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1

Gas-holdup measurements in bubble columns using computed tomography  

SciTech Connect

Bubble columns are used in the chemical and process industry as contactors for mass-transfer processes and chemical reaction between gases and liquids. A computed tomographic scanner was developed for imaging gas-holdup distributions in two-phase flow systems such as bubble columns and fluidized beds. The scanner has been used to study the effects of various operating parameters (such as column diameter, superficial gas velocity, and distributor type) on the gas holdup and its distribution in an air-water bubble column. The experimental investigation shows that the column dimensions have no significant effect on the void fraction when the column diameter is greater than 0.15 m. Differences in the holdup distribution due to the kind of distributor used are significant only at low gas flow rates. Surface tension of the liquid has a profound influence on the gas holdup and its distribution.

Kumar, S.B.; Moslemian, D.; Dudukovic, M.P. [Washington Univ., St. Louis, MO (United States)] [Washington Univ., St. Louis, MO (United States)

1997-06-01

2

Gas hold-up and bubble diameters in a gassed oscillatory baffled column  

Microsoft Academic Search

In this paper attempts are made to address how bubble behaviour in a batch oscillatory baffled column (OBC) contributes to the overall measured enhancement in mass transfer. A CCD camera is used to measure the bubble size distribution and the gas hold-up in the OBC. The experimental results of Sauter mean diameter and gas hold-up are correlated as a function

M. S. N Oliveira; X Ni

2001-01-01

3

The effect of bubble column diameter on gas holdup in fiber suspensions  

Microsoft Academic Search

Three bubble column diameters (D=10.2, 15.2, and 32.1cm) are employed to study the scale-up effect on gas holdup in air–water and air–water–cellulose fiber (hardwood, softwood, and BCTMP) systems. The effect of column diameter depends on flow regime and fiber mass fraction. When D?15.2cm, gas holdup decreases with increasing column diameter for the transitional and heterogeneous flow regime, and column diameter

Xuefeng Su; Philip D. Hol; Sarah M. Talcott; Ann K. Staudt; Theodore J. Heindel

2006-01-01

4

Artificial Neural Networks Modeling of Ozone Bubble Columns: Mass Transfer Coefficient, Gas Hold-Up, and Bubble Size  

Microsoft Academic Search

This study aims at applying artificial neural network (ANN) modeling approach in designing ozone bubble columns. Three multi-layer perceptron (MLP) ANN models were developed to predict the overall mass transfer coefficient (kLa, s), the gas hold-up (?G, dimensionless), and the Sauter mean bubble diameter (dS, m) in different ozone bubble columns using simple inputs such as bubble column's geometry and

Mahad S. Baawain; Mohamed Gamal El-Din; Daniel W. Smith

2007-01-01

5

Gas holdup and bubble size behavior in a large-scale slurry bubble column reactor operating with an organic liquid under elevated pressures and temperatures  

Microsoft Academic Search

The holdups of small and large gas bubbles, bubble size distribution and the Sauter-mean bubble diameter were measured for N2 and He in isoparaffinic organic liquid mixture (Isopar-M) in the absence and presence of Alumina powder under various pressures (0.67–3MPa), temperatures (300–473K), superficial gas velocities (0.07–0.39m\\/s), and solid concentrations (0–20vol.%) in a large-scale bubble column and slurry bubble column reactor

Arsam Behkish; Romain Lemoine; Laurent Sehabiague; Rachid Oukaci; Badie I. Morsi

2007-01-01

6

Evaluation of micro-bubble size and gas hold-up in two-phase gas–liquid columns via scattered light measurements  

Microsoft Academic Search

In this paper, potential use of an elliptically polarized light scattering (EPLS) method to monitor both bubble size and gas hold-up in a bubble-laden medium is explored. It is shown that with the use of the new EPLS system, normalized scattering matrix elements (Mij's) measured at different side and back-scattering angles can be used to obtain the desired correlations between

Mustafa M. Aslan; Czarena Crofcheck; Daniel Tao; M. Pinar Mengüç

2006-01-01

7

Bubble and bubble wake characteristics in a gas-liquid-solid fluidized bed  

SciTech Connect

A light transmittance technique involving a dual optical fiber probe was used to measure the local solids holdup in a three-dimensional gas-liquid-solid fluidized bed. The bubble could be clearly identified in the same signal, thus permitting the simultaneous determination of the local solids holdup profile in the wake of a single bubble and the rise velocity and chord length of the bubble. The solids holdup behavior was studied in the wake of single bubbles rising in a liquid-solid fluidized bed for different liquid velocities, particle sizes, and bubble sizes. The wake solids holdup was found to decrease with decreasing mean solids holdup in the bed, to be essentially independent of the bubble Reynolds number over the range investigated in this study (4000 < Re{sub b} < 8000), and to decrease with increasing particle size. In freely bubbling bed at low gas holdups ({epsilon}{sub g} < 0.03), both the solids holdup in the wake and the particulate phase solids holdup were measured. The light transmittance probe developed for the single bubble system was also used for these measurements. Axial variations in the particulate solids holdup indicated that the relative wake solids holdup increased with axial distance from the distributor. The best agreement between the single bubble measurements and the measurements in the freely bubbling bed occurred in the bubble formation region. And finally, a simple model of the bubble wake was developed based on equations available in the literature for a spherical vortex to predict both the wake size and the relative wake solids holdup. The predictions showed good agreement with the experimentally observed values.

Kreischer, B.E.

1989-01-01

8

Statistical analysis of the phase holdup characteristics of a gas-liquid-solid fluidized bed  

Microsoft Academic Search

Experiments have been carried out to study the individual phase holdup characteristics in a cocurrent three-phase fluidized bed. An antenna type modified air sparger has been used in the gas-liquid distributor section, for uniform mixing of the fluids with the gas moving as fine bubbles to the fluidizing section. This arrangement also reduces the pressure drop encountered through a conventional

H. M. Jena; B. K. Sahoo; G. K. Roy; B. C. Meikap

2009-01-01

9

Solids holdup in the wake of a single bubble in a liquid-solid fluidized bed  

SciTech Connect

The wake structure behind large bubbles rising in a three-dimensional fluidized bed was investigated through measurements of the local solids holdup. A dual light transmittance probe allowed the measurement of the local solids concentration both in the bed and immediately above the bed surface. 160, 326, 460, and 760 micron glass beads were used as the fluidized solids and the large single bubbles were of spherical-cap shape. The light transmittance probe proved effective in measuring the solids concentration profile behind a single bubble for both 160 and 326 micron glass bead systems. The solids holdup profile was found to depend on position within the wake relative to the central axis and a stable wake size could be identified. The ratio of the average solids holdup in the wake to the mean solids holdup was found to decrease with a decrease in the mean solids holdup in the liquid-solid fluidized bed, but this decrease was less extensive for beds of smaller size particles. Comparison of the in-bed wake solids holdup data with visual observation of the single bubble immediately above the bed surface show good agreement. Observed stable wake size data is in reasonable agreement with published data for two-dimensional fluidized beds.

Kreischer, B.; Moritomi, H.; Fan, L.S. (Ohio State Univ., Columbus, OH (USA). Dept. of Chemical Engineering)

1988-01-01

10

Solids holdup in the wake of a single bubble in a liquid-solid fluidized bed  

Microsoft Academic Search

The wake structure behind large bubbles rising in a three-dimensional fluidized bed was investigated through measurements of the local solids holdup. A dual light transmittance probe allowed the measurement of the local solids concentration both in the bed and immediately above the bed surface. 160, 326, 460, and 760 micron glass beads were used as the fluidized solids and the

B. Kreischer; H. Moritomi; L. S. Fan

1988-01-01

11

Gas bubble detector  

NASA Technical Reports Server (NTRS)

A gas bubble detector having a modulated IR source focused through a bandpass filter onto a venturi, formed in a sample tube, to illuminate the venturi with modulated filtered IR to detect the presence of gas bubbles as small as 0.01 cm or about 0.004 in diameter in liquid flowing through the venturi. Means are provided to determine the size of any detected bubble and to provide an alarm in the absence of liquid in the sample tube.

Mount, Bruce E. (Inventor); Burchfield, David E. (Inventor); Hagey, John M. (Inventor)

1995-01-01

12

EFFECTS OF ALTERNATE ANTIFOAM AGENTS, NOBLE METALS, MIXING SYSTEMS AND MASS TRANSFER ON GAS HOLDUP AND RELEASE FROM NONNEWTONIAN SLURRIES  

SciTech Connect

Gas holdup tests performed in a small-scale mechanically-agitated mixing system at the Savannah River National Laboratory (SRNL) were reported in 2006. The tests were for a simulant of waste from the Hanford Tank 241-AZ-101 and featured additions of DOW Corning Q2-3183A Antifoam agent. Results indicated that this antifoam agent (AFA) increased gas holdup in the waste simulant by about a factor of four and, counter intuitively, that the holdup increased as the simulant shear strength decreased (apparent viscosity decreased). These results raised questions about how the AFA might affect gas holdup in Hanford Waste Treatment and Immobilization Plant (WTP) vessels mixed by air sparging and pulse-jet mixers (PJMs). And whether the WTP air supply system being designed would have the capacity to handle a demand for increased airflow to operate the sparger-PJM mixing systems should the AFA increase retention of the radiochemically generated flammable gases in the waste by making the gas bubbles smaller and less mobile, or decrease the size of sparger bubbles making them mix less effectively for a given airflow rate. A new testing program was developed to assess the potential effects of adding the DOW Corning Q2-3183A AFA to WTP waste streams by first confirming the results of the work reported in 2006 by Stewart et al. and then determining if the AFA in fact causes such increased gas holdup in a prototypic sparger-PJM mixing system, or if the increased holdup is just a feature of the small-scale agitation system. Other elements of the new program include evaluating effects other variables could have on gas holdup in systems with AFA additions such as catalysis from trace noble metals in the waste, determining mass transfer coefficients for the AZ-101 waste simulant, and determining whether other AFA compositions such as Dow Corning 1520-US could also increase gas holdup in Hanford waste. This new testing program was split into two investigations, prototypic sparger-PJM tests and modeling being conducted at the Pacific Northwest National Laboratory (PNNL), and small-scale agitation tests and evaluations of effects waste and AFA ingredients have on gas retention and mass transfer being conducted at SRNL. Only work conducted at SRNL is reported here. Key results are: (1) The unexpected gas holdup behavior reported in 2006 for a small-scale agitation system is confirmed. The gas holdup data from small-scale and bench-scale impeller-type mixing systems reported herein show very different trends than the behavior exhibited by the prototypic sparger-PJM mixing system tested in the PNNL APEL facility. Results obtained from testing this 1/4-scale prototypic mixing system will be reported by PNNL. The reason for this difference in holdup behavior between the two different mixing systems is not known at this time. Consequently, data from the small mechanical agitation systems should not be extrapolated to prototypic plant conditions. (2) Bench-scale and small-scale tests conducted with Dow Corning 1520-US AFA show it to be a viable replacement to Dow Corning Q2-3183A AFA. This alternative AFA will, however, require significantly higher dosage (concentration) to perform the same antifoam function. (3) Addition of noble metals to the AZ-101 waste simulant does not produce a catalytic gas retention effect with the AFA. The Gas holdup is similar whether or not noble metals are present in the AZ-101 simulant. (4) Mass transfer tests were performed in a large (0.76 m diameter) bubble column filled to 1.3, 3.4, and 7.4 m elevations with water and the AZ-101 waste simulant. Mass transfer coefficients for air bubbles emanating from a prototypic 0.051 m diameter sparger were obtained from the transient decay of dissolved oxygen concentration in the initially saturated fluids. Adding AFA to water reduces the mass transfer coefficient slightly. AFA addition reduces the mass transfer coefficient for AZ-101 simulant more than it does for water because the shear strength of the simulant allows for larger bubble sizes, and larger bubbles have smaller surf

Guerrero, H; Mark Fowley, M; Charles Crawford, C; Michael Restivo, M; Robert Leishear, R

2007-12-24

13

Gas-Liquid flow characterization in bubble columns with various gas-liquid using electrical resistance tomography  

NASA Astrophysics Data System (ADS)

Electrical resistance tomography (ERT) is an advanced and new detecting technique that can measure and monitor the parameters of two-phase flow on line, such as gas-liquid bubble column. It is fit for the industrial process where the conductible medium serves as the disperse phase to present the key bubble flow characteristics in multi-phase medium. Radial variation of the gas holdup and mean holdups are investigated in a 0.160 m i. d. bubble column using ERT with two axial locations (Plane 1 and Plane 2). In all the experiments, air was used as the gas phase, tap water as liquid phase, and a series of experiments were done by adding KCl, ethanol, oil sodium, and glycerol to change liquid conductivity, liquid surface tension and viscosity. The superficial gas velocity was varied from 0.02 to 0.2 m/s. The effect of conductivity, surface tension, viscosity on the mean holdups and radial gas holdup distribution is discussed. The results showed that the gas holdup decrease with the increase of surface tension and increase with the increase of viscosity. Meanwhile, the settings of initial liquid conductivity slightly influence the gas holdup values, and the experimental data increases with the increase of the initial setting values in the same conditions.

Jin, Haibo; Yuhuan, Han; Suohe, Yang

2009-02-01

14

Gas void ratio and bubble diameter inside a deep airlift reactor  

Microsoft Academic Search

Void ratio (gas holdup) and bubble diameter measurements were made inside a 1.06-m diameter column containing bubbly flow at depths up to 24m. Experiments were performed in order to identify differences in trends with column geometry and operating conditions from those found in smaller columns. Void ratio was found to increase as depth decreased regardless of the sparger type or

J. P. Giovannettone; E. Tsai; J. S. Gulliver

2009-01-01

15

Finite element simulation of turbulent bubbly flows in gas-liquid reactors  

Microsoft Academic Search

A mathematical model for turbulent gas-liquid flows is presented. It is shown that bubble-induced buoyancy resembles natural convection and can be readily incor- porated into an incompressible flow solver by using an analog of the Boussinesq approximation. Extra transport equations are introduced to describe the evolution of the gas holdup and compute the turbulent eddy viscosity in the framework of

D. Kuzmin; S. Turek; H. Haario

16

Experimental study on solids mixing and bubble behavior in a pseudo-2D, freely bubbling, gas-solid fluidized bed using PIV and DIA  

Microsoft Academic Search

The hydrodynamics of a freely bubbling, gas-solid fluidized bed has been investigated experimentally with non-invasive measuring techniques in a pseudo-2D column filled with glass beads of 400-600 ?m fluidized with air. Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA) has been used to determine simultaneously the emulsion phase circulation patterns, bubble hold-up and bubble size and velocity distributions.

J. A. Laverman; Ivo Roghair; Sint Annaland van M; J. A. M. Kuipers

2007-01-01

17

Experimental study on solids mixing and bubble behavior in a pseudo-2D, freely bubbling, gas-solid fluidized bed using PIV and DIA  

Microsoft Academic Search

The hydrodynamics of a freely bubbling, gas-solid fluidized bed has been investigated experimentally with non-invasive measuring techniques in a pseudo-2D column filled with glass beads of 400-600 µm fluidized with air. Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA) has been used to determine simultaneously the emulsion phase circulation patterns, bubble hold-up and bubble size and velocity distributions.

18

Gas-Liquid flow characterization in bubble columns with various gas-liquid using electrical resistance tomography  

Microsoft Academic Search

Electrical resistance tomography (ERT) is an advanced and new detecting technique that can measure and monitor the parameters of two-phase flow on line, such as gas-liquid bubble column. It is fit for the industrial process where the conductible medium serves as the disperse phase to present the key bubble flow characteristics in multi-phase medium. Radial variation of the gas holdup

Haibo Jin; Han Yuhuan; Yang Suohe

2009-01-01

19

Effect of the ejector configuration on the gas suction rate and gas hold-up in ejector loop reactors  

Microsoft Academic Search

An experimental study has been aimed at examining the effect of ejector configuration on the rate and energy effectiveness of gas suction and on the values of gas hold-up in ejector loop reactors. Experimental data showed that insertion of a swirl body into the ejector nozzle increased the suction rate and dispersion efficiency of the ejector distributor and significantly improved

P. Havelka; V. Linek; J. Sinkule; J. Zahradník; M. Fialova

1997-01-01

20

Resonance properties of soluble gas bubbles  

Microsoft Academic Search

Soluble gas bubbles in a liquid experiencing radial oscillations created by an acoustic field are considered. It is shown that the resonance frequency of large soluble gas bubbles practically coincides with the natural frequency of gas bubbles as determined by the Minnaert formula. In the case of small gas bubbles, the presence of capillary effects and solubility of the gas

Nail S. Khabeev

2006-01-01

21

EFFECTS OF ALTERNATE ANTIFOAM AGENTS, NOBLE METALS, MIXING SYSTEMS AND MASS TRANSFER ON GAS HOLDUP AND RELEASE FROM NONNEWTONIAN SLURRIES  

Microsoft Academic Search

Gas holdup tests performed in a small-scale mechanically-agitated mixing system at the Savannah River National Laboratory (SRNL) were reported in 2006. The tests were for a simulant of waste from the Hanford Tank 241-AZ-101 and featured additions of DOW Corning Q2-3183A Antifoam agent. Results indicated that this antifoam agent (AFA) increased gas holdup in the waste simulant by about a

H Guerrero; M Mark Fowley; C Charles Crawford; M Michael Restivo; R Robert Leishear

2007-01-01

22

Electrogenerated Gas Bubbles in Flotation  

Microsoft Academic Search

Electrolytic gas evolution plays a very significant part in a number of electrochemical processes. In the electrowinning of metals the evolution of gases at the electrodes is a very important phenonenon. Gas evolution is common in chlorine and water electrolysis and in a number of other processes. Electro-generated gas bubbles have been used in the treatment of waste water and

S. VENKATACHALAM

1992-01-01

23

CFD simulation of effects of the configuration of gas distributors on gas–liquid flow and mixing in a bubble column  

Microsoft Academic Search

Numerical simulations of gas–liquid flow in a cylindrical bubble column of 400mm in diameter at the superficial gas velocity Ug=0.10ms-1 were conducted to investigate effects of the configuration of gas distributors on hydrodynamic behaviour, gas hold-up and mixing characteristics. Eight different gas distributors were adopted in the simulation. The simulation results clearly show that the configuration of gas distributor have

Guang Li; Xiaogang Yang; Gance Dai

2009-01-01

24

Fluid dynamic parameters in bubble columns with internals  

Microsoft Academic Search

The knowledge of gas holdup, liquid recirculation and turbulent parameters is important for design and performance calculation of bubble column reactors. Although numerous experimental studies have been reported on this subject, most are point measurements limited to columns without internals operated at low gas velocities. In this study, we present the results obtained for the gas holdup profiles, time-averaged liquid

Jinwen Chen; Fan Li; Sujatha Degaleesan; Puneet Gupta; Muthanna H. Al-Dahhan; Milorad P. Dudukovic; Bernard A. Toseland

1999-01-01

25

Bubble column bioreactors  

Microsoft Academic Search

The present article investigates the behavior of bubble column bioreactors with yeast culture media in the absence of cells.\\u000a To aid in the assessment of these reactors the following properties were estimated and partly theoretically treated: relative\\u000a mean gas hold-up, bubble swarm velocity, bubble size, gas\\/liquid interfacial area, energy requirement for aeration, oxygen\\u000a transfer coefficient across the gas\\/liquid interface and

K. Schügerl; J. Lücke; U. Oels

26

The influence of pressure on the liquid hold-up in a cocurrent gas-liquid trickle-bed reactor operating at low gas velocities  

Microsoft Academic Search

The influence of reactor pressure up to 6.0 MPa on the dynamic liquid hold-up in the trickle-flow regime with superficial gas velocities up to 5.2 cm\\/s has been investigated for water, ethanol and aqueous 40% ethyleneglycol, with nitrogen as the gas phase. Without gas flow, i.e. single-liquid trickle-flow operation, the reactor pressure has no influence on the dynamic liquid hold-up,

W. J. A. Wammes; S. J. Mechielsen; K. R. Westerterp

1991-01-01

27

CFD SIMULATION AND EXPERIMENTAL STUDY OF FLOW IN PACKED BUBBLE COLUMNS  

Microsoft Academic Search

The gas holdup in a small-scale packed bubble column with dimensions of 35?mm wide and 10?mm deep was measured for air-water system. The effect of gas flow rate on gas holdup was investigated for various packings such as spheres, Berl saddles, and knitted meshes. In all cases it was found that the gas holdup increases with increasing gas flow rate.

F. H. YIN; J. L. MIDGLEY; A. AFACAN; K. NANDAKUMAR; K. T. CHUANG

2004-01-01

28

Etiology of gas bubble disease  

SciTech Connect

Gas bubble disease is a noninfectious, physically induced process caused by uncompensated hyperbaric pressure of total dissolved gases. When pressure compensation is inadequate, dissolved gases may form emboli (in blood) and emphysema (in tissues). The resulting abnormal physical presence of gases can block blood vessels (hemostasis) or tear tissues, and may result in death. Population mortality is generally skewed, in that the median time to death occurs well before the average time to death. Judged from mortality curves, three stages occur in gas bubble disease: (1) a period of gas pressure equilibrium, nonlethal cavitation, and increasing morbidity; (2) a period of rapid and heavy mortality; and (3) a period of protracted survival, despite lesions, and dysfunction that eventually terminates in total mortality. Safe limits for gas supersaturation depend on species tolerance and on factors that differ among hatcheries and rivers, between continuous and intermittent exposures, and across ranges of temperature and salinity.

Bouck, G.R.

1980-11-01

29

Gas hold-up and oxygen mass transfer in three pneumatic bioreactors operating with sugarcane bagasse suspensions.  

PubMed

Sugarcane bagasse is a low-cost and abundant by-product generated by the bioethanol industry, and is a potential substrate for cellulolytic enzyme production. The aim of this work was to evaluate the effects of air flow rate (QAIR), solids loading (%S), sugarcane bagasse type, and particle size on the gas hold-up (?G) and volumetric oxygen transfer coefficient (kLa) in three different pneumatic bioreactors, using response surface methodology. Concentric tube airlift (CTA), split-cylinder airlift (SCA), and bubble column (BC) bioreactor types were tested. QAIR and %S affected oxygen mass transfer positively and negatively, respectively, while sugarcane bagasse type and particle size (within the range studied) did not influence kLa. Using large particles of untreated sugarcane bagasse, the loop-type bioreactors (CTA and SCA) exhibited higher mass transfer, compared to the BC reactor. At higher %S, SCA presented a higher kLa value (0.0448 s?1) than CTA, and the best operational conditions in terms of oxygen mass transfer were achieved for %S < 10.0 g L?1 and QAIR > 27.0 L min?1. These results demonstrated that pneumatic bioreactors can provide elevated oxygen transfer in the presence of vegetal biomass, making them an excellent option for use in three-phase systems for cellulolytic enzyme production by filamentous fungi. PMID:24078146

Esperança, M N; Cunha, F M; Cerri, M O; Zangirolami, T C; Farinas, C S; Badino, A C

2014-05-01

30

Effect of dissolved gas on bubble nucleation  

Microsoft Academic Search

Experiments studying the extinction of a gas bubble in a liquid droplet and the possibility of bubble formation in a droplet containing dissolved gas are used to investigate the effect of dissolved gas on liquid-gas phase transitions (boiling, caviation, etc.). The superheat limit of the liquid was studied using a technique in which a droplet containing a dissolved gas was

Y. Mori; K. Hijikata; T. Nagatani

1976-01-01

31

Gas–liquid simulation of an airlift bubble column reactor  

Microsoft Academic Search

The simulation of two-phase flow for an experimental airlift reactor (32-l volume) using commercially available software from Fluent Incorporated is presented here (http:\\/\\/www.fluent.co.uk). Data from the simulation is compared with the experimental data obtained by the tracking of a magnetic particle and analysis of the pressure drop to determine the gas hold-up. Comparisons between vertical velocity and gas hold-up were

M. Blažej; G. M. Cartland Glover; S. C. Generalis; J. Markoš

2004-01-01

32

Gas-liquid simulation of an airlift bubble column reactor  

Microsoft Academic Search

The simulation of two-phase flow for an experimental airlift reactor (32-l volume) using commercially available software from Fluent Incorporated is presented here (http:\\/\\/www.fluent.co.uk ). Data from the simulation is compared with the experimental data obtained by the tracking of a magnetic particle and analysis of the pressure drop to determine the gas hold-up. Comparisons between vertical velocity and gas hold-up

M. Bla; G. M. Cartland Glover; S. C. Generalis; J. Markoš

2004-01-01

33

PARAMETRIC EFFECTS OF ANTIFOAM COMPOSITION, SIMULANT PROPERTIES AND NOBLE METALS ON THE GAS HOLDUP AND RELEASE OF A NON-NEWTONIAN WASTE SLURRY SIMULANT  

Microsoft Academic Search

Gas holdup tests were performed in bench-scale and small-scale mechanically-agitated mixing systems at the Savannah River National Laboratory (SRNL) for a simulant of waste from the Hanford Tank 241-AZ-101. These featured additions of DOW Corning Q2-3183A anti-foam agent. Results indicated that this anti-foam agent (AFA) increased gas holdup in the waste simulant by about a factor of four and, counter-intuitively,

H Guerrero; C Charles Crawford; M Mark Fowley

2008-01-01

34

Determination of optimum gas holdup conditions in a three-phase fluidized bed by genetic algorithm  

Microsoft Academic Search

Experiments have been carried out in a 0.1m internal diameter, 1.88m height vertical Plexiglas column with an antenna type modified air sparger in the gas–liquid distributor section. This arrangement provides uniform mixing of the fluids, ensures the gas entering the fluidizing section as fine bubbles and reduces the pressure drop encountered through a conventional distributor used for the purpose. The

H. M. Jena; G. K. Roy; S. S. Mahapatra

2010-01-01

35

Structure of nanoscale gas bubbles in metals  

NASA Astrophysics Data System (ADS)

A usual way to estimate the amount of gas in a bubble inside a metal is to assume thermodynamic equilibrium, i.e., the gas pressure P equals the capillarity force 2?/R, with ? the surface energy of the host material and R the bubble radius; under this condition there is no driving force for vacancies to be emitted or absorbed by the bubble. In contrast to the common assumption that pressure inside a gas or fluid bubble is constant, we show that at the nanoscale this picture is no longer valid. P and density can no longer be defined as global quantities determined by an equation of state (EOS), but they become functions of position because the bubble develops a core-shell structure. We focus on He in Fe and solve the problem using both continuum mechanics and empirical potentials to find a quantitative measure of this effect. We point to the need of redefining an EOS for nanoscale gas bubbles in metals, which can be obtained via an average pressure inside the bubble. The resulting EOS, which is now size dependent, gives pressures that differ by a factor of two or more from the original EOS for bubble diameters of 1 nm and below.

Caro, A.; Schwen, D.; Martinez, E.

2013-11-01

36

Bubble nucleation from gas cavities — a review  

Microsoft Academic Search

This review is concerned with the nucleation of bubbles in solutions supersaturated with a gas, in particular the bubble nucleation that occurs at specific sites, as a cycle. A classification system for the kinds of nucleation that occur is defined and discussed in order to place this specific form of nucleation into a better defined context. It is noted that

S. F. Jones; G. M. Evans; K. P. Galvin

1999-01-01

37

Acoustic manifestations of gas hydrate shelled bubbles  

NASA Astrophysics Data System (ADS)

The hydrocarbon seeps emitting buoyant bubble plumes from seafloor vents—gas flares have been actively investigated in different regions of the World Ocean, in particular, on the Sakhalin slope in the Sea of Okhotsk. The gas flares can be easily detected by regular echo sounders, because the scattering cross section of a gas bubble is large. Within the gas-hydrate stability zone—for high hydrostatic pressures and low temperatures, methane-hydrate ice skins are formed on rising seep bubbles which are typically methane. The objective of the present study was to develop a suitable model describing rheological characteristics of gas-hydrate shell and to analyze acoustic manifestations of such bubbles for the frequency range used in marine field experiments.

Maksimov, A. O.; Sosedko, E. V.

2009-11-01

38

Experimental determination of bubble size distributions in bubble columns: prediction of mean bubble diameter and gas hold up  

Microsoft Academic Search

Bubble diameters were measured photographically in a bubble column, which was operating in the homogeneous regime with air and aqueous isopropanol solutions. The bubble size data were determined for several values of the superficial gas velocity, and used to fit bubble size distributions. The gas hold up was measured under the same conditions and its values were calculated from the

P. L. C. Lage; R. O. Espósito

1999-01-01

39

Effect of point defect interaction with bubble surface on the nucleation and growth of gas bubbles  

Microsoft Academic Search

The influence of absorption ability of gas bubble surface on bubble kinetics in supersaturated solid solution of vacancies self-interstitial and gas atoms is investigated. Depending on the peculiarities of point defect absorption\\/desorption at the bubble surface possible cases of gas bubble ensemble kinetics are described.

Roman E. Voskoboinikov; Alexander E. Volkov

2001-01-01

40

Gas bubbles in shaped sapphire  

Microsoft Academic Search

Shaped sapphire single crystals almost always contain a typical defect: small bubbles also known as “micro-voids”. The goal of this paper is to review the existing literature and give a survey of our recent work on this specific defect. As a conclusion to our review we propose a mechanism for bubble formation and its occurrence and distribution in shaped sapphire.The

O. M. Bunoiu; Th. Duffar; I. Nicoara

2010-01-01

41

Hydrodynamic studies of Fischer-Tropsch bubble-column systems  

SciTech Connect

Scoping hydrodynamic studies of slurry Fischer-Tropsch bubble-column reactors were performed using small hot-flow non-reacting bubble-columns. Various liquid mediums were studied including actual reactor-waxes from our pilot plant runs. Results indicate that different waxes can produce vastly different gas holdups under similar conditions. The type of gas distributor has a major effect on holdup and bubble size in certain waxes and photographs are presented to illustrate this. The effect of pressure and gas type are negligible.

Gupte, K.; Kuo, J.C.W.; Leib, T.M.; Smith, J.

1984-08-01

42

Wall-To-Bulk Mass Transfer in a Gas Liquid Upflow Bubble Column  

NASA Astrophysics Data System (ADS)

Experiments have been carried out to investigate the effect of liquid and gas velocities, viscosity and gas hold-up on wall-to-bulk mass transfer coefficient in a gas-liquid upflow bubble column using limiting current technique. The system chosen was an electrolyte as liquid phase and inert nitrogen as gas phase. The electrolyte was an equimolar solution of potassium ferricyanide and potassium ferrocyanide of 0.01 N with 0.5 N sodium hydroxide as indifferent electrolyte. To vary the viscosity carboxy methyl cellulose sodium salt (CMC) in 0.1, 0.2 and 0.4 wt% was added to the electrolyte. The reaction considered was the reduction of ferricyanide ion. The experiments were carried out at constant temperature of 25 °C at which the physical property values of the electrolyte were known from literature. The mass transfer coefficient was computed from the measured limiting current. It was found that the mass transfer coefficient was relatively independent of liquid velocity with in the range covered in the present experiment. The kL increased with increasing gas velocity and gas holdup. The kL was observed to decrease with increasing CMC concentration. The entire experimental data have been correlated in terms of Colburn j-factor, Reynolds number and modified Froude number.

Raju, G. M. J.; Ramesh, K. V.; Sarma, G. V. S.

2013-09-01

43

Morphology of Gas Bubbles in Mud: A Microcomputed Tomographic Evaluation.  

National Technical Information Service (NTIS)

Free gas in surficial sediments commonly forms gas bubbles that attenuate and dampen acoustic waves, influence slope stability, and contribute to greenhouse gas concentrations. Therefore, determining the mechanisms that control bubble shape, size, growth,...

A. H. Reed B. P. Boudreau C. Algar Y. Furukawa

2005-01-01

44

Fluid inclusions with gas bubbles as geothermometers  

Microsoft Academic Search

Two types of fluid inclusions can be distinguished. The first is based on the assumption of Sorby (1858) that a homogeneous phase, such as water, salt solution, or CO2, is entrapped, meaning that the bubbles result from the gas of the enclosed fluid. The second type includes foreign gas entrapped with the fluid. \\

C. W. Correns; Geol Rundsch

2002-01-01

45

Dynamics of gas bubbles in monolayers  

Microsoft Academic Search

We present a study of the temporal evolution of a two-dimensional bubble pattern in the liquid-gas coexistence region of monolayers. Using fluorescence microscopy of pentadecanoic acid or dipalmitoyl phosphotidylcholine on the surface of water, we study the coarsening of the pattern for several days. Two different regimes appear, depending on the percentage of gas phase observed on the surface. At

Bruno Berge; Adam J. Simon; Albert Libchaber

1990-01-01

46

REMARKS ABOUT GAS BUBBLE CHAMBER CHARACTERISTICS  

Microsoft Academic Search

The effect of ionizing radiation on strongly supersaturated gas--liquid ; solutions has been observed by the Genoa research group during the Spring of 1958. ; The group established, in a first approximation, the conditions which the gas--; liquid systems must satisfy in order to turn this effect into formation of bubble ; tracks along the ionizing path. Some of the

P. E. Argan; A. Gigli; E. Picasso; G. Tomasini; L. Gonella

1959-01-01

47

Heat transfer and bubble dynamics in bubble and slurry bubble columns with internals for Fischer-Tropsch synthesis of clean alternative fuels and chemicals  

NASA Astrophysics Data System (ADS)

Synthesis gas, a mixture of CO and H2 obtained from coal, natural gas and biomass are increasingly becoming reliable sources of clean synthetic fuels and chemicals and via Fischer-Tropsch (F-T) synthesis process. Slurry bubble column reactor is the reactor of choice for the commercialization of the F-T synthesis. Even though the slurry bubble column reactors and contactors are simple in structures, their design, scale-up, operation, and performance prediction are still challenging and not well understood due to complex interaction of phases. All the studies of heat transfer have been performed without simultaneously investigating the bubble dynamics adjacent to the heat transfer surfaces, particularly in slurry with dense internals. This dissertation focuses on enhancing the understanding of the role of local and overall gas holdup, bubble passage frequency, bubble sizes and bubble velocity on the heat transfer characteristics by means of a hybrid measurement technique comprising an advanced four-point optical probe and a fast response heat transfer probe used simultaneously, in the presence and absence of dense internals. It also seeks to advance a mechanistic approach for estimating the needed parameters for predicting the heat transfer rate in two phase and three phase systems. The results obtained suggest that the smaller diameter internals gives higher heat transfer coefficient, higher local and overall gas holdup, bubble passage frequency and specific interfacial area but smaller bubble sizes and lower axial bubble velocities. The presence of dense internals enhances the heat transfer coefficient in both the large and smaller columns, while increased column diameter increases the heat transfer coefficient, axial bubble velocity, local and overall gas holdup, bubble chord lengths and specific interfacial area. Addition of solids (glass beads) leads to increased bubble chord lengths and increase in axial bubble velocity, but a decrease in local and overall gas holdup, a decrease in bubble passage frequency and decrease in the heat transfer coefficient. Further, a mechanistic assessment of the dependence of the heat transfer coefficient on the bubble dynamics shows that the contact time needed in the heat transfer coefficient estimation is indeed a function of the bubble passage frequency and local gas holdup. Hence the variation of the heat transfer coefficient with contact time is via bubble passage frequency and local gas phase holdup, which are related with sizes and velocity.

Kagumba, Moses Odongo O.

48

Homogeneous nucleation of gas bubbles in vivo.  

PubMed

Several current theories of decompression sickness (DCS) presume the preexistence of gas bubble nuclei in tissue, because the de novo nucleation of gas bubbles in the body is thought to be theoretically impossible. Reexamination of nucleation theory reveals the overwhelming importance of two parameters: gas supersaturation and tissue surface tension (gamma). For the high gamma of pure water nucleation theoretically requires more than 1,000 ATA supersaturation. Lower values of gamma allow nucleation to occur with vastly smaller supersaturations. Application of homogeneous nucleation theory can provide reasonable fits to both rat and human pressure-reduction data with values of gamma within the range reported for biological fluids (below 5 dyn/cm). The initial bubble sizes predicted are 0.1 micron or less. The presence of heterogeneous sites, for example crevices and lipid surfaces, makes nucleation even more likely. PMID:6295990

Weathersby, P K; Homer, L D; Flynn, E T

1982-10-01

49

Gas–vapor bubble nucleation—a unified approach  

Microsoft Academic Search

In a solution which is saturated with gas near the superheat limit, one might expect a bubble formed from both dissolved gas and vapor molecules to appear. The integration of the surface-energy concepts, that are postulated on completely different physical bases for gas and vapor bubble formation is a major issue. In this paper, we reformulate gas and vapor bubble

Ho-Young Kwak; Si-Doek Oh

2004-01-01

50

In-Situ Measurements of Low Enrichment Uranium Holdup Process Gas Piping at K-25-Paper for Waste Management Symposia 2010 East Tennessee Technology Park, Oak Ridge, Tennessee.  

