Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LD: Multiphase Bubbly Flows II |
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Chair: Ellen Longmire, University of Minnesota Room: Hilton Chicago Continental A |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LD.00001: Bubbly flow around microcantilevers. Matthew Stegmeir, Ellen Longmire In the current study, we investigate the flow of bubbles that impact cantilever obstacles with thickness 26-38$\mu $m in a confined channel. The cantilevers are mounted in a vertical channel with thickness of 1-4mm, width of 10mm, and length of 75mm. Steady flows upward with channel Reynolds numbers based on mean fluid velocity 0-2000 are established. Bubbles of diameter 40-1000$\mu $m are introduced upstream of the test section. Bubble number density can be controlled independent of liquid velocity. Bubble motion in the vicinity of the cantilever obstacle is observed using a microscope equipped with a high frame rate camera. Observations are made perpendicular to and along the length of the cantilevers using reflected white light. Preliminary results show three types of interactions: bubbles bounce off of the cantilever, are sliced in two, or exhibit significant deformation around the cantilever before rebounding and continuing on one side. The flow studies are part of a larger research program examining the effect of fluid properties and flow on the reliability and performance of vibrating beams. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LD.00002: Multibubble Dynamics: Phase Shift, Transition Frequency, and Avoided Crossing Masato Ida The oscillation phases and resonance frequencies of multibubble systems in a sound field are considered to show hidden complexities of bubbles. In recent papers [e.g. Ida, Phys. Lett. A 297, 210 (2002)] we have shown that bubbles in a multibubble system can reverse their own oscillation phase not only at their resonance frequencies but also around some other driving frequencies. In those studies we introduced the notion of a transition frequency which is the driving frequency at which the phase reversal of a bubble occurs. This notion has already been utilized to understand the sign reversal of the secondary Bjerknes force [e.g. Ida, Phys. Rev. E 67, 056617 (2003)], showing that the sign reversal takes place at the transition frequencies that do not correspond to the resonance frequencies. In the present study [Phys. Rev. E, accepted], we show that in certain cases the phenomenon of avoided crossing appears in the resonance frequencies of a multibubble system as the separation distances between the bubbles are varied, and a kind of state exchange takes place among the bubbles at a point, detectable by observing the transition frequencies, in the avoided crossing region. [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LD.00003: The boiling bubble dynamics under gamma ray irradiation Yasuyuki Imai, Koji Okamoto, Haruki Madarame, Tomoji Takamasa The understanding of heat transfer under irradiation environment is still inadequate. The boiling experiment has never been carried out under irradiation environment. In this study, the boiling conditions under gamma-ray irradiation were investigated to evaluate the effect of irradiation so that the pool vessel with a test piece was placed in the irradiation room. The test piece in the water vessel was irradiated by $^{60}$Co gamma rays at a predetermined dose rate and for a predetermined period. The boiling curve of nucleate boiling for oxidized titanium wire under irradiation had been measured. Also, the images of the boiling conditions under irradiation had been captured using a high-speed video camera. Using a high-speed camera, motion of the bubbles could be clearly visualized. The active nucleation site density decreased with increasing dose. The several nucleation sites have been deactivated under the irradiation condition. The decrease of heat transfer by reduction of active nucleation site density causes the shift of boiling curve to higher wall superheat temperature. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LD.00004: Three-Dimensional Simulation of Vapor Bubble Dynamics in Nucleate Boiling Damir Juric, Gretar Tryggvason, Seungwon Shin The ability to apply numerical simulation to three-dimensional multiphase flows has existed now for nearly two decades. However, only in the last 2 or 3 years has this technology advanced into the realm of boiling flows. The difficulties inherent when computing solutions to these flows lie in the fact that not only do we need to accurately incorporate the usual physics of fluid flow, surface tension and deformable interfaces found in multiphase flows but now with boiling and phase change these must be coupled to the thermal transport and latent heat at the vaporizing or condensing interface. In addition, any simulation for real fluids and systems such as water must be prepared to handle the specific volume ratios and thus large volume expansions upon vaporization (1600 to 1 for water at standard conditions). In our numerical investigations we couple an explicit front tracking of the liquid-vapor interface with an advanced interface reconstruction technique and wall-refined grids to obtain high accuracy three-dimensional simulations of the large scale dynamic behavior of water vapor bubbles in nucleate boiling from active surface nucleation sites. We compare the overall heat transfer as a function of wall superheat to existing correlations and discuss various models for heat transfer in the microlayer and contact line. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LD.00005: A Dissipative Particle Dynamics model for two-phase flows Anupam Tiwari, John Abraham A Dissipative Particle Dynamics (DPD) model for two-phase flows is presented. The new model, unlike existing models [1, 2], uses different cut-off radii for the attractive and repulsive components of the inter-particle interaction potential and allows for larger density ratios between the phases. Surface tension arises due to the attractive component and a forcing term that depends on higher order density gradients. The model is shown to reproduce the Laplace law and analytical results for drop oscillations. A new method that couples a Lennard-Jones type potential with a coarse-grained potential is also presented. \newline \newline References: \newline [1] Pagonabarraga, I. and Frenkel, D. (2001). \textit{Journal of Chemical Physics, }115(11): 5015-5026. \newline [2] Warren, P.B. (2003). \textit{Physical Review E}\textbf{\textit{. }}68. 066702: 1-8. [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LD.00006: Lattice-Boltzmann Simulations of Bubble Suspensions in Vertical and Inclined Channels Xiaolong Yin, Donald L. Koch We have developed a lattice-Boltzmann boundary method to recover the slip boundary condition at the gas-liquid interface. This rule enables one to use a single-component lattice-Boltzmann solver to simulate gas-liquid flows. The method is applied to suspensions of spherical, non-coalescing bubbles with Re=O(10). We first studied the hindered rising velocity and microstructures of bubble suspensions in periodic domains. We observed that the bubbles form a distinctive structure with strong correlations in the horizontal positions of neighboring bubbles at all bubble volume fractions. We then simulated the rise of bubbles in vertical and slightly inclined channels bounded by solid walls in the horizontal direction. In vertical channels, the bubbles are pushed away from the walls. A strong backflow is observed near the wall. In inclined channels, the gravity component normal to the walls breaks the symmetry and creates a bubble-rich layer next to the upper wall. A weak shear flow then develops. The shear rate is just sufficient so that the lift force on the bubbles balances the cross-channel buoyancy, thus keeping most of the bubbles suspended. [Preview Abstract] |
Tuesday, November 22, 2005 9:18AM - 9:31AM |
LD.00007: Study on bubble shape interacted with vortex motion via mathematical approach Yukihiro Yonemoto, Tomoaki Kunugi, Akimi Serizawa There are many unclear mechanisms regarding bubble coalescence and breakup both experimentally and numerically. In general, it is considered that the processes of bubble coalescence and breakup are composed of several microscopic interfacial phenomena such as intermolecular force, electric double layer, surfactant and so on. On the other hand, a hydrodynamic force like a vortex motion is a dominant factor in fluid flows. A geometrical change of a bubble due to the hydrodynamic force could be related to the microscopic phenomena at a gas-liquid interface. In this study, we focus on the relation between the shape of bubble and the hydrodynamic force by means of numerical analysis and mathematical approach based on differential geometry. In particular, we make vortex dipoles impinge on the bubble in liquid and investigate the relation between the circulation of vortex dipoles and the feature of bubble shape after impingement such as a surface curvature singularity. This singularity can be estimated from the distribution of the curvature, its gradient and the Gauss-mapping of the bubble surface. [Preview Abstract] |
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