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Correlação entre imagens e sinal elétrico para determinação do diâmetro de bolhas em líquidos ; Correlation between images and electrical signals for determination of bubble diameters in liquids

Marinho, Marcelo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/12/2006 PT
Relevância na Pesquisa
36.51%
A distribuição do tamanho de bolhas é uma importante característica em sistemas bifásicos. A área interfacial de bolhas está fortemente relacionada às taxas de reações químicas e de transferência de massa em aplicações industriais como colunas de destilação e fermentação, sistemas biológicos, oxidação, hidrogenação, tratamento de água, e em processos naturais, como dinâmicas de aerossóis e transferência de gás oceano-atmosfera. Pontas de provas intrusivas são largamente usadas para determinar a distribuição do tamanho de bolhas em colunas de borbulhamento bifásicas. Embora o tamanho de bolhas não possa ser obtido diretamente pelo uso de uma simples ponta de prova porque estas medem somente comprimentos perfurados em bolhas, é possível relacionar distribuições de cordas à distribuição de tamanho de bolhas usando análises estatísticas. Este trabalho apresenta a implementação de um sistema capaz de medir distribuição de tamanho de bolhas em uma coluna de borbulhamento composta por água e ar através de uma ponta de prova condutiva. Imagens obtidas por uma câmera de vídeo CCD (Charge-Coupled Devices) monocromática são usadas para validar e calibrar o sistema.; The distribution of bubble sizes is a critical feature in two–phase systems. The interfacial area of bubbles is strongly related to chemical reaction and mass transfer rates in industrial applications such as distillation and fermentation columns...

Effect of solids on gas-liquid mass transfer and bubble characteristics in three-phase systems

Mena, P. C.; Pons, M. N.; Teixeira, J. A.; Rocha, F. A.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /07/2005 ENG
Relevância na Pesquisa
36.38%
Comunicação apresentada no "7th World Congress of Chemical Engineering" em Glasgow, Escócia, em Julho de 2005.; The effect of the solids on the mass transfer characteristics in a bubble column was studied experimentally for the system air/water/beads of calcium alginate. Volumetric liquid side mass transfer coefficient, kLα, specific interfacial area, α, and liquid side mass transfer coefficient, kL, were determined under different solid concentrations, gas flow rates and solid sizes. Bubble characteristics were obtained using an image analysis technique. The presence of solids affect negatively kLα, decreasing both α and kL and the effect is more pronounced for the smaller particles. For these particles the variation of kLα is due to the variation of its two components, while for larger particles kLα variation is due, essentially, to changes in kL as no significant differences in α were observed. An optical probe technique was also used to obtain gas holdup radial profiles for higher solids loadings and gas flow rates. It was observed that increasing the solids loading, the gas holdup decreases and the shape of the gas holdup profiles is also influenced by the solids concentration.; Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/3427/2000...

Measurement of gas phase characteristics using amonofibre optical probe in a three-phase flow

Mena, P. C.; Rocha, F. A.; Teixeira, J. A.; Sechet, P.; Cartellier, C.
Fonte: Elsevier Ltd. Publicador: Elsevier Ltd.
Tipo: Artigo de Revista Científica
Publicado em /08/2008 ENG
Relevância na Pesquisa
36.44%
The study of gas–liquid–solid systems structure requires reliable measurement tools. In this paper, preliminary results on the potential use of a monofibre optical probe to investigate such flow are presented. This probe, manufactured at LEGI, allows the simultaneous measurement of the gas phase residence time and gas phase velocity. This specificity makes this probe more interesting than classical single tip probes (which measure only the gas residence time) or double tip probes (which are more intrusive). Although extensively used in two-phase gas–liquid, this probe was never used in gas–liquid–solid systems. First, the probe signal response is studied for three-phase flow conditions in the presence of solids. Results show that for soft solids, the probe tips can be contaminated when the probe pierces the solid. The signal processing procedure was modified accordingly to take into account these events. Second, the probe results are validated by comparing global results (global void fraction, gas flowrate) deduced from profile measurements with measurements performed by independent means. Lastly, void fraction profiles and interfacial area are studied more in detail. Depending on the solid loading, these profiles exhibit different behaviours. These features are associated to characteristics of the flow such as the transition from an homogeneous regime to an heterogenous regime...

