A comparative study of two-phase flow models relevant to bubble column dynamics
Minev, P. D.; Lange, U.; Nandakumar, K.
1999-09-01
Multiphase flow modelling is still a major challenge in fluid dynamics and, although many different models have been derived, there is no clear evidence of their relevance to certain flow situations. That is particularly valid for bubbly flows, because most of the studies have considered the case of fluidized beds. In the present study we give a general formulation to five existing models and study their relevance to bubbly flows. The results of the linear analysis of those models clearly show that only two of them are applicable to that case. They both show a very similar qualitative linear stability behaviour. In the subsequent asymptotic analysis we derive an equation hierarchy which describes the weakly nonlinear stability of the models. Their qualitative behaviour up to first order with respect to the small parameter is again identical. A permanent-wave solution of the first two equations of the hierarchy is found. It is shown, however, that the permanent-wave (soliton) solution is very unlikely to occur for the most common case of gas bubbles in water. The reason is that the weakly nonlinear equations are unstable due to the low magnitude of the bulk modulus of elasticity. Physically relevant stabilization can eventually be achieved using some available experimental data. Finally, a necessary condition for existence of a fully nonlinear soliton is derived.
DEFF Research Database (Denmark)
Dholakia, Nikhilesh; Turcan, Romeo V.
2013-01-01
A goal of our ongoing research stream is to develop a multidisciplinary metatheory of bubbles. In this viewpoint paper we put forward a typology of bubbles by comparing four types of assets – entertainment, commodities, financial securities (stocks), and housing properties – where bubbles could and...... do form occasionally. Cutting across and comparing such varied asset types provides some rich insights into the nature of bubbles – and offers an inductive way to arrive at the typology of bubbles....
Cox, D. P.
Modeling the Local Bubble is one of those activities fraught with danger. It is very easy to be too naive, to fail to consider the dependence of the model on assumptions about the nearby ambient state, or the likelihood of such a structure. It is similarly easy to become so caught up in the details of the vicinity that it is unclear where to begin a necessarily idealized modeling effort. And finally, it is important to remember that the data we have may in some cases be lying to us, and that we have not yet learned to read their facial expressions quite carefully enough. That said, I've tried in this paper to be helpful to those who may wish to take the risks. I surveyed the very most basic stories that the data seem to tell, and pointed out the standard coincidences that may be telling us a lot about what is happening, but may turn out once again to have been just coincidences. I've described 5 distinct conceptions that in one flavor or another pretty well survey the collection of mental images that have so far been carried by those who've attempted models. One may be right, or something entirely different may be more appropriate. It's at least vital to realize that a conception comes first, followed by a simplified model of details. I've also included a long list of questions directed at observers. Some have partial answers, some one wouldn't know today quite how to approach. But it is a list that students of the soft x-ray background, interstellar absorption lines, possible instrumentation, and the heliosphere may wish to review from time to time, just to see whether they can figure out how to be more helpful. There is another list for modelers, things the models must address, however-so-flimsily if necessary, because there are strong observational constraints (and stronger ones coming) on what can and cannot be present in the local ISM. To that I've added a few remarks concerning x-ray emission coming from beyond the Local Bubble, and another few on how x
Large-Scale Clustering in Bubble Models
Borgani, S
1993-01-01
We analyze the statistical properties of bubble models for the large-scale distribution of galaxies. To this aim, we realize static simulations, in which galaxies are mostly randomly arranged in the regions surrounding bubbles. As a first test, we realize simulations of the Lick map, by suitably projecting the three-dimensional simulations. In this way, we are able to safely compare the angular correlation function implied by a bubbly geometry to that of the APM sample. We find that several bubble models provide an adequate amount of large-scale correlation, which nicely fits that of APM galaxies. Further, we apply the statistics of the count-in-cell moments to the three-dimensional distribution and compare them with available observational data on variance, skewness and kurtosis. Based on our purely geometrical constructions, we find that a well defined hierarchical scaling of higher order moments up to scales $\\sim 70\\hm$. The overall emerging picture is that the bubbly geometry is well suited to reproduce ...
Argonne Bubble Experiment Thermal Model Development II
Energy Technology Data Exchange (ETDEWEB)
Buechler, Cynthia Eileen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-07-01
This report describes the continuation of the work reported in “Argonne Bubble Experiment Thermal Model Development”. 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 three beam power levels, 6, 12 and 15 kW. Solution temperatures were measured by thermocouples, and gas bubble behavior was observed. This report will describe the Computational Fluid Dynamics (CFD) model that was developed to calculate the temperatures and gas volume fractions in the solution vessel during the irradiations. The previous report described an initial analysis performed on a geometry that had not been updated to reflect the as-built solution vessel. Here, the as-built geometry is used. Monte-Carlo N-Particle (MCNP) calculations were performed on the updated geometry, and these results were used to define the power deposition profile for the CFD analyses, which were performed using Fluent, Ver. 16.2. CFD analyses were performed for the 12 and 15 kW irradiations, and further improvements to the model were incorporated, including the consideration of power deposition in nearby vessel components, gas mixture composition, and bubble size distribution. The temperature results of the CFD calculations are compared to experimental measurements.
Modeling of bubble dynamics in relation to medical applications
International Nuclear Information System (INIS)
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
Modeling bubble collapse aggressiveness in traveling bubble cavitation using bubble breakup model
Czech Academy of Sciences Publication Activity Database
Zima, Patrik; Sedlář, M.
Singapore : Research Publishing Services, 2012 - (Ohl, C.; Klaseboer, E.; Ohl, S.; Gong, S.; Khoo, B.), s. 182-186 ISBN 978-981-07-2826-7. [International Symposium on Cavitation /8./ CAV 2012. Singapur (SG), 13.08.2012-16.08.2012] R&D Projects: GA ČR GAP101/10/1428 Institutional research plan: CEZ:AV0Z20760514 Keywords : bubble collapse * traveling bubble cavitation * numerical modeling Subject RIV: BK - Fluid Dynamics http://rpsonline.com.sg/proceedings/9789810728267/html/209.xml51.xml
Bubbles in Non-Newtonian Fluids: A Multiscale Modeling
Directory of Open Access Journals (Sweden)
Frank X.
2013-06-01
Full Text Available In this paper, the concept of a multiscale modeling approach is highlighted with which physical phenomena at different scales can be studied. The work reports a multiscale approach to describe the dynamics of a chain of bubbles rising in non-Newtonian fluids. By means of the Particle Image Velocimetry (PIV and the Lattice Boltzmann (LB simulation, a deep understanding of the complex flow pattern around a single bubble is gained at microscale. The interactions and coalescences between bubbles rising in non-Newtonian fluids are experimentally investigated by the PIV measurements, birefringence and rheological characterization for both an isolated bubble and a chain of bubbles formed from a submerged orifice. Two aspects are identified as central to interactions and coalescence: the stress creation by the passage of bubbles and their relaxation due to the fluid’s memory. This competition between the creation and relaxation of stresses displays non-linear complex dynamics. Along with the detailed knowledge around a single bubble, these fundamental mechanisms governing bubbles’ collective behavior in a train of bubbles at mesoscale lead to a cognitive modeling based on behavioral rules. By simulating bubbles as adaptive agents with the surround fluid via residual stresses, model predictions for consecutive coalescence between a great number of bubbles compare very satisfactorily with the experimental investigation at macroscale. Obviously this new approach captures important quantitative and qualitative features of the collective behaviors of bubbles at macroscale level which are predicted by the mesoscopic cognitive modeling approach of the interactions rules which are deduced from the understanding of the microscopic mechanism of the flow around a single bubble.
Bubble models, data acquisition and model applicability
Czech Academy of Sciences Publication Activity Database
Jebavá, Marcela; Kloužek, Jaroslav; Němec, Lubomír
Vsetín : GLASS SERVICE ,INC, 2005, s. 182-191. ISBN 80-239-4687-0. [International Seminar on Mathematical Modeling and Advanced Numerical Methods in Furnace Design and Operation /8./. Velké Karlovice (CZ), 19.05.2005-20.05.2005] Institutional research plan: CEZ:AV0Z40320502 Keywords : bubble models Subject RIV: CA - Inorganic Chemistry
IMPROVEMENT OF BUBBLE MODEL FOR CAVITATING FLOW SIMULATIONS
Institute of Scientific and Technical Information of China (English)
TAMURA Y.; MATSUMOTO Y.
2009-01-01
In the present research,a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications.The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction.The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius(or void fraction)reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem.This procedure is expected to stabilize the numerical calculation.The results of simple two-dimensional flow field are presented compared with the existing bubble model.
Modeling bubbly-cap flows using two-group average bubble number density
International Nuclear Information System (INIS)
The basic concept of two-group average bubble number density equations along with three-fluid model has been demonstrated for vertical gas-liquid flow. Specifically, the current study focused on: (i)classification of bubble interaction between spherical bubbles (Group-1) and cap bubbles (Group- 2), (ii) preliminary consideration of source and sink terms in the averaged bubble number density equations via the model of Hibiki and Ishii [1] and (iii) assessment by means of experimental data sets at bubbly-to-cap flow transition. Reasonable agreement was achieved between measured and predicted distributions of void fraction, interfacial area concentration (IAC) and volume equivalent bubble diameter. (author)
The parton bubble model compared to central Au Au collisions (0% to 5%) at $\\sqrt{s_{NN}}$=200 GeV
Longacre, R S
2010-01-01
In an earlier paper we developed a Parton Bubble Model (PBM) for RHIC, high-energy heavy-ion collisions. PBM was based on a substructure of a ring of localized bubbles (gluonic hot spots) which initially contain 3-4 partons composed of almost entirely gluons. The bubbles emitted correlated particles at kinetic freezeout, leading to a lumpy fireball surface. For a selection of charged particles (0.8 GeV/c $<$ $p_t$ $<$ 4.0 GeV/c), the PBM reasonably quantitatively (within a few percent) explained high precision RHIC experimental correlation analyses in a manner which was consistent with the small observed HBT source size in this transverse momentum range. We demonstrated that surface emission from a distributed set of surface sources (as in the PBM) was necessary to obtain this consistency. In this paper we give a review of the above comparison to central Au Au collisions. The bubble formation can be associated with gluonic objects predicted by a Glasma Flux Tube Model (GFTM) that formed longitudinal flu...
Modeling and simulation of bubbles and particles
Dorgan, Andrew James
negligible (in terms of particle concentration predictions) when terminal velocity was oriented in the wall-normal direction. The history force was shown to damp particle diffusion and have some minor impacts on particle concentration. This effect was augmented by using the creeping flow Basset expression and shows that the creeping flow expression should not be used in finite-Reynolds number conditions. The effects due to the finite-size extensions are also considered as are effects due to spatial reconstruction of the fluid properties. In general, little effect of the finite-size model or choice of spatial interpolation was observed in terms of particle concentration. However, Lagrangian statistics show some interesting sensitivities. Finally, the new equation of motion was applied to air bubbles and sand particles of several different diameters. Particle-fluid interactions observed through flow-visualization, particle concentration, particle-wall interactions, and Lagrangian statistics were all considered. These results were interpreted and compared to heavy-particle results where appropriate. Particle deposition was found to be well-described by the heavy-particle model of Young & Leeming and root-mean-square relative velocities were found to also agree with previous heavy-particle work. A model for the latter is suggested for heavy-particles and found to work similarly well for low-density particles. Non-tracer behavior was observed for bubbles with small Stokes numbers, a result not expected based on heavy-particle expectations. Local clustering of particles was observed in certain fluid structures which may indicate the importance of modeling particle collisions in future studies.
Modeling of Wall Effects on Drag and Lift Acting on Bubbles in Bubbly Flow
International Nuclear Information System (INIS)
The two-fluid model based on Eulerian-Eulerian approach has been widely used for simulating two-phase flows in many industrial applications. However, the two-fluid approach needs accurate modeling for interfacial momentum exchange such as drag, shear induced lift, and wall-induced lift. In particular, it is important to accurately model the wall effect in order to predict 'wall peaking' or 'core peaking' phenomena observed in bubbly pipe flow. Those phenomena characterized by the radial distribution of void fraction are mainly determined by the balance between shear induced lift and wall-induced lift usually called 'wall lubrication force'. However, the wall effect is not fully understood yet and the wall force coefficient in previous studies has a wide range of values, probably tuned to the experimental results. Therefore, we propose a new model considering the wall effect on drag and lift forces and evaluate its accuracy by simulating laminar bubbly flows with available data for comparison. In this study, we proposed a new model for interfacial momentum exchange for wall-bounded bubbly flow. In particular, to accurately consider the wall effects on drag and lift, separate simulations were performed for the flow around a moving sphere near the wall. The present model was verified by solving the laminar bubbly flow in a vertical pipe and comparing the results with previous ones. The present void fraction and water velocity profiles showed good results
Directory of Open Access Journals (Sweden)
K. Ekambara
2012-01-01
Full Text Available Modelling of gas-liquid bubbly flows is achieved by coupling a population balance equation with the three-dimensional, two-fluid, hydrodynamic model. For gas-liquid bubbly flows, an average bubble number density transport equation has been incorporated in the CFD code CFX 5.7 to describe the temporal and spatial evolution of the gas bubbles population. The coalescence and breakage effects of the gas bubbles are modeled. The coalescence by the random collision driven by turbulence and wake entrainment is considered, while for bubble breakage, the impact of turbulent eddies is considered. Local spatial variations of the gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, and liquid velocity are compared against experimental data in a horizontal pipe, covering a range of gas (0.25 to 1.34 m/s and liquid (3.74 to 5.1 m/s superficial velocities and average volume fractions (4% to 21%. The predicted local variations are in good agreement with the experimental measurements reported in the literature. Furthermore, the development of the flow pattern was examined at three different axial locations of L/D = 25, 148, and 253. The first location is close to the entrance region where the flow is still developing, while the second and the third represent nearly fully developed bubbly flow patterns.
Hydrodynamic models for slurry bubble column reactors
Energy Technology Data Exchange (ETDEWEB)
Gidaspow, D. [IIT Center, Chicago, IL (United States)
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, 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.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A model for a bubble column slurry reactor is developed based on the experiment of Rhenpreussen Koppers demonstration plant for slurry phase Fischer-Tropsch synthesis reported by Koelble et al. This model is applicable to the operation in the churn-turbulent regime and incorporates the information on the bubble size. The axial dispersion model is adopted to describe the flow characteristics of the Fischer-Tropsch slurry reactor. With the model developed, simulations are performed to identify the steady state behavior of a Fischer-Tropsch slurry reactor of commercial size. Predictions of the two-bubble class model is compared with that of the conventional single- bubble class model. The results show that under a variety of conditions, the two-bubble class model gives results different from those for the single-bubble class model.
Modelling of boiling bubbly flows using a polydisperse approach
International Nuclear Information System (INIS)
The objective of this work was to improve the modelling of boiling bubbly flows.We focused on the modelling of the polydisperse aspect of a bubble population, i.e. the fact that bubbles have different sizes and different velocities. The multi-size aspect of a bubble population can originate from various mechanisms. For the bubbly flows we are interested in, bubble coalescence, bubble break-up, phase change kinematics and/or gas compressibility inside the bubbles can be mentioned. Since, bubble velocity depends on bubble size, the bubble size spectrum also leads to a bubble velocity spectrum. An averaged model especially dedicated to dispersed flows is introduced in this thesis. Closure of averaged interphase transfer terms are written in a polydisperse framework, i.e. using a distribution function of the bubble sizes and velocities. A quadratic law and a cubic law are here proposed for the modelling of the size distribution function, whose evolution in space and time is then obtained with the use of the moment method. Our averaged model has been implemented in the NEPTUNE-CFD computation code in order to simulate the DEBORA experiment. The ability of our model to deal with sub-cooled boiling flows has therefore been evaluated. (author)
Free Surface Lattice Boltzmann with Enhanced Bubble Model
Anderl, Daniela; Rauh, Cornelia; Rüde, Ulrich; Delgado, Antonio
2016-01-01
This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid-gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.
A computational model of gas bubble evolution in liquid filled straight tubes
Himm, Jeff; Halpern, David
1996-11-01
Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too quick. When the ambient pressure drops, inert gas bubbles are usually formed in blood vessels and tissues of divers. It is believed that the existence of gas bubbles is the cause of DCS that manifests itself as itching, joint pain, and neurological abnormalities. While models of gas bubbles in tissues are relatively well developed, the mechanism of bubble growth in the circulation is far less well understood. The existence of gas bubbles may affect gas exchange in small blood vessels by blocking the flow of blood. Gas bubble evolution in the circulation is investigated using an analytical method for small bubbles and the boundary element method for bubbles whose effective radius is close to the tube radius. The concentration field for the dissolved gas surrounding the bubble is solved numerically using finite differences. The bubble volume is adjusted over time according to the mass flux at the surface. It is shown that the effect of increasing the flow rate is to enhance bubble evolution, up to a factor of two compared with the evolution in tissue where there is no flow. This work was supported by the Naval Medical Research and Development Command work unit 62233N.MM33P30.0041509.
Photon Number Conserving Models of HII Bubbles during Reionization
Paranjape, Aseem; Choudhury, T. Roy; Padmanabhan, Hamsa
2016-05-01
Traditional excursion set based models of HII bubble growth during the epoch of reionization are known to violate photon number conservation, in the sense that the mass fraction in ionized bubbles in these models does not equal the ratio of the number of ionizing photons produced by sources and the number of hydrogen atoms in the intergalactic medium. E.g., for a Planck13 cosmology with electron scattering optical depth τ ≃ 0.066, the discrepancy is ˜15 per cent for xHII = 0.1 and ˜5 per cent for xHII = 0.5. We demonstrate that this problem arises from a fundamental conceptual shortcoming of the excursion set approach (already recognised in the literature on this formalism) which only tracks average mass fractions instead of the exact, stochastic source counts. With this insight, we build an approximately photon number conserving Monte Carlo model of bubble growth based on partitioning regions of dark matter into halos. Our model, which is formally valid for white noise initial conditions (ICs), shows dramatic improvements in photon number conservation, as well as substantial differences in the bubble size distribution, as compared to traditional models. We explore the trends obtained on applying our algorithm to more realistic ICs, finding that these improvements are robust to changes in the ICs. Since currently popular semi-numerical schemes of bubble growth also violate photon number conservation, we argue that it will be worthwhile to pursue new, explicitly photon number conserving approaches. Along the way, we clarify some misconceptions regarding this problem that have appeared in the literature.
Studies on modelling of bubble driven flows in chemical reactors
Energy Technology Data Exchange (ETDEWEB)
Grevskott, Sverre
1997-12-31
Multiphase reactors are widely used in the process industry, especially in the petrochemical industry. They very often are characterized by very good thermal control and high heat transfer coefficients against heating and cooling surfaces. This thesis first reviews recent advances in bubble column modelling, focusing on the fundamental flow equations, drag forces, transversal forces and added mass forces. The mathematical equations for the bubble column reactor are developed, using an Eulerian description for the continuous and dispersed phase in tensor notation. Conservation equations for mass, momentum, energy and chemical species are given, and the k-{epsilon} and Rice-Geary models for turbulence are described. The different algebraic solvers used in the model are described, as are relaxation procedures. Simulation results are presented and compared with experimental values. Attention is focused on the modelling of void fractions and gas velocities in the column. The energy conservation equation has been included in the bubble column model in order to model temperature distributions in a heated reactor. The conservation equation of chemical species has been included to simulate absorption of CO{sub 2}. Simulated axial and radial mass fraction profiles for CO{sub 2} in the gas phase are compared with measured values. Simulations of the dynamic behaviour of the column are also presented. 189 refs., 124 figs., 1 tab.
Modelling for three dimensional coalescence of two bubbles
Han, R.; Li, S.; Zhang, A. M.; Wang, Q. X.
2016-06-01
This paper is concerned with the three dimensional (3D) interaction and coalescence of two bubbles subject to buoyancy and the dynamics of the subsequent joined bubble using the boundary integral method (BIM). An improved density potential method is implemented to control the mesh quality. It helps to avoid the numerical instabilities, which occur after coalescence. Numerical convergence tests are conducted in terms of mesh sizes and time steps. The 3D numerical model agrees well with an axisymmetric BIM model for axisymmetric cases as well as experimental results captured by high-speed camera. The bubble jetting, interaction, and coalescence of the two bubbles depend on the maximum bubble radii, the centre distance between two bubbles at inception, and the angle β between the centre line and the direction of buoyancy. We investigate coalescence of two bubbles for β = 0, π/4, and π/2, respectively, and at various centre distances at inception. Numerical results presented include the bubble and jet shapes, the velocity, and pressure fields surrounding the bubbles, as well as the time histories of bubble volumes, jet velocities, and positions of centroid of the bubble system.
A mechanistic model of separation bubble
Krechetnikov, R; Nagib, H M
2007-01-01
This work uncovers the low-dimensional nature the complex dynamics of actuated separated flows. Namely, motivated by the problem of model-based predictive control of separated flows, we identify the requirements on a model-based observer and the key variables and propose a prototype model in the case of thick airfoils as motivated by practical applications. The approach in this paper differs fundamentally from the logic behind known models, which are either linear or based on POD-truncations and are unable to reflect even the crucial bifurcation and hysteresis inherent in separation phenomena. This new look at the problem naturally leads to several important implications, such as, firstly, uncovering the physical mechanisms for hysteresis, secondly, predicting a finite amplitude instability of the bubble, and thirdly to new issues to be studied theoretically and tested experimentally. More importantly, by employing systematic reasoning, the low-dimensional nature of these complex phenomena at the coarse level...
Force Balance Model for Bubble Rise, Impact, and Bounce from Solid Surfaces.
Manica, Rogerio; Klaseboer, Evert; Chan, Derek Y C
2015-06-23
A force balance model for the rise and impact of air bubbles in a liquid against rigid horizontal surfaces that takes into account effects of buoyancy and hydrodynamic drag forces, bubble deformation, inertia of the fluid via an added mass force, and a film force between the bubble and the rigid surface is proposed. Numerical solution of the governing equations for the position and velocity of the center of mass of the bubbles is compared against experimental data taken with ultraclean water. The boundary condition at the air-water interface is taken to be stress free, which is consistent for bubbles in clean water systems. Features that are compared include bubble terminal velocity, bubbles accelerating from rest to terminal speed, and bubbles impacting and bouncing off different solid surfaces for bubbles that have already or are yet to attain terminal speed. Excellent agreement between theory and experiments indicates that the forces included in the model constitute the main physical ingredients to describe the bouncing phenomenon. PMID:26035016
A new pressure formulation for gas-compressibility dampening in bubble dynamics models.
Gadi Man, Yezaz Ahmed; Trujillo, Francisco J
2016-09-01
We formulated a pressure equation for bubbles performing nonlinear radial oscillations under ultrasonic high pressure amplitudes. The proposed equation corrects the gas pressure at the gas-liquid interface on inertial bubbles. This pressure formulation, expressed in terms of gas-Mach number, accounts for dampening due to gas compressibility during the violent collapse of cavitation bubbles and during subsequent rebounds. We refer to this as inhomogeneous pressure, where the gas pressure at the gas-liquid interface can differ to the pressure at the centre of the bubble, in contrast to homogenous pressure formulations that consider that pressure inside the bubble is spatially uniform from the wall to the centre. The pressure correction was applied to two bubble dynamic models: the incompressible Rayleigh-Plesset equation and the compressible Keller and Miksis equation. This improved the predictions of the nonlinear radial motion of the bubble vs time obtained with both models. Those simulations were also compared with other bubble dynamics models that account for liquid and gas compressibility effects. It was found that our corrected models are in closer agreement with experimental data than alternative models. It was concluded that the Rayleigh-Plesset family of equations improve accuracy by using our proposed pressure correction. PMID:27150768
THE SEMIEMPIRICAL MODEL OF THE MULTICOMPONENT BUBBLE BEHAVIOUR IN GLASS MELTS
Directory of Open Access Journals (Sweden)
LUBOMÍR NĚMEC
2012-12-01
Full Text Available A semi-empirical model of the bubble growth and dissolution in glasses with a fining agent has been derived. This model applies the experimental data from bubble observation at melting and fining temperatures. The experimental data needed for the model involved the temperature dependences of the average growth rate of the bubble radius and the average concentration of the fining gas in the bubbles. Both sets of values were measured in the laboratory in the glass of the float type and applied in the model. The measurements of the solubilities and diffusion coefficients of the gases present in the glass – needed for the analytical model of multicomponent bubbles – were thus avoided. The course of the partial bubble absorption with the temperature decreasing was simulated by means of two factors modifying the experimental values of the bubble growth rates at constant temperature. The temperature dependence of the resulting bubble growth rate qualitatively corresponded to the experimental observations in the soda-lime-silica glass, but a more detailed experimental and comparative study has yet to be performed. Such a study is being prepared.
Extension of the inhomogeneous MUSIG model for bubble condensation
International Nuclear Information System (INIS)
Highlights: ► The inhomogenous MUSIG model allows 3D simulations for poly-dispersed bubbly flows. ► The model is now extended to consider flows with phase transfer. ► Experimental data for the condensation of steam bubbles in sub-cooled vertical pipe flow are used for validation. ► There is a good agreement between experimental data and CFD simulations with the ANSYS-CFX code. - Abstract: Bubble condensation plays an important role, e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done previously at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Recently the Inhomogeneous MUSIG model was implemented into the CFD code CFX from ANSYS enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Here an extension of the model is proposed to include the effects due to phase transfer. The paper focuses on the derivation of equations for the extension of the Inhomogeneous MUSIG model and presents some first results for verification and validation.
The effect of high viscosity on compressible and incompressible Rayleigh–Plesset-type bubble models
International Nuclear Information System (INIS)
Highlights: • Spherical gas bubbles in glycerol have been examined numerically and experimentally. • The bubble was generated using a Q-switched Nd:YAG laser. • The radius was measured with a novel shadowing technique of a He–Ne laser beam. • The measurements were compared with a compressible and an incompressible bubble models. • The validity domain of the incompressible assumption has been given. -- Abstract: Free oscillations of a single spherical gas bubble in glycerol have been examined numerically and experimentally at different ambient temperatures and pressures. The bubble was generated using a Q-switched Nd:YAG laser and the unsteady radius measurement was based on a shadowing technique of a He–Ne laser beam. The measurements were compared to computations obtained from two models, first taking into consideration the liquid compressibility and then assuming an incompressible liquid domain, respectively. In both cases the temperature fields inside and outside the bubble were computed by solving the energy equation in both phases as the thermodynamic processes have great importance to the bubble behavior. For high amplitude oscillations the incompressible model provides poor agreement with the measurements and the modeling of the liquid compressibility becomes necessary. In contrast to the standard method, a practical region of applicability for the incompressible approach was determined as a function of the instantaneous Mach and Reynolds numbers, rather than specifying a simple threshold Mach number
International Nuclear Information System (INIS)
In previous theoretical studies of the behaviour of the fission gases in nuclear fuel, the Nelson single knock-on model of the fission induced re-solution of gas atoms from fission gas bubbles has been employed. In the present investigation, predictions from this model are compared with those from a complete bubble destruction model of the re-solution process. The main conclusions of the study are that the complete bubble destruction model predicts more gas release after a particular irradiation time than the single knock-on model, for the same choice of the model parameters, and that parameter sets chosen to give the same gas release predict significantly different bubble size distribution functions. (author)
Li, Linmin; Li, Baokuan
2016-03-01
In ladle metallurgy, bubble-liquid interaction leads to complex phase structures. Gas bubble behavior, as well as the induced slag layer behavior, plays a significant role in the refining process and the steel quality. In the present work, a mathematical model using the large eddy simulation (LES) is developed to investigate the bubble transport and slag layer behavior in a water model of an argon-stirred ladle. The Eulerian volume of fluid model is adopted to track the liquid steel-slag-air free surfaces while the Lagrangian discrete phase model is used for tracking and handling the dynamics of discrete bubbles. The bubble coalescence is considered using O'Rourke's algorithm to solve the bubble diameter redistribution and bubbles are removed after leaving the air-liquid interface. The turbulent liquid flow that is induced by bubble-liquid interaction is solved by LES. The slag layer fluactuation, slag droplet entrainment and spout eye open-close phenomenon are well revealed. The bubble diameter distribution and the spout eye size are compared with the experiment. The results show that the hybrid Eulerian-Lagrangian-LES model provides a valid modeling framework to predict the unsteady gas bubble-slag layer coupled behaviors.
International Nuclear Information System (INIS)
Under decompression, bubbles can form in the human body, and these can be found both within the body tissues and the bloodstream. Mathematical models for the growth of both types of bubbles have previously been presented, but they have not been coupled together. This work thus explores the interaction between the growth of tissue and blood-borne bubbles under decompression, specifically looking at the extent to which they compete for the common resource of inert gas held in solution in the tissues. The influence of tissue bubbles is found to be significant for densities as low as 10 ml-1 for tissues which are poorly perfused. However, the effects of formation of bubbles in the blood are not found until the density of bubble production sites reaches 106 ml-1. From comparison of the model predictions with experimental evidence for bubbles produced in animals and man under decompression, it is concluded that the density of tissue bubbles is likely to have a significant effect on the number of bubbles produced in the blood. However, the density of nucleation sites in the blood is unlikely to be sufficiently high in humans for the formation of bubbles in the blood to have a significant impact on the growth of the bubbles in the tissue
Bubble Size Models for the Prediction of Bubbly Flow with CMFD Code
Energy Technology Data Exchange (ETDEWEB)
Bak, Jin-yeong; Yun, Byong-jo; Jeong, Jae-jun [Pusan National Univ., Busan (Korea, Republic of)
2015-05-15
In recent years, the use of computational multi-fluid dynamics (CMFD) codes has been extended to the analysis of multi-dimensional two-phase flow for the operation and safety analysis of nuclear power plants (NPP). In these applications, an accurate prediction of bubble behaviors is one of major concerns. Yao and Morel and Yeoh and Tu respectively applied interfacial area concentration transport (IACT) equation and bubble number density transport equation into CMFD code. Recently Lo and Zhang tried to apply the generalized S{sub γ} model to the predictions of not only droplet size in the oil-water flow but also bubble size in the air-water flow. In this paper, three-dimensional numerical simulations for the gas-liquid two-phase flow were conducted to validate and confirm the performance of S{sub γ} bubble size model for the further application to the narrow rectangular boiling channel for the research reactor core, using the commercial CFD code STAR CCM''+ ver. 9.06. For this, S{sub γ} model was evaluated against air-water data of DEDALE and Hibiki et al.'s experiment. These experimental data were obtained in a vertically arranged pipe under upwards air-water flow condition. Detailed descriptions on the S{sub γ} with its breakup and coalescence model are presented in the present manuscript.
A 3D Bubble Merger Model for RTI Mixing
Cheng, Baolian
2015-11-01
In this work we present a model for the merger processes of bubbles at the edge of an unstable acceleration driven mixing layer. Steady acceleration defines a self-similar mixing process, with a time-dependent inverse cascade of structures of increasing size. The time evolution is itself a renormalization group evolution. The model predicts the growth rate of a Rayleigh-Taylor chaotic fluid-mixing layer. The 3-D model differs from the 2-D merger model in several important ways. Beyond the extension of the model to three dimensions, the model contains one phenomenological parameter, the variance of the bubble radii at fixed time. The model also predicts several experimental numbers: the bubble mixing rate, the mean bubble radius, and the bubble height separation at the time of merger. From these we also obtain the bubble height to the radius aspect ratio, which is in good agreement with experiments. Applications to recent NIF and Omega experiments will be discussed. This work was performed under the auspices of the U.S. Department of Energy by the Los Alamos National Laboratory under Contract No. W-7405-ENG-36.
Time-Dependent Stochastic Acceleration Model for the Fermi Bubbles
Sasaki, Kento; Terasawa, Toshio
2015-01-01
We study stochastic acceleration models for the Fermi bubbles. Turbulence is excited just behind the shock front via Kelvin-Helmholtz, Rayleigh-Taylor or Richtmyer-Meshkov instabilities, and plasma particles are continuously accelerated by the interaction with the turbulence. The turbulence gradually decays as it goes away from the shock fronts. Adopting a phenomenological model for the stochastic acceleration, we explicitly solve the temporal evolution of the particle energy distribution in the turbulence. Our results show that the spatial distribution of high-energy particles is different from those for a steady solution. We also show that the contribution of electrons escaped from the acceleration regions significantly softens the photon spectrum. The photon spectrum and surface brightness profile are reproduced by our models. If the escape efficiency is very high, the radio flux from the escaped low-energy electrons can be comparable to that of the WMAP haze. We also demonstrate hadronic models with the s...
Modeling the dynamics of single-bubble sonoluminescence
Vignoli, Lucas L; Thomé, Roberto C A; Nogueira, A L M A; Paschoal, Ricardo C; Rodrigues, Hilario
2014-01-01
Sonoluminescence (SL) is the phenomenon in which acoustic energy is (partially) transformed into light. It may occur by means of many or just one bubble of gas inside a liquid medium, giving rise to the terms multi-bubble- and single-bubble sonoluminescence (MBSL and SBSL). In the last years some models have been proposed to explain this phenomenon, but there is still no complete theory for the light emission mechanism (especially in the case of SBSL). In this work, we will not address this more complicated particular issue, but only present a simple model describing the dynamical behaviour of the sonoluminescent bubble, in the SBSL case. Using simple numerical techniques within the software Matlab, we discuss solutions considering various possibilities for some of the parameters involved: liquid compressibility, superficial tension, viscosity, and type of gas. The model may be used as an introductory study of sonoluminescence in physics courses at undergraduate or graduate levels, as well as a quite clarifyi...
Experimental investigation and mechanistic modelling of dilute bubbly bulk boiling
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During evaporation the geometric shape of the vapour is not described using thermodynamics. In bubbly flows the bubble shape is considered spheric with small diameters and changing into various shapes upon growth. The heat and mass transfer happens at the interfacial area. The forces acting on the bubbles depend on the bubble diameter and shape. In this work the prediction of the bubble diameter and/or bubble number density in bulk boiling was considered outside the vicinity of the heat input area. Thus the boiling effects that happened inside the nearly saturated bulk were under investigation. This situation is relevant for nuclear safety analysis concerning a stagnant coolant in the spent fuel pool. In this research project a new experimental set-up to investigate was built. The experimental set-up consists of an instrumented, partly transparent, high and slender boiling container for visual observation. The direct visual observation of the boiling phenomena is necessary for the identification of basic mechanisms, which should be incorporated in the simulation model. The boiling process has been recorded by means of video images and subsequently was evaluated by digital image processing methods, and by that data concerning the characteristics of the boiling process were generated for the model development and validation. Mechanistic modelling is based on the derivation of relevant mechanisms concluded from observation, which is in line with physical knowledge. In this context two mechanisms were identified; the growth/-shrink mechanism (GSM) of the vapour bubbles and sudden increases of the bubble number density. The GSM was implemented into the CFD-Code ANSYS-CFX using the CFX Expression Language (CEL) by calculation of the internal bubble pressure using the Young-Laplace-Equation. This way a hysteresis is realised as smaller bubbles have an increased internal pressure. The sudden increases of the bubble number density are explainable by liquid super
Experimental investigation and mechanistic modelling of dilute bubbly bulk boiling
Energy Technology Data Exchange (ETDEWEB)
Kutnjak, Josip
2013-06-27
During evaporation the geometric shape of the vapour is not described using thermodynamics. In bubbly flows the bubble shape is considered spheric with small diameters and changing into various shapes upon growth. The heat and mass transfer happens at the interfacial area. The forces acting on the bubbles depend on the bubble diameter and shape. In this work the prediction of the bubble diameter and/or bubble number density in bulk boiling was considered outside the vicinity of the heat input area. Thus the boiling effects that happened inside the nearly saturated bulk were under investigation. This situation is relevant for nuclear safety analysis concerning a stagnant coolant in the spent fuel pool. In this research project a new experimental set-up to investigate was built. The experimental set-up consists of an instrumented, partly transparent, high and slender boiling container for visual observation. The direct visual observation of the boiling phenomena is necessary for the identification of basic mechanisms, which should be incorporated in the simulation model. The boiling process has been recorded by means of video images and subsequently was evaluated by digital image processing methods, and by that data concerning the characteristics of the boiling process were generated for the model development and validation. Mechanistic modelling is based on the derivation of relevant mechanisms concluded from observation, which is in line with physical knowledge. In this context two mechanisms were identified; the growth/-shrink mechanism (GSM) of the vapour bubbles and sudden increases of the bubble number density. The GSM was implemented into the CFD-Code ANSYS-CFX using the CFX Expression Language (CEL) by calculation of the internal bubble pressure using the Young-Laplace-Equation. This way a hysteresis is realised as smaller bubbles have an increased internal pressure. The sudden increases of the bubble number density are explainable by liquid super
ONE-DIMENSIONAL DYNAMICAL MODELS OF THE CARINA NEBULA BUBBLE
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We have tested the two main theoretical models of bubbles around massive star clusters, Castor et al. and Chevalier and Clegg, against observations of the well-studied Carina nebula. The Castor et al. theory overpredicts the X-ray luminosity in the Carina bubble by a factor of 60 and expands too rapidly, by a factor of 4; if the correct radius and age are used, the predicted X-ray luminosity is even larger. In contrast, the Chevalier and Clegg model underpredicts the X-ray luminosity by a factor of 10. We modify the Castor et al. theory to take into account lower stellar wind mass-loss rates, radiation pressure, gravity, and escape of or energy loss from the hot shocked gas. We argue that energy is advected rather than radiated from the bubble. We undertake a parameter study for reduced stellar mass-loss rates and for various leakage rates and are able to find viable models. The X-ray surface brightness in Carina is highest close to the bubble wall, which is consistent with conductive evaporation from cold clouds. The picture that emerges is one in which the hot gas pressure is far below that found by dividing the time-integrated wind luminosity by the bubble volume; rather, the pressure in the hot gas is set by pressure equilibrium with the photoionized gas at T = 104 K. It follows that the shocked stellar winds are not dynamically important in forming the bubbles.
Numerical simulations of bubbly flows using an averaged equations' model
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The paper discusses a numerical method for solving a two phase flow model based on the interpenetrating continua hypothesis. The model incorporates terms to account for the effects of virtual mass force, different pressures for the two phases and the viscous dissipation. Our numerical scheme extends the incremental projection scheme for the incompressible Navier-Stokes equation toward the multiphase flows. An optimal stability is obtained by slightly modifying the Galerkin formulation. The stabilized Galerkin technique we used is based on a two-level hierarchical decomposition of the approximation space. Numerical simulations of the three-dimensional bubbly flows in a periodic domain are presented. These simulations are compared with experiments. The stability of this flow with respect to 3D perturbations is studied numerically and a discussion of the results is presented. (author)
Fluid dynamic modelling of bubble column reactors
Khan, Khurram Imran
2014-01-01
Numerical simulations of rectangular shape bubble column reactors (BCR) are validated starting from preliminary simulations aimed at identifying proper simulation parameters for a given system and resulting up to the numerical simulation with mass transfer and chemical reactions. The transient, three dimensional simulations are carried out using FLUENT software and the results obtained for a system with low gas flow rate (48 L/h) indicated that we need enough fine mesh grid and appropriate cl...
Algebraic model for bubble tracking in horizontal gas-liquid flow
Energy Technology Data Exchange (ETDEWEB)
Freitas, Felipe G.C. de; Tisserant, Hendy R. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba, PR (Brazil); Morales, Rigoberto E.M. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba, PR (Brazil). Programa de Pos-Graduacao em Engenharia Mecanica e de Materiais; Mazza, Ricardo A.; Rosa, Eugenio S. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Mecanica
2008-07-01
The current work extends the concept of unit-cell applied in gas-liquid slug flow models to predict the evolution of the gas and liquid flow properties along a horizontal pipe. The motivation of this model is its simplicity, easiness of application and low computational cost. It is a useful tool of reference data generation in order to check the consistency of numerical slug tracking models. The potential of the model is accessed by comparing the gas bubbles and liquid slug sizes, the translational bubble velocity and the pressure drop against experimental data. (author)
Using a dynamic point-source percolation model to simulate bubble growth
International Nuclear Information System (INIS)
Accurate modeling of nucleation, growth and clustering of helium bubbles within metal tritide alloys is of high scientific and technological importance. Of interest is the ability to predict both the distribution of these bubbles and the manner in which these bubbles interact at a critical concentration of helium-to-metal atoms to produce an accelerated release of helium gas. One technique that has been used in the past to model these materials, and again revisited in this research, is percolation theory. Previous efforts have used classical percolation theory to qualitatively and quantitatively model the behavior of interstitial helium atoms in a metal tritide lattice; however, higher fidelity models are needed to predict the distribution of helium bubbles and include features that capture the underlying physical mechanisms present in these materials. In this work, we enhance classical percolation theory by developing the dynamic point-source percolation model. This model alters the traditionally binary character of site occupation probabilities by enabling them to vary depending on proximity to existing occupied sites, i.e. nucleated bubbles. This revised model produces characteristics for one and two dimensional systems that are extremely comparable with measurements from three dimensional physical samples. Future directions for continued development of the dynamic model are also outlined
Using a dynamic point-source percolation model to simulate bubble growth.
Energy Technology Data Exchange (ETDEWEB)
Zimmerman, Jonathan A.; Zeigler, David A.; Cowgill, Donald F.
2004-05-01
Accurate modeling of nucleation, growth and clustering of helium bubbles within metal tritide alloys is of high scientific and technological importance. Of interest is the ability to predict both the distribution of these bubbles and the manner in which these bubbles interact at a critical concentration of helium-to-metal atoms to produce an accelerated release of helium gas. One technique that has been used in the past to model these materials, and again revisited in this research, is percolation theory. Previous efforts have used classical percolation theory to qualitatively and quantitatively model the behavior of interstitial helium atoms in a metal tritide lattice; however, higher fidelity models are needed to predict the distribution of helium bubbles and include features that capture the underlying physical mechanisms present in these materials. In this work, we enhance classical percolation theory by developing the dynamic point-source percolation model. This model alters the traditionally binary character of site occupation probabilities by enabling them to vary depending on proximity to existing occupied sites, i.e. nucleated bubbles. This revised model produces characteristics for one and two dimensional systems that are extremely comparable with measurements from three dimensional physical samples. Future directions for continued development of the dynamic model are also outlined.
Argonne Bubble Experiment Thermal Model Development
Energy Technology Data Exchange (ETDEWEB)
Buechler, Cynthia Eileen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-12-03
This report will describe the Computational Fluid Dynamics (CFD) model that was developed to calculate the temperatures and gas volume fractions in the solution vessel during the irradiation. It is based on the model used to calculate temperatures and volume fractions in an annular vessel containing an aqueous solution of uranium . The experiment was repeated at several electron beam power levels, but the CFD analysis was performed only for the 12 kW irradiation, because this experiment came the closest to reaching a steady-state condition. The aim of the study is to compare results of the calculation with experimental measurements to determine the validity of the CFD model.
Numerical modeling of bubble dynamics in viscoelastic media with relaxation
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.
Using DNS and Statistical Learning to Model Bubbly Channel Flow
Ma, Ming; Lu, Jiacai; Tryggvason, Gretar
2015-11-01
The transient evolution of laminar bubbly flow in a vertical channel is examined by direct numerical simulation (DNS). Nearly spherical bubbles, initially distributed evenly in a fully developed parabolic flow, are driven relatively quickly to the walls, where they increase the drag and reduce the flow rate on a longer time scale. Once the flow rate has been decreased significantly, some of the bubbles move back into the channel interior and the void fraction there approaches the value needed to balance the weight of the mixture and the imposed pressure gradient. A database generated by averaging the DNS results is used to model the closure terms in a simple model of the average flow. Those terms relate the averaged lateral flux of the bubbles, the velocity fluctuations and the averaged surface tension force to the fluid shear, the void fraction and its gradient, as well as the distance to the nearest wall. An aggregated neural network is used for the statistically leaning of unknown closures, and closure relationships are tested by following the evolution of bubbly channel flow with different initial conditions. It is found that the model predictions are in reasonably good agreement with DNS results. Supported by NSF.
CFD Approaches for Modelling Bubble Entrainment by an Impinging Jet
Directory of Open Access Journals (Sweden)
Martin Schmidtke
2009-01-01
Full Text Available This contribution presents different approaches for the modeling of gas entrainment under water by a plunging jet. Since the generation of bubbles happens on a scale which is smaller than the bubbles, this process cannot be resolved in meso-scale simulations, which include the full length of the jet and its environment. This is why the gas entrainment has to be modeled in meso-scale simulations. In the frame of a Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example, the gas is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed. The algebraic interface area density (AIAD model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g., correlations for the gas entrainment.
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. PMID:26044460
Modeling DNA bubble formation at the atomic scale
International Nuclear Information System (INIS)
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 sequence 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.
Time-dependent Stochastic Acceleration Model for Fermi Bubbles
Sasaki, Kento; Asano, Katsuaki; Terasawa, Toshio
2015-12-01
We study stochastic acceleration models for the Fermi bubbles. Turbulence is excited just behind the shock front via Kelvin-Helmholtz, Rayleigh-Taylor, or Richtmyer-Meshkov instabilities, and plasma particles are continuously accelerated by the interaction with the turbulence. The turbulence gradually decays as it goes away from the shock fronts. Adopting a phenomenological model for the stochastic acceleration, we explicitly solve the temporal evolution of the particle energy distribution in the turbulence. Our results show that the spatial distribution of high-energy particles is different from those for a steady solution. We also show that the contribution of electrons that escaped from the acceleration regions significantly softens the photon spectrum. The photon spectrum and surface brightness profile are reproduced by our models. If the escape efficiency is very high, the radio flux from the escaped low-energy electrons can be comparable to that of the WMAP haze. We also demonstrate hadronic models with the stochastic acceleration, but they are unlikely in the viewpoint of the energy budget.
Development and validation of models for bubble coalescence and breakup
International Nuclear Information System (INIS)
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model. For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the
Modeling Air Bubble Transport in Hydraulic Jump Flows using Population Balance Approach
Directory of Open Access Journals (Sweden)
Min Xiang
2016-01-01
Full Text Available This paper proposed a numerical model aiming at coupling the MUltiple-SIze-Group (MUSIG with the semiempirical air entrainment model based on the Euler-Euler two-fluid framework to handle the bubble transport in hydraulic jump flows. The internal flow structure including the recirculation region, the shear layer region and the jet region was accurately predicted. The flow parameters such as the water velocity and void fraction distributions were examined and compared with the experimental data, validating the effectiveness of the numerical model. Prediction of the Sauter mean bubble diameter distributions by the population balance approach at different axial locations confirmed the dominance of breakage due to the high turbulent intensity in the shear layer region which led to the generation of small gas bubbles at high void fraction. Comparison between different cases indicates that high Froude number not only give rise to longer recirculation region and higher void fraction due to larger air entrainment rate, but also generate larger bubble number density and smaller bubble size because of the stronger turbulence intensity in the same axial position.
Evolutionary thinking in microeconomic models: prestige bias and market bubbles.
Bell, Adrian Viliami
2013-01-01
Evolutionary models broadly support a number of social learning strategies likely important in economic behavior. Using a simple model of price dynamics, I show how prestige bias, or copying of famed (and likely successful) individuals, influences price equilibria and investor disposition in a way that exacerbates or creates market bubbles. I discuss how integrating the social learning and demographic forces important in cultural evolution with economic models provides a fruitful line of inquiry into real-world behavior. PMID:23544100
A modelling and experimental study of the bubble trajectory in a non-Newtonian crystal suspension
Energy Technology Data Exchange (ETDEWEB)
Hassan, N M S [Process Engineering and Light Metals (PELM) Centre, Faculty of Sciences, Engineering and Health, CQUniversity, Rockhampton, QLD 4702 (Australia); Khan, M M K; Rasul, M G, E-mail: m.rasul@cqu.edu.a [School of Engineering and Built Environment, Faculty of Sciences, Engineering and Health, CQUniversity, Rockhampton, QLD 4702 (Australia)
2010-12-15
This paper presents an experimental and computational study of air bubbles rising in a massecuite-equivalent non-Newtonian crystal suspension. The bubble trajectory inside the stagnant liquid of a 0.05% xanthan gum crystal suspension was investigated and modelled using the computational fluid dynamics (CFD) model to gain an insight into the bubble flow characteristics. The CFD code FLUENT was used for numerical simulation, and the bubble trajectory calculations were performed through a volume of fluid (VOF) model. The influences of the Reynolds number (Re), the Weber number (We) and the bubble aspect ratio (E) on the bubble trajectory are discussed. The conditions for the bubbles' path oscillations are identified. The experimental results showed that the path instability for the crystal suspension was less rapid than in water. The trajectory analysis indicated that 5.76 mm diameter bubbles followed a zigzag motion in the crystal suspension. Conversely, the smaller bubbles (5.76 mm) followed a path of least horizontal movement and larger bubbles (21.21 mm) produced more spiral motion within the crystal suspension. Path instability occurred for bubbles of 15.63 and 21.21 mm diameter, and they induced both zigzag and spiral trajectories within the crystal suspension. At low Re and We, smaller bubbles (5.76 mm) produced a zigzag trajectory, whereas larger bubbles (15.63 and 21.21 mm) showed both zigzag and spiral trajectories at intermediate and moderately high Re and We in the crystal suspension. The simulation results illustrated that a repeating pattern of swirling vortices was created for smaller bubbles due to the unstable wake and unsteady flow of these bubbles. This is the cause of the smaller bubbles moving in a zigzag way. Larger bubbles showed two counter-rotating trailing vortices at the back of the bubble. These vortices induced a velocity component to the gas-liquid interface and caused a deformation. Hence, the larger bubbles produced a path
A modelling and experimental study of the bubble trajectory in a non-Newtonian crystal suspension
International Nuclear Information System (INIS)
This paper presents an experimental and computational study of air bubbles rising in a massecuite-equivalent non-Newtonian crystal suspension. The bubble trajectory inside the stagnant liquid of a 0.05% xanthan gum crystal suspension was investigated and modelled using the computational fluid dynamics (CFD) model to gain an insight into the bubble flow characteristics. The CFD code FLUENT was used for numerical simulation, and the bubble trajectory calculations were performed through a volume of fluid (VOF) model. The influences of the Reynolds number (Re), the Weber number (We) and the bubble aspect ratio (E) on the bubble trajectory are discussed. The conditions for the bubbles' path oscillations are identified. The experimental results showed that the path instability for the crystal suspension was less rapid than in water. The trajectory analysis indicated that 5.76 mm diameter bubbles followed a zigzag motion in the crystal suspension. Conversely, the smaller bubbles (5.76 mm) followed a path of least horizontal movement and larger bubbles (21.21 mm) produced more spiral motion within the crystal suspension. Path instability occurred for bubbles of 15.63 and 21.21 mm diameter, and they induced both zigzag and spiral trajectories within the crystal suspension. At low Re and We, smaller bubbles (5.76 mm) produced a zigzag trajectory, whereas larger bubbles (15.63 and 21.21 mm) showed both zigzag and spiral trajectories at intermediate and moderately high Re and We in the crystal suspension. The simulation results illustrated that a repeating pattern of swirling vortices was created for smaller bubbles due to the unstable wake and unsteady flow of these bubbles. This is the cause of the smaller bubbles moving in a zigzag way. Larger bubbles showed two counter-rotating trailing vortices at the back of the bubble. These vortices induced a velocity component to the gas-liquid interface and caused a deformation. Hence, the larger bubbles produced a path transition.
Development of bubble-induced turbulence model for advanced two-fluid model
International Nuclear Information System (INIS)
diameter pipes. As a result, the analysis results of void fraction distribution were improved by using the suggested model. However, the analytical velocity distribution was flat compared with the experiments. As the main cause of this, we thought that turbulent viscosity in two-phase flow was overestimated in these analyses. To express the velocity distribution, we improved the two-phase k-ε turbulent model in this study. Especially, turbulent dissipation rate transport equation was introduced in order to consider the influence of bubble-induced turbulence. These models were incorporated to the advanced two-fluid model code ACE-3D, and numerical simulations for air-water two-phase flow experiment in 200 mm-, 60 mm- and 38 mm-diameter vertical pipe were performed. From these results, the qualitative phenomena could be expressed and the dependency of the suggested model was confirmed. (author)
Directory of Open Access Journals (Sweden)
Kálal Zbyněk
2014-09-01
Full Text Available The main topic of this study is the mathematical modelling of bubble size distributions in an aerated stirred tank using the population balance method. The air-water system consisted of a fully baffled vessel with a diameter of 0.29 m, which was equipped with a six-bladed Rushton turbine. The secondary phase was introduced through a ring sparger situated under the impeller. Calculations were performed with the CFD software CFX 14.5. The turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the MUSIG method with 24 bubble size groups. For the bubble size distribution modelling, the breakup model by Luo and Svendsen (1996 typically has been used in the past. However, this breakup model was thoroughly reviewed and its practical applicability was questioned. Therefore, three different breakup models by Martínez-Bazán et al. (1999a, b, Lehr et al. (2002 and Alopaeus et al. (2002 were implemented in the CFD solver and applied to the system. The resulting Sauter mean diameters and local bubble size distributions were compared with experimental data.
