Gas depletion through single gas bubble diffusive growth and its effect on subsequent bubbles

NASA Astrophysics Data System (ADS)

Moreno Soto, Alvaro; Prosperetti, Andrea; Lohse, Detlef; van der Meer, Devaraj; Physics of Fluid Group Collaboration; MCEC Netherlands CenterMultiscale Catalytic Energy Conversion Collaboration

2016-11-01

In weakly supersaturated mixtures, bubbles are known to grow quasi-statically as diffusion-driven mass transfer governs the process. In the final stage of the evolution, before detachment, there is an enhancement of mass transfer, which changes from diffusion to natural convection. Once the bubble detaches, it leaves behind a gas-depleted area. The diffusive mass transfer towards that region cannot compensate for the amount of gas which is taken away by the bubble. Consequently, the consecutive bubble will grow in an environment which contains less gas than for the previous one. This reduces the local supersaturation of the mixture around the nucleation site, leading to a reduced bubble growth rate. We present quantitative experimental data on this effect and the theoretical model for depletion during the bubble growth rate. This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands.

Hydrodynamic models for slurry bubble column reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gidaspow, D.

1995-12-31

The objective of this investigation is to convert a {open_quotes}learning gas-solid-liquid{close_quotes} fluidization model into a predictive design model. This model is capable of predicting local gas, liquid and solids hold-ups and the basic flow regimes: the uniform bubbling, the industrially practical churn-turbulent (bubble coalescence) and the slugging regimes. Current reactor models incorrectly assume that the gas and the particle hold-ups (volume fractions) are uniform in the reactor. They must be given in terms of empirical correlations determined under conditions that radically differ from reactor operation. In the proposed hydrodynamic approach these hold-ups are computed from separate phase momentum balances. Furthermore,more » the kinetic theory approach computes the high slurry viscosities from collisions of the catalyst particles. Thus particle rheology is not an input into the model.« less

Hidden Attractors in a Model of a Bubble Contrast Agent Oscillating Near an Elastic Wall

NASA Astrophysics Data System (ADS)

Garashchuk, Ivan; Sinelshchikov, Dmitry; Kudryashov, Nikolay

2018-02-01

A model describing the dynamics of a spherical gas bubble in a compressible viscous liquid is studied. The bubble is oscillating close to an elastic wall of finite thickness under the influence of an external pressure field which simulates a contrast agent oscillating close to a blood vessel wall. Here we investigate numerically the coexistence of chaotic and periodic attractors in this model. One of the tools applied for seeking coexisting attractors is the perpetual points method. This method can be helpful for localizing coexisting attractors, occurring in various physically realistic ranges of variation of the control parameters. We provide some examples of coexisting attractors to demonstrate the importance of the multistability problem for the applications.

Analytical study of the acoustic field in a spherical resonator for single bubble sonoluminescence.

PubMed

Dellavale, Damián; Urteaga, Raúl; Bonetto, Fabián J

2010-01-01

The acoustic field in the liquid within a spherical solid shell is calculated. The proposed model takes into account Stoke's wave equation in the viscous fluid, the membrane theory to describe the solid shell motion and the energy loss through the external couplings of the system. A point source at the resonator center is included to reproduce the acoustic emission of a sonoluminescence bubble. Particular calculations of the resulting acoustic field are performed for viscous liquids of interest in single bubble sonoluminescence. The model reveals that in case of radially symmetric modes of low frequency, the quality factor is mainly determined by the acoustic energy flowing through the mechanical coupling of the resonator. Alternatively, for high frequency modes the quality factor is mainly determined by the viscous dissipation in the liquid. Furthermore, the interaction between the bubble acoustic emission and the resonator modes is analyzed. It was found that the bubble acoustic emission produces local maxima in the resonator response. The calculated amplitudes and relative phases of the harmonics constituting the bubble acoustic environment can be used to improve multi-frequency driving in sonoluminescence.

Simulating the universe(s) III: observables for the full bubble collision spacetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Matthew C.; Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5; Wainwright, Carroll L.

2016-07-14

This is the third paper in a series establishing a quantitative relation between inflationary scalar field potential landscapes and the relic perturbations left by the collision between bubbles produced during eternal inflation. We introduce a new method for computing cosmological observables from numerical relativity simulations of bubble collisions in one space and one time dimension. This method tiles comoving hypersurfaces with locally-perturbed Friedmann-Robertson-Walker coordinate patches. The method extends previous work, which was limited to the spacetime region just inside the future light cone of the collision, and allows us to explore the full bubble-collision spacetime. We validate our new methodsmore » against previous work, and present a full set of predictions for the comoving curvature perturbation and local negative spatial curvature produced by identical and non-identical bubble collisions, in single scalar field models of eternal inflation. In both collision types, there is a non-zero contribution to the spatial curvature and cosmic microwave background quadrupole. Some collisions between non-identical bubbles excite wall modes, giving extra structure to the predicted temperature anisotropies. We comment on the implications of our results for future observational searches. For non-identical bubble collisions, we also find that the surfaces of constant field can readjust in the presence of a collision to produce spatially infinite sections that become nearly homogeneous deep into the region affected by the collision. Contrary to previous assumptions, this is true even in the bubble into which the domain wall is accelerating.« less

Simulating the universe(s) III: observables for the full bubble collision spacetime

NASA Astrophysics Data System (ADS)

Johnson, Matthew C.; Wainwright, Carroll L.; Aguirre, Anthony; Peiris, Hiranya V.

2016-07-01

This is the third paper in a series establishing a quantitative relation between inflationary scalar field potential landscapes and the relic perturbations left by the collision between bubbles produced during eternal inflation. We introduce a new method for computing cosmological observables from numerical relativity simulations of bubble collisions in one space and one time dimension. This method tiles comoving hypersurfaces with locally-perturbed Friedmann-Robertson-Walker coordinate patches. The method extends previous work, which was limited to the spacetime region just inside the future light cone of the collision, and allows us to explore the full bubble-collision spacetime. We validate our new methods against previous work, and present a full set of predictions for the comoving curvature perturbation and local negative spatial curvature produced by identical and non-identical bubble collisions, in single scalar field models of eternal inflation. In both collision types, there is a non-zero contribution to the spatial curvature and cosmic microwave background quadrupole. Some collisions between non-identical bubbles excite wall modes, giving extra structure to the predicted temperature anisotropies. We comment on the implications of our results for future observational searches. For non-identical bubble collisions, we also find that the surfaces of constant field can readjust in the presence of a collision to produce spatially infinite sections that become nearly homogeneous deep into the region affected by the collision. Contrary to previous assumptions, this is true even in the bubble into which the domain wall is accelerating.

Radical production inside an acoustically driven microbubble.

PubMed

Stricker, Laura; Lohse, Detlef

2014-01-01

The chemical production of radicals inside acoustically driven bubbles is determined by the local temperature inside the bubbles and by their composition at collapse. By means of a previously validated ordinary differential equations (ODE) model [L. Stricker, A. Prosperetti, D. Lohse, Validation of an approximate model for the thermal behavior in acoustically driven bubbles, J. Acoust. Soc. Am. 130 (5) (2011) 3243-3251], based on boundary layer assumption for mass and heat transport, we study the influence of different parameters on the radical production. We perform different simulations by changing the driving frequency and pressure, the temperature of the surrounding liquid and the composition of the gas inside the bubbles. In agreement with the experimental conditions of new generation sonochemical reactors, where the bubbles undergo transient cavitation oscillations [D. F. Rivas, L. Stricker, A. Zijlstra, H. Gardeniers, D. Lohse, A. Prosperetti, Ultrasound artificially nucleated bubbles and their sonochemical radical production, Ultrason. Sonochem. 20 (1) (2013) 510-524], we mainly concentrate on the initial chemical transient and we suggest optimal working ranges for technological applications. The importance of the chemical composition at collapse is reflected in the model, including the role of entrapped water vapor. We in particular study the exothermal reactions taking place in H2 and O2 mixtures. At the exact stoichiometric mixture 2:1 the highest internal bubble temperatures are achieved. Copyright © 2013 Elsevier B.V. All rights reserved.

The Origin of the Local 1/4-KeV X-Ray Flux in Both Charge Exhange and a Hot Bubble

NASA Technical Reports Server (NTRS)

Galeazzi, M.; Chiao, M.; Collier, M. R.; Cravens, T.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Lepri, S. T.; McCammon, D.; Morgan, K.;

The origin of the local 1/4-keV X-ray flux in both charge exchange and a hot bubble.

PubMed

Galeazzi, M; Chiao, M; Collier, M R; Cravens, T; Koutroumpa, D; Kuntz, K D; Lallement, R; Lepri, S T; McCammon, D; Morgan, K; Porter, F S; Robertson, I P; Snowden, S L; Thomas, N E; Uprety, Y; Ursino, E; Walsh, B M

2014-08-14

The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.

Ultrasound-induced oscillations of gas bubbles in contact with gelatin gel surfaces

NASA Astrophysics Data System (ADS)

Fukui, Sosuke; Ando, Keita

2017-11-01

Ultrasound-induced dynamics of gas bubbles in the vicinity of deformable boundaries are studied experimentally, as a simplified model of sonoporation in medicine. In our experiment, 28-kHz underwater ultrasound was irradiated to a gas bubble nuclei (of radius from 60 μm to 200 μm) sitting at gel surfaces (of gelatin concentration from 6 wt% to 16 wt%) and the bubble dynamics were recorded by a high-speed camera. The repeated deformation of the gel surface was found to be in phase with volumetric oscillation of the bubble. A liquid jet, which can appear toward the collapse phase in the bubble oscillation in volume, produced localized surface deformation, which is an important observation in the context of sonoporation. We characterize the maximum displacement of the gel surface with varying the bubble nuclei radius (in comparison to the resonant radius fixed approximately at 117 μm). We also examine the phase difference between the ultrasound and the bubble dynamics under the influence of the deformable boundary. The Research Grant of Keio Leading-edge Laboratory of Science & Technology.

Interaction, coalescence, and collapse of localized patterns in a quasi-one-dimensional system of interacting particles

NASA Astrophysics Data System (ADS)

Dessup, Tommy; Coste, Christophe; Saint Jean, Michel

2017-01-01

We study the path toward equilibrium of pairs of solitary wave envelopes (bubbles) that modulate a regular zigzag pattern in an annular channel. We evidence that bubble pairs are metastable states, which spontaneously evolve toward a stable single bubble. We exhibit the concept of topological frustration of a bubble pair. A configuration is frustrated when the particles between the two bubbles are not organized in a modulated staggered row. For a nonfrustrated (NF) bubble pair configuration, the bubbles interaction is attractive, whereas it is repulsive for a frustrated (F) configuration. We describe a model of interacting solitary wave that provides all qualitative characteristics of the interaction force: It is attractive for NF systems and repulsive for F systems and decreases exponentially with the bubbles distance. Moreover, for NF systems, the bubbles come closer and eventually merge as a single bubble, in a coalescence process. We also evidence a collapse process, in which one bubble shrinks in favor of the other one, overcoming an energetic barrier in phase space. This process is relevant for both NF systems and F systems. In NF systems, the coalescence prevails at low temperature, whereas thermally activated jumps make the collapse prevail at high temperature. In F systems, the path toward equilibrium involves a collapse process regardless of the temperature.

Bubbling in unbounded coflowing liquids.

PubMed

Gañán-Calvo, Alfonso M; Herrada, Miguel A; Garstecki, Piotr

2006-03-31

An investigation of the stability of low density and viscosity fluid jets and spouts in unbounded coflowing liquids is presented. A full parametrical analysis from low to high Weber and Reynolds numbers shows that the presence of any fluid of finite density and viscosity inside the hollow jet elicits a transition from an absolute to a convective instability at a finite value of the Weber number, for any value of the Reynolds number. Below that critical value of the Weber number, the absolute character of the instability leads to local breakup, and consequently to local bubbling. Experimental data support our model.

Bubble driven quasioscillatory translational motion of catalytic micromotors.

PubMed

Manjare, Manoj; Yang, Bo; Zhao, Y-P

2012-09-21

A new quasioscillatory translational motion has been observed for big Janus catalytic micromotors with a fast CCD camera. Such motional behavior is found to coincide with both the bubble growth and burst processes resulting from the catalytic reaction, and the competition of the two processes generates a net forward motion. Detailed physical models have been proposed to describe the above processes. It is suggested that the bubble growth process imposes a growth force moving the micromotor forward, while the burst process induces an instantaneous local pressure depression pulling the micromotor backward. The theoretic predictions are consistent with the experimental data.

Bubble Driven Quasioscillatory Translational Motion of Catalytic Micromotors

NASA Astrophysics Data System (ADS)

Manjare, Manoj; Yang, Bo; Zhao, Y.-P.

2012-09-01

A new quasioscillatory translational motion has been observed for big Janus catalytic micromotors with a fast CCD camera. Such motional behavior is found to coincide with both the bubble growth and burst processes resulting from the catalytic reaction, and the competition of the two processes generates a net forward motion. Detailed physical models have been proposed to describe the above processes. It is suggested that the bubble growth process imposes a growth force moving the micromotor forward, while the burst process induces an instantaneous local pressure depression pulling the micromotor backward. The theoretic predictions are consistent with the experimental data.

Long-lived oscillons from asymmetric bubbles: Existence and stability

NASA Astrophysics Data System (ADS)

Adib, Artur B.; Gleiser, Marcelo; Almeida, Carlos A.

2002-10-01

The possibility that extremely long-lived, time-dependent, and localized field configurations (``oscillons'') arise during the collapse of asymmetrical bubbles in (2+1)-dimensional φ4 models is investigated. It is found that oscillons can develop from a large spectrum of elliptically deformed bubbles. Moreover, we provide numerical evidence that such oscillons are (a) circularly symmetric and (b) linearly stable against small arbitrary radial and angular perturbations. The latter is based on a dynamical approach designed to investigate the stability of nonintegrable time-dependent configurations that is capable of probing slowly growing instabilities not seen through the usual ``spectral'' method.

Flow of foams in two-dimensional disordered porous media

NASA Astrophysics Data System (ADS)

Dollet, Benjamin; Geraud, Baudouin; Jones, Sian A.; Meheust, Yves; Cantat, Isabelle; Institut de Physique de Rennes Team; Geosciences Rennes Team

2015-11-01

Liquid foams are a yield stress fluid with elastic properties. When a foam flow is confined by solid walls, viscous dissipation arises from the contact zones between soap films and walls, giving very peculiar friction laws. In particular, foams potentially invade narrow pores much more efficiently than Newtonian fluids, which is of great importance for enhanced oil recovery. To quantify this effect, we study experimentally flows of foam in a model two-dimensional porous medium, consisting of an assembly of circular obstacles placed randomly in a Hele-Shaw cell, and use image analysis to quantify foam flow at the local scale. We show that bubbles split as they flow through the porous medium, by a mechanism of film pinching during contact with an obstacle, yielding two daughter bubbles per split bubble. We quantify the evolution of the bubble size distribution as a function of the distance along the porous medium, the splitting probability as a function of bubble size, and the probability distribution function of the daughter bubbles. We propose an evolution equation to model this splitting phenomenon and compare it successfully to the experiments, showing how at long distance, the porous medium itself dictates the size distribution of the foam.

A computational efficient modelling of laminar separation bubbles

NASA Technical Reports Server (NTRS)

Dini, Paolo; Maughmer, Mark D.

1990-01-01

In predicting the aerodynamic characteristics of airfoils operating at low Reynolds numbers, it is often important to account for the effects of laminar (transitional) separation bubbles. Previous approaches to the modelling of this viscous phenomenon range from fast but sometimes unreliable empirical correlations for the length of the bubble and the associated increase in momentum thickness, to more accurate but significantly slower displacement-thickness iteration methods employing inverse boundary-layer formulations in the separated regions. Since the penalty in computational time associated with the more general methods is unacceptable for airfoil design applications, use of an accurate yet computationally efficient model is highly desirable. To this end, a semi-empirical bubble model was developed and incorporated into the Eppler and Somers airfoil design and analysis program. The generality and the efficiency was achieved by successfully approximating the local viscous/inviscid interaction, the transition location, and the turbulent reattachment process within the framework of an integral boundary-layer method. Comparisons of the predicted aerodynamic characteristics with experimental measurements for several airfoils show excellent and consistent agreement for Reynolds numbers from 2,000,000 down to 100,000.

Bubble clustering in a glass of stout beer

NASA Astrophysics Data System (ADS)

Iwatsubo, Fumiya; Watamura, Tomoaki; Sugiyama, Kazuyasu

2017-11-01

To clarify why the texture in stout beer poured into a pint glass descends, we investigated local time development of the void fraction and velocity of bubbles. The propagation of the number density distribution, i.e. the texture, appearing near the inclined wall is observed. We visualized individual advective bubbles near the inclined wall by microscope and measured the local void fraction using brightness of images while the velocity of bubbles by means of Particle Tracking Velocimetry. As the result of measurements, we found the local void fraction and the bubbles advection velocity increase and decrease repeatedly with a time delay. We conclude the texture pattern is composed of fluid blobs which contain less bubbles; extruding and suction flows respectively toward and from the interior of the container form respectively in front and back of the blobs.

Molecular dynamics simulations of bubble nucleation in dark matter detectors.

PubMed

Denzel, Philipp; Diemand, Jürg; Angélil, Raymond

2016-01-01

Bubble chambers and droplet detectors used in dosimetry and dark matter particle search experiments use a superheated metastable liquid in which nuclear recoils trigger bubble nucleation. This process is described by the classical heat spike model of F. Seitz [Phys. Fluids (1958-1988) 1, 2 (1958)PFLDAS0031-917110.1063/1.1724333], which uses classical nucleation theory to estimate the amount and the localization of the deposited energy required for bubble formation. Here we report on direct molecular dynamics simulations of heat-spike-induced bubble formation. They allow us to test the nanoscale process described in the classical heat spike model. 40 simulations were performed, each containing about 20 million atoms, which interact by a truncated force-shifted Lennard-Jones potential. We find that the energy per length unit needed for bubble nucleation agrees quite well with theoretical predictions, but the allowed spike length and the required total energy are about twice as large as predicted. This could be explained by the rapid energy diffusion measured in the simulation: contrary to the assumption in the classical model, we observe significantly faster heat diffusion than the bubble formation time scale. Finally we examine α-particle tracks, which are much longer than those of neutrons and potential dark matter particles. Empirically, α events were recently found to result in louder acoustic signals than neutron events. This distinction is crucial for the background rejection in dark matter searches. We show that a large number of individual bubbles can form along an α track, which explains the observed larger acoustic amplitudes.

Quasiopen inflation

NASA Astrophysics Data System (ADS)

García-Bellido, Juan; Garriga, Jaume; Montes, Xavier

1998-04-01

We show that a large class of two-field models of single-bubble open inflation does not lead to infinite open universes, as was previously thought, but to an ensemble of very large but finite inflating ``islands.'' The reason is that the quantum tunneling responsible for the nucleation of the bubble does not occur simultaneously along both field directions and equal-time hypersurfaces in the open universe are not synchronized with equal-density or fixed-field hypersurfaces. The most probable tunneling trajectory corresponds to a zero value of the inflaton field; large values, necessary for the second period of inflation inside the bubble, only arise as localized fluctuations. The interior of each nucleated bubble will contain an infinite number of such inflating regions of comoving size of order γ-1, where γ is the supercurvature eigenvalue, which depends on the parameters of the model. Each one of these islands will be a quasi-open universe. Since the volume of the hyperboloid is infinite, inflating islands with all possible values of the field at their center will be realized inside of a single bubble. We may happen to live in one of those patches of comoving size d<~γ-1, where the universe appears to be open. In particular, we consider the ``supernatural'' model proposed by Linde and Mezhlumian. There, an approximate U(1) symmetry is broken by a tunneling field in a first order phase transition, and slow-roll inflation inside the nucleated bubble is driven by the pseudo Goldstone field. We find that the excitations of the pseudo Goldstone field produced by the nucleation and subsequent expansion of the bubble place severe constraints on this model. We also discuss the coupled and uncoupled two-field models.

Modeling DNA bubble formation at the atomic scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beleva, V; Rasmussen, K. O.; Garcia, A. E.

We describe the fluctuations of double stranded DNA molecules using a minimalist Go model over a wide range of temperatures. Minimalist models allow us to describe, at the atomic level, the opening and formation of bubbles in DNA double helices. This model includes all the geometrical constraints in helix melting imposed by the 3D structure of the molecule. The DNA forms melted bubbles within double helices. These bubbles form and break as a function of time. The equilibrium average number of broken base pairs shows a sharp change as a function of T. We observe a temperature profile of sequencemore » dependent bubble formation similar to those measured by Zeng et al. Long nuclei acid molecules melt partially through the formations of bubbles. It is known that CG rich sequences melt at higher temperatures than AT rich sequences. The melting temperature, however, is not solely determined by the CG content, but by the sequence through base stacking and solvent interactions. Recently, models that incorporate the sequence and nonlinear dynamics of DNA double strands have shown that DNA exhibits a very rich dynamics. Recent extensions of the Bishop-Peyrard model show that fluctuations in the DNA structure lead to opening in localized regions, and that these regions in the DNA are associated with transcription initiation sites. 1D and 2D models of DNA may contain enough information about stacking and base pairing interactions, but lack the coupling between twisting, bending and base pair opening imposed by the double helical structure of DNA that all atom models easily describe. However, the complexity of the energy function used in all atom simulations (including solvent, ions, etc) does not allow for the description of DNA folding/unfolding events that occur in the microsecond time scale.« less

Foam Flow Through a 2D Porous Medium: Evolution of the Bubble Size Distribution

NASA Astrophysics Data System (ADS)

Meheust, Y.; Géraud, B.; Cantat, I.; Dollet, B.

2017-12-01

Foams have been used for decades as displacing fluids for EOR and aquifer remediation, and more recently as carriers of chemical amendments for remediation of the vadose zone. Bulk foams are shear-thinning fluids; but for foams with bubbles of order at least the typical pore size of the porous medium, the rheology cannot be described at the continuum scale, as viscous dissipation occurs mostly at the contact between soap films and solid walls. We have investigated the flow of an initially monodisperse foam through a transparent 2D porous medium[1]. The resulting complex flow phenomenology has been characterized quantitatively from optical measurements of the bubble dynamics. In addition to preferential flow path and local flow intermittency, we observe an irreversible evolution of the probability density function (PDF) for bubbles size as bubbles travel along the porous medium. This evolution is due to bubble fragmentation by lamella division, which is by far the dominant mechanism of film creation/destruction. We measure and characterize this evolution of the PDF as a function of the experimental parameters, and model it numerically based on a fragmentation equation, with excellent agreement. The model uses two ingredients obtained from the experimental data, namely the statistics of the bubble fragmentation rate and of the fragment size distributions[2]. It predicts a nearly-universal scaling of all PDFs as a function of the bubble area normalized by the initial mean bubble area. All the PDFs measured in various experiments, with different mean flow velocities, initial bubble sizes and foam qualities, collapse on a master distribution which is only dependent on the geometry of the medium.References:[1] B. Géraud, S. A. Jones, I. Cantat, B. Dollet & Y. Méheust (2016), WRR 52(2), 773-790. [2] B. Géraud, Y. Méheust, I. Cantat & B. Dollet (2017), Lamella division in a foam flowing through a two-dimensional porous medium: A model fragmentation process, PRL 118, 098003.

A non-local free boundary problem arising in a theory of financial bubbles

PubMed Central

Berestycki, Henri; Monneau, Regis; Scheinkman, José A.

2014-01-01

We consider an evolution non-local free boundary problem that arises in the modelling of speculative bubbles. The solution of the model is the speculative component in the price of an asset. In the framework of viscosity solutions, we show the existence and uniqueness of the solution. We also show that the solution is convex in space, and establish several monotonicity properties of the solution and of the free boundary with respect to parameters of the problem. To study the free boundary, we use, in particular, the fact that the odd part of the solution solves a more standard obstacle problem. We show that the free boundary is and describe the asymptotics of the free boundary as c, the cost of transacting the asset, goes to zero. PMID:25288815

Effect of Shock-Induced Cavitation Bubble Collapse on the damage in the Simulated Perineuronal Net of the Brain.

PubMed

Wu, Yuan-Ting; Adnan, Ashfaq

2017-07-13

The purpose of this study is to conduct modeling and simulation to understand the effect of shock-induced mechanical loading, in the form of cavitation bubble collapse, on damage to the brain's perineuronal nets (PNNs). It is known that high-energy implosion due to cavitation collapse is responsible for corrosion or surface damage in many mechanical devices. In this case, cavitation refers to the bubble created by pressure drop. The presence of a similar damage mechanism in biophysical systems has long being suspected but not well-explored. In this paper, we use reactive molecular dynamics (MD) to simulate the scenario of a shock wave induced cavitation collapse within the perineuronal net (PNN), which is the near-neuron domain of a brain's extracellular matrix (ECM). Our model is focused on the damage in hyaluronan (HA), which is the main structural component of PNN. We have investigated the roles of cavitation bubble location, shockwave intensity and the size of a cavitation bubble on the structural evolution of PNN. Simulation results show that the localized supersonic water hammer created by an asymmetrical bubble collapse may break the hyaluronan. As such, the current study advances current knowledge and understanding of the connection between PNN damage and neurodegenerative disorders.

Advanced subgrid-scale modeling for convection-dominated species transport at fluid interfaces with application to mass transfer from rising bubbles

NASA Astrophysics Data System (ADS)

Weiner, Andre; Bothe, Dieter

2017-10-01

This paper presents a novel subgrid scale (SGS) model for simulating convection-dominated species transport at deformable fluid interfaces. One possible application is the Direct Numerical Simulation (DNS) of mass transfer from rising bubbles. The transport of a dissolving gas along the bubble-liquid interface is determined by two transport phenomena: convection in streamwise direction and diffusion in interface normal direction. The convective transport for technical bubble sizes is several orders of magnitude higher, leading to a thin concentration boundary layer around the bubble. A true DNS, fully resolving hydrodynamic and mass transfer length scales results in infeasible computational costs. Our approach is therefore a DNS of the flow field combined with a SGS model to compute the mass transfer between bubble and liquid. An appropriate model-function is used to compute the numerical fluxes on all cell faces of an interface cell. This allows to predict the mass transfer correctly even if the concentration boundary layer is fully contained in a single cell layer around the interface. We show that the SGS-model reduces the resolution requirements at the interface by a factor of ten and more. The integral flux correction is also applicable to other thin boundary layer problems. Two flow regimes are investigated to validate the model. A semi-analytical solution for creeping flow is used to assess local and global mass transfer quantities. For higher Reynolds numbers ranging from Re = 100 to Re = 460 and Péclet numbers between Pe =104 and Pe = 4 ṡ106 we compare the global Sherwood number against correlations from literature. In terms of accuracy, the predicted mass transfer never deviates more than 4% from the reference values.

Probing the Local Bubble with diffuse interstellar bands. I. Project overview and southern hemisphere survey

NASA Astrophysics Data System (ADS)

Bailey, Mandy; van Loon, Jacco Th.; Farhang, Amin; Javadi, Atefeh; Khosroshahi, Habib G.; Sarre, Peter J.; Smith, Keith T.

2016-01-01

Context. The Sun traverses a low-density, hot entity called the Local Bubble. Despite its relevance to life on Earth, the conditions in the Local Bubble and its exact configuration are not very well known. Besides that, there is some unknown interstellar substance that causes a host of absorption bands across the optical spectrum, called diffuse interstellar bands (DIBs). Aims: We have started a project to chart the Local Bubble in a novel way and learn more about the carriers of the DIBs, by using DIBs as tracers of diffuse gas and environmental conditions. Methods: We conducted a high signal-to-noise spectroscopic survey of 670 nearby early-type stars to map DIB absorption in and around the Local Bubble. The project started with a southern hemisphere survey conducted at the European Southern Observatory's New Technology Telescope and has since been extended to an all-sky survey using the Isaac Newton Telescope. Results: In this first paper in the series, we introduce the overall project and present the results from the southern heiphere survey. We make aviable a catalogue of equivalent-width measurements of the DIBs at 5780, 5797, 5850, 6196, 6203, 6270, 6283, and 6614 Å, of the interstellar Na I D lines at 5890 and 5896 Å, and of the stellar He I line at 5876 Å. We find that the 5780 Å DIB is relatively strong throughout, as compared to the 5797 Å DIB, but especially within the Local Bubble and at the interface iwth a more neutral medium. The 6203 Å DIB shows similar behaviour with respect to the 6196 Å DIB. Some nearby stars show surprisingly strong DIBs, whereas some distant stars show very weak DIBs, indicating small-scale structure within, as well as outside, the Local Bubble. The sight lines with non-detections trace the extent of the Local Bubble especially clearly and show it opening out into the halo. Conclusions: The Local Bubble has a wall that is in contact with hot gas and/or a harsh interstellar radiation field. That wall is perforated, though, causing leakage of radiation and possibly hot gas. On the other hand, compact self-shielded cloudlets are present much closer to the Sun, probably within the Local Bubble itself. As for the carriers of the DIBs, our observations confirm the notion that these are large molecules whose differences in behaviour are mainly governed by their differing resilience and/or electrical charge, with more subtle differences possibly related to varying excitation. Full Tables 1 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or I http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A12

Drug delivery with microsecond laser pulses into gelatin.

PubMed

Shangguan, H; Casperson, L W; Shearin, A; Gregory, K W; Prahl, S A

1996-07-01

Photo acoustic drug delivery is a technique for localized drug delivery by laser-induced hydrodynamic pressure following cavitation bubble expansion and collapse. Photoacoustic drug delivery was investigated on gelatin-based thrombus models with planar and cylindrical geometries by use of one microsecond laser pulses. Solutions of a hydrophobic dye in mineral oil permitted monitoring of delivered colored oil into clear gelatin-based thrombus models. Cavitation bubble development and photoacoustic drug delivery were visualized with flash photography. This study demonstrated that cavitation is the governing mechanism for photoacoustic drug delivery, and the deepest penetration of colored oil in gels followed the bubble collapse. Spatial distribution measurements revealed that colored oil could be driven a few millimeters into the gels in both axial and radial directions, and the penetration was less than 500 µm when the gelatin structure was not fractured.

Light Scattering by Ice Crystals Containing Air Bubbles

NASA Astrophysics Data System (ADS)

Zhang, J.; Panetta, R. L.; Yang, P.; Bi, L.

2014-12-01

The radiative effects of ice clouds are often difficult to estimate accurately, but are very important for interpretation of observations and for climate modeling. Our understanding of these effects is primarily based on scattering calculations, but due to the variability in ice habit it is computationally difficult to determine the required scattering and absorption properties, and the difficulties are only compounded by the need to include consideration of air and carbon inclusions of the sort frequently observed in collected samples. Much of the previous work on effects of inclusions in ice particles on scattering properties has been conducted with variants of geometric optics methods. We report on simulations of scattering by ice crystals with enclosed air bubbles using the pseudo-spectral time domain method (PSTD) and improved geometric optics method (IGOM). A Bouncing Ball Model (BBM) is proposed as a parametrization of air bubbles, and the results are compared with Monte Carlo radiative transfer calculations. Consistent with earlier studies, we find that air inclusions lead to a smoothing of variations in the phase function, weakening of halos, and a reduction of backscattering. We extend these studies by examining the effects of the particular arrangement of a fixed number of bubbles, as well as the effects of splitting a given number of bubbles into a greater number of smaller bubbles with the same total volume fraction. The result shows that the phase function will not change much for stochastic distributed air bubbles. It also shows that local maxima of phase functions are smoothed out for backward directions, when we break bubbles into small ones, single big bubble scatter favors more forward scattering than multi small internal scatters.

Controlled single bubble cavitation collapse results in jet-induced injury in brain tissue.

PubMed

Canchi, Saranya; Kelly, Karen; Hong, Yu; King, Michael A; Subhash, Ghatu; Sarntinoranont, Malisa

2017-10-01

Multiscale damage due to cavitation is considered as a potential mechanism of traumatic brain injury (TBI) associated with explosion. In this study, we employed a TBI relevant hippocampal ex vivo slice model to induce bubble cavitation. Placement of single reproducible seed bubbles allowed control of size, number, and tissue location to visualize and measure deformation parameters. Maximum strain value was measured at 45 µs after bubble collapse, presented with a distinct contour and coincided temporally and spatially with the liquid jet. Composite injury maps combined this maximum strain value with maximum measured bubble size and location along with histological injury patterns. This facilitated the correlation of bubble location and subsequent jet direction to the corresponding regions of high strain which overlapped with regions of observed injury. A dynamic threshold strain range for tearing of cerebral cortex was estimated to be between 0.5 and 0.6. For a seed bubble placed underneath the hippocampus, cavitation induced damage was observed in hippocampus (local), proximal cerebral cortex (marginal) and the midbrain/forebrain (remote) upon histological evaluation. Within this test model, zone of cavitation injury was greater than the maximum radius of the bubble. Separation of apposed structures, tissue tearing, and disruption of cellular layers defined early injury patterns that were not detected in the blast-exposed half of the brain slice. Ultrastructural pathology of the neurons exposed to cavitation was characterized by disintegration of plasma membrane along with loss of cellular content. The developed test system provided a controlled experimental platform to study cavitation induced high strain deformations on brain tissue slice. The goal of the future studies will be to lower underpressure magnitude and cavitation bubble size for more sensitive evaluation of injury. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cavitation in ultrasound and shockwave therapy

NASA Astrophysics Data System (ADS)

Colonius, Tim

2014-11-01

Acoustic waves, especially high-intensity ultrasound and shock waves, are used for medical imaging and intra- and extra-corporeal manipulation of cells, tissue, and urinary calculi. Waves are currently used to treat kidney stone disease, plantar fasciitis, and bone nonunion, and they are being investigated as a technique to ablate cancer tumors and mediate drug delivery. In many applications, acoustic waves induce the expansion and collapse of preexisting or newly cavitating bubbles whose presence can either mediate the generation of localized stresses or lead to collateral damage, depending on how effectively they can be controlled. We describe efforts aimed at simulating the collapse of bubbles, both individually and in clusters, with the aim to characterize the induced mechanical stresses and strains. To simulate collapse of one or a few bubbles, compressible Euler and Navier-Stokes simulations of multi-component materials are performed with WENO-based shock and interface capturing schemes. Repetitive insonification generates numerous bubbles that are difficult to resolve numerically. Such clouds are also important in traditional engineering applications such as caveating hydrofoils. Models that incorporate the dynamics of an unresolved dispersed phase consisting of the bubble cloud are also developed. The results of several model problems including bubble collapse near rigid surfaces, bubble collapse near compliant surfaces and in small capillaries are analyzed. The results are processed to determine the potential for micron-sized preexisting gas bubbles to damage capillaries. The translation of the fundamental fluid dynamics into improvements in the design and clinical application of shockwave lithotripters will be discussed. NIH Grant PO1-DK043881.

Bubble and Slug Flow at Microgravity Conditions: State of Knowledge and Open Questions

NASA Technical Reports Server (NTRS)

Colin, C.; Fabre, J.; McQuillen, J.

1996-01-01

Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.

PROBING THE LOCAL BUBBLE WITH DIFFUSE INTERSTELLAR BANDS. II. THE DIB PROPERTIES IN THE NORTHERN HEMISPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh

2015-02-10

We present a new high signal-to-noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the λ5780 Å and λ5797 Å diffuse interstellar bands (DIBs). We observed 432 sightlines to a distance of 200 pc over a duration of three years. In this study, we establish the λ5780 and λ5797 correlations with Na I, Ca II and E {sub B-V}, for both inside and outside the Local Bubble. The correlations show that among all neutral and ionized atoms, the correlation between Ca II and λ5780 is stronger than its correlation with λ5797, suggestingmore » that λ5780 is more associated with regions where Ca{sup +} is more abundant. We study the λ5780 correlation with λ5797, which shows a tight correlation within and outside the Local Bubble. In addition, we investigate the DIB properties in UV irradiated and UV shielded regions. We find that, within and beyond the Local Bubble, λ5797 is located in denser parts of clouds, protected from UV irradiation, while λ5780 is located in the low-density regions of clouds.« less

Bubble Combustion

NASA Technical Reports Server (NTRS)

Corrigan, Jackie

2004-01-01

A method of energy production that is capable of low pollutant emissions is fundamental to one of the four pillars of NASA s Aeronautics Blueprint: Revolutionary Vehicles. Bubble combustion, a new engine technology currently being developed at Glenn Research Center promises to provide low emissions combustion in support of NASA s vision under the Emissions Element because it generates power, while minimizing the production of carbon dioxide (CO2) and nitrous oxides (NOx), both known to be Greenhouse gases. and allows the use of alternative fuels such as corn oil, low-grade fuels, and even used motor oil. Bubble combustion is analogous to the inverse of spray combustion: the difference between bubble and spray combustion is that spray combustion is spraying a liquid in to a gas to form droplets, whereas bubble combustion involves injecting a gas into a liquid to form gaseous bubbles. In bubble combustion, the process for the ignition of the bubbles takes place on a time scale of less than a nanosecond and begins with acoustic waves perturbing each bubble. This perturbation causes the local pressure to drop below the vapor pressure of the liquid thus producing cavitation in which the bubble diameter grows, and upon reversal of the oscillating pressure field, the bubble then collapses rapidly with the aid of the high surface tension forces acting on the wall of the bubble. The rapid and violent collapse causes the temperatures inside the bubbles to soar as a result of adiabatic heating. As the temperatures rise, the gaseous contents of the bubble ignite with the bubble itself serving as its own combustion chamber. After ignition, this is the time in the bubble s life cycle where power is generated, and CO2, and NOx among other species, are produced. However, the pollutants CO2 and NOx are absorbed into the surrounding liquid. The importance of bubble combustion is that it generates power using a simple and compact device. We conducted a parametric study using CAVCHEM, a computational model developed at Glenn, that simulates the cavitational collapse of a single bubble in a liquid (water) and the subsequent combustion of the gaseous contents inside the bubble. The model solves the time-dependent, compressible Navier-Stokes equations in one-dimension with finite-rate chemical kinetics using the CHEMKIN package. Specifically, parameters such as frequency, pressure, bubble radius, and the equivalence ratio were varied while examining their effect on the maximum temperature, radius, and chemical species. These studies indicate that the radius of the bubble is perhaps the most critical parameter governing bubble combustion dynamics and its efficiency. Based on the results of the parametric studies, we plan on conducting experiments to study the effect of ultrasonic perturbations on the bubble generation process with respect to the bubble radius and size distribution.

Ray-based acoustic localization of cavitation in a highly reverberant environment.

PubMed

Chang, Natasha A; Dowling, David R

2009-05-01

Acoustic detection and localization of cavitation have inherent advantages over optical techniques because cavitation bubbles are natural sound sources, and acoustic transduction of cavitation sounds does not require optical access to the region of cavitating flow. In particular, near cavitation inception, cavitation bubbles may be visually small and occur infrequently, but may still emit audible sound pulses. In this investigation, direct-path acoustic recordings of cavitation events are made with 16 hydrophones mounted on the periphery of a water tunnel test section containing a low-cavitation-event-rate vortical flow. These recordings are used to localize the events in three dimensions via cross correlations to obtain arrival time differences. Here, bubble localization is hindered by reverberation, background noise, and the fact that both the pulse emission time and waveform are unknown. These hindrances are partially mitigated by a signal-processing scheme that incorporates straight-ray acoustic propagation and Monte-Carlo techniques for compensating ray-path, sound-speed, and hydrophone-location uncertainties. The acoustic localization results are compared to simultaneous optical localization results from dual-camera high-speed digital-video recordings. For 53 bubbles and a peak-signal to noise ratio frequency of 6.7 kHz, the root-mean-square spatial difference between optical and acoustic bubble location results was 1.94 cm. Parametric dependences in acoustic localization performance are also presented.

Oscillating microbubbles for selective particle sorting in acoustic microfluidic devices

NASA Astrophysics Data System (ADS)

Rogers, Priscilla; Xu, Lin; Neild, Adrian

2012-05-01

In this study, acoustic waves were used to excite a microbubble for selective particle trapping and sorting. Excitation of the bubble at its volume resonance, as necessary to drive strong fluid microstreaming, resulted in the particles being either selectively attracted to the bubble or continuing to follow the local microstreamlines. The operating principle exploited two acoustic phenomena acting on the particle suspension: the drag force arising from the acoustic microstreaming and the secondary Bjerknes force, i.e. the attractive radiation force produced between an oscillating bubble and a non-buoyant particle. It was also found that standing wave fields within the fluid chamber could be used to globally align bubbles and particles for local particle sorting by the bubble.

Laser irradiated fluorescent perfluorocarbon microparticles in 2-D and 3-D breast cancer cell models

NASA Astrophysics Data System (ADS)

Niu, Chengcheng; Wang, Long; Wang, Zhigang; Xu, Yan; Hu, Yihe; Peng, Qinghai

2017-03-01

Perfluorocarbon (PFC) droplets were studied as new generation ultrasound contrast agents via acoustic or optical droplet vaporization (ADV or ODV). Little is known about the ODV irradiated vaporization mechanisms of PFC-microparticle complexs and the stability of the new bubbles produced. In this study, fluorescent perfluorohexane (PFH) poly(lactic-co-glycolic acid) (PLGA) particles were used as a model to study the process of particle vaporization and bubble stability following excitation in two-dimensional (2-D) and three-dimensional (3-D) cell models. We observed localization of the fluorescent agent on the microparticle coating material initially and after vaporization under fluorescence microscopy. Furthermore, the stability and growth dynamics of the newly created bubbles were observed for 11 min following vaporization. The particles were co-cultured with 2-D cells to form 3-D spheroids and could be vaporized even when encapsulated within the spheroids via laser irradiation, which provides an effective basis for further work.

Radiation pressure injection in laser-wakefield acceleration

NASA Astrophysics Data System (ADS)

Liu, Y. L.; Kuramitsu, Y.; Isayama, S.; Chen, S. H.

2018-01-01

We investigated the injection of electrons in laser-wakefield acceleration induced by a self-modulated laser pulse by a two dimensional particle-in-cell simulation. The localized electric fields and magnetic fields are excited by the counter-streaming flows on the surface of the ion bubble, owing to the Weibel or two stream like instability. The electrons are injected into the ion bubble from the sides of it and then accelerated by the wakefield. Contrary to the conventional wave breaking model, the injection of monoenergetic electrons are mainly caused by the electromagnetic process. A simple model was proposed to address the instability, and the growth rate was verified numerically and theoretically.

The Mesoscale Ionospheric Simulation Testbed (MIST) Regional Data Assimilation Model (Invited)

NASA Astrophysics Data System (ADS)

Comberiate, J.; Kelly, M. A.; Miller, E.; Paxton, L.

2013-12-01

The Mesoscale Ionospheric Simulation Testbed (MIST) provides a regional nowcast and forecast of electron density values and has sufficient resolution to include equatorial plasma bubbles. The SSUSI instrument on the DMSP F18 satellite has high-resolution nightly observations of plasma bubbles at 8 PM local time throughout the current solar maximum. MIST can assimilate SSUSI UV observations, GPS TEC measurements, and SCINDA S4 readings simultaneously into a single scintillation map over a region of interest. MIST also models ionospheric physics to provide a short-term UHF scintillation forecast based on assimilated data. We will present examples of electron density and scintillation maps from MIST. We will also discuss the potential to predict scintillation occurrence up to 6 hours in advance using observations of the equatorial arcs from SSUSI observations at 5:30 PM local time on the DMSP F17 satellite.

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles

PubMed Central

Fernandez Rivas, David; Verhaagen, Bram; Seddon, James R. T.; Zijlstra, Aaldert G.; Jiang, Lei-Meng; van der Sluis, Luc W. M.; Versluis, Michel; Lohse, Detlef; Gardeniers, Han J. G. E.

2012-01-01

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip. PMID:23964308

Analysis of transitional separation bubbles on infinite swept wings

NASA Technical Reports Server (NTRS)

Davis, R. L.; Carter, J. E.

1986-01-01

A previously developed two-dimensional local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been extended for the calculation of transitional separation bubbles over infinite swept wings. As part of this effort, Roberts' empirical correlation, which is interpreted as a separated flow empirical extension of Mack's stability theory for attached flows, has been incorporated into the ALESEP procedure for the prediction of the transition location within the separation bubble. In addition, the viscous procedure used in the ALESEP techniques has been modified to allow for wall suction. A series of two-dimensional calculations is presented as a verification of the prediction capability of the interaction techniques with the Roberts' transition model. Numerical tests have shown that this two-dimensional natural transition correlation may also be applied to transitional separation bubbles over infinite swept wings. Results of the interaction procedure are compared with Horton's detailed experimental data for separated flow over a swept plate which demonstrates the accuracy of the present technique. Wall suction has been applied to a similar interaction calculation to demonstrate its effect on the separation bubble. The principal conclusion of this paper is that the prediction of transitional separation bubbles over two-dimensional or infinite swept geometries is now possible using the present interacting boundary layer approach.

Influence of cavitation bubble growth by rectified diffusion on cavitation-enhanced HIFU

NASA Astrophysics Data System (ADS)

Okita, Kohei; Sugiyama, Kazuyasu; Takagi, Shu; Matsumoto, Yoichiro

2017-11-01

Cavitation is becoming increasingly important in therapeutic ultrasound applications such as diagnostic, tumor ablation and lithotripsy. Mass transfer through gas-liquid interface due to rectified diffusion is important role in an initial stage of cavitation bubble growth. In the present study, influences of the rectified diffusion on cavitation-enhanced high-intensity focused ultrasound (HIFU) was investigated numerically. Firstly, the mass transfer rate of gas from the surrounding medium to the bubble was examined as function of the initial bubble radius and the driving pressure amplitude. As the result, the pressure required to bubble growth was decreases with increasing the initial bubble radius. Next, the cavitation-enhanced HIFU, which generates cavitation bubbles by high-intensity burst and induces the localized heating owing to cavitation bubble oscillation by low-intensity continuous waves, was reproduced by the present simulation. The heating region obtained by the simulation is agree to the treatment region of an in vitro experiment. Additionally, the simulation result shows that the localized heating is enhanced by the increase of the equilibrium bubble size due to the rectified diffusion. This work was supported by JSPS KAKENHI Grant Numbers JP26420125,JP17K06170.

Mechanical algal disruption for efficient biodiesel extraction

NASA Astrophysics Data System (ADS)

Krehbiel, Joel David

Biodiesel from algae provides several benefits over current biodiesel feedstocks, but the energy requirements of processing algae into a useable fuel are currently so high as to be prohibitive. One route to improving this is via disruption of the cells prior to lipid extraction, which can significantly increase energy recovery. Unfortunately, several obvious disruption techniques require more energy than can be gained. This dissertation examines the use of microbubbles to improve mechanical disruption of algal cells using experimental, theoretical, and computational methods. New laboratory experiments show that effective ultrasonic disruption of algae is achieved by adding microbubbles to an algal solution. The configuration studied flows the solution through a tube and insonifies a small section with a high-pressure ultrasound wave. Previous biomedical research has shown effective cell membrane damage on animal cells with similar methods, but the present research is the first to extend such study to algal cells. Results indicate that disruption increases with peak negative pressure between 1.90 and 3.07 MPa and with microbubble concentration up to 12.5 x 107 bubbles/ml. Energy estimates of this process suggest that it requires only one-fourth the currently most-efficient laboratory-scale disruption process. Estimates of the radius near each bubble that causes disruption (i.e. the disruption radius) suggest that it increases with peak negative pressure and is near 9--20 microm for all cases tested. It is anticipated that these procedures can be designed for better efficiency and efficacy, which will be facilitated by identifying the root mechanisms of the bubble-induced disruption. We therefore examine whether bubble expansion alone creates sufficient cell deformation for cell rupture. The spherically-symmetric Marmottant model for bubble dynamics allows estimation of the flow regime under experimental conditions. Bubble expansion is modeled as a point source of mass at the bubble center, and if the bubble-to-cell spacing is much larger than the cell radius, the flow around the cell is approximately extensional in the cell's frame of reference. It is known that the present algae are quasi-spherical with cytoplasmic viscosity approximately 100 times that of water, so the cell is approximated as a viscous sphere. Thus, conditions that cause cell disruption from an expanding microbubble are modeled as either steady inviscid extensional flow or steady point source flow over a viscous sphere. In the inviscid extensional flow model, the flow inside the sphere is dominated by viscous forces so the Stokes equation is solved with matched stresses at the sphere surface from the exterior inviscid extensional flow. The short-time deformation of the sphere surface suggests that inviscid extensional flow is insufficient to disrupt cells. This indicates that asymmetry of the flow over the sphere may be required to provide sufficient surface areal strain to rupture the cell. In a more detailed model, the bubble expansion is modeled as an expansion near a viscous sphere using finite element software. For conditions similar to those seen in the experiment, deformation shows similar scaling to disruption. The deformation in this model is significantly higher than predicted from the inviscid extensional flow model due to the effect of asymmetric flow on the cell membrane. Estimates suggest 21% average areal strain on the algal membrane is required to disrupt algal cells, and this result agrees well with areal strains typically required to disrupt cell membranes although the actual value would be lessened by the effect of an elastic membrane, which is neglected in the present model. The local areal strain on the sphere surface is a maximum closest to the point source, and there is compressive strain near theta = +/-pi/4 with theta the angle from the line between the cell center and the point source. The maximum local areal strain shows less sensitivity to the viscosity of the interior fluid than the average areal strain. Overall, the dissertation lays the groundwork for more efficient algal disruption through the judicious use of microbubbles. Separation of bubble generation and bubble growth provides the ability to improve the efficiency of each process and localize energy. Results suggest that effective disruption can occur by pulsing high-pressure ultrasound waves to a solution of cells co-suspended with microbubbles. The models are thought to represent basic phenomenological mechanisms of disruption that could be exploited to improve the overall energy efficiency of schemes. Analysis suggests that extensional flow alone cannot be the cause of cell disruption near an expanding microbubble. Additionally, this work provides an estimate of the areal strain required disrupt an algal cell membrane. This research suggests a couple routes toward reducing the energy required for production of algal biodiesel.

Stability, diffusion and interactions of nonlinear excitations in a many body system

NASA Astrophysics Data System (ADS)

Coste, Christophe; Jean, Michel Saint; Dessup, Tommy

2017-04-01

When repelling particles are confined in a quasi-one-dimensional trap by a transverse potential, a configurational phase transition happens. All particles are aligned along the trap axis at large confinement, but below a critical transverse confinement they adopt a staggered row configuration (zigzag phase). This zigzag transition is a subcritical pitchfork bifurcation in extended systems and in systems with cyclic boundary conditions in the longitudinal direction. Among many evidences, phase coexistence is exhibited by localized nonlinear patterns made of a zigzag phase embedded in otherwise aligned particles. We give the normal form at the bifurcation and we show that these patterns can be described as solitary wave envelopes that we call bubbles. They are stable in a large temperature range and can diffuse as quasi-particles, with a diffusion coefficient that may be deduced from the normal form. The potential energy of a bubble is found to be lower than that of the homogeneous bifurcated phase, which explains their stability. We observe also metastable states, that are pairs of solitary wave envelopes which spontaneously evolve toward a stable single bubble. We evidence a strong effect of the discreteness of the underlying particles system and introduce the concept of topological frustration of a bubble pair. A configuration is frustrated when the particles between the two bubbles are not organized in a modulated staggered row. For a nonfrustrated (NF) bubble pair configuration, the bubbles interaction is attractive so that the bubbles come closer and eventually merge as a single bubble. In contrast, the bubbles interaction is found to be repulsive for a frustrated (F) configuration. We describe a model of interacting solitary wave that provides all qualitative characteristics of the interaction force: it is attractive for NF-systems, repulsive for F-systems, and decreases exponentially with the bubbles distance.

The North Galactic Pole Rift and the Local Hot Bubble

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Puspitarini, L.

2015-01-01

The North Galactic Pole Rift (NGPR) is one of the few distinct neutral hydrogen clouds at high Galactic latitudes that have well-defined distances. It is located at the edge of the Local Cavity (LC) and provides an important test case for understanding the Local Hot Bubble (LHB), the presumed location for the hot diffuse plasma responsible for much of the observed 1/4 keV emission originating in the solar neighborhood. Using data from the ROSAT All- Sky Survey and the Planck reddening map, we find the path length within the LC (LHB plus Complex of Local Interstellar Clouds) to be 98 plus or minus 27 pc, in excellent agreement with the distance to the NGPR of 98 +/- 6 pc. In addition, we examine another 14 directions that are distributed over the sky where the LC wall is apparently optically thick at 1/4 keV. We find that the data in these directions are also consistent with the LHB model and a uniform emissivity plasma filling most of the LC.

JET TRAILS AND MACH CONES: THE INTERACTION OF MICROQUASARS WITH THE INTERSTELLAR MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, D.; Morsony, B.; Heinz, S.

2011-11-20

A subset of microquasars exhibits high peculiar velocity with respect to the local standard of rest due to the kicks they receive when being born in supernovae. The interaction between the radio plasma released by microquasar jets from such high-velocity binaries with the interstellar medium must lead to the production of trails and bow shocks similar to what is observed in narrow-angle tailed radio galaxies and pulsar wind nebulae. We present a set of numerical simulations of this interaction that illuminate the long-term dynamical evolution and the observational properties of these microquasar bow-shock nebulae and trails. We find that thismore » interaction always produces a structure that consists of a bow shock, a trailing neck, and an expanding bubble. Using our simulations to model emission, we predict that the shock surrounding the bubble and the neck should be visible in H{sub {alpha}} emission, the interior of the bubble should be visible in synchrotron radio emission, and only the bow shock is likely to be detectable in X-ray emission. We construct an analytic model for the evolution of the neck and bubble shape and compare this model with observations of the X-ray binary SAX J1712.6-3739.« less

XMM-Newton Observations of MBM 12: More Constraints on the Solar Wind Charge Exchange and Local Bubble Emissions

NASA Technical Reports Server (NTRS)

Koutroumpa, Dimitra; Smith, Randall K.; Edgar, Richard J.; Kuntz, Kip D.; Plucinsky, Paul P.; Snowden, Steven L.

2010-01-01

We present the first analysis of an XMM-Newton observation of the nearby molecular cloud MBM 12. We find that in the direction of MBM 12 the total O VII (0.57 keV) triplet emission is 1.8(+0.5/-0.6) photons/sq cm/s/sr (or Line Units - LU) while for the O VIII (0.65 keV) line emission we find a 3(sigma) upper limit of <1 LU. We also use a heliospheric model to calculate the O VII and O VIII emission generated by Solar Wind Charge-eXchange (SWCX) which we compare to the XMM-Newton observations. This comparison provides new constraints on the relative heliospheric and Local Bubble contributions to the local diffuse X-ray background. The heliospheric SWCX model predicts 0.82 LU for O VII, which accounts for approx. 46+/-15% of the observed value, and 0.33 LU for the O VIII line emission consistent with the XMM-Newton observed value. We discuss our results in combination with previous observations of the MBM 12 with CHANDRA and Suzaku.

Jet formation of SF6 bubble induced by incident and reflected shock waves

NASA Astrophysics Data System (ADS)

Zhu, Yuejin; Yu, Lei; Pan, Jianfeng; Pan, Zhenhua; Zhang, Penggang

2017-12-01

The computational results of two different cases on the evolution of the shock-SF6 heavy bubble interaction are presented. The shock focusing processes and jet formation mechanisms are analyzed by using the high resolution of computation schemes, and the influence of reflected shock waves is also investigated. It is concluded that there are two steps in the shock focusing process behind the incident shock wave, and the density and pressure values increase distinctly when the shock focusing process is completed. The local high pressure and vorticities in the vicinity of the downstream pole can propel the formation of the jet behind the incident shock wave. In addition, the gas is with the rightward velocity before the reflected shock wave impinges on the bubble; therefore, the evolutions of the waves and the bubble are more complicated when the reflected shock wave impinges on the SF6 bubble. Furthermore, the different end wall distances would affect the deformation degree of the bubble before the interaction of the reflected shock wave; therefore, the different left jet formation processes are found after the impingement of reflected shock waves when L = 27 mm. The local high pressure zones in the vicinity of the left bubble interface and the impingement of different shock waves can induce the local gas to shift the rightward velocity to the leftward velocity, which can further promote the formation of jets.

Effect of air bubble localization after transfer on embryo transfer outcomes.

PubMed

Tiras, Bulent; Korucuoglu, Umit; Polat, Mehtap; Saltik, Ayse; Zeyneloglu, Hulusi Bulent; Yarali, Hakan

2012-09-01

Our study aimed to provide information about the effects of air bubble localization after transfer on embryo transfer outcomes. Retrospective analysis of 7489 ultrasound-guided embryo transfers. Group 1 included 6631 embryo transfers in which no movement of the air bubbles was observed after transfer. Group 2 consisted of 407 embryo transfers in which the air bubbles moved towards the uterine fundus spontaneously, a little time after transfer. Group 3 included 370 embryo transfers in which the air bubbles moved towards the uterine fundus with ejection, immediately after transfer. Group 4 consisted of 81 embryo transfers in which the air bubbles moved towards the cervical canal. The four patient groups were different from one another with respect to positive pregnancy tests. Post hoc test revealed that this difference was between group 4 and other groups. An initial finding of our study was significantly decreased positive pregnancy test rates and clinical pregnancy rates with air bubbles moving towards the cervical canal after transfer. Although air bubbles moving towards the uterine fundus with ejection were associated with higher pregnancy rates, higher miscarriage rates and similar live birth rates were observed compared to air bubbles remaining stable after transfer. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Cluster Dynamics Modeling with Bubble Nucleation, Growth and Coalescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Almeida, Valmor F.; Blondel, Sophie; Bernholdt, David E.

The topic of this communication pertains to defect formation in irradiated solids such as plasma-facing tungsten submitted to helium implantation in fusion reactor com- ponents, and nuclear fuel (metal and oxides) submitted to volatile ssion product generation in nuclear reactors. The purpose of this progress report is to describe ef- forts towards addressing the prediction of long-time evolution of defects via continuum cluster dynamics simulation. The di culties are twofold. First, realistic, long-time dynamics in reactor conditions leads to a non-dilute di usion regime which is not accommodated by the prevailing dilute, stressless cluster dynamics theory. Second, long-time dynamics callsmore » for a large set of species (ideally an in nite set) to capture all possible emerging defects, and this represents a computational bottleneck. Extensions beyond the dilute limit is a signi cant undertaking since no model has been advanced to extend cluster dynamics to non-dilute, deformable conditions. Here our proposed approach to model the non-dilute limit is to monitor the appearance of a spatially localized void volume fraction in the solid matrix with a bell shape pro le and insert an explicit geometrical bubble onto the support of the bell function. The newly cre- ated internal moving boundary provides the means to account for the interfacial ux of mobile species into the bubble, and the growth of bubbles allows for coalescence phenomena which captures highly non-dilute interactions. We present a preliminary interfacial kinematic model with associated interfacial di usion transport to follow the evolution of the bubble in any number of spatial dimensions and any number of bubbles, which can be further extended to include a deformation theory. Finally we comment on a computational front-tracking method to be used in conjunction with conventional cluster dynamics simulations in the non-dilute model proposed.« less

Bubbles and denaturation in DNA

NASA Astrophysics Data System (ADS)

van Erp, T. S.; Cuesta-López, S.; Peyrard, M.

2006-08-01

The local opening of DNA is an intriguing phenomenon from a statistical-physics point of view, but is also essential for its biological function. For instance, the transcription and replication of our genetic code cannot take place without the unwinding of the DNA double helix. Although these biological processes are driven by proteins, there might well be a relation between these biological openings and the spontaneous bubble formation due to thermal fluctuations. Mesoscopic models, like the Peyrard-Bishop-Dauxois (PBD) model, have fairly accurately reproduced some experimental denaturation curves and the sharp phase transition in the thermodynamic limit. It is, hence, tempting to see whether these models could be used to predict the biological activity of DNA. In a previous study, we introduced a method that allows to obtain very accurate results on this subject, which showed that some previous claims in this direction, based on molecular-dynamics studies, were premature. This could either imply that the present PBD model should be improved or that biological activity can only be predicted in a more complex framework that involves interactions with proteins and super helical stresses. In this article, we give a detailed description of the statistical method introduced before. Moreover, for several DNA sequences, we give a thorough analysis of the bubble-statistics as a function of position and bubble size and the so-called l-denaturation curves that can be measured experimentally. These show that some important experimental observations are missing in the present model. We discuss how the present model could be improved.

Design of an Improved Heater Array to Measure Microscale Wall Heat Transfer

NASA Technical Reports Server (NTRS)

Kim, Jungho; Chng, Choon Ping; Kalkur, T. S.

1996-01-01

An improved array of microscale heaters is being developed to measure the heat transfer coefficient at many points underneath individual bubbles during boiling as a function of space and time. This heater array enables the local heat transfer from a surface during the bubble growth and departure process to be measured with very high temporal and spatial resolution, and should allow better understanding of the boiling heat transfer mechanisms by pin-pointing when and where in the bubble departure cycle large amounts of wall heat transfer occur. Such information can provide much needed data regarding the important heat transfer mechanisms during the bubble departure cycle, and can serve as benchmarks to validate many of the analytical and numerical models used to simulate boiling. The improvements to the heater array include using a silicon-on-quartz substrate to reduce thermal cross-talk between the heaters, decreased space between the heaters, increased pad sizes on the heaters, and progressive heater sizes. Some results using the present heater array are discussed.

New impact sensitivity test of liquid explosives

NASA Astrophysics Data System (ADS)

Tiutiaev, Andrei; Trebunskih, Valeri

The sensitivity of liquid explosive in the presence of gas bubbles increases many times as compared with the liquid without gas bubbles. Local hot spot in this case formed as a result of compression and heating of the gas inside the bubbles. If we consider that in the liquid as a result of convection, wave motion, shock, etc. gas bubbles are easily generated, the need to develop a method for determining sensitivity of liquid explosives to impact and a detailed study of the ignition explosives with bubbles is obvious. On a mathematical model of a single steam bubbles in the fluid theoretically considered the process of initiating explosive liquid systems to impact. For the experimental investigation, the well-known K-44 -II with the metal cap were used. Instead of the metal cap in the standard method in this paper there was polyurethane foam cylindrical container with LHE, which is easily deforms by impact. A large number of tests with different liquid explosives were made. It was found that the test LHE to impact with polyurethane foam to a large extent reflect the real mechanical sensitivity due to the small loss of impact energy on the deformation of the metal cap, as well as the best differentiation LHE sensitivity due to the higher resolution method . Results obtained in the samara state technical university.

Impurity bubbles in a BEC

NASA Astrophysics Data System (ADS)

Timmermans, Eddy; Blinova, Alina; Boshier, Malcolm

2013-05-01

Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. This work was funded by the Los Alamos LDRD program.

ALESEP. Part 2: A computer program for the analysis of leading edge separation bubbles on infinite swept wings

NASA Technical Reports Server (NTRS)

Davis, R. L.

1986-01-01

A program called ALESEP is presented for the analysis of the inviscid-viscous interaction which occurs due to the presence of a closed laminar-transitional separation bubble on an airfoil or infinite swept wing. The ALESEP code provides an iterative solution of the boundary layer equations expressed in an inverse formulation coupled to a Cauchy integral representation of the inviscid flow. This interaction analysis is treated as a local perturbation to a known solution obtained from a global airfoil analysis; hence, part of the required input to the ALESEP code are the reference displacement thickness and tangential velocity distributions. Special windward differencing may be used in the reversed flow regions of the separation bubble to accurately account for the flow direction in the discretization of the streamwise convection of momentum. The ALESEP code contains a forced transition model based on a streamwise intermittency function, a natural transition model based on a solution of the integral form of the turbulent kinetic energy equation, and an empirical natural transition model.

Modeling quiescent phase transport of air bubbles induced by breaking waves

NASA Astrophysics Data System (ADS)

Shi, Fengyan; Kirby, James T.; Ma, Gangfeng

Simultaneous modeling of both the acoustic phase and quiescent phase of breaking wave-induced air bubbles involves a large range of length scales from microns to meters and time scales from milliseconds to seconds, and thus is computational unaffordable in a surfzone-scale computational domain. In this study, we use an air bubble entrainment formula in a two-fluid model to predict air bubble evolution in the quiescent phase in a breaking wave event. The breaking wave-induced air bubble entrainment is formulated by connecting the shear production at the air-water interface and the bubble number intensity with a certain bubble size spectra observed in laboratory experiments. A two-fluid model is developed based on the partial differential equations of the gas-liquid mixture phase and the continuum bubble phase, which has multiple size bubble groups representing a polydisperse bubble population. An enhanced 2-DV VOF (Volume of Fluid) model with a k - ɛ turbulence closure is used to model the mixture phase. The bubble phase is governed by the advection-diffusion equations of the gas molar concentration and bubble intensity for groups of bubbles with different sizes. The model is used to simulate air bubble plumes measured in laboratory experiments. Numerical results indicate that, with an appropriate parameter in the air entrainment formula, the model is able to predict the main features of bubbly flows as evidenced by reasonable agreement with measured void fraction. Bubbles larger than an intermediate radius of O(1 mm) make a major contribution to void fraction in the near-crest region. Smaller bubbles tend to penetrate deeper and stay longer in the water column, resulting in significant contribution to the cross-sectional area of the bubble cloud. An underprediction of void fraction is found at the beginning of wave breaking when large air pockets take place. The core region of high void fraction predicted by the model is dislocated due to use of the shear production in the algorithm for initial bubble entrainment. The study demonstrates a potential use of an entrainment formula in simulations of air bubble population in a surfzone-scale domain. It also reveals some difficulties in use of the two-fluid model for predicting large air pockets induced by wave breaking, and suggests that it may be necessary to use a gas-liquid two-phase model as the basic model framework for the mixture phase and to develop an algorithm to allow for transfer of discrete air pockets to the continuum bubble phase. A more theoretically justifiable air entrainment formulation should be developed.

Bubble-based acoustic radiation force using chirp insonation to reduce standing wave effects.

PubMed

Erpelding, Todd N; Hollman, Kyle W; O'Donnell, Matthew

2007-02-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young's modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200 and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size.

Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects

PubMed Central

Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

2007-01-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

Impact of methane flow through deformable lake sediments on atmospheric release

NASA Astrophysics Data System (ADS)

Scandella, B.; Juanes, R.

2010-12-01

Methane is a potent greenhouse gas that is generated geothermally and biologically in lake and ocean sediments. Free gas bubbles may escape oxidative traps and contribute more to the atmospheric source than dissolved methane, but the details of the methane release depend on the interactions between the multiple fluid phases and the deformable porous medium. We present a model and supporting laboratory experiments of methane release through “breathing” dynamic flow conduits that open in response to drops in the hydrostatic load on lake sediments, which has been validated against a high-resolution record of free gas flux and hydrostatic pressure in Upper Mystic Lake, MA. In contrast to previous linear elastic fracture mechanics analysis of gassy sediments, the evolution of gas transport in a deformable compliant sediment is presented within the framework of multiphase poroplasticity. Experiments address how strongly the mode and rate of gas flow, captured by our model, impacts the size of bubbles released into the water column. A bubble's size in turn determines how efficiently it transports methane to the atmosphere, and integrating this effect will be critical to improving estimates of the atmospheric methane source from lakes. Cross-sectional schematic of lake sediments showing two venting sites: one open at left and one closed at right. The vertical release of gas bubbles (red) at the open venting site creates a local pressure drop, which drives both bubble formation from the methane-rich pore water (higher concentrations shaded darker red) and lateral advection of dissolved methane (purple arrows). Even as bubbles in the open site escape, those at the closed site remain trapped.

Bubble induced flow field modulation for pool boiling enhancement over a tubular surface

NASA Astrophysics Data System (ADS)

Raghupathi, P. A.; Joshi, I. M.; Jaikumar, A.; Emery, T. S.; Kandlikar, S. G.

2017-06-01

We demonstrate the efficacy of using a strategically placed enhancement feature to modify the trajectory of bubbles nucleating on a horizontal tubular surface to increase both the critical heat flux (CHF) and the heat transfer coefficient (HTC). The CHF on a plain tube is shown to be triggered by a local dryout at the bottom of the tube due to vapor agglomeration. To mitigate this effect and delay CHF, the nucleating bubble trajectory is modified by incorporating a bubble diverter placed axially at the bottom of the tube. The nucleating bubble at the base of the diverter experiences a tangential evaporation momentum force (EMF) which causes the bubble to grow sideways away from the tube and avoid localized bubble patches that are responsible for CHF initiation. High speed imaging confirmed the lateral displacement of the bubbles away from the diverter closely matched with the theoretical predictions using EMF and buoyancy forces. Since the EMF is stronger at higher heat fluxes, bubble displacement increases with heat flux and results in the formation of separate liquid-vapor pathways wherein the liquid enters almost unobstructed at the bottom and the vapor bubble leaves sideways. Experimental results yielded CHF and HTC enhancements of ˜60% and ˜75%, respectively, with the diverter configuration when compared to a plain tube. This work can be used for guidance in developing enhancement strategies to effectively modulate the liquid-vapor flow around the heater surface at various locations to enhance HTC and CHF.

Evaluation of stability and size distribution of sunflower oil-coated micro bubbles for localized drug delivery.

PubMed

Filho, Walter Duarte de Araujo; Schneider, Fábio Kurt; Morales, Rigoberto E M

2012-09-20

Micro bubbles were initially introduced as contrast agents for ultrasound examinations as they are able to modify the signal-to-noise ratio in imaging, thus improving the assessment of clinical information on human tissue. Recent developments have demonstrated the feasibility of using these bubbles as drug carriers in localized delivery. In micro fluidics devices for generation of micro bubbles, the bubbles are formed at interface of liquid gas through a strangulation process. A device that uses these features can produce micro bubbles with small size dispersion in a single step. A T-junction micro fluidic device constructed using 3D prototyping was made for the production of mono dispersed micro bubbles. These micro bubbles use sunflower oil as a lipid layer. Stability studies for micro bubbles with diameters different generated from a liquid phase of the same viscosity were conducted to evaluate whether micro bubbles can be used as drug carriers. The biocompatibility of coating layer, the ability to withstand environmental pressure variations combined with echogenicity, are key factors that they can safely play the role of drug transporters. The normal distribution curve with small dispersion of the diameter of bubbles validates the process of generating micro bubbles with low value of variation coefficient, i.e., 0.381 at 1.90%. The results also showed the feasibility of using sunflower oil as the lipid matrix with stable population of bubbles over 217 minutes for micro bubbles with an average diameter of 313.04 μm and 121 minutes for micro bubbles with an average diameter of 73.74 μm, considering bubbles with air as gaseous phase. The results indicate that the micro fluidic device designed can be used for producing micro bubbles with low variation coefficient using sunflower oil as a coating of micro bubbles. These carriers were stable for periods of time that are long enough for clinical applications even when regular air is used as the gas phase. Improved stability can be achieved when biocompatible gas with lower permeability is used.

Localized and delocalized motion of colloidal particles on a magnetic bubble lattice.

