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Mecanismo de flotação de partículas grossas em células mecânicas: influência das variáveis hidrodinâmicas e suas implicações cinéticas.; Mechanisms of coarse particle flotation in mechanical cell: influence of the hydrodynamic parameters and kinetics involvement.

Rodrigues, Wendel Johnson
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/08/2010 PT
Relevância na Pesquisa
55.36%
A seletividade e eficiência do processo de flotação não estão fundamentadas tão somente nas diferenças das propriedades físico-químicas das superfícies dos minerais, mas também na hidrodinâmica do sistema de concentração. Via de regra, a eficácia da flotação diminui quando o tamanho de partícula ultrapassa 150 micrômetros. Esta pesquisa visou estudar a influência de variáveis hidrodinâmicas sobre mecanismos de flotação de partículas grossas em células mecânicas e suas implicações cinéticas. Os ensaios utilizaram células com agitação mecânica e cada situação experimental esteve associada a um conjunto de variáveis hidrodinâmicas: números de hidrodinâmicos adimensionais, características geométricas do impelidor, velocidade mínima de suspensão da polpa, energia dissipada média e energia de preservação do agregado partícula-bolha. Desta forma, a influência dos parâmetros hidrodinâmicos na flotação de apatita e esferas de vidro (diâmetro médio248 micrômetros) foi determinada na presença de oleato de sódio e acetato de eteramina em pH 10. Em condições hidrodinâmicas pouco turbulenta, a recuperação de partículas grossas decresce em função da falta de suspensão de partículas...

Modelagem matemática e simulação numérica do transporte de metano em reservatórios de hidrelétricas; Mathematical modeling and numerical simulation of the methane transport in hydroelectric reservoirs

Cirilo, Eliandro Rodrigues
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/09/2012 PT
Relevância na Pesquisa
95.64%
É notório que a degradação ambiental vem ao longo do tempo posicionando-se como um dos principais problemas do mundo moderno. Dentre as várias questões do interesse ambiental podemos destacar a ascensão da bolha de metano, em reservatórios hidrelétricos, desde o sedimento anóxico no fundo do reservatório até a interface água atmosfera. Neste contexto, a presente tese vêm propor uma nova modelagem matemática para a ascensão da bolha axissimétrica em fluidos newtonianos/nãonewtonianos e mostrar resultados numéricos simulados. Desta forma, o estado da arte estaria elevado a posição de permitir, via Matemática e Simulação Numérica-Computacional, a análise do transporte de metano em reservatórios de hidrelétricas através da bolha; It is well-known that environmental degradation has come along the time positioning as one of the main problems from modern world. Among several questions of the environmental interest may emphasize the methane bubble rise in hydroelectric reservoirs from the anoxic sediment in the bottom of reservoir until water interface atmosphere. In this context, the current thesis has come to propose a new mathematic modeling to the rise of the axisymmetric bubble in the newtonian/non-newtonian fluids and display numerical results simulated. Therefore...

Experimentação física do escoamento gás-líquido em uma coluna de bolhas retangular utilizando a técnica PIV e a técnica de sombras SHADOW; Gas- liquid experimentation in a rectangular bubble column using PIV and Shadow techniques

Diana Isabel Sánchez Forero
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/07/2012 PT
Relevância na Pesquisa
45.64%
Colunas de bolhas são dispositivos de contato multifásico para transferência de massa e calor, intensamente utilizados em diferentes áreas industriais. O escoamento e a turbulência destes equipamentos são induzidos pelo movimento ascendente das bolhas. A hidrodinâmica e o comportamento das bolhas em regime homogêneo foram analisados em uma coluna de bolhas retangular em escala de laboratório (50 cm x 20 cm x 220 cm), utilizando as técnicas de velocimetria por imagem de partícula (PIV) e a técnica de sombras Shadow para o estudo das fases contínua e dispersa, respectivamente. O gás foi alimentado através de um distribuidor de 18 furos a várias condições de velocidade superficiais de gás na entrada. As propriedades do escoamento para as duas fases foram determinadas por meio de uma quantidade suficiente de imagens duplas. O campo de velocidade para a fase contínua (líquido) foi obtido por adição de partículas traçadoras fluorescentes. Além disso, a intensidade de turbulência, energia cinética turbulenta e os tensores de Reynolds, foram determinados a partir dos dados obtidos pelas medições experimentais. Os resultados mostram o perfil típico da velocidade axial média do líquido, ascendente na região central e descendente nas proximidades das paredes da coluna. Também...