International Nuclear Information System (INIS)
Highlights: • Flow behaviors with H and Vg were simulated using CFD coupled with PBM. • Bubble size and gas holdup are mainly determined by vortical flow. • Interfacial area enhanced by increasing Vg and H, but the enhancement effect is not obvious while the Vg is too fast. - Abstract: Using bubble column to extract tritium from lead lithium (Pb–17Li) eutectic is an effective way in the process of tritium extraction in liquid blanket system, where the hydrodynamic characteristics of the gas–liquid two-phase flow in the columns play a very important role. In order to understand the two-phase flow details and investigate the influence factors on the hydrodynamic performance, in this paper the flow behaviors in the cylindrical bubble columns with different heights and purge gas inlet velocities using computational fluid dynamics coupled with population balance model were simulated. Liquid flow field, bubble Sauter mean diameter, time-averaged gas holdup and two-phase interfacial area for the different cases were obtained and compared. The simulation results showed good agreement with previous studies, and which indicated that bubble size and gas holdup formation are mainly determined by vortical flow. In addition, interfacial area can be enhanced by increasing the purge gas inlet velocity and column height. However, the enhancement effect will trail away when the gas inlet velocity is too fast, and the contribution of column height is relatively small
Numerical Modeling and Prediction of Bubbling Fluidized Beds
England, Jonas Andrew
2011-01-01
Numerical modeling and prediction techniques are used to determine pressure drop, minimum fluidization velocity and segregation for bubbling fluidized beds. The computational fluid dynamics (CFD) code Multiphase Flow with Interphase eXchange (MFIX) is used to study a two-stage reactor geometry with a binary mixture. MFIX is demonstrated to accurately predict pressure drop versus inlet gas velocity for binary mixtures. A new method is developed to predict the pressure drop versus inlet gas v...
Horizontal bubbly flow with elbow restrictions: Interfacial area transport modeling
International Nuclear Information System (INIS)
The present study develops an interfacial area transport equation applicable to an air-water horizontal bubbly flow, along which two types of horizontal elbows are installed as flow restrictions. Two sets of experiments are performed in a round glass tube of 50.3 mm inner diameter. Along the test section, a 90-degree elbow is installed at L/D = 206.6 from the two-phase mixture inlet and then a 45-degree elbow is installed at L/D = 353.5. In total, 15 different flow conditions in the bubbly flow regime for each of the two flow restriction experiments are studied. Detailed local two-phase flow parameters are acquired by a double-sensor conductivity probe at four different axial locations in the 90-degree experiment and three different axial locations in the 45-degree experiment. The effect of the elbows is found to be evident in the distribution of local parameters as well as in the development of interfacial structures. It is clear that the elbows make an effect on the bubble interactions resulting in significant changes to both the void fraction and interfacial area concentration. In the present analysis, the interfacial area transport equation is developed in one-dimensional form via area averaging. In the averaging process, characteristic non-uniform distributions of the flow parameters in horizontal two-phase flow are treated mathematically through a distribution parameter. The mechanistic models for the major bubble interaction phenomena developed in vertical flow analysis are employed in the present study. Furthermore, the change in pressure due to the minor loss of an elbow is taken into consideration by using a newly developed correlation analogous to Lockhart and Martinelli's. In total, 105 area-averaged data points are employed to benchmark the present model. The present model predicts the data relatively well with an average percent difference of approximately ±20%.
Bubbling phenomenon in a discrete economic model for the interaction of demand and supply
Energy Technology Data Exchange (ETDEWEB)
Yang Xiaozhong [School of Mathematics and Statistics, North China Electric Power University, Beijing 102 206 (China)], E-mail: yxiaozh@ncepu.edu.cn; Peng Mingshu [School of Science, Beijing Jiao Tong University, Beijing 100 044 (China)], E-mail: mshpeng@bjtu.edu.cn; Hu Jiping [School of Civil Engineering, Beijing Jiao Tong University, Beijing 100 044 (China)], E-mail: jphu@bjtu.edu.cn; Jiang Xiaoxia [School of Science, Beijing Jiao Tong University, Beijing 100 044 (China)
2009-11-15
In this paper, we study rich dynamics of a nonlinear economic model. Chaotic and bubbling phenomena are shown by numerical simulation, which clearly parallels with phenomena from technology bubbling during 1999-2000, or economic bubbling such as in the global industry of real state/stock market/production (oil) market since 2006.
Liang, Mingchao; Wei, Junhong; Han, Hongmei; Fu, Chengguo; Liu, Jianjun
2015-09-01
The capillary pressure is one of the crucial parameters in many science and engineering applications such as composite materials, interface science, chemical engineering, oil exploration, etc. The drop/bubble formation and its mechanisms that affect the permeability of porous media have steadily attracted much attention in the past. When a drop/bubble moves from a larger capillary to a smaller one, it is often obstructed by an additional pressure difference caused by the capillary force. In this paper, a comprehensive model is derived for the capillary pressure difference when a drop/bubble flows through a constricted capillary, i.e. a geometrically constricted passage with an abrupt change in radius. The proposed model is expressed as a function of the smaller capillary radius, pore-throat ratio, contact angle, surface tension and length of the drop/bubble in the smaller capillary. The model predictions are compared with the available experimental data, and good agreement is found between them.
An application of the method of moments to the modeling of bubbly flow
International Nuclear Information System (INIS)
Bubbly flows are relevant in nuclear reactors thermalhydraulics and safety analysis. Regularly, empirical constitutive laws are required to close the two-fluid equations, particularly in relating the interfacial area and the bubble number densities to the local void fraction. In this article, starting from a generalized Boltzmann transport equation for the bubble size spectrum, a convection equation for the bubble number density is derived using the method of moments. The equation is analyzed for a vertical bubbly flow in stagnated liquid, showing excellent agreement with experimental data. The model is useful as a mean to provide conservation-based correlations to complement the existing two-fluid models
Bubbly flows with fixed polydispersity: Validation of a baseline closure model
Energy Technology Data Exchange (ETDEWEB)
Rzehak, Roland, E-mail: R.Rzehak@hzdr.de; Krepper, Eckhard, E-mail: E.Krepper@hzdr.de
2015-06-15
Highlights: • Consideration of regime with significant but non-varying polydispersity. • Facilitates qualification of closure models. • Including bubble forces and bubble-induced turbulence. • Validation of the models with an experimental database for developing flow. • Shows reversing direction of shear lift force with bubble size. - Abstract: For practical applications the Euler–Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas–liquid multiphase flow, closures are needed for bubble forces, bubble-induced turbulence, as well as bubble-coalescence and -breakup. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture. Reasonable success has been achieved so far for flows that are amenable to a monodisperse approximation for the bubble size which limits the latter to no more than a few mm. In the present work we extend the validation to flow in which bubbles with a broad distribution of sizes up to ∼10 mm are present, but the shape of the distribution remains unchanged during the flow development. The existence of such conditions, which we term “fixed polydispersity”, is deduced from the experimental data. For this kind of situation the complexity of the closure problem is reduced since a balance between bubble-coalescence and -breakup prevails that allows to neglect these processes and simply impose a fixed bubble size distribution. Conclusions towards best practice guidelines for modeling bubbly flows are drawn and needs for further research identified.
Bubbly flows with fixed polydispersity: Validation of a baseline closure model
International Nuclear Information System (INIS)
Highlights: • Consideration of regime with significant but non-varying polydispersity. • Facilitates qualification of closure models. • Including bubble forces and bubble-induced turbulence. • Validation of the models with an experimental database for developing flow. • Shows reversing direction of shear lift force with bubble size. - Abstract: For practical applications the Euler–Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas–liquid multiphase flow, closures are needed for bubble forces, bubble-induced turbulence, as well as bubble-coalescence and -breakup. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture. Reasonable success has been achieved so far for flows that are amenable to a monodisperse approximation for the bubble size which limits the latter to no more than a few mm. In the present work we extend the validation to flow in which bubbles with a broad distribution of sizes up to ∼10 mm are present, but the shape of the distribution remains unchanged during the flow development. The existence of such conditions, which we term “fixed polydispersity”, is deduced from the experimental data. For this kind of situation the complexity of the closure problem is reduced since a balance between bubble-coalescence and -breakup prevails that allows to neglect these processes and simply impose a fixed bubble size distribution. Conclusions towards best practice guidelines for modeling bubbly flows are drawn and needs for further research identified
Hydrodynamics of Bubble Bouncing on a Wall, Experiment and Modelling
Czech Academy of Sciences Publication Activity Database
Zedníková, Mária; Vejražka, Jiří; Růžička, Marek; Drahoš, Jiří
Prague: Institute of Hydrodynamics ASCR, v.v.i, 2008 - (Chára, Z.; Klaboch, L.), s. 20-27 ISBN 978-80-87117-04-0. [XXII. Symposium on Anemometry. Holany-Litice (CZ), 03.06.2008-04.06.2008] R&D Projects: GA ČR GA104/07/1110; GA AV ČR(CZ) IAA200720801; GA AV ČR(CZ) KJB200720801 Institutional research plan: CEZ:AV0Z40720504 Keywords : hydrodynamics of bubble * experiments * modelling Subject RIV: CI - Industrial Chemistry, Chemical Engineering
The Accretion Wind Model of Fermi Bubbles. II. Radiation
Mou, Guobin; Yuan, Feng; Gan, Zhaoming; Sun, Mouyuan
2015-09-01
In a previous work, we have shown that the formation of Fermi bubbles can be due to the interaction between winds launched from the hot accretion flow in Sgr A* and the interstellar medium (ISM). In that work, we focus only on the morphology. In this paper we continue our study by calculating the gamma-ray radiation. Some cosmic-ray protons (CRp) and electrons (CRe) must be contained in the winds, which are likely formed by physical processes such as magnetic reconnection. We have performed MHD simulations to study the spatial distribution of CRp, considering the advection and diffusion of CRp in the presence of magnetic field. We find that a permeated zone is formed just outside of the contact discontinuity between winds and the ISM, where the collisions between CRp and thermal nuclei mainly occur. The decay of neutral pions generated in the collisions, combined with the inverse Compton scattering of background soft photons by the secondary leptons generated in the collisions and primary CRe, can well explain the observed gamma-ray spectral energy distribution. Other features such as the uniform surface brightness along the latitude and the boundary width of the bubbles are also explained. The advantage of this “accretion wind” model is that the adopted wind properties come from the detailed small-scale MHD numerical simulation of accretion flows and the value of mass accretion rate has independent observational evidences. The success of the model suggests that we may seriously consider the possibility that cavities and bubbles observed in other contexts such as galaxy clusters may be formed by winds rather than jets.
Modeling high-energy gamma-rays from the Fermi Bubbles
Energy Technology Data Exchange (ETDEWEB)
Splettstoesser, Megan
2015-09-17
In 2010, the Fermi Bubbles were discovered at the galactic center of the Milky Way. These giant gamma-ray structures, extending 55° in galactic latitude and 20°-30° in galactic longitude, were not predicted. We wish to develop a model for the gamma-ray emission of the Fermi Bubbles. To do so, we assume that second order Fermi acceleration requires charged particles and irregular magnetic fields- both of which are present in the disk of the Milky Way galaxy. By solving the steady-state case of the transport equation, I compute the proton spectrum due to second order Fermi acceleration. I compare the analytical solutions of the proton spectrum to a numerical solution. I find that the numerical solution to the transport equation converges to the analytical solution in all cases. The gamma-ray spectrum due to proton-proton interaction is compared to Fermi Bubble data (from Ackermann et al. 2014), and I find that second order Fermi acceleration is a good fit for the gamma-ray spectrum of the Fermi Bubbles at low energies with an injection source term of S = 1.5 x 10⁻¹⁰ GeV⁻¹cm⁻³yr⁻¹. I find that a non-steady-state solution to the gamma-ray spectrum with an injection source term of S = 2 x 10⁻¹⁰ GeV⁻¹cm⁻³yr⁻¹ matches the bubble data at high energies.
Modeling Space-Time Dependent Helium Bubble Evolution in Tungsten Armor under IFE Conditions
International Nuclear Information System (INIS)
The High Average Power Laser (HAPL) program is a coordinated effort to develop Laser Inertial Fusion Energy. The implosion of the D-T target produces a spectrum of neutrons, X-rays, and charged particles, which arrive at the first wall (FW) at different times within about 2.5 μs at a frequency of 5 to 10 Hz. Helium is one of several high-energy charged particle constituents impinging on the candidate tungsten armored low activation ferritic steel First Wall. The spread of the implanted debris and burn helium energies results in a unique space-time dependent implantation profile that spans about 10 μm in tungsten. Co-implantation of X-rays and other ions results in spatially dependent damage profiles and rapid space-time dependent temperature spikes and gradients. The rate of helium transport and helium bubble formation will vary significantly throughout the implanted region. Furthermore, helium will also be transported via the migration of helium bubbles and non-equilibrium helium-vacancy clusters. The HEROS code was developed at UCLA to model the spatial and time-dependent helium bubble nucleation, growth, coalescence, and migration under transient damage rates and transient temperature gradients. The HEROS code is based on kinetic rate theory, which includes clustering of helium and vacancies, helium mobility, helium-vacancy cluster stability, cavity nucleation and growth and other microstructural features such as interstitial loop evolution, grain boundaries, and precipitates. The HEROS code is based on space-time discretization of reaction-diffusion type equations to account for migration of mobile species between neighboring bins as single atoms, clusters, or bubbles. HAPL chamber FW implantation conditions are used to model helium bubble evolution in the implanted tungsten. Helium recycling rate predictions are compared with experimental results of helium ion implantation experiments. (author)
Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue
Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.
2003-01-01
Models of gas bubble dynamics employed in probabilistic analyses of decompression sickness incidence in man must be theoretically consistent and simple, if they are to yield useful results without requiring excessive computations. They are generally formulated in terms of ordinary differential equations that describe diffusion-limited gas exchange between a gas bubble and the extravascular tissue surrounding it. In our previous model (Ann. Biomed. Eng. 30: 232-246, 2002), we showed that with appropriate representation of sink pressures to account for gas loss or gain due to heterogeneous blood perfusion in the unstirred diffusion region around the bubble, diffusion-limited bubble growth in a tissue of finite volume can be simulated without postulating a boundary layer across which gas flux is discontinuous. However, interactions between two or more bubbles caused by competition for available gas cannot be considered in this model, because the diffusion region has a fixed volume with zero gas flux at its outer boundary. The present work extends the previous model to accommodate interactions among multiple bubbles by allowing the diffusion region volume of each bubble to vary during bubble evolution. For given decompression and tissue volume, bubble growth is sustained only if the bubble number density is below a certain maximum.
Pseudopotential MRT lattice Boltzmann model for cavitation bubble collapse with high density ratio
Shan, Ming-Lei; Yao, Cheng; Yin, Cheng; Jiang, Xiao-Yan
2016-01-01
The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q. et al. is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. The independence between the kinematic viscosity and the thermodynamic consistency, surface tension is founded. By homogeneous and heterogeneous cavitation simulation, the capability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of collapsing bubble is consistent with the results from experiments and simulations by other numerical method. It is demonstrated that the present pseudopotential...
Multiple bifurcations and periodic 'bubbling' in a delay population model
International Nuclear Information System (INIS)
In this paper, the flip bifurcation and periodic doubling bifurcations of a discrete population model without delay influence is firstly studied and the phenomenon of Feigenbaum's cascade of periodic doublings is also observed. Secondly, we explored the Neimark-Sacker bifurcation in the delay population model (two-dimension discrete dynamical systems) and the unique stable closed invariant curve which bifurcates from the nontrivial fixed point. Finally, a computer-assisted study for the delay population model is also delved into. Our computer simulation shows that the introduction of delay effect in a nonlinear difference equation derived from the logistic map leads to much richer dynamic behavior, such as stable node → stable focus → an lower-dimensional closed invariant curve (quasi-periodic solution, limit cycle) or/and stable periodic solutions → chaotic attractor by cascading bubbles (the combination of potential period doubling and reverse period-doubling) and the sudden change between two different attractors, etc
Energy Technology Data Exchange (ETDEWEB)
Hu, Shenyang Y.; Burkes, Douglas; Lavender, Curt A.; Senor, David J.; Setyawan, Wahyu; Xu, Zhijie
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 along 〈110〉 directions in the body-centered cubic U matrix causes the gas bubble alignment along 〈110〉 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.
A model of the interaction of bubbles and solid particles under acoustic excitation
Hay, Todd Allen
The Lagrangian formalism utilized by Ilinskii, Hamilton and Zabolotskaya [J. Acoust. Soc. Am. 121, 786-795 (2007)] to derive equations for the radial and translational motion of interacting bubbles is extended here to obtain a model for the dynamics of interacting bubbles and elastic particles. The bubbles and particles are assumed to be spherical but are otherwise free to pulsate and translate. The model is accurate to fifth order in terms of a nondimensional expansion parameter R/d, where R is a characteristic radius and d is a characteristic distance between neighboring bubbles or particles. The bubbles and particles may be of nonuniform size, the particles elastic or rigid, and external acoustic sources are included to an order consistent with the accuracy of the model. Although the liquid is assumed initially to be incompressible, corrections accounting for finite liquid compressibility are developed to first order in the acoustic Mach number for a cluster of bubbles and particles, and to second order in the acoustic Mach number for a single bubble. For a bubble-particle pair consideration is also given to truncation of the model at fifth order in R/d via automated derivation of the model equations to arbitrary order. Numerical simulation results are presented to demonstrate the effects of key parameters such as particle density and size, liquid compressibility, particle elasticity and model order on the dynamics of single bubbles, pairs of bubbles, bubble-particle pairs and clusters of bubbles and particles under both free response conditions and sinusoidal or shock wave excitation.
Energy Technology Data Exchange (ETDEWEB)
Pellacani, Filippo
2012-12-04
A local mechanistic model for bubble coalescence and breakup for the one-group interfacial area transport equation has been developed, in agreement and within the limits of the current understanding, based on an exhaustive survey of the theory and of the state of the art models for bubble dynamics simulation. The new model has been tested using the commercial 3D CFD code ANSYS CFX. Upward adiabatic turbulent air-water bubbly flow has been simulated and the results have been compared with the data obtained in the experimental facility PUMA. The range of the experimental data available spans between 0.5 to 2 m/s liquid velocity and 5 to 15 % volume fraction. For the implementation of the models, both the monodispersed and the interfacial area transport equation approaches have been used. The first one to perform a detailed analysis of the forces and models to reproduce the dynamic of the dispersed phase adequately and to be used in the next phases of the work. Also two different bubble induced turbulence models have been tested to consider the effect of the presence of the gas phase on the turbulence of the liquid phase. The interfacial area transport equation has been successfully implemented into the CFD code and the state of the art breakup and coalescence models have been used for simulation. The limitations of the actual theory have been shown and a new bubble interactions model has been developed. The simulations showed that a considerable improvement is achieved if compared to the state of the art closure models. Limits in the implementation derive from the actual understanding and formulation of the bubbly dynamics. A strong dependency on the interfacial non-drag force models and coefficients have been shown. More experimental and theory work needs to be done in this field to increase the prediction capability of the simulation tools regarding the distribution of the phases along the pipe radius.
International Nuclear Information System (INIS)
A local mechanistic model for bubble coalescence and breakup for the one-group interfacial area transport equation has been developed, in agreement and within the limits of the current understanding, based on an exhaustive survey of the theory and of the state of the art models for bubble dynamics simulation. The new model has been tested using the commercial 3D CFD code ANSYS CFX. Upward adiabatic turbulent air-water bubbly flow has been simulated and the results have been compared with the data obtained in the experimental facility PUMA. The range of the experimental data available spans between 0.5 to 2 m/s liquid velocity and 5 to 15 % volume fraction. For the implementation of the models, both the monodispersed and the interfacial area transport equation approaches have been used. The first one to perform a detailed analysis of the forces and models to reproduce the dynamic of the dispersed phase adequately and to be used in the next phases of the work. Also two different bubble induced turbulence models have been tested to consider the effect of the presence of the gas phase on the turbulence of the liquid phase. The interfacial area transport equation has been successfully implemented into the CFD code and the state of the art breakup and coalescence models have been used for simulation. The limitations of the actual theory have been shown and a new bubble interactions model has been developed. The simulations showed that a considerable improvement is achieved if compared to the state of the art closure models. Limits in the implementation derive from the actual understanding and formulation of the bubbly dynamics. A strong dependency on the interfacial non-drag force models and coefficients have been shown. More experimental and theory work needs to be done in this field to increase the prediction capability of the simulation tools regarding the distribution of the phases along the pipe radius.
A mathematical model and numerical simulation of pressure wave in horizontal gas-liquid bubbly flow
Institute of Scientific and Technical Information of China (English)
HUANG Fei; BAI Bofeng; GUO Liejin
2004-01-01
By using an ensemble-averaged two-fluid model,with valid closure conditions of interfacial momentum exchange due to virtual mass force,viscous shear stress and drag force,a model for pressure wave propagation in a horizontal gas-liquid bubbly flow is proposed.According to the small perturbation theory and solvable condition of one-order linear uniform equations,a dispersion equation of pressure wave is induced.The pressure wave speed calculated from the model is compared and in good agreement with existing data.According to the dispersion equation,the propagation and attenuation of pressure wave are investigated systemically.The factors affecting pressure wave,such as void fraction,pressure,wall shear stress,perturbation frequency,virtual mass force and drag force,are analyzed.The result shows that the decrease in system pressure,the increase in void fraction and the existence of wall shear stress,will cause a decrease in pressure wave speed and an increase in the attenuation coefficient in the horizontal gas-liquid bubbly flow.The effects of perturbation frequency,virtual mass and drag force on pressure wave in the horizontal gas-liquid bubbly flow at low perturbation frequency are different from that at high perturbation frequency.
Bubble Economics and Structural Change: The Cases of Spain and France Compared
Agnese, Pablo; Hromcová, Jana
2015-01-01
This paper delves into the recent events that led to the formation of the housing bubble in Spain and the resulting structural change that is arguably needed to put the economy back into the right track. For this purpose we calibrate a model with different equilibria descriptive of the labor markets in Spain and France, where the unemployment rates went from the same initial spot to very different levels. In addition to this, we run two counterfactual analyses that throw some more light on th...
COMPUTATIONAL AND EXPERIMENTAL MODELING OF SLURRY BUBBLE COLUMN REACTORS
Energy Technology Data Exchange (ETDEWEB)
Paul C.K. Lam; Isaac K. Gamwo; Dimitri Gidaspow
2002-05-01
The objective of this study was to develop a predictive experimentally verified computational fluid dynamics (CFD) model for gas-liquid-solid flow. A three dimensional transient computer code for the coupled Navier-Stokes equations for each phase was developed and is appended in this report. The principal input into the model is the viscosity of the particulate phase which was determined from a measurement of the random kinetic energy of the 800 micron glass beads and a Brookfield viscometer. The details are presented in the attached paper titled ''CFD Simulation of Flow and Turbulence in a Slurry Bubble Column''. This phase of the work is in press in a referred journal (AIChE Journal, 2002) and was presented at the Fourth International Conference on Multiphase Flow (ICMF 2001) in New Orleans, May 27-June 1, 2001 (Paper No. 909). The computed time averaged particle velocities and concentrations agree with Particle Image Velocimetry (PIV) measurements of velocities and concentrations, obtained using a combination of gamma-ray and X-ray densitometers, in a slurry bubble column, operated in the bubbly-coalesced fluidization regime with continuous flow of water. Both the experiment and the simulation show a down-flow of particles in the center of the column and up-flow near the walls and nearly uniform particle concentration. Normal and shear Reynolds stresses were constructed from the computed instantaneous particle velocities. The PIV measurement and the simulation produced instantaneous particle velocities. The PIV measurement and the simulation produced similar nearly flat horizontal profiles of turbulent kinetic energy of particles. To better understand turbulence we studied fluidization in a liquid-solid bed. This work was also presented at the Fourth International Conference on Multiphase Flow (ICMF 2001, Paper No. 910). To understand turbulence in risers, measurements were done in the IIT riser with 530 micron glass beads using a PIV
An Axial Dispersion Model for Evaporating Bubble Column Reactor
Institute of Scientific and Technical Information of China (English)
谢刚; 李希
2004-01-01
Evaporating bubble column reactor (EBCR) is a kind of aerated reactor in which the reaction heat is removed by the evaporation of volatile reaction mixture. In this paper, a mathematical model that accounts for the gas-liquid exothermic reaction and axial dispersions of both gas and liquid phase is employed to study the performance of EBCR for the process of p-xylene(PX) oxidation. The computational results show that there are remarkable concentration and temperature gradients in EBCR for high ratio of height to diameter (H/DT). The temperature is lower at the bottom of column and higher at the top, due to rapid evaporation induced by the feed gas near the bottom. The concentration profiles in the gas phase are more nonuniform than those (except PX) in the liquid phase, which causes more solvent burning consumption at high H/DT ratio. For p-xylene oxidation, theo ptimal H/DT is around 5.
Energy Technology Data Exchange (ETDEWEB)
Cheung, S.C.P.; Deju, L. [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Victoria 3083 (Australia); Yeoh, G.H. [Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, New South Wales 2232 (Australia); School of Mechanical and Manufacturing Engineering, University of New South Wales, New South Wales 2052 (Australia); Tu, J.Y., E-mail: jiyuan.tu@rmit.edu.au [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Victoria 3083 (Australia)
2013-12-15
Highlights: • Analyze gas–liquid flow in medium and large pipe under various flow regimes. • Identifying relative merits and capabilities of DQMOM. • Comparison of DQMOM with ABND and homogeneous MUSIG model. • Numerical results validation against gas–liquid flow experiments. - Abstract: Gas–liquid flows are commonly encountered in many industrial flow systems. In many cases, the evolution of bubble size distribution is a crucial factor governing the momentum, heat and mass transfer between phases within the system. Aiming to evaluate the capability of existing models, numerical assessment of three different population balance approaches – direct quadrature method of moments (DQMOM), average bubble number density (ABND) model and homogeneous MUlti-SIze-Group (MUSIG) models – is presented in this paper. Model predictions were validated against experimental measurements from medium and large scale bubble columns where bubble sizes within the system were found to be dominant by coalescence and break-up mechanism, respectively. In result of the bubble size change, transitions of phase distribution from wall peak to core peak profile were also found in both experiments. In general, predictions of the three models were in satisfactory agreement with experiment measurements clearly demonstrating its applicability for large scale practical systems. Encouraging results have also been obtained in capturing the evolution of bubble size distribution. Nevertheless, noticeable errors were also found in predictions of the MUSIG and DQMOM model indicating some potential deficiencies of the model. To evaluate the numerical efficiency of the three models, computational requirements of each model were also compared.
International Nuclear Information System (INIS)
Highlights: • Analyze gas–liquid flow in medium and large pipe under various flow regimes. • Identifying relative merits and capabilities of DQMOM. • Comparison of DQMOM with ABND and homogeneous MUSIG model. • Numerical results validation against gas–liquid flow experiments. - Abstract: Gas–liquid flows are commonly encountered in many industrial flow systems. In many cases, the evolution of bubble size distribution is a crucial factor governing the momentum, heat and mass transfer between phases within the system. Aiming to evaluate the capability of existing models, numerical assessment of three different population balance approaches – direct quadrature method of moments (DQMOM), average bubble number density (ABND) model and homogeneous MUlti-SIze-Group (MUSIG) models – is presented in this paper. Model predictions were validated against experimental measurements from medium and large scale bubble columns where bubble sizes within the system were found to be dominant by coalescence and break-up mechanism, respectively. In result of the bubble size change, transitions of phase distribution from wall peak to core peak profile were also found in both experiments. In general, predictions of the three models were in satisfactory agreement with experiment measurements clearly demonstrating its applicability for large scale practical systems. Encouraging results have also been obtained in capturing the evolution of bubble size distribution. Nevertheless, noticeable errors were also found in predictions of the MUSIG and DQMOM model indicating some potential deficiencies of the model. To evaluate the numerical efficiency of the three models, computational requirements of each model were also compared
COMPUTATIONAL AND EXPERIMENTAL MODELING OF SLURRY BUBBLE COLUMN REACTORS
Energy Technology Data Exchange (ETDEWEB)
Paul Lam; Dimitri Gidaspow
2000-09-01
The objective if this study was to develop a predictive experimentally verified computational fluid dynamics (CFD) model for gas-liquid-solid flow. A three dimensional transient computer code for the coupled Navier-Stokes equations for each phase was developed. The principal input into the model is the viscosity of the particulate phase which was determined from a measurement of the random kinetic energy of the 800 micron glass beads and a Brookfield viscometer. The computed time averaged particle velocities and concentrations agree with PIV measurements of velocities and concentrations, obtained using a combination of gamma-ray and X-ray densitometers, in a slurry bubble column, operated in the bubbly-coalesced fluidization regime with continuous flow of water. Both the experiment and the simulation show a down-flow of particles in the center of the column and up-flow near the walls and nearly uniform particle concentration. Normal and shear Reynolds stresses were constructed from the computed instantaneous particle velocities. The PIV measurement and the simulation produced instantaneous particle velocities. The PIV measurement and the simulation produced similar nearly flat horizontal profiles of turbulent kinetic energy of particles. This phase of the work was presented at the Chemical Reaction Engineering VIII: Computational Fluid Dynamics, August 6-11, 2000 in Quebec City, Canada. To understand turbulence in risers, measurements were done in the IIT riser with 530 micron glass beads using a PIV technique. The results together with simulations will be presented at the annual meeting of AIChE in November 2000.
GISAXS modelling of helium-induced nano-bubble formation in tungsten and comparison with TEM
Thompson, Matt; Sakamoto, Ryuichi; Bernard, Elodie; Kirby, Nigel; Kluth, Patrick; Riley, Daniel; Corr, Cormac
2016-05-01
Grazing-incidence small angle x-ray scattering (GISAXS) is a powerful non-destructive technique for the measurement of nano-bubble formation in tungsten under helium plasma exposure. Here, we present a comparative study between transmission electron microscopy (TEM) and GISAXS measurements of nano-bubble formation in tungsten exposed to helium plasma in the Large Helical Device (LHD) fusion experiment. Both techniques are in excellent agreement, suggesting that nano-bubbles range from spheroidal to ellipsoidal, displaying exponential diameter distributions with mean diameters μ=0.68 ± 0.04 nm and μ=0.6 ± 0.1 nm measured by TEM and GISAXS respectively. Depth distributions were also computed, with calculated exponential depth distributions with mean depths of 8.4 ± 0.5 nm and 9.1 ± 0.4 nm for TEM and GISAXS. In GISAXS modelling, spheroidal particles were fitted with an aspect ratio ε=0.7 ± 0.1. The GISAXS model used is described in detail.
Development of Bubble Lift-off Diameter Model for Subcooled Boiling Flows
International Nuclear Information System (INIS)
A lot of models and correlations for predicting the bubble departure/lift-off diameter are available in the literature. Most of them were developed based on a hydrodynamic principle, which balances forces acting on a bubble at the departure/lift-off point. One difficulty of these models is lack of essential information, such as bubble front velocity, liquid velocity, or relative velocity, to estimate the active force elements. Hence, the lift-off bubble diameter predicted by these hydrodynamic-controlled models may be suffered a large uncertainty. In contract to the hydrodynamic approach, there are few models developed based on the heat transfer aspect. By balancing the heat conducted through a microlayer underneath a bubble with the heat taken away by condensation at the upper part of the bubble, Unal derived a heat-controlled model of the bubble lift-off diameter. This model did not consider the role of superheat liquid layer surrounding the bubble as well as the effect of liquid properties on the heat transfer process. Beside these two approaches, several empirical correlations have been proposed based on dimensionless analyses for measured experimental databases. The application of these correlations to different experiments conditions is, of course, questionable because of the lack of physical bases. Regarding the heat transfer accompanied by a vapor bubble, four involved heat transfer regions surrounding this bubble can be defined as in Fig. 1. These are dry region, microlayer, superheated liquid layer (SpLL) and subcooled liquid layer (SbLL). The existing of the microlayer is confirmed by experiments, and it is considered to be very effective in the heat transfer. Sernas and Hoper defined five types of the microlayer and indicated that the microlayer acting as a very thick liquid layer gives a best prediction for the bubble growth. However, beside the microlayer, the SpLL might play an important role in the heat transfer if its effective heat transfer area
Modeling and Measurements of Multiphase Flow and Bubble Entrapment in Steel Continuous Casting
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.
International Nuclear Information System (INIS)
To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with a very high resolution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary conditions. Local bubble size distributions are calculated from the data. The measurements were done in different distances from the gas injection device. As a result the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe. (orig.)
Mathematical models for tritium permeation analysis in liquid metal flows with helium bubbles
International Nuclear Information System (INIS)
Highlights: • Tritium transport in wall-attached He bubbles is studied. • Tritium mainly by-passes the bubble and its partial pressure in the bubble is homogeneous. • The bubble boundary layer depth is about twice the bubble radius. • Simplified tritium transport models are developed and validated. • A preliminary tritium wall function is proposed for wall-attached He bubbles flows. - Abstract: In LIBRETTO-2 test, evidence was obtained that helium bubbles nucleated and grew in the neutron irradiated PbLi probes. If such phenomenon occurs inside liquid metal (LM) breeding blanket channels, the study of its effect on tritium permeation and heat transfer in the near wall region will acquire utmost importance. The T4F research group has developed in the past a nucleation, growth and transport model for helium bubbles in LM flows, as well as a tritium transport model in such a multi-fluid system. In the present study, we are focused on the near-wall region analysis in order to obtain a wall function that allow reproducing the tritium permeation with coarse meshes and, hence, reduce the computational time. First, we perform some detailed CFD simulations of the near-wall region where bubbles might be attached. In these simulations, tritium diffusion processes as well as tritium recombination and dissociation are modelled. The analysis of such simulations allows us to further understand the complex phenomena and justify the use of simplified models. As a result, a new model for tritium transport across a LM–solid interface partially covered by helium bubbles is developed, implemented and validated. This simplified model can be seen as a wall function for the CFD simulation which substantially reduces computational time
Modeling High-Energy Gamma-Rays from the Fermi Bubbles - Oral Presentation
Energy Technology Data Exchange (ETDEWEB)
Splettstoesser, Megan [SLAC National Accelerator Lab., Menlo Park, CA (United States)
2015-08-25
In 2010, the Fermi Bubbles were discovered at the galactic center of the Milky Way. These giant gamma-ray structures, extending 50 degrees in galactic latitude and 20-30 degrees in galactic longitude, were not predicted. We wish to develop a model for the gamma-ray emission of the Fermi Bubbles. To do so, we assume that second order Fermi acceleration is responsible for the high-energy emission of the bubbles. Second order Fermi acceleration requires charged particles and irregular magnetic fields—both of which are present in the disk of the Milky Way galaxy. I use the assumption of second order Fermi acceleration in the transport equation, which describes the diffusion of particles. By solving the steady-state case of the transport equation, I compute the proton spectrum due to Fermi second order acceleration and compare this analytical solution to a numerical solution provided by Dr. P. Mertsch. Analytical solutions to the transport equation are taken from Becker, Le, & Dermer and are used to further test the numerical solution. I find that the numerical solution converges to the analytical solution in all cases. Thus, we know the numerical solution accurately calculates the proton spectrum. The gamma-ray spectrum follows the proton spectrum, and will be computed in the future.
Numerical and physical modelling of bubbly flow phenomena
Sangani, A. S.
1991-01-01
The objective of this study is to develop theoretical tools -- analytical as well as numerical -- for understanding how the flows of bubbly liquids are affected by its microstructure, i.e., the detailed spatial, size, and velocity distribution of bubbles, and how the microstructure, in turn, is affected by the flow. This report describes the progress made to date on the several problems that are being studied. The first problem is concerned with the molecular-dynamics type simulations of monodispersed bubbly liquids under equilibrium and homogeneous conditions and their application to slightly inhomogeneous flows. The Reynolds number is large and the Weber and Froud numbers are small in these simulations. The second problem is concerned with the simulations of flows of bubbly liquids undergoing small amplitude oscillatory motion. Both the cases of bubbles with rigid (due to impurities) and stress-free interfaces are examined. The results are related to the added mass, Basset, and viscous drag coefficients. The third problem is concerned with the acoustic wave propagation in bubbly liquids at frequencies above natural frequency of the bubbles. The second problem is completed as of this writing. Work on the other two problems is currently in progress. A summary of the work to be carried out during the period 1/91 to 6/92 is given in the last section.
Micro-bubble drag reduction on a high speed vessel model
Yanuar; Gunawan; Sunaryo; Jamaluddin, A.
2012-09-01
Ship hull form of the underwater area strongly influences the resistance of the ship. The major factor in ship resistance is skin friction resistance. Bulbous bows, polymer paint, water repellent paint (highly water-repellent wall), air injection, and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships. Micro-bubble injection is a promising technique for lowering frictional resistance. The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction. The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat (FPB) 57 m type model with the following main dimensions: L=2 450 mm, B=400 mm, and T=190 mm. The influence of the location of micro bubble injection and bubble velocity was also investigated. The ship model was pulled by an electric motor whose speed could be varied and adjusted. The ship model resistance was precisely measured by a load cell transducer. Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number. It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction, and the drag reduction caused by the micro-bubbles can reach 6%-9%.
Corrigan, Jackie
2004-01-01
, 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.
International Nuclear Information System (INIS)
To predict the behavior of air-water two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed based on a bubbly flow model. If it is assumed that the mixtures are homogeneous bubbly flow containing fine bubbles compared with the characteristic length of the impeller channel, then the equations of motion of the mixtures are represented by those of liquid phase and its velocity is expressed as a potential for the quasi-harmonic equation. The equations are solved by use of the finite element method to obtain the velocities and pressures, and the equation of motion of an air bubble is integrated numerically on this flow field to obtain the void fraction. These calculations are repeated until the solutions converge. The results obtained show good agreement with experiments within the range of bubbly flow regime. (author)
A model of phase distribution in bubble flow
International Nuclear Information System (INIS)
The knowledge of phase distribution in a channel with bubble flow is important for several problems in nuclear reactor technology. It is possible to assume the random bubble motion as a Markov diffusion process caused by turbulent liquid velocity fluctuations. A diffusion coefficient can be evaluated in this case. Diffusion equations and their boundary conditions are given to calculate bubble distribution in some cases of practical interest. The solution is possible for the most problems on numerical way only. Analytical solutions are shown in the case of a small bubble source near the wall, for instance a water to sodium microleak in a sodium-heated steam generator. Results of a two-dimensional calculation are discussed from the point of view of microleak detection. (author)
Modelling of bubble trajectories in a pump impeller
Dupoiron, Marine; Linden, Paul
2015-11-01
A vertical rotating flow in an annulus gap with an increasing diameter is used to approximate the flow in a pump impeller. We study a spherical gas bubble released at the flow inlet, subject to turbulent drag and added mass forces. Bubbles trajectories have been computed for different geometries, rotation speeds and bubble size, showing a deviation from the liquid streamlines in the angular and radial directions. This effect is related to the pump performance in multiphase conditions: the velocity difference between the gas and the liquid phases changes the final pressure rise produced by the impeller. In some extreme cases, the centrifugal force can be large enough to prevent bubbles from exiting the impeller at all, leading to an unwanted gas accumulation and the blockage of the pump. We eventually quantify the effects of geometrical and operational parameters on the pump behaviour. Work done in collaboration with Schlumberger Gould Research, Cambridge.
Comment on "Simple improvements to classical bubble nucleation models"
Schmelzer, Jürn W. P.; Baidakov, Vladimir G.
2016-08-01
A critical analysis of several statements concerning experimental studies, molecular dynamics simulations, and the theoretical interpretation of bubble nucleation processes is performed. In particular, it is shown that the Tolman equation does not supply us, in general, with a satisfactory theoretically founded description of the curvature dependence of the surface tension and the dependence of the steady-state nucleation rate of bubbles and droplets on supersaturation in the framework of classical nucleation theory.
Inhomogeneous MUSIG Model - a population balance approach for polydispersed bubbly flows
International Nuclear Information System (INIS)
Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase is characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model. Within this model the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 test case data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow. (author)
Time and Space Dependent Stochastic Acceleration Model for the Fermi Bubbles
Sasaki, K; Terasawa, T
2015-01-01
Fermi-LAT reveals two huge gamma-ray bubbles existing in the Galactic Center, called 'Fermi Bubbles'. The existence of two microwave bubbles at the same region are also reported by the observation by WMAP, dubbed 'WMAP haze'. In order to explain these components, It has been argued that the gamma-rays arise from Inverse-Compton scattering of relativistic electrons accelerated by plasma turbulence, and the microwaves are radiated by synchrotron radiation. But no previous research reproduces both the Fermi Bubbles and WMAP haze under typical magnetic fields in the galaxy. We assume that shocks present in the bubbles and the efficiency of the acceleration by plasma turbulence, 'stochastic acceleration', changes with the distance from the shock front. The distance from the shock front increases with time, accordingly the efficiency of the acceleration changes with time. We also consider the time development of the electrons escape from the turbulence by diffusive loss. Our model succeed to reproduce both the obse...
A heat transfer model for evaporating micro-channel coalescing bubble flow
Energy Technology Data Exchange (ETDEWEB)
Consolini, L.; Thome, J.R. [Ecole Polytechnique Federale de Lausanne (Switzerland). Lab. de Transfert de Chaleur et de Masse], e-mail: lorenzo.consolini@epfl.ch, E-mail: john.thome@epfl.ch
2009-07-01
The current study presents a one-dimensional model of confined coalescing bubble flow for the prediction of micro-channel convective boiling heat transfer. Coalescing bubble flow has recently been identified as one of the characteristic flow patterns to be found in micro-scale systems, occurring at intermediate vapor qualities between the isolated bubble and the fully annular regimes. As two or more bubbles bond under the action of inertia and surface tension, the passage frequency of the bubble liquid slug pair declines, with a redistribution of liquid among the remaining flow structures. Assuming heat transfer to occur only by conduction through the thin evaporating liquid film surrounding individual bubbles, the present model includes a simplified description of the dynamics of the thin film evaporation process that takes into account the added mass transfer by breakup of the bridging liquid slugs. The new model has been confronted against experimental data taken within the coalescing bubble flow mode that have been identified by a diabatic micro-scale flow pattern map. The comparisons for three different fluids (R-134a, R-236fa and R-245fa) gave encouraging results with 83% of the database predicted within a {+-} 30% error band. (author)
International Nuclear Information System (INIS)
A new condensation model for the FLUENT 6 code was developed. This model is based on a chemical species mixing model. In the areas where condensation takes place, the model modifies the terms in the transfer equations. The model allows condensation in the bulk and condensation on walls to be calculated. Condensation during steam passage over the area with water is modelled in a simplified manner by means of a porous body. Condensation during steam passage through the lattice can be modelled in a simplified manner by means of the 'porous jump' area. The condensation model was tested on a model of the EREC facility and on a model of the VVER-440/213 vacuum bubble condenser in LB LOCA circumstances. The calculated pressure levels in the EREC facility were compared with the observed data, the pressure levels in the bubble condensation tower was compared with COCOSYS data. The fit was reasonable in both cases. The results point to and unbalanced load of the caps in the EREC facility: the condenser right side is loaded more than the left side. In the bubble condenser tower, the lower plates are stressed more than the upper plates
A Revised Nuclear Star Formation Driven, Hadronic Model for the Fermi Bubbles
Crocker, Roland M; Carretti, Ettore; Hill, Alex S; Sutherland, Ralph S
2013-01-01
The Fermi Bubbles are enigmatic \\gamma-ray features of the Galactic bulge. Both putative activity (within $\\sim$ few $\\times$ Myr) connected to the Galactic center super-massive black hole and, alternatively, nuclear star formation have been claimed as the energising source of the Bubbles. Likewise, both inverse-Compton emission by non-thermal electrons (`leptonic' models) and collisions between non-thermal protons and gas (`hadronic' models) have been advanced as the process supplying the Bubbles' \\gamma -ray emission. An issue for any steady state hadronic model is that the very low density of the Bubbles' plasma seems to require that they accumulate protons over a multi-Gyr timescale, much longer than other natural timescales occurring in the problem. Here we present a hadronic model where the timescale for generating the Bubbles' hadronic \\gamma -ray emission is $\\sim$ few $\\times 10^8$ years. Our model invokes collapse of the Bubbles' thermally-unstable plasma, leading to an accumulation of cosmic rays a...
Widera, Paweł
2011-01-01
The process of comparison of computer generated protein structural models is an important element of protein structure prediction. It has many uses including model quality evaluation, selection of the final models from a large set of candidates or optimisation of parameters of energy functions used in template free modelling and refinement. Although many protein comparison methods are available online on numerous web servers, their ability to handle a large scale model comparison is often very limited. Most of the servers offer only a single pairwise structural comparison, and they usually do not provide a model-specific comparison with a fixed alignment between the models. To bridge the gap between the protein and model structure comparison we have developed the Protein Models Comparator (pm-cmp). To be able to deliver the scalability on demand and handle large comparison experiments the pm-cmp was implemented "in the cloud". Protein Models Comparator is a scalable web application for a fast distributed comp...
Modeling the impediment of methane ebullition bubbles by seasonal lake ice
Directory of Open Access Journals (Sweden)
S. Greene
2014-07-01
Full Text Available Microbial methane (CH4 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 CH4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH4 cycle in Goldstream Lake, a thermokarst (thaw lake in interior Alaska. We find that summertime ebullition dominates annual CH4 emissions to the atmosphere. Eighty percent of CH4 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 CH4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH4 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 CH4 dissolution from trapped bubbles, and greater CH4 emissions from northern lakes.
Measuring and modeling the bubble population produced by an underwater explosion.
Holt, Fred D; Lee Culver, R
2011-11-01
Underwater explosions have been studied intensively in the United States since 1941 [e.g., R. H. Cole, Underwater Explosions (Princeton University Press, Princeton, NJ, 1945), pp. 3-13]. Research to date has primarily focused on the initial shock and subsequent pressure waves caused by the oscillations of the "gas-globe" resulting from charge detonation. These phenomena have relatively short timescales (typically less than 2 s). However, after the gas-globe rises through the water column and breaks the surface, there remains behind a cloud of bubbles and perhaps debris from the explosion container which has been markedly less studied. A recent experiment measured the spatial and temporal acoustic response of the bubble cloud resulting from a 13.6 kg PBXN-111 charge detonated at 15.2 m (50 ft) depth. A directional projector was used to propagate linear frequency-modulated (5-65 kHz) and 40 kHz tonal pulses through the bubble cloud. Two hydrophone arrays were positioned so as to measure the energy lost in propagating through the bubble cloud. Three methods have been utilized to invert measurements and estimate the bubble population. The bubble population estimates have been used to develop a model for the bubble population resulting from an underwater explosion. PMID:22088003
A multi-size model for sub-cooled boiling bubbly flows
International Nuclear Information System (INIS)
In this paper we present a model which takes into account the multi-size aspect of a bubble population in a two-phase flow. Several methods exist in the literature to deal with such problematic. For its relative simplicity, the method of moments is here used in addition to a classical two-fluid model. It consists in determining the evolution of the topological and statistical quantities of the two-phase flow by solving additional transport equations on the bubble size distribution moment densities. These so-called geometrical equations involve all phenomena responsible for the changes in the bubble size distribution, namely coalescence and break-up but also dispersed phase compressibility and phase change. To close the bubble size distribution appearing in different source terms of the geometrical equations, a two-parameter quadratic expression is here proposed. The simplicity of this quadratic law allows to derived quite easily the geometrical equation source terms and implies to solve only two additional equations. The resulting multi-size model is therefore easy to implement and numerically efficient. Numerical simulation of a DEBORA test case (upward bubbly boiling flow in a vertical tube) has been performed with the NEPTUNE-CFD code to test the ability of the multi-size model to represent sub-cooled boiling bubbly flows. (authors)
An equation of motion for bubble growth
International Nuclear Information System (INIS)
A mathematical model is developed which describes asymmetric bubble growth, either during boiling or bubble injection from submerged orifices. The model is developed using the integral form of the continuity and momentum equations, resulting in a general expression for the acceleration of the bubble's centre of gravity. The proposed model highlights the need to include acceleration due to an asymmetric gain or loss of mass in order to accurately predict bubble motion. Some scenarios are posed by which the growth of bubbles, particularly idealized bubbles that remain a section of a sphere, must include the fact that bubble growth can be asymmetric. In particular, for approximately hemispherical bubble growth the sum of the forces acting on the bubble is negligible compared with the asymmetric term. Further, for bubble injection from a submerged needle this component in the equation of motion is very significant during the initial rapid growth phase as the bubble issues from the nozzle changing from a near hemisphere to truncated sphere geometry. (author)
Prediction of bubble departure in forced convection boiling: a mechanistic model
Colombo, M; Fairweather, M.
2015-01-01
In the context of computational fluid dynamic simulations of boiling flows using time-averaged Eulerian multi-phase approaches, the many sub-models required to describe such a complex phenomena are of particular importance. Of interest here, wall boiling requires calculation of the contribution of evaporation to global heat transfer, which in turn relies on determination of the active nucleation site density, bubble departure diameter and frequency of bubble departure. In this paper, an impro...
Computational Model for Determination of Vapor Bubble Growth Speed Maximimum in Superheated Liquids
Turlajs, D; Grivcovs, V; Jaundālders, S
2008-01-01
The article deals with problems of investigation of boiling of liquids - the most intensive heat transfer phenomena. There are a lot of research reports of boiling dynamics and heat transfer studies in micro- and nanoscopic levels, carried out with aim to understund phenomena in whole. Simulation model for vapor bubble growth speed maximum calculations in the region of bubble critical radius is elaborated. Numerical calculations were carried out for water in the region of system p...
Zhang, L. C.; Zhu, X. L.; Huang, Y. F.; Liu, Z.; Yan, K.
2016-07-01
In this paper, a simple model was developed to predict the dynamics of a spark-induced bubble under different ambient pressures. This work helps in developing a deep-towed plasma sparker, as the model can predict the dynamics of bubbles subjected to very high ambient pressures (about 20 MPa) which normally are difficult to obtain experimentally. Experimental results indicate that the maximum bubble radius for a fixed discharge energy decreases as a power-law function of the ambient pressure up to 1.0 MPa; the bubble period also decreases quickly with increasing ambient pressure. For a constant value of the ratio of bubble energy to discharge energy, the modeling results for both maximum radius and bubble period are in good agreement with the experimental results. Both sets of results indicate that the bubble period is proportional to the maximum radius under different ambient pressures.
Micro-bubble Drag Reduction on a High Speed Vessel Model
Institute of Scientific and Technical Information of China (English)
Yanuar; Gunawan; Sunaryo; A. Jamaluddin
2012-01-01
Ship hull form of the underwater area strongly influences the resistance of the ship.The major factor in ship resistance is skin friction resistance.Bulbous bows,polymer paint,water repellent paint (highly water-repellent wall),air injection,and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships.Micro-bubble injection is a promising technique for lowering frictional resistance.The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction.The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat (FPB) 57 m type model with the following main dimensions:L=2 450 mm,B=400 mm,and T=190 mm.The influence of the location of micro bubble injection and bubble velocity was also investigated.The ship model was pulled by an electric motor whose speed could be varied and adjusted.The ship model resistance was precisely measured by a load cell transducer.Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number.It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction,and the drag reduction caused by the micro-bubbles can reach 6％-9％.
Barnaveli, A T; Barnaveli, Andro; Gogberashvili, Merab
1995-01-01
We investigate the gravitational behavior of spherical domain walls (bubbles) arising during the phase transitions in the early Universe. In the thin-wall approximation we show the existence of the new solution of Einstein equations with negative gravitational mass of bubbles and the reversed direction of time flow on the shell. This walls exhibit gravitational repulsion just as the planar walls are assumed to do. The equilibrium radius and critical mass of such objects are found for realistic models.
Mario Forni; Luca Gambetti; Marco Lippi; Luca Sala
2014-01-01
We introduce noisy information into a standard present value stock price model. Agents receive a noisy signal about the structural shock driving future dividend variations. The resulting equilibrium stock price includes a transitory component — the "noise bubble" — which can be responsible for boom and bust episodes unrelated to economic fundamentals. We propose a non-standard VAR procedure to estimate the structural shock and the "noise" shock, their impulse response functions and the bubble...