PubMed

Tierno, Pietro; Johansen, Tom H; Fischer, Thomas M

2007-07-20

We study the motion of paramagnetic colloidal particles placed above magnetic bubble domains of a uniaxial garnet film and driven through the lattice by external magnetic field modulation. An external tunable precessing field propels the particles either in localized orbits around the bubbles or in superdiffusive or ballistic motion through the bubble array. This motion results from the interplay between the driving rotating signal, the viscous drag force and the periodic magnetic energy landscape. We explain the transition in terms of the incommensurability between the transit frequency of the particle through a unit cell and the modulation frequency. Ballistic motion dynamically breaks the symmetry of the array and the phase locked particles follow one of the six crystal directions.

First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All-Sky Airglow Imager and GNSS Receivers

NASA Astrophysics Data System (ADS)

Okoh, Daniel; Rabiu, Babatunde; Shiokawa, Kazuo; Otsuka, Yuichi; Segun, Bolaji; Falayi, Elijah; Onwuneme, Sylvester; Kaka, Rafiat

2017-12-01

This is the first paper that reports the occurrence frequency of equatorial plasma bubbles and their dependences of local time, season, and geomagnetic activity based on airglow imaging observations at West Africa. The all-sky imager, situated in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S), has a 180° fisheye view covering almost the entire airspace of Nigeria. Plasma bubbles are observed for 70 nights of the 147 clear-sky nights from 9 June 2015 to 31 January 2017. Differences between nighttime and daytime ROTIs were also computed as a proxy of plasma bubbles using Global Navigation Satellite Systems (GNSS) receivers within the coverage of the all-sky imager. Most plasma bubble occurrences are found during equinoxes and least occurrences during solstices. The occurrence rate of plasma bubbles was highest around local midnight and lower for hours farther away. Most of the postmidnight plasma bubbles were observed around the months of December to March, a period that coincides with the harmattan period in Nigeria. The on/off status of plasma bubble in airglow and GNSS observations were in agreement for 67.2% of the total 768 h, while we suggest several reasons responsible for the remaining 32.8% when the airglow and GNSS bubble status are inconsistent. A majority of the plasma bubbles were observed under relatively quiet geomagnetic conditions (Dst ≥ -40 and Kp ≤ 3), but there was no significant pattern observed in the occurrence rate of plasma bubbles as a function of geomagnetic activity. We suggest that geomagnetic activities could have either suppressed or promoted the occurrence of plasma bubbles.

A Microfluidic System with Surface Patterning for Investigating Cavitation Bubble(s)-Cell Interaction and the Resultant Bioeffects at the Single-cell Level.

PubMed

Li, Fenfang; Yuan, Fang; Sankin, Georgy; Yang, Chen; Zhong, Pei

2017-01-10

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass substrate, that precisely controls the generation of tandem bubbles and individual cells patterned nearby with well-defined locations and shapes. We then demonstrate the generation of tandem bubbles by using two pulsed lasers illuminating a pair of gold dots with a few-microsecond time delay. We visualize the bubble-bubble interaction and jet formation by high-speed imaging and characterize the resultant flow field using particle image velocimetry (PIV). Finally, we present some applications of this technique for single cell analysis, including cell membrane poration with macromolecule uptake, localized membrane deformation determined by the displacements of attached integrin-binding beads, and intracellular calcium response from ratiometric imaging. Our results show that a fast and directional jetting flow is produced by the tandem bubble interaction, which can impose a highly localized shear stress on the surface of a cell grown in close proximity. Furthermore, different bioeffects can be induced by altering the strength of the jetting flow by adjusting the standoff distance from the cell to the tandem bubbles.

Raman Spectral Band Oscillations in Large Graphene Bubbles

NASA Astrophysics Data System (ADS)

Huang, Yuan; Wang, Xiao; Zhang, Xu; Chen, Xianjue; Li, Baowen; Wang, Bin; Huang, Ming; Zhu, Chongyang; Zhang, Xuewei; Bacsa, Wolfgang S.; Ding, Feng; Ruoff, Rodney S.

2018-05-01

Raman spectra of large graphene bubbles showed size-dependent oscillations in spectral intensity and frequency, which originate from optical standing waves formed in the vicinity of the graphene surface. At a high laser power, local heating can lead to oscillations in the Raman frequency and also create a temperature gradient in the bubble. Based on Raman data, the temperature distribution within the graphene bubble was calculated, and it is shown that the heating effect of the laser is reduced when moving from the center of a bubble to its edge. By studying graphene bubbles, both the thermal conductivity and chemical reactivity of graphene were assessed. When exposed to hydrogen plasma, areas with bubbles are found to be more reactive than flat graphene.

A Mechanistic Study of Nucleate Boiling Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Dhir, V. K.; Warrier, G. R.; Hasan, M. M.

2002-01-01

The overall objective of this work is to study nucleate boiling heat transfer under microgravity conditions in such a way that while providing basic knowledge of the phenomena, it also leads to development of simulation models and correlations that can be used as design tools for a wide range of gravity levels. In the study a building block type of approach is used and both pool and low velocity flow boiling are investigated. Starting with experiments using a single bubble, the complexity of the experiments is increased to two or three inline bubbles, to five bubbles placed on a two-dimensional grid. Finally, experiments are conducted where a large number of prescribed cavities nucleate on the heater and when a commercial surface is used. So far experiments have been conducted at earth normal gravity and in the reduced gravity environment of the KC-135 aircraft whereas experiments on the space station are planned. Modeling/complete numerical simulation of the boiling process is an integral part of the total effort. Experiments conducted with single bubbles formed on a nucleation site microfabricated on a polished silicon wafer show that for gravity levels (g) varying from 1.5g(sub e) to 0.01g(sub e), the bubble diameter at departure varies approximately as (g(sub e)/g)(exp 1/2) and the growth period as (g(sub e)/g). When bubbles merge either inline or in a plane, the bubble diameter at departure is found to be smaller than that obtained for a single bubble and shows a weaker dependence on the level of gravity. The possible reason is that as the bubbles merge they create fluid circulation around the bubbles, which in turn induces a lift force that is responsible for the earlier departure of the bubbles. The verification of this proposition is being sought through numerical simulations. There is a merger of two inline, three inline, and several bubbles in a plane in the low gravity environment of the KC-135 aircraft. After merger and before departure, a mushroom type of bubble with several stems attached to the heater surface is clearly evident. Local heat fluxes during growth and departure of a single bubble were also measured. It was found that during most of the growth period of the bubble, generally the wall heat flux decreased with time because of the increased dry area under the bubble. However, the heat flux increased rapidly just prior to departure of the bubble because of the transient conduction into the cold liquid rushing to fill the space vacated by the bubble as the bubble base shrinks. The measured heat fluxes at various radial locations are found to be in qualitative agreement with the numerical predictions. Single bubble studies at earth normal gravity have also been performed on surfaces oriented at different angles to the gravitational acceleration with flow parallel to the surface. It is found that in all cases the bubbles slide along the surface before lift-off from the surface. The lift force generated as a result of the relative motion between the sliding bubbles and the imposed flow is found to play an important role when the normal force due to buoyancy is reduced. An experimental apparatus for the study of the bubble behavior with imposed flow under reduced gravity conditions has been developed and will soon be employed for experiments in the KC-135 aircraft.

Gas exchange in the ice zone: the role of small waves and big animals

NASA Astrophysics Data System (ADS)

Loose, B.; Takahashi, A.; Bigdeli, A.

2016-12-01

The balance of air-sea gas exchange and net biological carbon fixation determine the transport and transformation of carbon dioxide and methane in the ocean. Air-sea gas exchange is mostly driven by upper ocean physics, but biology can also play a role. In the open ocean, gas exchange increases proportionate to the square of wind speed. When sea ice is present, this dependence breaks down in part because breaking waves and air bubble entrainment are damped out by interactions between sea ice and the wave field. At the same time, sea ice motions, formation, melt, and even sea ice-associated organisms can act to introduce turbulence and air bubbles into the upper ocean, thereby enhancing air-sea gas exchange. We take advantage of the knowledge advances of upper ocean physics including bubble dynamics to formulate a model for air-sea gas exchange in the sea ice zone. Here, we use the model to examine the role of small-scale waves and diving animals that trap air for insulation, including penguins, seals and polar bears. We compare these processes to existing parameterizations of wave and bubble dynamics in the open ocean, to observe how sea ice both mitigates and locally enhances air-sea gas transfer.

Potential Flow Model for Compressible Stratified Rayleigh-Taylor Instability

NASA Astrophysics Data System (ADS)

Rydquist, Grant; Reckinger, Scott; Owkes, Mark; Wieland, Scott

2017-11-01

The Rayleigh-Taylor Instability (RTI) is an instability that occurs when a heavy fluid lies on top of a lighter fluid in a gravitational field, or a gravity-like acceleration. It occurs in many fluid flows of a highly compressive nature. In this study potential flow analysis (PFA) is used to model the early stages of RTI growth for compressible fluids. In the localized region near the bubble tip, the effects of vorticity are negligible, so PFA is applicable, as opposed to later stages where the induced velocity due to vortices generated from the growth of the instability dominate the flow. The incompressible PFA is extended for compressibility effects by applying the growth rate and the associated perturbation spatial decay from compressible linear stability theory. The PFA model predicts theoretical values for a bubble terminal velocity for single-mode compressible RTI, dependent upon the Atwood (A) and Mach (M) numbers, which is a parameter that measures both the strength of the stratification and intrinsic compressibility. The theoretical bubble terminal velocities are compared against numerical simulations. The PFA model correctly predicts the M dependence at high A, but the model must be further extended to include additional physics to capture the behavior at low A. Undergraduate Scholars Program - Montana State University.

Electron Bubbles in Superfluid (3) 3 He-A: Exploring the Quasiparticle-Ion Interaction

NASA Astrophysics Data System (ADS)

Shevtsov, Oleksii; Sauls, J. A.

2017-06-01

When an electron is forced into liquid ^3He, it forms an "electron bubble", a heavy ion with radius, R˜eq 1.5 nm, and mass, M˜eq 100 m_3, where m_3 is the mass of a ^3He atom. These negative ions have proven to be powerful local probes of the physical properties of the host quantum fluid, especially the excitation spectra of the superfluid phases. We recently developed a theory for Bogoliubov quasiparticles scattering off electron bubbles embedded in a chiral superfluid that provides a detailed understanding of the spectrum of Weyl Fermions bound to the negative ion, as well as a theory for the forces on moving electron bubbles in superfluid ^3He-A (Shevtsov and Sauls in Phys Rev B 94:064511, 2016). This theory is shown to provide quantitative agreement with measurements reported by the RIKEN group (Ikegami et al. in Science 341(6141):59, 2013) for the drag force and anomalous Hall effect of moving electron bubbles in superfluid ^3He-A. In this report, we discuss the sensitivity of the forces on the moving ion to the effective interaction between normal-state quasiparticles and the ion. We consider models for the quasiparticle-ion (QP-ion) interaction, including the hard-sphere potential, constrained random-phase-shifts, and interactions with short-range repulsion and intermediate-range attraction. Our results show that the transverse force responsible for the anomalous Hall effect is particularly sensitive to the structure of the QP-ion potential and that strong short-range repulsion, captured by the hard-sphere potential, provides an accurate model for computing the forces acting on the moving electron bubble in superfluid 3He-A.

The excitation and characteristic frequency of the long-period volcanic event: An approach based on an inhomogeneous autoregressive model of a linear dynamic system

USGS Publications Warehouse

Nakano, M.; Kumagai, H.; Kumazawa, M.; Yamaoka, K.; Chouet, B.A.

1998-01-01

We present a method to quantify the source excitation function and characteristic frequencies of long-period volcanic events. The method is based on an inhomogeneous autoregressive (AR) model of a linear dynamic system, in which the excitation is assumed to be a time-localized function applied at the beginning of the event. The tail of an exponentially decaying harmonic waveform is used to determine the characteristic complex frequencies of the event by the Sompi method. The excitation function is then derived by operating an AR filter constructed from the characteristic frequencies to the entire seismogram of the event, including the inhomogeneous part of the signal. We apply this method to three long-period events at Kusatsu-Shirane Volcano, central Japan, whose waveforms display simple decaying monochromatic oscillations except for the beginning of the events. We recover time-localized excitation functions lasting roughly 1 s at the start of each event and find that the estimated functions are very similar to each other at all the stations of the seismic network for each event. The phases of the characteristic oscillations referred to the estimated excitation function fall within a narrow range for almost all the stations. These results strongly suggest that the excitation and mode of oscillation are both dominated by volumetric change components. Each excitation function starts with a pronounced dilatation consistent with a sudden deflation of the volumetric source which may be interpreted in terms of a choked-flow transport mechanism. The frequency and Q of the characteristic oscillation both display a temporal evolution from event to event. Assuming a crack filled with bubbly water as seismic source for these events, we apply the Van Wijngaarden-Papanicolaou model to estimate the acoustic properties of the bubbly liquid and find that the observed changes in the frequencies and Q are consistently explained by a temporal change in the radii of the bubbles characterizing the bubbly water in the crack.

A computationally efficient modelling of laminar separation bubbles

NASA Technical Reports Server (NTRS)

Dini, Paolo; Maughmer, Mark D.

1989-01-01

The goal is to accurately predict the characteristics of the laminar separation bubble and its effects on airfoil performance. Toward this end, a computational model of the separation bubble was developed and incorporated into the Eppler and Somers airfoil design and analysis program. Thus far, the focus of the research was limited to the development of a model which can accurately predict situations in which the interaction between the bubble and the inviscid velocity distribution is weak, the so-called short bubble. A summary of the research performed in the past nine months is presented. The bubble model in its present form is then described. Lastly, the performance of this model in predicting bubble characteristics is shown for a few cases.

A combined three-dimensional in vitro–in silico approach to modelling bubble dynamics in decompression sickness

PubMed Central

Stride, E.; Cheema, U.

2017-01-01

The growth of bubbles within the body is widely believed to be the cause of decompression sickness (DCS). Dive computer algorithms that aim to prevent DCS by mathematically modelling bubble dynamics and tissue gas kinetics are challenging to validate. This is due to lack of understanding regarding the mechanism(s) leading from bubble formation to DCS. In this work, a biomimetic in vitro tissue phantom and a three-dimensional computational model, comprising a hyperelastic strain-energy density function to model tissue elasticity, were combined to investigate key areas of bubble dynamics. A sensitivity analysis indicated that the diffusion coefficient was the most influential material parameter. Comparison of computational and experimental data revealed the bubble surface's diffusion coefficient to be 30 times smaller than that in the bulk tissue and dependent on the bubble's surface area. The initial size, size distribution and proximity of bubbles within the tissue phantom were also shown to influence their subsequent dynamics highlighting the importance of modelling bubble nucleation and bubble–bubble interactions in order to develop more accurate dive algorithms. PMID:29263127

A Microfluidic System with Surface Patterning for Investigating Cavitation Bubble(s)-Cell Interaction and the Resultant Bioeffects at the Single-Cell Level

PubMed Central

Li, Fenfang; Yuan, Fang; Sankin, Georgy; Yang, Chen; Zhong, Pei

2017-01-01

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass substrate that precisely controls the generation of tandem bubbles and individual cells patterned nearby with well-defined locations and shapes. We then demonstrate the generation of tandem bubbles by using two pulsed lasers illuminating a pair of gold dots with a few-microsecond time delay. We visualize the bubble-bubble interaction and jet formation by high-speed imaging and characterize the resultant flow field using particle image velocimetry (PIV). Finally, we present some applications of this technique for single cell analysis, including cell membrane poration with macromolecule uptake, localized membrane deformation determined by the displacements of attached integrin-binding beads, and intracellular calcium response from ratiometric imaging. Our results show that a fast and directional jetting flow is produced by the tandem bubble interaction, which can impose a highly-localized shear stress on the surface of a cell grown in close proximity. Furthermore, different bioeffects can be induced by altering the strength of the jetting flow by adjusting the standoff distance from the cell to the tandem bubbles. PMID:28117807

Collective organization in aerotactic motion

NASA Astrophysics Data System (ADS)

Mazza, Marco G.

Some bacteria exhibit interesting behavior in the presence of an oxygen concentration. They perform an aerotactic motion along the gradient until they reach their optimal oxygen concentration. But they often organize collectively by forming dense regions, called 'bands', that travel towards the oxygen source. We have developed a model of swimmers with stochastic interaction rules moving in proximity of an air bubble. We perform molecular dynamics simulations and also solve advection-diffusion equations that reproduce the aerotactic behavior of mono-flagellated, facultative anaerobic bacteria. If the oxygen concentration in the system sinks locally below a threshold value, the formation of a migrating aerotactic band toward the bubble can be observed.

On the effect of irradiation-induced resolution in modelling fission gas release in UO2 LWR fuel

NASA Astrophysics Data System (ADS)

Lösönen, Pekka

2017-12-01

Irradiation resolution of gas atoms and vacancies from intra- and intergranular bubbles in sintered UO2 fuel was studied by comparing macroscopic models with a more mechanistic approach. The applied macroscopic models imply the resolution rate of gas atoms to be proportional to gas concentration in intragranular bubbles and at grain boundary (including intergranular bubbles). A relation was established between the macroscopic models and a single encounter of an energetic fission fragment with a bubble. The effect of bubble size on resolution was quantified. The number of resoluted gas atoms per encounter of a fission fragment per bubble was of the same order of magnitude for intra- and intergranular bubbles. However, the resulting macroscopic resolution rate of gas atoms was about two orders of magnitude larger from intragranular bubbles. The number of vacancies resoluted from a grain face bubble by a passing fission fragment was calculated. The obtained correlations for resolution of gas atoms from intragranular bubbles and grain boundaries and for resolution of vacancies from grain face bubbles were used to demonstrate the effect of irradiation resolution on fission gas release.

The rheology of three-phase suspensions at low bubble capillary number

PubMed Central

Truby, J. M.; Mueller, S. P.; Llewellin, E. W.; Mader, H. M.

2015-01-01

We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an ‘effective-medium’ approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0≤ϕp≲0.5) and bubble volume fraction (0≤ϕb≲0.3). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases. PMID:25568617

Photothermally controlled Marangoni flow around a micro bubble

NASA Astrophysics Data System (ADS)

Namura, Kyoko; Nakajima, Kaoru; Kimura, Kenji; Suzuki, Motofumi

2015-01-01

We have experimentally investigated the control of Marangoni flow around a micro bubble using photothermal conversion. Using a focused laser spot acting as a highly localized heat source on Au nanoparticles/dielectric/Ag mirror thin film enables us to create a micro bubble and to control the temperature gradient around the bubble at a micrometer scale. When we irradiate the laser next to the bubble, a strong main flow towards the bubble and two symmetric rotation flows on either side of it develop. The shape of this rotation flow shows a significant transformation depending on the relative position of the bubble and the laser spot. Using this controllable rotation flow, we have demonstrated sorting of the polystyrene spheres with diameters of 2 μm and 0.75 μm according to their size.

Modelling of Dispersed Gas-Liquid Flow using LBGK and LPT Approach

NASA Astrophysics Data System (ADS)

Agarwal, Alankar; Prakash, Akshay; Ravindra, B.

2017-11-01

The dynamics of gas bubbles play a significant, if not crucial, role in a large variety of industrial process that involves using reactors. Many of these processes are still not well understood in terms of optimal scale-up strategies.An accurate modeling of bubbles and bubble swarms become important for high fidelity bioreactor simulations. This study is a part of the development of robust bubble fluid interaction modules for simulation of industrial-scale reactors. The work presents the simulation of a single bubble rising in a quiescent water tank using current models presented in the literature for bubble-fluid interaction. In this multiphase benchmark problem, the continuous phase (water) is discretized using the Lattice Bhatnagar-Gross and Krook (LBGK) model of Lattice Boltzmann Method (LBM), while the dispersed gas phase (i.e. air-bubble) modeled with the Lagrangian particle tracking (LPT) approach. The cheap clipped fourth order polynomial function is used to model the interaction between two phases. The model is validated by comparing the simulation results for terminal velocity of a bubble at varying bubble diameter and the influence of bubble motion in liquid velocity with the theoretical and previously available experimental data. This work is supported by the ``Centre for Development of Advanced Computing (C-DAC), Pune'' by providing the advanced computational facility in PARAM Yuva-II.

Visualizing the Histotripsy Process: Bubble Cloud-Cancer Cell Interactions in a Tissue-Mimicking Environment.

PubMed

Vlaisavljevich, Eli; Maxwell, Adam; Mancia, Lauren; Johnsen, Eric; Cain, Charles; Xu, Zhen

2016-10-01

Histotripsy is a non-invasive ultrasonic ablation method that uses cavitation to mechanically fractionate tissue into acellular debris. With a sufficient number of pulses, histotripsy can completely fractionate tissue into a liquid-appearing homogenate with no cellular structures. The location, shape and size of lesion formation closely match those of the cavitation cloud. Previous work has led to the hypothesis that the rapid expansion and collapse of histotripsy bubbles fractionate tissue by inducing large stress and strain on the tissue structures immediately adjacent to the bubbles. In the work described here, the histotripsy bulk tissue fractionation process is visualized at the cellular level for the first time using a custom-built 2-MHz transducer incorporated into a microscope stage. A layer of breast cancer cells were cultured within an optically transparent fibrin-based gel phantom to mimic cells inside a 3-D extracellular matrix. To test the hypothesis, the cellular response to single and multiple histotripsy pulses was investigated using high-speed optical imaging. Bubbles were always generated in the extracellular space, and significant cell displacement/deformation was observed for cells directly adjacent to the bubble during both bubble expansion and collapse. The largest displacements were observed during collapse for cells immediately adjacent to the bubble, with cells moving more than 150-300 μm in less than 100 μs. Cells often underwent multiple large deformations (>150% strain) over multiple pulses, resulting in the bisection of cells multiple times before complete removal. To provide theoretical support to the experimental observations, a numerical simulation was conducted using a single-bubble model, which indicated that histotripsy exerts the largest strains and cell displacements in the regions immediately adjacent to the bubble. The experimental and simulation results support our hypothesis, which helps to explain the formation of the sharp lesions formed in histotripsy therapy localized to the regions directly exposed to the bubbles. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

A Generalized Eulerian-Lagrangian Analysis, with Application to Liquid Flows with Vapor Bubbles

NASA Technical Reports Server (NTRS)

Dejong, Frederik J.; Meyyappan, Meyya

1993-01-01

Under a NASA MSFC SBIR Phase 2 effort an analysis has been developed for liquid flows with vapor bubbles such as those in liquid rocket engine components. The analysis is based on a combined Eulerian-Lagrangian technique, in which Eulerian conservation equations are solved for the liquid phase, while Lagrangian equations of motion are integrated in computational coordinates for the vapor phase. The novel aspect of the Lagrangian analysis developed under this effort is that it combines features of the so-called particle distribution approach with those of the so-called particle trajectory approach and can, in fact, be considered as a generalization of both of those traditional methods. The result of this generalization is a reduction in CPU time and memory requirements. Particle time step (stability) limitations have been eliminated by semi-implicit integration of the particle equations of motion (and, for certain applications, the particle temperature equation), although practical limitations remain in effect for reasons of accuracy. The analysis has been applied to the simulation of cavitating flow through a single-bladed section of a labyrinth seal. Models for the simulation of bubble formation and growth have been included, as well as models for bubble drag and heat transfer. The results indicate that bubble formation is more or less 'explosive'. for a given flow field, the number density of bubble nucleation sites is very sensitive to the vapor properties and the surface tension. The bubble motion, on the other hand, is much less sensitive to the properties, but is affected strongly by the local pressure gradients in the flow field. In situations where either the material properties or the flow field are not known with sufficient accuracy, parametric studies can be carried out rapidly to assess the effect of the important variables. Future work will include application of the analysis to cavitation in inducer flow fields.

Convective mass transfer around a dissolving bubble

NASA Astrophysics Data System (ADS)

Duplat, Jerome; Grandemange, Mathieu; Poulain, Cedric

2017-11-01

Heat or mass transfer around an evaporating drop or condensing vapor bubble is a complex issue due to the interplay between the substrate properties, diffusion- and convection-driven mass transfer, and Marangoni effects, to mention but a few. In order to disentangle these mechanisms, we focus here mainly on the convective mass transfer contribution in an isothermal mass transfer problem. For this, we study the case of a millimetric carbon dioxide bubble which is suspended under a substrate and dissolved into pure liquid water. The high solubility of CO2 in water makes the liquid denser and promotes a buoyant-driven flow at a high (solutal) Rayleigh number (Ra˜104 ). The alteration of p H allows the concentration field in the liquid to be imaged by laser fluorescence enabling us to measure both the global mass flux (bubble volume, contact angle) and local mass flux around the bubble along time. After a short period of mass diffusion, where the boundary layer thickens like the square root of time, convection starts and the CO2 is carried by a plume falling at constant velocity. The boundary layer thickness then reaches a plateau which depends on the bubble cross section. Meanwhile the plume velocity scales like (dV /d t )1 /2 with V being the volume of the bubble. As for the rate of volume loss, we recover a constant mass flux in the diffusion-driven regime followed by a decrease in the volume V like V2 /3 after convection has started. We present a model which agrees well with the bubble dynamics and discuss our results in the context of droplet evaporation, as well as high Rayleigh convection.

Impact of boundaries on velocity profiles in bubble rafts.

PubMed

Wang, Yuhong; Krishan, Kapilanjan; Dennin, Michael

2006-03-01

Under conditions of sufficiently slow flow, foams, colloids, granular matter, and various pastes have been observed to exhibit shear localization, i.e., regions of flow coexisting with regions of solidlike behavior. The details of such shear localization can vary depending on the system being studied. A number of the systems of interest are confined so as to be quasi two-dimensional, and an important issue in these systems is the role of the confining boundaries. For foams, three basic systems have been studied with very different boundary conditions: Hele-Shaw cells (bubbles confined between two solid plates); bubble rafts (a single layer of bubbles freely floating on a surface of water); and confined bubble rafts (bubbles confined between the surface of water below and a glass plate on top). Often, it is assumed that the impact of the boundaries is not significant in the "quasistatic limit," i.e., when externally imposed rates of strain are sufficiently smaller than internal kinematic relaxation times. In this paper, we directly test this assumption for rates of strain ranging from 10(-3) to 10(-2) s(-1). This corresponds to the quoted rate of strain that had been used in a number of previous experiments. It is found that the top plate dramatically alters both the velocity profile and the distribution of nonlinear rearrangements, even at these slow rates of strain. When a top is present, the flow is localized to a narrow band near the wall, and without a top, there is flow throughout the system.

Void fraction and velocity measurement of simulated bubble in a rotating disc using high frame rate neutron radiography.

PubMed

Saito, Y; Mishima, K; Matsubayashi, M

2004-10-01

To evaluate measurement error of local void fraction and velocity field in a gas-molten metal two-phase flow by high-frame-rate neutron radiography, experiments using a rotating stainless-steel disc, which has several holes of various diameters and depths simulating gas bubbles, were performed. Measured instantaneous void fraction and velocity field of the simulated bubbles were compared with the calculated values based on the rotating speed, the diameter and the depth of the holes as parameters and the measurement error was evaluated. The rotating speed was varied from 0 to 350 rpm (tangential velocity of the simulated bubbles from 0 to 1.5 m/s). The effect of shutter speed of the imaging system on the measurement error was also investigated. It was revealed from the Lagrangian time-averaged void fraction profile that the measurement error of the instantaneous void fraction depends mainly on the light-decay characteristics of the fluorescent converter. The measurement error of the instantaneous local void fraction of simulated bubbles is estimated to be 20%. In the present imaging system, the light-decay characteristics of the fluorescent converter affect the measurement remarkably, and so should be taken into account in estimating the measurement error of the local void fraction profile.

Further experimentation on bubble generation during transformer overload

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oommen, T.V.

1992-03-01

This report covers additional work done during 1990 and 1991 on gas bubble generation under overload conditions. To improve visual bubble detection, a single disc coil was used. To further improve detection, a corona device was also used which signaled the onset of corona activity in the early stages of bubble formation. A total of fourteen model tests were conducted, half of which used the Inertaire system, and the remaining, a conservator (COPS). Moisture content of paper in the coil varied from 1.0% to 8.0%; gas (nitrogen) content varied from 1.0% to 8.8%. The results confirmed earlier observations that themore » mathematical bubble prediction model was not valid for high gas content model with relatively low moisture levels in the coil. An empirical relationship was formulated to accurately predict bubble evolution temperatures from known moisture and gas content values. For low moisture content models (below 2%), the simple Piper relationship was sufficient to predict bubble evolution temperatures, regardless of gas content. Moisture in the coil appears to be the key factor in bubble generation. Gas blanketed (Inertaire) systems do not appear to be prone to premature bubble generation from overloads as previously thought. The new bubble prediction model reveals that for a coil with 2% moisture, the bubble evolution temperature would be about 140{degrees}C. Since old transformers in service may have as much as 2% moisture in paper, the 140{degrees}C bubble evolution temperature may be taken as the lower limit of bubble evolution temperature under overload conditions for operating transformers. Drier insulation would raise the bubble evolution temperature.« less

Buoyancy effects in steeply inclined air-water bubbly shear flow in a rectangular channel

NASA Astrophysics Data System (ADS)

Sanaullah, K.; Arshad, M.; Khan, A.; Chughtai, I. R.

2015-07-01

We report measurements of two-dimensional ( B/ D = 5) fully turbulent and developed duct flows (overall length/depth, L/ D = 60; D-based Reynolds number Re > 104) for inclinations to 30° from vertical at low voidages (< 5 % sectional average) representative of disperse regime using tap water bubbles (4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10 % local value) discrimination of main aspects of the mean velocity and voidage profiles at representative streamwise station i.e L/ D = 40. Our results can be divided into three categories of behaviour. For vertical flow (0°) the evidence is inconclusive as to whether bubbles are preferentially trapped within the wall-layer as found in some, may be most earlier experimental works. Thus, the 4-mm bubbles showed indication of voidage retention but the 2-mm bubbles did not. For nearly vertical flow (5°) there was pronounced profiling of voidage especially with 4-mm bubbles but the transverse transport was not suppressed sufficiently to induce any obvious layering. In this context, we also refer to similarities with previous work on one-phase vertical and nearly vertical mixed convection flows displaying buoyancy inhibited mean shear turbulence. However, with inclined flow (10+ degrees) a distinctively layered pattern was invariably manifested in which voidage confinement increased with increasing inclination. In this paper we address flow behavior at near vertical conditions. Eulerian, mixed and VOF models were used to compute voidage and mean velocity profiles.

Ultrasonic bubbles in medicine: influence of the shell.

PubMed

Postema, Michiel; Schmitz, Georg

2007-04-01

Ultrasound contrast agents consist of microscopically small bubbles encapsulated by an elastic shell. These microbubbles oscillate upon ultrasound insonification, and demonstrate highly nonlinear behavior, ameliorating their detectability. (Potential) medical applications involving the ultrasonic disruption of contrast agent microbubble shells include release-burst imaging, localized drug delivery, and noninvasive blood pressure measurement. To develop and enhance these techniques, predicting the cracking behavior of ultrasound-insonified encapsulated microbubbles has been of importance. In this paper, we explore microbubble behavior in an ultrasound field, with special attention to the influence of the bubble shell. A bubble in a sound field can be considered a forced damped harmonic oscillator. For encapsulated microbubbles, the presence of a shell has to be taken into account. In models, an extra damping parameter and a shell stiffness parameter have been included, assuming that Hooke's Law holds for the bubble shell. At high acoustic amplitudes, disruptive phenomena have been observed, such as microbubble fragmentation and ultrasonic cracking. We analyzed the occurrence of ultrasound contrast agent fragmentation, by simulating the oscillating behavior of encapsulated microbubbles with various sizes in a harmonic acoustic field. Fragmentation occurs exclusively during the collapse phase and occurs if the kinetic energy of the collapsing microbubble is greater than the instantaneous bubble surface energy, provided that surface instabilities have grown big enough to allow for break-up. From our simulations it follows that the Blake critical radius is not a good approximation for a fragmentation threshold. We demonstrated how the phase angle differences between a damped radially oscillating bubble and an incident sound field depend on shell parameters.

Methodology Development of a Gas-Liquid Dynamic Flow Regime Transition Model

NASA Astrophysics Data System (ADS)

Doup, Benjamin Casey

Current reactor safety analysis codes, such as RELAP5, TRACE, and CATHARE, use flow regime maps or flow regime transition criteria that were developed for static fully-developed two-phase flows to choose interfacial transfer models that are necessary to solve the two-fluid model. The flow regime is therefore difficult to identify near the flow regime transitions, in developing two-phase flows, and in transient two-phase flows. Interfacial area transport equations were developed to more accurately predict the dynamic nature of two-phase flows. However, other model coefficients are still flow regime dependent. Therefore, an accurate prediction of the flow regime is still important. In the current work, the methodology for the development of a dynamic flow regime transition model that uses the void fraction and interfacial area concentration obtained by solving three-field the two-fluid model and two-group interfacial area transport equation is investigated. To develop this model, detailed local experimental data are obtained, the two-group interfacial area transport equations are revised, and a dynamic flow regime transition model is evaluated using a computational fluid dynamics model. Local experimental data is acquired for 63 different flow conditions in bubbly, cap-bubbly, slug, and churn-turbulent flow regimes. The measured parameters are the group-1 and group-2 bubble number frequency, void fraction, interfacial area concentration, and interfacial bubble velocities. The measurements are benchmarked by comparing the prediction of the superficial gas velocities, determined using the local measurements with those determined from volumetric flow rate measurements and the agreement is generally within +/-20%. The repeatability four-sensor probe construction process is within +/-10%. The repeatability of the measurement process is within +/-7%. The symmetry of the test section is examined and the average agreement is within +/-5.3% at z/D = 10 and +/-3.4% at z/D = 32. Revised source/sink terms for the two-group interfacial area transport equations are derived and fit to area-averaged experimental data to determine new model coefficients. The average agreement between this model and the experiment data for the void fraction and interfacial area concentration is 10.6% and 15.7%, respectively. This revised two-group interfacial area transport equation and the three-field two-fluid model are used to solve for the group-1 and group-2 interfacial area concentration and void fraction. These values and a dynamic flow regime transition model are used to classify the flow regimes. The flow regimes determined using this model are compared with the flow regimes based on the experimental data and on a flow regime map using Mishima and Ishii's (1984) transition criteria. The dynamic flow regime transition model is shown to predict the flow regimes dynamically and has improved the prediction of the flow regime over that using a flow regime map. Safety codes often employ the one-dimensional two-fluid model to model two-phase flows. The area-averaged relative velocity correlation necessary to close this model is derived from the drift flux model. The effects of the necessary assumptions used to derive this correlation are investigated using local measurements and these effects are found to have a limited impact on the prediction of the area-averaged relative velocity.

Bubble generation during transformer overload

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oommen, T.V.

1990-03-01

Bubble generation in transformers has been demonstrated under certain overload conditions. The release of large quantities of bubbles would pose a dielectric breakdown hazard. A bubble prediction model developed under EPRI Project 1289-4 attempts to predict the bubble evolution temperature under different overload conditions. This report details a verification study undertaken to confirm the validity of the above model using coil structures subjected to overload conditions. The test variables included moisture in paper insulation, gas content in oil, and the type of oil preservation system. Two aged coils were also tested. The results indicated that the observed bubble temperatures weremore » close to the predicted temperatures for models with low initial gas content in the oil. The predicted temperatures were significantly lower than the observed temperatures for models with high gas content. Some explanations are provided for the anomalous behavior at high gas levels in oil. It is suggested that the dissolved gas content is not a significant factor in bubble evolution. The dominant factor in bubble evolution appears to be the water vapor pressure which must reach critical levels before bubbles can be released. Further study is needed to make a meaningful revision of the bubble prediction model. 8 refs., 13 figs., 11 tabs.« less

Axisymmetric bubble pinch-off at high Reynolds numbers.

PubMed

Gordillo, J M; Sevilla, A; Rodríguez-Rodríguez, J; Martínez-Bazán, C

2005-11-04

Analytical considerations and potential-flow numerical simulations of the pinch-off of bubbles at high Reynolds numbers reveal that the bubble minimum radius, rn, decreases as tau proportional to r2n sqrt[1lnr2n], where tau is the time to break up, when the local shape of the bubble near the singularity is symmetric. However, if the gas convective terms in the momentum equation become of the order of those of the liquid, the bubble shape is no longer symmetric and the evolution of the neck changes to a rn proportional to tau1/3 power law. These findings are verified experimentally.

Bubble snap-off and capillary-back pressure during counter-current spontaneous imbibition into model pores.

PubMed

Unsal, Evren; Mason, Geoffrey; Morrow, Norman R; Ruth, Douglas W

2009-04-09

A previous paper (Unsal, E.; Mason, G.; Ruth, D. W.; Morrow, N. R. J. Colloid Interface Sci. 2007, 315, 200-209) reported experiments involving counter-current spontaneous imbibition into a model pore system consisting of a rod in an angled slot covered by a glass plate. Such an arrangement gives two tubes with different cross-sections (both size and shape) with an interconnection through the gap between the rod and the plate. In the previous experiments, the wetting phase advanced in the small tube and nonwetting phase retreated in the large tube. No bubbles were formed. In this paper, we study experimentally and theoretically the formation of bubbles at the open end of the large tube and their subsequent snap-off. Such bubbles reduce the capillary back pressure produced by the larger tube and can thus have an effect on the local rate of imbibition. In the model pore system, the rod was either in contact with the glass, forming two independent tubes, or the rod was spaced from the glass to allow cross-flow between the tubes. For small gaps, there were three distinct menisci. The one with the highest curvature was between the rod and the plate. The next most highly curved was in the smaller tube, and the least highly curved meniscus was in the large tube and this was the tube from which the bubbles developed. The pressure in the dead end of the system was recorded during imbibition. Once the bubble starts to form outside of the tube, the pressure drops rapidly and then steadies. After the bubble snaps off, the pressure rises to almost the initial value and stays essentially constant until the next bubble starts to form. After snap-off, the meniscus in the large tube appears to invade the large tube for some distance. The snap-off is the result of capillary instability; it takes place significantly inside the large tube with flow of wetting phase moving in the angular corners. As imbibition into the small tube progresses, the rate of imbibition decreases and the time taken for each bubble to form increases, slightly increasing the pressure at which snap-off occurs. The snap-off curvature is only about two-thirds of the curvature of a theoretical cylindrical meniscus within the large tube and about 40% of the curvature of the actual meniscus spanning the large tube.

Wetting of soap bubbles on hydrophilic, hydrophobic, and superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Arscott, Steve

2013-06-01

Wetting of sessile bubbles on various wetting surfaces (solid and liquid) has been studied. A model is presented for the apparent contact angle of a sessile bubble based on a modified Young's equation--the experimental results agree with the model. Wetting a hydrophilic surface results in a bubble contact angle of 90° whereas using a superhydrophobic surface one observes 134°. For hydrophilic surfaces, the bubble angle diminishes with bubble radius whereas on a superhydrophobic surface, the bubble angle increases. The size of the plateau borders governs the bubble contact angle, depending on the wetting of the surface.

TOPICAL REVIEW: Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering

NASA Astrophysics Data System (ADS)

Qin, Shengping; Caskey, Charles F.; Ferrara, Katherine W.

2009-03-01

Microbubble contrast agents and the associated imaging systems have developed over the past 25 years, originating with manually-agitated fluids introduced for intra-coronary injection. Over this period, stabilizing shells and low diffusivity gas materials have been incorporated in microbubbles, extending stability in vitro and in vivo. Simultaneously, the interaction of these small gas bubbles with ultrasonic waves has been extensively studied, resulting in models for oscillation and increasingly sophisticated imaging strategies. Early studies recognized that echoes from microbubbles contained frequencies that are multiples of the microbubble resonance frequency. Although individual microbubble contrast agents cannot be resolved—given that their diameter is on the order of microns—nonlinear echoes from these agents are used to map regions of perfused tissue and to estimate the local microvascular flow rate. Such strategies overcome a fundamental limitation of previous ultrasound blood flow strategies; the previous Doppler-based strategies are insensitive to capillary flow. Further, the insonation of resonant bubbles results in interesting physical phenomena that have been widely studied for use in drug and gene delivery. Ultrasound pressure can enhance gas diffusion, rapidly fragment the agent into a set of smaller bubbles or displace the microbubble to a blood vessel wall. Insonation of a microbubble can also produce liquid jets and local shear stress that alter biological membranes and facilitate transport. In this review, we focus on the physical aspects of these agents, exploring microbubble imaging modes, models for microbubble oscillation and the interaction of the microbubble with the endothelium.

Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering

PubMed Central

Qin, Shengping; Caskey, Charles F; Ferrara, Katherine W

2010-01-01

Microbubble contrast agents and the associated imaging systems have developed over the past twenty-five years, originating with manually-agitated fluids introduced for intra-coronary injection. Over this period, stabilizing shells and low diffusivity gas materials have been incorporated in microbubbles, extending stability in vitro and in vivo. Simultaneously, the interaction of these small gas bubbles with ultrasonic waves has been extensively studied, resulting in models for oscillation and increasingly sophisticated imaging strategies. Early studies recognized that echoes from microbubbles contained frequencies that are multiples of the microbubble resonance frequency. Although individual microbubble contrast agents cannot be resolved—given that their diameter is on the order of microns—nonlinear echoes from these agents are used to map regions of perfused tissue and to estimate the local microvascular flow rate. Such strategies overcome a fundamental limitation of previous ultrasound blood flow strategies; the previous Doppler-based strategies are insensitive to capillary flow. Further, the insonation of resonant bubbles results in interesting physical phenomena that have been widely studied for use in drug and gene delivery. Ultrasound pressure can enhance gas diffusion, rapidly fragment the agent into a set of smaller bubbles or displace the microbubble to a blood vessel wall. Insonation of a microbubble can also produce liquid jets and local shear stress that alter biological membranes and facilitate transport. In this review, we focus on the physical aspects of these agents, exploring microbubble imaging modes, models for microbubble oscillation and the interaction of the microbubble with the endothelium. PMID:19229096

Numerical and Experimental Study of Mechanisms Involved in Boiling Histotripsy.

PubMed

Pahk, Ki Joo; Gélat, Pierre; Sinden, David; Dhar, Dipok Kumar; Saffari, Nader

2017-12-01

The aim of boiling histotripsy is to mechanically fractionate tissue as an alternative to thermal ablation for therapeutic applications. In general, the shape of a lesion produced by boiling histotripsy is tadpole like, consisting of a head and a tail. Although many studies have demonstrated the efficacy of boiling histotripsy for fractionating solid tumors, the exact mechanisms underpinning this phenomenon are not yet well understood, particularly the interaction of a boiling vapor bubble with incoming incident shockwaves. To investigate the mechanisms involved in boiling histotripsy, a high-speed camera with a passive cavitation detection system was used to observe the dynamics of bubbles produced in optically transparent tissue-mimicking gel phantoms exposed to the field of a 2.0-MHz high-intensity focused ultrasound (HIFU) transducer. We observed that boiling bubbles were generated in a localized heated region and cavitation clouds were subsequently induced ahead of the expanding bubble. This process was repeated with HIFU pulses and eventually resulted in a tadpole-shaped lesion. A simplified numerical model describing the scattering of the incident ultrasound wave by a vapor bubble was developed to help interpret the experimental observations. Together with the numerical results, these observations suggest that the overall size of a lesion induced by boiling histotripsy is dependent on the sizes of (i) the heated region at the HIFU focus and (ii) the backscattered acoustic field by the original vapor bubble. Copyright © 2017 World Federation for Ultrasound in Medicine and Biology. Published by Elsevier Inc. All rights reserved.

Magnetic field and radiative transfer modelling of a quiescent prominence

NASA Astrophysics Data System (ADS)

Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel, P.; Jurčák, J.

2014-07-01

Aims: The aim of this work is to analyse the multi-instrument observations of the June 22, 2010 prominence to study its structure in detail, including the prominence-corona transition region and the dark bubble located below the prominence body. Methods: We combined results of the 3D magnetic field modelling with 2D prominence fine structure radiative transfer models to fully exploit the available observations. Results: The 3D linear force-free field model with the unsheared bipole reproduces the morphology of the analysed prominence reasonably well, thus providing useful information about its magnetic field configuration and the location of the magnetic dips. The 2D models of the prominence fine structures provide a good representation of the local plasma configuration in the region dominated by the quasi-vertical threads. However, the low observed Lyman-α central intensities and the morphology of the analysed prominence suggest that its upper central part is not directly illuminated from the solar surface. Conclusions: This multi-disciplinary prominence study allows us to argue that a large part of the prominence-corona transition region plasma can be located inside the magnetic dips in small-scale features that surround the cool prominence material located in the dip centre. We also argue that the dark prominence bubbles can be formed because of perturbations of the prominence magnetic field by parasitic bipoles, causing them to be devoid of the magnetic dips. Magnetic dips, however, form thin layers that surround these bubbles, which might explain the occurrence of the cool prominence material in the lines of sight intersecting the prominence bubbles. Movie and Appendix A are available in electronic form at http://www.aanda.org

Further experimentation on bubble generation during transformer overload. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oommen, T.V.

1992-03-01

This report covers additional work done during 1990 and 1991 on gas bubble generation under overload conditions. To improve visual bubble detection, a single disc coil was used. To further improve detection, a corona device was also used which signaled the onset of corona activity in the early stages of bubble formation. A total of fourteen model tests were conducted, half of which used the Inertaire system, and the remaining, a conservator (COPS). Moisture content of paper in the coil varied from 1.0% to 8.0%; gas (nitrogen) content varied from 1.0% to 8.8%. The results confirmed earlier observations that themore » mathematical bubble prediction model was not valid for high gas content model with relatively low moisture levels in the coil. An empirical relationship was formulated to accurately predict bubble evolution temperatures from known moisture and gas content values. For low moisture content models (below 2%), the simple Piper relationship was sufficient to predict bubble evolution temperatures, regardless of gas content. Moisture in the coil appears to be the key factor in bubble generation. Gas blanketed (Inertaire) systems do not appear to be prone to premature bubble generation from overloads as previously thought. The new bubble prediction model reveals that for a coil with 2% moisture, the bubble evolution temperature would be about 140{degrees}C. Since old transformers in service may have as much as 2% moisture in paper, the 140{degrees}C bubble evolution temperature may be taken as the lower limit of bubble evolution temperature under overload conditions for operating transformers. Drier insulation would raise the bubble evolution temperature.« less

Controllable bioeffects of laser-generated intracellular microbubbles

NASA Astrophysics Data System (ADS)

Zohdy, Marwa Joy

Laser-induced optical breakdown (LIOB) is a nonlinear energy absorption process that can generate precise damage in biological tissues. With femtosecond laser pulses, disruption is highly localized with minimal thermal and mechanical effects to the surrounding region. Cavitation bubbles are produced as a result of LIOB, and these bubbles can be detected and monitored with high-frequency ultrasound. In this work, the controllable viability effects of LIOB bubbles in single cells were characterized. Using a high-frequency acoustic transducer synchronized with a 793 nm, 100 fs laser pulsed at 250 kHz, thermal effects in the vicinity of an LIOB event were directly assessed. Temperaturedependent pulse-echo displacements were calculated using phase-sensitive correlation tracking and fit to a finite-element heat transfer model to estimate thermal distribution. Results indicate a minimal temperature increase (<1 degree C) within 100 microns of a bubble created with multiple laser pulses, confirming that LIOB can be controlled to be thermally noninvasive in the bubble vicinity. Acoustically detectable microbubbles were generated in individual cells with femtosecond LIOB. By adjusting laser fluence, exposure time, and focal location, LIOB could be controlled to produce distinctly different cellular effects. Small (1-2 micron) bubbles with short lifetimes (10100 ms) could be generated in cells without affecting their viability; and, alternatively, large (510 micron) bubbles with long lifetimes (1-5 s) could be generated for selective cell killing without affecting immediately neighboring cells. Experiments were performed in Chinese hamster ovary (CHO) cells in vitro, and LIOB was detected with both optical and acoustic microscopy. A long-term proliferation assay was also performed using green-fluorescent MCA207 mouse sarcoma cells targeted for LIOB. This assay confirmed that nondestructive bubbles did not affect target cell proliferation over several generations, and that destructive bubbles could indeed eliminate target cells and prevent further proliferation with no effect on immediately neighboring cells. These studies help to outline future applications for site-activated, acoustically monitored intracellular microbubbles. Nondestructive bubbles can potentially be used for functional cell measurements without introducing exogenous agents or affecting subsequent cell proliferation, and destructive bubbles can be used for highly precise biologically-targeted cancer cell therapy with real-time acoustic validation.

Gas Diffusion in Fluids Containing Bubbles

NASA Technical Reports Server (NTRS)

Zak, M.; Weinberg, M. C.

1982-01-01

Mathematical model describes movement of gases in fluid containing many bubbles. Model makes it possible to predict growth and shrink age of bubbles as function of time. New model overcomes complexities involved in analysis of varying conditions by making two simplifying assumptions. It treats bubbles as point sources, and it employs approximate expression for gas concentration gradient at liquid/bubble interface. In particular, it is expected to help in developing processes for production of high-quality optical glasses in space.

Mathematical and experimental modelling of the dynamic bubble processes occurring in a two-phase cyclonic separation device

NASA Astrophysics Data System (ADS)

Schrage, Dean Stewart

1998-11-01

This dissertation presents a combined mathematical and experimental analysis of the fluid dynamics of a gas- liquid, dispersed-phase cyclonic separation device. The global objective of this research is to develop a simulation model of separation process in order to predict the void fraction field within a cyclonic separation device. The separation process is approximated by analyzing the dynamic motion of many single-bubbles, moving under the influence of the far-field, interacting with physical boundaries and other bubbles. The dynamic motion of the bubble is described by treating the bubble as a point-mass and writing an inertial force balance, equating the force applied to the bubble-point-location to the inertial acceleration of the bubble mass (also applied to the point-location). The forces which are applied to the bubble are determined by an integration of the surface pressure over the bubble. The surface pressure is coupled to the intrinsic motion of the bubble, and is very difficult to obtain exactly. However, under moderate Reynolds number, the wake trailing a bubble is small and the near-field flow field can be approximated as an inviscid flow field. Unconventional potential flow techniques are employed to solve for the surface pressure; the hydrodyamic forces are described as a hydrodynamic mass tensor operating on the bubble acceleration vector. The inviscid flow model is augmented with adjunct forces which describe: drag forces, dynamic lift, far-field pressure forces. The dynamic equations of motion are solved both analytically and numerically for the bubble trajectory in specific flow field examples. A validation of these equations is performed by comparing to an experimentally-derived trajectory of a single- bubble, which is released into a cylindrical Couette flow field (inner cylinder rotating) at varying positions. Finally, a simulation of a cyclonic separation device is performed by extending the single-bubble dynamic model to a multi-bubble ensemble. A simplified model is developed to predict the effects of bubble-interaction. The simulation qualitatively depicts the separation physics encountered in an actual cyclonic separation device, supporting the original tenet that the separation process can be approximated by the collective motions of single- bubbles.

Using Improved Equation of State to Model Simultaneous Nucleation and Bubble Growth in Thermoplastic Foams

NASA Astrophysics Data System (ADS)

Khan, Irfan; Costeux, Stephane; Adrian, David; Cristancho, Diego

2013-11-01

Due to environmental regulations carbon-dioxide (CO2) is increasingly being used to replace traditional blowing agents in thermoplastic foams. CO2 is dissolved in the polymer matrix under supercritical conditions. In order to predict the effect of process parameters on foam properties using numerical modeling, the P-V-T relationship of the blowing agents should accurately be represented at the supercritical state. Previous studies in the area of foam modeling have all used ideal gas equation of state to predict the behavior of the blowing agent. In this work the Peng-Robinson equation of state is being used to model the blowing agent during its diffusion into the growing bubble. The model is based on the popular ``Influence Volume Approach,'' which assumes a growing boundary layer with depleted blowing agent surrounds each bubble. Classical nucleation theory is used to predict the rate of nucleation of bubbles. By solving the mass balance, momentum balance and species conservation equations for each bubble, the model is capable of predicting average bubble size, bubble size distribution and bulk porosity. The effect of the improved model on the bubble growth and foam properties are discussed.

One-group interfacial area transport in vertical air-water bubbly flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Q.; Kim, S.; Ishii, M.

In the two-fluid model for two-phase flows, interfacial area concentration is one of the most important closure relations that should be obtained from careful mechanistic modeling. The objective of this study is to develop a one-group interfacial area transport equation together with the modeling of the source and sink terms due to bubble breakage and coalescence. For bubble coalescence, two mechanisms are considered to be dominant in vertical two-phase bubbly flow. These are the random collisions between bubbles due to turbulence in the flow field, and the wake entrainment process due to the relative motion of the bubbles in themore » wake region of a seeding bubble. For bubble breakup, the impact of turbulent eddies is considered. These phenomena are modeled individually, resulting in a one-group interfacial area concentration transport equation with certain parameters to be determined from experimental data. Compared to the measured axial distribution of the interfacial area concentration under various flow conditions, these parameters are obtained for the reduced one-group, one-dimensional transport equation. The results indicate that the proposed models for bubble breakup and coalescence are appropriate.« less

A genetic algorithm-based optimization model for pool boiling heat transfer on horizontal rod heaters at isolated bubble regime

NASA Astrophysics Data System (ADS)

Alavi Fazel, S. Ali

2017-09-01

A new optimized model which can predict the heat transfer in the nucleate boiling at isolated bubble regime is proposed for pool boiling on a horizontal rod heater. This model is developed based on the results of direct observations of the physical boiling phenomena. Boiling heat flux, wall temperature, bubble departing diameter, bubble generation frequency and bubble nucleation site density have been experimentally measured. Water and ethanol have been used as two different boiling fluids. Heating surface was made by several metals and various degrees of roughness. The mentioned model considers various mechanisms such as latent heat transfer due to micro-layer evaporation, transient conduction due to thermal boundary layer reformation, natural convection, heat transfer due to the sliding bubbles and bubble super-heating. The fractional contributions of individual mentioned heat transfer mechanisms have been calculated by genetic algorithm. The results show that at wall temperature difference more that about 3 K, bubble sliding transient conduction, non-sliding transient conduction, micro-layer evaporation, natural convection, radial forced convection and bubble super-heating have higher to lower fractional contributions respectively. The performance of the new optimized model has been verified by comparison of the existing experimental data.

Development of bubble microstructure in ErT2 films during aging

NASA Astrophysics Data System (ADS)

Bond, Gillian M.; Browning, James F.; Snow, Clark S.

2010-04-01

Helium bubbles form in metal tritide films as tritium decays into H3e, influencing mechanical properties and long-term film stability. The bubble nucleation and growth mechanisms comprise an active research area, but there has been only one previous systematic experimental study of helium bubble growth in metal tritides, on zirconium tritides. There have been no such studies on tritides such as ErT2 that form platelike bubbles and lack a secondary bubble population on a network of line dislocations, and yet such a study is needed to inform the modeling of helium bubble microstructure development in a broader range of metal tritides. Transmission electron microscopy has been used to study the growth and evolution of helium bubbles in ErT2 films over a four-year period. The results have been used to test the present models of helium bubble nucleation and growth in metal tritides, particularly those forming platelike bubbles. The results support the models of Trinkaus and Cowgill. The observations of nonuniform bubble thicknesses and the pattern of grain-boundary bubble formation, however, indicate that these models could be strengthened by closer attention to details of interfacial energy. It is strongly recommended that efforts be made (either experimentally or by calculation) to determine anisotropy of tritide/helium interfacial energy, both for clean, stoichiometric interfaces, and also allowing for such factors as nonstoichiometry and segregation.

A model describing intra-granular fission gas behaviour in oxide fuel for advanced engineering tools

NASA Astrophysics Data System (ADS)

Pizzocri, D.; Pastore, G.; Barani, T.; Magni, A.; Luzzi, L.; Van Uffelen, P.; Pitts, S. A.; Alfonsi, A.; Hales, J. D.

2018-04-01

The description of intra-granular fission gas behaviour is a fundamental part of any model for the prediction of fission gas release and swelling in nuclear fuel. In this work we present a model describing the evolution of intra-granular fission gas bubbles in terms of bubble number density and average size, coupled to gas release to grain boundaries. The model considers the fundamental processes of single gas atom diffusion, gas bubble nucleation, re-solution and gas atom trapping at bubbles. The model is derived from a detailed cluster dynamics formulation, yet it consists of only three differential equations in its final form; hence, it can be efficiently applied in engineering fuel performance codes while retaining a physical basis. We discuss improvements relative to previous single-size models for intra-granular bubble evolution. We validate the model against experimental data, both in terms of bubble number density and average bubble radius. Lastly, we perform an uncertainty and sensitivity analysis by propagating the uncertainties in the parameters to model results.

Well-posed Euler model of shock-induced two-phase flow in bubbly liquid

NASA Astrophysics Data System (ADS)

Tukhvatullina, R. R.; Frolov, S. M.

2018-03-01

A well-posed mathematical model of non-isothermal two-phase two-velocity flow of bubbly liquid is proposed. The model is based on the two-phase Euler equations with the introduction of an additional pressure at the gas bubble surface, which ensures the well-posedness of the Cauchy problem for a system of governing equations with homogeneous initial conditions, and the Rayleigh-Plesset equation for radial pulsations of gas bubbles. The applicability conditions of the model are formulated. The model is validated by comparing one-dimensional calculations of shock wave propagation in liquids with gas bubbles with a gas volume fraction of 0.005-0.3 with experimental data. The model is shown to provide satisfactory results for the shock propagation velocity, pressure profiles, and the shock-induced motion of the bubbly liquid column.

Determination of surface tension from the measurement of internal pressure of mini soap bubbles

NASA Astrophysics Data System (ADS)

Behroozi, F.; Behroozi, P. S.

2011-11-01

We review the elementary theory that gives the internal pressure of a soap bubble in terms of its radius and surface tension. The theory is generalized to relate the pressure difference across any element of a soap film to its local curvature. This result is used to introduce the concept of the mean curvature of a surface element and is applied to a double soap bubble to obtain the relation between the three radii that characterize its geometry. We also describe a simple setup, suitable for the undergraduate laboratory, to produce mini bubbles and to obtain the surface tension of the soap solution by measuring the radius and internal pressure of the bubbles.

Sinking bubbles in stout beers

NASA Astrophysics Data System (ADS)

Lee, W. T.; Kaar, S.; O'Brien, S. B. G.

2018-04-01

A surprising phenomenon witnessed by many is the sinking bubbles seen in a settling pint of stout beer. Bubbles are less dense than the surrounding fluid so how does this happen? Previous work has shown that the explanation lies in a circulation of fluid promoted by the tilted sides of the glass. However, this work has relied heavily on computational fluid dynamics (CFD) simulations. Here, we show that the phenomenon of sinking bubbles can be predicted using a simple analytic model. To make the model analytically tractable, we work in the limit of small bubbles and consider a simplified geometry. The model confirms both the existence of sinking bubbles and the previously proposed mechanism.

A computationally efficient modelling of laminar separation bubbles

NASA Technical Reports Server (NTRS)

Maughmer, Mark D.

1988-01-01

The goal of this research is to accurately predict the characteristics of the laminar separation bubble and its effects on airfoil performance. To this end, a model of the bubble is under development and will be incorporated in the analysis section of the Eppler and Somers program. As a first step in this direction, an existing bubble model was inserted into the program. It was decided to address the problem of the short bubble before attempting the prediction of the long bubble. In the second place, an integral boundary-layer method is believed more desirable than a finite difference approach. While these two methods achieve similar prediction accuracy, finite-difference methods tend to involve significantly longer computer run times than the integral methods. Finally, as the boundary-layer analysis in the Eppler and Somers program employs the momentum and kinetic energy integral equations, a short-bubble model compatible with these equations is most preferable.

Improvement of ore recovery efficiency in a flotation column cell using ultra-sonic enhanced bubbles

NASA Astrophysics Data System (ADS)

Filippov, L. O.; Royer, J. J.; Filippova, I. V.

2017-07-01

The ore process flotation technique is enhanced by using external ultra-sonic waves. Compared to the classical flotation method, the application of ultrasounds to flotation fluids generates micro-bubbles by hydrodynamic cavitation. Flotation performances increase was modelled as a result of increased probabilities of the particle-bubble attachment and reduced detachment probability under sonication. A simplified analytical Navier-Stokes model is used to predict the effect of ultrasonic waves on bubble behavior. If the theory is verified by experimentation, it predicts that the ultrasonic waves would create cavitation micro-bubbles, smaller than the flotation bubble added by the gas sparger. This effect leads to increasing the number of small bubbles in the liquid which promote particle-bubble attachment through coalescence between bubbles and micro-bubbles. The decrease in the radius of the flotation bubbles under external vibration forces has an additional effect by enhancing the bubble-particle collision. Preliminary results performed on a potash ore seem to confirm the theory.

Prediction of Cavitation Depth in an Al-Cu Alloy Melt with Bubble Characteristics Based on Synchrotron X-ray Radiography

NASA Astrophysics Data System (ADS)

Huang, Haijun; Shu, Da; Fu, Yanan; Zhu, Guoliang; Wang, Donghong; Dong, Anping; Sun, Baode

2018-06-01

The size of cavitation region is a key parameter to estimate the metallurgical effect of ultrasonic melt treatment (UST) on preferential structure refinement. We present a simple numerical model to predict the characteristic length of the cavitation region, termed cavitation depth, in a metal melt. The model is based on wave propagation with acoustic attenuation caused by cavitation bubbles which are dependent on bubble characteristics and ultrasonic intensity. In situ synchrotron X-ray imaging of cavitation bubbles has been made to quantitatively measure the size of cavitation region and volume fraction and size distribution of cavitation bubbles in an Al-Cu melt. The results show that cavitation bubbles maintain a log-normal size distribution, and the volume fraction of cavitation bubbles obeys a tanh function with the applied ultrasonic intensity. Using the experimental values of bubble characteristics as input, the predicted cavitation depth agrees well with observations except for a slight deviation at higher acoustic intensities. Further analysis shows that the increase of bubble volume and bubble size both leads to higher attenuation by cavitation bubbles, and hence, smaller cavitation depth. The current model offers a guideline to implement UST, especially for structural refinement.

Prediction of Cavitation Depth in an Al-Cu Alloy Melt with Bubble Characteristics Based on Synchrotron X-ray Radiography

NASA Astrophysics Data System (ADS)

Huang, Haijun; Shu, Da; Fu, Yanan; Zhu, Guoliang; Wang, Donghong; Dong, Anping; Sun, Baode

2018-04-01

The size of cavitation region is a key parameter to estimate the metallurgical effect of ultrasonic melt treatment (UST) on preferential structure refinement. We present a simple numerical model to predict the characteristic length of the cavitation region, termed cavitation depth, in a metal melt. The model is based on wave propagation with acoustic attenuation caused by cavitation bubbles which are dependent on bubble characteristics and ultrasonic intensity. In situ synchrotron X-ray imaging of cavitation bubbles has been made to quantitatively measure the size of cavitation region and volume fraction and size distribution of cavitation bubbles in an Al-Cu melt. The results show that cavitation bubbles maintain a log-normal size distribution, and the volume fraction of cavitation bubbles obeys a tanh function with the applied ultrasonic intensity. Using the experimental values of bubble characteristics as input, the predicted cavitation depth agrees well with observations except for a slight deviation at higher acoustic intensities. Further analysis shows that the increase of bubble volume and bubble size both leads to higher attenuation by cavitation bubbles, and hence, smaller cavitation depth. The current model offers a guideline to implement UST, especially for structural refinement.

Nonlinear Bubble Dynamics And The Effects On Propagation Through Near-Surface Bubble Layers

NASA Astrophysics Data System (ADS)

Leighton, Timothy G.

2004-11-01

Nonlinear bubble dynamics are often viewed as the unfortunate consequence of having to use high acoustic pressure amplitudes when the void fraction in the near-surface oceanic bubble layer is great enough to cause severe attenuation (e.g. >50 dB/m). This is seen as unfortunate since existing models for acoustic propagation in bubbly liquids are based on linear bubble dynamics. However, the development of nonlinear models does more than just allow quantification of the errors associated with the use of linear models. It also offers the possibility of propagation modeling and acoustic inversions which appropriately incorporate the bubble nonlinearity. Furthermore, it allows exploration and quantification of possible nonlinear effects which may be exploited. As a result, high acoustic pressure amplitudes may be desirable even in low void fractions, because they offer opportunities to gain information about the bubble cloud from the nonlinearities, and options to exploit the nonlinearities to enhance communication and sonar in bubbly waters. This paper presents a method for calculating the nonlinear acoustic cross-sections, scatter, attenuations and sound speeds from bubble clouds which may be inhomogeneous. The method allows prediction of the time dependency of these quantities, both because the cloud may vary and because the incident acoustic pulse may have finite and arbitrary time history. The method can be readily adapted for bubbles in other environments (e.g. clouds of interacting bubbles, sediments, structures, in vivo, reverberant conditions etc.). The possible exploitation of bubble acoustics by marine mammals, and for sonar enhancement, is explored.

Numerical modeling of ultrasonic cavitation in ionic liquids

NASA Astrophysics Data System (ADS)

Calvisi, Michael L.; Elder, Ross M.

2017-11-01

Ionic liquids have favorable properties for sonochemistry applications in which the high temperatures and pressures achieved by cavitation bubbles are important drivers of chemical processes. Two different numerical models are presented to simulate ultrasonic cavitation in ionic liquids, each with different capabilities and physical assumptions. A model based on a compressible form of the Rayleigh-Plesset equation (RPE) simulates ultrasonic cavitation of a spherical bubble with a homogeneous interior, incorporating evaporation and condensation at the bubble surface, and temperature-varying thermodynamic properties in the interior. A second, more computationally intensive model of a spherical bubble uses the finite element method (FEM) and accounts for spatial variations in pressure and temperature throughout the flow domain. This model provides insight into heat transfer across the bubble surface and throughout the bubble interior and exterior. Parametric studies are presented for sonochemistry applications involving ionic liquids as a solvent, examining a range of realistic ionic liquid properties and initial conditions to determine their effect on temperature and pressure. Results from the two models are presented for parametric variations including viscosity, thermal conductivity, water content of the ionic liquid solvent, acoustic frequency, and initial bubble pressure. An additional study performed with the FEM model examines thermal penetration into the surrounding ionic liquid during bubble oscillation. The results suggest the prospect of tuning ionic liquid properties for specific applications.

A theoretical insight into H accumulation and bubble formation by applying isotropic strain on the W-H system under a fusion environment

NASA Astrophysics Data System (ADS)

Han, Quan-Fu; Liu, Yue-Lin; Zhang, Ying; Ding, Fang; Lu, Guang-Hong

2018-04-01

The solubility and bubble formation of hydrogen (H) in tungsten (W) are crucial factors for the application of W as a plasma-facing component under a fusion environment, but the data and mechanism are presently scattered, indicating some important factors might be neglected. High-energy neutron-irradiated W inevitably causes a local strain, which may change the solubility of H in W. Here, we performed first-principles calculations to predict the H solution behaviors under isotropic strain combined with temperature effect in W and found that the H solubility in interstitial lattice can be promoted/impeded by isotropic tensile/compressive strain over the temperature range 300-1800 K. The calculated H solubility presents good agreement with the experiment. Together, our previous results of anisotropic strain, except for isotropic compression, both isotropic tension and anisotropic tension/compression enhance H solution so as to reveal an important physical implication for H accumulation and bubble formation in W: strain can enhance H solubility, resulting in the preliminary nucleation of H bubble that further causes the local strain of W lattice around H bubble, which in turn improves the H solubility at the strained region that promotes continuous growth of the H bubble via a chain-reaction effect in W. This result can also interpret the H bubble formation even if no radiation damage is produced in W exposed to low-energy H plasma.

Nonlinear interaction between underwater explosion bubble and structure based on fully coupled model

NASA Astrophysics Data System (ADS)

Zhang, A. M.; Wu, W. B.; Liu, Y. L.; Wang, Q. X.

2017-08-01

The interaction between an underwater explosion bubble and an elastic-plastic structure is a complex transient process, accompanying violent bubble collapsing, jet impact, penetration through the bubble, and large structural deformation. In the present study, the bubble dynamics are modeled using the boundary element method and the nonlinear transient structural response is modeled using the explicit finite element method. A new fully coupled 3D model is established through coupling the equations for the state variables of the fluid and structure and solving them as a set of coupled linear algebra equations. Based on the acceleration potential theory, the mutual dependence between the hydrodynamic load and the structural motion is decoupled. The pressure distribution in the flow field is calculated with the Bernoulli equation, where the partial derivative of the velocity potential in time is calculated using the boundary integral method to avoid numerical instabilities. To validate the present fully coupled model, the experiments of small-scale underwater explosion near a stiffened plate are carried out. High-speed imaging is used to capture the bubble behaviors and strain gauges are used to measure the strain response. The numerical results correspond well with the experimental data, in terms of bubble shapes and structural strain response. By both the loosely coupled model and the fully coupled model, the interaction between a bubble and a hollow spherical shell is studied. The bubble patterns vary with different parameters. When the fully coupled model and the loosely coupled model are advanced with the same time step, the error caused by the loosely coupled model becomes larger with the coupling effect becoming stronger. The fully coupled model is more stable than the loosely coupled model. Besides, the influences of the internal fluid on the dynamic response of the spherical shell are studied. At last, the case that the bubble interacts with an air-backed stiffened plate is simulated. The associated interesting physical phenomenon is obtained and expounded.

Single-bubble sonoluminescence in sulfuric acid and water: bubble dynamics, stability, and continuous spectra.

PubMed

Puente, Gabriela F; García-Martínez, Pablo; Bonetto, Fabián J

2007-01-01

We present theoretical calculations of an argon bubble in a liquid solution of 85%wt sulfuric acid and 15%wt water in single-bubble sonoluminescence. We used a model without free parameters to be adjusted. We predict from first principles the region in parameter space for stable bubble evolution, the temporal evolution of the bubble radius, the maximum temperature, pressures, and the light spectra due to thermal emissions. We also used a partial differential equation based model (hydrocode) to compute the temperature and pressure evolutions at the center of the bubble during maximum compression. We found the behavior of this liquid mixture to be very different from water in several aspects. Most of the models in sonoluminescence were compared with water experimental results.

Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion

NASA Astrophysics Data System (ADS)

Nigmatulin, Robert I.; Akhatov, Iskander Sh.; Topolnikov, Andrey S.; Bolotnova, Raisa Kh.; Vakhitova, Nailya K.; Lahey, Richard T.; Taleyarkhan, Rusi P.

