Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R25: Surface Tension: General; Superfluids |
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Chair: Yongkang Chen, Portland State University Room: E145 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R25.00001: Revisiting the first fluid interface experiment in space Yongkang Chen, Mark Weislogel, William Masica, Fred Kohl, Robert Green This year marks the 54th anniversary of the first fluid physics experiment performed aboard a spacecraft during the Mercury-Atlas 7 mission (MA7). The MA7 experiment test cell served as an early model for a spacecraft liquid fuel tank consisting of a circular standpipe mounted within a spherical container. The low-g free surface configuration was dependent on contact angle, fluid fill fraction, standpipe dimensions, and initial conditions. Well-behaved symmetric equilibrium interfaces in the symmetric tank were expected and observed during the historic flight. We revisit the problem here employing a modern numerical tool and discover a rich variety of asymmetric fluid interface configurations that were not observed during the experiment. Interestingly, experimental support for these newly-computed outcomes may be found in 54 year old drop tower data collected by the original NASA investigator team. In short, rotationally symmetric nodoidal surfaces are unstable in a certain domain giving rise to highly asymmetric surfaces with significant shifts in the mass center of the liquid. The NASA team selected a fluid fill level for MA7 that `fortunately' fell outside this domain. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R25.00002: Marangoni effects on a thin liquid film coating a sphere with axial or radial thermal gradients Di Kang, Ali Nadim, Marina Chugunova We study the time evolution of a thin liquid film coating the outer surface of a sphere in the presence of gravity, surface tension and thermal gradients. We derive the fourth-order nonlinear partial differential equation that models the thin film dynamics, including Marangoni terms arising from the dependence of surface tension on temperature. We consider two different heating regimes with axial or radial thermal gradients. We analyze the stability of a uniform coating under small perturbations and carry out numerical simulations in COMSOL for a range of parameter values. In the case of an axial temperature gradient, we find steady states with either uniform film thickness, or with drops forming at the top or bottom of the sphere, depending on the total volume of liquid in the film, dictating whether gravity or Marangoni effects dominate. In the case of a radial temperature gradient, a stability analysis reveals the most unstable non-axisymmetric modes on an initially uniform coating film. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R25.00003: Electrostatic Assist of Liquid Transfer in Printing Processes Chung-Hsuan Huang, Satish Kumar Transfer of liquid from one surface to another plays an important role in many printing processes. Incomplete liquid transfer can produce defects that are detrimental to the operation of printed electronic devices, and one strategy for minimizing these defects is to apply an electric field, a technique known as electrostatic assist (ESA). However, the underlying physical mechanisms of ESA remain a mystery. To better understand these mechanisms, slender-jet models for both perfect dielectric and leaky dielectric Newtonian liquid bridges with moving contact lines are developed. Nonlinear partial differential equations describing the time- and axial-evolution of the bridge radius and interfacial charge are derived, and then solved using finite-element methods. For perfect dielectrics, it is found that application of an electric field enhances transfer of liquid to the more wettable surface. For leaky dielectrics, application of an electric field can augment or oppose the influence of wettability differences, depending on the direction of the electric field and the sign of the interfacial charge. The physical mechanisms underlying these observations will be discussed. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R25.00004: Experiments on chemically enhanced immiscible fluid displacements Tejaswi Soori, Thomas Ward This talk focuses on experiments conducted by displacing a vegetable oil within a capillary tube (diameter $<$ 1 mm) using an aqueous alkali solution. Estimates of the residual film were measured as a function of Reynolds (Re), viscous Atwood (At) and capillary (Ca) numbers. The pendant drop method was used to measure surface tension of the aqueous alkali solutions. We observed a decrease in surface tension for an increase in alkali concentration, which beyond a critical concentration forms a stable micro-emulsion. We estimate the shear viscosity of the emulsion as a function of alkali and aqueous/oil concentrations. Separately we attempt to measure the average bulk diffusion coefficient of the emulsion in both phases which is necessary to estimate the P{\'e}clet number (P{\'e}) and subsequent mass transport phenomena. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R25.00005: Grooves drain dew Henri Lhuissier, Pierre-Brice Bintein, Laurent Royon, Anne Mongruel, Daniel Beysens The yield of natural dew harvesting is often limited by the amount of water remaining on the collector plate at sunrise. By cooling inclined and partially wetting plates in a controlled atmosphere, we show that this immobilized amount is significantly reduced when the plate is dug with vertical sub-millimeter-sized grooves. As condensation proceeds, the grooves rapidly fill up with water and hasten drop shedding by two mechanisms. First, they connect and provoke the coalescence of distant drops, which accelerates the emergence of large drops. Second, they reduce the drop pinning to the plate, which decreases the drop size at the onset of shedding. We will discuss how these mechanisms depend on the rate of condensation, the plate inclination and the grooves dimensions, as well as the consequences for dew harvesting. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R25.00006: Three Dimensional Particle Tracking in Superfluid Helium Peter Megson, Daniel Lathrop, Itamar Shani Superfluid helium is a macroscopic quantum state which exhibits exotic physical properties, such as flow without friction and ballistic heat transport. Superfluid flow is irrotational except about line-like topological phase defects with quantized circulation, known as quatized vortices. The presence of these vortices and their dynamics is the dominating factor of turbulence in superfluid flows. One commonly studied regime of superfluid turbulence is thermal counterflow, where a local heat flux drives the formation and growth of a tangle of vortices. This talk will present experimental studies of counterflow turbulence performed using a multi-camera three-dimensional imaging apparatus with micron-sized ice tracer particles as well as fluorescent nanoparticles. In particular, we will discuss the measurement of three-dimensional velocties and their autocorrelations. Additionally, we are developing new techniques for optical studies of bulk superfluid helium, with particular focus on characterizing tracer particles and particle dispersal mechanisms. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R25.00007: Vortex reconnections and rebounds in trapped atomic Bose–Einstein condensates Luca Galantucci, Simone Serafini, Elena Iseni, Tom Bienaime', Russell Bisset, Franco Dalfovo, Giacomo Lamporesi, Gabriele Ferrari, Carlo F. Barenghi Reconnections and interactions of filamentary coherent structures play a fundamental role in the dynamics of classical and quantum fluids, plasmas and nematic liquid crystals. In quantum fluids vorticity is concentrated into discrete (quantised) vortex lines (unlike ordinary fluids where vorticity is a continuous field), turning vortex reconnections into isolated events, conceptually easier to study. In order to investigate the impact of non-homogeneous density fields on the dynamics of quantum reconnections, we perform a numerical study of two-vortex interactions in magnetically trapped elongated Bose--Einstein condensates in the T=0 limit. We observe different vortex interactions regimes depending on the vortex orientations and their relative velocity: unperturbed orbiting, bounce dynamics, single and double reconnection events. The key ingredients driving the dynamics are the anti-parallel preferred alignment of the vortices and the impact of density gradients arising from the inhomogeneity of the trapping potential. The results are confirmed by ongoing experiments in Trento performed employing an innovative non--destrutive real--time imaging technique capable of determining the axial dynamics and the orientation of the vortices. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R25.00008: The latent heat of vaporization of supercritical fluids Daniel Banuti, Muralikrishna Raju, Jean-Pierre Hickey, Matthias Ihme The enthalpy of vaporization is the energy required to overcome intermolecular attractive forces and to expand the fluid volume against the ambient pressure when transforming a liquid into a gas. It diminishes for rising pressure until it vanishes at the critical point. Counterintuitively, we show that a latent heat is in fact also required to heat a supercritical fluid from a liquid to a gaseous state. Unlike its subcritical counterpart, the supercritical pseudoboiling transition is spread over a finite temperature range. Thus, in addition to overcoming intermolecular attractive forces, added energy simultaneously heats the fluid. Then, considering a transition from a liquid to an ideal gas state, we demonstrate that the required enthalpy is invariant to changes in pressure for $0 |
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