Feasibility of an in situ measurement device for bubble size and distribution

Junker, Beth; Maciejak, Walter; Darnell, Branson; Lester, Michael; Pollack, Michael
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.38%
The feasibility of in situ measurement device for bubble size and distribution was explored. A novel in situ probe measurement system, the EnviroCam™, was developed. Where possible, this probe incorporated strengths, and minimized weaknesses of historical and currently available real-time measurement methods for bubbles. The system was based on a digital, high-speed, high resolution, modular camera system, attached to a stainless steel shroud, compatible with standard Ingold ports on fermenters. Still frames and/or video were produced, capturing bubbles passing through the notch of the shroud. An LED light source was integral with the shroud. Bubbles were analyzed using customized commercially available image analysis software and standard statistical methods. Using this system, bubble sizes were measured as a function of various operating parameters (e.g., agitation rate, aeration rate) and as a function of media properties (e.g., viscosity, antifoam, cottonseed flour, and microbial/animal cell broths) to demonstrate system performance and its limitations. For selected conditions, mean bubble size changes qualitatively compared favorably with published relationships. Current instrument measurement capabilities were limited primarily to clear solutions that did not contain large numbers of overlapping bubbles.

In vitro surfactant mitigation of gas bubble contact-induced endothelial cell death

Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
26.55%
Interactions of gas embolism bubbles with endothelial cells, as can occur during decompression events or other forms of intravascular gas entry, are poorly characterized. Endothelial cells respond to microbubble contact via mechanotransduction responses that can lead to cell death or aberrant cellular function. Cultured bovine aortic endothelial cells were individually contacted with microbubbles. Cells were loaded with fluorescent dyes indicating calcium- and nitric oxide signaling and cell viability. A surfactant, Pluronic F-127, and/or albumin were added to the culture media. Control experiments utilized calcium-free media as well as probe-poking in place of microbubble contact. We acquired fluorescence microscopy time-lapse images of cell responses to bubble and probe contact and determined contact effects on cell signaling and cell death. Calcium influx was essential for cell death to occur with bubble contact. Bubble contact stimulated extracellular calcium entry without altering nitric oxide levels unless cell death was provoked. Cell responses were independent of bubble contact duration lasting either one or 30 seconds. Microbubble contact provoked cell death over 7 times more frequently than micropipette poking. Albumin and the surfactant each attenuated the calcium response to bubble contact and also reduced the lethality of microbubble contact by 67.4% and 76.0%...

Dual-Beam Histotripsy: A Low-Frequency Pump Enabling a High-Frequency Probe for Precise Lesion Formation

Lin, Kuang-Wei; Duryea, Alexander P.; Kim, Yohan; Hall, Timothy L.; Xu, Zhen; Cain, Charles A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/2014 EN
Relevância na Pesquisa
26.52%
Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. When using pulses shorter than 2 cycles, the generation of these energetic bubble clouds only depends on where the peak negative pressure (P–) exceeds an intrinsic threshold of a medium (26 – 30 MPa in soft tissue with high water content). This paper investigates a strategic method for precise lesion generation in which a low-frequency pump pulse is applied to enable a sub-threshold high-frequency probe pulse to exceed the intrinsic threshold. This pump-probe method of controlling a supra-threshold volume can be called “dual-beam histotripsy.” A 20-element dual-frequency (500 kHz and 3 MHz elements confocally aligned) array transducer was used to generate dual-beam histotripsy pulses in RBC phantoms and porcine hepatic tissue specimens. The results showed that, when sub-intrinsic-threshold pump (500 kHz) and probe (3 MHz) pulses were applied together, dense bubble clouds (and resulting lesions) were only generated when their peak negative pressures combined constructively to exceed the intrinsic threshold. The smallest reproducible lesion varied with the relative amplitude between the pump and probe pulses...