2005-10-01

This paper provides the theoretical basis for energetic vapor bubble implosions induced by a standing acoustic wave. Its primary goal is to describe, explain, and demonstrate the plausibility of the experimental observations by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] of thermonuclear fusion for imploding cavitation bubbles in chilled deuterated acetone. A detailed description and analysis of these data, including a resolution of the criticisms that have been raised, together with some preliminary HYDRO code simulations, has been given by Nigmatulin et al. [Vestnik ANRB (Ufa, Russia) 4, 3 (2002); J. Power Energy 218-A, 345 (2004)] and Lahey et al. [Adv. Heat Transfer (to be published)]. In this paper a hydrodynamic shock (i.e., HYDRO) code model of the spherically symmetric motion for a vapor bubble in an acoustically forced liquid is presented. This model describes cavitation bubble cluster growth during the expansion period, followed by a violent implosion during the compression period of the acoustic cycle. There are two stages of the bubble dynamics process. The first, low Mach number stage, comprises almost all the time of the acoustic cycle. During this stage, the radial velocities are much less than the sound speeds in the vapor and liquid, the vapor pressure is very close to uniform, and the liquid is practically incompressible. This process is characterized by the inertia of the liquid, heat conduction, and the evaporation or condensation of the vapor. The second, very short, high Mach number stage is when the radial velocities are the same order, or higher, than the sound speeds in the vapor and liquid. In this stage high temperatures, pressures, and densities of the vapor and liquid take place. The model presented herein has realistic equations of state for the compressible liquid and vapor phases, and accounts for nonequilibrium evaporation/condensation kinetics at the liquid/vapor interface. There are interacting shock waves in both phases, which converge toward and reflect from the center of the bubble, causing dissociation, ionization, and other related plasma physics phenomena during the final stage of bubble collapse. For a vapor bubble in a deuterated organic liquid (e.g., acetone), during the final stage of collapse there is a nanoscale region (diameter ˜100nm) near the center of the bubble in which, for a fraction of a picosecond, the temperatures and densities are extremely high (˜108K and ˜10g/cm3, respectively) such that thermonuclear fusion may take place. To quantify this, the kinetics of the local deuterium/deuterium (D/D) nuclear fusion reactions was used in the HYDRO code to determine the intensity of the fusion reactions. Numerical HYDRO code simulations of the bubble implosion process have been carried out for the experimental conditions used by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] at Oak Ridge National Laboratory. The results show good agreement with the experimental data on bubble fusion that was measured in chilled deuterated acetone.

Analytic model of electron self-injection in a plasma wakefield accelerator in the strongly nonlinear bubble regime

NASA Astrophysics Data System (ADS)

Yi, Sunghwan; Khudik, Vladimir; Shvets, Gennady

2012-10-01

We study self-injection into a plasma wakefield accelerator in the blowout (or bubble) regime, where the bubble evolves due to background density inhomogeneities. To explore trapping, we generalize an analytic model for the wakefields inside the bubble [1] to derive expressions for the fields outside. With this extended model, we show that a return current in the bubble sheath layer plays an important role in determining the trapped electron trajectories. We explore an injection mechanism where bubble growth due to a background density downramp causes reduction of the electron Hamiltonian in the co-moving frame, trapping the particle in the dynamically deepening potential well [2]. Model calculations agree quantitatively with PIC simulations on the bubble expansion rate required for trapping, as well as the range of impact parameters for which electrons are trapped. This is an improvement over our previous work [3] using a simplified spherical bubble model, which ignored the fields outside of the bubble and hence overestimated the expansion rate required for trapping. [4pt] [1] W. Lu et al., Phys. Plasmas 13, 056709 (2006).[0pt] [2] S. Kalmykov et al., Phys. Rev. Lett 103, 135004 (2009).[0pt] [3] S.A. Yi et al., Plasma Phys. Contr. Fus. 53, 014012 (2011).

Thermodynamic stability of nanosized multicomponent bubbles/droplets: the square gradient theory and the capillary approach.

PubMed

Wilhelmsen, Øivind; Bedeaux, Dick; Kjelstrup, Signe; Reguera, David

2014-01-14

Formation of nanosized droplets/bubbles from a metastable bulk phase is connected to many unresolved scientific questions. We analyze the properties and stability of multicomponent droplets and bubbles in the canonical ensemble, and compare with single-component systems. The bubbles/droplets are described on the mesoscopic level by square gradient theory. Furthermore, we compare the results to a capillary model which gives a macroscopic description. Remarkably, the solutions of the square gradient model, representing bubbles and droplets, are accurately reproduced by the capillary model except in the vicinity of the spinodals. The solutions of the square gradient model form closed loops, which shows the inherent symmetry and connected nature of bubbles and droplets. A thermodynamic stability analysis is carried out, where the second variation of the square gradient description is compared to the eigenvalues of the Hessian matrix in the capillary description. The analysis shows that it is impossible to stabilize arbitrarily small bubbles or droplets in closed systems and gives insight into metastable regions close to the minimum bubble/droplet radii. Despite the large difference in complexity, the square gradient and the capillary model predict the same finite threshold sizes and very similar stability limits for bubbles and droplets, both for single-component and two-component systems.

Thermodynamic stability of nanosized multicomponent bubbles/droplets: The square gradient theory and the capillary approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilhelmsen, Øivind, E-mail: oivind.wilhelmsen@ntnu.no; Bedeaux, Dick; Kjelstrup, Signe

Formation of nanosized droplets/bubbles from a metastable bulk phase is connected to many unresolved scientific questions. We analyze the properties and stability of multicomponent droplets and bubbles in the canonical ensemble, and compare with single-component systems. The bubbles/droplets are described on the mesoscopic level by square gradient theory. Furthermore, we compare the results to a capillary model which gives a macroscopic description. Remarkably, the solutions of the square gradient model, representing bubbles and droplets, are accurately reproduced by the capillary model except in the vicinity of the spinodals. The solutions of the square gradient model form closed loops, which showsmore » the inherent symmetry and connected nature of bubbles and droplets. A thermodynamic stability analysis is carried out, where the second variation of the square gradient description is compared to the eigenvalues of the Hessian matrix in the capillary description. The analysis shows that it is impossible to stabilize arbitrarily small bubbles or droplets in closed systems and gives insight into metastable regions close to the minimum bubble/droplet radii. Despite the large difference in complexity, the square gradient and the capillary model predict the same finite threshold sizes and very similar stability limits for bubbles and droplets, both for single-component and two-component systems.« less

Transformer overload characteristics---Bubble evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woods, E.E.; Wendel, R.C.; Dresser, R.D.

1988-08-01

Project RP1289-3 explores significant parameters affecting bubble evolution from transformer oil under high temperature operating conditions to address the question: Does ''real life'' operation of a transformer cause harmful bubbling conditions. Studies outlined in the project are designed to determine when bubbling occurs in transformers and if bubbling can be harmful during the normal operation of these transformers. Data obtained from these studies should provide a basis for utilities to perform risk assessments in relation to their loading practices. The program is designed to demonstrate those conditions under which bubbling occurs in transformers by using controlled models and actual signalmore » phase transformers that were designed to give access to both high and low voltage windings for the purpose of viewing bubble generation. Results and observations from tests on the full-size transformers, thermal models, and electrical models have led to the conclusion that bubbles can occur under operating conditions. The electrical models show that dielectric strength can be reduced by as much as 40 percent due to the presence of bubbles. Because of factory safety considerations, the transformers could not be tested at hot spot temperatures greater than 140/degree/C. Therefore, there is no information on the dielectric strength of the full-size transformers under bubbling conditions. 4 refs., 28 figs., 45 tabs.« less

Localized Tissue Surrogate Deformation due to Controlled Single Bubble Cavitation

DTIC Science & Technology

2014-08-27

calculate liquid jet formation with collapse of an empty spherical bubble due to the high surrounding fluid pressure 18. Experimental evidence of...maximum collapse pressures over a wide range between 8 MPa 13 to 2.5 GPa 11 have also been calculated . 5 A fundamental problem in the study of...and a digital image correlation (DIC) technique was used to calculate strain fields during bubble growth and collapse. The subsequent response of the

Modeling and Measurements of Multiphase Flow and Bubble Entrapment in Steel Continuous Casting

NASA Astrophysics Data System (ADS)

Jin, Kai; Thomas, Brian G.; Ruan, Xiaoming

2016-02-01

In steel continuous casting, argon gas is usually injected to prevent clogging, but the bubbles also affect the flow pattern, and may become entrapped to form defects in the final product. To investigate this behavior, plant measurements were conducted, and a computational model was applied to simulate turbulent flow of the molten steel and the transport and capture of argon gas bubbles into the solidifying shell in a continuous slab caster. First, the flow field was solved with an Eulerian k- ɛ model of the steel, which was two-way coupled with a Lagrangian model of the large bubbles using a discrete random walk method to simulate their turbulent dispersion. The flow predicted on the top surface agreed well with nailboard measurements and indicated strong cross flow caused by biased flow of Ar gas due to the slide-gate orientation. Then, the trajectories and capture of over two million bubbles (25 μm to 5 mm diameter range) were simulated using two different capture criteria (simple and advanced). Results with the advanced capture criterion agreed well with measurements of the number, locations, and sizes of captured bubbles, especially for larger bubbles. The relative capture fraction of 0.3 pct was close to the measured 0.4 pct for 1 mm bubbles and occurred mainly near the top surface. About 85 pct of smaller bubbles were captured, mostly deeper down in the caster. Due to the biased flow, more bubbles were captured on the inner radius, especially near the nozzle. On the outer radius, more bubbles were captured near to narrow face. The model presented here is an efficient tool to study the capture of bubbles and inclusion particles in solidification processes.

Dissolution of spherical cap CO2 bubbles attached to flat surfaces in air-saturated water

NASA Astrophysics Data System (ADS)

Peñas, Pablo; Parrales, Miguel A.; Rodriguez-Rodriguez, Javier

2014-11-01

Bubbles attached to flat surfaces immersed in quiescent liquid environments often display a spherical cap (SC) shape. Their dissolution is a phenomenon commonly observed experimentally. Modelling these bubbles as fully spherical may lead to an inaccurate estimate of the bubble dissolution rate. We develop a theoretical model for the diffusion-driven dissolution or growth of such multi-component SC gas bubbles under constant pressure and temperature conditions. Provided the contact angle of the bubble with the surface is large, the concentration gradients in the liquid may be approximated as spherically symmetric. The area available for mass transfer depends on the instantaneous bubble contact angle, whose dynamics is computed from the adhesion hysteresis model [Hong et al., Langmuir, vol. 27, 6890-6896 (2011)]. Numerical simulations and experimental measurements on the dissolution of SC CO2 bubbles immersed in air-saturated water support the validity of our model. We verify that contact line pinning slows down the dissolution rate, and the fact that any bubble immersed in a saturated gas-liquid solution eventually attains a final equilibrium size. Funded by the Spanish Ministry of Economy and Competitiveness through Grant DPI2011-28356-C03-0.

Bubble number saturation curve and asymptotics of hypobaric and hyperbaric exposures.

PubMed

Wienke, B R

1991-12-01

Within bubble number limits of the varying permeability and reduced gradient bubble models, it is shown that a linear form of the saturation curve for hyperbaric exposures and a nearly constant decompression ratio for hypobaric exposures are simultaneously recovered from the phase volume constraint. Both limits are maintained within a single bubble number saturation curve. A bubble term, varying exponentially with inverse pressure, provides closure. Two constants describe the saturation curve, both linked to seed numbers. Limits of other decompression models are also discussed and contrasted for completeness. It is suggested that the bubble number saturation curve thus provides a consistent link between hypobaric and hyperbaric data, a link not established by earlier decompression models.

Microbubbles and ultrasound: a bird's eye view.

PubMed

Kaul, Sanjiv

2004-01-01

Gas-filled microbubbles were initially used as ultrasound contrast agent because of their intravascular rheology, which is similar to that of red blood cells. Their transit through tissue can thus be quantified with ultrasound. More recently, these bubbles have been successfully used for molecular imaging by incorporating ligands on their surfaces that will adhere to cellular and other components within the microvasculature and can be detected by ultrasound. These bubbles have also been used for delivery of genes and drugs which can be released locally by disruption of the bubbles with high-energy ultrasound. Finally, bioeffects produced by localized ultrasound disruption of microbubbles have been shown to induce angiogenesis. This brief review will provide a bird's eye view of these applications.

Effect of an entrained air bubble on the acoustics of an ink channel.

PubMed

Jeurissen, Roger; de Jong, Jos; Reinten, Hans; van den Berg, Marc; Wijshoff, Herman; Versluis, Michel; Lohse, Detlef

2008-05-01

Piezo-driven inkjet systems are very sensitive to air entrapment. The entrapped air bubbles grow by rectified diffusion in the ink channel and finally result in nozzle failure. Experimental results on the dynamics of fully grown air bubbles are presented. It is found that the bubble counteracts the pressure buildup necessary for the droplet formation. The channel acoustics and the air bubble dynamics are modeled. For good agreement with the experimental data it is crucial to include the confined geometry into the model: The air bubble acts back on the acoustic field in the channel and thus on its own dynamics. This two-way coupling limits further bubble growth and thus determines the saturation size of the bubble.

Influence of mass transfer on bubble plume hydrodynamics.

PubMed

Lima Neto, Iran E; Parente, Priscila A B

2016-03-01

This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.

Regimes of Micro-bubble Formation Using Gas Injection into Ladle Shroud

NASA Astrophysics Data System (ADS)

Chang, Sheng; Cao, Xiangkun; Zou, Zongshu

2018-03-01

Gas injection into a ladle shroud is a practical approach to produce micro-bubbles in tundishes, to promote inclusion removal from liquid steel. A semi-empirical model was established to characterize the bubble formation considering the effect of shearing action combined with the non-fully bubble break-up by turbulence. The model shows a good accuracy in predicting the size of bubbles formed in complex flow within the ladle shroud.

Bubble Dynamics and Resulting Noise from Traveling Bubble Cavitation.

DTIC Science & Technology

1982-04-13

proportional to the gas content. The subjectivity of visual cavitation determination is evidenced by the maximum standard deviation. As mentioned before...bubble radii at the maximum radius position on the model. The point on the model where the bubble will be at its maximum volume was determined by...48 3.7 Recording Bubble Dynamics . • . * . . . . 52 3.8 Measurement of Gas Nuclei in Water 0 • 52 3 TABLE OF CONTENTS (continued) Paqe

Regimes of Micro-bubble Formation Using Gas Injection into Ladle Shroud

NASA Astrophysics Data System (ADS)

Chang, Sheng; Cao, Xiangkun; Zou, Zongshu

2018-06-01

Gas injection into a ladle shroud is a practical approach to produce micro-bubbles in tundishes, to promote inclusion removal from liquid steel. A semi-empirical model was established to characterize the bubble formation considering the effect of shearing action combined with the non-fully bubble break-up by turbulence. The model shows a good accuracy in predicting the size of bubbles formed in complex flow within the ladle shroud.

Acoustic measurement of bubble size and position in a piezo driven inkjet printhead

NASA Astrophysics Data System (ADS)

van der Bos, Arjan; Jeurissen, Roger; de Jong, Jos; Stevens, Richard; Versluis, Michel; Reinten, Hans; van den Berg, Marc; Wijshoff, Herman; Lohse, Detlef

2008-11-01

A bubble can be entrained in the ink channel of a piezo-driven inkjet printhead, where it grows by rectified diffusion. If large enough, the bubble counteracts the pressure buildup at the nozzle, resulting in nozzle failure. Here an acoustic sizing method for the volume and position of the bubble is presented. The bubble response is detected by the piezo actuator itself, operating in a sensor mode. The method used to determine the volume and position of the bubble is based on a linear model in which the interaction between the bubble and the channel are included. This model predicts the acoustic signal for a given position and volume of the bubble. The inverse problem is to infer the position and volume of the bubble from the measured acoustic signal. By solving it, we can thus acoustically measure size and position of the bubble. The validity of the presented method is supported by time-resolved optical observations of the dynamics of the bubble within an optically accessible ink-jet channel.

A detection algorithm for scale analysis of post-sunset low-latitude plasma depletions as observed by the Swarm constellation mission

NASA Astrophysics Data System (ADS)

Kervalishvili, Guram; Stolle, Claudia; Xiong, Chao

2016-04-01

ESA's constellation mission Swarm was successfully launched on 22 November 2013. The three satellites achieved their final constellation on 17 April 2014 and since then Swarm-A and Swarm-C orbiting the Earth at about 470 km (flying side-by-side) and Swarm-B at about 520 km altitude. The satellites carry instruments to monitor the F-region electron density with a sampling frequency of 2 Hz. This paper will present a detection algorithm for low-latitude post-sunset plasma bubbles (depletions), which uses local minima and maxima to detect depletions directly from electron density readings from Swarm. Our analyses were performed in the magnetic latitude (MLat) and local time (MLT) coordinate system. The detection procedure also captures the amplitude of depletion, which is called depth in the following. The width of a bubble corresponds to the length the satellite is located inside a depletion. We discuss the global distribution of depth and width of plasma bubbles and its seasonal and local time dependence for all three Swarm satellites from April 2015 through September 2015. As expected, on global average the bubble occurrence rate is highest for combined equinoxes (Mar, Apr, Sep, and Oct) and smallest for June solstice (May, Jun, Jul, and Aug). MLT distribution of the bubble occurrence number shows a sharp increase at about 19 MLT and decreases towards post-midnight hours. Interestingly, there is an inverse relation between depth and width of bubbles as function of MLT. This is true for all seasons and for all Swarm satellites. The bubble depth (width) is decreasing (increasing) from post-sunset to post-midnight for December solstice (Jan, Feb, Nov, and Dec) and combined equinoxes with about the same amplitude values for bubbles depth (width). Therefore we suggest that at post midnight when the depletions are less steep the structures of the depletions is broader than early after sunset. However for June solstice the depletions are less deep and the bubble depth and width do not change significantly throughout the evening. Deepest depletions occur at around +/- 10° magnetic latitude that is at the inner edge of the ionisation anomaly with density maxima at around 15° MLat. Therefore, the level of background electron density does not only determine the depth of a post-sunset depletion.

A reduced-order, single-bubble cavitation model with applications to therapeutic ultrasound

PubMed Central

Kreider, Wayne; Crum, Lawrence A.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2011-01-01

Cavitation often occurs in therapeutic applications of medical ultrasound such as shock-wave lithotripsy (SWL) and high-intensity focused ultrasound (HIFU). Because cavitation bubbles can affect an intended treatment, it is important to understand the dynamics of bubbles in this context. The relevant context includes very high acoustic pressures and frequencies as well as elevated temperatures. Relative to much of the prior research on cavitation and bubble dynamics, such conditions are unique. To address the relevant physics, a reduced-order model of a single, spherical bubble is proposed that incorporates phase change at the liquid-gas interface as well as heat and mass transport in both phases. Based on the energy lost during the inertial collapse and rebound of a millimeter-sized bubble, experimental observations were used to tune and test model predictions. In addition, benchmarks from the published literature were used to assess various aspects of model performance. Benchmark comparisons demonstrate that the model captures the basic physics of phase change and diffusive transport, while it is quantitatively sensitive to specific model assumptions and implementation details. Given its performance and numerical stability, the model can be used to explore bubble behaviors across a broad parameter space relevant to therapeutic ultrasound. PMID:22088026

A reduced-order, single-bubble cavitation model with applications to therapeutic ultrasound.

PubMed

Kreider, Wayne; Crum, Lawrence A; Bailey, Michael R; Sapozhnikov, Oleg A

2011-11-01

Cavitation often occurs in therapeutic applications of medical ultrasound such as shock-wave lithotripsy (SWL) and high-intensity focused ultrasound (HIFU). Because cavitation bubbles can affect an intended treatment, it is important to understand the dynamics of bubbles in this context. The relevant context includes very high acoustic pressures and frequencies as well as elevated temperatures. Relative to much of the prior research on cavitation and bubble dynamics, such conditions are unique. To address the relevant physics, a reduced-order model of a single, spherical bubble is proposed that incorporates phase change at the liquid-gas interface as well as heat and mass transport in both phases. Based on the energy lost during the inertial collapse and rebound of a millimeter-sized bubble, experimental observations were used to tune and test model predictions. In addition, benchmarks from the published literature were used to assess various aspects of model performance. Benchmark comparisons demonstrate that the model captures the basic physics of phase change and diffusive transport, while it is quantitatively sensitive to specific model assumptions and implementation details. Given its performance and numerical stability, the model can be used to explore bubble behaviors across a broad parameter space relevant to therapeutic ultrasound.

A hydrodynamical model of the circumstellar bubble created by two massive stars

NASA Astrophysics Data System (ADS)

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2012-05-01

Context. Numerical models of the wind-blown bubble of massive stars usually only account for the wind of a single star. However, since massive stars are usually formed in clusters, it would be more realistic to follow the evolution of a bubble created by several stars. Aims: We develop a two-dimensional (2D) model of the circumstellar bubble created by two massive stars, a 40 M⊙ star and a 25 M⊙ star, and follow its evolution. The stars are separated by approximately 16 pc and surrounded by a cold medium with a density of 20 particles per cm3. Methods: We use the MPI-AMRVAC hydrodynamics code to solve the conservation equations of hydrodynamics on a 2D cylindrical grid using time-dependent models for the wind parameters of the two stars. At the end of the stellar evolution (4.5 and 7.0 million years for the 40 and 25 M⊙ stars, respectively), we simulate the supernova explosion of each star. Results: Each star initially creates its own bubble. However, as the bubbles expand they merge, creating a combined, aspherical bubble. The combined bubble evolves over time, influenced by the stellar winds and supernova explosions. Conclusions: The evolution of a wind-blown bubble created by two stars deviates from that of the bubbles around single stars. In particular, once one of the stars has exploded, the bubble is too large for the wind of the remaining star to maintain and the outer shell starts to disintegrate. The lack of thermal pressure inside the bubble also changes the behavior of circumstellar features close to the remaining star. The supernovae are contained inside the bubble, which reflects part of the energy back into the circumstellar medium. Movies are available in electronic form at http://www.aanda.org

Theoretical study on bubble formation and flow condensation in downflow channel with horizontal gas injection

NASA Astrophysics Data System (ADS)

Zhu, Kang; Li, Yanzhong; Wang, Jiaojiao; Ma, Yuan; Wang, Lei; Xie, Fushou

2018-05-01

Bubble formation and condensation in liquid pipes occur widely in industrial systems such as cryogenic propellant feeding system. In this paper, an integrated theoretical model is established to give a comprehensive description of the bubble formation, motion and condensation process. The model is validated by numerical simulations and bubble condensation experiments from references, and good agreements are achieved. The bubble departure diameter at the orifice and the flow condensation length in the liquid channel are predicted by the model, and effects of various influencing parameters on bubble behaviors are analyzed. Prediction results indicate that the orifice diameter, the gas feeding rate, and the liquid velocity are the primary influence factors on the bubble departure diameter. The interfacial heat transfer as well as the bubble departure diameter has a direct impact on the bubble flow condensation length, which increases by 2.5 times over a system pressure range of 0.1 0.4 MPa, and decreases by 85% over a liquid subcooling range of 5 30 K. This work could be beneficial to the prediction of bubble formation and flow condensation processes and the design of cryogenic transfer pipes.

Effect of added mass on the interaction of bubbles in a low-Reynolds-number shear flow.

PubMed

Lavrenteva, Olga; Prakash, Jai; Nir, Avinoam

2016-02-01

Equal size air bubbles that are entrapped by a Taylor vortex of the secondary flow in a Couette device, thereby defying buoyancy, slowly form a stable ordered ring with equal separation distances between all neighbors. We present two models of the process dynamics based on force balance on a bubble in the presence of other bubbles positioned on the same streamline in a simple shear flow. The forces taken into account are the viscous resistance, the added mass force, and the inertia-induced repulsing force between two bubbles in a low-Reynolds-number shear flow obtained in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)]. The first model of the process assumes that each bubble interacts solely with its nearest neighbors. The second model takes into account pairwise interactions among all the bubbles in the ring. The performed dynamic simulations were compared to the experimental results reported in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)] and to the results of quasistationary models (ignoring the added mass effect) suggested in that paper. It is demonstrated that taking into account the effect of added mass, the models describe the major effect of the bubbles' ordering, provide good estimation of the relaxation time, and also predict nonmonotonic behavior of the separation distance between the bubbles, which exhibit over- and undershooting of equilibrium separations. The latter effects were observed in experiments, but are not predicted by the quasistationary models.

One-dimensional bubble model of pulsed discharge in water

NASA Astrophysics Data System (ADS)

Lu, XinPei

2007-09-01

In this paper, a one-dimensional bubble model of pulsed discharge in water is presented. With a total input energy of 0.63J, the simulation results show that when the bubble collapses at the center of the bubble, the plasma pressure oscillates strongly. It oscillates between 800 and 1150atm with an oscillation frequency of about 6.9MHz, while at r =R/2 (R: bubble radius), the gas velocity oscillates intensely at the same frequency. It oscillates between -235 and 229m/s when the bubble radius reaches its minimum. But it does not oscillate at r =R because of the inertia of the surrounding water. The bubble collapses and reexpands with almost the same speed as that of the zero-dimensional (0D) model. This further confirms why the shock wave pressure from the 0D mode has a good agreement with the experimental results since the shock wave pressure is only determined by the bubble wall velocity v(R ).

Investigation of Nucleate Boiling Mechanisms Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Dhir, V. K.; Qiu, D. M.; Ramanujapu, N.; Hasan, M. M.

1999-01-01

The present work is aimed at the experimental studies and numerical modeling of the bubble growth mechanisms of a single bubble attached to a heating surface and of a bubble sliding along an inclined heated plate. Single artificial cavity of 10 microns in diameter was made on the polished Silicon wafer which was electrically heated at the back side in order to control the surface nucleation superheat. Experiments with a sliding bubble were conducted at different inclination angles of the downward facing heated surface for the purpose of studying the effect of magnitude of components of gravity acting parallel to and normal to the heat transfer surface. Information on the bubble shape and size, the bubble induced liquid velocities as well as the surface temperature were obtained using the high speed imaging and hydrogen bubble techniques. Analytical/numerical models were developed to describe the heat transfer through the micro-macro layer underneath and around a bubble formed at a nucleation site. In the micro layer model the capillary and disjoining pressures were included. Evolution of the bubble-liquid interface along with induced liquid motion was modeled. As a follow-up to the studies at normal gravity, experiments are being conducted in the KC-135 aircraft to understand the bubble growth/detachment under low gravity conditions. Experiments have been defined to be performed under long duration of microgravity conditions in the space shuttle. The experiment in the space shuttle will provide bubble growth and detachment data at microgravity and will lead to validation of the nucleate boiling heat transfer model developed from the preceding studies conducted at normal and low gravity (KC-135) conditions.

Numerical simulation of cavitation bubble dynamics induced by ultrasound waves in a high frequency reactor.

PubMed

Servant, G; Caltagirone, J P; Gérard, A; Laborde, J L; Hita, A

2000-10-01

The use of high frequency ultrasound in chemical systems is of major interest to optimize chemical procedures. Characterization of an open air 477 kHz ultrasound reactor shows that, because of the collapse of transient cavitation bubbles and pulsation of stable cavitation bubbles, chemical reactions are enhanced. Numerical modelling is undertaken to determine the spatio-temporal evolution of cavitation bubbles. The calculus of the emergence of cavitation bubbles due to the acoustic driving (by taking into account interactions between the sound field and bubbles' distribution) gives a cartography of bubbles' emergence within the reactor. Computation of their motion induced by the pressure gradients occurring in the reactor show that they migrate to the pressure nodes. Computed bubbles levitation sites gives a cartography of the chemical activity of ultrasound. Modelling of stable cavitation bubbles' motion induced by the motion of the liquid gives some insight on degassing phenomena.

Bubble video experiments in the marine waters off Panarea Island (Italy): real-world data for modelling CO2 bubble dissolution and evolution

NASA Astrophysics Data System (ADS)

Beaubien, Stan; De Vittor, Cinzia; McGinnis, Dan; Bigi, Sabina; Comici, Cinzia; Ingrosso, Gianmarco; Lombardi, Salvatore; Ruggiero, Livio

2014-05-01

Carbon capture and storage is expected to provide an important, short-term contribution to mitigate global climate change due to anthropogenic emissions of CO2. Offshore reservoirs are particularly favourable, however concerns exist regarding the potential for CO2 leakage into the water column (with possible ecosystem impacts) and the atmosphere. Although laboratory experiments and modelling can examine these issues, the study of natural systems can provide a more complete and realistic understanding. For this reason the natural CO2 emission site off the coast of Panarea Island (Italy) was chosen for study within the EC-funded ECO2 project. The present paper discusses the results of field experiments conducted at this site to better understand the fate of CO2 gas bubbles as they rise through the water column, and to use this real-world data as input to test the predictive capabilities of a bubble model. Experiments were conducted using a 1m wide x 1m deep x 3m tall, hollow-tube structure equipped with a vertical guide on the front face and a dark, graduated cloth for contrast and depth reference on the back. A Plexiglas box was filled with the naturally emitted gas and fixed on the seafloor inside the structure. Tubes exit the top of the box to make bubbles of different diameters, while valves on each tube control bubble release rate. Bubble rise velocity was measured by tracking each bubble with a HD video camera mounted in the guide and calculating values over 20 cm intervals. Bubble diameter was measured by filming the bubbles as they collide with a graduated Plexiglas sheet deployed horizontally at the measurement height. Bubble gas was collected at different heights using a funnel and analysed in the laboratory for CO2, O2+Ar, N2, and CH4. Water parameters were measured by performing a CTD cast beside the structure and collecting water samples at four depths using a Niskin bottle; samples were analysed in the laboratory for all carbonate system species, DO, and dissolved gases. An in-house developed GasPro sensor was also mounted on the structure to monitor pCO2 over the entire 2.5 hour duration of the experiment. The obtained data were used as input into the Discrete Bubble Model (DBM) (e.g., McGinnis et al., 2011, doi:10.1029/2010JC006557). The DBM uses mass balance to predict the gas flux across the bubble surface, whereby gas flux direction depends on internal bubble gas concentration and ambient concentration, and considering the Henry's coefficient and partial pressure of the gas. The model uses bubble-size dependent relationships for the mass transfer rate and the bubble rise velocity. Important model input parameters include: bubble size; depth; ambient dissolved gas concentrations, temperature and salinity; and initial bubble gas concentrations. Measured and modelled results are compared, showing good general agreement. Based on the concentrations measured at the lowest level, the modelled and measured bubble concentrations match very closely. Bubble size values do not match as well if this initial concentration is used, however they improve as a value closer to 100% CO2 is applied. This preliminary study has shown promising results and highlight areas where experimental design and data quality should be improved in the next phase of the study.

Experimental study on bubble dynamics and wall heat transfer arising from a single nucleation site at subcooled flow boiling conditions – Part 2: Data analysis on sliding bubble characteristics and associated wall heat transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yooa, Junsoo; Estrada-Perez, Carlos E.; Hassan, Yassin A.

In this second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single nucleation site for better observation of both the sliding bubbles’ characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. Our results showed that slidingmore » bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the nucleation site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single nucleation site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the nucleation site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur<0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the nucleation site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. Particularly, the sliding bubble characteristics such as bubble growth behavior observed near the nucleation site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.« less

Experimental study on bubble dynamics and wall heat transfer arising from a single nucleation site at subcooled flow boiling conditions – Part 2: Data analysis on sliding bubble characteristics and associated wall heat transfer

DOE PAGES

Yooa, Junsoo; Estrada-Perez, Carlos E.; Hassan, Yassin A.

2016-04-28

In this second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single nucleation site for better observation of both the sliding bubbles’ characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. Our results showed that slidingmore » bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the nucleation site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single nucleation site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the nucleation site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur<0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the nucleation site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. Particularly, the sliding bubble characteristics such as bubble growth behavior observed near the nucleation site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.« less

Layered storage of biogenic methane-enriched gas bubbles in peat: A lumped capacitance model controlled by soil structure

NASA Astrophysics Data System (ADS)

Chen, X.; Comas, X.; Binley, A. M.; Slater, L. D.

2017-12-01

Methane can accumulate in the gaseous phase in peats, and enter the atmosphere as gas bubbles with a mass flux higher than that via diffusion and plant-mediated pathways. A complete understanding of the mechanisms regulating bubble storage in peats remains incomplete. We developed a layered model to quantify the storage of gas bubbles over a peat column based on a general lumped capacitance model. This conceptual model was applied to explain the effects of peat structure on bubble storage at different depths observed in a laboratory experiment. A peat monolith was collected from the Everglades, a subtropical wetland located in Florida (USA), and kept submerged in a cuboid chamber over 102 days until gas bubble saturation was achieved. Time-lapse ground-penetrating radar (GPR) was used to estimate changes in gas content of each layer and the corresponding average dimensions of stored gas bubbles. The results highlight a hotspot layer of bubble accumulation at depths between 5 and 10 cm below the monolith surface. Bubbles in this shallow hotspot layer were larger relative to those in deeper layers, whilst the degree of decomposition of the upper layers was generally smaller than that of the lower layers based on von Post humification tests. X-ray Computer tomography (CT) was applied to resin-impregnated peat sections from different depths and the results showed that a higher porosity promotes bubbles storage. The stored gas bubbles were released by changing water levels and the air CH4 concentrations above the peat monolith were measured using a flow-through chamber system to confirm the high CH4 concentration in the stored bubbles. Our findings suggest that bubble capacitance is related to the difference in size between gas bubbles and peat pores. This work has implications for better understanding how changes in water table elevation associated with climate change and sea level rise (particularly for freshwater wetlands near coastal areas like the Everglades) may potentially alter bubble sizes, thus bubble storage in peats.

Are winds in cities always slower than in the countryside? Modelling the Urban Wind Island Effect

NASA Astrophysics Data System (ADS)

Droste, Arjan; Steeneveld, Gert-Jan

2017-04-01

Though the Urban Heat Island has been extensively studied, relatively little has been documented about differences in wind between the city as a whole and the countryside. Urban winds are difficult to capture in both observations and modelling, due to the complex urban canyon and neighbourhood geometry. This study uses a straightforward mixed-layer model (Tennekes & Driedonks, 1981) to investigate the contrast between the diurnal cycle of wind in the urban and the rural environment. The model contains one urban and one rural column, to identify differences in wind patterns between city and countryside under equal geostrophic forcing. The model has been evaluated against rural observations from the 213 m. Cabauw tower (the Netherlands), and the urban observations from the BUBBLE campaign (Basel, Rotach et al., 2005). The influence of the urban fabric on the wind is investigated by varying the surface underneath the column model using the 10 urban Local Climate Zones, thereby altering building height, fraction of impervious surface, and initial boundary-layer depth. First results show that for high initial urban boundary-layer depths compared to the rural boundary-layer depth, the urban column can be much windier than its rural counterpart: i.e. the urban Wind Island Effect. The effect appears to be most prominent in the morning and the late afternoon (up to 1 m/s), for Local Climate Zones with lower buildings (3 or 7). BUBBLE observations confirm the timing of the Wind Island Effect, though with weaker magnitude.

Physics of puffing and microexplosion of emulsion fuel droplets

NASA Astrophysics Data System (ADS)

Shinjo, J.; Xia, J.; Ganippa, L. C.; Megaritis, A.

2014-10-01

The physics of water-in-oil emulsion droplet microexplosion/puffing has been investigated using high-fidelity interface-capturing simulation. Varying the dispersed-phase (water) sub-droplet size/location and the initiation location of explosive boiling (bubble formation), the droplet breakup processes have been well revealed. The bubble growth leads to local and partial breakup of the parent oil droplet, i.e., puffing. The water sub-droplet size and location determine the after-puffing dynamics. The boiling surface of the water sub-droplet is unstable and evolves further. Finally, the sub-droplet is wrapped by boiled water vapor and detaches itself from the parent oil droplet. When the water sub-droplet is small, the detachment is quick, and the oil droplet breakup is limited. When it is large and initially located toward the parent droplet center, the droplet breakup is more extensive. For microexplosion triggered by the simultaneous growth of multiple separate bubbles, each explosion is local and independent initially, but their mutual interactions occur at a later stage. The degree of breakup can be larger due to interactions among multiple explosions. These findings suggest that controlling microexplosion/puffing is possible in a fuel spray, if the emulsion-fuel blend and the ambient flow conditions such as heating are properly designed. The current study also gives us an insight into modeling the puffing and microexplosion of emulsion droplets and sprays.

Size distributions of micro-bubbles generated by a pressurized dissolution method

NASA Astrophysics Data System (ADS)

Taya, C.; Maeda, Y.; Hosokawa, S.; Tomiyama, A.; Ito, Y.

2012-03-01

Size of micro-bubbles is widely distributed in the range of one to several hundreds micrometers and depends on generation methods, flow conditions and elapsed times after the bubble generation. Although a size distribution of micro-bubbles should be taken into account to improve accuracy in numerical simulations of flows with micro-bubbles, a variety of the size distribution makes it difficult to introduce the size distribution in the simulations. On the other hand, several models such as the Rosin-Rammler equation and the Nukiyama-Tanazawa equation have been proposed to represent the size distribution of particles or droplets. Applicability of these models to the size distribution of micro-bubbles has not been examined yet. In this study, we therefore measure size distribution of micro-bubbles generated by a pressurized dissolution method by using a phase Doppler anemometry (PDA), and investigate the applicability of the available models to the size distributions of micro-bubbles. Experimental apparatus consists of a pressurized tank in which air is dissolved in liquid under high pressure condition, a decompression nozzle in which micro-bubbles are generated due to pressure reduction, a rectangular duct and an upper tank. Experiments are conducted for several liquid volumetric fluxes in the decompression nozzle. Measurements are carried out at the downstream region of the decompression nozzle and in the upper tank. The experimental results indicate that (1) the Nukiyama-Tanasawa equation well represents the size distribution of micro-bubbles generated by the pressurized dissolution method, whereas the Rosin-Rammler equation fails in the representation, (2) the bubble size distribution of micro-bubbles can be evaluated by using the Nukiyama-Tanasawa equation without individual bubble diameters, when mean bubble diameter and skewness of the bubble distribution are given, and (3) an evaluation method of visibility based on the bubble size distribution and bubble number density is proposed, and the evaluated visibility agrees well with the visibility measured in the upper tank.

Local-Scale Simulations of Nucleate Boiling on Micrometer Featured Surfaces: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sitaraman, Hariswaran; Moreno, Gilberto; Narumanchi, Sreekant V

2017-08-03

A high-fidelity computational fluid dynamics (CFD)-based model for bubble nucleation of the refrigerant HFE7100 on micrometer-featured surfaces is presented in this work. The single-fluid incompressible Navier-Stokes equations, along with energy transport and natural convection effects are solved on a featured surface resolved grid. An a priori cavity detection method is employed to convert raw profilometer data of a surface into well-defined cavities. The cavity information and surface morphology are represented in the CFD model by geometric mesh deformations. Surface morphology is observed to initiate buoyancy-driven convection in the liquid phase, which in turn results in faster nucleation of cavities. Simulationsmore » pertaining to a generic rough surface show a trend where smaller size cavities nucleate with higher wall superheat. This local-scale model will serve as a self-consistent connection to larger device scale continuum models where local feature representation is not possible.« less

Local-Scale Simulations of Nucleate Boiling on Micrometer-Featured Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sitaraman, Hariswaran; Moreno, Gilberto; Narumanchi, Sreekant V

2017-07-12

A high-fidelity computational fluid dynamics (CFD)-based model for bubble nucleation of the refrigerant HFE7100 on micrometer-featured surfaces is presented in this work. The single-fluid incompressible Navier-Stokes equations, along with energy transport and natural convection effects are solved on a featured surface resolved grid. An a priori cavity detection method is employed to convert raw profilometer data of a surface into well-defined cavities. The cavity information and surface morphology are represented in the CFD model by geometric mesh deformations. Surface morphology is observed to initiate buoyancy-driven convection in the liquid phase, which in turn results in faster nucleation of cavities. Simulationsmore » pertaining to a generic rough surface show a trend where smaller size cavities nucleate with higher wall superheat. This local-scale model will serve as a self-consistent connection to larger device scale continuum models where local feature representation is not possible.« less

Field testing model predictions of foam coverage and bubble content in the surf zone

NASA Astrophysics Data System (ADS)

Shi, F.; Kirby, J. T.; Ma, G.; Holman, R. A.; Chickadel, C. C.

2012-12-01

Field-scale modeling of surfzone bubbles and foam coverage is challenging in terms of the computational intensity of multi-phase bubble models based on Navier-Stokes/VOF formulation. In this study, we developed the NHWAVE-bubble package, which includes a 3D non-hydrostatic wave model NHWAVE (Ma et al., 2012), a multi-phase bubble model and a foam model. NHWAVE uses a surface and bottom following sigma coordinate system, making it more applicable to 3D modeling of nearshore waves and circulation in a large-scale field domain. It has been extended to include a multiphase description of polydisperse bubble populations following the approach applied in a 3D VOF model by Ma et al. (2012). A model of a foam layer on the water surface is specified in the model package using a shallow water formulation based on a balance of drag forces due to wind and water column motion. Foam mass conservation includes source and sink terms representing outgassing of the water column, direct foam generation due to surface agitation, and erosion due to bubble bursting. The model is applied in a field scale domain at FRF, Duck, NC where optical data in either visible band (ARGUS) or infrared band were collected during 2010 Surf Zone Optics experiments. The decay of image brightness or intensity following the passage of wave crests is presumably tied to both decay of bubble populations and foam coverage after passage of a broken wave crest. Infrared imagery is likely to provide more detailed information which could separate active breaking from passive foam decay on the surface. Model results will be compared with the measurements with an attention to distinguishing between active generation and passive decay of the foam signature on the water surface.

Development of an Acoustic Localization Method for Cavitation Experiments in Reverberant Environments

NASA Astrophysics Data System (ADS)

Ranjeva, Minna; Thompson, Lee; Perlitz, Daniel; Bonness, William; Capone, Dean; Elbing, Brian

2011-11-01

Cavitation is a major concern for the US Navy since it can cause ship damage and produce unwanted noise. The ability to precisely locate cavitation onset in laboratory scale experiments is essential for proper design that will minimize this undesired phenomenon. Measuring the cavitation onset is more accurately determined acoustically than visually. However, if other parts of the model begin to cavitate prior to the component of interest the acoustic data is contaminated with spurious noise. Consequently, cavitation onset is widely determined by optically locating the event of interest. The current research effort aims at developing an acoustic localization scheme for reverberant environments such as water tunnels. Currently cavitation bubbles are being induced in a static water tank with a laser, allowing the localization techniques to be refined with the bubble at a known location. The source is located with the use of acoustic data collected with hydrophones and analyzed using signal processing techniques. To verify the accuracy of the acoustic scheme, the events are simultaneously monitored visually with the use of a high speed camera. Once refined testing will be conducted in a water tunnel. This research was sponsored by the Naval Engineering Education Center (NEEC).

Piercing the Bubble: How Management Students Can Confront Poverty in Colombia

ERIC Educational Resources Information Center

Rosenbloom, Al; Cortes, Juan Alejandro

2008-01-01

This article describes the current relationship between management education in Colombia and the efforts of the management program at Universidad Pontificia Bolivariana (UPB) in Medellin to reduce local poverty. The article uses the metaphor of "the bubble" to illustrate how social class, family socialization, and the current UPB…

Model for the dynamics of two interacting axisymmetric spherical bubbles undergoing small shape oscillations

PubMed Central

Kurihara, Eru; Hay, Todd A.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

2011-01-01

Interaction between acoustically driven or laser-generated bubbles causes the bubble surfaces to deform. Dynamical equations describing the motion of two translating, nominally spherical bubbles undergoing small shape oscillations in a viscous liquid are derived using Lagrangian mechanics. Deformation of the bubble surfaces is taken into account by including quadrupole and octupole perturbations in the spherical-harmonic expansion of the boundary conditions on the bubbles. Quadratic terms in the quadrupole and octupole amplitudes are retained, and surface tension and shear viscosity are included in a consistent manner. A set of eight coupled second-order ordinary differential equations is obtained. Simulation results, obtained by numerical integration of the model equations, exhibit qualitative agreement with experimental observations by predicting the formation of liquid jets. Simulations also suggest that bubble-bubble interactions act to enhance surface mode instability. PMID:22088009

Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Burkes, Douglas E.; Lavender, Curt A.

2016-07-08

Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the for- mation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was devel- oped. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials alongmore » $$\\langle$$110$$\\rangle$$ directions in the body-centered cubic U matrix causes the gas bubble alignment along $$\\langle$$110$$\\rangle$$ directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.« less

Experimental study on interfacial area transport in downward two-phase flow

NASA Astrophysics Data System (ADS)

Wang, Guanyi

In view of the importance of two group interfacial area transport equations and lack of corresponding accurate downward flow database that can reveal two group interfacial area transport, a systematic database for adiabatic, air-water, vertically downward two-phase flow in a round pipe with inner diameter of 25.4 mm was collected to gain an insight of interfacial structure and provide benchmarking data for two-group interfacial area transport models. A four-sensor conductivity probe was used to measure the local two phase flow parameters and data was collected with data sampling frequency much higher than conventional data sampling frequency to ensure the accuracy. Axial development of local flow parameter profiles including void fraction, interfacial area concentration, and Sauter mean diameter were presented. Drastic inter-group transfer of void fraction and interfacial area was observed at bubbly to slug transition flow. And the wall peaked interfacial area concentration profiles were observed in churn-turbulent flow. The importance of local data about these phenomenon on flow structure prediction and interfacial area transport equation benchmark was analyzed. Bedsides, in order to investigate the effect of inlet conditions, all experiments were repeated after installing the flow straightening facility, and the results were briefly analyzed. In order to check the accuracy of current data, the experiment results were cross-checked with rotameter measurement as well as drift-flux model prediction, the averaged error is less than 15%. Current models for two-group interfacial area transport equation were evaluated using these data. The results show that two-group interfacial area transport equations with current models can predict most flow conditions with error less than 20%, except some bubbly to slug transition flow conditions and some churn-turbulent flow conditions. The disagreement between models and experiments could result from underestimate of inter-group void transfer.

Modelling the global efficiency of dissolved air flotation.

PubMed

Leppinen, D M; Dalziel, S B; Linden, P F

2001-01-01

The purpose of this paper is to examine how the efficiency of dissolved air flotation is affected by the size of bubbles and particles. The rise speed of bubble/particle agglomerates is modelled as a function of bubble and particle size, while the kinematics of the bubble attachment process is modelled using the population balance approach adopted by Matsui, Fukushi and Tambo. It is found that flotation, in general, is enhanced by the use of larger particles and larger bubbles. In particular, it is concluded that for the ultra-high surface loading rates of 25 m/hr or more planned for future flotation tanks, bubble size will have to be increased by a factor of two over the size currently employed in many facilities during dissolved air flotation.

On the role of sea-state in bubble-mediated air-sea gas flux during a winter storm

NASA Astrophysics Data System (ADS)

Liang, Jun-Hong; Emerson, Steven R.; D'Asaro, Eric A.; McNeil, Craig L.; Harcourt, Ramsey R.; Sullivan, Peter P.; Yang, Bo; Cronin, Meghan F.

2017-04-01

Oceanic bubbles play an important role in the air-sea exchange of weakly soluble gases at moderate to high wind speeds. A Lagrangian bubble model embedded in a large eddy simulation model is developed to study bubbles and their influence on dissolved gases in the upper ocean. The transient evolution of mixed-layer dissolved oxygen and nitrogen gases at Ocean Station Papa (50°N, 145°W) during a winter storm is reproduced with the model. Among different physical processes, gas bubbles are the most important in elevating dissolved gas concentrations during the storm, while atmospheric pressure governs the variability of gas saturation anomaly (the relative departure of dissolved gas concentration from the saturation concentration). For the same wind speed, bubble-mediated gas fluxes are larger during rising wind with smaller wave age than during falling wind with larger wave age. Wave conditions are the primary cause for the bubble gas flux difference: when wind strengthens, waves are less-developed with respect to wind, resulting in more frequent large breaking waves. Bubble generation in large breaking waves is favorable for a large bubble-mediated gas flux. The wave-age dependence is not included in any existing bubble-mediated gas flux parameterizations.

The Role of Contact Line (Pinning) Forces on Bubble Blockage in Microchannels.

PubMed

Mohammadi, Mahshid; Sharp, Kendra V

2015-03-01

This paper highlights the influence of contact line (pinning) forces on the mobility of dry bubbles in microchannels. Bubbles moving at velocities less than the dewetting velocity of liquid on the surface are essentially dry, meaning that there is no thin liquid film around the bubbles. For these "dry" bubbles, contact line forces and a possible capillary pressure gradient induced by pinning act on the bubbles and resist motion. Without sufficient driving force (e.g., external pressure), a dry bubble is brought to stagnation. For the first time, a bipartite theoretical model that estimates the required pressure difference across the length of stagnant bubbles with concave and convex back interfaces to overcome the contact line forces and stimulate motion is proposed. To validate our theory, the pressure required to move a single dry bubble in square microchannels exhibiting contact angle hysteresis has been measured. The working fluid was deionized water. The experiments have been conducted on coated glass channels with different surface hydrophilicities that resulted in concave and convex back interfaces for the bubbles. The experimental results were in agreement with the model's predictions for square channels. The predictions of the concave and convex back models were within 19% and 27% of the experimental measurements, respectively.

Scanning force microscopy at the air-water interface of an air bubble coated with pulmonary surfactant.

PubMed Central

Knebel, D; Sieber, M; Reichelt, R; Galla, H-J; Amrein, M

2002-01-01

To study the structure-function relationship of pulmonary surfactant under conditions close to nature, molecular films of a model system consisting of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, and surfactant-associated protein C were prepared at the air-water interface of air bubbles about the size of human alveoli (diameter of 100 microm). The high mechanical stability as well as the absence of substantial film flow, inherent to small air bubbles, allowed for scanning force microscopy (SFM) directly at the air-water interface. The SFM topographical structure was correlated to the local distribution of fluorescent-labeled dipalmitoylphosphatidylcholine, as revealed from fluorescence light microscopy of the same bubbles. Although SFM has proven before to be exceptionally well suited to probe the structure of molecular films of pulmonary surfactant, the films so far had to be transferred onto a solid support from the air-water interface of a film balance, where they had been formed. This made them prone to artifacts imposed by the transfer. Moreover, the supported monolayers disallowed the direct observation of the structural dynamics associated with expansion and compression of the films as upon breathing. The current findings are compared in this respect to our earlier findings from films, transferred onto a solid support. PMID:11751334

Bubble suspension rheology and implications for conduit flow

NASA Astrophysics Data System (ADS)

Llewellin, E. W.; Manga, M.

2005-05-01

Bubbles are ubiquitous in magma during eruption and influence the rheology of the suspension. Despite this, bubble-suspension rheology is routinely ignored in conduit-flow and eruption models, potentially impairing accuracy and resulting in the loss of important phenomenological richness. The omission is due, in part, to a historical confusion in the literature concerning the effect of bubbles on the rheology of a liquid. This confusion has now been largely resolved and recently published studies have identified two viscous regimes: in regime 1, the viscosity of the two-phase (magma-gas) suspension increases as gas volume fraction ϕ increases; in regime 2, the viscosity of the suspension decreases as ϕ increases. The viscous regime for a deforming bubble suspension can be determined by calculating two dimensionless numbers, the capillary number Ca and the dynamic capillary number Cd. We provide a didactic explanation of how to include the effect of bubble-suspension rheology in continuum, conduit-flow models. Bubble-suspension rheology is reviewed and a practical rheological model is presented, followed by an algorithmic, step-by-step guide to including the rheological model in conduit-flow models. Preliminary results from conduit-flow models which have implemented the model presented are discussed and it is concluded that the effect of bubbles on magma rheology may be important in nature and results in a decrease of at least 800 m in calculated fragmentation-depth and an increase of between 40% and 250% in calculated eruption-rate compared with the assumption of Newtonian rheology.

Lyα-emitting galaxies as a probe of reionization: large-scale bubble morphology and small-scale absorbers

NASA Astrophysics Data System (ADS)

Kakiichi, Koki; Dijkstra, Mark; Ciardi, Benedetta; Graziani, Luca

2016-12-01

The visibility of Lyα-emitting galaxies during the Epoch of Reionization is controlled by both diffuse H I patches in large-scale bubble morphology and small-scale absorbers. To investigate their impacts on Lyα transfer, we apply a novel combination of analytic modelling and cosmological hydrodynamical, radiative transfer simulations to three reionization models: (I) the `bubble' model, where only diffuse H I outside ionized bubbles is present; (II) the `web' model, where H I exists only in overdense self-shielded gas; and (III) the hybrid `web-bubble' model. The three models can explain the observed Lyα luminosity function equally well, but with very different H I fractions. This confirms a degeneracy between the ionization topology of the intergalactic medium (IGM) and the H I fraction inferred from Lyα surveys. We highlight the importance of the clustering of small-scale absorbers around galaxies. A combined analysis of the Lyα luminosity function and the Lyα fraction can break this degeneracy and provide constraints on the reionization history and its topology. Constraints can be improved by analysing the full MUV-dependent redshift evolution of the Lyα fraction of Lyman break galaxies. We find that the IGM-transmission probability distribution function is unimodal for bubble models and bimodal in web models. Comparing our models to observations, we infer that the neutral fraction at z ˜ 7 is likely to be of the order of tens of per cent when interpreted with bubble or web-bubble models, with a conservative lower limit ˜1 per cent when interpreted with web models.

What Can Be Learned from X-Ray Spectroscopy Concerning Hot Gas in the Local Bubble and Charge Exchange Processes?

NASA Technical Reports Server (NTRS)

Snowden, S. L.

2008-01-01

Both solar wind charge exchange emission and diffuse thermal emission from the Local Bubble are strongly dominated in the soft X-ray band by lines from highly ionized elements. While both processes share many of the same lines, the spectra should differ significantly due to the different production mechanisms, abundances, and ionization states. Despite their distinct spectral signatures, current and past observatories have lacked the spectral resolution to adequately distinguish between the two sources. High-resolution X-ray spectroscopy instrumentation proposed for future missions has the potential to answer fundamental questions such as whether there is any hot plasma in the Local Hot Bubble, and if so, what are the abundances of the emitting plasma and whether the plasma is in equilibrium. Such instrumentation will provide dynamic information about the solar wind including data on ion species which are currently difficult to track. It will also make possible remote sensing of the solar wind.

Analysis of the three-dimensional structure of a bubble wake using PIV and Galilean decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassan, Y.A.; Schmidl, W.D.; Ortiz-Villafuerte, J.

1999-07-01

Bubbly flow plays a key role in a variety of natural and industrial processes. An accurate and complete description of the phase interactions in two-phase bubbly flow is not available at this time. These phase interactions are, in general, always three-dimensional and unsteady. Therefore, measurement techniques utilized to obtain qualitative and quantitative data from two-phase flow should be able to acquire transient and three-dimensional data, in order to provide information to test theoretical models and numerical simulations. Even for dilute bubble flows, in which bubble interaction is at a minimum, the turbulent motion of the liquid generated by the bubblemore » is yet to be completely understood. For many years, the design of systems with bubbly flows was based primarily on empiricism. Dilute bubbly flows are an extension of single bubble dynamics, and therefore improvements in the description and modeling of single bubble motion, the flow field around the bubble, and the dynamical interactions between the bubble and the flow will consequently improve bubbly flow modeling. The improved understanding of the physical phenomena will have far-reaching benefits in upgrading the operation and efficiency of current processes and in supporting the development of new and innovative approaches. A stereoscopic particle image velocimetry measurement of the flow generated by the passage of a single air-bubble rising in stagnant water, in a circular pipe is presented. Three-dimensional velocity fields within the measurement zone were obtained. Ensemble-averaged instantaneous velocities for a specific bubble path were calculated and interpolated to obtain mean three-dimensional velocity fields. A Galilean velocity decomposition is used to study the vorticity generated in the flow.« less

An Analysis of Bubble Deformation by a Sphere Relevant to the Measurements of Bubble-Particle Contact Interaction and Detachment Forces.

PubMed

Sherman, H; Nguyen, A V; Bruckard, W

2016-11-22

Atomic force microscopy makes it possible to measure the interacting forces between individual colloidal particles and air bubbles, which can provide a measure of the particle hydrophobicity. To indicate the level of hydrophobicity of the particle, the contact angle can be calculated, assuming that no interfacial deformation occurs with the bubble retaining a spherical profile. Our experimental results obtained using a modified sphere tensiometry apparatus to detach submillimeter spherical particles show that deformation of the bubble interface does occur during particle detachment. We also develop a theoretical model to describe the equilibrium shape of the bubble meniscus at any given particle position, based on the minimization of the free energy of the system. The developed model allows us to analyze high-speed video captured during detachment. In the system model deformation of the bubble profile is accounted for by the incorporation of a Lagrange multiplier into both the Young-Laplace equation and the force balance. The solution of the bubble profile matched to the high-speed video allows us to accurately calculate the contact angle and determine the total force balance as a function of the contact point of the bubble on the particle surface.

Numerical simulation of bubble plumes and an analysis of their seismic attributes

NASA Astrophysics Data System (ADS)

Li, Canping; Gou, Limin; You, Jiachun

2017-04-01

To study the bubble plume's seismic response characteristics, the model of a plume water body has been built in this article using the bubble-contained medium acoustic velocity model and the stochastic medium theory based on an analysis of both the acoustic characteristics of a bubble-contained water body and the actual features of a plume. The finite difference method is used for forward modelling, and the single-shot seismic record exhibits the characteristics of a scattered wave field generated by a plume. A meaningful conclusion is obtained by extracting seismic attributes from the pre-stack shot gather record of a plume. The values of the amplitude-related seismic attributes increase greatly as the bubble content goes up, and changes in bubble radius will not cause seismic attributes to change, which is primarily observed because the bubble content has a strong impact on the plume's acoustic velocity, while the bubble radius has a weak impact on the acoustic velocity. The above conclusion provides a theoretical reference for identifying hydrate plumes using seismic methods and contributes to further study on hydrate decomposition and migration, as well as on distribution of the methane bubble in seawater.

DXL: A Sounding Rocket Mission for the Study of Solar Wind Charge Exchange and Local Hot Bubble X-Ray Emission

NASA Technical Reports Server (NTRS)

Galeazzi, M.; Prasai, K.; Uprety, Y.; Chiao, M.; Collier, M. R.; Koutroumpa, D.; Porter, F. S.; Snowden, S.; Cravens, T.; Robertson, I.;

A novel bubble-forming material for preparing hydrophobic-agent-loaded bubbles with theranostic functionality.

PubMed

Yang, Pei-Sin; Tung, Fu-I; Chen, Hsiao-Ping; Liu, Tse-Ying; Lin, Yi-Ying

2014-08-01

In the present study, a new bubble-forming material (carboxymethyl hexanoyl chitosan, CHC), together with superparamagnetic iron oxide (SPIO) nanoparticles, was employed to prepare image-guided bubbles for efficiently encapsulating and delivering hydrophobic agents to kill tumor cells. The results showed that CHC could be used for preparing not only micronized bubbles (CHC/SPIO MBs) to exhibit ultrasound imaging functionality but also nanosized bubbles (CHC/SPIO NBs) to exhibit magnetic resonance T2 image contrast. It was found that the amounts of SPIO nanoparticles and hexane during preparation process were the key factors to obtaining CHC/SPIO NBs. Most importantly, under in vitro cell culture conditions with the same amount of camptothecin (CPT) and therapeutic sonication, CPT-loaded CHC/SPIO NBs demonstrated more significant transcellular delivery and cytotoxicity than free CPT. Subsequently, an intratumoral injection was proposed for the in vivo administration of hydrophobic-agent-loaded CHC/SPIO NBs. After injection, the distribution of a hydrophobic dye (DiR, an agent with near-infrared (NIR) fluorescence used as a model drug) released from the CHC/SPIO NBs was tracked by an NIR imaging technique. A significant tumor-specific accumulation was observed in the mouse that received the DiR-loaded CHC/SPIO NBs; the same was not observed in the mouse that received the free dye (without incorporating with CHC/SPIO NBs). It is expected, in the future, both the dose of the therapeutic agent administered and its side effects can be significantly lowered by using novel CHC/SPIO NBs together with local delivery (intratumoral injection), targeted imaging and enhanced cellular uptake of the drug. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Amplification of seismic waves beneath active volcanoes

NASA Astrophysics Data System (ADS)

Navon, O.; Lensky, N. G.; Collier, L.; Neuberg, J.; Lyakhovsky, V.

2003-04-01

Long-period (LP) seismic events are typical of many volcanoes and are attributed to energy leaking from waves traveling through the volcanic conduit or along the conduit - country-rock interface. The LP events are triggered locally, at the volcanic edifice, but the source of energy for the formation of tens of events per day is not clear. Energy may be supplied by volatile-release from a supersaturated melt. If bubbles are present in equilibrium with the melt in the conduit, and the melt is suddenly decompressed, transfer of volatiles from the supersaturated melt into the bubbles transforms stored potential energy into expansion work. For example, small dome collapses may decompress the conduit by a few bars and lead to solubility decrease, exsolution of volatiles and, consequently, to work done by the expansion of the bubbles under pressure. This energy is released over a timescale that is similar to that of LP events and may amplify the original weak seismic signals associated with the collapse. Using the formulation of Lensky et al. (2002), following the decompression, when the transfer of volatiles into bubbles is fast enough, expansion accelerates and the bulk viscosity of the bubbly magma is negative. New calculations show that under such conditions a sinusoidal P-wave is amplified. We note that seismic waves created by tectonic earthquakes that are not associated with net decompression, do not lead to net release of volatiles or to net expansion. In this case, the bulk viscosity is positive and waves traveling through the magma should attenuate. The proposed model explains how weak seismic signals may be amplified as they travel through a conduit that contains supersaturated bubbly magma. It provides the general framework for amplifying volcanic seismicity such as the signals associated with long-period events.

Growth and Detachment of Oxygen Bubbles Induced by Gold-Catalyzed Decomposition of Hydrogen Peroxide.

PubMed

Lv, Pengyu; Le The, Hai; Eijkel, Jan; Van den Berg, Albert; Zhang, Xuehua; Lohse, Detlef

2017-09-28

Whereas bubble growth out of gas-oversatured solutions has been quite well understood, including the formation and stability of surface nanobubbles, this is not the case for bubbles forming on catalytic surfaces due to catalytic reactions , though it has important implications for gas evolution reactions and self-propulsion of micro/nanomotors fueled by bubble release. In this work we have filled this gap by experimentally and theoretically examining the growth and detachment dynamics of oxygen bubbles from hydrogen peroxide decomposition catalyzed by gold. We measured the bubble radius R ( t ) as a function of time by confocal microscopy and find R ( t ) ∝ t 1/2 . This diffusive growth behavior demonstrates that the bubbles grow from an oxygen-oversaturated environment. For several consecutive bubbles detaching from the same position in a short period of time, a well-repeated growing behavior is obtained from which we conclude the absence of noticeable depletion effect of oxygen from previous bubbles or increasing oversaturation from the gas production. In contrast, for two bubbles far apart either in space or in time, substantial discrepancies in their growth rates are observed, which we attribute to the variation in the local gas oversaturation. The current results show that the dynamical evolution of bubbles is influenced by comprehensive effects combining chemical catalysis and physical mass transfer. Finally, we find that the size of the bubbles at the moment of detachment is determined by the balance between buoyancy and surface tension and by the detailed geometry at the bubble's contact line.

Modeling the kinetics of bubble nucleation in champagne and carbonated beverages.

PubMed

Liger-Belair, Gérard; Parmentier, Maryline; Jeandet, Philippe

2006-10-26

In champagne and carbonated beverages, bubble nucleation was mostly found to take place from tiny Taylor-like bubbles trapped inside immersed cellulose fibers stuck on the glass wall. The present paper complements a previous paper about the thorough examination of the bubble nucleation process in a flute poured with champagne (Liger-Belair et al. J. Phys. Chem. B 2005, 109, 14573). In this previous paper, a model was built that accurately reproduces the dynamics of these tiny Taylor-like bubbles that grow inside the fiber's lumen by diffusion of CO(2)-dissolved molecules. In the present paper, by use of the model recently developed, the frequency of bubble formation from cellulose fibers is accessed and linked with various liquid and fiber parameters, namely, the concentration c(L) of CO(2)-dissolved molecules, the liquid temperature theta, its viscosity eta, the ambient pressure P, the course of the gas pocket growing trapped inside the fiber's lumen before releasing a bubble, and the radius r of the fiber's lumen. The relative influence of the latter parameters on the bubbling frequency is discussed and supported with recent experimental observations and data.

Prediction of Bubble Diameter at Detachment from a Wall Orifice in Liquid Cross Flow Under Reduced and Normal Gravity Conditions

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Kamotani, Y.

2003-01-01

Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to theoretically investigate the effects of liquid cross-flow velocity, gas flow rate embodied in the momentum flux force, and orifice diameter on bubble formation in a wall-bubble injection configuration. A two-dimensional one-stage theoretical model based on a global force balance on the bubble evolving from a wall orifice in a cross liquid flow is presented in this work. In this model, relevant forces acting on the evolving bubble are expressed in terms of the bubble center of mass coordinates and solved simultaneously. Relevant forces in low gravity included the momentum flux, shear-lift, surface tension, drag and inertia forces. Under normal gravity conditions, the buoyancy force, which is dominant under such conditions, can be added to the force balance. Two detachment criteria were applicable depending on the gas to liquid momentum force ratio. For low ratios, the time when the bubble acceleration in the direction of the detachment angle is greater or equal to zero is calculated from the bubble x and y coordinates. This time is taken as the time at which all the detaching forces that are acting on the bubble are greater or equal to the attaching forces. For high gas to liquid momentum force ratios, the time at which the y coordinate less the bubble radius equals zero is calculated. The bubble diameter is evaluated at this time as the diameter at detachment from the fact that the bubble volume is simply given by the product of the gas flow rate and time elapsed. Comparison of the model s predictions was also made with predictions from a two-dimensional normal gravity model based on Kumar-Kuloor formulation and such a comparison is presented in this work.

Quantifying dynamic rheology, phase interactions and strain localisation in deforming three phase magmas using high-speed x-ray tomography

NASA Astrophysics Data System (ADS)

Dobson, Katherine; Pistone, Mattia; Fife, Julie; Cordonnier, Benoit; Blundy, Jon; Dingwell, Don; Lee, Peter

2015-04-01

The crystal and bubble cargoes of magmas are critical to controlling magma mobility and rheology. These cargos vary in both time and space and the local, and bulk, rheological behaviour are correspondingly heterogeneous. Tracking how these heterogeneous cargoes evolve, and how crystals and bubbles interact with each other in deforming systems is a critical challenge in volcanology, as these processes control both the chemical and physical evolution of the magma, including phenomena such as melt-crystal segregation, strain localisation, and fragmentation. The only methodology available to track these processes in real time, and at the scale of individual melt-crystal-bubble interactions is high speed x-ray tomography. This non-destructive imaging technique allows the rapid acquisition of sequential 3D images that capture the physical, and to some degree chemical, microstructure of the sample during a deformation cycle. We utilise in situ tomographic methods developed in materials science to perfume magmatic deformation experiments on synthesized three phase systems at magmatic temperatures. Through a novel combination of a high temperature laser heating system [1] in situ micro-precision deformation apparatus [2] and the temporal and spatial resolution available at the TOMCAT beam line at the Swiss Light Source synchrotron facility we performed in situ observations of the microstructural evolution of a synthesized anhydrous borosilicate melt seeded with a variable concentration of non-reactive rutile crystals and air bubbles (30-70 volume %). The experiments were conducted at 800-1000C, under constant deformation rates of 0.25-5.00 microns/second. Each 3D image has 2D and 3D spatial resolution of approximately 3 microns per pixel, and each 3D image took ~3 seconds to acquire. Here we present this innovative high speed, high temperature, syn-deformation tomographic data , and show how it can be used to trace the location and local distribution of each crystal and bubble within a small volume cylindrical experimental charge (3mm diameter, 5mm length) undergoing shear along a single vertical plane. By qualitative and quantitative analysis of the sequential images collected over 5-15 minute deformation cycles we track the local bubble, crystal and melt concentrations on a range of spatial scales. From this we calculate a spatially heterogeneous and dynamic local viscosity [3] and assess our results against recently developed 3-phase rheological models [4]. We will present how this real time 4D information can be used to quantify the dynamics of magma motion, discuss the implications of spatially and temporally variable rheological behaviours, and show how this novel technique can be integrated with other volcanology methods to improve our understanding of volcanic and magmatic processes. [1] Fife et al. 2012. J. Synchrotron Rad. 19, 352-358 [2] Kareh et al. 2014 Nature Comm. 5 4464. [3] Giordano, et al. 2008 EPSL 271 123-134. [4] Truby et al. 2015 P.Roy.Soc.A. 2015471 20140557

The motion of bubbles inside drops in containerless processing

NASA Technical Reports Server (NTRS)

Shankar, N.; Annamalai, P.; Cole, R.; Subramanian, R. S.

1982-01-01

A theoretical model of thermocapillary bubble motion inside a drop, located in a space laboratory, due to an arbitrary axisymmetric temperature distribution on the drop surface was constructed. Typical results for the stream function and temperature fields as well as the migration velocity of the bubble were obtained in the quasistatic limit. The motion of bubbles in a rotating body of liquid was studied experimentally, and an approximate theoretical model was developed. Comparison of the experimental observations of the bubble trajectories and centering times with theoretical predictions lends qualified support to the theory.

Decompression models: review, relevance and validation capabilities.

PubMed

Hugon, J

2014-01-01

For more than a century, several types of mathematical models have been proposed to describe tissue desaturation mechanisms in order to limit decompression sickness. These models are statistically assessed by DCS cases, and, over time, have gradually included bubble formation biophysics. This paper proposes to review this evolution and discuss its limitations. This review is organized around the comparison of decompression model biophysical criteria and theoretical foundations. Then, the DCS-predictive capability was analyzed to assess whether it could be improved by combining different approaches. Most of the operational decompression models have a neo-Haldanian form. Nevertheless, bubble modeling has been gaining popularity, and the circulating bubble amount has become a major output. By merging both views, it seems possible to build a relevant global decompression model that intends to simulate bubble production while predicting DCS risks for all types of exposures and decompression profiles. A statistical approach combining both DCS and bubble detection databases has to be developed to calibrate a global decompression model. Doppler ultrasound and DCS data are essential: i. to make correlation and validation phases reliable; ii. to adjust biophysical criteria to fit at best the observed bubble kinetics; and iii. to build a relevant risk function.

A measurement model for real estate bubble size based on the panel data analysis: An empirical case study

PubMed Central

Liu, Fengyun; Liu, Deqiang; Malekian, Reza; Li, Zhixiong; Wang, Deqing

2017-01-01

Employing the fundamental value of real estate determined by the economic fundamentals, a measurement model for real estate bubble size is established based on the panel data analysis. Using this model, real estate bubble sizes in various regions in Japan in the late 1980s and in recent China are examined. Two panel models for Japan provide results, which are consistent with the reality in the 1980s where a commercial land price bubble appeared in most area and was much larger than that of residential land. This provides evidence of the reliability of our model, overcoming the limit of existing literature with this method. The same models for housing prices in China at both the provincial and city levels show that contrary to the concern of serious housing price bubble in China, over-valuing in recent China is much smaller than that in 1980s Japan. PMID:28273141

A measurement model for real estate bubble size based on the panel data analysis: An empirical case study.

PubMed

Liu, Fengyun; Liu, Deqiang; Malekian, Reza; Li, Zhixiong; Wang, Deqing

2017-01-01

Employing the fundamental value of real estate determined by the economic fundamentals, a measurement model for real estate bubble size is established based on the panel data analysis. Using this model, real estate bubble sizes in various regions in Japan in the late 1980s and in recent China are examined. Two panel models for Japan provide results, which are consistent with the reality in the 1980s where a commercial land price bubble appeared in most area and was much larger than that of residential land. This provides evidence of the reliability of our model, overcoming the limit of existing literature with this method. The same models for housing prices in China at both the provincial and city levels show that contrary to the concern of serious housing price bubble in China, over-valuing in recent China is much smaller than that in 1980s Japan.