Numerical study of wall effects on buoyant gas-bubble rise in a liquid-filled finite cylinder

Mukundakrishnan, Karthik; Quan, Shaoping; Eckmann, David M.; Ayyaswamy, Portonovo S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.76%
The wall effects on the axisymmetric rise and deformation of an initially spherical gas bubble released from rest in a liquid-filled, finite circular cylinder are numerically investigated. The bulk and gas phases are considered incompressible and immiscible. The bubble motion and deformation are characterized by the Morton number (Mo), Eötvös number (Eo), Reynolds number (Re), Weber number (We), density ratio, viscosity ratio, the ratios of the cylinder height and the cylinder radius to the diameter of the initially spherical bubble (H* = H/d0, R* = R/d0). Bubble rise in liquids described by Eo and Mo combinations ranging from (1,0.01) to (277.5,0.092), as appropriate to various terminal state Reynolds numbers (ReT) and shapes have been studied. The range of terminal state Reynolds numbers includes 0.02 < ReT < 70. Bubble shapes at terminal states vary from spherical to intermediate spherical-cap–skirted. The numerical procedure employs a front tracking finite difference method coupled with a level contour reconstruction of the front. This procedure ensures a smooth distribution of the front points and conserves the bubble volume. For the wide range of Eo and Mo examined, bubble motion in cylinders of height H* = 8 and R* ≥ 3...

Evolution of Acoustically Vaporized Microdroplets in Gas Embolotherapy

Qamar, Adnan; Wong, Zheng Z.; Fowlkes, J. Brian; Bull, Joseph L.
Fonte: American Society of Mechanical Engineers Publicador: American Society of Mechanical Engineers
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.59%
Acoustic vaporization dynamics of a superheated dodecafluoropentane (DDFP) microdroplet inside a microtube and the resulting bubble evolution is investigated in the present work. This work is motivated by a developmental gas embolotherapy technique that is intended to treat cancers by infarcting tumors using gas bubbles. A combined theoretical and computational approach is utilized and compared with the experiments to understand the evolution process and to estimate the resulting stress distribution associated with vaporization event. The transient bubble growth is first studied by ultra-high speed imaging and then theoretical and computational modeling is used to predict the entire bubble evolution process. The evolution process consists of three regimes: an initial linear rapid spherical growth followed by a linear compressed oval shaped growth and finally a slow asymptotic nonlinear spherical bubble growth. Although the droplets are small compared to the tube diameter, the bubble evolution is influenced by the tube wall. The final bubble radius is found to scale linearly with the initial droplet radius and is approximately five times the initial droplet radius. A short pressure pulse with amplitude almost twice as that of ambient conditions is observed. The width of this pressure pulse increases with increasing droplet size whereas the amplitude is weakly dependent. Although the rise in shear stress along the tube wall is found to be under peak physiological limits...

