Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session B15: Current Fluid Mechanics |
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Sponsoring Units: DFD Chair: Shelley Anna, Carnegie Mellon University Room: 316 |
Monday, March 16, 2009 11:15AM - 11:27AM |
B15.00001: Walking on water: why your feet get wet Michael Shelley, Jake Fontana, Peter Palffy-Muhoray Walking on wet pavement during or after heavy rain results in wet shoes, and often, wet feet. We describe a peculiar transport process associated with walking on wet surfaces which results in the vamps, and frequently, the insides, of shoes getting wet. We discuss details of this process and compare experimental results with simple model predictions. Strategies for keeping feet dry will be considered. [Preview Abstract] |
Monday, March 16, 2009 11:27AM - 11:39AM |
B15.00002: Breaking beer bottles with cavitation Sunny Jung, Jake Fontana, Peter Palffy-Muhoray, Michael Shelley Hitting the top of a beer bottle, nearly full of water, with an open hand can cause the bottle to break, with the bottom separating from upper section. We have studied this phenomenon using a high-speed camera, and observed the formation, coalescence and collapse of bubbles. The breaking of glass is due to cavitation, typically occurring near the bottom edge. We make numerical estimates of the relevant physical parameters, and compare these with experimental observations. [Preview Abstract] |
Monday, March 16, 2009 11:39AM - 11:51AM |
B15.00003: Optical Tweezer as a Viscometer Daniel Erenso, Samuel Elrod, Taylor Barns, Anthony Farone , Mary Farone An optical tweezer (OT) has been widely used to study the mechanical properties of microscopic living biological systems like red blood cells. These studies are based on measurement of deformations caused by a force exerted directly or indirectly by an optical trap. The trap is usually pre-calibrated using Stokes viscous force of the suspension fluids for the biological system which is directly proportional to the viscosity of the fluids. Therefore, calibration of the trap depends on the viscosity of the fluid which depends on temperature. In this work, we have demonstrated that OT can be used to precisely measure the viscosity of biological fluids affected by temperature. Using a an infrared laser trap which is calibrated using silica sphere suspended in a distilled deionized water and measuring the power as function of escape velocity, we have measured the viscosities of a newborn and unborn bovine serum with a different concentration of antibodies. [Preview Abstract] |
Monday, March 16, 2009 11:51AM - 12:03PM |
B15.00004: Fabrication of a Nanoscale Thermal Anemometry Probe Via Electric Field Assisted Assembly Jason Kawasaki, Sean Bailey, Lex Smits, Craig Arnold A nanoscale thermal anemometry probe (NSTAP) is being developed to measure instantaneous fluid velocity at ultra-small scales using conventional constant temperature anemometry principles. The probe consists of a 50 nm by 10 um platinum nanowire (NW) suspended between two current carrying electrodes. Previous nanoscale anemometry wires had been fabricated via metal deposition on a photolithography-patterned substrate; however, deposited NWs are not free-standing and thus must later be lifted off the substrate resulting in low process yields. In this presentation, we discuss alternative methods of shrinking the probes further and increasing the yield of successful probes, including growing nanowires from solution to bridge the electrodes, and using dielectrophoresis to align pregrown nanowires between the electrodes. In each of these methods, the NWs are directly assembled in the desired structure eliminating the need for additional processing steps. NSTAP probes manufactured using these methods will also exhibit higher spatial resolution and temporal response than previous NSTAP designs. [Preview Abstract] |
Monday, March 16, 2009 12:03PM - 12:15PM |
B15.00005: A Front Tracking Algorithm for Liquid Jet Breakup Wurigen Bo, James Glimm, Xingtao Liu A numerical study of breakup of a high speed jet is presented using the Front Tracking method in 3D. A robust locally grid based method is applied to handle the topological change of the surface mesh in the simulation, the validation of the method is proved mathematically. Numerical results are presented for 3D simulation of the primary breakup of a liquid jet with turbulent inflow. [Preview Abstract] |
Monday, March 16, 2009 12:15PM - 12:27PM |
B15.00006: Coalescence and Pinch-Off in Viscous Liquids Joseph Paulsen, Justin Burton, Sidney Nagel When two fluid drops come into contact, a topological transformation occurs as they rapidly coalesce into a single drop. Because of its speed and geometry, this finite time singularity is difficult to study optically. We therefore use an electrical method to probe viscous coalescence as early as 10 ns after contact. This technique was developed by Burton \textit{et al}.[1] to study mercury drop pinch-off and adapted for salt-water coalescence by Case \textit{et al}.,[2] revealing a breakdown of the expected universal dynamics in early-time inviscid coalescence. For viscous coalescence, we measure a resistance that decreases as t$^{-1}$ at early times and as t$^{-1/2}$ at late times, with a crossover time that increases with viscosity. In the inviscid case, these power laws had been interpreted with a model in which the drops coalesce at a slightly deformed interface.[2] We explore this possibility as well as others, such as an anomalously long viscous regime. This electrical technique is also used to study viscous fluid pinch-off, which we compare with previous optical studies. [1] J. C. Burton, J. E. Rutledge, and P. Taborek, Phys. Rev. Lett. \textbf{92}, 244505 (2004). [2] S. C. Case and S. R. Nagel, Phys. Rev. Lett. \textbf{100}, 084503 (2008). [Preview Abstract] |