Influences of non-uniform pressure field outside bubbles on the propagation of acoustic waves in dilute bubbly liquids.

PubMed

Zhang, Yuning; Du, Xiaoze

2015-09-01

Predictions of the propagation of the acoustic waves in bubbly liquids is of great importance for bubble dynamics and related applications (e.g. sonochemistry, sonochemical reactor design, biomedical engineering). In the present paper, an approach for modeling the propagation of the acoustic waves in dilute bubbly liquids is proposed through considering the non-uniform pressure field outside the bubbles. This approach is validated through comparing with available experimental data in the literature. Comparing with the previous models, our approach mainly improves the predictions of the attenuation of acoustic waves in the regions with large kR0 (k is the wave number and R0 is the equilibrium bubble radius). Stability of the oscillating bubbles under acoustic excitation are also quantitatively discussed based on the analytical solution. Copyright © 2015 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, B.; The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610207; Wang, L.

With large-scale molecular dynamics simulations, we investigate shock response of He nanobubbles in single crystal Cu. For sufficient bubble size or internal pressure, a prismatic dislocation loop may form around a bubble in unshocked Cu. The internal He pressure helps to stabilize the bubble against plastic deformation. However, the prismatic dislocation loops may partially heal but facilitate nucleation of new shear and prismatic dislocation loops. For strong shocks, the internal pressure also impedes internal jetting, while a bubble assists local melting; a high speed jet breaks a He bubble into pieces dispersed among Cu. Near-surface He bubbles may burst andmore » form high velocity ejecta containing atoms and small fragments, while the ejecta velocities do not follow the three-dimensional Maxwell-Boltzmann distributions expected for thermal equilibrium. The biggest fragment size deceases with increasing shock strength. With a decrease in ligament thickness or an increase in He bubble size, the critical shock strength required for bubble bursting decreases, while the velocity range, space extension and average velocity component along the shock direction, increase. Small bubbles are more efficient in mass ejecting. Compared to voids and perfect single crystal Cu, He bubbles have pronounced effects on shock response including bubble/void collapse, Hugoniot elastic limit (HEL), deformation mechanisms, and surface jetting. HEL is the highest for perfect single crystal Cu with the same orientations, followed by He bubbles without pre-existing prismatic dislocation loops, and then voids. Complete void collapse and shear dislocations occur for embedded voids, as opposed to partial collapse, and shear and possibly prismatic dislocations for He bubbles. He bubbles lower the threshhold shock strength for ejecta formation, and increase ejecta velocity and ejected mass.« less

Detection and 3D representation of pulmonary air bubbles in HRCT volumes

NASA Astrophysics Data System (ADS)

Silva, Jose S.; Silva, Augusto F.; Santos, Beatriz S.; Madeira, Joaquim

2003-05-01

Bubble emphysema is a disease characterized by the presence of air bubbles within the lungs. With the purpose of identifying pulmonary air bubbles, two alternative methods were developed, using High Resolution Computer Tomography (HRCT) exams. The search volume is confined to the pulmonary volume through a previously developed pulmonary contour detection algorithm. The first detection method follows a slice by slice approach and uses selection criteria based on the Hounsfield levels, dimensions, shape and localization of the bubbles. Candidate regions that do not exhibit axial coherence along at least two sections are excluded. Intermediate sections are interpolated for a more realistic representation of lungs and bubbles. The second detection method, after the pulmonary volume delimitation, follows a fully 3D approach. A global threshold is applied to the entire lung volume returning candidate regions. 3D morphologic operators are used to remove spurious structures and to circumscribe the bubbles. Bubble representation is accomplished by two alternative methods. The first generates bubble surfaces based on the voxel volumes previously detected; the second method assumes that bubbles are approximately spherical. In order to obtain better 3D representations, fits super-quadrics to bubble volume. The fitting process is based on non-linear least squares optimization method, where a super-quadric is adapted to a regular grid of points defined on each bubble. All methods were applied to real and semi-synthetical data where artificial and randomly deformed bubbles were embedded in the interior of healthy lungs. Quantitative results regarding bubble geometric features are either similar to a priori known values used in simulation tests, or indicate clinically acceptable dimensions and locations when dealing with real data.

Models and observations of foam coverage and bubble content in the surf zone

NASA Astrophysics Data System (ADS)

Kirby, J. T.; Shi, F.; Holman, R. A.

2010-12-01

Optical and acoustical observations and communications are hampered in the nearshore by the presence of bubbles and foam generated by breaking waves. Bubble clouds in the water column provide a highly variable (both spatially and temporally) obstacle to direct acoustic and optical paths. Persistent foam riding on the water surface creates a primary occlusion of optical penetration into the water column. In an effort to better understand and predict the level of bubble and foam content in the surfzone, we have been pursuing the development of a detailed phase resolved model of fluid and gaseous components of the water column, using a Navier-Stokes/VOF formulation extended to include a multiphase description of polydisperse bubble populations. This sort of modeling provides a detailed description of large scale turbulent structures and associated bubble transport mechanisms under breaking wave crests. The modeling technique is too computationally intensive, however, to provide a wider-scale description of large surfzone regions. In order to approach the larger scale problem, we are developing a model for spatial and temporal distribution of foam and bubbles within the framework of a Boussinesq model. The basic numerical framework for the code is described by Shi et al (2010, this conference). Bubble effects are incorporated both in the mass and momentum balances for weakly dispersive, fully nonlinear waves, with spatial and temporal bubble distributions parameterized based on the VOF modeling and measurements and tied to the computed rate of dissipation of energy during breaking. A model of a foam layer on the water surface is specified using a shallow water formulation. Foam mass conservation includes source and sink terms representing outgassing of the water column, direct foam generation due to surface agitation, and erosion due to bubble bursting. The foam layer motion in the plane of the water surface arises due to a balance of drag forces due to wind and water column motion. Preliminary steps to calibrate and verify the resulting models will be taken based on results to be collected during the Surf Zone Optics experiment at Duck, NC in September 2010. Initial efforts will focus on an examination of breaking wave patterns and persistent foam distributions, using ARGUS imagery.

Effects of floc and bubble size on the efficiency of the dissolved air flotation (DAF) process.

PubMed

Han, Mooyoung; Kim, Tschung-il; Kim, Jinho

2007-01-01

Dissolved air flotation (DAF) is a method for removing particles from water using micro bubbles instead of settlement. The process has proved to be successful and, since the 1960s, accepted as an alternative to the conventional sedimentation process for water and wastewater treatment. However, limited research into the process, especially the fundamental characteristics of bubbles and particles, has been carried out. The single collector collision model is not capable of determining the effects of particular characteristics, such as the size and surface charge of bubbles and particles. Han has published a set of modeling results after calculating the collision efficiency between bubbles and particles by trajectory analysis. His major conclusion was that collision efficiency is maximum when the bubbles and particles are nearly the same size but have opposite charge. However, experimental verification of this conclusion has not been carried out yet. This paper describes a new method for measuring the size of particles and bubbles developed using computational image analysis. DAF efficiency is influenced by the effect of the recycle ratio on various average floc sizes. The larger the recycle ratio, the higher the DAF efficiency at the same pressure and particle size. The treatment efficiency is also affected by the saturation pressure, because the bubble size and bubble volume concentration are controlled by the pressure. The highest efficiency is obtained when the floc size is larger than the bubble size. These results, namely that the highest collision efficiency occurs when the particles and bubbles are about the same size, are more in accordance with the trajectory model than with the white water collector model, which implies that the larger the particles, the higher is the collision efficiency.

Microhydrodynamics of flotation processes in the sea surface layer

NASA Astrophysics Data System (ADS)

Grammatika, Marianne; Zimmerman, William B.

2001-10-01

The uppermost surface of the ocean forms a peculiarly important ecosystem, the sea surface microlayer (SML). Comprising the top 1-1000 μm of the ocean surface, the SML concentrates many chemical substances, particularly those that are surface active. Important economically as a nursery for fish eggs and larvae, the SML unfortunately is also especially vulnerable to pollution. Contaminants that settle out from the air, have low solubility, or attach to floatable matter tend to accumulate in the SML. Bubbles contribute prominently to the dynamics of air-sea exchanges, playing an important role in geochemical cycling of material in the upper ocean and SML. In addition to the movement of bubbles, the development of a bubble cloud interrelates with the single particle dynamics of all other bubbles and particles. In the early sixties, several in situ oceanographic techniques revealed an "unbelievably immense" number of coastal bubbles of radius 15-300 μm. The spatial and temporal variation of bubble numbers were studied; acoustical oceanographers now use bubbles as tracers to determine ocean processes near the ocean surface. Sea state and rain noises have both been definitively ascribed to the radiation from huge numbers of infant micro bubbles [The Acoustic Bubble. Academic Press, San Diego]. Our research programme aims at constructing a hydrodynamic model for particle transport processes occurring at the microscale, in multi-phase flotation suspensions. Current research addresses bubble and floc microhydrodynamics as building blocks for a microscale transport model. This paper reviews sea surface transport processes in the microlayer and the lower atmosphere, and identifies those amenable to microhydrodynamic modelling and simulation. It presents preliminary simulation results including the multi-body hydrodynamic mobility functions for the modelling of "dynamic bubble filters" and floc suspensions. Hydrodynamic interactions versus spatial anisotropy and size of particle clouds are investigated.

A fractional Fourier transform analysis of a bubble excited by an ultrasonic chirp.

PubMed

Barlow, Euan; Mulholland, Anthony J

2011-11-01

The fractional Fourier transform is proposed here as a model based, signal processing technique for determining the size of a bubble in a fluid. The bubble is insonified with an ultrasonic chirp and the radiated pressure field is recorded. This experimental bubble response is then compared with a series of theoretical model responses to identify the most accurate match between experiment and theory which allows the correct bubble size to be identified. The fractional Fourier transform is used to produce a more detailed description of each response, and two-dimensional cross correlation is then employed to identify the similarities between the experimental response and each theoretical response. In this paper the experimental bubble response is simulated by adding various levels of noise to the theoretical model output. The method is compared to the standard technique of using time-domain cross correlation. The proposed method is shown to be far more robust at correctly sizing the bubble and can cope with much lower signal to noise ratios.

Modeling bubble dynamics and radical kinetics in ultrasound induced microalgal cell disruption.

PubMed

Wang, Meng; Yuan, Wenqiao

2016-01-01

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process. Copyright © 2015 Elsevier B.V. All rights reserved.

Jumping acoustic bubbles on lipid bilayers.

PubMed

Der Loughian, Christelle; Muleki Seya, Pauline; Pirat, Christophe; Inserra, Claude; Béra, Jean-Christophe; Rieu, Jean-Paul

2015-05-07

In the context of sonoporation, we use supported lipid bilayers as a model for biological membranes and investigate the interactions between the bilayer and microbubbles induced by ultrasound. Among the various types of damage caused by bubbles on the surface, our experiments exhibit a singular dynamic interaction process where bubbles are jumping on the bilayer, forming a necklace pattern of alteration on the membrane. This phenomenon was explored with different time and space resolutions and, based on our observations, we propose a model for a microbubble subjected to the combined action of van der Waals, acoustic and hydrodynamic forces. Describing the repeated jumps of the bubble, this model explains the lipid exchanges between the bubble and bilayer.

Droplets, Bubbles and Ultrasound Interactions.

PubMed

Shpak, Oleksandr; Verweij, Martin; de Jong, Nico; Versluis, Michel

2016-01-01

The interaction of droplets and bubbles with ultrasound has been studied extensively in the last 25 years. Microbubbles are broadly used in diagnostic and therapeutic medical applications, for instance, as ultrasound contrast agents. They have a similar size as red blood cells, and thus are able to circulate within blood vessels. Perfluorocarbon liquid droplets can be a potential new generation of microbubble agents as ultrasound can trigger their conversion into gas bubbles. Prior to activation, they are at least five times smaller in diameter than the resulting bubbles. Together with the violent nature of the phase-transition, the droplets can be used for local drug delivery, embolotherapy, HIFU enhancement and tumor imaging. Here we explain the basics of bubble dynamics, described by the Rayleigh-Plesset equation, bubble resonance frequency, damping and quality factor. We show the elegant calculation of the above characteristics for the case of small amplitude oscillations by linearizing the equations. The effect and importance of a bubble coating and effective surface tension are also discussed. We give the main characteristics of the power spectrum of bubble oscillations. Preceding bubble dynamics, ultrasound propagation is introduced. We explain the speed of sound, nonlinearity and attenuation terms. We examine bubble ultrasound scattering and how it depends on the wave-shape of the incident wave. Finally, we introduce droplet interaction with ultrasound. We elucidate the ultrasound-focusing concept within a droplets sphere, droplet shaking due to media compressibility and droplet phase-conversion dynamics.

Ideas of Flat and Curved Space in History of Physics

NASA Astrophysics Data System (ADS)

Berezin, Alexander A.

2006-04-01

Since ``everything which is not prohibited is compulsory'' (assigned to Gell-Mann) we can postulate infinite flat Cartesian N-dimensional (N: any integer) space-time (ST) as embedding for any curved ST. Ergodicity raises quest of whether total number of inflationary and/or Everett bubbles (mini-verses) is finite, countably infinite (aleph-zero) or uncountably infinite (aleph-one). Are these bubbles form Gaussian distribution or form some non-random subsetting? Perhaps, communication between mini-verses (idea of D.Deutsch) can be facilitated by a kind of minimax non-local dynamics akin to Fermat principle? (Minimax Principle in Bubble Cosmology). Even such classical effects as magnetism and polarization have some non-local features. Can we go below the Planck length to perhaps Compton wavelength of our ``Hubble's bubble'' (h/Mc = 10 to minus 95 m, if M = 10 to 54 kg)? When talking about time loops and ergodicity (eternal return paradigm) is there some hysterisis in the way quantum states are accessed in ``forward'' or ``reverse'' direction? (reverse direction implies backward causality of J.Wheeler and/or Aristotelian final causation).

Origin of crashes in three US stock markets: shocks and bubbles

NASA Astrophysics Data System (ADS)

Johansen, Anders

2004-07-01

This paper presents an exclusive classification of the largest crashes in Dow Jones industrial average, SP500 and NASDAQ in the past century. Crashes are objectively defined as the top-rank filtered drawdowns (loss from the last local maximum to the next local minimum disregarding noise fluctuations), where the size of the filter is determined by the historical volatility of the index. It is shown that all crashes can be linked to either an external shock, e.g., outbreak of war, or a log-periodic power law (LPPL) bubble with an empirically well-defined complex value of the exponent. Conversely, with one sole exception all previously identified LPPL bubbles are followed by a top-rank drawdown. As a consequence, the analysis presented suggest a one-to-one correspondence between market crashes defined as top-rank filtered drawdowns on one hand and surprising news and LPPL bubbles on the other. We attribute this correspondence to the efficient market hypothesis effective on two quite different time scales depending on whether the market instability the crash represent is internally or externally generated.

Perturbations of the magnetic induction in a bubbly liquid metal flow

NASA Astrophysics Data System (ADS)

Guichou, Rafael; Tordjeman, Philippe; Bergez, Wladimir; Zamansky, Remi; Paumel, Kevin

2017-11-01

The presence of bubbles in liquid metal flow subject to AC magnetic field modifies the distribution of eddy currents in the fluid. This situation is encountered in metallurgy and nuclear industry for Sodium Fast Reactors. We will show that the perturbation of the eddy currents can be measured by an Eddy Current Flowmeter coupled with a lock-in amplifier. The experiments point out that the demodulated signal allows to detect the presence of a single bubble in the flow. The signal is sensitive both to the diameter and the relative position of the bubble. Then, we will present a model of a potential perturbation of the current density caused by a bubble and the distortion of the magnetic field. The eddy current distribution is calculated from the induction equation. This model is derived from a potential flow around a spherical particle. The total vector potential is the sum of the vector potential in the liquid metal flow without bubbles and the perturbated vector potential due to the presence of a bubble. The model is then compared to the experimental measurements realized with the eddy current flow meter for various bubble diameters in galinstan. The very good agreement between model and experiments validates the relevance of the perturbative approach.

The gas fluxing of aluminum: Mathematical modeling and experimental investigations

NASA Astrophysics Data System (ADS)

Fjeld, Autumn Marie

Chlorine fluxing is an essential purification step in aluminum refining in which impurities such as Ca, Na, Li, and Mg are removed by bubbling a mixture of chlorine and argon gas through molten aluminum. The gas is injected into the fluxing vessel through a rotating shaft and impeller which simultaneously agitates the melt, while breaking up and dispersing gas bubbles through the liquid phase. The efficiency of impurity removal and control of toxic chlorine and chloride emissions are dependent upon the extent of gas dispersion or mixing, residence time of the bubbles, and surface area of the bubbles. Clearly the gas injection and distribution within the liquid metal cannot be directly observed and such operations are often poorly controlled and not well understood. Problems arise when the injection gas, i.e. chlorine, is not completely consumed by reaction with impurities and the excess is reported as emissions of chlorides such as toxic HCl. The intention is to improve the technology to eliminate this waste (saving on the energy entailed in the chlorine production and reducing pollution) by better dispersion of the injected gas throughout the metal. Previous experimental investigations using a capacitance probe, capable of immersion in liquid aluminum for several hours, have been carried out to detect bubbles in an industrial fluxing unit at the Alcoa Technical Center. Bubble frequency data have shown the bubbles to be fairly well dispersed in the areas of the fluxing unit, decreasing in observed bubble frequency with increasing distance from the impeller (source of gas injection). To gain further insight and add to our experimental findings, two computational models have been developed to simulate the complex two-phase fluid dynamics of a rotary gas injection system. The results of these two modeling approaches are presented and analyzed and compared to experimental bubble measurements gathered using the capacitance probe. Bubble size distributions and residence times from the discrete phase model were incorporated in an external demagging reaction model to predict chlorine utilization efficiency. This simplified model included several assumptions regarding the kinetics and reaction path, however the model showed reasonable agreement to prior experimental magnesium removal data and provides valuable information related to the interplay of reaction progress in a fluxing unit and the fluid dynamics, in terms of bubble size, trajectory and resulting bubble residence time.

Bubble Proliferation or Dissolution of Cavitation Nuclei in the Beam Path of a Shock-Wave Lithotripter

NASA Astrophysics Data System (ADS)

Frank, Spencer; Lautz, Jaclyn; Sankin, Georgy N.; Szeri, Andrew J.; Zhong, Pei

2015-03-01

It is hypothesized that the decreased treatment efficiency in contemporary shock-wave lithotripters is related to tensile wave attenuation due to cavitation in the prefocal beam path. Utilizing high-speed imaging of the beam path and focal pressure waveform measurements, tensile attenuation is associated with bubble proliferation. By systematically testing different combinations of pulse-repetition frequency and gas concentration, we modulate the bubble-dissolution time to identify which conditions lead to bubble proliferation and show that reducing bubble proliferation in the beam path significantly improves acoustic transmission and stone comminution efficiency in vitro. In addition to experiments, a bubble-proliferation model is developed that takes gas diffusion across the bubble wall and bubble fragmentation into account. By aligning the model with experimental observations, the number of daughter bubbles produced after a single lithotripter bubble collapse is estimated to be in the range of 253 ˜510 . This finding is on the same order of magnitude with previous measurements of an isolated bubble collapse in a lithotripter field by Pishchalnikov, McAteer, and Williams [BJU Int. 102, 1681 (2008), 10.1111/j.1464-410X.2008.07896.x], and this estimate improves the general understanding of lithotripsy bubble dynamics in the beam path.

Growth and Detachment of Oxygen Bubbles Induced by Gold-Catalyzed Decomposition of Hydrogen Peroxide

PubMed Central

2017-01-01

Whereas bubble growth out of gas-oversatured solutions has been quite well understood, including the formation and stability of surface nanobubbles, this is not the case for bubbles forming on catalytic surfaces due to catalytic reactions, though it has important implications for gas evolution reactions and self-propulsion of micro/nanomotors fueled by bubble release. In this work we have filled this gap by experimentally and theoretically examining the growth and detachment dynamics of oxygen bubbles from hydrogen peroxide decomposition catalyzed by gold. We measured the bubble radius R(t) as a function of time by confocal microscopy and find R(t) ∝ t1/2. This diffusive growth behavior demonstrates that the bubbles grow from an oxygen-oversaturated environment. For several consecutive bubbles detaching from the same position in a short period of time, a well-repeated growing behavior is obtained from which we conclude the absence of noticeable depletion effect of oxygen from previous bubbles or increasing oversaturation from the gas production. In contrast, for two bubbles far apart either in space or in time, substantial discrepancies in their growth rates are observed, which we attribute to the variation in the local gas oversaturation. The current results show that the dynamical evolution of bubbles is influenced by comprehensive effects combining chemical catalysis and physical mass transfer. Finally, we find that the size of the bubbles at the moment of detachment is determined by the balance between buoyancy and surface tension and by the detailed geometry at the bubble’s contact line. PMID:28983387

Argon Bubble Transport and Capture in Continuous Casting with an External Magnetic Field Using GPU-Based Large Eddy Simulations

NASA Astrophysics Data System (ADS)

Jin, Kai

Continuous casting produces over 95% of steel in the world today, hence even small improvements to this important industrial process can have large economic impact. In the continuous casting of steel process, argon gas is usually injected at the slide gate or stopper rod to prevent clogging, but entrapped bubbles may cause defects in the final product. Many defects in this process are related to the transient fluid flow in the mold region of the caster. Electromagnetic braking (EMBr) device is often used at high casting speed to modify the mold flow, reduce the surface velocity and fluctuation. This work studies the physics in continuous casting process including effects of EMBr on the motion of fluid flow in the mold region, and transport and capture of bubbles in the solidification processes. A computational effective Reynolds-averaged Navier-Stokes (RANS) model and a high fidelity Large Eddy Simulation (LES) model are used to understand the motion of the molten steel flow. A general purpose multi-GPU Navier-Stokes solver, CUFLOW, is developed. A Coherent-Structure Smagorinsky LES model is implemented to model the turbulent flow. A two-way coupled Lagrangian particle tracking model is added to track the motion of argon bubbles. A particle/bubble capture model based on force balance at dendrite tips is validated and used to study the capture of argon bubbles by the solidifying steel shell. To investigate the effects of EMBr on the turbulent molten steel flow and bubble transport, an electrical potential method is implemented to solve the magnetohydrodynamics equations. Volume of Fluid (VOF) simulations are carried out to understand the additional resistance force on moving argon bubbles caused by adding transverse magnetic field. A modified drag coefficient is extrapolated from the results and used in the two-way coupled Eulerian-Lagrangian model to predict the argon bubble transport in a caster with EMBr. A hook capture model is developed to understand the effects of hooks on argon bubble capture.

High frequency acoustic propagation under variable sea surfaces

NASA Astrophysics Data System (ADS)

Senne, Joseph

This dissertation examines the effects of rough sea surfaces and sub-surface bubbles on high frequency acoustic transmissions. Owing to the strong attenuation of electromagnetic waves in seawater, acoustic waves are used in the underwater realm much in the same way that electromagnetic waves are used in the atmosphere. The transmission and reception of acoustic waves in the underwater environment is important for a variety of fields including navigation, ocean observation, and real-time communications. Rough sea surfaces and sub-surface bubbles alter the acoustic signals that are received not only in the near-surface water column, but also at depth. This dissertation demonstrates that surface roughness and sub-surface bubbles notably affect acoustic transmissions with frequency ranges typical of underwater communications systems (10-50 kHz). The influence of rough surfaces on acoustic transmissions is determined by modeling forward propagation subject to sea surface dynamics that vary with time scales of less than a second to tens of seconds. A time-evolving rough sea surface model is combined with a rough surface formulation of a parabolic equation model for predicting time-varying acoustic fields. Linear surface waves are generated from surface wave spectra, and evolved in time using a Runge-Kutta integration technique. This evolving, range-dependent surface information is combined with other environmental parameters and fed into the acoustic model, giving an approximation of the time-varying acoustic field. The wide-angle parabolic equation model manages the rough sea surfaces by molding them into the boundary conditions for calculations of the near-surface acoustic field. The influence of sub-surface bubbles on acoustic transmissions is determined by modeling the population of bubbles near the surface and using those populations to approximate the effective changes in sound speed and attenuation. Both range-dependent and range-independent bubble models are considered, with the range-dependent model varying over the same time scales as the sea surface model and the range-independent model invariant over time. The bubble-induced sound speed and attenuation fluctuations are read in by the parabolic equation model, which allows for the effects of surface roughness and sub-surface bubbles to be computed separately or together. These merged acoustic models are validated using concurrently-collected acoustic and environmental information, including surface wave spectra. Data to model comparisons demonstrate that the models are able to approximate the ensemble-averaged acoustic intensity at ranges of at least a kilometer for acoustic signals of 10-20 kHz. The rough surface model is shown to capture variations due to surface fluctuations occurring over time scales of less than a second to tens of seconds. The separate bubble models demonstrate the abilities to account for the intermittency of bubble plumes and to determine overall effect of bubbly layers, respectively. The models are shown to capture variations in the acoustic field occurring over time scales of less than a second to tens of seconds. Comparisons against data demonstrate the ability of the model to track acoustic transmissions under evolving sea surfaces. The effects of the evolving bubble field are demonstrated through the use of idealized test cases. For frequency ranges important to communications, surface roughness is shown to have the more dominant effect, with bubbles having an ancillary effect.

Bubbling at high flow rates in inviscid and viscous liquids (slags)

NASA Astrophysics Data System (ADS)

Engh, T. Abel; Nilmani, M.

1988-02-01

The behavior of gas discharging into melts at high velocities but still in the bubbling regime has been investigated in a laboratory modeling study for constant flow conditions. Air or helium was injected through a vertical tuyere into water, zinc-chloride, and aqueous glycerol solutions. High speed cinematography and pressure measurements in the tuyere have been carried out simultaneously. Pressure fluctuations at the injection point were monitored and correlated to the mode of bubble formation. The effects of high gas flow rates and high liquid viscosities have been examined in particular. Flow rates were employed up to 10-3 m3/s and viscosity to 0.5 Ns/m2. In order to attain a high gas momentum, the tuyere diameter was only 3 x 10-3 m. The experimental conditions and modeling liquids were chosen with special reference to the established practice of submerged gas injection to treat nonferrous slags. Such slags can be highly viscous. Bubble volume is smaller than that calculated from existing models such as those given by Davidson and Schüler10,11 due to the effect of gas momentum elongating the bubbles. On the other hand, viscosity tends to retard the bubble rise velocity, thus increasing volumes. To take elongation into account, a mathematical model is presented that assumes a prolate ellipsoidal shape of the bubbles. The unsteady potential flow equations for the liquid are solved for this case. Viscous effects are taken into account by noting that flow deviates from irrotational motion only in a thin boundary layer along the surface of the bubble. Thus, drag on the bubble can be obtained by calculating the viscous energy dissipation for potential flow past an ellipse. The time-dependent inertia coefficient for the ellipsoid is found by equating the vertical pressure increase inside and outside the bubble. This pressure change in the bubble is obtained by assuming that gas enters as a homogeneous jet and then calculating the stagnation pressure at the apex of the bubble.

The Ultra-Soft X-ray Background: A Probe of the Hot Interstellar Medium and the Local Bubble - ADP-99

NASA Technical Reports Server (NTRS)

Smith, Randall

2003-01-01

The Ultra-Soft X-ray Telescope (UXT) was a sounding rocket mission flown three times in 1984 - 1986. At the beginning of the project, the data existed solely in form of raw telemetry data stored on 9 track tapes. The primary goal of this proposal has been to extract event files from the raw telemetry stream and to create instrument response models and calibrated spectra from it. We have completed this project, and the data will soon be available to all via the HEASARC archive of high-energy data at Goddard Space Flight Center. We are in the process of combining the results with the ALEXIS and DXS observations of the Local Bubble in modelling the 72 eV iron line (recently observed by the X-ray Quantum Calorimeter) and the carbon emission lines that are uniquely visible in this dataset. Our results agree with the XQC observation which predicts a maximum emission in the 72 eV iron lines that is below the limit observable with UXT. However, this leaves an open question as to what lines were responsible for the observed Be-band emission. The answer to this question will likely require more observations of soft X-rays with the Chandra LETGS and new atomic data models of potentially emitting ions.

Modeling of bubble dynamics in relation to medical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amendt, P.A.; London, R.A.; Strauss, M.

1997-03-12

In various pulsed-laser medical applications, strong stress transients can be generated in advance of vapor bubble formation. To better understand the evolution of stress transients and subsequent formation of vapor bubbles, two-dimensional simulations are presented in channel or cylindrical geometry with the LATIS (LAser TISsue) computer code. Differences with one-dimensional modeling are explored, and simulated experimental conditions for vapor bubble generation are presented and compared with data. 22 refs., 8 figs.

Numerical Modelling and Simulation of Chemical Reactions in a Nano-Pulse Discharged Bubble for Water Treatment

NASA Astrophysics Data System (ADS)

He, Yuchen; Satoshi, Uehara; Hidemasa, Takana; Hideya, Nishiyama

2016-09-01

A zero-dimensional model to simulate a nano-pulse-discharged bubble in water was developed. The model consists of gas and liquid phases corresponding to the inside and outside of the bubble, respectively. The diffusions of chemical species from the gas to the liquid phase through the bubble interface was also investigated. The initial gas is Ar, but includes a little H2O and O2 in the bubble. The time evolution of the OH concentration in the liquid phase was mainly investigated as an important species for water treatment. It was shown that OH was generated in the bubble and then diffused into the liquid. With the application of a continuous nano-pulse discharge, more OH radicals were generated as the frequency increased at a low voltage for a given power consumption. supported partially by Japan Society for the Promotion of Science (JSPS) KAKENHI (No. 26249015)

Bubble Formation and Detachment in Reduced Gravity Under the Influence of Electric Fields

NASA Technical Reports Server (NTRS)

Herman, Cila; Iacona, Estelle; Chang, Shinan

2002-01-01

The objective of the study is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Both uniform and nonuniform electric field configurations were considered. Bubble formation and detachment were recorded and visualized in reduced gravity (corresponding to gravity levels on Mars, on the Moon as well as microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angle at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. Measured data and model predictions show good agreement and indicate that the level of gravity and the electric field magnitude significantly affect bubble shape, volume and dimensions.

Collapse dynamics of ultrasound contrast agent microbubbles

NASA Astrophysics Data System (ADS)

King, Daniel Alan

Ultrasound contrast agents (UCAs) are micron-sized gas bubbles encapsulated with thin shells on the order of nanometers thick. The damping effects of these viscoelastic coatings are widely known to significantly alter the bubble dynamics for linear and low-amplitude behavior; however, their effects on strongly nonlinear and destruction responses are much less studied. This dissertation examines the behaviors of single collapsing shelled microbubbles using experimental and theoretical methods. The study of their dynamics is particularly relevant for emerging experimental uses of UCAs which seek to leverage localized mechanical forces to create or avoid specialized biomedical effects. The central component in this work is the study of postexcitation rebound and collapse, observed acoustically to identify shell rupture and transient inertial cavitation of single UCA microbubbles. This time-domain analysis of the acoustic response provides a unique method for characterization of UCA destruction dynamics. The research contains a systematic documentation of single bubble postexcitation collapse through experimental measurement with the double passive cavitation detection (PCD) system at frequencies ranging from 0.9 to 7.1 MHz and peak rarefactional pressure amplitudes (PRPA) ranging from 230 kPa to 6.37 MPa. The double PCD setup is shown to improve the quality of collected data over previous setups by allowing symmetric responses from a localized confocal region to be identified. Postexcitation signal percentages are shown to generally follow trends consistent with other similar cavitation metrics such as inertial cavitation, with greater destruction observed at both increased PRPA and lower frequency over the tested ranges. Two different types of commercially available UCAs are characterized and found to have very different collapse thresholds; lipid-shelled Definity exhibits greater postexcitation at lower PRPAs than albumin-shelled Optison. Furthermore, by altering the size distributions of these UCAs, it is shown that the shell material has a large influence on the occurrence of postexcitation rebound at all tested frequencies while moderate alteration of the size distribution may only play a significant role within certain frequency ranges. Finally, the conditions which generate the experimental postexcitation signal are examined theoretically using several forms of single bubble models. Evidence is provided for the usefulness of modeling this large amplitude UCA behavior with a size-varying surface tension as described in the Marmottant model; better agreement for lipid-shelled Definity UCAs is obtained by considering the dynamic response with a rupturing shell rather than either a non-rupturing or nonexistent shell. Moreover, the modeling indicates that maximum radial expansion from the initial UCA size is a suitable metric to predict postexcitation collapse, and that both shell rupture and inertial cavitation are necessary conditions to generate this behavior. Postexcitation analysis is found to be a beneficial characterization metric for studying the destruction behaviors of single UCAs when measured with the double PCD setup. This work provides quantitative documentation of UCA collapse, exploration into UCA material properties which affect this collapse, and comparison of existing single bubble models with experimentally measured postexcitation signals.

Visualization of airflow growing soap bubbles

NASA Astrophysics Data System (ADS)

Al Rahbi, Hamood; Bock, Matthew; Ryu, Sangjin

2016-11-01

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.

Analysis of intergranular fission-gas bubble-size distributions in irradiated uranium-molybdenum alloy fuel

NASA Astrophysics Data System (ADS)

Rest, J.; Hofman, G. L.; Kim, Yeon Soo

2009-04-01

An analytical model for the nucleation and growth of intra and intergranular fission-gas bubbles is used to characterize fission-gas bubble development in low-enriched U-Mo alloy fuel irradiated in the advanced test reactor in Idaho as part of the Reduced Enrichment for Research and Test Reactor (RERTR) program. Fuel burnup was limited to less than ˜7.8 at.% U in order to capture the fuel-swelling stage prior to irradiation-induced recrystallization. The model couples the calculation of the time evolution of the average intergranular bubble radius and number density to the calculation of the intergranular bubble-size distribution based on differential growth rate and sputtering coalescence processes. Recent results on TEM analysis of intragranular bubbles in U-Mo were used to set the irradiation-induced diffusivity and re-solution rate in the bubble-swelling model. Using these values, good agreement was obtained for intergranular bubble distribution compared against measured post-irradiation examination (PIE) data using grain-boundary diffusion enhancement factors of 15-125, depending on the Mo concentration. This range of enhancement factors is consistent with values obtained in the literature.

Modeling of single film bubble and numerical study of the plateau structure in foam system

NASA Astrophysics Data System (ADS)

Sun, Zhong-guo; Ni, Ni; Sun, Yi-jie; Xi, Guang

2018-02-01

The single-film bubble has a special geometry with a certain amount of gas shrouded by a thin layer of liquid film under the surface tension force both on the inside and outside surfaces of the bubble. Based on the mesh-less moving particle semi-implicit (MPS) method, a single-film double-gas-liquid-interface surface tension (SDST) model is established for the single-film bubble, which characteristically has totally two gas-liquid interfaces on both sides of the film. Within this framework, the conventional surface free energy surface tension model is improved by using a higher order potential energy equation between particles, and the modification results in higher accuracy and better symmetry properties. The complex interface movement in the oscillation process of the single-film bubble is numerically captured, as well as typical flow phenomena and deformation characteristics of the liquid film. In addition, the basic behaviors of the coalescence and connection process between two and even three single-film bubbles are studied, and the cases with bubbles of different sizes are also included. Furthermore, the classic plateau structure in the foam system is reproduced and numerically proved to be in the steady state for multi-bubble connections.

Pore-scale analysis of the minimum liquid film thickness around elongated bubbles in confined gas-liquid flows

NASA Astrophysics Data System (ADS)

Magnini, M.; Beisel, A. M.; Ferrari, A.; Thome, J. R.

2017-11-01

The fluid mechanics of elongated bubbles in confined gas-liquid flows in micro-geometries is important in pore-scale flow processes for enhanced oil recovery and mobilization of colloids in unsaturated soil. The efficiency of such processes is traditionally related to the thickness of the liquid film trapped between the elongated bubble and the pore's wall, which is assumed constant. However, the surface of long bubbles presents undulations in the vicinity of the rear meniscus, which may significantly decrease the local thickness of the liquid film, thus impacting the process of interest. This study presents a systematic analysis of these undulations and the minimum film thickness induced in the range Ca = 0.001- 0.5 and Re = 0.1- 2000 . Pore-scale Computational Fluid Dynamics (CFD) simulations are performed with a self-improved version of the opensource solver ESI OpenFOAM which is based on a Volume of Fluid method to track the gas-liquid interface. A lubrication model based on the extension of the classical axisymmetric Bretherton theory is utilized to better understand the CFD results. The profiles of the rear meniscus of the bubble obtained with the lubrication model agree fairly well with those extracted from the CFD simulations. This study shows that the Weber number of the flow, We = Ca Re , is the parameter that best describes the dynamics of the interfacial waves. When We < 0.1, a single wave crest is observed and the minimum film thickness tends to an asymptotic value, which depends on the capillary number, as We → 0. Undulations dampen as the capillary number increases and disappear completely when Ca = 0.5 . When We > 0.1, a larger number of wave crests becomes evident on the surface of the rear meniscus of the bubble. The liquid film thickness at the crests of the undulations thins considerably as the Reynolds number is increased, down to less than 60% of the value measured in the flat film region. This may significantly influence important environmental processes, such as the detachment and mobilization of micron-sized pollutants and pathogenic micro-organisms adhering at the pore's wall in unsaturated soil.

Statistical mechanics of two-dimensional shuffled foams: Geometry-topology correlation in small or large disorder limits

NASA Astrophysics Data System (ADS)

Durand, Marc; Kraynik, Andrew M.; van Swol, Frank; Käfer, Jos; Quilliet, Catherine; Cox, Simon; Ataei Talebi, Shirin; Graner, François

2014-06-01

Bubble monolayers are model systems for experiments and simulations of two-dimensional packing problems of deformable objects. We explore the relation between the distributions of the number of bubble sides (topology) and the bubble areas (geometry) in the low liquid fraction limit. We use a statistical model [M. Durand, Europhys. Lett. 90, 60002 (2010), 10.1209/0295-5075/90/60002] which takes into account Plateau laws. We predict the correlation between geometrical disorder (bubble size dispersity) and topological disorder (width of bubble side number distribution) over an extended range of bubble size dispersities. Extensive data sets arising from shuffled foam experiments, surface evolver simulations, and cellular Potts model simulations all collapse surprisingly well and coincide with the model predictions, even at extremely high size dispersity. At moderate size dispersity, we recover our earlier approximate predictions [M. Durand, J. Kafer, C. Quilliet, S. Cox, S. A. Talebi, and F. Graner, Phys. Rev. Lett. 107, 168304 (2011), 10.1103/PhysRevLett.107.168304]. At extremely low dispersity, when approaching the perfectly regular honeycomb pattern, we study how both geometrical and topological disorders vanish. We identify a crystallization mechanism and explore it quantitatively in the case of bidisperse foams. Due to the deformability of the bubbles, foams can crystallize over a larger range of size dispersities than hard disks. The model predicts that the crystallization transition occurs when the ratio of largest to smallest bubble radii is 1.4.

Effects of fluid viscosity on a moving sonoluminescing bubble.

PubMed

Sadighi-Bonabi, Rasoul; Mirheydari, Mona; Rezaee, Nastaran; Ebrahimi, Homa

2011-08-01

Based on the quasi-adiabatic model, the parameters of the bubble interior for a moving single bubble sonoluminescence in water, adiponitrile, and N-methylformamide are calculated for various fluid viscosities. By using a complete form of the hydrodynamic force, the bubble trajectory is calculated for a moving single bubble sonoluminescence (m-SBSL). It is found that as the fluid viscosity increases, the unique circular path changes to an ellipsoidal and then linear form and along this incrementally increase of viscosity the light intensity increases. By using the Bremsstrahlung model to describe the bubble radiation, gradual increase of the viscosity results in brighter emissions. It is found that in fluids with higher viscosity the light intensity decreases as time passes.

Dynamic morphology of gas hydrate on a methane bubble in water: Observations and new insights for hydrate film models

NASA Astrophysics Data System (ADS)

Warzinski, Robert P.; Lynn, Ronald; Haljasmaa, Igor; Leifer, Ira; Shaffer, Frank; Anderson, Brian J.; Levine, Jonathan S.

2014-10-01

Predicting the fate of subsea hydrocarbon gases escaping into seawater is complicated by potential formation of hydrate on rising bubbles that can enhance their survival in the water column, allowing gas to reach shallower depths and the atmosphere. The precise nature and influence of hydrate coatings on bubble hydrodynamics and dissolution is largely unknown. Here we present high-definition, experimental observations of complex surficial mechanisms governing methane bubble hydrate formation and dissociation during transit of a simulated oceanic water column that reveal a temporal progression of deep-sea controlling mechanisms. Synergistic feedbacks between bubble hydrodynamics, hydrate morphology, and coverage characteristics were discovered. Morphological changes on the bubble surface appear analogous to macroscale, sea ice processes, presenting new mechanistic insights. An inverse linear relationship between hydrate coverage and bubble dissolution rate is indicated. Understanding and incorporating these phenomena into bubble and bubble plume models will be necessary to accurately predict global greenhouse gas budgets for warming ocean scenarios and hydrocarbon transport from anthropogenic or natural deep-sea eruptions.

The life and death of film bubbles

NASA Astrophysics Data System (ADS)

Poulain, S.; Villermaux, E.; Bourouiba, L.

2017-11-01

Following its burst, the fragmentation of a large bubble (film bubble) at the air-water interface can release hundreds of micrometer-sized film-drops in the air we breathe. This mechanism of droplet formation is one of the most prominent sources of sea spray. Indoor or outdoor, pathogens from contaminated water are transported by these droplets and have also been linked to respiratory infection. The lifetime and thickness of bubbles govern the number and size of the droplets they produce. Despite these important implications, little is known about the factors influencing the life and death of surface film bubbles. In particular, the fundamental physical mechanisms linking bubble aging, thinning, and lifetime remain poorly understood. To address this gap, we present the results of an extensive investigation of the aging of film-drop-producing bubbles in various ambient air, water composition, and temperature conditions. We present and validate a generalized physical picture and model of bubble cap thickness evolution. The model and physical picture are linked to the lifetime of bubbles via a series of cap rupture mechanisms of increasing efficiency.

Molecular Dynamics Investigation of Each Bubble Behavior in Coarsening of Cavitation Bubbles in a Finite Space

NASA Astrophysics Data System (ADS)

Tsuda, Shin-Ichi; Nakano, Yuta; Watanabe, Satoshi

2017-11-01

Recently, several studies using Molecular Dynamics (MD) simulation have been conducted for investigation of Ostwald ripening of cavitation bubbles in a finite space. The previous studies focused a characteristic length of bubbles as one of the spatially-averaged quantities, but each bubble behavior was not been investigated in detail. The objective of this study is clarification of the characteristics of each bubble behavior in Ostwald ripening, and we conducted MD simulation of a Lennard-Jones fluid in a semi-confined space. As a result, the time dependency of the characteristic length of bubbles as a spatially-averaged quantity suggested that the driving force of the Ostwald ripening is Evaporation/Condensation (EC) across liquid-vapor surface, which is the same result as the previous works. The radius change of the relatively larger bubbles also showed the same tendency to a classical EC model. However, the sufficiently smaller bubbles than the critical size, e.g., the bubbles just before collapsing, showed a different characteristic from the classical EC model. Those smaller bubbles has a tendency to be limited by mechanical non-equilibrium in which viscosity of liquid is dominant rather than by EC across liquid-vapor surface. This work was supported by JSPS KAKENHI Grant Number JP16K06085.

Swelling and gas release in oxide fuels during fast temperature transients

NASA Astrophysics Data System (ADS)

Dollins, C. C.; Jursich, M.

1982-05-01

A previously reported intergranular swelling and gas release model for oxide fuels has been modified to predict fission gas behavior during fast temperature transients. Under steady state or slowly varying conditions it has been assumed in the previous model that the pressure caused by the fission gas within the gas bubbles is in equilibrium with the surface tension of the bubbles. During a fast transient, however, net vacancy migration to the bubbles may be insufficient to maintain this equilibrium. In order to ascertain the net vacancy flow, it is necessary to model the point defect behavior in the fuel. Knowing the net flow of vacancies to the bubble and the bubble size, the bubble diffusivity can be determined and the long range migration of the gas out of the fuel can be calculated. The model has also been modified to allow release of all the gas on the grain boundaries during a fast temperature transient. The gas release predicted by the revised model shows good agreement to fast transient gas release data from an EBR-II TREAT H-3 (Transient Reactor Test Facility) test. Agreement has also been obtained between predictions using the model and gas release data obtained by Argonne National Laboratory from out-of-reactor transient heating experiments on irradiated UO 2. It was found necessary to increase the gas bubble diffusivity used in the model by a factor of thirty during the transient to provide agreement between calculations and measurements. Other workers have also found that such an increase is necessary for agreement and attribute the increased diffusivity to yielding at the bubble surface due to the increased pressure.

Forced convection in the wakes of sliding bubbles

NASA Astrophysics Data System (ADS)

Meehan, O'Reilly; Donnelly, B.; Persoons, T.; Nolan, K.; Murray, D. B.

2016-09-01

Both vapour and gas bubbles are known to significantly increase heat transfer rates between a heated surface and the surrounding fluid, even with no phase change. However, the complex wake structures means that the surface cooling is not fully understood. The current study uses high speed infra-red thermography to measure the surface temperature and convective heat flux enhancement associated with an air bubble sliding under an inclined surface, with a particular focus on the wake. Enhancement levels of 6 times natural convection levels are observed, along with cooling patterns consistent with a possible hairpin vortex structure interacting with the thermal boundary layer. Local regions of suppressed convective heat transfer highlight the complexity of the bubble wake in two-phase applications.

Measurement and modeling on hydrodynamic forces and deformation of an air bubble approaching a solid sphere in liquids.

PubMed

Shahalami, Mansoureh; Wang, Louxiang; Wu, Chu; Masliyah, Jacob H; Xu, Zhenghe; Chan, Derek Y C

2015-03-01

The interaction between bubbles and solid surfaces is central to a broad range of industrial and biological processes. Various experimental techniques have been developed to measure the interactions of bubbles approaching solids in a liquid. A main challenge is to accurately and reliably control the relative motion over a wide range of hydrodynamic conditions and at the same time to determine the interaction forces, bubble-solid separation and bubble deformation. Existing experimental methods are able to focus only on one of the aspects of this problem, mostly for bubbles and particles with characteristic dimensions either below 100 μm or above 1 cm. As a result, either the interfacial deformations are measured directly with the forces being inferred from a model, or the forces are measured directly with the deformations to be deduced from the theory. The recently developed integrated thin film drainage apparatus (ITFDA) filled the gap of intermediate bubble/particle size ranges that are commonly encountered in mineral and oil recovery applications. Equipped with side-view digital cameras along with a bimorph cantilever as force sensor and speaker diaphragm as the driver for bubble to approach a solid sphere, the ITFDA has the capacity to measure simultaneously and independently the forces and interfacial deformations as a bubble approaches a solid sphere in a liquid. Coupled with the thin liquid film drainage modeling, the ITFDA measurement allows the critical role of surface tension, fluid viscosity and bubble approach speed in determining bubble deformation (profile) and hydrodynamic forces to be elucidated. Here we compare the available methods of studying bubble-solid interactions and demonstrate unique features and advantages of the ITFDA for measuring both forces and bubble deformations in systems of Reynolds numbers as high as 10. The consistency and accuracy of such measurement are tested against the well established Stokes-Reynolds-Young-Laplace model. The potential to use the design principles of the ITFDA for fundamental and developmental research is demonstrated. Copyright © 2014. Published by Elsevier B.V.

Foam flow in a model porous medium: II. The effect of trapped gas.

PubMed

Jones, S A; Getrouw, N; Vincent-Bonnieu, S

2018-05-09

Gas trapping is an important mechanism in both Water or Surfactant Alternating Gas (WAG/SAG) and foam injection processes in porous media. Foams for enhanced oil recovery (EOR) can increase sweep efficiency as they decrease the gas relative permeability, and this is mainly due to gas trapping. However, gas trapping mechanisms are poorly understood. Some studies have been performed during corefloods, but little work has been carried out to describe the bubble trapping behaviour at the pore scale. We have carried out foam flow tests in a micromodel etched with an irregular hexagonal pattern. Image analysis of the foam flow allowed the bubble centres to be tracked and local velocities to be obtained. It was found that the flow in the micromodel is dominated by intermittency and localized zones of trapped gas. The quantity of trapped gas was measured both by considering the fraction of bubbles that were trapped (via velocity thresholding) and by measuring the area fraction containing immobile gas (via image analysis). A decrease in the quantity of trapped gas was observed for both increasing total velocity and increasing foam quality. Calculations of the gas relative permeability were made with the Brooks Corey equation, using the measured trapped gas saturations. The results showed a decrease in gas relative permeabilities, and gas mobility, for increasing fractions of trapped gas. It is suggested that the shear thinning behaviour of foam could be coupled to the saturation of trapped gas.

Fearless versus fearful speculative financial bubbles

NASA Astrophysics Data System (ADS)

Andersen, J. V.; Sornette, D.

2004-06-01

Using a recently introduced rational expectation model of bubbles, based on the interplay between stochasticity and positive feedbacks of prices on returns and volatility, we develop a new methodology to test how this model classifies nine time series that have been previously considered as bubbles ending in crashes. The model predicts the existence of two anomalous behaviors occurring simultaneously: (i) super-exponential price growth and (ii) volatility growth, that we refer to as the “fearful singular bubble” regime. Out of the nine time series, we find that five pass our tests and can be characterized as “fearful singular bubbles”. The four other cases are the information technology Nasdaq bubble and three bubbles of the Hang Seng index ending in crashes in 1987, 1994 and 1997. According to our analysis, these four bubbles have developed with essentially no significant increase of their volatility. This paper thus proposes that speculative bubbles ending in crashes form two groups hitherto unrecognized, namely those accompanied by increasing volatility (reflecting increasing risk perception) and those without change of volatility (reflecting an absence of risk perception).

Study on characteristics of single cavitation bubble considering condensation and evaporation of kerosene steam under ultrasonic vibration honing.

PubMed

Ye, Linzheng; Zhu, Xijing; Wang, Lujie; Guo, Ce

2018-01-01

Ultrasonic vibration honing technology is an effective means for materials difficult to machine, where cavitation occurs in grinding fluid under the action of ultrasound. To investigate the changes of single cavitation bubble characteristics in the grinding area and how honing parameters influence bubble characteristics, a dynamic model of single cavitation bubble in the ultrasonic vibration honing grinding area was established. The model was based on the bubble dynamics and considered the condensation and evaporation of kerosene steam and honing processing environment. The change rules of bubble radius, temperature, pressure and number of kerosene steam molecules inside the bubble were numerically simulated in the process of bubble moving. The results show that the condensation and evaporation of kerosene steam can help to explain the changes of temperature and pressure inside the bubble. Compared with ultrasonic vibration, the amplitude of bubble radius is greatly suppressed in the ultrasonic honing environment. However, the rate of movement of the bubble is faster. Meanwhile, the minimum values of pressure and temperature are larger, and the number of kerosene steam molecules is less. By studying the effect of honing factors on the movement of the cavitation bubble, it is found that honing pressure has a greater influence on bubble evolution characteristics, while rotation speed of honing head has a minor effect and the reciprocating speed of honing head has little impacts. Copyright © 2017 Elsevier B.V. All rights reserved.

Targeted Nanoparticle Thermometry: A Method to Measure Local Temperature at the Nanoscale Point Where Water Vapor Nucleation Occurs.

PubMed

Alaulamie, Arwa A; Baral, Susil; Johnson, Samuel C; Richardson, Hugh H

2017-01-01

An optical nanothermometer technique based on laser trapping, moving and targeted attaching an erbium oxide nanoparticle cluster is developed to measure the local temperature. The authors apply this new nanoscale temperature measuring technique (limited by the size of the nanoparticles) to measure the temperature of vapor nucleation in water. Vapor nucleation is observed after superheating water above the boiling point for degassed and nondegassed water. The average nucleation temperature for water without gas is 560 K but this temperature is lowered by 100 K when gas is introduced into the water. The authors are able to measure the temperature inside the bubble during bubble formation and find that the temperature inside the bubble spikes to over 1000 K because the heat source (optically-heated nanorods) is no longer connected to liquid water and heat dissipation is greatly reduced. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microbubbles and Ultrasound: A Bird's Eye View.

PubMed Central

Kaul, Sanjiv

2004-01-01

Gas-filled microbubbles were initially used as ultrasound contrast agent because of their intravascular rheology, which is similar to that of red blood cells. Their transit through tissue can thus be quantified with ultrasound. More recently, these bubbles have been successfully used for molecular imaging by incorporating ligands on their surfaces that will adhere to cellular and other components within the microvasculature and can be detected by ultrasound. These bubbles have also been used for delivery of genes and drugs which can be released locally by disruption of the bubbles with high-energy ultrasound. Finally, bioeffects produced by localized ultrasound disruption of microbubbles have been shown to induce angiogenesis. This brief review will provide a bird's eye view of these applications. Images Fig. 1 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 PMID:17060963

Structural characteristics of the shock-induced boundary layer separation extended to the leading edge

NASA Astrophysics Data System (ADS)

Tao, Y.; Liu, W. D.; Fan, X. Q.; Zhao, Y. L.

2017-07-01

For a better understanding of the local unstart of supersonic/hypersonic inlet, a series of experiments has been conducted to investigate the shock-induced boundary layer separation extended to the leading edge. Using the nanoparticle-based planar laser scattering, we recorded the fine structures of these interactions under different conditions and paid more attention to their structural characteristics. According to their features, these interactions could be divided into four types. Specifically, Type A wave pattern is similar to the classic shock wave/turbulent boundary layer interaction, and Type B wave configuration consists of an overall Mach reflection above the large scale separation bubble. Due to the gradual decrease in the size of the separation bubble, the separation bubble was replaced by several vortices (Type C wave pattern). Besides, for Type D wave configuration which exists in the local unstart inlet, there appears to be some flow spillage around the leading edge.

Exploring a Method for Improving Turbulent Separated-Flow Predictions with kappa-omega Models

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.

2009-01-01

A particular failing of Reynolds-averaged Navier-Stokes separated turbulent flow computations is addressed within the context of a kappa-omega two-equation turbulence model. The failing is the tendency for turbulence models to under-predict turbulent shear stress in the shear layers of some separation bubbles, yielding late boundary layer reattachment and recovery. Inspired by unpublished work of Volker, Langtry, and Menter, the author undertook an independent investigation in an attempt to improve the ability of the Menter shear stress transport (SST) model to predict flowfield characteristics in and downstream of separation bubbles. The fix is an ad hoc term that is a function of the local ratio of turbulent production to dissipation; it is used to multiply the omega-destruction term, increasing eddy viscosity in separated regions. With this fix, several flowfields are investigated. Results show that, although the "separation fix" can provide dramatic improvement in some cases, it is not consistently good for all flows. Thus, although it may prove helpful in many situations in its current form, this model may benefit from further refinements, including better sensitization to the energetics of turbulence in the separated region.

Shock-initiated Combustion of a Spherical Density Inhomogeneity

NASA Astrophysics Data System (ADS)

Haehn, Nicholas; Oakley, Jason; Rothamer, David; Anderson, Mark; Ranjan, Devesh; Bonazza, Riccardo

2010-11-01

A spherical density inhomogeneity is prepared using fuel and oxidizer at a stoichiometric ratio and Xe as a diluent that increases the overall density of the bubble mixture (55% Xe, 30% H2, 15% O2). The experiments are performed in the Wisconsin Shock Tube Laboratory in a 9.2 m vertical shock tube with a 25.4 cm x 25.4 cm square cross-section. An injector is used to generate a 5 cm diameter soap film bubble filled with the combustible mixture. The injector retracts flush into the side of the tube releasing the bubble into a state of free fall. The combustible bubble is accelerated by a planar shock wave in N2 (2.0 < M < 2.8). The mismatch of acoustic impedances results in shock-focusing at the downstream pole of the bubble. The shock focusing results in localized temperatures and pressures significantly larger than nominal conditions behind a planar shock wave, resulting in auto-ignition at the focus. Planar Mie scattering and chemiluminescence are used simultaneously to visualize the bubble morphology and combustion characteristics. During the combustion phase, both the span-wise and stream-wise lengths of the bubble are seen to increase compared to the non-combustible scenario. Additionally, smaller instabilities are observed on the upstream surface, which are absent in the non-combustible bubbles.

Do volcanic gases represent equilibrium volatile concentrations? Some insights from a model of diffusive fractionation during rapid bubble growth

NASA Astrophysics Data System (ADS)

Baker, D. R.

2012-12-01

Measurements of volcanic gas compositions are often presumed to be directly related to equilibrium compositions of fluids exsolved at depth in magmatic systems that rapidly escape into the atmosphere. In particular, changes in the ratios of volatile species concentrations in volcanic gases have been interpreted to reflect influx of new magma batches or changes in the degassing depth. However, other mechanisms can also yield changes in volcanic gas compositions. One such mechanism is diffusive fractionation during rapid bubble growth. Such fractionation can occur because radial growth rates of bubbles in magmas are estimated to be in the range of 10-6 to 10-3 m s-1 and diffusion coefficients of minor volatiles (e.g., Cl, F, S, CO2) are orders of magnitude slower, 10-12 to 10-9 m2 s-1. Thus a bubble that rapidly grows and subsequently loses its volatiles to the surface may contribute a fluid sample whose concentration is affected by the interplay between the kinetics of bubble growth and volatile diffusion in the melt. A finite difference code was developed to calculate the effects of rapid bubble growth on the concentration of minor elements in the bubble for a spherical growth geometry. The bubble is modeled with a fixed growth rate and a constant equilibrium fluid-melt partition coefficient, KD. Bubbles were modeled to grow to a radius of 50 μm, the size at which the dominant bubble growth mechanism appears to change from diffusion to coalescence. The critical variables that control the departure from equilibrium behavior are the K D and the ratio of the growth velocity, V, to the diffusivity, D. Modeling bubble growth in a magma chamber at 100 MPa demonstrates that when KD is in the range of 10 to 1000 at low V/D values (e.g., 103 m-1) the composition of the fluid is at, or near, equilibrium with the melt. However, as V/D increases the bubble composition deviates increasingly from equilibrium. For V/D ratios of 105 and equilibrium KD's of either 50 or 100 (similar to estimates for S), a bubble with a 50 μm radius will contain a fluid whose concentration was apparently determined by a KD of less than 10. These models also demonstrate that the combination of rapid bubble growth with slow diffusion can deplete the melt in the volatile species only within the immediate neighborhood, on the order of 100 μm. If bubbles are spaced further apart the melts may retain significant concentrations of dissolved volatiles, which could lead to secondary and tertiary nucleation events. These models for diffusive fractionation during rapid bubble growth suggest that changes in the ratios of minor elements in volcanic gases may be influenced by bubble growth rate changes. Volatiles with lower diffusivities and volatiles with very high or very low partition coefficients will be more influenced by this process. Diffusive fractionation may be responsible for the drop in the CO2/SO2 ratios sometimes observed prior to large eruptions of Stromboli volcano.

Modeling of Mixing Behavior in a Combined Blowing Steelmaking Converter with a Filter-Based Euler-Lagrange Model

NASA Astrophysics Data System (ADS)

Li, Mingming; Li, Lin; Li, Qiang; Zou, Zongshu

2018-05-01

A filter-based Euler-Lagrange multiphase flow model is used to study the mixing behavior in a combined blowing steelmaking converter. The Euler-based volume of fluid approach is employed to simulate the top blowing, while the Lagrange-based discrete phase model that embeds the local volume change of rising bubbles for the bottom blowing. A filter-based turbulence method based on the local meshing resolution is proposed aiming to improve the modeling of turbulent eddy viscosities. The model validity is verified through comparison with physical experiments in terms of mixing curves and mixing times. The effects of the bottom gas flow rate on bath flow and mixing behavior are investigated and the inherent reasons for the mixing result are clarified in terms of the characteristics of bottom-blowing plumes, the interaction between plumes and top-blowing jets, and the change of bath flow structure.

Approaching behavior of a pair of spherical bubbles in quiescent liquids

NASA Astrophysics Data System (ADS)

Sanada, Toshiyuki; Kusuno, Hiroaki

2015-11-01

Some unique motions related bubble-bubble interaction, such as equilibrium distance, wake induced lift force, have been proposed by theoretical analysis or numerical simulations. These motions are different from the solid spheres like DKT model (Drafting, Kissing and Tumbling). However, there is a lack of the experimental verification. In this study, we experimentally investigated the motion of a pair of bubbles initially positioned in-line configuration in ultrapure water or an aqueous surfactant solution. The bubble motion were observed by two high speed video cameras. The bubbles Reynolds number was ranged from 50 to 300 and bubbles hold the spherical shape in this range. In ultrapure water, initially the trailing bubble deviated from the vertical line on the leading bubble owing to the wake of the leading bubble. And then, the slight difference of the bubble radius changed the relative motion. When the trailing bubble slightly larger than the leading bubble, the trailing bubble approached to the leading bubble due to it's buoyancy difference. The bubbles attracted and collided only when the bubbles rising approximately side by side configuration. In addition, we will also discuss the motion of bubbles rising in an aqueous surfactant solution.

Bubble migration in a compacting crystal-liquid mush

NASA Astrophysics Data System (ADS)

Boudreau, Alan

2016-04-01

Recent theoretical models have suggested that bubbles are unlikely to undergo significant migration in a compaction crystal mush by capillary invasion while the system remains partly molten. To test this, experiments of bubble migration during compaction in a crystal-liquid mush were modeled using deformable foam crystals in corn syrup in a volumetric burette, compacted with rods of varying weights. A bubble source was provided by sodium bicarbonate (Alka-Seltzer®). Large bubbles (>several crystal sizes) are pinched by the compacting matrix and become overpressured and deformed as the bubbles experience a load change from hydrostatic to lithostatic. Once they begin to move, they move much faster than the compaction-driven liquid. Bubbles that are about the same size as the crystals but larger than the narrower pore throats move by deformation or breaking into smaller bubbles as they are forced through pore restrictions. Bubbles that are less than the typical pore diameter generally move with the liquid: The liquid + bubble mixture behaves as a single phase with a lower density than the bubble-free liquid, and as a consequence it rises faster than bubble-free liquid and allows for faster compaction. The overpressure required to force a bubble through the matrix (max grain size = 5 mm) is modest, about 5 %, and it is estimated that for a grain size of 1 mm, the required overpressure would be about 25 %. Using apatite distribution in a Stillwater olivine gabbro as an analog for bubble nucleation and growth, it is suggested that relatively large bubbles initially nucleate and grow in liquid-rich channels that develop late in the compaction history. Overpressure from compaction allows bubbles to rise higher into hotter parts of the crystal pile, where they redissolve and increase the volatile content of the liquid over what it would have without the bubble migration, leading to progressively earlier vapor saturation during crystallization of the interstitial liquid. Bubbles can also move rapidly by `surfing' on porosity waves that can develop in a compacting mush.

Abundances of Deuterium, Oxygen and Nitrogen in the Local Interstellar Medium: Overview of First Results from the Far Ultraviolet Spectroscopic Explorer Mission

NASA Technical Reports Server (NTRS)

Moos, H. W.; Sembach, K. R.; Vidal-Madjar, A.; York, D. G.; Friedman, S. D.; Hebrard, G.; Kruk, J. W.; Lehner, N.; Lemoine, M.; Sonneborn, G.;

The rate of bubble growth in a superheated liquid in pool boiling

NASA Astrophysics Data System (ADS)

Abdollahi, Mohammad Reza; Jafarian, Mehdi; Jamialahmadi, Mohammad

2017-12-01

A semi-empirical model for the estimation of the rate of bubble growth in nucleate pool boiling is presented, considering a new equation to estimate the temperature history of the bubble in the bulk of liquid. The conservation equations of energy, mass and momentum have been firstly derived and solved analytically. The present analytical model of the bubble growth predicts that the radius of the bubble grows as a function of √{t}.{\\operatorname{erf}}( N√{t}) , while so far the bubble growth rate has been mainly correlated to √{t} in the previous studies. In the next step, the analytical solutions were used to develop a new semi-empirical equation. To achieve this, firstly the analytical solution were non-dimensionalised and then the experimental data, available in the literature, were applied to tune the dimensionless coefficients appeared in the dimensionless equation. Finally, the reliability of the proposed semi-empirical model was assessed through comparison of the model predictions with the available experimental data in the literature, which were not applied in the tuning of the dimensionless parameters of the model. The comparison of the model predictions with other proposed models in the literature was also performed. These comparisons show that this model enables more accurate predictions than previously proposed models with a deviation of less than 10% in a wide range of operating conditions.

Modeling of Vapor Bubble Growth Under Nucleate Boiling Conditions in Reduced Gravity

NASA Technical Reports Server (NTRS)

Buyevich, Yu A.; Webbon, Bruce W.

1995-01-01

A dynamic model is developed to describe the evolution of a vapor bubble growing at a nucleation site on a superheated surface under arbitrary gravity. The bubble is separated from the surface by a thin microlayer and grows due to the evaporation from the microlayer interface. The average thickness of the microlayer increases as the bubble expands along the surface if the evaporation rate is lower than some critical value. The corresponding threshold value of the surface temperature has to be associated with the burn-out crisis. Two main reasons make for bubble separation, which are the buoyancy force and a force caused by the vapor momentum that comes to the bubble with vapor molecules. The latter force is somewhat diminished if condensation takes place at the upper bubble surface in subcooled liquids. The action of the said forces is opposed by inertia of the additional mass of liquid as the bubble center rises above the surface and by inertia of liquid being expelled by the growing bubble in radial directions. An extra pressure force arises due to the liquid inflow into the microlayer with a finite velocity. The last force helps in holding the bubble close to the surface during an initial stage of bubble evolution. Two limiting regimes with distinctly different properties can be singled out, depending on which of the forces that favor bubble detachment dominates. Under conditions of moderately reduced gravity, the situation is much the same as in normal gravity, although the bubble detachment volume increases as gravity diminishes. In microgravity, the buoyancy force is negligible. Then the bubble is capable of staying near the surface for a long time, with intensive evaporation from the microlayer. It suggests a drastic change in the physical mechanism of heat removal as gravity falls below a certain sufficiently low level. Inferences of the model and conclusions pertaining to effects caused on heat transfer processes by changes in bubble hydrodynamics induced by gravity are discussed in connection with experimental evidence, both available in current and in as yet unpublished literature.

Bubble Generation in a Continuous Liquid Flow Under Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Pais, Salvatore Cezar

1999-01-01

The present work reports a study of bubble generation under reduced gravity conditions for both co-flow and cross-flow configurations. Experiments were performed aboard the DC-9 Reduced Gravity Aircraft at NASA Glenn Research Center, using an air-water system. Three different flow tube diameters were used: 1.27, 1.9, and 2.54 cm. Two different ratios of air injection nozzle to tube diameters were considered: 0.1 and 0.2. Gas and liquid volumetric flow rates were varied from 10 to 200 ml/s. It was experimentally observed that with increasing superficial liquid velocity, the bubbles generated decreased in size. The bubble diameter was shown to increase with increasing air injection nozzle diameters. As the tube diameter was increased, the size of the detached bubbles increased. Likewise, as the superficial liquid velocity was increased, the frequency of bubble formation increased and thus the time to detach forming bubbles decreased. Independent of the flow configuration (for either single nozzle or multiple nozzle gas injection), void fraction and hence flow regime transition can be controlled in a somewhat precise manner by solely varying the gas and liquid volumetric flow rates. On the other hand, it is observed that uniformity of bubble size can be controlled more accurately by using single nozzle gas injection than by using multiple port injection, since this latter system gives rise to unpredictable coalescence of adjacent bubbles. A theoretical model, based on an overall force balance, is employed to study single bubble generation in the dynamic and bubbly flow regime. Under conditions of reduced gravity, the gas momentum flux enhances bubble detachment; however, the surface tension forces at the nozzle tip inhibits bubble detachment. Liquid drag and inertia can act either as attaching or detaching force, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with performed experiments. However, at higher superficial,liquid velocities, the bubble neck length begins to significantly deviate from the value of the air injection nozzle diameter and thus the theory no longer predicts the experiment behavior. Effects of fluid properties, injection geometry and flow conditions on generated bubble size are investigated using the theoretical model. It is shown that bubble diameter is larger in a reduced gravity environment than in a normal gravity environment at similar flow condition and flow geometry.

Bubble Formation Modeling in IE-911

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fondeur, F.F.

2000-09-27

The author used diffusion modeling to determine the hydrogen and oxygen concentration inside IE-911. The study revealed gas bubble nucleation will not occur in the bulk solution inside the pore or on the pore wall. This finding results from the fast oxygen and hydrogen gas molecular diffusion and a very confined pore space. The net steady state concentration of these species inside the pore proves too low to drive bubble nucleation. This study did not investigate other gas bubble nucleating mechanism such as suspended particles in solution.

Mathematical Models of Diffusion-Limited Gas Bubble Evolution in Perfused Tissue

DTIC Science & Technology

2013-08-01

the Generation of New Bubbles,” Undersea Biomedical Research, Vol. 18, No. 4 (1991), pp. 333-345. 10. H. D. Van Liew and M. E. Burkard, “Density of...and R. D. Vann, “Probabilistic Gas and Bubble Dynamics Models of Decompression Sickness Occurrence in Air and Nitrogen-Oxygen Diving,” Undersea and...Gas Bubbles During Decompression,” Undersea and Hyperbaric Medicine, Vol. 23, No. 3 (1996), pp. 131-140. 13. R. L. Riley and A. Cournand, “’Ideal

Theoretical model of ice nucleation induced by acoustic cavitation. Part 1: Pressure and temperature profiles around a single bubble.

PubMed

Cogné, C; Labouret, S; Peczalski, R; Louisnard, O; Baillon, F; Espitalier, F

2016-03-01

This paper deals with the inertial cavitation of a single gas bubble in a liquid submitted to an ultrasonic wave. The aim was to calculate accurately the pressure and temperature at the bubble wall and in the liquid adjacent to the wall just before and just after the collapse. Two different approaches were proposed for modeling the heat transfer between the ambient liquid and the gas: the simplified approach (A) with liquid acting as perfect heat sink, the rigorous approach (B) with liquid acting as a normal heat conducting medium. The time profiles of the bubble radius, gas temperature, interface temperature and pressure corresponding to the above models were compared and important differences were observed excepted for the bubble size. The exact pressure and temperature distributions in the liquid corresponding to the second model (B) were also presented. These profiles are necessary for the prediction of any physical phenomena occurring around the cavitation bubble, with possible applications to sono-crystallization. Copyright © 2015 Elsevier B.V. All rights reserved.