Experimental and computational study on the bubble behavior in a 3-D fluidized bed

Acosta-Iborra, Antonio; Sobrino, Celia; Hernández-Jiménez, Fernando; Vega, Mercedes de
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf; text/plain
Publicado em 01/08/2011 ENG
Relevância na Pesquisa
36.34%
The results from a two-fluid Eulerian–Eulerian three-dimensional (3-D) simulation of a cylindrical bed, filled with Geldart-B particles and fluidized with air in the bubbling regime, are compared with experimental data obtained from pressure and optical probe measurements in a real bed of similar dimensions and operative conditions. The main objectives of this comparison are to test the validity of the simulation results and to characterize the bubble behavior and bed dynamics. The fluidized bed is 0.193 m internal diameter and 0.8 m height, and it is filled with silica sand particles, reaching a settle height of 0.22 m. A frequency domain analysis of absolute and differential pressure signals in both the measured and the simulated cases shows that the same principal phenomena are reproduced with similar distributions of peak frequencies in the power spectral density (PSD) and width of the spectrum. The local dynamic behavior is also studied in the present work by means of the PSD of the simulated particle fraction and the PSD of the measured optical signal, which reveals as well good agreement between both the spectra. This work also presents, for the first time, comparative results of the measured and the simulated bubble size and velocity in a fully 3-D bed configuration. The values of bubble pierced length and velocity retrieved from the experimental optical signals and from the simulated particle fraction compare fairly well in different radial and axial positions. Very similar values are obtained when these bubble parameters are deduced from either simulated pressure signals or simulated particle volume fraction. In addition...

Characteristic lengths and maximum entropy estimation from probe signals in the ellipsoidal bubble regime

Santana Santana, Domingo José; Rodríguez-Rodríguez, Javier; Almendros-Ibáñez, José Antonio; Martínez-Bazán, C.
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em 09/09/2006 ENG
Relevância na Pesquisa
36.57%
The bubble size, surface and volume distributions in two and three phase flows are essential to determine energy and mass transfer processes. The traditional approaches commonly use a conditional probability density function of chordlengths to calculate the bubble size distribution, when the bubble size, shape and velocity are known. However, the approach used in this paper obtains the above distributions from statistical relations, requiring only the moments inferred from the measurements given by a sampling probe. Using image analysis of bubbles injected in a water tank, and placing an ideal probe on the image, a sample of bubble diameter, shape factor and velocity angle are obtained. The samples of the bubble chord-length are synthetically generated from these variables. Thus, we propose a semi-parametric approach based on the maximum entropy (MaxEnt) distribution estimation subjected to a number of moment constraints avoiding the use of the complex backward transformation. Therefore, the method allows us to obtain the distributions in close form. The probability density functions of the most important length scales (D,D20,D30,D32), obtained applying the semi-parametric approach proposed here in the ellipsoidal bubble regime...

Three-dimensional two-fluid modeling of a cylindrical fluidized bed and validation of the Maximum Entropy method to determine bubble properties

Sobrino, Celia; Acosta-Iborra, Antonio; Izquierdo-Barrientos, María Asunción; Vega, Mercedes de
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article
Publicado em /02/2015 ENG
Relevância na Pesquisa
36.42%
Diameter and velocity of bubbles from a three-dimensional two-fluid model simulation of a cylindrical fluidized bed are presented. Two methods for obtaining the bubble size and velocity are compared: (i) estimation from the chord lengths and velocities of the detected bubbles using information from two virtual voidage probes (pierced bubble method) and (ii) calculation from the bubble volume and velocity directly obtained from the instantaneous 3D voidage field (tomography method). The Maximum Entropy method (MaxEnt) is employed to convert probability density functions of chord lengths into the corresponding diameter distributions. The algorithm for the direct evaluation of the bubble volume and velocity, based on the tomography reconstruction of the 3D field, is explicitly explained and used to evaluate the results obtained from the virtual void probe signals. Results show a good agreement between the bubble sizes obtained using the MaxEnt treatment of the chord lengths and the directly obtained bubble sizes, which confirms the robustness of the MaxEnt.method to infer bubble behavior in 3D bubbling beds. In particular, the mean bubble diameter obtained with the MaxEnt method applied to chord lengths was less than 4.5% different to the result from the tomography reconstruction. It was found that the bubble velocities obtained from virtual voidage probes are higher than the bubble velocities calculated with the tomography method...