National Technical Information Service (NTIS)

This document is the final version of a paper submitted to the Waste Management Symposia, Phoenix, 2010, abstract BJC/OR-3280. The primary document from which this paper was condensed is In-Situ Measurement of Low Enrichment Uranium Holdup in Process Gas ...

B. Rasmussen

2010-01-01

51

Dynamics of gas-liquid flows in bubble column reactors  

Microsoft Academic Search

Wall pressure fluctuations were measured in bubble columns at different locations and for different gas velocities and height to diameter ratios. Non-linear analysis of the acquired data of pressure fluctuations was carried out to quantify dynamic characteristics. A bubble–bubble interaction model was developed to simulate voidage fluctuations in bubble columns. Dynamic characteristics of the simulated voidage fluctuations were compared with

V. V. Ranade; R. P. Utikar

1999-01-01

52

STUDIES ON THE DYNAMICS OF GAS BUBBLES IN MAGNETIZABLE NANOFLUIDS  

Microsoft Academic Search

The paper presents results of experimental work on the dynamics of single gas bubbles in magnetizable nanofluids, with emphasis on the bubble frequency and average volume at departure. The effects of magnetic properties of the magnetizable nanofluid and of gradient of the applied magnetic field on bubble frequency and average bubble volume at departure were determined.

Gheorghe POP; Floriana D. STOIAN; Doina BICA; Virgil STOICA

53

Flow regimes and gas holdup in paper pulp–water–gas three-phase slurry flow  

Microsoft Academic Search

Hydrodynamic flow characteristics of solid–liquid–gas slurry made by intimately mixing fibrous paper pulp with water and air were investigated in a short, vertical circular column. The pulp consistency (weight fraction of pulp in the pulp–water mixture) was varied in the low consistency range of 0.0–1.5%. The test section was 1.8m long, with 5.08cm inner diameter. Mixing of the slurry prior

T Xie; S. M Ghiaasiaan; S Karrila; T McDonough

2003-01-01

54

Heterogeneous nucleation of fission gas bubbles and gas migration in uranium dioxide  

Microsoft Academic Search

The number and size of fission gas bubbles precipitated in irradiated uranium dioxide are calculated from a theory based on a balance between nucleation of bubbles at vacancy clusters produced by fission fragments and the agglomeration of bubbles by random motion. The distribution of bubble sizes is determined by gas atom capture, bubble agglomeration and irradiation re-solution. Irradiation re-solution exceeds

A. D. Whapham

1972-01-01

55

Nucleation and Growth of Gas Bubbles in Elastomers  

Microsoft Academic Search

An experimental study is described of the formation and growth of gas bubbles in crosslinked elastomers. A critical condition for bubble formation is found to hold in most cases: The gas supersaturation pressure must exceed 5G?2, where G is the shear modulus of the elastomer. The kinetics of bubble growth are shown to be in good accord with a simple

A. N. Gent; D. A. Tompkins

1969-01-01

56

Suppression of cavitation inception by gas bubble injection: A numerical study focusing on bubble-bubble interaction  

NASA Astrophysics Data System (ADS)

The dynamic behavior of cavitation and gas bubbles under negative pressure has been studied numerically to evaluate the effect of gas bubble injection into a liquid on the suppression of cavitation inception. In our previous studies, it was demonstrated by direct observation that cavitation occurs in liquid mercury when mechanical impacts are imposed, and this will cause cavitation damage in spallation neutron sources, in which liquid mercury is bombarded by a high-power proton beam. In the present paper, we describe numerical investigations of the dynamics of cavitation bubbles in liquid mercury using a multibubble model that takes into account the interaction of a cavitation bubble with preexisting gas bubbles through bubble-radiated pressure waves. The numerical results suggest that, if the mercury includes gas bubbles whose equilibrium radius is much larger than that of the cavitation bubble, the explosive expansion of the cavitation bubble (i.e., cavitation inception) is suppressed by the positive-pressure wave radiated by the injected bubbles, which decreases the magnitude of the negative pressure in the mercury.

Ida, Masato; Naoe, Takashi; Futakawa, Masatoshi

2007-10-01

57

Enhancement of Oxygen Mass Transfer and Gas Holdup Using Palm Oil in Stirred Tank Bioreactors with Xanthan Solutions as Simulated Viscous Fermentation Broths  

PubMed Central

Volumetric mass transfer coefficient (kLa) is an important parameter in bioreactors handling viscous fermentations such as xanthan gum production, as it affects the reactor performance and productivity. Published literatures showed that adding an organic phase such as hydrocarbons or vegetable oil could increase the kLa. The present study opted for palm oil as the organic phase as it is plentiful in Malaysia. Experiments were carried out to study the effect of viscosity, gas holdup, and kLa on the xanthan solution with different palm oil fractions by varying the agitation rate and aeration rate in a 5?L bench-top bioreactor fitted with twin Rushton turbines. Results showed that 10% (v/v) of palm oil raised the kLa of xanthan solution by 1.5 to 3 folds with the highest kLa value of 84.44?h?1. It was also found that palm oil increased the gas holdup and viscosity of the xanthan solution. The kLa values obtained as a function of power input, superficial gas velocity, and palm oil fraction were validated by two different empirical equations. Similarly, the gas holdup obtained as a function of power input and superficial gas velocity was validated by another empirical equation. All correlations were found to fit well with higher determination coefficients.

Mohd Sauid, Suhaila; Huey Ling, Tan; Veluri, Murthy V. P. S.

2013-01-01

58

A novel method of measuring electrophoretic mobility of gas bubbles  

Microsoft Academic Search

Accurate measurement of electrophoretic mobility for gas bubbles is a challenging task as it requires the creation of a desired number of very small air bubbles to ensure negligible rise velocities during the course of the measurement. Here, we report a simple and reliable method for generating stable dispersions of “nano-bubbles.” Preparation of such dispersions relies on the nucleation of

Aref Seyyed Najafi; Jaroslaw Drelich; Anthony Yeung; Zhenghe Xu; Jacob Masliyah

2007-01-01

59

Nucleation and growth of a gas bubble in magma  

NASA Astrophysics Data System (ADS)

The dynamics of a "collective" gas bubble in the magma melt during its decompression was numerically studied on the basis of a complete mathematical models of an explosive volcanic eruption. It is shown that the bubble size distribution obtained for the nucleation process has one peak, which allows considering a "collective" bubble. The main stages of bubble growth due to gas diffusion and changes in the viscosity of the medium are determined. It is shown that the high viscosity of the melt makes possible the transition from the Rayleigh equation to a simpler relation for the radial velocity of the bubble.

Davydov, M. N.

2012-05-01

60

GAS BUBBLE FORMATION IN IRRADIATED PLASTICS AND REACTOR FUELS  

Microsoft Academic Search

A transparent plastic, in which gas was formed by gamma irradiation was ; used to investigate the mechanisms of gas bubble formation and growth. Babble ; formation and swelling were studied for several environments, both external and ; internal to the plastic-gas systems. During irradiation at lOO deg C, larger but ; fewer bubbles form in the plastic than on

Bentle

1959-01-01

61

Modelling of large-scale dense gas–solid bubbling fluidised beds using a novel discrete bubble model  

Microsoft Academic Search

In order to model the complex hydrodynamic phenomena prevailing in industrial scale gas–solid bubbling fluidised bed reactors and especially the macro-scale emulsion phase circulation patterns induced by bubble–bubble interactions and bubble coalescence, a discrete bubble model (DBM) has been developed. In the DBM, the (larger) bubbles are modelled as discrete elements and are tracked individually during their rise through the

G. A. Bokkers; J. A. Laverman; M. van Sint Annaland; J. A. M. Kuipers

2006-01-01

62

Gas nuclei, their origin, and their role in bubble formation.  

PubMed

Gas bubbles are the primary agent in producing the pathogenic effects of decompression sickness. Bubble formation during decompression is not simply the consequence of inert gas supersaturation. Numerous experiments indicate that bubbles originate as pre-existing gas nuclei. Radii are on the order of 1 microm or less. Heterogeneous nucleation processes are involved in generating these gas entities. Musculoskeletal activity could be the main promoter of gas nuclei from stress-assisted nucleation. The half-life and faculty for nuclei to initiate bubble formation during decompression depend on many factors. Oxygen window and surface tension are involved in resolving bubbles. Two factors have been proposed to stabilize gas nuclei against dissolution: gas nuclei trapped in hydrophobic crevices and gas nuclei coated with surface-active molecules such as surfactants. Diffusion and surface tension could play an important role in the formation of gas nuclei crevices. However, while the concept of in vivo hydrophobic crevices remains a theoretical possibility, none have yet been identified in tissues and/or in microcapillaries. Moreover, while surfactants seem present in numerous tissues and could play a role in gas nuclei stabilization, they could also be involved in bubble elimination. The understanding of such mechanisms is of primary importance to neutralize nuclei and for modeling bubble growth. Here we present in a single document a summary of the original findings and views from authors in this field. PMID:17042253

Blatteau, Jean-Eric; Souraud, Jean-Baptiste; Gempp, Emmanuel; Boussuges, Alain

2006-10-01

63

Gas separation and bubble behavior at a woven screen  

NASA Astrophysics Data System (ADS)

Gas-liquid two phase flows are widespread and in many applications the separation of both phases is necessary. Chemical reactors, water treatment devices or gas-free delivery of liquids like propellant are only some of them. We study the performance of a woven metal screen in respect to its phase separation behavior under static and dynamic conditions. Beside hydraulic screen resistance and static bubble point, our study also comprises the bubble detachment from the screen upon gas breakthrough. Since a woven screen is essentially an array of identical pores, analogies to bubble detachment from a needle can be established. While the bubble point poses an upper limit for pressurized gas at a wetted screen to preclude gas breakthrough, the necessary pressure for growing bubbles to detach from the screen pores a lower limit when breakthrough is already in progress. Based on that inside, the dynamic bubble point effects were constituted that relate to a trapped bubble at such a screen in liquid flow. A trapped is caused to break through the screen by the flow-induced pressure drop across it. Our model includes axially symmetric bubble shapes, degree of coverage of the screen and bubble pressurization due to hydraulic losses in the rest of the circuit. We have built an experiment that consists of a Dutch Twilled woven screen made of stainless steel in a vertical acrylic glass tube. The liquid is silicon oil SF0.65. The screen is suspended perpendicular to the liquid flow which is forced through it at variable flow rate. Controlled injection of air from a needle allows us to examine the ability of the screen to separate gas and liquid along the former mentioned effects. We present experimental data on static bubble point and detachment pressure for breakthrough at different gas supply rates that suggest a useful criterion for reliable static bubble point measurements. Results for the dynamic bubble point are presented that include i) screen pressure drop for different trapped bubble volumes, liquid flow rates and flow-induced compression, ii) typical breakthrough of a trapped bubble at rising liquid flow rate and iii) steady gas supply in steady liquid flow. It shows that our model can explain the experimental observations. One of the interesting findings for the dynamic bubble point is that hydraulic losses in the rest of the circuit will shift the breakthrough of gas to higher liquid flow rates.

Conrath, Michael; Dreyer, Michael E.

64

Gas Bubble Formation in Stagnant and Flowing Mercury  

SciTech Connect

Investigations in the area of two-phase flow at the Oak Ridge National Laboratory's (ORNL) Spallation Neutron Source (SNS) facility are progressing. It is expected that the target vessel lifetime could be extended by introducing gas into the liquid mercury target. As part of an effort to validate the two-phase computational fluid dynamics (CFD) model, simulations and experiments of gas injection in stagnant and flowing mercury have been completed. The volume of fluid (VOF) method as implemented in ANSYS-CFX, was used to simulate the unsteady two-phase flow of gas injection into stagnant mercury. Bubbles produced at the upwards-oriented vertical gas injector were measured with proton radiography at the Los Alamos Neutron Science Center. The comparison of the CFD results to the radiographic images shows good agreement for bubble sizes and shapes at various stages of the bubble growth, detachment, and gravitational rise. Although several gas flows were measured, this paper focuses on the case with a gas flow rate of 8 cc/min through the 100-micron-diameter injector needle. The acoustic waves emitted due to the detachment of the bubble and during subsequent bubble oscillations were recorded with a microphone, providing a precise measurement of the bubble sizes. As the mercury flow rate increases, the drag force causes earlier bubble detachment and therefore smaller bubbles.

Wendel, Mark W [ORNL; Abdou, Ashraf A [ORNL; Riemer, Bernie [ORNL; Felde, David K [ORNL

2007-01-01

65

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

Microsoft Academic Search

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets

Y. Matsumoto

1988-01-01

66

Gas-vapor bubble nucleation--a unified approach.  

PubMed

In a solution which is saturated with gas near the superheat limit, one might expect a bubble formed from both dissolved gas and vapor molecules to appear. The integration of the surface-energy concepts, that are postulated on completely different physical bases for gas and vapor bubble formation is a major issue. In this paper, we reformulate gas and vapor bubble nucleation by a scaling transformation, which turns the surface energy for the bubble formation from both dissolved gases and vapor molecules to the translational energy of a molecule, (3/2)kBT. With this unified approach, one could estimate the dissolved gas effect on the superheat limit of the liquid. The driving force and the molecular volume are important quantities for determining the number of gas and vapor molecules composed of a critical cluster. This approach, of course, can predict pure gas bubble formation, as well as pure vapor bubble formation, as limiting cases. Also, this approach makes it possible to find that the possible occurrence of gas bubble nucleation by dissolved gases prevents measuring the theoretical superheat limit of water at atmospheric pressure, 300 degrees C. PMID:15450464

Kwak, Ho-Young; Oh, Si-Doek

2004-10-15

67

Downward bubbly gas–liquid flow in a vertical pipe  

Microsoft Academic Search

Local characteristics of downward bubbly flow in a 42.3mm i.d. vertical pipe were investigated. An electrochemical technique was used to measure wall shear stress, local void fraction, liquid velocity, wall shear stress and velocity fluctuations. A gas–liquid mixer was used permitting the change in size of gas bubbles for the same gas and liquid flow rates. Special attention was paid

O. N. Kashinsky; V. V. Randin

1999-01-01

68

Measurement Of Gas Bubbles In Mercury Using Proton Radiography  

SciTech Connect

An experiment using proton radiography on a small mercury loop for testing gas bubble injection was conducted at the Los Alamos Neutron Science Center (LANSCE) in December 2006. Small gas bubble injection is one of the approaches under development to reduce cavitation damage in the U.S. Spallation Neutron Source mercury target vessel. Several hundred radiograph images were obtained as the test loop was operated over range of conditions that included two jet type bubble generators, two needle type bubble generators, various mercury flow speeds and gas injection rates, and use of helium, argon and xenon. This paper will describe the analysis of the radiograph images and present the obtained bubble measurement data.

Riemer, Bernie [ORNL; Bingham, Philip R [ORNL; Mariam, Fesseha G [Los Alamos National Laboratory (LANL); Merrill, Frank E [ORNL

2007-01-01

69

Gas bubble nucleation kinetics in a live heavy oil  

Microsoft Academic Search

The current primary production of heavy oil and bitumen is highly dependent on the development of ‘foamy oil’, heavy oils containing dispersions of long-lived bubbles of gas. The nucleation and initial growth of these bubbles are key elements of the behavior of foamy oils. The tremendous levels of supersaturation associated with the expansion of live heavy oils within a porous

D. A. Lillico; A. J. Babchin; W. E. Jossy; R. P. Sawatzky; J.-Y. Yuan

2001-01-01

70

Pulsed Electrical Discharge in a Gas Bubble in Water  

NASA Astrophysics Data System (ADS)

This experiment is an investigation of the electrical and optical characteristics of a pulsed electrical discharge ignited in a gas bubble in water in a needle-to-plane electrode geometry. Argon or oxygen gas is fed through a platinum hypodermic needle that serves as the high voltage electrode. The gas filled bubble forms at the high voltage electrode with the tip of the needle inside the bubble. The discharge in the gas bubble in water is produced by applying 5 -- 15 kV, microsecond long rectangular pulses between the electrodes submerged in water. The voltage across the electrodes and the current are measured as functions of time. Electrical measurements suggest a discharge ignited in the bubble (composed of the bubbled gas and water vapor) without breakdown of the entire water filled electrode gap. Time-resolved optical emission measurements are taken in the areas of the spectrum corresponding to the main reactive species produced in the discharge, e.g. OH 309 nm, Ar 750 nm, and O 777 nm emissions using optical filters. The discharge properties are investigated as a function of the applied voltage, the distance between the electrodes, the gas in the bubble (Ar or O2). Work supported by the US Army, Picatinny Arsenal, NJ and the US DOE (Contract number DE-AC02-76CH03073).

Schaefer, Erica; Gershman, Sophia; Mozgina, Oksana

2005-10-01

71

Holdup measurements under realistic conditions  

Microsoft Academic Search

This paper reviews the documentation of the precision and bias of holdup (residual nuclear material remaining in processing equipment) measurements and presents previously unreported results. Precision and bias results for holdup measurements are reported from training seminars with simulated holdup, which represent the best possible results, and compared to actual plutonium processing facility measurements. Holdup measurements for plutonium and uranium

J. K. Jr. Sprinkel; R. Marshall; P. A. Russo; R. Siebelist

1997-01-01

72

Bubble coalescence dynamics and supersaturation in electrolytic gas evolution  

SciTech Connect

The apparatus and procedures developed in this research permit the observation of electrolytic bubble coalescence, which heretofore has not been possible. The influence of bubble size, electrolyte viscosity, surface tension, gas type, and pH on bubble coalescence was examined. The Navier-Stokes equations with free surface boundary conditions were solved numerically for the full range of experimental variables that were examined. Based on this study, the following mechanism for bubble coalescence emerges: when two gas bubbles coalesce, the surface energy decreases as the curvature and surface area of the resultant bubble decrease, and the energy is imparted into the surrounding liquid. The initial motion is driven by the surface tension and slowed by the inertia and viscosity of the surrounding fluid. The initial velocity of the interface is approximately proportional to the square root of the surface tension and inversely proportional to the square root of the bubble radius. Fluid inertia sustains the oblate/prolate oscillations of the resultant bubble. The period of the oscillations varies with the bubble radius raised to the 3/2 power and inversely with the square root of the surface tension. Viscous resistance dampens the oscillations at a rate proportional to the viscosity and inversely proportional to the square of the bubble radius. The numerical simulations were consistent with most of the experimental results. The differences between the computed and measured saddle point decelerations and periods suggest that the surface tension in the experiments may have changed during each run. By adjusting the surface tension in the simulation, a good fit was obtained for the 150-{micro}m diameter bubbles. The simulations fit the experiments on larger bubbles with very little adjustment of surface tension. A more focused analysis should be done to elucidate the phenomena that occur in the receding liquid film immediately following rupture.

Stover, R.L. [Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering]|[Lawrence Berkeley National Lab., CA (United States). Energy and Environment Div.

1996-08-01

73

Gas-vapor bubble dynamics in therapeutic ultrasound  

NASA Astrophysics Data System (ADS)

In applications of therapeutic ultrasound such as shock wave lithotripsy (SWL) and high-intensity focused ultrasound (HIFU), cavitation and the associated bubble dynamics play an important role. Moreover, bubble dynamics have not been fully studied in the context of the large acoustic excitations, elevated temperatures, and gas-saturated conditions that characterize therapeutic ultrasound treatments. Because acoustic cavitation has been typically explored in the context of bubbles containing only non-condensable gases, relatively little is understood about the role of vapor under relevant conditions. Accordingly, the primary goal of this effort is to elucidate the role of vapor in the dynamics of gas-vapor bubbles. Given the large acoustic excitations of SWL and HIFU, the dynamics of violent inertial collapses are of particular interest. To investigate the impact of vapor, both numerical modeling and experiments were utilized. The model was developed for a single, spherical bubble and was designed to capture behavior associated with the collapse and rebound of a gas-vapor bubble. Numerical difficulties in modeling violent collapses were addressed by using scaling principles to approximate the spatial gradients used for estimating heat and mass transport in both liquid and gaseous phases, Model predictions demonstrate thermal effects from vapor transport through the coupling of the saturated vapor pressure to temperature changes in the surrounding liquid. Also, the model suggests that vapor transport affects the dynamics mechanically when vapor is diffusively trapped in the bubble interior. Moreover, predictions imply that the collapses of millimeter-sized lithotripsy bubbles are principally governed by the aforementioned mechanical effects. To test the model, collapses and rebounds of lithotripsy bubbles were experimentally observed using high-speed photography. Although bubble asymmetries added scatter to the data, experimental observations agree very well with the range of model predictions obtained with feasible length scales for mass diffusion in the bubble interior. Statistically significant variations observed in the experimental data imply that both temperature and dissolved gas concentration in the surrounding liquid affect mass diffusion inside the bubble. To complement experimental observations, bubble clusters in an incompressible liquid were modeled; simulations yielded insights related to bubble collapse times.

Kreider, Wayne

74

Production of Gas Bubbles in Reduced Gravity Environments  

NASA Technical Reports Server (NTRS)

In a wide variety of applications such as waste water treatment, biological reactors, gas-liquid reactors, blood oxygenation, purification of liquids, etc., it is necessary to produce small bubbles in liquids. Since gravity plays an essential role in currently available techniques, the adaptation of these applications to space requires the development of new tools. Under normal gravity, bubbles are typically generated by forcing gas through an orifice in a liquid. When a growing bubble becomes large enough, the buoyancy dominates the surface tension force causing it to detach from the orifice. In space, the process is quite different and the bubble may remain attached to the orifice indefinitely. The most practical approach to simulating gravity seems to be imposing an ambient flow to force bubbles out of the orifice. In this paper, we are interested in the effect of an imposed flow in 0 and 1 g. Specifically, we investigate the process of bubble formation subject to a parallel and a cross flow. In the case of parallel flow, we have a hypodermic needle in a tube from which bubbles can be produced. On the other hand, the cross flow condition is established by forcing bubbles through an orifice on a wall in a shear flow. The first series of experiments have been performed under normal gravity conditions and the working fluid was water. A high quality microgravity facility has been used for the second type and silicone oil is used as the host liquid.

Oguz, Hasan N.; Takagi, Shu; Misawa, Masaki

1996-01-01

75

Determination and evaluation of gas holdup time with the quadratic equation model and comparison with nonlinear models for isothermal gas chromatography.  

PubMed

Gas holdup time (tM) is a basic parameter in isothermal gas chromatography (GC). Determination and evaluation of tM and retention behaviors of n-alkanes under isothermal GC conditions have been extensively studied since the 1950s, but still remains unresolved. The difference equation (DE) model [J. Chromatogr. A 1260: 215-223] reveals retention behaviors of n-alkanes excluding tM, while the quadratic equation (QE) model [J. Chromatogr. A 1260: 224-231] including tM is suitable for applications. In the present study, tM values were calculated with the QE model, which is referred to as tMT, evaluated and compared with other three typical nonlinear models. The QE model gives an accurate estimation of tM in isothermal GC. The tMT values are highly accurate, stable, and easy to calculate and use. There is only one tMT value at each GC condition. The proper classification of tM values can clarify their disagreement and facilitate GC retention data standardization for which tMT values are promising reference tM values. PMID:23726077

Wu, Liejun; Chen, Maoxue; Chen, Yongli; Li, Qing X

2013-07-01

76

Determination and evaluation of gas holdup time with the quadratic equation model and comparison with nonlinear equation models for isothermal gas chromatography  

PubMed Central

Gas holdup time (tM) is a basic parameter in isothermal gas chromatography (GC). Determination and evaluation of tM and retention behaviors of n-alkanes under isothermal GC conditions have been extensively studied since the 1950s, but still remains unresolved. The difference equation (DE) model [J. Chromatogr. A 1260:215–223] reveals retention behaviors of n-alkanes excluding tM, while the quadratic equation (QE) model [J. Chromatogr. A 1260:224–231] including tM is suitable for applications. In the present study, tM values were calculated with the QE model, which is referred to as tMT, evaluated and compared with other three typical nonlinear models. The QE model gives an accurate estimation of tM in isothermal GC. The tMT values are highly accurate, stable, and easy to calculate and use. There is only one tMT value at each GC condition. The proper classification of tM values can clarify their disagreement and facilitate GC retention data standardization for which tMT values are promising reference tM values.

Wu, Liejun; Chen, Maoxue; Chen, Yongli; Li, Qing X.

2013-01-01

77

Phase-field simulations of gas density within bubbles in metals under irradiation  

Microsoft Academic Search

Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles in solids. In our simulations, which use copper as a model material, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid

Paul C. Millett; Michael Tonks

2011-01-01

78

Measurement and Prediction of Tritium Holdup.  

National Technical Information Service (NTIS)

Total inventory of tritium requires quantitation of the residual tritium that remains in the process after a normal measurement of bulk gas inventory by PVT/Gas Analysis methods. Two process elements known to exhibit this holdup are uranium getter pumps (...

R. E. Ellefson C. N. Lindsay E. E. Johns

1988-01-01

79

Theory of gas bubble nucleation in supersaturated solution of vacancies, interstitials and gas atoms  

Microsoft Academic Search

A general form of the kinetic coefficients of the Fokker–Planck equation describing gas bubble nucleation in supersaturated solution of vacancies, interstitials and gas atoms is obtained. No assumptions concerning the detailed balance are used to describe the absorption and desorption of point defects and gas atoms at the bubble surface. This allows us to investigate limits of the usual formalisms

A. E. Volkov; A. I. Ryazanov

1999-01-01

80

Bubble bursting phenomenon in Gas\\/Metal\\/Slag systems  

Microsoft Academic Search

Iron droplets can be ejected into the surrounding atmosphere or entrained into the slag phase when gas bubbles pass through\\u000a the metal surface or the metal\\/slag interface. The phenomena occurring during passage of single bubbles through the free surface\\u000a and the interface were investigated by using the in-situ X-ray transmission technique. The mass of droplets ejected into the atmosphere attained

Zhijun Han; Lauri Holappa

2003-01-01

81

Structure of Shock Waves in a Liquid Containing Gas Bubbles  

Microsoft Academic Search

\\u000a Transient shock wave phenomena in a liquid containing noncondensable gas bubbles are investigated experimentally and numerically.\\u000a In the experiment, time evolution of the shock wave is measured using two vertical glass shock tubes with different diameters,\\u000a 18 mm and 52 mm. In the numerical simulation, thermal processes inside each bubble are directly calculated by using full equations\\u000a for mass, momentum

Masaharu Kameda; Yoichiro Matsumoto

82

Phase holdups in three-phase fluidized beds in the presence of disc promoter  

SciTech Connect

Three-phase fluidized beds are found to have wide applications in process industries. The present investigation essentially comprises of the studies on gas holdup, liquid holdup and bed porosity in three-phase fluidized beds with coaxially placed disc promoter. Holdup data were obtained from bed expansion and pressure drop measurements. Analysis of the data was done to elucidate the effects of dynamic and geometric parameters on gas holdup, liquid holdup and bed porosity. Data were correlated and useful equations were obtained from empirical modeling. (author)

Murty, M.S.N. [Department of Chemical Engineering, GVP College of Engineering, Visakhapatnam 530 048 (India); Ramesh, K.V.; Venkateswarlu, P. [Department of Chemical Engineering, Andhra University, Visakhapatnam 530 003 (India); Prabhakar, G. [Department of Chemical Engineering, Sri Venkateswara University, Tirupati 517 502 (India)

2011-02-15

83

Progression and Severity of Gas Bubble Trauma in Juvenile Salmonids  

Microsoft Academic Search

We conducted laboratory experiments to assess the progression and to quantify the severity of signs of gas bubble trauma (GBT) in juvenile chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss exposed to different levels of total dissolved gas (TDG), and we attempted to relate these signs to the likelihood of mortality. When fish were exposed to 110% TDG for up

Matthew G. Mesa; Lisa K. Weiland; Alec G. Maule

2000-01-01

84

Enhanced diffusion of liquid-coated gas bubbles in solids  

Microsoft Academic Search

Gas bubble diffusion in solids is typically due to surface diffusion of matrix atoms along the gas-solid interface. Insoluble impurities that segregate to the interface tend to suppress surface diffusion by chemically combining with the surface atoms, as in the creation of a metal oxide layer, or by simply presenting a physical barrier to the kinetic jump process. We propose

C. De W. Van Siclen; R. N. Wright

1993-01-01

85

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

NASA Technical Reports Server (NTRS)

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.

Matsumoto, Y.

1988-01-01

86

Transient Flow Dynamics in Optical Micro Well Involving Gas Bubbles  

NASA Technical Reports Server (NTRS)

The Lab-On-a-Chip Application Development (LOCAD) team at NASA s Marshall Space Flight Center is utilizing Lab-On-a-Chip to support technology development specifically for Space Exploration. In this paper, we investigate the transient two-phase flow patterns in an optic well configuration with an entrapped bubble through numerical simulation. Specifically, the filling processes of a liquid inside an expanded chamber that has bubbles entrapped. Due to the back flow created by channel expansion, the entrapped bubbles tend to stay stationary at the immediate downstream of the expansion. Due to the huge difference between the gas and liquid densities, mass conservation issues associated with numerical diffusion need to be specially addressed. The results are presented in terms of the movement of the bubble through the optic well. Bubble removal strategies are developed that involve only pressure gradients across the optic well. Results show that for the bubble to be moved through the well, pressure pulsations must be utilized in order to create pressure gradients across the bubble itself.

Johnson, B.; Chen, C. P.; Jenkins, A.; Spearing, S.; Monaco, L. A.; Steele, A.; Flores, G.

2006-01-01

87

Gas-liquid bubbly flow in vertical pipes  

SciTech Connect

Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained demonstrate the existence of universal near-wall velocity distribution in a downward bubbly flow. The reduction of turbulent fluctuations is observed in downward flow as compared to a single-phase turbulent flow. The development of bubble-induced liquid velocity fluctuations in a laminar bubbly flow was studied.

Nakoryakov, V.E.; Kashinsky, O.N.; Randin, V.V.; Timkin, L.S. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. of Thermophysics

1996-06-01

88

Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury  

SciTech Connect

ABSTRACT Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic. Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations. After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions. The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into an actual SNS target.

Wendel, Mark W [ORNL; Riemer, Bernie [ORNL; Abdou, Ashraf A [ORNL

2012-01-01

89

Effect of dense heat exchanging internals on the hydrodynamics of bubble column reactors using non-invasive measurement techniques  

NASA Astrophysics Data System (ADS)

Given their efficiency and capital cost reduction, bubble/slurry bubble column reactors are the reactors of choice for Fischer-Tropsch (FT) synthesis, offering clean alternative fuels and chemicals. FT synthesis is an exothermic process that requires many heat exchanging tubes in order to remove heat efficiently and maintain the desired temperature and isothermal operating condition. The impact of the heat exchanging tubes (internals) on the hydrodynamics is not fully understood. Reliably designing and scaling up bubble column reactors requires proper understanding of hydrodynamics, as well as heat and mass transfer parameters. The main objective of this work is to advance the understanding of the effect of internals (25% covered cross-sectional area to meet FT needs) on hydrodynamics (gas holdup distribution, 3D liquid velocity, Reynolds stresses, turbulent kinetic energy, eddy diffusivity, etc.) in bubble columns. Single-source gamma-ray Computed Tomography (CT) and Radioactive Particle Tracking (RPT) were used for the first time to study the effect of dense internals and gas velocity on the phase holdup distribution and radial profiles, liquid velocity field and turbulent parameter profiles. The main findings obtained for the first time in this study can be summarized as follows: The presence of internals at a given superficial gas velocity causes: An increase in gas holdup and the axial centerline liquid velocity. A sharp decrease in turbulence parmeters. The increase in superficial gas velocity in the presence of internals causes: An increase in gas holdup, axial centerline liquid velocity and turbulent parameters.

Al Mesfer, Mohammed Khloofh

90

Homogeneous nucleation and macroscopic growth of gas bubble in organic solutions  

Microsoft Academic Search

This work concerns the spontaneous gas bubble nucleation after rapid decompression in organic solution initially saturated with dissolved gas and the subsequent bubble growth to macroscopic size. The decompression limit for gas bubble formation was obtained from the stability condition of the critical cluster of dissolved gas molecules. This work also clarifies how the critical cluster grows to the critical

Yong W. Kim

1998-01-01

91

Behavior of bubbles in glassmelts. II - Dissolution of a stationary bubble containing a diffusing and a nondiffusing gas  

NASA Technical Reports Server (NTRS)

The effect of a foreign nondiffusing gas on the rate of shrinkage of an oxygen bubble in a soda-lime-silica melt was studied. The rate of change of bubble radius with time was computed using the quasi-stationary approximation. The effects of melt undersaturation and initial fraction of foreign gas in the bubble are considered and compared with those calculated using previously derived expressions.

Weinberg, M. C.; Onorato, P. I. K.; Uhlmann, D. R.

1980-01-01

92

Theory of heterogeneous decay of a gas-supersaturated solution on passive gas bubbles  

Microsoft Academic Search

It is shown that there can be barrierless heterogeneous nucleation of bubbles of a mixture of active and passive gases on bubbles of a passive gas in a solution supersaturated with active gas. The threshold solution supersaturation above which barrierless heterogeneous nucleation commences is found. All the thermodynamic data on heterogeneous formation of nucleating centers needed to describe the kinetics

F. M. Kuni; A. A. Melikhov

1993-01-01

93

Experimental study of detonating gas bubble oscillations using a shock tube  

NASA Astrophysics Data System (ADS)

Oscillations of bubbles containing a mixture of a detonating gas with argon in their interior are studied. The bubbles are excited for oscillations by a pressure step generated in a shock tube. A bubble wall motion is observed by a rotating mirror camera and a radiated pressure wave by a needle hydrophone. For weak pressure steps the bubble behaves as an ordinary gas bubble. However, above a certain pressure step threshold ignition of the detonating gas occurs. Due to released heat the bubble oscillation intensity is amplified. The data obtained are used to estimate pressures and temperatures in the compressed bubble.

Vokurka, K.

1993-11-01

94

An apparatus to measure electrical charge of bubble swarms.  

PubMed

An apparatus has been developed to characterize bubble charge by measuring the swarm potential of gas bubbles. The technique allows in-process measurement of all system variables associated with bubble surface electrical charge: swarm potential, solution conductivity, gas holdup, pH and bubble size distribution. The method was validated by comparing with literature iso-electric point (iep) values. Bubble swarm potential was measured as a function of concentration and pH for a series of non-ionic surfactant frothers, ionic surfactant collectors and multivalent metal ions. Results showed good agreement with established theory and prior experimental findings. The setup is a step towards measurement of charge on flotation size range of bubble swarms. PMID:23031493

Uddin, S; Jin, L; Mirnezami, M; Finch, J A

2013-01-01

95

The velocity of gas bubble rise in a tube  

NASA Astrophysics Data System (ADS)

The solutions of the Laplace equation involving the diverging infinite series are used in the classical works at the analysis of the problem of the gravitational rise of a gas bubble in a tube filled with ideal fluid (the Taylor bubble). In the present work, an approximate method is proposed for a correct analysis of the above problem. The ideal fluid flow around a body of revolution in a tube is constructed by the method of the superposition of elementary solutions. The satisfaction of the free surface condition in the critical point neighborhood and the passage of the main parameter to the limit lead to the sought expression for the dimensionless velocity of the gas bubble — Froude number.

Zudin, Yu. B.

2013-03-01

96

Concentration distribution around a growing gas bubble in tissue.  