Subcooled flow boiling heat transfer of ethanol aqueous solutions in vertical annulus space

Sarafraz, M.M.; Peyghambarzadeh, S.M.; Vaeli, N.
Fonte: Association of the Chemical Engineers Publicador: Association of the Chemical Engineers
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
65.36%
The subcooled flow boiling heat-transfer characteristics of water and ethanol solutions in a vertical annulus have been investigated up to heat flux 132kW/m2. The variations in the effects of heat flux and fluid velocity, and concentration of ethanol on the observed heat-transfer coefficients over a range of ethanol concentrations implied an enhanced contribution of nucleate boiling heat transfer in flow boiling, where both forced convection and nucleate boiling heat transfer occurred. Increasing the ethanol concentration led to a significant deterioration in the observed heat-transfer coefficient because of a mixture effect, that resulted in a local rise in the saturation temperature of ethanol/water solution at the vapor-liquid interface. The reduction in the heat-transfer coefficient with increasing ethanol concentration is also attributed to changes in the fluid properties (for example, viscosity and heat capacity) of tested solutions with different ethanol content. The experimental data were compared with some well-established existing correlations. Results of comparisons indicate existing correlations are unable to obtain the acceptable values. Therefore a modified correlation based on Gnielinski correlation has been proposed that predicts the heat transfer coefficient for ethanol/water solution with uncertainty about 8% that is the least in comparison to other well-known existing correlations.; M.M. Sarafraz...

Numerical simulation of bubble dispersion in turbulent Taylor-Couette flow

CHOUIPPE, Agathe; CLIMENT, Eric; LEGENDRE, Dominique; GABILLET, Céline
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
Relevância na Pesquisa
45.6%
We investigate bubble dispersion in turbulent Taylor-Couette flow. The aim of this study is to describe the main mechanisms yielding preferential bubble accumulation in near-wall structures of the flow. We first proceed to direct numerical simulation of Taylor-Couette flows for three different geometrical configurations (three radius ratios η = R 1/R 2: η = 0.5, η = 0.72, and η = 0.91 with the outer cylinder at rest) and Reynolds numbers corresponding to turbulent regime ranging from 3000 to 8000. The statistics of the flow are discussed using two different averaging procedures that permit to characterize the mean azimuthal velocity, the Taylor vortices contribution and the small-scale turbulent fluctuations. The simulations are compared and validated with experimental and numerical data from literature. The second part of this study is devoted to bubble dispersion. Bubble accumulation is analyzed by comparing the dispersion obtained with the full turbulent flow field to bubble dispersion occurring at lower Reynolds numbers in previous works. Several patterns of preferential accumulation of bubbles have been observed depending on bubble size and the effect of gravity. For the smaller size considered, bubbles disperse homogeneously throughout the gap...

An experimental study of nanobubbles on hydrophobic surfaces

Agarwal, Abhinandan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 127 p.; 4752156 bytes; 5086346 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
55.57%
With the recent development of microfluidic systems, miniaturization of flow devices has become a real challenge. Microchannels, however, are characterized by a large surface area-to-volume ratio so that surface properties strongly affect flow resistance in sub-micrometer devices. Recent studies in the literature have opened up the possibility of a controlled realization of nanobubbles- found to exist primarily on hydrophobic surfaces- that can play all important role in changing the hydrodynamic boundary condition at the fluid-solid interface giving rise to considerable reduction in friction of the fluid flow past the solid boundaries. In this study, we seek to increase our understanding of the formation, morphology, and stability of nanobubbles. Further. we seek to exploit the dependence of nanobubble formation on surface to provide a means for controlling hydrodynamic boundary conditions at the solid-liquid interface. The formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase.; (cont.) First, a number of homogeneous surfaces are used as solid substrates to understand and analyze the formation and distribution of nanobubbles on homogeneous surfaces with differing degrees of hydrophobicity. While nanobubbles do not form on flat hydrophilic surfaces immersed in water. they appear spontaneously at the interface of water against smooth...