International Nuclear Information System (INIS)
The universal applicability of the bubble model is examined and attention is drawn to a number of situations in which it is inadequate. Some possible areas of improvements are considered. The effects of van der Waals forces on the bubble radius are estimated to be insignificant, but the problem of the potential well depth and shape is more intractable. We find that when a linear combination of finite potential components is used, the Ps pressure can become independent of well depth when the infinite component becomes large, as may be the case in certain liquids. We have developed the idea of Tao on the description of the wavefunction overlap occurring in a thin skin in the inside of the bubble surface. By considering the contribution from the protrusion of hydrogen atoms from a hard core bubble surface, we calculate that the pick-off rate can be significantly altered. (orig.)
Numerical Modeling of the Photothermal Processing for Bubble Forming around Nanowire in a Liquid
Directory of Open Access Journals (Sweden)
Anis Chaari
2014-01-01
Full Text Available 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.
PERTURBANCE ANALYSIS AND FISSION MODEL OF COLLAPSING BUBBLE
Czech Academy of Sciences Publication Activity Database
Petrík, P.; Zima, Patrik; Ridha, A.
Vol. 1. Liberec: Technical University of Liberec, 2010 - (Vít, T.; Dančová, P.), s. 507-514 ISBN 978-80-7372-670-6. [International Conference Experimental Fluid Mechanics 2010. Liberec (CZ), 24.11.2010-26.11.2010] R&D Projects: GA ČR GAP101/10/1428 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation bubble * collapse * fission Subject RIV: BK - Fluid Dynamics
Modelling of Methane Bubble Dissolution in Freshwater Lakes
Czech Academy of Sciences Publication Activity Database
Štiková, L.; Stanovský, Petr; Orvalho, Sandra; Kordač, M.
Bratislava: Slovak Society of Chemical Engineering, 2015 - (Markoš, J.), s. 161 ISBN 978-80-89475-14-8. [International Conference of Slovak Society of Chemical Engineering /42./. Tatranské Matliare (SK), 25.05.2015-29.05.2015] R&D Projects: GA ČR GAP504/12/1186 Institutional support: RVO:67985858 Keywords : methane ebullition * mass transfer * single bubbles Subject RIV: EH - Ecology, Behaviour
Some Misconceptions in Bubble and Drops Hydrodynamics Models
Czech Academy of Sciences Publication Activity Database
Wichterle, Kamil; Smutná, K.; Večeř, M.; Růžička, Marek
Bratislava: Slovak University of Technology, 2010 - (Markoš, J.), s. 288 ISBN 978-80-227-3290-1. [International Conference of Slovak Society of Chemical Engineering /37./. Tatranské Matliare (SK), 24.05.2010-28.05.2010] R&D Projects: GA ČR GA104/07/1110 Institutional research plan: CEZ:AV0Z40720504 Keywords : bubbles * surface tension * viscosity Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Institute of Scientific and Technical Information of China (English)
袁德文; 潘良明; 陈德奇
2009-01-01
The process of bubble growth on heating wall in subcooled boiling includes the micro-layer evaporation on heating wall and the bubble top coagulation when the bubbles grow to a certain size and emerge into the subcooled mainstream fluid. Based on this consideration, a model for the single bubble growth of subcooled flow boiling in vertical narrow rectangular channel was proposed. Compared with experimental results, the error of the simulation results using the proposed model is less than ?5%. The simulation results indicated that as the wall superheat increases, the bubble growth gets faster, with the subcooled degree of mainstream increases, the bubble growth in later stage would be slowed, with the contact angle increases, the contact radius of the bubble bottom and the wall tension would be strengthened, resulting in faster bubble growth to make the bubble to be flat and more easily exposed to the mainstream. The velocity of mainstream has no significant effects on bubble growth rate.%@@ 引言 沸腾具有极高的换热效率的原因就在于沸腾过程中大量气相对周围液体的扰动.对汽泡形成、生长、脱离等过程机理的了解是理解和优化沸腾换热过程的关键.
Kochetkov, I. I.; Pinaev, A. V.
2013-03-01
Strong shock and detonation waves in inert and chemically active bubble media, which are generated by a wire explosion initiated by a capacitor with a stored energy W_0 =12.3-1,600 J, is experimentally studied. The measurements are performed near the wire and far from the wire in a vertical shock tube 4.5 m long with a volume fraction of the gas in the medium β _0 =1-4 %. It is shown that in inert bubble medium, a short intensely decaying shock wave (SW) with intense pressure oscillations is formed in the vicinity of wire explosion point; near the explosion point at β _0 le 2 % the SW propagates with the velocity of sound in a liquid. In chemically active bubble medium, an unsteady detonation wave generated by a wire explosion is formed. The pressure amplitude and the velocity of this wave are greater and the length is smaller than those of SW in an inert bubble medium in the same range of explosion energy. It is found that in the interval of low energy explosion from {˜ }12 to 64 J, the formation of the bubble detonation wave occurs faster than that at high energies (3× 102-103 J).
A mathematical model of particles entrainment in the freeboard of bubbling fluidized bed
International Nuclear Information System (INIS)
A two-component flow with a low concentration occurs in the freeboard after the eruption of the bubbles at the free surface of the bubbling fluidized beds. A three-dimensional mathematical model of gas-particle mixture turbulent flow is developed in this work. The gas turbulence is modeled using standard k-ε turbulence model. The dispersed phase is treated by the Lagrangian approach. Coupling between the gas phase and the dispersed particles is modeled by adding, source term in the momentum equation for gas phase. By using the equation for determining the drag coefficient, the particle's shape is involved in the model, as well. Experimental investigations for determining the conditions at the bed surface, the origin of erupting bubbles and their erupting mechanism and for selecting dominant influencing parameters are done. Comparisons of the experimentally obtained results with the results of other authors, which are in reasonable agreement, are used for determining the dominant influencing parameter related to the phenomena of bursting bubbles. On a base of observation, the dynamic eruption mechanism of single bursting bubble is proposed. This bubble eruption mechanism is used like a boundary condition in the numerical experimentation for investigation of the entrainment of particles and its separation along the freeboard height. The numerical solving of the developed mathematical model is accomplished by using the CFD technology. For graphical design and mesh generation of the flow domain and for numerical solving of the equations of the developed mathematical model, the software packages Gambit and FLUENT are used, respectively. The testing and verification of the proposed erupting bubble mechanism and the developed mathematical model for two-component flow in the freeboard, is made by numerical experimentation in 3D cylindrical flow domain, in the following conditions: eruption of isolated central bursting bubble; determining of particles terminal velocity
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.
Gleiser, Marcello
1994-01-01
The evolution of spherically symmetric unstable scalar field configurations (``bubbles'') is examined for both symmetric (SDWP) and asymmetric (ADWP) double-well potentials. Bubbles with initial static energies $E_0\\la E_{{\\rm crit}}$, where $E_{{\\rm crit}}$ is some critical value, shrink in a time scale determined by their linear dimension, or ``radius''. Bubbles with $E_0\\ga E_{{\\rm crit}}$ evolve into time-dependent, localized configurations which are {\\it very} long-lived compared to characteristic time-scales in the models examined. The stability of these configurations is investigated and possible applications are briefly discussed.tic time-scales in the models examined. The stability of these configurations is investigated and possible applications are briefly discussed.
Hydrodynamics of Bubble Bouncing on a Wall, Experiment and Modelling
Czech Academy of Sciences Publication Activity Database
Zedníková, Mária; Vejražka, Jiří; Růžička, Marek; Drahoš, Jiří
Praha: Process Engineering Publisher, 2008, s. 878. ISBN 978-80-02-02050-9. [18th International Congress of Chemical and Process Engineering CHISA 2008. Praha (CZ), 24.08.2008-28.08.2008] R&D Projects: GA ČR GA104/07/1110; GA AV ČR(CZ) KJB200720801; GA AV ČR(CZ) IAA200720801 Institutional research plan: CEZ:AV0Z40720504 Keywords : bubble-wall collision * impact velocity * contact time Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Bubble burst as jamming phase transition
Nishinari, Katsuhiro; Saito, Yukiko Umeno; Watanabe, Tsutomu
2010-01-01
Recently research on bubble and its burst attract much interest of researchers in various field such as economics and physics. Economists have been regarding bubble as a disorder in prices. However, this research strategy has overlooked an importance of the volume of transactions. In this paper, we have proposed a bubble burst model by focusing the transactions incorporating a traffic model that represents spontaneous traffic jam. We find that the phenomenon of bubble burst shares many similar properties with traffic jam formation by comparing data taken from US housing market. Our result suggests that the transaction could be a driving force of bursting phenomenon.
A force balance model for the motion, impact, and bounce of bubbles
Klaseboer, Evert; Manica, Rogerio; Hendrix, Maurice H. W.; Ohl, Claus-Dieter; Chan, Derek Y. C.
2014-09-01
A force balance model has been developed to predict the terminal velocity of a sub-millimetric bubble as its rises in water under buoyancy. The dynamics of repeated collisions and rebounds of the bubble against a horizontal solid surface is modeled quantitatively by including forces due to buoyancy, added mass, drag, and hydrodynamic lubrication—the last arises from the drainage of water trapped in the thin film between the solid surface and the surface of the deformable bubble. The result is a self-contained, parameter-free model that is capable of giving quantitative agreement with measured trajectories and observed collisions and rebounds against a solid surface as well as the spatio-temporal evolution of the thin film during collision as measured by interferometry.
Bubble nucleation in $\\phi^{4}$ models at all temperatures
Ferrera, A
1995-01-01
One possible way in which phase transitions in the early universe may have ocurred is via nucleation of bubbles of the new phase (true vacuum) in the old phase (false vacuum). The technique most widely used to compute the probability of bubble nucleation is based on instanton methods in the context of the semiclassical approximation. At zero temperature in (3+1) dimensions the nucleation rate is dominated by the O(4) symmetric instanton, a sphere of radius R, while at temperatures T >> R^{-1}, the decay is dominated by a ``cylindrical'' (static) instanton wtih O(3) invariance. There has been discussion in the literature as to whether the transition between these two regimens would be first order (discontinuity in the first derivative of the nucleation rate at the transition temperature T_{c}), or second order (continuity of the first derivative, but discontinuity of the second derivative at T_{c}). In this paper we obtain the finite temperature solutions corresponding to the quantum and the thermal regimes, a...
Energy Technology Data Exchange (ETDEWEB)
Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin
2012-05-30
Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas
Modeling of reaction kinetics in bubbling fluidized bed biomass gasification reactor
Energy Technology Data Exchange (ETDEWEB)
Thapa, R.K.; Halvorsen, B.M. [Telemark University College, Kjolnes ring 56, P.O. Box 203, 3901 Porsgrunn (Norway); Pfeifer, C. [University of Natural Resources and Life Sciences, Vienna (Austria)
2013-07-01
Bubbling fluidized beds are widely used as biomass gasification reactors as at the biomass gasification plant in Gussing, Austria. The reactor in the plant is a dual circulating bubbling fluidized bed gasification reactor. The plant produces 2MW electricity and 4.5MW heat from the gasification of biomass. Wood chips as biomass and olivine particles as hot bed materials are fluidized with high temperature steam in the reactor. As a result, biomass undergoes endothermic chemical reaction to produce a mixture of combustible gases in addition to some carbon-dioxide (CO2). The combustible gases are mainly hydrogen (H2), carbon monoxide (CO) and methane (CH4). The gas is used to produce electricity and heat via utilization in a gas engine. Alternatively, the gas is further processed for gaseous or liquid fuels, but still on the process of development level. Composition and quality of the gas determine the efficiency of the reactor. A computational model has been developed for the study of reaction kinetics in the gasification rector. The simulation is performed using commercial software Barracuda virtual reactor, VR15. Eulerian-Lagrangian approach in coupling of gas-solid flow has been implemented. Fluid phase is treated with an Eulerian formulation. Discrete phase is treated with a Lagrangian formulation. Particle-particle and particle-wall interactions and inter-phase heat and mass transfer have been taken into account. Series of simulations have been performed to study model prediction of the gas composition. The composition is compared with data from the gasifier at the CHP plant in Güssing, Austria. The model prediction of the composition of gases has good agreements with the result of the operating plant.
Bubble and kink solitons in the φ6-model of nonlinear field theory
International Nuclear Information System (INIS)
We have studied the φ6-model in the parameter domain A>1, with A being the relevant parameter of the model. For this case we have found localized soliton-like solutions: kinks and bubbles. The investigation of waves propagating through a stable vacuum shows that the sound velocity provides a rigid constraint for these oscillations to be stable or not. (orig.)
Mechanism of the Dark Matter and Condensed Bubble Objects Formation in the Model of Extended Space
Andreev, V A
2004-01-01
Within the framework of Extended Space Model (ESM) the processes connected to birth of photons in a gravitational field are studied. These photons have a nonzero mass. It can be both positive, and negative, and photon's energy and strength of the gravitational field determine its absolute value. It is shown that in ESM model formation of bubble gravitational structures is possible. In the frame of ESM one can obtain the follow physical picture. Bubble gravitational objects have a halo formed by dark matter generated by photons with a positive mass. The photons with a negative mass are throw away in free deep space and create there antigravitating vacuum with negative pressure. The comparison ESM bubble structures with similar objects of a type "gravastar", existing in a General Theory of Relativity (GR) is made.
Modeling of Liquid Level and Bubble Behavior in Vacuum Chamber of RH Process
Institute of Scientific and Technical Information of China (English)
Yi-hong LI; Yan-ping BAO; Rui WANG; Min WANG; Qing-xue HUANG; Yu-gui LI
2016-01-01
In the Ruhrstahl-Heraeus (RH)refining process,liquid steel flow pattern in a ladle is controlled by the fluid flow behavior in the vacuum chamber.Potassium chloride solution and NaOH solution saturated with CO 2 were respectively used as a tracer to investigate the liquid and gas flow behaviors in the vacuum chamber.Principal compo-nent and comparative analysis were made to show the factors controlling mixing and circulation flow rate.The liquid level and bubble behavior in the vacuum chamber greatly affect fluid flow in RH process.Experiments were per-formed to investigate the effects of liquid steel level,gas flow rate,bubble residence time,and gas injection mode on mixing,decarburization,and void fraction.The results indicate that the mixing process can be divided into three re-gions:the flow rate-affected zone,the concentration gradient-affected zone,and their combination.The liquid steel level in the vacuum chamber of 300 mm is a critical point in the decarburization transition.For liquid level lower than 300 mm,liquid steel circulation controls decarburization,while for liquid level higher than 300 mm,bubble behavior is the main controlling factor.During the RH process,it is recommended to use the concentrated bubble injection mode for low gas flow rates and the uniform bubble injection mode for high gas flow rates.
Modelling chemical reactions in dc plasma inside oxygen bubbles in water
Takeuchi, N.; Ishii, Y.; Yasuoka, K.
2012-02-01
Plasmas generated inside oxygen bubbles in water have been developed for water purification. Zero-dimensional numerical simulations were used to investigate the chemical reactions in plasmas driven by dc voltage. The numerical and experimental results of the concentrations of hydrogen peroxide and ozone in the solution were compared with a discharge current between 1 and 7 mA. Upon increasing the water vapour concentration inside bubbles, we saw from the numerical results that the concentration of hydrogen peroxide increased with discharge current, whereas the concentration of ozone decreased. This finding agreed with the experimental results. With an increase in the discharge current, the heat flux from the plasma to the solution increased, and a large amount of water was probably vaporized into the bubbles.
Bubble spreading during the boiling crisis: modelling and experimenting in microgravity
Nikolayev, Vadim; Garrabos, Y; Lecoutre, C; Chatain, D
2016-01-01
Boiling is a very efficient way to transfer heat from a heater to the liquid carrier. We discuss the boiling crisis, a transition between two regimes of boiling: nucleate and film boiling. The boiling crisis results in a sharp decrease in the heat transfer rate, which can cause a major accident in industrial heat exchangers. In this communication, we present a physical model of the boiling crisis based on the vapor recoil effect. Under the action of the vapor recoil the gas bubbles begin to spread over the heater thus forming a germ for the vapor film. The vapor recoil force not only causes its spreading, it also creates a strong adhesion to the heater that prevents the bubble departure, thus favoring the further spreading. Near the liquid-gas critical point, the bubble growth is very slow and allows the kinetics of the bubble spreading to be observed. Since the surface tension is very small in this regime, only microgravity conditions can preserve a convex bubble shape. In the experiments both in the Mir spa...
A vapour bubble collapse model to describe the fragmentation of low-melting materials
International Nuclear Information System (INIS)
By means of a model, the fragmentation of a hot melt of metal in consequence of collapsing vapour-bubbles is investigated. In particular the paper deals with the development of the physical model-ideas for calculation of the temperature of contact that adjusts between the temperature of the melt and the coolant, of the waiting-time until bubble-nucleation occurs and of the maximal obtainable vapour-bubble-radius in dependence of the coolant-temperature. After that follows the description of the computing-program belonging to this model and of the results of an extensive parameter-study. The study examined the influence of the temperature of melt and coolant, the melted mass, the nucleation-site-density, the average maximum bubble-radius, the duration of film-breakdown and the coefficient of heat-transition. The calculation of the process of fragmentation turns out to be according to expectation, whereas the duration of this process seems to be somewhat too long. The dependence of the surface-enlargement on the subcooling of the water-bath and the initial temperature of the melt is not yet reproduced satisfactorily by the model. The reasons for this are the temperature-increase of the water-bath as well as the fact that the coupling of heat-flux-density and nucleation-site-density are not taken into consideration. Further improvement of the model is necessary and may improve the results in the sense of the experimental observations. (orig.)
Directory of Open Access Journals (Sweden)
Mahood Hameed B.
2016-01-01
Full Text Available An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct contact condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.
A gas bubble-based parallel micro manipulator: conceptual design and kinematics model
International Nuclear Information System (INIS)
The parallel mechanism has become an alternative solution when micro manipulators are demanded in the fields of micro manipulation and micro assembly. In this technical note, a three-degree-of-freedom (3-DOF) parallel micro manipulator is presented, which is directly driven by three micro gas bubbles. Since the micro gas bubbles are generated and maintained due to the surface tension between the gas and liquid media, the proposed novel system can be used in the liquid environment which allows for rotation about the X and Y axes and translation along the Z axis. In this technical note, the conceptual design of micro gas bubble-based parallel manipulator is introduced and the input/output characteristic of the actuator is analyzed in detail. The kinematics model of the parallel micro manipulator is also established, based on which the workspace and the system motion resolution are analyzed as a criterion and reference for future prototype development. (technical note)
A MODEL OF MIRA'S COMETARY HEAD/TAIL ENTERING THE LOCAL BUBBLE
International Nuclear Information System (INIS)
We model the cometary structure around Mira as the interaction of an asymptotic giant branch stellar wind from Mira A with a streaming environment. Our simulations introduce the following new element: we assume that after 200 kyr of evolution in a dense environment, Mira entered the Local Bubble (low-density coronal gas). As Mira enters the bubble, the head of the comet expands quite rapidly, while the tail remains well collimated for a >100 kyr timescale. The result is a broad-head/narrow-tail structure that resembles the observed morphology of Mira's comet. The simulations were carried out with our new adaptive grid code WALICXE, which is described in detail.
A model of Mira's cometary head/tail entering the Local Bubble
Esquivel, A; Canto, J; Rodriguez-Gonzalez, A; Lopez-Camara, D; Velazquez, P F; De Colle, F
2010-01-01
We model the cometary structure around Mira as the interaction of an AGB wind from Mira A, and a streaming environment. Our simulations introduce the following new element: we assume that after 200 kyr of evolution in a dense environment Mira entered the Local Bubble (low density coronal gas). As Mira enters the bubble, the head of the comet expands quite rapidly, while the tail remains well collimated for a 100 kyr timescale. The result is a broad-head/narrow-tail structure that resembles the observed morphology of Mira's comet. The simulations were carried out with our new adaptive grid code WALICXE, which is described in detail.
Directory of Open Access Journals (Sweden)
Javed Bin Kamal
2012-09-01
Full Text Available The paper aims at constructing an optimal portfolio by applying Sharpe’s single index model of capital asset pricing in different scenarios, one is ex ante stock price bubble scenario and stock price bubble and bubble burst is second scenario. Here we considered beginning of year 2010 as rise of stock price bubble in Dhaka Stock Exchange. Hence period from 2005 -2009 is considered as ex ante stock price bubble period. Using DSI (All share price index in Dhaka Stock Exchange as market index and considering daily indices for the March 2005 to December 2009 period, the proposed method formulates a unique cut off point (cut off rate of return and selects stocks having excess of their expected return over risk-free rate of return surpassing this cut-off point. Here, risk free rate considered to be 8.5% per annum (Treasury bill rate in 2009. Percentage of an investment in each of the selected stocks is then decided on the basis of respective weights assigned to each stock depending on respective ‘β’ value, stock movement variance representing unsystematic risk, return on stock and risk free return vis-à-vis the cut off rate of return. Interestingly, most of the stocks selected turned out to be bank stocks. Again we went for single index model applied to same stocks those made to the optimum portfolio in ex ante stock price bubble scenario considering data for the period of January 2010 to June 2012. We found that all stocks failed to make the pass Single Index Model criteria i.e. excess return over beta must be higher than the risk free rate. Here for the period of 2010 to 2012, the risk free rate considered to be 11.5 % per annum (Treasury bill rate during 2012.
International Nuclear Information System (INIS)
The dynamic behaviour of SonoVue microbubbles, a new generation ultrasound contrast agent, is investigated in real time with light scattering method. Highly diluted SonoVue microbubbles are injected into a diluted gel made of xanthan gum and water. The responses of individual SonoVue bubbles to driven ultrasound pulses are measured. Both linear and nonlinear bubble oscillations are observed and the results suggest that SonoVue microbubbles can generate strong nonlinear responses. By fitting the experimental data of individual bubble responses with Sarkar's model, the shell coating parameter of the bubbles and dilatational viscosity is estimated to be 7.0 nm·s·Pa
Numerical Modeling of Air-Water Flows in Bubble Columns and Airlift Reactors
Studley, Allison F
2010-01-01
Bubble columns and airlift reactors were modeled numerically to better understand the hydrodynamics and analyze the mixing characteristics for each configuration. An Eulerian-Eulerian approach was used to model air as the dispersed phase within a continuous phase of water using the commercial software FLUENT. The Schiller-Naumann drag model was employed along with virtual mass and the standard k-e turbulence model. The equations were discretized using the QUICK scheme and solved with the SIMP...
Effect of Water Vapour to Temperature Inside Sonoluminescing Bubble
Institute of Scientific and Technical Information of China (English)
安宇; 谢崇国; 应崇福
2003-01-01
Using the model based on the homo-pressure approximation, we explain why the maximum temperature is sensitive to the ambient temperature in the single bubble sonoluminescence. The numerical simulation shows that the maximum temperature inside a sonoluminescing bubble depends on how much water vapour evaporates or coagulates at the bubble wall during the bubble shrinking to its minimum size. While the amount of water vapour inside the bubble at the initial and the final state of the compression depends on the saturated water vapour pressure which is sensitive to the ambient temperature. The lower the saturated vapour pressure is, the higher the maximum temperature is. This may lead to more general conclusion that those liquids with lower saturated vapour pressure are more favourable for the single bubble sonoluminescence. We also compare those bubbles with different noble gases, the result shows that the maximum temperatures in the different gas bubbles are almost the same for those with the same ambient temperature.
Bubble generation in a twisted and bent DNA-like model
DEFF Research Database (Denmark)
Larsen, Peter Ulrik Vingaard; Christiansen, Peter Leth; Bang, Ole;
2004-01-01
The DNA molecule is modeled by a parabola embedded chain with long-range interactions between twisted base pair dipoles. A mechanism for bubble generation is presented and investigated in two different configurations. Using random normally distributed initial conditions to simulate thermal fluctu...
Hong, Ban Zhen; Keong, Lau Kok; Shariff, Azmi Mohd
2016-05-01
The employment of different mathematical models to address specifically for the bubble nucleation rates of water vapour and dissolved air molecules is essential as the physics for them to form bubble nuclei is different. The available methods to calculate bubble nucleation rate in binary mixture such as density functional theory are complicated to be coupled along with computational fluid dynamics (CFD) approach. In addition, effect of dissolved gas concentration was neglected in most study for the prediction of bubble nucleation rates. The most probable bubble nucleation rate for the water vapour and dissolved air mixture in a 2D quasi-stable flow across a cavitating nozzle in current work was estimated via the statistical mean of all possible bubble nucleation rates of the mixture (different mole fractions of water vapour and dissolved air) and the corresponding number of molecules in critical cluster. Theoretically, the bubble nucleation rate is greatly dependent on components' mole fraction in a critical cluster. Hence, the dissolved gas concentration effect was included in current work. Besides, the possible bubble nucleation rates were predicted based on the calculated number of molecules required to form a critical cluster. The estimation of components' mole fraction in critical cluster for water vapour and dissolved air mixture was obtained by coupling the enhanced classical nucleation theory and CFD approach. In addition, the distribution of bubble nuclei of water vapour and dissolved air mixture could be predicted via the utilisation of population balance model.
International Nuclear Information System (INIS)
This paper describes the updating of the sub-cooled boiling model with the more recent and better sub-models. The improved sub-models include: Hibiki and Ishii [1] correlation for nucleation site density, Kocamustafaogullari [2] correlation for bubble departure diameter and the S-gamma model of Lo and Rao [3] for bubble size distribution in the flow. The new model has been tested against measured data from Debora [4] and Bartolomei [5]. The results show that improvement in the bubble size prediction has the most significant impact on the accuracy of the model. (author)
Dynamics of micro-bubble sonication inside a phantom vessel
Qamar, Adnan
2013-01-10
A model for sonicated micro-bubble oscillations inside a phantom vessel is proposed. The model is not a variant of conventional Rayleigh-Plesset equation and is obtained from reduced Navier-Stokes equations. The model relates the micro-bubble oscillation dynamics with geometric and acoustic parameters in a consistent manner. It predicts micro-bubble oscillation dynamics as well as micro-bubble fragmentation when compared to the experimental data. For large micro-bubble radius to vessel diameter ratios, predictions are damped, suggesting breakdown of inherent modeling assumptions for these cases. Micro-bubble response with acoustic parameters is consistent with experiments and provides physical insight to the micro-bubble oscillation dynamics.
How do the models to measure bubbles in the stock market
Ding, Yun
2007-01-01
Bubble economy is a phenomenon frequently occurs in the process of finance opening and an essential factor contributing to financial crisis. Once bubbles burst, financial crisis is quite possible. Stock market bubble is a key component of a countrys economic bubble, thus it is important to analyze the developing process of stock market bubble and to find out the method to eliminate harmful bubble component. The thesis organizes a static index system to measure the bubble component in a st...
The Accretion Wind Model of the Fermi Bubbles (II): Radiation
Mou, Guobin; Gan, Zhaoming; Sun, Mouyuan
2015-01-01
In a previous work, we have shown that the formation of the Fermi bubbles can be due to the interaction between winds launched from the hot accretion flow in Sgr A* and the interstellar medium (ISM). In that work, we focus only on the morphology. In this paper we continue our study by calculating the gamma-ray radiation. Some cosmic ray protons (CRp) and electrons must be contained in the winds, which are likely formed by physical processes such as magnetic reconnection. We have performed MHD simulations to study the spatial distribution of CRp, considering the advection and diffusion of CRp in the presence of magnetic field. We find that a permeated zone is formed just outside of the contact discontinuity between winds and ISM, where the collisions between CRp and thermal nuclei mainly occur. The decay of neutral pions generated in the collisions, combined with the inverse Compton scattering of background soft photons by the secondary leptons generated in the collisions and primary CR electrons can well expl...
Bubble merger model for the nonlinear Rayleigh-Taylor instability driven by a strong blast wave
International Nuclear Information System (INIS)
A bubble merger model is presented for the nonlinear evolution of the Rayleigh-Taylor instability driven by a strong blast wave. Single bubble motion is determined by an extension of previous buoyancy-drag models extended to the blast-wave-driven case, and a simple bubble merger law in the spirit of the Sharp-Wheeler model allows for the generation of larger scales. The blast-wave-driven case differs in several respects from the classical case of incompressible fluids in a uniform gravitational field. Because of material decompression in the rarefaction behind the blast front, the asymptotic bubble velocity and the merger time depend on time as well as the transverse scale and the drive. For planar blast waves, this precludes the emergence of a self-similar regime independent of the initial conditions. With higher-dimensional blast waves, divergence restores the properties necessary for the establishment of the self-similar state, but its establishment requires a very high initial characteristic mode number and a high Mach number for the incident blast wave
A hierarchy of simple hyperbolic two-fluid models for bubbly flows
Drui, Florence; Kokh, Samuel; Massot, Marc
2016-01-01
With the objective of modeling both separate and disperse two-phase flows, we use in this paper a methodology for deriving two-fluid models that do not assume any flow topology. This methodology is based on a variational principle and on entropy dissipation requirement. Some of the models that are such derived and studied are already known in the contexts of the description of separate-or disperse-phase flows. However, we here propose an arrangement of these models into a hierarchy based on their links through relaxation parameters. Moreover, the models are shown to be compatible with the description of a monodisperse bubbly flow and, within this frame, the relaxation parameters can be identified. This identification is finally verified and discussed through comparisons with experimental measures of sound dispersion and with dispersion relations of a reference model for bubbly media.
Prediction of a subcooled boiling flow with mechanistic wall boiling and bubble size models
International Nuclear Information System (INIS)
Subcooled boiling is one of the crucial phenomena for the design, operation and safety analysis of a nuclear power plant. In recent years, developers of multiphase CFD (Computational Fluid Dynamics) codes focused their development activity on the mechanistic prediction of DNB (Departure from Nucleate Boiling) in PWR. Wall boiling model is one of the key parameters for this purpose. In order to enhance prediction capability of the subcooled boiling flow, an advanced wall boiling model consisting of a mechanistic bubble departure model (Klausner et al., 1993), Hibiki et al.'s (2009) active nucleate site model and Cole's bubble departure frequency model was explored for the CFD code. To ensure a wide range applicability of the advanced wall boiling model, each model was evaluated separately according to the flow conditions such as pressure, temperature and flow rate. Finally, the advanced wall boiling model was implemented into the STAR-CD as a form of user FORTRAN file. One of the other important parameters for an accurate prediction of the subcooled boiling flow is bubble size which governs interfacial transfer terms between two phases. In this study, the S-gamma model, which was developed for the STAR-CD (Lo, 2006), was applied as a bubble size model. For the validation of the present wall boiling and bubble size models, benchmark calculations were carried out against SUBO and DEBORA subcooled boiling flow data. Working fluid of SUBO test is steam/water and its pressure condition is about 2 bars. In contrast to this, working fluid of DEBORA test is Refrigerant-12 (R-12) and phasic density ratio of the tests is equivalent to that of steam/water around 90 to 170 bars. Therefore, present benchmark calculation covers wide range pressure condition of steam/water. The calculation results confirms that the new mechanistic wall boiling and bubble size models follow well the tendency on the change of flow conditions and they can be applicable to the wide range of flow
Multifluid modeling of the desulfurization process within a bubbling fluidized bed coal gasifier
Armstrong, L-M.; Gu, Sai; Luo, K. H.; P Mahanta
2013-01-01
The desulfurization process to a two-dimensional (2-D) and three-dimensional (3-D) Eulerian-Eulerian computational fluid dynamic (CFD) model of a coal bubbling fluidized gasifier is introduced. The desulfurization process is important for the reduction of harmful SOx emissions; therefore, the development of a CFD model capable of predicting chemical reactions involving desulfurization is key to the optimization of reactor designs and operating conditions. To model the process, one gaseous pha...
International Nuclear Information System (INIS)
To enhance the multi-dimensional analysis capability for a subcooled boiling two-phase flow, the one-group interfacial area transport equation was improved with a source term for the bubble lift-off. It included the bubble lift-off diameter model and the lift-off frequency reduction factor model. The bubble lift-off diameter model took into account the bubble's sliding on a heated wall after its departure from a nucleate site, and the lift-off frequency reduction factor was derived by considering the coalescences of the sliding bubbles. To implement the model, EAGLE (elaborated analysis of gas-liquid evolution) code was developed for a multi-dimensional analysis of two-phase flow. The developed model and EAGLE code were validated with the experimental data of SUBO (subcooled boiling) and SNU (Seoul National University) test, where the subcooled boiling phenomena in a vertical annulus channel were observed. Locally measured two-phase flow parameters included a void fraction, interfacial area concentration, and bubble velocity. The results of the computational analysis revealed that the interfacial area transport equation with the bubble lift-off model showed a good agreement with the experimental results of SUBO and SNU. It demonstrates that the source term for the wall nucleation by considering a bubble sliding and lift-off mechanism enhanced the prediction capability for the multi-dimensional behavior of void fraction or interfacial area concentration in the subcooled boiling flow. From the point of view of the bubble velocity, the modeling of an increased turbulence induced by boiling bubbles at the heated wall enhanced the prediction capability of the code.
Thomas, Johannes
2014-01-01
An extended analytical model for particle dynamics in fields of a highly-nonlinear plasma wake field (the bubble or blow out regime) is derived. A recently proposed piecewise model (Kostyukov et al., New J. Phys., {\\bf 12}, 045009 (2010)) is generalized to include a time dependent bubble radius and full field solution in the acceleration direction. Incorporation of the cavity dynamics in the model is required to simulate the particle trapping properly. On the other hand, it is shown that the previously reported piecewise model does not reproduce the formation of a mono energetic peak in the particle spectrum. The mono energetic electron beams are recovered only when the full longitudinal field gradient is included in the model.
On the modelling of bubble entrainment by impinging jets in CFD-simulations
International Nuclear Information System (INIS)
This contribution presents different approaches for the modeling of air entrainment under water by plunging jets in CFD codes. In simulations which include the full length of the jet and its environment, the process of bubble generation cannot be resolved due to computational limitations. This is why the air entrainment has to be modeled in meso-scale simulations. In the frame of an Euler- Euler simulation, the local morphology of the phases has to be considered in the drag model. In the impinging jet configuration, the air is a continuous phase above the water level but bubbly below the water level. Various drag models are implemented in the CFD solver CFX11 and their influence on the gas void fraction below the water level is discussed. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g. correlations) for the gas entrainment. (authors)
Predictions of bubbly flows in vertical pipes using two-fluid models in CFDS-FLOW3D code
Energy Technology Data Exchange (ETDEWEB)
Banas, A.O.; Carver, M.B. [Chalk River Laboratories (Canada); Unrau, D. [Univ. of Toronto (Canada)
1995-09-01
This paper reports the results of a preliminary study exploring the performance of two sets of two-fluid closure relationships applied to the simulation of turbulent air-water bubbly upflows through vertical pipes. Predictions obtained with the default CFDS-FLOW3D model for dispersed flows were compared with the predictions of a new model (based on the work of Lee), and with the experimental data of Liu. The new model, implemented in the CFDS-FLOW3D code, included additional source terms in the {open_quotes}standard{close_quotes} {kappa}-{epsilon} transport equations for the liquid phase, as well as modified model coefficients and wall functions. All simulations were carried out in a 2-D axisymmetric format, collapsing the general multifluid framework of CFDS-FLOW3D to the two-fluid (air-water) case. The newly implemented model consistently improved predictions of radial-velocity profiles of both phases, but failed to accurately reproduce the experimental phase-distribution data. This shortcoming was traced to the neglect of anisotropic effects in the modelling of liquid-phase turbulence. In this sense, the present investigation should be considered as the first step toward the ultimate goal of developing a theoretically sound and universal CFD-type two-fluid model for bubbly flows in channels.
PROGRESS TOWARDS MODELING OF FISCHER TROPSCH SYNTHESIS IN A SLURRY BUBBLE COLUMN REACTOR
Energy Technology Data Exchange (ETDEWEB)
Donna Post Guillen; Tami Grimmett; Anastasia M. Gandrik; Steven P. Antal
2010-11-01
The Hybrid Energy Systems Testing (HYTEST) Laboratory is being established at the Idaho National Laboratory to develop and test hybrid energy systems with the principal objective to safeguard U.S. Energy Security by reducing dependence on foreign petroleum. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions will be performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. SBCRs are cylindrical vessels in which gaseous reactants (for example, synthesis gas or syngas) is sparged into a slurry of liquid reaction products and finely dispersed catalyst particles. The catalyst particles are suspended in the slurry by the rising gas bubbles and serve to promote the chemical reaction that converts syngas to a spectrum of longer chain hydrocarbon products, which can be upgraded to gasoline, diesel or jet fuel. These SBCRs operate in the churn-turbulent flow regime which is characterized by complex hydrodynamics, coupled with reacting flow chemistry and heat transfer, that effect reactor performance. The purpose of this work is to develop a computational multiphase fluid dynamic (CMFD) model to aid in understanding the physico-chemical processes occurring in the SBCR. Our team is developing a robust methodology to couple reaction kinetics and mass transfer into a four-field model (consisting of the bulk liquid, small bubbles, large bubbles and solid catalyst particles) that includes twelve species: (1) CO reactant, (2) H2 reactant, (3) hydrocarbon product, and (4) H2O product in small bubbles, large bubbles, and the bulk fluid. Properties of the hydrocarbon product were specified by vapor liquid equilibrium calculations. The absorption and kinetic models, specifically changes in species concentrations, have been incorporated into the mass continuity equation. The reaction rate is determined based on the macrokinetic model for a cobalt catalyst developed by Yates and Satterfield [1]. The
International Nuclear Information System (INIS)
In this paper, a computational simulation study is presented on the prediction of helium bubble evolution during repair welding of irradiated 304 stainless steel. Realistic spatial and temporal temperature and stress evolution during welding were obtained from simulation of the repair welding operation using the finite element model approach. The helium bubble evolution model by Kawano et al. was adopted as a user subroutine in the finite element model to predict the spatial distribution and temporal evolution of the helium bubble size and density in the heat-affected zone (HAZ) of partial penetration welds. Comparisons with experimental results available in open literature show that the predicted average helium bubble sizes were consistent with those observed experimentally under similar conditions. In addition, the computer simulation revealed strong spatial variation of helium bubble size due to the differences in combined thermal and stress conditions experienced in different locations in the HAZ. The predicted location of the maximum helium bubble agreed well with the observed helium-induced cracking site. The effect of welding heat input and welding speed was also investigated numerically. The modeling approach adopted in this study could be used as a cost-effective tool to quantitatively correlate the welding condition, radiation damage, and the likelihood of cracking, under the influence of welding-induced thermal and stress cycles. The model will also be useful in studying the degradation of properties from helium bubble formation of post-welded structures, even if a successful weld is made. (authors)
Bubble Growth in Lunar Basalts
Zhang, Y.
2009-05-01
Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth
Implementation of a new bubbly-slug interphase drag model in RELAP5/MOD2
International Nuclear Information System (INIS)
The implementation of a new bubbly-slug interphase drag model in the RELAP5/MOD2 code is described. The model is based on the determination of an effective interphase drag coefficient from a set of best-estimate void fraction correlations covering the full range of geometries and flow conditions encountered in PWR safety analysis. Calculations are reported which show that the new model leads to a much better prediction of void fraction profile for low flows in rod bundles than the standard model. Further work is necessary to derive a model formulation which can be guaranteed to produce physical drag coefficients in all flow situations. (author)
Modeling of Bubble Column Slurry Reactor for Dimethyl Ether Synthesis from Syngas
Institute of Scientific and Technical Information of China (English)
张海涛; 应卫勇; 房鼎业
2005-01-01
A mathematical model for a bubble column slurry reactor is presented for dimethyl ether synthesis from syngas. Methanol synthesis from carbon monoxide and carbon dioxide by hydrogenation and the methanol dehydration are considered as independent reactions, in which methanol, dimethyl ether and carbon dioxide are the key components. In this model, the gas phase is considered to be in plug flow and the liquid phase to be in partly back mixing with axial distribution of solid catalyst. The simulation results show that the axial dispersion of solid catalysts, the operational height of the slurry phase in the bubble column slurry reactor, and the reaction results are influenced by the reaction temperature and pressure, which are the basic data for the scale-up of reactor.
Prediction of bubble detachment diameter in flow boiling based on force analysis
International Nuclear Information System (INIS)
Highlights: ► All the forces acting on the growing bubbles are taken into account in the model. ► The bubble contact diameter has significant effect on bubble detachment. ► Bubble growth force and surface tension are more significant in narrow channel. ► A good agreement between the predicted and the measured results is achieved. - Abstract: Bubble detachment diameter is one of the key parameters in the study of bubble dynamics and boiling heat transfer, and it is hard to be measured in a boiling system. In order to predict the bubble detachment diameter, a theoretical model is proposed based on forces analysis in this paper. All the forces acting on a bubble are taken into account to establish a model for different flow boiling configurations, including narrow and conventional channels, upward, downward and horizontal flows. A correlation of bubble contact circle diameter is adopted in this study, and it is found that the bubble contact circle diameter has significant effect on bubble detachment. A new correlation taking the bubble contact circle diameter into account for the evaluation of bubble growth force is proposed in this study, and it is found that the bubble growth force and surface tension force are more significant in narrow channel when comparing with that in conventional channel. A visual experiment was carried out in order to verify present model; and the experimental data from published literature are used also. A good agreement between predicted and measured results is achieved.
Soap bubble hadronic states in a QCD-motivated Nambu-Jona-Lasinio model
Kutnii, Sergii
2015-01-01
Inhomogeneous solutions of the gap equation in the mean field approach to Nambu-Jona-Lasinio model are studied. An approximate Ginzburg-Landau-like gap equation is obtained and the domain wall solution is found. Binding of fermions to the domain wall is demonstrated. Compact domain wall with bound fermions is studied and stabilisation by fermion pressure is demonstrated which opens a possibility for existence of "soap bubble" hadronic states.
On the Dynamics of a Fluid-Particle Interaction Model: The Bubbling Regime
Carrillo, Jose' A.; Karper, Trygve; Trivisa, Konstantina
2010-01-01
This article deals with the issues of global-in-time existence and asymptotic analysis of a fluid-particle interaction model in the so-called bubbling regime. The mixture occupies the physical space $\\Omega \\subset \\mathbb{R}^3$ which may be unbounded. The system under investigation describes the evolution of particles dispersed in a viscous compressible fluid and is expressed by the conservation of fluid mass, the balance of momentum and the balance of particle density often referred as the ...
Modeling and simulation of the bubble-induced flow in wine fermentation vessels
Schmidt Dominik; Velten Kai
2015-01-01
Detailed flow pattern analyses regarding wine fermentations conducted without mechanical agitation are limited to lab-scale investigations, as industrial size measurements are expensive and difficult to realize. Computational fluid dynamic (CFD) methods can offer an alternative and more flexible approach to gain insight into such bubble induced fluid flows. Therefore, the aim of this study was to transfer the findings of existing research onto a CFD model capable of capturing the three- dimen...
Implementation of two-phase tritium models for helium bubbles in HCLL breeding blanket modules
Fradera, Jordi; Sedano, L.A.; Mas de les Valls Ortiz, Elisabet; Batet Miracle, Lluís
2011-01-01
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 phen...
Modelling of bubble-mediated gas transfer: Fundamental principles and a laboratory test
Woolf, D.K.; Leifer, I.S.; Nightingale, P.D.; Rhee, T.S.; Bowyer, P.; Caulliez, G.; Leeuw, G. de; Larsen, S.E.; Liddicoat, M.; Baker, J.; Andreae, M.O.
2007-01-01
The air-water exchange of gases can be substantially enhanced by wave breaking and specifically by bubble-mediated transfer. A feature of bubble-mediated transfer is the additional pressure on bubbles resulting from the hydrostatic forces on a submerged bubble and from surface tension and curvature.
Indian Academy of Sciences (India)
Debasish Majumdar; Kamakshya Prasad Modak; Subhendu Rakshit
2016-02-01
We propose a two-component dark matter (DM) model, each component of which is a real singlet scalar, to explain results from both direct and indirect detection experiments. We put the constraints on the model parameters from theoretical bounds, PLANCK relic density results and direct DM experiments. The -ray flux is computed from DM annihilation in this framework and is then compared with the Fermi-LAT observations from galactic centre region and Fermi bubble.
Passive Underwater Noise Attenuation Using Large Encapsulated Air Bubbles.
Lee, Kevin M; Wochner, Mark S; Wilson, Preston S
2016-01-01
Measurements demonstrating low-frequency underwater sound attenuation using arrays of large, tethered, stationary encapsulated bubbles to surround a sound source were compared with various effective medium models for the acoustic dispersion relationship in bubbly liquids. Good agreement was observed between measurements for the large bubbles (on the order of 10 cm) at frequencies below 1 kHz and a model originally intended to describe the acoustic behavior of ultrasound contrast agents. The primary goal is to use the model for designing encapsulated-bubble-based underwater noise abatement systems and to reduce uncertainty in system performance. PMID:26611010
DEFF Research Database (Denmark)
Hendricks, Vincent Fella; Pedersen, David Budtz
2013-01-01
Much like the trade and trait sof bubbles in financial markets,similar bubbles appear on the science market. When economic bubbles burst, the drop in prices causes the crash of unsustainable investments leading to an investor confidence crisis possibly followed by a financial panic. But when...... bubbles appear in science, truth and reliability are the first victims. This paper explores how fashions in research funding and research management may turn science into something like a bubble economy....
Sonochemical effects on single-bubble sonoluminescence
Yuan, L
2005-01-01
A refined hydro-chemical model for single-bubble sonoluminescence is presented. The processes of water vapor evaporation and condensation, mass diffusion, and chemical reactions are taken into account. Numerical simulations of Xe-, Ar- and He-filled bubbles are carried out. The results show that the trapped water vapor in conjunction with its endothermic chemical reactions significantly reduces the temperature within the bubble so that the degrees of ionization are generally very low. The chemical radicals generated from water vapor are shown to play an increasingly important role in the light emission from Xe to He bubbles. Light spectra and pulses computed from an optically thin model and from an essentially blackbody model are compared with recent experimental results. It is found that the results of the blackbody model generally match better with the experiment ones than those of the optically thin model. Suggestions on how to reconcile the conflict are given.
Bubbles tomorrow and bubbles yesterday, but never bubbles today?
Williams, John C.
2013-01-01
Standard asset price models have generally failed to detect bubbles, with enormous costs to the economy. Economists are now creating promising new models that account for bubbles by relaxing the assumption of rational expectations and allowing people’s decisions to be driven by their perceptions of what the future may hold. ; This letter is adapted from a presentation by the president and CEO of the Federal Reserve Bank of San Francisco to the National Association for Business Economics in Sa...
Shape of isolated bubble in downwardly inclined gas-liquid two-phase flows
International Nuclear Information System (INIS)
Experimental and theoretical studies on the shape of a single bubble in downwardly inclined gas-liquid two-phase flows are carried out. Measurements of the shape are made using conductance probes and visual observation in this paper. The experimental results show that bubble turning phenomenon of bubble shape happens at low Froude number, which is defined by gas/liquid mixture velocity. The turning phenomenon significantly affects the bubble velocity. It is also found that the shape of bubble is mainly determined by the Froude number rather than the bubble length. A hydrodynamics model for the shape of bubble tail is derived based on a one-dimension two-fluid model. The model well predicts the characteristics of the bubble tail when compared with the experimental results. The theoretical analysis shows that the critical Froude number, at which the turning phenomenon happens, increases as the downward inclination and pipe diameter increase. (authors)
Lindenbaum, S J
2008-01-01
In an earlier paper we developed a QCD inspired theoretical parton bubble model (PBM) for RHIC/LHC. The PBM quantitatively agreed with the strong charged particle pair correlations observed by the STAR collaboration at RHIC in the highest energy Au + Au central collisions, and also agreed with the Hanbury Brown and Twiss (HBT) observed small final state source size approximately 2f radii in the transverse momentum range above 0.8 GeV/c. The model assumed a substructure of a ring of localized adjoining 2f radius bubbles(gluonic hot spots) perpendicular to the collider beam direction, centered on the beam, at mid-rapidity and located on the expanding fireball surface of the Au + Au collisions. In this paper we extend the model (PBME) to include the changing development of bubbles with centrality from the most central region where bubbles are very important to the most peripheral where the bubbles are gone. Energy density is found to be related to bubble formation and as centrality decreases the maximum energy d...
Institute of Scientific and Technical Information of China (English)
TU Juan; GUAN J.F.; MATULA T.J.; Crum L.A.; WEI Rong-jue
2008-01-01
The dynamic behaviour of SonoVue microbubbles a new generation ultrasound contrast agent is investigated in real time with light scattering method.Highly diluted SonoVue microbubbles are injected into a diluted gel made of xanthan gum and water.The responses of individual SonoVue bubbles to driven ultrasound pulses are measured.Both linear and nonlinear bubble oscillations are observed and the results suggest that SonoVue microbubbles can generate strong nonlinear responses.By fitting the experimental data of individual bubble responses with Sarkar's model,the shell coating parameter of the bubbles and dilatational viscosity is estimated to be 7.0 nm·s·Pa.
Models for viscosity and shear localization in bubble-rich magmas
Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia
2016-09-01
Bubble content influences magma rheology and, thus, styles of volcanic eruption. Increasing magma vesicularity affects the bulk viscosity of the bubble-melt suspension and has the potential to promote non-Newtonian behavior in the form of shear localization or brittle failure. Here, we present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. The starting materials are cores of natural rhyolitic obsidian synthesized to have variable vesicularity (ϕ = 0- 66%). The foamed cores were deformed isothermally (T = 750 °C) at atmospheric conditions using a high-temperature uniaxial press under constant displacement rates (strain rates between 0.5- 1 ×10-4 s-1) and to total strains of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods to establish a baseline for experiments on the vesicle rich cores. At the experimental conditions, rising vesicle content produces a marked decrease in bulk viscosity that is best described by a two-parameter empirical equation: log10 ηBulk =log10 η0 - 1.47[ ϕ / (1 - ϕ) ] 0.48. Our parameterization of the bubble-melt rheology is combined with Maxwell relaxation theory to map the potential onset of non-Newtonian behavior (shear localization) in magmas as a function of melt viscosity, vesicularity, and strain rate. For low degrees of strain (i.e. as in our study), the rheological properties of vesicular magmas under different flow types (pure vs. simple shear) are indistinguishable. For high strain or strain rates where simple and pure shear viscosity values may diverge, our model represents a maximum boundary condition. Vesicular magmas can behave as non-Newtonian fluids at lower strain rates than unvesiculated melts, thereby, promoting shear localization and (explosive or non-explosive) magma fragmentation. The extent of shear localization in magma influences outgassing efficiency
Models for viscosity and shear localization in bubble-rich magmas
Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia
2016-09-01
Bubble content influences magma rheology and, thus, styles of volcanic eruption. Increasing magma vesicularity affects the bulk viscosity of the bubble-melt suspension and has the potential to promote non-Newtonian behavior in the form of shear localization or brittle failure. Here, we present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. The starting materials are cores of natural rhyolitic obsidian synthesized to have variable vesicularity (ϕ = 0- 66%). The foamed cores were deformed isothermally (T = 750 °C) at atmospheric conditions using a high-temperature uniaxial press under constant displacement rates (strain rates between 0.5- 1 ×10-4 s-1) and to total strains of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods to establish a baseline for experiments on the vesicle rich cores. At the experimental conditions, rising vesicle content produces a marked decrease in bulk viscosity that is best described by a two-parameter empirical equation: log10 ηBulk =log10 η0 - 1.47[ ϕ / (1 - ϕ) ] 0.48. Our parameterization of the bubble-melt rheology is combined with Maxwell relaxation theory to map the potential onset of non-Newtonian behavior (shear localization) in magmas as a function of melt viscosity, vesicularity, and strain rate. For low degrees of strain (i.e. as in our study), the rheological properties of vesicular magmas under different flow types (pure vs. simple shear) are indistinguishable. For high strain or strain rates where simple and pure shear viscosity values may diverge, our model represents a maximum boundary condition. Vesicular magmas can behave as non-Newtonian fluids at lower strain rates than unvesiculated melts, thereby, promoting shear localization and (explosive or non-explosive) magma fragmentation. The extent of shear localization in magma influences outgassing efficiency
The Ising model and bubbles in the quark-gluon plasma
Svetitsky, B
1997-01-01
I review evidence for the stability of bubbles in the quark-gluon plasma near the confinement phase transition. In analogy with the much-studied oil-water emulsions, this raises the possibility that there are many phases between the pure plasma and the pure hadron gas, characterized by spontaneous inhomogeneity and modulation. In studying emulsions, statistical physicists have reproduced many of their phases with microscopic models based on Ising-like theories with competing interactions. Hence we seek an effective Ising Hamiltonian for the SU(3) gauge theory near its transition.