PubMed

This paper presents the concentration distribution around a growing nitrogen gas bubble in the blood and other tissues of divers who surface too quickly, when the ambient pressure through the decompression process is variable and constant. This effort is a modification of Sirinivasan et al. model (1999) [9]. The mathematical model is solved analytically to find the growth rate of a gas bubble in a tissue after decompression in the ambient pressure. Moreover, the concentration distribution around the growing bubble is introduced. The growth process is affected by ascent rate alpha (t), tissue diffusivity D(T), initial concentration difference DeltaC(0), surface tension sigma and void fraction varphi(0). PMID:20085775

Mohammadein, S A; Mohamed, K G

2010-05-01

97

Suspension viscosity and bubble rise velocity in liquid-solid fluidized beds  

Microsoft Academic Search

The effective viscosity which characterizes the pseudo-homogeneous property of the liquid-solid suspension in gas-liquid-solid fluidization is examined in light of the velocity of single bubbles rising through the suspension. Experiments conducted in this study cover a wide range of bubble diameters (2–23 mm) under high solids holdup (0.48 – 0.57) conditions. The study reveals that the liquid-solid medium exhibits a

Katsumi Tsuchiya; Akihiko Furumoto; Liang-Shih Fan; Jianping Zhang

1997-01-01

98

Gas-bubble enhanced heating in rabbit thigh in vivo  

Microsoft Academic Search

In this study, we propose a focused ultrasound surgery protocol that induces and then uses gas bubbles at the focus to enhance the ultrasound absorption and ultimately create larger lesions in vivo. MRI and ultrasound visualization and monitoring methods for this heating method are also investigated. Larger lesions created with a carefully monitored single ultrasound exposure could greatly improve the

S. Sokka; R. King; N. McDannold; K. Hynynen

2002-01-01

99

Gas bubble nucleation and growth in cohesive sediments  

Microsoft Academic Search

Sediment often contains a significant amount of organic material, which can be decomposed by bacterial activity. During this process and under anaerobic conditions that prevail in sediments, mainly methane and carbon dioxide are formed. These compounds will dissolve in the pore water, until the level of saturation is attained.Experiments show that gas bubble nucleation occurs already at a small oversaturation

Walther van Kesteren; Thijs van Kessel

2002-01-01

100

NUCLEATION AND GROWTH OF GAS BUBBLES IN IRRADIATED METALS  

Microsoft Academic Search

Several metals undergo nuclear reactions when subjected to neutron ; irradiation which result in the formation of gases in the metal. At elevated ; temperatures these gases tend to nucleate and form gas bubbles which result in ; over-all inportant technological implications. The available experi mental data ; on this phenomenon are rummarized, attention being concentrated on the cases of

Hickman

1960-01-01

101

Determination of Gas and Vapor Nuclei for Bubble Nucleation.  

National Technical Information Service (NTIS)

Nucleation in a given liquid depends on many variables, one of the most important of which is the size distribution and concentration of gas vapor nuclei. The present work applies a new technique to the investigation of bubble nucleation and the required ...

O. Ahmed F. G. Hammitt

1968-01-01

102

Analysis of gas flow through erupting bubbles in a gas fluidized bed  

SciTech Connect

As bubbles erupt from the surface of a gas fluidized bed, particles are projected upwards into the freeboard. Some are subsequently carried from the bed by their initial momentum and by the gas motion and others fall back onto the bed surface. In order to relate the design and operating characteristics of the fluidized bed to elutriation rate, it is necessary to have information on quantities such as the rate of flow of gas across the free surface of the bed in the vicinity of the erupting bubble and the variation of gas velocities at the free surface during the course of the bubble eruption. As a bubble moves upward towards the free surface, it carries gas with it, but there can also be a net flow of gas through the bubble. During the period of the actual eruption, vertical gas velocities in excess of those in the surrounding emulsion phase occur, resulting in a brief transient vertical flow of gas through the site of the erupting bubble. Precisely when this burst of gas flow begins and how long it lasts during a typical bubble eruption are not known. Only very limited quantitative information is available on the nature of the gas flow patterns which issue from the top of an erupting bubble. Measurements previously made using hot film probes, a laser Doppler anemometer and with flow visualization techniques show that the burst of gas flowing through the site of the erupting bubble forms a vortex motion at the free surface. The vortex has also been linked to the turbulent fluctuation patterns occurring in the freeboard above the surface of the bed.

Levy, E.K.; Chen, H.K.; Radcliff, R.; Caram, H.S.

1986-01-01

103

Measurement of the Zeta Potential of Gas Bubbles in Aqueous Solutions by Microelectrophoresis Method  

Microsoft Academic Search

An electrophoresis technique is used to measure the zeta potential of fine bubbles dispersed in aqueous solutions. An improved apparatus of a microelectrophoretic type is developed for the bubble zeta potential measurements. Electrodes for generating either oxygen or hydrogen gas bubbles are designed in such a manner that micrometer-sized bubbles can be produced over the entire cross section of the

Chun Yang; Tadeusz Dabros; Dongqing Li; Jan Czarnecki; Jacob H. Masliyah

2001-01-01

104

Micropumping of liquid by directional growth and selective venting of gas bubbles  

Microsoft Academic Search

We introduce a new mechanism to pump liquid in microchannels based on the directional growth and displacement of gas bubbles in conjunction with the non-directional and selective removal of the bubbles. A majority of the existing bubble-driven micropumps employs boiling despite the unfavorable scaling of energy consumption for miniaturization because the vapor bubbles can be easily removed by condensation. Other

Dennis Desheng Meng; Chang-Jin “CJ” Kim

2008-01-01

105

Eulerian simulations of bubbling behaviour in gas-solid fluidised beds  

Microsoft Academic Search

In literature little attempt has been made to verify experimentally Eulerian-Eulerian gas-solid model simulations of bubbling fluidised beds with existing correlations for bubble size or bubble velocity. In the present study, a CFD model for a free bubbling fluidised bed was implemented in the commercial code CFX of AEA Technology. This CFD model is based on a two fluid model

B. G. M. van Wachem; J. C. Schouten; R. Krishna; C. M. van den Bleek

1998-01-01

106

Anterior chamber gas bubbles in open globe injury.  

PubMed

We present a case of a 40-year-old soldier who was in close proximity to the detonation of an improvised explosive device (IED). Bubbles of gas were visible within the anterior chamber of his left eye. The authors propose that intraocular gas, present acutely after trauma, is diagnostic of open globe injury and is of particular importance in remote military environments. PMID:24079202

Barnard, E B G; Baxter, D; Blanch, R

2013-01-01

107

Analyzing the ability of peat to trap gas bubbles  

NASA Astrophysics Data System (ADS)

Peatlands, thick deposits of partially decayed plant matter, are a globally important carbon store. Peat soils make up one third of the global soil carbon pool and provide one of the largest natural sources of methane to the atmosphere. Bubbles of methane, an important greenhouse gas, are produced by the decomposition of peat under waterlogged conditions. These bubbles increase in size until their buoyancy exceeds the forces keeping them in place, at which point methane bubbles move upward through the soil and are released at the surface in what is known as an ebullition event. These ebullition events are important because they may account for a large proportion of methane lost from peatlands. (Journal of Geophysical Research Biogeosciences, doi:10.1029/2010JG001478, 2011)

Tretkoff, Ernie

2011-05-01

108

Behavior of bubbles in glassmelts. III - Dissolution and growth of a rising bubble containing a single gas  

NASA Technical Reports Server (NTRS)

Finite difference solutions of the mass transport equations governing the dissolution (growth) of a rising gas bubble, containing a single gas, in a glassmelt were obtained. These solutions were compared with those obtained from an approximate procedure for a range of the controlling parameters. Applications were made to describe various aspects of O2 and CO2 gas-bubble behavior in a soda-lime-silicate melt.

Onorato, P. I. K.; Weinberg, M. C.; Uhlmann, D. R.

1981-01-01

109

Gas bubbles in marine mud-How small are they?  

NASA Astrophysics Data System (ADS)

Free gas in marine mud poses a challenging problem in the realm of ocean acoustics as it readily attenuates (i.e., scatters or absorbs) energy, such that objects lying below the gassy sediment are acoustically masked. Gas-laden sediments were located in 10- to 120-m water depth adjacent to the South Pass of the Mississippi River in East Bay using a 12-kHz transducer and the Acoustic Sediment Classification System. Several cores were collected in this region for physical property measurements. Some of the cores were x-rayed on medical and industrial computed tomography (CT) scanners. Volumetric CT images were used to locate gas bubbles, determine shapes and sizes to within the limits of the CT resolution. Free gas in the East Bay sediments was relegated to worm tubes as well as isolated pockets as was the case in Eckernförde Bay sediments [Abegg and Anderson, Mar. Geol. 137, 137-147 (1997)]. The primary significance of the present work is that gas bubbles have been determined to exist in the tens of ?m size range, which is significantly smaller than the smallest bubbles that were previously resolved with medical CT (~440 ?m) with NRL's HD-500 micro-CT System. [Work supported by ONR and NRL.

Reed, Allen H.; Briggs, Kevin B.

2003-10-01

110

Porosity formation and gas bubble retention in laser metal deposition  

NASA Astrophysics Data System (ADS)

One of the inherent problems associated with laser metal deposition using gas-assisted powder transfer is the formation of porosity, which can be detrimental to the mechanical properties of the bulk material. In this work, a comprehensive investigation of porosity is carried out using gas atomised Inconel 718 powder. In the analysis, a clear distinction is made between two types of porosity; namely lack of fusion and gas porosity. The results show that the two types of porosity are attributed by different factors. The gas porosity, which is more difficult to eliminate than the lack of fusion, can be as high as 0.7%. The study shows that the gas porosity is dependent on the process parameters and the melt pool dynamics. The flotation of entrapped gas bubbles was analysed, showing that in a stationary melt pool the gas would be retained by Marangoni-driven flow. The overall Marangoni-driven flow of the melt pool is in the order of five times higher than the flotation effect, and this is the reason why the melt pool geometry would tend to dominate the flow direction of the gas bubbles. Through optimisation, the gas porosity can be reduced to 0.037%.

Ng, G. K. L.; Jarfors, A. E. W.; Bi, G.; Zheng, H. Y.

2009-11-01

111

Modelling of bubble-mediated gas transfer: Fundamental principles and a laboratory test  

Microsoft Academic Search

The air–water exchange of gases can be substantially enhanced by wave breaking and specifically by bubble-mediated transfer. A feature of bubble-mediated transfer is the additional pressure on bubbles resulting from the hydrostatic forces on a submerged bubble and from surface tension and curvature. This peculiarity results in asymmetry of bubble-mediated gas transfer and equilibrium supersaturations of dissolved gases in a

D. K. Woolf; I. S. Leifer; P. D. Nightingale; T. S. Rhee; P. Bowyer; G. Caulliez; G. de Leeuw; S. E. Larsen; M. Liddicoat; J. Baker; M. O. Andreae

2007-01-01

112

Phase-field simulation of irradiated metals Part II : Gas bubble kinetics.  

SciTech Connect

The phase-field model developed in Part I of this work is expanded to include fission gas generation, diffusion, and segregation within bubbles nucleated both homogeneously and heterogeneously along grain boundaries. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of the irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy and bubble density are investigated.

Millett, P. C.; El-Azab, A.; Wolf, D. (Materials Science Division); (INL); (Florida State Univ.)

2011-01-01

113

Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume  

NASA Technical Reports Server (NTRS)

Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.

Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.

2002-01-01

114

HUBBLE PICTURES SHOW HOT GAS BUBBLE EJECTED BY YOUNG STAR  

NASA Technical Reports Server (NTRS)

These images taken with the Hubble Space Telescope's Wide Field and Planetary Camera 2 reveal the evolution of bubbles of glowing gas being blown out from the young binary star system XZ Tauri. Gas from an unseen disk around one or both of the stars is channeled through magnetic fields surrounding the binary system and then is forced out into space at nearly 300,000 miles per hour (540,000 kilometers per hour). This outflow, which is only about 30 years old, extends nearly 60 billion miles (96 billion kilometers). Hubble first discovered this unique bubble in 1995, and additional observations were made between 1998 and 2000. These images show that there was a dramatic change in its appearance between 1995 and 1998. In 1995, the bubble's edge was the same brightness as its interior. However, when Hubble took another look at XZ Tauri in 1998, the edge was suddenly brighter. This brightening is probably caused by the hot gas cooling off, which allows electrons in the gas to recombine with atoms, a process that gives off light. This is the first time that astronomers have seen such a cooling zone 'turn on.' These images provide an unprecedented opportunity to study the development of a very recent outflow from young (about 1 million years old) stars. Credits: NASA, John Krist (Space Telescope Science Institute), Karl Stapelfeldt (Jet Propulsion Laboratory), Jeff Hester (Arizona State University), Chris Burrows (European Space Agency/Space Telescope Science Institute)

2002-01-01

115

Progression and severity of gas bubble trauma in juvenile salmonids  

USGS Publications Warehouse

We conducted laboratory experiments to assess the progression and to quantify the severity of signs of gas bubble trauma (GBT) in juvenile chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss exposed to different levels of total dissolved gas (TDG), and we attempted to relate these signs to the likelihood of mortality. When fish were exposed to 110% TDG for up to 22 d, no fish died, and there were few signs of GBT in the lateral line or gills. Bubbles in the fins, however, were relatively common, and they progressively worsened over the experimental period. When fish were exposed to 120% TDG for up to 140 h, chinook salmon had an LT20 (time necessary to kill 20% of the fish) ranging from 40 to 120 h, whereas steelhead had LT20s ranging from 20 to 35 h. In steelhead, bubbles in the lateral line, fins, and gills displayed poor trends of worsening over time, showed substantial interindividual variability, and were poorly related to mortality. In chinook salmon, only bubbles in the lateral line showed a distinct worsening over time, and the severity of bubbles in the lateral line was highly correlated with mortality. When fish were exposed to 130% TDG for up to 11 h, LT20s for chinook salmon ranged from 3 to 6 h, whereas those for steelhead ranged from 5 to 7 h. In chinook salmon, bubbles in the lateral line and fins, but not those in the gills, showed distinct trends of worsening over time. In steelhead, bubbles in the lateral line displayed the most significant trend of progressive severity. In both species at 130% TDG, the severity of all GBT signs was highly correlated with mortality. The progressive nature of GBT and the methods we developed to examine fish for GBT may be useful for monitoring programs that aim to assess the severity of dissolved gas supersaturation exposures experienced by fish in the wild. However, the efficacy of such programs seems substantially hindered by problems associated with (1) the variable persistence of GBT signs; (2) the inconsistent relation of GBT signs to mortality; (3) the insufficient knowledge of the relation between exposure history and GBT sign development for fish in the wild; and (4) an extreme amount of interindividual variation in terms of susceptibility to GBT.

Mesa, M. G.; Weiland, L. K.; Maule, A. G.

2000-01-01

116

Holdup measurements under realistic conditions  

SciTech Connect

This paper reviews the documentation of the precision and bias of holdup (residual nuclear material remaining in processing equipment) measurements and presents previously unreported results. Precision and bias results for holdup measurements are reported from training seminars with simulated holdup, which represent the best possible results, and compared to actual plutonium processing facility measurements. Holdup measurements for plutonium and uranium processing plants are also compared to reference values. Recommendations for measuring holdup are provided for highly enriched uranium facilities and for low enriched uranium facilities. The random error component of holdup measurements is less than the systematic error component. The most likely factor in measurement error is incorrect assumptions about the measurement, such as background, measurement geometry, or signal attenuation. Measurement precision on the order of 10% can be achieved with some difficulty. Bias of poor quality holdup measurement can also be improved. However, for most facilities, holdup measurement errors have no significant impact on inventory difference, sigma, or safety (criticality, radiation, or environmental); therefore, it is difficult to justify the allocation of more resources to improving holdup measurements. 25 refs., 10 tabs.

Sprinkel, J.K. Jr.; Marshall, R.; Russo, P.A.; Siebelist, R. [and others

1997-11-01

117

PHASE-FIELD SIMULATION OF IRRADIATED METALS: PART II: GAS BUBBLE KINETICS  

SciTech Connect

We present a phase-field model for inert gas bubble formation and evolution in irradiated metals. The model evolves vacancy, self-interstitial, and fission gas atoms through a coupled set of Cahn-Hilliard and Allen-Cahn equations, capturing the processes of defect generation, recombination, annihilation at GB sinks, as well as intragranular and intergranular bubble nucleation and growth in polycrystalline microstructures. Illustrative results are presented that characterize bubble growth and shrinkage, as well as the bubble density, size and nucleation rate as a function of varying irradiation conditions. Finally, intergranular bubble characteristics such as shape, pinning energy on GB motion, and bubble density are investigated.

Paul C Millett; Anter El-Azab

2011-01-01

118

Calculation and Analysis of Liquid Holdup in Lower Blast Furnace by Model Experiments  

NASA Astrophysics Data System (ADS)

A hydromechanics experiment on the countercurrent flow of gas and liquid simulating the flow conditions in the lower blast furnace was carried out. A cold model of a packed bed with various packing materials and liquids was used to study the holdup of liquid. Correlations for static holdup, dynamic holdup, and total holdup were obtained. A good agreement was found between the calculated and experimental data. A mathematical model simulating the flow fields was applied to study the effect of liquid holdup in blast furnace. The results of the model calculation show that static holdup is the determinant of the total holdup of molten materials when the blast furnace works in stable condition. The slag phase generally reaches flooding holdup ahead of the hot metal. The radial distribution of gas flow is almost not influenced by the holdup of molten materials, but it has a greater influence on the pressure drop. The size of coke has far greater influence on static holdup than liquid properties does. The study is useful for acquiring a deeper understanding of the complex phenomena in the blast furnace and for determining appropriate operational actions under different production conditions.

Xiong, Wei; Bi, Xue-Gong; Wang, Guo-Qiang; Yang, Fu

2012-06-01

119

Gas-liquid bubbly flow in vertical pipes  

Microsoft Academic Search

Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained

V. E. Nakoryakov; O. N. Kashinsky; V. V. Randin; L. S. Timkin

1996-01-01

120

Gas–liquid–solid flow modelling in a bubble column  

Microsoft Academic Search

An alternative approach to the modelling of solid–liquid and gas–liquid–solid flows for a 5:1 height to width aspect ratio bubble column is presented here. A modified transport equation for the volume fraction of a dispersed phase has been developed for the investigation of turbulent buoyancy driven flows (Chem. Eng. Proc., in press). In this study, a modified transport equation has

G. M. Cartland Glover; S. C. Generalis

2004-01-01

121

Behavior of Helium Gas Bubbles in Neutron-Irradiated Beryllium  

Microsoft Academic Search

Transmission electron microscopic observations were made on hot-rolled Be sheet prepared from cast ingots irradiated to about 5 × 10 nvt(fast) in JRR-2.The aim of the study was to elucidate the effect of irradiation on changes in microstructure and the effect of pre-irradiation heat treatment on the formation of He gas bubbles during post-irradiation annealing.The formation and growth of He

Ryukichi NAGASAKI; Shozo OHASHI; Satoru KAWASAKI; Yoichi KARITA; Nobuo TSUNO

1971-01-01

122

Gas bubble dynamics model for shallow volcanic tremor at Stromboli  

Microsoft Academic Search

Volcanic tremor at Stromboli (Aeolian islands, Italy) is correlated to small infrasonic transients [Ripepe et al., 1996] which repeat almost rythmically in time in a range between 0.8 and 1.2 s. We demonstrate that infrasonic transients are associated to small gas bubble (~0.5 m) burstings which produces no transients in the seismic signal. Tremor ground displacement attenuates with the inverse

Maurizio Ripepe; Evgenii Gordeev

1999-01-01

123

Gas bubble dynamics model for shallow volcanic tremor  

Microsoft Academic Search

Volcanic tremor at Stromboli (Aeolian islands, Italy) is correlated to small infrasonic transients (Ripepe et al., 1996) which repeat almost rythmically in time in a range between 0.8 and 1.2 s. We demonstrate that infrasonic transients are associated to small gas bubble (-0.5 m) burstings which produces no transients in the seismic signal. Tremor ground displacement attenuates with the inverse

Maurizio Ripepe; Evgenii Gordeev

1999-01-01

124

Bubble-included chocolate: relating structure with sensory response.  

PubMed

Bubbles impart a very unique texture, chew, and mouth-feel to foods. However, little is known about the relationship between structure of such products and consumer response in terms of mouth-feel and eating experience. The objective of this article is to investigate the sensory properties of 4 types of bubble-containing chocolates, produced by using different gases: carbon dioxide, nitrogen, nitrous oxide, and argon. The structure of these chocolates were characterized in terms of (1) gas hold-up values determined by density measurements and (2) bubble size distribution which was measured by undertaking an image analysis of X-ray microtomograph sections. Bubble size distributions were obtained by measuring bubble volumes after reconstructing 3D images from the tomographic sections. A sensory study was undertaken by a nonexpert panel of 20 panelists and their responses were analyzed using qualitative descriptive analysis (QDA). The results show that chocolates made from the 4 gases could be divided into 2 groups on the basis of bubble volume and gas hold-up: the samples produced using carbon dioxide and nitrous oxide had a distinctly higher gas hold-up containing larger bubbles in comparison with those produced using argon and nitrogen. The sensory study also demonstrated that chocolates made with the latter were perceived to be harder, less aerated, slow to melt in the mouth, and having a higher overall flavor intensity. These products were further found to be creamier than the chocolates made by using carbon dioxide and nitrous oxide; the latter sample also showed a higher intensity of cocoa flavor. PMID:17995803

Haedelt, J; Beckett, S T; Niranjan, K

2007-04-01

125

Bubbles  

NSDL National Science Digital Library

Learners engage in a scientific investigation to answer the question, "Are free-floating bubbles always round?" By experimenting with different-shaped bubble wands and then reading a nonfiction book to support their findings, learners collect evidence to answer the question and then share their findings with others by creating a poster.

Morgan, Emily; Ansberry, Karen

2007-01-01

126

Dynamic simulation of dispersed gas-liquid two-phase flow using a discrete bubble model  

Microsoft Academic Search

In this paper a detailed hydrodynamic model for gas-liquid two-phase flow will be presented. The model is based on a mixed Eulerian-Lagrangian approach and describes the time-dependent two-dimensional motion of small, spherical gas bubbles in a bubble column operating in the homogeneous regime. The motion of these bubbles is calculated from a force balance for each individual bubble, accounting for

E. Delnoij; F. A. Lammers; J. A. M. Kuipers; W. P. M. van Swaaij

1997-01-01

127

GAS TRANSFER FROM SMALL SPHERICAL BUBBLES IN NATURAL AND INDUSTRIAL SYSTEMS  

Microsoft Academic Search

The bubble terminal velocity and the mass transfer behavior of a small (diameter 0.2 cm) spherical bubble rising through stagnant water are reviewed. Equations relating the bubble diameter and gas composition as a function of depth are presented. The gas-liquid mass transfer co-efficient was estimated from observed bubble diameter versus time data reported in the literature. The system of equations

TARIQ AHMED; MICHAEL J. SEMMENS

2003-01-01

128

Pulsed electrical discharge in gas bubbles in water  

NASA Astrophysics Data System (ADS)

A phenomenological picture of pulsed electrical discharge in gas bubbles in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying one microsecond long 5 to 20 kilovolt pulses between the needle and disk electrodes submerged in water. A gas bubble is generated at the tip of the needle electrode. The study includes detailed experimental investigation of the discharge in argon bubbles and a brief look at the discharge in oxygen bubbles. Imaging, electrical characteristics, and time-resolved optical emission data point to a fast streamer propagation mechanism and formation of a plasma channel in the bubble. Spectroscopic methods based on line intensity ratios and Boltzmann plots of line intensities of argon, atomic hydrogen, and argon ions and the examination of molecular emission bands from molecular nitrogen and hydroxyl radicals provide evidence of both fast beam-like electrons and slow thermalized ones with temperatures of 0.6 -- 0.8 electron-volts. The collisional nature of plasma at atmospheric pressure affects the decay rates of optical emission. Spectroscopic study of rotational-vibrational bands of hydroxyl radical and molecular nitrogen gives vibrational and rotational excitation temperatures of the discharge of about 0.9 and 0.1 electron-volt, respectively. Imaging and electrical evidence show that discharge charge is deposited on the bubble wall and water serves as a dielectric barrier for the field strength and time scales of this experiment. Comparing the electrical and imaging information for consecutive pulses applied at a frequency of 1 Hz indicates that each discharge proceeds as an entirely new process with no memory of the previous discharge aside from long-lived chemical species, such as ozone and oxygen. Intermediate values for the discharge gap and pulse duration, low repetition rate, and unidirectional character of the applied voltage pulses make the discharge process here unique compared to the traditional corona or dielectric barrier discharges. These conditions make the experimental evidence presented in this work valuable for the advancement of modeling and the theoretical understanding of the discharge in bubbles in water.

Gershman, Sophia

129

Modelling of Spherical Gas Bubble Oscillations and Sonoluminescence  

NASA Technical Reports Server (NTRS)

The discovery of single-bubble sonoluminescence has led to a renewed interest in the forced radial oscillations of gas bubbles. Many of the more recent studies devoted to this topic have used several simplifications in the modelling, and in particular in accounting for liquid compressibility and thermal processes in the bubble. In this paper the significance of these simplifications is explored by contrasting the results of Lohse and co-workers with those of a more detailed model. It is found that, even though there may be little apparent difference between the radius-versus time behaviour of the bubble as predicted by the two models, quantities such as the spherical stability boundary and the threshold for rectified diffusion are affected in a quantitatively significant way. These effects are a manifestation of the subtle dependence upon dissipative processes of the phase of radial motion with respect to the driving sound field. The parameter space region, where according to the theory of Lohse and co-workers, sonoluminescence should be observable, is recalculated with the new model and is found to be enlarged with respect to the earlier estimate. The dependence of this parameter region on sound frequency is also illustrated.

Prosperetti, A.; Hao, Y.

1999-01-01

130

A computational model of gas bubble evolution in liquid filled straight tubes  

NASA Astrophysics Data System (ADS)

Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too quick. When the ambient pressure drops, inert gas bubbles are usually formed in blood vessels and tissues of divers. It is believed that the existence of gas bubbles is the cause of DCS that manifests itself as itching, joint pain, and neurological abnormalities. While models of gas bubbles in tissues are relatively well developed, the mechanism of bubble growth in the circulation is far less well understood. The existence of gas bubbles may affect gas exchange in small blood vessels by blocking the flow of blood. Gas bubble evolution in the circulation is investigated using an analytical method for small bubbles and the boundary element method for bubbles whose effective radius is close to the tube radius. The concentration field for the dissolved gas surrounding the bubble is solved numerically using finite differences. The bubble volume is adjusted over time according to the mass flux at the surface. It is shown that the effect of increasing the flow rate is to enhance bubble evolution, up to a factor of two compared with the evolution in tissue where there is no flow. This work was supported by the Naval Medical Research and Development Command work unit 62233N.MM33P30.0041509.

Himm, Jeff; Halpern, David

1996-11-01

131

Comparison of Holdup Measurement Techniques  

SciTech Connect

The measurement of uranium holdup, the residual material left in process equipment such as pipes or ducts, is an integral element of material control and accountability. Not only are the measurements important for accountability, they are also important for criticality safety. The goal in measuring holdup is to quantify the amount of material in the pipes to verify that all material is accounted for (inventory in [inventory out + holdup] = 0) and to ensure that the amount of material heldup is not a criticality risk. There are a number of ways to measure holdup in process equipment; however, this paper will evaluate only two methods (i.e., Holdup Measurement System 4 (HMS-4) and In Situ Object Counting Software (ISOCS)) for specific measurement scenarios. The comparison will use measurements of well-known reference materials in various configurations and will examine the results, uncertainties, repeatability, time required, portability, and cost of each system.

Lousteau, Angela L [ORNL; Stooksbury, John C [ORNL; Cleveland, Steven L [ORNL

2012-01-01

132

Ultrasound-induced dissolution of lipid-coated and uncoated gas bubbles.  

PubMed

The 1.1 MHz ultrasound response of micrometer-scale perfluorobutane gas bubbles, coated with a mixture of 90 mol % saturated phospholipid (disteroylphosphatidylcholine, DSPC) or unsaturated phospholipid (dioleoylphosphatidylcholine, DOPC) and 10 mol % PEG-lipid, was studied by optical microscopy. Uncoated bubbles were also studied. Bubbles, resting buoyantly against the wall of a polystyrene cuvette, were exposed to brief pulses of ultrasound (?200 kPa amplitude) at a repetition rate of 25 Hz; images of the bubbles were taken after every other pulse. The coating had little effect on the initial response: large (>10 ?m diameter) bubbles showed no size change, while smaller bubbles rapidly shrank (or fragmented) to reach a stable or metastable diameter-ca. 2 ?m for coated bubbles and 4 ?m for uncoated bubbles. The coating had a significant effect on further bubble evolution: after reaching a metastable size, uncoated bubbles and DOPC-coated bubbles continued to shrink slowly and ultimately vanished entirely, while DSPC-coated bubbles did not change perceptibly during the duration of the exposure. Numerical modeling using the modified Herring equation showed that the size range in which DSPC bubbles responded does correspond well with the bubble resonance; the long-term stability of these bubbles may be related to the ability of the DSPC to form a two-dimensional solid at ambient temperature or to phase separate from the PEG-lipid. PMID:20722377

Cox, Debra J; Thomas, James L

2010-09-21

133

Natural frequency of a gas bubble in a tube: Experimental and simulation results  

PubMed Central

Use of ultrasonically excited microbubbles within blood vessels has been proposed for a variety of clinical applications. In this paper, an axisymmetric coupled boundary element and finite element code and experiments have been used to investigate the effects of a surrounding tube on a bubble’s response to acoustic excitation. A balloon model allowed measurement of spherical gas bubble response. Resonance frequencies match one-dimensional cylindrical model predictions for a bubble well within a rigid tube but deviate for a bubble near the tube end. Simulations also predict bubble translation along the tube axis and aspherical oscillations at higher amplitudes.

Jang, Neo W.; Gracewski, Sheryl M.; Abrahamsen, Ben; Buttaccio, Travis; Halm, Robert; Dalecki, Diane

2009-01-01

134

Phase-field simulations of gas density within bubbles under irradiation  

SciTech Connect

Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles. In our simulations, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid regions. We find that gas densities within bubbles fluctuate drastically in the early nucleation stages, when growth rates are highest, but converge to steady-state values during the later coarsening stages. The steady-state gas densities within bubbles correspond with the ratio of total accumulated vacancy content divided by the total accumulated gas content, in agreement with a thermodynamic analysis concerning free-energy minimization.

Paul C. Millett; Anter El-Azab; Michael Tonks

2011-05-01

135

A physiological model of the release of gas bubbles from crevices under decompression  

Microsoft Academic Search

Moving bubbles have been observed in the blood during or after decompression using ultrasonic techniques. It has been proposed that these may grow from nuclei housed on the blood vessel wall. One candidate for bubble nucleation is hydrophobic crevices. This work explores the growth of gas pockets that might exist in conical crevices and the release of bubbles from these

M. A. Chappell; S. J. Payne

2006-01-01

136

Bubble nucleation algorithm for the simulation of gas evolving electrodes  

Microsoft Academic Search

We propose a bubble nucleation algorithm to link a Lagrangian bubble tracker to the multi-ion transport and reaction model. This algorithm computes the bubble growth rate and the surface blocking effect at nucleation sites.

Steven Van Damme; Pedro Maciel; Heidi Van Parys; Johan Deconinck; Annick Hubin; Herman Deconinck

2010-01-01

137

Observation and quantification of gas bubble formation on a mechanical heart valve.  

PubMed

Clinical studies using transcranial Doppler ultrasonography in patients with mechanical heart valves (MHV) have detected gaseous emboli. The relationship of gaseous emboli release and cavitation on MHV has been a subject of debate in the literature. To study the influence of cavitation and gas content on the formation and growth of stable gas bubbles, a mock circulatory loop, which employed a Medtronic-Hall pyrolytic carbon disk valve in the mitral position, was used. A high-speed video camera allowed observation of cavitation and gas bubble release on the inflow valve surfaces as a function of cavitation intensity and carbon dioxide (CO2) concentration, while an ultrasonic monitoring system scanned the aortic outflow tract to quantify gas bubble production by calculating the gray scale levels of the images. In the absence of cavitation, no stable gas bubbles were formed. When gas bubbles were formed, they were first seen a few milliseconds after and in the vicinity of cavitation collapse. The volume of the gas bubbles detected in the aortic track increased with both increased CO2 and increased cavitation intensity. No correlation was observed between O2 concentration and bubble volume. We conclude that cavitation is an essential precursor to stable gas bubble formation, and CO2, the most soluble blood gas, is the major component of stable gas bubbles. PMID:11036552

Lin, H Y; Bianccucci, B A; Deutsch, S; Fontaine, A A; Tarbell, J M

2000-08-01

138

Comparative hydrodynamics study in a bubble column using computer-automated radioactive particle tracking (CARPT)\\/computed tomography (CT) and particle image velocimetry (PIV)  

Microsoft Academic Search

The hydrodynamics of a 10-cm-diameter cylindrical bubble column at the superficial gas velocity of 2, 4, and 8cm\\/s are investigated by computer-automated radioactive particle tracking (CARPT), particle image velocimetry (PIV), and computed tomography (CT). These experimental techniques are capable of providing the knowledge of velocity and holdup fields in a bubble column system, which are essential as the experimental benchmark

Jinwen Chen; Abdenour Kemoun; Muthanna H. Al-Dahhan; Milorad P. Dudukovi?; D. J. Lee; Liang-Shih Fan

1999-01-01

139

Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue  

NASA Technical Reports Server (NTRS)

Models of gas bubble dynamics employed in probabilistic analyses of decompression sickness incidence in man must be theoretically consistent and simple, if they are to yield useful results without requiring excessive computations. They are generally formulated in terms of ordinary differential equations that describe diffusion-limited gas exchange between a gas bubble and the extravascular tissue surrounding it. In our previous model (Ann. Biomed. Eng. 30: 232-246, 2002), we showed that with appropriate representation of sink pressures to account for gas loss or gain due to heterogeneous blood perfusion in the unstirred diffusion region around the bubble, diffusion-limited bubble growth in a tissue of finite volume can be simulated without postulating a boundary layer across which gas flux is discontinuous. However, interactions between two or more bubbles caused by competition for available gas cannot be considered in this model, because the diffusion region has a fixed volume with zero gas flux at its outer boundary. The present work extends the previous model to accommodate interactions among multiple bubbles by allowing the diffusion region volume of each bubble to vary during bubble evolution. For given decompression and tissue volume, bubble growth is sustained only if the bubble number density is below a certain maximum.

Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.

2003-01-01

140

A model for fission-gas-bubble behavior in amorphous uranium silicide compounds  

Microsoft Academic Search

A model for the behavior of fission gas in irradiated amorphous materials is developed. The model proposes that gas bubble nucleation occurs within shear bands initiated around free volume regions. Small gas–atom clusters that form within these regions are susceptible to dissolution by forces generated by the plastic flow of material around the cluster. The bubble coarsening process depends on

J. Rest

2004-01-01

141

Phase-field modeling of gas bubbles and thermal conductivity evolution in nuclear fuels  

Microsoft Academic Search

A phase-field model was developed to simulate the accumulation and transport of fission products and the evolution of gas bubble microstructures in nuclear fuels. The model takes into account the generation of gas atoms and vacancies, and the elastic interaction between diffusive species and defects as well as the inhomogeneity of elasticity and diffusivity. The simulations show that gas bubble

Shenyang Y. Hu; Charles H. Henager Jr.; Howard L. Heinisch; Marius Stan; Michael I. Baskes; Steven M. Valone

2009-01-01

142

Measurement of local specific interfacial area in bubble columns via a non-isokinetic withdrawal method coupled to electro-optical detector  

Microsoft Academic Search

Precise measurement of gas–liquid interfacial surface area is essential to reactor design and operation. Mass transfer from the gas phase to the liquid phase is often a key feature that controls the overall process. Measurement of gas–liquid interfacial area is often made through a separate measurement of the gas holdup and bubble size with complex and\\/or sophisticated methods. In this

Sergio García-Salas; M. E. Rosales Peña Alfaro; R. Michael Porter; Frederic Thalasso

2008-01-01

143

Sparger Effect on Bubble-Column Gas Distributions  

NASA Astrophysics Data System (ADS)

The effect of sparger geometry (hole number, size, and orientation) on gas distribution in bubble columns is examined. Experiments are performed in a cylindrical vessel with an inner diameter D of 0.48 m and a height of 3 m. The vessel is filled to a height of 4 D with liquid, gas is injected near the bottom through the sparger, and the gas distribution is measured using gamma-densitometry tomography (GDT). Drakeol 10 (a lightweight mineral oil) is typically the liquid (Drakeol 5 and water are also used). The gas is air, with column pressures of 100-500 kPa and superficial velocities up to 30 cm/s. Cross spargers (four hole-lined tubes radiating from a central hub) are examined that have 4-120 holes with 1-8 mm diameters oriented upward, downward, or sideways (swirling). For a given liquid, column pressure, and gas flow rate, the gas radial distribution above a few diameters is independent of sparger selection and vertical location. The development length is less than D with downward holes, ( 1 - 2 ) D with upward holes, and about 3 D with sideways holes. The gas volume fraction decreases with height for upward holes but increases with height for sideways holes. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Torczynski, J. R.; George, D. L.; Shollenberger, K. A.