Numerical Modeling of Nanocellular Foams Using Classical Nucleation Theory and Influence Volume Approach

NASA Astrophysics Data System (ADS)

Khan, Irfan; Costeux, Stephane; Bunker, Shana; Moore, Jonathan; Kar, Kishore

2012-11-01

Nanocellular porous materials present unusual optical, dielectric, thermal and mechanical properties and are thus envisioned to find use in a variety of applications. Thermoplastic polymeric foams show considerable promise in achieving these properties. However, there are still considerable challenges in achieving nanocellular foams with densities as low as conventional foams. Lack of in-depth understanding of the effect of process parameters and physical properties on the foaming process is a major obstacle. A numerical model has been developed to simulate the simultaneous nucleation and bubble growth during depressurization of thermoplastic polymers saturated with supercritical blowing agents. The model is based on the popular ``Influence Volume Approach,'' which assumes a growing boundary layer with depleted blowing agent surrounds each bubble. Classical nucleation theory is used to predict the rate of nucleation of bubbles. By solving the mass balance, momentum balance and species conservation equations for each bubble, the model is capable of predicting average bubble size, bubble size distribution and bulk porosity. The model is modified to include mechanisms for Joule-Thompson cooling during depressurization and secondary foaming. Simulation results for polymer with and without nucleating agents will be discussed and compared with experimental data.

Corner-transport-upwind lattice Boltzmann model for bubble cavitation

NASA Astrophysics Data System (ADS)

Sofonea, V.; Biciuşcǎ, T.; Busuioc, S.; Ambruş, Victor E.; Gonnella, G.; Lamura, A.

2018-02-01

Aiming to study the bubble cavitation problem in quiescent and sheared liquids, a third-order isothermal lattice Boltzmann model that describes a two-dimensional (2D) fluid obeying the van der Waals equation of state, is introduced. The evolution equations for the distribution functions in this off-lattice model with 16 velocities are solved using the corner-transport-upwind (CTU) numerical scheme on large square lattices (up to 6144 ×6144 nodes). The numerical viscosity and the regularization of the model are discussed for first- and second-order CTU schemes finding that the latter choice allows to obtain a very accurate phase diagram of a nonideal fluid. In a quiescent liquid, the present model allows us to recover the solution of the 2D Rayleigh-Plesset equation for a growing vapor bubble. In a sheared liquid, we investigated the evolution of the total bubble area, the bubble deformation, and the bubble tilt angle, for various values of the shear rate. A linear relation between the dimensionless deformation coefficient D and the capillary number Ca is found at small Ca but with a different factor than in equilibrium liquids. A nonlinear regime is observed for Ca≳0.2 .

Volume I: fluidized-bed code documentation, for the period February 28, 1983-March 18, 1983

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piperopoulou, H.; Finson, M.; Bloomfield, D.

1983-03-01

This documentation supersedes the previous documentation of the Fluidized-Bed Gasifier code. Volume I documents a simulation program of a Fluidized-Bed Gasifier (FBG), and Volume II documents a systems model of the FBG. The FBG simulation program is an updated version of the PSI/FLUBED code which is capable of modeling slugging beds and variable bed diameter. In its present form the code is set up to model a Westinghouse commercial scale gasifier. The fluidized bed gasifier model combines the classical bubbling bed description for the transport and mixing processes with PSI-generated models for coal chemistry. At the distributor plate, the bubblemore » composition is that of the inlet gas and the initial bubble size is set by the details of the distributor plate. Bubbles grow by coalescence as they rise. The bubble composition and temperature change with height due to transport to and from the cloud as well as homogeneous reactions within the bubble. The cloud composition also varies with height due to cloud/bubble exchange, cloud/emulsion, exchange, and heterogeneous coal char reactions. The emulsion phase is considered to be well mixed.« less

Analysis of airfoil leading edge separation bubbles

NASA Technical Reports Server (NTRS)

Carter, J. E.; Vatsa, V. N.

1982-01-01

A local inviscid-viscous interaction technique was developed for the analysis of low speed airfoil leading edge transitional separation bubbles. In this analysis an inverse boundary layer finite difference analysis is solved iteratively with a Cauchy integral representation of the inviscid flow which is assumed to be a linear perturbation to a known global viscous airfoil analysis. Favorable comparisons with data indicate the overall validity of the present localized interaction approach. In addition numerical tests were performed to test the sensitivity of the computed results to the mesh size, limits on the Cauchy integral, and the location of the transition region.

Multifocal laser surgery: cutting enhancement by hydrodynamic interactions between cavitation bubbles.

PubMed

Toytman, I; Silbergleit, A; Simanovski, D; Palanker, D

2010-10-01

Transparent biological tissues can be precisely dissected with ultrafast lasers using optical breakdown in the tight focal zone. Typically, tissues are cut by sequential application of pulses, each of which produces a single cavitation bubble. We investigate the hydrodynamic interactions between simultaneous cavitation bubbles originating from multiple laser foci. Simultaneous expansion and collapse of cavitation bubbles can enhance the cutting efficiency, by increasing the resulting deformations in tissue, and the associated rupture zone. An analytical model of the flow induced by the bubbles is presented and experimentally verified. The threshold strain of the material rupture is measured in a model tissue. Using the computational model and the experimental value of the threshold strain one can compute the shape of the rupture zone in tissue resulting from application of multiple bubbles. With the threshold strain of 0.7 two simultaneous bubbles produce a continuous cut when applied at the distance 1.35 times greater than that required in sequential approach. Simultaneous focusing of the laser in multiple spots along the line of intended cut can extend this ratio to 1.7. Counterpropagating jets forming during collapse of two bubbles in materials with low viscosity can further extend the cutting zone-up to approximately a factor of 1.5.

Investigation of Mechanisms Associated with Nucleate Boiling Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Dhir, Vijay K.

1996-01-01

The focus of the present work is to experimentally study and to analytically/numerically model the mechanisms of growth of bubbles attached to, and sliding along, a heated surface. To control the location of the active cavities, the number, the spacing, and the nucleation superheat, artificial cavities will be formed on silicon wafers. In order to study the effect of magnitude of components of gravitational acceleration acting parallel to, and normal to the surface, experiments will be conducted on surfaces inclined at different angles including a downward facing surface. Information on the temperature field around bubbles, bubble shape and size, and bubble induced liquid velocities will be obtained through the use of holography, video/high speed photography and hydrogen bubble techniques, respectively. Analytical/numerical models will be developed to describe the heat transfer including that through the micro-macro layer underneath and around a bubble. In the micro layer model capillary and disjoining pressures will be included. Evolution of the interface along with induced liquid motion will be modelled. Subsequent to the world at normal gravity, experiments will be conducted in the KC-135 or the Lear jet especially to learn about bubble growth/detachment under low gravity conditions. Finally, an experiment will be defined to be conducted under long duration of microgravity conditions in the space shuttle. The experiment in the space shuttle will provide microgravity data on bubble growth and detachment and will lead to a validation of the nucleate boiling heat transfer model developed from the preceding studies performed at normal and low gravity (KC-135 or Lear jet) conditions.

Effect of the Inhomogeneity of Ice Crystals on Retrieving Ice Cloud Optical Thickness and Effective Particle Size

NASA Technical Reports Server (NTRS)

Xie, Yu; Minnis, Patrick; Hu, Yong X.; Kattawar, George W.; Yang, Ping

2008-01-01

Spherical or spheroidal air bubbles are generally trapped in the formation of rapidly growing ice crystals. In this study the single-scattering properties of inhomogeneous ice crystals containing air bubbles are investigated. Specifically, a computational model based on an improved geometric-optics method (IGOM) has been developed to simulate the scattering of light by randomly oriented hexagonal ice crystals containing spherical or spheroidal air bubbles. A combination of the ray-tracing technique and the Monte Carlo method is used. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22deg and 46deg halo peaks, and substantially reduce the backscatter relative to bubble-free particles. These features vary with the number, sizes, locations and shapes of the air bubbles within ice crystals. Moreover, the asymmetry factors of inhomogeneous ice crystals decrease as the volume of air bubbles increases. Cloud reflectance lookup tables were generated at wavelengths 0.65 m and 2.13 m with different air-bubble conditions to examine the impact of the bubbles on retrieving ice cloud optical thickness and effective particle size. The reflectances simulated for inhomogeneous ice crystals are slightly larger than those computed for homogenous ice crystals at a wavelength of 0.65 microns. Thus, the retrieved cloud optical thicknesses are reduced by employing inhomogeneous ice cloud models. At a wavelength of 2.13 microns, including air bubbles in ice cloud models may also increase the reflectance. This effect implies that the retrieved effective particle sizes for inhomogeneous ice crystals are larger than those retrieved for homogeneous ice crystals, particularly, in the case of large air bubbles.

Separated two-phase flow and basaltic eruptions

NASA Astrophysics Data System (ADS)

Vergniolle, Sylvie; Jaupart, Claude

1986-11-01

Fluid dynamical models of volcanic eruptions are usually made in the homogeneous approximation where gas and liquid are constrained to move at the same velocity. Basaltic eruptions exhibit the characteristics of separated flows, including transitions in their flow regime, from bubbly to slug flow in Strombolian eruptions and from bubbly to annular flow in Hawaiian ones. These regimes can be characterized by a parameter called the melt superficial velocity, or volume flux per unit cross section, which takes values between 10-3 and 10-2 m/s for bubbly and slug flow, and about 1 m/s for annular flow. We use two-phase flow equations to determine under which conditions the homogeneous approximation is not valid. In the bubbly regime, in which many bubbles rise through the moving liquid, there are large differences between the two-phase and homogeneous models, especially in the predictions of gas content and pressure. The homogeneous model is valid for viscous lavas such as dacites because viscosity impedes bubble motion. It is not valid for basaltic lavas if bubble sizes are greater than 1 cm, which is the case. Accordingly, basaltic eruptions should be characterized by lower gas contents and lower values of the exit pressure, and they rarely erupt in the mist and froth regimes, which are a feature of more viscous lavas. The two-phase flow framework allows for the treatment of different bubble populations, including vesicles due to exsolution by pressure release in the volcanic conduit and bubbles from the magma chamber. This yields information on poorly constrained parameters including the effective friction coefficient for the conduit, gas content, and bubble size in the chamber. We suggest that the observed flow transitions record changes in the amount and size of gas bubbles in the magma chamber at the conduit entry.

Simulation of the ultrasound-induced growth and collapse of a near-wall bubble

NASA Astrophysics Data System (ADS)

Boyd, Bradley; Becker, Sid

2017-11-01

In this study, we consider the acoustically driven growth and collapse of a cavitation bubble in a fluid medium exposed to an ultrasound field. The bubble dynamics are modelled using a compressible, inviscid, multiphase model. The numerical scheme consists of a conservative interface capturing scheme which uses the fifth-order WENO reconstruction with a maximum-principle-satisfying and positivity-preserving limiter, and the HLLC approximate Riemann flux. To model the ultrasound input, a moving boundary oscillates through a fixed grid of finite-volume cells. The growth phase of the simulation shows the rapid non-spherical growth of the near-wall bubble. Once the bubble reaches its maximum size and the collapse phase begins, the simulation shows the formation of a jet which penetrates the bubble towards the wall at the later stages of the collapse. For a bubble with an initial radius of 50 μ m and an ultrasound pressure amplitude of 200 kPa, the pressure experienced by the wall increased rapidly nearing the end of the collapse, reaching a peak pressure of 13 MPa. This model is an important development in the field as it represents the physics of acoustic cavitation in more detail than before. This work was supported by the Royal Society of New Zealand's Marsden Fund.

Predicting the fate of methane emanating from the seafloor using a marine two-phase gas model in one dimension (M2PG1) - Example from a known Arctic methane seep site offshore Svalbard

NASA Astrophysics Data System (ADS)

Jansson, Pär; Ferré, Benedicte

2017-04-01

Transport of methane in seawater occurs by diffusion and advection in the dissolved phase, and/or as free gas in form of bubbles. The fate of methane in bubbles emitted from the seafloor depends on both bubble size and ambient conditions. Larger bubbles can transport methane higher into the water column, potentially reaching the atmosphere and contributing to greenhouse gas concentrations and impacts. Single bubble or plume models have been used to predict the fate of bubble mediated methane gas emissions. Here, we present a new process based two-phase (free and dissolved) gas model in one dimension, which has the capability to dynamically couple water column properties such as temperature, salinity and dissolved gases with the free gas species contained in bubbles. The marine two-phase gas model in one dimension (M2PG1) uses a spectrum of bubbles and an Eulerian formulation, discretized on a finite-volume grid. It employs the most up-to-date equations for solubility and compressibility of the included gases, nitrogen, oxygen, carbon dioxide and methane. M2PG1 is an extension of PROBE (Omstedt, 2011), which facilitates atmospheric coupling and turbulence closures to realistically predict vertical mixing of all properties, including dissolved methane. This work presents the model's first application in an Arctic Ocean environment at the landward limit of the methane-hydrate stability zone west of Svalbard, where we observe substantial methane bubble release over longer time periods. The research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) and is supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259 and UiT. Omstedt, A. (2011). Guide to process based modeling of lakes and coastal seas: Springer.

Deformation behaviors of peat with influence of organic matter.

PubMed

Yang, Min; Liu, Kan

2016-01-01

Peat is a kind of special material rich in organic matter. Because of the high content of organic matter, it shows different deformation behaviors from conventional geotechnical materials. Peat grain has a non-negligible compressibility due to the presence of organic matter. Biogas can generate from peat and can be trapped in form of gas bubbles. Considering the natural properties of peat, a special three-phase composition of peat is described which indicates the existence of organic matter and gas bubbles in peat. A stress-strain-time model is proposed for the compression of organic matter, and the surface tension effect is considered in the compression model of gas bubbles. Finally, a mathematical model has been developed to simulate the deformation behavior of peat considering the compressibility of organic matter and entrapped gas bubbles. The deformation process is the coupling of volume variation of organic matter, gas bubbles and water drainage. The proposed model is used to simulate a series of peat laboratory oedometer tests, and the model can well capture the test results with reasonable model parameters. Effects of model parameters on deformation of peat are also analyzed.

CFD-PBM coupled simulation of a nanobubble generator with honeycomb structure

NASA Astrophysics Data System (ADS)

Ren, F.; Noda, N. A.; Ueda, T.; Sano, Y.; Takase, Y.; Umekage, T.; Yonezawa, Y.; Tanaka, H.

2018-06-01

In recent years, nanobubble technologies have drawn great attention due to their wide applications in many fields of science and technology. The nitrogen nanobubble water circulation can be used to slow the progressions of oxidation and spoilage for the seafood long- term storage. From previous studies, a kind of honeycomb structure for high-efficiency nanobubble generation has been proposed. In this paper, the bubbly flow in the honeycomb structure was studied. The numerical simulations of honeycomb structure were performed by using a computational fluid dynamics–population balance model (CFD-PBM) coupled model. The numerical model was based on the Eulerian multiphase model and the population balance model (PBM) was used to calculate the gas bubble size distribution. The bubble coalescence and breakage were included. Considering the effect of bubble diameter on the fluid flow, the phase interactions were coupled with the PBM. The bubble size distributions in the honeycomb structure under different work conditions were predicted. The experimental results were compared with the simulation predictions.

Implementation of two-phase tritium models for helium bubbles in HCLL breeding blanket modules

NASA Astrophysics Data System (ADS)

Fradera, J.; Sedano, L.; Mas de les Valls, E.; Batet, L.

2011-10-01

Tritium self-sufficiency requirement of future DT fusion reactors involves large helium production rates in the breeding blankets; this might impact on the conceptual design of diverse fusion power reactor units, such as Liquid Metal (LM) blankets. Low solubility, long residence-times and high production rates create the conditions for Helium nucleation, which could mean effective T sinks in LM channels. A model for helium nano-bubble formation and tritium conjugate transport phenomena in liquid Pb17.5Li and EUROFER is proposed. In a first approximation, it has been considered that He bubbles can be represented as a passive scalar. The nucleation model is based on the classical theory and includes a simplified bubble growth model. The model captures the interaction of tritium with bubbles and tritium diffusion through walls. Results show the influence of helium cavitation on tritium inventory and the importance of simulating the system walls instead of imposing fixed boundary conditions.

Numerical and experimental study of dissociation in an air-water single-bubble sonoluminescence system.

PubMed

Puente, Gabriela F; Urteaga, Raúl; Bonetto, Fabián J

2005-10-01

We performed a comprehensive numerical and experimental analysis of dissociation effects in an air bubble in water acoustically levitated in a spherical resonator. Our numerical approach is based on suitable models for the different effects considered. We compared model predictions with experimental results obtained in our laboratory in the whole phase parameter space, for acoustic pressures from the bubble dissolution limit up to bubble extinction. The effects were taken into account simultaneously to consider the transition from nonsonoluminescence to sonoluminescence bubbles. The model includes (1) inside the bubble, transient and spatially nonuniform heat transfer using a collocation points method, dissociation of O2 and N2, and mass diffusion of vapor in the noncondensable gases; (2) at the bubble interface, nonequilibrium evaporation and condensation of water and a temperature jump due to the accommodation coefficient; (3) in the liquid, transient and spatially nonuniform heat transfer using a collocation points method, and mass diffusion of the gas in the liquid. The model is completed with a Rayleigh-Plesset equation with liquid compressible terms and vapor mass transfer. We computed the boundary for the shape instability based on the temporal evolution of the computed radius. The model is valid for an arbitrary number of dissociable gases dissolved in the liquid. We also obtained absolute measurements for R(t) using two photodetectors and Mie scattering calculations. The robust technique used allows the estimation of experimental results of absolute R0 and P(a). The technique is based on identifying the bubble dissolution limit coincident with the parametric instability in (P(a),R0) parameter space. We take advantage of the fact that this point can be determined experimentally with high precision and replicability. We computed the equilibrium concentration of the different gaseous species and water vapor during collapse as a function of P(a) and R0. The model obtains from first principles the result that in sonoluminescence the bubble is practically 100% argon for air dissolved in water. Therefore, the dissociation reactions in air bubbles must be taken into account for quantitative computations of maximum temperatures. The agreement found between the numerical and experimental data is very good in the whole parameter space explored. We do not fit any parameter in the model. We believe that we capture all the relevant physics with the model.

Influence of bubble size and thermal dissipation on compressive wave attenuation in liquid foams

NASA Astrophysics Data System (ADS)

Monloubou, M.; Saint-Jalmes, A.; Dollet, B.; Cantat, I.

2015-11-01

Acoustic or blast wave absorption by liquid foams is especially efficient and bubble size or liquid fraction optimization is an important challenge in this context. A resonant behavior of foams has recently been observed, but the main local dissipative process is still unknown. In this paper, we evidence the thermal origin of the dissipation, with an optimal bubble size close to the thermal boundary layer thickness. Using a shock tube, we produce typical pressure variation at time scales of the order of the millisecond, which propagates in the foam in linear and slightly nonlinear regimes.

A large bubble around the Crab Nebula

NASA Technical Reports Server (NTRS)

Romani, Roger W.; Reach, William T.; Koo, Bon Chul; Heiles, Carl

1990-01-01

IRAS and 21 cm observations of the interstellar medium around the Crab nebula show evidence of a large bubble surrounded by a partial shell. If located at the canonical 2 kpc distance of the Crab pulsar, the shell is estimated to have a radius of about 90 pc and to contain about 50,000 solar masses of swept-up gas. The way in which interior conditions of this bubble can have important implications for observations of the Crab are described, and the fashion in which presupernova evolution of the pulsar progenitor has affected its local environment is described.

Acoustic bubble dynamics in a microvessel surrounded by elastic material

NASA Astrophysics Data System (ADS)

Wang, S. P.; Wang, Q. X.; Leppinen, D. M.; Zhang, A. M.; Liu, Y. L.

2018-01-01

This paper is concerned with microbubble dynamics in a blood vessel surrounded by elastic tissue subject to ultrasound, which are associated with important applications in medical ultrasonics. Both the blood flow inside the vessel and the tissue flow external to the vessel are modeled using the potential flow theory coupled with the boundary element method. The elasticity of tissue is modeled through the inclusion of a pressure term in the dynamic boundary condition at the interface between the two fluids. Weakly viscous effects are considered using viscous potential flow theory. The numerical model is validated by comparison with the theoretical results of the Rayleigh-Plesset equation for spherical bubbles, the numerical results for acoustic bubbles in an unbounded flow, and the experimental images for a spark generated bubble in a rigid circular cylinder. Numerical analyses are then performed for the bubble oscillation, jet formation and penetration through the bubble, and the deformation of the vessel wall in terms of the ultrasound amplitude and the vessel radius.

How many bubbles in your glass of bubbly?

PubMed

Liger-Belair, Gérard

2014-03-20

The issue about how many carbon dioxide bubbles are likely to nucleate in a glass of champagne (or bubbly) is of concern for sommeliers, wine journalists, experienced tasters, and any open minded physical chemist wondering about complex phenomena at play in a glass of bubbly. The whole number of bubbles likely to form in a single glass is the result of the fine interplay between dissolved CO2, tiny gas pockets trapped within particles acting as bubble nucleation sites, and ascending bubble dynamics. Based on theoretical models combining ascending bubble dynamics and mass transfer equations, the falsely naı̈ve question of how many bubbles are likely to form per glass is discussed in the present work. A theoretical relationship is derived, which provides the whole number of bubbles likely to form per glass, depending on various parameters of both the wine and the glass itself.

Modeling the failure of magmatic foams with application to Stromboli volcano, Italy

NASA Astrophysics Data System (ADS)

O'Shaughnessy, Cedrick; Brun, Francesco; Mancini, Lucia; Fife, Julie L.; Baker, Don R.

2014-10-01

The failure of magmatic foams has been implicated as a fundamental process in eruptions occurring at open-conduit, basaltic volcanoes. In order to investigate the failure of magmatic foams we applied the fiber bundle model using global load sharing. The strengths of the fibers for the model were taken from bubble wall widths measured in four computer-simulated foams of low-porosity and from one very low-porosity and two high-porosity foams produced in the laboratory by heating hydrated basaltic glasses to 1200 °C. The relative strength of an individual fiber in the model was calculated from the square of a bubble wall's average width and absolute strengths of the foams were calculated based upon the correlation of the strength of one modeled foam with experimental data. The fiber bundle model is shown to successfully reproduce measured tensile strengths of porous volcanic rocks studied by other researchers and confirms previous findings of the primary importance of foam porosity, as well as the secondary importance of structural details that affect the number and size of bubble walls and permeability. Because of the success of the fiber bundle model in reproducing experimental foam failure, its results are compared to infrasonic measurements associated with bubbles at Stromboli (Italy) and demonstrate that within uncertainty the power-law exponents of the infrasonic energies and of the fiber bundle model energies are in agreement; both show a crossover from an exponent of 5/2 associated with the bursting of small bubbles in the infrasonic measurements to an exponent of 3/2 for normal Strombolian eruptions associated with infrasonic signals from meter-scale bubbles. The infrasonic signals for major explosions and a paroxysmal eruption at Stromboli fall near the extrapolation of the power law defined by the low-amplitude, bubble bursting events and are interpreted to reflect the bursting of multitudes of small bubbles, rather than a few large bubbles. The measurement of small-amplitude infrasonic events at Stromboli appears useful in predicting the recurrence interval of paroxysmal eruptions at this volcano and may also provide a tool that uses common, small-amplitude infrasonic events to constrain the frequency of larger eruptions at other volcanoes.

The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites.

PubMed

Jordt, Anne; Zelenka, Claudius; von Deimling, Jens Schneider; Koch, Reinhard; Köser, Kevin

2015-12-05

Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information.

The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites

PubMed Central

Jordt, Anne; Zelenka, Claudius; Schneider von Deimling, Jens; Koch, Reinhard; Köser, Kevin

2015-01-01

Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information. PMID:26690168

Suppression of shocked-bubble expansion due to tissue confinement with application to shock-wave lithotripsy

PubMed Central

Freund, Jonathan B.

2008-01-01

Estimates are made of the effect of tissue confinement on the response of small bubbles subjected to lithotriptor shock pressures. To do this the Rayleigh–Plesset equation, which governs the dynamics of spherical bubbles, is generalized to treat a bubble in a liquid region (blood), which is in turn encased within an elastic membrane (like a vessel’s basement membrane), beyond which a Voigt viscoelastic material models the exterior tissue. Material properties are estimated from a range of measurements available for kidneys and similar soft tissues. Special attention is given to the constitutive modeling of the basement membranes because of their expected importance due to their proximity to the bubble and their toughness. It is found that the highest expected values for the elasticity of the membrane and surrounding tissue are insufficient to suppress bubble growth. The reduced confinement of a cylindrical vessel should not alter this conclusion. Tissue viscosities taken from ultrasound measurements suppress bubble growth somewhat, though not to a degree expected to resist injury. However, the higher reported viscosities measured by other means, which are arguably more relevant to the deformations caused by growing bubbles, do indeed significantly suppress bubble expansion. PMID:18529202

Suppression of shocked-bubble expansion due to tissue confinement with application to shock-wave lithotripsy.

PubMed

Freund, Jonathan B

2008-05-01

Estimates are made of the effect of tissue confinement on the response of small bubbles subjected to lithotriptor shock pressures. To do this the Rayleigh-Plesset equation, which governs the dynamics of spherical bubbles, is generalized to treat a bubble in a liquid region (blood), which is in turn encased within an elastic membrane (like a vessel's basement membrane), beyond which a Voigt viscoelastic material models the exterior tissue. Material properties are estimated from a range of measurements available for kidneys and similar soft tissues. Special attention is given to the constitutive modeling of the basement membranes because of their expected importance due to their proximity to the bubble and their toughness. It is found that the highest expected values for the elasticity of the membrane and surrounding tissue are insufficient to suppress bubble growth. The reduced confinement of a cylindrical vessel should not alter this conclusion. Tissue viscosities taken from ultrasound measurements suppress bubble growth somewhat, though not to a degree expected to resist injury. However, the higher reported viscosities measured by other means, which are arguably more relevant to the deformations caused by growing bubbles, do indeed significantly suppress bubble expansion.

Microbubble transport through a bifurcating vessel network with pulsatile flow.

PubMed

Valassis, Doug T; Dodde, Robert E; Esphuniyani, Brijesh; Fowlkes, J Brian; Bull, Joseph L

2012-02-01

Motivated by two-phase microfluidics and by the clinical applications of air embolism and a developmental gas embolotherapy technique, experimental and theoretical models of microbubble transport in pulsatile flow are presented. The one-dimensional time-dependent theoretical model is developed from an unsteady Bernoulli equation that has been modified to include viscous and unsteady effects. Results of both experiments and theory show that roll angle (the angle the plane of the bifurcating network makes with the horizontal) is an important contributor to bubble splitting ratio at each bifurcation within the bifurcating network. When compared to corresponding constant flow, pulsatile flow was shown to produce insignificant changes to the overall splitting ratio of the bubble despite the order one Womersley numbers, suggesting that bubble splitting through the vasculature could be modeled adequately with a more modest constant flow model. However, bubble lodging was affected by the flow pulsatility, and the effects of pulsatile flow were evident in the dependence of splitting ratio of bubble length. The ability of bubbles to remain lodged after reaching a steady state in the bifurcations is promising for the effectiveness of gas embolotherapy to occlude blood flow to tumors, and indicates the importance of understanding where lodging will occur in air embolism. The ability to accurately predict the bubble dynamics in unsteady flow within a bifurcating network is demonstrated and suggests the potential for bubbles in microfluidics devices to encode information in both steady and unsteady aspects of their dynamics.

A high-fidelity approach towards simulation of pool boiling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yazdani, Miad; Radcliff, Thomas; Soteriou, Marios

2016-01-15

A novel numerical approach is developed to simulate the multiscale problem of pool-boiling phase change. The particular focus is to develop a simulation technique that is capable of predicting the heat transfer and hydrodynamic characteristics of nucleate boiling and the transition to critical heat flux on surfaces of arbitrary shape and roughness distribution addressing a critical need to design enhanced boiling heat transfer surfaces. The macro-scale of the phase change and bubble dynamics is addressed through employing off-the-shelf Computational Fluid Dynamics (CFD) methods for interface tracking and interphase mass and energy transfer. The micro-scale of the microlayer, which forms atmore » early stage of bubble nucleation near the wall, is resolved through asymptotic approximation of the thin-film theory which provides a closed-form solution for the distribution of the micro-layer and its influence on the evaporation process. In addition, the sub-grid surface roughness is represented stochastically through probabilistic density functions and its role in bubble nucleation and growth is then represented based on the thermodynamics of nucleation process. This combination of deterministic CFD, local approximation, and stochastic representation allows the simulation of pool boiling on any surface with known roughness and enhancement characteristics. The numerical model is validated for dynamics and hydrothermal characteristics of a single nucleated bubble on a flat surface against available literature data. In addition, the prediction of pool-boiling heat transfer coefficient is verified against experimental measurements as well as reputable correlations for various roughness distributions and different surface orientations. Finally, the model is employed to demonstrate pool-boiling phenomenon on enhanced structures with reentrance cavities and to explore the effect of enhancement feature design on thermal and hydrodynamic characteristics of these surfaces.« less

Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamaguchi, Fumiya; Ando, Keita, E-mail: kando@mech.keio.ac.jp

2015-11-15

Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows frommore » the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh–Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh–Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.« less

Gas Bubble Migration and Trapping in Porous Media: Pore-Scale Simulation

NASA Astrophysics Data System (ADS)

Mahabadi, Nariman; Zheng, Xianglei; Yun, Tae Sup; van Paassen, Leon; Jang, Jaewon

2018-02-01

Gas bubbles can be naturally generated or intentionally introduced in sediments. Gas bubble migration and trapping affect the rate of gas emission into the atmosphere or modify the sediment properties such as hydraulic and mechanical properties. In this study, the migration and trapping of gas bubbles are simulated using the pore-network model extracted from the 3D X-ray image of in situ sediment. Two types of bubble size distribution (mono-sized and distributed-sized cases) are used in the simulation. The spatial and statistical bubble size distribution, residual gas saturation, and hydraulic conductivity reduction due to the bubble trapping are investigated. The results show that the bubble size distribution becomes wider during the gas bubble migration due to bubble coalescence for both mono-sized and distributed-sized cases. And the trapped bubble fraction and the residual gas saturation increase as the bubble size increases. The hydraulic conductivity is reduced as a result of the gas bubble trapping. The reduction in hydraulic conductivity is apparently observed as bubble size and the number of nucleation points increase.

Nanoscale dynamics of Joule heating and bubble nucleation in a solid-state nanopore.

PubMed

Levine, Edlyn V; Burns, Michael M; Golovchenko, Jene A

2016-01-01

We present a mathematical model for Joule heating of an electrolytic solution in a nanopore. The model couples the electrical and thermal dynamics responsible for rapid and extreme superheating of the electrolyte within the nanopore. The model is implemented numerically with a finite element calculation, yielding a time and spatially resolved temperature distribution in the nanopore region. Temperatures near the thermodynamic limit of superheat are predicted to be attained just before the explosive nucleation of a vapor bubble is observed experimentally. Knowledge of this temperature distribution enables the evaluation of related phenomena including bubble nucleation kinetics, relaxation oscillation, and bubble dynamics.

Getting the gas out - developing gas networks in magmatic systems

NASA Astrophysics Data System (ADS)

Cashman, Katharine; Rust, Alison; Oppenheimer, Julie; Belien, Isolde

2015-04-01

Volcanic eruption style, and explosive potential, are strongly controlled by the pre-eruptive history of the magmatic volatiles: specifically, the more efficient the gas loss prior to eruption, the lower the likelihood of primary (magmatic) explosive activity. Commonly considered gas loss mechanisms include separated flow, where individual bubbles (or bubble clouds) travel at a rate that is faster than the host magma, and permeable flow, where gas escapes through permeable (connected) pathways developed within a (relatively) static matrix. Importantly, gas loss via separated flow is episodic, while gas loss via permeable flow is likely to be continuous. Analogue experiments and numerical models on three phase (solid-liquid-gas) systems also suggest a third mechanism of gas loss that involves the opening and closing of 'pseudo fractures'. Pseudo fractures form at a critical crystallinity that is close to the maximum particle packing. Fractures form by local rearrangement of solid particles and liquid to form a through-going gas fracture; gas escape is episodic, and modulated by the available gas volume and the rate of return flow of interstitial liquid back into the fracture. In all of the gas escape scenarios described above, a fundamental control on gas behaviour is the melt viscosity, which affects the rate of individual bubble rise, the rate of bubble expansion, the rate of film thinning (required for bubble coalescence), and the rate of melt flow into gas-generated fractures. From the perspective of magma degassing, rates of gas expansion and film thinning are key to the formation of an interconnected (permeable) gas pathway. Experiments with both analogue and natural materials show that bubble coalescence is relatively slow, and, in particle-poor melts, does not necessarily create permeable gas networks. As a result, degassing efficiency is modulated by the time scales required either (1) to produce large individual bubbles or bubble clouds (in low viscosity melts) or (2) to develop sufficient porosity for full connectivity of a bubble network (in high viscosity melts). In contrast, our experiments suggest that the presence of solid particles may greatly enhance gas escape. On the one hand, the addition of solid particles increases the bulk viscosity of the mixture, which reduces the migration rate of large single bubbles. On the other hand, the strength of networks created by touching crystals inhibits bulk magma deformation and forces smaller bubbles to deform to occupy the spaces between particles, thereby increasing both the bubble shape anisotropy and, correspondingly, the probability of bubble coalescence. Gas pathways created in this way take advantage of inhomogeneities in the spatial distribution of crystals and allow large-scale gas release at relatively low vesicularities. This mechanism of gas escape is likely to be important not only in mafic arc volcanoes, where shallow conduits are likely to be highly crystalline, but also for degassing of crystal-mush-dominated magmatic systems.

The footprint of CO2 leakage in the water-column: Insights from numerical modeling based on a North Sea gas release experiment

NASA Astrophysics Data System (ADS)

Vielstädte, L.; Linke, P.; Schmidt, M.; Sommer, S.; Wallmann, K.; McGinnis, D. F.; Haeckel, M.

2013-12-01

Assessing the environmental impact of potential CO2 leakage from offshore carbon dioxide storage sites necessitates the investigation of the corresponding pH change in the water-column. Numerical models have been developed to simulate the buoyant rise and dissolution of CO2 bubbles in the water-column and the subsequent near-field dispersion of dissolved CO2 in seawater under ocean current and tidal forcing. In order to test and improve numerical models a gas release experiment has been conducted at 80 m water-depth within the Sleipner area (North Sea). CO2 and Kr (used as inert tracer gas) were released on top of a benthic lander at varying gas flows (<140 kg/day) and bubble sizes (de: 1-6 mm). pCO2 and pH were measured by in situ sensors to monitor the spread of the solute in different vertical heights and distances downstream of the artificial leak. The experiment and numerical analysis show that the impact of such leakage rates is limited to the near-field bottom waters, due to the rapid dissolution of CO2 bubbles in seawater (CO2 is being stripped within the first two to five meters of bubble rise). In particular, small bubbles, which will dissolve close to the seafloor, may cause a dangerous low-pH environment for the marine benthos. However, on the larger scale, the advective transport by e.g. tidal currents, dominates the CO2 dispersal in the North Sea and dilutes the CO2 peak quickly. The model results show that at the small scales (<100 m) of the CO2 plume the lateral eddy diffusion (~0.01 m2/s) has only a negligible effect. Overall, we can postulate that CO2 leakage at a rate of ~ 100 kg per day as in our experiment will only have a localized impact on the marine environment, thereby reducing pH substantially (by 0.4 units) within a diameter of less than 50 m around the release spot (depending on the duration of leakage and the current velocities). Strong currents and tidal cycles significantly reduce the spreading of low-pH water masses into the far-field by efficiently diluting the amount of CO2 in ambient seawater.

Wall function treatment for bubbly boundary layers at low void fractions.

PubMed

Soares, Daniel V; Bitencourt, Marcelo C; Loureiro, Juliana B R; Silva Freire, Atila P

2018-01-01

The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction of bubbly flows. Two different wall function formulations are tested against experimental data obtained for bubbly boundary layers: (i) a new analytical solution derived through asymptotic techniques and (ii) the previous formulation of Troshko and Hassan (IJHMT, 44, 871-875, 2001a). A modified k-e model is used to close the averaged Navier-Stokes equations together with the hypothesis that turbulence can be modelled by a linear superposition of bubble and shear induced eddy viscosities. The work shows, in particular, how four corrections must the implemented in the standard single-phase k-e model to account for the effects of bubbles. The numerical implementation of the near wall functions is made through a finite elements code.

Sound synchronization of bubble trains in a viscous fluid: experiment and modeling.

PubMed

Pereira, Felipe Augusto Cardoso; Baptista, Murilo da Silva; Sartorelli, José Carlos

2014-10-01

We investigate the dynamics of formation of air bubbles expelled from a nozzle immersed in a viscous fluid under the influence of sound waves. We have obtained bifurcation diagrams by measuring the time between successive bubbles, having the air flow (Q) as a parameter control for many values of the sound wave amplitude (A), the height (H) of the solution above the top of the nozzle, and three values of the sound frequency (fs). Our parameter spaces (Q,A) revealed a scenario for the onset of synchronization dominated by Arnold tongues (frequency locking) which gives place to chaotic phase synchronization for sufficiently large A. The experimental results were accurately reproduced by numerical simulations of a model combining a simple bubble growth model for the bubble train and a coupling term with the sound wave added to the equilibrium pressure.

Foam flows through a local constriction

NASA Astrophysics Data System (ADS)

Chevalier, T.; Koivisto, J.; Shmakova, N.; Alava, M. J.; Puisto, A.; Raufaste, C.; Santucci, S.

2017-11-01

We present an experimental study of the flow of a liquid foam, composed of a monolayer of millimetric bubbles, forced to invade an inhomogeneous medium at a constant flow rate. To model the simplest heterogeneous fracture medium, we use a Hele-Shaw cell consisting of two glass plates separated by a millimetric gap, with a local constriction. This single defect localized in the middle of the cell reduces locally its gap thickness, and thus its local permeability. We investigate here the influence of the geometrical property of the defect, specifically its height, on the average steady-state flow of the foam. In the frame of the flowing foam, we can observe a clear recirculation around the obstacle, characterized by a quadrupolar velocity field with a negative wake downstream the obstacle, which intensity evolves systematically with the obstacle height.

Study on drag coefficient of rising bubble in still water

NASA Astrophysics Data System (ADS)

Shi, M. Y.; Qi, Mei; Yi, C. G.; Liu, D. Y.; Zhang, K. X.

2017-09-01

Research on the behavior of a rising bubble in still water is on the basis of Newton's theory of classical mechanics. Develop a calculation analysis and an experimental process of bubble rising behavior in order to search for an appropriate way of valuing drag coefficient, which is the key element toward this issue. Analyze the adaptability of the drag coefficient; compare the theoretical model to the real experimental model of rising bubble behavior. The result turns out that the change rate of radius could be ignored according to the analysis; the acceleration phase is transient; final velocity and the diameter of bubble do relate to the drag coefficient, but have no obvious relation with the depth of water. After series of inference analysis of the bubble behavior and experimental demonstration, a new drag coefficient and computing method is proposed.

Acoustic measurement of bubble size in an inkjet printhead.

PubMed

Jeurissen, Roger; van der Bos, Arjan; Reinten, Hans; van den Berg, Marc; Wijshoff, Herman; de Jong, Jos; Versluis, Michel; Lohse, Detlef

2009-11-01

The volume of a bubble in a piezoinkjet printhead is measured acoustically. The method is based on a numerical model of the investigated system. The piezo not only drives the system but it is also used as a sensor by measuring the current it generates. The numerical model is used to predict this current for a given bubble volume. The inverse problem is to infer the bubble volume from an experimentally obtained piezocurrent. By solving this inverse problem, the size and position of the bubble can thus be measured acoustically. The method is experimentally validated with an inkjet printhead that is augmented with a glass connection channel, through which the bubble was observed optically, while at the same time the piezocurrent was measured. The results from the acoustical measurement method correspond closely to the results from the optical measurement.

Volume Oscillations Delivered to a Lung Model Using 4 Different Bubble CPAP Systems.

PubMed

Poli, Jonathan A; Richardson, C Peter; DiBlasi, Robert M

2015-03-01

High-frequency pressure oscillations created by gas bubbling through an underwater seal during bubble CPAP may enhance ventilation and aid in lung recruitment in premature infants. We hypothesized that there are no differences in the magnitude of oscillations in lung volume (ΔV) in a preterm neonatal lung model when different bubble CPAP systems are used. An anatomically realistic replica of an infant nasal airway model was attached to a Silastic test lung sealed within a calibrated plethysmograph. Nasal prongs were affixed to the simulated neonate and supported using bubble CPAP systems set at 6 cm H2O. ΔV was calculated using pressure measurements obtained from the plethysmograph. The Fisher & Paykel Healthcare bubble CPAP system provided greater ΔV than any of the other devices at all of the respective bias flows (P < .05). The Fisher & Paykel Healthcare and Babi.Plus systems generally provided ΔV at lower frequencies than the other bubble CPAP systems. The magnitude of ΔV increased at bias flows of > 4 L/min in the Fisher & Paykel Healthcare, Airways Development, and homemade systems, but appeared to decrease as bias flow increased with the Babi.Plus system. The major finding of this study is that bubble CPAP can provide measureable ventilation effects in an infant lung model. We speculate that the differences noted in ΔV between the different devices are a combination of the circuit/nasal prong configuration, bubbler configuration, and frequency of oscillations. Additional testing is needed in spontaneously breathing infants to determine whether a physiologic benefit exists when using the different bubble CPAP systems. Copyright © 2015 by Daedalus Enterprises.

Use of ultrasound in altitude decompression modeling

NASA Technical Reports Server (NTRS)

Olson, Robert M.; Pilmanis, Andrew A.

1993-01-01

A model that predicts the probability of developing decompression sickness (DCS) with various denitrogenation schedules is being developed by the Armstrong Laboratory, using human data from previous exposures. It was noted that refinements are needed to improve the accuracy and scope of the model. A commercially developed ultrasonic echo imaging system is being used in this model development. Using this technique, bubbles images from a subject at altitude can be seen in the gall bladder, hepatic veins, vena cava, and chambers of the heart. As judged by their motion and appearance in the vena cava, venous bubbles near the heart range in size from 30 to 300 M. The larger bubbles skim along the top, whereas the smaller ones appear as faint images near the bottom of the vessel. Images from growing bubbles in a model altitude chamber indicate that they grow rapidly, going from 20 to 100 M in 3 sec near 30,000 ft altitude. Information such as this is valuable in verifying those aspects of the DCS model dealing with bubble size, their growth rate, and their site of origin.

Studies on the Tempo of Bubble Formation in Recently Cavitated Vessels: A Model to Predict the Pressure of Air Bubbles1

PubMed Central

Wang, Yujie; Pan, Ruihua; Tyree, Melvin T.

2015-01-01

A cavitation event in a vessel replaces water with a mixture of water vapor and air. A quantitative theory is presented to argue that the tempo of filling of vessels with air has two phases: a fast process that extracts air from stem tissue adjacent to the cavitated vessels (less than 10 s) and a slow phase that extracts air from the atmosphere outside the stem (more than 10 h). A model was designed to estimate how water tension (T) near recently cavitated vessels causes bubbles in embolized vessels to expand or contract as T increases or decreases, respectively. The model also predicts that the hydraulic conductivity of a stem will increase as bubbles collapse. The pressure of air bubbles trapped in vessels of a stem can be predicted from the model based on fitting curves of hydraulic conductivity versus T. The model was validated using data from six stem segments each of Acer mono and the clonal hybrid Populus 84K (Populus alba × Populus glandulosa). The model was fitted to results with root mean square error less than 3%. The model provided new insight into the study of embolism formation in stem tissue and helped quantify the bubble pressure immediately after the fast process referred to above. PMID:25907963

Studies on the tempo of bubble formation in recently cavitated vessels: a model to predict the pressure of air bubbles.

PubMed

Wang, Yujie; Pan, Ruihua; Tyree, Melvin T

2015-06-01

A cavitation event in a vessel replaces water with a mixture of water vapor and air. A quantitative theory is presented to argue that the tempo of filling of vessels with air has two phases: a fast process that extracts air from stem tissue adjacent to the cavitated vessels (less than 10 s) and a slow phase that extracts air from the atmosphere outside the stem (more than 10 h). A model was designed to estimate how water tension (T) near recently cavitated vessels causes bubbles in embolized vessels to expand or contract as T increases or decreases, respectively. The model also predicts that the hydraulic conductivity of a stem will increase as bubbles collapse. The pressure of air bubbles trapped in vessels of a stem can be predicted from the model based on fitting curves of hydraulic conductivity versus T. The model was validated using data from six stem segments each of Acer mono and the clonal hybrid Populus 84 K (Populus alba × Populus glandulosa). The model was fitted to results with root mean square error less than 3%. The model provided new insight into the study of embolism formation in stem tissue and helped quantify the bubble pressure immediately after the fast process referred to above. © 2015 American Society of Plant Biologists. All Rights Reserved.

Effect of oxygen breathing on micro oxygen bubbles in nitrogen-depleted rat adipose tissue at sea level and 25 kPa altitude exposures.

PubMed

Randsoe, Thomas; Hyldegaard, Ole

2012-08-01

The standard treatment of altitude decompression sickness (aDCS) caused by nitrogen bubble formation is oxygen breathing and recompression. However, micro air bubbles (containing 79% nitrogen), injected into adipose tissue, grow and stabilize at 25 kPa regardless of continued oxygen breathing and the tissue nitrogen pressure. To quantify the contribution of oxygen to bubble growth at altitude, micro oxygen bubbles (containing 0% nitrogen) were injected into the adipose tissue of rats depleted from nitrogen by means of preoxygenation (fraction of inspired oxygen = 1.0; 100%) and the bubbles studied at 101.3 kPa (sea level) or at 25 kPa altitude exposures during continued oxygen breathing. In keeping with previous observations and bubble kinetic models, we hypothesize that oxygen breathing may contribute to oxygen bubble growth at altitude. Anesthetized rats were exposed to 3 h of oxygen prebreathing at 101.3 kPa (sea level). Micro oxygen bubbles of 500-800 nl were then injected into the exposed abdominal adipose tissue. The oxygen bubbles were studied for up to 3.5 h during continued oxygen breathing at either 101.3 or 25 kPa ambient pressures. At 101.3 kPa, all bubbles shrank consistently until they disappeared from view at a net disappearance rate (0.02 mm(2) × min(-1)) significantly faster than for similar bubbles at 25 kPa altitude (0.01 mm(2) × min(-1)). At 25 kPa, most bubbles initially grew for 2-40 min, after which they shrank and disappeared. Four bubbles did not disappear while at 25 kPa. The results support bubble kinetic models based on Fick's first law of diffusion, Boyles law, and the oxygen window effect, predicting that oxygen contributes more to bubble volume and growth during hypobaric conditions. As the effect of oxygen increases, the lower the ambient pressure. The results indicate that recompression is instrumental in the treatment of aDCS.

Numerical Simulations of Inclusion Behavior in Gas-Stirred Ladles

NASA Astrophysics Data System (ADS)

Lou, Wentao; Zhu, Miaoyong

2013-06-01

A computation fluid dynamics-population balance model (CFD-PBM) coupled model has been proposed to investigate the bubbly plume flow and inclusion behavior including growth, size distribution, and removal in gas-stirred ladles, and some new and important phenomena and mechanisms were presented. For the bubbly plume flow, a modified k- ɛ model with extra source terms to account for the bubble-induced turbulence was adopted to model the turbulence, and the bubble turbulent dispersion force was taken into account to predict gas volume fraction distribution in the turbulent gas-stirred system. For inclusion behavior, the phenomena of inclusions turbulent random motion, bubbles wake, and slag eye forming on the molten steel surface were considered. In addition, the multiple mechanisms both that promote inclusion growth due to inclusion-inclusion collision caused by turbulent random motion, shear rate in turbulent eddy, and difference inclusion Stokes velocities, and the mechanisms that promote inclusion removal due to bubble-inclusion turbulence random collision, bubble-inclusion turbulent shear collision, bubble-inclusion buoyancy collision, inclusion own floatation near slag-metal interface, bubble wake capture, and wall adhesion were investigated. The importance of different mechanisms and total inclusion removal ratio under different conditions, and the distribution of inclusion number densities in ladle, were discussed and clarified. The results show that at a low gas flow rate, the inclusion growth is mainly attributed to both turbulent shear collision and Stokes collision, which is notably affected by the Stokes collision efficiency, and the inclusion removal is mainly attributed to the bubble-inclusion buoyancy collision and inclusion own floatation near slag-metal interface. At a higher gas flow rate, the inclusions appear as turbulence random motion in bubbly plume zone, and both the inclusion-inclusion and inclusion-bubble turbulent random collisions become important for inclusion growth and removal. With the increase of the gas flow rate, the total removal ratio increases, but when the gas flow rate exceeds 200 NL/min in 150-ton ladle, the total removal ration almost does not change. For the larger size inclusions, the number density in bubbly plume zone is less than that in the sidewall recirculation zones, but for the small size inclusions, the distribution of number density shows the opposite trend.

Modeling of sonochemistry in water in the presence of dissolved carbon dioxide.

PubMed

Authier, Olivier; Ouhabaz, Hind; Bedogni, Stefano

2018-07-01

CO 2 capture and utilization (CCU) is a process that captures CO 2 emissions from sources such as fossil fuel power plants and reuses them so that they will not enter the atmosphere. Among the various ways of recycling CO 2 , reduction reactions are extensively studied at lab-scale. However, CO 2 reduction by standard methods is difficult. Sonochemistry may be used in CO 2 gas mixtures bubbled through water subjected to ultrasound waves. Indeed, the sonochemical reduction of CO 2 in water has been already investigated by some authors, showing that fuel species (CO and H 2 ) are obtained in the final products. The aim of this work is to model, for a single bubble, the close coupling of the mechanisms of bubble dynamics with the kinetics of gas phase reactions in the bubble that can lead to CO 2 reduction. An estimation of time-scales is used to define the controlling steps and consequently to solve a reduced model. The calculation of the concentration of free radicals and gases formed in the bubble is undertaken over many cycles to look at the effects of ultrasound frequency, pressure amplitude, initial bubble radius and bubble composition in CO 2 . The strong effect of bubble composition on the CO 2 reduction rate is confirmed in accordance with experimental data from the literature. When the initial fraction of CO 2 in the bubble is low, bubble growth and collapse are slightly modified with respect to simulation without CO 2 , and chemical reactions leading to CO 2 reduction are promoted. However, the peak collapse temperature depends on the thermal properties of the CO 2 and greatly decreases as the CO 2 increases in the bubble. The model shows that initial bubble radius, ultrasound frequency and pressure amplitude play a critical role in CO 2 reduction. Hence, in the case of a bubble with an initial radius of around 5 μm, CO 2 reduction appears to be more favorable at a frequency around 300 kHz than at a low frequency of around 20 kHz. Finally, the industrial application of ultrasound to CO 2 reduction in water would be largely dependent on sonochemical efficiency. Under the conditions tested, this process does not seem to be sufficiently efficient. Copyright © 2018 Elsevier B.V. All rights reserved.

Small-bubble transport and splitting dynamics in a symmetric bifurcation.

PubMed

Qamar, Adnan; Warnez, Matthew; Valassis, Doug T; Guetzko, Megan E; Bull, Joseph L

2017-08-01

Simulations of small bubbles traveling through symmetric bifurcations are conducted to garner information pertinent to gas embolotherapy, a potential cancer treatment. Gas embolotherapy procedures use intra-arterial bubbles to occlude tumor blood supply. As bubbles pass through bifurcations in the blood stream nonhomogeneous splitting and undesirable bioeffects may occur. To aid development of gas embolotherapy techniques, a volume of fluid method is used to model the splitting process of gas bubbles passing through artery and arteriole bifurcations. The model reproduces the variety of splitting behaviors observed experimentally, including the bubble reversal phenomenon. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Small bubbles, having initial length less than twice the vessel diameter, were found unlikely to split in the presence of gravitational asymmetry. Maximum shear stresses were found to decrease exponentially with increasing Reynolds number. Vortex-induced shearing near the bifurcation is identified as a possible mechanism for endothelial cell damage.

Developing a bubble number-density paleoclimatic indicator for glacier ice

USGS Publications Warehouse

Spencer, M.K.; Alley, R.B.; Fitzpatrick, J.J.

2006-01-01

Past accumulation rate can be estimated from the measured number-density of bubbles in an ice core and the reconstructed paleotemperature, using a new technique. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. An empirical model of these processes, optimized to fit published data on recently formed bubbles, reconstructs accumulation rates using recent temperatures with an uncertainty of 41% (P < 0.05). For modern sites considered here, no statistically significant trend exists between mean annual temperature and the ratio of bubble number-density to grain number-density at the time of pore close-off; optimum modeled accumulation-rate estimates require an eventual ???2.02 ?? 0.08 (P < 0.05) bubbles per close-off grain. Bubble number-density in the GRIP (Greenland) ice core is qualitatively consistent with independent estimates for a combined temperature decrease and accumulation-rate increase there during the last 5 kyr.

Bubble transport in bifurcations

NASA Astrophysics Data System (ADS)

Bull, Joseph; Qamar, Adnan

2017-11-01

Motivated by a developmental gas embolotherapy technique for cancer treatment, we examine the transport of bubbles entrained in liquid. In gas embolotherapy, infarction of tumors is induced by selectively formed vascular gas bubbles that originate from acoustic vaporization of vascular droplets. In the case of non-functionalized droplets with the objective of vessel occlusion, the bubbles are transported by flow through vessel bifurcations, where they may split prior to eventually reach vessels small enough that they become lodged. This splitting behavior affects the distribution of bubbles and the efficacy of flow occlusion and the treatment. In these studies, we investigated bubble transport in bifurcations using computational and theoretical modeling. The model reproduces the variety of experimentally observed splitting behaviors. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Maximum shear stresses were found to decrease with increasing Reynolds number. The initial bubble length was found to affect the splitting behavior in the presence of gravitational asymmetry. This work was supported by NIH Grant R01EB006476.

Bremsstrahlung of nitrogen and noble gases in single-bubble sonoluminescence

NASA Astrophysics Data System (ADS)

Xu, Ning; Wang, Long; Hu, Xiwei

2000-03-01

A hydrodynamic model, discussing neutral gases as well as plasmas, is applied to simulate single-bubble sonoluminescence. In this model, thermal conduction and various inelastic impact processes such as dissociation, ionization, and recombination are considered. Bremsstrahlung is assumed as the mechanism of the picosecond light pulse in sonoluminescence. Diatomic nitrogen and noble gas bubbles are studied. The results show that the sonoluminescing bubbles are completely optically thin for bremsstrahlung. The calculated spectra agree with previous observations, and can explain the observed differences in spectra of different gases.

Study on the bubble transport mechanism in an acoustic standing wave field.

PubMed

Xi, Xiaoyu; Cegla, Frederic B; Lowe, Michael; Thiemann, Andrea; Nowak, Till; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2011-12-01

The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller-Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton's second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of pressure amplitude or a decrease of bubble size forces bubbles larger than their resonant size to arrive at the target plate at lower heights, while the trajectories of smaller bubbles are less influenced by these factors. The test cell is also suitable for testing the effects of drag force on the bubble motion and for studying the bubble behavior near a surface. Copyright © 2011 Elsevier B.V. All rights reserved.

Bubble dynamics and bubble-induced turbulence of a single-bubble chain

NASA Astrophysics Data System (ADS)

Lee, Joohyoung; Park, Hyungmin

2016-11-01

In the present study, the bubble dynamics and liquid-phase turbulence induced by a chain of bubbles injected from a single nozzle have been experimentally investigated. Using a high-speed two-phase particle image velociemtry, measurements on the bubbles and liquid-phase velocity field are conducted in a transparent tank filled with water, while varying the bubble release frequency from 0.1 to 35 Hz. The tested bubble size ranges between 2.0-3.2 mm, and the corresponding bubble Reynolds number is 590-1100, indicating that it belongs to the regime of path instability. As the release frequency increases, it is found that the global shape of bubble dispersion can be classified into two regimes: from asymmetric (regular) to axisymmetric (irregular). In particular, at higher frequency, the wake vortices of leading bubbles cause an irregular behaviour of the following bubble. For the liquid phase, it is found that a specific trend on the bubble-induced turbulence appears in a strong relation to the above bubble dynamics. Considering this, we try to provide a theoretical model to estimate the liquid-phase turbulence induced by a chain of bubbles. Supported by a Grant funded by Samsung Electronics, Korea.

CONSTRAINING THE MILKY WAY'S HOT GAS HALO WITH O VII AND O VIII EMISSION LINES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Matthew J.; Bregman, Joel N., E-mail: mjmil@umich.edu, E-mail: jbregman@umich.edu

2015-02-10

The Milky Way hosts a hot (≈2 × 10{sup 6} K), diffuse, gaseous halo based on detections of z = 0 O VII and O VIII absorption lines in quasar spectra and emission lines in blank-sky spectra. Here we improve constraints on the structure of the hot gas halo by fitting a radial model to a much larger sample of O VII and O VIII emission line measurements from XMM-Newton/EPIC-MOS spectra compared to previous studies (≈650 sightlines). We assume a modified β-model for the halo density distribution and a constant-density Local Bubble from which we calculate emission to compare withmore » the observations. We find an acceptable fit to the O VIII emission line observations with χ{sub red}{sup 2} (dof) = 1.08 (644) for best-fit parameters of n{sub o}r{sub c}{sup 3β}=1.35±0.24 cm{sup –3} kpc{sup 3β} and β = 0.50 ± 0.03 for the hot gas halo and negligible Local Bubble contribution. The O VII observations yield an unacceptable χ{sub red}{sup 2} (dof) = 4.69 (645) for similar best-fit parameters, which is likely due to temperature or density variations in the Local Bubble. The O VIII fitting results imply hot gas masses of M(<50 kpc) = 3.8{sub −0.3}{sup +0.3}×10{sup 9} M{sub ⊙} and M(<250 kpc) = 4.3{sub −0.8}{sup +0.9}×10{sup 10} M{sub ⊙}, accounting for ≲50% of the Milky Way's missing baryons. We also explore our results in the context of optical depth effects in the halo gas, the halo gas cooling properties, temperature and entropy gradients in the halo gas, and the gas metallicity distribution. The combination of absorption and emission line analyses implies a sub-solar gas metallicity that decreases with radius, but that also must be ≥0.3 Z {sub ☉} to be consistent with the pulsar dispersion measure toward the Large Magellanic Cloud.« less

Possible Mechanism for Formation of Nonwettable "Dry Spots" on a Heated Surface during Nucleate Pool Boiling: II. Feedwater Stop Regime

NASA Astrophysics Data System (ADS)

Zhukov, Yu. M.; Urtenov, D. S.

2017-12-01

The problems of simulation of heterogeneous nucleate pool boiling on a horizontal surface on the ascending branch of the boiling curve from the formation of a steam lens (SL) to the boiling crisis are considered. The proposed hypothesis provides in a number of cases a logically consistent interpretation of experiments and outlines the organizational principle of transferring the wall-liquid-steam system into the regime of nonwettable "dry spot" formation. The model includes the following types of nucleate boiling: (a) cyclic boiling with the contact line reverse to the bubble bottom center and bubble departure from the surface (at low heat flux q and the contact angle θ < 90°); (b) single steam bubble conversion into a steam lens, i.e., local film boiling with the possibility of spreading of a single "dry spot" at the variation of the contact angle θ ≥ 90°, and substantial growth of the departure diameter D d and SL lifetime τd; (c) formation of a single steam cluster of four SLs at a given pressure, the liquid underheating, and the average wall overheating.

Real-cinematographic visualization of droplet ejection in thermal ink jets

NASA Astrophysics Data System (ADS)

Rembe, Christian; Patzer, Joachim; Hofer, Eberhard P.; Krehl, Peter

1996-03-01

Although thermal ink jet printers have gained a high market share there are still open questions left in the understanding of the processes in ink jet firing chambers. The experimental investigation of these processes is difficult due to the extremely short time durations of the different phenomena. For example, the bubble life time amounts to approximately 20 microsecond(s) . A new experimental set-up is presented to record phenomena of very short time duration like the bubble nucleation process and the beginning of droplet ejection. This set-up allows realcinematographic visualization with a local resolution of less than 1 micrometers and a time resolution of 10 ns. This also offers the possibility to investigate transient processes like the droplet ejection at high printing frequencies. The essential part of the set-up is a new high speed camera. With an exact evaluation of the digitized images the locus, velocity, and acceleration distributions of the phase interface from liquid to vapor/air can be measured. In addition the results of a numerical model with realistic geometry of the firing chamber and the nozzle have been compared with the experimental results to draw conclusions for pressure propagation in the vapor bubble.

Visualization of irrigant flow and cavitation induced by Er:YAG laser within a root canal model.

PubMed

Matsumoto, Himeka; Yoshimine, Yoshito; Akamine, Akifumi

2011-06-01

Laser-activated irrigation (LAI) has recently been introduced as an innovative method for root canal irrigation. However, there is limited information about the cleaning mechanism of an Er:YAG laser. In this study, we visualized the action of laser-induced bubbles and fluid flow in vitro to better understand the physical mechanisms underlying LAI. An Er:YAG laser was equipped with a novel cone-shaped tip with a lateral emission rate of approximately 80%. Laser light was emitted at a pulse energy of 30, 50, or 70 mJ (output energy: 11, 18, or 26 mJ) and a repetition rate of 1 or 20 pulses per second, without air or water spray. Fluid flow dynamics in a root canal model were observed by using glass-bead tracers under a high-speed camera. Moreover, laser-induced bubble patterns were visualized in both free water and the root canal model. Tracers revealed high-speed motion of the fluid. A full cycle of expansion and implosion of vapor and secondary cavitation bubbles were clearly observed. In free water, the vapor bubble expanded for 220 microseconds, and its shape resembled that of an apple. In the root canal model, the vapor bubble expanded in a vertical direction along the canal wall, and bubble expansion continued for ≥700 microseconds. Furthermore, cavitation bubbles were created much more frequently in the canal model than in free water. These results suggest that the cleaning mechanism of an Er:YAG laser within the root canal might depend on rapid fluid motion caused by expansion and implosion of laser-induced bubbles. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Dynamics of diffusive bubble growth and pressure recovery in a bubbly rhyolitic melt embedded in an elastic solid

USGS Publications Warehouse

Chouet, Bernard A.; Dawson, Phillip B.; Nakano, Masaru

2006-01-01

We present a model of gas exsolution and bubble expansion in a melt supersaturated in response to a sudden pressure drop. In our model, the melt contains a suspension of gas bubbles of identical sizes and is encased in a penny-shaped crack embedded in an elastic solid. The suspension is modeled as a three-dimensional lattice of spherical cells with slight overlap, where each elementary cell consists of a gas bubble surrounded by a shell of volatile-rich melt. The melt is then subjected to a step drop in pressure, which induces gas exsolution and bubble expansion, resulting in the compression of the melt and volumetric expansion of the crack. The dynamics of diffusion-driven bubble growth and volumetric crack expansion span 9 decades in time. The model demonstrates that the speed of the crack response depends strongly on volatile diffusivity in the melt and bubble number density and is markedly sensitive to the ratio of crack thickness to crack radius and initial bubble radius but is relatively insensitive to melt viscosity. The net drop in gas concentration in the melt after pressure recovery represents only a small fraction of the initial concentration prior to the drop, suggesting the melt may undergo numerous pressure transients before becoming significantly depleted of gases. The magnitude of pressure and volume recovery in the crack depends sensitively on the size of the input-pressure transient, becoming relatively larger for smaller-size transients in a melt containing bubbles with initial radii less than 10-5 m. Amplification of the input transient may be large enough to disrupt the crack wall and induce brittle failure in the rock matrix surrounding the crack. Our results provide additional basis for the interpretation of volume changes in the magma conduit under Popocatépetl Volcano during Vulcanian degassing bursts in its eruptive activity in April–May 2000.

Eternal inflation, bubble collisions, and the persistence of memory

NASA Astrophysics Data System (ADS)

Garriga, Jaume; Guth, Alan H.; Vilenkin, Alexander

2007-12-01

A “bubble universe” nucleating in an eternally inflating false vacuum will experience, in the course of its expansion, collisions with an infinite number of other bubbles. In an idealized model, we calculate the rate of collisions around an observer inside a given reference bubble. We show that the collision rate violates both the homogeneity and the isotropy of the bubble universe. Each bubble has a center which can be related to “the beginning of inflation” in the parent false vacuum, and any observer not at the center will see an anisotropic bubble collision rate that peaks in the outward direction. Surprisingly, this memory of the onset of inflation persists no matter how much time elapses before the nucleation of the reference bubble.

A boundary element model of the transport of a semi-infinite bubble through a microvessel bifurcation

NASA Astrophysics Data System (ADS)

Calderon, Andres J.; Eshpuniyani, Brijesh; Fowlkes, J. Brian; Bull, Joseph L.

2010-06-01

Motivated by a developmental gas embolotherapy technique for selective occlusion of blood flow to tumors, we examined the transport of a pressure-driven semi-infinite bubble through a liquid-filled bifurcating channel. Homogeneity of bubble splitting as the bubble passes through a vessel bifurcation affects the degree to which the vascular network near the tumor can be uniformly occluded. The homogeneity of bubble splitting was found to increase with bubble driving pressure and to decrease with increased bifurcation angle. Viscous losses at the bifurcation were observed to affect the bubble speed significantly. The potential for oscillating bubble interfaces to induce flow recirculation and impart high stresses on the vessel endothelium was also observed.

Bubbles in Sediments

DTIC Science & Technology

1999-09-30

saturated poroelastic medium. The transition matrix scattering formalism was used to develop the scattered acoustic field(s) such that appropriate...sediment increases from a fluid model (simplest) to a fluid-saturated poroelastic model (most complex). Laboratory experiments in carefully quantified...of a linear acoustic field from a bubble, collection of bubbles, or other targets embedded in a fluid-saturated sediment are not well known. This

Radiation, Gas and Magnetic Fields: Understanding Accretion Disks with Real Physics

NASA Astrophysics Data System (ADS)

Tao, Ted

2011-01-01

This dissertation studies some of the fundamental physics ingredients that underlie the theory of astrophysical accretion disks. We begin by focusing on local radiation magnetohydrodynamic instabilities in static, optically thick, vertically stratified media with constant flux mean opacity. Our analysis includes the effects of vertical gradients in a horizontal background magnetic field. Assuming rapid radiative diffusion, we use the zero gas pressure limit as an entry point for investigating the coupling between the photon bubble instability and the Parker instability. We find that the two instabilities transition smoothly into each other at a characteristic wavelength that is approximately equal to the magnetic pressure scale height times the ratio of radiation to magnetic pressure gradient forces. The Parker instability exists for longer wavelengths, while photon bubbles exist for wavelengths shorter than the transition wavelength. We also consider the effects of finite gas pressure on the coupled instabilities. Finite gas pressure introduces an additional short wavelength limit to the Parker-like behavior, and also limits the growth rate of the photon bubble instability to a constant value at high wave numbers. Finally, our analytic infinite wavenumber perturbation calculation strongly suggest that magnetic pressure gradients do not modify the photon bubble growth rate in the asymptotic regime. Our results may explain why photon bubbles have not yet been observed in recent stratified shearing box accretion disk simulations. Photon bubbles may physically exist in simulations with high radiation to gas pressure ratios, but higher spatial resolution will be needed to resolve the asymptotically growing unstable wavelengths. Next, we turn to the effects of local dissipation physics on the spectra and vertical structure of high luminosity stellar mass black hole X-ray binary accretion disks. More specifically, we present spectral calculations of non-LTE accretion disk models. We first use a dissipation profile based on scaling the results of shearing box simulations to a range of annuli parameters. We simultaneously scale the effective temperature, orbital frequency and surface density of a disk annulus according to the standard Shakura & Sunyaev model in order to bring increased dissipation to the disk surface layers (around the photosphere). We find that annuli spectrum transitions directly from that of a modified black body to one characteristic of saturated Compton scattering without first going through an intermediate power law regime as we increased the effective temperature and orbital frequency while decreasing mid-plane surface density. Next, we construct annuli models based on the parameters of a 0.8 Eddington disk orbiting a 6.62 solar mass black hole (with accretion efficiency approximately 0.083) using two modified dissipation profiles that explicitly put more dissipation per unit mass near the disk surface. The new dissipation profiles are qualitatively similar to the one found by Hirose et al. (2009) and produce strong and distinct non-thermal spectral tails. Our models also include physically motivated magnetic acceleration support based once again on scaling the Hirose et al. (2009) results. We present three full-disk spectra each based on one of the dissipation prescriptions. Our most aggressive dissipation profile results in a disk spectrum that is in approximate quantitative agreement with certain observations of the steep power law (SPL) spectral state from some black hole X-ray binaries.

An analysis of contact stiffness between a finger and an object when wearing an air-cushioned glove: the effects of the air pressure.

PubMed

Wu, John Z; Wimer, Bryan M; Welcome, Daniel E; Dong, Ren G

2012-04-01

Air-cushioned gloves have the advantages of lighter weight, lower cost, and unique mechanical performance, compared to gloves made of conventional engineering materials. The goal of this study is to analyze the contact interaction between fingers and object when wearing an air-cushioned glove. The contact interactions between the the fingertip and air bubbles, which is considered as a cell of a typical air-cushioned glove, has been analyzed theoretically. Two-dimensional finite element models were developed for the analysis. The fingertip model was assumed to be composed of skin layers, subcutaneous tissue, bone, and nail. The air bubbles were modeled as air sealed in the container of nonelastic membrane. We simulated two common scenarios: a fingertip in contact with one single air bubble and with two air cushion bubbles simultaneously. Our simulation results indicated that the internal air pressure can modulate the fingertip-object contact characteristics. The contact stiffness reaches a minimum when the initial air pressure is equal to 1.3 and 1.05 times of the atmosphere pressure for the single air bubble and the double air bubble contact, respectively. Furthermore, the simulation results indicate that the double air bubble contact will result in smaller volumetric tissue strain than the single air bubble contact for the same force. Published by Elsevier Ltd.

THE AGE OF THE LOCAL INTERSTELLAR BUBBLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abt, Helmut A., E-mail: abt@noao.edu

2011-05-15

The Local Interstellar Bubble is an irregular region from 50 to 150 pc from the Sun in which the interstellar gas density is 10{sup -2}-10{sup -3} of that outside the bubble and the interstellar temperature is 10{sup 6} K. Evidently most of the gas was swept out by one or more supernovae. I explored the stellar contents and ages of the region from visual double stars, spectroscopic doubles, single stars, open clusters, emission regions, X-ray stars, planetary nebulae, and pulsars. The bubble has three sub-regions. The region toward the galactic center has stars as early as O9.5 V and withmore » ages of 2-4 M yr. It also has a pulsar (PSRJ1856-3754) with a spin-down age of 3.76 Myr. That pulsar is likely to be the remnant of the supernova that drove away most of the gas. The central lobe has stars as early as B7 V and therefore an age of about 160 Myr or less. The Pleiades lobe has stars as early as B3 and therefore an age of about 50 Myr. There are no obvious pulsars that resulted from the supernovae that cleared out those areas. As found previously by Welsh and Lallement, the bubble has five B stars along its perimeter that show high-temperature ions of O VI and C II along their lines of sight, confirming its high interstellar temperature.« less

Effect of Slotted Anode on Gas Bubble Behaviors in Aluminum Reduction Cell

NASA Astrophysics Data System (ADS)

Sun, Meijia; Li, Baokuan; Li, Linmin; Wang, Qiang; Peng, Jianping; Wang, Yaowu; Cheung, Sherman C. P.

