Distribution by Scientific Domains

Kinds of Bubbles

  • air bubble
  • gas bubble
  • hydrogen bubble
  • large bubble
  • market bubble
  • radio bubble
  • single bubble
  • small bubble
  • stock market bubble

  • Terms modified by Bubbles

  • bubble coalescence
  • bubble column
  • bubble column reactor
  • bubble diameter
  • bubble dynamics
  • bubble formation
  • bubble function
  • bubble growth
  • bubble length
  • bubble nucleation
  • bubble size
  • bubble size distribution
  • bubble velocity

  • Selected Abstracts


    First page of article [source]

    Financial markets can go mad: evidence of irrational behaviour during the South Sea Bubble1

    This paper explores investor behaviour during the South Sea Bubble,the first major speculative boom and bust on the stock markets. Previous literature debates whether investors during this episode acted rationally. Newly acquired data involving parallel markets for the South Sea Company's stock and subscription receipts are analysed, and widening valuation gaps are observed between these substitutable financial instruments. Rational explanations do not prove adequate, and the anomalies are explained by the biased decision-making of investors, and their tendency to view financial markets as wagering markets. The implications of these findings for the current debate on rationality in financial markets are identified. [source]

    What Is an Asset Price Bubble?

    An Operational Definition
    This paper reviews and analyses the current definitions of bubbles in asset prices. It makes the case that one cannot identify a bubble immediately, but one has to wait a sufficient amount of time to determine whether the previous prices can be justified by subsequent cash flows. The paper proposes an operational definition of a bubble as any time the realised asset return over given future period is more than two standard deviations from its expected return. Using this framework, the paper shows how the great crash of 1929 and 1987,both periods generally characterised as bubbles,prove not to be bubbles but the low point in stock prices in 1932 is a ,negative bubble.' The paper then extends this analysis to the internet stocks and concludes that it is virtually certain that it is a bubble. [source]

    Global Debt Markets in 2007: New Paradigm or the Great Credit Bubble?

    Edward I. Altman

    Discussion of,The Relevance of Accounting Information in a Stock Market Bubble: Evidence from Internet IPOs

    Ana SimpsonArticle first published online: 10 MAY 2010
    First page of article [source]

    Beyond the Green Bubble

    Reid Lifset
    No abstract is available for this article. [source]

    PVLAS experiment: some astrophysical consequences

    Yu. N. Gnedin
    ABSTRACT The birefringent effects of photon,pseudo-scalar boson (Goldstone) particle mixing in intergalactic magnetic field are calculated for cosmological objects. We use the recent results of PVLAS collaboration that reported recently the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such result was interpreted as arising due to conversion of photon into pseudo-scalar with coupling strength ga,, 4 × 10,6 GeV,1. This result contradicts to data of stellar evolution that excluded standard axion model and seems to claim existence of supersymmetry (SUSY) pseudo-scalars. We estimate the intergalactic magnetic field magnitude as ,10,16 G based on Hatsemekers et al. observations of extreme-scale alignments of quasar polarization vectors. We analysed some additional results of astronomical observations that could be explained by axion interpretation of the PVLAS data: a sharp steepening of the quasi-stellar object (QSO) continuum shortward of ,1100 Å, observed circular polarization of active galactic nuclei (AGNs) and QSOs, discrepancy between observed intrinsic polarization of stars in the Local Bubble and stellar spectral classification. The observed polarization of stars in the Local Bubble cannot be explained by interstellar origin. [source]

    Infrared mergers and infrared quasi-stellar objects with galactic winds , III.

    Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)
    ABSTRACT We present a study of outflow (OF) and broad absorption line (BAL) systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects (QSOs). This study is based mainly on one-dimensional and two-dimensional spectroscopy (obtained at La Palma/William Herschel Telescope, Hubble Space Telescope, International Ultraviolet Explorer, European Southern Observatory/New Technology Telescope, Kitt Peak National Observatory, Apache Point Observatory and Complejo Astronomico El Leoncito observatories) plus Hubble Space Telescope images. For Mrk 231, we report evidence that the extreme nuclear OF process has at least three main components on different scales, which are probably associated with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at parsec and kiloparsec scale. This OF has generated at least four concentric expanding superbubbles and the BAL systems. Specifically, inside and very close to the nucleus the two-dimensional spectra show the presence of an OF emission bump in the blend H,+[N ii], with a peak at the same velocity of the main BAL-I system (VEjection BAL-I,,4700 km s,1). This bump was more clearly detected in the area located at 0.6,1.5 arcsec (490,1220 pc), to the south-west of the nucleus core, showing a strong and broad peak. In addition, in the same direction [at position angle (PA) ,,120°, i.e. close to the PA of the small-scale radio jet] at 1.7,2.5 arcsec, we also detected multiple narrow emission-line components, with ,greatly' enhanced [N ii]/H, ratio (very similar to the spectra of jets bow shocks). These results suggest that the BAL-I system is generated in OF clouds associated with the parsec-scale jet. The Hubble Space Telescope images show four (or possibly five) nuclear superbubbles or shells with radii r, 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For these bubbles, the two-dimensional H, velocity field map and two-dimensional spectra show the following. (i) At the border of the more extended bubble (S1), a clear expansion of the shell with blueshifted velocities (with circular shape and at a radius r, 5.0 arcsec). This bubble shows a rupture arc , to the south , suggesting that the bubble is in the blowout phase. The axis of this rupture or ejection (at PA , 00°) is coincident with the axis of the intermediate and large-scale structures detected at radio wavelengths. (ii) In addition, in the three more external bubbles (S1, S2, S3), the two-dimensional William Herschel Telescope spectra show multiple emission-line components with OF velocities, of ,VOF Bubble, S1, S2 and S3 =[,(650 , 420) ± 30], [,500 ± 30] and [,230 ± 30] km s,1. (iii) In the whole circumnuclear region (1.8 < r < 5 arcsec), the [N ii]/H, and [S ii]/H, narrow emission-line ratios show high values (>0.8), which are consistent with low-ionization nuclear emission-line region/OF processes associated with fast velocity shocks. Therefore, we suggest that these giant bubbles are associated with the large-scale nuclear OF component, which is generated , at least in part , by the extreme nuclear starburst: giant supernova/hypernova explosions. The variability of the short-lived BAL-III Na i D system was studied, covering almost all the period in which this system appeared (between ,1984 and 2004). We have found that the BAL-III light curve is clearly asymmetric with a steep increase, a clear maximum and an exponential fall (similar to the shape of a supernova light curve). The origin of this BAL-III system is discussed, mainly in the framework of an extreme explosive event, probably associated with giant supernova/hypernova explosions. Finally, the IR colour diagram and the ultraviolet BAL systems of IR + GW/OF + Fe ii QSOs are analysed. This study shows two new BAL IR QSOs and suggests/confirms that these objects could be nearby young BAL QSOs, similar to those detected recently at z, 6.0. We propose that the phase of young QSOs is associated with accretion of a large amount of gas (by the supermassive black hole) + extreme starbursts + extreme composite OFs/BALs. [source]

    The Effect of Bed Temperature on Mass Transfer between the Bubble and Emulsion Phases in a Fluidized Bed

    Wenyuan Wu
    Abstract The rate of interphase mass transfer between the bubble and emulsion phases of a bubbling fluidized bed is of primary importance in all models for fluidized bed reactors. Many experimental studies have been reported, however, all these investigations have been carried out in fluidized beds operated at room temperature. In this work, the effect of the bed temperature on the interphase mass transfer is reported. Single bubbles containing argon , used as a tracer , were injected into an incipiently fluidized bed maintained at the required temperature. The change in argon concentration in the bubble was measured using a suction probe connected to a mass spectrometer. The effects of bed particle type and size, bubble size, and bed temperature on the mass transfer coefficient were examined experimentally. The interphase mass transfer coefficient was found to decrease with the increase in bed temperature and bubble size, and increase slightly with increase in particle size. Experimental data obtained in this study were compared with some frequently used correlations for estimation of the mass transfer coefficient. Le taux de transfert de matière interphasique entre les phases à bulles et à émulsion d'un lit fluidisé bullant est de première importance dans tous les modèles de réacteurs à lits fluidisés. Beaucoup d'études expérimentales ont été présentées; toutefois, toutes ces recherches ont été menées dans des lits fluidisés fonctionnant à la température ambiante. Dans ce travail, on décrit l'effet de la température du lit sur le taux de transfert de matière. Des bulles simples contenant de l'argon &#0150; utilisé comme traceur &#0150; ont été injectées dans un lit fluidisé naissant maintenu à la température requise. Le changement de concentration d'argon dans la bulle est mesuré à l'aide d'une sonde de succion reliée à un spectromètre de masse. Les effets du type et de la taille des particules de lit, de la taille des bulles et de la température de lit sur le coefficient de transfert de matière sont examinés de façon expérimentale. On a trouvé que le coefficient de transfert de matière interphasique diminuait avec l'augmentation de la température du lit et de la taille des bulles, et augmentait légèrement avec l'augmentation de la taille des particules. Les données expérimentales obtenues dans cette étude sont comparées avec quelques corrélations fréquemment utilisées pour l'estimation du coefficient de transfert de matière. [source]