2000-11-01

144

Hydrodynamics and mass transfer in a draft tube gas-liquid solid spouted bed  

SciTech Connect

Experiments were conducted using various types of solid particles to investigate the hydrodynamic properties of a draft tube gas-liquid-solid spouted bed. The hydrodynamic properties under study include flow modes, pressure profile and pressure drop, bubble penetration, depth, overall gas holdup, apparent liquid circulation rate, and bubble size distribution. Three flow modes were classified: a packed bed mode, a fluidized bed mode, and a circulated bed mode. The bubble penetration depth in the annular region, overall gas holdup, and apparent liquid circulation rate increase with an increase in gas or liquid velocity. A model was proposed to describe the liquid circulation behavior in the draft tube gas-liquid-solid spouted bed. The optimal design of a draft tube gas-liquid-solid spouted bed was evaluated by considering four design variables including draft tube diameter, gas-liquid injector, top (above draft tube) spacing, and bottom (below draft tube) spacing. The effects of these design variables on the overall gas holdup were comprehensively examined for various gas and liquid velocities and solid particle properties. The 7.62 cm ID draft tube has highest overall gas holdup. The overall gas holdup increases with decreasing top spacing. The concentric tube gas-liquid injector with the smallest pore size gas distributor plate placed on the top of the outer tube gives rise to the holdup. Dissolution of benzoic acid pellets into water was used to obtain the solid liquid mass transfer coefficient in a draft tube gas-liquid-solid spouted bed. The in-bed benzoic acid concentration was examined to justify the use of the continuous flow stirred tank reactor (CSTR) model in the evaluation of the mass transfer coefficient.

Hwang, S.J.

1985-01-01

145

Theoretical and experimental investigation of the liquid flow around a gas bubble  

NASA Astrophysics Data System (ADS)

The relation between the shape of gas bubbles and the flow pattern around them is studied in order to improve understanding of the interaction between the gas and liquid phases. The equilibrium shapes of the free surfaces of the bubbles in different liquids are numerically computed. The liquid flow in the region of single rising bubbles with terminal velocities and high Reynolds numbers is investigated. A theoretical model for the shape of the free surface of a gas bubble and the flow field around it is presented. The usefulness and applicability of this model is tested by comparing experimental and calculated results.

van Bekkum, A. J.

146

Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments  

SciTech Connect

About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions. The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.

Krishna, R.; Baten, J.M. van

1999-10-01

147

Formation of a single micro bubble by controlled acoustic gas pressure wave  

NASA Astrophysics Data System (ADS)

We have developed micro bubble generator which can control both bubble size and generation frequency independently and accurately, by using acoustic gas pressure wave. However, though, the mechanism of this generator has not been fully understood. We further investigated the role of the acoustic gas pressure wave and found the optimal pressure wave for a single micro bubble formation. We succeeded in forming a bubble, whose radius was ranging from 0.3 to 0.8 mm, with extremely small standard deviation of less than 1 micro meter. By analyzing images taken by high-speed photography, detachment of a bubble from a nozzle, especially shrinkage of a capillary bridge connecting a bubble and a nozzle, is investigated in detail. Force balance on a growing bubble is evaluated with the help of experimental data of time rate of both bubble radius and position of the center of mass of a bubble, by applying a spherical bubble formation model. As results, we find that with the decrease in gas pressure, the capillary bridge is sucked down into a nozzle and added mass force is exerted in the upward direction, both of which promote detachment of a bubble from a nozzle.

Watanabe, Masao; Shirota, Minori; Sanada, Toshiyuki

2006-11-01

148

A three-dimensional CFD model for gas–liquid bubble columns  

Microsoft Academic Search

This paper discusses the development of a three-dimensional Euler–Lagrange CFD model for a gas–liquid bubble column. The model resolves the time-dependent, three-dimensional motion of small, spherical gas bubbles in a liquid. Our model incorporates all relevant forces acting on a bubble rising in a liquid, and accounts for two-way momentum coupling between the phases. The liquid-phase hydrodynamics are described using

E. Delnoij; J. A. M. Kuipers; W. P. M. van Swaaij

1999-01-01

149

Hydrodynamics of an endothermic gas with application to bubble cavitation.  

PubMed

The hydrodynamics for a gas of hard spheres which sometimes experience inelastic collisions resulting in the loss of a fixed, velocity-independent, amount of energy Delta is investigated with the goal of understanding the coupling between hydrodynamics and endothermic chemistry. The homogeneous cooling state of a uniform system and the modified Navier-Stokes equations are discussed and explicit expressions given for the pressure, cooling rates, and all transport coefficients for D dimensions. The Navier-Stokes equations are solved numerically for the case of a two-dimensional gas subject to a circular piston so as to illustrate the effects of the energy loss on the structure of shocks found in cavitating bubbles. It is found that the maximal temperature achieved is a sensitive function of Delta with a minimum occurring near the physically important value of Delta approximately 12,000 K approximately 1 eV. PMID:17092085

Lutsko, James F

2006-10-28

150

Expansion of long-acting gas bubbles for intraocular use. Principles and practice.  

PubMed

Expansion of long-acting gas bubbles used in vitreoretinal surgery may lead to increased intraocular pressure and central retinal artery occlusion. To further understand the principles controlling the expansion of long-acting gases, we compared the expansion of perfluoropropane gas bubbles with that of sulfur hexafluoride gas bubbles in an in vitro model, as well as in rabbits. We found that perfluoropropane bubbles expand more rapidly and to a greater extent than do sulfur hexafluoride bubbles in the first 24 hours. The early rate of expansion of a long-acting gas is largely dependent on convection of the surrounding fluid and is independent of the type of long-acting gas. Early postoperative monitoring of intraocular pressure is, therefore, equally important when using any long-acting gas. PMID:4004624

Crittenden, J J; de Juan, E; Tiedeman, J

1985-06-01

151

Phase-field Modeling of Gas Bubbles and Thermal Conductivity Evolution in Nuclear Fuels  

SciTech Connect

The major factors that influence the thermal conductivity of the ceramics and metals are temperature, stoichiometry, microstructure, porosity, and point defects. Nuclear fuels and structure materials are subject to a severe radiation environment and their properties, including thermal conductivity change significantly with time and irradiation level. In particular, the accumulation of fission products and the formation of He bubbles can decrease the heat transfer, leading to overheating of the fuel element. In this work, we use the phase-field method to study the effect of microstructural changes on thermal conductivity. We developed a phase-field model to simulate the He bubble formation and growth in a single/polycrystalline material with defects. The model takes into account the generation of gas atoms and defects, gas atom diffusivity inhomogeneity, gas atom segregation, and gas bubble nucleation. With the model, we simulated the gas bubble and temperature evolution, and calculated the effect of gas bubble volume fraction on effective thermal conductivity.

Hu, Shenyang Y.; Henager, Charles H.; Heinisch, Howard L.; Stan, Marius; Baskes, Michael I.; Valone, Steven

2009-07-15

152

Analysis of the bubbling behaviour of 2D gas solid fluidized beds  

Microsoft Academic Search

In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in

Antonio Busciglio; Giuseppa Vella; Giorgio Micale; Lucio Rizzuti

2009-01-01

153

On the formation of gas bubbles in fissile material during reactor irradiation  

Microsoft Academic Search

The formation of fission gas bubbles in solids has been considered in conditions where the re-solution of gas from bubbles is appreciable. In such conditions the Greenwood theory is shown to apply only at high temperatures and short irradiation times. At low temperatures precipitation is delayed at short irradiation times. For longer irradiation times at all temperatures, the irradiation-enhanced generation

A. D. Whapham

1971-01-01

154

Effect of electrolyte composition on the dynamics of hydrogen gas bubble evolution at copper microelectrodes  

Microsoft Academic Search

The dynamics of hydrogen gas bubble evolution at copper microelectrodes in H2SO4 and HCl solutions of various compositions have been studied by means of galvanostatic polarization experiments and simultaneous video taping. As long as the solution contains acid only, gas evolution is dominated by the growth of a single bubble at the electrode at any one time. The transients in

P. Kristof; M. Pritzker

1997-01-01

155

Dynamics of gas bubble growth in a supersaturated solution with Sievert's solubility law  

Microsoft Academic Search

This paper presents a theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution. We study systems where gas molecules completely dissociate in the solvent into two parts, thus making Sievert's solubility law valid. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth

G. Yu. Gor; A. E. Kuchma

2009-01-01

156

Bubble Bubble  

NSDL National Science Digital Library

With magic bubble solution, a boy discovers that he can blow any kind of bubble imaginable: a kangaroo, a bird, a car, or a boat. Mercer Mayer's colorful illustrations enliven this engaging tale of mysterious bubbles.

Mayer, Mercer

2009-11-11

157

Effect of surface contaminants on oxygen transfer in bubble column reactors  

Microsoft Academic Search

Gas hold-up (?g), sauter mean bubble diameter (d32) and oxygen transfer coefficient (kLa) were evaluated at four different alkane concentrations (0.05, 0.1, 0.3 and 0.5vol.%) in water over the range of superficial gas velocity (ug) of (1.18–23.52)×10?3m\\/s at 25°C in a laboratory-scale bubble column bioreactor. Immiscible hydrocarbons (n-decane, n-tridecane and n-hexadecane) were utilized in the experiments as impurity. A type

Maryam Asgharpour; Mohammad Reza Mehrnia; Navid Mostoufi

2010-01-01

158

Dynamics of gas bubble growth in a supersaturated solution with Sievert's solubility law.  

PubMed

This paper presents a theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution. We study systems where gas molecules completely dissociate in the solvent into two parts, thus making Sievert's solubility law valid. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth dynamics. Assuming that diffusion flux is steady we obtain a differential equation on bubble radius. Bubble dynamics equation is solved analytically for the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop. We also obtain conditions of diffusion flux steadiness. The fulfillment of these conditions is studied for the case of nucleation of water vapor bubbles in magmatic melts. PMID:19624209

Gor, G Yu; Kuchma, A E

2009-07-21

159

Free energy wells for small gas bubbles in soft deformable materials  

NASA Astrophysics Data System (ADS)

Thermodynamic expressions are derived for the system relative Gibbs free energy, and the relative Gibbs free energy per bubble, for all possible equilibrium bubble states that can form in a soft slightly rigid material, initially supersaturated with a dissolved inert gas (N2). While the thermodynamic manipulations are exact, the final expressions are approximate, due to an approximation made in deriving the expression for the elastic free energy of a soft material containing more than a single bubble. The expressions predict that provided the shear modulus of the soft material is not negligibly small, free energy wells which stabilize small gas bubbles for finite periods of time exist in such materials. This is consistent with a previous calculation, based solely on the bubble pressure equation, which resulted in the conjecture that bubbles found in soft materials with some rigidity (or shear resistance) are likely to be small. The possible relevance of this to the field of decompression sickness is outlined.

Goldman, Saul

2010-04-01

160

Shock-wave propagation in a sonoluminescing gas bubble  

NASA Technical Reports Server (NTRS)

The motion of the bubble radius and of the air trapped inside the bubble during sonoluminescence are determined self-consistently by coupling the solution of the Rayleigh-Plesset equation governing the bubble radius to the solution of Euler's equations for the motion of air in the bubble. Results are presented for three slightly different conditions of excitation, in two of which shocks are formed during the collapse of the bubble, and in which such high temperatures are attained that the air is ionized. Estimates are made of the duration and intensity of the light then radiated by the plasma.

Wu, C. C.; Roberts, Paul H.

1993-01-01

161

A study of changes in the temperature profile of a liquid agitated by gas bubbles  

NASA Astrophysics Data System (ADS)

A simple mathematical model is developed which described changes in the temperature profile of a liquid during bubbling. The model consists of a system of equations which allow both for temperature leveling due to agitation and for cooling due to evaporation of the liquid into the gas bubbles. The model is validated by comparing calculated results with experimental data for water bubbling in an isolated container.

Kutznetsov, V. I.

162

Ultrasonic methods for locating hold-up  

SciTech Connect

Hold-up remains one of the major contributing factors to unaccounted for materials and can be a costly problem in decontamination and decommissioning activities. Ultrasonic techniques are being developed to noninvasively monitor hold-up in process equipment where the inner surface of such equipment may be in contact with the hold-up material. These techniques may be useful in improving hold-up measurements as well as optimizing decontamination techniques.

Sinha, D.N.; Olinger, C.T.

1995-09-01

163

Flow Field Prediction and Bubble Trajectory Model in Gas-Liquid Cylindrical Cyclone (GLCC) Separators  

Microsoft Academic Search

Several mechanistic models have been already developed for predicting the onset of liquid carry-over in Gas-Liquid Cylindrical Cyclone (GLCC) Separators. However, currently no model is available to predict gas carry-under. A bubble trajectory model has been developed that can be used to determine the initiation of gas carry-under in the GLCC and to design GLCC for field applications. The bubble

Ivan Mantilla; S. A. Shirazi; O. Shoham

1999-01-01

164

Heat transfer and bubble dynamics in slurry bubble columns for Fischer-Tropsch clean alternative energy  

NASA Astrophysics Data System (ADS)

With the increasing demand for alternative energy resources, the Fischer-Tropsch (FT) process that converts synthesis gas into clean liquid fuels has attracted more interest from the industry. Slurry bubble columns are the most promising reactors for FT synthesis due to their advantages over other reactors. Successful operation, design, and scale-up of such reactors require detailed knowledge of hydrodynamics, bubble dynamics, and transport characteristics. However, most previous studies have been conducted at ambient pressure or covered only low superficial gas velocities. The objectives of this study were to experimentally investigate the heat transfer coefficient and bubble dynamics in slurry bubble columns at conditions that can mimic FT conditions. The air-C9C 11-FT catalysts/glass beads systems were selected to mimic the physical properties of the gas, liquid, and solid phases at commercial FT operating conditions. A heat transfer coefficient measurement technique was developed, and for the first time, this technique was applied in a pilot scale (6-inch diameter) high pressure slurry bubble column. The effects of superficial gas velocity, pressure, solids loading, and liquid properties on the heat transfer coefficients were investigated. Since the heat transfer coefficient can be affected by the bubble properties (Kumar et al., 1992), in this work bubble dynamics (local gas holdup, bubble chord length, apparent bubble frequency, specific interfacial area, and bubble velocity) were studied using the improved four-point optical probe technique (Xue et al., 2003; Xue, 2004). Because the four-point optical technique had only been successfully applied in a churn turbulent flow bubble column (Xue, 2004), this technique was first assessed in a small scale slurry bubble column in this study. Then the bubble dynamics were studied at the same conditions as the heat transfer coefficient investigation in the same pilot scale column. The results from four-point probe bubble dynamics study advanced the understanding of heat transfer in the slurry bubble column. This study also provides important benchmark information for the slurry bubble column design and the evaluation of computational fluid dynamics (CFD) simulations.

Wu, Chengtian

165

Multi-scale analysis of gas–liquid interaction and CFD simulation of gas–liquid flow in bubble columns  

Microsoft Academic Search

The ratio of effective drag coefficient to bubble diameter is of critical importance for CFD simulation of gas–liquid flow in bubble columns. In this study, a novel model is proposed to calculate the ratio on the basis of the Dual-Bubble-Size (DBS) model. The motivation of the study is that a stability condition reflecting the compromise between different dominant mechanisms can

Ning Yang; Zongying Wu; Jianhua Chen; Yuhua Wang; Jinghai Li

2011-01-01

166

Impacts of ratio of asymptotic bubble width to diameter of circular tube and Reynolds number in a gas bubble driven flow  

Microsoft Academic Search

This study investigates the steady-state flow field in a circular tube filled with a viscous fluid expelled by a long gas bubble. We use a finite difference method (FDM) with successive over-relaxation (SOR) in the computation of the viscous fluid flows. An empirical deduced bubble profile is employed to simplify the complex computation of the interface shape between the gas

Cheng-Hsing Hsu; Po-Chuang Chen; Kuang-Yuan Kung; Chuan Lai

2005-01-01

167

Gas bubbles in a Hele-Shaw cell manipulated by a light beam  

Microsoft Academic Search

The action of a light beam upon a gas bubble in a light-absorbing solution of a tensoactive substance is studied. The light-assisted\\u000a manipulations, including the partition of large bubbles and the translation of small ones according to the solutocapillary\\u000a mechanism, are demonstrated for the first time.

B. A. Bezuglyi; N. A. Ivanova

2002-01-01

168

Dissipation of the energy of sound waves in small gas bubbles  

Microsoft Academic Search

One of the main factors affecting the dynamics of homogeneous solution type pulse reactors is the formation of gas bubbles on the fission-fragment tracks [1, 2]. The behavior of the reactor depends very considerably on the size (10-5 cm) and growth rate of these bubbles [2], and it is, accordingly, a very important matter to study these properties. One convenient

A. N. Sizov

1975-01-01

169

Coupled pulsation and translation of two gas bubbles in a liquid  

Microsoft Academic Search

We present and analyse a model for the spherical pulsations and translational motions of a pair of interacting gas bubbles in an incompressible liquid. The model is derived rigorously in the context of potential flow theory and contains all terms up to and including fourth order in the inverse separation distance between the bubbles. We use this model to study

Anthony Harkin; Tasso J. Kaper; Ali Nadim

2001-01-01

170

A study of changes in the temperature profile of a liquid agitated by gas bubbles  

Microsoft Academic Search

A simple mathematical model is developed which described changes in the temperature profile of a liquid during bubbling. The model consists of a system of equations which allow both for temperature leveling due to agitation and for cooling due to evaporation of the liquid into the gas bubbles. The model is validated by comparing calculated results with experimental data for

V. I. Kutznetsov

1985-01-01

171

Studies of the Hot Gas in the Galactic halo and Local Bubble  

NASA Technical Reports Server (NTRS)

This paper presents a report on the progress made on Studies of the Hot Gas in the Galactic halo and Local Bubble at Johns Hopkins University. The broad goals of this project are to determine the physical conditions and history of the hot phase of the Galaxy's interstellar medium. Such gas resides in the Galactic halo, the Local Bubble surrounding the solar neighborhood, other bubbles, and supernova remnants. A better understanding of the hot gas and the processes occurring within it requires several types of work, including ultraviolet and X-ray data analyses and computer modeling.

Shelton, Robin L.

2003-01-01

172

Role of gas density in the stability of single-bubble sonoluminescence.  

PubMed

Recent full hydrodynamic simulations of a sonoluminescing bubble interior have shown that the bubble content is compressed to a very dense state during the violent collapse. In this paper, we numerically studied the shape stability of a radially oscillating gas bubble by using Hilgenfeldt et al. theoretical model with corrections taking into account the gas density effect. Our results show that gas density variations not only significantly suppress the Rayleigh-Taylor instability, but also enhance the threshold of the parametric instability under sonoluminescence conditions. PMID:11461401

Yuan, L; Ho, C Y; Chu, M C; Leung, P T

2001-07-01

173

Role of gas density in the stability of single-bubble sonoluminescence  

NASA Astrophysics Data System (ADS)

Recent full hydrodynamic simulations of a sonoluminescing bubble interior have shown that the bubble content is compressed to a very dense state during the violent collapse. In this paper, we numerically studied the shape stability of a radially oscillating gas bubble by using Hilgenfeldt et al. theoretical model with corrections taking into account the gas density effect. Our results show that gas density variations not only significantly suppress the Rayleigh-Taylor instability, but also enhance the threshold of the parametric instability under sonoluminescence conditions.

Yuan, L.; Ho, C. Y.; Chu, M.-C.; Leung, P. T.

2001-07-01

174

Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate  

PubMed Central

The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.

Ohta, Aaron T.; Jamshidi, Arash; Valley, Justin K.; Hsu, Hsan-Yin; Wu, Ming C.

2009-01-01

175

Effect of gas expansion on the front shape of a Taylor bubble: an experimental contribution  

NASA Astrophysics Data System (ADS)

An experimental study where an individual Taylor bubble rises through water with different bubble volume expansion rates is presented with the (front) bubble shape determination as main objective. A combination of two techniques, Particle Image Velocimetry (PIV) and Pulsed Shadowgraphy (PS), was used to collect images for further treatment in order to characterize the liquid flow pattern in front of the bubble and the bubble shape. Processing the images acquired with pulsed illumination from behind the bubble it was possible to define with precision the bubble shape at different stages when it was expanding. The operation conditions used allowed a wide range of volume expansion rates (0 to 28.5 × 10-6 m3/s) with a significant effect on the Taylor bubble velocity; increases in bubble velocity up to 21% were observed relatively to constant volume system condition. Nevertheless, it seems that the front shape of Taylor bubbles does not change significantly with the upward liquid flow rates induced by gas expansion, at least for the volume expansion rates used in the experiments.

Santos, Laura; Esteves, Teresa; Coelho Pinheiro, Nazaré

2014-03-01

176

A molecular dynamics study of helium bubble formation and gas release near titanium surfaces  

NASA Astrophysics Data System (ADS)

Helium bubble formation and gas release near titanium surfaces have been studied using molecular dynamics. The results show that the formation of helium bubbles near a titanium surface is accompanied by the production of defects and the drift of defects toward the metal surfaces as well as an increase in the number of surface metal atoms. It is also shown that the helium bubbles burst at the mechanical stability limit of the metal. The metal surface morphology is modified by the bursting of the helium bubbles, with an increase in the surface roughness and the formation of surface pores as well as the re-deposition of the helium atoms. In contrast, the subsurface metal will retain its perfect crystal structure. The size of the resultant surface pore depends on the initial bubble diameter. For a small bubble, the pore can be healed by the thermal evolution of the substrate.

Zhang, B. L.; Wang, J.; Li, M.; Hou, Q.

2013-07-01

177

ENGINEERING DEVELOPMENT OF SLURRY BUBBLE COLUMN REACTOR (SBCR) TECHNOLOGY  

SciTech Connect

The major technical objectives of this program are threefold: (1) to develop the design tools and a fundamental understanding of the fluid dynamics of a slurry bubble column reactor to maximize reactor productivity, (2) to develop the mathematical reactor design models and gain an understanding of the hydrodynamic fundamentals under industrially relevant process conditions, and (3) to develop an understanding of the hydrodynamics and their interaction with the chemistries occurring in the bubble column reactor. Successful completion of these objectives will permit more efficient usage of the reactor column and tighter design criteria, increase overall reactor efficiency, and ensure a design that leads to stable reactor behavior when scaling up to large diameter reactors. The past three months of research have been focused on two major areas of bubble column hydrodynamics: (1) pressure and temperature effects on gas holdup and (2) region transition using a sparger as a gas distributor.

Bernard A. Toseland, Ph.D.

1999-03-01

178

Perturbed breakup of gas bubbles in water: Memory, gas flow, and coalescence  

NASA Astrophysics Data System (ADS)

The pinch-off of an air bubble from an underwater nozzle ends in a singularity with a remarkable sensitivity to a variety of perturbations. I report on experiments that break both the axial (i.e., vertical) and azimuthal symmetry of the singularity formation. The density of the inner gas influences the axial asymmetry of the neck near pinch-off. For denser gases, flow through the neck late in collapse changes the pinch-off dynamics. Gas density is also implicated in the formation of satellite bubbles. The azimuthal shape oscillations described by Schmidt can be initiated by anisotropic boundary conditions in the liquid as well as with an asymmetric nozzle shape. I measure the n=3 oscillatory mode and observe the nonlinear, highly three-dimensional outcomes of pinch-off with large azimuthal perturbations. These are consistent with prior theory.

Keim, Nathan C.

2011-05-01

179

Perturbed breakup of gas bubbles in water: memory, gas flow, and coalescence.  

PubMed

The pinch-off of an air bubble from an underwater nozzle ends in a singularity with a remarkable sensitivity to a variety of perturbations. I report on experiments that break both the axial (i.e., vertical) and azimuthal symmetry of the singularity formation. The density of the inner gas influences the axial asymmetry of the neck near pinch-off. For denser gases, flow through the neck late in collapse changes the pinch-off dynamics. Gas density is also implicated in the formation of satellite bubbles. The azimuthal shape oscillations described by Schmidt et al. can be initiated by anisotropic boundary conditions in the liquid as well as with an asymmetric nozzle shape. I measure the n=3 oscillatory mode and observe the nonlinear, highly three-dimensional outcomes of pinch-off with large azimuthal perturbations. These are consistent with prior theory. PMID:21728665

Keim, Nathan C

2011-05-01

180

Controlling bubbles using bubbles--microfluidic synthesis of ultra-small gold nanocrystals with gas-evolving reducing agents.  

PubMed

Microfluidic wet-chemical synthesis of nanoparticles is a growing area of research in chemical microfluidics, enabling the development of continuous manufacturing processes that overcome the drawbacks of conventional batch-based synthesis methods. The synthesis of ultra-small (<5 nm) metallic nanocrystals is an interesting area with many applications in diverse fields, but is typically very challenging to accomplish in a microfluidics-based system due to the use of a strong gas-evolving reducing agent, aqueous sodium borohydride (NaBH(4)), which causes uncontrolled out-gassing and bubble formation, flow disruption and ultimately reactor failure. Here we present a simple method, rooted in the concepts of multiphase mass transfer that completely overcomes this challenge-we simply inject a stream of inert gas bubbles into our channels that essentially capture the evolving gas from the reactive aqueous solution, thereby preventing aqueous dissolved gas concentration from reaching the solubility threshold for bubble nucleation. We present a simple model for coupled mass transfer and chemical reaction that adequately captures device behaviour. We demonstrate the applicability of our method by synthesizing ultra-small gold nanocrystals (<5 nm); the quality of nanocrystals thus synthesized is further demonstrated by their use in an off-chip synthesis of high-quality gold nanorods. This is a general approach that can be extended to a variety of metallic nanomaterials. PMID:22456754

Khan, Saif A; Duraiswamy, Suhanya

2012-04-24

181

A Model for Surface Induced Growth of Inert Gas Bubbles in Irradiated Copper-Boron Alloys  

SciTech Connect

A matrix containing inert gas bubbles dilates in direct proportion to the growth experienced by the gas bubbles. This phenomenon is termed as swelling. A model for the swelling induced by the growth of the helium gas bubbles in irradiated copper-boron alloys is presented. The bubbles grow by acquiring vacancies from the external surface, which acts as a source of vacancies. The vacancies reach the surface of the bubbles mainly via lattice diffusion and to a limited extent via diffusion through short-circuiting paths such as grain boundaries and dislocation pipes. The model predicts that overall swelling of the matrix varies as 1.5 power of time. Another consequence of the present model is that the growth rate of a gas bubble varies inversely as the cube of its distance from the external surface. The model has been applied to the data on irradiated copper-boron alloys and found to be in accord with the experimental results. The model is general and can be applied to the growth of all kinds of stationary inert gas bubbles trapped within a crystalline matrix. (authors)

Tiwari, G.P.; Ramadasan, E. [Post Irradiation Examination Division, Bhabha Atomic Research Division (India)

2006-07-01

182

Guinier-Preston Zones and Gas Bubbles Clustering Studied by Dechanneling.  

National Technical Information Service (NTIS)

Dechanneling due to precipitation of heteroatoms in aluminium is studied theoretically and experimentally. Precipitation of copper atoms leads to Guinier-Preston zones (G.P.Z.) clustering. Helium, which is insoluble in aluminium, forms gas bubbles. An iso...

G. Desarmot

1976-01-01

183

Phase-field simulations of intragranular fission gas bubble evolution in UO2 under post-irradiation thermal annealing  

SciTech Connect

Fission gas bubble is one of evolving microstructures, which affect thermal mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking, in operating nuclear fuels. Therefore, fundamental understanding of gas bubble evolution kinetics is essential to predict the thermodynamic property and performance changes of fuels. In this work, a generic phasefield model was developed to describe the evolution kinetics of intra-granular fission gas bubbles in UO2 fuels under post-irradiation thermal annealing conditions. Free energy functional and model parameters are evaluated from atomistic simulations and experiments. Critical nuclei size of the gas bubble and gas bubble evolution were simulated. A linear relationship between logarithmic bubble number density and logarithmic mean bubble diameter is predicted which is in a good agreement with experimental data.

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

2013-05-15

184

Bubble Size Control to Improve Oxygen-Based Bleaching: Characterization of Flow Regimes in Pulp-Water-Gas Three-Phase Flows  

SciTech Connect

Flow characteristics of fibrous paper pulp-water-air slurries were investigated in a vertical circular column 1.8 m long, with 5.08 cm diameter. Flow structures, gas holdup (void fraction), and the geometric and population characteristics of gas bubbles were experimentally investigated, using visual observation, Gamma-ray densitometry, and flash X-ray photography. Five distinct flow regimes could be visually identified: dispersed bubbly, layered bubbly, plug, churn-turbulent, and slug. Flow regime maps were constructed, and the regime transition lines were found to be sensitive to consistency. The feasibility of using artificial neural networks (ANNs) for the identification of the flow regimes, using the statistical characteristics of pressure fluctuations measured by a single pressure sensor, was demonstrated. Local pressure fluctuations at a station were recorded with a minimally-intrusive transducer. Three-layer, feed-forward ANNs were designed that could identify the four major flow patterns (bubbly, plug, churn, and slug) well. The feasibility of a transportable artificial neural network (ANN) - based technique for the classification of flow regimes was also examined. Local pressures were recorded at three different locations using three independent but similar transducers. An ANN was designed, trained and successfully tested for the classification of the flow regimes using one of the normalized pressure signals (from Sensor 1). The ANN trained and tested for Sensor 1 predicted the flow regimes reasonably well when applied directly to the other two sensors, indicating a good deal of transportability. An ANN-based method was also developed, whereby the power spectrum density characteristics of other sensors were adjusted before they were used as input to the ANN that was based on Sensor 1 alone. The method improved the predictions. The gas-liquid interfacial surface area concentration was also measured in the study. The gas absorption technique was applied, using CO2 as the transferred species and sodium hydroxide as the alkaline agent in water. Statistical analysis was performed to identify the parametric dependencies. The experimental data were empirically correlated.

S.M. Ghiaasiaan and Seppo Karrila

2006-03-20

185

Comments on ``Behaviour of inert gas bubbles under chemical concentration gradients'' by G.P. Tiwari  

NASA Astrophysics Data System (ADS)

The motion of inert gas bubbles induced by thermal vacancy gradients has previously been used by the present authors to understand gas bubble release in UO 2 and metals. This approach has been recently questioned by Tiwari. In the present letter, a critical discussion of his viewpoint is presented, together with an analysis of the important experimental results of Marachov et al. There appears to be good evidence for the disputed effect.

Evans, J. H.; van Veen, A.

1998-01-01

186

Dynamics of gas bubble growth in a supersaturated solution with Sievert’s solubility law  

Microsoft Academic Search

This paper presents a theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution. We study systems where gas molecules completely dissociate in the solvent into two parts, thus making Sievert’s solubility law valid. We show that the difference between Henry’s and Sievert’s laws for chemical equilibrium conditions causes the difference in bubble growth

G. Yu. Gor; A. E. Kuchma

2009-01-01

187

Evolution of fission-gas-bubble-size distribution in recrystallized U–10Mo nuclear fuel  

Microsoft Academic Search

An analytical model for the nucleation and growth of intra and intergranular fission-gas bubbles, used to characterize fission-gas bubble development in U–Mo alloy fuel with burnup limited to less than 10at.% U in order to capture the fuel swelling stage prior to irradiation-induced recrystallization, is extended to recrystallized fuel at a burnup of ?16at.% U. During recrystallization the grain size

J. Rest

2010-01-01

188

Gas-bubble growth mechanisms in the analysis of metal fuel swelling  

Microsoft Academic Search

During steady-state irradiation, swelling rates associated with growth of fission-gas bubbles in metallic fast reactor fuels may be expected to remain small. As a consequence, bubble-growth mechanisms are not a major consideration in modeling the steady-state fuel behavior, and it is usually adequate to consider the gas pressure to be in equilibrium with the external pressure and surface tension restraint.

E. E. Gruber; J. M. Kramer

1986-01-01

189

Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2  

SciTech Connect

Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas bubbles at grain boundaries for given grain boundary properties. More validation of the model capability in polycrystalline is underway.

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

2012-05-30

190

Measurement and Analysis of Gas Bubbles Near a Reference Electrode in Aqueous Solutions  

SciTech Connect

Bubble size distributions (BSDs) near a reference electrode (RE) in aqueous glycerol solutions of an electrolyte NaCl have been investigated under various gas superficial velocities (U{sub S}). BSD and voltage reading of the solution were measured by using a high-speed digital camera and a pH/voltage meter, respectively. The results show that bubble size (b) increases with liquid viscosity ({mu}{sub c}) and U{sub S}. Self-similarity is seen and can be described by the log-normal form of the continuous number frequency distribution. The result shows that b controls the voltage reading in each solution. As b increases, the voltage increases because of gas bubbles interrupting their electrolyte paths in the solutions. An analysis of bubble rising velocity reveals that Stokes Law should be used cautiously to describe the system. The fundamental equation for bubble formation was developed via Newton's second law of motion and shown to be the function of three dimensionless groups--Weber number, Bond number, and Capillary number. After linking an electrochemical principle in the practical application, the result indicates that the critical bubble size is {approx}177 {micro}m. Further analysis suggests that there may be 3000 to 70,000 bubbles generated on the anode surface depending on the size of initial bubbles and provides the potential cause of the efficiency drop observed in the practical application.

Supathorn Phongikaroon; Steve Herrmann; Shelly Li; Michael Simpson

2005-10-01

191

A study of gas bubbles in liquid mercury in a vertical Hele-Shaw cell  

NASA Astrophysics Data System (ADS)

High-quality observations of mesoscopic gas bubbles in liquid metal are vital for a further development of pyrometallurgical gas injection reactors. However, the opacity of metals enforces the use of indirect imaging techniques with limited temporal or spatial resolution. In addition, accurate interface tracking requires tomography which further complicates the design of a high-temperature experimental setup. In this paper, an alternative approach is suggested that circumvents these two main restrictions. By injecting gas in a thin layer of liquid metal entrapped between two flat and closely spaced plates, bubbles in a Hele-Shaw flow regime are generated. The resulting quasi-2D multiphase flow phenomena can be fully captured from a single point of view and, when using a non-wetted transparent plate material, the bubbles can be observed directly. The feasibility of this approach is demonstrated by observations on buoyancy-driven nitrogen bubbles in liquid mercury in a vertical Hele-Shaw cell. By using a moving high-speed camera to make continuous close up recordings of individual bubbles, the position and geometry of these bubbles are quantified with a high resolution along their entire path. After a thorough evaluation of the experimental accuracy, this information is used for a detailed analysis of the bubble expansion along the path. While the observed bubble growth is mainly caused by the hydrostatic pressure gradient, a careful assessment of the volume variations for smaller bubbles shows that an accurate bubble description should account for significant dynamic pressure variations that seem to be largely regime dependent.

Klaasen, B.; Verhaeghe, F.; Blanpain, B.; Fransaer, J.

2014-01-01

192

Velocity field in isothermal turbulent bubbly gas-liquid flow through a pipe  

Microsoft Academic Search

Velocity field was measured by laser Doppler velocimetry in isothermal, turbulent bubbly gas-liquid flow through a 26.6 mm inner diameter vertical pipe. The measurements were made about 33 diameters downstream from the pipe entrance, gas injection being just upstream of the entrance. The gas phase radial distribution at the measurement plane exhibited influence of the injection device in that higher

V. Velidandla; S. Putta; R. P. Roy

1996-01-01

193

Nucleation of Gas Bubbles in Extrusion Foaming of High-Pressure Polyethylene  

Microsoft Academic Search

The nucleation of gas bubbles in extrusion foaming of high-pressure polyethylene is considered. Experiments show that undissolved gas microbubbles in the solution being foamed can have a significant effect on the number density of pores in the foam. A simple model for estimating the number density of supercritical nuclei is proposed. The effect of the time of mixing of gas

B. V. Kichatov; A. M. Korshunov

2005-01-01

194

The Dynamic Effects of Surfactants on Gas Bubbles in Liquid Flows  

NASA Astrophysics Data System (ADS)

We have experimentally examined the effects of soluble surfactants on gas bubbles in liquid flows in inclined tubes. Air bubbles of known size (? = 0.8, 1.0, 1.5) are suspended under minimum flow conditions in tubes oriented at inclination angles of ? = 25^o, 45^o, 65^o, or 90^o. Sodium Dodecyl Sulfate or Triton X-100 is infused into the flow to give a bulk concentration of ? = 10% CMC or 100% CMC. Pressure and flow waveforms in the test section are continuously recorded. >From video images, the time-dependent contact angles, contact perimeter, and the gas-solid interfacial area are measured. The modification of these interfacial properties by the surfactant produces three general regimes of bubble response: 1) bubble deformation, 2) deformation plus axial translation, 3) deformation with detachment from the wall plus translation. Correspondingly, we observe modifications of the pressure gradient. These surfactant mediated responses are dependent upon the interrelated effects of ?, ?, ? and the surfactant characteristics. High bulk concentration of surfactant more rapidly alters bubble shape and promotes bubble detachment. This investigation demonstrates the potential ability of surfactants to dislodge dried gas bubbles by the alteration of interfacial properties. Supported by NIH HL R01-60230.