Mitigation of underwater explosion effects by bubble curtains : experiments and modelling

CROCI, Kilian; ARRIGONI, Michel; BOYCE, P; GABILLET, Céline; GRANDJEAN, Hervé; JACQUES, Nicolas; KERAMPRAN, Steven
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
Relevância na Pesquisa
26.39%
Mine fields and UneXploded Ordnances (UXO) become a danger regarding maritime activities. Since UXOs are strongly affected by marine corrosion after decades, they cannot be handled safely. A safe solution to get rid of them would be to explode them in their locations. However, this method generates noise pollution and damaging shock waves. Mitigation of shocks and noises is made possible by the use of a bubble curtain set around the explosive charge. Physical aspects of shock propagation in bubbly flows have been the subject of numerous investigations in the past decades and theoretical models of aerated liquids now reproduce main shock features with acceptable accuracy in the case of a uniform distribution of bubbles of the same size. However, the bubble distribution obtained by air blown in a porous pipe is far to be monodisperse. So the modeling of the interaction of a shock wave with a polydisperse medium still remains a challenge. In the present study, the transmission of a shock wave propagating through a bubble curtain is investigated experimentally on a water filled tank. A microporous pipe, connected to a compressed air supply system and a flowmeter, is placed on the floor in the tank. A dual-tip fiber optical probe is used to measure the gas fraction distribution...

Lyman-Alpha Emitting Galaxies as a Probe of Reionization: Large-Scale Bubble Morphology and Small-Scale Absorbers

Kakiichi, Koki; Dijkstra, Mark; Ciardi, Benedetta; Graziani, Luca
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/10/2015
Relevância na Pesquisa
26.32%
The visibility of LyA emitting galaxies during the Epoch of Reionization is controlled by both diffuse HI patches in large-scale bubble morphology and small-scale absorbers. To investigate the impact on LyA photons, we apply a novel combination of analytic and numerical calculations to three scenarios: (i) the `bubble' model, where only diffuse HI outside ionized bubbles is present; (ii) the `web' model, where HI exists only in overdense self-shielded gas; and (iii) the more realistic 'web-bubble' model, which contains both. Our analysis confirms that there is a degeneracy between the ionization structure of the intergalactic medium (IGM) and the HI fraction inferred from LyA surveys, as the three models suppress LyA flux equally with very different HI fractions. We argue that a joint analysis of the LyA luminosity function and the rest-frame equivalent width distribution/LyA fraction can break this degeneracy and provide constraints on the reionization history and its topology. We further show that constraints can improve if we consider the full shape of the M_UV-dependent redshift evolution of the LyA fraction of Lyman break galaxies. Contrary to conventional wisdom, we find that (i) a drop of LyA fraction larger for UV-faint than for UV-bright galaxies can be reproduced with web and web-bubble models and therefore does not provide exclusive evidence of patchy reionization...

Multi-wavelength study of triggered star formation around mid-infrared bubble N14

Dewangan, L. K.; Ojha, D. K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/11/2012
Relevância na Pesquisa
26.39%
We present multi-wavelength analysis around mid-infrared bubble N14 to probe the signature of triggered star formation as well as the formation of new massive star(s) and/or cluster(s) on the borders of the bubble by the expansion of the H II region. Spitzer-IRAC ratio maps reveal that the bubble is traced by the polycyclic aromatic hydrocarbon emission following an almost circular morphology except in the south-west direction towards the low molecular density environment. The observational signatures of the collected molecular and cold dust material have been found around the bubble. We have detected 418 YSOs in the selected region around the bubble N14. Interestingly, the detected YSO clusters are associated with the collected molecular and cold dust material on the borders of the bubble. One of the clusters is found with deeply embedded intermediate mass and massive Class I YSOs associated with one of the dense dust clumps in the east of the bubble N14. We do not find a good agreement between the dynamical age of the H II region and the fragmentation time of the accumulated molecular materials to explain possible "collect-and-collapse" process around the bubble N14. Therefore, we suggest the possibility of triggered star formation by compression of the pre-existing dense clumps by the shock wave and/or small scale Jeans gravitational instabilities in the collected materials. We have also investigated 5 young massive embedded protostars (8 to 10 M_sun) and 15 intermediate mass (3 to 7 M_sun) Class I YSOs which are associated with the dust and molecular fragmented clumps at the borders of the bubble. We conclude that the expansion of the H II region is also leading to the formation of these intermediate and massive Class I YSOs around the bubble N14.; Comment: 14 pages...