Intense spreading of radar echoes from ionospheric plasmas

Dorfman, Seth E
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 59 leaves; 2292344 bytes; 2293745 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
55.46%
On December 25, 2004, a large-scale ionospheric plasma bubble was observed over Arecibo Observatory in Puerto Rico, inducing significant range spreading on ionograms. This phenomena may be explained by means of the E x B instability and gravitational Rayleigh-Taylor instability. A derivation of the dispersion relations for X and O mode waves transmitted from an ionosonde and an analysis of the collisional Rayleigh-Taylor instability leading to an expression for the growth rate are presented as background information. Ray tracing code developed by Nathan Dalrymple, a previous graduate student of Professor Min-Chang Lee, is extended, first to draw refractive index surfaces to illustrate a key principle in ray tracing and later to simulate range spreading due to depleted ionospheric ducts [1]. Data from Arecibo incoherent scatter radar and Arecibo's CADI digisonde is examined showing strong evidence for the development of a plasma bubble following a rise in the plasma layer and the appearance of a horizontal density gradient. In one portion of the ionosphere, this gradient is found to be at an angle of approximately 70 degrees to the Earth's magnetic field, a favorable condition for the excitation of the Rayleigh-Taylor instability over Arecibo.; by Seth E. Dorfman.; Thesis (S.B.)--Massachusetts Institute of Technology...

The mismatched nucleotides in the 5'-terminal hairpin of minute virus of mice are required for efficient viral DNA replication.

Costello, E; Sahli, R; Hirt, B; Beard, P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1995 EN
Relevância na Pesquisa
45.67%
The 5'-terminal sequence in the DNA of the parvovirus minute virus of mice (MVM) is a palindrome. It can form a hairpin, the stem of which is entirely base-paired except for three consecutive unpaired nucleotides which form a bubble. Since this structure is well conserved among different parvoviruses, we examined its importance for viral replication by generating MVM mutants with alterations in this region. A clone of MVMp DNA which contained the entire 3' end and more than half of the 5' palindrome was made. Although it lacked the sequence information to form a wild-type bubble, this DNA was infectious. On transfection into A9 fibroblasts, it gave rise to a virus (MVMs) which had a bubble in its 5' palindrome. The bubble consisted of four mismatched nucleotides in the same location as the unpaired nucleotides of the wild-type palindrome. Apparently, neighboring plasmid sequences were incorporated into the viral DNA, enabling formation of the mismatch. This observation suggested that a bubble is critical for growth of MVM but that its sequence is not. To find out whether MVM lacking a bubble in the 5' palindrome is viable, we made a second clone in which the plasmid sequences incorporated in MVMs were removed. Transfection of this DNA gave rise to a virus (MVMx) in which the nucleotides unpaired in the wild-type hairpin are now fully base-paired. Although MVMx can be propagated...

A Study of the Vertical Motion of Supernova Remnant Bubbles in the Interstellar Medium Drawn from the Results of Three-Dimensional MHD Simulations

Raley, E. A.; Shelton, R. L.; Plewa, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/07/2007
Relevância na Pesquisa
65.51%
In order to determine the circumstances under which isolated SNRs are capable of rising into and enriching the thick disk and galactic halo, simulations of supernova remnants are performed with the FLASH magnetohydrodynamic code. We performed simulations in which the interstellar magnetic field is parallel to or perpendicular to the galactic plane as well as a simulation without a magnetic field. The ambient gas density distribution and gravitational potential are based on observations of our galaxy. We evolve the remnants to ages of roughly 10,000,000 years. For our simulation without a magnetic field, we compare the evolution of the hot bubble's velocity with the velocity evolution calculated from the buoyant and drag accelerations. We found surprisingly small vertical velocities of the hot gas, from which we estimated the drag coefficient to be ten for the non-magnetic simulation. Although we found little buoyant motion of the hot gas during the remnant's lifetime, we found rapid vertical motion of the associated cool dense gas near the end of the remnants life. This motion deformed the remnant into a mushroom cloud structure similar to those found in previous simulations. The simulation in which we have a 4 micro-Gauss magnetic field parallel to the galactic mid-plane shows a dramatically elongated bubble parallel to the magnetic field. The magnetic field pins the supernova remnant preventing it from rising. In the simulation with the 4 micro-Gauss magnetic field perpendicular to the midplane the hot bubble rises more...

