Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S03: Surface Tension IV |
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Chair: Irmgard Bischofberger, MIT Room: 201 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S03.00001: Reverse Marangoni Propulsion of Disks and Hemispheres at Finite Reynolds Numbers Samrat Sur, Hassan Masoud, Jonathan Rothstein In this presentation, the experimentally observed phenomenon of Reverse Marangoni propulsion will be presented for both a thin cylindrical disk and a hemisphere floating on an air-water interface. Each particle was propelled by an asymmetric release of a surfactant to locally reduce the surface tension. Marangoni surfers typically propel themselves forward in the direction of high surface. However, by systematically varying the water depth we will show that increasing confinement initially causes the velocity of the Marangoni surfer to slow, then come to rest and finally to reverse direction resulting in the Marangoni surfers moving in the direction of lower surface tension. Particle tracking and PIV measurements will be used to measure flow field induced by Marangoni flow underneath the disk and hemisphere and understand the origin of the reverse Marangoni flow. This phenomenon of reverse Marangoni flow has been predicted theoretically for Stokes flow at zero Reynolds number. We will show that the reverse Marangoni motion is not only dependent on the water depth confinement but also on Reynolds number. With increasing Reynolds number, increased confinement is needed to observed reverse Marangoni flow. These experimental results are in excellent agreement with the prediction of numerical simulations. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S03.00002: Analytical study for vapor-driven solutal Marangoni flows inside a sessile droplet Junil Ryu, Junkyu Kim, Jonghyeok Park, Hyoungsoo Kim Flow control inside a sessile droplet is important in microfluidic mixing, materials patterning and coating applications. Recently, a solutal Marangoni flow driven by a vapor of volatile liquid has been introduced as a novel way of flow controller and mixer, which does not require external devices and pollute mixing samples. In this talk, we will present the controlled flow patterns and efficient mixing inside a sessile droplet using solutal Marangoni effects. Furthermore, we developed a theoretical model to predict the vapor-driven solutal Marangoni flows. By matching the experimental and theoretical results, we estimate the profile of vapor distribution of volatile liquid, which is very difficult to directly measure from experiments. Using this analytical model, we further investigate how the boundary condition changes the internal flow pattern. Several possible cases will be discussed during the talk. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S03.00003: Hydrodynamic Doppler effect in a weakly compressible two-dimensional medium Ildoo Kim This study is based on two experimental observations in flowing soap film channels. First, the vorticity field is strongly correlated with the thickness field. Second, the thickness field propagates at the Marangoni wave speed. Using the two observations, we propose and review the hypothesis that the vorticity field propagates at the Marangoni wave speed $c$. It is inferred from the hypothesis that a retarded hydrodynamic potential function can be solved in an approach similar to the Lienard-Wiechert potential of the relativistic electromagnetic theory, and the retarded potential implies an elongation effect of a vortex array by $1/(1+v/c)$ when the array recedes from the origin at $v$. The theory is compared with the experiment, and they agree within the margin of measurement error. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S03.00004: Marangoni-driven film climbing on a draining pre-wetted film Nan Xue, Min Pack, Howard Stone In this experimental study, we report a Marangoni flow generated when a bath of surfactant contacts a pre-wetted film, which is set by gravitational drainage on a vertical substrate. High-speed interferometry is used to measure the front position of the climbing film and the film thickness profile, and the effect of the surfactant concentration and the pre-wetted film thickness on the film climbing is studied. As a result, higher surfactant concentration induces a faster and thicker climbing film. Also, for high surfactant concentrations, where Marangoni driving dominates, increasing the film thickness increases the rise speed of the climbing front since viscous resistance is less important. In contrast, for low surfactant concentrations, where Marangoni driving balances with gravitational drainage, increasing the film thickness decreases the rise speed of the climbing front while enhancing gravitational drainage. We rationalize these observations by establishing a model that analyzes the climbing front, either in the Marangoni driving dominated region or in the Marangoni balanced, drainage region. Our work highlights the possible effects of the gravitational drainage on the Marangoni flow, both by setting a pre-wetted film and by resisting the film climbing. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S03.00005: Marangoni Instability and Interfacial Turbulence of a Water Drop at an Oil/Alcohol Interface Sami Yamanidouzisorkhabi, Gareth H. McKinley, Irmgard Bischofberger Water and ethanol are fully miscible, while anise oil and ethanol are partially miscible and anise oil and water are immiscible. Mixing of all three liquids; however, result in an equilibrium state emulsion of anise microdroplets in water/ethanol solution. Here, we study the mixing of a water drop at the interface of anise oil and ethanol until the equilibrium emulsion state is achieved. We use a combination of regular imaging and Schlieren imaging to visualize the mixing phenomenon. This mixing involves two processes: (i) introduction of a water drop at the anise oil/ethanol interface and formation of a vortex ring due to natural convection caused by exothermic mixing of water and ethanol, (ii) growth of the vortex ring at the interface due to Marangoni forces until the equilibrium state is achieved. We show that the inhomogeneities at the anise oil/ethanol interface apply non-uniform Marangoni forces on the vortex ring resulting in its deformation and a non-uniform distribution of the final mixing product, i.e., the equilibrium state emulsion, at the interface. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S03.00006: Solutal Marangoni flow induced by a solute source. Islam Benouaguef, Naga Munsunuri, Denis Blackmore, Ian S. Fischer, Pushpendra Singh The study of the solutocapillary flow induced in a waterbody due to the presence of a solute source or sink on its surface is reported. The surface tension of water increases with increasing salt concentration, and so, for example, when a freshwater source is present on the surface the local salt concentration is reduced which in turn makes the interfacial tension near the source smaller than that away from the source where the salt concentration is larger. This gives rise to an interfacial gradient away from the source which drives the flow. We have analytically studied the axially symmetric analytic solution to this problem and have made a comparison with the experimental data obtained by the PIV (Particle Image Velocimetry) and PLIF (planer laser-induced fluorescence) techniques. It is shown that a freshwater source gives rise to a doublet flow such that the flow comes towards the source within a conical region with its vertex at the source and outside the conical region the flow moves away from the source. The half cone angle increases with increasing source strength and for a typical solutocapillary flow it is \textasciitilde 70-80 degrees. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S03.00007: Influence of nonlinear temperature dependence of surface tension on longwave oscillatory Marangoni patterns Alexander Mikishev, Alexander Nepomnyashchy In most theoretical papers on Marangoni convection the authors assume the linear dependence of the surface tension on temperature. However, according to experiments, that dependence is more complex. In the present work, we consider the influence of nonlinear temperature dependence of surface tension on the nonlinear dynamics of waves created by an oscillatory instability recently discovered in [1] in the limit of small Biot number \textit{Bi} and wavenumber $k$, \textit{k \textasciitilde Bi}$^{\mathrm{1/2}}$. Near the critical Marangoni number, that dependence is described by a Taylor series around the reference temperature value. The set of amplitude equations governing the nonlinear interaction of waves has been derived. The stability of different wave patterns and wave pattern selection are investigated. REFERENCE. [1] S. Shklyaev, A. Alabuzhev, and M. Khenner, Phys. Rev. E, \textbf{85}, 016328 (2012). [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S03.00008: Surface tension-driven flows induced by polymerization waves Reda Tiani, John A. Pojman, Laurence Rongy Thermal frontal polymerization (FP) is a process in which a monomer-initiator mixture is converted into a polymer via a localized reaction zone that propagates due to the interplay between heat diffusion and exothermic polymerization whose reaction rate increases with temperature following Arrhenius' dependence. Recent experiments considering horizontally propagating FP have evidenced the presence of hydrodynamic flows that interfere with the dynamics of polymerization waves and even possibly prevent their initiation. Since those experiments are conducted in systems \textit{open to the air}, \textit{surface tension-driven (or Marangoni) flows}, due to temperature gradients between the cold monomer-initiator mixture and the hot polymer solution, are expected to play an important role in the observed experimental results. In this context, we propose a two-dimensional model that includes the incompressible Navier-Stokes (NS) equations coupled to the reaction-diffusion equations for temperature and for the degree of polymerization. Preliminary numerical results of surface tension-driven flows induced by polymerization waves are discussed. A particular attention is devoted to the remarkable possibility of Marangoni flows to prevent the formation of polymerization waves. [Preview Abstract] |
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