Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H36: Bubbles: Micro-bubbles and Nano-bubbles |
Hide Abstracts |
Chair: Jose Gordillo, Universidad de Sevilla Room: Ballroom C |
Monday, November 23, 2015 10:35AM - 10:48AM |
H36.00001: Contact line pinning favors the mass production of monodisperse microbubbles. Jose Manuel Gordillo, Francisco Campo-Cortes, Guillaume Riboux A robust method for the generation of phospholipid covered monodisperse microbubbles of diameters $\sim $10 microns at production rates exceeding 0.1 MHz, is presented here. We show that bubbles are periodically formed from the tip of a long and thin gas ligament stabilized thanks to both the strong favorable pressure gradient existing at the entrance region of a long rectangular PDMS-PDMS channel and to the pinning of the gas-liquid interface at a centered groove of several microns width placed on one of its walls. Moreover, the long exit channel incorporated in our design, favors the transport of phospholipid molecules towards the gas-liquid interface. Our experiments show that the resulting phospholipid shell inhibit both the diffusion of the gas in the surrounding liquid as well as the coalescence between contacting bubbles. These evidences indicate that the proposed method is suitable for the generation of monodisperse microbubbles for diagnosis or therapeutical applications. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H36.00002: Pressure gradient induced generation of microbubbles Alvaro Evangelio, Francisco Campo-Cortes, Jose Manuel Gordillo It is well known that the controlled production of monodisperse bubbles possesses uncountable applications in medicine, pharmacy and industry. Here we provide with a detailed physical description of the bubble formation processes taking place in a type of flow where the liquid pressure gradient can be straightforwardly controlled. In our experiments, a gas flow rate discharges through a cylindrical needle into a pressurized chamber. The pressure gradient created from the exit of the injection needle towards the entrance of a extraction duct promotes the stretching of the gas ligament downstream. In our analysis, which is supported by an exhaustive experimental study in which the liquid viscosity is varied by three orders of magnitude, different regimes can be distinguished depending mainly on the Reynolds number. Through our physical modeling, we provide closed expressions for both the bubbling frequencies and for the bubble diameters as well as the conditions under which a monodisperse generation is obtained in all regimes found. The excellent agreement between our expressions and the experimental data fully validates our physical modeling. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H36.00003: Surface elastic waves on a viscoelastic boundary generated by an oscillating microbubble Marc Tinguely, Matthew Hennessy, Angelo Pommella, Omar Matar, Valeria Garbin Acoustically-driven microbubbles are used as contrast agents for ultrasound medical imaging, or to enhance the uptake of molecules by cells in drug delivery. For both applications, the microbubbles oscillate near soft interfaces, whose viscoelastic properties vary depending on neighbouring tissues. The effect of these properties on the deformation of the boundary, and on the stresses generated by the microbubbles, is still poorly understood. We use high-speed video microscopy to investigate the deformation of agarose gels of controlled viscoelastic properties by an oscillating microbubble via tracking the displacement of embedded particles. We observe the propagation of surface elastic waves (Rayleigh waves) whose velocity of propagation, phase shift, and particle trajectories depend on the viscoelastic properties of the boundary. We develop a Kelvin-Voigt viscoelastic model to predict the deformation of the gels. The results of the model are in good agreement with the experimental observations, which permits the estimation of the magnitude of the stresses generated on the surface of the gel by the oscillating bubble. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H36.00004: Nano bubble migration in a tapered conduit in the asymptotic limits of zero capillary and Bond Numbers - Theory and Experiments Michael Norton, Frances Ross, Haim Bau Using a hermetically sealed liquid cell, we observed the growth and migration of bubbles (tens to hundreds of nanometers in diameter) in a tapered conduit and supersaturated solution with a transmission electron microscope. To better understand bubble shape and migration dynamics, we developed simple 2D and 3D models valid in the limit of zero capillary and Bond numbers. The 3D model is restricted to small taper slope, weakly non-circular contact line geometries and large bubble aspect ratio (high confinement), and was solved using a pseudo-spectral decomposition. Both models utilize the Blake-Haynes mechanism to relate dynamic contact angle to local contact line velocity The influence of pinning of a portion of the contact line on bubble geometry is also considered. Contact line dissipation controls curvature and regulates growth rate. Our 2D and 3D models predict growth rates in agreement with experimental observations, but several orders of magnitude lower than predicted by the classical Epstein -- Plesset theory. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H36.00005: Stability of surface nanobubbles Shantanu Maheshwari, Martin van der Hoef, Xuehua Zhang, Detlef Lohse We have studied the stability and dissolution of surface nanobubbles on the chemical heterogenous surface by performing Molecular Dynamics (MD) simulations of binary mixture consists of Lennard-Jones (LJ) particles. Recently our group has derived the exact expression for equilibrium contact angle of surface nanobubbles as a function of oversaturation of the gas concentration in bulk liquid and the lateral length of bubble. It has been showed that the contact line pinning and the oversaturation of gas concentration in bulk liquid is crucial in the stability of surface nanobubbles. Our simulations showed that how pinning of the three-phase contact line on the chemical heterogenous surface lead to the stability of the nanobubble. We have calculated the equilibrium contact angle by varying the gas concentration in bulk liquid and the lateral length of the bubble. Our results showed that the equilibrium contact angle follows the expression derived analytically by our group. We have also studied the bubble dissolution dynamics and showed the "stick-jump" mechanism which was also observed experimentally in case of dissolution of nanodrops. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H36.00006: Distinguishing between microscale gaseous bubbles and liquid drops Beng Hau Tan, Hongjie An, Chon U Chan, Claus-Dieter Ohl In recent years, there has been strong research interest in decorating surfaces with tiny bubbles and drops due to their potential applications in reducing slippage in micro and nanofluidic devices. Both nanobubbles and nanodrops are typically nucleated by exchanging fluids over a suitable substrate. However, the nucleation experiments present many challenges, such as reproducibility and the possibility of contamination. The use of one-use plastic syringes and needle cannulas in nucleation experiments can introduce polymeric contamination. A contaminated experiment may nucleate bubbles, drops or both. Moreover, it is surprisingly difficult to distinguish between bubbles and drops under the usual atomic force microscopy or optical techniques. Here we present an experimental study comparing bubbles and oil (PDMS) drops on an atomically smooth surface (HOPG). Instead of nucleating the objects via solvent exchange, we directly introduced bubbles via electrolysis, and oil drops by injecting a dilute solution. Contrary to previous reports, we find that under careful AFM characterisation, liquid drops and gaseous bubbles respond differently to a change in imaging force, and moreover present different characteristic force curves. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H36.00007: Analysis of cavitation effect for water purifier using electrolysis Dong Ho Shin, Han Seo Ko, Seung Ho Lee Water is a limited and vital resource, so it should not be wasted by pollution. A development of new water purification technology is urgent nowadays since the original and biological treatments are not sufficient. The microbubble-aided method was investigated for removal of algal in this study since it overcomes demerits of the existing purification technologies. Thus, the cavitation effect in a venturi-type tube using the electrolysis was analyzed. Ruthenium-coated titanium plates were used as electrodes. Optimum electrode interval and applied power were determined for the electrolysis. Then, the optimized electrodes were installed in the venturi-type tube for generating cavitation. The cavitation effect could be enhanced without any byproduct by the bubbly flow induced by the electrolysis. The optimum mass flow rate and current were determined for the cavitation with the electrolysis. Finally, the visualization techniques were used to count the cell number of algal and microbubbles for the confirmation of the performance. As a result, the energy saving and high efficient water purifier was fabricated in this study. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H36.00008: Surface nanobubble nucleation dynamics during water-ethanol exchange Chon U Chan, Claus-dieter Ohl Water-ethanol exchange has been a promising nucleation method for surface attached nanobubbles since their discovery. In this process, water and ethanol displace each other sequentially on a substrate. As the gas solubility is 36 times higher in ethanol than water, it was suggested that the exchange process leads to transient supersaturation and is responsible for the nanobubble nucleation. In this work, we visualize the nucleation dynamics by controllably mixing water and ethanol. It depicts the temporal evolution of the conventional exchange in a single field of view, detailing the conditions for surface nanobubble nucleation and the flow field that influences their spatial organization. This technique can also pattern surface nanobubbles with variable size distribution. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H36.00009: Hot Microbubble Injection in Thin Liquid Film Layers for Ammonia-Water Separation Pratik Desai, William Zimmerman 140 MT of NH$_{3}$ produced p.a. barely keeps up with the global usage of this ubiquitously used commodity. NH$_{3}$ manufacture {\&} later remediation from landfill leachate to lower eco-toxicity makes further~demands on the energy utilised for this ``NH$_{3}$ cycle.'' Moreover, current methods for lowering eco-toxicity destroy NH$_{3}$ rather than recovering it. Air stripping is a widely employed low energy industrial process used for NH$_{3}$ recovery but has a long processing time-$\cong $24h for 60{\%} efficiency {\&} 100h for 95{\%} efficiency. The solution presented herein is based on hot microbubble injection in thin liquid film layers designed to separate NH$_{3}$ from NH$_{3}$-H$_{2}$O solutions. The transport phenomena exhibited by the microbubbles helps them separate volatile liquids effectively with negligible sensible heat transfer. This process is nearly isothermal simply because evaporation by microbubbles is controlled by internal mixing, which is fast relative to sensible heat transfer, when limited to short contact times in thin films. A 1000-3000-fold increase in mass transfer, over conventional stripping, and a 100{\%} separation efficiency achieved in a processing time of 30 minutes is observed, potentially, if persisting with industrial scale up, resulting in a 200-fold reduction in processing time. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H36.00010: Bubble dynamics in a micro-channel with a virtual check valve Rou Chen, Likun Zhu, Huidan (Whitney) Yu Bubble dynamics plays a critical role in the design of a self-circulation and self-regulation gas generator with little or zero parasitic power consumption (Zhu \textit{et al}, Microfluidics and Nanofluidics, 2011). We numerically study bubble dynamics in the micro-channel with a virtual check valve using lattice Boltzmann method. The lattice Boltzmann model has been validated through several static cases with a bubble sitting inside a liquid and on a solid surface with a triple contact among bubble, liquid, and solid. In this work, we simulate bubble transport driven via unbalanced capillary forces. Focus will be on the bubble merging phenomena between the moving bubble and a static bubble prior siting downstream in the channel with same and different sizes. By varying the size of the check valve, we study the effects of channel ratio between the check valve and channel on the dynamics of bubble-driven liquid circulation and seek for an optimal channel ratio to support experimental design. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700