Cavanagh, Daniel; Eckmann, David

2000-11-01

195

Rate of disappearance of gas bubble trauma signs in juvenile salmonids  

USGS Publications Warehouse

To assess the rate of disappearance of gas bubble trauma (GBT) signs in juvenile salmonids, we exposed spring chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss to water containing high levels of dissolved gas supersaturation (DGS) for a time period sufficient to induce signs of GBT, reduced the DGS to minimal levels, and then sampled fish through time to document changes in severity of GBT. Because of the tendency of GBT signs to dissipate at different rates, we conducted trials focusing on emboli (bubbles) in the gill filaments and lateral line and separate trials that focused on bubbles in the external surfaces (fins, eyes, and opercula). Bubbles in gill filaments dissipated almost completely within 2 h after transfer of fish to water of nearly normal DGS (104%), whereas bubbles in the lateral line dissipated to negligible levels within 5 h. Bubbles on external surfaces were more persistent through time than they were in gill filaments and the lateral line. Although typically dissipating to low levels within 48 h, external bubbles sometimes remained for 4 d. Assuming a direct relation exists between easily observable signs and direct mortality, our results suggest that fish can recover quickly from the potentially lethal effects of DGS once they move from water with high DGS to water of almost normal gas saturation. These results should be of fundamental importance to fishery managers interpreting the results of monitoring for the severity and prevalence of GBT in juvenile salmonids in the Columbia River system and perhaps elsewhere.

Hans, K. M.; Mesa, M. G.; Maule, A. G.

1999-01-01

196

Heterogeneous bubble nucleation and conditions for growth in a liquid–gas system of constant mass and volume  

Microsoft Academic Search

The conditions are considered under which heterogeneous bubble nucleation takes place in a conical pit in the boundary of a constant size volume containing a liquid–gas solution, and the size to which the nucleate bubble grows is predicted. Four possible equilibrium states are found for the nucleate bubble: two unstable, one metastable, and one stable. The unstable state corresponding to

C. A. Ward; W. R. Johnson; R. D. Venter; S. Ho; T. W. Forest; W. D. Fraser

1983-01-01

197

Histopathology and ultrastructure of ocular lesions associated with gas bubble disease in salmonids.  

PubMed

Ocular lesions associated with natural and experimental outbreaks of gas bubble disease (GBD) in commercial salmonids were assessed histologically and by scanning electron microscopy. Small gas emboli were first detected in the choroid gland of the posterior uvea. In subacute and chronic cases, bubble size increased markedly and localization in retrobulbar and periocular sites was favoured. During the acute phase of GBD, ocular lesions were limited to anatomical displacement of tissue and local degeneration of compressed tissues around the perimeter of bubbles. Subacute sequelae included the formation of anterior synechia, lens cataract, and suppurative panophthalmitis. During chronic stages, when large retrobulbar bubbles had caused severe exophthalmia, there was stretching of the optic nerve and of retinal blood vessels and severe distortion of the posterior aspects of the globe. The sequential development, pathogenesis and persistence of ocular lesions associated with GBD in fish are discussed. PMID:2079557

Speare, D J

1990-11-01

198

[Growth dynamics and the largest size of gas bubbles emerging in body tissues due to decompression].  

PubMed

Symptoms of decompression sickness (DCS) develop when the total volume of gas bubbles due to decompression reaches the magnitude critical for a body tissue. Number of the bubbles is a function of random nucleation intensity before, during or after decompression and tissue superaeration dynamics, whereas their size is unambiguously dependent on a tissue, decompression phase and bubbling time. A mathematical model of bubble tissue dynamics has been proposed for calculating the dynamics of mathematical expectation of the total gas in tissues and mounting a method for comparative analysis of the maximal DCS probability as a result of implementation of different decompression tables. Unequal intensity of nucleation during spaceflight EVA and its ground simulation w/o spacesuit is the course of inequality of decompression safety of these operations. PMID:16193924

Nikolaev, V P

2005-01-01

199

Gas bubble formation in fused silica generated by ultra-short laser pulses.  

PubMed

During processing of glass using ultra-fast lasers the formation of bubble-like structures can be observed in several glass types such as fused silica. Their formation can be exploited to generate periodic gratings in glasses but for other glass processing techniques such as waveguide-writing or glass welding by ultra-fast lasers the bubble formation proves often detrimental. In this work we present experiments and their results in order to gain understanding of the origins and on the underlying formation and transportation mechanisms of the gas bubbles. PMID:24977843

Cvecek, Kristian; Miyamoto, Isamu; Schmidt, Michael

2014-06-30

200

AN INVESTIGATION OF THE EFFECT OF BUBBLE DIAMETER ON THE PERFORMANCE OF GAS-SOLID FLUIDIZED BED REACTOR AND TWO-PHASE MODELING OF BUBBLING FLUIDIZED BED REACTOR IN MELAMINE PRODUCTION  

Microsoft Academic Search

Bubble diameter is an important parameter in the modeling of gas-solid fluidized bed reactor and plays an important role in the performance of the fluidized bed reactor. Determination of the actual bubble diameter in the fluidized bed is very important. Bubble diameter starts at the initial bubble diameter ( 0

Amir Farshi; Houman Javaherizadeh; M. A. Hamzavi

201

Analysis of an oscillatory oil squeeze film containing a central gas bubble  

NASA Technical Reports Server (NTRS)

A squeeze-film damper, consisting of two circular plates, having only normal oscillatory relative motion is considered. The liquid lubricant between the plates is assumed to contain a single central gas bubble. The effect of the bubble on the damper performance is analyzed. Comparison is made with the performance of a pure liquid damper. Substantial deviations in peak dynamic pressures are predicted which explain discrepancies between experimental and theoretical results reported in the literature.

Haber, S.; Etsion, I.

1985-01-01

202

Force of a gas bubble on a foreign particle in front of a freezing interface  

Microsoft Academic Search

We monitored the formation and development of a single gas bubble on the surface of a spherical particle of size 1.676 mm under unidirectional freezing and thawing (4.6–5.0 ?m\\/s) and for the first time quantitatively estimated the force exerted on this particle by measuring the deformation of an attached elastic stick. The bubble would nucleate and grow on the particle

T. Tao; X. F. Peng; D. J. Lee

2004-01-01

203

Effect of fluctuations on the surface tension of liquid droplets and gas bubbles and their nucleation  

Microsoft Academic Search

Correlations are established between the surface tension of liquid droplets and gas bubbles, and fluctuations in the volume,\\u000a density, and number of particles in their core,. The smallest droplet or bubble size below which the homogeneity of its core\\u000a starts to disturb is estimated. It is shown that, for the nuclei containing as few as several tens of microparticles (molecules

E. V. Veitsman

2007-01-01

204

Experimental investigation of a strongly shocked gas bubble.  

PubMed

A free-falling, spherical, soap-film bubble filled with argon is subjected to a planar M=2.88 shock in atmospheric nitrogen; vorticity is deposited on the surface of the bubble during shock interaction, and the Richtmyer-Meshkov instability ensues. The geometrical development of the shocked bubble is diagnosed with laser sheet imaging and a planar slice showing two cross sections of both the major vortex ring and a secondary vortex ring is revealed experimentally for the first time. Quantitative measurements of the experimental data include the vortex velocity defect, and subsequent circulation calculations, along with a new set of relevant length scales. The shock wave strength, leading to a post-shock compressible regime, allows the study of the instability development in a regime between low Mach number shock tube experiments and high Mach number laser driven experiments that has not been investigated previously. PMID:15904378

Ranjan, Devesh; Anderson, Mark; Oakley, Jason; Bonazza, Riccardo

2005-05-13

205

Experimental Investigation of a Strongly Shocked Gas Bubble  

NASA Astrophysics Data System (ADS)

A free-falling, spherical, soap-film bubble filled with argon is subjected to a planar M=2.88 shock in atmospheric nitrogen; vorticity is deposited on the surface of the bubble during shock interaction, and the Richtmyer-Meshkov instability ensues. The geometrical development of the shocked bubble is diagnosed with laser sheet imaging and a planar slice showing two cross sections of both the major vortex ring and a secondary vortex ring is revealed experimentally for the first time. Quantitative measurements of the experimental data include the vortex velocity defect, and subsequent circulation calculations, along with a new set of relevant length scales. The shock wave strength, leading to a post-shock compressible regime, allows the study of the instability development in a regime between low Mach number shock tube experiments and high Mach number laser driven experiments that has not been investigated previously.

Ranjan, Devesh; Anderson, Mark; Oakley, Jason; Bonazza, Riccardo

2005-05-01

206

Dynamics of gas–liquid flow in a rectangular bubble column: experiments and single\\/multi-group CFD simulations  

Microsoft Academic Search

Several flow processes influence overall dynamics of gas–liquid flow and hence mixing and transport processes in bubble columns. In the present work, we have experimentally as well as computationally studied the effect of gas velocity, sparger design and coalescence suppressing additives on dynamics of gas–liquid flow in a rectangular bubble column. Wall pressure fluctuations were measured to characterize the low

Vivek V. Buwa; Vivek V. Ranade

2002-01-01

207

The stability of bubbles formed from supersaturated solutions, and homogeneous nucleation of gas bubbles from solution, both revisited.  

PubMed

The solution of the problem of the relative stability of all possible equilibrium bubble states that can form from a closed, finite, supersaturated gas-liquid solution, maintained at a fixed temperature and a fixed external pressure is given. The supersaturated solution may contain any number of dissolved volatile solutes. The full solution to this problem has remained elusive for decades, because of the complication of pressure inequalities between the bubbles and the constant external (or reservoir) pressure. The method of solution is one that had been used previously to solve the related problem of the stability of a liquid droplet in a supersaturated vapor, where the same complication occurred. The derived equations were found to reduce correctly when simplified; they were consistent with experiment, and the system Gibbs free energy appropriately obeyed the Law of Corresponding States. The expressions were used in the context of transition state theory to provide semiempirical predictions of the rate of homogeneous bubble formation from a supersaturated solution, and the "critical pressure for homogeneous nucleation (P(crit))". The nucleation Gibbs free energy expression derived here had a lower barrier height and resulted in a reduction of P(crit) values, relative to what was obtained from the basis of a pre-existing approximate expression taken from the literature. Applications to chemical engineering and human decompression modeling are briefly described. PMID:19032116

Goldman, Saul

2008-12-25

208

A gas bubble-based parallel micro manipulator: conceptual design and kinematics model  

NASA Astrophysics Data System (ADS)

The parallel mechanism has become an alternative solution when micro manipulators are demanded in the fields of micro manipulation and micro assembly. In this technical note, a three-degree-of-freedom (3-DOF) parallel micro manipulator is presented, which is directly driven by three micro gas bubbles. Since the micro gas bubbles are generated and maintained due to the surface tension between the gas and liquid media, the proposed novel system can be used in the liquid environment which allows for rotation about the X and Y axes and translation along the Z axis. In this technical note, the conceptual design of micro gas bubble-based parallel manipulator is introduced and the input/output characteristic of the actuator is analyzed in detail. The kinematics model of the parallel micro manipulator is also established, based on which the workspace and the system motion resolution are analyzed as a criterion and reference for future prototype development.

Dong, Wei; Gauthier, Michaël; Lenders, Cyrille; Lambert, Pierre

2012-05-01

209

Bubble dispersion and coalescence in turbulent pipe flow  

NASA Astrophysics Data System (ADS)

An experiment for investigating bubble coalescence rate in turbulent pipe flow was designed based on measuring evolution of the specific interfacial area at two locations along the pipeline. A broad range of operating conditions (i.e. 0.008 < phiG < 0.5, 4 < epsilonp < 26 w/kg, 25 mum < d32 < 8,700 mum, and sodium dodecyl sulfate (SDS) concentration range of 0--50 ppm) were investigated. Three bubble coalescence rates were developed based on the temporal rate of variation of Sauter mean diameter, specific interfacial area, and bubble population density and the resulting findings were discussed in terms of hydrodynamic factors (including gas hold-up, energy dissipation rate and bubble size) and interfacial properties. The bubble coalescence rate was found to increase as the gas hold-up and the energy dissipation rate increase, and decrease as the bubble size and SAA concentration increase. Compared to tap water, the normalized coalescence rates were found to decrease radically by the presence of minute dosage of SAA due to the decisive role interfacial characteristics play. The exponential format of interfacial parameters can be used to characterize their effect on bubble coalescence processes, which implies that the interfacial characteristics affect the bubble coalescence through influencing coalescence efficiency which leads to decreasing bubble coalescence rate in gas/liquid turbulent flow. A theoretical collision model was adapted to the case of bubble coalescence rate in turbulent two-phase flow in pipes, and the resulting expression was found to apply not only to pure water system but also to contaminated streams displaying surface activity. The use of different interfacial parameters (such as the static surface tension, surface pressure, Gibbs surface excess and surface excess based on long-term approximation) to explain how SAA retards bubble coalescence rate was evaluated and it was found although the dimensionless forms of these interfacial parameters are correlated with bubble coalescence rate for SDS aqueous solutions to the similar degrees, the surface excess based on the long-term approximation could prevail due to its revealing the underlying mechanism of coalescence hindrance. Factors affecting bubble dispersion and sparger performance were systematically investigated though the use of a 25.4 mm pipe loop in which liquid velocities of up to 3.2 m/s, and gas holdup varying between 0.008 and 0.5 were tested. Trace dosage of either MIBC or SDS was added to simulate the industrial streams. The use of novel dynamic spargers results in the formation of large interfacial area of contact (up to 5,400 m2/m3) and small bubbles (d32 down to 25 mum). The efficiency by which dynamic spargers utilize energy for the formation of interfacial area was found to be one order of magnitude higher than that obtained in mechanically-agitated tanks and traditional pipe nozzles, and more efficient than some of the commonly used static mixers operating at the same power input per unit mass of the stream processed. The interfacial area and the Sauter mean bubble size can be predicted by using correlation equations for MIBC and SDS aqueous solutions. (Abstract shortened by UMI.)

Luo, Jianjun

2002-04-01

210

A physiological model of the release of gas bubbles from crevices under decompression.  

PubMed

Moving bubbles have been observed in the blood during or after decompression using ultrasonic techniques. It has been proposed that these may grow from nuclei housed on the blood vessel wall. One candidate for bubble nucleation is hydrophobic crevices. This work explores the growth of gas pockets that might exist in conical crevices and the release of bubbles from these crevices under decompression. An existing dynamic mathematical model for the stability of gas pockets in crevices [Chappell, M.A., Payne, S.J., in press. A physiological model of gas pockets in crevices and their behavior under compression. Respir. Physiol. Neurobiol.] is extended to include the behavior as the gas pocket reaches the crevice mouth and bubbles seed into the bloodstream. The behavior of the crevice bubble is explored for a single inert gas, both alone and with metabolic gases included. It was found that the presence of metabolic gases has a significant effect on the behavior under decompression and that this appears to be due to the high diffusivity of these gases. PMID:16309977

Chappell, M A; Payne, S J

2006-09-28

211

Lack of intracellular bubble formation in microorganisms at very high gas supersaturations.  

PubMed

Eucaryotic unicellular (a yeast, a cellular slime mold, and various protozoans) and two multicellular (aschelminths) microorganisms were saturated with gas at high pressures and rapidly decompressed. No effect was observed with pressures of argon up to 125 atm, nitrogen up to 175 atm, and helium up to 350 atm, showing that the induced gas supersaturations did not cause intracellular bubbles to form. With 25--50 atm higher gas pressures, the decompression usually produced killing and cell rupture, although differences in tolerances existed among the various organisms. Substantial fractions of the populations survived gas supersaturations well above the threshold values for massive spontaneous nucleation of bubbles in the water. When killing occurred, external rather than internal bubbles appeared to be the cause. Even with the 300 atm argon or nitrogen pressures, yeast cells were unaffected, apparently because of the external protection provided by their cell wall. It is concluded that the gas supersaturations required for intracellular formation of bubbles generally are at least equal to and probably higher than the bubble nucleation thresholds for water or aqueous solutions. PMID:395143

Hemmingsen, E A; Hemmingsen, B B

1979-12-01

212

Gas Bubble Disease Monitoring and Research of Juvenile Salmonids : Annual Report 1996.  

SciTech Connect

This document describes the project activities 1996--1997 contract year. This report is composed of three chapters which contain data and analyses of the three main elements of the project: field research to determine the vertical distribution of migrating juvenile salmonids, monitoring of juvenile migrants at dams on the Snake and Columbia rivers, and laboratory experiments to describe the progression of gas bubble disease signs leading to mortality. The major findings described in this report are: A miniature pressure-sensitive radio transmitter was found to be accurate and precise and, after compensation for water temperature, can be used to determine the depth of tagged-fish to within 0.32 m of the true depth (Chapter 1). Preliminary data from very few fish suggest that depth protects migrating juvenile steelhead from total dissolved gas supersaturation (Chapter 1). As in 1995, few fish had any signs of gas bubble disease, but it appeared that prevalence and severity increased as fish migrated downstream and in response to changing gas supersaturation (Chapter 2). It appeared to gas bubble disease was not a threat to migrating juvenile salmonids when total dissolved gas supersaturation was < 120% (Chapter 2). Laboratory studies suggest that external examinations are appropriate for determining the severity of gas bubble disease in juvenile salmonids (Chapter 3). The authors developed a new method for examining gill arches for intravascular bubbles by clamping the ventral aorta to reduce bleeding when arches were removed (Chapter 3). Despite an outbreak of bacterial kidney disease in the experimental fish, the data indicate that gas bubble disease is a progressive trauma that can be monitored (Chapter 3).

Maule, Alec G.; Beeman, John W.; Hans, Karen M.; Mesa, M.G.; Haner, P.; Warren, J.J. [Geological Survey, Cook, WA (United States). Columbia River Research Lab.

1997-10-01

213

Methanotrophic microbial communities associated with bubble plumes above gas seeps in the Black Sea  

Microsoft Academic Search

Bubbles evolving from active gas seeps can be traced by hydroacoustic imaging up to 1000 m high in the Black Sea water column. Although methane concentrations are not distinguishable between the water column above the deep seep and reference sites, atmospheric noble gas measurements clearly show the constant input of gases (mainly methane) via seepage into the Black Sea. Archaea

Carsten J. Schubert; Edith Durisch-Kaiser; Christian P. Holzner; Lucia Klauser; Bernhard Wehrli; Oliver Schmale; Jens Greinert; Daniel F. McGinnis; Marc De Batist; Rolf Kipfer

2006-01-01

214

Two-phase flow equations for a dilute dispersion of gas bubbles in liquid  

Microsoft Academic Search

Equations of motion correct to the first order of the gas concentration by volume are derived for a dispersion of gas bubbles in liquid through systematic averaging of the equations on the microlevel. First, by ensemble averaging, an expression for the average stress tensor is obtained, which is non-isotropic although the local stress tensors in the constituent phases are isotropic

A. Biesheuvel; L. van Wijngaarden

1984-01-01

215

Experiment and Numerical Simulation of Bubble Behaviors in Argon Gas Injection Into Lead-Bismuth Pool  

SciTech Connect

In a lead-bismuth alloy (45%Pb-55%Bi) cooled direct contact boiling water fast reactor (PBWFR), steam can be produced by direct contact of feed water with primary Pb-Bi coolant in the upper core plenum, and Pb-Bi coolant can be circulated by buoyancy forces of steam bubbles. As a basic study to investigate the two-phase flow characteristics in the chimneys of PBWFR, a two-dimensional two-phase flow was simulated by injecting argon gas into Pb-Bi pool in a rectangular vessel (400 mm in length, 1500 mm in height, 50 mm in width), and bubble behaviors were investigated experimentally. Bubble sizes, bubble rising velocities and void fractions were measured using void probes. Argon gas was injected through five nozzles of 4 mm in diameter into Pb-Bi at two locations. The experimental conditions are the pressure of atmospheric pressure, Pb-Bi temperatures of 443 K, and the flow rate of injection Ar gas is 10, 20, and 30 NL/min. The measured bubble rising velocities were distributed in the range from 1 to 3 m/s. The average velocity was about 0.6 m/s. The measured bubble chord lengths were distributed from 1 mm up to 30 mm. The average chord length was about 7 mm. An analysis was performed by two-dimensional and two-fluid model. The experimental results were compared with the analytical results to evaluate the validity of the analytical model. Although large diameter bubbles were observed in the experiment, the drag force model for spherical bubbles performed better for simulation of the experimental result because of high surface tension force of Pb-Bi. (authors)

Yumi Yamada [Advanced Reactor Technology Company, Ltd. (Japan); Toyou Akashi; Minoru Takahashi [Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 (Japan)

2006-07-01

216

Can Propagation of Gas Bubbles Lead to Detached Solidification? Experiments on Freezing of Water  

NASA Technical Reports Server (NTRS)

A vertical Bridgman-Stockbarger apparatus was used to directionally solidify water upward, in the hope that detached solidification would evolve from gas bubbles forming on the wall. A large contact angle of the water on the ampoule wall and a high solubility of the dissolved gas caused gas bubbles or tubes to form only at the ampoule wall, and not in the interior. Gas tubes were often nearly periodically spaced around the ampoule wall, with a spacing that increased with ampoule diameter and decreased with freezing rate. The width of the gas tubes was nearly independent of the ampoule diameter and freezing rate. A high degree of detachment was obtained with a rough, nonwetting coating on the ampoule wall, but full detachment was not achieved. This indicates that detachment does not occur by propagation of a single gas bubble around the periphery of the freezing interface. The convection near the freezing interface influenced gas bubble formation, and was outward for a concave freezing interface and inward for a convex interface.

Wang, Yazhen; Regel, Liya; Wilcox, William R.

2002-01-01

217

Dissolution without disappearing: multicomponent gas exchange for CO2 bubbles in a microfluidic channel.  

PubMed

We studied the dissolution dynamics of CO2 gas bubbles in a microfluidic channel, both experimentally and theoretically. In the experiments, spherical CO2 bubbles in a flow of a solution of sodium dodecyl sulfate (SDS) first shrink rapidly before attaining an equilibrium size. In the rapid dissolution regime, the time to obtain a new equilibrium is 30 ms regardless of SDS concentration, and the equilibrium radius achieved varies with the SDS concentration. To explain the lack of complete dissolution, we interpret the results by considering the effects of other gases (O2, N2) that are already dissolved in the aqueous phase, and we develop a multicomponent dissolution model that includes the effect of surface tension and the liquid pressure drop along the channel. Solutions of the model for a stationary gas bubble show good agreement with the experimental results, which lead to our conclusion that the equilibrium regime is obtained by gas exchange between the bubbles and liquid phase. Also, our observations from experiments and model calculations suggest that SDS molecules on the gas-liquid interface form a diffusion barrier, which controls the dissolution behaviour and the eventual equilibrium radius of the bubble. PMID:24874437

Shim, Suin; Wan, Jiandi; Hilgenfeldt, Sascha; Panchal, Prathamesh D; Stone, Howard A

2014-06-17

218

Random-walk Monte Carlo simulation of intergranular gas bubble nucleation in UO2 fuel  

NASA Astrophysics Data System (ADS)

Using a random-walk particle algorithm, we investigate the clustering of fission gas atoms on grain boundaries in oxide fuels. The computational algorithm implemented in this work considers a planar surface representing a grain boundary on which particles appear at a rate dictated by the Booth flux, migrate two dimensionally according to their grain boundary diffusivity, and coalesce by random encounters. Specifically, the intergranular bubble nucleation density is the key variable we investigate using a parametric study in which the temperature, grain boundary gas diffusivity, and grain boundary segregation energy are varied. The results reveal that the grain boundary bubble nucleation density can vary widely due to these three parameters, which may be an important factor in the observed variability in intergranular bubble percolation among grain boundaries in oxide fuel during fission gas release.

Millett, Paul C.; Zhang, Yongfeng; Andersson, D. A.; Tonks, Michael R.; Biner, S. B.

2012-11-01

219

Numerical investigation of gas-driven flow in 2-D bubble columns  

SciTech Connect

Gas-liquid bubbly flow in 2-D bubble columns was studied by numerical simulation. A Eulerian-Eulerian two-fluid model used describes the time-dependent motion of liquid driven by small, spherical gas bubbles injected at the bottom of the columns. Such equations, numerically implemented in this work, were derived by Zhang and Prosperetti. A distinctive feature of this method is the derivation of the disperse-phase momentum equation by averaging the particle (here, the bubble) equation of motion directly, not the macroscopic equation for the particle phase. Both the time-averaged quantities and dynamic characteristics of the macroscopic coherent structures agree with the experimental data of Lin et al. and Muddle et al. The comparison of simulated results with data demonstrates that this physical model and numerical approach can provide the key features of the time-dependent behavior of dispersed bubbly flows qualitatively with reasonable quantitative accuracy. Effects of the number of injectors, magnitude of bubble-induced viscosity, and various parameters in the interphase momentum exchange were also studied by simulating various cases and comparing with measurements. The applicability of different boundary conditions and the sensitivity to the mesh system used are also examined.

Pan, Y.; Dudukovic, M.P.; Chang, M.

2000-03-01

220

Experiment and Numerical Simulation of Bubble Behavior in Argon Gas Injection into Lead-Bismuth Pool  

NASA Astrophysics Data System (ADS)

In a lead-bismuth alloy (45%Pb-55%Bi) cooled direct contact boiling water fast reactor (PBWFR), steam can be produced by direct contact of feed water with primary Pb-Bi coolant in the upper core plenum, and Pb-Bi coolant can be circulated by buoyancy forces of steam bubbles. As a basic study to investigate the two-phase flow characteristics in the chimneys of PBWFR, a two-dimensional two-phase flow was simulated by injecting argon gas into Pb-Bi pool in a rectangular vessel (400mm in length, 1500mm in height), and bubble behavior were investigated experimentally. Bubble sizes, bubble rising velocities and void fractions were measured using void probes. The experimental conditions are the atmospheric pressure and the flow rate of injection Ar gas is 10, 20, and 30 NL/min. The average of measured bubble rising velocity was about 0.6 m/s. The average chord length was about 7mm. An analysis was performed by two-dimensional and two-fluid model. The experimental results were compared with the analytical results to evaluate the validity of the analytical model. Although large diameter bubbles were observed in the experiment, the drag force model of lower value performed better for simulation of the experimental result.

Yamada, Yumi; Akashi, Toyou; Takahashi, Minoru

221

Evolution of a gas bubble in porous matrix filled by methane hydrate  

NASA Astrophysics Data System (ADS)

Behavior of a small isolated hydrate-free inclusion (a bubble) within hydrate-bearing porous matrix is studied analytically and numerically. An infinite porous matrix of uniform properties with pores filled by methane hydrates and either water (excessive water situation) or methane gas (excessive gas situation) is considered. A small spherical hydrate-free bubble of radius R0 exists at initial moment within the matrix due to overheating relative to the surrounding medium. There is no continuing heat supply within the bubble, so new hydrate forms on its boundary, and its radius decreases with time. The process is analysed in the framework of the model that takes into account the phase transition and accompanying heat and mass transport processes and assumes spherical symmetry. It is shown that in the case of small (~ 10-2-10-1 m) bubbles, convective fluxes are negligible and the process is fully described by heat conduction and phase change equations. A spherically symmetric Stefan problem for purely conduction-controlled evolution is solved analytically for the case of equilibrium initial temperature and pressure within the bubble. The self-similar solution is verified, with good results, in numerical simulations based on the full filtration and heat transfer model and using the isotherm migration method. Numerical simulations are also conducted for a wide range of cases not amenable to analytical solution. It is found that, except for initial development of an overheated bubble, its radius evolves with time following the self-similar formula: R(t) ( t)1-2 R0-= 1 - tm- , (1) where tm is the life-time of bubble (time of its complete freezing). The analytical solution shows that tm follows 2 tm ~ (R0-?) , (2) where ? is a constant determined by the temperature difference ?T between the bubble's interior and far field. We consider implications for natural hydrate deposits. As an example, for a bubble with R0 = 4 cm and ?T = 0.001 K, we find tm ~ 5.7 ? 106 s (2 months) in a water excess system, and ~ 2.9 ? 107 s (11 months) in a gas excess system. Motion of the bubble is not considered in our study, but it can be estimated that at the typical velocity of buoyancy-driven transport, a small bubble does not move a significant distance over its life-time and, thus, cannot survive filtration through the hydrate stability zone. Work was financially supported by the Civilian Research and Development Foundation (Grant RUP1-2945-PE-09) and the Russian Foundation for Basic Research (Grant 09-01-92505).

Tsiberkin, Kirill; Lyubimov, Dmitry; Lyubimova, Tatyana; Zikanov, Oleg

2013-04-01

222

Improved Background Corrections for Uranium Holdup Measurements.  

National Technical Information Service (NTIS)

In the original Generalized Geometry Holdup (GGH) model, all holdup deposits were modeled as points, lines, and areas. Two improvements were recently made to the GGH model and are currently in use at the Y-12 National Security Complex. These two improveme...

R. B. Oberer C. A. Gunn L. G. Chian

2004-01-01

223

Measurement and Analysis of Gas Bubbles near a Reference Electrode in Aqueous Solutions  

SciTech Connect

Bubble size distributions (BSD) near a reference electrode (RE) in aqueous glycerol solutions of an electrolyte NaCl have been investigated under various gas superficial velocities (Us). BSD and RE voltage were measured by using a high-speed digital camera and a pH/voltage meter, respectively. Self-similarity is seen in the normalized cumulative number distribution through BSD. The percent relative difference (PRD) based on the baseline voltage shows that bubble size (b) has a strong impact on PRD at low liquid viscosity and both PRD and b increase at diverging rates as Us increases. An analysis on bubble rising velocity reveals that the system is in an intermediate region. A fundamental equation for spherical bubble formation is developed via Newton’s second law of motion and is linked to an electrochemical principle in the practical application.

Steven D. Herrmann; Shelly X. Li; Michael F. Simpson; Supathorn Phongikaroon

2006-10-01

224

Creating Small Gas Bubbles in Flowing Mercury Using Turbulence at an Orifice  

SciTech Connect

Pressure waves created in liquid mercury pulsed spallation targets have been shown to create cavitation damage to the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating such a population in mercury is difficult due to the high surface tension and particularly the non-wetting behavior of mercury on gas-injection hardware. If the larger injected gas bubbles can be broken down into small bubbles after they are introduced to the flow, then the material interface problem is avoided. Research at the Oak Ridge National Labarotory is underway to develop a technique that has shown potential to provide an adequate population of small-enough bubbles to a flowing spallation target. This technique involves gas injection at an orifice of a geometry that is optimized to the turbulence intensity and pressure distribution of the flow, while avoiding coalescence of gas at injection sites. The most successful geometry thus far can be described as a square-toothed orifice having a 2.5 bar pressure drop in the nominal flow of 12 L/s for one of the target inlet legs. High-speed video and high-resolution photography have been used to quantify the bubble population on the surface of the mercury downstream of the gas injection sight. Also, computational fluid dynamics has been used to optimize the dimensions of the toothed orifice based on a RANS computed mean flow including turbulent energies such that the turbulent dissipation and pressure field are best suited for turbulent break-up of the gas bubbles.

Wendel, Mark W [ORNL; Abdou, Ashraf A [ORNL; Paquit, Vincent C [ORNL; Felde, David K [ORNL; Riemer, Bernie [ORNL

2010-01-01

225

An analytical study of gas-bubble nucleation mechanisms in uranium-alloy nuclear fuel at high temperature  

Microsoft Academic Search

A multi-atom gas-bubble nucleation mechanism in uranium-alloy nuclear fuel operating in the high-temperature equilibrium gamma phase is proposed based on interpretation of measured intragranular bubble-size distribution data. This model is contrasted with the conventional two-atom nucleation mechanism within the context of a mechanistic calculation of the fission-gas bubble-size distribution. The results of the analysis enable the calculation of safety margins

J. Rest

2010-01-01

226

Evolution of microstructure of bubbles and gas permeability in sheared rhyolite (Invited)  

NASA Astrophysics Data System (ADS)

The microstructure of bubbles in magmas ascending in volcanic conduits is strongly changed by shear deformation. Because the microstructure controls the magma rheology and degassing behavior, clarifying its evolution in sheared magmas will help to understand the dynamics of magma ascent in volcanic conduits and predict the explosivity and style of volcanic eruptions. We have experimentally investigated the evolution of the microstructure of bubbles and the corresponding change in the gas permeability in shared rhyolite. The deformation experiments were performed using a piston-cylinder-type torsional deformation apparatus. Natural obsidians with a water content of 0.5 wt% were vesiculated in a cell with constant volume (ca. 5 mm? and ~5 mm in length) and then twisted at a temperature of around 1000°C. The maximum strain rate and total strain were of the order of 10-2 s-1 and ~35. After the deformation experiments, the microstructure of bubbles in run products was observed using synchrotron radiation X-ray CT at SPring-8 (BL20B2). The gas permeability of the run products was measured using an originally-manufactured gas permeameter. The size distribution and connectivity of bubbles in the run products indicated that shear strongly enhanced bubble coalescence. The coalescence resulted in the formation of bubble networks and an increase in the connectivity with total strain. The shear also elongated bubbles in a direction parallel to the shear. These results imply that shear increases the gas permeability in a direction parallel to the shear, and indeed, the measured gas permeabilities in this direction were two to five orders of magnitude larger than those of non-sheared samples. Once the connectivity and gas permeability increased because of shear deformation, compaction started to occur. During compaction, the connectivity remained large although the vesicularity decreased, and finally, bubble networks were pinched off, leaving elongated and aligned fine bubbles. The compaction of samples with a vesicularity of ~60 vol% resulted in the formation of dense rhyolite with only ~5 vol% vesicularity. Our experimental results imply that under a large shear strain, for example, in a narrow and long volcanic conduit, degassing is enhanced and magma compaction occurs, resulting in the effusion of lava and non-explosive eruptions.

Okumura, S.; Nakamura, M.; Fujioka, T.; Tsuchiyama, A.; Takeuchi, S.; Nakano, T.; Uesugi, K.

2010-12-01

227

ADVANCED DIAGNOSTIC TECHNIQUES FOR THREE-PHASE SLURRY BUBBLE COLUMN REACTORS (SBCR)  

SciTech Connect

This report summarizes the accomplishment made during the second year of this cooperative research effort between Washington University, Ohio State University and Air Products and Chemicals. The technical difficulties that were encountered in implementing Computer Automated Radioactive Particle Tracking (CARPT) in high pressure SBCR have been successfully resolved. New strategies for data acquisition and calibration procedure have been implemented. These have been performed as a part of other projects supported by Industrial Consortium and DOE via contract DE-2295PC95051 which are executed in parallel with this grant. CARPT and Computed Tomography (CT) experiments have been performed using air-water-glass beads in 6 inch high pressure stainless steel slurry bubble column reactor at selected conditions. Data processing of this work is in progress. The overall gas holdup and the hydrodynamic parameters are measured by Laser Doppler Anemometry (LDA) in 2 inch slurry bubble column using Norpar 15 that mimic at room temperature the Fischer Tropsch wax at FT reaction conditions of high pressure and temperature. To improve the design and scale-up of bubble column, new correlations have been developed to predict the radial gas holdup and the time averaged axial liquid recirculation velocity profiles in bubble columns.

M.H. Al-Dahhan; M.P. Dudukovic; L.S. Fan

2001-07-25

228

Decompression sickness bubbles: are gas micronuclei formed on a flat hydrophobic surface?  

PubMed

It is a long-standing hypothesis that the bubbles which evolve as a result of decompression have their origin in stable gas micronuclei lodged in hydrophobic crevices, micelles of surface-active molecules, or tribonucleation. Recent findings supported by atomic force microscopy have indicated that tiny, flat nanobubbles form spontaneously on smooth, hydrophobic surfaces submerged in water. We propose that these nanobubbles may be the gas micronuclei responsible for the bubbles that evolve to cause decompression sickness. To support our hypothesis, we used hydrophilic and monolayer-covered hydrophobic smooth silicon wafers. The experiment was conducted in three main stages. Double distilled water was degassed at the low pressure of 5.60 kPa; hydrophobic and hydrophilic silicon wafers were placed in a bowl of degassed water and left overnight at normobaric pressure. The bowl was then placed in the hyperbaric chamber for 15 h at a pressure of 1013 kPa (=90 m sea water). After decompression, bubbles were observed and photographed. The results showed that bubbles only evolved on the hydrophobic surfaces following decompression. There are numerous hydrophobic surfaces within the living body (e.g., in the large blood vessels), which may thus be the sites where nanobubbles that serve as gas micronuclei for bubble evolution following decompression are formed. PMID:21376842

Arieli, R; Marmur, A

2011-06-30

229

Gas-bubble effects on the formation of colloidal iron oxide nanocrystals.  