Monday, March 16, 2009 12:27PM - 12:39PM |
B15.00007: Scaling Law for Driven Spreading and Coalescence of Sessile Droplets Pilgyu Kang, Shahab Shojaei-Zadeh, Christine Appleby, Shelley Anna This study investigates the dynamics of spreading and coalescence of droplets on a surface, a process important in applications such as inkjet printing, spray coating, and flooding of fuel cells. We use a simple microfluidic device to control the spreading and merging processes. Droplet diameter and maximum height are monitored as functions of time. We compare the dynamics with existing scaling models modified to incorporate time dependent volume, and we extend the model to describe the scaling behavior of the liquid bridge growing between merging droplets on a surface. The experiments agree well with the expected scaling. [Preview Abstract] |
Monday, March 16, 2009 12:39PM - 12:51PM |
B15.00008: Temperature profiles near a pinned nucleating bubble Scott Parker, Chang-Ki Min, Sung Chul Bae, David Cahill, Steve Granick We have measured the temperature distribution on solid surfaces in contact with a nucleating vapor bubble by thermal surface plasmon imaging. Vapor bubbles are created by focused laser heating of an underlying metal substrate. Bubbles are pinned in place by suitable surface functionalization and their shape is characterized by interferometry. Varying the wettability of the surface to control the shape and surface lifetimes of bubbles, we have correlated contact angle, lift-off diameter, and local temperature. [Preview Abstract] |
Monday, March 16, 2009 12:51PM - 1:03PM |
B15.00009: Effect of Encapsulated Polymers and Nanoparticles on Deformation of Droplets O. Berk Usta, Dennis Perchak, Andrew Clarke, Julia M. Yeomans, Anna C. Balazs We investigate the effects of polymer chains and nanoparticles on the deformation of a droplet in shear and extensional flow using computational modeling; Our model accounts for both the solid and fluid phases explicitly. We show that under shear flow, both the nanoparticles and the encapsulated polymers reduce the shear-induced deformation of the droplet at intermediate capillary numbers; nevertheless, long polymer chains can induce the breakup of the droplet at high capillary numbers. In contrast, under extensional flow we find that the long polymer chains inhibit the breakup and reduce deformation. We study the chain-length and concentration dependence and also present the effects of various parameters such as the wetting strength. [Preview Abstract] |
Monday, March 16, 2009 1:03PM - 1:15PM |
B15.00010: Electrorheology Leads to Efficient Combustion R. Tao, K. Huang, H. Tang, D. Bell Improving engine efficiency and reducing pollutant emissions are important. Since combustion starts at the interface between fuel and air and most harmful emissions come from incomplete burning, reducing the size of fuel droplets for the fuel injection would increase the total surface area to start burning, leading to a cleaner and more efficient engine. While most efforts are focused on ultra-dilute mixtures at extremely high pressure to produce much finer mist of fuel for combustion, the new technology is still under development and only for next generation vehicles. Here we report our fuel injection technology based on new physics principle that proper application of electrorheology can reduce the viscosity of petroleum fuels. A small device is thus introduced just before the fuel injection for the engine, producing a strong electric field to reduce the fuel viscosity, resulting in much smaller fuel droplets in atomization. Both lab tests and road tests confirm our theory and indicate that such a device improves fuel mileage significantly and reduces emission. The technology is expected to have broad applications, applicable to current internal combustion engines and future engines as well. Supported by STWA and RAND. [Preview Abstract] |
Monday, March 16, 2009 1:15PM - 1:27PM |
B15.00011: Evolution of Electrified Films on a Porous Inclined Plane Uma Balakrishnan, Usha Ranganathan The nonlinear stability of a thin conducting film flow down a porous inclined plane, when an electric field acts normal to the plane is considered. It is assumed that the flow through the porous medium is governed by Darcy's law and the characteristic length of the pore space is much smaller than the depth of the fluid layer above. Integral Boundary Layer method is employed in obtaining a set of exact averaged equations for the film flow system. Linear stability results through normal mode analysis reveal that the destabilizing influence of the electric field is further enhanced by the porosity of the medium. Critical Reynolds number for the onset of instability decreases with the increase in the permeability of the porous plane. Weakly nonlinear stability analysis using method of multiple scales divulges the existence of zones due to supercritical stability and subcritical instability. Permanent finite-amplitude waves in the supercritical stable region are portrayed by solving the nonlinear evolution equation numerically in a periodic domain. The parameter ranges that support complex nonlinear dynamics is obtained through a combination of theoretical analysis and numerical experiments. [Preview Abstract] |