    Options and the Bubble

    THE JOURNAL OF FINANCE, Issue 5 2006
    ABSTRACT Many believe that a bubble existed in Internet stocks in the 1999 to 2000 period, and that short-sale restrictions prevented rational investors from driving Internet stock prices to reasonable levels. In the presence of such short-sale constraints, option and stock prices could decouple during a bubble. Using intraday options data from the peak of the Internet bubble, we find almost no evidence that synthetic stock prices diverged from actual stock prices. We also show that the general public could cheaply short synthetically using options. In summary, we find no evidence that short-sale restrictions affected Internet stock prices. [source]

    Hedge Funds and the Technology Bubble

    THE JOURNAL OF FINANCE, Issue 5 2004
    ABSTRACT This paper documents that hedge funds did not exert a correcting force on stock prices during the technology bubble. Instead, they were heavily invested in technology stocks. This does not seem to be the result of unawareness of the bubble: Hedge funds captured the upturn, but, by reducing their positions in stocks that were about to decline, avoided much of the downturn. Our findings question the efficient markets notion that rational speculators always stabilize prices. They are consistent with models in which rational investors may prefer to ride bubbles because of predictable investor sentiment and limits to arbitrage. [source]

    Measuring the Interaction Forces between Protein Inclusion Bodies and an Air Bubble Using an Atomic Force Microscope

    N. D. Wangsa-Wirawan
    Interaction forces between protein inclusion bodies and an air bubble have been quantified using an atomic force microscope (AFM). The inclusion bodies were attached to the AFM tip by covalent bonds. Interaction forces measured in various buffer concentrations varied from 9.7 nN to 25.3 nN (± 4,11%) depending on pH. Hydrophobic forces provide a stronger contribution to overall interaction force than electrostatic double layer forces. It also appears that the ionic strength affects the interaction force in a complex way that cannot be directly predicted by DLVO theory. The effects of pH are significantly stronger for the inclusion body compared to the air bubble. This study provides fundamental information that will subsequently facilitate the rational design of flotation recovery system for inclusion bodies. It has also demonstrated the potential of AFM to facilitate the design of such processes from a practical viewpoint. [source]

    Rapid Confirmation of Central Venous Catheter Placement Using an Ultrasonographic "Bubble Test"

    Matthew E. Prekker MD
    No abstract is available for this article. [source]

    UK Assessment: A Tale of Two Bubbles?

    ECONOMIC OUTLOOK, Issue 4 2002
    Article first published online: 16 DEC 200
    First page of article [source]

    Syntactic Iron Foams with Integrated Microglass Bubbles Produced by Means of Metal Powder Injection Moulding,

    Jörg Weise
    Systematic tests for the production of pure iron (99%) foams with integrated microglass bubbles by means of metal powder injection moulding (MIM) have been carried out with variation of the glass bubble contents. Process parameters were optimized and the resulting materials characterized using density measurements, tensile and compression tests, metallographic sections, and scanning electron microscopy. The corrosion behavior of this novel material was characterized using potentiodynamic polarization measurements and immersion tests. [source]

    The spirit of capitalism, stock market bubbles and output fluctuations

    Takashi Kamihigashi
    E20; E32 This paper presents a representative agent model in which stock market bubbles cause output fluctuations. Assuming that utility depends directly on wealth, we show that stock market bubbles arise if the marginal utility of wealth does not decline to zero as wealth goes to infinity. Bubbles can affect output positively or negative depending on whether the production function exhibits increasing or decreasing returns to scale. In sunspot equilibria, the bursting of a bubble is followed by a sharp decline in output one period later. Various numerical examples are given to illustrate the behavior of stochastic bubbles and the relationship between bubbles and output. [source]