PubMed

This paper reports that gas bubbles can be used to tailor the kinetics of the nucleation and growth of inorganic-nanocrystals in a colloidal synthesis. We conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. We identified that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals. Our results show that gas bubbles display a stronger effect on the nucleation of iron oxide nanocrystals than on their growth. These results indicate that the nucleation and growth of iron oxide nanocrystals may rely on different types of chemical reactions between the iron-oleate decomposition products: the nucleation relies on the strongly exothermic, multiple-bond formation reactions, whereas the growth of iron oxide nanocrystals may primarily depend upon single-bond formation reactions. The identification of exothermic reactions is further consistent with our results in the synthesis of iron oxide nanocrystals with boiling solvents at reaction temperatures ranging from 290 to 365 °C, by which we determined the reaction enthalpy in the nucleation of iron oxide nanocrystals to be -142 ± 12 kJ/mol. Moreover, our results suggest that a prerequisite for effectively suppressing secondary nucleation in a colloidal synthesis is that the primary nucleation must produce a critical amount of nuclei, and this finding is important for a priori design of colloidal synthesis of monodispersed nanocrystals in general. PMID:21702497

Lynch, Jared; Zhuang, Jiaqi; Wang, Tie; LaMontagne, Derek; Wu, Huimeng; Cao, Y Charles

2011-08-17

230

Acoustic monitoring of gas emissions from the seafloor. Part I: quantifying the volumetric flow of bubbles  

NASA Astrophysics Data System (ADS)

Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en-route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0-200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance.

Leblond, Isabelle; Scalabrin, Carla; Berger, Laurent

2014-06-01

231

Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling  

NASA Astrophysics Data System (ADS)

In many natural and contaminated aquifers, geochemical processes result in the production or consumption of dissolved gases. In cases where methanogenesis or denitrification occurs, the production of gases may result in the formation and growth of gas bubbles below the water table. Near the water table, entrapment of atmospheric gases during water table rise may provide a significant source of O 2 to waters otherwise depleted in O 2. Furthermore, the presence of bubbles will affect the hydraulic conductivity of an aquifer, resulting in changes to the groundwater flow regime. The interactions between physical transport, biogeochemical processes, and gas bubble formation, entrapment and release is complex and requires suitable analysis tools. The objective of the present work is the development of a numerical model capable of quantitatively assessing these processes. The multicomponent reactive transport code MIN3P has been enhanced to simulate bubble growth and contraction due to in-situ gas production or consumption, bubble entrapment due to water table rise and subsequent re-equilibration of the bubble with ambient groundwater, and permeability changes due to trapped gas phase saturation. The resulting formulation allows for the investigation of complex geochemical systems where microbially mediated redox reactions both produce and consume gases as well as affect solution chemistry, alkalinity, and pH. The enhanced model has been used to simulate processes in a petroleum hydrocarbon contaminated aquifer where methanogenesis is an important redox process. The simulations are constrained by data from a crude oil spill site near Bemidji, MN. Our results suggest that permeability reduction in the methanogenic zone due to in-situ formation of gas bubbles, and dissolution of entrapped atmospheric bubbles near the water table, both work to attenuate the dissolved gas plume emanating from the source zone. Furthermore, the simulations demonstrate that under the given conditions more than 50% of all produced CH 4 partitions to the gas phase or is aerobically oxidised near the water table, suggesting that these processes should be accounted for when assessing the rate and extent of methanogenic degradation of hydrocarbons.

Amos, Richard T.; Ulrich Mayer, K.

2006-09-01

232

Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling.  

PubMed

In many natural and contaminated aquifers, geochemical processes result in the production or consumption of dissolved gases. In cases where methanogenesis or denitrification occurs, the production of gases may result in the formation and growth of gas bubbles below the water table. Near the water table, entrapment of atmospheric gases during water table rise may provide a significant source of O(2) to waters otherwise depleted in O(2). Furthermore, the presence of bubbles will affect the hydraulic conductivity of an aquifer, resulting in changes to the groundwater flow regime. The interactions between physical transport, biogeochemical processes, and gas bubble formation, entrapment and release is complex and requires suitable analysis tools. The objective of the present work is the development of a numerical model capable of quantitatively assessing these processes. The multicomponent reactive transport code MIN3P has been enhanced to simulate bubble growth and contraction due to in-situ gas production or consumption, bubble entrapment due to water table rise and subsequent re-equilibration of the bubble with ambient groundwater, and permeability changes due to trapped gas phase saturation. The resulting formulation allows for the investigation of complex geochemical systems where microbially mediated redox reactions both produce and consume gases as well as affect solution chemistry, alkalinity, and pH. The enhanced model has been used to simulate processes in a petroleum hydrocarbon contaminated aquifer where methanogenesis is an important redox process. The simulations are constrained by data from a crude oil spill site near Bemidji, MN. Our results suggest that permeability reduction in the methanogenic zone due to in-situ formation of gas bubbles, and dissolution of entrapped atmospheric bubbles near the water table, both work to attenuate the dissolved gas plume emanating from the source zone. Furthermore, the simulations demonstrate that under the given conditions more than 50% of all produced CH(4) partitions to the gas phase or is aerobically oxidised near the water table, suggesting that these processes should be accounted for when assessing the rate and extent of methanogenic degradation of hydrocarbons. PMID:16797104

Amos, Richard T; Ulrich Mayer, K

2006-09-10

233

Characterization of intergranular fission gas bubbles in U-Mo fuel.  

SciTech Connect

This report can be divided into two parts: the first part, which is composed of sections 1, 2, and 3, is devoted to report the analyses of fission gas bubbles; the second part, which is in section 4, is allocated to describe the mechanistic model development. Swelling data of irradiated U-Mo alloy typically show that the kinetics of fission gas bubbles is composed of two different rates: lower initially and higher later. The transition corresponds to a burnup of {approx}0 at% U-235 (LEU) or a fission density of {approx}3 x 10{sup 21} fissions/cm{sup 3}. Scanning electron microscopy (SEM) shows that gas bubbles appear only on the grain boundaries in the pretransition regime. At intermediate burnup where the transition begins, gas bubbles are observed to spread into the intragranular regions. At high burnup, they are uniformly distributed throughout fuel. In highly irradiated U-Mo alloy fuel large-scale gas bubbles form on some fuel particle peripheries. In some cases, these bubbles appear to be interconnected and occupy the interface region between fuel and the aluminum matrix for dispersion fuel, and fuel and cladding for monolithic fuel, respectively. This is a potential performance limit for U-Mo alloy fuel. Microscopic characterization of the evolution of fission gas bubbles is necessary to understand the underlying phenomena of the macroscopic behavior of fission gas swelling that can lead to a counter measure to potential performance limit. The microscopic characterization data, particularly in the pre-transition regime, can also be used in developing a mechanistic model that predicts fission gas bubble behavior as a function of burnup and helps identify critical physical properties for the future tests. Analyses of grain and grain boundary morphology were performed. Optical micrographs and scanning electron micrographs of irradiated fuel from RERTR-1, 2, 3 and 5 tests were used. Micrographic comparisons between as-fabricated and as-irradiated fuel revealed that the site of first bubble appearance is the grain boundary. Analysis using a simple diffusion model showed that, although the difference in the Mo-content between the grain boundary and grain interior region decreased with burnup, a complete convergence in the Mo-content was not reached at the end of the test for all RERTR tests. A total of 13 plates from RERTR-1, 2, 3 and 5 tests with different as-fabrication conditions and irradiation conditions were included for gas bubble analyses. Among them, two plates contained powders {gamma}-annealed at {approx}800 C for {approx}100 hours. Most of the plates were fabricated with as-atomized powders except for two as-machined powder plates. The Mo contents were 6, 7 and 10wt%. The irradiation temperature was in the range 70-190 C and the fission rate was in the range 2.4 x 10{sup 14} - 7 x 10{sup 14} f/cm{sup 3}-s. Bubble size for both of the {gamma}-annealed powder plates is smaller than the as-atomized powder plates. The bubble size for the as-atomized powder plates increases as a function of burnup and the bubble growth rate shows signs of slowing at burnups higher than {approx}40 at% U-235 (LEU). The bubble-size distribution for all plates is a quasi-normal, with the average bubble size ranging 0.14-0.18 {micro}m. Although there are considerable errors, after an initial incubation period the average bubble size increases with fission density and shows saturation at high fission density. Bubble population (density) per unit grain boundary length was measured. The {gamma}-annealed powder plates have a higher bubble density per unit grain boundary length than the as-atomized powder plates. The measured bubble number densities per unit grain boundary length for as-atomized powder plates are approximately constant with respect to burnup. Bubble density per unit cross section area was calculated using the density per unit grain boundary length data. The grains were modeled as tetrakaidecahedrons. Direct measurements for some plates were also performed and compared with the calculated quantities. Bubble density per unit

Kim, Y. S.; Hofman, G.; Rest, J.; Shevlyakov, G. V.; Nuclear Engineering Division; SSCR RIAR

2008-04-14

234

Observation of bubble-involving spontaneous gas dissolution in superheated Al alloy melt  

NASA Astrophysics Data System (ADS)

We present a direct visualization of spontaneous gas dissolution in Al-7.7 mass% Ca eutectic alloy melt during superheating using high-brilliance synchrotron X-ray imaging. A bubble-involving gas dissolution process was observed, which can be understood within the framework of adsorption-diffusion-dissolution mechanism. The heterogenous nucleation and combined effect of hydrogen diffusivity and solubility results in the growth of individual bubbles in a stochastic way with Gaussian distribution. This also applies to the behavior of group bubbles in early stage, while which in final stage can be treated as reverse Ostwald ripening dominated by Lifshitz-Slyozov-Wagner diffusion mechanism when pure diffusive condition is satisfied.

Zhang, S. G.; Zhang, L.; Lu, W. Q.; Zhang, W.; Yu, J. D.; Fu, Y. N.; Li, J. G.

2013-10-01

235

Bubble Suspension  

NSDL National Science Digital Library

In this activity, learners observe as soap bubbles float on a cushion of carbon dioxide gas. Learners blow bubbles into an aquarium filled with a slab of dry ice. Learners will be amazed as the bubbles hover on the denser layer of carbon dioxide gas, then begin to expand and sink before freezing on the dry ice. Use this activity to discuss sublimation, density, and osmosis as well as principles of buoyancy, semipermeability, and interference.

Exploratorium, The

2011-10-11

236

Large-Scale Testing of Effects of AntiFoam Agent on Gas Holdup in Process Vessels in the Hanford Waste Treatment Plant - 8280  

Microsoft Academic Search

The Hanford Waste Treatment Plant (WTP) will vitrify the radioactive wastes stored in underground tanks. These wastes generate and retain hydrogen and other flammable gases that create safety concerns for the vitrification process tanks in the WTP. An anti-foam agent (AFA) will be added to the WTP process streams. Prior testing in a bubble column and a small-scale impeller-mixed vessel

Lenna A. Mahoney; James M. Alzheimer; Stuart T. Arm; Consuelo E. Guzman-Leong; Lynette K. Jagoda; Charles W. Stewart; Beric E. Wells; Satoru T. Yokuda

2008-01-01

237

Network simulation method applied to models of diffusion-limited gas bubble dynamics in tissue  

NASA Astrophysics Data System (ADS)

In this work the Network Simulation Method is used to study decompression sickness (DCS) in human subjects after diving and/or flying exposures. Bubble dynamics models suitable for these applications assume the bubble to be either contained in an unstirred tissue (two-region model) or surrounded by a boundary layer within a well stirred tissue (three-region model). The main results are obtained using the three-region model of gas bubble dynamics, which consists of a bubble and a well-stirred tissue region with an intervening unperfused diffusion region previously assumed to have a constant thickness and uniform gas diffusivity. Spatial discretization is used to numerically solve the diffusion equation considering the transitory term, where programming does not involve manipulation of the sophisticated mathematical software that is inherent in other numerical methods. The technique in question is always stable and convergent. Different effects (among them, tissue volume, initial bubble radius, surface tension of intercellular fluid and boundary layer thickness) are studied and plotted.

Zueco, Joaquín; Hernández-González, A.

2010-08-01

238

Steady-state composition of a two-component gas bubble growing in a liquid solution: self-similar approach.  

PubMed

The paper presents an analytical description of the growth of a two-component bubble in a binary liquid-gas solution. We obtain asymptotic self-similar time dependence of the bubble radius and analytical expressions for the nonsteady profiles of dissolved gases around the bubble. We show that the necessary condition for the self-similar regime of bubble growth is the constant, steady-state composition of the bubble. The equation for the steady-state composition is obtained. We reveal the dependence of the steady-state composition on the solubility laws of the bubble components. Besides, the universal, independent from the solubility laws, expressions for the steady-state composition are obtained for the case of strong supersaturations, which are typical for the homogeneous nucleation of a bubble. PMID:20025340

Gor, G Yu; Kuchma, A E

2009-12-21

239

Reconstructing recent atmospheric trace gas concentrations from polar firn and bubbly ice data by inverse methods  

Microsoft Academic Search

We present a method to extract the atmospheric signal of trace gas mixing ratios from firn and bubbly ice measurements. This method, validated using data from Antarctic sites (Vostok and DE08), includes a numerical model that simulates air transport in the firn, and inverse theory. We focus here on atmospheric CH4 reconstruction, but the method can be used to reconstruct

Vincent Rommelaere; Laurent Arnaud; Jean-Marc Barnola

1997-01-01

240

Decompression sickness bubbles: Are gas micronuclei formed on a flat hydrophobic surface?  

Microsoft Academic Search

It is a long-standing hypothesis that the bubbles which evolve as a result of decompression have their origin in stable gas micronuclei lodged in hydrophobic crevices, micelles of surface-active molecules, or tribonucleation. Recent findings supported by atomic force microscopy have indicated that tiny, flat nanobubbles form spontaneously on smooth, hydrophobic surfaces submerged in water. We propose that these nanobubbles may

R. Arieli; A. Marmur

2011-01-01

241

Generation of micro gas bubbles of uniform diameter in an ultrasonic field  

Microsoft Academic Search

Consecutive images of the fragmentation of capillary waves in an ultrasonic field were obtained using a high-speed video camera through a microscope at a frame rate of 500000 frames per second. The images showed that micro bubbles of uniform diameter from 4 to 15mum were generated at a constant periodic rate when a small amount of gas was introduced (via

Toshinori Makuta; Fumio Takemura; Eiji Hihara; Yoichiro Matsumoto; Masahiro Shoji

2006-01-01

242

A Model for the Simultaneous Heterogeneous and Homogeneous Nucleation of Gas Bubbles  

Microsoft Academic Search

Electron microscope observations of cavities in steels have shown that they are often associated with microstructural features as well as occurring randomly in the matrix. Previous theoretical studies of gas bubble nucleation have concentrated on either homogeneous or heterogeneous nucleation. In the present work we extend the homogeneous nucleation rate theory for rare gases in solids to include, for the

M. R. Hayns; M. H. Wood

1979-01-01

243

Field nano-localization of gas bubble production from water electrolysis  

NASA Astrophysics Data System (ADS)

Using a tip shaped electrode and ac voltages, we show that the production of micro bubbles of gas from water electrolysis is localized at the tip apex inside a domain in the voltage frequency phase space. A model taking into account the electrode shape and dimensions explains these results which suggest a field effect control of the electrolysis reaction rate at a nanometer scale.

Hammadi, Z.; Morin, R.; Olives, J.

2013-11-01

244

Single-Gas Bubble Neutron Detectors for Alpha Knock-On Tail Measurements  

Microsoft Academic Search

Measurement of the neutron energy spectrum above ~16 MeV will yield information on the spatial and energy distributions of confined fast alphas in DT tokamaks. Standard two-gas bubble neutron detectors, designed to only detect neutrons with energies above a selectable threshold determined by the gas mixture, were used in preliminary attempts to measure the knock-on neutrons from DT plasmas in

R. K. Fisher; P. B. Parks; A. Belian; E. Morse

1999-01-01

245

Hydrodynamic simulation of methanol synthesis in gas–liquid slurry bubble column reactors  

Microsoft Academic Search

A transient, two-dimensional hydrodynamic model for the production of methanol from syn-gas in an Air Products\\/DOE LaPorte slurry bubble column reactor was developed. The model predicts downflow of catalyst at the walls and oscillatory particle and gas flow at the center, with a frequency of about 0.7H. The computed temperature variation in the reactor with heat exchangers was only about

Yuanxiang Wu; Dimitri Gidaspow

2000-01-01

246

The effect of numerical diffusion on simulation of isolated bubbles in a gas–solid fluidized bed  

Microsoft Academic Search

A two-fluid hydrodynamic model of a two-dimensional gas–solids fluidized bed is used to calculate the shape of an isolated bubble. The calculations are done by applying four different discretization schemes to the convection term. The bubble shape calculated by using the first-order upwind (FOW) scheme is unphysical and pointed, where as the bubble shape calculated by the second-order schemes SMART,

C. Guenther; M. Syamlal

2001-01-01

247

The Experimental Study of Dynamics of Scaled Gas-Filled Bubble Collapse in Liquid  

NASA Astrophysics Data System (ADS)

The article provides results of analyzing special features of the single-bubble sonoluminescence, developing the special apparatus to investigate this phenomenon on a larger-scale basis. Certain very important effects of high energy density physics, i.e. liquid compressibility, shock-wave formation under the collapse of the gas cavity in liquid, shock-wave focusing in the gas-filled cavity, occurrence of hot dense plasma in the focusing area, and high-temperature radiation yield are observed in this phenomenon. Specificity of the process is conditioned by the ``ideal'' preparation and sphericity of the gas-and-liquid contact boundary what makes the collapse process efficient due to the reduced influence of hydrodynamic instabilities. Results of experimental investigations; results of developing the facilities, description of methods used to register parameters of facilities and the system under consideration; analytical estimates how gas-filled bubbles evolve in liquid with the regard for scale effects; results of preliminary 1-D gas dynamic calculations of the gas bubble evolution are presented. The work supported by ISTC Project #2116.

Pavlenko, Alexander

2011-06-01

248

Helium gas bubble trapped in liquid helium in high magnetic field  

NASA Astrophysics Data System (ADS)

High magnetic field magnets are used widely in the area of the condensed matter physics, material science, chemistry, geochemistry, and biology at the National High Magnetic Field Laboratory. New high field magnets of state-of-the-art are being pursued and developed at the lab, such as the current developing 32 T, 32 mm bore fully superconducting magnet. Liquid Helium (LHe) is used as the coolant for superconducting magnets or samples tested in a high magnetic field. When the magnetic field reaches a relatively high value the boil-off helium gas bubble generated by heat losses in the cryostat can be trapped in the LHe bath in the region where BzdBz/dz is less than negative 2100 T2/m, instead of floating up to the top of LHe. Then the magnet or sample in the trapped bubble region may lose efficient cooling. In the development of the 32 T magnet, a prototype Yttrium Barium Copper Oxide coil of 6 double pancakes with an inner diameter of 40 mm and an outer diameter of 140 mm was fabricated and tested in a resistive magnet providing a background field of 15 T. The trapped gas bubble was observed in the tests when the prototype coil was ramped up to 7.5 T at a current of 200 A. This letter reports the test results on the trapped gas bubble and the comparison with the analytical results which shows they are in a good agreement.

Bai, H.; Hannahs, S. T.; Markiewicz, W. D.; Weijers, H. W.

2014-03-01

249

Removal of dichloromethane from waste gas streams using a hybrid bubble column/biofilter bioreactor  

PubMed Central

The performance of a hybrid bubble column/biofilter (HBCB) bioreactor for the removal of dichloromethane (DCM) from waste gas streams was studied in continuous mode for several months. The HBCB bioreactor consisted of two compartments: bubble column bioreactor removing DCM from liquid phase and biofilter removing DCM from gas phase. Effect of inlet DCM concentration on the elimination capacity was examined in the DCM concentration range of 34–359 ppm with loading rates ranged from 2.2 to 22.8 g/m3.h and constant total empty bed retention time (EBRT) of 200 s. In the equal loading rates, the elimination capacity and removal efficiency of the biofilter were higher than the corresponding values of the bubble column bioreactor. The maximum elimination capacity of the HBCB bioreactor was determined to be 15.7 g/m3.h occurred in the highest loading rate of 22.8 g/m3.h with removal efficiency of 69%. The overall mineralization portion of the HBCB bioreactor was in the range of 72-79%. The mixed liquor acidic pH especially below 5.5 inhibited microbial activity and decreased the elimination capacity. Inhibitory effect of high ionic strength was initiated in the mixed liquor electrical conductivity of 12.2 mS/cm. This study indicated that the HBCB bioreactor could benefit from advantages of both bubble column and biofilter reactors and could remove DCM from waste gas streams in a better manner.

2014-01-01

250

Removal of dichloromethane from waste gas streams using a hybrid bubble column/biofilter bioreactor.  

PubMed

The performance of a hybrid bubble column/biofilter (HBCB) bioreactor for the removal of dichloromethane (DCM) from waste gas streams was studied in continuous mode for several months. The HBCB bioreactor consisted of two compartments: bubble column bioreactor removing DCM from liquid phase and biofilter removing DCM from gas phase. Effect of inlet DCM concentration on the elimination capacity was examined in the DCM concentration range of 34-359 ppm with loading rates ranged from 2.2 to 22.8 g/m3.h and constant total empty bed retention time (EBRT) of 200 s. In the equal loading rates, the elimination capacity and removal efficiency of the biofilter were higher than the corresponding values of the bubble column bioreactor. The maximum elimination capacity of the HBCB bioreactor was determined to be 15.7 g/m3.h occurred in the highest loading rate of 22.8 g/m3.h with removal efficiency of 69%. The overall mineralization portion of the HBCB bioreactor was in the range of 72-79%. The mixed liquor acidic pH especially below 5.5 inhibited microbial activity and decreased the elimination capacity. Inhibitory effect of high ionic strength was initiated in the mixed liquor electrical conductivity of 12.2 mS/cm. This study indicated that the HBCB bioreactor could benefit from advantages of both bubble column and biofilter reactors and could remove DCM from waste gas streams in a better manner. PMID:24406056

Abtahi, Mehrnoosh; Naddafi, Kazem; Mesdaghinia, Alireza; Yaghmaeian, Kamyar; Nabizadeh, Ramin; Jaafarzadeh, Nematollah; Rastkari, Noushin; Nazmara, Shahrokh; Saeedi, Reza

2014-01-01

251

Tracer Techniques in Estimating Nuclear Materials Holdup.  

National Technical Information Service (NTIS)

Residual inventory of nuclear materials remaining in processing facilities (holdup) is recognized as an insidious problem for safety of plant operations and safeguarding of special nuclear materials (SNM). This paper reports on an experimental study where...

K. K. S. Pillay

1987-01-01

252

Nucleation stage with nonsteady growth of supercritical gas bubbles in a strongly supersaturated liquid solution and the effect of excluded volume.  

PubMed

An approach to the kinetics of barrier formation of supercritical gas bubbles in a strongly supersaturated liquid solution is presented. A common assumption of uniform reduction of a dissolved gas supersaturation in a liquid solution via stationary diffusion to nucleating gas bubbles is shown to be not applicable to the case of high gas supersaturations. The approach recognizes that the diffusion growth of supercritical bubbles at high gas supersaturation is essentially nonstationary. Nonstationary growth of an individual gas bubble is described by a self-similar solution of the diffusion equation which predicts a renormalized growth rate and thin highly nonuniform diffusion layer around the bubble. The depletion of a dissolved gas due to intake of gas molecules by the bubble occurs only within this thin layer. An integral equation for the total volume of an ensemble of supercritical gas bubbles within a liquid solution is derived. This equation describes the effect of excluding a total volume of the depleted diffusion layers around the growing bubbles nucleated at all previous moments of time until nucleation of new bubbles ceases due to elimination of the nondepleted volume of the solution. An analytical solution of this equation is found. The swelling of the liquid solution, the number of gas bubbles nucleated, the distribution function of bubbles in their sizes, and the mean radius of the bubbles are determined in their dependence on time. PMID:20365136

Kuchma, Anatoly E; Kuni, Fedor M; Shchekin, Alexander K

2009-12-01

253

Temperature and dose dependence of fission-gas-bubble swelling in U 3Si 2  

NASA Astrophysics Data System (ADS)

Large fission gas bubbles were observed during metallographic examination of an irradiated U 3Si 2 dispersion fuel plate (U0R040) in the Advanced Test Reactor (ATR). The fuel temperature of this plate was higher than for most of the previous silicide-fuel tests where much smaller bubble growth was observed. The apparent conditions for the large bubble growth are high fission density (6.1 × 10 21 f/cm 3) and high fuel temperature (life-average 160 °C). After analysis of PIE results of U0R040 and previous ANL test plates, a modification to the existing athermal bubble growth model appears to be necessary for high temperature application (above 130 °C). A detailed analysis was performed using a model for the irradiation-induced viscosity of binary alloys to explain the effect of the increased fuel temperature. Threshold curves are proposed in terms of fuel temperature and fission density above which formation and interconnection of bubbles larger than 5 ? are possible.

Kim, Yeon Soo; Hofman, G. L.; Rest, J.; Robinson, A. B.

2009-06-01

254

Kinetics of the formation of gas bubbles during polarization of copper and graphite electrodes in electrolytic aqueous solutions  

Microsoft Academic Search

The adsorption and kinetic processes of the formation of gas bubbles passivating the surface during polarization of copper\\u000a and graphite electrodes in 1% aqueous solution of sulfuric acid have been investigated. Three stages of the process related\\u000a to the recharging of the double electric layer—adsorption accumulation of the gas escaping from the surface, the critical\\u000a nucleation of the gas bubbles,

A. M. Orlov; I. O. Yavtushenko; M. V. Churilov

2010-01-01

255

A Mathematical Model of Diffusion-Limited Gas Bubble Dynamics in Tissue with Varying Diffusion Region Thickness  

NASA Technical Reports Server (NTRS)

A three-region mathematical model of gas bubble dynamics has been shown suitable for describing diffusion-limited dynamics of more than one bubble in a given volume of extravascular tissue. The model is based on the dynamics of gas exchange between a bubble and a well-stirred tissue region through an intervening unperfused diffusion region previously assumed to have constant thickness and uniform gas diffusivity. As a result, the gas content of the diffusion region remains constant as the volume of the region increases with bubble growth, causing dissolved gas in the region to violate Henry's law. Earlier work also neglected the relationship between the varying diffusion region volume and the fixed total tissue volume, because only cases in which the diffusion region volume is a small fraction of the overall tissue volume were considered. We herein extend the three-region model to correct these theoretical inconsistencies by allowing both the thickness and gas content of the diffusion region to vary during bubble evolution. A postulated difference in gas diffusivity between an infinitesimally thin layer at the bubble surface and the remainder of the diffusion region leads to variation in diffusion region gas content and thickness during bubble growth and resolution. This variable thickness, differential diffusivity (VTDD) model can yield bubble lifetimes considerably longer than those yielded by earlier three-region models for given model and decompression parameters, and meets a need for theoretically consistent but relatively simple bubble dynamics models for use in studies of decompression sickness (DCS) in human subjects, Keywords: decompression sickness, gas diffusion in tissue, diffusivity

Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.; Paloski, William H. (Technical Monitor)

2000-01-01

256

Simultaneous measurement of gas hold-up and mass transfer coefficient by tracer dynamic technique in “Emulsair” reactor with an emulsion-venturi distributor  

Microsoft Academic Search

Hydrodynamics and gas–liquid mass transfer have been investigated in an “Emulsair” reactor with cocurrent downflow of gas and liquid. This consists of a cylindrical tank with conical bottom topped by an emulsion-venturi as the gas–liquid distributor in which the gas is self-aspired by action of the kinetic energy of the liquid recirculation. An original tracer dynamic technique using the CO2–N2\\/water

B. Gourich; M. Belhaj Soulami; A. Zoulalian; M. Ziyad

2005-01-01

257

Iodine Mass Transfer from Xenon-Iodine Mixed Gas Bubble to Liquid Sodium Pool, (II) Development of Analytical Model  

Microsoft Academic Search

Iodine mass transfer in a xenon-iodine mixed gas bubble rising through a liquid sodium pool is analyzed on the basis of a diffusion model applied to the first short stage just after the bubble generation and a convection model applied to the successive stage. In the diffusion model, production of sodium iodide aerosols and generation of the heat caused by

Shinya MIYAHARA; Norihiko SAGAWA

1996-01-01

258

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE FIELD APPROACH  

Microsoft Academic Search

In this paper, we study the nucleation and growth of gas bubbles in a Newtonian fluid. We employ a general energetic variational formulation with a phase-field method, and compare the analytical and numerical predictions of this new formulation with those of classical models. The new approach allows the study of bubble nucleation, growth and coalescence in a unified framework, and

AARON NABER; CHUN LIU; JAMES J. FENG

259

Compositional Discrimination of Decompression and Decomposition Gas Bubbles in Bycaught Seals and Dolphins  

PubMed Central

Gas bubbles in marine mammals entangled and drowned in gillnets have been previously described by computed tomography, gross examination and histopathology. The absence of bacteria or autolytic changes in the tissues of those animals suggested that the gas was produced peri- or post-mortem by a fast decompression, probably by quickly hauling animals entangled in the net at depth to the surface. Gas composition analysis and gas scoring are two new diagnostic tools available to distinguish gas embolisms from putrefaction gases. With this goal, these methods have been successfully applied to pathological studies of marine mammals. In this study, we characterized the flux and composition of the gas bubbles from bycaught marine mammals in anchored sink gillnets and bottom otter trawls. We compared these data with marine mammals stranded on Cape Cod, MA, USA. Fresh animals or with moderate decomposition (decomposition scores of 2 and 3) were prioritized. Results showed that bycaught animals presented with significantly higher gas scores than stranded animals. Gas composition analyses indicate that gas was formed by decompression, confirming the decompression hypothesis.

Bernaldo de Quiros, Yara; Seewald, Jeffrey S.; Sylva, Sean P.; Greer, Bill; Niemeyer, Misty; Bogomolni, Andrea L.; Moore, Michael J.

2013-01-01

260

Lagrangian coherent structures analysis of gas-liquid flow in a bubble column  

NASA Astrophysics Data System (ADS)

The objective of this paper is to apply a new identifying method to investigating the gas-liquid two-phase flow behaviors in a bubble column with air injected into water. In the numerical simulations, the standard k-? turbulence model is employed to describe the turbulence phenomenon occurring in the continuous fluid. The Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures (LCS) are applied to analyze the vortex structures in multiphase flow. Reasonable agreements are obtained between the numerical and experimental data. The numerical results show that the evolution of gas-liquid in the column includes initial and periodical developing stages. During the initial stage, the bubble hose is forming and extending along the vertical direction with the vortex structures formed symmetrically. During the periodical developing stage, the bubble hose starts to oscillate periodically, and the vortexes move along the bubble hose to the bottom of column alternately. Compared to the Euler-system-based identification criterion of a vortex, the FTLE field presents the boundary of a vortex without any threshold defined and the LCS represents the divergence extent of infinite neighboring particles. During the initial stage, the interfaces between the forward and backward flows are highlighted by the LCS. As for the periodical developing stage, the LCS curls near the vortex centers, providing a method of analyzing a flow field from a dynamical system perspective.

Wu, Qin; Wang, GuoYu; Huang, Biao; Bai, ZeYu

2014-04-01

261

Lagrangian coherent structures analysis of gas-liquid flow in a bubble column  

NASA Astrophysics Data System (ADS)

The objective of this paper is to apply a new identifying method to investigating the gas-liquid two-phase flow behaviors in a bubble column with air injected into water. In the numerical simulations, the standard k- ? turbulence model is employed to describe the turbulence phenomenon occurring in the continuous fluid. The Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures (LCS) are applied to analyze the vortex structures in multiphase flow. Reasonable agreements are obtained between the numerical and experimental data. The numerical results show that the evolution of gas-liquid in the column includes initial and periodical developing stages. During the initial stage, the bubble hose is forming and extending along the vertical direction with the vortex structures formed symmetrically. During the periodical developing stage, the bubble hose starts to oscillate periodically, and the vortexes move along the bubble hose to the bottom of column alternately. Compared to the Euler-system-based identification criterion of a vortex, the FTLE field presents the boundary of a vortex without any threshold defined and the LCS represents the divergence extent of infinite neighboring particles. During the initial stage, the interfaces between the forward and backward flows are highlighted by the LCS. As for the periodical developing stage, the LCS curls near the vortex centers, providing a method of analyzing a flow field from a dynamical system perspective.

Wu, Qin; Wang, GuoYu; Huang, Biao; Bai, ZeYu

2014-06-01

262

Gas Bubble Trauma Monitoring and Research of Juvenile Salmonids, 1994-1995 Progress Report.  

SciTech Connect

This report describes laboratory and field monitoring studies of gas bubble trauma (GBT) in migrating juvenile salmonids in the Snake and Columbia rivers. The first chapter describes laboratory studies of the progression of GBT signs leading to mortality and the use of the signs for GBT assessment. The progression and severity of GBT signs in juvenile salmonids exposed to different levels of total dissolved gas (TDG) and temperatures was assessed and quantified. Next, the prevalence, severity, and individual variation of GBT signs was evaluated to attempt to relate them to mortality. Finally, methods for gill examination in fish exposed to high TDG were developed and evaluated. Primary findings were: (1) no single sign of GBT was clearly correlated with mortality, but many GBT signs progressively worsened; (2) both prevalence and severity of GBT signs in several tissues is necessary; (3) bubbles in the lateral line were the earliest sign of GBT, showed progressive worsening, and had low individual variation but may develop poorly during chronic exposures; (4) fin bubbles had high prevalence, progressively worsened, and may be a persistent sign of GBT; and (5) gill bubbles appear to be the proximate cause of death but may only be relevant at high TDG levels and are difficult to examine. Chapter Two describes monitoring results of juvenile salmonids for signs of GBT. Emigrating fish were collected and examined for bubbles in fins and lateral lines. Preliminary findings were: (1) few fish had signs of GBT, but prevalence and severity appeared to increase as fish migrated downstream; (2) there was no apparent correlation between GBT signs in the fins, lateral line, or gills; (3) prevalence and severity of GBT was suggestive of long-term, non-lethal exposure to relatively low level gas supersaturated water; and (4) it appeared that GBT was not a threat to migrating juvenile salmonids. 24 refs., 26 figs., 3 tabs.

Hans, Karen M.

1997-07-01

263

Coated gas bubbles for the continuous synthesis of hollow inorganic particles.  

PubMed

We present a microfluidic approach for the controlled encapsulation of individual gas bubbles in micrometer-diameter aqueous droplets with high gas volume fractions and demonstrate this approach to making a liquid shell, which serves as a template for the synthesis of hollow inorganic particles. In particular, we find that an increase in the viscosity of the aqueous phase facilitates the encapsulation of individual gas bubbles in an aqueous droplet and allows control of the thickness of a thin aqueous shell. Furthermore, because such droplets contain a finite amount of water, uncontrolled hydrolysis reactions between reactive inorganic precursors and bulk water can be avoided. We demonstrate this approach by introducing reactive inorganic precursors, such as silane and titanium butoxide, for sol-gel reactions downstream from the formation of the bubble in a droplet and consequently fabricate hollow particles of silica or titania in one continuous flow process. These approaches provide a route to controlling double-emulsion-type gas-liquid microstructures and offer a new fabrication method for thin-shell-covered microbubbles and hollow microparticles. PMID:22129137

Wan, Jiandi; Stone, Howard A

2012-01-10

264

Shock waves in water with Freon-12 bubbles and formation of gas hydrates  

NASA Astrophysics Data System (ADS)

The evolution of a shock wave and its reflection from a wall in a gas-liquid medium with dissolution and hydration are experimentally investigated. Dissolution and hydration behind the front of a moderate-amplitude shock wave are demonstrated to be caused by fragmentation of gas bubbles, resulting in a drastic increase in the area of the interphase surface and in a decrease in size of gas inclusions. The mechanisms of hydration behind the wave front are examined. Hydration behind the front of a shock wave with a stepwise profile is theoretically analyzed.

Dontsov, V. E.; Nakoryakov, V. E.; Chernov, A. A.