Bubble fluctuations in $\Omega<1$ inflation

Garriga, Jaume
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/02/1995
Relevância na Pesquisa
45.58%
In the context of the open inflationary universe, we calculate the amplitude of quantum fluctuations which deform the bubble shape. These give rise to scalar field fluctuations in the open Friedman-Robertson-Walker universe which is contained inside the bubble. One can transform to a new gauge in which matter looks perfectly smooth, and then the perturbations behave as tensor modes (gravitational waves of very long wavelength). For $(1-\Omega)<<1$, where $\Omega$ is the density parameter, the microwave temperature anisotropies produced by these modes are of order $\delta T/T\sim H(R_0\mu l)^{-1/2} (1-\Omega)^{l/2}$. Here, $H$ is the expansion rate during inflation, $R_0$ is the intrinsic radius of the bubble at the time of nucleation, $\mu$ is the bubble wall tension and $l$ labels the different multipoles ($l>1$). The gravitational backreaction of the bubble has been ignored. In this approximation, $G\mu R_0<<1$, and the new effect can be much larger than the one due to ordinary gravitational waves generated during inflation (unless, of course, $\Omega$ gets too close to one, in which case the new effect disappears).; Comment: 17 pages, 3 figs, LaTeX, epsfig.sty, available at ftp://ftp.ifae.es/preprint/ft/uabft387.ps

The Centaurus A Northern Middle Lobe as a Buoyant Bubble

Saxton, Curtis J.; Sutherland, Ralph S.; Bicknell, Geoffrey V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/07/2001
Relevância na Pesquisa
55.67%
We model the northern middle radio lobe of Centaurus A (NGC 5128) as a buoyant bubble of plasma deposited by an intermittently active jet. The extent of the rise of the bubble and its morphology imply that the ratio of its density to that of the surrounding ISM is less than 10^{-2}, consistent with our knowledge of extragalactic jets and minimal entrainment into the precursor radio lobe. Using the morphology of the lobe to date the beginning of its rise through the atmosphere of Centaurus A, we conclude that the bubble has been rising for approximately 140Myr. This time scale is consistent with that proposed by Quillen et al. (1993) for the settling of post-merger gas into the presently observed large scale disk in NGC 5128, suggesting a strong connection between the delayed re-establishment of radio emission and the merger of NGC 5128 with a small gas-rich galaxy. This suggests a connection, for radio galaxies in general, between mergers and the delayed onset of radio emission. In our model, the elongated X-ray emission region discovered by Feigelson et al. (1981), part of which coincides with the northern middle lobe, is thermal gas that originates from the ISM below the bubble and that has been uplifted and compressed. The "large-scale jet" appearing in the radio images of Morganti et al. (1999) may be the result of the same pressure gradients that cause the uplift of the thermal gas...

Vibration and Nonlinear Resonance in the Break-up of an Underwater Bubble

Lai, Lipeng; Keim, Nathan C.; Fezzaa, Kamel; Zhang, Wendy W.; Nagel, Sidney R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/07/2013
Relevância na Pesquisa
45.58%
We use high-speed X-ray phase-contrast imaging, weakly nonlinear analysis and boundary integral simulations to characterize the final stage of underwater bubble break-up. The X-ray imaging study shows that an initial azimuthal perturbation to the shape of the bubble neck gives rise to oscillations that increasingly distort the cross-section shape. These oscillations terminate in a pinch-off where the bubble surface develops concave regions that contact similar to what occurs when two liquid drops coalesce. We also present a weakly nonlinear analysis that shows that this coalescence-like mode of pinch-off occurs when the initial shape oscillation interferes constructively with the higher harmonics it generates and thus reinforce each other's effects in bringing about bubble break-up. Finally we present numerical results that confirm the weakly nonlinear analysis scenario as well as provide insight into observed shape reversals. They demonstrate that when the oscillations interfere destructively, a qualitatively different mode of pinch-off results where the cross-section profile of the bubble neck develops sharply-curved regions.; Comment: 30 pages, 16 figures, submitted to Journal of Fluid Mechanics