International Nuclear Information System (INIS)
Highlights: • RANS simulation of laminar separation bubbles. • Spalart–Allamaras unexpected capability. • Straightforward implementation of our SA modifications. • Applications of a high order DG incompressible solver. - Abstract: The present paper deals with the Reynolds Averaged Navier–Stokes (RANS) simulation of Laminar Separation Bubble (LSB). This phenomenon is of large interest in several engineering fields, such as the study of wind turbines, unmanned aerial vehicles (UAV) and micro-air vehicles (MAV) characterized by a low operating Reynolds number. In such contexts a laminar boundary layer separation followed by a turbulent transition and afterwards by a turbulent reattachment may appear in the flow-field. The main novelty of this work is that an almost standard Spalart–Allmaras (SA) model, without additional equations for transition modeling, was successfully employed. The result achieved is very surprising being the model not developed for this purpose, but for fully-turbulent flows or for cases with imposed transition location. This result is of large interest, since the SA model is widely used in commercial, open-source and research codes. However, our approach cannot be advocated to predict natural transition within an attached boundary layer, indeed it is only able to deal with transitions triggered by a separated flow. The reliability and accuracy of our approach are here proved computing, by means of a high-order Discontinuous Galerkin (DG) incompressible solver, the flow-field over two airfoils at different flow regimes showing the formation of a LSB
Insights in hydrodynamics of bubbling fluidized beds at elevated pressure by DEM-CFD approach
Institute of Scientific and Technical Information of China (English)
Zahra Mansourpour; Sedighe Karimi; Reza Zarghami; Navid Mostoufi; Rahmat Sotudeh-Gharebagh
2010-01-01
A numerical simulation was conducted to study the effect of pressure on bubble dynamics in a gas-solid fluidized bed. The gas flow was modeled using the continuum theory and the solid phase, by the dis-crete element method (DEM). To validate the simulation results, calculated local pressure fluctuations were compared with corresponding experimental data of 1-mm polyethylene particles. It was shown that the model successfully predicts the hydrodynamic features of the fluidized bed as observed in the experiments. Influence of pressure on bubble rise characteristics such as bubble rise path, bubble sta-bility, average bubbles diameter and bubble velocity through the bed was investigated. The simulation results are in conformity with current hydrodynamic theories and concepts for fluidized beds at high pressures. The results show further that elevated pressure reduces bubble growth, velocity and stability and enhances bubble gyration through the bed, leading to change in bed flow structure.
Measurements of sub-surface bubble populations and the modelling of air-sea gas flux
Coles, David Geoffrey Hallstaff
2010-01-01
Bubbles, formed by breaking waves, play an important role in the transfer of gases between the Earth’s oceans and atmosphere and have been shown to increase the flux of gases during periods of heightened sea state. Having been formed, these bubble clouds evolve through the effects of buoyancy, gas exsolution and dissolution, and the fragmentation and coalescence of bubbles. A number of experimenters have successfully measured sub-surface bubble clouds using a variety of acoustic and opt...
Primary Particles from different bubble generation techniques
Butcher, A. C.; King, S. M.; Rosenoern, T.; Nilsson, E. D.; Bilde, M.
2011-12-01
Sea spray aerosols (SSA) are of major interest to global climate models due to large uncertainty in their emissions and ability to form Cloud Condensation Nuclei (CCN). In general, SSA are produced from wind breaking waves that entrain air and cause bubble bursting on the ocean surface. Preliminary results are presented for bubble generation, bubble size distribution, and CCN activity for laboratory generated SSA. In this study, the major processes of bubble formation are examined with respect to particle emissions. It has been suggested that a plunging jet closely resembles breaking wave bubble entrainment processes and subsequent bubble size distributions (Fuentes, Coe et al. 2010). Figure 1 shows the different particle size distributions obtained from the various bubble generation techniques. In general, frits produce a higher concentration of particles with a stronger bimodal particle size distribution than the various jet configurations used. The experiments consist of a stainless steel cylinder closed at both ends with fittings for aerosol sampling, flow connections for the recirculating jet, and air supply. Bubble generation included a recirculating jet with 16 mm or 4 mm nozzles, a stainless steel frit, or a ceramic frit. The chemical composition of the particles produced via bubble bursting processes has been probed using particle CCN activity. The CCN activity of sodium chloride, artificial sea salt purchased from Tropic Marin, and laboratory grade artificial sea salt (Kester, Duedall et al. 1967) has been compared. Considering the the limits of the shape factor as rough error bars for sodium chloride and bubbled sea salt, the CCN activity of artificial sea salt, Tropic Marin sea salt, and sodium chloride are not significantly different. This work has been supported by the Carlsberg Foundation.
Jones, T. B.; Bliss, G. W.
1977-01-01
The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements, static-levitation experiments, and dynamic-force measurements.
Sonochemistry and bubble dynamics.
Mettin, Robert; Cairós, Carlos; Troia, Adriano
2015-07-01
The details of bubble behaviour in chemically active cavitation are still not sufficiently well understood. Here we report on experimental high-speed observations of acoustically driven single-bubble and few-bubble systems with the aim of clarification of the connection of their dynamics with chemical activity. Our experiment realises the sonochemical isomerization reaction of maleic acid to fumaric acid, mediated by bromine radicals, in a bubble trap set-up. The main result is that the reaction product can only be observed in a parameter regime where a small bubble cluster occurs, while a single trapped bubble stays passive. Evaluations of individual bubble dynamics for both cases are given in form of radius-time data and numerical fits to a bubble model. A conclusion is that a sufficiently strong collapse has to be accompanied by non-spherical bubble dynamics for the reaction to occur, and that the reason appears to be an efficient mixing of liquid and gas phase. This finding corroborates previous observations and literature reports on high liquid phase sonochemical activity under distinct parameter conditions than strong sonoluminescence emissions. PMID:25194210
Long scale evolution of a nonlinear stochastic dynamic system for modeling market price bubbles
Kiselev, S. A.; Phillips, Andy; Gabitov, I.
2000-07-01
This Letter investigates the stochastic dynamics of a simplified agent-based microscopic model describing stock market evolution. Our mathematical model includes a stochastic market and a sealed-bid double auction. The dynamics of the model are determined by the game of two types of traders: (i) `intelligent' traders whose strategy is based on nonlinear technical data analysis 1 and (ii) `random' traders that act without a consistent strategy. We demonstrate the effect of time-scale separations on the market dynamics. We study the characteristics of the market relaxation in response to perturbations caused by large cash flows generated between these two groups of traders. We also demonstrate that our model exhibits the formation of a price bubble 2 and the subsequent transition to a bear market 3. Bear market - a macroscopically long stage of a market evolution when the stock price declines significantly, 15% or more.
Lu, Yurong; Wang, Zhongtong; Yong, Huadong; Zhou, Youhe
2016-07-01
Due to the larger current-carrying property, Bi2Sr2CaCu2Ox (Bi2212) superconductors have a great potential application in high field magnet. Bi2212 superconducting material can be fabricated as an isotropic round wire. However, there is 30% void space in the wire, such as gas bubbles. The void space has a larger influence on the property of the wire. In this paper, we will study the effect of gas bubble on the fracture behavior. Based on the double cantilever beam model and critical state theory, the mechanical behavior of Bi2212 wire is studied for decreasing field. Two different damage mechanisms are discussed using the strain energy release rate and strain of bridge. The results show that the large gas bubble can increase the strain of bridge. The central filaments with gas bubble are easier to be damaged than the edge filaments with gas bubble.
Liquid-bubble Interaction under Surf Zone Breaking Waves
Derakhti, M.; Kirby, J. T., Jr.
2014-12-01
Liquid-bubble interaction, especially in complex two-phase bubbly flow under breaking waves, is still poorly understood. Derakhti and Kirby (2014a,b) have recently studied bubble entrainment and turbulence modulation by dispersed bubbles under isolated unsteady breaking waves along with extensive model verifications and convergence tests. In this presentation, we continue this examination with attention turned to the simulation of periodic surf zone breaking waves. In addition, the relative importance of preferential accumulation of dispersed bubbles in coherent vortex cores is investigated. Heavier-than-liquid particles, i.e. sediment, tend to accumulate in regions of high strain rate and avoid regions of intense vorticity. In contrast, lighter-than-liquid particles such as bubbles tend to congregate in vortical regions. We perform a three dimensional (3D) large-eddy simulation (LES) using a Navier-Stokes solver extended to incorporate entrained bubble populations, using an Eulerian-Eulerian formulation for the polydisperse bubble phase. The volume of fluid (VOF) method is used for free surface tracking. The model accounts for momentum exchange between dispersed bubbles and liquid phase as well as bubble-induced dissipation. We investigate the formation and evolution of breaking-induced turbulent coherent structures (BTCS) under both plunging and spilling periodic breaking waves as well as BTCS's role on the intermittent 3D distributions of bubble void fraction in the surf zone. We particularly examine the correlation between bubble void fractions and Q-criterion values to quantify this interaction. Also, the vertical transport of dispersed bubbles by downburst type coherent structures in the transition region is compared to that by obliquely descending eddies. All the results are summarized at different zones from outer to inner surf zone.
Simulation of hydrogen bubble growth in tungsten by a hybrid model
International Nuclear Information System (INIS)
A two dimensional hybrid code (HIIPC-MC) joining rate-theory and Monte Carlo (MC) methods is developed in this work. We evaluate the cascade-coalescence mechanism contribution to the bubble growth by MC. First, effects of the starting radius and solute deuterium concentration on the bubble growth are studied; then the impacts of the wall temperature and implantation ion flux on the bubble growth are assessed. The simulation indicates that the migration-coalescence of the bubbles and the high pressure inside the bubbles are the main driving forces for the bubble growth, and that neglect of the migration and coalescence would lead to an underestimation of the bubble growth or blistering
Potential and energy of the monoenergetic electrons in an alternative ellipsoid bubble model
International Nuclear Information System (INIS)
The electron acceleration in the bubble regime is considered during the intense laser-plasma interaction. The presented ellipsoid cavity model is more consistent than the previous spherical model, and it explains the monoenergetic electron trajectory more accurately. At the relativistic region, the maximum energy of electrons in the ellipsoid model is about 24% more than the spherical model, and this is confirmed by PIC and the measured experimental results reported here. The electron energy spectrum is also calculated, and it is found that the energy distribution ratio of electrons ΔE/E for the ellipsoid model in the here reported condition is about 11% which is less than the one third that of the spherical model. It is in good agreement with the experimentally measured value in the same condition. In this regime, the parameters of the quasi-monoenergetic electrons output beam can be described more appropriately. In this work, 10 TW from 16.6 TW, 500 mJ, and 30-fs laser pulse was focused on the best matched point above a 2-mm-diameter pulsed He gas jet to obtain a stable ellipsoid bubble. Laser intensity of 1.42x1019 W cm-2 corresponding to a normalized vector potential of a0=2.6 focused in a 100-μm2 spot at the focal point and 1 mm above the edge of the gas jet with an electron density of 1x1019 cm-3 accelerates electrons to the relativistic velocities. The obtained monoenergetic electron energy spectrum is properly explained by the ellipsoid model introduced here.
Bubble rupture in bubble electrospinning
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Chen Rouxi
2015-01-01
Full Text Available As the distinctive properties and different applications of nanofibers, the demand of nanofibers increased sharply in recently years. Bubble electrospinning is one of the most effective and industrialized methods for nanofiber production. To optimize the set-up of bubble electrospinning and improve its mass production, the dynamic properties of un-charged and charged bubbles are studied experimentally, the growth and rupture process of a bubble are also discussed in this paper.
Measurements of local interfacial area concentration in two-phase bubbly flow
International Nuclear Information System (INIS)
The local interfacial characteristics of an air-water, bubbly upflow in a circular pipe has been investigated experimentally cased on the measurements of a miniature two-sensor resistivity probe. Radial profiles of interfacial area concentration (IAC), together with other structural parameters (void fraction, bubble frequency, bubble velocity and Sauter mean bubble diameter) were simultaneously measured at four axial positions with entrance length (L)-to-internal diameter (D) ratios of 30, 60, 90 and 120. The experiments were carried out under various fixed gas and liquid fluxes, with only the bubble size being changed at the flow entrance. It is found that the phase distribution ana IAC are very sensitive to the variation oi the bubble size and the bubble coalescence effects during the development of bubbly flow. This paper summarizes the experimental results on the associated local interfacial parameters and compares the present data with the existing models used in predicting the IAC. (author)
Extended two-fluid model applied to analysis of bubbly flow in multiphase rotodynamic pump impeller
Institute of Scientific and Technical Information of China (English)
Zhiyi YU; Guoyu WANG; Shuliang CAO
2009-01-01
This paper presents an extended two-fluid model based on the Navier-Stokes equations and the standard k-e turbulence model, to simulate the three-dimensional air-water bubbly flow in turbo machinery. In the governing equations, the drag force and added mass force are added and the additional source terms arising from fluctuations of gas volume fraction are considered. The discrete equations are solved using a developed two-phase semi-implicit method for pressure-linked equations, consistent (SIMPLEC) algorithm in body-fitted coordi-nates with a staggered grid system. Simulation is then carried out for the pure liquid flow and air-water two-phase flow with the inlet gas volume fraction being 15% in a multiphase rotodynamic pump impeller and the pump head performance is predicted. Comparison with experimental results shows the reliability and commonality of the numerical model.
A study on models of the inhomogeneity of the decompression in a bubble chamber
International Nuclear Information System (INIS)
Before building a hydrogen bubble chamber with liquid decompression the 'Saturne' cyclotron department wished to study for this chamber a shape leading to a homogeneous decompression as far as possible, without the production of vortices even after prolonged operation. The 'Office National d'Etudes et de Recherches Aeronautiques' (ONERA) were ready to carry out experiments on a model by strioscopy. The model was filled with air but an attempt was made to simulate the actual conditions as far as possible by varying the speed of the piston. The model was placed at one end of a tunnel, at the other end of which were produced alternatively compression and decompression waves. The study made it possible to conclude that it was necessary to make the base of the chamber round and that, in the space between the decompression cylinder and the body of the chamber it was advantageous to use 5 fins instead of 3. (author)
International Nuclear Information System (INIS)
Full text of publication follows: A computational code has been developed for inert gas behavior in the primary system of sodium cooled fast reactor (SFR). The inert gas exists in the circulating coolant sodium as resolved gas or free gas bubbles. The primary coolant system of the SFR has free surfaces which are covered by argon gas. The cover gas system is slightly pressurized above the atmospheric pressure. Therefore, the argon cover gas would dissolve in the liquid sodium and dispersed in the primary coolant system by diffusion and convection. In addition, helium gas is generated in the control rods of the reactor core and is emitted as small bubbles from the B4C pellet. Another source of gas bubbles is gas entrainment at the free surface of the reactor vessel if the sodium flow velocity at the free surface is large enough. From the viewpoint of design and safety of the SFR, the gas in the primary system may cause disturbance in reactivity, nucleation site for boiling and cavitation, flow instability, and/or influence on heat transfer. In the present method, the concentration distribution of the dissolved gas and free gas bubble are evaluated for steady state and transient conditions according to the mass and heat transfer in the cooling system. The bubble diameter is assumed to follow the lognormal distribution and discretized into numbers of representative diameters. Physical modeling of the gas behavior is described in the following. In the intermediate heat exchanger, nucleation of bubbles caused by the temperature decrease is evaluated at the heat transfer tube surface. The bubbles on the tube surface are detached from the wall according to the balance of drag, surface tension and buoyancy forces. At the gas liquid interface (free surface and bubble surface), evaporation, dissolution and diffusion are calculated. Bubbles traveling the primary system would break up at turbulent region such as core fuel assembly and mechanical coolant pump. At the free
Energy Technology Data Exchange (ETDEWEB)
McDeavitt, Sean [Texas A & M Univ., College Station, TX (United States); Shao, Lin [Texas A & M Univ., College Station, TX (United States); Tsvetkov, Pavel [Texas A & M Univ., College Station, TX (United States); Wirth, Brian [Univ. of Tennessee, Knoxville, TN (United States); Kennedy, Rory [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2014-04-07
Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. Many mechanistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, research, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.
International Nuclear Information System (INIS)
Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. Many mechanistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, research, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.
Laser-Generated Shocks and Bubbles as Laboratory-Scale Models of Underwater Explosions
Directory of Open Access Journals (Sweden)
Theodore G. Jones
2003-01-01
Full Text Available Underwater shocks and bubbles were generated using a high energy pulsed laser system. The advantages of this experimental approach are: (1 precisely controlled and measured experimental conditions; (2 improved diagnostics, including extensive imaging capabilities; (3 unique experiments, including a simultaneously detonated line charge; and (4 the ability to provide validation quality data for hydrodynamic simulation codes. Bubble sensitivity to variation of several experimental parameters was examined. Numerical simulations were performed corresponding to the experimental shots, showing that empirical bubble theory, experimental bubble data, and simulations were all in good agreement.
Atomistic modeling of growth and coalescence of helium nano-bubbles in tungsten
International Nuclear Information System (INIS)
The mechanisms of growth and coalescence of helium nano-bubbles in tungsten are investigated using molecular dynamics simulations. It is shown that crystal symmetries and governed by them properties of dislocations, generated by the growing nano-bubbles, are responsible for main nano-bubble features revealed, including non-spherical shape and anisotropy of surrounding stress field. The transport of helium atoms in non-uniform stress field is simulated at different temperatures and the transport coefficients are determined. The implications of the considered dislocation and helium dynamics on nucleation and growth of bubbles in tungsten with implanted helium are discussed
Atomistic modeling of growth and coalescence of helium nano-bubbles in tungsten
Smirnov, R. D.; Krasheninnikov, S. I.; Guterl, J.
2015-08-01
The mechanisms of growth and coalescence of helium nano-bubbles in tungsten are investigated using molecular dynamics simulations. It is shown that crystal symmetries and governed by them properties of dislocations, generated by the growing nano-bubbles, are responsible for main nano-bubble features revealed, including non-spherical shape and anisotropy of surrounding stress field. The transport of helium atoms in non-uniform stress field is simulated at different temperatures and the transport coefficients are determined. The implications of the considered dislocation and helium dynamics on nucleation and growth of bubbles in tungsten with implanted helium are discussed.
Interfacial area concentration in gas–liquid bubbly to churn flow regimes in large diameter pipes
International Nuclear Information System (INIS)
Highlights: • A systematic method to predict interfacial area concentration (IAC) is presented. • A correlation for group 1 bubble void fraction is proposed. • Correlations of IAC and bubble diameter are developed for group 1 bubbles. • Correlations of IAC and bubble diameter are developed for group 2 bubbles. • The newly-developed two-group IAC model compares well with collected databases. - Abstract: This study performed a survey on existing correlations for interfacial area concentration (IAC) prediction and collected an IAC experimental database of two-phase flows taken under various flow conditions in large diameter pipes. Although some of these existing correlations were developed by partly using the IAC databases taken in the low-void-fraction two-phase flows in large diameter pipes, no correlation can satisfactorily predict the IAC in the two-phase flows changing from bubbly, cap bubbly to churn flow in the collected database of large diameter pipes. So this study presented a systematic way to predict the IAC for the bubbly-to-churn flows in large diameter pipes by categorizing bubbles into two groups (group 1: spherical or distorted bubble, group 2: cap bubble). A correlation was developed to predict the group 1 void fraction by using the void fraction for all bubble. The group 1 bubble IAC and bubble diameter were modeled by using the key parameters such as group 1 void fraction and bubble Reynolds number based on the analysis of Hibiki and Ishii (2001, 2002) using one-dimensional bubble number density and interfacial area transport equations. The correlations of IAC and bubble diameter for group 2 cap bubbles were developed by taking into account the characteristics of the representative bubbles among the group 2 bubbles and the comparison between a newly-derived drift velocity correlation for large diameter pipes and the existing drift velocity correlation of Kataoka and Ishii (1987) for large diameter pipes. The predictions from the newly
Avdeev, Alexander A
2016-01-01
This monograph presents a systematic analysis of bubble system mathematics, using the mechanics of two-phase systems in non-equilibrium as the scope of analysis. The author introduces the thermodynamic foundations of bubble systems, ranging from the fundamental starting points to current research challenges. This book addresses a range of topics, including description methods of multi-phase systems, boundary and initial conditions as well as coupling requirements at the phase boundary. Moreover, it presents a detailed study of the basic problems of bubble dynamics in a liquid mass: growth (dynamically and thermally controlled), collapse, bubble pulsations, bubble rise and breakup. Special emphasis is placed on bubble dynamics in turbulent flows. The analysis results are used to write integral equations governing the rate of vapor generation (condensation) in non-equilibrium flows, thus creating a basis for solving a number of practical problems. This book is the first to present a comprehensive theory of boil...
Mathematical modeling of cold cap: Effect of bubbling on melting rate
Energy Technology Data Exchange (ETDEWEB)
Pokorny, Richard; Kruger, Albert A.; Hrma, Pavel R.
2014-12-31
The rate of melting is a primary concern in the vitrification of radioactive wastes because it directly influences the life cycle of nuclear waste cleanup efforts. To increase glass melting performance, experimental and industrial all-electric waste glass melters employ various melt-rate enhancement techniques, the most prominent being the application of bubblers submerged into molten glass. This study investigates various ways in which bubbling affects melting rate in a waste glass melter. Using the recently developed cold cap model, we suggest that forced convection of molten glass, which increases the cold cap bottom temperature, is the main factor. Other effects, such as stirring the feed into molten glass or reducing the insulating effect of foaming, also play a role.
Identifying bubble collapse in a hydrothermal system using hiddden Markov models
Dawson, Phillip B.; Benitez, M.C.; Lowenstern, Jacob B.; Chouet, Bernard A.
2012-01-01
Beginning in July 2003 and lasting through September 2003, the Norris Geyser Basin in Yellowstone National Park exhibited an unusual increase in ground temperature and hydrothermal activity. Using hidden Markov model theory, we identify over five million high-frequency (>15 Hz) seismic events observed at a temporary seismic station deployed in the basin in response to the increase in hydrothermal activity. The source of these seismic events is constrained to within ~100 m of the station, and produced ~3500–5500 events per hour with mean durations of ~0.35–0.45 s. The seismic event rate, air temperature, hydrologic temperatures, and surficial water flow of the geyser basin exhibited a marked diurnal pattern that was closely associated with solar thermal radiance. We interpret the source of the seismicity to be due to the collapse of small steam bubbles in the hydrothermal system, with the rate of collapse being controlled by surficial temperatures and daytime evaporation rates.
Directory of Open Access Journals (Sweden)
Nur-E- Mostafa
2016-01-01
Full Text Available This paper presents a numerical study with pressure-based finite volume method for prediction of non-cavitating and time dependent cavitating flow on hydrofoil. The phenomenon of cavitation is modeled through a mixture model. For the numerical simulation of cavitating flow, a bubble dynamics cavitation model is used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. The non-cavitating study focuses on choosing mesh size and the influence of the turbulence model. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST k-ω model and Re-Normalization Group (RNG k-ε model with enhanced wall treatment are used to capture the turbulent boundary layer on the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ=0.8. Moreover, this study focuses on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers. Finally, the flow pattern and hydrodynamic characteristics are also studied at different angles of attack.
Numerical analyses of boiling two-phase bubbly flows in pipes with particle tracking method
International Nuclear Information System (INIS)
The present study deals with the numerical modeling of two-phase bubbly flows with subcooled boiling in a flow channel using Particle Tracking Method. It is an on-going project whose final aim is to develop a computer code to more accurately predict, and better understand, the Departure from Nuclear Boiling (DNB) under PWR accidental conditions. At the first stage of the present study, this presentation reports the development of bubble dynamics models such as the bubble coalesces/break models and bubble heat transfer models. The validation of the models by comparing simulation results with experimental data in literature is also reported. (author)
Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes
Lynn, Alan; Zhang, Yue; Hsu, Scott
2010-11-01
The Plasma Bubble Expansion Experiment (PBEX) is conducting laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (˜10 kV, ˜100 kA, ˜2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. Experimental data from plasma bubble injection into a background plasma, particularly magnetic probe measurements, will be discussed. [4pt] [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).
Bubbles, shocks and elementary technical trading strategies
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.
Bubble Dynamics and Shock Waves
2013-01-01
This volume of the Shock Wave Science and Technology Reference Library is concerned with the interplay between bubble dynamics and shock waves. It is divided into four parts containing twelve chapters written by eminent scientists. Topics discussed include shock wave emission by laser generated bubbles (W Lauterborn, A Vogel), pulsating bubbles near boundaries (DM Leppinen, QX Wang, JR Blake), interaction of shock waves with bubble clouds (CD Ohl, SW Ohl), shock propagation in polydispersed bubbly liquids by model equations (K Ando, T Colonius, CE Brennen. T Yano, T Kanagawa, M Watanabe, S Fujikawa) and by DNS (G Tryggvason, S Dabiri), shocks in cavitating flows (NA Adams, SJ Schmidt, CF Delale, GH Schnerr, S Pasinlioglu) together with applications involving encapsulated bubble dynamics in imaging (AA Doinikov, A Novell, JM Escoffre, A Bouakaz), shock wave lithotripsy (P Zhong), sterilization of ships’ ballast water (A Abe, H Mimura) and bubbly flow model of volcano eruptions ((VK Kedrinskii, K Takayama...
Directory of Open Access Journals (Sweden)
Lu Zhang
2015-07-01
Full Text Available The RNA polymerase II (Pol II is a eukaryotic enzyme that catalyzes the synthesis of the messenger RNA using a DNA template. Despite numerous biochemical and biophysical studies, it remains elusive whether the "secondary channel" is the only route for NTP to reach the active site of the enzyme or if the "main channel" could be an alternative. On this regard, crystallographic structures of Pol II have been extremely useful to understand the structural basis of transcription, however, the conformation of the unpaired non-template DNA part of the full transcription bubble (TB is still unknown. Since diffusion routes of the nucleoside triphosphate (NTP substrate through the main channel might overlap with the TB region, gaining structural information of the full TB is critical for a complete understanding of Pol II transcription process. In this study, we have built a structural model of Pol II with a complete transcription bubble based on multiple sources of existing structural data and used Molecular Dynamics (MD simulations together with structural analysis to shed light on NTP entry pathways. Interestingly, we found that although both channels have enough space to allow NTP loading, the percentage of MD conformations containing enough space for NTP loading through the secondary channel is twice higher than that of the main channel. Further energetic study based on MD simulations with NTP loaded in the channels has revealed that the diffusion of the NTP through the main channel is greatly disfavored by electrostatic repulsion between the NTP and the highly negatively charged backbones of nucleotides in the non-template DNA strand. Taken together, our results suggest that the secondary channel is the major route for NTP entry during Pol II transcription.
Lohse, Detlef
2003-01-01
With their ubiquitous occurrence in a multitude of fluid systems, bubbles occupy an important place in contemporary science and technology. One can readily cite several examples: the production and transport of oil, in which bubbles are purposely injected to help lift heavy oil to the surface; energ
Proposals for improving interphase drag modelling for the bubbly and slug regimes in RELAP5
International Nuclear Information System (INIS)
The proposal is put forward that the effective interphase drag coefficient for the bubbly and slug regimes in RELAP5 should be calculated using best-estimate void fraction correlations. It is argued that this will lead to improvements in the code's modelling of interphase drag and evidence is given to corroborate this. The need for such improvements has been prompted by the poor performance of the current models in simulating rod bundle experiments. There is also concern that the models do not account for profile slip effects, which could be important in a variety of geometries, and that the slug flow equations may not be appropriate for large diameter vertical pipes. To support the proposal, a set of void fraction correlations is identified which is believed to cover the full range of geometries and flow conditions encountered in PWR safety analysis including the analysis of small-scale experimental facilities. This set is selected from a detailed appraisal of the most appropriate correlations found in the literature which takes account of comparisons with experimental data and physical considerations. This Report forms part of the UK's commitment to the ICAP Code Improvement Plan. The recommendations will now be implemented in a development version of RELAP5/MOD3 and a preliminary assessment made. The interphase drag models used in the annular-mist regime will also be examined and, if necessary, appropriate improvements will be proposed. (author)
Energy Technology Data Exchange (ETDEWEB)
De Backer, A., E-mail: andree.debacker@ccfe.ac.uk [UMET, UMR 8207, Université Lille 1, Villeneuve d’Ascq (France); CCFE, Culham Centre for Fusion Energy, Abingdon, Oxon (United Kingdom); Adjanor, G.; Domain, C.; Lescoat, M.L. [EDF R& D, MMC Centre des Renardières, Moret-sur-Loing (France); Jublot-Leclerc, S.; Fortuna, F.; Gentils, A. [CSNSM, Univ Paris-Sud, CNRS/IN2P3, Orsay (France); Ortiz, C.J. [CIEMAT, Laboratorio Nacional de Fusión por Confinamiento Magnético, Madrid (Spain); Souidi, A. [Université Dr. Tahar Moulay de Saida, Saida (Algeria); Becquart, C.S. [UMET, UMR 8207, Université Lille 1, Villeneuve d’Ascq (France)
2015-06-01
Implantation of 10 keV helium in 316L steel thin foils was performed in JANNuS-Orsay facility and modeled using a multiscale approach. Density Functional Theory (DFT) atomistic calculations [1] were used to obtain the properties of He and He-vacancy clusters, and the Binary Collision Approximation based code MARLOWE was applied to determine the damage and He-ion depth profiles as in [2,3]. The processes involved in the homogeneous He bubble nucleation and growth were defined and implemented in the Object Kinetic Monte Carlo code LAKIMOCA [4]. In particular as the He to dpa ratio was high, self-trapping of He clusters and the trap mutation of He-vacancy clusters had to be taken into account. With this multiscale approach, the formation of bubbles was modeled up to nanometer-scale size, where bubbles can be observed by Transmission Electron Microscopy. Their densities and sizes were studied as functions of fluence (up to 5 × 10{sup 19} He/m{sup 2}) at two temperatures (473 and 723 K) and for different sample thicknesses (25–250 nm). It appears that the damage is not only due to the collision cascades but is also strongly controlled by the He accumulation in pressurized bubbles. Comparison with experimental data is discussed and sensible agreement is achieved.
Louisnard, Olivier
2013-01-01
In a companion paper, a reduced model for propagation of acoustic waves in a cloud of inertial cavitation bubbles was proposed. The wave attenuation was calculated directly from the energy dissipated by a single bubble, the latter being estimated directly from the fully nonlinear radial dynamics. The use of this model in a mono-dimensional configuration has shown that the attenuation near the vibrating emitter was much higher than predictions obtained from linear theory, and that this strong attenuation creates a large traveling wave contribution, even for closed domain where standing waves are normally expected. In this paper, we show that, owing to the appearance of traveling waves, the primary Bjerknes force near the emitter becomes very large and tends to expel the bubbles up to a stagnation point. Two-dimensional axi-symmetric computations of the acoustic field created by a large area immersed sonotrode are also performed, and the paths of the bubbles in the resulting Bjerknes force field are sketched. C...
International Nuclear Information System (INIS)
were compared with several experimental data sets of steam-water two-phase flow in large-diameter pipes. One-dimensional and axi-symmetric two-dimensional two-fluid models were used for this purpose. Since the present interfacial drag force model would be applicable only to bubbly two-phase flow, the experimental data in which the mean void fraction is less than 0.3 were used for this purpose. As a result, it was demonstrated that the new model is effective for accurate prediction in these experimental conditions. (author)
A One-Dimensional (1-D) Three-Region Model for a Bubbling Fluidized-Bed Adsorber
Energy Technology Data Exchange (ETDEWEB)
Lee, Andrew; Miller, David C.
2012-01-01
A general one-dimensional (1-D), three-region model for a bubbling fluidized-bed adsorber with internal heat exchangers has been developed. The model can predict the hydrodynamics of the bed and provides axial profiles for all temperatures, concentrations, and velocities. The model is computationally fast and flexible and allows for any system of adsorption and desorption reactions to be modeled, making the model applicable to any adsorption process. The model has been implemented in both gPROMS and Aspen Custom Modeler, and the behavior of the model has been verified.
Evaluation of two bubble-detachment models for two-phase flow
International Nuclear Information System (INIS)
Two-phase flows with attached wall bubbles are considered as flows in roughened ducts with roughness elements equal in magnitude to the bubble detachment diameters determined by a force balance analysis. Two methods for determining the drag component of the forces acting on a bubble give distinctly different mixing-length theory expressions for velocity profile, friction factor, and void fraction. Available data are shown to be compatible with that set of expressions in which drag is due primarily to skin friction rather than form drag
Bubble, Bubble, Toil and Trouble.
Journal of Chemical Education, 2001
2001-01-01
Bubbles are a fun way to introduce the concepts of surface tension, intermolecular forces, and the use of surfactants. Presents two activities in which students add chemicals to liquid dishwashing detergent with water in order to create longer lasting bubbles. (ASK)
Dirk G Baur; Kristoffer Glover
2012-01-01
In this paper we use a test developed by Phillips et al. (2011) to identify a bubble in the gold market. We find that the price of gold followed an explosive price process between 2002 and 2012 interrupted only briefly by the subprime crisis in 2008. We also provide a theoretical foundation for such bubble tests based on a behavioural model of heterogeneous agents and demonstrate that periods of explosive price behaviour are consistent with increased chartist activity in the gold market. The ...
A Hadronic-Leptonic Model for the Fermi Bubbles: Cosmic-Rays in the Galactic Halo and Radio Emission
Fujita, Yutaka; Yamazaki, Ryo
2014-01-01
We investigate non-thermal emission from the Fermi bubbles on a hadronic model. Cosmic-ray (CR) protons are accelerated at the forward shock of the bubbles. They interact with the background gas in the Galactic halo and create $\\pi^0$-decay gamma-rays and secondary electrons through proton-proton interaction. We follow the evolution of the CR protons and electrons by calculating their distribution functions. We find that the spectrum and the intensity profile of $\\pi^0$-decay gamma-rays are consistent with observations. We predict that the shock front is located far ahead of the gamma-ray boundary of the Fermi bubbles. This naturally explains the fact that a clear temperature jump of thermal gas was not discovered at the gamma-ray boundary in recent Suzaku observations. We also consider re-acceleration of the background CRs in the Galactic halo at the shock front. We find that it can significantly affect the gamma-rays from the Fermi bubbles, unless the density of the background CRs is $\\lesssim 10$\\% of that...
Powering of cool filaments in cluster cores by buoyant bubbles - I. Qualitative model
Churazov, E.; Ruszkowski, M.; Schekochihin, A.
2013-11-01
Cool-core clusters (e.g. Perseus or M87) often possess a network of bright gaseous filaments, observed in radio, infrared, optical and X-ray bands. We propose that these filaments are powered by the reconnection of the magnetic field in the wakes of buoyant bubbles. Active galactic nucleus (AGN)-inflated bubbles of relativistic plasma rise buoyantly in the cluster atmosphere, stretching and amplifying the field in the wake to values of β = 8πPgas/B2 ˜ 1. The field lines in the wake have opposite directions and are forced together as the bubble motion stretches the filament. This setup bears strong similarity to the coronal loops on the Sun or to the Earth's magnetotail. The reconnection process naturally explains both the required level of local dissipation rate in filaments and the overall luminosity of filaments. The original source of power for the filaments is the potential energy of buoyant bubbles, inflated by the central AGN.
Powering of cool filaments in cluster cores by buoyant bubbles. I. Qualitative model
Churazov, E; Schekochihin, A
2013-01-01
Cool-core clusters (e.g., Perseus or M87) often possess a network of bright gaseous filaments, observed in radio, IR, optical and X-ray bands. We propose that these filaments are powered by the reconnection of the magnetic field in the wakes of buoyant bubbles. AGN-inflated bubbles of relativistic plasma rise buoyantly in the cluster atmosphere, stretching and amplifying the field in the wake to values of $\\beta =8\\pi P_{gas}/B^2\\sim 1$. The field lines in the wake have opposite directions and are forced together as the bubble motion stretches the filament. This setup bears strong similarity to the coronal loops on the Sun or the Earth magneto-tail. The reconnection process naturally explains both the required level of local dissipation rate in filaments and the overall luminosity of filaments. The original source of power for the filaments is the potential energy of buoyant bubbles, inflated by the central AGN.
Modeling and simulation of the bubble-induced flow in wine fermentation vessels
Directory of Open Access Journals (Sweden)
Schmidt Dominik
2015-01-01
Full Text Available Detailed flow pattern analyses regarding wine fermentations conducted without mechanical agitation are limited to lab-scale investigations, as industrial size measurements are expensive and difficult to realize. Computational fluid dynamic (CFD methods can offer an alternative and more flexible approach to gain insight into such bubble induced fluid flows. Therefore, the aim of this study was to transfer the findings of existing research onto a CFD model capable of capturing the three- dimensional flow pattern in industrial scale wine fermentation vessels. First results were obtained by using an extended version of the OpenFOAM® (v.2.2.x solver multiphaseEulerFoam for modeling the gas-liquid two phase system. With parameters from the most vigorous phase of wine fermentation a fully developed, unsteady flow regime could be established after approx. 120 s of real time. Thereby the groundwork for further evaluations of e.g. mixing efficiency or cooling equipment optimizations with CFD methods is laid.
A gas bubble-based parallel micro manipulator : conceptual design and kinematics model.
Dong, Wei; Gauthier, Michaël; Lenders, Cyrille; Lambert, Pierre
2012-01-01
The parallel mechanism has become an alternative solution when micro manipulators are demanded in the fields of micro manipulation and micro assembly. In this paper, a three-Degree-Of-Freedom (3-DOF) parallel micro manipulator is presented, which is directly driven by three micro gas bubbles. Since the micro gas bubbles are generated and maintained due to the surface tension between the gas and liquid media, the proposed novel system can be used in the liquid environment which allows for rota...
Characteristics of a bubble jet near a vertical wall
Institute of Scientific and Technical Information of China (English)
ZHANG A-man; YAO Xiong-liang; LI Jia
2008-01-01
A numerical model of a coupled bubble jet and wall was built on the assumption of potential flow and calculated by the boundary integral method. A three-dimensional computing program was then developed. Starting with the basic phenomenon of the interaction between a bubble and a wall, the dynamics of bubbles near rigid walls were studied systematically with the program. Calculated results agreed well with experimental results. The relationship between the Bjerknes effect of a wall and characteristic parameters was then studied and the calculated results of various cases were compared and discussed with the Blake criterion based on the Kelvin-impulse theory. Our analyses show that the angle of the jet's direction and the pressure on the rigid wall have a close relationship with collapse force and the bubble's characteristic parameters. From this, the application range of Blake criterion can be determined. This paper aims to provide a basis for future research on the dynamics of bubbles near a wall.
A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime
Energy Technology Data Exchange (ETDEWEB)
Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
1997-12-31
This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)
International Nuclear Information System (INIS)
The aim of this thesis is the 3-D modeling and numerical simulation of liquid/gas (water/vapor or water/air) two-phase flows in cooling circuits of nuclear power plants during normal and accidental situations. The development of a multidimensional dual-fluid model encounters two problems: the statistical effects of turbulence and the interface mass, momentum and energy transfers. The models developed in this study were introduced in the 3-D module of the CATHARE code developed by the CEA and the results were compared to experimental results available in the literature. The first chapter describes the equations of the local dual-fluid model for the 3-D description of two-phase flows. Closing relations adapted to dispersed flows with isothermal bubbles and without phase transformation are proposed and focus on the momentum transfer at the interfaces. The theoretical study of turbulence in the liquid phase of a bubble flow is modelled in chapter 2. Chapter 3 deals with the voluminal interface area used in the interface mass, momentum and energy transfers, and chapters 4 and 5 concern the application of the developed models to concrete situations. Chapter 4 describes in details the 3-D module of the CATHARE code while chapter 5 gives a comparison of numerical results obtained using the CATHARE code with other experimental results obtained at EdF. (J.S.)
Energy Technology Data Exchange (ETDEWEB)
Donna Post Guillen; Tami Grimmett; Anastasia M. Gribik; Steven P. Antal
2010-09-01
The Hybrid Energy Systems Testing (HYTEST) Laboratory is being established at the Idaho National Laboratory to develop and test hybrid energy systems with the principal objective to safeguard U.S. Energy Security by reducing dependence on foreign petroleum. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions will be performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. SBCRs are cylindrical vessels in which gaseous reactants (for example, synthesis gas or syngas) is sparged into a slurry of liquid reaction products and finely dispersed catalyst particles. The catalyst particles are suspended in the slurry by the rising gas bubbles and serve to promote the chemical reaction that converts syngas to a spectrum of longer chain hydrocarbon products, which can be upgraded to gasoline, diesel or jet fuel. These SBCRs operate in the churn-turbulent flow regime which is characterized by complex hydrodynamics, coupled with reacting flow chemistry and heat transfer, that effect reactor performance. The purpose of this work is to develop a computational multiphase fluid dynamic (CMFD) model to aid in understanding the physico-chemical processes occurring in the SBCR. Our team is developing a robust methodology to couple reaction kinetics and mass transfer into a four-field model (consisting of the bulk liquid, small bubbles, large bubbles and solid catalyst particles) that includes twelve species: (1) CO reactant, (2) H2 reactant, (3) hydrocarbon product, and (4) H2O product in small bubbles, large bubbles, and the bulk fluid. Properties of the hydrocarbon product were specified by vapor liquid equilibrium calculations. The absorption and kinetic models, specifically changes in species concentrations, have been incorporated into the mass continuity equation. The reaction rate is determined based on the macrokinetic model for a cobalt catalyst developed by Yates and Satterfield [1]. The
Energy Technology Data Exchange (ETDEWEB)
Veshchunov, M.S. [Russian Academy of Sciences, Nuclear Safety Institute (IBRAE), 52, B. Tulskaya, Moscow 115191 (Russian Federation)]. E-mail: vms@ibrae.ac.ru
2005-11-15
A new mechanism of the lenticular grain face bubble migration which controls the bubble mobility and determines the drag force exerted on the grain boundary, is developed. It is shown that besides a more complicated (so called 'lenticular') shape of grain face bubbles, the migration mechanism of these bubbles might be essentially different from the intragranular bubbles, owing to their specific location on and interaction with a grain boundary. The model is validated against tests on grain growth kinetics during steady irradiation exposure and during post-irradiation annealing of UO{sub 2} fuel samples, and allows explanation of a strong retarding effect of irradiation on the grain growth observed in these tests.
International Nuclear Information System (INIS)
To predict the behavior of gas-liquid two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed on the basis of a bubbly flow model. Under the assumption of homogeneous bubbly flow entraining fine bubbles, the equation of motion of the mixture is represented by that of liquid-phase and the liquid velocity is expressed as a potential for a quasi-harmonic equation. This equation is solved with a finite element method to obtain the velocities, and the equation of motion of an air bubble is integrated numerically in the flow field to obtain the void fraction. These calculations are iterated to obtain a converged solution. The method has been applied to a radial-flow pump, and the results obtained have been confirmed by experiments within the range of bubbly flow regime
O'Geary, Melissa A.
Bubbles provide an enjoyable and festive medium through which to teach many concepts within the science topics of light, color, chemistry, force, air pressure, electricity, buoyancy, floating, density, among many others. In order to determine the nature of children's engagement within a museum setting and the learning opportunities of playing with bubbles, I went to a children's interactive museum located in a metropolitan city in the Northeastern part of the United States.
Modeling and simulation of bubbling hot well deaerator in condensers of ships
International Nuclear Information System (INIS)
Highlights: • The model was based on the specific structure and heat transfer process. • The solubility of Oxygen could be calculated. • The simulation results are consistent with the theoretical analysis. - Abstract: Application of deaerators in ship has been restricted due to space limitation. Thus far, the function of deaerator has been integrated into the hot well of the condenser. The condensate water would be heated to saturation by extracting steam from turbine, which would make the solubility of Oxygen in condensate water fall to zero according to Henry’s law and Dalton’s law. The purpose of this paper was to build a mathematical model of bubbling hot well deaerator in the condensers of ships. In this paper, the heat exchange rate was calculated by empirical formulas which took the specific structure and process of heat exchange into account. When the operating conditions were in the application ranges of the empirical formulas, the simulation model would be performed by utilizing them; otherwise, calculations would be done by the conservation of energy, which assured the simulation model could be used at any operating condition. Different from previous works, the solubility of Oxygen in heated condensate water could be calculated by an empirical formula. The simulation results showed that the structure and heat exchange process considered could be highly accurate at the steady-state operations, and the main parameters trend curves during dynamic-state operations were consistent with theoretical analysis. The solubility of Oxygen could be calculated and the simulation results at the steady-state operations were verified against the practical situation, the trend curves during dynamic-state operations were consistent with theoretical analysis
A non-equilibrium ionization model of the Local Bubble (I)
de Avillez, Miguel A
2012-01-01
Aims. We present the first high-resolution non-equilibrium ionization simulation of the joint evolution of the Local Bubble (LB) and Loop I superbubbles in the turbulent supernova-driven interstellar medium (ISM). The time variation and spatial distribution of the Li-like ions Civ, Nv, and Ovi inside the LB are studied in detail. Methods. This work uses the parallel adaptive mesh refinement code EAF-PAMR coupled to the newly developed atomic and molecular plasma emission module E(A+M)PEC, featuring the time-dependent calculation of the ionization structure of H through Fe, using the latest revision of solar abundances. The finest AMR resolution is 1 pc within a grid that covers a representative patch of the Galactic disk (with an area of 1 kpc^2 in the midplane) and halo (extending up to 10 kpc above and below the midplane). Results. The evolution age of the LB is derived by the match between the simulated and observed absorption features of the Li-like ions Civ, Nv, and Ovi . The modeled LB current evolution...
Issues for Achieving an Experimental Model Concerning Bubble Deck Concrete Slab with Spherical Gaps
Directory of Open Access Journals (Sweden)
Sergiu Călin
2010-01-01
Full Text Available After realizing numerous constructions in the world, which use Bubble Deck concrete slabs with spherical gaps, valuable information were gathered, allowing a rigorous processing and systematization, with the purpose of realizing an experimental and documentary study. The paper presents some experimental programs which refer to concrete slabs with spherical gaps, existing in similar execution and loading conditions as those from a real construction; this implies the realization of a monolithic slab element at a scale of 1:1, which will be subjected to static gravitational loadings in order to determine the deformation (deflection, cracking and failing characteristics. The resultant conclusions will be used in defining the failing mechanisms, very useful in the formulation of an adequate mathematical model. The research proposed in the project offers an answer to the major objectives of the development of calculus methods and existent prescriptions of the concrete slabs with spherical gaps. The realization of the proposed objectives involves documentation activities, theoretical study, collaboration with different other partners, gathering and processing of the results obtained in laboratory and even in situ.
Identifying bubble collapse in a hydrothermal system using hidden Markov models
Dawson, P.B.; Benitez, M.C.; Lowenstern, J. B.; Chouet, B.A.
2012-01-01
Beginning in July 2003 and lasting through September 2003, the Norris Geyser Basin in Yellowstone National Park exhibited an unusual increase in ground temperature and hydrothermal activity. Using hidden Markov model theory, we identify over five million high-frequency (>15Hz) seismic events observed at a temporary seismic station deployed in the basin in response to the increase in hydrothermal activity. The source of these seismic events is constrained to within ???100 m of the station, and produced ???3500-5500 events per hour with mean durations of ???0.35-0.45s. The seismic event rate, air temperature, hydrologic temperatures, and surficial water flow of the geyser basin exhibited a marked diurnal pattern that was closely associated with solar thermal radiance. We interpret the source of the seismicity to be due to the collapse of small steam bubbles in the hydrothermal system, with the rate of collapse being controlled by surficial temperatures and daytime evaporation rates. copyright 2012 by the American Geophysical Union.
International Nuclear Information System (INIS)
Bubble chambers may have almost vanished from the front line of physics research, but the vivid memory of their intricate and sometimes beautiful patterns of particle tracks lives on, and has greatly influenced the computer graphics of track reconstruction in today's big experiments. 'Seeing' an interaction makes it more understandable. Bubble chambers, with their big collaborations of physicists from many widely scattered research institutes, started another ball rolling. The groups formed are even now only surpassed in size by the big collaborations working on today's major detectors at colliding beam machines. From 14-16 July, about 130 physicists gathered at CERN to commemorate the 40th anniversary of the invention of the bubble chamber by Donald Glaser. The meeting, organized by Derek C. Colley from Birmingham, gave a comprehensive overview of bubble chamber contributions to physics, their challenging technology, and the usefulness of bubble chamber photographs in education, both for physics and the public at large. After opening remarks by CERN Director Carlo Rubbia, Donald Glaser began with a brief review of the work which led to his invention - there was much more to it than idly watching beer bubbles rise up the wall of the glass - before turning to his present line of research, biophysics, also very visually oriented
Movahed, Pooya; Kreider, Wayne; Maxwell, Adam D; Hutchens, Shelby B; Freund, Jonathan B
2016-08-01
A generalized Rayleigh-Plesset-type bubble dynamics model with a damage mechanism is developed for cavitation and damage of soft materials by focused ultrasound bursts. This study is linked to recent experimental observations in tissue-mimicking polyacrylamide and agar gel phantoms subjected to bursts of a kind being considered specifically for lithotripsy. These show bubble activation at multiple sites during the initial pulses. More cavities appear continuously through the course of the observations, similar to what is deduced in pig kidney tissues in shock-wave lithotripsy. Two different material models are used to represent the distinct properties of the two gel materials. The polyacrylamide gel is represented with a neo-Hookean elastic model and damaged based upon a maximum-strain criterion; the agar gel is represented with a strain-hardening Fung model and damaged according to the strain-energy-based Griffith's fracture criterion. Estimates based upon independently determined elasticity and viscosity of the two gel materials suggest that bubble confinement should be sufficient to prevent damage in the gels, and presumably injury in some tissues. Damage accumulation is therefore proposed to occur via a material fatigue, which is shown to be consistent with observed delays in widespread cavitation activity. PMID:27586763
Bubble point pressures of the selected model system for CatLiq® bio-oil process
DEFF Research Database (Denmark)
Toor, Saqib Sohail; Rosendahl, Lasse; Baig, Muhammad Noman; Robbins, Phil; Santos, Regina; Nørgaard, Kristian
2010-01-01
work, the bubble point pressures of a selected model mixture (CO2 + H2O + Ethanol + Acetic acid + Octanoic acid) were measured to investigate the phase boundaries of the CatLiq® process. The bubble points were measured in the JEFRI-DBR high pressure PVT phase behavior system. The experimental results......The CatLiq® process is a second generation catalytic liquefaction process for the production of bio-oil from WDGS (Wet Distillers Grains with Solubles) at subcritical conditions (280-350 oC and 225-250 bar) in the presence of a homogeneous alkaline and a heterogeneous Zirconia catalyst. In this...... predicted data is 8.7% in the selected model mixture....
International Nuclear Information System (INIS)
Investigation of two-phase flow around obstacles is important for thermal-hydraulic design and safety analyses of various equipments in nuclear power plants. The examples of obstacles are spacers in nuclear fuel rod bundles or in steam generator tube bundles, as well as perforated plates submerged in two-phase mixture in order to equalize void fraction and swell level spatial distribution in large volumes. In this paper the numerical simulation of a bubble column flow in a rectangular water pool is performed. The gas is injected in form of bubbles near the pool bottom through the short perforated pipe. A horizontal plate with a slit is introduced at the half-length of the pool and it forms an obstacle to the bubble column flow. The simulation is performed with the multidimensional transient two-fluid model. The model is based on the mass and momentum balance equations for the liquid and gas phase. The model is numerically solved with the application of the SIMPLE type algorithm developed for the conditions of two-phase flow. Obtained results show the ability of the applied modelling approach to simulate complex liquid and gas flow conditions around obstacles. The bubble column rise along the pool and passing through the plate slit is shown, together with the recirculation of water below and above the horizontal plate. The problem of achieving symmetric velocity and void fraction fields for symmetric rectangular pool geometry and boundary conditions is encountered. The simulations without and with the lateral force are performed, showing the importance of lateral force inclusion in the momentum balance equations. (author)
A Phase-Field Approach to Modeling Hydrate Formation on Methane Gas Bubbles in a Water Column
Fu, X.; Cueto-Felgueroso, L.; Waite, W. F.; Ruppel, C. D.; Juanes, R.
2014-12-01
Methane hydrates are water-based crystalline solids, where gas molecules are trapped inside the lattice structure formed by water. Most commonly found in deep ocean floors where low temperature and high pressure are primal conditions for hydrate to form, gas hydrates contain most of the world's mobile carbon and yet it remains an important and open question how methane leakage from gas hydrate impacts ocean and the atmosphere. While current work focus on the breakdown of gas hydrate in marine environment and the the release of methane from seafloor, few studies explore the fate of a single or a plume of methane bubbles when entering the water column after the release. We propose to study the fate of an individual and a series of methane bubbles through mathematical modeling, specifically using a phase-field approach. Phase-field modeling is a mathematical framework that describes systems that are out of thermodynamic equilibrium. First introduced in the context of solidification process and phase transitions, it has since been adopted in the field of multiphase flow. In this work, we present a new phase-field formulation for multiphase/multicomponent flows that allows us to model the fate of methane bubbles in the water system as a nonequilibrium process.