2007-05-01

265

A Philippinite with an Unusually Large Bubble: Gas Pressure and Noble Gas Composition  

Microsoft Academic Search

Bubbles are common in tektites, but usually their sizes range up to only a few mm. They are most abundant in Muong Nong-type tektites. The gases contained in these bubbles are of terrestrial atmospheric composition, with pressures below 1 atm (e.g., [1]). The abundances of light noble gases (He, Ne) are controlled by diffusion from the atmosphere [2], and noble

J. Matsuda; T. Maruoka; D. L. Pinti; C. Koeberl

1995-01-01

266

IR dust bubbles: gas, dust and star formation in the S21-S24 complex  

NASA Astrophysics Data System (ADS)

Churchwell et al. (2006) identified many IR dust bubbles in the GLIMPSE images at 8 ?m. Among these bubbles, S21, S22, S23, and S24 conform a poorly studied complex plenty of small scale bubbles, with IRDCs and signposts of recent star formation, located at about 4.5 kpc. Based on 12CO(2-1), 13CO(2-1), and 13CO(3-2) line observations obtained with the APEX telescope (angular resolution of 20"-30"), LABOCA continuum observations at 870 ?m (angular resolution of 18.5") also from APEX, Spitzer-IRAC and -MIPS images in the near and mid IR (3.6 to 24 ?m, and Herschel-PACS and -SPIRE images in the far infrared (70-500 ?m), we performed an analysis of the characteristics of the gas and dust in this high density complex. This study allowed molecular shells linked to these bubbles to be revealed, and to estimate new distances, excitation conditions, masses, and ambient densities. Cold dust counterparts were revealed by Herschel and LABOCA images, showing the material available for new generations of stars. In addition to the presence of EGOs and methanol masers, a search for young stellar objets in the complex using the available data at several wavelengths in the infrared revealed many active areas of star formation coincident with the densest regions. We compare our results with those for other IR dust bubbles and investigate the possibility that the expansion of the bubbles has triggered the star formation activity.

Cappa, E. C.; Romero, A. G.; Vasquez, J.; Firpo, V.; Dorunea, N.; Rubio, M.; Kobilnicky, C.

2013-06-01

267

Perturbed breakup of air bubbles in water: Memory, gas flow, and coalescence  

NASA Astrophysics Data System (ADS)

The pinch-off of an air bubble from an underwater nozzle ends in a singularity with a remarkable sensitivity to a variety of perturbations. I report on experiments that break both the axial (i.e., vertical) and azimuthal symmetry of the singularity formation. The density of the inner gas influences the axial asymmetry of the neck near pinch-off. For denser gases, flow through the neck late in collapse changes the pinch-off dynamics. Gas density is also implicated in the formation of satellite bubbles. The azimuthal shape oscillations described by Schmidt et al., can be initiated by anisotropic boundary conditions in the liquid as well as with an asymmetric nozzle shape. I measure the n = 3 oscillatory mode, and observe the nonlinear, highly three-dimensional outcomes of pinch-off with large azimuthal perturbations. These are consistent with prior theory.

Keim, Nathan C.

268

The concentration distribution around a growing gas bubble in a bio tissue under the effect of suction process.  

PubMed

The concentration distribution around a growing nitrogen gas bubble in the blood and other bio tissues of divers who ascend to surface too quickly is obtained by Mohammadein and Mohamed model (2010) for variant and constant ambient pressure through the decompression process. In this paper, the growing of gas bubbles and concentration distribution under the effect of suction process are studied as a modification of Mohammadein and Mohamed model (zero suction). The growth of gas bubble is affected by ascent rate, tissue diffusivity, initial concentration difference, surface tension and void fraction. Mohammadein and Mohamed model (2010) is obtained as a special case from the present model. Results showed that, the suction process activates the systemic blood circulation and delay the growth of gas bubbles in the bio tissues to avoid the incidence of decompression sickness (DCS). PMID:24813454

Mohammadein, S A

2014-07-01

269

Ebullition of biogenic gas bubbles from samples of near-surface peat.  

NASA Astrophysics Data System (ADS)

There is evidence that peat soils are not water-saturated below the water table (e.g. Rosenberry et al. 2003; Baird and Waldron, 2003), owing to accumulations of biogenic gas bubbles, consisting of poorly-soluble gases such as CH4. It has been shown that gas bubbles can block pores and reduce rates of water flow in peat soils (Baird and Waldron, 2003). It has also been shown that, beyond certain levels, biogenic gas bubble accumulations become unstable, giving rise to large but episodic ebullition events, and that ebullition may be an important mechanism of CH4 transfer between peat soils and the atmosphere (e.g. Romanowicz et al., 1995; Rosenberry et al., 2003). However, the studies that have been done on ebullition have looked at relatively deep peat where the bubbles were apparently held below a confining layer of low hydraulic conductivity. Very little is known about the degree to which gas bubbles accumulate in near-surface peat (i.e. the upper 40 cm) and whether they accumulate to such an extent that ebullition and transfer of carbon gases to the atmosphere occur. To address this lack of knowledge we conducted experiments on eight `undisturbed' samples of near-surface (depths of c. 8 cm to 30 cm) peat taken from two lowland raised bogs, one in SW Scotland and one in W Wales. The samples were c. 10 l in volume and were incubated at 12 deg. C with the water table maintained above the sample surface. Water was allowed to flow through the samples periodically for the measurement of hydraulic conductivity (not reported here). Gas traps were fitted to the tops of the samples and the volume of gas in these was measured c. every 2-3 days. Finally, the samples were fitted with TDR probes and gas permeation samplers to measure gas volume and to take gas samples for the measurement of gas content (CH4 and CO2) using a GC. Ebullition was recorded in every sample but only after a build up of biogenic gas bubbles had occurred. We found that ebullition was not episodic and that it appeared to match gas production. The amount of ebullition varied substantially between samples. In two samples from the Scottish bog consisting respectively of Sphagnum papillosum and S. magellanicum litter, over 400 ml of gas per sample was lost over a 90-day period. At the other extreme, virtually no ebullition occurred from one of the Welsh peat samples, with only 14.5 ml being lost in 125 days. Provisional calculations based on CH4 concentrations in our gas permeation samplers suggest that CH4 efflux from the peatland surface via ebullition is potentially as important as that via diffusional transfer. We consider how transportable our data are to field conditions.

Baird, A.; Waldron, S.

2004-05-01

270

Bubble dielectrophoresis  

Microsoft Academic Search

The force due to polarization exerted on dielectric particles, vapor or gas bubbles, and voids in insulating dielectric liquids is an example of dielectrophoresis. This force is directly proportional to the gradient of the electric field intensity. Bubbles and voids are attracted into regions of lower electric field intensity, while dielectric particles (with higher relative polarizability) are attracted into regions

T. B. Jones; G. W. Bliss

1977-01-01

271

Proteomics of Juvenile Senegal Sole ( Solea senegalensis ) Affected by Gas Bubble Disease in Hyperoxygenated Ponds  

Microsoft Academic Search

Solea senegalensis is a commercial flat fish traditionally farmed in earth ponds in coastal wetlands that might also become important to more\\u000a intensive aquaculture. Gas bubble disease (GBD) is a potential risk for outdoor fish farming, particularly in certain periods\\u000a of the year, related to improper management leading to macroalgae blooms. Physical-chemical conditions inducing hyperoxia,\\u000a including radiation, temperature, and high

E. Salas-Leiton; B. Cánovas-Conesa; R. Zerolo; J. López-Barea; J. P. Cañavate; J. Alhama

2009-01-01

272

Radiation-generated prismatic loops around gas bubbles in alumnium-lithium alloy  

Microsoft Academic Search

Prismatic dislocation loops were observed to emanate from a gas bubble in neutron-irradiated aluminum-lithium alloy during electron irradiation at 200°C in a 200 kV electron microscope. The loops aligned in the ?110? directions were analysed to be vacancy loops on ?111? plane with a\\/2 ?110? Burgers vector. In a 1000 kV electron microscope, the prismatic punching were observed to occur

K. Shiraishi; A. Hishinuma; Y. Katano

1974-01-01

273

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

Microsoft Academic Search

An analytical model for the nucleation and growth of intra and intergranular fission-gas bubbles is used to characterize fission-gas bubble development in low-enriched U–Mo alloy fuel irradiated in the advanced test reactor in Idaho as part of the Reduced Enrichment for Research and Test Reactor (RERTR) program. Fuel burnup was limited to less than ?7.8 at.% U in order to

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

2009-01-01

274

A horizontal packed-bed bioreactor to reduce CO 2 gas holdup in the continuous production of ethanol by immobilized yeast cells  

Microsoft Academic Search

Summary  CO2 gas, evolved during alcohol fermentation using immobilized yeast, causes several undesirable problems in a packed-bed bioreactor\\u000a installed vertically as it increases the dead space and causes hydrostatic pressure. In order to reduce this “CO2 gas phase effect” which lowers the efficiency of ethanol production, a shallow, horizontal packed-bed bioreactor has been\\u000a developed with a free space above the gel

Takeshi Shiotani; Tsuneo Yamané

1981-01-01

275

Mass Transfer from Gas Bubbles to Impinging Flow of Biological Fluids with Chemical Reaction  

PubMed Central

The rates of mass transfer from a gas bubble to an impinging flow of a biological fluid such as whole blood and plasma are investigated analytically and experimentally. Gases commonly found dissolved in body fluids are included. Consideration is given to the effects of the chemical reaction between the dissolved gas and the liquid on the rate of mass transfer. Through the application of boundary layer theory the over-all transfer is found to be Sh/(Re)1/2 = 0.845 Sc1/3 in the absence of chemical reaction, and Sh/(Re) 1/2 = F? (0) in the presence of chemical reaction, where Sh, Re, and Sc are the Sherwood, Reynolds, and Schmidt numbers, respectively, and F? (0) is a function of Sc and the dimensionless reaction rate constant. Analytical results are also obtained for the bubble lifetime and the bubble radius-time history. These results, which are not incompatible with experimental results, can be applied to predict the dissolution of the entrapped gas emboli in the circulatory system of the human body.

Yang, Wen-Jei; Echigo, R.; Wotton, D. R.; Ou, J. W.; Hwang, J. B.

1972-01-01

276

Shock-induced collapse of a gas bubble in shockwave lithotripsy  

PubMed Central

The shock-induced collapse of a pre-existing nucleus near a solid surface in the focal region of a lithotripter is investigated. The entire flow field of the collapse of a single gas bubble subjected to a lithotripter pulse is simulated using a high-order accurate shock- and interface-capturing scheme, and the wall pressure is considered as an indication of potential damage. Results from the computations show the same qualitative behavior as that observed in experiments: a re-entrant jet forms in the direction of propagation of the pulse and penetrates the bubble during collapse, ultimately hitting the distal side and generating a water-hammer shock. As a result of the propagation of this wave, wall pressures on the order of 1 GPa may be achieved for bubbles collapsing close to the wall. The wall pressure decreases with initial stand-off distance and pulse width and increases with pulse amplitude. For the stand-off distances considered in the present work, the wall pressure due to bubble collapse is larger than that due to the incoming shockwave; the region over which this holds may extend to ten initial radii. The present results indicate that shock-induced collapse is a mechanism with high potential for damage in shockwave lithotripsy.

Johnsen, Eric; Colonius, Tim

2008-01-01

277

Methanotrophic microbial communities associated with bubble plumes above gas seeps in the Black Sea  

NASA Astrophysics Data System (ADS)

Bubbles evolving from active gas seeps can be traced by hydroacoustic imaging up to 1000 m high in the Black Sea water column. Although methane concentrations are not distinguishable between the water column above the deep seep and reference sites, atmospheric noble gas measurements clearly show the constant input of gases (mainly methane) via seepage into the Black Sea. Archaea (ANME-1, ANME-2) and methanotrophic bacteria detected with specific 16S rRNA-targeted oligonucleotide probes are related to active gas seeps in the oxic and anoxic water column. It is suggested that methane seeps have a much greater influence on the Black Sea methane budget than previously acknowledged and that ANME-1 and ANME-2 are injected via gas bubbles from the sediment into the anoxic water column mediating methane oxidation. Our results show further that only minor amounts of methane evolving from Black Sea gas seeps reach the atmosphere due to the very effective microbial barrier. Hence only major thermodynamically and/or tectonically triggered gas hydrate dissociation has the potential to induce rapid climate changes as suggested by the "clathrate gun hypothesis."

Schubert, Carsten J.; Durisch-Kaiser, Edith; Holzner, Christian P.; Klauser, Lucia; Wehrli, Bernhard; Schmale, Oliver; Greinert, Jens; McGinnis, Daniel F.; de Batist, Marc; Kipfer, Rolf

2006-04-01

278

Single-Gas Bubble Neutron Detectors for Alpha Knock-On Tail Measurements  

NASA Astrophysics Data System (ADS)

Measurement of the neutron energy spectrum above ~16 MeV will yield information on the spatial and energy distributions of confined fast alphas in DT tokamaks. Standard two-gas bubble neutron detectors, designed to only detect neutrons with energies above a selectable threshold determined by the gas mixture, were used in preliminary attempts to measure the knock-on neutrons from DT plasmas in TFTR and JET. Subsequent measurements at accelerator neutron sources showed an unexpected below-threshold detector response that prevented observations of the alpha-induced neutron tails. Spontaneous bubble nucleation measurements show that this below-threshold response is due to slight variations in the gas mixture, and is not present in single-gas detectors. Single-gas detectors will be tested at Ohio University and at UC Berkeley to determine the neutron energy threshold as a function of detector operating temperature, and to confirm the lack of a below-threshold response. An array of single-gas detectors operating at different temperatures should allow measurements of the alpha knock-on neutron tail during the planned DTE2 experiments on JET.

Fisher, R. K.; Parks, P. B.; Belian, A.; Morse, E.

1999-11-01

279

Lateral line pore diameters correlate with the development of gas bubble trauma signs in several Columbia River fishes  

USGS Publications Warehouse

Gas bubble trauma (GBT) caused by gas supersaturation of river water continues to be a problem in the Columbia River Basin. A common indicator of GBT is the percent of the lateral line occluded with gas bubbles; however, this effect has never been examined in relation to lateral line morphology. The effects of 115, 125 and 130% total dissolved gas levels were evaluated on five fish species common to the upper Columbia River. Trunk lateral line pore diameters differed significantly (Plargescale sucker>northern pikeminnow???chinook salmon???redside shiner). At all supersaturation levels evaluated, percent of lateral line occlusion exhibited an inverse correlation to pore size but was not generally related to total dissolved gas level or time of exposure. This study suggests that the differences in lateral line pore diameters between species should be considered when using lateral line occlusion as an indicator of gas bubble trauma. ?? 2003 Elsevier Science Inc. All rights reserved.

Morris, R. G.; Beeman, J. W.; VanderKooi, S. P.; Maule, A. G.

2003-01-01

280

Nucleation stage with nonsteady growth of supercritical gas bubbles in a strongly supersaturated liquid solution and the effect of excluded volume  

Microsoft Academic Search

An approach to the kinetics of barrier formation of supercritical gas bubbles in a strongly supersaturated liquid solution is presented. A common assumption of uniform reduction of a dissolved gas supersaturation in a liquid solution via stationary diffusion to nucleating gas bubbles is shown to be not applicable to the case of high gas supersaturations. The approach recognizes that the

Anatoly E. Kuchma; Fedor M. Kuni; Alexander K. Shchekin

2009-01-01

281

Aerobic exercise before diving reduces venous gas bubble formation in humans.  

PubMed

We have previously shown in a rat model that a single bout of high-intensity aerobic exercise 20 h before a simulated dive reduces bubble formation and after the dive protects from lethal decompression sickness. The present study investigated the importance of these findings in man. Twelve healthy male divers were compressed in a hyperbaric chamber to 280 kPa at a rate of 100 kPa min(-1) breathing air and remaining at pressure for 80 min. The ascent rate was 9 m min(-1) with a 7 min stop at 130 kPa. Each diver underwent two randomly assigned simulated dives, with or without preceding exercise. A single interval exercise performed 24h before the dive consisted of treadmill running at 90% of maximum heart rate for 3 min, followed by exercise at 50% of maximum heart rate for 2 min; this was repeated eight times for a total exercise period of 40 min. Venous gas bubbles were monitored with an ultrasonic scanner every 20 min for 80 min after reaching surface pressure. The study demonstrated that a single bout of strenuous exercise 24h before a dive to 18 m of seawater significantly reduced the average number of bubbles in the pulmonary artery from 0.98 to 0.22 bubbles cm(-2)(P= 0.006) compared to dives without preceding exercise. The maximum bubble grade was decreased from 3 to 1.5 (P= 0.002) by pre-dive exercise, thereby increasing safety. This is the first report to indicate that pre-dive exercise may form the basis for a new way of preventing serious decompression sickness. PMID:14755001

Dujic, Zeljko; Duplancic, Darko; Marinovic-Terzic, Ivana; Bakovic, Darija; Ivancev, Vladimir; Valic, Zoran; Eterovic, Davor; Petri, Nadan M; Wisløff, Ulrik; Brubakk, Alf O

2004-03-16

282

The Holdup Measurement System II (HMSII)  

SciTech Connect

A project is in progress that addresses two of problems with existing holdup measurement technology; the need for compact instrumentation and a more efficient means of reducing the massive amounts of data to quantities of Special Nuclear Materials (SNM). The approach taken by the project utilizes the Miniature Modular MultiChannel Analyzer (M{sup 3}CA) a complete and truly portable gamma-ray spectroscopy system, under development at Los Alamos National Laboratory. The hardware is then integrated and automated by the Holdup Measurement System II (HMSII) software being developed by the Oak Ridge Y-12 Plant. Together they provide the hardware components, measurement control in the field, automated data acquisition, data storage and manipulation which simplify holdup measurements.

Finch, T.L.; Gibson, J.S.; Smith, S.E. [Oak Ridge Y-12 Plant, TN (United States); Halbig, J.K.; Klosterbuer, S.F.; Russo, P.A.; Siebelist, R.; Sprinkle, J.K. Jr. [Los Alamos National Lab., NM (United States)

1994-10-04

283

Electrical-Impedance Tomography Measurements of Gas Distribution in a Bubble Column  

NASA Astrophysics Data System (ADS)

Electrical-impedance tomography (EIT) has been successfully used to measure gas distribution in a bubble column. The bubble column is a lexan tube (19-cm diameter) filled with salt water into which air is injected at the bottom. The EIT system employs 16 strip electrodes (7.62-cm length, 0.635-cm width) flush-mounted at equal azimuthal intervals around the inner perimeter of the column. Gamma-densitometry tomography (GDT) is also used to measure the gas distribution for comparison purposes. Five gas superficial velocities were examined: 1.5, 2.9, 4.4, 5.8, and 8.8 cm/s. For every flow rate, EIT and GDT yielded nearly identical gas-volume-fraction profiles even for the strong radial variations that were observed (for example, gas volume fractions of 0.05 at the wall and 0.25 at the axis for 8.8 cm/s). The close agreement between EIT and GDT enables EIT to be used for fast, inexpensive, quantitative measurements of material distribution in two-phase flows and, in combination with GDT, measurements of material distribution in three-phase flows. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Torczynski, J. R.; Shollenberger, K. A.; O'Hern, T. J.; George, D. L.; Ceccio, S. L.

1998-11-01

284

Kinetics of CH4 and CO2 hydrate dissociation and gas bubble evolution via MD simulation.  

PubMed

Molecular dynamics simulations of gas hydrate dissociation comparing the behavior of CH4 and CO2 hydrates are presented. These simulations were based on a structurally correct theoretical gas hydrate crystal, coexisting with water. The MD system was first initialized and stabilized via a thorough energy minimization, constant volume-temperature ensemble and constant volume-energy ensemble simulations before proceeding to constant pressure-temperature simulations for targeted dissociation pressure and temperature responses. Gas bubble evolution mechanisms are demonstrated as well as key investigative properties such as system volume, density, energy, mean square displacements of the guest molecules, radial distribution functions, H2O order parameter, and statistics of hydrogen bonds. These simulations have established the essential similarities between CH4 and CO2 hydrate dissociation. The limiting behaviors at lower temperature (no dissociation) and higher temperature (complete melting and formation of a gas bubble) have been illustrated for both hydrates. Due to the shift in the known hydrate stability curves between guest molecules caused by the choice of water model as noted by other authors, the intermediate behavior (e.g., 260 K) showed distinct differences however. Also, because of the more hydrogen-bonding capability of CO2 in water, as reflected in its molecular parameters, higher solubility of dissociated CO2 in water was observed with a consequence of a smaller size of gas bubble formation. Additionally, a novel method for analyzing hydrate dissociation based on H-bond breakage has been proposed and used to quantify the dissociation behaviors of both CH4 and CO2 hydrates. Activation energies Ea values from our MD studies were obtained and evaluated against several other published laboratory and MD values. Intrinsic rate constants were estimated and upscaled. A kinetic reaction model consistent with macroscale fitted kinetic models has been proposed to indicate the macroscopic consequences of this analysis. PMID:24571292

Uddin, M; Coombe, D

2014-03-20

285

Acoustic emission associated with the bursting of a gas bubble at the free surface of a non-Newtonian fluid  

NASA Astrophysics Data System (ADS)

We report experimental measurements of the acoustic emission associated with the bursting of a gas bubble at the free surface of a non-Newtonian fluid. On account of the viscoelastic properties of the fluid, the bubble is generally elongated. The associated frequency and duration of the acoustic signal are discussed with regard to the shape of the bubble and successfully accounted for by a simple linear model. The acoustic energy exhibits a high sensitivity to the dynamics of the thin film bursting, which demonstrates that, in practice, it is barely possible to deduce from the acoustic measurements the total amount of energy released by the event. Our experimental findings provide clues for the understanding of the signals from either volcanoes or foams, where one observes respectively, the bursting of giant bubbles at the free surface of lava and bubble bursting avalanches.

Divoux, T.; Vidal, V.; Melo, F.; Géminard, J.-C.

2008-05-01

286

The Effect of Viscosity on the Spherical Stability of Oscillating Gas Bubbles  

NASA Technical Reports Server (NTRS)

Gas bubbles driven in radial oscillations are subject to an instability of the spherical shape that is opposed by surface tension and viscosity. An exact linear formulation for the study of the phenomenon has been available for many years, but its complexity has discouraged a detailed investigation. With the recent theory of sonoluminescence of Lohse and co-workers, there has been a renewed interest in the problem and new data have become available. This paper presents a numerical method for the solution of the pertinent equations and compares the theory with these new data. The coupling of the strong nonlinearity of the bubble radial oscillations with the parametric mechanism of the surface instability results in a very complex structure for the stability boundary. Nevertheless, a good agreement between theory and data is found. A comparison with earlier approximate models is also made.

Hao, Y.; Prosperetti, A.

1999-01-01

287

Feasibility study of using microfluidic platforms for visualizing bubble flows in electrolyzer gas diffusion layers  

NASA Astrophysics Data System (ADS)

In this study, microfluidic platforms were used to visualize air bubble transport in two-dimensional (2D) representations of gas diffusion layers (GDLs) to gain insight into how the geometric features of the GDL impact multiphase flow in polymer electrolyte membrane (PEM) electrolyzers. Two-dimensional porous networks were designed using volumetric pore space information, including average porosity and average throat size obtained from micro-computed tomography (micro CT) visualizations. Microfluidic chips were fabricated to represent felt, sintered powder, and foam GDLs and used to simulate the transfer of oxygen bubbles generated at the catalyst layer, through the GDL towards the flow channels of a PEM electrolyzer. The results of this work indicate that the use of microfluidic platforms for evaluating PEM electrolyzer GDLs is highly promising.

Arbabi, F.; Kalantarian, A.; Abouatallah, R.; Wang, R.; Wallace, J. S.; Bazylak, A.

288

Free gas bubbles in the hydrate stability zone: evidence from CT investigation under in situ conditions  

NASA Astrophysics Data System (ADS)

Determination of the internal structures and the fabric of natural marine gas hydrate as well as its distribution in shallow subseafloor depth was restricted because of dissociation during recovery. Investigation under in situ conditions becomes possible with a pressure coring device. The newly developed MultiAutoclaveCorer (MAC) can take up to four cores which are housed in a pressure vessel called LabTransferChamber (LTC), which is compatible with CT imaging technology. During a video-guided deployment on Hydrate Ridge, a well known near-surface gas hydrate-rich environment, two LTCs were filled and recovered under pressure. CT imaging was performed four days after retrieval in a medical clinic in Palo Alto/Ca., a second round was run 2 months later in Kiel/Germany, still under pressure. The same type of scanner was used for both rounds of imaging. The function and the pressure preserving capability of the MAC was confirmed. Although only 0.8 m apart, both cores showed different gas hydrate contents, varying between a maximum of 5 vol-% in LTC 3 and 48 vol-% in LTC 4, documenting the high variability of gas hydrate occurrences in near-surface sediments. The uppermost layer of gas hydrate was observed 0.1 m below the seafloor. The high gas hydrate content in LTC 4 is concentrated in a horizon between 0.28 and 0.32 m subseafloor depth. Within this hoizon a significant quantity of bubbles was detected with a free gas content of up to 2.4 vol-%. Bubble sizes reach a maximum of 1.8 x 10-2 m in either x, y or z direction. Integrating across the mentioned core interval, the gas hydrate content is 19 vol-% and the free gas content is 0.8 vol-%. Assuming several simplifications, the normalised calculated methane volume of the gas hydrate is 9.15 x 10-3 m^3 and the amount of methane in the bubbles is 1.49 x 10-4 m^3.

Abegg, F.; Freitag, J.; Bohrmann, G.; Brueckmann, W.; Eisenhauer, A.; Amann, H.; Hohnberg, H.-J.

2003-04-01

289

Hydrodynamic models for slurry bubble column reactors. Seventh technical progress report, January--March 1996  

SciTech Connect

The objective of this investigation is to convert our ``learning gas solid-liquid`` fluidization model into a predictive design model. The IIT hydrodynamic model computes the phase velocities and the volume fractions of gas, liquid and particulate phase. Model verification involves a comparison of these computed velocities and volume fractions to experimental values. A hydrodynamic model for multiphase flows, based on the principles of mass, momentum and energy conservation for each phase, was developed and applied to model gas-liquid, gas-liquid-solid fluidization and gas-solid-solid separation. To simulate the industrial slurry bubble column reactors, a computer program based on the hydrodynamic model was written with modules for chemical reactions (e.g. the synthesis of methanol), phase changes and heat exchangers. In the simulations of gas-liquid two phases flow system, the gas hold-ups, computed with a variety of operating conditions such as temperature, pressure, gas and liquid velocities, agree well with the measurements obtained at Air Products` pilot plant. The hydrodynamic model has more flexible features than the previous empirical correlations in predicting the gas hold-up of gas-liquid two-phase flow systems. In the simulations of gas-liquid-solid bubble column reactors with and without slurry circulation, the code computes volume fractions, temperatures and velocity distributions for the gas, the liquid and the solid phases, as well as concentration distributions for the species (CO, H{sub 2}, CH{sub 3}0H, ... ), after startup from a certain initial state. A kinetic theory approach is used to compute a solid viscosity due to particle collisions. Solid motion and gas-liquid-solid mixing are observed on a color PCSHOW movie made from computed time series data. The steady state and time average catalyst concentration profiles, the slurry height and the rates of methanol production agree well with the measurements obtained at an Air Products` pilot plant.

Gidaspow, D.

1996-04-01

290

Bubble Combustion  

NASA Technical Reports Server (NTRS)

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

Corrigan, Jackie

2004-01-01

291

Studies in vacuum degassing: Mass and momentum transfer to gas bubbles rising in melts, the freeboard of which is evacuated  

Microsoft Academic Search

A mathematical formulation is presented describing the growth of gas bubbles rising in melts, the freeboard of which is evacuated.\\u000a A novel aspect of the paper is that in the statement of the problem account is taken of the role played by liquid inertia\\u000a and surface kinetics in limiting the growth rate and affecting the rising velocity of the bubble.

J. Szekely; S. D. Fang

1974-01-01

292

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

PubMed Central

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, is noted to correspond to the rise in an infinite medium, both in terms of Reynolds number and shape at terminal state. In a thin cylindrical vessel (small R*), the motion of the bubble is retarded due to increased total drag and the bubble achieves terminal conditions within a short distance from release. The wake effects on bubble rise are reduced, and elongated bubbles may occur at appropriate conditions. For a fixed volume of the bubble, increasing the cylinder radius may result in the formation of well-defined rear recirculatory wakes that are associated with lateral bulging and skirt formation. The paper includes figures of bubble shape regimes for various values of R*, Eo, Mo, and ReT. Our predictions agree with existing results reported in the literature.

Mukundakrishnan, Karthik; Quan, Shaoping; Eckmann, David M.; Ayyaswamy, Portonovo S.

2009-01-01

293

Observations of three-dimensional Richtmyer-Meshkov instability on a membraneless gas bubble.  

PubMed

We investigate the three-dimensional evolution of shock impact on a membraneless gas bubble. When a shock wave impacts a gas interface, gas layer is generally perturbed via the Richtmyer-Meshkov instability. We show the vortex structure evolves from the merging process of the extending spikes on the compressed D-shaped surface via the Richtmyer-Meshkov instability. The spikes are found to have a linear growth before 11 ?s (of 1.4 mm). A ripple-typed fluctuating ring structure is observed and discussed with the scaling relation. We also notice that a thin layer exists in the intersection of the counterpropagating shock shells. The superposition of the rarefaction waves from both sides of the intersection is suspected to be responsible for the density change. PMID:23767479

Chu, Hong-Yu; Chen, Dong-Kai

2013-05-01

294

A Study of Vertical Gas Jets in a Bubbling Fluidized Bed  

SciTech Connect

A detailed experimental study of a vertical gas jet impinging a fluidized bed of particles has been conducted with the help of Laser Doppler Velocimetry measurements. Mean and fluctuating velocity profiles of the two phases have been presented and analyzed for different fluidization states of the emulsion. The results of this work would be greatly helpful in understanding the complex two-phase mixing phenomenon that occurs in bubbling beds, such as in coal and biomass gasification, and also in building more fundamental gas-solid Eulerian/Lagrangian models which can be incorporated into existing CFD codes. Relevant simulations to supplement the experimental findings have also been conducted using the Department of Energyâ??s open source code MFIX. The goal of these simulations was two-fold. One was to check the two-dimensional nature of the experimental results. The other was an attempt to improve the existing dense phase Eulerian framework through validation with the experimental results. In particular the sensitivity of existing frictional models in predicting the flow was investigated. The simulation results provide insight on wall-bounded turbulent jets and the effect frictional models have on gas-solid bubbling flows. Additionally, some empirical minimum fluidization correlations were validated for non-spherical particles with the idea of extending the present study to non-spherical particles which are more common in industries.

Steven Ceccio; Jennifer Curtis

2011-01-18

295

Method for gas bubble and void control and removal from metals  

DOEpatents

A method for enhancing the diffusion of gas bubbles or voids attached to impurity precipitates, and biasing their direction of migration out of the host metal (or metal alloy) by applying a temperature gradient across the host metal (or metal alloy). In the preferred embodiment of the present invention, the impurity metal is insoluble in the host metal and has a melting point lower than the melting point of the host material. Also, preferably the impurity metal is lead or indium and the host metal is aluminum or a metal alloy.

Van Siclen, Clinton D. (Idaho Falls, ID); Wright, Richard N. (Idaho Falls, ID)

1996-01-01

296

Noble gas dependence of single-bubble sonoluminescence in phosphoric acid  

NASA Astrophysics Data System (ADS)

Single-bubble sonoluminescence (SL) from a concentrated solution of phosphoric acid doped with various noble gases has been studied using a hydrochemical model. The results indicate that in agreement with experiment, the SL temperature increases with the atomic mass of the noble gases. Also, both the temperature and the intensity of SL are remarkably higher for lower partial pressures of a noble gas. Our calculations show that the maximum acquirable SL intensity from phosphoric acid is considerably greater than that of water. This mainly originates from the lower vapor pressure and the higher viscosity of phosphoric acid relative to water making the instability mechanisms completely different for these liquids.

Faraji, Mehdi; Moshaii, Ahmad

2012-09-01

297

Gas Bubbles Electrolytically Generated At Microcavity Electrodes (MCE) Used For The Measurement Of The Dynamic Surface Tension In Liquids  

Microsoft Academic Search

A new method is proposed for the measurement of dynamic surface tension in aqueous solutions. The advantage of this method with respect to the classical method based on sparging is that the use (of gas pumps is avoided, resulting in a miniaturised system. This method is based on the in-situ generation of gas bubbles by means of electrolysis at Microcavity

A. Volanschi; W. Olthuis; P. Bergveld

1995-01-01

298

Gas bubbles electrolytically generated at microcavity electrodes used for the measurement of the dynamic surface tension in liquids  

Microsoft Academic Search

A new method is proposed for the measurement of dynamic surface tension in aqueous solutions. The advantage of this method with respect to the classical method based on sparging is that the use of gas pumps is avoided, resulting in a miniaturized system. This method is based on the in situ generation of gas bubbles by means of electrolysis at

A. Volanschi; W. Olthuis; P. Bergveld

1996-01-01

299

Microstructure and fission gas bubbles in irradiated mixed carbide fuels at 2 to 11 a/o burnup  

NASA Astrophysics Data System (ADS)

An analysis of the defect structure and of small fission gas bubbles has been performed on mixed carbide fuels with burn-ups between 1.8 and 11 a/o by transmission electron microscopy (TEM). A complex defect structure consisting of dislocations, loops and at least 3 types of solid fission product precipitates was observed. Na-bonded carbides develop predominantly a dislocation network increasing in density with burn-up whereas He-bonded carbides showed mainly a corresponding network of crystallographic needle precipitates. Locally the nucleation and growth of small fission gas bubbles with 1 to 20 nm diameters (bubble population P 1) is closely related to their dislocation or needle environment, larger bubbles with diameters 30 to 50 nm appear to be mostly associated with platelike precipitates or dislocation boundaries. The local swelling contribution ? 1 of bubble population P 1 is ? 0.5% and its fission gas content G 1 is 4 to 5% of the total amount of gas created over the whole burn-up range investigated.

Ray, I. L. F.; Blank, H.

1984-05-01

300

Experimental formation of massive hydrate deposits from accumulation of CH4 gas bubbles within synthetic and natural sediments  

SciTech Connect

In order for methane to be economically produced from the seafloor, prediction and detection of massive hydrate deposits will be necessary. In many cases, hydrate samples recovered from seafloor sediments appear as veins or nodules, suggesting that there are strong geologic controls on where hydrate is likely to accumulate. Experiments have been conducted examining massive hydrate accumulation from methane gas bubbles within natural and synthetic sediments in a large volume pressure vessels through temperature and pressure data, as well as visual observations. Observations of hydrate growth suggest that accumulation of gas bubbles within void spaces and at sediment interfaces likely results in the formation of massive hydrate deposits. Methane hydrate was first observed as a thin film forming at the gas/water interface of methane bubbles trapped within sediment void spaces. As bubbles accumulated, massive hydrate growth occurred. These experiments suggest that in systems containing free methane gas, bubble pathways and accumulation points likely control the location and habit of massive hydrate deposits.

Madden, Megan Elwood [ORNL; Szymcek, Phillip [ORNL; Ulrich, Shannon M [ORNL; McCallum, Scott D [ORNL; Phelps, Tommy Joe [ORNL

2009-01-01

301

Bubble Suspension  

NSDL National Science Digital Library

This activity from the Exploratorium illustrates the principles of buoyancy, semipermeability, and interference as soap bubbles float on a cushion of carbon dioxide gas. Dry ice, gloves, and adult supervision are required to view the beautiful effect. The site also includes an explanation of the physics involved and other quick experiments that can be done with bubbles. This activity is part of Exploratorium's Science Snacks series.

2006-07-16

302

Measurement of Entrapped Biogenic Gas Bubbles in Northern Peat Soils: Application of Resistivity and X-ray Computed Tomography.  

NASA Astrophysics Data System (ADS)

Peatlands are the largest natural source per annum of CH4 emissions to the atmosphere. CH4 is lost from peatlands via diffusion or active transport through vascular plants, and as bubbles moving to the peatland surface - ebullition. The build up and ebullition of biogenic gas bubbles within northern peatlands is spatially variable and depends on the rate of CH4 production, the transport of dissolved CH4 to bubbles through pore water, and the physical properties of the peat. Recent measurements suggest a threshold bubble volume must be reached to trigger episodic or cyclic ebullition, which is assumed to be dependent on peat type. However, this threshold theory lacks a secure physical basis and therefore cannot be applied to simulate methane ebullition from northern peatlands with any confidence. We develop an approach to examine the structural attributes of the peat that cause and promote the trapping and release of bubbles by combining resistivity and X-ray computed tomography (CT). The spatial and temporal variation in the biogenic gas content of peat cores are identified from resistivity measurements. Areas of high and low entrapped gas content are subsequently correlated with the pore structure of the peat samples, characterised using CT. The CT images of the peat structure are vectorised to allow them to be analysed for metrics which relate to the ability of the peat to trap bubbles: e.g. stem length and width, number of branches, angle of branches. Difficulties applying these approaches within northern peatlands are examined. The low pore water conductivity of poorly decomposed near surface peat can hamper resistivity measurements at the laboratory scale, and electrolytic reactions induce the development of artificial gas bubbles. The similarity in linear attenuations between poorly decomposed Sphagnum and pore water also makes the peat structure indistinguishable from the pore water within standard CT scans. The peat samples must, therefore, first be doped with a solution of lead(II) nitrate which is adsorbed by the peat fibres, making them visible.

