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 H21: Bubbles: General |
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Chair: James Bird, Boston University Room: D139-140 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H21.00001: The equilibrium shape of bubbles on curved interfaces James Bird, Daniel Poe, Peter Walls The equilibrium shape for a bubble resting at a free surface depends on a balance of hydrostatic and capillary forces, with the smallest bubbles approximating a sphere and a hemisphere for the largest. This shape has been shown to be important to several processes ranging from gas transfer across the thin film cap to the production of jet droplets. Past works calculating the equilibrium shape assume that the interface is flat. However, there are instances where the curvature of the boundary may be comparable to the bubble itself. For example, a bubble bursting on the surface of a rain droplet. Here we relax the assumption of a flat interface and extend the classic bubble shape calculations to account for a curved interface boundary. An understanding of the extent of this deformation and the precise equilibrium bubble shape is important to applications in fields ranging from air-sea exchange to combustion dynamics. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H21.00002: History effects on the gas exchange between a bubble and a liquid Shigan Chu, Andrea Prosperetti History effects are a distinctive feature of diffusive processes. For a diffusing gas bubble at rest in a liquid, such effects arise when the concentration of dissolved gas at the bubble surface, connected to the gas pressure by Henry’s law, depends on time. This time dependence can be caused by several factors, such as varying ambient pressure, mole fraction in a multicomponent gas bubble, surface tension and others. In this study we consider history effects in the three situations mentioned above. More specifically, rectified diffusion in an oscillating ambient pressure field is explored under conditions when the diffusion length is larger than the bubble radius. History effects are found to be important in determining the threshold conditions for rectified diffusion. In contrast, history effects are small in the other two cases. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H21.00003: Effect of surfactants on bubble collisions with an air-water interface Shiyan WANG, Tianqi Guo, Sadegh Dabiri, Pavlos P. Vlachos, Arezoo M. Ardekani Collisions of bubbles on an air-water interface are frequently observed in natural environments and industrial applications. We study the coefficient of restitution of a bubble colliding on an air-water interface in the presence of surfactants through a combination of experimental and numerical approaches. In a high concentration surfactant solution, bubbles experience perfectly inelastic collisions, and bubbles are arrested by the interface after the collision. As the surfactant concentration decreases, collisions are altered to partially inelastic, and eventually, elastic collisions occur in the pure water. In a high concentration surfactant solution, the reduced bouncing is attributed to the Marangoni stress. We identify the Langmuir number, the ratio between absorption and desorption rates, as the fundamental parameter to quantify the Marangoni effect on collision processes in surfactant solutions. The effect of Marangoni stress on the bubble's coefficient of restitution is non-monotonic, where the coefficient of restitution first decreases with Langmuir number, and then increases. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H21.00004: Visualization of airflow growing soap bubbles Hamood Al Rahbi, Matthew Bock, Sangjin Ryu Visualizing airflow inside growing soap bubbles can answer questions regarding the fluid dynamics of soap bubble blowing, which is a model system for flows with a gas-liquid-gas interface. Also, understanding the soap bubble blowing process is practical because it can contribute to controlling industrial processes similar to soap bubble blowing. In this study, we visualized airflow which grows soap bubbles using the smoke wire technique to understand how airflow blows soap bubbles. The soap bubble blower setup was built to mimic the human blowing process of soap bubbles, which consists of a blower, a nozzle and a bubble ring. The smoke wire was placed between the nozzle and the bubble ring, and smoke-visualized airflow was captured using a high speed camera. Our visualization shows how air jet flows into the growing soap bubble on the ring and how the airflow interacts with the soap film of growing bubble. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H21.00005: How to make a giant bubble Justin Burton, Stephen Frazier Soap and water solutions can form massive, free floating films encompassing volumes in excess of 50 m$^{\mathrm{3}}$ with thicknesses of only 1-10 microns when mixed with polymeric additives. These films are interesting from a physical standpoint due to their long lifetime and stability in ambient environments. We have investigated a variety of mixtures which are deemed ``optimal'' for making large bubbles, such as solutions made from guar seeds and polyethylene oxide (PEO). Making a giant bubble requires a balance between viscous and elastic forces. Drawing out a large soap film requires a low-viscosity solution, while elasticity enhances stability. Using a combination of shear rheology, drop-based extensional rheology, and time-dependent thickness measurements, we found that ``optimal'' solutions showed similar extensional properties even though their shear viscosity differed by more than an order of magnitude. Soap and water solutions with polymers lived 2-3 times longer and drained more slowly than typical soap and water solutions, even though their initial thicknesses were similar. In addition, polymeric bubbles showed increased stability to aging in dry environments. By varying the molecular weight and concentration of PEO in the solutions, we are able to optimize the lifetime of the film and determine the best way to make a giant bubble. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H21.00006: Long-life of a bubble on the surface of a water-alcohol mixture Gibran Rage, J. Federico Hernandez-Sanchez, Monica M. Wilhelmus, Roberto Zenit The lifetime of superficial bubbles has been used traditionally to determine the alcohol content in destilled beverages and spirits. With the proper alcohol content, the bubbles, known as pearls, have a particularly long life which is much longer than that in either pure water or pure ethanol. To understand this peculiar behavior, we conducted controlled experiments in water-ethanol mixtures and in samples of mezcal, an artisanal agave spirit. We assess the effect of the changes in viscosity, surface tension and density of the liquids. Also, we analyzed the effects of surfactants and evaporation rate differences, which lead to Marangoni convection in the draining film. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H21.00007: Purging dissolved oxygen by nitrogen bubble aeration Tatsuya Yamashita, Keita Ando We apply aeration with nitrogen microbubbles to water in order to see whether oxygen gas originally dissolved in the water at one atmosphere is purged by the aeration. The concentration of dissolved oxygen (DO) is detected by a commercial DO meter. To detect the dissolved nitrogen (DN) level, we observe the growth of millimetre-sized bubbles nucleated at glass surfaces in contact with the aerated water and compare it with the Epstein-Plesset theory that accounts for DO/DN diffusions and the presence of the glass surfaces. Comparisons between the experiment and the theory suggest that the DO in the water are effectively purged by the aeration. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H21.00008: ``Jumping'' of Bubbles in Viscoplastic Fluids with Elasticity Dimitrios Fraggedakis, Yannis Dimakopoulos, John Tsamopoulos Recently, it has been shown that phenomena known to be observed in viscoelastic liquids (e.g. the negative wake formation past deformable or rigid obstacles, cusp formation in bubbles), are present in elastoviscoplastic materials too, due to elasticity effects, Fraggedakis et al., \textit{Soft Matter} (2016). Based on the numerical results for bubbles in viscoelastic materials, Fraggedakis et al. \textit{J. Fluid Mech. }(2016), we focus our study on the rise of a confined air bubble in materials which exhibit elasto-viscoplastic behavior. Based on the rheological data by Mougin et al. (2012), the present study examines the conditions under which cusped bubble shapes are evident in yield stress materials. Moreover, the distance of the yield surface to the bubble is found to play a crucial role in both the rise velocity and the shape of the bubble. Additionally, if the yield stress effects are increased, the rise velocity is found to exhibit a discontinuous behavior. The mechanism which leads to such phenomena is found to be related with that discussed in Fraggedakis et al. (2016). Ultimately, the existence of the yield surface near the bubble enhances the formation of the negative wake, irrespective of the position of the confinement in relation to the air bubble. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H21.00009: Growth and collapse of laser-induced bubbles in gas-supersaturated gelatin gels. Keita Ando, Nobuyuki Nakamura We study, with experiments and theory, the growth and collapse of laser-induced bubbles in a gelatin gel. The gel sample is prepared so as to obtain gas supersaturation, according to a difference between heat and gas diffusion rates. Spherical gas bubbles are created by focusing a nano-second laser pulse at 532 nm into the gas-supersaturated gel. The bubble dynamics are recorded by a high-speed camera. To explore effects of the gel elasticity on the bubble collapse, the experimental observations are compared to an extended Rayleigh-Plesset model that accounts for linear/nonlinear elasticity of the gel surrounding bubbles. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H21.00010: Boundary effects on streaming flow around a bubble located at the velocity antinode of a standing wave Mohammad Alhamli A stable bubble trapped in a standing sound wave with frequency less than the resonance frequency of the bubble will be located at the velocity antinode. Steady streaming flow will develop around the bubble and is directly dependent on the bubble’s boundary. Four boundary conditions are possible: 1) nonpulsating; no slip, 2) nonpulsating; free shear, 3) pulsating; no slip, and 4) pulsating; free shear. To solve for these conditions, we expanded the equations of motion with the dimensionless lateral oscillation amplitude,$\epsilon$, using the singular perturbation method. The lateral oscillation amplitude is much smaller than the bubble radius $\epsilon< [Preview Abstract] |
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