Mechanisms of gas bubble retention
International Nuclear Information System (INIS)
Retention and episodic release of flammable gases are critical safety concerns regarding double-shell tanks (DSTs) containing waste slurries. Previous investigations have concluded that gas bubbles are retained by the slurry that has settled at the bottom of the DST. However, the mechanisms responsible for the retention of these bubbles are not well understood. In addition, the presence of retained gas bubbles is expected to affect the physical properties of the sludge, but essentially no literature data are available to assess the effect of these bubbles. The rheological behavior of the waste, particularly of the settled sludge, is critical to characterizing the tendency of the waste to retain gas bubbles. The objectives of this study are to elucidate the mechanisms contributing to gas bubble retention and release from sludge such as is in Tank 241-SY-101, understand how the bubbles affect the physical properties of the sludge, develop correlations of these physical properties to include in computer models, and collect experimental data on the physical properties of simulated sludges with bubbles. This report presents a theory and experimental observations of bubble retention in simulated sludge and gives correlations and new data on the effect of gas bubbles on sludge yield strength
Rational Bubbles in Stock Prices?
Behzad T. Diba; Grossman, Herschel I.
1985-01-01
This paper reports empirical tests for the existence of rational bubbles in stock prices. The analysis focuses on a familiar model that defines market fundamentals to be the expected present value of dividends, discounted at a constantrate, and defines a rational bubble to be a self-confirming divergence of stock prices from market fundamentals in response to extraneous variables. The tests are based on the theoretical result that, if rational bubbles exist, time series obtained by differenci...
Rational Asset Pricing Bubbles Revisited
Jan Werner
2012-01-01
Price bubble arises when the price of an asset exceeds the asset's fundamental value, that is, the present value of future dividend payments. The important result of Santos and Woodford (1997) says that price bubbles cannot exist in equilibrium in the standard dynamic asset pricing model with rational agents as long as assets are in strictly positive supply and the present value of total future resources is finite. This paper explores the possibility of asset price bubbles when either one of ...
A criterion for the occurrence of bubble fission and its modeling
Czech Academy of Sciences Publication Activity Database
Delale, C. F.; Pasinlioğlu, S.; Zima, Patrik
Singapore: Research Publishing Services, 2012 - (Ohl, C.; Klaseboer, E.; Ohl, S.; Gong, S.; Khoo, B.), s. 78-82 ISBN 978-981-07-2826-7. [International Symposium on Cavitation /8./ CAV 2012. Singapur (SG), 13.08.2012-16.08.2012] R&D Projects: GA ČR GAP101/10/1428 Institutional research plan: CEZ:AV0Z20760514 Keywords : bubble dynamics * bubble fission * cavitation Subject RIV: BK - Fluid Dynamics http://rpsonline.com.sg/proceedings/9789810728267/html/192.xml59.xml
International Nuclear Information System (INIS)
In the channels of liquid metal (ML) regenerating sheaths of a fusion reactor, the possibility of bubbles of helium is not remote. Bubbles adhering to the wall of the ML channels would affect heat transfer and the permeation of tritium. Detailed analysis has been conducted (fine mesh), using OpenFOAM, from the environment of a bubble attached to the wall and has developed a model for permeation of tritium through a partially covered with bubbles of helium surface of contact Ml-solid. The model developed has implemented as wall function in OpenFOAM, has validated and has been applied to a case study, using a relatively thick mesh. The developed model substantially reduces the need for computing on the detailed calculation power.
Solares, H A Ayala; Hüntemeyer, P
2015-01-01
The Fermi Bubbles, which comprise two large and homogeneous regions of spectrally hard gamma-ray emission extending up to $55^{o}$ above and below the Galactic Center, were first noticed in GeV gamma-ray data from the Fermi Telescope in 2010. The mechanism or mechanisms which produce the observed hard spectrum are not understood. Although both hadronic and lep- tonic models can describe the spectrum of the bubbles, the leptonic model can also explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff in the energy range of 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain the origin of the bubbles. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With...
Muñoz-Cobo, José; Chiva, Sergio; El Aziz Essa, Mohamed; Mendes, Santos
2012-08-01
Two phase flow experiments with different superficial velocities of gas and water were performed in a vertical upward isothermal cocurrent air-water flow column with conditions ranging from bubbly flow, with very low void fraction, to transition flow with some cap and slug bubbles and void fractions around 25%. The superficial velocities of the liquid and the gas phases were varied from 0.5 to 3 m/s and from 0 to 0.6 m/s, respectively. Also to check the effect of changing the surface tension on the previous experiments small amounts of 1-butanol were added to the water. These amounts range from 9 to 75 ppm and change the surface tension. This study is interesting because in real cases the surface tension of the water diminishes with temperature, and with this kind of experiments we can study indirectly the effect of changing the temperature on the void fraction distribution. The following axial and radial distributions were measured in all these experiments: void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter and turbulence intensity. The range of values of the gas superficial velocities in these experiments covered the range from bubbly flow to the transition to cap/slug flow. Also with transition flow conditions we distinguish two groups of bubbles in the experiments, the small spherical bubbles and the cap/slug bubbles. Special interest was devoted to the transition region from bubbly to cap/slug flow; the goal was to understand the physical phenomena that take place during this transition A set of numerical simulations of some of these experiments for bubbly flow conditions has been performed by coupling a Lagrangian code, that tracks the three dimensional motion of the individual bubbles in cylindrical coordinates inside the field of the carrier liquid, to an Eulerian model that computes the magnitudes of continuous phase and to a 3D random walk model that takes on account the fluctuation in the velocity field of the
International Nuclear Information System (INIS)
Highlights: • We simulate convective nucleate pool boiling with a novel phase-change model. • We simulate four cases at different sub-cooling and wall superheat levels. • We investigate the flow structures around the growing bubble and analyze the accompanying physics. • We accurately simulate bubble shape elongation and enhanced wall cooling due to the sliding and slanting motions of bubbles. • Bubble cycle durations show good agreement with experimental observations. - Abstract: With the long-term objective of Critical Heat Flux (CHF) prediction, bubble dynamics in convective nucleate boiling flows has been studied using a Direct Numerical Simulation (DNS). A sharp-interface phase change model which was originally developed for pool boiling flows is extended to convective boiling flows. For physical scales smaller than the smallest flow scales (smaller than the grid size), a micro-scale model was used. After a grid dependency study and a parametric study for the contact angle, four cases of simulation were carried out with different wall superheat and degree of subcooling. The flow structures around the growing bubble were investigated together with the accompanying physics. The relation between the heat flux evolution and the bubble growth was studied, along with investigations of bubble diameter and bubble base diameter evolutions across the four cases. As a validation, the evolutions of bubble diameter and bubble base diameter were compared to experimental observations. The bubble departure period and the bubble shapes show good agreement between the experiment and the simulation, although the Reynolds number of the simulation cases is relatively low
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The shift of China’s monetary policy stance from "moderately loose" to "prudent" in 2011 indicates curbing inflation and asset bubbles have become the Central Government’s top priority. But is China’s bubble problem short-term or long-term? Is it only monetary or related to economic structure? Is it the cause of China’s economic imbalance or the result? And what kind of deep-rooted problems in the macro economy does it reflect? All these questions call for deep thought,said Zhang Monan,a
CFD Model for Pneumatic Mixing with Bubble Chains: Application to Glass Melts
Czech Academy of Sciences Publication Activity Database
Šimčík, Miroslav; Růžička, Marek
2015-01-01
Roč. 127, MAY 4 (2015), s. 344-361. ISSN 0009-2509 R&D Projects: GA MŠk(CZ) LD13018 Institutional support: RVO:67985858 Keywords : bubble chain * viscous liquid * flow simulation Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.337, year: 2014
Energy Technology Data Exchange (ETDEWEB)
Donna Guillen, PhD; Anastasia Gribik; Daniel Ginosar, PhD; Steven P. Antal, PhD
2008-11-01
This paper describes the development of a computational multiphase fluid dynamics (CMFD) model of the Fischer Tropsch (FT) process in a Slurry Bubble Column Reactor (SBCR). The CMFD model is fundamentally based which allows it to be applied to different industrial processes and reactor geometries. The NPHASE CMFD solver [1] is used as the robust computational platform. Results from the CMFD model include gas distribution, species concentration profiles, and local temperatures within the SBCR. This type of model can provide valuable information for process design, operations and troubleshooting of FT plants. An ensemble-averaged, turbulent, multi-fluid solution algorithm for the multiphase, reacting flow with heat transfer was employed. Mechanistic models applicable to churn turbulent flow have been developed to provide a fundamentally based closure set for the equations. In this four-field model formulation, two of the fields are used to track the gas phase (i.e., small spherical and large slug/cap bubbles), and the other two fields are used for the liquid and catalyst particles. Reaction kinetics for a cobalt catalyst is based upon values reported in the published literature. An initial, reaction kinetics model has been developed and exercised to demonstrate viability of the overall solution scheme. The model will continue to be developed with improved physics added in stages.
Shekhar, R.; Evans, J. W.
1994-06-01
The need for energy reduction in the electrolytic production of aluminum led to the concept of advanced Hall cells that can be operated at lower interelectrode gaps compared to existing cells. However, gas bubbles generated by the anodic reaction increase the resistivity of electrolyte and cancel out part of the reduction in interelectrode resistance expected from bringing the electrodes closer together. Therefore, the primary objective of this work was to determine a cell design in which flow can be managed to promote the removal of anode gas bubbles from the interelectrode gap. In particular, this article focuses on advanced Hall cells equipped with “flat” anodes, similar to those used in existing cells. The principal experimental tool has been a “water” model consisting of a large tank in which simulated anodes can be suspended in either the horizontal or near-horizontal configurations. Gas was generated by forcing compressed air through porous graphite, and the fine bubbles characteristic of inert anodes used in advanced Hall cells were produced by adding butanol to water. Velocities were measured using a laser-Doppler velocimeter (LDV). This study indicates that the existing cell configuration might not be the optimum configuration for advanced Hall cells. The results also show that operation of an advanced Hall cell with a fully submerged anode should give rise to higher electrolyte velocities and thus rapid removal of bubbles. The bubble effect should be further lowered in a near-horizontal configuration; however, the flow pattern could have an adverse effect on current efficiency and alumina distribution in the cell. It has also been shown that the bubble size, and, therefore, the physical properties of the electrolyte, can have a significant effect on the electrolyte flow pattern in the interelectrode gap.
Analyzing Cosmic Bubble Collisions
Gobbetti, Roberto
2012-01-01
We develop a set of controlled, analytic approximations to study the effects of bubble collisions on cosmology. We expand the initial perturbation to the inflaton field caused by the collision in a general power series, and determine its time evolution during inflation in terms of the coefficients in the expansion. In models where the observer's bubble undergoes sufficient slow-roll inflation to solve the flatness problem, in the thin wall limit only one coefficient in the expansion is relevant to observational cosmology, allowing nearly model-independent predictions. We discuss two approaches to determining the initial perturbation to the inflaton and the implications for the sign of the effect (a hot or cold spot on the Cosmic Microwave Background temperature map). Lastly, we analyze the effects of collisions with thick-wall bubbles, i.e. away from the thin-wall limit.
Developed ‘laminar’ bubbly flow with non-uniform bubble sizes
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Bubbles with different sizes have different dynamic and kineticbehavior in a two-phase bubbly flow. A common two-fluid model based on the uniform bubble size assumption is not suitable for a bubbly flow with non-uniform bubble sizes. To deal with non-uniform bubbly flows, a multi-fluid model is established, with which bubbles are divided into several groups according to their sizes and a set of basic equations is derived for each group of bubbles with almost the same size. Through analyzing the bubble-bubble and bubble-pipe wall interactions, two new constitutive laws for the wall-force and pressure difference between the liquid phase and interface are developed to close the averaged basic equations. The respective phase distributions for each group of bubbles measured by a specially designed three-dimensional photographic method are used to check the model. Comparison between model-predicted values and experimental data shows that the model can describe laminar bubbly flow with non-uniform bubble sizes.
Numerical simulation of vapor bubble condensation in turbulent subcooled flow boiling
International Nuclear Information System (INIS)
Highlights: • The two-phase flow was modeled using VOF interface tracking method. • Bubble dynamics at high pressure, high velocity conditions was captured using LES. • Reverse bubble velocity trends occur for varying pressure with zero and nonzero bulk velocity. • Condensation rate increases with subcooling temperature and bulk velocity. • Bubble distortion increases with system pressure and bulk velocity. - Abstract: Subcooled flow boiling is a significant heat transfer regime in pressurized water reactors (PWRs) and also occurs in boiling water reactors (BWRs) prior to the onset of saturated nucleate boiling. In subcooled boiling, individual bubbles experience a life-cycle of nucleation from the wall, (possible) departure from the wall, and transport along the channel during condensation/collapse. The present paper focuses on the last stage of this life cycle. CFD analysis of a single bubble behavior in upward subcooled flow boiling was performed using volume-of-fluid (VOF) interface tracking method and large eddy simulation (LES) turbulence model. High pressure steam-water conditions at high flow velocity were simulated due to their relevance to the nuclear application. The numerical solutions were compared with terminal velocity correlations. Bubble behavior was investigated at different system pressure, subcooling temperature, bubble diameter, pipe diameter, and bulk fluid velocity, corresponding to bulk Reynolds number range of 0–410,000. The effects of these parametric variations on bubble rise velocity, deformation rate, trajectory, and distortion are presented. Results show that bubble rise velocity increases with bulk velocity, and bubble size, but decreases with increasing pipe diameter. A reverse bubble velocity trend with varying system pressure is observed with and without bulk velocity. Bubble condensation rate decreased with increasing system pressure, bubble size and pipe diameter, but increased with increasing subcooling temperature
Numerical simulation of vapor bubble condensation in turbulent subcooled flow boiling
Energy Technology Data Exchange (ETDEWEB)
Owoeye, Eyitayo James, E-mail: msgenius10@ufl.edu; Schubring, DuWanye, E-mail: dlschubring@ufl.edu
2015-08-15
Highlights: • The two-phase flow was modeled using VOF interface tracking method. • Bubble dynamics at high pressure, high velocity conditions was captured using LES. • Reverse bubble velocity trends occur for varying pressure with zero and nonzero bulk velocity. • Condensation rate increases with subcooling temperature and bulk velocity. • Bubble distortion increases with system pressure and bulk velocity. - Abstract: Subcooled flow boiling is a significant heat transfer regime in pressurized water reactors (PWRs) and also occurs in boiling water reactors (BWRs) prior to the onset of saturated nucleate boiling. In subcooled boiling, individual bubbles experience a life-cycle of nucleation from the wall, (possible) departure from the wall, and transport along the channel during condensation/collapse. The present paper focuses on the last stage of this life cycle. CFD analysis of a single bubble behavior in upward subcooled flow boiling was performed using volume-of-fluid (VOF) interface tracking method and large eddy simulation (LES) turbulence model. High pressure steam-water conditions at high flow velocity were simulated due to their relevance to the nuclear application. The numerical solutions were compared with terminal velocity correlations. Bubble behavior was investigated at different system pressure, subcooling temperature, bubble diameter, pipe diameter, and bulk fluid velocity, corresponding to bulk Reynolds number range of 0–410,000. The effects of these parametric variations on bubble rise velocity, deformation rate, trajectory, and distortion are presented. Results show that bubble rise velocity increases with bulk velocity, and bubble size, but decreases with increasing pipe diameter. A reverse bubble velocity trend with varying system pressure is observed with and without bulk velocity. Bubble condensation rate decreased with increasing system pressure, bubble size and pipe diameter, but increased with increasing subcooling temperature
Differential criterion of a bubble collapse in viscous liquids
Bogoyavlenskiy, V A
1999-01-01
The present work is devoted to a model of bubble collapse in a Newtonian viscous liquid caused by an initial bubble wall motion. The obtained bubble dynamics described by an analytic solution significantly depends on the liquid and bubble parameters. The theory gives two types of bubble behavior: collapse and viscous damping. This results in a general collapse condition proposed as the sufficient differential criterion. The suggested criterion is discussed and successfully applied to the analysis of the void and gas bubble collapses.
Energy Technology Data Exchange (ETDEWEB)
Beaumont, Christopher N.; Williams, Jonathan P. [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Goodman, Alyssa A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kendrew, Sarah; Simpson, Robert, E-mail: beaumont@ifa.hawaii.edu [Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)
2014-09-01
We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10%-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to the mid-plane, and display a stronger excess of young stellar objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches—particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machine learning techniques. In cases where ''untrained' citizens can identify patterns that machines cannot detect without training, machine learning algorithms like Brut can use the output of citizen science projects as input training sets, offering tremendous opportunities to speed the pace of scientific discovery. A hybrid model of machine learning combined with crowdsourced training data from citizen scientists can not only classify large quantities of data, but also address the weakness of each approach if deployed alone.
International Nuclear Information System (INIS)
We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10%-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to the mid-plane, and display a stronger excess of young stellar objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches—particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machine learning techniques. In cases where ''untrained' citizens can identify patterns that machines cannot detect without training, machine learning algorithms like Brut can use the output of citizen science projects as input training sets, offering tremendous opportunities to speed the pace of scientific discovery. A hybrid model of machine learning combined with crowdsourced training data from citizen scientists can not only classify large quantities of data, but also address the weakness of each approach if deployed alone
Comparing Simple Quasar Demographics Models
Veale, Melanie; Conroy, Charlie
2014-01-01
This paper explores several simple model variations for the connections among quasars, galaxies, and dark matter halos for redshifts 1 < z < 6. A key component of these models is that we enforce a self-consistent black hole (BH) history by tracking both BH mass and BH growth rate at all redshifts. We connect objects across redshift with a simple constant-number-density procedure, and choose a fiducial model with a relationship between BH and galaxy growth rates that is linear and evolves in a simple way with redshift. Within this fiducial model, we find the quasar luminosity function (QLF) by calculating an "intrinsic" luminosity based on either the BH mass or BH growth rate, and then choosing a model of quasar variability with either a lognormal or truncated power-law distribution of instantaneous luminosities. This gives four model variations, which we fit to the observed QLF at each redshift. With the best-fit models in hand, we undertake a detailed comparison of the four fiducial models, and explore...
Prakash, Manu
2011-11-01
Metamorphosis presents a puzzling challenge where, triggered by a signal, an organism abruptly transforms its entire shape and form. Here I describe the role of physical fluid dynamic processes during pupal metamorphosis in flies. During early stages of pupation of third instar larvae into adult flies, a physical gas bubble nucleates at a precise temporal and spatial location, as part of the normal developmental program in Diptera. Although its existence has been known for the last 100 years, the origin and control of this ``cavitation'' event has remained completely mysterious. Where does the driving negative pressure for bubble nucleation come from? How is the location of the bubble nucleation site encoded in the pupae? How do molecular processes control such a physical event? What is the role of this bubble during development? Via developing in-vivo imaging techniques, direct bio-physical measurements in live insect pupal structures and physical modeling, here I elucidate the physical mechanism for appearance and disappearance of this bubble and predict the site of nucleation and its exact timing. This new physical insight into the process of metamorphosis also allows us to understand the inherent design of pupal shell architectures in various species of insects. Milton Award, Harvard Society of Fellows; Terman Fellowship, Stanford
International Nuclear Information System (INIS)
The present paper summarises recent studies by the author in which the removal of intragranular fission gas to grain boundaries during post-irradiation annealing of high burn-up UO2 has been modelled in terms of known bubble behaviour. The difficulties of matching random bubble migration to experimental results and the fundamental difficulties of using simple gas atom diffusion have been avoided by utilising the strong 'directed' bubble migration that must occur in the vacancy gradient induced between the grain boundary and over-pressurised bubble concentrations within a grain during annealing. The present paper summarises the approach used to simulate these processes, leading to quantitative predictions and providing information on the parameters of importance. Comparison with experimental data from the literature shows excellent agreement with the main trends, particularly the increase in release fraction with burn-up. (author)
Engineering patterns of wrinkles and bubbles in supported graphene through modeling and simulation
Zhang, Kuang
2015-01-01
Graphene deposited on a substrate often exhibits out-of-plane deformations with different features and origins. Networks of localized wrinkles have been observed in graphene synthesized through CVD, as a result of compressive stresses transmitted by the substrate. Graphene blisters have been reported with various sizes and shapes, and have been shown to be caused by gas trapped between graphene and substrate. Such wrinkles or bubbles locally modify the electronic properties and are often seen...
Sand dissolution and bubble removal in a model glass-melting channel with melt circulation
Czech Academy of Sciences Publication Activity Database
Cincibusová, Petra; Němec, Lubomír
2012-01-01
Roč. 53, č. 4 (2012), s. 150-157. ISSN 1753-3546 R&D Projects: GA TA ČR TA01010844 Institutional research plan: CEZ:AV0Z30460519 Keywords : glass melting * sand dissolution * bubble removal Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 0.729, year: 2012 http://www.ingentaconnect.com/content/sgt/gt/2012/00000053/00000004/art00004
Nakao, K; Suenaga, S.; Furumoto, K.; Yoshimoto, M; Fukunaga, K.
2007-01-01
The effects of suspended solid particles on the hydrodynamic and mass transfer properties were experimentally studied in a wide range of the superficial gas velocity, solid particle property and liquid viscosity in an external loop airlift bubble column in comparison with those in an internal loop airlift bubble column as well as a normal bubble column. The circulating liquid velocities UL, gas holdups G and volumetric gas liquid oxygen transfer coefficients kLa in the riser of the external ...
International Nuclear Information System (INIS)
Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs
Energy Technology Data Exchange (ETDEWEB)
Bottoni, M.; Ajuha, S. [Argonne National Lab., IL (United States). Energy Technology Div.; Sengpiel, W. [Kernforschungszentrum Karlsruhe (Germany). Inst. fur Reaktorsicherheit
1994-12-31
Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy derived for a two-phase flow by volume-averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration; bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities makes the rigorously formulated terms useless for computational purposes, modeling of these terms is discussed.
Bubble drag reduction requires large bubbles
Verschoof, Ruben A; Sun, Chao; Lohse, Detlef
2016-01-01
In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.
International Nuclear Information System (INIS)
In order to prevent the expansion of tube damages and to maintain structural safety in steam generators (SG) of fast breeder reactors (FBR), it is necessary to detect precisely and immediately the leakage of water from tubes of heat exchangers. Therefore, an active acoustic method, which detects the sound attenuation due to bubbles generated in the sodium-water reactions, it being developed. In this paper, the attenuation characteristics of sound attenuated by bubbles and influence of background noise are investigated experimentally by using an SG full sector model (diameter ratio about 1/1, height ratio about 1/7) simulating the actual SG. As an experimental result, the received sound attenuation for ten seconds was more than 10 dB from air bubble injection when injected bubble of 10 l/s (equivalence water leak rate about 10 g/s). The attenuation of sound are least affected by bubble injection position of heat exchanger tube bunch department. And the time was about 25 seconds till the sound attenuation became 10 dB in case of quantity of air bubble 1 l/s (equivalent water leak rate about 1 g/s). It is clarified that the background noise hardly influenced water leak detection performance as a result of having examined influence of background noise. (author)
The Fermi Bubbles as Starburst Wind Termination Shocks
Lacki, Brian C
2013-01-01
The enhanced star formation in the inner 100 pc of the Galaxy launches a superwind, reaching ~1600 km/s for M82-like parameters. The ram pressure of the wind is very low compared to more powerful starburst winds. I show that halo gas stops the wind a few kpc from the Galactic Center. I argue that the termination shock accelerates cosmic rays, and that the resulting Inverse Compton gamma-rays are visible as the Fermi Bubbles. The Bubbles are thus wind bubbles, which the starburst can inflate within 10 Myr. They remain in steady state as long as the starburst lasts. The shock may accelerate PeV electrons and ultra-high energy protons. The Bubbles may be analogs of galactic wind termination shocks in the intergalactic medium. I discuss the advantages and problems of this model.
Calibration of PICO Bubble Chamber Dark Matter Detectors
Jin, Miaotianzi; PICO Collaboration
2016-03-01
The PICO Collaboration builds bubble chambers for the direct detection of WIMP dark matter. I will present the suite of calibration experiments performed to measure the sensitivity of these chambers to nuclear recoils (the expected WIMP signal) and to gamma rays (a common background to the WIMP signal). These calibrations include measurements with a 10-ml C3F8 bubble chamber at Northwestern University and with a 30-ml C3F8 bubble chamber deployed in the University of Montreal's tandem Van de Graaf facility, giving the bubble chamber response to a variety of gamma rays, broad-spectrum neutron sources, and mono-energetic low energy neutrons. I will compare our measured sensitivities to those predicted by a simple thermodynamic model and will show how the results impact our ability to detect dark matter, with a focus on light WIMP searches. Supported by DOE Grant: DE-SC0012161.
Experimental Investigation of Large-Scale Bubbly Plumes
International Nuclear Information System (INIS)
Carefully planned and instrumented experiments under well-defined boundary conditions have been carried out on large-scale, isothermal, bubbly plumes. The data obtained is meant to validate newly developed, high-resolution numerical tools for 3D transient, two-phase flow modelling. Several measurement techniques have been utilised to collect data from the experiments: particle image velocimetry, optical probes, electromagnetic probes, and visualisation. Bubble and liquid velocity fields, void-fraction distributions, bubble size and interfacial-area-concentration distributions have all been measured in the plume region, as well as recirculation velocities in the surrounding pool. The results obtained from the different measurement techniques have been compared. In general, the two-phase flow data obtained from the different techniques are found to be consistent, and of high enough quality for validating numerical simulation tools for 3D bubbly flows. (author)
The impact and bounce of air bubbles at a flat fluid interface.
Manica, Rogerio; Klaseboer, Evert; Chan, Derek Y C
2016-04-01
The rise and impact of bubbles at an initially flat but deformable liquid-air interface in ultraclean liquid systems are modelled by taking into account the buoyancy force, hydrodynamic drag, inertial added mass effect and drainage of the thin film between the bubble and the interface. The bubble-surface interaction is analyzed using lubrication theory that allows for both bubble and surface deformation under a balance of normal stresses and surface tension as well as the long-range nature of deformation along the interface. The quantitative result for collision and bounce is sensitive to the impact velocity of the rising bubble. This velocity is controlled by the combined effects of interfacial tension via the Young-Laplace equation and hydrodynamic stress on the surface, which determine the deformation of the bubble. The drag force that arises from the hydrodynamic stress in turn depends on the hydrodynamic boundary conditions on the bubble surface and its shape. These interrelated factors are accounted for in a consistent manner. The model can predict the rise velocity and shape of millimeter-size bubbles in ultra-clean water, in two silicone oils of different densities and viscosities and in ethanol without any adjustable parameters. The collision and bounce of such bubbles with a flat water/air, silicone oil/air and ethanol/air interface can then be predicted with excellent agreement when compared to experimental observations. PMID:26924623
International Nuclear Information System (INIS)
This report describes the results of seven series of experiments conducted to investigate heat and mass transfer phenomena in multicomponent bubbling pools with application to the modeling of interlayer heat and mass transfer between immiscible liquid layers and interfacial heat transfer to vertical and horizontal boundaries for the CORCON computer code. Criteria for the onset of entrainment between immiscible liquids, as well as the rate of entrainment and the rate of settling are developed, which are applicable for modeling of mass transport during core-concrete interactions. Heat transfer models are developed for the case of stratified layers as well as the case with mass entrainment between the layers. Finally, models for heat transfer with bubbling to horizontal, drilled surfaces as well as bubbling along vertical surfaces are presented which are appropriate for boundary heat transfer analyses during molten core- concrete interactions
Comparation of Models for Datamining
Gabriš, Ondrej
2009-01-01
S prudkým rozvojem informačních technologií neustále stoupá i množství vyprodukovaných dat a narůstá potřeba je rychle a efektivně zpracovávat za účelem odhalení skrytých znalostí obsažených v datech. Tahle práce se zabývá procesem dolování dat z databází, jeho jednotlivými fázemi, různými metodami pro dolování v datech a jejich porovnáním. Podrobně je analyzován model regrese, neuronové sítě a rozhodovacího stromu.V práci je též představen jeden z&nbs...
International Nuclear Information System (INIS)
Turbulent mixing zones that appear at the various interfaces of Inertial Confined Fusion (ICF) facilities can be modeled in 1D as multiphase flows mixtures. The difficulty with this type of modeling relies in the closure relations. We have started a research program based on a new homogenization method for multiphase flows. This method, used also for other applications (detonations and front propagations), is named the Discrete Equations Method (DEM). and is detailed in Abgrall and Saurel (2003) and Saurel et al. (2003a). The main advantage for the present application is that important closure relations like drag force and pressure relaxation rate are automatically. determined. Thank to this nice property, the rate of kinetic energy stored as turbulence has been determined in Saurel et al. (2003a) for a two-phase mixture of heavy and Light gases. It has been validated against direct numerical simulation of shock-bubble interaction. In the present paper we first recall the main results of this study. Second, we introduce plasma effects in both phases. The resulting multiphase model couples the dynamics of the two mixtures of ions and electrons under thermal non equilibrium. Turbulent effects are involved in each fluid. Turbulence is involved in the model by the way of an equation of state for thermodynamic turbulent variables. This thermodynamics of turbulence provides a simple and nice structure of equations. In this context, each fluid possesses its own density, velocity, pressures (ions, electrons. and turbulence) as well as associated internal energies. The resulting model involves 11 partial differential equations. It is unconditionally hyperbolic and involves non conservative terms that are correctly computed by the numerical scheme, even in the presence of shock wave and volume fraction discontinuities. A discrete equation method (DEM) based on the averaging of the discrete equations of pure inviscid turbulent plasmas has been proposed. It approximates
Molecular dynamics simulation of helium bubble coalescence in titanium
International Nuclear Information System (INIS)
Molecular dynamics simulations were performed to study the helium bubble coalescence in titanium. The influence of helium bubble coalescence on the metal microstructure was analyzed. The bubble coalescences in the bulk metal and near the metal surface were compared. When helium bubbles lie in the bulk metal, a lot of defects are induced around by the bubbles coalescence and extend outward. The coalescence of helium bubbles with 1.77 nm diameter can form a dislocation loop around them. The helium bubbles after coalescence evolve from dumbbell shape toward ellipsoid shape. When helium bubbles lie near the metal surface, the defects induced by bubbles coalescence are likely to move to the top surface, and the metal around bubble tends to restore the crystal structure. The helium bubbles evolve from dumbbell shape toward hemispherical shape. (authors)
Directory of Open Access Journals (Sweden)
Nemoda Stevan Đ.
2016-01-01
Full Text Available The paper presents a two-dimensional CFD model of liquid fuel combustion in bubbling fluidized bed. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The model is taking into account also the third - liquid phase, as well as its interaction with the solid and gas phase. The proposed numerical model comprise energy equations for all three phases, as well as the transport equations of chemical components with source terms originated from the component conversion. In the frame of the proposed model, user sub-models were developed for heterogenic fluidized bed combustion of liquid fuels, with or without water. The results of the calculation were compared with experiments on a pilot-facility (power up to 100 kW, combusting, among other fuels, oil. The temperature profiles along the combustion chamber were compared for the two basic cases: combustion with or without water. On the basis of numerical experiments, influence of the fluid-dynamic characteristics of the fluidized bed on the combustion efficiency was analyzed, as well as the influence of the fuel characteristics (reactivity, water content on the intensive combustion zone. [Projekat Ministarstva nauke Republike Srbije, br. TR33042: Improvement of the industrial fluidized bed facility, in scope of technology for energy efficient and environmentally feasible combustion of various waste materials in fluidized bed
Hydrodynamics of circulating and bubbling fluidized beds
International Nuclear Information System (INIS)
This paper reports that a review of modeling of the hydrodynamics of fluidization of bubbling beds showed that inviscid two-fluid models were able to predict a great deal of the behavior of bubbling beds because the dominant mechanism of energy dissipation is the drag between the particles and the fluid. The formation, the growth and the bursting of bubbles were predicted. Predicted wall-to-bed heat transfer coefficients and velocity profiles of jets agreed with measurements. Time average porosity distributions agreed with measurements done using gamma-ray densitometers without the use of any adjustable parameters. However, inviscid models could not correctly predict rates of erosion around tubes immersed into fluidized beds. To correctly model such behavior, granular stresses involving solids viscosity were added into the computer model. This viscosity arises due to random collision of particles. Several models fro this viscosity were investigated and the results compared to measurements of solids distributions in two-dimensional beds and to particle velocities reported in the literature. While in the case of bubbling beds the solids viscosity plays the role of a correction, modeling of a circulating fluidized bed (CFB) without a viscosity is not possible. Recent experimental data obtained at IIT and at IGT show that in CFB the solids viscous dissipation is responsible for as much as half of the pressure drop. From such measurement, solids viscosities were computed. These were used in the two fluid hydrodynamic model, to predict radial solids distributions and solids velocities which matched the experimental distributions. Most important, the model predicted cluster formation and transient internal circulation which is responsible for the favorable characteristics of CFBs, such as good wall-to-bed heat transfer. Video tape movies of computations compared favorably with high speed movies of the experiments
Computational analysis of ozonation in bubble columns
International Nuclear Information System (INIS)
This paper presents a new computational ozonation model based on the principle of computational fluid dynamics along with the kinetics of ozone decay and microbial inactivation to predict the performance of ozone disinfection in fine bubble columns. The model can be represented using a mixture two-phase flow model to simulate the hydrodynamics of the water flow and using two transport equations to track the concentration profiles of ozone and microorganisms along the height of the column, respectively. The applicability of this model was then demonstrated by comparing the simulated ozone concentrations with experimental measurements obtained from a pilot scale fine bubble column. One distinct advantage of this approach is that it does not require the prerequisite assumptions such as plug flow condition, perfect mixing, tanks-in-series, uniform radial or longitudinal dispersion in predicting the performance of disinfection contactors without carrying out expensive and tedious tracer studies. (author)
Directory of Open Access Journals (Sweden)
S. M. Burrows
2014-12-01
Full Text Available The presence of a large fraction of organic matter in primary sea spray aerosol (SSA can strongly affect its cloud condensation nuclei activity and interactions with marine clouds. Global climate models require new parameterizations of the SSA composition in order to improve the representation of these processes. Existing proposals for such a parameterization use remotely sensed chlorophyll a concentrations as a proxy for the biogenic contribution to the aerosol. However, both observations and theoretical considerations suggest that existing relationships with chlorophyll a, derived from observations at only a few locations, may not be representative for all ocean regions. We introduce a novel framework for parameterizing the fractionation of marine organic matter into SSA based on a competitive Langmuir adsorption equilibrium at bubble surfaces. Marine organic matter is partitioned into classes with differing molecular weights, surface excesses, and Langmuir adsorption parameters. The classes include a lipid-like mixture associated with labile dissolved organic carbon (DOC, a polysaccharide-like mixture associated primarily with semilabile DOC, a protein-like mixture with concentrations intermediate between lipids and polysaccharides, a processed mixture associated with recalcitrant surface DOC, and a deep abyssal humic-like mixture. Box model calculations have been performed for several cases of organic adsorption to illustrate the underlying concepts. We then apply the framework to output from a global marine biogeochemistry model, by partitioning total dissolved organic carbon into several classes of macromolecules. Each class is represented by model compounds with physical and chemical properties based on existing laboratory data. This allows us to globally map the predicted organic mass fraction of the nascent submicron sea spray aerosol. Predicted relationships between chlorophyll a and organic fraction are similar to existing empirical
Directory of Open Access Journals (Sweden)
Anna Sivachenko
2016-04-01
Full Text Available Debilitating neurodegenerative conditions with metabolic origins affect millions of individuals worldwide. Still, for most of these neurometabolic disorders there are neither cures nor disease-modifying therapies, and novel animal models are needed for elucidation of disease pathology and identification of potential therapeutic agents. To date, metabolic neurodegenerative disease has been modeled in animals with only limited success, in part because existing models constitute analyses of single mutants and have thus overlooked potential redundancy within metabolic gene pathways associated with disease. Here, we present the first analysis of a very-long-chain acyl-CoA synthetase (ACS double mutant. We show that the Drosophila bubblegum (bgm and double bubble (dbb genes have overlapping functions, and that the consequences of double knockout of both bubblegum and double bubble in the fly brain are profound, affecting behavior and brain morphology, and providing the best paradigm to date for an animal model of adrenoleukodystrophy (ALD, a fatal childhood neurodegenerative disease associated with the accumulation of very-long-chain fatty acids. Using this more fully penetrant model of disease to interrogate brain morphology at the level of electron microscopy, we show that dysregulation of fatty acid metabolism via disruption of ACS function in vivo is causal of neurodegenerative pathologies that are evident in both neuronal cells and their supporting cell populations, and leads ultimately to lytic cell death in affected areas of the brain. Finally, in an extension of our model system to the study of human disease, we describe our identification of an individual with leukodystrophy who harbors a rare mutation in SLC27a6 (encoding a very-long-chain ACS, a human homolog of bgm and dbb.
Bubble Generation in a Continuous Liquid Flow Under Reduced Gravity Conditions
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
Jumper, Kevin; Fisher, Robert
2012-03-01
Type Ia supernovae are astronomical events in which a white dwarf, the cold remnant of a star that has exhausted its hydrogen fuel, detonates and briefly produces an explosion brighter than most galaxies. Many researchers think that they could occur as the white dwarf approaches a critical mass of 1.4 solar masses by accreting matter from a companion main sequence star, a scenario that is referred to as the single-degenerate channel. Assuming such a progenitor, we construct a semi-analytic model of the propagation of a flame bubble ignited at a single off-center point within the white dwarf. The bubble then rises under the influences of buoyancy and drag, burning the surrounding fuel material in a process called deflagration. We contrast the behavior of the deflagration phase in the presence of a physically high Reynolds number regime with the low Reynolds number regimes inherent to three-dimensional simulations, which are a consequence of numerical viscosity. Our work may help validate three-dimensional deflagration results over a range of initial conditions.
Wetting of soap bubbles on hydrophilic, hydrophobic and superhydrophobic surfaces
Arscott, Steve
2013-01-01
Wetting of sessile bubbles on solid and liquid surfaces has been studied. A model is presented for the contact angle of a sessile bubble based on a modified Young equation - the experimental results agree with the model. A hydrophilic surface results in a bubble contact angle of 90 deg whereas on a superhydrophobic surface one observes 134 deg. 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.
Hydrodynamics in a swarm of rising bubbles
International Nuclear Information System (INIS)
In many applications, bubbles are used to agitate a liquid in order to enhance mixing and transfer. This work is devoted to the study of the hydrodynamics in a stable bubble column. Experimentally, we have determined the properties of the velocity fluctuations inside and behind a homogeneous swarm of rising bubbles for different bubble sizes and gas volume fractions α: self-similarity in α0,4, spectrum in k-3 and integral length scale controlled by buoyancy. Numerically, we have reproduced these properties by means of large-scale simulations, the bubbles being modeled by volume-forces. This confirms that the dynamics is controlled by wake interactions. (author)
High-speed photography of the bubble generated by an airgun
Energy Technology Data Exchange (ETDEWEB)
Langhammer, J.; Landroe, M. [IKU Petroleum Research, Trondheim (Norway)
1996-01-01
High-speed photography has been used visually to study the shape, surface, turbulence and behavior of an underwater oscillating bubble generated by an airgun. The source wa a BOLT airgun with a chamber volume of 1.6 cu.in., placed in a 0.85 m{sup 3} tank at 0.5 m depth. Near-field signatures were also recorded in order to compare the instant photographs of the oscillating bubble with the pressure field recorded about 25 cm from the gun. Estimations of the bubble-wall velocity and bubble radius estimated from high-speed film sequences are also presented, and are compared with modeled results. The deviation between the modeled and measured bubble radii was at most 9%. In order to check the capacity for transmission of light through the bubble, a concentrated laser beam was used as illumination. The authors found that the air bubble is a strong scattering medium of laser light, hence the bubble is opaque.
Chakraborty, Shubhankar; Roy Chaudhuri, Partha; Das, Prasanta Kr.
2016-07-01
In this communication, a novel optical technique has been proposed for the reconstruction of the shape of a Taylor bubble using measurements from multiple arrays of optical sensors. The deviation of an optical beam passing through the bubble depends on the contour of bubble surface. A theoretical model of the deviation of a beam during the traverse of a Taylor bubble through it has been developed. Using this model and the time history of the deviation captured by the sensor array, the bubble shape has been reconstructed. The reconstruction has been performed using an inverse algorithm based on Bayesian inference technique and Markov chain Monte Carlo sampling algorithm. The reconstructed nose shape has been compared with the true shape, extracted through image processing of high speed images. Finally, an error analysis has been performed to pinpoint the sources of the errors.
Comparing the Discrete and Continuous Logistic Models
Gordon, Sheldon P.
2008-01-01
The solutions of the discrete logistic growth model based on a difference equation and the continuous logistic growth model based on a differential equation are compared and contrasted. The investigation is conducted using a dynamic interactive spreadsheet. (Contains 5 figures.)
V&V Of CFD Modeling Of The Argonne Bubble Experiment: FY15 Summary Report
Energy Technology Data Exchange (ETDEWEB)
Hoyt, Nathaniel C. [Argonne National Lab. (ANL), Argonne, IL (United States); Wardle, Kent E. [Argonne National Lab. (ANL), Argonne, IL (United States); Bailey, James L. [Argonne National Lab. (ANL), Argonne, IL (United States); Basavarajappa, Manjunath [Univ. of Utah, Salt Lake City, UT (United States)
2015-09-30
In support of the development of accelerator-driven production of the fission product Mo 99, computational fluid dynamics (CFD) simulations of an electron-beam irradiated, experimental-scale bubble chamber have been conducted in order to aid in interpretation of existing experimental results, provide additional insights into the physical phenomena, and develop predictive thermal hydraulic capabilities that can be applied to full-scale target solution vessels. Toward that end, a custom hybrid Eulerian-Eulerian-Lagrangian multiphase solver was developed, and simulations have been performed on high-resolution meshes. Good agreement between experiments and simulations has been achieved, especially with respect to the prediction of the maximum temperature of the uranyl sulfate solution in the experimental vessel. These positive results suggest that the simulation methodology that has been developed will prove to be suitable to assist in the development of full-scale production hardware.
V&V Of CFD Modeling Of The Argonne Bubble Experiment: FY15 Summary Report
International Nuclear Information System (INIS)
In support of the development of accelerator-driven production of the fission product Mo 99, computational fluid dynamics (CFD) simulations of an electron-beam irradiated, experimental-scale bubble chamber have been conducted in order to aid in interpretation of existing experimental results, provide additional insights into the physical phenomena, and develop predictive thermal hydraulic capabilities that can be applied to full-scale target solution vessels. Toward that end, a custom hybrid Eulerian-Eulerian-Lagrangian multiphase solver was developed, and simulations have been performed on high-resolution meshes. Good agreement between experiments and simulations has been achieved, especially with respect to the prediction of the maximum temperature of the uranyl sulfate solution in the experimental vessel. These positive results suggest that the simulation methodology that has been developed will prove to be suitable to assist in the development of full-scale production hardware.
Black holes as bubble nucleation sites
International Nuclear Information System (INIS)
We consider the effect of inhomogeneities on the rate of false vacuum decay. Modelling the inhomogeneity by a black hole, we construct explicit Euclidean instantons which describe the nucleation of a bubble of true vacuum centred on the inhomogeneity. We find that inhomogeneity significantly enhances the nucleation rate over that of the Coleman-de Luccia instanton — the black hole acts as a nucleation site for the bubble. The effect is larger than previously believed due to the contributions to the action from conical singularities. For a sufficiently low initial mass, the original black hole is replaced by flat space during this process, as viewed by a single causal patch observer. Increasing the initial mass, we find a critical value above which a black hole remnant survives the process. This resulting black hole can have a higher mass than the original black hole, but always has a lower entropy. We compare the process to bubble-to-bubble transitions, where there is a semi-classical Lorentzian description in the WKB approximation
Effects of Gas Dynamics on Rapidly Collapsing Bubbles
Bauman, Spenser; Fomitchev-Zamilov, Max
2013-01-01
The dynamics of rapidly collapsing bubbles are of great interest due to the high degree of energy focusing that occurs withing the bubble. Molecular dynamics provides a way to model the interior of the bubble and couple the gas dynamics with the equations governing the bubble wall. While much theoretical work has been done to understand how a bubble will respond to an external force, the internal dynamics of the gas system are usually simplified greatly in such treatments. This paper shows ho...
Energy Technology Data Exchange (ETDEWEB)
Modak, Kamakshya Prasad; Majumdar, Debasish [Astroparticle Physics and Cosmology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Rakshit, Subhendu [Discipline of Physics, Indian Institute of Technology Indore, IET-DAVV Campus, Indore 452017 (India)
2015-03-09
We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of Ω{sub DM}, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles.
International Nuclear Information System (INIS)
We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of ΩDM, these candidates have larger annihilation cross-sections compared to the single-component DM models. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: the existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy γ-ray from galactic centre and Fermi bubble by Fermi Gamma-ray Space Telescope (FGST) already have the capability to distinguish between different DM halo profiles
Loss Given Default Modelling: Comparative Analysis
Yashkir, Olga; Yashkir, Yuriy
2013-01-01
In this study we investigated several most popular Loss Given Default (LGD) models (LSM, Tobit, Three-Tiered Tobit, Beta Regression, Inflated Beta Regression, Censored Gamma Regression) in order to compare their performance. We show that for a given input data set, the quality of the model calibration depends mainly on the proper choice (and availability) of explanatory variables (model factors), but not on the fitting model. Model factors were chosen based on the amplitude of their correlati...
Thermodynamic property of gases in the sonoluminescing bubble
Institute of Scientific and Technical Information of China (English)
AN Yu; LI Guiqin; ZHOU Tieying
2001-01-01
With the theory of statistical physics dealing with chemical reaction (the law of mass action), the different thermodynamic property of noble gases (mono-atomic gases) in a small bubble and diatomic gases in a small bubble semi-quantitatively are analyzed. As bubbles of the mono-atomic and the diatomic gases are compressed, shock waves are produced in both bubbles. Though shock wave leads to sharp increase of pressure and temperature of gases in the bubble, diatomic gas will excitated vibrations and dissociate themselves to mono-atomic gas,these processes will consume many accumulated heat energy and block the further increase of the temperature. Therefore, compare with the mono-atomic gases in the bubble, there will be no enough charged particles ionized to flash for diatomic gases in the bubble, this may be the reason why a bubble of diatomic gases has no single bubble sonoluminescence while a bubble of noble gases has.
Generation of pulsed discharge plasma in water with fine bubbles
Hayashi, Yui; Takada, Noriharu; Kanda, Hideki; Goto, Motonobu; Goto laboratory Team
2015-09-01
Recently, some researchers have proposed electric discharge methods with bubbles in water because the discharge plasma inside bubble was easy to be generated compared to that in water. Almost all of these methods introduced bubbles in the order of millimeter size from a nozzle placed in water. In these methods, bubbles rose one after another owing to high rising speed of millibubble, leading to inefficient gas consumption. We proposed fine bubbles introduction at the discharge area in water. A fine bubble is determined a bubble with less than 100 μm in a diameter. Fine bubbles exhibit extremely slow rising speed. Fine bubbles decrease in size during bubble rising and subsequently collapse in water with OH radical generation. Therefore, combining the discharge plasma with fine bubbles is expected to generate more active species with small amount of gas consumption. In this work, fine bubbles were introduced in water and pulsed discharge plasma was generated between two cylindrical electrodes which placed in water. We examined effects of fine bubbles on electric discharge in water when argon or oxygen gas was utilized as feed gas. Fine bubbles enhanced optical emission of hydrogen and oxygen atoms from H2O molecules, but that of feed gas was not observed. The formation mechanism of H2O2 by electric discharge was supposed to be different from that with no bubbling. Dissolved oxygen in water played a role in H2O2 formation by the discharge with fine bubbles.
Nemoda Stevan Đ.; Mladenović Milica R.; Paprika Milijana J.; Erić Aleksandar M.; Grubor Borislav D.
2016-01-01
The paper presents a two-dimensional CFD model of liquid fuel combustion in bubbling fluidized bed. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The model is taking into account also the third - liquid phase, as well as its interaction with the solid and gas phase. The proposed numerical model comprise energy equations for all three...
Merouani, Slimane; Hamdaoui, Oualid; Rezgui, Yacine; Guemini, Miloud
2013-05-01
Numerical simulation of chemical reactions inside an isolated spherical bubble of oxygen has been performed for various ambient bubble radii at different frequencies and acoustic amplitudes to study the effects of these two parameters on the range of ambient radius for an active bubble in sonochemical reactions. The employed model combines the dynamic of bubble collapse with the chemical kinetics of single cavitation bubble. Results from this model were compared with some experimental results presented in the literature and good apparent trends between them were observed. The numerical calculations of this study showed that there always exists an optimal ambient bubble radius at which the production of oxidizing species at the end of the bubble collapse attained their upper limit. It was shown that the range of ambient radius for an active bubble increased with increasing acoustic amplitude and decreased with increasing ultrasound frequency. The optimal ambient radius decreased with increasing frequency. Analysis of curves showing optimal ambient radius versus acoustic amplitude for different ultrasonic frequencies indicated that for 200 and 300kHz, the optimal ambient radius increased linearly with increasing acoustic amplitude up to 3atm. However, slight minima of optimal radius were observed for the curves obtained at 500 and 1000kHz. PMID:23187064
Neelakantaswamy, P. S.; Rajaratnam, A.; Kisdnasamy, S.; Das, N. P.
1985-02-01
Systematic errors in conductimetric measurements are often encountered due to partial screening of interelectrode current paths resulting from adhesion of bubbles on the electrode surfaces of the cell. A method of assessing this error quantitatively by a simulated electrolytic tank technique is proposed here. The experimental setup simulates the bubble-curtain effect in the electrolytic tank by means of a pair of electrodes partially covered by a monolayer of small polystyrene-foam spheres representing the bubble adhesions. By varying the number of spheres stuck on the electrode surface, the fractional area covered by the bubbles is controlled; and by measuring the interelectrode impedance, the systematic error is determined as a function of the fractional area covered by the simulated bubbles. A theoretical model which depicts the interelectrode resistance and, hence, the systematic error caused by bubble adhesions is calculated by considering the random dispersal of bubbles on the electrodes. Relevant computed results are compared with the measured impedance data obtained from the electrolytic tank experiment. Results due to other models are also presented and discussed. A time-domain measurement on the simulated cell to study the capacitive effects of the bubble curtain is also explained.
International Nuclear Information System (INIS)
Using Tc-99m as a radioactive tracer in a laboratory vortex bubble channel, it has been shown that the Markov-chain model is suitable for describing technical mixing processes with the aid of site-dependent diffusion coefficients. (author)
A Comparative of business process modelling techniques
Tangkawarow, I. R. H. T.; Waworuntu, J.
2016-04-01
In this era, there is a lot of business process modeling techniques. This article is the research about differences of business process modeling techniques. For each technique will explain about the definition and the structure. This paper presents a comparative analysis of some popular business process modelling techniques. The comparative framework is based on 2 criteria: notation and how it works when implemented in Somerleyton Animal Park. Each technique will end with the advantages and disadvantages. The final conclusion will give recommend of business process modeling techniques that easy to use and serve the basis for evaluating further modelling techniques.
SELF-SIMILARITY OF VERTICAL BUBBLY JETS
Directory of Open Access Journals (Sweden)
I. E. Lima Neto
2015-06-01
Full Text Available AbstractAn integral model for vertical bubbly jets with nearly monodisperse bubble sizes is presented. The model is based on the Gaussian type self-similarity of mean liquid velocity, bubble velocity and void fraction, as well as on functional relationships for initial liquid jet velocity and radius, bubble diameter and relative velocity. Adjusting the model to experimental data available in the literature for a wide range of densimetric Froude numbers provide constant values for the entrainment coefficient, momentum amplification factor, and spreading ratio of the bubble core for different flow conditions. Consistency and sensitivity of key model parameters are also verified. Overall, the deviations between model predictions and axial/radial profiles of mean liquid velocity, bubble velocity and void fraction are lower than about 20%, which suggests that bubbly jets tend to behave as self-preserving shear flows, similarly to single-phase jets and plumes. Furthermore, model simulations indicate a behavior similar to those of single-phase buoyant jets and slurry jets, but some differences with respect to confined bubbly jets are highlighted. This article provides not only a contribution to the problem of self-similarity in two-phase jets, but also a comprehensive model that can be used for analysis of artificial aeration/mixing systems involving bubbly jets.