2017-12-01

In the aluminum reduction cells, gas bubbles are generated at the bottom of the anode which eventually reduces the effective current contact area and the system efficiency. To encourage the removal of gas bubbles, slotted anode has been proposed and increasingly adopted by some industrial aluminum reduction cells. Nonetheless, the exact gas bubble removal mechanisms are yet to be fully understood. A three-dimensional (3D) transient, multiphase flow mathematical model coupled with magnetohydrodynamics has been developed to investigate the effect of slotted anode on the gas bubble movement. The Eulerian volume of fluid approach is applied to track the electrolyte (bath)-molten aluminum (metal) interface. Meanwhile, the Lagrangian discrete particle model is employed to handle the dynamics of gas bubbles with considerations of the buoyancy force, drag force, virtual mass force, and pressure gradient force. The gas bubble coalescence process is also taken into account based on the O'Rourke's algorithm. The two-way coupling between discrete bubbles and fluids is achieved by the inter-phase momentum exchange. Numerical predictions are validated against the anode current variation in an industrial test. Comparing the results using slotted anode with the traditional one, the time-averaged gas bubble removal rate increases from 36 to 63 pct; confirming that the slotted anode provides more escaping ways and shortens the trajectories for gas bubbles. Furthermore, the slotted anode also reduces gas bubble's residence time and the probability of coalescence. Moreover, the bubble layer thickness in aluminum cell with slotted anode is reduced about 3.5 mm (17.4 pct), so the resistance can be cut down for the sake of energy saving and the metal surface fluctuation amplitude is significantly reduced for the stable operation due to the slighter perturbation with smaller bubbles.

Period adding cascades: experiment and modeling in air bubbling.

PubMed

Pereira, Felipe Augusto Cardoso; Colli, Eduardo; Sartorelli, José Carlos

2012-03-01

Period adding cascades have been observed experimentally/numerically in the dynamics of neurons and pancreatic cells, lasers, electric circuits, chemical reactions, oceanic internal waves, and also in air bubbling. We show that the period adding cascades appearing in bubbling from a nozzle submerged in a viscous liquid can be reproduced by a simple model, based on some hydrodynamical principles, dealing with the time evolution of two variables, bubble position and pressure of the air chamber, through a system of differential equations with a rule of detachment based on force balance. The model further reduces to an iterating one-dimensional map giving the pressures at the detachments, where time between bubbles come out as an observable of the dynamics. The model has not only good agreement with experimental data, but is also able to predict the influence of the main parameters involved, like the length of the hose connecting the air supplier with the needle, the needle radius and the needle length.

Cardiovascular microbubble transport in vessel bifurcations with pulsatile flow: experimental model and theory

NASA Astrophysics Data System (ADS)

Valassis, Doug; Dodde, Robert; Eshpuniyani, Brijesh; Fowlkes, J. Brian; Bull, Joseph

2008-11-01

The behavior of long gas bubbles suspended in liquid flowing through successive bifurcations was investigated experimentally and theoretically as a model of cardiovascular bubble transport in gas embolotherapy. In this developmental cancer therapy, perflurocarbon droplets are vaporized in the vasculature and travel through a bifurcating network of vessels before lodging. The homogeneity of tumor necrosis is directly correlated with the transport and lodging of the emboli. An experimental model was used to explore the effects of flow pulsatility, frequency, gravity, and bifurcation roll angle on bubble splitting and lodging. At a bifurcation roll angle of 45-degrees, the most distinct difference in splitting ratios between three physiologic frequencies (1, 1.5, 2 Hz) was observed. As roll angle increased, lodged bubble volume in the first generation channel increased while bubble volume beyond the second bifurcation proportionately decreased. A corresponding time-dependent one-dimensional theoretical model was also developed. The results elucidate the effects of pulsatile flow and suggest the potential of gas embolotherapy to occlude blood flow to tumors.

Dynamics of sonoluminescing bubbles within a liquid hammer device.

PubMed

Urteaga, Raúl; García-Martínez, Pablo Luis; Bonetto, Fabián J

2009-01-01

We studied the dynamics of a single sonoluminescing bubble (SBSL) in a liquid hammer device. In particular, we investigated the phosphoric acid-xenon system, in which pulses up to four orders of magnitude brighter than SBSL in water systems (about 10;{12} photons per pulse) have been previously reported [Chakravarty, Phys. Rev. E 69, 066317 (2004)]. We used stroboscopic photography and a Mie scattering technique in order to measure the radius evolution of the bubbles. Under adequate conditions we may position a bubble at the bottom of the tube (cavity) and a second bubble trapped at the middle of the tube (upper bubble). During its collapse, the cavity produces the compression of the liquid column. This compression drives impulsively the dynamics of the upper bubble. Our measurements reveal that the observed light emissions produced by the upper bubble are generated at its second collapse. We employed a simple numerical model to investigate the conditions that occur during the upper bubble collapse. We found good agreement between numerical and experimental values for the light intensity (fluence) and light pulse widths. Results from the model show that the light emission is increased mainly due to an increase in noble gas ambient radius and not because the maximum temperature increases. Even for the brightest pulses obtained ( 2x10;{13} photons, about 20W of peak power) the maximum temperatures computed for the upper bubble are always lower than 20000K .

Linear bubble plume model for hypolimnetic oxygenation: Full-scale validation and sensitivity analysis

NASA Astrophysics Data System (ADS)

Singleton, V. L.; Gantzer, P.; Little, J. C.

2007-02-01

An existing linear bubble plume model was improved, and data collected from a full-scale diffuser installed in Spring Hollow Reservoir, Virginia, were used to validate the model. The depth of maximum plume rise was simulated well for two of the three diffuser tests. Temperature predictions deviated from measured profiles near the maximum plume rise height, but predicted dissolved oxygen profiles compared very well with observations. A sensitivity analysis was performed. The gas flow rate had the greatest effect on predicted plume rise height and induced water flow rate, both of which were directly proportional to gas flow rate. Oxygen transfer within the hypolimnion was independent of all parameters except initial bubble radius and was inversely proportional for radii greater than approximately 1 mm. The results of this work suggest that plume dynamics and oxygen transfer can successfully be predicted for linear bubble plumes using the discrete-bubble approach.

Attenuation of low-frequency underwater sound using an array of air-filled balloons and comparison to effective medium theory.

PubMed

Lee, Kevin M; Wilson, Preston S; Wochner, Mark S

2017-12-01

The ultimate goal of this work is to accurately predict the attenuation through a collection of large (on the order of 10-cm-radius) tethered encapsulated bubbles used in underwater noise abatement systems. Measurements of underwater sound attenuation were performed during a set of lake experiments, where a low-frequency compact electromechanical sound source was surrounded by different arrays of encapsulated bubbles with various individual bubbles sizes and void fractions. The measurements were compared with an existing predictive model [Church, J. Acoust. Soc. Am. 97, 1510-1521 (1995)] of the dispersion relation for linear propagation in liquid containing encapsulated bubbles. Although the model was originally intended to describe ultrasound contrast agents, it is evaluated here for large bubbles, and hence low frequencies, as a design tool for future underwater noise abatement systems, and there is good quantitative agreement between the observations and the model.

Bubble formation in water with addition of a hydrophobic solute.

PubMed

Okamoto, Ryuichi; Onuki, Akira

2015-07-01

We show that phase separation can occur in a one-component liquid outside its coexistence curve (CX) with addition of a small amount of a solute. The solute concentration at the transition decreases with increasing the difference of the solvation chemical potential between liquid and gas. As a typical bubble-forming solute, we consider O2 in ambient liquid water, which exhibits mild hydrophobicity and its critical temperature is lower than that of water. Such a solute can be expelled from the liquid to form gaseous domains while the surrounding liquid pressure is higher than the saturated vapor pressure p cx. This solute-induced bubble formation is a first-order transition in bulk and on a partially dried wall, while a gas film grows continuously on a completely dried wall. We set up a bubble free energy ΔG for bulk and surface bubbles with a small volume fraction ϕ. It becomes a function of the bubble radius R under the Laplace pressure balance. Then, for sufficiently large solute densities above a threshold, ΔG exhibits a local maximum at a critical radius and a minimum at an equilibrium radius. We also examine solute-induced nucleation taking place outside CX, where bubbles larger than the critical radius grow until attainment of equilibrium.

Low threshold lasing of bubble-containing glass microspheres by non-whispering gallery mode excitation over a wide wavelength range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumagai, Tsutaru, E-mail: kumagai.t.af@m.titech.ac.jp; Kishi, Tetsuo; Yano, Tetsuji

2015-03-21

Bubble-containing Nd{sup 3+}-doped tellurite glass microspheres were fabricated by localized laser heating technique to investigate their optical properties for use as microresonators. Fluorescence and excitation spectra measurements were performed by pumping with a tunable CW-Ti:Sapphire laser. The excitation spectra manifested several sharp peaks due to the conventional whispering gallery mode (WGM) when the pumping laser was irradiated to the edge part of the microsphere. However, when the excitation light was irradiated on the bubble position inside the microsphere, “non-WGM excitation” was induced, giving rise to numerous peaks at a broad wavelength range in the excitation spectra. Thus, efficient excitation wasmore » achieved over a wide wavelength range. Lasing threshold excited at the bubble position was much lower than that for the excitation at the edges of the microsphere. The lowest value of the laser threshold was 34 μW for a 4 μm sphere containing a 0.5 μm bubble. Efficiency of the excitation at the bubble position with broadband light was calculated to be 5 times higher than that for the edge of the microsphere. The bubble-containing microsphere enables efficient utilization of broadband light excitation from light-emitting diodes and solar light.« less

How are soap bubbles blown? Fluid dynamics of soap bubble blowing

NASA Astrophysics Data System (ADS)

Davidson, John; Lambert, Lori; Sherman, Erica; Wei, Timothy; Ryu, Sangjin

2013-11-01

Soap bubbles are a common interfacial fluid dynamics phenomenon having a long history of delighting not only children and artists but also scientists. In contrast to the dynamics of liquid droplets in gas and gas bubbles in liquid, the dynamics of soap bubbles has not been well documented. This is possibly because studying soap bubbles is more challenging due to there existing two gas-liquid interfaces. Having the thin-film interface seems to alter the characteristics of the bubble/drop creation process since the interface has limiting factors such as thickness. Thus, the main objective of this study is to determine how the thin-film interface differentiates soap bubbles from gas bubbles and liquid drops. To investigate the creation process of soap bubbles, we constructed an experimental model consisting of air jet flow and a soap film, which consistently replicates the conditions that a human produces when blowing soap bubbles, and examined the interaction between the jet and the soap film using the high-speed videography and the particle image velocimetry.

Bubble dynamics in viscoelastic soft tissue in high-intensity focal ultrasound thermal therapy.

PubMed

Zilonova, E; Solovchuk, M; Sheu, T W H

2018-01-01

The present study is aimed to investigate bubble dynamics in a soft tissue, to which HIFU's continuous harmonic pulse is applied by introducing a viscoelastic cavitation model. After a comparison of some existing cavitation models, we decided to employ Gilmore-Akulichev model. This chosen cavitation model should be coupled with the Zener viscoelastic model in order to be able to simulate soft tissue features such as elasticity and relaxation time. The proposed Gilmore-Akulichev-Zener model was investigated for exploring cavitation dynamics. The parametric study led us to the conclusion that the elasticity and viscosity both damp bubble oscillations, whereas the relaxation effect depends mainly on the period of the ultrasound wave. The similar influence of elasticity, viscosity and relaxation time on the temperature inside the bubble can be observed. Cavitation heat source terms (corresponding to viscous damping and pressure wave radiated by bubble collapse) were obtained based on the proposed model to examine the cavitation significance during the treatment process. Their maximum values both overdominate the acoustic ultrasound term in HIFU applications. Elasticity was revealed to damp a certain amount of deposited heat for both cavitation terms. Copyright © 2017 Elsevier B.V. All rights reserved.

Models of cylindrical bubble pulsation

PubMed Central

Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hay, Todd A.; Hamilton, Mark F.

2012-01-01

Three models are considered for describing the dynamics of a pulsating cylindrical bubble. A linear solution is derived for a cylindrical bubble in an infinite compressible liquid. The solution accounts for losses due to viscosity, heat conduction, and acoustic radiation. It reveals that radiation is the dominant loss mechanism, and that it is 22 times greater than for a spherical bubble of the same radius. The predicted resonance frequency provides a basis of comparison for limiting forms of other models. The second model considered is a commonly used equation in Rayleigh-Plesset form that requires an incompressible liquid to be finite in extent in order for bubble pulsation to occur. The radial extent of the liquid becomes a fitting parameter, and it is found that considerably different values of the parameter are required for modeling inertial motion versus acoustical oscillations. The third model was developed by V. K. Kedrinskii [Hydrodynamics of Explosion (Springer, New York, 2005), pp. 23–26] in the form of the Gilmore equation for compressible liquids of infinite extent. While the correct resonance frequency and loss factor are not recovered from this model in the linear approximation, it provides reasonable agreement with observations of inertial motion. PMID:22978863

Liquid phase stabilization versus bubble formation at a nanoscale curved interface

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Luo, Tengfei

2018-03-01

We investigate the nature of vapor bubble formation near a nanoscale-curved convex liquid-solid interface using two models: an equilibrium Gibbs model for homogenous nucleation, and a nonequilibrium dynamic van der Waals-diffuse-interface model for phase change in an initially cool liquid. Vapor bubble formation is shown to occur for sufficiently large radius of curvature and is suppressed for smaller radii. Solid-fluid interactions are accounted for and it is shown that liquid-vapor interfacial energy, and hence Laplace pressure, has limited influence over bubble formation. The dominant factor is the energetic cost of creating the solid-vapor interface from the existing solid-liquid interface, as demonstrated via both equilibrium and nonequilibrium arguments.

Bubble nucleation and migration in a lead-iron hydr(oxide) core-shell nanoparticle

DOE PAGES

Niu, Kaiyang; Frolov, Timofey; Xin, Huolin L.; ...

2015-10-05

Iron hydroxide is found in a wide range of contexts ranging from biominerals to steel corrosion, and it can transform to anhydrous oxide via releasing O 2 gas and H 2O. However, it is not well understood how gases transport through a crystal lattice. Here, we present in situ observation of the nucleation and migration of gas bubbles in iron (hydr)oxide using transmission electron microscopy. We create Pb–FeOOH model core–shell nanoparticles in a liquid cell. Under electron irradiation, iron hydroxide transforms to iron oxide, during which bubbles are generated, and they migrate through the shell to the nanoparticle surface. Geometricmore » phase analysis of the shell lattice shows an inhomogeneous stain field at the bubbles. In conclusion, our modeling suggests that the elastic interaction between the core and the bubble provides a driving force for bubble migration.« less

Bubble nucleation and migration in a lead–iron hydr(oxide) core–shell nanoparticle

PubMed Central

Niu, Kaiyang; Frolov, Timofey; Xin, Huolin L.; Wang, Junling; Asta, Mark; Zheng, Haimei

2015-01-01

Iron hydroxide is found in a wide range of contexts ranging from biominerals to steel corrosion, and it can transform to anhydrous oxide via releasing O2 gas and H2O. However, it is not well understood how gases transport through a crystal lattice. Here, we present in situ observation of the nucleation and migration of gas bubbles in iron (hydr)oxide using transmission electron microscopy. We create Pb–FeOOH model core–shell nanoparticles in a liquid cell. Under electron irradiation, iron hydroxide transforms to iron oxide, during which bubbles are generated, and they migrate through the shell to the nanoparticle surface. Geometric phase analysis of the shell lattice shows an inhomogeneous stain field at the bubbles. Our modeling suggests that the elastic interaction between the core and the bubble provides a driving force for bubble migration. PMID:26438864

Thermodynamics of ultra-sonic cavitation bubbles in flotation ore processes

NASA Astrophysics Data System (ADS)

Royer, J. J.; Monnin, N.; Pailot-Bonnetat, N.; Filippov, L. O.; Filippova, I. V.; Lyubimova, T.

2017-07-01

Ultra-sonic enhanced flotation ore process is a more efficient technique for ore recovery than classical flotation method. A classical simplified analytical Navier-Stokes model is used to predict the effect of the ultrasonic waves on the cavitations bubble behaviour. Then, a thermodynamics approach estimates the temperature and pressure inside a bubble, and investigates the energy exchanges between flotation liquid and gas bubbles. Several gas models (including ideal gas, Soave-Redlich-Kwong, and Peng-Robinson) assuming polytropic transformations (from isothermal to adiabatic) are used to predict the evolution of the internal pressure and temperature inside the bubble during the ultrasonic treatment, together with the energy and heat exchanges between the gas and the surrounding fluid. Numerical simulation illustrates the suggest theory. If the theory is verified experimentally, it predicts an increase of the temperature and pressure inside the bubbles. Preliminary ultrasonic flotation results performed on a potash ore seem to confirm the theory.

Monte Carlo simulation of spectral reflectance and BRDF of the bubble layer in the upper ocean.

PubMed

Ma, Lanxin; Wang, Fuqiang; Wang, Chengan; Wang, Chengchao; Tan, Jianyu

2015-09-21

The presence of bubbles can significantly change the radiative properties of seawater and these changes will affect remote sensing and underwater target detection. In this work, the spectral reflectance and bidirectional reflectance characteristics of the bubble layer in the upper ocean are investigated using the Monte Carlo method. The Hall-Novarini (HN) bubble population model, which considers the effect of wind speed and depth on the bubble size distribution, is used. The scattering coefficients and the scattering phase functions of bubbles in seawater are calculated using Mie theory, and the inherent optical properties of seawater for wavelengths between 300 nm and 800 nm are related to chlorophyll concentration (Chl). The effects of bubble coating, Chl, and bubble number density on the spectral reflectance of the bubble layer are studied. The bidirectional reflectance distribution function (BRDF) of the bubble layer for both normal and oblique incidence is also investigated. The results show that bubble populations in clear waters under high wind speed conditions significantly influence the reflection characteristics of the bubble layer. Furthermore, the contribution of bubble populations to the reflection characteristics is mainly due to the strong backscattering of bubbles that are coated with an organic film.

Bubbles, shocks and elementary technical trading strategies

NASA Astrophysics Data System (ADS)

Fry, John

2014-01-01

In this paper we provide a unifying framework for a set of seemingly disparate models for bubbles, shocks and elementary technical trading strategies in financial markets. Markets operate by balancing intrinsic levels of risk and return. This seemingly simple observation is commonly over-looked by academics and practitioners alike. Our model shares its origins in statistical physics with others. However, under our approach, changes in market regime can be explicitly shown to represent a phase transition from random to deterministic behaviour in prices. This structure leads to an improved physical and econometric model. We develop models for bubbles, shocks and elementary technical trading strategies. The list of empirical applications is both interesting and topical and includes real-estate bubbles and the on-going Eurozone crisis. We close by comparing the results of our model with purely qualitative findings from the finance literature.

Tapered Screened Channel PMD for Cryogenic Liquids

NASA Astrophysics Data System (ADS)

Dodge, Franklin T.; Green, Steve T.; Walter, David B.

2004-02-01

If a conventional spacecraft propellant management device (PMD) of the screened channel type were employed with a cryogenic liquid, vapor bubbles generated within the channel by heat transfer could ``dry out'' the channel screens and thereby cause the channels to admit large amounts of vapor from the tank into the liquid outflow. This paper describes a new tapered channel design that passively `pumps' bubbles away from the outlet port and vents them into the tank. A predictive mathematical model of the operating principle is presented and discussed. Scale-model laboratory tests were conducted and the mathematical model agreed well with the measured rates of bubble transport velocity. Finally, an example of the use of the predictive model for a realistic spacecraft application is presented. The model predicts that bubble clearing rates are acceptable even in tanks up to 2 m in length.

Sound propagation in water containing large tethered spherical encapsulated gas bubbles with resonance frequencies in the 50 Hz to 100 Hz range.

PubMed

Lee, Kevin M; Hinojosa, Kevin T; Wochner, Mark S; Argo, Theodore F; Wilson, Preston S; Mercier, Richard S

2011-11-01

The efficacy of large tethered encapsulated gas bubbles for the mitigation of low frequency underwater noise was investigated with an acoustic resonator technique. Tethered latex balloons were used as the bubbles, which had radii of approximately 5 cm. Phase speeds were inferred from the resonances of a water and balloon-filled waveguide approximately 1.8 m in length. The Commander and Prosperetti effective-medium model [J. Acoust. Soc. Am. 85, 732-746 (1989)] quantitatively described the observed dispersion from well below to just below the individual bubble resonance frequency, and it qualitatively predicted the frequency range of high attenuation for void fractions between 2% and 5% for collections of stationary balloons within the waveguide. A finite-element model was used to investigate the sensitivity of the waveguide resonance frequencies, and hence the inferred phase speeds, to changes in individual bubble size and position. The results indicate that large tethered encapsulated bubbles could be used mitigate low frequency underwater noise and that the Commander and Prosperetti model would be useful in the design of such a system.

FAR-ULTRAVIOLET OBSERVATIONS OF THE SPICA NEBULA AND THE INTERACTION ZONE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Yeon-Ju; Min, Kyoung-Wook; Lim, Tae-Ho

2013-09-01

We report the analysis results of far-ultraviolet (FUV) observations, made for a broad region around {alpha} Vir (Spica) including the interaction zone of Loop I and the Local Bubble. The whole region was optically thin and a general correlation was seen between the FUV continuum intensity and the dust extinction, except in the neighborhood of the bright central star, indicating the dust scattering nature of the FUV continuum. We performed Monte Carlo radiative transfer simulations to obtain the optical parameters related to the dust scattering as well as to the geometrical structure of the region. The albedo and asymmetry factormore » were found to be 0.38 {+-} 0.06 and 0.46 {+-} 0.06, respectively, in good agreement with the Milky Way dust grain models. The distance to and the thickness of the interaction zone were estimated to be 70{sup +4}{sub -8} pc and 40{sup +8}{sub -10} pc, respectively. The diffuse FUV continuum in the northern region above Spica was mostly the result of scattering of the starlight from Spica, while that in the southern region was mainly due to the background stars. The C IV {lambda}{lambda}1548, 1551 emission was found throughout the whole region, in contrast to the Si II* {lambda}1532 emission which was bright only within the H II region. This indicates that the C IV line arises mostly at the shell boundaries of the bubbles, with a larger portion likely from the Loop I than from the Local Bubble side, whereas the Si II* line is from the photoionized Spica Nebula.« less

The Structure of the Local Hot Bubble

NASA Technical Reports Server (NTRS)

Liu, W.; Chiao, M.; Collier, M. R.; Cravens, T.; Galeazzi, M.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Lepri, S. T.; McCammon, Dan;

Dynamic colloidal sorting on a magnetic bubble lattice

NASA Astrophysics Data System (ADS)

Tierno, Pietro; Soba, Alejandro; Johansen, Tom H.; Sagués, Francesc

2008-11-01

We use a uniaxial garnet film with a magnetic bubble lattice to sort paramagnetic colloidal particles with different diameters, i.e., 1.0 and 2.8μm. We apply an external magnetic field which precesses around an axis normal to the film with a frequency Ω =62.8s-1 and intensity 3120A/m

Numerical simulation of the distribution of individual gas bubbles in shaped sapphire crystals

NASA Astrophysics Data System (ADS)

Borodin, A. V.; Borodin, V. A.

2017-11-01

The simulation of the effective density of individual gas bubbles in a two-phase melt, consisting of a liquid and gas bubbles, is performed using the virtual model of the thermal unit. Based on the studies, for the first time the theoretically and experimentally grounded mechanism of individual gas bubbles formation in shaped sapphire is proposed. It is shown that the change of the melt flow pattern in crucible affects greatly the bubble density at the crystallization front, and in the crystal. The obtained results allowed reducing the number of individual gas bubbles in sapphire sheets.

Robust acoustic wave manipulation of bubbly liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gumerov, N. A., E-mail: gumerov@umiacs.umd.edu; Center for Micro- and Nanoscale Dynamics of Dispersed Systems, Bashkir State University, Ufa 450076; Akhatov, I. S.

Experiments with water–air bubbly liquids when exposed to acoustic fields of frequency ∼100 kHz and intensity below the cavitation threshold demonstrate that bubbles ∼30 μm in diameter can be “pushed” away from acoustic sources by acoustic radiation independently from the direction of gravity. This manifests formation and propagation of acoustically induced transparency waves (waves of the bubble volume fraction). In fact, this is a collective effect of bubbles, which can be described by a mathematical model of bubble self-organization in acoustic fields that matches well with our experiments.

The ISM From the Soft X-ray Background Perspective

NASA Technical Reports Server (NTRS)

Snowden, S. L.

2003-01-01

In the past few years progress in understanding the local and Galactic ISM in terms of the diffuse X-ray background has been as much about what hasn't been seen as it has been about detections. High resolution spectra of the local SXRB have been observed, but are inconsistent with current thermal emission models. An excess over the extrapolation of the high-energy (most clearly visible at E greater than 1.5 keV) extragalactic power law down to 3/4 keV has been observed but only at the level consistent with cosmological models, implying the absence of at least a bright hot Galactic halo. A very recent FUSE result indicates that O VI emission from the Local Hot Bubble is insignificant, if it exists at all, a result which is also inconsistent with current thermal emission models. A short review of the current status of our (well, at least my) understanding of the Galactic SXRB and ISM is presented here.

Predawn plasma bubble cluster observed in Southeast Asia

NASA Astrophysics Data System (ADS)

Watthanasangmechai, Kornyanat; Yamamoto, Mamoru; Saito, Akinori; Tsunoda, Roland; Yokoyama, Tatsuhiro; Supnithi, Pornchai; Ishii, Mamoru; Yatini, Clara

2016-06-01

Predawn plasma bubble was detected as deep plasma depletion by GNU Radio Beacon Receiver (GRBR) network and in situ measurement onboard Defense Meteorological Satellite Program F15 (DMSPF15) satellite and was confirmed by sparse GPS network in Southeast Asia. In addition to the deep depletion, the GPS network revealed the coexisting submesoscale irregularities. A deep depletion is regarded as a primary bubble. Submesoscale irregularities are regarded as secondary bubbles. Primary bubble and secondary bubbles appeared together as a cluster with zonal wavelength of 50 km. An altitude of secondary bubbles happened to be lower than that of the primary bubble in the same cluster. The observed pattern of plasma bubble cluster is consistent with the simulation result of the recent high-resolution bubble (HIRB) model. This event is only a single event out of 76 satellite passes at nighttime during 3-25 March 2012 that significantly shows plasma depletion at plasma bubble wall. The inside structure of the primary bubble was clearly revealed from the in situ density data of DMSPF15 satellite and the ground-based GRBR total electron content.

Multiphase fluid-solid coupled analysis of shock-bubble-stone interaction in shockwave lithotripsy.

PubMed

Wang, Kevin G

2017-10-01

A novel multiphase fluid-solid-coupled computational framework is applied to investigate the interaction of a kidney stone immersed in liquid with a lithotripsy shock wave (LSW) and a gas bubble near the stone. The main objective is to elucidate the effects of a bubble in the shock path to the elastic and fracture behaviors of the stone. The computational framework couples a finite volume 2-phase computational fluid dynamics solver with a finite element computational solid dynamics solver. The surface of the stone is represented as a dynamic embedded boundary in the computational fluid dynamics solver. The evolution of the bubble surface is captured by solving the level set equation. The interface conditions at the surfaces of the stone and the bubble are enforced through the construction and solution of local fluid-solid and 2-fluid Riemann problems. This computational framework is first verified for 3 example problems including a 1D multimaterial Riemann problem, a 3D shock-stone interaction problem, and a 3D shock-bubble interaction problem. Next, a series of shock-bubble-stone-coupled simulations are presented. This study suggests that the dynamic response of a bubble to LSW varies dramatically depending on its initial size. Bubbles with an initial radius smaller than a threshold collapse within 1 μs after the passage of LSW, whereas larger bubbles do not. For a typical LSW generated by an electrohydraulic lithotripter (p max  = 35.0MPa, p min  =- 10.1MPa), this threshold is approximately 0.12mm. Moreover, this study suggests that a noncollapsing bubble imposes a negative effect on stone fracture as it shields part of the LSW from the stone. On the other hand, a collapsing bubble may promote fracture on the proximal surface of the stone, yet hinder fracture from stone interior. Copyright © 2016 John Wiley & Sons, Ltd.

An analytical approach to the rise velocity of periodic bubble trains in non-Newtonian fluids.

PubMed

Frank, X; Li, H Z; Funfschilling, D

2005-01-01

The present study aims at providing insight into the acceleration mechanism of a bubble chain rising in shear-thinning viscoelastic fluids. The experimental investigation by the Particle Image Velocimetry (PIV), birefringence visualisation and rheological simulation shows that two aspects are central to bubble interactions in such media: the stress creation by the passage of bubbles, and their relaxation due to the fluid's memory forming an evanescent corridor of reduced viscosity. Interactions between bubbles were taken into account mainly through a linear superposition of the stress evolution behind each bubble. An analytical approach together with the rheological consideration was developed to compute the rise velocity of a bubble chain in function of the injection period and bubble volume. The model predictions compare satisfactorily with the experimental investigation.

Numerical simulation of high Reynolds number bubble motion

DOE Office of Scientific and Technical Information (OSTI.GOV)

McLaughlin, J.B.

This paper presents the results of numerical simulations of bubble motion. All the results are for single bubbles in unbounded fluids. The liquid phase is quiescent except for the motion created by the bubble, which is axisymmetric. The main focus of the paper is on bubbles that are of order 1 mm in diameter in water. Of particular interest is the effect of surfactant molecules on bubble motion. Results for the {open_quotes}insoluble surfactant{close_quotes} model will be presented. These results extend research by other investigators to finite Reynolds numbers. The results indicate that, by assuming complete coverage of the bubble surface,more » one obtains good agreement with experimental observations of bubble motion in tap water. The effect of surfactant concentration on the separation angle is discussed.« less

Biomedical device prototype based on small scale hydrodynamic cavitation

NASA Astrophysics Data System (ADS)

Ghorbani, Morteza; Sozer, Canberk; Alcan, Gokhan; Unel, Mustafa; Ekici, Sinan; Uvet, Huseyin; Koşar, Ali

2018-03-01

This study presents a biomedical device prototype based on small scale hydrodynamic cavitation. The application of small scale hydrodynamic cavitation and its integration to a biomedical device prototype is offered as an important alternative to other techniques, such as ultrasound therapy, and thus constitutes a local, cheap, and energy-efficient solution, for urinary stone therapy and abnormal tissue ablation (e.g., benign prostate hyperplasia (BPH)). The destructive nature of bubbly, cavitating, flows was exploited, and the potential of the prototype was assessed and characterized. Bubbles generated in a small flow restrictive element (micro-orifice) based on hydrodynamic cavitation were utilized for this purpose. The small bubbly, cavitating, flow generator (micro-orifice) was fitted to a small flexible probe, which was actuated with a micromanipulator using fine control. This probe also houses an imaging device for visualization so that the emerging cavitating flow could be locally targeted to the desired spot. In this study, the feasibility of this alternative treatment method and its integration to a device prototype were successfully accomplished.

Local phase transitions in driven colloidal suspensions

NASA Astrophysics Data System (ADS)

Scacchi, A.; Brader, J. M.

2018-02-01

Using dynamical density functional theory and Brownian dynamics simulations, we investigate the influence of a driven tracer particle on the density distribution of a colloidal suspension at a thermodynamic state point close to the liquid side of the binodal. In bulk systems, we find that a localised region of the colloid-poor phase, a 'cavitation bubble', forms behind the moving tracer. The extent of the cavitation bubble is investigated as a function of both the size and velocity of the tracer. The addition of a confining boundary enables us to investigate the interaction between the local phase instability at the substrate and that at the particle surface. When both the substrate and tracer interact repulsively with the colloids we observe the formation of a colloid-poor bridge between the substrate and the tracer. When a shear flow is applied parallel to the substrate the bridge becomes distorted and, at sufficiently high shear-rates, disconnects from the substrate to form a cavitation bubble.

Effects of Particle Size and Bubble Characteristics on Transport of Micro- and Nano-Bubbles in Saturated Porous Media

NASA Astrophysics Data System (ADS)

Hamamoto, S.; Nihei, N.; Ueda, Y.; Moldrup, P.; Nishimura, T.

2016-12-01

The micro- and nano-bubbles (MNBs) have considerable potentials for the remediation of soil contaminated by organic compounds when used in conjunction with bioremediation technology. Understanding a transport mechanism of MNBs in soils is essential to optimize remediation techniques using MNBs. In this study, column transport experiments using glass beads with different size fractions (average particles size: 0.1 mm and 0.4 mm) were conducted, where MNBs created by oxygen gas were injected to the column with different flow rates. Effects of particle size and bubble characteristics on MNB transport in porous media were investigated based on the column experiments. The results showed that attachments of MNBs were enhanced under lower flow rate. Under higher flow rate condition, there were not significant differences of MNBs transport in porous media with different particle size. A convection-dispersion model including bubble attachment, detachment, and straining terms was applied to the obtained breakthrough curves for each experiment, showing good fitness against the measured data. Further investigations will be conducted to understand bubble characteristics including bubble size and zeta potential on MNB transport in porous media. Relations between in model parameters in the transport model and physical and chemical properties in porous media and MNBs will be discussed.

Hydrodynamics and propulsion mechanism of self-propelled catalytic micromotors: model and experiment.

PubMed

Li, Longqiu; Wang, Jiyuan; Li, Tianlong; Song, Wenping; Zhang, Guangyu

2014-10-14

The hydrodynamic behavior and propulsion mechanism of self-propelled micromotors are studied theoretically and experimentally. A hydrodynamic model to describe bubble growth and detachment is proposed to investigate the mechanism of a self-propelled conical tubular catalytic micromotor considering bubble geometric asymmetry and buoyancy force. The growth force caused by the growth of the bubble surface against the fluid is the driving force for micromotor motion. Also, the buoyancy force plays a primary role in bubble detachment. The effect of geometrical parameters on the micromotor velocity and drag force is presented. The bubble radius ratio is investigated for different micromotor radii to determine its hydrodynamic behavior during bubble ejection. The average micromotor velocity is found to be strongly dependent on the semi-cone angle, expelling frequency and bubble radius ratio. The semi-cone angle has a significant effect on the expelling frequency for conical tubular micromotors. The predicted results are compared to already existing experimental data for cylindrical micromotors (semi-cone angle δ = 0°) and conical micromotors. A good agreement is found between the theoretical calculation and experimental results. This model provides a profound explanation for the propulsion mechanism of a catalytic micromotor and can be used to optimize the micromotor design for its biomedical and environmental applications.

Effects of Intergranular Gas Bubbles on Thermal Conductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

K. Chockalingam; Paul C. Millett; M. R. Tonks

2012-11-01

Model microstructures obtained from phase-field simulations are used to study the effective heat transfer across bicrys- tals with stationary grain boundary bubble populations. We find that the grain boundary coverage, irrespective of the intergranular bubble radii, is the most relevant parameter to the thermal resistance, which we use to derive effec- tive Kapitza resistances that are dependent on the grain boundary coverage and Kaptiza resistance of the intact grain boundary. We propose a model to predict thermal conductivity as a function of porosity, grain-size, Kaptiza resistance of the intact grain boundary, and grain boundary bubble coverage.

Feasibility of self-structured current accessed bubble devices in spacecraft recording systems

NASA Technical Reports Server (NTRS)

Nelson, G. L.; Krahn, D. R.; Dean, R. H.; Paul, M. C.; Lo, D. S.; Amundsen, D. L.; Stein, G. A.

1985-01-01

The self-structured, current aperture approach to magnetic bubble memory is described. Key results include: (1) demonstration that self-structured bubbles (a lattice of strongly interacting bubbles) will slip by one another in a storage loop at spacings of 2.5 bubble diameters, (2) the ability of self-structured bubbles to move past international fabrication defects (missing apertures) in the propagation conductors (defeat tolerance), and (3) moving bubbles at mobility limited speeds. Milled barriers in the epitaxial garnet are discussed for containment of the bubble lattice. Experimental work on input/output tracks, storage loops, gates, generators, and magneto-resistive detectors for a prototype device are discussed. Potential final device architectures are described with modeling of power consumption, data rates, and access times. Appendices compare the self-structured bubble memory from the device and system perspectives with other non-volatile memory technologies.

The collapse of a cavitation bubble in a corner

NASA Astrophysics Data System (ADS)

Peters, Ivo; Tagawa, Yoshiyuki

2017-11-01

The collapse of cavitation bubbles is influenced by the surrounding geometry. A classic example is the collapse of a bubble near a solid wall, where a fast jet is created towards the wall. The addition of a second wall creates a non-axisymmetric flow field, which influences the displacement and jet formation during the collapse of a bubble. In this experimental study we generate mm-sized vapor bubbles using a focused pulsed laser, giving us full control over the position of the bubble. The corner geometry is formed by two glass slides. High-speed imaging reveals the directional motion of the bubble during the collapse. We find that the bubble displacement cannot be fully described by a simple superposition of the bubble dynamics of the two walls individually. Comparison of our experimental results to a model based on potential flow shows a good agreement for the direction of displacement.

Bubble nucleation in simple and molecular liquids via the largest spherical cavity method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gonzalez, Miguel A., E-mail: m.gonzalez12@imperial.ac.uk; Department of Chemistry, Imperial College London, London SW7 2AZ; Abascal, José L. F.

2015-04-21

In this work, we propose a methodology to compute bubble nucleation free energy barriers using trajectories generated via molecular dynamics simulations. We follow the bubble nucleation process by means of a local order parameter, defined by the volume of the largest spherical cavity (LSC) formed in the nucleating trajectories. This order parameter simplifies considerably the monitoring of the nucleation events, as compared with the previous approaches which require ad hoc criteria to classify the atoms and molecules as liquid or vapor. The combination of the LSC and the mean first passage time technique can then be used to obtain themore » free energy curves. Upon computation of the cavity distribution function the nucleation rate and free-energy barrier can then be computed. We test our method against recent computations of bubble nucleation in simple liquids and water at negative pressures. We obtain free-energy barriers in good agreement with the previous works. The LSC method provides a versatile and computationally efficient route to estimate the volume of critical bubbles the nucleation rate and to compute bubble nucleation free-energies in both simple and molecular liquids.« less

Numerical simulation and experimental validation of the dynamics of multiple bubble merger during pool boiling under microgravity conditions.

PubMed

Abarajith, H S; Dhir, V K; Warrier, G; Son, G

2004-11-01

Numerical simulation and experimental validation of the growth and departure of multiple merging bubbles and associated heat transfer on a horizontal heated surface during pool boiling under variable gravity conditions have been performed. A finite difference scheme is used to solve the equations governing mass, momentum, and energy in the vapor liquid phases. The vapor-liquid interface is captured by a level set method that is modified to include the influence of phase change at the liquid-vapor interface. Water is used as test liquid. The effects of reduced gravity condition and orientation of the bubbles on the bubble diameter, interfacial structure, bubble merger time, and departure time, as well as local heat fluxes, are studied. In the experiments, multiple vapor bubbles are produced on artificial cavities in the 2-10 micrometer diameter range, microfabricated on the polished silicon wafer with given spacing. The wafer was heated electrically from the back with miniature strain gage type heating elements in order to control the nucleation superheat. The experiments conducted in normal Earth gravity and in the low gravity environment of KC-135 aircraft are used to validate the numerical simulations.

Collective dissolution of microbubbles

NASA Astrophysics Data System (ADS)

Michelin, Sébastien; Guérin, Etienne; Lauga, Eric

2018-04-01

A microscopic bubble of soluble gas always dissolves in finite time in an undersaturated fluid. This diffusive process is driven by the difference between the gas concentration near the bubble, whose value is governed by the internal pressure through Henry's law, and the concentration in the far field. The presence of neighboring bubbles can significantly slow down this process by increasing the effective background concentration and reducing the diffusing flux of dissolved gas experienced by each bubble. We develop theoretical modeling of such diffusive shielding process in the case of small microbubbles whose internal pressure is dominated by Laplace pressure. We first use an exact semianalytical solution to capture the case of two bubbles and analyze in detail the shielding effect as a function of the distance between the bubbles and their size ratio. While we also solve exactly for the Stokes flow around the bubble, we show that hydrodynamic effects are mostly negligible except in the case of almost-touching bubbles. In order to tackle the case of multiple bubbles, we then derive and validate two analytical approximate yet generic frameworks, first using the method of reflections and then by proposing a self-consistent continuum description. Using both modeling frameworks, we examine the dissolution of regular one-, two-, and three-dimensional bubble lattices. Bubbles located at the edge of the lattices dissolve first, while innermost bubbles benefit from the diffusive shielding effect, leading to the inward propagation of a dissolution front within the lattice. We show that diffusive shielding leads to severalfold increases in the dissolution time, which grows logarithmically with the number of bubbles in one-dimensional lattices and algebraically in two and three dimensions, scaling respectively as its square root and 2 /3 power. We further illustrate the sensitivity of the dissolution patterns to initial fluctuations in bubble size or arrangement in the case of large and dense lattices, as well as nonintuitive oscillatory effects.

Effects of viscosity on endothelial cell damage under acoustic droplet vaporization

NASA Astrophysics Data System (ADS)

Seda, Robinson; Singh, Rahul; Li, David; Pitre, John; Putnam, Andrew; Fowlkes, J. Brian; Bull, Joseph

2014-11-01

Acoustic droplet vaporization (ADV) is a process by which stabilized superheated microdroplets are able to undergo phase transition with the aid of focused ultrasound. Gas bubbles resulting from ADV can provide local occlusion of the blood vessels supplying diseased tissue, such as tumors. The ADV process can also induce bioeffects that increase vessel permeability, which is beneficial for localized drug delivery. Previous in vitro studies have demonstrated that vaporization at the endothelial layer will affect cell attachment and viability. Several hypotheses have been proposed to elucidate the mechanism of damage including the generation of normal and shear stresses during bubble expansion. A single 3.5 MHz ultrasound pulse consisting of 8 cycles (~2.3 μs) and a 6 MPa peak rarefactional pressure was used to induce ADV on endothelial cells in media of different viscosities. Carboxylmethyl cellulose was added to the cell media to increase the viscosity up to 300 cP to and aid in the reduction of stresses during bubble expansion. The likelihood of cell damage was decreased when compared to our control (~1 cP), but it was still present in some cases indicating that the mechanism of damage does not depend entirely on viscous stresses associated with bubble expansion. This work was supported by NIH Grant R01EB006476.

Bubble dynamics in a compressible liquid in contact with a rigid boundary

PubMed Central

Wang, Qianxi; Liu, Wenke; Zhang, A. M.; Sui, Yi

2015-01-01

A bubble initiated near a rigid boundary may be almost in contact with the boundary because of its expansion and migration to the boundary, where a thin layer of water forms between the bubble and the boundary thereafter. This phenomenon is modelled using the weakly compressible theory coupled with the boundary integral method. The wall effects are modelled using the imaging method. The numerical instabilities caused by the near contact of the bubble surface with the boundary are handled by removing a thin layer of water between them and joining the bubble surface with its image to the boundary. Our computations correlate well with experiments for both the first and second cycles of oscillation. The time history of the energy of a bubble system follows a step function, reducing rapidly and significantly because of emission of shock waves at inception of a bubble and at the end of collapse but remaining approximately constant for the rest of the time. The bubble starts being in near contact with the boundary during the first cycle of oscillation when the dimensionless stand-off distance γ = s/Rm < 1, where s is the distance of the initial bubble centre from the boundary and Rm is the maximum bubble radius. This leads to (i) the direct impact of a high-speed liquid jet on the boundary once it penetrates through the bubble, (ii) the direct contact of the bubble at high temperature and high pressure with the boundary, and (iii) the direct impingement of shock waves on the boundary once emitted. These phenomena have clear potential to damage the boundary, which are believed to be part of the mechanisms of cavitation damage. PMID:26442148

The physiological kinetics of nitrogen and the prevention of decompression sickness.

PubMed

Doolette, D J; Mitchell, S J

2001-01-01

Decompression sickness (DCS) is a potentially crippling disease caused by intracorporeal bubble formation during or after decompression from a compressed gas underwater dive. Bubbles most commonly evolve from dissolved inert gas accumulated during the exposure to increased ambient pressure. Most diving is performed breathing air, and the inert gas of interest is nitrogen. Divers use algorithms based on nitrogen kinetic models to plan the duration and degree of exposure to increased ambient pressure and to control their ascent rate. However, even correct execution of dives planned using such algorithms often results in bubble formation and may result in DCS. This reflects the importance of idiosyncratic host factors that are difficult to model, and deficiencies in current nitrogen kinetic models. Models describing the exchange of nitrogen between tissues and blood may be based on distributed capillary units or lumped compartments, either of which may be perfusion- or diffusion-limited. However, such simplistic models are usually poor predictors of experimental nitrogen kinetics at the organ or tissue level, probably because they fail to account for factors such as heterogeneity in both tissue composition and blood perfusion and non-capillary exchange mechanisms. The modelling of safe decompression procedures is further complicated by incomplete understanding of the processes that determine bubble formation. Moreover, any formation of bubbles during decompression alters subsequent nitrogen kinetics. Although these factors mandate complex resolutions to account for the interaction between dissolved nitrogen kinetics and bubble formation and growth, most decompression schedules are based on relatively simple perfusion-limited lumped compartment models of blood: tissue nitrogen exchange. Not surprisingly, all models inevitably require empirical adjustment based on outcomes in the field. Improvements in the predictive power of decompression calculations are being achieved using probabilistic bubble models, but divers will always be subject to the possibility of developing DCS despite adherence to prescribed limits.

Sharp Interface Tracking in Rotating Microflows of Solvent Extraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glimm, James; Almeida, Valmor de; Jiao, Xiangmin

2013-01-08

The objective of this project is to develop a specialized sharp interface tracking simulation capability for predicting interaction of micron-sized drops and bubbles in rotating flows relevant to optimized design of contactor devices used in solvent extraction processes of spent nuclear fuel reprocessing. The primary outcomes of this project include the capability to resolve drops and bubbles micro-hydrodynamics in solvent extraction contactors, determining from first principles continuum fluid mechanics how micro-drops and bubbles interact with each other and the surrounding shearing fluid for realistic flows. In the near term, this effort will play a central role in providing parameters andmore » insight into the flow dynamics of models that average over coarser scales, say at the millimeter unit length. In the longer term, it will prove to be the platform to conduct full-device, detailed simulations as parallel computing power reaches the exaflop level. The team will develop an accurate simulation tool for flows containing interacting droplets and bubbles with sharp interfaces under conditions that mimic those found in realistic contactor operations. The main objective is to create an off-line simulation capability to model drop and bubble interactions in a domain representative of the averaged length scale. The technical approach is to combine robust interface tracking software, subgrid modeling, validation quality experiments, powerful computational hardware, and a team with simulation modeling, physical modeling and technology integration experience. Simulations will then fully resolve the microflow of drops and bubbles at the microsecond time scale. This approach is computationally intensive but very accurate in treating important coupled physical phenomena in the vicinity of interfaces. The method makes it possible to resolve spatial scales smaller than the typical distance between bubbles and to model some non-equilibrium thermodynamic features such as finite critical tension in cavitating liquids« less

Modelling the Composition of Outgassing Bubbles at Basaltic Open Vent Volcanoes

NASA Astrophysics Data System (ADS)

Edmonds, M.; Clements, N.; Houghton, B. F.; Oppenheimer, C.; Jones, R. L.; Burton, M. R.

2015-12-01

Basaltic open vent volcanoes exhibit a wide range in eruption styles, from passive outgassing to Strombolian and Hawaiian explosive activity. Transitions between these styles are linked to contrasting two-phase (melt and gas) flow regimes in the conduit system. A wealth of data now exists characterising the fluxes and compositions of gases emitted from these volcanoes, alongside detailed observations of patterns of outgassing at the magma free surfaces. Complex variations in gas composition are apparent from high temporal resolution measurement techniques such as open path spectroscopy. This variability with time is likely a function of individual bubbles' histories of growth during ascent, with variable degrees of kinetic inhibition. Our previous studies at Kilauea and Stromboli have, for example, linked CO2-rich gases with the bursting of bubbles that last equilibrated at some depth beneath the surface. However, very few studies have attempted to reconcile such observations with quantitative models of diffusion-limited bubble growth in magmas prior to eruption. We present here an analytical model that simulates the growth of populations of bubbles by addition of volatile mass during decompression, with growth limited by diffusion. The model simulates a range of behaviors between the end members of separated two-phase flow and homogeneous bubbly flow in the conduit, tied to thermodynamic models of solubility and partitioning of volatile species (carbon, water, sulfur). We explore the effects of the form of bubble populations at depth, melt viscosity, total volatile content, magma decompression rate and other intrinsic parameters on expected gas compositions at the surface and consider implications for transitions between eruption styles. We compare the the model to data suites from Stromboli and Kilauea.

Turbulent water flow in a channel at Reτ = 400 laden with 0.25 mm diameter air-bubbles clustered near the wall

NASA Astrophysics Data System (ADS)

Lakehal, D.; Métrailler, D.; Reboux, S.

2017-06-01

This paper presents Direct Numerical Simulation (DNS) results of a turbulent water flow in a channel at Reτ = 400 laden with 0.25 mm diameter air bubbles clustered near the wall (maximum void fraction of α = 8% at y+ ˜ 20). The bubbles were fully resolved using the level set approach built within the CFD/CMFD code TransAT. The fluid properties (air and water) were kept real, including density, viscosity, and surface tension coefficient. The aim of this work is to understand the effects of the bubbles on near-wall turbulence, paving the way towards convective wall-boiling flow studies. The interactions between the gas bubbles and the water stream were studied through an in-depth analysis of the turbulence statistics. The near-wall flow is overall affected by the bubbles, which act like roughness elements during the early phase, prior to their departure from the wall. The average profiles are clearly altered by the bubbles dynamics near the wall, which somewhat contrasts with the findings from similar studies [J. Lu and G. Tryggvason, "Dynamics of nearly spherical bubbles in a turbulent channel upflow," J. Fluid Mech. 732, 166 (2013)], most probably because the bubbles were introduced uniformly in the flow and not concentrated at the wall. The shape of the bubbles measured as the apparent to initial diameter ratio is found to change by a factor of at least two, in particular at the later stages when the bubbles burst out from the boundary layer. The clustering of the bubbles seems to be primarily localized in the zone populated by high-speed streaks and independent of their size. More importantly, the bubbly flow seems to differ from the single-phase flow in terms of turbulent stress distribution and energy exchange, in which all the stress components seem to be increased in the region very close to the wall, by up to 40%. The decay in the energy spectra near the wall was found to be significantly slower for the bubbly flow than for a single-phase flow, which confirms that the bubbles increase the energy at smaller scales. The coherent structures in the boundary layer are broken by the bubbles, which disrupts the formation of long structures, reducing the streamwise integral length scale.

Experimental Study of the Morphology and Dynamics of Gas-Laden Layers Under the Anodes in an Air-Water Model of Aluminum Reduction Cells

NASA Astrophysics Data System (ADS)

Vékony, Klára; Kiss, László I.

2012-10-01

The bubble layer formed under an anode and the bubble-induced flow play a significant role in the aluminum electrolysis process. The bubbles covering the anode bottom reduce the efficient surface that can carry current. In our experiments, we filmed and studied the bubble layer under the anode in a real-size air-water electrolysis cell model. Three different flow regimes were found depending on the gas generation rate. The covering factor was found to be proportional to the gas generation rate and inversely proportional to the angle of inclination. A correlation between the average height of the entire bubble layer and the position under the anode was determined. From this correlation and the measured contact sizes, the volume of the accumulated gas was calculated. The sweeping effect of large bubbles was observed. Moreover, the small bubbles under the inner edge of the anode were observed to move backward as a result of the escape of huge gas pockets, which means large momentum transport occurs in the bath.

Dissolution of methane bubbles with hydrate armoring in deep ocean conditions

NASA Astrophysics Data System (ADS)

Kovalchuk, Margarita; Socolofsky, Scott

2017-11-01

The deep ocean is a storehouse of natural gas. Methane bubble moving upwards from marine sediments may become trapped in gas hydrates. It is uncertain precisely how hydrate armoring affects dissolution, or mass transfer from the bubble to the surrounding water column. The Texas A&M Oilspill Calculator was used to simulate a series of gas bubble dissolution experiments conducted in the United States Department of Energy National Energy Technology Laboratory High Pressure Water Tunnel. Several variations of the mass transfer coefficient were calculated based on gas or hydrate phase solubility and clean or dirty bubble correlations. Results suggest the mass transfer coefficient may be most closely modeled with gas phase solubility and dirty bubble correlation equations. Further investigation of hydrate bubble dissolution behavior will refine current numeric models which aid in understanding gas flux to the atmosphere and plumes such as oil spills. Research funded in part by the Texas A&M University 2017 Undergraduate Summer Research Grant and a Grant from the Methane Gas Hydrates Program of the US DOE National Energy Technology Laboratory.

Formation and evolution of bubbly screens in confined oscillating bubbly liquids.

PubMed

Shklyaev, Sergey; Straube, Arthur V

2010-01-01

We consider the dynamics of dilute monodisperse bubbly liquid confined by two plane solid walls and subject to small-amplitude high-frequency oscillations normal to the walls. The initial state corresponds to the uniform distribution of bubbles and motionless liquid. The period of external driving is assumed much smaller than typical relaxation times for a single bubble but larger than the period of volume eigenoscillations. The time-averaged description accounting for the two-way coupling between the liquid and the bubbles is applied. We show that the model predicts accumulation of bubbles in thin sheets parallel to the walls. These singular structures, which are formally characterized by infinitely thin width and infinitely high concentration, are referred to as bubbly screens. The formation of a bubbly screen is described analytically in terms of a self-similar solution, which is in agreement with numerical simulations. We study the evolution of bubbly screens and detect a one-dimensional stationary state, which is shown to be unconditionally unstable.

Formation and evolution of bubbly screens in confined oscillating bubbly liquids

NASA Astrophysics Data System (ADS)

Shklyaev, Sergey; Straube, Arthur V.

2010-01-01

We consider the dynamics of dilute monodisperse bubbly liquid confined by two plane solid walls and subject to small-amplitude high-frequency oscillations normal to the walls. The initial state corresponds to the uniform distribution of bubbles and motionless liquid. The period of external driving is assumed much smaller than typical relaxation times for a single bubble but larger than the period of volume eigenoscillations. The time-averaged description accounting for the two-way coupling between the liquid and the bubbles is applied. We show that the model predicts accumulation of bubbles in thin sheets parallel to the walls. These singular structures, which are formally characterized by infinitely thin width and infinitely high concentration, are referred to as bubbly screens. The formation of a bubbly screen is described analytically in terms of a self-similar solution, which is in agreement with numerical simulations. We study the evolution of bubbly screens and detect a one-dimensional stationary state, which is shown to be unconditionally unstable.

Rational Speculative Bubble Size in Gold, Hang Seng, S&P 500 and Nikkei 225 Index During Year 2008 to 2016

NASA Astrophysics Data System (ADS)

Borhan, Nurharyanti; Halim, Nurfadhlina Abdul; Amir, W. Ahmad Wan Muhammad

2017-09-01

A rational speculative bubble is a surge in asset prices that exceed its intrinsic value. Rational speculative bubbles are among the ascription which may lead to the collapse of an economic system. Rational speculative bubble cannot be created but it comes into existence when assets started to be traded. Financial rational speculative bubble and burst have negative effect on the economy and markets. Financial rational speculative bubbles are difficult to detect. This study aims to shows the size of rational speculative bubble in four markets, which are gold, Hang Seng, S&P500 and Nikkei 225 during year 2008 to 2016. In this study, generalized Johansen-Ledoit-Sornette model are used to find the size of the rational speculative bubble. Bubble detection is important for both sides of macro-economic decision makers and to the trader. Especially for a trading system that requires detailed knowledge about the time and the stage of the bubble burst.

Nanoscale Dynamics of Joule heating and Bubble Nucleation in a Solid-State Nanopore

PubMed Central

Levine, Edlyn V.; Burns, Michael M.; Golovchenko, Jene A.

2016-01-01

We present a mathematical model for Joule heating of an electrolytic solution in a nanopore. The model couples the electrical and thermal dynamics responsible for rapid and extreme superheating of the electrolyte within the nanopore. The model is implemented numerically with a finite element calculation, yielding a time and spatially resolved temperature distribution in the nanopore region. Temperatures near the thermodynamic limit of superheat are predicted to be attained just before the explosive nucleation of a vapor bubble is observed experimentally. Knowledge of this temperature distribution enables the evaluation of related phenomena including bubble nucleation kinetics, relaxation oscillation, and bubble dynamics. PACS numbers 47.55.dp, 47.55.db, 85.35.-p, 05.70Fh PMID:26871171

Collective bubble oscillations as a component of surf infrasound.

PubMed

Park, Joseph; Garcés, Milton; Fee, David; Pawlak, Geno

2008-05-01

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.

Methane rising from the Deep: Hydrates, Bubbles, Oil Spills, and Global Warming

NASA Astrophysics Data System (ADS)

Leifer, I.; Rehder, G. J.; Solomon, E. A.; Kastner, M.; Asper, V. L.; Joye, S. B.

2011-12-01

Elevated methane concentrations in near-surface waters and the atmosphere have been reported for seepage from depths of nearly 1 km at the Gulf of Mexico hydrate observatory (MC118), suggesting that for some methane sources, deepsea methane is not trapped and can contribute to atmospheric greenhouse gas budgets. Ebullition is key with important sensitivity to the formation of hydrate skins and oil coatings, high-pressure solubility, bubble size and bubble plume processes. Bubble ROV tracking studies showed survival to near thermocline depths. Studies with a numerical bubble propagation model demonstrated that consideration of structure I hydrate skins transported most methane only to mid-water column depths. Instead, consideration of structure II hydrates, which are stable to far shallower depths and appropriate for natural gas mixtures, allows bubbles to survive to far shallower depths. Moreover, model predictions of vertical methane and alkane profiles and bubble size evolution were in better agreement with observations after consideration of structure II hydrate properties as well as an improved implementation of plume properties, such as currents. These results demonstrate the importance of correctly incorporating bubble hydrate processes in efforts to predict the impact of deepsea seepage as well as to understand the fate of bubble-transported oil and methane from deepsea pipeline leaks and well blowouts. Application to the DWH spill demonstrated the importance of deepsea processes to the fate of spilled subsurface oil. Because several of these parameters vary temporally (bubble flux, currents, temperature), sensitivity studies indicate the importance of real-time monitoring data.

Experimental and numerical study on bubble-sphere interaction near a rigid wall

NASA Astrophysics Data System (ADS)

Li, S.; Zhang, A. M.; Han, R.; Liu, Y. Q.

2017-09-01

This study is concerned with the interaction between a violently oscillating bubble and a movable sphere with comparable size near a rigid wall, which is an essential physical phenomenon in many applications such as cavitation, underwater explosion, ultrasonic cleaning, and biomedical treatment. Experiments are performed in a cubic water tank, and the underwater electric discharge technique (580 V DC) is employed to generate a bubble that is initiated between a rigid wall and a sphere in an axisymmetric configuration. The bubble-sphere interactions are captured using a high-speed camera operating at 52 000 frames/s. A classification of the bubble-sphere interaction is proposed, i.e., "weak," "intermediate," and "strong" interactions, identified with three distinct bubble shapes at the maximum volume moment. In the numerical simulations, the boundary integral method and the auxiliary function method are combined to establish a full coupling model that decouples the mutual dependence between the force and the sphere motion. The main features of bubble dynamics in different experiments are well reproduced by our numerical model. Meanwhile, the pressure and velocity fields are also provided for clarifying the associated mechanisms. The effects of two dimensionless standoff parameters, namely, γs (defined as ds/Rm, where ds is the minimum distance between the initial bubble center and the sphere surface and Rm is the maximum bubble radius) and γw (defined as dw/Rm, where dw is the distance between the initial bubble center and the rigid wall), are also discussed.

Numerical Modeling of the Photothermal Processing for Bubble Forming around Nanowire in a Liquid

PubMed Central

Chaari, Anis; Giraud-Moreau, Laurence

2014-01-01

An accurate computation of the temperature is an important factor in determining the shape of a bubble around a nanowire immersed in a liquid. The study of the physical phenomenon consists in solving a photothermic coupled problem between light and nanowire. The numerical multiphysic model is used to study the variations of the temperature and the shape of the created bubble by illumination of the nanowire. The optimization process, including an adaptive remeshing scheme, is used to solve the problem through a finite element method. The study of the shape evolution of the bubble is made taking into account the physical and geometrical parameters of the nanowire. The relation between the sizes and shapes of the bubble and nanowire is deduced. PMID:24795538

A model for large amplitude oscillations of coated bubbles accounting for buckling and rupture

NASA Astrophysics Data System (ADS)

Marmottant, Philippe; van der Meer, Sander; Emmer, Marcia; Versluis, Michel; de Jong, Nico; Hilgenfeldt, Sascha; Lohse, Detlef

2005-12-01

We present a model applicable to ultrasound contrast agent bubbles that takes into account the physical properties of a lipid monolayer coating on a gas microbubble. Three parameters describe the properties of the shell: a buckling radius, the compressibility of the shell, and a break-up shell tension. The model presents an original non-linear behavior at large amplitude oscillations, termed compression-only, induced by the buckling of the lipid monolayer. This prediction is validated by experimental recordings with the high-speed camera Brandaris 128, operated at several millions of frames per second. The effect of aging, or the resultant of repeated acoustic pressure pulses on bubbles, is predicted by the model. It corrects a flaw in the shell elasticity term previously used in the dynamical equation for coated bubbles. The break-up is modeled by a critical shell tension above which gas is directly exposed to water.

Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishna, R.; Baten, J.M. van

About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions.more » The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.« less

In silico investigation of blast-induced intracranial fluid cavitation as it potentially leads to traumatic brain injury

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haniff, S.; Taylor, P. A.

In this paper, we conducted computational macroscale simulations predicting blast-induced intracranial fluid cavitation possibly leading to brain injury. To further understanding of this problem, we developed microscale models investigating the effects of blast-induced cavitation bubble collapse within white matter axonal fiber bundles of the brain. We model fiber tracks of myelinated axons whose diameters are statistically representative of white matter. Nodes of Ranvier are modeled as unmyelinated sections of axon. Extracellular matrix envelops the axon fiber bundle, and gray matter is placed adjacent to the bundle. Cavitation bubbles are initially placed assuming an intracranial wave has already produced them. Pressuremore » pulses, of varied strengths, are applied to the upper boundary of the gray matter and propagate through the model, inducing bubble collapse. Simulations, conducted using the shock wave physics code CTH, predict an increase in pressure and von Mises stress in axons downstream of the bubbles after collapse. This appears to be the result of hydrodynamic jetting produced during bubble collapse. Interestingly, results predict axon cores suffer significantly lower shear stresses from proximal bubble collapse than does their myelin sheathing. Finally, simulations also predict damage to myelin sheathing, which, if true, degrades axonal electrical transmissibility and general health of the white matter structures in the brain.« less

In silico investigation of blast-induced intracranial fluid cavitation as it potentially leads to traumatic brain injury

DOE PAGES

Haniff, S.; Taylor, P. A.

2017-10-17

In this paper, we conducted computational macroscale simulations predicting blast-induced intracranial fluid cavitation possibly leading to brain injury. To further understanding of this problem, we developed microscale models investigating the effects of blast-induced cavitation bubble collapse within white matter axonal fiber bundles of the brain. We model fiber tracks of myelinated axons whose diameters are statistically representative of white matter. Nodes of Ranvier are modeled as unmyelinated sections of axon. Extracellular matrix envelops the axon fiber bundle, and gray matter is placed adjacent to the bundle. Cavitation bubbles are initially placed assuming an intracranial wave has already produced them. Pressuremore » pulses, of varied strengths, are applied to the upper boundary of the gray matter and propagate through the model, inducing bubble collapse. Simulations, conducted using the shock wave physics code CTH, predict an increase in pressure and von Mises stress in axons downstream of the bubbles after collapse. This appears to be the result of hydrodynamic jetting produced during bubble collapse. Interestingly, results predict axon cores suffer significantly lower shear stresses from proximal bubble collapse than does their myelin sheathing. Finally, simulations also predict damage to myelin sheathing, which, if true, degrades axonal electrical transmissibility and general health of the white matter structures in the brain.« less

Numerical modeling of bubble dynamics in viscoelastic media with relaxation

NASA Astrophysics Data System (ADS)

Warnez, M. T.; Johnsen, E.

2015-06-01

Cavitation occurs in a variety of non-Newtonian fluids and viscoelastic materials. The large-amplitude volumetric oscillations of cavitation bubbles give rise to high temperatures and pressures at collapse, as well as induce large and rapid deformation of the surroundings. In this work, we develop a comprehensive numerical framework for spherical bubble dynamics in isotropic media obeying a wide range of viscoelastic constitutive relationships. Our numerical approach solves the compressible Keller-Miksis equation with full thermal effects (inside and outside the bubble) when coupled to a highly generalized constitutive relationship (which allows Newtonian, Kelvin-Voigt, Zener, linear Maxwell, upper-convected Maxwell, Jeffreys, Oldroyd-B, Giesekus, and Phan-Thien-Tanner models). For the latter two models, partial differential equations (PDEs) must be solved in the surrounding medium; for the remaining models, we show that the PDEs can be reduced to ordinary differential equations. To solve the general constitutive PDEs, we present a Chebyshev spectral collocation method, which is robust even for violent collapse. Combining this numerical approach with theoretical analysis, we simulate bubble dynamics in various viscoelastic media to determine the impact of relaxation time, a constitutive parameter, on the associated physics. Relaxation time is found to increase bubble growth and permit rebounds driven purely by residual stresses in the surroundings. Different regimes of oscillations occur depending on the relaxation time.

In silico investigation of blast-induced intracranial fluid cavitation as it potentially leads to traumatic brain injury

NASA Astrophysics Data System (ADS)

Haniff, S.; Taylor, P. A.

2017-11-01

We conducted computational macroscale simulations predicting blast-induced intracranial fluid cavitation possibly leading to brain injury. To further understanding of this problem, we developed microscale models investigating the effects of blast-induced cavitation bubble collapse within white matter axonal fiber bundles of the brain. We model fiber tracks of myelinated axons whose diameters are statistically representative of white matter. Nodes of Ranvier are modeled as unmyelinated sections of axon. Extracellular matrix envelops the axon fiber bundle, and gray matter is placed adjacent to the bundle. Cavitation bubbles are initially placed assuming an intracranial wave has already produced them. Pressure pulses, of varied strengths, are applied to the upper boundary of the gray matter and propagate through the model, inducing bubble collapse. Simulations, conducted using the shock wave physics code CTH, predict an increase in pressure and von Mises stress in axons downstream of the bubbles after collapse. This appears to be the result of hydrodynamic jetting produced during bubble collapse. Interestingly, results predict axon cores suffer significantly lower shear stresses from proximal bubble collapse than does their myelin sheathing. Simulations also predict damage to myelin sheathing, which, if true, degrades axonal electrical transmissibility and general health of the white matter structures in the brain.

Study of CO2 bubble dynamics in seawater from QICS field Experiment

NASA Astrophysics Data System (ADS)

Chen, B.; Dewar, M.; Sellami, N.; Stahl, H.; Blackford, J.

2011-12-01

One of the concerns of employing CCS at engineering scale is the risk of leakage of storage CO2 on the environment and especially on the marine life. QICS, a scientific research project was launched with an aim to study the effects of a potential leak from a CCS system on the UK marine environment [1]. The project involves the injection of CO2 from a shore-based lab into shallow marine sediments. One of the main objectives of the project is to generate experimental data to be compared with the developed physical models. The results of the models are vital for the biogeochemical and ecological models in order to predict the impact of a CO2 leak in a variety of situations. For the evaluation of the fate of the CO2 bubbles into the surrounding seawater, the physical model requires two key parameters to be used as input which are: (i) a correlation of the drag coefficient as function of the CO2 bubble Reynolds number and (ii) the CO2 bubble size distribution. By precisely measuring the CO2 bubble size and rising speed, these two parameters can be established. For this purpose, the dynamical characteristics of the rising CO2 bubbles in Scottish seawater were investigated experimentally within the QICS project. Observations of the CO2 bubbles plume rising freely in the in seawater column were captured by video survey using a ruler positioned at the leakage pockmark as dimension reference. This observation made it possible, for the first time, to discuss the dynamics of the CO2 bubbles released in seawater. [1] QICS, QICS: Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage. (Accessed 15.07.13), http://www.bgs.ac.uk/qics/home.html

Study of CO2 bubble dynamics in seawater from QICS field Experiment

NASA Astrophysics Data System (ADS)

Chen, B.; Dewar, M.; Sellami, N.; Stahl, H.; Blackford, J.

2013-12-01

One of the concerns of employing CCS at engineering scale is the risk of leakage of storage CO2 on the environment and especially on the marine life. QICS, a scientific research project was launched with an aim to study the effects of a potential leak from a CCS system on the UK marine environment [1]. The project involves the injection of CO2 from a shore-based lab into shallow marine sediments. One of the main objectives of the project is to generate experimental data to be compared with the developed physical models. The results of the models are vital for the biogeochemical and ecological models in order to predict the impact of a CO2 leak in a variety of situations. For the evaluation of the fate of the CO2 bubbles into the surrounding seawater, the physical model requires two key parameters to be used as input which are: (i) a correlation of the drag coefficient as function of the CO2 bubble Reynolds number and (ii) the CO2 bubble size distribution. By precisely measuring the CO2 bubble size and rising speed, these two parameters can be established. For this purpose, the dynamical characteristics of the rising CO2 bubbles in Scottish seawater were investigated experimentally within the QICS project. Observations of the CO2 bubbles plume rising freely in the in seawater column were captured by video survey using a ruler positioned at the leakage pockmark as dimension reference. This observation made it possible, for the first time, to discuss the dynamics of the CO2 bubbles released in seawater. [1] QICS, QICS: Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage. (Accessed 15.07.13), http://www.bgs.ac.uk/qics/home.html

DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

X. Wang; X. Sun; H. Zhao

In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do notmore » exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in which flow regime transition occurs.« less

Critical evaluation and modeling of algal harvesting using dissolved air flotation. DAF Algal Harvesting Modeling

DOE PAGES

Zhang, Xuezhi; Hewson, John C.; Amendola, Pasquale; ...

