Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session R04: Bubbles: Microbubbles and Nanobubbles and Rupture (5:00pm - 5:45pm CST)Interactive On Demand
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R04.00001: Pool boiling investigations via non-equilibrium molecular dynamics: the role of surface topography in heterogenous nanobubble nucleation Alessio Lavino, Edward Smith, Mirco Magnini, Omar Matar Molecular dynamics (MD) is emerging as a robust and powerful tool in the modelling of pool boiling processes. The main advantage of discrete molecular models over a continuum based approach is the ability to capture the atomistic nature of phase transition together with solid-liquid and liquid-vapor interfacial phenomena. Here, we study the onset of nanobubble nucleation and transition to film-like boiling regimes at the molecular scale by means of non-equilibrium molecular dynamics (NEMD). We investigate the surface topography effects on pool boiling using a cavity on the solid surface. The interplay of the cavity aspect ratio, surface wettability and wall superheat is investigated to explore the main mechanisms that control nanobubble nucleation. NEMD results are summarized in a phase diagram which captures the main phenomena observed at the different operating conditions. Classical nucleation theory (CNT) and continuum-scale heat transfer models are applied to reach a solid understanding of the MD results, showing a promising way to link the latter to larger-scale models in a more general multi-scale framework. [Preview Abstract] |
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R04.00002: The Nature of Bubble Entrapment in a Lamb-Oseen Vortex Ryan Kelly, Marcos Botto, David Goldstein, Saikishan Suryanarayanan, Robert Handler We are interested in bubble trajectories in the presence of a vortex as a step in understanding the bubble dynamics in turbulent, wall-bounded flows. Specifically, we have studied trajectories of non-deforming bubbles through a Lamb-Oseen vortex by solving modified Maxey-Riley equations for low-Reynolds-Number flows with lift. We found that, under appropriate physical conditions, a bubble will spiral around inside the vortex core with a decaying periodic nature until it comes to a quasi-equilibrium state at a particular equilibrium point which varies with time. The bubble spends most of its time in the core close to these points until the core dissipates enough for the bubble to escape. To study this entrapment, we look at quasi-steady-state solutions, which are a system of nonlinear algebraic equations that can be solved numerically. These equations reveal where these equilibrium points will be at a given time, as well as at what time the bubble will escape the vortex. The nature of these equilibrium points, the periodic spiraling, and the bubble trap times will be discussed in terms of nondimensional parameters and related to the properties of a turbulent boundary layer. [Preview Abstract] |
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R04.00003: The Formation of Gas Jets and Vortex Rings from Bursting Bubbles Ali Dasouqi, Geum-Su Yeom, David Murphy Bubble bursting is important in ocean-atmosphere processes (e.g. marine aerosol formation), industrial processes (e.g. gas fluxing of molten metal), and food science (e.g. beer). The fluid mechanics of the liquid component of bubble bursting, including film cap retraction and droplet formation, has been well investigated. However, the ejection of pressurized gas from inside a bursting bubble, which may affect the spatial distribution of generated droplets, is much less understood. Here, we analyze the fluid dynamics of gas jets and vortex rings produced by the bursting of 440 \textmu m to 4 cm diameter smoke-filled bubbles resting at an air-water interface by using high speed stereophotogrammetry. The slow, low Reynolds number jets characteristic of small bubbles are attributed to high film retraction speeds which produce relatively large holes in the bubble cap; these jets roll up into spherical, slowly growing vortex rings traveling short distances. In contrast, the low film retraction speeds typical of large bubbles generate high speed, high Reynolds number jets ejected through relatively small apertures which roll up into highly oblate, fast-growing, far-traveling vortex rings. A quasi-one-dimensional nozzle model also is used to predict the initial velocity of the gas jet. [Preview Abstract] |
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R04.00004: The Making and Breaking of Viscous Bubbles Phalguni Shah, Eleanor Ward, Michelle Driscoll A Newtonian soap bubble ruptures on the timescale of milliseconds, and this rupture grows at a constant rate, known as the Culick velocity [1]. This rupture speed is believed to be independent of fluid viscosity, after a short transient [2]. We experimentally studied the rupture of soap films made of varied concentration of glycerol and water, covering over two orders of magnitudes in fluid viscosity. The constant-thickness films were formed by stretching a known fluid volume to a specific size on a custom film stretcher. The rupture speed of films was observed to decrease with the increase in viscosity. One hypothesis for this decrease is that the thickness profile of the stretched film is a function of fluid viscosity. To test this hypothesis, we measure the film thickness using an ultrafast multi-wavelength interferometry setup. [1] F. E. C. Culick, Journal of Applied Physics(1960) [2] N. Savva and J. W. M. Bush, Journal of Fluid Mechanics (2009) [Preview Abstract] |
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R04.00005: Jet Drops Produced by Bubble Bursting at an Oil-covered Interface Zhengyu Yang, Bingqiang Ji, Jie Feng Bursting of bubbles at a fluid-fluid interface is ubiquitous in a wide range of physical, biological, and geological phenomena. It mediates the mass transport across the interface and has consequently received significant attention. Here, we study the jet dynamics produced by bubble bursting at an aqueous surface coated by a layer of oil. The configuration of such a compound air/oil/water interface could represent the natural state of the sea surface microlayer that typifies the oceans, or it can be considered as a model of an oil spill. With high-speed imaging, we document the change of the jet drop size with different oil viscosities and layer thicknesses. We observe that the oil layer damps the capillary waves during cavity collapsing and influences the jetting process, thus changing the jet drop size. Our study not only advances the fundamental understandings of bubble bursting, but may also shed light on the formation of oily aerosols in the ocean regarding pollutant transport. [Preview Abstract] |
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