Constraining Quasar and IGM Properties Through Bubble Detection in Redshifted 21-cm Maps

Majumdar, Suman; Bharadwaj, Somnath; Choudhury, T. Roy
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.34%
The infrared detection of a z>7 quasar has opened up a new window to directly probe the IGM during the epoch of reionization. In this paper we theoretically consider the possibility of detecting the ionized bubble around a z=8 quasar using targeted redshifted 21-cm observations with the GMRT. The apparent shape and size of the ionized bubble, as seen by a distant observer, depends on the parameters \dot{N}_{phs}/C, x_HI/C and \tau_Q where \dot{N}_{phs}, \tau_Q, x_HI and C are respectively the photon emission rate, age of the quasar, the neutral fraction and clumping factor of the IGM.Here we have analytically estimated the shape and size of a quasar's ionized bubble assuming an uniform IGM and ignoring other ionizing sources besides the quasar, and used this as a template for matched filter bubble search with the GMRT visibility data. We have assumed that \dot{N}_{phs} is known from the infrared spectrum and C from theoretical considerations, which gives us two free parameters x_HI and \tau_Q for bubble. Considering 1,000 hr of observation, we find that there is a reasonably large region of parameter space where a 3\sigma detection is possible. We also find that it will be possible to place lower limits on x_HI and \tau_Q with this observation. Deeper follow up observations can place upper limits on \tau_Q and x_HI. Value of C affect the estimation of x_HI but the estimation of \tau_Q remains unaffected.We have used a semi-numerical technique to simulate the apparent shape and size of quasar ionized bubbles considering the presence of other ionizing sources and inhomogeneities in the IGM. The presence of other sources increase the size of the quasar bubble...

Probing the Local Bubble with Diffuse Interstellar Bands. II. The DIB properties in the Northern hemisphere

Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; van Loon, Jacco Th.; Bailey, Mandy; Molaeinezhad, Alireza; Tavasoli, Saeed; Habibi, Farhang; Kourkchi, Ehsan; Rezaei, Sara; Saberi, Maryam; Hardy, Liam
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/11/2014
Relevância na Pesquisa
26.29%
We present a new high signal to noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the $\lambda 5780$ \AA\ and $\lambda 5797$ \AA\ Diffuse Interstellar Bands (DIBs). We observed 432 sightlines to a distance of 200 pc over a duration of 3 years. In this study, we establish the $\lambda 5780$ and $\lambda 5797$ correlations with Na I, Ca II and E(B-V), for both inside and outside the Local Bubble. The correlations show that among all neutral and ionized atoms, the correlation between Ca II and $\lambda5780$ is stronger than its correlation with $\lambda5797$, suggesting that $\lambda5780$ is more associated with regions where Ca$^{+}$ is more abundant. We study the $\lambda5780$ correlation with $\lambda5797$, which shows a tight correlation within and outside the Local Bubble. In addition we investigate the DIB properties in UV irradiated and UV shielded regions. We find that, within and beyond the Local Bubble, $\lambda5797$ is located in denser parts of clouds, protected from UV irradiation, while $\lambda5780$ is located in the low density regions of clouds.

On the magnetic field through the Upper Centaurs-Lupus Super bubble, in the vicinity of the Southern Coalsack

Bhat, N. D. Ramesh; Andersson, B-G
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/12/2010
Relevância na Pesquisa
26.38%
The Southern Coalsack is located in the interior of the Upper Centaurus-Lupus (UCL) super bubble and shows many traits that point to a much more energetic environment than might be expected from a dark, starless molecular cloud. A hot, X-ray emitting, envelope surrounds the cloud, it has a very strong internal magnetic field and its darkest core seems to be on astronomical time scales "just about" to start forming stars. In order to probe the magnetic environment of the cloud and to compare with the optical/near infrared polarimetry-based field estimates for the cloud, we have acquired Faraday Rotation measurements towards the pulsar PSR J1210$-$6550, probing the magnetic field in the vicinity of the cloud, and a comparison target, PSR J1435$-$5954, at a similar line of sight distance but several degrees from the cloud. Both lines of sight hence primarily probe the UCL super bubble. The earlier estimates of the magnetic field inside the Coalsack, using the Chandrasekhar-Fermi method on optical and near-infrared polarimetry, yield B$_\perp$ = 64--93 $\mu$G. However, even though PSR J1210$-$6550 is located only $\sim$30 arc minutes from the (CO) edge of the cloud, the measured field strength is only B$_\parallel$ = 1.1$\pm$0.2 $\mu$G. While thus yielding a very high field contrast to the cloud we argue that this might be understood as due to the effects on the cloud by the super bubble.; Comment: 8 pages...