Monday, March 16, 2009 1:27PM - 1:39PM |
B15.00012: Universal cone angle of ac electrosprays due to net charge entrainment Nishant Chetwani, Siddharth Maheshwari, H.C. Chang The slender meniscus that is obtained by the application of high frequency AC field is quite distinct from DC Taylor Cone. This AC cone shows a continuous longitudinal growth and has much smaller half cone of $\sim $ 11$^{o}$. Mass spectrometry on the microjet from the AC cone shows that dissociation reaction occurs at the tip but only the low- mobility anionic species are entrained to produce a charged cone. These free negative charges relax to the interface to produce a non-uniform surface charge density that scales with respect to the azimuthal radius as $\rho ^{-\frac{1}{2}}$ to balance the singular normal capillary pressure. Repulsion of this entrained surface charge and the Maxwell pressure they induce are estimated with an elliptic integral and a variational formulation produces anormal stress balance with capillary pressure that is only satisfied at a universal angle of 12.6$^{o}$ degrees for the liquids with high dielectric constant in good agreement with the measured values for the organic solvents used in experiments [Preview Abstract] |
Monday, March 16, 2009 1:39PM - 1:51PM |
B15.00013: Impact of Elasticity on Coating Flow near A Moving Contact Line Yuli Wei, Stephen Garoff, Enrique Ram\'e, Lynn Walker The impact of fluid elasticity and shear thinning on the dynamic wetting of polymer solutions is important because many fluids, even those that are normally considered Newtonian, exhibit non-Newtonian behaviors in the high shear environment of the wedge-like geometry near a moving contact line. Even though this behavior is on the microscopic scale, it has significant impact on wetting on the millimeter scale. Shear thinning dramatically modifies the flow field near a moving contact line and results in a reduced curvature of the free surface. In this talk, we will focus on the effects due to fluid elasticity. Both experimental and theoretical results are presented. The fluids we use are the dilute solutions of high molecular weight polyisobutylene (PIB) which exhibit elasticity-dominated rheology with minimal shear thinning. Their wetting behaviors are compared to their oligomer ``solvent,'' which is considered Newtonian based on standard rheometry. We will also discuss a lubrication analysis of the wedge-like flow field using an Oldroyd-B constitutive relation to mimic the stress evolution of the elastic solution. [Preview Abstract] |
Monday, March 16, 2009 1:51PM - 2:03PM |
B15.00014: Field-dependent thermal transfer in magnetic fluids Jun Huang, Zhenyu Zhou, Geoff Huston, Weili Luo The temperature gradient across a quasi one-dimensional magnetic fluid was measured as a function of the magnetic field and field gradient. It was found that when the field gradient, $\nabla B$, is anti-parallel to the temperature gradient, $\nabla T$, the temperature gradient increases with increasing field and field gradient, but decreases for $\nabla B$ parallel to $\nabla T$. For B and $\nabla B$ perpendicular to $\nabla T$ and gravity, the results are complex and depend on the local configuration of the field and field gradient. We will discuss the results in terms of the effect of local magnetic body force that originates from the local field and the local susceptibility on thermal transfer in magnetic fluids. [Preview Abstract] |
Monday, March 16, 2009 2:03PM - 2:15PM |
B15.00015: How does the viscosity of a lubricant effect its tribological behavior? M. Aggleton, P. Taborek The viscosity of many conventional lubricants varies by many orders of magnitude over a small temperature range. We have exploited this variation to explore the effect of large viscosity changes on lubrication. We have used a sliding block tribometer to measure the coefficient of friction of a steel on steel system with a variety of vacuum compatible hydrocarbon lubricants. Each lubricant was thermally cycled in ultrahigh vacuum from room temperature to below the glass transition temperature. This varies the viscosity without changing the chemistry. Several theoretical models for the temperature dependence of the viscosity of hydrocarbons are applied. The theory described in Cameron (1981) is used to relate the change in viscosity to the coefficient of friction. Some lubricants are found to fit these models up to viscosities as high as $10^6$ centiStokes, while for others the model does not even qualitatively describe the data. [Preview Abstract] |
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