2014-07-14

In our study, Chlorella zofingiensis harvesting by dissolved air flotation (DAF) was critically evaluated with regard to algal concentration, culture conditions, type and dosage of coagulants, and recycle ratio. Harvesting efficiency increased with coagulant dosage and leveled off at 81%, 86%, 91%, and 87% when chitosan, Al 3+, Fe 3+, and cetyl trimethylammonium bromide (CTAB) were used at dosages of 70, 180, 250, and 500 mg g -1, respectively. The DAF efficiency-coagulant dosage relationship changed with algal culture conditions. In evaluating the influence of the initial algal concentration and recycle ratio revealed that, under conditions typical for algal harvesting, wemore » found that it is possible that the number of bubbles is insufficient. A DAF algal harvesting model was developed to explain this observation by introducing mass-based floc size distributions and a bubble limitation into the white water blanket model. Moreover, the model revealed the importance of coagulation to increase floc-bubble collision and attachment, and the preferential interaction of bubbles with larger flocs, which limited the availability of bubbles to the smaller sized flocs. The harvesting efficiencies predicted by the model agree reasonably with experimental data obtained at different Al 3+ dosages, algal concentrations, and recycle ratios. Based on this modeling, critical parameters for efficient algal harvesting were identified.« less

Critical evaluation and modeling of algal harvesting using dissolved air flotation. DAF Algal Harvesting Modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xuezhi; Hewson, John C.; Amendola, Pasquale

In our study, Chlorella zofingiensis harvesting by dissolved air flotation (DAF) was critically evaluated with regard to algal concentration, culture conditions, type and dosage of coagulants, and recycle ratio. Harvesting efficiency increased with coagulant dosage and leveled off at 81%, 86%, 91%, and 87% when chitosan, Al 3+, Fe 3+, and cetyl trimethylammonium bromide (CTAB) were used at dosages of 70, 180, 250, and 500 mg g -1, respectively. The DAF efficiency-coagulant dosage relationship changed with algal culture conditions. In evaluating the influence of the initial algal concentration and recycle ratio revealed that, under conditions typical for algal harvesting, wemore » found that it is possible that the number of bubbles is insufficient. A DAF algal harvesting model was developed to explain this observation by introducing mass-based floc size distributions and a bubble limitation into the white water blanket model. Moreover, the model revealed the importance of coagulation to increase floc-bubble collision and attachment, and the preferential interaction of bubbles with larger flocs, which limited the availability of bubbles to the smaller sized flocs. The harvesting efficiencies predicted by the model agree reasonably with experimental data obtained at different Al 3+ dosages, algal concentrations, and recycle ratios. Based on this modeling, critical parameters for efficient algal harvesting were identified.« less

Dynamics of Ultrasound Contrast Agents and Nonlinear Acoustic Waves: Experiments, Modeling, and Theories

NASA Astrophysics Data System (ADS)

Xia, Lang

Bubbles occur in many natural and biological flows as well as in numerous industrial phenomena, such as pumps, propellers, turbines, and chemical processing plants. They have been widely studied in the past leading to a large body of literature. However, bubbles appearing in different situations differ significantly in their physical characteristics and behaviors. Recently, bubbles of diameter less than 10 micrometers have found applications in diagnostic ultrasound imaging. These microbubble-based ultrasound contrast agents (UCA) are intravenously administered in patients before ultrasound imaging. Due to the compressive gas core, they generate substantial ultrasound echoes leading to significant enhancement of image quality and contrast. Free bubbles of a micrometer diameter experience a large surface tension induced Laplace pressure leading to their quick dissolution in milliseconds. UCAs are stabilized by coating them with a shell of lipids, polymers, proteins, and other surface-active materials and changing the gas content from air to a high molecular weight low solubility gas such as perfluorocarbon. The past literature of bubble dynamics are mostly restricted to free bubbles. The stabilizing shell of UCAs, however, critically affects their dynamics. In this thesis, we performed acoustic characterization of several UCAs coated with polymer and lipids. We experimentally measured their acoustic attenuation and scattering, of which the data were used in mathematical models to determine shell properties and nonlinear dynamics. Several different interfacial rheological models were employed. Experimental acoustic characterization was also extended to a novel type of nanoparticle suspension--polymersomes, vesicles encapsulated by amphiphilic polymers. The later part of the thesis is devoted to modeling the effects of the presence of coated microbubbles to the overall effective bulk properties of bubbly liquids. Introduction of microbubbles in the liquids does not only modify the bulk properties of the medium (bubbly liquids) but also significantly changes the natures of the propagating waves (e.g., the sound velocity in bubble suspension was found to be as low as 20 m/s). We investigate the nonlinear nature of the acoustic wave in bubbly liquids. Specifically, we theoretically show that microbubbles could change the nonlinearity of the medium, characterized by quantity B/A.

Two-Dimensional Numerical Simulations of Ultrasound in Liquids with Gas Bubble Agglomerates: Examples of Bubbly-Liquid-Type Acoustic Metamaterials (BLAMMs)

PubMed Central

Vanhille, Christian

2017-01-01

This work deals with a theoretical analysis about the possibility of using linear and nonlinear acoustic properties to modify ultrasound by adding gas bubbles of determined sizes in a liquid. We use a two-dimensional numerical model to evaluate the effect that one and several monodisperse bubble populations confined in restricted areas of a liquid have on ultrasound by calculating their nonlinear interaction. The filtering of an input ultrasonic pulse performed by a net of bubbly-liquid cells is analyzed. The generation of a low-frequency component from a single cell impinged by a two-frequency harmonic wave is also studied. These effects rely on the particular dispersive character of attenuation and nonlinearity of such bubbly fluids, which can be extremely high near bubble resonance. They allow us to observe how gas bubbles can change acoustic signals. Variations of the bubbly medium parameters induce alterations of the effects undergone by ultrasound. Results suggest that acoustic signals can be manipulated by bubbles. This capacity to achieve the modification and control of sound with oscillating gas bubbles introduces the concept of bubbly-liquid-based acoustic metamaterials (BLAMMs). PMID:28106748

Repeated bubble breakup and coalescence in perturbed Hele-Shaw channels

NASA Astrophysics Data System (ADS)

Thompson, Alice; Franco-Gomez, Andres; Hazel, Andrew; Juel, Anne

2017-11-01

The introduction of an axially-uniform, centred constriction in a Hele-Shaw channel leads to multiple propagation modes for both air fingers and bubbles, including symmetric and asymmetric steadily propagating modes along with oscillations. These multiple modes correspond to a non-trivial bifurcation structure, and relate to the plethora of steadily propagating bubbles and fingers which exist in the Saffman-Taylor system. In both experiments and depth-averaged computations, a very small centred occlusion can be enough to trigger bubble breakup, with a single large centred bubble splitting into two smaller bubbles which propagate along each side of the channel. We present numerical simulations for the depth-averaged model, implementing geometric criteria for pinchoff and coalescence in order to track the bubble before and beyond breakup. We find that the two-bubble state is itself unstable, with finger competition causing one bubble to move ahead; the trailing bubble then moves across the channel to merge with the leading bubble. However, the story is not always so simple, enabling complicated cascades of splitting and merging bubbles. We compare the general dynamical behaviour, basins of attraction, and the details of merging and splitting, to experimental observations.

Two-Dimensional Numerical Simulations of Ultrasound in Liquids with Gas Bubble Agglomerates: Examples of Bubbly-Liquid-Type Acoustic Metamaterials (BLAMMs).

PubMed

Vanhille, Christian

2017-01-17

This work deals with a theoretical analysis about the possibility of using linear and nonlinear acoustic properties to modify ultrasound by adding gas bubbles of determined sizes in a liquid. We use a two-dimensional numerical model to evaluate the effect that one and several monodisperse bubble populations confined in restricted areas of a liquid have on ultrasound by calculating their nonlinear interaction. The filtering of an input ultrasonic pulse performed by a net of bubbly-liquid cells is analyzed. The generation of a low-frequency component from a single cell impinged by a two-frequency harmonic wave is also studied. These effects rely on the particular dispersive character of attenuation and nonlinearity of such bubbly fluids, which can be extremely high near bubble resonance. They allow us to observe how gas bubbles can change acoustic signals. Variations of the bubbly medium parameters induce alterations of the effects undergone by ultrasound. Results suggest that acoustic signals can be manipulated by bubbles. This capacity to achieve the modification and control of sound with oscillating gas bubbles introduces the concept of bubbly-liquid-based acoustic metamaterials (BLAMMs).

Informative frame detection from wireless capsule video endoscopic images

NASA Astrophysics Data System (ADS)

Bashar, Md. Khayrul; Mori, Kensaku; Suenaga, Yasuhito; Kitasaka, Takayuki; Mekada, Yoshito

2008-03-01

Wireless capsule endoscopy (WCE) is a new clinical technology permitting the visualization of the small bowel, the most difficult segment of the digestive tract. The major drawback of this technology is the high amount of time for video diagnosis. In this study, we propose a method for informative frame detection by isolating useless frames that are substantially covered by turbid fluids or their contamination with other materials, e.g., faecal, semi-processed or unabsorbed foods etc. Such materials and fluids present a wide range of colors, from brown to yellow, and/or bubble-like texture patterns. The detection scheme, therefore, consists of two stages: highly contaminated non-bubbled (HCN) frame detection and significantly bubbled (SB) frame detection. Local color moments in the Ohta color space are used to characterize HCN frames, which are isolated by the Support Vector Machine (SVM) classifier in Stage-1. The rest of the frames go to the Stage-2, where Laguerre gauss Circular Harmonic Functions (LG-CHFs) extract the characteristics of the bubble-structures in a multi-resolution framework. An automatic segmentation method is designed to extract the bubbled regions based on local absolute energies of the CHF responses, derived from the grayscale version of the original color image. Final detection of the informative frames is obtained by using threshold operation on the extracted regions. An experiment with 20,558 frames from the three videos shows the excellent average detection accuracy (96.75%) by the proposed method, when compared with the Gabor based- (74.29%) and discrete wavelet based features (62.21%).

Of drops and bubbles - The technology of space processing

NASA Technical Reports Server (NTRS)

Subramanian, R. Shankar

1984-01-01

It is possible to manipulate a large, molten mass of material, such as a glass, aboard an orbital platform using acoustic fields. Attention is presently given to the problem of bubble removal from such a melt; it is desirable to make small bubbles coalesce into larger ones through floating melt rotation, to create an artificial convective field in which the bubbles will move centripetally to the axis of rotation. Computer models of bubble migration have been developed in order to define the operational conditions required aboard such experiment platforms as the Space Shuttle Orbiter.

A stochastic differential equations approach for the description of helium bubble size distributions in irradiated metals

NASA Astrophysics Data System (ADS)

Seif, Dariush; Ghoniem, Nasr M.

2014-12-01

A rate theory model based on the theory of nonlinear stochastic differential equations (SDEs) is developed to estimate the time-dependent size distribution of helium bubbles in metals under irradiation. Using approaches derived from Itô's calculus, rate equations for the first five moments of the size distribution in helium-vacancy space are derived, accounting for the stochastic nature of the atomic processes involved. In the first iteration of the model, the distribution is represented as a bivariate Gaussian distribution. The spread of the distribution about the mean is obtained by white-noise terms in the second-order moments, driven by fluctuations in the general absorption and emission of point defects by bubbles, and fluctuations stemming from collision cascades. This statistical model for the reconstruction of the distribution by its moments is coupled to a previously developed reduced-set, mean-field, rate theory model. As an illustrative case study, the model is applied to a tungsten plasma facing component under irradiation. Our findings highlight the important role of stochastic atomic fluctuations on the evolution of helium-vacancy cluster size distributions. It is found that when the average bubble size is small (at low dpa levels), the relative spread of the distribution is large and average bubble pressures may be very large. As bubbles begin to grow in size, average bubble pressures decrease, and stochastic fluctuations have a lessened effect. The distribution becomes tighter as it evolves in time, corresponding to a more uniform bubble population. The model is formulated in a general way, capable of including point defect drift due to internal temperature and/or stress gradients. These arise during pulsed irradiation, and also during steady irradiation as a result of externally applied or internally generated non-homogeneous stress fields. Discussion is given into how the model can be extended to include full spatial resolution and how the implementation of a path-integral approach may proceed if the distribution is known experimentally to significantly stray from a Gaussian description.

Global distribution and surface activity of macromolecules in offline simulations of marine organic chemistry

DOE PAGES

Ogunro, Oluwaseun O.; Burrows, Susannah M.; Elliott, Scott; ...

2015-10-13

Here, organic macromolecules constitute high percentage components of remote sea spray. They enter the atmosphere through adsorption onto bubbles followed by bursting at the ocean surface, and go on to influence the chemistry of the fine mode aerosol. We present a global estimate of mixed-layer organic macromolecular distributions, driven by offline marine systems model output. The approach permits estimation of oceanic concentrations and bubble film surface coverages for several classes of organic compound. Mixed layer levels are computed from the output of a global ocean biogeochemistry model by relating the macromolecules to standard biogeochemical tracers. Steady state is assumed formore » labile forms, and for longer-lived components we rely on ratios to existing transported variables. Adsorption is then represented through conventional Langmuir isotherms, with equilibria deduced from laboratory analogs. Open water concentrations locally exceed one micromolar carbon for the total of protein, polysaccharide and refractory heteropolycondensate. The shorter-lived lipids remain confined to regions of strong biological activity. Results are evaluated against available measurements for all compound types, and agreement is generally quite reasonable. Global distributions are further estimated for both fractional coverage of bubble films at the air-water interface and the two-dimensional concentration excess. Overall, we show that macromolecular mapping provides a novel tool for the comprehension of oceanic surfactant distributions. Results may prove useful in planning field experiments and assessing the potential response of surface chemical behaviors to global change.« less

MR-based detection of individual histotripsy bubble clouds formed in tissues and phantoms.

PubMed

Allen, Steven P; Hernandez-Garcia, Luis; Cain, Charles A; Hall, Timothy L

2016-11-01

To demonstrate that MR sequences can detect individual histotripsy bubble clouds formed inside intact tissues. A line-scan and an EPI sequence were sensitized to histotripsy by inserting a bipolar gradient whose lobes bracketed the lifespan of a histotripsy bubble cloud. Using a 7 Tesla, small-bore scanner, these sequences monitored histotripsy clouds formed in an agar phantom and in vitro porcine liver and brain. The bipolar gradients were adjusted to apply phase with k-space frequencies of 10, 300 or 400 cm -1 . Acoustic pressure amplitude was also varied. Cavitation was simultaneously monitored using a passive cavitation detection system. Each image captured local signal loss specific to an individual bubble cloud. In the agar phantom, this signal loss appeared only when the transducer output exceeded the cavitation threshold pressure. In tissues, bubble clouds were immediately detected when the gradients created phase with k-space frequencies of 300 and 400 cm -1 . When the gradients created phase with a k-space frequency of 10 cm -1 , individual bubble clouds were not detectable until many acoustic pulses had been applied to the tissue. Cavitation-sensitive MR-sequences can detect single histotripsy bubble clouds formed in biologic tissue. Detection is influenced by the sensitizing gradients and treatment history. Magn Reson Med 76:1486-1493, 2016. © 2015 International Society for Magnetic Resonance in Medicine. © 2015 International Society for Magnetic Resonance in Medicine.

Oxygen quenching in a LAB based liquid scintillator and the nitrogen bubbling model

NASA Astrophysics Data System (ADS)

Xiao, Hua-Lin; Deng, Jing-Shan; Wang, Nai-Yan

2010-05-01

The oxygen quenching effect in a Linear Alkl Benzene (LAB) based liquid scintillator (LAB as the solvent, 3 g/L 2, 5 diphe-nyloxazole (PPO) as the fluor and 15 mg/L p-bis-(o-methylstyryl)-benzene (bis-MSB) as the λ-shifter) is studied by measuring the light yield as a function of the nitrogen bubbling time. It is shown that the light yield of the fully purged liquid scintillator is increased by 11% at room temperature and the room atmospheric pressure. A simple nitrogen bubbling model is proposed to describe the relationship between the relative light yield (oxygen quenching factor) and the bubbling time.

Sound Shell Model for Acoustic Gravitational Wave Production at a First-Order Phase Transition in the Early Universe.

PubMed

Hindmarsh, Mark

2018-02-16

A model for the acoustic production of gravitational waves at a first-order phase transition is presented. The source of gravitational radiation is the sound waves generated by the explosive growth of bubbles of the stable phase. The model assumes that the sound waves are linear and that their power spectrum is determined by the characteristic form of the sound shell around the expanding bubble. The predicted power spectrum has two length scales, the average bubble separation and the sound shell width when the bubbles collide. The peak of the power spectrum is at wave numbers set by the sound shell width. For a higher wave number k, the power spectrum decreases to k^{-3}. At wave numbers below the inverse bubble separation, the power spectrum goes to k^{5}. For bubble wall speeds near the speed of sound where these two length scales are distinguished, there is an intermediate k^{1} power law. The detailed dependence of the power spectrum on the wall speed and the other parameters of the phase transition raises the possibility of their constraint or measurement at a future space-based gravitational wave observatory such as LISA.

Sound Shell Model for Acoustic Gravitational Wave Production at a First-Order Phase Transition in the Early Universe

NASA Astrophysics Data System (ADS)

Hindmarsh, Mark

2018-02-01

A model for the acoustic production of gravitational waves at a first-order phase transition is presented. The source of gravitational radiation is the sound waves generated by the explosive growth of bubbles of the stable phase. The model assumes that the sound waves are linear and that their power spectrum is determined by the characteristic form of the sound shell around the expanding bubble. The predicted power spectrum has two length scales, the average bubble separation and the sound shell width when the bubbles collide. The peak of the power spectrum is at wave numbers set by the sound shell width. For a higher wave number k , the power spectrum decreases to k-3. At wave numbers below the inverse bubble separation, the power spectrum goes to k5. For bubble wall speeds near the speed of sound where these two length scales are distinguished, there is an intermediate k1 power law. The detailed dependence of the power spectrum on the wall speed and the other parameters of the phase transition raises the possibility of their constraint or measurement at a future space-based gravitational wave observatory such as LISA.

Dissolution without disappearing: multicomponent gas exchange for CO2 bubbles in a microfluidic channel.

PubMed

Shim, Suin; Wan, Jiandi; Hilgenfeldt, Sascha; Panchal, Prathamesh D; Stone, Howard A

2014-07-21

We studied the dissolution dynamics of CO2 gas bubbles in a microfluidic channel, both experimentally and theoretically. In the experiments, spherical CO2 bubbles in a flow of a solution of sodium dodecyl sulfate (SDS) first shrink rapidly before attaining an equilibrium size. In the rapid dissolution regime, the time to obtain a new equilibrium is 30 ms regardless of SDS concentration, and the equilibrium radius achieved varies with the SDS concentration. To explain the lack of complete dissolution, we interpret the results by considering the effects of other gases (O2, N2) that are already dissolved in the aqueous phase, and we develop a multicomponent dissolution model that includes the effect of surface tension and the liquid pressure drop along the channel. Solutions of the model for a stationary gas bubble show good agreement with the experimental results, which lead to our conclusion that the equilibrium regime is obtained by gas exchange between the bubbles and liquid phase. Also, our observations from experiments and model calculations suggest that SDS molecules on the gas-liquid interface form a diffusion barrier, which controls the dissolution behaviour and the eventual equilibrium radius of the bubble.

Infrared imaging and acoustic sizing of a bubble inside a micro-electro-mechanical system piezo ink channel

NASA Astrophysics Data System (ADS)

van der Bos, Arjan; Segers, Tim; Jeurissen, Roger; van den Berg, Marc; Reinten, Hans; Wijshoff, Herman; Versluis, Michel; Lohse, Detlef

2011-08-01

Piezo drop-on-demand inkjet printers are used in an increasing number of applications because of their reliable deposition of droplets onto a substrate. Droplets of a few picoliters are ejected from an inkjet nozzle at frequencies of up to 100 kHz. However, the entrapment of an air microbubble in the ink channel can severely impede the productivity and reliability of the printing system. The air bubble disturbs the channel acoustics, resulting in disrupted drop formation or failure of the jetting process. Here we study a micro-electro-mechanical systems-based printhead. By using the actuating piezo transducer in receive mode, the acoustical field inside the channel was monitored, clearly identifying the presence of an air microbubble inside the channel during failure of the jetting process. The infrared visualization technique allowed for the accurate sizing of the bubble, including its dynamics, inside the intact printhead. A model was developed to calculate the mutual interaction between the channel acoustics and the bubble dynamics. The model was validated by simultaneous acoustical and infrared detection of the bubble. The model can predict the presence and size of entrapped air bubbles inside an operating ink channel purely from the acoustic response.

Argonne Bubble Experiment Thermal Model Development III

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buechler, Cynthia Eileen

This report describes the continuation of the work reported in “Argonne Bubble Experiment Thermal Model Development” and “Argonne Bubble Experiment Thermal Model Development II”. The experiment was performed at Argonne National Laboratory (ANL) in 2014. A rastered 35 MeV electron beam deposited power in a solution of uranyl sulfate, generating heat and radiolytic gas bubbles. Irradiations were performed at beam power levels between 6 and 15 kW. Solution temperatures were measured by thermocouples, and gas bubble behavior was recorded. The previous report2 described the Monte-Carlo N-Particle (MCNP) calculations and Computational Fluid Dynamics (CFD) analysis performed on the as-built solution vesselmore » geometry. The CFD simulations in the current analysis were performed using Ansys Fluent, Ver. 17.2. The same power profiles determined from MCNP calculations in earlier work were used for the 12 and 15 kW simulations. The primary goal of the current work is to calculate the temperature profiles for the 12 and 15 kW cases using reasonable estimates for the gas generation rate, based on images of the bubbles recorded during the irradiations. Temperature profiles resulting from the CFD calculations are compared to experimental measurements.« less

Modelling of Spherical Gas Bubble Oscillations and Sonoluminescence

NASA Technical Reports Server (NTRS)

Prosperetti, A.; Hao, Y.

1999-01-01

The discovery of single-bubble sonoluminescence has led to a renewed interest in the forced radial oscillations of gas bubbles. Many of the more recent studies devoted to this topic have used several simplifications in the modelling, and in particular in accounting for liquid compressibility and thermal processes in the bubble. In this paper the significance of these simplifications is explored by contrasting the results of Lohse and co-workers with those of a more detailed model. It is found that, even though there may be little apparent difference between the radius-versus time behaviour of the bubble as predicted by the two models, quantities such as the spherical stability boundary and the threshold for rectified diffusion are affected in a quantitatively significant way. These effects are a manifestation of the subtle dependence upon dissipative processes of the phase of radial motion with respect to the driving sound field. The parameter space region, where according to the theory of Lohse and co-workers, sonoluminescence should be observable, is recalculated with the new model and is found to be enlarged with respect to the earlier estimate. The dependence of this parameter region on sound frequency is also illustrated.

Computational Fluid Dynamics-Population Balance Model Simulation of Effects of Cell Design and Operating Parameters on Gas-Liquid Two-Phase Flows and Bubble Distribution Characteristics in Aluminum Electrolysis Cells

NASA Astrophysics Data System (ADS)

Zhan, Shuiqing; Wang, Junfeng; Wang, Zhentao; Yang, Jianhong

2018-02-01

The effects of different cell design and operating parameters on the gas-liquid two-phase flows and bubble distribution characteristics under the anode bottom regions in aluminum electrolysis cells were analyzed using a three-dimensional computational fluid dynamics-population balance model. These parameters include inter-anode channel width, anode-cathode distance (ACD), anode width and length, current density, and electrolyte depth. The simulations results show that the inter-anode channel width has no significant effect on the gas volume fraction, electrolyte velocity, and bubble size. With increasing ACD, the above values decrease and more uniform bubbles can be obtained. Different effects of the anode width and length can be concluded in different cell regions. With increasing current density, the gas volume fraction and electrolyte velocity increase, but the bubble size keeps nearly the same. Increasing electrolyte depth decreased the gas volume fraction and bubble size in particular areas and the electrolyte velocity increased.

Numerical modeling of Stokes flows over a superhydrophobic surface containing gas bubbles

NASA Astrophysics Data System (ADS)

Ageev, A. I.; Golubkina, I. V.; Osiptsov, A. N.

2017-10-01

This paper continues the numerical modeling of Stokes flows near cavities of a superhydrophobic surface, occupied by gas bubbles, based on the Boundary Element Method (BEM). The aim of the present study is to estimate the friction reduction (pressure drop) in a microchannel with a bottom superhydrophobic surface, the texture of which is formed by a periodic system of striped rectangular microcavities containing compressible gas bubbles. The model proposed takes into account the streamwise variation of the bubble shift into the cavities, caused by the longitudinal pressure gradient in the channel flow. The solution for the macroscopic (averaged) flow in the microchannel, constructed using an effective slip boundary condition on the superhydrophobic bottom wall, is matched with the solution of the Stokes problem at the microscale of a single cavity containing a gas bubble. The 2D Stokes problems of fluid flow over single cavities containing curved phase interfaces with the condition of zero shear stress are reduced to the boundary integral equations which are solved using the BEM method.

Influence of grid resolution, parcel size and drag models on bubbling fluidized bed simulation

DOE PAGES

Lu, Liqiang; Konan, Arthur; Benyahia, Sofiane

2017-06-02

Here in this paper, a bubbling fluidized bed is simulated with different numerical parameters, such as grid resolution and parcel size. We examined also the effect of using two homogeneous drag correlations and a heterogeneous drag based on the energy minimization method. A fast and reliable bubble detection algorithm was developed based on the connected component labeling. The radial and axial solids volume fraction profiles are compared with experiment data and previous simulation results. These results show a significant influence of drag models on bubble size and voidage distributions and a much less dependence on numerical parameters. With a heterogeneousmore » drag model that accounts for sub-scale structures, the void fraction in the bubbling fluidized bed can be well captured with coarse grid and large computation parcels. Refining the CFD grid and reducing the parcel size can improve the simulation results but with a large increase in computation cost.« less

Diffusion of dissolved CO2 in water propagating from a cylindrical bubble in a horizontal Hele-Shaw cell

NASA Astrophysics Data System (ADS)

Peñas-López, Pablo; van Elburg, Benjamin; Parrales, Miguel A.; Rodríguez-Rodríguez, Javier

2017-06-01

The dissolution of a gas bubble in a confined geometry is a problem of interest in technological applications such as microfluidics or carbon sequestration, as well as in many natural flows of interest in geophysics. While the dissolution of spherical or sessile bubbles has received considerable attention in the literature, the case of a two-dimensional bubble in a Hele-Shaw cell, which constitutes perhaps the simplest possible confined configuration, has been comparatively less studied. Here, we use planar laser-induced fluorescence to experimentally investigate the diffusion-driven transport of dissolved CO2 that propagates from a cylindrical mm-sized bubble in air-saturated water confined in a horizontal Hele-Shaw cell. We observe that the radial trajectory of an isoconcentration front, rf(t ) , evolves in time as approximately rf-R0∝√{t } , where R0 denotes the initial bubble radius. We then characterize the unsteady CO2 concentration field via two simple analytical models, which are then validated against a numerical simulation. The first model treats the bubble as an instantaneous line source of CO2, whereas the second assumes a constant interfacial concentration. Finally, we provide an analogous Epstein-Plesset equation with the intent of predicting the dissolution rate of a cylindrical bubble.

From bubble bursting to droplet evaporation in the context of champagne aerosols

NASA Astrophysics Data System (ADS)

Seon, Thomas; Ghabache, Elisabeth; Antkowiak, Arnaud; Liger-Belair, Gerard

2015-11-01

As champagne or sparkling wine is poured into a glass, a myriad of ascending bubbles collapse and therefore radiate a multitude of tiny droplets above the free surface into the form of very characteristic and refreshing aerosols. Because these aerosols have been found to hold the organoleptic ``essence'' of champagne they are believed to play a crucial role in the flavor release in comparison with that from a flat wine for example. Based on the model experiment of a single bubble bursting in idealized champagnes, the velocity, radius and maximum height of the first jet drop following bubble collapse have been characterized, with varying bubble size and liquid properties in the context of champagne aerosols. Using the experimental results and simple theoretical models for drop and surface evaporation, we show that bubble bursting aerosols drastically enhance the transfer of liquid in the atmosphere with respect to a flat liquid surface. Contrary to popular opinion, we exhibit that small bubbles are negative in terms of aroma release, and we underline bubble radii enabling to optimize the droplet height and evaporation in the whole range of champagne properties. These results pave the road to the fine tuning of champagne aroma diffusion, a major issue of the sparkling wine industry.

Correlation between Gas Bubble Formation and Hydrogen Evolution Reaction Kinetics at Nanoelectrodes.

PubMed

Chen, Qianjin; Luo, Long

2018-04-17

We report the correlation between H 2 gas bubble formation potential and hydrogen evolution reaction (HER) activity for Au and Pt nanodisk electrodes (NEs). Microkinetic models were formulated to obtain the HER kinetic information for individual Au and Pt NEs. We found that the rate-determining steps for the HER at Au and Pt NEs were the Volmer step and the Heyrovsky step, respectively. More interestingly, the standard rate constant ( k 0 ) of the rate-determining step was found to vary over 2 orders of magnitude for the same type of NEs. The observed variations indicate the HER activity heterogeneity at the nanoscale. Furthermore, we discovered a linear relationship between bubble formation potential ( E bubble ) and log( k 0 ) with a slope of 125 mV/decade for both Au and Pt NEs. As log ( k 0 ) increases, E bubble shifts linearly to more positive potentials, meaning NEs with higher HER activities form H 2 bubbles at less negative potentials. Our theoretical model suggests that such linear relationship is caused by the similar critical bubble formation condition for Au and Pt NEs with varied sizes. Our results have potential implications for using gas bubble formation to evaluate the HER activity distribution of nanoparticles in an ensemble.

Modeling the impediment of methane ebullition bubbles by seasonal lake ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greene, S.; Walter Anthony, K. M.; Archer, D.

Microbial methane (CH 4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH 4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH 4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH 4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We findmore » that summertime ebullition dominates annual CH 4 emissions to the atmosphere. Eighty percent of CH 4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH 4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH 4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH 4 dissolution from trapped bubbles, and greater CH 4 emissions from northern lakes.« less

Modeling the impediment of methane ebullition bubbles by seasonal lake ice

DOE PAGES

Greene, S.; Walter Anthony, K. M.; Archer, D.; ...

2014-12-08

Microbial methane (CH 4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH 4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH 4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH 4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We findmore » that summertime ebullition dominates annual CH 4 emissions to the atmosphere. Eighty percent of CH 4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH 4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH 4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH 4 dissolution from trapped bubbles, and greater CH 4 emissions from northern lakes.« less

What can be Learned from X-ray Spectroscopy Concerning Hot Gas in Local Bubble and Charge Exchange Processes?

NASA Technical Reports Server (NTRS)

Snowden, Steve

2007-01-01

What can be learned from x-ray spectroscopy in observing hot gas in local bubble and charge exchange processes depends on spectral resolution, instrumental grasp, instrumental energy band, signal-to-nose, field of view, angular resolution and observatory location. Early attempts at x-ray spectroscopy include ROSAT; more recently, astronomers have used diffuse x-ray spectrometers, XMM Newton, sounding rocket calorimeters, and Suzaku. Future observations are expected with calorimeters on the Spectrum Roentgen Gamma mission, and the Solar Wind Charge Exchange (SWCX). The Geospheric SWCX may provide remote sensing of the solar wind and magnetosheath and remote observations of solar CMEs moving outward from the sun.

Dynamics of Vapour Bubbles in Nucleate Boiling. 2; Evolution of Thermally Controlled Bubbles

NASA Technical Reports Server (NTRS)

Buyevich, Yu A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

1995-01-01

The previously developed dynamic theory of growth and detachment of vapour bubbles under conditions of nucleate pool boiling is applied to study motion and deformation of a bubble evolving at a single nucleation site. The bubble growth is presumed to be thermally controlled, and two components of heat transfer to the bubble are accounted of: the one from the bulk of surrounding liquid and the one due to heat conduction across a liquid microlayer formed underneath the bubble. Bubble evolution is governed by the buoyancy and an effective surface tension force, both the forces making the bubble centre of mass move away from the wall and, thus, assisting its detachment. Buoyancy-controlled and surface-tension-controlled regimes are considered separately in a meticulous way. The duration of the whole process of bubble evolution till detachment, the rate of growth, and the bubble departure size are found as functions of time and physical and operating parameters. Some repeatedly observed phenomena, such as an influence of gravity on the growth rate, are explained. Inferences of the model agree qualitatively with available experimental evidence, and conclusions pertaining to the dependence on gravity of the bubble radius at detachment and the whole time of the bubble development when being attached to the wall are confirmed quantitatively.

Assessing the Performance of a Machine Learning Algorithm in Identifying Bubbles in Dust Emission

NASA Astrophysics Data System (ADS)

Xu, Duo; Offner, Stella S. R.

2017-12-01

Stellar feedback created by radiation and winds from massive stars plays a significant role in both physical and chemical evolution of molecular clouds. This energy and momentum leaves an identifiable signature (“bubbles”) that affects the dynamics and structure of the cloud. Most bubble searches are performed “by eye,” which is usually time-consuming, subjective, and difficult to calibrate. Automatic classifications based on machine learning make it possible to perform systematic, quantifiable, and repeatable searches for bubbles. We employ a previously developed machine learning algorithm, Brut, and quantitatively evaluate its performance in identifying bubbles using synthetic dust observations. We adopt magnetohydrodynamics simulations, which model stellar winds launching within turbulent molecular clouds, as an input to generate synthetic images. We use a publicly available three-dimensional dust continuum Monte Carlo radiative transfer code, HYPERION, to generate synthetic images of bubbles in three Spitzer bands (4.5, 8, and 24 μm). We designate half of our synthetic bubbles as a training set, which we use to train Brut along with citizen-science data from the Milky Way Project (MWP). We then assess Brut’s accuracy using the remaining synthetic observations. We find that Brut’s performance after retraining increases significantly, and it is able to identify yellow bubbles, which are likely associated with B-type stars. Brut continues to perform well on previously identified high-score bubbles, and over 10% of the MWP bubbles are reclassified as high-confidence bubbles, which were previously marginal or ambiguous detections in the MWP data. We also investigate the influence of the size of the training set, dust model, evolutionary stage, and background noise on bubble identification.

Observation of interaction of shock wave with gas bubble by image converter camera

NASA Astrophysics Data System (ADS)

Yoshii, M.; Tada, M.; Tsuji, T.; Isuzugawa, Kohji

1995-05-01

When a spark discharge occurs at the first focal point of a semiellipsoid or a reflector located in water, a spherical shock wave is produced. A part of the wave spreads without reflecting on the reflector and is called direct wave in this paper. Another part reflects on the semiellipsoid and converges near the second focal point, that is named the focusing wave, and locally produces a high pressure. This phenomenon is applied to disintegrators of kidney stone. But it is concerned that cavitation bubbles induced in the body by the expansion wave following the focusing wave will injure human tissue around kidney stone. In this paper, in order to examine what happens when shock waves strike bubbles on human tissue, the aspect that an air bubble is truck by the spherical shock wave or its behavior is visualized by the schlieren system and its photographs are taken using an image converter camera. Besides,the variation of the pressure amplitude caused by the shock wave and the flow of water around the bubble is measured with a pressure probe.

Optofluidic microvalve-on-a-chip with a surface plasmon-enhanced fiber optic microheater

PubMed Central

Zhang, Zhijian; Kusimo, Abisola; Yu, Miao

2014-01-01

We present an optofluidic microvalve utilizing an embedded, surface plasmon-enhanced fiber optic microheater. The fiber optic microheater is formed by depositing a titanium thin film on the roughened end-face of a silica optical fiber that serves as a waveguide to deliver laser light to the titanium film. The nanoscale roughness at the titanium-silica interface enables strong light absorption enhancement in the titanium film through excitation of localized surface plasmons as well as facilitates bubble nucleation. Our experimental results show that due to the unique design of the fiber optic heater, the threshold laser power required to generate a bubble is greatly reduced and the bubble growth rate is significantly increased. By using the microvalve, stable vapor bubble generation in the microchannel is demonstrated, which does not require complex optical focusing and alignment. The generated vapor bubble is shown to successfully block a liquid flow channel with a size of 125 μm × 125 μm and a flow rate of ∼10 μl/min at ∼120 mW laser power. PMID:25538813

Hemolytic potential of hydrodynamic cavitation.

PubMed

Chambers, S D; Bartlett, R H; Ceccio, S L

2000-08-01

The purpose of this study was to determine the hemolytic potentials of discrete bubble cavitation and attached cavitation. To generate controlled cavitation events, a venturigeometry hydrodynamic device, called a Cavitation Susceptibility Meter (CSM), was constructed. A comparison between the hemolytic potential of discrete bubble cavitation and attached cavitation was investigated with a single-pass flow apparatus and a recirculating flow apparatus, both utilizing the CSM. An analytical model, based on spherical bubble dynamics, was developed for predicting the hemolysis caused by discrete bubble cavitation. Experimentally, discrete bubble cavitation did not correlate with a measurable increase in plasma-free hemoglobin (PFHb), as predicted by the analytical model. However, attached cavitation did result in significant PFHb generation. The rate of PFHb generation scaled inversely with the Cavitation number at a constant flow rate, suggesting that the size of the attached cavity was the dominant hemolytic factor.

Morphology of Two-Phase Layers with Large Bubbles

NASA Astrophysics Data System (ADS)

Vékony, Klára; Kiss, László I.

2010-10-01

The understanding of formation and movement of bubbles nucleated during aluminum reduction is essential for a good control of the electrolysis process. In our experiments, we filmed and studied the formation of a bubble layer under the anode in a real-size air-water electrolysis cell model. The maximum height of the bubbles was found to be up to 2 cm because of the presence of the so-called Fortin bubbles. Also, the mean height of the bubble layer was found to be much higher than published previously. The Fortin bubbles were investigated more closely, and their shape was found to be induced by a gravity wave formed at the gas-liquid interface. In addition, large bubbles were always observed to break up into smaller parts right before escaping from under the anode. This breakup and escape led to a large momentum transfer in the bath.

Pressure and tension waves from bubble collapse near a solid boundary: A numerical approach.

PubMed

Lechner, Christiane; Koch, Max; Lauterborn, Werner; Mettin, Robert

2017-12-01

The acoustic waves being generated during the motion of a bubble in water near a solid boundary are calculated numerically. The open source package OpenFOAM is used for solving the Navier-Stokes equation and extended to include nonlinear acoustic wave effects via the Tait equation for water. A bubble model with a small amount of gas is chosen, the gas obeying an adiabatic law. A bubble starting from a small size with high internal pressure near a flat, solid boundary is studied. The sequence of events from bubble growth via axial microjet formation, jet impact, annular nanojet formation, torus-bubble collapse, and bubble rebound to second collapse is described. The different pressure and tension waves with their propagation properties are demonstrated.

Bernoulli Suction Effect on Soap Bubble Blowing?

NASA Astrophysics Data System (ADS)

Davidson, John; Ryu, Sangjin

2015-11-01

As a model system for thin-film bubble with two gas-liquid interfaces, we experimentally investigated the pinch-off of soap bubble blowing. Using the lab-built bubble blower and high-speed videography, we have found that the scaling law exponent of soap bubble pinch-off is 2/3, which is similar to that of soap film bridge. Because air flowed through the decreasing neck of soap film tube, we studied possible Bernoulli suction effect on soap bubble pinch-off by evaluating the Reynolds number of airflow. Image processing was utilized to calculate approximate volume of growing soap film tube and the volume flow rate of the airflow, and the Reynolds number was estimated to be 800-3200. This result suggests that soap bubbling may involve the Bernoulli suction effect.

Simulation Studies on Cooling of Cryogenic Propellant by Gas Bubbling

NASA Astrophysics Data System (ADS)

Sandilya, Pavitra; Saha, Pritam; Sengupta, Sonali

Injection cooling was proposed to store cryogenic liquids (Larsen et al. [1], Schmidt [2]). When a non-condensable gas is injected through a liquid, the liquid component would evaporate into the bubble if its partial pressure in the bubble is lower than its vapour pressure. This would tend to cool the liquid. Earlier works on injection cooling was analysed by Larsen et al. [1], Schmidt [2], Cho et al. [3] and Jung et al. [4], considering instantaneous mass transfer and finite heat transfer between gas bubble and liquid. It is felt that bubble dynamics (break up, coalescence, deformation, trajectory etc.) should also play a significant role in liquid cooling. The reported work are based on simple assumptions like single bubble, zero bubble deformation, and no inter-bubble interactions. Hence in this work, we propose a lumped parameter model considering both heat and mass interactions between bubble and the liquid to gain a preliminary insight into the cooling phenomenon during gas injection through a liquid.

Pinch-off Scaling Law of Soap Bubbles

NASA Astrophysics Data System (ADS)

Davidson, John; Ryu, Sangjin

2014-11-01

Three common interfacial phenomena that occur daily are liquid drops in gas, gas bubbles in liquid and thin-film bubbles. One aspect that has been studied for these phenomena is the formation or pinch-off of the drop/bubble from the liquid/gas threads. In contrast to the formation of liquid drops in gas and gas bubbles in liquid, thin-film bubble pinch-off has not been well documented. Having thin-film interfaces may alter the pinch-off process due to the limiting factor of the film thickness. We observed the pinch-off of one common thin-film bubble, soap bubbles, in order to characterize its pinch-off behavior. We achieved this by constructing an experimental model replicating the process of a human producing soap bubbles. Using high-speed videography and image processing, we determined that the minimal neck radius scaled with the time left till pinch-off, and that the scaling law exponent was 2/3, similar to that of liquid drops in gas.

Size limits the formation of liquid jets during bubble bursting

PubMed Central

Lee, Ji San; Weon, Byung Mook; Park, Su Ji; Je, Jung Ho; Fezzaa, Kamel; Lee, Wah-Keat

2011-01-01

A bubble reaching an air–liquid interface usually bursts and forms a liquid jet. Jetting is relevant to climate and health as it is a source of aerosol droplets from breaking waves. Jetting has been observed for large bubbles with radii of R≫100 μm. However, few studies have been devoted to small bubbles (R<100 μm) despite the entrainment of a large number of such bubbles in sea water. Here we show that jet formation is inhibited by bubble size; a jet is not formed during bursting for bubbles smaller than a critical size. Using ultrafast X-ray and optical imaging methods, we build a phase diagram for jetting and the absence of jetting. Our results demonstrate that jetting in bubble bursting is analogous to pinching-off in liquid coalescence. The coalescence mechanism for bubble bursting may be useful in preventing jet formation in industry and improving climate models concerning aerosol production. PMID:21694715

Evaluation of Interfacial Forces and Bubble-Induced Turbulence Using Direct Numerical Simulation

NASA Astrophysics Data System (ADS)

Feng, Jinyong

High fidelity prediction of multiphase flows is important in a wide range of engineering applications. While some multiphase flow scenarios can be successfully modeled, many questions remain unanswered regarding the interaction between the bubbles and the turbulence, and present significant challenges in the development of closure laws for the multiphase computational fluid dynamics (M-CFD) models. To address these challenges, we propose to evaluate the interfacial forces and bubble-induced turbulence in both laminar and turbulent flow field with direct numerical simulation (DNS) approach. Advanced finite-element based flow solver (PHASTA) with level-set interface tracking method is utilized for these studies. The proportional-integral-derivative (PID) controller is adopted to ensure the statistically steady state bubble position and perform the detailed study of the turbulent field around the bubble. Selected numerical capabilities and post-processing codes are developed to achieve the research goals. The interface tracking approach is verified and validated by comparing the interfacial forces with the experiment-based data and correlations. The sign change of transverse lift force is observed as the bubble becomes more deformable. A new correlation is proposed to predict the behavior of the drag coefficient over the wide range of conditions. The wall effect on the interfacial forces are also investigated. In homogeneous turbulent flow, the effect of bubble deformability, turbulent intensity and relative velocity on the bubble-induced turbulence are analyzed. The presented method and novel results will complement the experimental database, provide insight to the bubbleinduced turbulence mechanism and help the development of M-CFD closure models.

Dynamics of two-dimensional bubbles.

PubMed

Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón

2015-06-01

The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.

Bubble Motion through a Generalized Power-Law Fluid Flowing in a Vertical Tube

PubMed Central

Mukundakrishnan, Karthik; Eckmann, David M.; Ayyaswamy, P. S.

2009-01-01

Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow. PMID:19426324

A physics based multiscale modeling of cavitating flows.

PubMed

Ma, Jingsen; Hsiao, Chao-Tsung; Chahine, Georges L

2017-03-02

Numerical modeling of cavitating bubbly flows is challenging due to the wide range of characteristic lengths of the physics at play: from micrometers (e.g., bubble nuclei radius) to meters (e.g., propeller diameter or sheet cavity length). To address this, we present here a multiscale approach which integrates a Discrete Singularities Model (DSM) for dispersed microbubbles and a two-phase Navier Stokes solver for the bubbly medium, which includes a level set approach to describe large cavities or gaseous pockets. Inter-scale schemes are used to smoothly bridge the two transitioning subgrid DSM bubbles into larger discretized cavities. This approach is demonstrated on several problems including cavitation inception and vapor core formation in a vortex flow, sheet-to-cloud cavitation over a hydrofoil, cavitation behind a blunt body, and cavitation on a propeller. These examples highlight the capabilities of the developed multiscale model in simulating various form of cavitation.

A physics based multiscale modeling of cavitating flows

PubMed Central

Ma, Jingsen; Hsiao, Chao-Tsung; Chahine, Georges L.

2018-01-01

Numerical modeling of cavitating bubbly flows is challenging due to the wide range of characteristic lengths of the physics at play: from micrometers (e.g., bubble nuclei radius) to meters (e.g., propeller diameter or sheet cavity length). To address this, we present here a multiscale approach which integrates a Discrete Singularities Model (DSM) for dispersed microbubbles and a two-phase Navier Stokes solver for the bubbly medium, which includes a level set approach to describe large cavities or gaseous pockets. Inter-scale schemes are used to smoothly bridge the two transitioning subgrid DSM bubbles into larger discretized cavities. This approach is demonstrated on several problems including cavitation inception and vapor core formation in a vortex flow, sheet-to-cloud cavitation over a hydrofoil, cavitation behind a blunt body, and cavitation on a propeller. These examples highlight the capabilities of the developed multiscale model in simulating various form of cavitation. PMID:29720773

Resonant Frequency Shifts of a Fluid Filled Cavity Caused by a Bubble

NASA Astrophysics Data System (ADS)

Zhang, Hailan; Wang, Xiuming; Chen, Dehua; Che, Chengxuan

2009-03-01

In the previous studies for estimating acoustic wave velocities and attenuations of a rock specimen in a low frequency range using an acoustic resonance spectroscopy method, it was found that bubbles in a fluid filled cavity reduce the resonant frequency of the cavity significantly, which makes the measurement unstable. In this paper, this phenomenon is explained by using a simple model of a spherical fluid filled cavity with a single air bubble. It is pointed out that air bubble effects are caused by the vibration of the bubble coupled with the vibration of the cavity and, therefore, the measurement must be carefully prepared to prevent any air bubbles from entering the cavity.

Physical Phenomena in Containerless Glass Processing

NASA Technical Reports Server (NTRS)

Subramanian, R. S.; Cole, R.

1985-01-01

An investigation into the various physical phenomena of importance in the space experiments is under way. Theoretical models of thermocapillary flow in drops, thermal migration of bubbles and droplets, the motion of bubbles inside drops, and the migration of bubbles in rotating liquid bodies are being developed. Experiments were conducted on the migration of bubbles and droplets to the axis of a rotating liquid body, and the rise of bubbles in molten glass. Also, experiments on thermocapillary motion in silicone oils as well as glass melts were performed. Experiments are currently being conducted on the migration of bubbles in a thermal gradient, and on their motion inside unconstrained liquid drops in a rotating liquid.

Investigation of transition from thermal- to solutal-Marangoni flow in dilute alcohol/water mixtures using nano-plasmonic heaters

NASA Astrophysics Data System (ADS)

Namura, Kyoko; Nakajima, Kaoru; Suzuki, Motofumi

2018-02-01

We experimentally investigated Marangoni flows around a microbubble in diluted 1-butanol/water, 2-propanol/water, and ethanol/water mixtures using the thermoplasmonic effect of gold nanoisland film. A laser spot on the gold nanoisland film acted as a highly localized heat source that was utilized to generate stable air microbubbles with diameters of 32-48 μm in the fluid and to induce a steep temperature gradient on the bubble surface. The locally heated bubble has a flow along the bubble surface, with the flow direction showing a clear transition depending on the alcohol concentrations. The fluid is driven from the hot to cold regions when the alcohol concentration is lower than the transition concentration, whereas it is driven from the cold to hot regions when the concentration is higher than the transition concentration. In addition, the transition concentration increases as the carbon number of the alcohol decreases. The observed flow direction transition is explained by the balance of the thermal- and solutal-Marangoni forces that are cancelled out for the transition concentration. The selective evaporation of the alcohol at the locally heated surface allows us to generate stable and rapid thermoplasmonic solutal-Marangoni flows in the alcohol/water mixtures.

The shape and motion of gas bubbles in a liquid flowing through a thin annulus

NASA Astrophysics Data System (ADS)

Lei, Qinghua; Xie, Zhihua; Pavlidis, Dimitrios; Salinas, Pablo; Veltin, Jeremy; Muggeridge, Ann; Pain, Christopher C.; Matar, Omar K.; Jackson, Matthew; Arland, Kristine; Gyllensten, Atle

2017-11-01

We study the shape and motion of gas bubbles in a liquid flowing through a horizontal or slightly-inclined thin annulus. Experimental data show that in the horizontal annulus, bubbles develop a unique ``tadpole'' shape with an elliptical cap and a highly-stretched tail, due to the confinement between the closely-spaced channel walls. As the annulus is inclined, the bubble tail tends to decrease in length, while the geometry of the cap remains almost invariant. To model the bubble evolution, the thin annulus is conceptualised as a ``Hele-Shaw'' cell in a curvilinear space. The three-dimensional flow within the cell is represented by a gap-averaged, two-dimensional model constrained by the same dimensionless quantities. The complex bubble dynamics are solved using a mixed control-volume finite-element method combined with interface-capturing and mesh adaptation techniques. A close match to the experimental data is achieved, both qualitatively and quantitatively, by the numerical simulations. The mechanism for the elliptical cap formation is interpreted based on an analogous irrotational flow field around a circular cylinder. The shape regimes of bubbles flowing through the thin annulus are further explored based on the simulation results. Funding from STATOIL gratefully acknowledged.

Microbubbles and Blood Brain Barrier Opening: A Numerical Study on Acoustic Emissions and Wall Stress Predictions

PubMed Central

Goertz, David E.; Hynynen, Kullervo

2015-01-01

Focused ultrasound with microbubbles is an emerging technique for blood brain barrier (BBB) opening. Here, a comprehensive theoretical model of a bubble-fluid-vessel system has been developed which accounts for the bubble’s non-spherical oscillations inside a microvessel, and its resulting acoustic emissions. Numerical simulations of unbound and confined encapsulated bubbles were performed to evaluate the effect of the vessel wall on acoustic emissions and vessel wall stresses. Using a Marmottant shell model, the normalized second harmonic to fundamental emissions first decreased as a function of pressure (>50 kPa) until reaching a minima ("transition point") at which point they increased. The transition point of unbound compared to confined bubble populations occurred at different pressures and was associated with an accompanying increase in shear and circumferential wall stresses. As the wall stresses depend on the bubble to vessel wall distance, the stresses were evaluated for bubbles with their wall at a constant distance to a flat wall. As a result, the wall stresses were bubble size and frequency dependent and the peak stress values induced by bubbles larger than resonance remained constant versus frequency at a constant mechanical index. PMID:25546853

FERMI BUBBLE γ-RAYS AS A RESULT OF DIFFUSIVE INJECTION OF GALACTIC COSMIC RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thoudam, Satyendra, E-mail: s.thoudam@astro.ru.nl

2013-11-20

Recently, the Fermi Space Telescope discovered two large γ-ray emission regions, the so-called Fermi bubbles, that extend up to ∼50° above and below the Galactic center (GC). The γ-ray emission from the bubbles is found to follow a hard spectrum with no significant spatial variation in intensity and spectral shape. The origin of the emission is still not clearly understood. Suggested explanations include the injection of cosmic-ray (CR) nuclei from the GC by high-speed Galactic winds, electron acceleration by multiple shocks, and stochastic electron acceleration inside the bubbles. In this Letter, it is proposed that the γ-rays may be themore » result of diffusive injection of Galactic CR protons during their propagation through the Galaxy. Considering that the bubbles are slowly expanding, and CRs undergo much slower diffusion inside the bubbles than in the average Galaxy and at the same time suffer losses due to adiabatic expansion and inelastic collisions with the bubble plasma, this model can explain the observed intensity profile, the emission spectrum and the measured luminosity without invoking any additional particle production processes, unlike other existing models.« less

An Euler-Lagrange method considering bubble radial dynamics for modeling sonochemical reactors.

PubMed

Jamshidi, Rashid; Brenner, Gunther

2014-01-01

Unsteady numerical computations are performed to investigate the flow field, wave propagation and the structure of bubbles in sonochemical reactors. The turbulent flow field is simulated using a two-equation Reynolds-Averaged Navier-Stokes (RANS) model. The distribution of the acoustic pressure is solved based on the Helmholtz equation using a finite volume method (FVM). The radial dynamics of a single bubble are considered by applying the Keller-Miksis equation to consider the compressibility of the liquid to the first order of acoustical Mach number. To investigate the structure of bubbles, a one-way coupling Euler-Lagrange approach is used to simulate the bulk medium and the bubbles as the dispersed phase. Drag, gravity, buoyancy, added mass, volume change and first Bjerknes forces are considered and their orders of magnitude are compared. To verify the implemented numerical algorithms, results for one- and two-dimensional simplified test cases are compared with analytical solutions. The results show good agreement with experimental results for the relationship between the acoustic pressure amplitude and the volume fraction of the bubbles. The two-dimensional axi-symmetric results are in good agreement with experimentally observed structure of bubbles close to sonotrode. Copyright © 2013 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Linyun; Mei, Zhi-Gang; Yacout, Abdellatif M.

We have developed a mesoscale phase-field model for studying the effect of recrystallization on the gas-bubble-driven swelling in irradiated U-Mo alloy fuel. The model can simulate the microstructural evolution of the intergranular gas bubbles on the grain boundaries as well as the recrystallization process. Our simulation results show that the intergranular gas-bubble-induced fuel swelling exhibits two stages: slow swelling kinetics before recrystallization and rapid swelling kinetics with recrystallization. We observe that the recrystallization can significantly expedite the formation and growth of gas bubbles at high fission densities. The reason is that the recrystallization process increases the nucleation probability of gasmore » bubbles and reduces the diffusion time of fission gases from grain interior to grain boundaries by increasing the grain boundary area and decreasing the diffusion distance. The simulated gas bubble shape, size distribution, and density on the grain boundaries are consistent with experimental measurements. We investigate the effect of the recrystallization on the gas-bubble-driven fuel swelling in UMo through varying the initial grain size and grain aspect ratio. We conclude that the initial microstructure of fuel, such as grain size and grain aspect ratio, can be used to effectively control the recrystallization and therefore reduce the swelling in U-Mo fuel.« less

Gas separation and bubble behavior at a woven screen

NASA Astrophysics Data System (ADS)

Conrath, Michael; Dreyer, Michael E.

Gas-liquid two phase flows are widespread and in many applications the separation of both phases is necessary. Chemical reactors, water treatment devices or gas-free delivery of liquids like propellant are only some of them. We study the performance of a woven metal screen in respect to its phase separation behavior under static and dynamic conditions. Beside hydraulic screen resistance and static bubble point, our study also comprises the bubble detachment from the screen upon gas breakthrough. Since a woven screen is essentially an array of identical pores, analogies to bubble detachment from a needle can be established. While the bubble point poses an upper limit for pressurized gas at a wetted screen to preclude gas breakthrough, the necessary pressure for growing bubbles to detach from the screen pores a lower limit when breakthrough is already in progress. Based on that inside, the dynamic bubble point effects were constituted that relate to a trapped bubble at such a screen in liquid flow. A trapped is caused to break through the screen by the flow-induced pressure drop across it. Our model includes axially symmetric bubble shapes, degree of coverage of the screen and bubble pressurization due to hydraulic losses in the rest of the circuit. We have built an experiment that consists of a Dutch Twilled woven screen made of stainless steel in a vertical acrylic glass tube. The liquid is silicon oil SF0.65. The screen is suspended perpendicular to the liquid flow which is forced through it at variable flow rate. Controlled injection of air from a needle allows us to examine the ability of the screen to separate gas and liquid along the former mentioned effects. We present experimental data on static bubble point and detachment pressure for breakthrough at different gas supply rates that suggest a useful criterion for reliable static bubble point measurements. Results for the dynamic bubble point are presented that include i) screen pressure drop for different trapped bubble volumes, liquid flow rates and flow-induced compression, ii) typical breakthrough of a trapped bubble at rising liquid flow rate and iii) steady gas supply in steady liquid flow. It shows that our model can explain the experimental observations. One of the interesting findings for the dynamic bubble point is that hydraulic losses in the rest of the circuit will shift the breakthrough of gas to higher liquid flow rates.

Numerical modeling of bubble dynamics in viscoelastic media with relaxation

PubMed Central

Warnez, M. T.; Johnsen, E.

2015-01-01

Cavitation occurs in a variety of non-Newtonian fluids and viscoelastic materials. The large-amplitude volumetric oscillations of cavitation bubbles give rise to high temperatures and pressures at collapse, as well as induce large and rapid deformation of the surroundings. In this work, we develop a comprehensive numerical framework for spherical bubble dynamics in isotropic media obeying a wide range of viscoelastic constitutive relationships. Our numerical approach solves the compressible Keller–Miksis equation with full thermal effects (inside and outside the bubble) when coupled to a highly generalized constitutive relationship (which allows Newtonian, Kelvin–Voigt, Zener, linear Maxwell, upper-convected Maxwell, Jeffreys, Oldroyd-B, Giesekus, and Phan-Thien-Tanner models). For the latter two models, partial differential equations (PDEs) must be solved in the surrounding medium; for the remaining models, we show that the PDEs can be reduced to ordinary differential equations. To solve the general constitutive PDEs, we present a Chebyshev spectral collocation method, which is robust even for violent collapse. Combining this numerical approach with theoretical analysis, we simulate bubble dynamics in various viscoelastic media to determine the impact of relaxation time, a constitutive parameter, on the associated physics. Relaxation time is found to increase bubble growth and permit rebounds driven purely by residual stresses in the surroundings. Different regimes of oscillations occur depending on the relaxation time. PMID:26130967

Analytical and numerical investigations of bubble behavior in electric fields

NASA Astrophysics Data System (ADS)

Vorreiter, Janelle Orae

The behavior of gas bubbles in liquids is important in a wide range of applications. This study is motivated by a desire to understand the motion of bubbles in the absence of gravity, as in many aerospace applications. Phase-change devices, cryogenic tanks and life-support systems are some of the applications where bubbles exist in space environments. One of the main difficulties in employing devices with bubbles in zero gravity environments is the absence of a buoyancy force. The use of an electric field is found to be an effective means of replacing the buoyancy force, improving the control of bubbles in space environments. In this study, analytical and numerical investigations of bubble behavior under the influence of electric fields are performed. The problem is a difficult one in that the physics of the liquid and the electric field need to be considered simultaneously to model the dynamics of the bubble. Simplifications are required to reduce the problem to a tractable form. In this work, for the liquid and the electric field, assumptions are made which reduce the problem to one requiring only the solution of potentials in the domain of interest. Analytical models are developed using a perturbation analysis applicable for small deviations from a spherical shape. Numerical investigations are performed using a boundary integral code. A number of configurations are found to be successful in promoting bubble motion by varying properties of the electric fields. In one configuration, the natural frequencies of a bubble are excited using time-varying electric and pressure fields. The applied electric field is spatially uniform with frequencies corresponding to shape modes of the bubble. The resulting bubble velocity is related to the strength of the electric field as well as the characteristics of the applied fields. In another configuration, static non-uniform fields are used to encourage bubble motion. The resulting motion is related to the degree of non-uniformity of the applied field. Several geometries are investigated to study the relationship between electrode geometry and bubble behavior.

Time and Space Resolved Heat Transfer Measurements Under Nucleate Bubbles with Constant Heat Flux Boundary Conditions

NASA Technical Reports Server (NTRS)

Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho

2003-01-01

Investigations into single bubble pool boiling phenomena are often complicated by the difficulties in obtaining time and space resolved information in the bubble region. This usually occurs because the heaters and diagnostics used to measure heat transfer data are often on the order of, or larger than, the bubble characteristic length or region of influence. This has contributed to the development of many different and sometimes contradictory models of pool boiling phenomena and dominant heat transfer mechanisms. Recent investigations by Yaddanapyddi and Kim and Demiray and Kim have obtained time and space resolved heat transfer information at the bubble/heater interface under constant temperature conditions using a novel micro-heater array (10x10 array, each heater 100 microns on a side) that is semi-transparent and doubles as a measurement sensor. By using active feedback to maintain a state of constant temperature at the heater surface, they showed that the area of influence of bubbles generated in FC-72 was much smaller than predicted by standard models and that micro-conduction/micro-convection due to re-wetting dominated heat transfer effects. This study seeks to expand on the previous work by making time and space resolved measurements under bubbles nucleating on a micro-heater array operated under constant heat flux conditions. In the planned investigation, wall temperature measurements made under a single bubble nucleation site will be synchronized with high-speed video to allow analysis of the bubble energy removal from the wall.

Extreme conditions in a dissolving air nanobubble

NASA Astrophysics Data System (ADS)

Yasui, Kyuichi; Tuziuti, Toru; Kanematsu, Wataru

2016-07-01

Numerical simulations of the dissolution of an air nanobubble in water have been performed taking into account the effect of bubble dynamics (inertia of the surrounding liquid). The presence of stable bulk nanobubbles is not assumed in the present study because the bubble radius inevitably passes the nanoscale in the complete dissolution of a bubble. The bubble surface is assumed to be clean because attachment of hydrophobic materials on the bubble surface could considerably change the gas diffusion rate. The speed of the bubble collapse (the bubble wall speed) increases to about 90 m/s or less. The shape of a bubble is kept nearly spherical because the amplitude of the nonspherical component of the bubble shape is negligible compared to the instantaneous bubble radius. In other words, a bubble never disintegrates into daughter bubbles during the dissolution. At the final moment of the dissolution, the temperature inside a bubble increases to about 3000 K due to the quasiadiabatic compression. The bubble temperature is higher than 1000 K only for the final 19 ps. However, the Knudsen number is more than 0.2 for this moment, and the error associated with the continuum model should be considerable. In the final 2.3 ns, only nitrogen molecules are present inside a bubble as the solubility of nitrogen is the lowest among the gas species. The radical formation inside a bubble is negligible because the probability of nitrogen dissociation is only on the order of 10-15. The pressure inside a bubble, as well as the liquid pressure at the bubble wall, increases to about 5 GPa at the final moment of dissolution. The pressure is higher than 1 GPa for the final 0.7 ns inside a bubble and for the final 0.6 ns in the liquid at the bubble wall. The liquid temperature at the bubble wall increases to about 360 K from 293 K at the final stage of the complete dissolution.

Morphological bubble evolution induced by air diffusion on submerged hydrophobic structures

NASA Astrophysics Data System (ADS)

Lv, Pengyu; Xiang, Yaolei; Xue, Yahui; Lin, Hao; Duan, Huiling

2017-03-01

Bubbles trapped in the cavities always play important roles in the underwater applications of structured hydrophobic surfaces. Air exchange between bubbles and surrounding water has a significant influence on the morphological bubble evolution, which in turn frequently affects the functionalities of the surfaces, such as superhydrophobicity and drag reduction. In this paper, air diffusion induced bubble evolution on submerged hydrophobic micropores under reduced pressures is investigated experimentally and theoretically. The morphological behaviors of collective and single bubbles are observed using confocal microscopy. Four representative evolution phases of bubbles are captured in situ. After depressurization, bubbles will not only grow and coalesce but also shrink and split although the applied pressure remains negative. A diffusion-based model is used to analyze the evolution behavior and the results are consistent with the experimental data. A criterion for bubble growth and shrinkage is also derived along with a phase diagram, revealing that the competition of effective gas partial pressures across the two sides of the diffusion layer dominates the bubble evolution process. Strategies for controlling the bubble evolution behavior are also proposed based on the phase diagram. The current work provides a further understanding of the general behavior of bubble evolution induced by air diffusion and can be employed to better designs of functional microstructured hydrophobic surfaces.

Dynamics of Two Interactive Bubbles in An Acoustic Field - Part II: Experiments

NASA Astrophysics Data System (ADS)

Ashgriz, Nasser; Barbat, Tiberiu; Liu, Ching-Shi

1996-11-01

The motion of two air bubbles levitated in water, in the presence of a high-frequency acoustic field is experimentally studied. The interaction force between them is named "secondary Bjerknes force" and may be significant in microgravity environments; in our experiments the buoyancy effect is compensated through the action of the "primary Bjerknes forces" - interaction between each bubble oscillation and external sound field. The stationary sound field is produced by a piezoceramic tranducer, in the range of 22-24 kHz. The experiments succesfully demonstrate the existence of three patterns of interaction between bubbles of various sizes: attraction, repulsion and oscillation. Bubbles attraction is quantitatively studied using a high speed video, for "large" bubbles (in the range 0.5-2 mm radius); bubbles repulsion and oscillations are only observed with a regular video, for "small" bubbles (around the resonance size at these frequencies, 0.12 mm). Velocities and accelerations of each bubble are computed from the time history of the motion. The theoretical equations of motion are completed with a drag force formula for single bubbles and solved numerically. Experimental results, for the case of two attracting bubbles, are in good agreement with the numerical model, especially for values of the mutual distance greater than 3 large bubble radii.

Optical shielding of nickel nanoparticle by a bubble: Optical limiting gets limited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Vijay; Jayabalan, J., E-mail: jjaya@rrcat.gov.in; Chari, Rama

2016-06-13

We have demonstrated that in a nickel nanoparticle colloid, the optical limiting action reduces if a vapor bubble forms around the nanoparticle. The energy-dependent transmission and z-scan measurements on nickel nanoparticles in toluene show the onset of an additional process. At high fluence excitation, the particle becomes less visible to the later part of the incoming pulse due to the heat generated bubble formed around it. We have proposed a simple “particle-in-bubble” model which fits the optical limiting and z-scan curves quite well. Using this model, we have also estimated that the bubble radius increases at a rate of 4.5 m/s.

Single-bubble boiling under Earth's and low gravity

NASA Astrophysics Data System (ADS)

Khusid, Boris; Elele, Ezinwa; Lei, Qian; Tang, John; Shen, Yueyang

2017-11-01

Miniaturization of electronic systems in terrestrial and space applications is challenged by a dramatic increase in the power dissipation per unit volume with the occurrence of localized hot spots where the heat flux is much higher than the average. Cooling by forced gas or liquid flow appears insufficient to remove high local heat fluxes. Boiling that involves evaporation of liquid in a hot spot and condensation of vapor in a cold region can remove a significantly larger amount of heat through the latent heat of vaporization than force-flow cooling can carry out. Traditional methods for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles from the heating surface. In contrast, we unexpectedly observed a new boiling regime of water under Earth's gravity and low gravity in which a bubble was pinned on a small heater up to 270°C and delivered a heat flux up to 1.2 MW/m2 that was as high as the critical heat flux in the classical boiling regime on Earth .Low gravity measurements conducted in parabolic flights in NASA Boeing 727. The heat flux in flight and Earth's experiments was found to rise linearly with increasing the heater temperature. We will discuss physical mechanisms underlying heat transfer in single-bubble boiling. The work supported by NASA Grants NNX12AM26G and NNX09AK06G.

Interpretations of phenocryst embayments

NASA Astrophysics Data System (ADS)

Rust, Alison; Cashman, Katharine

2017-04-01

Phenocryst embayments in volcanic samples tend to be filled with glass, regardless of the crystallinity and vesicularly of the groundmass surrounding the phenocryst. Embayments are important in volcanology and magma petrology because: 1) they often provide the only areas of matrix glass sufficient for compositional analysis in microlite-rich samples; 2) volatile gradients in embayments are used to constrain rates of magma ascent; 3) with further crystal growth, embayments may develop into melt inclusions, an essential source of data on melt composition evolution. Robust interpretations of data from embayments requires an understanding of why they form and why vesiculation and crystallisation are locally suppressed in these melt channels during ascent. We review instabilities in crystal growth and resorption, considering latent heat, local accumulation of elements, and interaction of the crystal growth front with pre-existing bubbles and other crystals. A survey of textures in volcanic samples from several volcanoes suggests that embayment formation by growth is more common than by resorption. Crystal nucleation suppression in the embayment of a growing phenocryst can be explained by buildup of excluded elements and continued growth (rather than nucleation) of the phenocryst phase. However, the suppression of bubble formation despite the accumulation of excluded volatiles is more difficult to explain but could be related to latent heat and difficulties in bubble formation in a restricted space. Finally, we flag complications in interpretations of embayment composition data due to element accumulation and bubble nucleation suppression.

THE STRUCTURE OF THE LOCAL HOT BUBBLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, W.; Galeazzi, M.; Uprety, Y.

Diffuse X-rays from the Local Galaxy ( DXL ) is a sounding rocket mission designed to quantify and characterize the contribution of Solar Wind Charge eXchange (SWCX) to the Diffuse X-ray Background and study the properties of the Local Hot Bubble (LHB). Based on the results from the DXL mission, we quantified and removed the contribution of SWCX to the diffuse X-ray background measured by the ROSAT All Sky Survey. The “cleaned” maps were used to investigate the physical properties of the LHB. Assuming thermal ionization equilibrium, we measured a highly uniform temperature distributed around kT  = 0.097 keV ± 0.013 keV (FWHM) ± 0.006more » keV (systematic). We also generated a thermal emission measure map and used it to characterize the three-dimensional (3D) structure of the LHB, which we found to be in good agreement with the structure of the local cavity measured from dust and gas.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Setyawan, Wahyu; Joshi, Vineet V.

Xe gas bubble superlattice formation is observed in irradiated uranium–10 wt% molybdenum (U10Mo) fuels. However, the thermodynamic properties of the bubbles (the relationship among bubble size, equilibrium Xe concentration, and bubble pressure) and the mechanisms of bubble growth and superlattice formation are not well known. In this work, molecular dynamics is used to study these properties and mechanisms. The results provide important inputs for quantitative mesoscale models of gas bubble evolution and fuel performance. In the molecular dynamics simulations, the embedded-atom method (EAM) potential of U10Mo-Xe (Smirnova et al. 2013) is employed. Initial gas bubbles with low Xe concentration aremore » generated in a U10Mo single crystal. Then Xe atom atoms are continuously added into the bubbles, and the evolution of pressure and dislocation emission around the bubbles is analyzed. The relationship between pressure, equilibrium Xe concentration, and radius of the bubbles is established. It was found that the gas bubble growth is accompanied by partial dislocation emission, which results in a star-shaped dislocation structure and an anisotropic stress field. The emitted partial dislocations have a Burgers vector along the <111> direction and a slip plane of (11-2). Dislocation loop punch-out was not observed. A tensile stress was found along <110> directions around the bubble, favoring the nucleation and formation of a face-centered cubic bubble superlattice in body-centered cubic U10Mo fuels.« less

Bubble-generating nano-lipid carriers for ultrasound/CT imaging-guided efficient tumor therapy.