A Comprehensive Study of the Radio Properties of Brightest Cluster Galaxies

Hogan, M. T.; Edge, A. C.; Hlavacek-Larrondo, J.; Grainge, K. J. B.; Hamer, S. L.; Mahony, E. K.; Russell, H. R.; Fabian, A. C.; McNamara, B. R.; Wilman, R. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/07/2015
Relevância na Pesquisa
55.36%
We examine the radio properties of the Brightest Cluster Galaxies (BCGs) in a large sample of X-ray selected galaxy clusters comprising the Brightest Cluster Sample (BCS), the extended BCS (eBCS) and ROSAT-ESO Flux Limited X-ray (REFLEX) cluster catalogues. We have multi-frequency radio observations of the BCG using a variety of data from the Australia Telescope Compact Array (ATCA), Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) telescopes. The radio spectral energy distributions (SEDs) of these objects are decomposed into a component attributed to on-going accretion by the active galactic nuclei (AGN) that we refer to as the 'core', and a more diffuse, ageing component we refer to as the 'non-core'. These BCGs are matched to previous studies to determine whether they exhibit emission lines (principally H-alpha), indicative of the presence of a strong cooling cluster core. We consider how the radio properties of the BCGs vary with cluster environmental factors. Line emitting BCGs are shown to generally host more powerful radio sources, exhibiting the presence of a strong, distinguishable core component in about 60% of cases. This core component more strongly correlates with the BCG's [OIII]5007A line emission. For BCGs in line-emitting clusters...

Determining the outcome of cosmic bubble collisions in full General Relativity

Johnson, Matthew C.; Peiris, Hiranya V.; Lehner, Luis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.59%
Cosmic bubble collisions provide an important possible observational window on the dynamics of eternal inflation. In eternal inflation, our observable universe is contained in one of many bubbles formed from an inflating metastable vacuum. The collision between bubbles can leave a detectable imprint on the cosmic microwave background radiation. Although phenomenological models of the observational signature have been proposed, to make the theory fully predictive one must determine the bubble collision spacetime, and thus the cosmological observables, from a scalar field theory giving rise to eternal inflation. Because of the intrinsically non-linear nature of the bubbles and their collision, this requires a numerical treatment incorporating General Relativity. In this paper, we present results from numerical simulations of bubble collisions in full General Relativity. These simulations allow us to accurately determine the outcome of bubble collisions, and examine their effect on the cosmology inside a bubble universe. We confirm the validity of a number of approximations used in previous analytic work, and identify qualitatively new features of bubble collision spacetimes. Both vacuum bubbles and bubbles containing a realistic inflationary cosmology are studied. We identify the constraints on the scalar field potential that must be satisfied in order to obtain collisions that are consistent with our observed cosmology...

On bubble clustering and energy spectra in pseudo-turbulence

Martinez, J.; Chehata, D.; van Gils, D. P. M.; Sun, C.; Lohse, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/12/2009
Relevância na Pesquisa
45.59%
3D-Particle Tracking (3D-PTV) and Phase Sensitive Constant Temperature Anemometry in pseudo-turbulence--i.e., flow solely driven by rising bubbles-- were performed to investigate bubble clustering and to obtain the mean bubble rise velocity, distributions of bubble velocities, and energy spectra at dilute gas concentrations ($\alpha \leq2.2$%). To characterize the clustering the pair correlation function $G(r,\theta)$ was calculated. The deformable bubbles with equivalent bubble diameter $d_b=4-5$ mm were found to cluster within a radial distance of a few bubble radii with a preferred vertical orientation. This vertical alignment was present at both small and large scales. For small distances also some horizontal clustering was found. The large number of data-points and the non intrusiveness of PTV allowed to obtain well-converged Probability Density Functions (PDFs) of the bubble velocity. The PDFs had a non-Gaussian form for all velocity components and intermittency effects could be observed. The energy spectrum of the liquid velocity fluctuations decayed with a power law of -3.2, different from the $\approx -5/3$ found for homogeneous isotropic turbulence, but close to the prediction -3 by \cite{lance} for pseudo-turbulence.