Closure relations for CFD simulation of bubble columns
Ziegenhein, Thomas; Lucas, Dirk; Rzehak, Roland; Krepper, Eckhard
2014-01-01
This paper describes the modelling of bubbly flow in a bubble column considering non-drag forces, polydispersity and bubble induced turbulence using the Eulerian two-fluid approach. The set of used closure models describing the momentum exchange between the phases was chosen on basis of broad experiences in modelling bubbly flows at the Helmholtz-Zentrum Dresden-Rossendorf. Polydispersity is modeled using the inhomogeneous multiple size group (iMUSIG) model, which was developed...
Three-dimensional CFD simulation of bubble-melt two-phase flow with air injecting and melt stirring
International Nuclear Information System (INIS)
Highlights: → Gas-metallic turbulent flow induced by an impeller with an inclined shaft was studied. → A two-fluid model incorporated with the multiple reference frames method was used. → The bubble number density function was accounted for bubble breakup and coalescence. → Effects of gas flow rate and impeller speed on bubble size distribution were studied. - Abstract: This paper reports on progress in developing CFD simulations of gas bubble-metallic melt turbulent flows induced by a pitched-blade impeller with an inclined shaft. Foaming process of aluminum foams, in which air is injected into molten aluminum composites and the melt is mechanical stirred by the impeller, has been investigated. A two-fluid model, incorporated with the Multiple Reference Frames (MRF) method is used to predict the three-dimensional gas-liquid flow in the foaming tank, in which a stirring shaft is positioned inclined into the melt. Locally average bubble size is also predicted by additively solving a transport equation for the bubble number density function, which accounts for effects of bubble breakup and coalescence phenomena. The computed bubble sizes are compared with experimental data from our water model measurement and reasonable agreements are obtained. Further, simulated results show that the volume averaged total and local gas fractions are generally increased with rising impeller speed and gas flow rate. The local averaged bubble size increases with increasing gas flow rate and orifice diameter and decreasing liquid viscosity, and decreases also with rising rotation speed of the impeller.
Three-dimensional CFD simulation of bubble-melt two-phase flow with air injecting and melt stirring
Energy Technology Data Exchange (ETDEWEB)
Liu Hong, E-mail: hongliu@dlut.edu.cn [School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024 (China); Xie Maozhao; Li Ke [School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024 (China); Wang Deqing [College of Material Science and Engineering, Dalian Jiaotong University, Dalian 116024 (China)
2011-10-15
Highlights: > Gas-metallic turbulent flow induced by an impeller with an inclined shaft was studied. > A two-fluid model incorporated with the multiple reference frames method was used. > The bubble number density function was accounted for bubble breakup and coalescence. > Effects of gas flow rate and impeller speed on bubble size distribution were studied. - Abstract: This paper reports on progress in developing CFD simulations of gas bubble-metallic melt turbulent flows induced by a pitched-blade impeller with an inclined shaft. Foaming process of aluminum foams, in which air is injected into molten aluminum composites and the melt is mechanical stirred by the impeller, has been investigated. A two-fluid model, incorporated with the Multiple Reference Frames (MRF) method is used to predict the three-dimensional gas-liquid flow in the foaming tank, in which a stirring shaft is positioned inclined into the melt. Locally average bubble size is also predicted by additively solving a transport equation for the bubble number density function, which accounts for effects of bubble breakup and coalescence phenomena. The computed bubble sizes are compared with experimental data from our water model measurement and reasonable agreements are obtained. Further, simulated results show that the volume averaged total and local gas fractions are generally increased with rising impeller speed and gas flow rate. The local averaged bubble size increases with increasing gas flow rate and orifice diameter and decreasing liquid viscosity, and decreases also with rising rotation speed of the impeller.
Transient bubbles, bublets and breakup
Keen, Giles; Blake, John
1999-11-01
The non-spherical nature of the collapse of bubbles has important ramifications in many practical situations such as ultrasonic cleaning, tanning of leather, and underwater explosions. In particular the high speed liquid jet that can thread a collapsing bubble is central to the functional performance. An impressive photographic record of a liquid jet was obtained by Crum using a bubble situated in the vicinity of a platform oscillating vertically at a frequency of 60 Hz. A boundary integral method is used to model this situation and is found to closely mimic some of the observations. However, a slight variation of parameters or a change in the phase of the driving frequency can lead to dramatically different bubble behaviour, a feature also observed by Crum.
Energy Technology Data Exchange (ETDEWEB)
Burrows, Susannah M.; Ogunro, O.; Frossard, Amanda; Russell, Lynn M.; Rasch, Philip J.; Elliott, S.
2014-12-19
The presence of a large fraction of organic matter in primary sea spray aerosol (SSA) can strongly affect its cloud condensation nuclei activity and interactions with marine clouds. Global climate models require new parameterizations of the SSA composition in order to improve the representation of these processes. Existing proposals for such a parameterization use remotely-sensed chlorophyll-a concentrations as a proxy for the biogenic contribution to the aerosol. However, both observations and theoretical considerations suggest that existing relationships with chlorophyll-a, derived from observations at only a few locations, may not be representative for all ocean regions. We introduce a novel framework for parameterizing the fractionation of marine organic matter into SSA based on a competitive Langmuir adsorption equilibrium at bubble surfaces. Marine organic matter is partitioned into classes with differing molecular weights, surface excesses, and Langmuir adsorption parameters. The classes include a lipid-like mixture associated with labile dissolved organic carbon (DOC), a polysaccharide-like mixture associated primarily with semi-labile DOC, a protein-like mixture with concentrations intermediate between lipids and polysaccharides, a processed mixture associated with recalcitrant surface DOC, and a deep abyssal humic-like mixture. Box model calculations have been performed for several cases of organic adsorption to illustrate the underlying concepts. We then apply the framework to output from a global marine biogeochemistry model, by partitioning total dissolved organic carbon into several classes of macromolecule. Each class is represented by model compounds with physical and chemical properties based on existing laboratory data. This allows us to globally map the predicted organic mass fraction of the nascent submicron sea spray aerosol. Predicted relationships between chlorophyll-\\textit{a} and organic fraction are similar to existing empirical
Directory of Open Access Journals (Sweden)
S. M. Burrows
2014-03-01
Full Text Available The presence of a large fraction of organic matter in primary sea spray aerosol (SSA can strongly affect its cloud condensation nuclei activity and interactions with marine clouds. Global climate models require new parameterizations of the SSA composition in order to improve the representation of these processes. Existing proposals for such a parameterization use remotely-sensed chlorophyll a concentrations as a proxy for the biogenic contribution to the aerosol. However, both observations and theoretical considerations suggest that existing relationships with chlorophyll a, derived from observations at only a few locations, may not be representative for all ocean regions. We introduce a novel framework for parameterizing the fractionation of marine organic matter into SSA based on a competitive Langmuir adsorption equilibrium at bubble surfaces. Marine organic matter is partitioned into classes with differing molecular weights, surface excesses, and Langmuir adsorption parameters. The classes include a lipid-like mixture associated with labile dissolved organic carbon (DOC, a polysaccharide-like mixture associated primarily with semi-labile DOC, a protein-like mixture with concentrations intermediate between lipids and polysaccharides, a processed mixture associated with recalcitrant surface DOC, and a deep abyssal humic-like mixture. Box model calculations have been performed for several cases of organic adsorption to illustrate the underlying concepts. We then apply the framework to output from a global marine biogeochemistry model, by partitioning total dissolved organic carbon into several classes of macromolecules. Each class is represented by model compounds with physical and chemical properties based on existing laboratory data. This allows us to globally map the predicted organic mass fraction of the nascent submicron sea spray aerosol. Predicted relationships between chlorophyll a and organic fraction are similar to existing empirical
Local measurements in turbulent bubbly flows
International Nuclear Information System (INIS)
Local measurements methods in bubbly flows are discussed. Concerning liquid velocity measurement, problems linked to HFA and LDA are first analysed. Then simultaneously recorded velocity signals obtained by both anemometers are compared. New signal processing are developed for the two techniques. Bubble sizes and velocities measurements methods using intrusive double optical sensor probe are presented. Plane bubbly mixing layer has been investigated. Local measurements using the described methods are presented as examples. (author)
Prediction of adiabatic bubbly flows in TRACE using the interfacial area transport equation
International Nuclear Information System (INIS)
The conventional thermal-hydraulic reactor system analysis codes utilize a two-field, two-fluid formulation to model two-phase flows. To close this model, static flow regime transition criteria and algebraic relations are utilized to estimate the interfacial area concentration (ai). To better reflect the continuous evolution of two-phase flow, an experimental version of TRACE is being developed which implements the interfacial area transport equation (IATE) to replace the flow regime based approach. Dynamic estimation of ai is provided through the use of mechanistic models for bubble coalescence and disintegration. To account for the differences in bubble interactions and drag forces, two-group bubble transport is sought. As such, Group 1 accounts for the transport of spherical and distorted bubbles, while Group 2 accounts for the cap, slug, and churn-turbulent bubbles. Based on this categorization, a two-group IATE applicable to the range of dispersed two-phase flows has been previously developed. Recently, a one-group, one-dimensional, adiabatic IATE has been implemented into the TRACE code with mechanistic models accounting for: (1) bubble breakup due to turbulent impact of an eddy on a bubble, (2) bubble coalescence due to random collision driven by turbulent eddies, and (3) bubble coalescence due to the acceleration of a bubble in the wake region of a preceding bubble. To demonstrate the enhancement of the code's capability using the IATE, experimental data for ai, void fraction, and bubble velocity measured by a multi-sensor conductivity probe are compared to both the IATE and flow regime based predictions. In total, 50 air-water vertical co-current upward and downward bubbly flow conditions in pipes with diameters ranging from 2.54 to 20.32 cm are evaluated. It is found that TRACE, using the conventional flow regime relation, always underestimates ai. Moreover, the axial trend of the ai prediction is always quasi-linear because ai in the conventional
Effect of added mass on the interaction of bubbles in a low-Reynolds-number shear flow.
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. PMID:26986411
International Nuclear Information System (INIS)
High helium (He) production rates support the conditions for He nucleation in liquid metal (LM) breeding blankets. The formation of bubbles in the LM might have an important impact on the hydrodynamics and on the tritium transport. The issue of He bubbles formation is, hence, highly relevant to tritium inventory control and recovery. Models for tritium and helium transport phenomena involving He nucleation, bubble growth, T absorption into He bubbles, T adsorption onto structural material and desorption to cooling system channels (CSC) are implemented into OpenFOAM CFD code (BelFoam solver). The code is capable of solving the mass transfer between different materials with a conjugated scalar transfer algorithm, so it takes into account LM-structural material interface T transport. In the present work, BelFoam solver results for a geometrically simplified horizontalU-bent channel of a helium cooled lithiumlead (HCLL) breeding unit (BU) are shown. In addition, for the T absortion model, a sensitivity analysis to the mass transfer coefficient is presented together with an analysis of the results.
Wellness Model of Supervision: A Comparative Analysis
Lenz, A. Stephen; Sangganjanavanich, Varunee Faii; Balkin, Richard S.; Oliver, Marvarene; Smith, Robert L.
2012-01-01
This quasi-experimental study compared the effectiveness of the Wellness Model of Supervision (WELMS; Lenz & Smith, 2010) with alternative supervision models for developing wellness constructs, total personal wellness, and helping skills among counselors-in-training. Participants were 32 master's-level counseling students completing their…
Comparing Forecast Performance of Exchange Rate Models
Lillie Lam; Laurence Fung; Ip-wing Yu
2008-01-01
Exchange-rate movement is regularly monitored by central banks for macroeconomic-analysis and market-surveillance purposes. Notwithstanding the pioneering study of Meese and Rogoff (1983), which shows the superiority of the random-walk model in out-of-sample exchange-rate forecast, there is some evidence that exchange-rate movement may be predictable at longer time horizons. This study compares the forecast performance of the Purchasing Power Parity model, Uncovered Interest Rate Parity model...
Bubble Universes With Different Gravitational Constants
Takamizu, Yu-ichi; Maeda, Kei-ichi
2015-01-01
We argue a scenario motivated by the context of string landscape, where our universe is produced by a new vacuum bubble embedded in an old bubble and these bubble universes have not only different cosmological constants, but also their own different gravitational constants. We study these effects on the primordial curvature perturbations. In order to construct a model of varying gravitational constants, we use the Jordan-Brans-Dicke (JBD) theory where different expectation values of scalar fi...
International Nuclear Information System (INIS)
To predict the behavior of air-water two-phase flows in centrifugal pumps, we have proposed a three-dimensional numerical method on the basis of an inviscid bubbly flow model with slippage between two phases. The void fractions calculated distribute unevenly and their maximum exceeds an applicability of the model. To extend its applicability, a newly modified model is proposed in this paper by assuming that the bubbles in such high void fraction regions coalesce with each other and adhere to the neighboring impeller walls so as to form a fixed cavity. Using this model, the flows in a radial-flow pump are solved. The cavity obtained increases progressively from the shroud to the hub in the section just after the impeller inlet when the inlet void fraction exceeds a critical value and finally fills the section, showing close relation with the experiments when the pump loses its function due to an air-filled blockade. (author)
Comparative Analysis of Parametric Engine Model and Engine Map Model
Zeeshan Ali Memon; Sadiq Ali Shah; Muhammas Saleh Jumani
2015-01-01
Two different engine models, parametric engine model and engine map model are employed to analyze the dynamics of an engine during the gear shifting. The models are analyzed under critical transitional manoeuvres to investigate their appropriateness for vehicle longitudinal dynamics. The simulation results for both models have been compared. The results show the engine map model matches well with the parametric model and can be used for the vehicle longitudinal dynamics model. The proposed ap...
Stable bubble oscillations beyond Blake's critical threshold.
Hegedűs, Ferenc
2014-04-01
The equilibrium radius of a single spherical bubble containing both non-condensable gas and vapor is determined by the mechanical balance at the bubble interface. This expression highlights the fact that decreasing the ambient pressure below the so called Blake's critical threshold, the bubble has no equilibrium state at all. In the last decade many authors have tried to find evidence for the existence of stable bubble oscillation under harmonic forcing in this regime, that is, they have tried to stabilize the bubble motion applying ultrasonic radiation on the bubble. The available numerical results provide only partial proof for the existence as they are usually based on linearized or weakly nonlinear (higher order approximation) bubble models. Here, based on numerical techniques of the modern nonlinear and bifurcation theory, the existence of stable bubble motion has been proven without any restrictions in nonlinearities. Although the model, applied in this paper, is the rather simple Rayleigh-Plesset equation, the presented technique can be extended to more complex bubble models easily. PMID:24485747
Comparing flood loss models of different complexity
Schröter, Kai; Kreibich, Heidi; Vogel, Kristin; Riggelsen, Carsten; Scherbaum, Frank; Merz, Bruno
2013-04-01
Any deliberation on flood risk requires the consideration of potential flood losses. In particular, reliable flood loss models are needed to evaluate cost-effectiveness of mitigation measures, to assess vulnerability, for comparative risk analysis and financial appraisal during and after floods. In recent years, considerable improvements have been made both concerning the data basis and the methodological approaches used for the development of flood loss models. Despite of that, flood loss models remain an important source of uncertainty. Likewise the temporal and spatial transferability of flood loss models is still limited. This contribution investigates the predictive capability of different flood loss models in a split sample cross regional validation approach. For this purpose, flood loss models of different complexity, i.e. based on different numbers of explaining variables, are learned from a set of damage records that was obtained from a survey after the Elbe flood in 2002. The validation of model predictions is carried out for different flood events in the Elbe and Danube river basins in 2002, 2005 and 2006 for which damage records are available from surveys after the flood events. The models investigated are a stage-damage model, the rule based model FLEMOps+r as well as novel model approaches which are derived using data mining techniques of regression trees and Bayesian networks. The Bayesian network approach to flood loss modelling provides attractive additional information concerning the probability distribution of both model predictions and explaining variables.
DEFF Research Database (Denmark)
Engsted, Tom
2016-01-01
While Eugene Fama has repeatedly expressed his discontent with the notion of an “irrational bubble,” he has never publicly expressed his opinion on “rational bubbles.” On empirical grounds Fama rejects bubbles by referring to the lack of reliable evidence that price declines are predictable....... However, this argument cannot be used to rule out rational bubbles because such bubbles do not necessarily imply return predictability, and return predictability of the kind documented by Fama does not rule out rational bubbles. On data samples that include the 1990s, there is evidence of an explosive...
DEFF Research Database (Denmark)
Engsted, Tom
Eugene Fama has repeatedly expressed his discontent with the notion of an irrational bubble. However, he has never publicly expressed his opinion on rational bubbles. This is peculiar since such bubbles build naturally from the rational efficient markets paradigm that Fama strongly adheres to....... On empirical grounds Fama rejects bubbles by referring to the lack of reliable evidence that price declines are predictable. However, this argument cannot be used to rule out rational bubbles because such bubbles do not necessarily imply return predictability. On data samples that include the 1990s...
Single DNA denaturation and bubble dynamics
International Nuclear Information System (INIS)
While the Watson-Crick double-strand is the thermodynamically stable state of DNA in a wide range of temperature and salt conditions, even at physiological conditions local denaturation bubbles may open up spontaneously due to thermal activation. By raising the ambient temperature, titration, or by external forces in single molecule setups bubbles proliferate until full denaturation of the DNA occurs. Based on the Poland-Scheraga model we investigate both the equilibrium transition of DNA denaturation and the dynamics of the denaturation bubbles with respect to recent single DNA chain experiments for situations below, at, and above the denaturation transition. We also propose a new single molecule setup based on DNA constructs with two bubble zones to measure the bubble coalescence and extract the physical parameters relevant to DNA breathing. Finally we consider the interplay between denaturation bubbles and selectively single-stranded DNA binding proteins.
Xiao, Qingtai; Xu, Jianxin; Wang, Hua
2016-01-01
A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target. PMID:27527065
Xiao, Qingtai; Xu, Jianxin; Wang, Hua
2016-01-01
A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target. PMID:27527065
Energy Technology Data Exchange (ETDEWEB)
Munoz-Cobo, Jose L., E-mail: jlcobos@iqn.upv.es [Instituto de Ingenieria Energetica, Universidad Politecnica de Valencia, Valencia (Spain); Chiva, Sergio [Department of Mechanical Engineering and Construction, Universitat Jaume I, Castellon (Spain); Essa, Mohamed Ali Abd El Aziz [Instituto de Ingenieria Energetica, Universidad Politecnica de Valencia, Valencia (Spain); Mendes, Santos [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon (Mexico)
2012-01-15
Highlights: Black-Right-Pointing-Pointer We have simulated bubbly flow in vertical pipes by coupling a Lagrangian model to an Eulerian one, and to a 3D random walk model. Black-Right-Pointing-Pointer A set of experiments in a vertical column with isothermal co-current two phase flow have been performed and used to validate the previous model. Black-Right-Pointing-Pointer We have investigated the influence of the turbulence induced by the bubbles on the results. Black-Right-Pointing-Pointer Comparison of experimental and computed results has been performed for different boundary conditions. - Abstract: A set of two phase flow experiments for different conditions ranging from bubbly flow to cap/slug flow have been performed under isothermal concurrent upward air-water flow conditions in a vertical column of 3 m height. Special attention in these experiments was devoted to the transition from bubbly to cap/slug flow. The interfacial velocity of the bubbles and the void fraction distribution was obtained using 2 and 4 sensors conductivity probes. Numerical simulations of these experiments for bubbly flow conditions were performed by coupling a Lagrangian code with an Eulerian one. The first one tracks the 3D motion of the individual bubbles in cylindrical coordinates (r, {phi}, z) inside the fluid field under the action of the following forces: buoyancy, drag, lift, wall lubrication. Also we have incorporated a 3D stochastic differential equation model to account for the random motion of the individual bubbles in the turbulent velocity field of the carrier liquid. Also we have considered the deformations undergone by the bubbles when they touch the walls of the pipe and are compressed until they rebound. The velocity and turbulence fields of the liquid phase were computed by solving the time dependent conservation equations in its Reynolds Averaged Transport Equation form (RANS). The turbulent kinetic energy k, and the dissipation rate {epsilon} transport equations
Comparative study of void fraction models
International Nuclear Information System (INIS)
Some models for the calculation of void fraction in water in sub-cooled boiling and saturated vertical upward flow with forced convection have been selected and compared with experimental results in the pressure range of 1 to 150 bar. In order to know the void fraction axial distribution it is necessary to determine the net generation of vapour and the fluid temperature distribution in the slightly sub-cooled boiling region. It was verified that the net generation of vapour was well represented by the Saha-Zuber model. The selected models for the void fraction calculation present adequate results but with a tendency to super-estimate the experimental results, in particular the homogeneous models. The drift flux model is recommended, followed by the Armand and Smith models. (F.E.)
FEASTING BLACK HOLE BLOWS BUBBLES
2002-01-01
A monstrous black hole's rude table manners include blowing huge bubbles of hot gas into space. At least, that's the gustatory practice followed by the supermassive black hole residing in the hub of the nearby galaxy NGC 4438. Known as a peculiar galaxy because of its unusual shape, NGC 4438 is in the Virgo Cluster, 50 million light-years from Earth. These NASA Hubble Space Telescope images of the galaxy's central region clearly show one of the bubbles rising from a dark band of dust. The other bubble, emanating from below the dust band, is barely visible, appearing as dim red blobs in the close-up picture of the galaxy's hub (the colorful picture at right). The background image represents a wider view of the galaxy, with the central region defined by the white box. These extremely hot bubbles are caused by the black hole's voracious eating habits. The eating machine is engorging itself with a banquet of material swirling around it in an accretion disk (the white region below the bright bubble). Some of this material is spewed from the disk in opposite directions. Acting like high-powered garden hoses, these twin jets of matter sweep out material in their paths. The jets eventually slam into a wall of dense, slow-moving gas, which is traveling at less than 223,000 mph (360,000 kph). The collision produces the glowing material. The bubbles will continue to expand and will eventually dissipate. Compared with the life of the galaxy, this bubble-blowing phase is a short-lived event. The bubble is much brighter on one side of the galaxy's center because the jet smashed into a denser amount of gas. The brighter bubble is 800 light-years tall and 800 light-years across. The observations are being presented June 5 at the American Astronomical Society meeting in Rochester, N.Y. Both pictures were taken March 24, 1999 with the Wide Field and Planetary Camera 2. False colors were used to enhance the details of the bubbles. The red regions in the picture denote the hot gas
Probing nuclear bubble configuration by the $\\pi^{-}/\\pi^{+}$ ratio in heavy-ion collisions
Yong, Gao-Chan
2016-01-01
It is theoretically and experimentally argued that there may exist bubble or toroid-shaped configurations in some nucleus systems. Based on the nuclear transport model, it is shown that compared with the collision of normal nuclei, there is a depletion of central density of compression with bubble configurations in projectile and target nuclei. This depletion of central compression density may affect some observables in heavy-ion collisions.
Cavitation and bubble dynamics: the Kelvin impulse and its applications.
Blake, John R; Leppinen, David M; Wang, Qianxi
2015-10-01
Cavitation and bubble dynamics have a wide range of practical applications in a range of disciplines, including hydraulic, mechanical and naval engineering, oil exploration, clinical medicine and sonochemistry. However, this paper focuses on how a fundamental concept, the Kelvin impulse, can provide practical insights into engineering and industrial design problems. The pathway is provided through physical insight, idealized experiments and enhancing the accuracy and interpretation of the computation. In 1966, Benjamin and Ellis made a number of important statements relating to the use of the Kelvin impulse in cavitation and bubble dynamics, one of these being 'One should always reason in terms of the Kelvin impulse, not in terms of the fluid momentum…'. We revisit part of this paper, developing the Kelvin impulse from first principles, using it, not only as a check on advanced computations (for which it was first used!), but also to provide greater physical insights into cavitation bubble dynamics near boundaries (rigid, potential free surface, two-fluid interface, flexible surface and axisymmetric stagnation point flow) and to provide predictions on different types of bubble collapse behaviour, later compared against experiments. The paper concludes with two recent studies involving (i) the direction of the jet formation in a cavitation bubble close to a rigid boundary in the presence of high-intensity ultrasound propagated parallel to the surface and (ii) the study of a 'paradigm bubble model' for the collapse of a translating spherical bubble, sometimes leading to a constant velocity high-speed jet, known as the Longuet-Higgins jet. PMID:26442141
Interactions between bubble formation and heating surface in nucleate boiling
Energy Technology Data Exchange (ETDEWEB)
Luke, Andrea [Leibniz University, Hannover (Denmark). Inst. of Thermodynamics], e-mail: ift@ift.uni-hannover.de
2009-07-01
The heat transfer and bubble formation is investigated in pool boiling of propane. Size distributions of active nucleation sites on single horizontal copper and steel tubes with different diameter and surface finishes have been calculated from heat transfer measurements over wide ranges of heat flux and selected pressure. The model assumptions of Luke and Gorenflo for the heat transfer near growing and departing bubbles, which were applied in the calculations, have been slightly modified and the calculated results have been compared to experimental investigations by high speed video techniques. The calculated number of active sites shows a good coincidence for the tube with smaller diameter, while the results for the tube with larger diameter describe the same relative increase of the active sites. The comparison of the cumulative size distribution of the active and potential nucleation sites demonstrates the same slope of the curve and that the critical radius of a stable bubble nuclei is smaller than the average cavity size. (author)
Levine, Shellie-helane; And Others
1986-01-01
Introduces questions and activities involving soap bubbles which provide students with experiences in prediction and logic. Examines commonly held false conceptions related to the shapes that bubbles take and provides correct explanations for the phenomenon. (ML)
CFD simulation of bubble column
Energy Technology Data Exchange (ETDEWEB)
Ekambara, K., E-mail: ekambara@ualberta.c [Department of Chemical and Materials Engineering, University of Alberta, 536 CME Building, Edmonton, AB, T6G 2G6 (Canada); Dhotre, M.T. [Thermal-Hydraulics Laboratory, Nuclear Energy and Safety Department, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)
2010-05-15
Three-dimensional simulations of gas-liquid flow in the bubble column using the Euler-Euler approach is presented. The attempt is made to assess the performance and applicability of different turbulence models namely, k-epsilon, k-epsilon RNG, k-omega, Reynolds stress model (RSM) and large eddy simulation (LES) using a commercial code (ANSYS-CFX). For this purpose, the predictions are compared against the experimental data of . Performance of the turbulence models is assessed on basis of comparison of axial liquid velocity, fractional gas hold-up, turbulent kinetic energy and turbulent eddy dissipation rate. All the non-drag (turbulent dispersion, virtual mass and lift force) and drag force were incorporated in the model. The low-Reynolds number treatment of the k-omega yields a better qualitative prediction than the k-epsilon model. The RSM predictions are comparable with LES results and seemed to give better prediction near the sparger, where the flow is more anisotropic and gives a clue why RANS approaches fails to predict the flow in this region. However, the large eddy simulations showed good agreement with the experimental data, but requires higher computational time than RSM.
Dynamics of bubble growth for Rayleigh--Taylor unstable interfaces
International Nuclear Information System (INIS)
A statistical model is analyzed for the growth of bubbles in a Rayleigh--Taylor unstable interface. The model is compared to solutions of the full Euler equations for compressible two phase flow, using numerical solutions based on the method of front tracking. The front tracking method has the distinguishing feature of being a predominantly Eulerian method in which sharp interfaces are preserved with zero numerical diffusion. Various regimes in the statistical model exhibiting qualitatively distinct behavior are explored
Energy Technology Data Exchange (ETDEWEB)
Bayod, R.; Rodriguez Rodriguez, J.; Martinez Bazan, C.
2005-07-01
In this report, a simplified model of the break-up of an air bubble in a turbulent water flow is proposed and analyzed numerically. According to Hinze's theory, and our experimental observations, the external flow field is assumed asymmetric and irrotational for away from the bubble. furthermore the turbulent flow-field is modelled by an asymmetric hyperbolic flow-field and the evolution of the air-water interface is calculated by the levels-set method for a wide range of Reynolds and Weber numbers. Therefore, the break-up times are obtained for super-critical weber numbers and different Reynolds numbers. Therefore, the break-up times are obtained for super-critical Weber and Reynolds numbers allows the comparison of the numeric with our experimental results. Other possible break-up mechanisms for subcritical Weber number, i. e. the break-up by resonance, are also considered. (Author) 20 refs.
Energy Technology Data Exchange (ETDEWEB)
Vallebuona, G.; Casali, A.; Kracht, W.
2005-07-01
In this work, bubble size distribution is determined for tests in a batch flotation cells, for different impeller speed and air flowrate. Bubbles are sampled and their sizes are measured using image analysis. Size distributions by surface are expressed as cumulative percent passing as well as percent retained. The distributions show a common shape for all tests and are represented with a unique model, selected due to its goodness of fit. This model corresponds to an equation used in heavy media separation and considers two parameters: x{sub 5}0, the 50% passing size, and 1, an adjustable parameter. The correlation coefficient for all tests averages 0.999 for the cumulative distributions and 0.912 for the retained distributions. (Author) 15 refs.
Preheating in Bubble Collision
Zhang, Jun
2010-01-01
In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatically oscillating of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually high inelastic. The cosmological implications of this result are discussed.
Global Structure of Isothermal Diffuse X-Ray Emission along the Fermi Bubbles
Kataoka, J.; Tahara, M.; Totani, T.; Sofue, Y.; Inoue, Y.; Nakashima, S.; Cheung, C. C.
2015-07-01
In our previous works, we found absorbed thermal X-ray plasma with kT ≃ 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes | l| NPS), SE-claw, and NW-clump features. Moreover, the EM distribution of kT ≃ 0.30 keV plasma is highly asymmetric in the northern and southern bubbles. Although the association of the X-ray emission with the bubbles is not conclusive, we compare the observed EM properties with simple models assuming (i) a filled halo without bubbles, whose gas density follows a hydrostatic isothermal model (King profile), and (ii) a bubble-in-halo in which two identical bubbles expand into the halo, forming thick shells of swept halo gas. We argue that the EM profile in the north (b > 0°) favors (ii), whereas that of the south (b NPS (South Polar Spur). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles’ axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial conditions.
The Fermi bubbles as starburst wind termination shocks
Lacki, Brian C.
2014-10-01
The enhanced star formation in the inner 100 pc of the Galaxy launches a superwind at ˜1600 km s-1 for M82-like parameters. The ram pressure of the wind is very low compared to more powerful starburst winds. I show that halo gas stops the wind a few kpc from the Galactic Centre. I suggest that the termination shock accelerates cosmic rays, and that the resulting inverse Compton γ-rays are visible as the Fermi bubbles. The bubbles are then wind bubbles, which the starburst can inflate within 10 Myr. They can remain in steady state as long as the starburst lasts. The shock may accelerate PeV electrons and EeV protons. The bubbles may be analogues of galactic wind termination shocks in the intergalactic medium. I discuss the advantages and problems of this model. I note that any jets from Sgr A* must burrow through the starburst wind bubble before reaching the halo gas, which could affect the early evolution of such jets.
Numerical analysis of the bubble detachment diameter in nucleate boiling
International Nuclear Information System (INIS)
The present paper presents a tri-dimensional CFD (Computational Fluid Dynamics) model to investigate the fluid flow around bubbles attached to heated walls. Transient solutions of the governing field equations in a domain containing the bubbles and the surrounding liquid have been obtained. The nucleation, growing and detachment processes have been analyzed. Concerning the software, the open source OpenFOAM has been used. Special attention has been given to the bubble detachment diameter. Two mechanisms have been considered as physically related to the detachment: surface tension and buoyancy. As expected, it has been verified that the bubble detachment diameter depends on the contact angle, operating pressure and properties of the fluid. Several fluids have been considered (water, R134a, ammonia and R123), as well as several operating pressures (between 0.1 and 10 bar) and contact angles (between 10 and 80°). It has been concluded that the detachment diameter depends strongly on the contact angle and fluid properties and slightly on the pressure. A correlation for the bubble detachment diameter has been developed based on the obtained numerical results. Data from this expression compare reasonably well with those from other correlations from the literature.
Conservation of bubble size distribution during gas reactive absorption in bubble column reactors
Directory of Open Access Journals (Sweden)
P. L.C. LAGE
1999-12-01
Full Text Available Conservation of the bubble size distribution function was applied to the reactive absorption of carbon dioxide in a bubble column reactor. The model developed was solved by the method of characteristics and by a Monte Carlo method. Simulations were carried out using simplified models for the liquid phase and for the gas-liquid mass transfer. Predictions of gas holdup and outlet gas composition showed that the concept of a mean bubble diameter is not applicable when the bubble size distribution is reasonably polydispersed. In these cases, the mass mean velocity and the numerical mean velocity of the bubbles are very different. Therefore, quantification of the polydispersion of bubbles was shown to be essential to gas-phase hydrodynamics modeling.
High-contrast active cavitation imaging technique based on multiple bubble wavelet transform.
Lu, Shukuan; Xu, Shanshan; Liu, Runna; Hu, Hong; Wan, Mingxi
2016-08-01
In this study, a unique method that combines the ultrafast active cavitation imaging technique with multiple bubble wavelet transform (MBWT) for improving cavitation detection contrast was presented. The bubble wavelet was constructed by the modified Keller-Miksis equation that considered the mutual effect among bubbles. A three-dimensional spatial model was applied to simulate the spatial distribution of multiple bubbles. The effects of four parameters on the signal-to-noise ratio (SNR) of cavitation images were evaluated, including the following: initial radii of bubbles, scale factor in the wavelet transform, number of bubbles, and the minimum inter-bubble distance. And the other two spatial models and cavitation bubble size distributions were introduced in the MBWT method. The results suggested that in the free-field experiments, the averaged SNR of images acquired by the MBWT method was improved by 7.16 ± 0.09 dB and 3.14 ± 0.14 dB compared with the values of images acquired by the B-mode and single bubble wavelet transform (SBWT) methods. In addition, in the tissue experiments, the averaged cavitation-to-tissue ratio of cavitation images acquired by the MBWT method was improved by 4.69 ± 0.25 dB and 1.74± 0.29 dB compared with that of images acquired by B-mode and SBWT methods. PMID:27586732
Bubble motion through a generalized power-law fluid flowing in a vertical tube.
Mukundakrishnan, Karthik; Eckmann, David M; Ayyaswamy, P S
2009-04-01
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
Institute of Scientific and Technical Information of China (English)
QIU Jia; LIANG Jian; CHEN GuangMing; DU RuXu
2009-01-01
This paper presents a novel solar-powered absorption air conditioning system driven by a bubble pump with energy storage. It solves the problem of unreliable solar energy supply by storing the working fluids and hence, functions 24 h per day. First, the working principles are described and the dynamic models for the primary energy storage components are developed. Then, the system is evaluated based on a numerical simulation. Based on the meteorological data of a typical day in a subtropical area, with the area of a solar collector being set at 19.15 m2, whilst the initial charging mass, mass fraction and temperature of the solution are respectively set at 379.5 kg, 54.16% and 34.5 ℃, it is found that the respective coefficients of performance (COP) of the air conditioning system and the en-tire system (including the solar panel) are 0.7771 and 0.4372. In particular, the energy storage density of the system is 206.69 MJ/m3 which is much greater than those of chilled water or hot water storage systems under comparable conditions. This makes the new system much more compact and efficient. Finally, an automatic control strategy is given to achieve the highest COP when solar energy fluctuates.
Financial frictions, bubbles, and macroprudential policies
Derviz, Alexis
2011-01-01
Writer explores the ability of a macroprudential policy instrument to dampen the consequences of equity mispricing (a bubble) and the correction thereof (the bubble bursting), as well as the consequences for real activity in a production economy. In the model, producers are financed by both bank debt and equity, and face a mix of systemic and idiosyncratic uncertainty.
Comparing coefficients of nested nonlinear probability models
DEFF Research Database (Denmark)
Kohler, Ulrich; Karlson, Kristian Bernt; Holm, Anders
2011-01-01
In a series of recent articles, Karlson, Holm and Breen have developed a method for comparing the estimated coeffcients of two nested nonlinear probability models. This article describes this method and the user-written program khb that implements the method. The KHB-method is a general decomposi......In a series of recent articles, Karlson, Holm and Breen have developed a method for comparing the estimated coeffcients of two nested nonlinear probability models. This article describes this method and the user-written program khb that implements the method. The KHB-method is a general...... decomposition method that is unaffected by the rescaling or attenuation bias that arise in cross-model comparisons in nonlinear models. It recovers the degree to which a control variable, Z, mediates or explains the relationship between X and a latent outcome variable, Y*, underlying the nonlinear probability...... model. It also decomposes effects of both discrete and continuous variables, applies to average partial effects, and provides analytically derived statistical tests. The method can be extended to other models in the GLM-family....
Henderson, Rita K; Parsons, Simon A; Jefferson, Bruce
2008-07-01
In this paper we present an investigation into the use of bubbles modified with surfactants in dissolved air flotation (DAF). Bubble modification was investigated by dosing surfactants of varying character into the saturator of a DAF unit in turn. The cell removal efficiency only improved when using a cationic surfactant where optimum removal of Microcystis aeruginosa cells was obtained when using 0.0022-0.004 mequiv L(-1) surfactant. However, the magnitude of the removal differed according to the hydrophobicity of the surfactant. Typically, the more efficiently the surfactant adsorbed at the bubble interface, the better the removal efficiency. When the dose to saturator ratio was kept constant and the recycle ratio varied, the removal efficiency improved with increasing recycle ratio, reaching a maximum removal efficiency of 87% for M. aeruginosa. This value was comparable with that predicted by a theoretical model. The bubble collection efficiency of a maximum of two cells per bubble was constant irrespective of the influent cell number or recycle ratio. Treatment of additional species in this way revealed a relationship between increasing size and both increasing removal efficiency and decreasing surfactant dose, which is supported by theoretical relationships. PMID:18678021
Efficient bubbles for visual categorization tasks.
Wang, Hong Fang; Friel, Nial; Gosselin, Frederic; Schyns, Philippe G
2011-06-21
Bubbles is a classification image technique that randomly samples visual information from input stimuli to derive the diagnostic features that observers use in visual categorization tasks. To reach statistical significance, Bubbles performs an exhaustive and repetitive search in the stimulus space. To reduce the search trials, we developed an adaptive method that uses reinforcement learning techniques to optimize sampling by exploiting the observer's history of categorization. We compared the performance of the original and the adaptive Bubbles algorithms in a model observer and eight human adults who all resolved the same visual categorization task (i.e., five facial expressions of emotion). We demonstrate the feasibility of a substantial reduction (by a factor of ∼2) in the number of search trials required to locate the same diagnostic features with the adaptive method, but only when the observer reaches a performance threshold of 50% correct for each expression category. When this threshold is not reached, both the original and adaptive algorithms converge in the same number of trials. PMID:21524660
Comparative analysis of parametric engine model and engine map model
International Nuclear Information System (INIS)
Two different engine models, parametric engine model and engine map model are employed to analyze the dynamics of an engine during the gear shifting. The models are analyzed under critical transitional manoeuvres to investigate their appropriateness for vehicle longitudinal dynamics. The simulation results for both models have been compared. The results show the engine map model matches well with the parametric model and can be used for the vehicle longitudinal dynamics model. The proposed approach can be useful for the selection of the appropriate vehicle for the given application. (author)
International Nuclear Information System (INIS)
This work is a part of a long term project that aims at using two-phase Direct Numerical Simulation (DNS) in order to give information to averaged models. For now, it is limited to isothermal bubbly flows with no phase change. It could be subdivided in two parts: Firstly, theoretical developments are made in order to build an equivalent of Large Eddy Simulation (LES) for two phase flows called Interfaces and Sub-grid Scales (ISS). After the implementation of the ISS model in our code called TrioU, a set of various cases is used to validate this model. Then, special test are made in order to optimize the model for our particular bubbly flows. Thus we showed the capacity of the ISS model to produce a cheap pertinent solution. Secondly, we use the ISS model to perform simulations of bubbly flows in column. Results of these simulations are averaged to obtain quantities that appear in mass, momentum and interfacial area density balances. Thus, we processed to an a priori test of a complete one dimensional averaged model.We showed that this model predicts well the simplest flows (laminar and monodisperse). Moreover, the hypothesis of one pressure, which is often made in averaged model like CATHARE, NEPTUNE and RELAP5, is satisfied in such flows. At the opposite, without a polydisperse model, the drag is over-predicted and the uncorrelated Ai flux needs a closure law. Finally, we showed that in turbulent flows, fluctuations of velocity and pressure in the liquid phase are not represented by the tested averaged model. (author)
DEFF Research Database (Denmark)
Hyldegaard, Ole; Kerem, Dikla; Melamed, Y
2011-01-01
while at 285 kPa or following immediate recompression to either 285 or 405 kPa, breathing 80:20 and 50:50 heliox mixtures. During the isobaric shifts, some bubbles in adipose tissue grew marginally for 10-30 min, subsequently they shrank and disappeared at a rate similar to or faster than during air...... shrinkage of all air bubbles, until they disappeared from view. Deep tissue isobaric counterdiffusion may cause some air bubbles to grow transiently in adipose tissue. The effect is marginal and of no clinical consequence. Bubble disappearance rate is faster with heliox breathing mixtures as compared to air......Deep tissue isobaric counterdiffusion that may cause unwanted bubble formation or transient bubble growth has been referred to in theoretical models and demonstrated by intravascular gas formation in animals, when changing inert breathing gas from nitrogen to helium after hyperbaric air breathing...
Vertical downward subcooled bubbly flow modelling with RELAP5/MOD3.2.2 gamma
International Nuclear Information System (INIS)
The presented paper will consider the correlation for void fraction distribution in the subcooled boiling flow regime of downward liquid flow at low velocities. More specifically, it will focus on the choice of the most appropriate heat and mass transfer correlation. The experimental findings and theoretical consideration of these processes and phenomena will be compared with RELAP5/MOD3.2.2 Gamma predictions. (author)
Numerical derivation of the drag force coefficient in bubble swarms using a Front Tracking model
Dijkhuizen, Wouter; Roghair, Ivo; Sint Annaland, van Martin; Kuipers, Hans
2008-01-01
Dispersed gas-liquid flows are often encountered in the chemical process industry. Large scale models which describe the overall behavior of these flows use closure relations to account for the interactions between the phases, such as the drag, lift and virtual mass forces. The closure relations for
Ammonia volatilization from treatment lagoons varies widely with the total ammonia concentration, pH, temperature, suspended solids, atmospheric ammonia concentration above the water surface, and wind speed. Ammonia emissions were estimated with a process-based mechanistic model integrating ammonia ...
Watson, C; Churchwell, E B; Babler, B L; Povich, M S; Meade, M R; Whitney, B A
2009-01-01
We present an analysis of late-O/early-B-powered, parsec-sized bubbles and associated star-formation using 2MASS, GLIMPSE, MIPSGAL and MAGPIS surveys. Three bubbles were selected from the Churchwell et al. (2007) catalog. We confirm that the structure identified in Watson et al. (2008) holds in less energetic bubbles, i.e. a PDR, identified by 8 um emission due to PAHs surrounds hot dust, identified by 24 um emission and ionized gas, identified by 20 cm continuum. We estimate the dynamical age of two bubbles by comparing bubble sizes to numerical models of Hosokawa & Inutsuka (2006). We also identify and analyze candidate young stellar objects (YSOs) using SED fitting and identify sites of possible triggered star-formation. Lastly, we identify likely ionizing sources for two sources based on SED fitting.
Gas-bubble growth mechanisms in the analysis of metal fuel swelling
International Nuclear Information System (INIS)
During steady-state irradiation, swelling rates associated with growth of fission-gas bubbles in metallic fast reactor fuels may be expected to remain small. As a consequence, bubble-growth mechanisms are not a major consideration in modeling the steady-state fuel behavior, and it is usually adequate to consider the gas pressure to be in equilibrium with the external pressure and surface tension restraint. On transient time scales, however, various bubble-growth mechanisms become important components of the swelling rate. These mechanisms include growth by diffusion, for bubbles within grains and on grain boundaries; dislocation nucleation at the bubble surface, or ''punchout''; and bubble growth by creep. Analyses of these mechanisms are presented and applied to provide information on the conditions and the relative time scales for which the various processes should dominate fuel swelling. The results are compared to a series of experiments in which the swelling of irradiated metal fuel was determined after annealing at various temperatures and pressures. The diffusive growth of bubbles on grain boundaries is concluded to be dominant in these experiments
Coarse-Grained Fluctuation Probabilities in the Standard Model and Subcritical Bubbles
Bettencourt, Luis M. A.
1995-01-01
We compute systematically the probability for fluctuations of the Higgs field, averaged over a given spatial scale, to exceed a specified value, in the Standard Model. For the particular case of interest of averages over one coherence volume we show that, even in the worst possible case of taking the one-loop improved effective potential parameters, the probability for the field to fluctuate from the symmetric to the asymmetric minimum before the latter becomes stable is very small for Higgs ...
Bubble spreading during the boiling crisis: modelling and experimenting in microgravity
Nikolayev, Vadim; Beysens, D.; Garrabos, Yves; Lecoutre, Carole; Chatain, D.
2006-01-01
International audience Boiling is a very efficient way to transfer heat from a heater to the liquid carrier. We discuss the boiling crisis, a transition between two regimes of boiling: nucleate and film boiling. The boiling crisis results in a sharp decrease in the heat transfer rate, which can cause a major accident in industrial heat exchangers. In this communication, we present a physical model of the boiling crisis based on the vapor recoil effect. Under the action of the vapor recoil ...
Bubble Manipulation by Self Organization of Bubbles inside Ultrasonic Wave
Yamakoshi, Yoshiki; Koganezawa, Masato
2005-06-01
Microbubble manipulation using ultrasonic waves is a promising technology in the fields of future medicine and biotechnology. For example, it is considered that bubble trapping using ultrasonic waves may play an important role in drug or gene delivery systems in order to trap the drugs or genes in the diseased tissue. Usually, when bubbles are designed so that they carry payloads, such as drug or gene, they tend to be harder than free bubbles. These hard bubbles receive a small acoustic radiation force, which is not sufficient for bubble manipulation. In this paper, a novel method of microbubble manipulation using ultrasonic waves is proposed. This method uses seed bubbles in order to manipulate target bubbles. When the seed bubbles are introduced into the ultrasonic wave field, they start to oscillate to produce a bubble aggregation of a certain size. Then the target bubbles are introduced, the target bubbles attach around the seed bubbles producing a bubble mass with bilayers (inner layer: seed bubbles, outer layer: target bubbles). The target bubbles are manipulated as a bilayered bubble mass. Basic experiments are carried out using polyvinyl chloride (PVC) shell bubbles. No target bubbles are trapped when only the target bubbles are introduced. However, they are trapped if the seed bubbles are introduced in advance.
Multiphase flow analysis using population balance modeling bubbles, drops and particles
Yeoh, Guan Heng; Tu, Jiyuan
2013-01-01
Written by leading multiphase flow and CFD experts, this book enables engineers and researchers to understand the use of PBM and CFD frameworks. Population balance approaches can now be used in conjunction with CFD, effectively driving more efficient and effective multiphase flow processes. Engineers familiar with standard CFD software, including ANSYS-CFX and ANSYS-Fluent, will be able to use the tools and approaches presented in this book in the effective research, modeling and control of multiphase flow problems. Builds a complete understanding of the theory behind the
Czech Academy of Sciences Publication Activity Database
Cincibusová, Petra; Němec, L.
2015-01-01
Roč. 56, č. 2 (2015), s. 52-62. ISSN 1753-3546 R&D Projects: GA TA ČR TA01010844 Institutional support: RVO:67985891 Keywords : glass melt * mathematical modelling * controlled flow * space utilization * temperature gradients Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 0.290, year: 2014 http://www.ingentaconnect.com/content/sgt/gta/2015/00000056/00000002/art00003
Directory of Open Access Journals (Sweden)
Steven P. Wrenn, Stephen M. Dicker, Eleanor F. Small, Nily R. Dan, Michał Mleczko, Georg Schmitz, Peter A. Lewin
2012-01-01
Full Text Available This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol (PEG - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented
Bursting SN 1996cr's Bubble: Hydrodynamic and X-ray Modeling of its Circumstellar Medium
Dwarkadas, Vikram V; Bauer, Franz
2010-01-01
SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with ...
A Non-Equilibrium Ionization Model of the Local and Loop I Bubbles - Tracing the Ovi Distribution
de Avillez, Miguel A; Spitoni, Emanuele; Carvalho, Nuno
2011-01-01
We present the first to date three-dimensional high-resolution hydrodynamical simulation tracing the non-equilibrium ionization evolution (using the Eborae Atomic and Molecular Plasma Emission Code - E(A+M)PEC) of the Local Bubble and Loop I superbubbles embedded in a turbulent supernova-driven interstellar medium.
Energy Technology Data Exchange (ETDEWEB)
Modekurti, Srinivasarao; Bhattacharyya, Debangsu; Zitney, Stephen E.
2013-07-31
A one-dimensional, non-isothermal, pressure-driven dynamic model has been developed for a two-stage bubbling fluidized bed (BFB) adsorber-reactor for solid-sorbent carbon dioxide (CO{sub 2}) capture using Aspen Custom Modeler® (ACM). The BFB model for the flow of gas through a continuous phase of downward moving solids considers three regions: emulsion, bubble, and cloud-wake. Both the upper and lower reactor stages are of overflow-type configuration, i.e., the solids leave from the top of each stage. In addition, dynamic models have been developed for the downcomer that transfers solids between the stages and the exit hopper that removes solids from the bottom of the bed. The models of all auxiliary equipment such as valves and gas distributor have been integrated with the main model of the two-stage adsorber reactor. Using the developed dynamic model, the transient responses of various process variables such as CO{sub 2} capture rate and flue gas outlet temperatures have been studied by simulating typical disturbances such as change in the temperature, flowrate, and composition of the incoming flue gas from pulverized coal-fired power plants. In control studies, the performance of a proportional-integral-derivative (PID) controller, feedback-augmented feedforward controller, and linear model predictive controller (LMPC) are evaluated for maintaining the overall CO{sub 2} capture rate at a desired level in the face of typical disturbances.
Bubble growth and rise in soft sediments
Boudreau, Bernard P.; Algar, Chris; Johnson, Bruce D.; Croudace, Ian; Reed, Allen; Furukawa, Yoko; Dorgan, Kelley M.; Jumars, Peter A.; Grader, Abraham S.; Gardiner, Bruce S.
2005-06-01
The mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance. We offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory. Natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids (disks) that grow either by fracturing the sediment or by reopening preexisting fractures. In contrast, bubbles in soft sandy sediment tend to be spherical, suggesting that sand acts fluidly or plastically in response to growth stresses. We also present bubble-rise results from gelatin, a mechanically similar but transparent medium, that suggest that initial rise is also accomplished by fracture. Given that muddy sediments are elastic and yield by fracture, it becomes much easier to explain physically related phenomena such as seafloor pockmark formation, animal burrowing, and gas buildup during methane hydrate melting.
Bubble Universes With Different Gravitational Constants
Takamizu, Yu-ichi
2015-01-01
We argue a scenario motivated by the context of string landscape, where our universe is produced by a new vacuum bubble embedded in an old bubble and these bubble universes have not only different cosmological constants, but also their own different gravitational constants. We study these effects on the primordial curvature perturbations. In order to construct a model of varying gravitational constants, we use the Jordan-Brans-Dicke (JBD) theory where different expectation values of scalar fields produce difference of constants. In this system, we investigate the nucleation of bubble universe and dynamics of the wall separating two spacetimes. In particular, the primordial curvature perturbation on superhorizon scales can be affected by the wall trajectory as the boundary effect. We show the effect of gravitational constant in the exterior bubble universe can provide a peak like a bump feature at a large scale in a modulation of power spectrum.
Microwave excitation of submerged plasma bubbles
International Nuclear Information System (INIS)
Steady-state models were formulated for spherical plasma bubbles, excited in water by an external microwave radiation source. The bubbles were assumed to be at rest relative to the surrounding water, and the energy absorbed by the plasma was balanced by energy loss through thermal conductance and convection to the surrounding water. Two regimes were considered: (1) bubbles with radii R less than the skin depth δ, i.e. R δ. A self-consistent system of equations was formulated. In the R δ case obtained for strong electric fields was larger than in the R δ bubbles had an isothermal core and power from the microwave field was absorbed in a relatively thin layer in the plasma bubble. (paper)
Fundamental of Inclusion Removal from Molten Steel by Rising Bubble
Institute of Scientific and Technical Information of China (English)
WANG Li-tao; ZHANG Qiao-ying; LI Zheng-bang; XUE Zheng-liang
2004-01-01
The mechanism of inclusion removal by attachment to rising bubble was analyzed, and the movement behavior of inclusion, the mechanism of bubbles/inclusion interaction, collision probability and adhesion probability were discussed. A mathematical model of inclusion removal from molten steel by attachment to fine bubble was developed. The results of theoretical analysis and mathematical model showed that the optimum bubble diameter for inclusion removal is 1 to 2 mm. A new method that argon is injected into the shroud from ladle to tundish during continuous casting has been proposed to produce fine bubble. It provides theoretical guides for production of super clean steel.