Optimal filters for detecting cosmic bubble collisions

McEwen, J. D.; Feeney, S. M.; Johnson, M. C.; Peiris, H. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.24%
A number of well-motivated extensions of the LCDM concordance cosmological model postulate the existence of a population of sources embedded in the cosmic microwave background (CMB). One such example is the signature of cosmic bubble collisions which arise in models of eternal inflation. The most unambiguous way to test these scenarios is to evaluate the full posterior probability distribution of the global parameters defining the theory; however, a direct evaluation is computationally impractical on large datasets, such as those obtained by the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck. A method to approximate the full posterior has been developed recently, which requires as an input a set of candidate sources which are most likely to give the largest contribution to the likelihood. In this article, we present an improved algorithm for detecting candidate sources using optimal filters, and apply it to detect candidate bubble collision signatures in WMAP 7-year observations. We show both theoretically and through simulations that this algorithm provides an enhancement in sensitivity over previous methods by a factor of approximately two. Moreover, no other filter-based approach can provide a superior enhancement of these signatures. Applying our algorithm to WMAP 7-year observations...

The Dynamics and Acoustics of Travelling Bubble Cavitation

Ceccio, S.; Brennen, C.
Fonte: National Academy Press Publicador: National Academy Press
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em //1991
Relevância na Pesquisa
26.29%
Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles were studied photographically, and these observations are related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse are analyzed and found to correlate with the maximum volume of the bubble for each headform. These results are compared to the observed bubble dynamics and numerical solutions of the Rayleigh-Plesset equation. Finally, the cavitation nuclei flux was measured and predicted cavitation event rates and bubble maximum size distributions are compared with the measurements of these quantities.

Observations of the Dynamics and Acoustics of Travelling Bubble Cavitation

Ceccio, S. L.; Brennen, C. E.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //1991
Relevância na Pesquisa
26.29%
Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles were studied photographically, and these observations are related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse are analysed and found to correlate with the maximum volume of the bubble for each headform. These results are compared to the observed bubble dynamics and numerical solutions of the Rayleigh-Plesset equation. Finally, the cavitation nuclei flux was measured and predicted cavitation event rates and bubble maximum size distributions are compared with the measurements of these quantities.

Observations of the Dynamics and Acoustics of Travelling Bubble Cavitation

Ceccio, Steven Louis
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em //1990
Relevância na Pesquisa
26.32%
Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles, almost all of which were quasi-spherical caps moving close to the headform surface, were studied photographically. Although the growth patterns for the two headforms were similar, the collapse mechanisms were quite different. These differences were related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse were analyzed and found to correlate with the maximum volume of the bubble for each headform. Numerical solutions of the Rayleigh-Plesset equation were generated for the same flows and compared with the experimental data. The experiments revealed that for smaller bubbles the impulse-volume relationship is determinate, but for larger bubbles the impulse becomes more uncertain. The theoretical impulse was at least a factor of two greater than the measured impulse, and the impulse-volume relationship was related to the details of the collapse mechanism. Acoustic emission of individual cavitation events was spectrally analyzed and the results were compared with relevant theoretical and empirical predictions. Finally...

THREE-FIBER OPTICAL PROBE FOR STUDYING FLUIDIZED GAS-SOLID BEDS IN BUBBLING REGIME

REYES-VERA,ERICK; DOMINGUEZ-GOMEZ,D. M.; CAUSADO-BUELVAS,JESÚS D.; TORRES,PEDRO; MORENO,YOLICE; LONDOÑO,CARLOS; MOLINA,ALEJANDRO
Fonte: DYNA Publicador: DYNA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 EN
Relevância na Pesquisa
36.45%
This work shows the development of a three-optical fiber probe to study the behavior of the bubble in bubbling fluidized gas-solid beds. Its compact design allows minimizing disturbance to the flow field, resulting in more accurate results than other probes. Bubbling fluidized beds are widely used in petrochemical processes, metallurgical, and thermoelectric plants. The behavior of the bubble is one of the most important parameters for the simulation and design of thermoelectric reactors, as it relates to the jumping phase, the interaction between solid and gaseous phases of the bed, and the behavior of mass transfer. Knowing both the speed and the size of the bubble helps to characterize these systems, bringing about a better design of large-scale reactors.