Experimental characterisation of bubbly flow using MRI

Tayler, Alexander B.
Fonte: University of Cambridge; Department of Chemical Engineering and Biotechnology; Trinity College Publicador: University of Cambridge; Department of Chemical Engineering and Biotechnology; Trinity College
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
55.67%
This thesis describes the first application of ultra-fast magnetic resonance imaging (MRI) towards the characterisation of bubbly flow systems. The principle goal of this study is to provide a hydrodynamic characterisation of a model bubble column using drift-flux analysis by supplying experimental closure for those parameters which are considered difficult to measure by conventional means. The system studied consisted of a 31 mm diameter semi-batch bubble column, with 16.68 mM dysprosium chloride solution as the continuous phase. This dopant served the dual purpose of stabilising the system at higher voidages, and enabling the use of ultra-fast MRI by rendering the magnetic susceptibilities of the two phases equivalent. Spiral imaging was selected as the optimal MRI scan protocol for application to bubbly flow on the basis of its high temporal resolution, and robustness to fluid flow and shear. A velocimetric variant of this technique was developed, and demonstrated in application to unsteady, single-phase pipe flow up to a Reynolds number of 12,000. By employing a compressed sensing reconstruction, images were acquired at a rate of 188 fps. Images were then acquired of bubbly flow for the entire range of voidages for which bubbly flow was possible (up to 40.8%). Measurements of bubble size distribution and interfacial area were extracted from these data. Single component velocity fields were also acquired for the entire range of voidages examined. The terminal velocity of single bubbles in the present system was explored in detail with the goal of validating a bubble rise model for use in drift-flux analysis. In order to provide closure to the most sophisticated bubble rise models...

Growth of vapor bubbles in a rapidly heated liquid

Zwick, S. A.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /09/1960
Relevância na Pesquisa
45.63%
The earlier theory of the growth of vapor bubbles in superheated liquids is extended to the situation in which the rate of temperature rise of the liquid is large. Numerical solutions are presented for the early stages of bubble growth for various rates of liquid temperature rise. The asymptotic behavior of a bubble is found explicitly for a temperature rise of the liquid which is linear in time. In this case the bubble radius grows initially as t^1/2, as in asymptotic solutions found previously for small rates of temperature rise, but then deviates toward a late t^3/2 variation.

The Centaurus A Northern Middle Lobe as a Buoyant Bubble

Saxton, Curtis; Sutherland, Ralph; Bicknell, Geoffrey
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.67%
We model the northern middle radio lobe of Centaurus A (NGC 5128) as a buoyant bubble of plasma deposited by an intermittently active jet. The extent of the rise of the bubble and its morphology imply that the ratio of its density to that of the surrounding ISM is less than 10-2, consistent with our knowledge of extragalactic jets and minimal entrainment into the precursor radio lobe. Using the morphology of the lobe to date the beginning of its rise through the atmosphere of Cen A, we conclude that the bubble has been rising for approximately 140 Myr. This timescale is consistent with that proposed by Quillen and coworkers for the settling of postmerger gas into the presently observed large-scale disk in NGC 5128, suggesting a strong connection between the delayed reestablishment of radio emission and the merger of NGC 5128 with a small gas-rich galaxy. This suggests a connection, for radio galaxies in general, between mergers and the delayed onset of radio emission. In our model, the elongated X-ray emission region discovered by Feigelson and coworkers, part of which coincides with the northern middle lobe, is thermal gas that originates from the interstellar medium below the bubble and that has been uplifted and compressed. The "large-scale jet" appearing in the radio images of Morganti and coworkers may be the result of the same pressure gradients that cause the uplift of the thermal gas...