Energy Technology Data Exchange (ETDEWEB)
Minemura, Kiyoshi; Uchiyama, Tomomi (Nagoya Univ. (Japan)); Ihara, Masaru; Furukawa, Hironori
1994-03-01
Effects of outlet blade angle and rotational speed on the two-phase-flow pump performance are discussed based on the results calculated by a three-dimensional bubbly flow model with fixed cavity. Critical volumetric flow ratio of air to whole fluid, at which the fixed cavity on the shroud near the impeller inlet section expands rapidly to fill the section, decreases with an increases in the outlet blade angle and increases with an increase in the rotational speed. To predict the theoretical head for the higher volumetric flow ratio, the one-dimensional two-fluid model by Furuya is also applied and modified for low-specific-speed pumps. (author).
Experiment and Numerical Simulation of Bubble Behavior in Argon Gas Injection into Lead-Bismuth Pool
Yamada, Yumi; Akashi, Toyou; Takahashi, Minoru
In a lead-bismuth alloy (45%Pb-55%Bi) cooled direct contact boiling water fast reactor (PBWFR), steam can be produced by direct contact of feed water with primary Pb-Bi coolant in the upper core plenum, and Pb-Bi coolant can be circulated by buoyancy forces of steam bubbles. As a basic study to investigate the two-phase flow characteristics in the chimneys of PBWFR, a two-dimensional two-phase flow was simulated by injecting argon gas into Pb-Bi pool in a rectangular vessel (400mm in length, 1500mm in height), and bubble behavior were investigated experimentally. Bubble sizes, bubble rising velocities and void fractions were measured using void probes. The experimental conditions are the atmospheric pressure and the flow rate of injection Ar gas is 10, 20, and 30 NL/min. The average of measured bubble rising velocity was about 0.6 m/s. The average chord length was about 7mm. An analysis was performed by two-dimensional and two-fluid model. The experimental results were compared with the analytical results to evaluate the validity of the analytical model. Although large diameter bubbles were observed in the experiment, the drag force model of lower value performed better for simulation of the experimental result.
Wildeman, Sander; Sun, Chao; Lohse, Detlef; Prosperetti, Andrea
2016-01-01
We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rubbing force and velocity exceed a certain threshold. Direct observation through a transparent solid shows that each bubble in the trail results from the early coalescence of several microscopic bubbles, themselves detaching from microscopic gas pockets forming between the solids. From a detailed study of the wear tracks, with atomic force and scanning electron microscopy imaging, we conclude that these microscopic gas pockets originate from a local fracturing of the surface asperities, possibly enhanced by chemical reactions at the freshly created surfaces. Our findings will be useful either for preventing undesired bubble formation or, on the contrary, for "writing with bubbles," i.e., creating controlled patterns ...
Mass transport by buoyant bubbles in galaxy clusters
Pope, Edward C. D.; Babul, Arif; Pavlovski, Georgi; Bower, Richard G.; Dotter, Aaron
2010-08-01
We investigate the effect of three important processes by which active galactic nuclei (AGN)-blown bubbles transport material: drift, wake transport and entrainment. The first of these, drift, occurs because a buoyant bubble pushes aside the adjacent material, giving rise to a net upward displacement of the fluid behind the bubble. For a spherical bubble, the mass of upwardly displaced material is roughly equal to half the mass displaced by the bubble and should be ~ 107-9 Msolar depending on the local intracluster medium (ICM) and bubble parameters. We show that in classical cool-core clusters, the upward displacement by drift may be a key process in explaining the presence of filaments behind bubbles. A bubble also carries a parcel of material in a region at its rear, known as the wake. The mass of the wake is comparable to the drift mass and increases the average density of the bubble, trapping it closer to the cluster centre and reducing the amount of heating it can do during its ascent. Moreover, material dropping out of the wake will also contribute to the trailing filaments. Mass transport by the bubble wake can effectively prevent the buildup of cool material in the central galaxy, even if AGN heating does not balance ICM cooling. Finally, we consider entrainment, the process by which ambient material is incorporated into the bubble. Studies of observed bubbles show that they subtend an opening angle much larger than predicted by simple adiabatic expansion. We show that bubbles that entrain ambient material as they rise will expand faster than the adiabatic prediction; however, the entrainment rate required to explain the observed opening angle is large enough that the density contrast between the bubble and its surroundings would disappear rapidly. We therefore conclude that entrainment is unlikely to be a dominant mass transport process. Additionally, this also suggests that the bubble surface is much more stable against instabilities that promote
Youssefmir, M; Hogg, T; Youssefmir, Michael; Huberman, Bernardo; Hogg, Tad
1994-01-01
We present a dynamical theory of asset price bubbles that exhibits the appearance of bubbles and their subsequent crashes. We show that when speculative trends dominate over fundamental beliefs, bubbles form, leading to the growth of asset prices away from their fundamental value. This growth makes the system increasingly susceptible to any exogenous shock, thus eventually precipitating a crash. We also present computer experiments which in their aggregate behavior confirm the predictions of the theory.
Inexperienced Investors and Bubbles
Robin Greenwood; Stefan Nagel
2008-01-01
We use mutual fund manager data from the technology bubble to examine the hypothesis that inexperienced investors play a role in the formation of asset price bubbles. Using age as a proxy for managers' investment experience, we find that around the peak of the technology bubble, mutual funds run by younger managers are more heavily invested in technology stocks, relative to their style benchmarks, than their older colleagues. Furthermore, young managers, but not old managers, exhibit trend-ch...
Sonoluminescence and bubble fusion
Arakeri, Vijay H
2003-01-01
Sonoluminescence (SL), the phenomenon of light emission from nonlinear motion of a gas bubble, involves an extreme degree of energy focusing. The conditions within the bubble during the last stages of the nearly catastrophic implosion are thought to parallel the efforts aimed at developing inertial confinement fusion. A limited review on the topic of SL and its possible connection to bubble nuclear fusion is presented here. The emphasis is on looking for a link between the various forms o...
Feng, Yuqing; Schwarz, M. Philip; Yang, William; Cooksey, Mark
2015-08-01
A two-phase computational fluid dynamics (CFD) model has been developed to simulate the time-averaged flow in the molten electrolyte layer of a Hall -Héroult aluminum cell. The flow is driven by the rise of carbon dioxide bubbles formed on the base of the anodes. The CFD model has been validated against detailed measurements of velocity and turbulence taken in a full-scale air-water physical model containing three anodes in four different configurations, with varying inter-anode gap and the option of slots. The model predictions agree with the measurements of velocity and turbulence energy for all configurations within the likely measurement repeatability, and therefore can be used to understand the overall electrolyte circulation patterns and mixing. For example, the model predicts that the bubble holdup under an anode is approximately halved by the presence of a slot aligned transverse to the cell long axis. The flow patterns do not appear to be significantly altered by halving the inter-anode gap width from 40 to 20 mm. The CFD model predicts that the relative widths of center, side, and end channels have a major influence on several critical aspects of the cell flow field.
Miller
2011-01-01
The book aims at describing the most important experimental methods for characterizing liquid interfaces, such as drop profile analysis, bubble pressure and drop volume tensiometry, capillary pressure technique, and oscillating drops and bubbles. Besides the details of experimental set ups, also the underlying theoretical basis is presented in detail. In addition, a number of applications based on drops and bubbles is discussed, such as rising bubbles and the very complex process of flotation. Also wetting, characterized by the dynamics of advancing contact angles is discussed critically. Spec
Magma mixing enhanced by bubble segregation
Wiesmaier, S.; Morgavi, D.; Renggli, C. J.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.
2015-08-01
In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be
International Nuclear Information System (INIS)
In this work, the dynamics of multiple cavitation bubbles produced by femtosecond laser ablation of a palladium target submerged in acetone is studied by means of time-resolved fast shadowgraphy technique. The data have evidenced the periodic growth and collapse of the bubbles and the consequent emission of material together with the role played by the laser focus position. Comparing the results with the previsions of the Rayleigh–Plesset model a good agreement is found. The nanoparticles obtained under different focusing conditions are characterized by means of TEM analysis. Their dimension and distribution are correlated with the bubbles dynamics. (paper)
The interaction between multiple bubbles and the free surface
Institute of Scientific and Technical Information of China (English)
Zhang A-Man; Yao Xiong-Liang
2008-01-01
The flow is assumed to be potential, and a boundary integral method is used to solve the Laplace equation for the velocity potential to investigate the shape and the position of the bubble. A 3D code to study the bubble dynamics is developed, and the calculation results agree well with the experimental data. Numerical analyses are carried out for the interaction between multiple bubbles near the free surface including in-phase and out-of-phase bubbles. The calculation result shows that the bubble period increases with the decrease of the distance between bubble centres because of the depression effect between multiple bubbles. The depression has no relationship with the free surface and it is more apparent for out-of-phase bubbles. There are great differences in dynamic behaviour between the in-phase bubbles and the out-of-phase bubbles due to the depression effect. Furthermore, the interaction among eight bubbles is simulated with a three-dimensional model, and the evolving process and the relevant physical phenomena are presented. These phenomena can give a reference to the future work on the power of bubbles induced by multiple charges exploding simultaneously or continuously.
涌泉根灌土壤湿润体运移模型%Prediction model of wetted front migration distance under bubbled-root irrigation
Institute of Scientific and Technical Information of China (English)
张智韬; 吴普特; 陈俊英; 朱德兰; 樊晓康
2013-01-01
In order to further research the characteristic variation of wetting body in bubbled-root irrigation , the following four factors as different soil bulk density, initial soil moisture, the length and burying depth of pervious sleeve of emitter of clay loam soil as an example were studied experimentally indoors to investigate the effects of these factors on wetting body in bubbled-root irrigation. The result shows that the velocity of wetted front decreases when the soil bulk density increases and increases when the initial soil moisture and the length of pervious sleeve of emitter increase while the burying depth has little effect on it. There is a power index relationship between wetted front and time and the index is 0. 32 and 0. 2 for horizontal and vertical orientation respectively. Prediction models were built for horizontal and vertical wetted front distance. Comprehensive prediction model with parameters of soil bulk density, initial soil moisture, the length of pervious sleeve of emitter and depth was built. After comparing the predicted and measured data, it is found that comprehensive prediction model has better prediction precision.%为了探明涌泉根灌土壤入渗湿润体运移的变化规律,以黏壤土为例,在室内选取不同土壤容重、初始含水率、灌水器套筒透水部长度和埋深等4个因素进行试验,研究这些因素对涌泉根灌土壤入渗湿润锋随时间运移关系的影响.结果表明:土壤入渗湿润锋运移速率随土壤容重的增大而减小,随土壤初始含水率的增大而增大,随套筒透水部管长的增长而增大,但不同埋深对灌水器湿润锋的推进速度无显著影响,涌泉根灌土壤入渗湿润体随时间的运移符合幂指数关系,幂指数在水平和垂直向分别为0.32和0.2.以此为基础分别建立了湿润锋在水平和垂直向运移距离的预测模型,并建立了包括土壤容重、初始含水率和灌水器套筒透水部长度的综合预测模
Sand dissolution and bubble removal in a model glass-melting channel with a uniform melt flow
Czech Academy of Sciences Publication Activity Database
Němec, Lubomír; Cincibusová, Petra
2012-01-01
Roč. 53, č. 6 (2012), s. 279-286. ISSN 1753-3546 R&D Projects: GA TA ČR TA01010844 Institutional research plan: CEZ:AV0Z30460519 Keywords : glass melting * sand dissolution * bubble removal Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 0.729, year: 2012 http://www.ingentaconnect.com/content/sgt/gt/2012/00000053/00000006/art00007
International Nuclear Information System (INIS)
In the present work, two common modeling concepts taking into account of the influence of bubbles on the turbulence of liquid phase were implemented in the EAGLE code and assessed against Hibiki's experiment data. The EAGLE (Elaborated Analysis of Gas-Liquid Evolution) code has been developed at KAERI based on the two-fluid model for a multi-dimensional analysis of two-phase flow with the implementations of non-drag force, standard k-ε turbulence model, and the interfacial area transport equation. In order to investigate the bubble size effect on two-phase flow evolution and to provide a data set for developing the physical models to describe the bubble-induced turbulence effect and also for validating the EAGLE code, a series of local parameter measurements as well as visualization tests were conducted in air-water vertical-upward flow condition in which the initial bubble size is controlled by a specially designed bubble generator. The numerical and experimental results are compared, analyzed and discussed in this paper. (author)
Brexit or Bremain ? Evidence from bubble analysis
Bianchetti, Marco; Galli, Davide; Ricci, Camilla; Salvatori, Angelo; Scaringi, Marco
2016-01-01
We applied the Johansen-Ledoit-Sornette (JLS) model to detect possible bubbles and crashes related to the Brexit/Bremain referendum scheduled for 23rd June 2016. Our implementation includes an enhanced model calibration using Genetic Algorithms. We selected a few historical financial series sensitive to the Brexit/Bremain scenario, representative of multiple asset classes. We found that equity and currency asset classes show no bubble signals, while rates, credit and real estate show super-ex...
Electronic structure of multielectron bubbles in liquid helium
International Nuclear Information System (INIS)
A quantum-statistical generalized Thomas-Fermi model is presented for the structure of multielectron bubbles observed in liquid helium-4 at low temperatures. The authors estimate bubbles with more than about 20 electrons to be stable against fissioning to single-electron bubbles. Electrons inside multielectron bubbles are found to concentrate in a narrow layer on the liquid helium surface. It is suggested that large bubbles in liquid helium constitute a new system and regime for testing electron density profiles; one which is quite clean from impurities, band structure effects and the background charge, all of which usually complicate the treatment of the electron density profile of metal surfaces. (Auth.)
Energy Technology Data Exchange (ETDEWEB)
Nigmatulin, R.I. [Tyumen Institute of Mechanics of Multiphase Systems (TIMMS), Marx (Russian Federation); Lahey, R.T. Jr. [Rensselaer Polytechnic Institute, Troy, NY (United States)
1995-09-01
In this paper a new method for the realization of fusion energy is presented. This method is based on the superhigh compression of a gas bubble (deuterium or deuterium/thritium) in heavy water or another liquid. The superhigh compression of a gas bubble in a liquid is achieved through forced non-linear, non-periodic resonance oscillations using moderate amplitudes of forcing pressure. The key feature of this new method is a coordination of the forced liquid pressure change with the change of bubble volume. The corresponding regime of the bubble oscillation has been called {open_quotes}basketball dribbling (BD) regime{close_quotes}. The analytical solution describing this process for spherically symmetric bubble oscillations, neglecting dissipation and compressibility of the liquid, has been obtained. This solution shown no limitation on the supercompression of the bubble and the corresponding maximum temperature. The various dissipation mechanisms, including viscous, conductive and radiation heat losses have been considered. It is shown that in spite of these losses it is possible to achieve very high gas bubble temperatures. This because the time duration of the gas bubble supercompression becomes very short when increasing the intensity of compression, thus limiting the energy losses. Significantly, the calculated maximum gas temperatures have shown that nuclear fusion may be possible. First estimations of the affect of liquid compressibility have been made to determine possible limitations on gas bubble compression. The next step will be to investigate the role of interfacial instability and breaking down of the bubble, shock wave phenomena around and in the bubble and mutual diffusion of the gas and the liquid.
A study of long separation bubble on thick airfoils and its consequent effects
International Nuclear Information System (INIS)
Highlights: • Effects of long separation bubbles on airfoil performance have been discussed. • The bubble is found to induce a camber-effect on the airfoil. • Effects of Re, TI and angle of attack on the bubble have been presented. • Appropriate modelling methodology of the separation-induced transition is presented. • Comparison of γ–Reθ and κ–κL–ω model for separation bubble in 2D is presented. - Abstract: A parametric study has been performed to analyse the flow around the thick-symmetric NACA 0021 airfoil in order to better understand the characteristics and effects of long separation bubbles (LoSBs) that exist on such airfoils at low Reynolds numbers and turbulence intensities. In the article, the prediction capabilities of two recently-developed transition models, the correlation-based γ–Reθ model and the laminar-kinetic-energy-based κ–κL–ω model are assessed. Two-dimensional steady-state simulations indicated that the κ–κL–ω model predicted the separation and reattachment process accurately when compared with published experimental work. The model was then used to study the attributes and the effects of LoSBs as a function of the angle of attack, freestream turbulence intensity and Reynolds number. It was observed that LoSBs considerably degrade the aerodynamic performance of airfoils and lead to abrupt stall behaviour. It is, furthermore, illustrated that the presence of the LoSB leads to an induced camber effect on the airfoil that increases as the airfoil angle of attack increases due to the upstream migration of the bubble. An increase in the Reynolds number or turbulence levels leads to a reduction in the bubble extent, considerably improving the airfoil performance and leading to a progressive trailing-edge stall
Numerical investigation of bubble nonlinear dynamics characteristics
Energy Technology Data Exchange (ETDEWEB)
Shi, Jie, E-mail: shijie@hrbeu.edu.cn; Yang, Desen; Shi, Shengguo; Hu, Bo [Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001 (China); College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001 (China); Zhang, Haoyang; Jiang, Wei [College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001 (China)
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.
Numerical investigation of bubble nonlinear dynamics characteristics
Shi, Jie; Yang, Desen; Zhang, Haoyang; Shi, Shengguo; Jiang, Wei; Hu, Bo
2015-10-01
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.
Numerical investigation of bubble nonlinear dynamics characteristics
International Nuclear Information System (INIS)
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
DEFF Research Database (Denmark)
Turcan, Romeo V.
prospects of a new venture and intended outcomes of that new venture; the higher the residue, the higher the likelihood of the bubble emergence; as residue increases, the likelihood of bubble burst increases. One question that arises is whether one can manage the hype, hence the residue. In this, it is...
Wildeman, Sander; Lhuissier, Henri; Sun, Chao; Lohse, Detlef; Prosperetti, Andrea
2014-01-01
We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rub
DEFF Research Database (Denmark)
Settnes, Mikkel; Power, Stephen; Lin, Jun;
2015-01-01
Strain-induced deformations in graphene are predicted to give rise to large pseudomagnetic fields. We examine theoretically the case of gas-inflated bubbles to determine whether signatures of such fields are present in the local density of states. Sharp-edged bubbles are found to induce Friedel...
Effect of internal bubbly flow on pipe vibrations
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
This paper presents an experimental investigation on wall vibrations of a pipe due to injection of a uniform bubble cloud into the pipe flow. For different bubble void fractions and averaged bubble sizes, the vibrations were measured using accelerometers. To understand the underlying physics, the evolution of the vibration spectra along the streamwise direction was examined. Results showed that wall vibrations were greatly enhanced up to 25 dB, compared with no bubble case. The characteristics of the vibration were mainly dependent on void fraction. These vibrations were believed to be caused by two mechanisms: acoustic resonance and normal modes of the bubble cloud. The former, originating from the interaction between the first mode of the bubble cloud and the first acoustic mode of the pipe, persisted along the entire pipe to enhance the vibration over a broad band frequency range, while the later, due to the process of bubble formation, successively decayed in the streamwise direction.
Institute of Scientific and Technical Information of China (English)
王一平; 陈为强; 黄群武; 冯加和; 崔勇
2016-01-01
Based on the momentum conservation approach, a theoretical model was developed to predict the su-perficial liquid velocity, and a correlation equation was established to calculate the gas holdup of an annular exter-nal-loop airlift reactor(AELAR)in the bubble flow and developing slug flow pattern. Experiments were performed by using tap-water and silicone oil with the viscosity of 2.0 mm2/s(2cs-SiO)and 5.0 mm2/s(5cs-SiO)as liquid phases. The effects of liquid viscosity and flow pattern on the AELAR performance were investigated. The predic-tions of the proposed model were in good agreement with the experimental results of the AELAR. In addition, the comparison of the experimental results shows that the proposed model has good accuracy and could be used to pre-dict the gas holdup and liquid velocity of an AELAR operating in bubble and developing flow pattern.
Test ventilation with smoke, bubbles, and balloons
Energy Technology Data Exchange (ETDEWEB)
Pickering, P.L.; Cucchiara, A.L.; McAtee, J.L.; Gonzales, M.
1987-01-01
The behavior of smoke, bubbles, and helium-filled balloons was videotaped to demonstrate the mixing of air in the plutonium chemistry laboratories, a plutonium facility. The air-distribution patterns, as indicated by each method, were compared. Helium-filled balloons proved more useful than bubbles or smoke in the visualization of airflow patterns. The replay of various segments of the videotape proved useful in evaluating the different techniques and in identifying airflow trends responsible for air mixing. 6 refs.
Surfactants for Bubble Removal against Buoyancy.
Raza, Md Qaisar; Kumar, Nirbhay; Raj, Rishi
2016-01-01
The common phenomenon of buoyancy-induced vapor bubble lift-off from a heated surface is of importance to many areas of science and technology. In the absence of buoyancy in zero gravity of space, non-departing bubbles coalesce to form a big dry patch on the heated surface and heat transfer deteriorates despite the high latent heat of vaporization of water. The situation is worse on an inverted heater in earth gravity where both buoyancy and surface tension act upwards to oppose bubble removal. Here we report a robust passive technique which uses surfactants found in common soaps and detergents to avoid coalescence and remove bubbles downwards, away from an inverted heater. A force balance model is developed to demonstrate that the force of repulsion resulting from the interaction of surfactants adsorbed at the neighboring liquid-vapor interfaces of the thin liquid film contained between bubbles is strong enough to overcome buoyancy and surface tension. Bubble removal frequencies in excess of ten Hz resulted in more than twofold enhancement in heat transfer in comparison to pure water. We believe that this novel bubble removal mechanism opens up opportunities for designing boiling-based systems for space applications. PMID:26743179
Surfactants for Bubble Removal against Buoyancy
Raza, Md. Qaisar; Kumar, Nirbhay; Raj, Rishi
2016-01-01
The common phenomenon of buoyancy-induced vapor bubble lift-off from a heated surface is of importance to many areas of science and technology. In the absence of buoyancy in zero gravity of space, non-departing bubbles coalesce to form a big dry patch on the heated surface and heat transfer deteriorates despite the high latent heat of vaporization of water. The situation is worse on an inverted heater in earth gravity where both buoyancy and surface tension act upwards to oppose bubble removal. Here we report a robust passive technique which uses surfactants found in common soaps and detergents to avoid coalescence and remove bubbles downwards, away from an inverted heater. A force balance model is developed to demonstrate that the force of repulsion resulting from the interaction of surfactants adsorbed at the neighboring liquid-vapor interfaces of the thin liquid film contained between bubbles is strong enough to overcome buoyancy and surface tension. Bubble removal frequencies in excess of ten Hz resulted in more than twofold enhancement in heat transfer in comparison to pure water. We believe that this novel bubble removal mechanism opens up opportunities for designing boiling-based systems for space applications.
Eternal inflation, bubble collisions, and the persistence of memory
International Nuclear Information System (INIS)
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
Numerical simulation of high Reynolds number bubble motion
International Nuclear Information System (INIS)
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 surfactantclose 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, one obtains good agreement with experimental observations of bubble motion in tap water. The effect of surfactant concentration on the separation angle is discussed
Morphology of Two-Phase Layers with Large Bubbles
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.
Numerical simulation of high Reynolds number bubble motion
Energy Technology Data Exchange (ETDEWEB)
McLaughlin, J.B. [Clarkson Univ., Potsdam, NY (United States)
1995-12-31
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, one obtains good agreement with experimental observations of bubble motion in tap water. The effect of surfactant concentration on the separation angle is discussed.
Comparing holographic dark energy models with statefinder
International Nuclear Information System (INIS)
We apply the statefinder diagnostic to the holographic dark energy models, including the original holographic dark energy (HDE) model, the new holographic dark energy model, the new agegraphic dark energy (NADE) model, and the Ricci dark energy model. In the low-redshift region the holographic dark energy models are degenerate with each other and with the ΛCDM model in the H(z) and q(z) evolutions. In particular, the HDE model is highly degenerate with the ΛCDM model, and in the HDE model the cases with different parameter values are also in strong degeneracy. Since the observational data are mainly within the low-redshift region, it is very important to break this lowredshift degeneracy in the H(z) and q(z) diagnostics by using some quantities with higher order derivatives of the scale factor. It is shown that the statefinder diagnostic r(z) is very useful in breaking the low-redshift degeneracies. By employing the statefinder diagnostic the holographic dark energy models can be differentiated efficiently in the low-redshift region. The degeneracy between the holographic dark energy models and the ΛCDM model can also be broken by this method. Especially for the HDE model, all the previous strong degeneracies appearing in the H(z) and q(z) diagnostics are broken effectively. But for the NADE model, the degeneracy between the cases with different parameter values cannot be broken, even though the statefinder diagnostic is used. A direct comparison of the holographic dark energy models in the r-s plane is also made, in which the separations between the models (including the ΛCDM model) can be directly measured in the light of the current values {r0, s0} of the models. (orig.)
Validation of Bubble Dynamics Equation for a Nano-scale Bubble via Molecular Dynamics Simulation
Tsuda, S.; Hyodo, H.; Watanabe, S.
2015-12-01
For a validation of the application of conventional bubble dynamics to a nano-scale bubble behaviour, we simulated a nano-scale bubble collapsing or vibration by Molecular Dynamics (MD) method and compared the result with the solution of Rayleigh-Plesset (RP) equation and that of Confined RP (CRP) equation, whose boundary condition was corrected to be consistent with that of MD simulation. As a result, a good coincidence was obtained between MD, RP, and CRP in the case of one-component fluid. In addition, also a good correspondence was obtained particularly in the comparison between MD and CRP in the case of two-component fluid containing non-condensable gas. The present results indicate that conventional bubble dynamics equation can be applied even to a nano-scale tiny bubble.
Rise of an argon bubble in liquid steel in the presence of a transverse magnetic field
Vanka, Surya Pratap; Jin, Kai; Kumar, Purushotam; Thomas, Brian
2015-11-01
In this work, the motion of a single argon gas bubble rising in quiescent liquid steel under an external magnetic field is studied numerically using a Volume-of-Fluid (VOF) method. To mitigate spurious velocities normally generated during numerical simulation of multiphase flows with large density differences, an improved algorithm for surface tension modeling, originally proposed by Wang and Tong is implemented, validated and used in present computations. The governing equations are integrated by a second-order space and time accurate numerical scheme, and implemented on multiple Graphics Processing Units (GPU) with high parallel efficiency. The motion and the terminal velocities of the rising bubble under different magnetic fields are compared and a reduction in rise velocity is seen in cases with the magnetic field applied. The shape deformation and the path of the bubble are discussed. An elongation of the bubble along the field direction is seen, and the physics behind these phenomena is discussed. The circulation inside of the bubble is seen to be affected by the magnetic field indirectly. The wake structures behind the bubble are visualized and effects of the magnetic field on the wake structures are presented.
The prediction of bubble defects in castings
Lawrence, James Andrew
2004-01-01
Objective of this research was to develop models that capture the entrainment, breakup and transport of gas bubbles in solidifying TiAl castings. The candidate has reviewed the literature, programmed in FORTRAN code, and validated a number of competing techniques for two phase flow relevant to the filling of moulds. He has developed a hybrid (Donor-acceptor/ Level Set) method, which captures the characteristics of gas bubbles based on the surface tension —fluid inertia balance on the free sur...
The dynamics of a non-equilibrium bubble near bio-materials
International Nuclear Information System (INIS)
In many medical treatments oscillating (non-equilibrium) bubbles appear. They can be the result of high-intensity-focused ultrasound, laser treatments or shock wave lithotripsy for example. The physics of such oscillating bubbles is often not very well understood. This is especially so if the bubbles are oscillating near (soft) bio-materials. It is well known that bubbles oscillating near (hard) materials have a tendency to form a high speed jet directed towards the material during the collapse phase of the bubble. It is equally well studied that bubbles near a free interface (air) tend to collapse with a jet directed away from this interface. If the interface is neither 'free' nor 'hard', such as often occurs in bio-materials, the resulting flow physics can be very complex. Yet, in many bio-applications, it is crucial to know in which direction the jet will go (if there is a jet at all). Some applications require a jet towards the tissue, for example to destroy it. For other applications, damage due to impacting jets is to be prevented at all cost. This paper tries to address some of the physics involved in these treatments by using a numerical method, the boundary element method (BEM), to study the dynamics of such bubbles near several bio-materials. In the present work, the behaviour of a bubble placed in a water-like medium near various bio-materials (modelled as elastic fluids) is investigated. It is found that its behaviour depends on the material properties (Young's modulus, Poisson ratio and density) of the bio-material. For soft bio-materials (fat, skin, brain and muscle), the bubble tends to split into smaller bubbles. In certain cases, the resulting bubbles develop opposing jets. For hard bio-materials (cornea, cartilage and bone), the bubble collapses towards the interface with high speed jets (between 100 and about 250 m s-1). A summary graph is provided identifying the combined effects of the dimensionless elasticity (κ) and density ratio (α) of the
Comparing Local, Collective, and Global Trust Models
Haydar, Charif; Roussanaly, Azim; Boyer, Anne
2014-01-01
—Today, trust modelling is a serious issue on the social web. Social web allows information exchange between anonymous users who have no prior knowledge to each other. The aim of a trust model is to rerank acquired information according to their reliability and the trustworthiness of their author. During the last decade, trust models were proposed to assist the user to state his opinion about the acquired information, and about their sources. We identify three paradigms for trust modelling: t...
Energy Technology Data Exchange (ETDEWEB)
Abanades, J.C.; Atares, S.; Grasa, G.
1999-07-01
Rapid solid mixing is important to avoid undesirable temperature profiles in fluidized beds combustors and gasifiers. In this work, two alternative mathematical models for solid axial mixing are compared and their suitability for coal based fluidized beds is discussed. The two models: the Dispersion Model (May (1959)) and the Countercurrent Backmixing Model (van Deemter (1967)) were postulated early in the development of fluidized beds and both have been applied successfully despite their fundamental differences in conception. A numerical analysis investigating the convergence in the predictions of both models under practical conditions has been carried out. There is a wide area of practical interest in which both models are close (relative to typical experimental errors). Reasonable values for the bubble/slug parameters in the CCBM model are able to fit data where the dispersion model has been previously successful. This result has been confirmed with both their experimental data and other published works. The conclusion from this analysis is that the CCBM model is more reliable idealization in describing and scaling up solid mixing in coal based fluidized beds.
Comparative study of hybrid RANS-LES models for separated flows
Kumar, G.; Lakshmanan, S. K.; Gopalan, H.; De, A.
2016-06-01
Hybrid RANS-LES models are proven to be capable of predicting massively separated flows with reasonable computation cost. In this paper, Spalart-Allmaras (S-A) based detached eddy simulation (DES) model and three SST based hybrid models with different RANS to LES switching criteriaare investigated. The flow over periodic hill at Re = 10,595 is chosen as the benchmark for comparing the performance of the different models due to the complex flow physics and reasonablecomputational cost. The model performances are evaluated based on their prediction capabilities of velocity and stress profiles, and separation and reattachment point. The simulated results are validatedagainst experimental and numerical results available in literature. The S-A DES model predicted separation bubble accurately at the top of the hill, as reported earlier in experiments and other numerical results. This model also correctly predicted velocity and stress profiles in recirculation region. However, the performance of this model was poor in the post reattachment region. On the other hand, the k-ω SST based hybrid models performed poorly in recirculation region, but it fairly predicted stress profiles in post reattachment region.
Predawn plasma bubble cluster observed in Southeast Asia
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.
Pulsed electrical discharge in gas bubbles in water
Gershman, Sophia
compared to the traditional corona or dielectric barrier discharges. These conditions make the experimental evidence presented in this work valuable for the advancement of modeling and the theoretical understanding of the discharge in bubbles in water.
Beaumont, Christopher; Williams, Jonathan; Kendrew, Sarah; Simpson, Robert
2014-01-01
We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to the mid plane, and display a stronger excess of Young Stellar Objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches -- particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machi...
On the dynamics of bubbles in boiling water
International Nuclear Information System (INIS)
Research highlights: → We devote this work to investigate the bubbles dynamics in boiling water. → A simple experiment of laser scattering was designed to obtain dynamical features. → Correlations and non-exponential distributions were found. → A simple model was able to describe several aspects of the system. - Abstract: We investigate the dynamics of many interacting bubbles in boiling water by using a laser scattering experiment. Specifically, we analyze the temporal variations of a laser intensity signal which passed through a sample of boiling water. Our empirical results indicate that the return interval distribution of the laser signal does not follow an exponential distribution; contrariwise, a heavy-tailed distribution has been found. Additionally, we compare the experimental results with those obtained from a minimalist phenomenological model, finding a good agreement.
Energy Technology Data Exchange (ETDEWEB)
DIMITRI GIDASPOW
1997-08-15
The objective of this study is to develop a predictive experimentally verified computational fluid dynamic (CFD) three phase model. It predicts the gas, liquid and solid hold-ups (volume fractions) and flow patterns in the industrially important bubble-coalesced (churn-turbulent) regime. The input into the model can be either particulate viscosities as measured with a Brookfield viscometer or effective restitution coefficient for particles. A combination of x-ray and {gamma}-ray densitometers was used to measure solid and liquid volume fractions. There is a fair agreement between the theory and the experiment. A CCD camera was used to measure instantaneous particle velocities. There is a good agreement between the computed time average velocities and the measurements. There is an excellent agreement between the viscosity of 800 {micro}m glass beads obtained from measurement of granular temperature (random kinetic energy of particles) and the measurement using a Brookfield viscometer. A relation between particle Reynolds stresses and granular temperature was found for developed flow. Such measurement and computations gave a restitution coefficient for a methanol catalyst to be about 0.9. A transient, two-dimensional hydrodynamic model for production of methanol from syn-gas in an Air Products/DOE LaPorte slurry bubble column reactor was developed. The model predicts downflow of catalyst at the walls and oscillatory particle and gas flow at the center, with a frequency of about 0.7 Hertz. The computed temperature variation in the rector with heat exchangers was only about 5 K, indicating good thermal management. The computed slurry height, the gas holdup and the rate of methanol production agree with LaPorte's reported data. Unlike the previous models in the literature, this model computes the gas and the particle holdups and the particle rheology. The only adjustable parameter in the model is the effective particle restitution coefficient.
Bolghasi, Alireza; Ghadimi, Parviz; Chekab, Mohammad A. Feizi
2016-08-01
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz-Kirchhoff-Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall-Novarini model and optimized HKF method. The extended Hall-Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
On thermonuclear processes in cavitation bubbles
International Nuclear Information System (INIS)
The theoretical and experimental foundations of so-called bubble nuclear fusion are reviewed. In the nuclear fusion process, a spherical cavitation cluster ∼10−2 m in diameter is produced of spherical bubbles at the center of a cylindrical chamber filled with deuterated acetone using a focused acoustic field having a resonant frequency of about 20 kHz. The acoustically-forced bubbles effectuate volume oscillations with sharp collapses during the compression stage. At the final stages of collapse, the bubble cluster emits 2.5 MeV D-D fusion neutron pulses at a rate of ∼2000 per second. The neutron yield is ∼105 s−1. In parallel, tritium nuclei are produced at the same yield. It is shown numerically that, for bubbles having sufficient molecular mass, spherical shock waves develop in the center of the cluster and that these spherical shock waves (microshocks) produce converging shocks within the interior bubbles, which focus energy on the centers of the bubbles. When these shock waves reflect from the centers of the bubbles, extreme conditions of temperature (∼108 K) and density (∼104 kg m−3) arise in a (nano)spherical region (∼10−7 m in size) that last for ∼10−12 s, during which time about ten D-D fusion neutrons and tritium nuclei are produced in the region. A paradoxical result in our experiments is that it is bubble cluster (not streamer) cavitation and the sufficiently high molecular mass of (and hence the low sound speed in) D-acetone (C3D6O) vapor (as compared, for example, to deuterated water D2O) which are necessary conditions for the formation of convergent spherical microshock waves in central cluster bubbles. It is these waves that allow the energy to be sufficiently focused in the nanospherical regions near the bubble centers for fusion events to occur. The criticism to which the concept of 'bubble fusion' has been subjected in the literature, in particular, most recently in Uspekhi Fizicheskikh Nauk (Physics
Rotating bubble membrane radiator
Webb, Brent J.; Coomes, Edmund P.
1988-12-06
A heat radiator useful for expelling waste heat from a power generating system aboard a space vehicle is disclosed. Liquid to be cooled is passed to the interior of a rotating bubble membrane radiator, where it is sprayed into the interior of the bubble. Liquid impacting upon the interior surface of the bubble is cooled and the heat radiated from the outer surface of the membrane. Cooled liquid is collected by the action of centrifical force about the equator of the rotating membrane and returned to the power system. Details regarding a complete space power system employing the radiator are given.
Jet flows from bubbles during subcooled pool boiling on micro wires
Institute of Scientific and Technical Information of China (English)
WANG; Hao; D.; M.; Christopher; PENG; Xiaofeng; WANG; Buxu
2005-01-01
An experimental investigation was conducted on subcooled nucleate boiling on ultra-small wires having diameters of 25―100 m. High-speed photography and laser PIV (Particle Image Velocimetry) technology were used to visually observe the bubble dynamics. For highly subcooled boiling at moderate heat fluxes, the bubbles generally remained attached to the micro heating wires and bubble-top jet flows were clearly observed. Smaller bubbles usually had stronger bubble-top jet flows, while larger bubbles seemed to produce multi-jet flows. The structures of the bubble-top jet flows, as well as multi-jet flows, were proposed from the experimental observation. A model was developed to describe jet flow phenomena from bubbles on micro wires. Numerical simulations for bubbles having diameter of 0.03 and 0.06 mm showed that both the bubble-top and multi-jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire. The predicted velocity magnitudes and flow structures agreed very well with experimental measurements. The bubble size relative to the wire is an important factor affecting the jet flow structure. For a 0.03 mm bubble on a 0.1 mm wire, only a bubble-top jet flow forms, while a complex multi-jet flow pattern forms around the bubble with a weak bubble-top jet and two side jet flows for a 0.06 mm bubble.
Comparing fluid mechanics models with experimental data.
Spedding, G R
2003-01-01
The art of modelling the physical world lies in the appropriate simplification and abstraction of the complete problem. In fluid mechanics, the Navier-Stokes equations provide a model that is valid under most circumstances germane to animal locomotion, but the complexity of solutions provides strong incentive for the development of further, more simplified practical models. When the flow organizes itself so that all shearing motions are collected into localized patches, then various mathemati...
A mechanical analysis of metallic tritide aging by helium bubble growth
Energy Technology Data Exchange (ETDEWEB)
Montheillet, F. [Ecole Nationale Superieure des Mines (SMS), CNRS UMR 5146 (PECM), 158 cours Fauriel, 42023 Saint-Etienne Cedex 2 (France)], E-mail: montheil@emse.fr; Delaplanche, D.; Fabre, A.; Munier, E.; Thiebaut, S. [Commissariat a l' Energie Atomique de Valduc, 21120 Is-sur-Tille (France)
2008-10-25
A simple mechanical model is proposed for the aging of a metallic tritide. The material is assumed to be elastic-power law viscoplastic. Part of the helium atoms generated by tritium decay form spherical bubbles that weaken the elastic moduli of the overall material. By contrast, others can be stored in solid solution in the matrix and are likely to increase the moduli. Two variants of the model are compared, assuming either instantaneous or finite rate diffusion of helium. They predict globally similar evolutions of the gas pressure inside the bubbles, the geometrical parameters (bubble radius, overall swelling), as well as the matrix and overall elastic moduli. The results are in good agreement with atomistic calculations of the pressure evolution. Furthermore, recent experimental measurements of the Young modulus changes during aging are better reproduced when He diffusion rate is finite, thus supporting the second variant of the model.
Bubble growth in decompression fields, 2
International Nuclear Information System (INIS)
Numerical analysis was performed for the growth of a vapor bubble in decompression fields of uniformly superheated water. The numerical solution obtained for the bubble growth was compared with experimental data reported in the 1st report. Bubble growth rates calculated were somewhat lower than the experimental data. The present solution was, however, shown to compare more favorably with the experimental bubble growth curves than the previous analytical solutions reported in the 1st report. In addition, existing solutions by other researchers provided that the sphericity correction factor was in agreement. Of course, the previous solutions with the correction factor of π/2 were the best-estimated solutions as reported in 1st report. Transient temperature distributions across the thermal boundary layer surrounding the bubble interface were also analyzed. It was found that, during the very short duration of the earlier bubble growth, the thermal boundary layer developed fully and the interfacial temperature approached that of saturation corresponding to the decompressed liquid pressure. (author)
Dynamics of buoyant bubbles in clusters of galaxies
Pavlovski, Georgi; Pope, Edward C D
2007-01-01
We present a phenomenological model of the dynamics of buoyant bubbles in the atmosphere of a cluster of galaxies. The derived equations describe velocity, size, mass, temperature and density of the buoyant bubbles as functions of time based on several simple approximations. The constructed model is then used to interpret results of a numerical experiment of heating of the cluster core with buoyant bubbles in a hydrodynamical approximation (i.e. in the absence of magnetic fields, viscosity, and thermal diffusion). Based on the model parameters we discuss possible limitations of the numerical treatment of the problem, and highlight the main physical processes that govern the dynamics of bubbles in the intracluster medium.
Jang, Neo W.; Zakrzewski, Aaron; Rossi, Christina; Dalecki, Diane; Gracewski, Sheryl
2011-01-01
Motivated by various clinical applications of ultrasound contrast agents within blood vessels, the natural frequencies of two bubbles in a compliant tube are studied analytically, numerically, and experimentally. A lumped parameter model for a five degree of freedom system was developed, accounting for the compliance of the tube and coupled response of the two bubbles. The results were compared to those produced by two different simulation methods: (1) an axisymmetric coupled boundary element and finite element code previously used to investigate the response of a single bubble in a compliant tube and (2) finite element models developed in comsol Multiphysics. For the simplified case of two bubbles in a rigid tube, the lumped parameter model predicts two frequencies for in- and out-of-phase oscillations, in good agreement with both numerical simulation and experimental results. For two bubbles in a compliant tube, the lumped parameter model predicts four nonzero frequencies, each asymptotically converging to expected values in the rigid and compliant limits of the tube material. PMID:22088008
Comparing of the dose forecasting models on radioactive farmland
International Nuclear Information System (INIS)
Three dose forecasting model was brief introduced, which include MEPAS model, MMSOILS model and PRESTO-EPA model. Every subschema in the models were compared each other, and the applicability of every model was analyzed. For result, the function of every subschema for MEPAS model was comprehensive which relative the other two models. Compared the approaches for dose forecasting which was aroused by the radioactive farmland, the MEPAS model was basic satisfied by the correspond requesting. (authors)
Stretching cells and delivering drugs with bubbles
Ohl, Claus-Dieter; Li, Fenfang; Chon U, Chan; Gao, Yu; Xu, Chenjie
2015-11-01
In this talk we'll review our work on impulsive cell stretching using cavitation bubbles and magnetic microbubbles for drug delivery. For sufficient short times cells can sustain a much larger areal strain than the yield strain obtained from quasi-static stretching. Experiments with red blood cells show that even then the rupture of the cell is slow process; it is caused by diffusive swelling rather than mechanical violation of the plasma membrane. In the second part we'll discuss bubbles coated with magnetic and drug loaded particles. These bubbles offer an interesting vector for on demand delivery of drugs using mild ultrasound and magnetic fields. We report on basic experiments in microfluidic channels revealing the release of the agent during bubble oscillations and first in vivo validation with a mouse tumor model. Singapore National Research Foundations Competitive Research Program funding (NRF-CRP9-2011-04).
Using sound to study bubble coalescence.
Kracht, W; Finch, J A
2009-04-01
Frothers are surfactants used in flotation to aid generation of small bubbles, an effect attributed to coalescence prevention. Studying coalescence at the moment of bubble creation is a challenge because events occur over a time frame of milliseconds. This communication introduces a novel acoustic technique to study coalescence as bubbles are generated at a capillary. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has the resolution to detect events that occur within 1-2 ms. The results show that for common flotation frothers and n-alcohols (C(4)-C(8)) coalescence prevention is not simply related to surface activity. A total stress model is used to give a qualitative explanation to the action observed. Results for salt (sodium chloride) are included for comparison. PMID:19128806
Bubbling the False Vacuum Away
Gleiser, Marcelo; Thorarinson, Joel
2007-01-01
We investigate the role of nonperturbative, bubble-like inhomogeneities on the decay rate of false-vacuum states in two and three-dimensional scalar field theories. The inhomogeneities are induced by setting up large-amplitude oscillations of the field about the false vacuum as, for example, after a rapid quench or in certain models of cosmological inflation. We show that, for a wide range of parameters, the presence of large-amplitude bubble-like inhomogeneities greatly accelerates the decay rate, changing it from the well-known exponential suppression of homogeneous nucleation to a power-law suppression. It is argued that this fast, power-law vacuum decay -- known as resonant nucleation -- is promoted by the presence of long-lived oscillons among the nonperturbative fluctuations about the false vacuum. A phase diagram is obtained distinguishing three possible mechanisms for vacuum decay: homogeneous nucleation, resonant nucleation, and cross-over. Possible applications are briefly discussed.
Cavitation inception from bubble nuclei
DEFF Research Database (Denmark)
Mørch, Knud Aage
2015-01-01
experimental investigations of bubbles and cavitation inception have been presented. These results suggest that cavitation nuclei in equilibrium are gaseous voids in the water, stabilized by a skin which allows diffusion balance between gas inside the void and gas in solution in the surrounding liquid. The...... cavitation nuclei may be free gas bubbles in the bulk of water, or interfacial gaseous voids located on the surface of particles in the water, or on bounding walls. The tensile strength of these nuclei depends not only on the water quality but also on the pressure-time history of the water. A recent model...... and associated experiments throw new light on the effects of transient pressures on the tensile strength of water, which may be notably reduced or increased by such pressure changes....
Bubble Collision in Curved Spacetime
International Nuclear Information System (INIS)
We study vacuum bubble collisions in curved spacetime, in which vacuum bubbles were nucleated in the initial metastable vacuum state by quantum tunneling. The bubbles materialize randomly at different times and then start to grow. It is known that the percolation by true vacuum bubbles is not possible due to the exponential expansion of the space among the bubbles. In this paper, we consider two bubbles of the same size with a preferred axis and assume that two bubbles form very near each other to collide. The two bubbles have the same field value. When the bubbles collide, the collided region oscillates back-and-forth and then the collided region eventually decays and disappears. We discuss radiation and gravitational wave resulting from the collision of two bubbles
Dynamics of diffusive bubble growth in magmas: Isothermal case
Prousevitch, A. A.; Sahagian, D. L.; Anderson, A. T.
1993-12-01
We have conducted a parametric study and developed a new cell model describing diffusion-induced growth of closely spaced bubbles in magmatic sytems. The model accounts for (1) the effects of advection of melt resulting from bubble growth, and its affect on the local concentration profile; (2) dynamic resistence of the viscous melt during diffusive growth; (3) diffusion of volatiles in response to evolving concentration gradients; (4) mass balance between dissolved volatiles and gas inside the bubble; (5) changes in the equilibrium saturation concentration at the bubble-melt interface; (6) total pressure within the bubble consisting of ambient, surface tension, and dynamic pressures. The results of this study reveal that bubble growth depends strongly on ambient pressure, volatile oversaturation in the melt, and diffusivity coefficients, but only weakly on bubble separation and inital bubble radius. Increased volatile oversaturation increases growth rate to the point at which it actually reduces time for complete bubble growth. This counterintuitive result is due to significant advective volatile flux toward the bubble interface during growth. Viscosity controls growth dynamics only for cases of high viscosity (greater than 10(exp 4) Pa s). The documentation of the evolution of gas fraction in the melt and bubble wall thickness as a function of time makes it possible to estimate bubble disruption thresholds which bear on volcanic eruption mechanisms. Model results can be applied to the larger-scale problem of magmatic degassing in terms of bubble coalescence, flotation and the development of foams in magma chambers and vent systems, and ultimately to the dynamics of eruption mechanisms.
Nonlinear Bubbling and Micro-Convection at a Submerged Orifice
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The present paper describes the nonlinear behavior of bubble formation from a single submerged orifice and induced liquid motion (micro-convection) surrounding the bubble. The experimental data reveals that departing periods of successive bubbles evolve multiple periods from single to triple periods when the gas flow rate is increased and that the micro-convection evolves bifurcation phenomena similar to the so-called "period doubling" in chaos dynamics. The photographic observation using high-speed video movies and data analysis indicate that the nonlinear features come from the deformation of the bubble and also the interaction between consecutive bubbles. A new comprehensive theoretical model is developed for describing the instantaneous bubble behaviors during formation and ascendance processes and for predicting the departing periods and sizes of successive bubbles for constant flow rate conditions. Owing to the estimation of instantaneous interactions between successive bubbles and the incorporation of the wake effect of previous bubbles, the present model describes the evolution process and mechanisms of bubble departing periods corresponding to different gas flow rate regimes. The theoretical results are in good agreement with experimental results.
Modelling and comparing maps with graphs
Le Ber, Florence; Metzger, Jean-Luc; Napoli, Amedeo
2002-01-01
This paper is concerned with the modelling of maps with conceptual graphs for the design of a knowledge-based system. We first describe the maps, which are synthetic descriptions of farm territories. We then explain the modelling principles we have used: the spatial objects of the map and the relations are represented into concepts linked with arcs. The reasoning principle of the system are briefly described. We finally focus on an example of graph comparison.
Energy Technology Data Exchange (ETDEWEB)
Zhongchun, Li, E-mail: zhongchun.lee@gmail.com [Tsinghua University, Beijing 100084 (China); Science and Technology on Reactor System Design Technology Laboratory, Chengdu 610041 (China); Xiaoming, Song [Nuclear Power Institute of China, Chengdu 610041 (China); Shengyao, Jiang; Jiyang, Yu [Tsinghua University, Beijing 100084 (China)
2014-07-01
Highlights: • A VOF simulation of bubble in low viscosity fluid was conducted. • Lift force in different viscosity fluid had different lateral migration characteristics. • Bubble with different size migrated to different direction. • Shear stress triggered the bubble deformation process and the bubble deformation came along with the oscillation behaviors. - Abstract: Two phase flow systems have been widely used in industrial engineering. Phase distribution characteristics are vital to the safety operation and optimization design of two phase flow systems. Lift force has been known as perpendicular to the bubbles’ moving direction, which is one of the mechanisms of interfacial momentum transfer. While most widely used lift force correlations, such as the correlation of Tomiyama et al. (2002), were obtained by experimentally tracking single bubble trajectories in high viscosity glycerol–water mixture, the applicability of these models into low viscosity fluid, such as water in nuclear engineering system, needs to be further evaluated. In the present paper, bubble in low viscosity fluid in shear flow was investigated in a full 3D numerical simulation and the volume of fluid (VOF) method was applied to capture the interface. The fluid parameter: fluid viscosity, bubble parameter: diameter and external flow parameters: shear stress magnitude and liquid velocity were examined. Comparing with bubble in high viscosity shear flow and bubble in low viscosity still flow, relative large bubble in low viscosity shear flow keep an oscillation way towards the moving wall and experienced a shape deformation process. The oscillation amplitude increased as the viscosity of fluid decreased. Small bubble migrated to the static wall in a line with larger migration velocity than that in high viscosity fluid and no deformation occurred. The shear stress triggered the oscillation behaviors while it had no direct influence with the behavior. The liquid velocity had no effect on
International Nuclear Information System (INIS)
Highlights: • A VOF simulation of bubble in low viscosity fluid was conducted. • Lift force in different viscosity fluid had different lateral migration characteristics. • Bubble with different size migrated to different direction. • Shear stress triggered the bubble deformation process and the bubble deformation came along with the oscillation behaviors. - Abstract: Two phase flow systems have been widely used in industrial engineering. Phase distribution characteristics are vital to the safety operation and optimization design of two phase flow systems. Lift force has been known as perpendicular to the bubbles’ moving direction, which is one of the mechanisms of interfacial momentum transfer. While most widely used lift force correlations, such as the correlation of Tomiyama et al. (2002), were obtained by experimentally tracking single bubble trajectories in high viscosity glycerol–water mixture, the applicability of these models into low viscosity fluid, such as water in nuclear engineering system, needs to be further evaluated. In the present paper, bubble in low viscosity fluid in shear flow was investigated in a full 3D numerical simulation and the volume of fluid (VOF) method was applied to capture the interface. The fluid parameter: fluid viscosity, bubble parameter: diameter and external flow parameters: shear stress magnitude and liquid velocity were examined. Comparing with bubble in high viscosity shear flow and bubble in low viscosity still flow, relative large bubble in low viscosity shear flow keep an oscillation way towards the moving wall and experienced a shape deformation process. The oscillation amplitude increased as the viscosity of fluid decreased. Small bubble migrated to the static wall in a line with larger migration velocity than that in high viscosity fluid and no deformation occurred. The shear stress triggered the oscillation behaviors while it had no direct influence with the behavior. The liquid velocity had no effect on
Bubble chamber: antiproton annihilation
1971-01-01
These images show real particle tracks from the annihilation of an antiproton in the 80 cm Saclay liquid hydrogen bubble chamber. A negative kaon and a neutral kaon are produced in this process, as well as a positive pion. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real tracks left by particles to be seen and photographed by expanding liquid that had been heated to boiling point.