    Bubbles and fads in the stock market: another look at the experience of the US

    Piergiorgio Alessandri
    Abstract This paper considers a standard present-value equity price formula where the discount factor is driven by the real return on short-term public debt. We discuss a state-space formulation by which prices can be decomposed into fundamental and non-fundamental components. The model is estimated on annual US data. The stochastic discount factor explains part of the volatility in equity values, but it is not sufficient per se to exclude the occurrence of near-exponential bubbles in the price-dividend ratio. These disappear if the dividend is replaced by a broader measure of the income flow generated by the firms. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Ultrasonic Investigation of the Effect of Vegetable Shortening and Mixing Time on the Mechanical Properties of Bread Dough

    K.L. Mehta
    ABSTRACT:, Mixing is a critical stage in breadmaking since it controls gluten development and nucleation of gas bubbles in the dough. Bubbles affect the rheology of the dough and largely govern the quality of the final product. This study used ultrasound (at a frequency where it is sensitive to the presence of bubbles) to nondestructively examine dough properties as a function of mixing time in doughs prepared from strong red spring wheat flour with various amounts of shortening (0%, 2%, 4%, 8% flour weight basis). The doughs were mixed for various times at atmospheric pressure or under vacuum (to minimize bubble nucleation). Ultrasonic velocity and attenuation (nominally at 50 kHz) were measured in the dough, and dough density was measured independently from specific gravity determinations. Ultrasonic velocity decreased substantially as mixing time increased (and more bubbles were entrained) for all doughs mixed in air; for example, in doughs made without shortening, velocity decreased from 165 to 105 ms,1, although superimposed on this overall decrease was a peak in velocity at optimum mixing time. Changes in attenuation coefficient due to the addition of shortening were evident in both air-mixed and vacuum-mixed doughs, suggesting that ultrasound was sensitive to changes in the properties of the dough matrix during dough development and to plasticization of the gluten polymers by the shortening. Due to its ability to probe the effect of mixing times and ingredients on dough properties, ultrasound has the potential to be deployed as an online quality control tool in the baking industry. [source]

    Passage of a bubble through a liquid,liquid interface

    AICHE JOURNAL, Issue 3 2008
    N. Dietrich
    Abstract The aim of this study is to investigate the bubble passage at a liquid,liquid interface using a high-speed video camera (950 images per second) and a Particle Image Velocimetry (PIV) system. Experiments were conducted in a square Plexiglas column of 0.1 m. Bubbles were generated through a submerged orifice (D = 1 × 10,3 m). The Newtonian Emkarox (HV45) solution was employed for the heavy phase whereas two different organic liquids of different viscosity (Silicone oil 10 mPa s and 100 mPa s) were used as light phase. Experimental results show the effect of the bubble size and the viscosity of the light phase on the retention time, the length of the column of fluid entrained behind the bubble, the bubble velocity as well as the velocity fields at the liquid,liquid interface. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

    Effects of Electrode Protrusion Length, Pre-Existing Bubbles, Solution Conductivity and Temperature, on Liquid Phase Pulsed Electrical Discharge

    Kai-Yuan Shih
    Abstract The effects of high voltage electrode needle protrusion length and the presence of low density pre-existing bubbles on liquid phase pulsed electrical discharge were investigated. Liquid phase pulsed corona discharge was operated with two different protrusion length needle electrodes (short , 2,mm and long , 20,mm) with different bulk solution conductivities (5,µS,·,cm,1 and 150,µS,·,cm,1) at room temperature (25,°C) and near boiling (95,°C). Chemical reactions formed in the discharge were also investigated by measuring the generation rates of hydrogen (H2), oxygen (O2) and hydrogen peroxide (H2O2). [source]

    Millimetre-scale bubble-like dielectric elastomer actuators

    Federico Carpi
    Abstract Hydrostatic coupling has recently been reported as a means to improve the versatility and safety of electromechanical actuators based on dielectric elastomers (DEs). Hydrostatically coupled DE actuators rely on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load. The work reported here was aimed at developing millimetre-scale bubble-like versions of such transducers. Silicone-made oil-filled actuators were manufactured as both single units and arrays of parallel elements. Bubbles had a base diameter of 6 mm and were driven up to a voltage of 2.25 kV, applied across a silicone film with a thickness of 42 µm. Active relative displacements and stresses up to 18% and 2.2 kPa, respectively, were recorded with static driving. Dynamic investigations reported a ,3 dB bandwidth of the order of 100 Hz and a resonance frequency of about 250 Hz. Millimetre-scale hydrostatically coupled DE actuators might play a useful role in several fields of application. Among them, we are currently exploring novel tactile displays and cutaneous stimulators, made of wearable, distributed and flexible devices. Although further miniaturization is required for high-resolution uses, this technology holds promise to properly combine performance with safe and compliant interfaces with users, low specific weight, no acoustic noise and low cost. Copyright © 2009 Society of Chemical Industry [source]