PubMed

Zhang, Nan; Li, Jia; Hou, Ruirui; Zhang, Jiangnan; Wang, Pei; Liu, Xinyang; Zhang, Zhenzhong

2017-12-20

Ideal therapeutic effectiveness of chemotherapy is obtained only when tumor cells are exposed to a maximal drug concentration, which is often hindered by dose-limiting toxicity. We designed a bubble-generating liposomal delivery system by introducing ammonium bicarbonate and gold nanorods into folic acid-conjugated liposomes to allow both multimodal imaging and the local release of drug (doxorubicin) with hyperthermia. The key component, ammonium bicarbonate, allows a controlled, rapid release of doxorubicin to provide an effective drug concentration in the tumor microenvironment. An in vitro temperature-triggered drug release study showed that cumulative release improved more than two-fold. In addition, in vitro and in vivo studies indicated that local heat treatment or ultrasonic cavitation enhanced the therapeutic efficiency greatly. The delivery system could also serve as an excellent contrast agent to allow ultrasonic imaging and computerized tomography imaging simultaneously to further achieve the aim of accurate diagnostics. Results of this study showed that this versatile bubble-generating liposome is a promising system to provide optimal therapeutic effects that are guided by multimodal imaging. Copyright © 2017 Elsevier B.V. All rights reserved.

A New Unsteady Model for Dense Cloud Cavitation in Cryogenic Fluids

NASA Technical Reports Server (NTRS)

Hosangadi, A.; Ahuja, V.

2005-01-01

A new unsteady, cavitation model is presented wherein the phase change process (bubble growth/collapse) is coupled to the acoustic field in a cryogenic fluid. It predicts the number density and radius of bubbles in vapor clouds by tracking both the aggregate surface area and volume fraction of the cloud. Hence, formulations for the dynamics of individual bubbles (e.g. Rayleigh-Plesset equation) may be integrated within the macroscopic context of a dense vapor cloud i.e. a cloud that occupies a significant fraction of available volume and contains numerous bubbles. This formulation has been implemented within the CRUNCH CFD, which has a compressible real fluid formulation, a multi-element, unstructured grid framework, and has been validated extensively for liquid rocket turbopump inducers. Detailed unsteady simulations of a cavitating ogive in liquid nitrogen are presented where time-averaged mean cavity pressure and temperature depressions due to cavitation are compared with experimental data. The model also provides the spatial and temporal history of the bubble size distribution in the vapor clouds that are shed, an important physical parameter that is difficult to measure experimentally and is a significant advancement in the modeling of dense cloud cavitation.

The influence of medium elasticity on the prediction of histotripsy-induced bubble expansion and erythrocyte viability

NASA Astrophysics Data System (ADS)

Bader, Kenneth B.

2018-05-01

Histotripsy is a form of therapeutic ultrasound that liquefies tissue mechanically via acoustic cavitation. Bubble expansion is paramount in the efficacy of histotripsy therapy, and the cavitation dynamics are strongly influenced by the medium elasticity. In this study, an analytic model to predict histotripsy-induced bubble expansion in a fluid was extended to include the effects of medium elasticity. Good agreement was observed between the predictions of the analytic model and numerical computations utilizing highly nonlinear excitations (shock-scattering histotripsy) and purely tensile pulses (microtripsy). No bubble expansion was computed for either form of histotripsy when the elastic modulus was greater than 20 MPa and the peak negative pressure was less than 50 MPa. Strain in the medium due to the expansion of a single bubble was also tabulated. The viability of red blood cells was calculated as a function of distance from the bubble wall based on empirical data of impulsive stretching of erythrocytes. Red blood cells remained viable at distances further than 44 µm from the bubble wall. As the medium elasticity increased, the distance over which bubble expansion-induced strain influenced red blood cells was found to decrease sigmoidally. These results highlight the relationship between tissue elasticity and the efficacy of histotripsy. In addition, an upper medium elasticity limit was identified, above which histotripsy may not be effective for tissue liquefaction.

Schema generation in recurrent neural nets for intercepting a moving target.

PubMed

Fleischer, Andreas G

2010-06-01

The grasping of a moving object requires the development of a motor strategy to anticipate the trajectory of the target and to compute an optimal course of interception. During the performance of perception-action cycles, a preprogrammed prototypical movement trajectory, a motor schema, may highly reduce the control load. Subjects were asked to hit a target that was moving along a circular path by means of a cursor. Randomized initial target positions and velocities were detected in the periphery of the eyes, resulting in a saccade toward the target. Even when the target disappeared, the eyes followed the target's anticipated course. The Gestalt of the trajectories was dependent on target velocity. The prediction capability of the motor schema was investigated by varying the visibility range of cursor and target. Motor schemata were determined to be of limited precision, and therefore visual feedback was continuously required to intercept the moving target. To intercept a target, the motor schema caused the hand to aim ahead and to adapt to the target trajectory. The control of cursor velocity determined the point of interception. From a modeling point of view, a neural network was developed that allowed the implementation of a motor schema interacting with feedback control in an iterative manner. The neural net of the Wilson type consists of an excitation-diffusion layer allowing the generation of a moving bubble. This activation bubble runs down an eye-centered motor schema and causes a planar arm model to move toward the target. A bubble provides local integration and straightening of the trajectory during repetitive moves. The schema adapts to task demands by learning and serves as forward controller. On the basis of these model considerations the principal problem of embedding motor schemata in generalized control strategies is discussed.

Evolution of the properties of helium nanobubbles during in situ annealing probed by spectrum imaging in the transmission electron microscope

NASA Astrophysics Data System (ADS)

Alix, K.; David, M.-L.; Dérès, J.; Hébert, C.; Pizzagalli, L.

2018-03-01

The evolution of nanometric helium bubbles in silicon has been investigated using spatially resolved electron energy-loss spectroscopy during in situ annealing in the transmission electron microscope. This approach allows the simultaneous determination of both the morphology and the helium density in the bubbles at each step of the annealing. Structural modification and helium emission from bubbles of various diameters in the range 7.5 to 20 nm and various aspect ratios of 1.1 to 1.9 have been studied. We clearly show that helium emission takes place at temperatures where bubble migration had hardly started. At higher temperatures, the migration (and coalescence) of voids is clearly revealed. For helium density lower than 150 He nm-3 , the Cerofolini's model taking into account the thermodynamical properties of an ultradense fluid reproduces well the helium emission from the bubbles, leading to an activation energy of 1.8 eV. When bubbles exhibit a higher initial helium density, the Cerofolini's model fails to reproduce the helium emission kinetics. We ascribe this to the fact that helium may be in the solid phase and we propose a tentative model to take into account the properties of the solid.

Effects of non-condensable gas on the dynamic oscillations of cavitation bubbles

NASA Astrophysics Data System (ADS)

Zhang, Yuning

2016-11-01

Cavitation is an essential topic of multiphase flow with a broad range of applications. Generally, there exists non-condensable gas in the liquid and a complex vapor/gas mixture bubble will be formed. A rigorous prediction of the dynamic behavior of the aforementioned mixture bubble is essential for the development of a complete cavitation model. In the present paper, effects of non-condensable gas on the dynamic oscillations of the vapor/gas mixture bubble are numerically investigated in great detail. For the completeness, a large parameter zone (e.g. bubble radius, frequency and ratio between gas and vapor) is investigated with many demonstrating examples. The mechanisms of mass diffusion are categorized into different groups with their characteristics and dominated regions given. Influences of non-condensable gas on the wave propagation (e.g. wave speed and attenuation) in the bubbly liquids are also briefly discussed. Specifically, the minimum wave speed is quantitatively predicted in order to close the pressure-density coupling relationship usually employed for the cavitation modelling. Finally, the application of the present finding on the development of cavitation model is demonstrated with a brief discussion of its influence on the cavitation dynamics. This work was financially supported by the National Natural Science Foundation of China (Project No.: 51506051).

Solar Wind Charge Exchange and Local Hot Bubble X-Ray Emission with the DXL Sounding Rocket Experiment

NASA Technical Reports Server (NTRS)

Galeazzi, M.; Collier, M. R.; Cravens, T.; Koutroumpa, D.; Kuntz, K. D.; Lepri, S.; McCammon, D.; Porter, F. S.; Prasai, K.; Robertson, I.;

Modelling and calculation of flotation process in one-dimensional formulation

NASA Astrophysics Data System (ADS)

Amanbaev, Tulegen; Tilleuov, Gamidulla; Tulegenova, Bibigul

2016-08-01

In the framework of the assumptions of the mechanics of the multiphase media is constructed a mathematical model of the flotation process in the dispersed mixture of liquid, solid and gas phases, taking into account the degree of mineralization of the surface of the bubbles. Application of the constructed model is demonstrated on the example of one-dimensional stationary flotation and it is shown that the equations describing the process of ascent of the bubbles are singularly perturbed ("rigid"). The effect of size and concentration of bubbles and the volumetric content of dispersed particles on the flotation process are analyzed.

A Study of Cavitation-Ignition Bubble Combustion

NASA Technical Reports Server (NTRS)

Nguyen, Quang-Viet; Jacqmin, David A.

2005-01-01

We present the results of an experimental and computational study of the physics and chemistry of cavitation-ignition bubble combustion (CIBC), a process that occurs when combustible gaseous mixtures are ignited by the high temperatures found inside a rapidly collapsing bubble. The CIBC process was modeled using a time-dependent compressible fluid-dynamics code that includes finite-rate chemistry. The model predicts that gas-phase reactions within the bubble produce CO and other gaseous by-products of combustion. In addition, heat and mechanical energy release through a bubble volume-expansion phase are also predicted by the model. We experimentally demonstrate the CIBC process using an ultrasonically excited cavitation flow reactor with various hydrocarbon-air mixtures in liquid water. Low concentrations (< 160 ppm) of carbon monoxide (CO) emissions from the ultrasonic reactor were measured, and found to be proportional to the acoustic excitation power. The results of the model were consistent with the measured experimental results. Based on the experimental findings, the computational model, and previous reports of the "micro-diesel effect" in industrial hydraulic systems, we conclude that CIBC is indeed possible and exists in ultrasonically- and hydrodynamically-induced cavitation. Finally, estimates of the utility of CIBC process as a means of powering an idealized heat engine are also presented.

Single Bubble Sonoluminescence in Low Gravity and Optical Radiation Pressure Positioning of the Bubble

NASA Technical Reports Server (NTRS)

Thiessen, D. B.; Young, J. E.; Marr-Lyon, M. J.; Richardson, S. L.; Breckon, C. D.; Douthit, S. G.; Jian, P. S.; Torruellas, W. E.; Marston, P. L.

1999-01-01

Several groups of researchers have demonstrated that high frequency sound in water may be used to cause the regular repeated compression and luminescence of a small bubble of gas in a flask. The phenomenon is known as single bubble sonoluminescence (SBSL). It is potentially important because light emitted by the bubble appears to be associated with a significant concentration of energy within the volume of the bubble. Unfortunately, the detailed physical mechanisms causing the radiation of light by oscillating bubbles are poorly understood and there is some evidence that carrying out experiments in a weightless environment may provide helpful clues. In addition, the radiation pressure of laser beams on the bubble may provide a way of simulating weightless experiments in the laboratory. The standard model of SBSL attributes the light emission to heating within the bubble by a spherically imploding shock wave to achieve temperatures of 50,000 K or greater. In an alternative model, the emission is attributed to the impact of a jet of water which is required to span the bubble and the formation of the jet is linked to the buoyancy of the bubble. The coupling between buoyancy and jet formation is a consequence of the displacement of the bubble from a velocity node (pressure antinode) of the standing acoustic wave that drives the radial bubble oscillations. One objective of this grant is to understand SBSL emission in reduced buoyancy on KC-135 parabolic flights. To optimize the design of those experiments and for other reasons which will help resolve the role of buoyancy, laboratory experiments are planned in simulated low gravity in which the radiation pressure of laser light will be used to position the bubble at the acoustic velocity node of the ultrasonic standing wave. Laser light will also be used to push the bubble away from the velocity node, increasing the effective buoyancy. The original experiments on the optical levitation and radiation pressure on bubbles in water by Unger and Marston noted above were carried out using a continuous wave (CW) beam of an Argon laser. For lateral stability the beam had a intensity minimum along its axis. Calculations of the optical radiation force on an SBSL bubble indicate that ion laser technology is a poor choice for providing the magnitude of the average optical radiation force required. Consequently it is necessary to examine various diode-pumped solid state laser technologies. The approach for this part of the research will be to achieve optical levitation of a quiescent bubble based on contemporary laser technology and then to strobe the laser synchronously with the SBSL bubble oscillations.

Effect of Supernovae on the Local Interstellar Material

NASA Astrophysics Data System (ADS)

Frisch, Priscilla; Dwarkadas, Vikram V.

A range of astronomical data indicates that ancient supernovae created the galactic environment of the Sun and sculpted the physical properties of the interstellar medium near the heliosphere. In this paper, we review the characteristics of the local interstellar medium that have been affected by supernovae. The kinematics, magnetic field, elemental abundances, and configuration of the nearest interstellar material support the view that the Sun is at the edge of the Loop I superbubble, which has merged into the low-density Local Bubble. The energy source for the higher temperature X-ray-emitting plasma pervading the Local Bubble is uncertain. Winds from massive stars and nearby supernovae, perhaps from the Sco-Cen association, may have contributed radioisotopes found in the geologic record and galactic cosmic ray population. Nested supernova shells in the Orion and Sco-Cen regions suggest spatially distinct sites of episodic star formation. The heliosphere properties vary with the pressure of the surrounding interstellar cloud. A nearby supernova would modify this pressure equilibrium and thereby severely disrupt the heliosphere as well as the local interstellar medium.

The relation between pre-eruptive bubble size distribution, ash particle morphology, and their internal density: Implications to volcanic ash transport and dispersion models

NASA Astrophysics Data System (ADS)

Proussevitch, Alexander

2014-05-01

Parameterization of volcanic ash transport and dispersion (VATD) models strongly depends on particle morphology and their internal properties. Shape of ash particles affects terminal fall velocities (TFV) and, mostly, dispersion. Internal density combined with particle size has a very strong impact on TFV and ultimately on the rate of ash cloud thinning and particle sedimentation on the ground. Unlike other parameters, internal particle density cannot be measured directly because of the micron scale sizes of fine ash particles, but we demonstrate that it varies greatly depending on the particle size. Small simple type ash particles (fragments of bubble walls, 5-20 micron size) do not contain whole large magmatic bubbles inside and their internal density is almost the same as that of volcanic glass matrix. On the other side, the larger compound type ash particles (>40 microns for silicic fine ashes) always contain some bubbles or the whole spectra of bubble size distribution (BSD), i.e. bubbles of all sizes, bringing their internal density down as compared to simple ash. So, density of the larger ash particles is a function of the void fraction inside them (magmatic bubbles) which, in turn, is controlled by BSD. Volcanic ash is a product of the fragmentation of magmatic foam formed by pre-eruptive bubble population and characterized by BSD. The latter can now be measured from bubble imprints on ash particle surfaces using stereo-scanning electron microscopy (SSEM) and BubbleMaker software developed at UNH, or using traditional high-resolution X-Ray tomography. In this work we present the mathematical and statistical formulation for this problem connecting internal ash density with particle size and BSD, and demonstrate how the TFV of the ash population is affected by variation of particle density.

Upper ocean bubble measurements from the NE Pacific and estimates of their role in air-sea gas transfer of the weakly soluble gases nitrogen and oxygen

NASA Astrophysics Data System (ADS)

Vagle, Svein; McNeil, Craig; Steiner, Nadja

2010-12-01

Simultaneous observations of upper-ocean bubble clouds, and dissolved gaseous nitrogen (N2) and oxygen (O2) from three winter storms are presented and analyzed. The data were collected on the Canadian Surface Ocean Lower Atmosphere Study (C-SOLAS) mooring located near Ocean Station Papa (OSP) at 50°N, 145°W in the NE Pacific during winter of 2003/2004. The bubble field was measured using an upward looking 200 kHz echosounder. Direct estimates of bubble mediated gas fluxes were made using assumed bubble size spectra and the upward looking echosounder data. A one-dimensional biogeochemical model was used to help compare data and various existing models of bubble mediated air-sea gas exchange. The direct bubble flux calculations show an approximate quadratic/cubic dependence on mean bubble penetration depth. After scaling from N2/O2 to carbon dioxide, near surface, nonsupersaturating, air-sea transfer rates, KT, for U10 > 12 m s-1 fall between quadratic and cubic relationships. Estimates of the subsurface bubble induced air injection flux, VT, show an approximate quadratic/cubic dependence on mean bubble penetration depth. Both KT and VT are much higher than those measured during Hurricane Frances over the wind speed range 12 < U10 < 23 m s-1. This result implies that over the open ocean and this wind speed range, older and more developed seas which occur during winter storms are more effective in exchanging gases between the atmosphere and ocean than younger less developed seas which occur during the rapid passage of a hurricane.

Champagne Patterns and Lake Nyos

ERIC Educational Resources Information Center

Science Teacher, 2005

2005-01-01

Carbon dioxide bubbles in a glass of champagne rise to the surface in fine threads, which are made of bubble groupings that change over time. Researchers from French and Brazilian universities have produced a new model that accounts for the patterns in strings of bubbles in champagne and other effervescent fluids. The research appears in Physical…

Bubble transport and sticking in gas embolotherapy

NASA Astrophysics Data System (ADS)

Bull, Joseph

2002-11-01

Pressure-driven bubble transport in a two-dimensional, bifurcating channel is investigated as a model of gas emboli transport in the microcirculation. Gas emboli are relevant to a number of clinical situations, and our particular interest is a novel gas embolotherapy technique, which involves using gas bubbles to occlude blood flow to tumors. This minimally invasive treatment modality allows selective delivery of emboli. The bubbles originate as 6 micron-diameter liquid droplets of perfluorocarbon (PFC), mixed in saline, and are injected into the vascular system. The droplet forms are small enough to pass through capillary beds, so they can circulate until the next stage of the therapy. By strategically placing an ultrasound source over the artery feeding the tumor, the droplets may be vaporized at that location. Our model is developed using the Stokes equation subject to interfacial and wall boundary conditions, and is solved using the boundary element method. The conditions under which bubbles 'stick' to the channel walls and occlude flow are investigated. Clinically, these results are important because the location and homogeneity of bubble sticking determines the degree of tumor necrosis and the efficacy of the treatment.

Midlatitude Plasma Bubbles Over China and Adjacent Areas During a Magnetic Storm on 8 September 2017

NASA Astrophysics Data System (ADS)

Aa, Ercha; Huang, Wengeng; Liu, Siqing; Ridley, Aaron; Zou, Shasha; Shi, Liqin; Chen, Yanhong; Shen, Hua; Yuan, Tianjiao; Li, Jianyong; Wang, Tan

2018-03-01

This paper presents observations of postsunset super plasma bubbles over China and adjacent areas during the second main phase of a storm on 8 September 2017. The signatures of the plasma bubbles can be seen or deduced from (1) deep field-aligned total electron content depletions embedded in regional ionospheric maps derived from dense Global Navigation Satellite System networks, (2) significant equatorial and midlatitudinal plasma bite-outs in electron density measurements on board Swarm satellites, and (3) enhancements of ionosonde virtual height and scintillation in local evening associated with strong southward interplanetary magnetic field. The bubbles/depletions covered a broad area mainly within 20°-45°N and 80°-110°E with bifurcated structures and persisted for nearly 5 hr (˜13-18 UT). One prominent feature is that the bubbles extended remarkably along the magnetic field lines in the form of depleted flux tubes, reaching up to midlatitude of around 50°N (magnetic latitude: 45.5°N) that maps to an altitude of 6,600 km over the magnetic equator. The maximum upward drift speed of the bubbles over the magnetic equator was about 700 m/s and gradually decreased with altitude and time. The possible triggering mechanism of the plasma bubbles was estimated to be storm time eastward prompt penetration electric field, while the traveling ionospheric disturbance could play a role in facilitating the latitudinal extension of the depletions.

Biophysical considerations for optimizing energy delivery during Erbium:YAG laser vitreoretinal surgery

NASA Astrophysics Data System (ADS)

Berger, Jeffrey W.; Bochow, Thomas W.; Kim, Rosa Y.; D'Amico, Donald J.

1996-05-01

Er:YAG laser-mediated tissue disruption and removal results from both direct ablation and the acousto-mechanical sequelae of explosive vaporization of the tissue water. We investigated the scaling laws for photoablative and photodisruptive interactions, and interpret these results towards optimizing energy delivery for vitreoretinal surgical maneuvers. Experimental studies were performed with a free-running Er:YAG laser (100 - 300 microseconds FWHM, 0.5 - 20 mJ, 1 - 30 Hz). Energy was delivered by fiberoptic to a custom-made handpiece with a 75 - 600 micrometer quartz tip, and applied to excised, en bloc samples of bovine vitreous or model systems of saline solution. Sample temperature was measured with 33 gauge copper- constantan thermocouples. Expansion and collapse of the bubble following explosive vaporization of tissue water was optically detected. The bubble size was calculated from the period of the bubble oscillation and known material properties. A model for bubble expansion is presented based on energy principles and adiabatic gas expansion. Pressure transients associated with bubble dynamics are estimated following available experimental and analytical data. The temperature rise in vitreous and model systems depends on the pulse energy and repetition rate, but is independent of the probe-tip diameter at constant laser power; at moderate repetition rates, the temperature rise depends only on the total energy (mJ) delivered. The maximum bubble diameter increases as the cube root of the pulse energy with a reverberation period of 110 microseconds and a maximum bubble diameter of 1.2 mm following one mJ delivery to saline through a 100 micrometer tip. Our modeling studies generate predictions similar to experimental data and predicts that the maximum bubble diameter increases as the cube root of the pulse energy. We demonstrate that tissue ablation depends on radiant exposure (J/cm2), while temperature rise, bubble size, and pressure depends on total pulse energy. Further, we show that mechanical injury should be minimized by delivering low pulse energy, through small diameter probe tips, at high repetition rates. These results allow for optimization strategies relevant to achieving vitreoretinal surgical goals while minimizing the potential for unintentional injury.

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

DOE PAGES

Hernandez-Alvarado, Freddy; Kalaga, Dinesh V.; Turney, Damon; ...

2017-05-06

Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fractionmore » and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m 2/m 3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%) in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.« less

Interaction of lithotripter shockwaves with single inertial cavitation bubbles

PubMed Central

Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K.; Khoo, Boo Cheong; Szeri, Andrew J.; Calvisi, Michael L.; Sankin, Georgy N.; Zhong, Pei

2008-01-01

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave–bubble interaction are discussed. PMID:19018296

Interaction of lithotripter shockwaves with single inertial cavitation bubbles.

PubMed

Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K; Khoo, Boo Cheong; Szeri, Andrew J; Calvisi, Michael L; Sankin, Georgy N; Zhong, Pei

2007-01-01

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed.

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez-Alvarado, Freddy; Kalaga, Dinesh V.; Turney, Damon

Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fractionmore » and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m 2/m 3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%) in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.« less

Gas embolotherapy: Bubble evolution in acoustic droplet vaporization and design of a benchtop microvascular model

NASA Astrophysics Data System (ADS)

Wong, Zheng Zheng

This work was motivated by an ongoing development of a potential embolotherapy technique to occlude blood flow to tumors using gas bubbles selectively formed by in vivo acoustic droplet vaporization (ADV) of liquid perfluorocarbon droplets. Mechanisms behind the ADV, transport and lodging of emboli need to be understood before gas embolotherapy can translate to the clinic. Evolution of a bubble from acoustic droplet vaporization in a rigid tube, under physiological and room temperature conditions, was observed via ultra-high speed imaging. Effective radii and radial expansion ratios were obtained by processing the images using Image] software. At physiological temperature, a radial expansion ratio of 5.05 was attained, consistent with theoretical prediction. The initial radial growth rate was linear, after which the growth rate increased proportionally with square root of time. Nondimensionalization revealed that the subsequent growth rate also varied inversely with square root of initial radius. Eventually growth became asymptotic. No collapse was observed. A theoretical model derived from a modified Bernoulli equation, and a computational model by Ye & Bull (2004), were compared respectively with experimental results. Initial growth rates were predicted correctly by both models. Experimental results showed heavy damping of growth rate as the bubble grew towards the wall, whereas both models predicted an overshoot in growth followed by multiple oscillations. The theoretical model broke down near the wall; the computational model gave a reasonable bubble shape near the wall but would require correct initial pressure values to be accurate. At room temperature, the expansion ratio shot to 1.43 initially and oscillated down to 1.11, far below the theoretical prediction. Failure of the bubble to expand fully could be due to unconsumed or condensed liquid perfluorocarbon. A new fabrication method via non-lithographic means was devised to make a circular-lumen microchannel out of PDMS, with a diameter as small as 80 microns to mimic the size of a medium arteriole. The microchannel was endothelialized successfully, with a fairly homogeneous distribution along the length. Cell viability assays confirmed the viability of cells maintained in the microchannel. Bubble motion experiments performed with the benchtop microvascular model demonstrated its feasibility.

Direct numerical simulation of reactor two-phase flows enabled by high-performance computing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Jun; Cambareri, Joseph J.; Brown, Cameron S.

Nuclear reactor two-phase flows remain a great engineering challenge, where the high-resolution two-phase flow database which can inform practical model development is still sparse due to the extreme reactor operation conditions and measurement difficulties. Owing to the rapid growth of computing power, the direct numerical simulation (DNS) is enjoying a renewed interest in investigating the related flow problems. A combination between DNS and an interface tracking method can provide a unique opportunity to study two-phase flows based on first principles calculations. More importantly, state-of-the-art high-performance computing (HPC) facilities are helping unlock this great potential. This paper reviews the recent researchmore » progress of two-phase flow DNS related to reactor applications. The progress in large-scale bubbly flow DNS has been focused not only on the sheer size of those simulations in terms of resolved Reynolds number, but also on the associated advanced modeling and analysis techniques. Specifically, the current areas of active research include modeling of sub-cooled boiling, bubble coalescence, as well as the advanced post-processing toolkit for bubbly flow simulations in reactor geometries. A novel bubble tracking method has been developed to track the evolution of bubbles in two-phase bubbly flow. Also, spectral analysis of DNS database in different geometries has been performed to investigate the modulation of the energy spectrum slope due to bubble-induced turbulence. In addition, the single-and two-phase analysis results are presented for turbulent flows within the pressurized water reactor (PWR) core geometries. The related simulations are possible to carry out only with the world leading HPC platforms. These simulations are allowing more complex turbulence model development and validation for use in 3D multiphase computational fluid dynamics (M-CFD) codes.« less

Shock-wave generation and bubble formation in the retina by lasers

NASA Astrophysics Data System (ADS)

Sun, Jinming; Gerstman, Bernard S.; Li, Bin

2000-06-01

The generation of shock waves and bubbles has been experimentally observed due to absorption of sub-nanosecond laser pulses by melanosomes, which are found in retinal pigment epithelium cells. Both the shock waves and bubbles may be the cause of retinal damage at threshold fluence levels. The theoretical modeling of shock wave parameters such as amplitude, and bubble size, is a complicated problem due to the non-linearity of the phenomena. We have used two different approaches for treating pressure variations in water: the Tait Equation and a full Equation Of State (EOS). The Tait Equation has the advantage of being developed specifically to model pressure variations in water and is therefore simpler, quicker computationally, and allows the liquid to sustain negative pressures. Its disadvantage is that it does not allow for a change of phase, which prevents modeling of bubbles and leads to non-physical behavior such as the sustaining of ridiculously large negative pressures. The full EOS treatment includes more of the true thermodynamic behavior, such as phase changes that produce bubbles and avoids the generation of large negative pressures. Its disadvantage is that the usual stable equilibrium EOS allows for no negative pressures at all, since tensile stress is unstable with respect to a transition to the vapor phase. In addition, the EOS treatment requires longer computational times. In this paper, we compare shock wave generation for various laser pulses using the two different mathematical approaches and determine the laser pulse regime for which the simpler Tait Equation can be used with confidence. We also present results of our full EOS treatment in which both shock waves and bubbles are simultaneously modeled.

A Physical Model to Study the Effects of Nozzle Design on Dispersed Two-Phase Flows in a Slab Mold Casting Ultra-Low-Carbon Steels

NASA Astrophysics Data System (ADS)

Salazar-Campoy, María M.; Morales, R. D.; Nájera-Bastida, A.; Calderón-Ramos, Ismael; Cedillo-Hernández, Valentín; Delgado-Pureco, J. C.

2018-04-01

The effects of nozzle design on dispersed, two-phase flows of the steel-argon system in a slab mold are studied using a water-air model with particle image velocimetry and ultrasound probe velocimetry techniques. Three nozzle designs were tested with the same bore size and different port geometries, including square (S), special bottom design with square ports (U), and circular (C). The meniscus velocities of the liquid increase two- or threefold in two-phase flows regarding one-phase flows using low flow rates of the gas phase. This effect is due to the dragging effects on bubbles by the liquid jets forming two-way coupled flows. Liquid velocities (primary phase) along the narrow face of the mold also are higher for two-phase flows. Flows using nozzle U are less dependent on the effects of the secondary phase (air). The smallest bubble sizes are obtained using nozzle U, which confirms that bubble breakup is dependent on the strain rates of the fluid and dissipation of kinetic energy in the nozzle bottom and port edges. Through dimensionless analysis, it was found that the bubble sizes are inversely proportional to the dissipation rate of the turbulent kinetic energy, ɛ 0.4. A simple expression involving ɛ, surface tension, and density of metal is derived to scale up bubble sizes in water to bubble sizes in steel with different degrees of deoxidation. The validity of water-air models to study steel-argon flows is discussed. Prior works related with experiments to model argon bubbling in steel slab molds under nonwetting conditions are critically reviewed.

One-dimensional model of inertial pumping

NASA Astrophysics Data System (ADS)

Kornilovitch, Pavel E.; Govyadinov, Alexander N.; Markel, David P.; Torniainen, Erik D.

2013-02-01

A one-dimensional model of inertial pumping is introduced and solved. The pump is driven by a high-pressure vapor bubble generated by a microheater positioned asymmetrically in a microchannel. The bubble is approximated as a short-term impulse delivered to the two fluidic columns inside the channel. Fluid dynamics is described by a Newton-like equation with a variable mass, but without the mass derivative term. Because of smaller inertia, the short column refills the channel faster and accumulates a larger mechanical momentum. After bubble collapse the total fluid momentum is nonzero, resulting in a net flow. Two different versions of the model are analyzed in detail, analytically and numerically. In the symmetrical model, the pressure at the channel-reservoir connection plane is assumed constant, whereas in the asymmetrical model it is reduced by a Bernoulli term. For low and intermediate vapor bubble pressures, both models predict the existence of an optimal microheater location. The predicted net flow in the asymmetrical model is smaller by a factor of about 2. For unphysically large vapor pressures, the asymmetrical model predicts saturation of the effect, while in the symmetrical model net flow increases indefinitely. Pumping is reduced by nonzero viscosity, but to a different degree depending on the microheater location.

One-dimensional model of inertial pumping.

PubMed

Kornilovitch, Pavel E; Govyadinov, Alexander N; Markel, David P; Torniainen, Erik D

2013-02-01

A one-dimensional model of inertial pumping is introduced and solved. The pump is driven by a high-pressure vapor bubble generated by a microheater positioned asymmetrically in a microchannel. The bubble is approximated as a short-term impulse delivered to the two fluidic columns inside the channel. Fluid dynamics is described by a Newton-like equation with a variable mass, but without the mass derivative term. Because of smaller inertia, the short column refills the channel faster and accumulates a larger mechanical momentum. After bubble collapse the total fluid momentum is nonzero, resulting in a net flow. Two different versions of the model are analyzed in detail, analytically and numerically. In the symmetrical model, the pressure at the channel-reservoir connection plane is assumed constant, whereas in the asymmetrical model it is reduced by a Bernoulli term. For low and intermediate vapor bubble pressures, both models predict the existence of an optimal microheater location. The predicted net flow in the asymmetrical model is smaller by a factor of about 2. For unphysically large vapor pressures, the asymmetrical model predicts saturation of the effect, while in the symmetrical model net flow increases indefinitely. Pumping is reduced by nonzero viscosity, but to a different degree depending on the microheater location.

The effect of gravity-induced pressure gradient on bubble luminescence

NASA Astrophysics Data System (ADS)

Supponen, Outi; Obreschkow, Danail; Kobel, Philippe; Dorsaz, Nicolas; Tinguely, Marc; Farhat, Mohamed

2014-11-01

The violent collapse of a bubble can heat up its gaseous contents to temperatures exceeding those on the sun's surface, resulting in a short luminescence flash. Occurring at the very moment of the collapse, luminescence must be highly sensitive to the bubble geometry at the preceding final stage. This represents an important feature as any pressure anisotropy in the surrounding liquid will result in a deformation of an initially spherical bubble, inducing a micro-jet that pierces the bubble and makes it experience a toroidal collapse. We therefore present these as complementary phenomena by investigating the link between jets and luminescence of laser-generated single bubbles. Through ultra-high-speed imaging, the micro-jet formation and evolution of a single bubble are observed with unprecedented detail, whilst the bubble light emission is analyzed by means of a spectrometer. The bubble energy and the micro-jet size are controlled by adjusting the laser-pulse and by varying the gravity level aboard ESA parabolic flights, respectively. We here provide systematic evidence on how bubble-jets suppress luminescence in a considerable manner, even in normal gravity where the jet is barely observable. We conclude that gravity must be accounted for in accurate models of luminescence.

Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Motil, Brian J.; Skor, Mark

2003-01-01

Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.

A derivation of the stable cavitation threshold accounting for bubble-bubble interactions.

PubMed

Guédra, Matthieu; Cornu, Corentin; Inserra, Claude

2017-09-01

The subharmonic emission of sound coming from the nonlinear response of a bubble population is the most used indicator for stable cavitation. When driven at twice their resonance frequency, bubbles can exhibit subharmonic spherical oscillations if the acoustic pressure amplitude exceeds a threshold value. Although various theoretical derivations exist for the subharmonic emission by free or coated bubbles, they all rest on the single bubble model. In this paper, we propose an analytical expression of the subharmonic threshold for interacting bubbles in a homogeneous, monodisperse cloud. This theory predicts a shift of the subharmonic resonance frequency and a decrease of the corresponding pressure threshold due to the interactions. For a given sonication frequency, these results show that an optimal value of the interaction strength (i.e. the number density of bubbles) can be found for which the subharmonic threshold is minimum, which is consistent with recently published experiments conducted on ultrasound contrast agents. Copyright © 2017 Elsevier B.V. All rights reserved.

Noise reduction by the application of an air-bubble curtain in offshore pile driving

NASA Astrophysics Data System (ADS)

Tsouvalas, A.; Metrikine, A. V.

2016-06-01

Underwater noise pollution is a by-product of marine industrial operations. In particular, the noise generated when a foundation pile is driven into the soil with an impact hammer is considered to be harmful for the aquatic species. In an attempt to reduce the ecological footprint, several noise mitigation techniques have been investigated. Among the various solutions proposed, the air-bubble curtain is often applied due to its efficacy in noise reduction. In this paper, a model is proposed for the investigation of the sound reduction during marine piling when an air-bubble curtain is placed around the pile. The model consists of the pile, the surrounding water and soil media, and the air-bubble curtain which is positioned at a certain distance from the pile surface. The solution approach is semi-analytical and is based on the dynamic sub-structuring technique and the modal decomposition method. Two main results of the paper can be distinguished. First, a new model is proposed that can be used for predictions of the noise levels in a computationally efficient manner. Second, an analysis is presented of the principal mechanisms that are responsible for the noise reduction due to the application of the air-bubble curtain in marine piling. The understanding of these mechanisms turns to be crucial for the exploitation of the maximum efficiency of the system. It is shown that the principal mechanism of noise reduction depends strongly on the frequency content of the radiated sound and the characteristics of the bubbly medium. For piles of large diameter which radiate most of the acoustic energy at relatively low frequencies, the noise reduction is mainly attributed to the mismatch of the acoustic impedances between the seawater and the bubbly layer. On the contrary, for smaller piles and when the radiated acoustic energy is concentrated at frequencies close to, or higher than, the resonance frequency of the air bubbles, the sound absorption within the bubbly layer becomes critical.

Inhibition of bubble coalescence: effects of salt concentration and speed of approach.

PubMed

Del Castillo, Lorena A; Ohnishi, Satomi; Horn, Roger G

2011-04-01

Bubble coalescence experiments have been performed using a sliding bubble apparatus, in which mm-sized bubbles in an aqueous electrolyte solution without added surfactant rose toward an air meniscus at different speeds obtained by varying the inclination of a closed glass cylinder containing the liquid. The coalescence times of single bubbles contacting the meniscus were monitored using a high speed camera. Results clearly show that stability against coalescence of colliding air bubbles is influenced by both the salt concentration and the approach speed of the bubbles. Contrary to the widespread belief that bubbles in pure water are unstable, we demonstrate that bubbles formed in highly purified water and colliding with the meniscus at very slow approach speeds can survive for minutes or even hours. At higher speeds, bubbles in water only survive for a few seconds, and at still higher speeds they coalesce instantly. Addition of a simple electrolyte (KCl) removes the low-speed stability and shifts the transition between transient stability and instant coalescence to higher approach speeds. At high electrolyte concentration no bubbles were observed to coalesce instantly. These observations are consistent with recent results of Yaminsky et al. (Langmuir 26 (2010) 8061) and the transitions between different regions of behavior are in semi-quantitative agreement with Yaminsky's model. Copyright © 2010 Elsevier Inc. All rights reserved.

Study of non-spherical bubble oscillations near a surface in a weak acoustic standing wave field.

PubMed

Xi, Xiaoyu; Cegla, Frederic; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2014-04-01

The interaction of acoustically driven bubbles with a wall is important in many applications of ultrasound and cavitation, as the close boundary can severely alter the bubble dynamics. In this paper, the non-spherical surface oscillations of bubbles near a surface in a weak acoustic standing wave field are investigated experimentally and numerically. The translation, the volume, and surface mode oscillations of bubbles near a flat glass surface were observed by a high speed camera in a standing wave cell at 46.8 kHz. The model approach is based on a modified Keller-Miksis equation coupled to surface mode amplitude equations in the first order, and to the translation equations. Modifications are introduced due to the adjacent wall. It was found that a bubble's oscillation mode can change in the presence of the wall, as compared to the bubble in the bulk liquid. In particular, the wall shifts the instability pressure thresholds to smaller driving frequencies for fixed bubble equilibrium radii, or to smaller equilibrium radii for fixed excitation frequency. This can destabilize otherwise spherical bubbles, or stabilize bubbles undergoing surface oscillations in the bulk. The bubble dynamics observed in experiment demonstrated the same trend as the theoretical results.

A Well-Posed, Objective and Dynamic Two-Fluid Model

NASA Astrophysics Data System (ADS)

Chetty, Krishna; Vaidheeswaran, Avinash; Sharma, Subash; Clausse, Alejandro; Lopez de Bertodano, Martin

The transition from dispersed to clustered bubbly flows due to wake entrainment is analyzed with a well-posed and objective one-dimensional (1-D) Two-Fluid Model, derived from variational principles. Modeling the wake entrainment force using the variational technique requires formulation of the inertial coupling coefficient, which defines the kinetic coupling between the phases. The kinetic coupling between a pair of bubbles and the liquid is obtained from potential flow over two-spheres and the results are validated by comparing the virtual mass coefficients with existing literature. The two-body interaction kinetic coupling is then extended to a lumped parameter model for viscous flow over two cylindrical bubbles, to get the Two-Fluid Model for wake entrainment. Linear stability analyses comprising the characteristics and the dispersion relation and non-linear numerical simulations are performed with the 1-D variational Two-Fluid Model to demonstrate the wake entrainment instability leading to clustering of bubbles. Finally, the wavelengths, amplitudes and propagation velocities of the void waves from non-linear simulations are compared with the experimental data.

Investigation of the properties of laser-induced cavitation bubble collapse and sound waves

NASA Astrophysics Data System (ADS)

Li, Shengyong; Ai, Xiaochuan; Wu, Ronghua; Cao, Jing

2017-02-01

The theoretical model of single bubble movement in an ideal solution, to carry on the numerical simulation of the process of cavitation in the liquid, the liquid in different laser energy, laser induced cavitation rules and acoustic characteristics were studied by high-speed camera, high frequency measurements of the hydrophone. The results show that with the increase of laser energy, the period of bubble pulsation and the maximum bubble radius increase gradually, and the amplitude of the laser acoustic signal becomes larger.

"Pressure Blocking" Effect in the Growing Vapor Bubble in a Highly Superheated Liquid

NASA Astrophysics Data System (ADS)

Zudin, Yu. B.; Zenin, V. V.

2016-09-01

The problem on the growth of a vapor bubble in a liquid whose superheating enthalpy exceeds the phase transition heat has been considered. A physical model of the "pressure blocking" in the bubble is presented. The problem for the conditions of the experiment on the effervescence of a butane drop has been solved numerically. An algorithm for constructing an analytical solution of the problem on the bubble growth in a highly superheated liquid is proposed.

Viscocapillary Response of Gas Bubbles Probed by Thermal Noise Atomic Force Measurement.

PubMed

Wang, Yuliang; Zeng, Binglin; Alem, Hadush Tedros; Zhang, Zaicheng; Charlaix, Elisabeth; Maali, Abdelhamid

2018-01-30

We present thermal noise measurements of a vibrating sphere close to microsized air bubbles in water with an atomic force microscope. The sphere was glued at the end of a cantilever with a resonance frequency of few kHz. The subangstrom thermal motion of the microsphere reveals an elastohydrodynamic coupling between the sphere and the air bubble. The results are in perfect agreement with a model incorporating macroscopic capillarity and fluid flow on the bubble surface with full slip boundary conditions.

Numerical investigation of bubble nonlinear dynamics characteristics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Jie, E-mail: shijie@hrbeu.edu.cn; Yang, Desen; Shi, Shengguo

2015-10-28

The complicated dynamical behaviors of bubble oscillation driven by acoustic wave can provide favorable conditions for many engineering applications. On the basis of Keller-Miksis model, the influences of control parameters, including acoustic frequency, acoustic pressure and radius of gas bubble, are discussed by utilizing various numerical analysis methods, Furthermore, the law of power spectral variation is studied. It is shown that the complicated dynamic behaviors of bubble oscillation driven by acoustic wave, such as bifurcation and chaos, further the stimulated scattering processes are revealed.

A New Theory of Nucleate Pool Boiling in Arbitrary Gravity

NASA Technical Reports Server (NTRS)

Buyevich, Y. A.; Webbon, Bruce W.

1995-01-01

Heat transfer rates specific to nucleate pool boiling under various conditions are determined by the dynamics of vapour bubbles that are originated and grow at nucleation sites of a superheated surface. A new dynamic theory of these bubbles has been recently developed on the basis of the thermodynamics of irreversible processes. In contrast to other existing models based on empirically postulated equations for bubble growth and motion, this theory does not contain unwarrantable assumptions, and both the equations are rigorously derived within the framework of a unified approach. The conclusions of the theory are drastically different from those of the conventional models. The bubbles are shown to detach themselves under combined action of buoyancy and a surface tension force that is proven to add to buoyancy in bubble detachment, but not the other way round as is commonly presumed. The theory ensures a sound understanding of a number of so far unexplained phenomena, such as effect caused by gravity level and surface tension on the bubble growth rate and dependence of the bubble characteristics at detachment on the liquid thermophysical parameters and relevant temperature differences. The theoretical predictions are shown to be in a satisfactory qualitative and quantitative agreement with observations. When being applied to heat transfer at nucleate pool boiling, this bubble dynamic theory offers an opportunity to considerably improve the main formulae that are generally used to correlate experimental findings and to design boiling heat removal in various industrial applications. Moreover, the theory makes possible to pose and study a great deal of new problems of essential impact in practice. Two such problems are considered in detail. One problem concerns the development of a principally novel physical model for the first crisis of boiling. This model allows for evaluating critical boiling heat fluxes under various conditions, and in particular at different gravity levels, with a good agreement with experimental evidence. The other problem bears upon equilibrium shapes of a detached bubble near a heated surface in exceedingly low gravity. In low gravity or in weightlessness, the bubble can remain in the close vicinity of the surface for a long time, and its shape is greatly affected by the Marangoni effect due to both temperature and possible surfactant concentration being nonuniform along the interface. The bubble performs at these conditions like a heat pipe, with evaporation at the bubble lower boundary and condensation at its upper boundary, and ultimately ensures a substantial increase in heat removal as compared with that in normal gravity. Some other problems relevant to nucleate pool and forced convection boiling heat transfer are also discussed.

Dynamics of primary and secondary microbubbles created by laser-induced breakdown of an optically trapped nanoparticle

PubMed Central

Arita, Y.; Antkowiak, M.; Venugopalan, V.; Gunn-Moore, F. J.; Dholakia, K.

2012-01-01

Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative position between the laser focus and the center of the optically trapped nanoparticle. We quantify the spatial and temporal dynamics of the cavitation and secondary bubbles created in this system and use hydrodynamic modeling to quantify the observed dynamic shear stress of the expanding bubble. In the final stage of bubble collapse, we visualize the formation of multiple submicrometer secondary bubbles around the toroidal bubble on the substrate. We show that the pattern of the secondary bubbles typically has its circular symmetry broken along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards the boundary upon bubble collapse near solid boundaries. PMID:22400669

Recognition and measurement gas-liquid two-phase flow in a vertical concentric annulus at high pressures

NASA Astrophysics Data System (ADS)

Li, Hao; Sun, Baojiang; Guo, Yanli; Gao, Yonghai; Zhao, Xinxin

2018-02-01

The air-water flow characteristics under pressure in the range of 1-6 MPa in a vertical annulus were evaluated in this report. Time-resolved bubble rising velocity and void fraction were also measured using an electrical void fraction meter. The results showed that the pressure has remarkable effect on the density, bubble size and rise velocity of the gas. Four flow patterns (bubble, cap-bubble, cap-slug, and churn) were also observed instead of Taylor bubble at high pressure. Additionally, the transition process from bubble to cap-bubble was investigated at atmospheric and high pressures, respectively. The results revealed that the flow regime transition criteria for atmospheric pressure do not work at high pressure, hence a new flow regime transition model for annular flow channel geometry was developed to predict the flow regime transition, which thereafter exhibited high accuracy at high pressure condition.

The Collapse of Vapor Bubbles in a Spatially Non-Uniform Flow

NASA Technical Reports Server (NTRS)

Hao, Y.; Prosperetti, A.

2000-01-01

Pressure gradients act differently on liquid particles and suspended bubbles and are, therefore, capable of inducing a relative motion between the phases even when no relative velocity initially exists. As a consequence of the enhanced heat transfer in the presence of convection, this fact may have a major impact on the evolution of a vapor bubble. The effect is particularly strong in the case of a collapsing bubble for which, due to the conservation of the system's impulse, the induced relative velocity tends to be magnified when the bubble volume shrinks. A practical application could be, for instance, the enhancement of the condensation rate of bubbles downstream of a heated region, thereby reducing the quality of a flowing liquid-vapor mixture. A simple model of the process, in which the bubble is assumed to be spherical and the flow potential, is developed in the paper.

Bubble evolution in Kr-irradiated UO2 during annealing

NASA Astrophysics Data System (ADS)

He, L.; Bai, X. M.; Pakarinen, J.; Jaques, B. J.; Gan, J.; Nelson, A. T.; El-Azab, A.; Allen, T. R.

2017-12-01

Transmission electron microscopy observation of Kr bubble evolution in polycrystalline UO2 annealed at high temperature was conducted in order to understand the inert gas behavior in oxide nuclear fuel. The average diameter of intragranular bubbles increased gradually from 0.8 nm in as-irradiated sample at room temperature to 2.6 nm at 1600 °C and the bubble size distribution changed from a uniform distribution to a bimodal distribution above 1300 °C. The size of intergranular bubbles increased more rapidly than intragranular ones and bubble denuded zones near grain boundaries formed in all the annealed samples. It was found that high-angle grain boundaries held bigger bubbles than low-angle grain boundaries. Complementary atomistic modeling was conducted to interpret the effects of grain boundary character on the Kr segregation. The area density of strong segregation sites in the high-angle grain boundaries is much higher than that in the low angle grain boundaries.

Formation of soap bubbles by gas jet

NASA Astrophysics Data System (ADS)

Zhou, Maolei; Li, Min; Chen, Zhiyuan; Han, Jifeng; Liu, Dong

2017-12-01

Soap bubbles can be easily generated by various methods, while their formation process is complicated and still worth studying. A model about the bubble formation process was proposed in the study by Salkin et al. [Phys. Rev. Lett. 116, 077801 (2016)] recently, and it was reported that the bubbles were formed when the gas blowing velocity was above one threshold. However, after a detailed study of these experiments, we found that the bubbles could be generated in two velocity ranges which corresponded to the laminar and turbulent gas jet, respectively, and the predicted threshold was only effective for turbulent gas flow. The study revealed that the bubble formation was greatly influenced by the aerodynamics of the gas jet blowing to the film, and these results will help to further understand the formation mechanism of the soap bubble as well as the interaction between the gas jet and the thin liquid film.

First observational tests of eternal inflation.

PubMed

Feeney, Stephen M; Johnson, Matthew C; Mortlock, Daniel J; Peiris, Hiranya V

2011-08-12

The eternal inflation scenario predicts that our observable Universe resides inside a single bubble embedded in a vast inflating multiverse. We present the first observational tests of eternal inflation, performing a search for cosmological signatures of collisions with other bubble universes in cosmic microwave background data from the WMAP satellite. We conclude that the WMAP 7-year data do not warrant augmenting the cold dark matter model with a cosmological constant with bubble collisions, constraining the average number of detectable bubble collisions on the full sky N(s) < 1.6 at 68% C.L. Data from the Planck satellite can be used to more definitively test the bubble-collision hypothesis.

Influence of the Fluid on the Parameters and Limits of Bubble Detonation

NASA Astrophysics Data System (ADS)

Pinaev, A. V.; Prokhorov, E. S.

2017-12-01

The compression and inflammation of reactive gas bubbles in bubble detonation waves have been studied, and the considerable influence of the fluid (liquid or vapor) on the detonation parameters has been found. It has been shown numerically that the final values of the pressure and temperature significantly decrease if the temperature dependence of the adiabatic index is taken into account at the compression stage. The parameters of reactive gas combustion products in the bubble have been calculated in terms of an equilibrium model, and the influence of the fluid that remains in the bubble in the form of microdroplets and vapor on these parameters has been investigated.

Numerical modeling of the 3D dynamics of ultrasound contrast agent microbubbles using the boundary integral method

NASA Astrophysics Data System (ADS)

Wang, Qianxi; Manmi, Kawa; Calvisi, Michael L.

2015-02-01

Ultrasound contrast agents (UCAs) are microbubbles stabilized with a shell typically of lipid, polymer, or protein and are emerging as a unique tool for noninvasive therapies ranging from gene delivery to tumor ablation. While various models have been developed to describe the spherical oscillations of contrast agents, the treatment of nonspherical behavior has received less attention. However, the nonspherical dynamics of contrast agents are thought to play an important role in therapeutic applications, for example, enhancing the uptake of therapeutic agents across cell membranes and tissue interfaces, and causing tissue ablation. In this paper, a model for nonspherical contrast agent dynamics based on the boundary integral method is described. The effects of the encapsulating shell are approximated by adapting Hoff's model for thin-shell, spherical contrast agents. A high-quality mesh of the bubble surface is maintained by implementing a hybrid approach of the Lagrangian method and elastic mesh technique. The numerical model agrees well with a modified Rayleigh-Plesset equation for encapsulated spherical bubbles. Numerical analyses of the dynamics of UCAs in an infinite liquid and near a rigid wall are performed in parameter regimes of clinical relevance. The oscillation amplitude and period decrease significantly due to the coating. A bubble jet forms when the amplitude of ultrasound is sufficiently large, as occurs for bubbles without a coating; however, the threshold amplitude required to incite jetting increases due to the coating. When a UCA is near a rigid boundary subject to acoustic forcing, the jet is directed towards the wall if the acoustic wave propagates perpendicular to the boundary. When the acoustic wave propagates parallel to the rigid boundary, the jet direction has components both along the wave direction and towards the boundary that depend mainly on the dimensionless standoff distance of the bubble from the boundary. In all cases, the jet directions for the coated and uncoated bubble are similar but the jet width and jet velocity are smaller for a coated bubble. The effects of shell thickness and shell viscosity are analyzed and determined to affect the bubble dynamics, including jet development.

Bioeffects due to acoustic droplet vaporization

NASA Astrophysics Data System (ADS)

Bull, Joseph

2015-11-01

Encapsulated micro- and nano-droplets can be vaporized via ultrasound, a process termed acoustic droplet vaporization. Our interest is primarily motivated by a developmental gas embolotherapy technique for cancer treatment. In this methodology, infarction of tumors is induced by selectively formed vascular gas bubbles that arise from the acoustic vaporization of vascular microdroplets. Additionally, the microdroplets may be used as vehicles for localized drug delivery, with or without flow occlusion. In this talk, we examine the dynamics of acoustic droplet vaporization through experiments and theoretical/computational fluid mechanics models, and investigate the bioeffects of acoustic droplet vaporization on endothelial cells and in vivo. Early timescale vaporization events, including phase change, are directly visualized using ultra-high speed imaging, and the influence of acoustic parameters on droplet/bubble dynamics is discussed. Acoustic and fluid mechanics parameters affecting the severity of endothelial cell bioeffects are explored. These findings suggest parameter spaces for which bioeffects may be reduced or enhanced, depending on the objective of the therapy. This work was supported by NIH grant R01EB006476.

Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

NASA Astrophysics Data System (ADS)

Miau, J. J.; Tsai, H. W.; Lin, Y. J.; Tu, J. K.; Fang, C. H.; Chen, M. C.

2011-10-01

Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 × 105-5.86 × 105. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured simultaneously at θ = ±90° further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident.

Shrinking microbubbles with microfluidics: mathematical modelling to control microbubble sizes.

PubMed

Salari, A; Gnyawali, V; Griffiths, I M; Karshafian, R; Kolios, M C; Tsai, S S H

2017-11-29

Microbubbles have applications in industry and life-sciences. In medicine, small encapsulated bubbles (<10 μm) are desirable because of their utility in drug/oxygen delivery, sonoporation, and ultrasound diagnostics. While there are various techniques for generating microbubbles, microfluidic methods are distinguished due to their precise control and ease-of-fabrication. Nevertheless, sub-10 μm diameter bubble generation using microfluidics remains challenging, and typically requires expensive equipment and cumbersome setups. Recently, our group reported a microfluidic platform that shrinks microbubbles to sub-10 μm diameters. The microfluidic platform utilizes a simple microbubble-generating flow-focusing geometry, integrated with a vacuum shrinkage system, to achieve microbubble sizes that are desirable in medicine, and pave the way to eventual clinical uptake of microfluidically generated microbubbles. A theoretical framework is now needed to relate the size of the microbubbles produced and the system's input parameters. In this manuscript, we characterize microbubbles made with various lipid concentrations flowing in solutions that have different interfacial tensions, and monitor the changes in bubble size along the microfluidic channel under various vacuum pressures. We use the physics governing the shrinkage mechanism to develop a mathematical model that predicts the resulting bubble sizes and elucidates the dominant parameters controlling bubble sizes. The model shows a good agreement with the experimental data, predicting the resulting microbubble sizes under different experimental input conditions. We anticipate that the model will find utility in enabling users of the microfluidic platform to engineer bubbles of specific sizes.

Root Causes of the Housing Bubble

NASA Astrophysics Data System (ADS)

Kaizoji, Taisei

In this chapter we investigate root causes of the recent US housing bubble which has been caused a serious downturn in US economic growth since autumn of 2008. We propose a simple model of housing markets in order to indicate the possible determinants of recent housing prices. Utilizing the model, we verify a number of hypotheses which have been proposed in the recent literature on the housing bubbles. We suggest that the main causes of the housing bubble from 2000 to 2006 are (1) non-elastic housing supply in the metropolitan areas, and (2) declines in the mortgage loan rate and the housing premium by the massive mortgage credit expansion. We also suggest that these factors were strongly influenced by policies that governments and the Federal Reserve Board performed.

Modes of self-organization of diluted bubbly liquids in acoustic fields: One-dimensional theory.

PubMed

Gumerov, Nail A; Akhatov, Iskander S

2017-02-01

The paper is dedicated to mathematical modeling of self-organization of bubbly liquids in acoustic fields. A continuum model describing the two-way interaction of diluted polydisperse bubbly liquids and acoustic fields in weakly-nonlinear approximation is studied analytically and numerically in the one-dimensional case. It is shown that the regimes of self-organization of monodisperse bubbly liquids can be controlled by only a few dimensionless parameters. Two basic modes, clustering and propagating shock waves of void fraction (acoustically induced transparency), are identified and criteria for their realization in the space of parameters are proposed. A numerical method for solving of one-dimensional self-organization problems is developed. Computational results for mono- and polydisperse systems are discussed.

Optimization of chlorine fluxing process for magnesium removal from molten aluminum

NASA Astrophysics Data System (ADS)

Fu, Qian

High-throughput and low operational cost are the keys to a successful industrial process. Much aluminum is now recycled in the form of used beverage cans and this aluminum is of alloys that contain high levels of magnesium. It is common practice to "demag" the metal by injecting chlorine that preferentially reacts with the magnesium. In the conventional chlorine fluxing processes, low reaction efficiency results in excessive reactive gas emissions. In this study, through an experimental investigation of the reaction kinetics involved in this process, a mathematical model is set up for the purpose of process optimization. A feedback controlled chlorine reduction process strategy is suggested for demagging the molten aluminum to the desired magnesium level without significant gas emissions. This strategy also needs the least modification of the existing process facility. The suggested process time will only be slightly longer than conventional methods and chlorine usage and emissions will be reduced. In order to achieve process optimization through novel designs in any fluxing process, a system is necessary for measuring the bubble distribution in liquid metals. An electro-resistivity probe described in the literature has low accuracy and its capability to measure bubble distribution has not yet been fully demonstrated. A capacitance bubble probe was designed for bubble measurements in molten metals. The probe signal was collected and processed digitally. Higher accuracy was obtained by higher discrimination against corrupted signals. A single-size bubble experiment in Belmont metal was designed to reveal the characteristic response of the capacitance probe. This characteristic response fits well with a theoretical model. It is suggested that using a properly designed deconvolution process, the actual bubble size distribution can be calculated. The capacitance probe was used to study some practical bubble generation devices. Preliminary results on bubble distribution generated by a porous plug in Belmont metal showed bubbles much bigger than those in a water model. Preliminary results in molten aluminum showed that the probe was applicable in this harsh environment. An interesting bubble coalescence phenomenon was also observed in both Belmont metal and molten aluminum.

Benefits of polidocanol endovenous microfoam (Varithena®) compared with physician-compounded foams

PubMed Central

Carugo, Dario; Ankrett, Dyan N; Zhao, Xuefeng; Zhang, Xunli; Hill, Martyn; O’Byrne, Vincent; Hoad, James; Arif, Mehreen; Wright, David DI

2015-01-01

Objective To compare foam bubble size and bubble size distribution, stability, and degradation rate of commercially available polidocanol endovenous microfoam (Varithena®) and physician-compounded foams using a number of laboratory tests. Methods Foam properties of polidocanol endovenous microfoam and physician-compounded foams were measured and compared using a glass-plate method and a Sympatec QICPIC image analysis method to measure bubble size and bubble size distribution, Turbiscan™ LAB for foam half time and drainage and a novel biomimetic vein model to measure foam stability. Physician-compounded foams composed of polidocanol and room air, CO2, or mixtures of oxygen and carbon dioxide (O2:CO2) were generated by different methods. Results Polidocanol endovenous microfoam was found to have a narrow bubble size distribution with no large (>500 µm) bubbles. Physician-compounded foams made with the Tessari method had broader bubble size distribution and large bubbles, which have an impact on foam stability. Polidocanol endovenous microfoam had a lower degradation rate than any physician-compounded foams, including foams made using room air (p < 0.035). The same result was obtained at different liquid to gas ratios (1:4 and 1:7) for physician-compounded foams. In all tests performed, CO2 foams were the least stable and different O2:CO2 mixtures had intermediate performance. In the biomimetic vein model, polidocanol endovenous microfoam had the slowest degradation rate and longest calculated dwell time, which represents the length of time the foam is in contact with the vein, almost twice that of physician-compounded foams using room air and eight times better than physician-compounded foams prepared using equivalent gas mixes. Conclusion Bubble size, bubble size distribution and stability of various sclerosing foam formulations show that polidocanol endovenous microfoam results in better overall performance compared with physician-compounded foams. Polidocanol endovenous microfoam offers better stability and cohesive properties in a biomimetic vein model compared to physician-compounded foams. Polidocanol endovenous microfoam, which is indicated in the United States for treatment of great saphenous vein system incompetence, provides clinicians with a consistent product with enhanced handling properties. PMID:26036246

Benefits of polidocanol endovenous microfoam (Varithena®) compared with physician-compounded foams.

PubMed

Carugo, Dario; Ankrett, Dyan N; Zhao, Xuefeng; Zhang, Xunli; Hill, Martyn; O'Byrne, Vincent; Hoad, James; Arif, Mehreen; Wright, David D I; Lewis, Andrew L

2016-05-01

To compare foam bubble size and bubble size distribution, stability, and degradation rate of commercially available polidocanol endovenous microfoam (Varithena®) and physician-compounded foams using a number of laboratory tests. Foam properties of polidocanol endovenous microfoam and physician-compounded foams were measured and compared using a glass-plate method and a Sympatec QICPIC image analysis method to measure bubble size and bubble size distribution, Turbiscan™ LAB for foam half time and drainage and a novel biomimetic vein model to measure foam stability. Physician-compounded foams composed of polidocanol and room air, CO2, or mixtures of oxygen and carbon dioxide (O2:CO2) were generated by different methods. Polidocanol endovenous microfoam was found to have a narrow bubble size distribution with no large (>500 µm) bubbles. Physician-compounded foams made with the Tessari method had broader bubble size distribution and large bubbles, which have an impact on foam stability. Polidocanol endovenous microfoam had a lower degradation rate than any physician-compounded foams, including foams made using room air (p < 0.035). The same result was obtained at different liquid to gas ratios (1:4 and 1:7) for physician-compounded foams. In all tests performed, CO2 foams were the least stable and different O2:CO2 mixtures had intermediate performance. In the biomimetic vein model, polidocanol endovenous microfoam had the slowest degradation rate and longest calculated dwell time, which represents the length of time the foam is in contact with the vein, almost twice that of physician-compounded foams using room air and eight times better than physician-compounded foams prepared using equivalent gas mixes. Bubble size, bubble size distribution and stability of various sclerosing foam formulations show that polidocanol endovenous microfoam results in better overall performance compared with physician-compounded foams. Polidocanol endovenous microfoam offers better stability and cohesive properties in a biomimetic vein model compared to physician-compounded foams. Polidocanol endovenous microfoam, which is indicated in the United States for treatment of great saphenous vein system incompetence, provides clinicians with a consistent product with enhanced handling properties. © The Author(s) 2015.

Bubble dynamics inside an outgassing hydrogel confined in a Hele-Shaw cell.

PubMed

Haudin, Florence; Noblin, Xavier; Bouret, Yann; Argentina, Médéric; Raufaste, Christophe

2016-08-01

We report an experimental study of bubble dynamics in a non-Newtonian fluid subjected to a pressure decrease. The fluid is a hydrogel, composed of water and a synthetic clay, prepared and sandwiched between two glass plates in a Hele-Shaw geometry. The rheological properties of the material can be tuned by the clay concentration. As the imposed pressure decreases, the gas initially dissolved in the hydrogel triggers bubble formation. Different stages of the process are observed: bubble nucleation, growth, interaction, and creation of domains by bubble contact or coalescence. Initially bubble behave independently. They are trapped and advected by the mean deformation of the hydrogel, and the bubble growth is mainly driven by the diffusion of the dissolved gas through the hydrogel and its outgassing at the reactive-advected hydrogel-bubble interface. In this regime, the rheology of the fluid does not play a significant role on the bubble growth. A model is proposed and gives a simple scaling that relates the bubble growth rate and the imposed pressure. Carbon dioxide is shown to be the gas at play, and the hydrogel is degassing at the millimeter scale as a water solution does at a smaller scale. Later, bubbles are not independent anymore. The growth rate decreases, and the morphology becomes more anisotropic as bubbles interact because they are separated by a distance smaller than the individual stress field extension. Our measurements show that the interaction distance scales with the bubbles' size.

Allostery through protein-induced DNA bubbles

DOE PAGES

Traverso, Joseph J.; Manoranjan, Valipuram S.; Bishop, A. R.; ...

2015-03-12

Allostery through DNA is increasingly recognized as an important modulator of DNA functions. Here, we show that the coalescence of protein-induced DNA bubbles can mediate allosteric interactions that drive protein aggregation. We propose that such allostery may regulate DNA's flexibility and the assembly of the transcription machinery. Mitochondrial transcription factor A (TFAM), a dual-function protein involved in mitochondrial DNA (mtDNA) packaging and transcription initiation, is an ideal candidate to test such a hypothesis owing to its ability to locally unwind the double helix. Numerical simulations demonstrate that the coalescence of TFAM-induced bubbles can explain experimentally observed TFAM oligomerization. The resultingmore » melted DNA segment, approximately 10 base pairs long, around the joints of the oligomers act as flexible hinges, which explains the efficiency of TFAM in compacting DNA. Since mitochondrial polymerase (mitoRNAP) is involved in melting the transcription bubble, TFAM may use the same allosteric interaction to both recruit mitoRNAP and initiate transcription.« less

Noise analysis of nucleate boiling

NASA Technical Reports Server (NTRS)

Mcknight, R. D.; Ram, K. S.

1971-01-01

The techniques of noise analysis have been utilized to investigate nucleate pool boiling. A simple experimental setup has been developed for obtaining the power spectrum of a nucleate boiling system. These techniques were first used to study single bubbles, and a method of relating the two-dimensional projected size and the local velocity of the bubbles to the auto-correlation functions is presented. This method is much less time consuming than conventional methods of measurement and has no probes to disturb the system. These techniques can be used to determine the contribution of evaporation to total heat flux in nucleate boiling. Also, these techniques can be used to investigate the effect of various parameters upon the frequency response of nucleate boiling. The predominant frequencies of the power spectrum correspond to the frequencies of bubble generation. The effects of heat input, degree of subcooling, and liquid surface tension upon the power spectra of a boiling system are presented. It was found that the degree of subcooling has a more pronounced effect upon bubble size than does heat flux. Also the effect of lowering surface tension can be sufficient to reduce the effect of the degree of subcooling upon the size of the bubbles.

The Regime Shift Associated with the 2004–2008 US Housing Market Bubble

PubMed Central

Cheong, Siew Ann

2016-01-01

The Subprime Bubble preceding the Subprime Crisis of 2008 was fueled by risky lending practices, manifesting in the form of a large abrupt increase in the proportion of subprime mortgages issued in the US. This event also coincided with critical slowing down signals associated with instability, which served as evidence of a regime shift or phase transition in the US housing market. Here, we show that the US housing market underwent a regime shift between alternate stable states consistent with the observed critical slowing down signals. We modeled this regime shift on a universal transition path and validated the model by estimating when the bubble burst. Additionally, this model reveals loose monetary policy to be a plausible cause of the phase transition, implying that the bubble might have been deflatable by a timely tightening of monetary policy. PMID:27583633

The effect of air bubbles on rabbit blood brain barrier.

PubMed

Hjelde, A; Bolstad, G; Brubakk, A O

2002-01-01

Several investigators have claimed that the blood brain barrier (BBB) may be broken by circulating bubbles, resulting in brain tissue edema. The aim of this study was to examine the effect of air bubbles on the permeability of BBB. Three groups of 6 rabbits were infused an isoosmotic solution of NaCl w/macrodex and 1% Tween. The solution was saturated with air bubbles and infused at rates of 50-100 ml hr(-1), a total of 1.6, 3.3, or 6.6 ml in each group, respectively. Two groups, each consisting of 6 rabbits, served as controls; one was infused by a degassed isoosmotic NaCl solution and one was sham-operated. All animals were left for 30 min before they were sacrificed. Specific gravity of brain tissue samples was determined using a brombenzene/kerosene gradient column, where a decrease in specific gravity indicates local brain edema. Specific gravity was significantly lower for left (P = 0.037) and right (P = 0.012) hemisphere white matter and left (P = 0.0015) and right (P = 0.002) hemisphere gray matter for the bubble-infused animals compared to the sham-operated ones. Infusion of degassed NaCl solution alone affected white left (P= 0.011) and right (P= 0.013), but not gray matter of both hemispheres. We speculate that insufficient degassing of the fluid may cause the effect of NaCl solution on the BBB of the white matter, indicating that the vessels of the white matter are more sensitive to gas bubbles than gray matter. Increasing the number of infused bubbles had no further impact on the development of cerebral edema, indicating that a threshold value was reached already at the lowest concentration of bubbles.

Modeling Cryptosporidium spp. Oocyst Inactivation in Bubble-Diffuser Ozone Contactors

DTIC Science & Technology

1998-07-01

requirements for Giardia lamblia (G. lamblia) and viruses under the Surface Water Treatment Rule (SWTR). Minimum CT requirements include relatively...parvum and C. muris ) oocysts in ozone bubble-diffuser contactors. The model is calibrated with semi-batch kinetic data, verified with pilot-scale

Interfacial bubbles formed by plunging thin liquid films in a pool

NASA Astrophysics Data System (ADS)

Salkin, Louis; Schmit, Alexandre; David, Richard; Delvert, Alexandre; Gicquel, Eric; Panizza, Pascal; Courbin, Laurent

2017-06-01

We show that the immersion of a horizontally suspended thin film of liquid in a pool of the same fluid creates an interfacial bubble, that is, a bubble at the liquid-air interface. Varying the fluid properties, the film's size, and its immersion velocity, our experiments unveil two formation regimes characterized by either a visco-capillary or an inertio-capillary mechanism that controls the size of a produced bubble. To rationalize these results, we compare the pressure exerted by the air flow under a plunging film with the Laplace pressure needed to generate film dimpling, which subsequently yields air entrapment and the production of a bubble. This physical model explains the power-law variations of the bubble size with the governing dimensionless number for each regime.

Influence of the bubble-bubble interaction on destruction of encapsulated microbubbles under ultrasound.

PubMed

Yasui, Kyuichi; Lee, Judy; Tuziuti, Toru; Towata, Atsuya; Kozuka, Teruyuki; Iida, Yasuo

2009-09-01

Influence of the bubble-bubble interaction on the pulsation of encapsulated microbubbles has been studied by numerical simulations under the condition of the experiment reported by Chang et al. [IEEE Trans. Ultrason Ferroelectr. Freq. Control 48, 161 (2001)]. It has been shown that the natural (resonance) frequency of a microbubble decreases considerably as the microbubble concentration increases to relatively high concentrations. At some concentration, the natural frequency may coincide with the driving frequency. Microbubble pulsation becomes milder as the microbubble concentration increases except at around the resonance condition due to the stronger bubble-bubble interaction. This may be one of the reasons why the threshold of acoustic pressure for destruction of an encapsulated microbubble increases as the microbubble concentration increases. A theoretical model for destruction has been proposed.