the position of the evaporating front and the total mass of water that is lost from the evapotranspiration of water out of the granular medium. The model also helps predict the lifetime of the plant -- an important application in agriculture. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G34.00007: Growth and densification of frost around a circular cylinder under humid air on cross flow Victor Madrid, Fausto Sanchez, Simon Martinez, Arturo Morales Formation, growth and densification of frost around a circular cylinder under humid air on cross flow at different Reynolds numbers has been numerically studied using the finite volume method. The frost formation phenomenon takes place when humidity goes through a desublimation phase change at a temperature lower than its solidification point. Continuity, momentum, energy and mass transport equations have been solved for a whole domain including both phases, gas and solid, and the two components in the gas phase, i.e. dry air and humidity. The mass of water that goes from the gas to the solid phase is used as a source term in the mass conservation equation for solid phase and as a sink for the gas phase, affecting source terms in all the other conservation equations (energy and momentum) also. A volume of fraction conservation equation for solid phase is used to obtain local fractions of ice droplets, considering formally as frost those fraction values greater than a critical value. Once those local fractions are known, local frost properties such as density and thermal conductivity can be calculated as functions of the phase fraction allowing to compute the evolution of growth and local properties of frost. [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G34.00008: Parallel magnetic resonance imaging of gas-liquid flows Christoph Mueller, Alexander Penn, Klaas P. Pruessmann Gas-liquids flows are commonly encountered in nature and industry. Experimental measurements of gas-liquid flows are challenging since such systems can be visually opaque and highly dynamic. Here we report the implementation of advanced magnetic resonance imaging (MRI) strategies allowing us to probe the dynamics (voidage and velocity measurements) of gas-liquid flows with ultra-fast acquisition speeds. Specifically, parallel MRI which exploits the spatial encoding capabilities of multiple receiver coils was implemented. To this end a tailored, 16 channels MR receive array was constructed and employed in the MR acquisition. A magnetic susceptibility matched gas-liquid system was set-up and used to probe the motion, splitting and coalescence of bubbles. The temporal and spatial resolution of our acquired data was 5 ms and 3.5 mm x 3.5 mm, respectively. The total field of view was 200 mm x 200 mm. We will conclude with an outlook of further possible advances in MRI that have the potential to reduce substantially the acquisition time, providing flexible gains in temporal and spatial resolution. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G34.00009: Air flows generated by an impacting drop Irmgard Bischofberger, Bahni Ray, Taehun Lee, Jeff Morris, Sidney R. Nagel A drop impacting a solid surface with sufficient velocity will splash and emit many small droplets. Lowering the ambient air pressure suppresses splashing completely. This effect, robustly found for different liquid and substrate properties, raises the fundamental question of how air affects a spreading drop. We visualize the flow of air induced by the drop after it hits the substrate using a modified Schlieren optics technique combined with high-speed video imaging. Comparison with the air flow created by an impacting solid sphere allows us to decouple the vorticity components of the falling drop from that of the spreading liquid. Our studies reveal the emergence of vorticity on two length scales. On larger scales, the airflow induced in the drop's wake leads to vortex structures due to interaction with the substrate. On smaller scales, the spreading of the drop generates a vortex ring above the outer edge of the spreading liquid. We show that this vorticity generation is governed by a balance between inertial and viscous forces. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G34.00010: Flow reversing in the gas layer in droplet impact Zhen Jian, Pascal Ray, Christophe Josserand, Stephane Zaleski Recent numerical and experimental studies demonstrated the crucial role of surrounding gas in droplet impact. Whereas, the mechanism of gas effect in droplet splashing is still far from a crystal clear comprehension. Complicated dynamics occur in a small temporal and spatial scale before direct contact with the target surface, which are related to the origin of the splashing. Direct numerical simulations were executed with a code called Gerris for both droplet impact on a liquid surface and on a solid subtract. New dynamics in the gas layer between the droplet and the target surface were discovered. Unexpectedly, a``reversing'' gas flow (towards the center) is observed as the droplet approaches the target surface. With further descending of the droplet, the flow is reversed and evacuates towards the outside. The reversing of the flow motion direction is followed by the pressure jump and the dimple formation which have been reported as some crucial gas dynamics in droplet splashing mechanism in our previous work. An aerodynamic mechanism is proposed for the flow reversing dynamics. [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G34.00011: Simulation of splashing of micro-scale droplets on a dry surface Arnout Boelens, Andrzej Latka, Cacey Stevens, Juan de Pablo Results are presented for the simulation of micro-scale droplets splashing on a dry surface. The simulations are performed using a Volume Of Fluid approach and a Finite Volume technique. The contact line is described using a Generalized Navier Boundary Condition with a dynamic microscopic contact angle. Both the gas phase and the liquid phase are assumed to be incompressible. The results of these simulations show good agreement with experiments. Independent of the wetting properties of the surface, simulations reveal the formation of a liquid sheet with an apparent contact angle approaching 180 degrees. This liquid sheet breaks up into smaller droplets as the spreading progresses. When the pressure of the system is reduced, the droplet does not break up and splashing is suppressed. Depending on the velocity with which the contact line moves, different flow regimes are observed. One of these regimes involves air bubbles becoming entrained in the liquid phase, similar to what is observed during wetting failure in coating processes. Mesh resolution is critical to describe contact line behavior, liquid sheet formation, and to reproduce the effect of pressure. In this work, the resolution is of the order of 10 nm, and the droplets are several hundred microns large. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G34.00012: Comparison of splashing of low- and high- viscosity liquids Cacey Stevens, Andrzej Latka, Sidney Nagel The splash of a liquid drop on a dry surface was shown to be suppressed at low ambient air pressure [1--3]. However the mechanism by which air causes a drop to splash remains unresolved. This is further complicated by the finding that there are two distinct splashing regimes that depend on the viscosity of the liquid. Accordingly, we determine the evolution of splashing at both low and high viscosities. A high-viscosity drop splashes by emitting a thin sheet of liquid from the spreading drop long after it has first contacted the solid. This film subsequently breaks up into smaller droplets to form the splash. We have found that there is also a delay in the ejection of a thin sheet when a low-viscosity drop splashes. This suggests a common mechanism of delayed thin sheet ejection for splashing in both viscosity regimes. We also show how the ejection time of the thin sheet depends on liquid viscosity and ambient air pressure. [1] L. Xu, W. W. Zhang, and S. R. Nagel, Phys. Rev. Lett., 94(18), 184505 (2005). [2] L. Xu, Phys. Rev. E, 75(5), 056316 (2007). [3] A. Latka et. al., Phys. Rev. Lett., 109(5), 054501 (2012). [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G34.00013: Force response of actively deformed polymer microdroplets: dependence on the solid/liquid boundary condition Jonas Heppe, Joshua D. McGraw, Roland Bennewitz, Karin Jacobs In fluid dynamics, the solid/liquid boundary condition can play a major role in the flow behavior of a liquid. For example, in the dewetting of identical polymer films on weak slip or strong slip substrates, large qualitative and quantitative differences are observed. Therefore, when applying an external load to a liquid resting on such substrates, the measured reaction forces and the ensuing flow should also depend on the boundary condition. We present atomic force microscopy measurements in which the reaction force of a cantilever is measured as the tip pierces liquid polymer micron sized droplets and films. These indentations are done on substrates with tuned slip. Accessing the size, depth and rate dependence of the resulting force distance curves, we show an influence of the slip condition on the dissipated energy and adhesion. [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G34.00014: Lyapunov Based Predictions of Droplet Shapes in Thermocapillary Driven Nanofilms Zachary Nicolaou, Sandra Troian Previous work in our group has focused on the spontaneous formation of pillar arrays in nanoscale molten films subject to an extremely large transverse thermal gradient.\footnote{M.Dietzel and S. M. Troian, Phys. Rev. Lett. 103 (7), 074501(2009)}$^,$\footnote{M. Dietzel and S. M. Troian, J. Appl. Phys.108, 074308 (2010)}$^,$\footnote{E. McLeod, Y. Liu and S. M.Troian, Phys. Rev. Lett. 106, 175501 (2011)}. The shape of these formations is influenced by the relative strength of thermocapillary to capillary forces which is strongly dependent on the system geometry, fluid properties, magnitude of the initial thermal gradient, and whether volume is conserved or not. Here we examine the parameter regime corresponding to steady state shapes resembling either isolated or extended sinusoidal-like waveforms. The stability of these one dimensional and axisymmetric shapes is investigated by a combination of Lyapunov analysis, asymptotic techniques and numerical simulations. Our findings indicate that radially symmetric arrays with small peak heights are linearly stable to perturbations. The existence of such stable states for parameter values accessible to experiment offers an intriguing route for non-contact fabrication of optical and photonic components. [Preview Abstract] |
Tuesday, March 3, 2015 2:03PM - 2:15PM |
G34.00015: Improved Measurement of the 3D Dominant Mode Wavelength in NanoBenard Instability Kevin Fiedler, Sandra Troian Molten nanofilms exposed to an initial uniform and very large transverse thermal gradient ($10^5$ to $10^7$ C/cm) are prone to spontaneous formation and growth of nanopillars typically separated by tens of microns or less. Linear stability analysis of the corresponding interface equations suggest these formations result either from electrostatic attraction between the molten film and proximate substrate due to fluctuation induced surface image charge\footnote{S. Y. Chou and L. Zhuang, J. Vac. Sci. Technol. B 17, 3197 (1999)}, interface radiation pressure from coherent reflections of acoustic phonons\footnote{E. Sch\"affer \emph{et al}., Macromolecules 36, 1645 (2003)}, or fluctuation induced thermocapillary forces leading to 3D B\'enard-like structures\footnote{M.Dietzel and S. M. Troian, Phys. Rev. Lett. 103 (7), 074501(2009); M. Dietzel and S. M. Troian, J. Appl. Phys. 108, 074308(2010)}. In this talk, we discuss a number of improvements to our original experimental system\footnote{E. McLeod, Y. Liu and S. M. Troian, Phys. Rev. Lett. 106, 175501 (2011)} including image analysis of structure formation at much earlier times. Our current measurements indicate even closer agreement with the thermocapillary mechanism proposed. [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