    Binary coalescence of air bubbles in viscous liquids in presence of non-ionic surfactant

    K. Giribabu
    Abstract Coalescence of air bubbles is important in gas,liquid reactors and food processing operations. Bubbles can be stabilized by using non-ionic surfactants. Binary coalescence of air bubbles in ethylene glycol and aqueous glycerol solutions were studied in this work in presence of Span 80. A novel set-up was developed to study long coalescence times. Coalescence time was observed to follow broad stochastic distributions in all systems. The distributions were fitted with a stochastic model developed earlier. The surface tension of ethylene glycol and glycerol solutions was measured at various concentrations of Span 80. These data were fitted using a surface equation of state derived from the Langmuir isotherm. The effect of surfactant concentration on coalescence time was explained in terms of the surface excess of the surfactant and the repulsive force generated at the air,liquid interface. The results from this work illustrate the stochastic nature of bubble coalescence in viscous liquids. This work also demonstrates how non-ionic surfactants can stabilize bubbles in such liquids. La coalescence des bulles d'air est importante dans les réacteurs gaz-liquide et les opérations de l'industrie alimentaire. Les bulles peuvent être stabilisées en utilisant des surfactants non ioniques. La coalescence binaire de bulles d'air dans des solutions aqueuses d'éthylène glycol et de glycérol a été étudiée dans ce travail en présence de Span 80. Un nouveau montage a été mis au point pour caractériser les temps de coalescence longs. Le temps de coalescence a été observé afin de suivre les distributions de modèle stochastique dans tous les systèmes. Les distributions ont été calées à un modèle stochastique mis au point antérieurement. La tension de surface des solutions d'éthylène glycol et de glycérol a été mesurée à différentes concentrations de Span 80. Ces données ont été calées à l'aide d'une équation d'état de surface calculée à partir de l'isotherme de Langmuir. L'effet de la concentration de surfactant sur le temps de coalescence est expliqué par l'excès de surface du surfactant et la force répulsive créée à l'interface air-liquide. Les résultats de ce travail illustrent la nature stochastique de la coalescence des bulles dans les liquides visqueux. Ce travail démontre également comment les surfactants non ioniques peuvent stabiliser les bulles dans de tels liquides. [source]

    Bubbles, drops and particles in non-newtonian fluids.


    No abstract is available for this article. [source]

    Capital Flows, Consumption Booms and Asset Bubbles: A Behavioural Alternative to the Savings Glut Hypothesis,

    THE ECONOMIC JOURNAL, Issue 544 2010
    David Laibson
    Bernanke (2005) hypothesised that a ,global savings glut' was causing large trade imbalances. However, we show that the global savings rates did not show a robust upward trend during the relevant period. Moreover, if there had been a global savings glut there should have been a large investment boom in the countries that imported capital. Instead, those countries experienced consumption booms. National asset bubbles explain the international imbalances. The bubbles raised consumption, resulting in large trade deficits. In a sample of 18 OECD countries plus China, movements in home prices alone explain half of the variation in trade deficits. [source]

    Asset Bubbles, Leverage and ,Lifeboats': Elements of the East Asian Crisis

    THE ECONOMIC JOURNAL, Issue 460 2000
    H. J. Edison
    Collapsing credit markets have been blamed for the depth and persistence of the Great Depression in the United States. Could similar mechanisms have played a role in ending the East Asian economic miracle , and in creating fragility in global financial markets? After a brief account of the nature of the East Asian crises of 1997/8, we use the framework of highly-leveraged, fully-collaterised firms due to Kiyotaki and Moore (1997) to explore the impact of a credit crunch. The paper emphasises the fragility of equilibrium and how rapidly boom can turn to bust. [source]

    Growth Effects of Bubbles in an Endogenous Growth Model

    Koichi Futagami
    This paper examines the possibility of the existence of bubbles and their effects on the growth rate by using an endogenous growth model. A necessary and sufficient condition for the existence of steady-state equilibrium with bubbles is provided. If non-zero rates of the useless asset supply are allowed, a steady-state equilibrium with bubbles exists even if the growth rate of the bubbleless equilibrium is lower than the market interest rate. The growth rate in the steady state with bubbles depends positively on the supply rate of the useless asset. Dynamic properties of bubbles are also analysed. JEL Classification Numbers: E52, O41, O42. [source]