CONDITIONS FOR BUBBLE FORMATION
Joffe, M
2010-01-01
A bubble is typically defined as ìtrade in high volume at prices that are considerably at variance from intrinsic valueî, which is compatible both with higher or lower prices, whereas the metaphor suggests something asymmetric that gradually inflates rather than deflates. Whether bubbles are symmetric or not is an empirical question; the historical record appears to be that they are asymmetric, but the literature is unclear on this point. In addition, in some types of market such as property,...
Buoyant Bubbles in a Cooling Intracluster Medium I. Hydrodynamic Bubbles
Gardini, A
2006-01-01
Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called "cool core" clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step. In this paper we present a first set of hydrodynamical, high resolution (1024^3 effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere while the ICM is subject to cooling. We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: th...
DNS based analysis of liquid phase turbulence kinetic energy equation for bubbly two-phase flow
International Nuclear Information System (INIS)
While the modeling of turbulent single phase flows has already reached a certain level of maturity, models for the turbulence in bubble flows are still under development. The majority of models is based on the transport equation for liquid phase turbulence kinetic energy (kL) which is recast by extending the k-equation for single phase flow with empirical closure terms to account for the dispersed phase. In this paper we investigate bubble-induced liquid phase pseudo-turbulence by direct numerical simulations (DNS) based on the volume-of-fluid method. Simulations are performed for a regular array of ellipsoidal bubbles (gas hold up a 0.8%) and for a monodisperse swarm of 8 bubbles (a 6.4 %) rising in a plane vertical channel within an otherwise stagnant liquid. In the three bubble swarm simulations the liquid viscosity is varied by a factor of 10, resulting in a change of the bubble shape from ellipsoidal to spherical, a decrease of the average bubble rise velocity by a factor of 5 and a decrease of kL by a factor of 20. The DNS data are used to perform a detailed quantitative analysis of the analytical balance equation for kL. The evaluation comprises single-phase-like terms (diffusion, dissipation, production) as well as the interfacial term that only exists for two-phase flows. The general conclusion to be drawn for the considered bubbly flows is the prominent role of the interfacial term. Because the production term due to shear stresses is so low that it can be neglected, the interfacial term is the only one that feeds the liquid phase turbulence. The different closure terms in the analytical kL-equation are compared with respective closure assumptions for the modeled kL-equation implemented in two-phase k-l, k-e and ASM turbulence models. We find that - for the bubbly flows studied here - the conventional modelling of single-phase-like terms totally fails. Encouraging results are, however, obtained for modeling of the interfacial term. A detailed analysis of
Dunn, R J H; Taylor, G B
2005-01-01
We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 < k/f < 1000. In the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte-Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have high...
Problems on holographic imaging technique and adapt lasers for bubble chambers
International Nuclear Information System (INIS)
Different types of holographic recording technique for bubble chambers are presented and compared. The influence of turbulence on resolution is discussed as well as the demand on laser equipment. Experiments on a test model of HOLEBC using a pulsed ruby laser are also presented. (orig.)
Problems on holographic imaging technique and adapt lasers for bubble chambers
Bjelkhagen, H I
1982-01-01
Different types of holographic recording technique for bubble chambers are presented and compared. The influence of turbulence on resolution is discussed as well as the demand on laser equipment. Experiments on a test model of HOLEBC using a pulsed ruby laser are also presented.
Interstellar Bubbles in Two Young HII Regions
Naze, Y; Points, S D; Danforth, C W; Rosado, M; Chen, C H R; Naze, Yael; Chu, You-Hua; Points, Sean D.; Danforth, Charles W.; Rosado, Margarita
2001-01-01
Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for wind-blown bubbles around main-sequence O stars, we have obtained high-resolution Hubble Space Telescope WFPC2 images and high-dispersion echelle spectra of two pristine HII regions, N11B and N180B, in the Large Magellanic Cloud. These HII regions are ionized by OB associations that still contain O3 stars, suggesting that the HII regions are young and have not hosted any supernova explosions. Our observations show that wind-blown bubbles in these HII regions can be detected kinematically but not morphologically because their expansion velocities are comparable to or only slightly higher than the isothermal sound velocity in the HII regions. Bubbles are detected around concentrations of massive stars, individual O stars, and even an evolved red supergiant (a fossil bubble). Comparisons between the observed bu...
A critical review of physiological bubble formation in hyperbaric decompression.
Papadopoulou, Virginie; Eckersley, Robert J; Balestra, Costantino; Karapantsios, Thodoris D; Tang, Meng-Xing
2013-05-01
Bubbles are known to form in the body after scuba dives, even those done well within the decompression model limits. These can sometimes trigger decompression sickness and the dive protocols should therefore aim to limit bubble formation and growth from hyperbaric decompression. Understanding these processes physiologically has been a challenge for decades and there are a number of questions still unanswered. The physics and historical background of this field of study is presented and the latest studies and current developments reviewed. Heterogeneous nucleation is shown to remain the prime candidate for bubble formation in this context. The two main theories to account for micronuclei stability are then to consider hydrophobicity of surfaces or tissue elasticity, both of which could also explain some physiological observations. Finally the modeling relevance of the bubble formation process is discussed, together with that of bubble growth as well as multiple bubble behavior. PMID:23523006
Mechanisms of stability of armored bubbles: FY 1995 progress report
International Nuclear Information System (INIS)
Experimental and theoretical studies of stabilization of liquid films between bubbles were undertaken as part of an effort to model gas release in waste tanks at the Hanford nuclear reservation. Synthetic Hanford waste created here showed solids accumulation at bubble surfaces and some stabilization of bubbles in a froth upon sparging with nitrogen. Dilational interfacial rheological measurements indicate increasing hydrophobicity with increasing EDTA concentration in the wastes. There is greater dilational elasticity of the interface with solid particles present on the interface. Theoretical modeling of a 2D liquid film between bubbles containing one row of solid particles suggests that in 3D such a film would be unstable unless the solids all touch. This hints at a possible mechanism for bubble stabilization, if it can be argued that slowly evolving interfaces, as bubbles grow toward each other in the sludge, have solids closely packed, but that rapid expansion of gas during a rollover event forces the films to expand without additional solids
Metal mixing by buoyant bubbles in galaxy clusters
Roediger, E; Rebusco, P; Böhringer, H; Churazov, E
2006-01-01
Using a series of three-dimensional, hydrodynamic simulations on an adaptive grid, we have performed a systematic study on the effect of bubble-induced motions on metallicity profiles in clusters of galaxies. In particular, we have studied the dependence on the bubble size and position, the recurrence times of the bubbles, the way these bubbles are inflated and the underlying cluster profile. We find that in hydrostatic cluster models, the resulting metal distribution is very elongated along the direction of the bubbles. Anisotropies in the cluster or ambient motions are needed if the metal distribution is to be spherical. In order to parametrise the metal transport by bubbles, we compute effective diffusion coefficients. The diffusion coefficients inferred from our simple experiments lie at values of around $\\sim 10^{29}$ cm$^2$s$^{-1}$ at a radius of 10 kpc. The runs modelled on the Perseus cluster yield diffusion coefficients that agree very well with those inferred from observations.
Comparative Distributions of Hazard Modeling Analysis
Directory of Open Access Journals (Sweden)
Rana Abdul Wajid
2006-07-01
Full Text Available In this paper we present the comparison among the distributions used in hazard analysis. Simulation technique has been used to study the behavior of hazard distribution modules. The fundamentals of Hazard issues are discussed using failure criteria. We present the flexibility of the hazard modeling distribution that approaches to different distributions.
The 1980s Price Bubble on (Post) Impressionism
Fabian Bocart; Ken Bastiaensen; Peter Cauwels
2011-01-01
The Log Periodic Power Law is a model used to define and measure speculative bubbles. This model has proven useful to track bubbles and even predict crashes of liquid asset classes. Using this methodology coupled with properties of cointegration between stocks and art, the 1980s price bubble on Impressionism and Post-Impressionism is analyzed. It is shown formally that there was a bubble in this market between 1986 and 1989. However, when denominating the art index in JPY rather than in USD, ...
Bubble shape in horizontal and near horizontal intermittent flow
International Nuclear Information System (INIS)
Highlights: • The bubble shapes in intermittent flows are presented experimentally. • The nose-tail inversion phenomenon appears at a low Froude number in downward pipe. • Transition from plug to slug flow occurs when the bubble tail changes from staircase pattern to hydraulic jump. - Abstract: This paper presents an experimental study of the shape of isolated bubbles in horizontal and near horizontal intermittent flows. It is found that the shapes of the nose and body of bubble depend on the Froude number defined by gas/liquid mixture velocity in a pipe, whereas the shape of the back of bubble region depends on both the Froude number and bubble length. The photographic studies show that the transition from plug to slug flow occurs when the back of the bubble changes from staircase pattern to hydraulic jump with the increase of the Froude number and bubble length. The effect of pipe inclination on characteristics of bubble is significant: The bubble is inversely located in a downwardly inclined pipe when the Froude number is low, and the transition from plug flow to slug flow in an upward inclined pipe is more ready to occur compared with that in a downwardly inclined pipe
Energy Technology Data Exchange (ETDEWEB)
Ryu, Seung Yeob [Korea Atomic Energy Research Institute (KAERI), Daejeon (Korea, Republic of); Ko, Sung Ho [Dept. of Mechanical Design Engineering, Chungnam National University, Daejeon (Korea, Republic of)
2012-08-15
The volume of fluid (VOF) model of FLUENT and the lattice Boltzmann method (LBM) are used to simulate two-phase flows. Both methods are validated for static and dynamic bubble test cases and then compared to experimental results. The VOF method does not reduce the spurious currents of the static droplet test and does not satisfy the Laplace law for small droplets at the acceptable level, as compared with the LBM. For single bubble flows, simulations are executed for various Eotvos numbers, Morton numbers and Reynolds numbers, and the results of both methods agree well with the experiments in the case of low Eotvos numbers. For high Eotvos numbers, the VOF results deviated from the experiments. For multiple bubbles, the bubble flow characteristics are related by the wake of the leading bubble. The coaxial and oblique coalescence of the bubbles are simulated successfully and the subsequent results are presented. In conclusion, the LBM performs better than the VOF method.
Beer tapping: dynamics of bubbles after impact
Mantič-Lugo, V.; Cayron, A.; Brun, P.-T.; Gallaire, F.
2015-12-01
Beer tapping is a well known prank where a bottle of beer is impacted from the top by a solid object, usually another bottle, leading to a sudden foam overflow. A description of the shock-driven bubble dynamics leading to foaming is presented based on an experimental and numerical study evoking the following physical picture. First, the solid impact produces a sudden downwards acceleration of the bottle creating a strong depression in the liquid bulk. The existing bubbles undergo a strong expansion and a sudden contraction ending in their collapse and fragmentation into a large amount of small bubbles. Second, the bubble clouds present a large surface area to volume ratio, enhancing the CO2 diffusion from the supersaturated liquid, hence growing rapidly and depleting the CO2. The clouds of bubbles migrate upwards in the form of plumes pulling the surrounding liquid with them and eventually resulting in the foam overflow. The sudden pressure drop that triggers the bubble dynamics with a collapse and oscillations is modelled by the Rayleigh-Plesset equation. The bubble dynamics from impact to collapse occurs over a time (tb ≃ 800 μs) much larger than the acoustic time scale of the liquid bulk (tac = 2H/c ≃ 80 μs), for the experimental container of height H = 6 cm and a speed of sound around c ≃ 1500 m/s. This scale separation, together with the comparison of numerical and experimental results, suggests that the pressure drop is controlled by two parameters: the acceleration of the container and the distance from the bubble to the free surface.
A Model for Comparing Free Cloud Platforms
Radu LIXANDROIU; Catalin MAICAN
2014-01-01
VMware, VirtualBox, Virtual PC and other popular desktop virtualization applications are used only by a few users of IT techniques. This article attempts to make a comparison model for choosing the best cloud platform. Many virtualization applications such as VMware (VMware Player), Oracle VirtualBox and Microsoft Virtual PC are free for home users. The main goal of the virtualization software is that it allows users to run multiple operating systems simultane-ously on one virtual environment...
Interaction of two three-dimensional explosion bubbles
Institute of Scientific and Technical Information of China (English)
YAO Xiong-liang; ZHANG A-man; LIU Yu-chen
2007-01-01
The interaction of two underwater explosion bubbles was mathematically analyzed in this paper. Based on the assumption of potential flow, high-order curved elements were used to discretize the boundary integral equation and solve it. Assuming that gas inside the bubble follows the isentropic rule,the Euler-Lagrange method was used to trace the evolution of the bubble, and when calculating the singular integral, the singularity of the double-layer singular integral was eliminated by reconstructing a principal-value integral of double-layer potential so that a more precise result could be obtained. Elastic mesh technique (EMT) was also used when tracing the evolution of the bubble interface, and numerical smoothing wasn't needed. A comparison of calculations using this three-dimensional model with results of the Reyleigh-Plesset bubble model shows that the three-dimensional model and calculation method in this paper is practical. This three-dimensional model was applied to simulate the interaction of two bubbles under the action of gravity, and the dynamic characteristics of two bubbles near the surface was also analyzed. Bubbles influenced by surface effects and gravity present severe non-linearity. This paper provides a reference for research into the dynamics of multi-bubbles.
Intensely oscillating cavitation bubble in microfluidics
Siew-Wan, Ohl; Tandiono; Klaseboer, Evert; Dave, Ow; Choo, Andre; Claus-Dieter, Ohl
2015-12-01
This study reports the technical breakthrough in generating intense ultrasonic cavitation in the confinement of a microfluidics channel [1], and applications that has been developed on this platform for the past few years [2,3,4,5]. Our system consists of circular disc transducers (10-20 mm in diameter), the microfluidics channels on PDMS (polydimethylsiloxane), and a driving circuitry. The cavitation bubbles are created at the gas- water interface due to strong capillary waves which are generated when the system is driven at its natural frequency (around 100 kHz) [1]. These bubbles oscillate and collapse within the channel. The bubbles are useful for sonochemistry and the generation of sonoluminescence [2]. When we add bacteria (Escherichia coli), and yeast cells (Pichia pastoris) into the microfluidics channels, the oscillating and collapsing bubbles stretch and lyse these cells [3]. Furthermore, the system is effective (DNA of the harvested intracellular content remains largely intact), and efficient (yield reaches saturation in less than 1 second). In another application, human red blood cells are added to a microchamber. Cell stretching and rapture are observed when a laser generated cavitation bubble expands and collapses next to the cell [4]. A numerical model of a liquid pocket surrounded by a membrane with surface tension which was placed next to an oscillating bubble was developed using the Boundary Element Method. The simulation results showed that the stretching of the liquid pocket occurs only when the surface tension is within a certain range.
Directory of Open Access Journals (Sweden)
Jorge Ramírez-Muñoz
2007-01-01
Full Text Available Se presenta un análisis hidrodinámico de la interacción de dos burbujas esféricas del mismo tamaño alineadas en la dirección de un flujo uniforme, laminar, newtoniano e incompresible. La burbuja puntera se considera aislada y la burbuja acarreada (segunda burbuja está sujeta a la acción de cuatro fuerzas: flotación, arrastre cuasiestacionario, impulso del fluido y masa agregada. Aplicando un balance de fuerzas sobre cada burbuja se obtuvo una nueva expresión para la velocidad de ascenso de la burbuja acarreada. La expresión se comparó con mediciones experimentales, realizadas por otros autores citados en la literatura, para números de Reynolds de 3.06, 21.5 y 35.4 y se obtuvo un error relativo promedio entre 1.2% y 2.1%. Se discuten dos alternativas para aproximar la reducción del arrastre sobre la burbuja acarreada. Se encontró que el arrastre cuasiestacionario no puede incorporar el efecto total de la estela sobre la burbuja acarreadaA hydrodynamic analysis on the interaction of two equal-size spherical bubbles aligned on the direction of a uniform, laminar, newtonian and incompressible flow, is presented. The leading bubble is considered as an isolated bubble and the trailing bubble (second bubble is subjected to four forces: buoyancy, quasisteady drag, fluid impulse and added mass. By applying a force balance on each bubble, an expression for the rising velocity of the trailing bubble was obtained. Comparison of this expression with existing experimental data for 3.06, 21.5 and 35.4 Reynolds number was performed, obtaining a relative average error between 1.2% and 2.1%. Two possible approaches on the trailing bubble drag reduction effect are discussed. It was found that a quasisteady drag is, by itself, unable to incorporate the whole wake effect on the trailing bubble.
Effects of interfacial surfactant contamination on bubble gas transfer
Rosso, D.; Huo, D L; Stenstrom, M K
2006-01-01
Surface active agents depress gas transfer at gas-liquid interfaces. They are present as measurable trace contaminants at all environmental and at most industrial interfaces. An experimental apparatus to concurrently measure dynamic surface tension and mass transfer was constructed and tested for single-bubble and multi-bubble experiments. In this work, the parameters describing time-dependent bubble surface contamination were characterized. The application of a Ward-Tordai transient model an...
ANALYSIS OF PRICE BUBBLES ON THE CZECH REAL ESTATE MARKET
Gevorgyan Kristine
2015-01-01
This thesis deals with the issue of price bubbles on the Czech real estate market. The theoretical part explains the price bubble in terms of behavioural finance, and describes the relationship between monetary policy and asset prices from the perspective of the Austrian school and representatives of traditional economics. In the empirical part, it presents ways of identifying bubbles on the property market using relative indicators and econometric models. By means of econometric methods, thi...
Oxygen quenching in LAB based liquid scintillator and nitrogen bubbling
Hua-Lin, Xiao
2009-01-01
Oxygen quenching effect in Linear Alkl Benzne (LAB) based liquid scintillator (LAB+3g/L POPOP+ 15 mg Bis--MSB) was studied by measuring the light yield as the function of nitrogen bubbling time. it shows that the light yield of fully purged liquid scintillator would increase of nearly 11% in room temperature and room atmosphere pressure. A simple model of nitrogen bubbling was built to describe the relationship between relative light yield (oxygen quenching factor) and bubbling time.
Non-intrusive measurements of bubble size and velocity
Tassin, A. L.; Nikitopoulos, D. E.
1995-06-01
A non-intrusive measuring technique based on video-imaging has been developed for the measurement of bubble size, velocity and frequency. Measurements carried out with this method have been compared to those obtained by an optimized phase-Doppler system in standard configuration, for a wide range of bubble sizes produced from single injectors in a quiescent environment. The two measuring techniques have yielded velocities and frequencies that are in very good agreement while the size of spherical bubbles was consistently measured by both methods. The phase-Doppler system was also used to size oblate-spheroidal bubbles moving with their equatorial plane parallel to the scattering plane, yielding measurements reasonably close to the average radius of curvature of the bubbles in the neighborhood of the equatorial plane, as calculated from the video-imaging data. Both methods were used for detailed velocity measurements of the bubble-stream in the neighborhood of the injector tip. The observed bubble-velocity variation with the distance from the injector tip does not always display the usual increasing trend leading into the terminal velocity. When injection conditions are near the transition from discrete to jet injection mode and the bubbles are small, the latter decelerate into a terminal velocity due to direct interaction of successive bubbles at the injector tip. The measured terminal velocities of bubble-chains for a variety of bubble sizes and injection frequencies, are successfully predicted by using a far-field wake approximation to account for the drafting effect which is responsible for bubble-chain velocities higher than those of single bubbles.
A Model for Comparing Free Cloud Platforms
Directory of Open Access Journals (Sweden)
Radu LIXANDROIU
2014-01-01
Full Text Available VMware, VirtualBox, Virtual PC and other popular desktop virtualization applications are used only by a few users of IT techniques. This article attempts to make a comparison model for choosing the best cloud platform. Many virtualization applications such as VMware (VMware Player, Oracle VirtualBox and Microsoft Virtual PC are free for home users. The main goal of the virtualization software is that it allows users to run multiple operating systems simultane-ously on one virtual environment, using one computer desktop.
Modele bicamerale comparate. Romania: Monocameralism versus bicameralism
Directory of Open Access Journals (Sweden)
Cynthia Carmen CURT
2007-06-01
Full Text Available The paper attempts to evaluate the Romanian bicameral model as well as to identify and critically asses which are the options our country has in choosing between unicameral and bicameral system. The analysis attempts to observe the characteristics of some Second Chambers that are related to Romanian bicameralism by influencing the configuration of the Romanian bicameral legislature, or which devised constitutional mechanisms can be used in order to preserve an efficient bicameral formula. Also the alternative of giving up the bicameral formula due to some arguments related to the simplification and the efficiency of the legislative procedure is explored.
Kumar, Anup; Guria, Chandan; Chitres, G; Chakraborty, Arunangshu; Pathak, A K
2016-10-01
A comprehensive mathematical model involving NPK-10:26:26 fertilizer, NaCl, NaHCO3, light and temperature operating variables for Dunaliella tertiolecta cultivation is formulated to predict microalgae-biomass and lipid productivity. Proposed model includes Monod/Andrews kinetics for the absorption of essential nutrients into algae-biomass and Droop model involving internal nutrient cell quota for microalgae growth, assuming algae-biomass is composed of sugar, functional-pool and neutral-lipid. Biokinetic model parameters are determined by minimizing the residual-sum-of-square-errors between experimental and computed microalgae-biomass and lipid productivity using genetic algorithm. Developed model is validated with the experiments of Dunaliella tertiolecta cultivation using air-agitated sintered-disk chromatographic glass-bubble column and the effects of operating variables on microalgae-biomass and lipid productivity is investigated. Finally, parametric sensitivity analysis is carried out to know the sensitivity of model parameters on the obtained results in the input parameter space. Proposed model may be helpful in scale-up studies and implementation of model-based control strategy in large-scale algal cultivation. PMID:27450983
Detached eddy simulations of Taylor bubbles rising in stagnant liquid columns
Shaban, Hassan; Tavoularis, Stavros
2015-11-01
The rise of a single air Taylor bubble in a vertical circular tube filled with stagnant water was investigated numerically using the Volume Of Fluid (VOF) method to model the phase distribution and the Detached Eddy Simulation (DES) method for turbulence modelling. The predictions were in good quantitative agreement with previous experimental results. The simulation results provided insight into bubble shedding in the wake of the Taylor bubble, frictional pressure drop along the tube and scalar dispersion caused by the passage of the Taylor bubble. The interaction between adjacent Taylor bubbles and the process of Taylor bubble coalescence were also examined in detail. Supported by NSERC and UNENE.
Comparative molecular modelling of biologically active sterols
Baran, Mariusz; Mazerski, Jan
2015-04-01
Membrane sterols are targets for a clinically important antifungal agent - amphotericin B. The relatively specific antifungal action of the drug is based on a stronger interaction of amphotericin B with fungal ergosterol than with mammalian cholesterol. Conformational space occupied by six sterols has been defined using the molecular dynamics method to establish if the conformational features correspond to the preferential interaction of amphotericin B with ergosterol as compared with cholesterol. The compounds studied were chosen on the basis of structural features characteristic for cholesterol and ergosterol and on available experimental data on the ability to form complexes with the antibiotic. Statistical analysis of the data obtained has been performed. The results show similarity of the conformational spaces occupied by all the sterols tested. This suggests that the conformational differences of sterol molecules are not the major feature responsible for the differential sterol - drug affinity.
Comparative analysis of enterprise risk management models
Nikolaev Igor V.
2012-01-01
The article is devoted to the analysis and the comparison of modern enterprise risk management models used in domestic and world practice. Some thesis to build such a model are proposed.Статья посвящена анализу и сравнению современных моделей управления рисками предприятий, которые используются в отечественной и зарубежной практике. Предложены некоторые положения, на которых должны базироваться такие модели....
Rapid vapor bubble growth during decompression of superheated water
International Nuclear Information System (INIS)
Both analytical and experimental investigations are performed for vapor bubble growth in a uniformly superheated water under rapid decompression. Numerical and analytical solutions are obtained by solving a complete set of governing equations for bubble growth, and compared with experimental data obtained in the present experiment and previously by Toda and Kitamura. Bubble growth rates calculated numerically are lower than the experimental data, however, they approach more favorably our experimental data than the analytical solutions without the added correction factor given by Toda and Kitamura. Their solutions with the correction factor of π/2 are the best-fit solutions reported thus far. Available solutions by other researchers are found to underpredict bubble growth rates. Transient temperature distributions across the thermal boundary layer on the bubble interface are also estimsted. It is found that for initial periods thermal boundary layer fully develops and the bubble interface temperature approaches that of saturation corresponding to decompressed liquid pressure. (author)
DIGITAL IMAGE MEASUREMENT OF BUBBLE MOTION IN AERATED WATER FLOWS
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Digital image measurement method, as an ex-tension of Particle Image Velocimetry of single-phase flowmeasurement, was investigated for application to air-watertwo-phase flows. The method has strong potential ability inmeasuring bubble geometrical features and moving velocitiesfor complex bubble motion in aerated water flow. Both dilutedand dense bubble rising flows are measured using the digitalimage method. Measured bubble shapes and sizes, and bubblevelocities are affected by threshold selection for binary image.Several algorithms for selecting threshold are compared andmethods for calculating the time-averaged void fraction arediscussed.
On the prediction of the phase distribution of bubbly flow in a horizontal pipe.
Yeoh, G H; Cheung, Sherman C P; Tu, J Y
2012-01-01
Horizontal bubbly flow is widely encountered in various industrial systems because of its ability to provide large interfacial areas for heat and mass transfer. Nonetheless, this particular flow orientation has received less attention when compared to vertical bubbly flow. Owing to the strong influence due to buoyancy, the migration of dispersed bubbles towards the top wall of the horizontal pipe generally causes a highly asymmetrical internal phase distributions, which are not experienced in vertical bubbly flow. In this study, the internal phase distribution of air-water bubbly flow in a long horizontal pipe with an inner diameter of 50.3 mm has been predicted using the population balance model based on direct quadrature method of moments (DQMOM) and multiple-size group (MUSIG) model. The predicted local radial distributions of gas void fraction, liquid velocity and interfacial area concentration have been validated against the experimental data of Kocamustafaogullari and Huang (1994). In general, satisfactory agreements between predicted and measured results were achieved. The numerical results indicated that the gas void fraction and interfacial area concentration have a unique internal structure with a prevailing maximum peak near the top wall of the pipe due to buoyancy effect. PMID:24415823
Dimensionless analysis of bubble departure frequency in forced convective subcooled boiling flow
International Nuclear Information System (INIS)
Forced convective subcooled boiling flow experiments were conducted in a vertical upward annular channel. Water was used as the testing fluid, and the tests were performed at atmospheric pressure. A high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process. Bubble departure frequencies were obtained from the video for a total of 58 test conditions. The non-dimensional analysis was performed on the current data as well as available data from literature. Existing models and correlations were compared with the experimental data of bubble waiting time, growth time, and departure frequency. The correlations developed for pool boiling flow do not work well for forced convective subcooled boiling flow, while the models proposed for subcooled boiling flow can not predict the bubble departure frequency in wide experimental ranges. Dimensionless bubble departure frequency is correlated with non-dimensional nucleate boiling heat flux. The new correlation agrees reasonably well with existing experimental data at lower wall superheat. (author)
Numerical simulation of Taylor bubble rising in liquid lead-bismuth eutectic based on MPS method
International Nuclear Information System (INIS)
The Taylor bubble rising in a vertical tube filled with liquid lead-bismuth eutectic was simulated based on MPS method. Several performed results including shape development, bubble rising terminal speed fitting line, and the thickness and axial velocity profile of the falling film were presented. The simulation results were compared with some experimental results from literature and reveal the corresponding laws obeyed by the terminal speed, velocity profile and film thickness. The computational results agree well with both theoretical analysis and experimental results, which demonstrates the reasonable selection of model as well as the accuracy and reliability of MPS method. (authors)
Novel techniques for slurry bubble column hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Dudukovic, M.P.
1999-05-14
The objective of this cooperative research effort between Washington University, Ohio State University and Exxon Research Engineering Company was to improve the knowledge base for scale-up and operation of slurry bubble column reactors for syngas conversion and other coal conversion processes by increased reliance on experimentally verified hydrodynamic models. During the first year (July 1, 1995--June 30, 1996) of this three year program novel experimental tools (computer aided radioactive particle tracking (CARPT), particle image velocimetry (PIV), heat probe, optical fiber probe and gamma ray tomography) were developed and tuned for measurement of pertinent hydrodynamic quantities, such as velocity field, holdup distribution, heat transfer and bubble size. The accomplishments were delineated in the First Technical Annual Report. The second year (July, 1996--June 30, 1997) was spent on further development and tuning of the novel experimental tools (e.g., development of Monte Carlo calibration for CARPT, optical probe development), building up the hydrodynamic data base using these tools and comparison of the two techniques (PIV and CARPT) for determination of liquid velocities. A phenomenological model for gas and liquid backmixing was also developed. All accomplishments were summarized in the Second Annual Technical Report. During the third and final year of the program (July 1, 1997--June 30, 1998) and during the nine months no cost extension, the high pressure facility was completed and a set of data was taken at high pressure conditions. Both PIV, CT and CARPT were used. More fundamental hydrodynamic modeling was also undertaken and model predictions were compared to data. The accomplishments for this period are summarized in this report.
Colliding with a crunching bubble
Energy Technology Data Exchange (ETDEWEB)
Freivogel, Ben; Freivogel, Ben; Horowitz, Gary T.; Shenker, Stephen
2007-03-26
In the context of eternal inflation we discuss the fate of Lambda = 0 bubbles when they collide with Lambda< 0 crunching bubbles. When the Lambda = 0 bubble is supersymmetric, it is not completely destroyed by collisions. If the domain wall separating the bubbles has higher tension than the BPS bound, it is expelled from the Lambda = 0 bubble and does not alter its long time behavior. If the domain wall saturates the BPS bound, then it stays inside the Lambda = 0 bubble and removes a finite fraction of future infinity. In this case, the crunch singularity is hidden behind the horizon of a stable hyperbolic black hole.
Theoretical aspects of appearing of bubbles in economy
Directory of Open Access Journals (Sweden)
Pronoza Pavlo V.
2014-01-01
Full Text Available The article considers theoretical aspects of appearing of bubbles in economy. It analyses vies of scientists regarding the essence of this phenomenon and, with the help of content analysis, specifies the essence of the bubble notion in economy. It considers main stages of appearance of such bubbles. It offers classification of their types. It analyses pre-requisites of appearance of bubbles in economy and their features. It considers main existing approaches to detection and modelling appearance of bubbles. It proves that bubbles negatively influence economy of the countries, that is why, the problem of their detection and prevention is one of the central problems in the process of development of policy of state regulation of economy.
Bubble migration in a compacting crystal-liquid mush
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
Institute of Scientific and Technical Information of China (English)
QU Jian-wu; MURAI Yuichi; YAMAMOTO Fujio
2005-01-01
Bubble-bubble interaction in free rising bubbly flows is experimentally investigated in the present study.The velocity vectors of the bubbles are measured by a stereoscopic bubble-tracking technique and then the relative velocity vectors of two nearest-neighbor bubbles are calculated with high statistical reliability.With the measurement data at Reynolds number ranging from 5 to 75, the vertical attraction and the horizontal repulsion are confirmed for Re＜10 as known by the past study based on Navier-Stokes simulation.The new finding of the present measurement is that the bubbles of Re＞30 have repulsive velocity bothin the horizontal and the vertical directions as those rise closely.Moreover, the three-dimensional structure of the bubble-bubble interaction is discussed with the data analysis of the interaction vector fields.
Comparative study between a dynamic food-chain model (DYNACON) and an equilibrium model (NRC model)
International Nuclear Information System (INIS)
The predictive results between a dynamic food-chain model (DYNACON) and an equilibrium model (NRC model) were compared to show the physical validity of DYNACON. Although the mathematical formulations and transport processes of radionuclides in the environment are different between two models, the comparative study shows good agreement for deposition events that occur during the growing season of plants
Buoyant Bubbles and the Disturbed Cool Core of Abell 133
Randall, Scott W.; Clarke, T.; Nulsen, P.; Owers, M.; Sarazin, C.; Forman, W.; Jones, C.; Murray, S.
2010-03-01
X-ray cavities, often filled with radio-emitting plasma, are routinely observed in the intracluster medium of clusters of galaxies. These cavities, or "bubbles", are evacuated by jets from central AGN and subsequently rise buoyantly, playing a vital role in the "AGN feedback" model now commonly evoked to explain the balance between heating and radiative cooling in cluster cores. As the bubbles rise, they can displace cool central gas, promoting mixing and the redistribution of metals. I will show a few examples of buoyant bubbles, then argue that the peculiar morphology of the Abell 133 is due to buoyant lifting of cool central gas by a radio-filled bubble.
Density of radiolytic gas bubbles in polymethyl methacrylate
Makkonen, T.; Tiainen, O. J. A.; Valkiainen, M.; Winberg, M.
The density of the radiolytic gas bubbles in irradiated polymethyl methacrylate was measured during subsequent heat treatment as a function of radiation dose. The samples were irradiated in the core of the Triga Mark II reactor in Otaniemi. After the irradiation periods the samples were heat treated at 393 K. The number of the bubbles could be explained by a thermal activation model. The bubbles are born in material inhomogeneities and the threshold dose for the bubble initiation was about 25 Mrad for the heat treatment at 393 K under the atmospheric pressure.
Energy Technology Data Exchange (ETDEWEB)
Legoll, F. [Service de Physique Theorique, CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France)
1998-07-22
For nuclei with very high electrical charge, the Coulomb field is expected to drive the protons away from the centre to the surface of the nucleus. Such a nucleus would be no more compact but look like a bubble. The goal of this work is to confirm this idea. We are interested in only the ground state of spherical nuclei. We use the Skyrme potential with the Sly4 parametrization to calculate the mean-field Hamiltonian. Paring correlations are described by a surface-active delta paring interaction. In its ground state the nucleus {sup A=900} X{sub Z=274} is shown to be a bubble. Another stable state is found with a little higher energy: it is also a bubble. (author) 11 refs., 18 figs., 33 tabs.
Energy Technology Data Exchange (ETDEWEB)
Fradera, J., E-mail: jfradera@ubu.es; Cuesta-López, S., E-mail: scuesta@ubu.es
2013-12-15
Highlights: • The work presented in this manuscript provides a reliable computational tool to quantify the He complex phenomena in a HCLL. • A model based on the self-consistent nucleation theory (SCT) is exposed. It includes radiation induced nucleation modelling and surface tension corrections. • Results informed reinforce the necessity of conducting experiments to determine nucleation conditions and bubble transport parameters in LM breeders. • Our findings and model provide a good qualitative insight into the helium nucleation phenomenon in LM systems for fusion technology and can be used to identify key system parameters. -- Abstract: Helium (He) nucleation in liquid metal breeding blankets of a DT fusion reactor may have a significant impact regarding system design, safety and operation. Large He production rates are expected due to tritium (T) fuel self-sufficiency requirement, as both, He and T, are produced at the same rate. Low He solubility, local high concentrations, radiation damage and fluid discontinuities, among other phenomena, may yield the necessary conditions for He nucleation. Hence, He nucleation may have a significant impact on T inventory and may lower the T breeding ratio. A model based on the self-consistent nucleation theory (SCT) with a surface tension curvature correction model has been implemented in OpenFOAM{sup ®} CFD code. A modification through a single parameter of the necessary nucleation condition is proposed in order to take into account all the nucleation triggering phenomena, specially radiation induced nucleation. Moreover, the kinetic growth model has been adapted so as to allow for the transition from a critical cluster to a macroscopic bubble with a diffusion growth process. Limitations and capabilities of the models are shown by means of zero-dimensional simulations and sensitivity analyses to key parameters under HCLL breeding unit conditions. Results provide a good qualitative insight into the helium
International Nuclear Information System (INIS)
Highlights: • The work presented in this manuscript provides a reliable computational tool to quantify the He complex phenomena in a HCLL. • A model based on the self-consistent nucleation theory (SCT) is exposed. It includes radiation induced nucleation modelling and surface tension corrections. • Results informed reinforce the necessity of conducting experiments to determine nucleation conditions and bubble transport parameters in LM breeders. • Our findings and model provide a good qualitative insight into the helium nucleation phenomenon in LM systems for fusion technology and can be used to identify key system parameters. -- Abstract: Helium (He) nucleation in liquid metal breeding blankets of a DT fusion reactor may have a significant impact regarding system design, safety and operation. Large He production rates are expected due to tritium (T) fuel self-sufficiency requirement, as both, He and T, are produced at the same rate. Low He solubility, local high concentrations, radiation damage and fluid discontinuities, among other phenomena, may yield the necessary conditions for He nucleation. Hence, He nucleation may have a significant impact on T inventory and may lower the T breeding ratio. A model based on the self-consistent nucleation theory (SCT) with a surface tension curvature correction model has been implemented in OpenFOAM® CFD code. A modification through a single parameter of the necessary nucleation condition is proposed in order to take into account all the nucleation triggering phenomena, specially radiation induced nucleation. Moreover, the kinetic growth model has been adapted so as to allow for the transition from a critical cluster to a macroscopic bubble with a diffusion growth process. Limitations and capabilities of the models are shown by means of zero-dimensional simulations and sensitivity analyses to key parameters under HCLL breeding unit conditions. Results provide a good qualitative insight into the helium nucleation
Turbulence kinetic energy budget in bubbly flows in a vertical duct
Energy Technology Data Exchange (ETDEWEB)
Hosokawa, Shigeo; Suzuki, Takashi; Tomiyama, Akio [Graduate School of Engineering, Kobe University, Department of Mechanical Engineering, Kobe, Hyogo (Japan)
2012-03-15
Understanding turbulence kinetic energy (TKE) budget in gas-liquid two-phase bubbly flows is indispensable to develop and improve turbulence models for the bubbly flows. In this study, a molecular tagging velocimetry based on photobleaching reaction was applied to turbulent bubbly flows with sub-millimeter bubbles in a vertical square duct to examine the applicability of the k-{epsilon} models to the bubbly flows. Effects of bubbles on TKE budget are discussed and a priori tests of the standard and low Reynolds number k-{epsilon} models are carried out to examine the applicability of these models to the bubbly flows. The conclusions obtained are as follows: (1) The photobleaching molecular tagging velocimetry is of use for validating turbulence models. (2) The bubbles increase the liquid velocity gradient in the near wall region, and therefore, enhance the production and dissipation rates of TKE. (3) The k-{epsilon} models can reasonably evaluate the production rate of TKE in the bubbly flows. (4) The modulations of diffusion due to the bubbles have different characteristics from the diffusion enhancement due to shear-induced turbulence. Hence, the k-{epsilon} models fail in evaluating the diffusion rate in the near wall region in the bubbly flows. (5) The k-{epsilon} models represent the trends of the production, dissipation, and diffusion rates of {epsilon} in the bubbly flow, although more accurate experimental data are required for quantitative validation of the {epsilon} equation. (orig.)
Voronoi analysis of bubbly flows via ultrafast X-ray tomographic imaging
Energy Technology Data Exchange (ETDEWEB)
Lau, Yuk Man; Mueller, Karolin; Azizi, Salar; Schubert, Markus [Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Fluid Dynamics, Dresden (Germany)
2016-03-15
Although clustering of bubbles plays a significant role in bubble column reactors regarding the heat and mass transfer due to bubble-bubble and flow field interactions, it has yet to be fully understood. Contrary to flows in bubble columns, most literature studies on clustering report numerical and experimental results on dilute or micro-bubbly flows. In this paper, clustering of bubbles in a cylindrical bubble column of 100 mm diameter is experimentally investigated. Ultrafast X-ray tomographic imaging is used to obtain the bubble positions within a hybrid Eulerian framework. By means of Voronoi analysis, the clustering behavior of bubbles is investigated. Experiments are performed with different superficial gas velocities, where Voronoi diagrams are constructed at several column heights. From the PDFs of the Voronoi diagrams, it is shown that the bubble structuring in terms of Voronoi cell volumes develops slower than the bubble size distribution. The latter reaches a steady state earlier with increasing column height. The measured PDFs are compared with the PDF of randomly distributed points, which showed that the amount of bubbles as part of clusters (Voronoi cells < V/ anti V{sub cluster}) as well as bubbles as part of voids (Voronoi cells > V/ anti V{sub void}) increases with the superficial gas velocity. It is found that all experiments have an approximate cluster limit V/ anti V{sub cluster} of 0.63, while the void limit V/ anti V{sub void} varies between 1.5 and 3.0. (orig.)
Fainerman, V B; Kovalchuk, V I; Aksenenko, E V; Miller, R
2016-06-01
The dilational viscoelasticity of adsorption layer was measured at different frequencies of drop and bubble surface area oscillations for aqueous C12EO5 solutions. The modulus values obtained by the two experimental protocols are the same for Π surface pressures the values from drop experiments exceed those from bubble profile analysis. The nature of this phenomenon was studied using stress deformation experiments. At high surfactant concentrations the magnitude of surface tension variations is essentially higher for drops as compared with bubbles, leading to an increased viscoelasticity modulus for oscillating drops. The observed effects are analyzed quantitatively using a diffusion controlled exchange of matter model. The viscoelasticity moduli for a number of surfactants (different CnEOm and Tritons, C13DMPO, and SDS) are reported, and it is shown that the discrepancies between the data obtained by the two methods for many surfactants agree well with the predictions made here. PMID:27164467
Bubble visualization in a simulated hydraulic jump
Witt, Adam; Shen, Lian
2013-01-01
This is a fluid dynamics video of two- and three-dimensional computational fluid dynamics simulations carried out at St. Anthony Falls Laboratory. A transient hydraulic jump is simulated using OpenFOAM, an open source numerical solver. A Volume of Fluid numerical method is employed with a realizable k-epsilon turbulence model. The goal of this research is to model the void fraction and bubble size in a transient hydraulic jump. This fluid dynamics video depicts the air entrainment characteristics and bubble behavior within a hydraulic jump of Froude number 4.82.
International Nuclear Information System (INIS)
This paper presents an analytical model of the bubble pump in a commercial diffusion–absorption refrigerator. Moreover, the energetic analysis achieved is integrated with a heat transfer model and coupled to a thermodynamic model to evaluate the cooling capacity and the coefficient of performance of the refrigeration system, based on geometrical and operational parameters such as heat input, diameter ratio and bubble tube length as well as the ammonia fraction at the inlet of the bubble pump. The results show that the cooling capacity and COP are mainly influenced by geometrical parameters, such as diameter ratio and tube length of the bubble pump, and slightly influenced by the heat input supplied to the bubble pump. The strong concentration range, which is also considered in this work, is a parameter that does not affect the cooling capacity and COP. Moreover, the results reveal that the lowest cooling capacity and COP are obtained when the refrigerator operates at the manufacture design conditions. An increase in cooling capacity and COP of about 150% can be obtained when the diameter ratio is expanded up to 1.5 when comparing with the original configuration. It is expected that these results help researchers and manufacturers extend their analysis to increase the energy performance in diffusion–absorption refrigeration systems. - Highlights: • An analytical model of the bubble pump of a commercial diffusion–absorption refrigerator is proposed. • The analysis presents a broadly characterization of the bubble pump. • A heat transfer model was included in order to evaluate the cooling capacity of all thermostat positions. • The model was validated using several operation conditions of the experimental refrigerator. • The cooling capacity and COP are mainly influenced by the geometrical parameters
Mass transport by buoyant bubbles in galaxy clusters
Pope, Edward C D; Pavlovski, Georgi; Bower, Richard G; Dotter, Aaron; Victoria, University of; Southampton, University of; Durham, University of
2010-01-01
We investigate the effect of three important processes by which AGN-blown bubbles transport material: drift, wake transport and entrainment. The first of these, drift, occurs because a buoyant bubble pushes aside the adjacent material, giving rise to a net upward displacement of the fluid behind the bubble. For a spherical bubble, the mass of upwardly displaced material is roughly equal to half the mass displaced by the bubble, and should be ~ 10^{7-9} solar masses depending on the local ICM and bubble parameters. We show that in classical cool core clusters, the upward displacement by drift may be a key process in explaining the presence of filaments behind bubbles. A bubble also carries a parcel of material in a region at its rear, known as the wake. The mass of the wake is comparable to the drift mass and increases the average density of the bubble, trapping it closer to the cluster centre and reducing the amount of heating it can do during its ascent. Moreover, material dropping out of the wake will also ...
Bubble growth in a narrow horizontal space
International Nuclear Information System (INIS)
The purpose of this work is to develop an axis-symmetric two-phase flow model describing the growth of a single bubble squeezed between a horizontal heated upward-facing disc and an insulating surface placed parallel to the heated surface. Heat transfers at the liquid-vapour interfaces are predicted by the kinetic limit of vaporisation. The depths of the liquid films deposed on the surfaces (heated surface and confinement space) are determined using the Moriyama and Inoue correlation (1996). Transient heat transfers within the heated wall are taken into account. The model is applied to pentane bubble growth. The influence of the gap size, the initial temperature of the system, the thermal effusivity of the heated wall and the kinetic limit of vaporisation are studied. The results show that the expansion of the bubbles strongly depends on the gap size and can be affected by the effusivity of the material. Mechanical inertia effects are mainly dominant at the beginning of the bubble expansion. Pressure drop induced by viscous effects have to be taken into account for high capillary numbers. Heat transfers at the meniscus are negligible except at the early stages of the bubble growth. (author)
Comparing model predictions for ecosystem-based management
DEFF Research Database (Denmark)
Jacobsen, Nis Sand; Essington, Timothy E.; Andersen, Ken Haste
2016-01-01
Ecosystem modeling is becoming an integral part of fisheries management, but there is a need to identify differences between predictions derived from models employed for scientific and management purposes. Here, we compared two models: a biomass-based food-web model (Ecopath with Ecosim (EwE)) and...... predictions, underscoring the importance of incorporating knowledge of model assumptions and limitation, possibly through using model ensembles, when providing model-based scientific advice to policy makers....
Bubble transport in subcooled flow boiling
Owoeye, Eyitayo James
Understanding the behavior of bubbles in subcooled flow boiling is important for optimum design and safety in several industrial applications. Bubble dynamics involve a complex combination of multiphase flow, heat transfer, and turbulence. When a vapor bubble is nucleated on a vertical heated wall, it typically slides and grows along the wall until it detaches into the bulk liquid. The bubble transfers heat from the wall into the subcooled liquid during this process. Effective control of this transport phenomenon is important for nuclear reactor cooling and requires the study of interfacial heat and mass transfer in a turbulent flow. Three approaches are commonly used in computational analysis of two-phase flow: Eulerian-Lagrangian, Eulerian-Eulerian, and interface tracking methods. The Eulerian- Lagrangian model assumes a spherical non-deformable bubble in a homogeneous domain. The Eulerian-Eulerian model solves separate conservation equations for each phase using averaging and closure laws. The interface tracking method solves a single set of conservation equations with the interfacial properties computed from the properties of both phases. It is less computationally expensive and does not require empirical relations at the fluid interface. Among the most established interface tracking techniques is the volume-of-fluid (VOF) method. VOF is accurate, conserves mass, captures topology changes, and permits sharp interfaces. This work involves the behavior of vapor bubbles in upward subcooled flow boiling. Both laminar and turbulent flow conditions are considered with corresponding pipe Reynolds number of 0 -- 410,000 using a large eddy simulation (LES) turbulence model and VOF interface tracking method. The study was performed at operating conditions that cover those of boiling water reactors (BWR) and pressurized water reactors (PWR). The analysis focused on the life cycle of vapor bubble after departing from its nucleation site, i.e. growth, slide, lift-off, rise
Bubbles of Nothing and Supersymmetric Compactifications
Blanco-Pillado, Jose J; Sousa, Kepa; Urrestilla, Jon
2016-01-01
We investigate the non-perturbative stability of supersymmetric compactifications with respect to decay via a bubble of nothing. We show examples where this kind of instability is not prohibited by the spin structure, i.e., periodicity of fermions about the extra dimension. However, such "topologically unobstructed" cases do exhibit an extra-dimensional analog of the well-known Coleman-De Luccia suppression mechanism, which prohibits the decay of supersymmetric vacua. We demonstrate this explicitly in a four dimensional Abelian-Higgs toy model coupled to supergravity. The compactification of this model to $M_3 \\times S_1$ presents the possibility of vacua with different windings for the scalar field. Away from the supersymmetric limit, these states decay by the formation of a bubble of nothing, dressed with an Abelian-Higgs vortex. We show how, as one approaches the supersymmetric limit, the circumference of the topologically unobstructed bubble becomes infinite, thereby preventing the realization of this dec...
Root Causes of the Housing Bubble
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.
Comparative study of turbulence models in predicting hypersonic inlet flows
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1992-01-01
A numerical study was conducted to analyze the performance of different turbulence models when applied to the hypersonic NASA P8 inlet. Computational results from the PARC2D code, which solves the full two-dimensional Reynolds-averaged Navier-Stokes equation, were compared with experimental data. The zero-equation models considered for the study were the Baldwin-Lomax model, the Thomas model, and a combination of the Baldwin-Lomax and Thomas models; the two-equation models considered were the Chien model, the Speziale model (both low Reynolds number), and the Launder and Spalding model (high Reynolds number). The Thomas model performed best among the zero-equation models, and predicted good pressure distributions. The Chien and Speziale models compared wery well with the experimental data, and performed better than the Thomas model near the walls.
Spiraling bubbles: How acoustic and hydrodynamic forces compete
Rensen, Judith; Bosman, Dennis; Magnaudet, Jacques; Ohl, Claus-Dieter; Prosperetti, Andrea; Togel, Rudiger; Versluis, Michel; Lohse, Detlef
2001-01-01
Experiments to study the effect of acoustic forces on individual bubbles in shear flows have been carried out. In the system that we have used, the competition between acoustic and fluid dynamical forces results in a spiraling bubble trajectory. This dynamics is modeled by expressing the balance bet
Scanning bubble chamber pictures
1974-01-01
These were taken at the 2 m hydrogen bubble chamber. The photo shows an early Shiva system where the pre-measurements needed to qualify the event were done manually (cf photo 7408136X). The scanning tables were located in bld. 12. Gilberte Saulmier sits on foreground, Inge Arents at centre.
Critical scattering by bubbles
International Nuclear Information System (INIS)
We apply the complex angular momentum theory to the problem of the critical scattering of light by spherical cavities in the high frequency limit (permittivity greater than the external media) (e.g, air bubble in water) (M.W.O.)
1972-01-01
Looking up into the interior of BEBC bubble chamber from the expansion cylinder. At the top of the chamber two fish-eye lenses are installed and three other fish-eye ports are blanked off. In the centre is a heat exchanger.
Glass Bubbles Insulation for Liquid Hydrogen Storage Tanks
Sass, J. P.; SaintCyr, W. W.; Barrett, T. M.; Baumgartner, R. G.; Lott, J. W.; Fesmire, J. E.
2009-01-01
A full-scale field application of glass bubbles insulation has been demonstrated in a 218,000 L liquid hydrogen storage tank. This work is the evolution of extensive materials testing, laboratory scale testing, and system studies leading to the use of glass bubbles insulation as a cost efficient and high performance alternative in cryogenic storage tanks of any size. The tank utilized is part of a rocket propulsion test complex at the NASA Stennis Space Center and is a 1960's vintage spherical double wall tank with an evacuated annulus. The original perlite that was removed from the annulus was in pristine condition and showed no signs of deterioration or compaction. Test results show a significant reduction in liquid hydrogen boiloff when compared to recent baseline data prior to removal of the perlite insulation. The data also validates the previous laboratory scale testing (1000 L) and full-scale numerical modeling (3,200,000 L) of boiloff in spherical cryogenic storage tanks. The performance of the tank will continue to be monitored during operation of the tank over the coming years. KEYWORDS: Glass bubble, perlite, insulation, liquid hydrogen, storage tank.