    Development of Air Micro Bubbles in the Venous Outlet Line: An In Vitro Analysis of Various Air Traps Used for Hemodialysis

    ARTIFICIAL ORGANS, Issue 6 2007
    Christofer J. Stegmayr
    Abstract:, Venous air traps were tested in vitro with respect to presence of micro bubbles. Three types of venous air traps were measured (Bioline, Bioline GmbH, Luckenwalde, Germany; Gambro, Gambro AB, Lund, Sweden; Fresenius M.C., Fresenius Medical Care AG & Co. KGaA, Bad Homburg, Germany). Measurements (n = 10) were taken for each air trap, fluid flow (50,600 mL/min), and fluid level (high/low). A 1.5-MHz ultrasound probe was used with an analysis device. The probe was mounted on the outlet line downstream of the venous air trap. A semisynthetic fluid was used to resemble blood viscosity. Occurrences of micro bubbles, without inducing an alarm of the dialysis device, were detected in almost all measurements. The amount of bubbles increased with increasing flow. There were more bubbles with low fluid level compared with high level. The Bioline tubing released the least bubbles in high fluid level. At low level, the Gambro tubing showed the least bubbles at flows 50,400 mL/min, and the Fresenius M.C. tubing showed the least bubbles at flows 400,600 mL/min. High fluid level in the air trap reduced generation of micro bubbles compared to low level, as did lower fluid flow versus high flow. The design of the air trap was also of importance. [source]

    Intensification of Rate of Diffusion Controlled Reactions in a Parallel Plate Electrochemical Reactor Stirred by a Curtain of Electrochemically Generated Gas Bubbles

    G. H. Sedahmed
    Abstract Rates of mass transfer were measured at a vertical plate stirred by a rising curtain of oxygen bubbles generated electrochemically at an upstream plate by measuring the limiting current of the cathodic reduction of K3Fe(CN)6 in alkaline solution. The rate of mass transfer was found to increase over the natural convection value by a factor ranging from 2.4 to 25 compared to the previously reported range of 2,5 in the case of copper deposition from acidified solutions. The high tendency of oxygen bubbles to coalesce in alkaline solutions is believed to be responsible for the high rates of mass transfer in alkaline solutions. The rate of mass transfer at a plate stirred by a curtain of oxygen bubbles was found to decrease with increasing plate height and electrolyte concentration. Curtains of H2 bubbles were found to be less effective in enhancing the rate of mass transfer compared to that of oxygen. Practical application of the results in designing a modified parallel plate electrochemical reactor stirred by a counterelectrode gas curtain was highlighted. The suggested design has the potential of saving part or all of the mechanical stirring energy as well as floor space since it extends vertically. [source]

    VOF-Simulation of the Lift Force for Single Bubbles in a Simple Shear Flow

    D. Bothe
    Abstract Bubbles in shear flows experience a lift force, causing them to migrate sideways while they are rising. This lateral migration is investigated in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force , expressed by the lift force coefficient CL , for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. An investigation of the dynamic pressure on the bubble surface explains why large bubbles migrate in the opposite direction compared to small bubbles. [source]

    Spatial Distribution of Acoustic Cavitation Bubbles at Different Ultrasound Frequencies

    CHEMPHYSCHEM, Issue 8 2010
    Muthupandian Ashokkumar Prof.
    Abstract Images of sonoluminescence, sonophotoluminescence and sonochemiluminescence are recorded in order to semi-quantitatively compare the spatial distribution of the cavitation activity at three different ultrasound frequencies (170 kHz, 440 kHz and 700 kHz) and at various acoustic amplitudes. At all ultrasound frequencies investigated, the sonochemically active cavitation zones are much larger than the cavitation zones where sonoluminescence is observed. Also, the sonochemically active bubbles are observed at relatively lower acoustic amplitudes than that required for sonoluminescence bubbles to appear. The acoustic power required for the observation of the initial cavitation bubbles increases with an increase in the ultrasound frequency. The cavitation bubbles are observed relatively uniformly throughout the reactor at 170 kHz whereas they are located away from the transducer at the higher frequencies used in this study. While these observations highlight the complexities involved in acoustic cavitation, possible reasons for the observed results are discussed. [source]