Kettridge, N.; Binley, A.; Baird, A.

2008-05-01

303

Comparison of single- and two-bubble class gas–liquid recirculation models — application to pilot-plant radioactive tracer studies during methanol synthesis  

Microsoft Academic Search

Radioactive gas tracer measurements conducted during liquid-phase methanol synthesis from syngas in a pilot-scale slurry bubble column at the alternate fuels development unit (AFDU), La Porte have been compared with simulations from two mechanistic reactor models — single-bubble class model (SBCM) and two-bubble class model (TBCM). The model parameters are estimated from an independent sub-model gas and liquid recirculation, and

Puneet Gupta; Muthanna H. Al-Dahhan; Milorad P. Dudukovic; Bernard A. Toseland

2001-01-01

304

The effects of total dissolved gas on chum salmon fry survival, growth, gas bubble disease, and seawater tolerance  

SciTech Connect

Chum salmon Oncorhynchus keta alevin developing in gravel habitats downstream of Bonneville Dam on the Columbia River are exposed to elevated levels of total dissolved gas (TDG) when water is spilled at the dam to move migrating salmon smolts downstream to the Pacific Ocean. Current water quality criteria for the management of dissolved gas in dam tailwaters were developed primarily to protect salmonid smolts and are assumed to be protective of alevin if adequate depth compensation is provided. We studied whether chum salmon alevin exposed to six levels of dissolved gas ranging from 100% to 130% TDG at three development periods between hatch and emergence (hereafter early, middle, and late stage) suffered differential mortality, growth, gas bubble disease, or seawater tolerance. Each life stage was exposed for 50 d (early stage), 29 d (middle stage), or 16 d (late stage) beginning at 13, 34, and 37 d post-hatch, respectively, through 50% emergence. The mortality for all stages from exposure to emergence was estimated to be 8% (95% confidence interval (CI) of 4% to 12%) when dissolved gas levels were between 100% and 117% TDG. Mortality significantly increased as dissolved gas levels rose above 117% TDG,; with the lethal concentration that produced 50% mortality (LC50 ) was estimated to be 128.7% TDG (95% CI of 127.2% to 130.2% TDG) in the early and middle stages. By contrast, there was no evidence that dissolved gas level significantly affected growth in any life stage except that the mean wet weight at emergence of early stage fish exposed to 130% TDG was significantly less than the modeled growth of unexposed fish. The proportion of fish afflicted with gas bubble disease increased with increasing gas concentrations and occurred most commonly in the nares and gastrointestinal tract. Early stage fish exhibited higher ratios of filament to lamellar gill chloride cells than late stage fish, and these ratios increased and decreased for early and late stage fish, respectively, as gas levels increased; however, there were no significant differences in mortality between life stages after 96 h in seawater. The study results suggest that current water quality guidelines for the management of dissolved gas appear to offer a conservative level of protection to chum salmon alevin incubating in gravel habitat downstream of Bonneville Dam.

Geist, David R.; Linley, Timothy J.; Cullinan, Valerie I.; Deng, Zhiqun

2013-02-01

305

The measurement of bubble diameter distributions and liquid side mass transfer coefficients in a gas-liquid agitated vessel using a real-time,high-speed image processing system  

Microsoft Academic Search

In this study, we report the measurement results of various spatial distributions, such as Sauter diameter, gas holdup ratio, and interface area per unit liquid volume, in a vessel using a real-time, high-speed image processing system developed by ourselves. We attempted to separate liquid side mass transfer coefficients, k L , from overall volumetric mass transfer coefficients, k L a,

Mitsuo Kamiwano; Meguru Kaminoyama; Kazuhiko Nishi; Daigo Shirota

2003-01-01

306

Computation of holdups in fluidized and trickle beds by computer-assisted tomography  

SciTech Connect

A fourth-generation X-ray computer-assisted tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas/solid fluidized beds were glass bead/nitrogen and polyethylene/nitrogen systems. The trickle bed was a glass bead/nitrogen/water system. The algorithms presented can be used to determine holdup from X-ray absorption data. These algorithms--extensions of similar algorithms used for the calculation of fluid saturations in porous media--are applied on data of CAT scanner images as they are generated by the scanner and after they are transferred to a workstation. The results of the presented tests demonstrate how detailed holdup calculations can be performed in a chemical reactor. Radial and longitudinal variances of the holdup can be easily defined. The proposed algorithms can assist in the design of chemical reactor prototypes.

Kantzas, A. (Novacor Research Technology Corp., Calgary, Alberta (Canada))

1994-07-01

307

Markets and regulatory hold-up problems  

SciTech Connect

Many regulatory programs such as environmental regulation are effective only if firms make irreversible investments that reduce the cost of compliance. A firm potentially subject to regulation may therefore behave strategically by not investing, thereby forcing the regulator to void the proposed regulation. The authors show that such incentives, which resemble a hold-up problem, may not be overcome when government`s only tool is the imposition of an emissions tax. The hold-up problem can be overcome by the issuance of tradeable permits. A time-consistent equilibrium exists with all firms investing and the government imposing regulations, even if no permits are traded and their market price is low. Indeed, an observation of no trade may indicate that pollution abatement is great.

Gersbach, H. [Univ. Heidelberg (Germany). Alfred-Weber-Inst.] [Univ. Heidelberg (Germany). Alfred-Weber-Inst.; Glazer, A. [Univ. of California, Irvine, CA (United States). Dept. of Economics] [Univ. of California, Irvine, CA (United States). Dept. of Economics

1999-03-01

308

Noninvasive measurement of the hydrostatic pressure in a fluid-filled cavity based on the disappearance time of micrometer-sized free gas bubbles.  

PubMed

A new method for noninvasive pressure measurement, based on the disappearance time of micrometer-sized free gas bubbles, is described in this article. An ultrasound (US) contrast agent, consisting of encapsulated gas bubbles, is used as a vehicle to transport the free gas bubbles to the desired region where the pressure is to be measured. The small free gas bubbles are generated at the region of interest (e.g., heart chambers), from the encapsulated gas bubbles, which rupture when they are exposed to a single low-frequency (e.g., 0.5 MHz), high acoustic amplitude US burst. The released gas bubbles persist for only a few ms and dissolve in the liquid, depending on their size, the gas, the liquid characteristics and ambient parameters such as temperature, gas concentration and pressure. A pressure-disappearance time relationship is determined using a sequence of high-frequency (e.g., 10 MHz), low acoustic amplitude US pulses. From in vitro experiments, reproducible results show a significant difference between the disappearance time of the bubbles as function of the local pressure, resulting in a quicker disappearance of the bubble for higher values of the pressure. The sensitivity of the method to small pressure changes (50 mmHg) is demonstrated. PMID:10626628

Bouakaz, A; Frinking, P J; de Jong, N; Bom, N

1999-11-01

309

Numerical Simulation of Separating Gas Mixtures via Hydrate Formation in Bubble Column 1 1 Supported by the National Natural Science Foundation of China (No.20490207)  

Microsoft Academic Search

To develop a new technique for separating gas mixtures via hydrate formation, a set of medium-sized experimental bubble column reactor equipment was constructed. On the basis of the structure parameters of the experimental bubble column reactor, assuming that the liquid phase was in the axial dispersion regime and the gas phase was in the plug flow regime, in the presence

Yantuo LUO; Jianhua ZHU; Guangjin CHEN

2007-01-01

310

Estimation methods for special nuclear materials holdup  

SciTech Connect

The potential value of statistical models for the estimation of residual inventories of special nuclear materials was examined using holdup data from processing facilities and through controlled experiments. Although the measurement of hidden inventories of special nuclear materials in large facilities is a challenging task, reliable estimates of these inventories can be developed through a combination of good measurements and the use of statistical models. 7 references, 5 figures.

Pillay, K.K.S.; Picard, R.R.

1984-01-01

311

Holdup Measurement System II (HMSII): Version 2.1. User's guide and software documentation.  

National Technical Information Service (NTIS)

The Holdup Measurement System II (HMSII) software is a database management package for doing Holdup Measurements. It is based on the generalized geometry holdup (GGH) methodology taught in the US Department of Energy Safeguards Technology Training Program...

S. E. Smith

1995-01-01

312

Passive acoustic derived bubble flux and applications to natural gas seepage in the Mackenzie Delta, NWT, Canada and Coal Oil Point, CA  

NASA Astrophysics Data System (ADS)

Methane is a prominent greenhouse gas that escapes naturally from thermogenic reservoirs as seepage from marine and lacustrine biogenic sources as bubble ebullition. Geologic methane emissions are critically important contributors to the global methane budget however, few quantitative flux measurements are available for shallow waters. This gap in knowledge is critical as in these settings gas can easily transit as bubbles through the water column and directly influence global atmospheric budgets. Video and active acoustic (sonar) measurements of bubble flux have spatial limitations requiring predictable bubble emission location. Passive acoustics are less affected by these limitations, in addition, they can provide data in water too shallow for effective sonar bubble observations. Lab tests were undertaken to quantify the acoustic signature of bubbles formed in non-cohesive sediments. specifically focusing on mechanisms that complicate interpretation of acoustic data. Lab tests then were compared to field data to provide measurement calibration/validation. The principles behind the acoustic analysis method are based on the Minnaert equation, which relates a bubble radius and acoustic frequency. Bubble size and the resultant acoustic frequency from known flows and capillary tube diameters are well documented; however changing sediment pathways adds to the complexity of bubble formation and the resultant bubble acoustic signal. These complex signals were investigated in a lab tank with a thick, cohesive fine-grained sediment bed, through which bubbles produced by a syringe pump migrated to the sediment-water interface. Then, the resultant bubbles were diverted into clear water and measured from high speed, high definition video, while the acoustic signature of bubble formation was recorded concurrently by a hydrophone. Bubble formation is influenced by currents, which shifts the acoustical signal towards a higher frequency with a more complex pattern than the Minnaert equation predicts. Furthermore, bubbles from a cohesive media escaped in pulses of multiple bubbles, which caused significant inter-bubble acoustic coupling and mud-bubble interaction. The acoustic signature of subsurface bubble migration and concurrent sediment movements, including bubble pinch off, presented additional complexities. Use of passive acoustic derived flux was applied to natural gas seepage in the Mackenzie Delta in the North West Territories, Canada as well as offshore Coal Oil Point (COP), CA. Video data were used to calibrate the COP acoustic observations and showed a strong current impact for non-cohesive sediments. Seepage flux in the delta (cohesive sediments) was calibrated using a custom turbine tent that directly measured flux. Further applications of passive acoustic-derived seep fluxes include monitoring of marine pipelines for leaks, and studying biogenic wetlands ebullition as well as thermogenic and hydrate seepage.

Culling, D.; Leifer, I.; Dallimore, S.; Alcala, K.

2012-12-01

313

Presentation and Discussion of Results from Measurements of the Velocity of Sliding Gas Bubbles in a Liquid Medium, Carried out by Different Methods.  

National Technical Information Service (NTIS)

Comparisons were made of the different methods used the measure the velocity of gas bubbles in a liquid medium. Of the methods compared, the radioactivation method did not appreciably change the physical and chemical properties of the gas which influences...

A. Campanile G. Galimi M. Goffi U. Magrini C. Pisoni

1975-01-01

314

3D mapping of the dense interstellar gas around the Local Bubble  

NASA Astrophysics Data System (ADS)

We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 Å are presented for the lines-of-sight towards some 311 new target stars lying within ~ 350 pc of the Sun. Using these data, together with NaI absorption measurements towards a further ~ 240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ~ 450 lines-of-sight already presented by (Sfeir et al. \\cite{sfeir99}), we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (\\cite{vergely01}). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas ``wall'', in the first quadrant, is at ~ 55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide ``interstellar tunnels'' which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void (Gry et al. \\cite{gry85}), which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles \\cite{heiles98}). High latitude lines-of-sight with the smallest absorption are found in two ``chimneys'', whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is ``squeezed'' by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 are closer than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41-43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192-67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc. Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447

Lallement, R.; Welsh, B. Y.; Vergely, J. L.; Crifo, F.; Sfeir, D.

2003-12-01

315

Ion-induced density bubble in a strongly correlated one-dimensional gas  

SciTech Connect

We consider a harmonically trapped Tonks-Girardeau gas of impenetrable bosons in the presence of a single embedded ion, which is assumed to be tightly confined in an RF trap. In an ultracold ion-atom collision the ion's charge induces an electric dipole moment in the atoms which leads to an attractive r{sup -4} potential asymptotically. We treat the ion as a static deformation of the harmonic trap potential and model its short range interaction with the gas in the framework of quantum defect theory. The molecular bound states of the ionic potential are not populated due to the lack of any possible relaxation process in the Tonks-Girardeau regime. Armed with this knowledge we calculate the density profile of the gas in the presence of a central ionic impurity and show that a density bubble of the order of 1{mu}m occurs around the ion for typical experimental parameters. From these exact results we show that an ionic impurity in a Tonks gas can be described using a pseudopotential approximation, allowing for significantly easier treatment.

Goold, J. [Department of Physics, University College Cork, Cork (Ireland); Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 (Singapore); Doerk, H. [Max-Planck-Institut fuer Plasmaphysik, Boltzmannstr. 3, D-85748 Garching (Germany); Idziaszek, Z. [Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Hoza 69, PL-00681 Warsaw (Poland); Calarco, T. [Institute for Quantum Information Processing, University of Ulm, Albert-Einstein-Allee 11, D-89069 Ulm (Germany); Busch, Th. [Department of Physics, University College Cork, Cork (Ireland)

2010-04-15

316

Hydrate film growth on the surface of a gas bubble suspended in water.  

PubMed

The lateral film growth rate of CH4, C2H4, CO2, CH4 + C2H4, and CH4 + C3H8 hydrates in pure water were measured at four fixed temperatures of 273.4, 275.4, 277.4, and 279.4 K by means of suspending a single gas bubble in water. The results showed that the lateral growth rates of mixed-gas CH4 + C2H4 hydrate films were slower than that of pure gas (CH4 or C2H4) for the same driving force and that of mixed-gas CH4 + C3H8 hydrate film growth was the slowest. The dependence of the thickness of hydrate film on the driving force was investigated, and it was demonstrated that the thickness of hydrate film was inversely proportional to the driving force. It was found that the convective heat transfer control model reported in the literature could be used to formulate the lateral film growth rate v(f) with the driving force DeltaT perfectly for all systems after introduction of the assumption that the thickness of hydrate films is inversely proportional to the driving force DeltaT; i.e., v(f) = psiDeltaT(5/2) is correct and independent of the composition of gas and the type of hydrate. The thicknesses of different gas hydrate films were estimated, and it is demonstrated that the thicknesses of mixed-gas hydrate films were thicker than those of pure gases, which was qualitatively consistent with the experimental result. PMID:17929860

Peng, B Z; Dandekar, A; Sun, C Y; Luo, H; Ma, Q L; Pang, W X; Chen, G J

2007-11-01

317

Review of scattering and extinction cross-sections, damping factors, and resonance frequencies of a spherical gas bubble.  

PubMed

Perhaps the most familiar concepts when discussing acoustic scattering by bubbles are the resonance frequency for bubble pulsation, the bubbles' damping, and their scattering and extinction cross-sections, all of which are used routinely in oceanography, sonochemistry, and biomedicine. The apparent simplicity of these concepts is illusory: there exist multiple, sometimes contradictory definitions for their components. This paper reviews expressions and definitions in the literature for acoustical cross-sections, resonance frequencies, and damping factors of a spherically pulsating gas bubble in an infinite liquid medium, deriving two expressions for "resonance frequency" that are compared and reconciled with two others from the reviewed literature. In order to prevent errors, care is needed by researchers when combining results from different publications that might have used internally correct but mutually inconsistent definitions. Expressions are presented for acoustical cross-sections associated with forced pulsations damped by liquid shear and (oft-neglected) bulk or dilatational viscosities, gas thermal diffusivity, and acoustic re-radiation. The concept of a dimensionless "damping coefficient" is unsuitable for radiation damping because different cross-sections would require different functional forms for this parameter. Instead, terms based on the ratio of bubble radius to acoustic wavelength are included explicitly in the cross-sections where needed. PMID:22087992

Ainslie, Michael A; Leighton, Timothy G

2011-11-01

318

Bubble nucleation in viscous material due to gas formation by a chemical reaction: application to coal pyrolysis  

Microsoft Academic Search

Most coals swell when heated, and their plastic properties change. These phenomena are explained qualitatively and semiquantitatively using a theory which combines classical nucleation theory and chemical kinetics. Classical bubble nucleation theory is modified to include cases where gases are formed in a liquid as a result of a chemical reaction. Part of the gas that is formed in the

Amir Attar

1978-01-01

319

A generalized bubble diameter correlation for gas-solid fluidized beds  

Microsoft Academic Search

A new bubble diameter correlation is derived to predict bubbling characteristics of fluidized beds of varieties of powders. The present model is founded on the postulate that the steady bubble size, which is often called the maximum stable diameter, observed in a bed of Geldart group A powder is formed as a result of an equilibrium of successive coalescence and

Masayuki Horio; Akira Nonaka

1987-01-01

320

The effect of magma flow on nucleation of gas bubbles in a volcanic conduit  

Microsoft Academic Search

We solve the dynamics of magma ascent and the kinetics of bubble nucleation and growth simultaneously, which allow us to predict bubble sizes and number densities under ascent conditions. As magma rises toward the surface, the pressure decreases and eventually becomes less than the solubility pressure. When the degree of supersaturation becomes great enough, bubbles nucleate. Nucleation will stop as

Hélène Massol; Takehiro Koyaguchi

2005-01-01

321

Gas Bubble Trauma Monitoring in the Clearwater River Drainage, Idaho 1998.  

SciTech Connect

Select portions of the Clearwater and North Fork of the Clearwater rivers were electroshocked to estimate the incidence of gas bubble trauma (GBT) occurring in resident fish populations for the spring and summer months of 1998. The study area was divided into four sections and sampled weekly during periods of spill and non-spill from Dworshak Dam. Five thousand five hundred and forty one fish, representing 22 different species, were captured and examined for GBT. Two fish were detected with signs of GBT; exhibiting the lowest incidence of GBT in the last four years (0.04%). Reduced discharge and lower levels of total dissolved gases may have resulted in lower incidence of GBT in the 1998 monitoring period.

Cochnauer, Tim

1998-12-01

322

HYDRODYNAMIC MODELS FOR SLURRY BUBBLE COLUMN REACTORS. FINAL TECHNICAL REPORT ALSO INCLUDES THE QUARTERLY TECHNICAL REPORT FOR THE PERIOD 01/01/1997 - 03/31/1997.  

SciTech Connect

The objective of this study is to develop a predictive experimentally verified computational fluid dynamic (CFD) three phase model. It predicts the gas, liquid and solid hold-ups (volume fractions) and flow patterns in the industrially important bubble-coalesced (churn-turbulent) regime. The input into the model can be either particulate viscosities as measured with a Brookfield viscometer or effective restitution coefficient for particles. A combination of x-ray and {gamma}-ray densitometers was used to measure solid and liquid volume fractions. There is a fair agreement between the theory and the experiment. A CCD camera was used to measure instantaneous particle velocities. There is a good agreement between the computed time average velocities and the measurements. There is an excellent agreement between the viscosity of 800 {micro}m glass beads obtained from measurement of granular temperature (random kinetic energy of particles) and the measurement using a Brookfield viscometer. A relation between particle Reynolds stresses and granular temperature was found for developed flow. Such measurement and computations gave a restitution coefficient for a methanol catalyst to be about 0.9. A transient, two-dimensional hydrodynamic model for production of methanol from syn-gas in an Air Products/DOE LaPorte slurry bubble column reactor was developed. The model predicts downflow of catalyst at the walls and oscillatory particle and gas flow at the center, with a frequency of about 0.7 Hertz. The computed temperature variation in the rector with heat exchangers was only about 5 K, indicating good thermal management. The computed slurry height, the gas holdup and the rate of methanol production agree with LaPorte's reported data. Unlike the previous models in the literature, this model computes the gas and the particle holdups and the particle rheology. The only adjustable parameter in the model is the effective particle restitution coefficient.

DIMITRI GIDASPOW

1997-08-15

323

Generalizations of the Young-Laplace equation for the pressure of a mechanically stable gas bubble in a soft elastic material  

NASA Astrophysics Data System (ADS)

The Young-Laplace equation for the pressure of a mechanically stable gas bubble is generalized to include the effects of both surface tension and elastic forces of its surroundings. The latter are taken to be comprised of a soft isotropic material. Generalizations are derived for conditions of constant external pressure and constant system volume. The derived equations are formally exact for a spherical bubble surrounded by a spherical shell of isotropic material, provided that the bubble is sufficiently large for the surface tension to be treated macroscopically, and that the bubble radius is much larger than the thickness of the bubble/soft material interface. The underlying equations are also used to derive a simple expression for the Gibbs free energy of deformation of an elastic medium that surrounds a gas bubble. The possible relevance of this expression to some recently published ideas on decompression sickness (``the bends'') is discussed.

Goldman, Saul

2009-11-01

324

Bubble diagnostics  

DOEpatents

The present invention is intended as a means of diagnosing the presence of a gas bubble and incorporating the information into a feedback system for opto-acoustic thrombolysis. In opto-acoustic thrombolysis, pulsed laser radiation at ultrasonic frequencies is delivered intraluminally down an optical fiber and directed toward a thrombus or otherwise occluded vessel. Dissolution of the occlusion is therefore mediated through ultrasonic action of propagating pressure or shock waves. A vapor bubble in the fluid surrounding the occlusion may form as a result of laser irradiation. This vapor bubble may be used to directly disrupt the occlusion or as a means of producing a pressure wave. It is desirable to detect the formation and follow the lifetime of the vapor bubble. Knowledge of the bubble formation and lifetime yields critical information as to the maximum size of the bubble, density of the absorbed radiation, and properties of the absorbing material. This information can then be used in a feedback system to alter the irradiation conditions.

Visuri, Steven R. (Livermore, CA) [Livermore, CA; Mammini, Beth M. (Walnut Creek, CA) [Walnut Creek, CA; Da Silva, Luiz B. (Danville, CA) [Danville, CA; Celliers, Peter M. (Berkeley, CA) [Berkeley, CA

2003-01-01

325

Sparger Effects on Gas Volume Fraction Distributions in Vertical Bubble-Column Flows as Measured by Gamma-Densitometry Tomography  

SciTech Connect

Gamma-densitometry tomography is applied to study the effect of sparger hole geometry, gas flow rate, column pressure, and phase properties on gas volume fraction profiles in bubble columns. Tests are conducted in a column 0.48 m in diameter, using air and mineral oil, superficial gas velocities ranging from 5 to 30 cm s{sup -1}, and absolute column pressures from 103 to 517 kPa. Reconstructed gas volume fraction profiles from two sparger geometries are presented. The development length of the gas volume fraction profile is found to increase with gas flow rate and column pressure. Increases in gas flow rate increase the local gas volume fraction preferentially on the column axis, whereas increases in column pressure produce a uniform rise in gas volume fraction across the column. A comparison of results from the two spargers indicates a significant change in development length with the number and size of sparger holes.

GEORGE,DARIN L.; SHOLLENBERGER,KIM ANN; TORCZYNSKI,JOHN R.

2000-01-18

326

Can high-frequency sound affect gas-bubble dynamics? A study in the intact prawn Palaemon elegans.  

PubMed

Underwater sound beacons (pingers) are employed in professional and scientific diving for location and navigation. Previous studies have demonstrated that exposure to acoustic fields may lead to the emergence of bubbles and cavities in tissues by rectified diffusion. However, this issue was studied mainly in vitro in various gels and isolated tissues. In the present study, we used the intact prawn Palaemon elegans, whose transparent shell makes it possible to conduct continuous microscopic observation of gas-bubble dynamics in the intact living prawn, to study the effect of high-frequency sound. In a crossover designed experiment, prawns were exposed to hyperbaric pressure of 203 kPa for 10 min, followed by decompression at 40 m/min (control). This procedure was carried out in the study group during transmission of a 37-kHz, 0.25-W, 10-ms pulse width, 1 pulse/s pulse interval. A significant increase was found in the mean volume of bubbles present for a longer period of time, in a higher percentage of the high-frequency sound-exposed prawns. We suggest that this sound exposure causes more gaseous micronuclei to grow into bubbles, and more of the dissolved gas to shift into the gas phase. PMID:11179625

Arieli, Y; Arieli, R; Shupak, A

2000-11-01

327

Fluid maldistribution effects on phase holdups in three-phase fluidized beds  

Microsoft Academic Search

Effects on the phase holdups and overall bed voidage of gas and liquid maldistribution due to partial blockage of the distributor and due to their premixing below the distributor have been determined for three-phase fluidized beds in a 127-mm-diameter column. The experiments were carried out with 3.3-mm polymer particles and 3.7-mm glass beads (densities of 1280 and 2510kg\\/m3), with water

DongHyun Lee; Arturo Macchi; John R Grace; Norman Epstein

2001-01-01

328

Computation of holdups in fluidized and trickle beds by computer-assisted tomography  

Microsoft Academic Search

A fourth-generation X-ray computer-assisted tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas\\/solid fluidized beds were glass bead\\/nitrogen and polyethylene\\/nitrogen systems. The trickle bed was a glass bead\\/nitrogen\\/water system. The algorithms

Apostolos Kantzas

1994-01-01

329

Inertial-Fusion-Related Hydrodynamic Instabilities in a Spherical Gas Bubble Accelerated by a Planar Shock Wave  

SciTech Connect

Experiments studying the compression and unstable growth of a dense spherical bubble in a gaseous medium subjected to a strong planar shock wave (2.8 < M < 3.4) are performed in a vertical shock tube. The test gas is initially contained in a free-falling spherical soap-film bubble, and the shocked bubble is imaged using planar laser diagnostics. Concurrently, simulations are carried out using a compressible hydrodynamics code in r-z axisymmetric geometry.Experiments and computations indicate the formation of characteristic vortical structures in the post-shock flow, due to Richtmyer-Meshkov and Kelvin-Helmholtz instabilities, and smaller-scale vortices due to secondary effects. Inconsistencies between experimental and computational results are examined, and the usefulness of the current axisymmetric approach is evaluated.

Niederhaus, John [University of Wisconsin-Madison (United States); Ranjan, Devesh [University of Wisconsin-Madison (United States); Anderson, Mark [University of Wisconsin-Madison (United States); Oakley, Jason [University of Wisconsin-Madison (United States); Bonazza, Riccardo [University of Wisconsin-Madison (United States); Greenough, Jeff [Lawrence Livermore National Laboratory (United States)

2005-05-15

330

Optical measurements of jet gas and bed particle velocity distributions in a 2D bubbling fluidized bed  

NASA Astrophysics Data System (ADS)

A laser Doppler velocimetry (LDV) measurement technique has been developed to obtain spatially and temporally resolved measurements of jet gas and bed particle velocities in a 2D bubbling fluidized bed. The LDV system was configured to eliminate spurious optical intensity fluctuations, which can contaminate velocity measurements in optically dense flows. The jet gas was seeded with ice crystals, which were formed by rapidly condensing and freezing the moisture in the jet air just prior to injection. LDV bursts from the bed particles and gas tracer ice crystals were simultaneously recorded to obtain the particulate and gas phase velocities at a given location within the jet plume in a non-intrusive manner.

Mychkovsky, Alexander; Ceccio, Steven

2009-11-01

331

Improved Background Corrections for Uranium Holdup Measurements  

SciTech Connect

In the original Generalized Geometry Holdup (GGH) model, all holdup deposits were modeled as points, lines, and areas[1, 5]. Two improvements[4] were recently made to the GGH model and are currently in use at the Y-12 National Security Complex. These two improvements are the finite-source correction CF{sub g} and the self-attenuation correction. The finite-source correction corrects the average detector response for the width of point and line geometries which in effect, converts points and lines into areas. The result of a holdup measurement of an area deposit is a density-thickness which is converted to mass by multiplying it by the area of the deposit. From the measured density-thickness, the true density-thickness can be calculated by correcting for the material self-attenuation. Therefore the self-attenuation correction is applied to finite point and line deposits as well as areas. This report demonstrates that the finite-source and self-attenuation corrections also provide a means to better separate the gamma rays emitted by the material from the gamma rays emitted by background sources for an improved background correction. Currently, the measured background radiation is attenuated for equipment walls in the case of area deposits but not for line and point sources. The measured background radiation is not corrected for attenuation by the uranium material. For all of these cases, the background is overestimated which causes a negative bias in the measurement. The finite-source correction and the self-attenuation correction will allow the correction of the measured background radiation for both the equipment attenuation and material attenuation for area sources as well as point and line sources.

Oberer, R.B.; Gunn, C.A.; Chiang, L.G.

2004-06-21

332

Tiny Bubbles.  

ERIC Educational Resources Information Center

A simple oxygen-collecting device (easily constructed from glass jars and a lid) can show bubbles released by water plants during photosynthesis. Suggestions are given for: (1) testing the collected gas; (2) using various carbon dioxide sources; and (3) measuring respiration. (DH)

Kim, Hy

1985-01-01

333

Measurements of the rise velocities of bubbles, slugs and pressure waves in a gas-solid fluidized bed using pressure fluctuation signals  

Microsoft Academic Search

The rise velocities of bubbles, slugs and pressure waves in a fluidized bed have been measured on-line through the use of pressure transducers coupled with the cross-correlation technique. Sand and glass beads with different particle sizes were tested. Effects of the gas flow rate and column diameter on the rise velocities of bubbles and slugs were investigated. The results were

L. T. Fan; Tho-Ching Ho; W. P. Walawender

1983-01-01

334

Hydrodynamical similarities between bubble column and bubbly pipe flow  

Microsoft Academic Search

The hydrodynamical similarities between the bubbly flow in a bubble column and in a pipe with vertical upward liquid flow are investigated. The system concerns air\\/water bubbly flow in a vertical cylinder of 14.9 cm inner diameter. Measurements of the radial distribution of the liquid velocity, gas fraction and the bubble velocity and size are performed using laser Doppler anemometry

Robert F. Mudde; Takayuki Saito

2001-01-01

335

Tiny Bubbles  

NSDL National Science Digital Library

In this activity, which can be performed as a demonstration by the teacher or by the students themselves, carbon dioxide is generated in a fish tank using sodium bicarbonate and vinegar. The students can observe as the accumulating carbon dioxide extinguishes candles of different heights, marking rising levels of CO2 in the tank. They can also blow soap bubbles (which contain air) into the tank and observe them floating on the denser CO2 at first, then sinking as the gas diffuses through the soap film that forms the bubbles.

Dolphin, Glenn

336

Free nonlinear oscillations of a thermally relaxing spherical gas bubble in an incompressible liquid  

Microsoft Academic Search

The quasi-adiabatic regime of free oscillation of a bubble in the presence of irreversible interphase heat transfer between\\u000a the bubble and the ambient liquid is studied. On the basis of simplified model equations of a rarefield bubble mixture, a\\u000a nonlinear-oscillation equation of the relaxation type is obtained. In constructing an exact particular solution of this equation,\\u000a the heat transfer law

G. G. Oganyan

2007-01-01

337

Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas  

USGS Publications Warehouse

Diffusive coarsening (Ostwald ripening) of H2O and H2O-CO2 bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H2O than in those with a CO2-rich mixed vapor probably due to faster diffusion of H2O than CO2 through the melt. None of the experimental series followed the time1/3 increase in mean bubble radius and time-1 decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 102–104 years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent.

Lautze, Nicole C.; Sisson, Thomas W.; Mangan, Margaret T.; Grove, Timothy L.

2011-01-01

338

Rise velocities and gas–liquid mass transfer of bubbles in organic solutions  

Microsoft Academic Search

Bubble size, shape, rise velocity and liquid side mass transfer coefficient have been experimentally determined for bubbles rising in organic systems, consisting of single or mutually soluble components, namely: alkanes (n-dodecane, n-hexadecane), alcohols (ethanol, 1-butanol, 1-octanol) and mixtures thereof. For pure solvents (alkanes and alcohols alike), it was found that the bubbles are non-spherical, and that both the rise velocity

Rocio Maceiras; Rui Santana; Sebastião S. Alves

2007-01-01

339

The cycle of bubble production from a gas cavity in a supersaturated solution  

Microsoft Academic Search

Bubble nucleation, classified according to the review by Jones et al. (Adv. Colloid Interface Sci. 80 (1999) 27–50) as type IV non-classical, was examined in this study. Trains of bubbles were produced in carbonated water solutions at low levels of supersaturation, typically less than about 2, at specific sites on the surface of the vessel in contact with the liquid.

S. F. Jones; G. M. Evans; K. P. Galvin

1999-01-01

340

Coupled effects of magma flow and nucleation of gas bubbles in a volcanic conduit  

Microsoft Academic Search

We solve the dynamics of magma ascent and the kinetics of bubble nucleation and growth simultaneously, which allow us to predict bubble sizes and number density under ascent conditions. As magma rises toward the surface the pressure decreases and eventually becomes less than the solubility pressure. When the difference between the concentration of volatiles in the melt and the concentration

H. Massol; T. Koyaguchi

2003-01-01

341

SNM holdup assessment of Los Alamos exhaust ducts. Final report  

SciTech Connect

Fissile material holdup in glovebox and fume hood exhaust ducting has been quantified for all Los Alamos duct systems. Gamma-based, nondestructive measurements were used to quantify holdup. The measurements were performed during three measurement campaigns. The first campaign, Phase I, provided foot-by-foot, semiquantitative measurement data on all ducting. These data were used to identify ducting that required more accurate (quantitative) measurement. Of the 280 duct systems receiving Phase I measurements, 262 indicated less than 50 g of fissile holdup and 19 indicated fissile holdup of 50 or more grams. Seven duct systems were measured in a second campaign, called Series 1, Phase II. Holdup estimates on these ducts ranged from 421 g of {sup 235}U in a duct servicing a shut-down uranium-machining facility to 39 g of {sup 239}Pu in a duct servicing an active plutonium-processing facility. Measurements performed in the second campaign proved excessively laborious, so a third campaign was initiated that used more efficient instrumentation at some sacrifice in measurement quality. Holdup estimates for the 12 duct systems measured during this third campaign ranged from 70 g of {sup 235}U in a duct servicing analytical laboratories to 1 g of {sup 235}U and 1 g of {sup 239}Pu in a duct carrying exhaust air to a remote filter building. These quantitative holdup estimates support the conclusion made at the completion of the Phase I measurements that only ducts servicing shut-down uranium operations contain about 400 g of fissile holdup. No ventilation ducts at Los Alamos contain sufficient fissile material holdup to present a criticality safety concern.

Marshall, R.S.

1994-02-01

342

Bubble-slug transition in two-phase, liquid-gas flow under microgravity conditions - A preliminary study  

Microsoft Academic Search

Existing microgravity flow-pattern observations in two-phase, gas-liquid flow, when compared against ground-based data, indicate a significant shift in the transition boundaries when gravity is reduced. Under those conditions of minimum or no gravitational forces acting on the flow, and a pronounced influence of surface tension forces; the transition from bubble to slug flow was repeatedly shown to be shifted during

K. S. Rezkallah

1990-01-01

343

Large eddy simulation of the Gas–Liquid flow in a square cross-sectioned bubble column  

Microsoft Academic Search

In this work the use of large eddy simulations (LES) in numerical simulations of the gas–liquid flow in bubble columns is studied. The Euler–Euler approach is used to describe the equations of motion of the two-phase flow. It is found that, when the drag, lift and virtual mass forces are used, the transient behaviour that was observed in experiments can

N. G. Deen; T. Solberg; B. H. Hjertager

2001-01-01

344

Homogeneous and bubbling fluidization regimes in DEM–CFD simulations: Hydrodynamic stability of gas and liquid fluidized beds  

Microsoft Academic Search

In recent years coupled DEM–CFD models have been successfully utilized to simulate fluidized particle systems in the bubbling regime. In this paper we report on DEM–CFD simulations of liquid-fluidization of glass beads and gas-fluidization of Geldart's Group A particles carried out to characterize hydrodynamically the stability of the fluidized state, in the absence of cohesive forces. Due to the importance

Alberto Di Renzo; Francesco Paolo Di Maio

2007-01-01

345

Adjustment of drag coefficient correlations in three dimensional CFD simulation of gas–solid bubbling fluidized bed  

Microsoft Academic Search

Fluidized beds have been widely used in power generation and in chemical, biochemical, and petroleum industries. 3D simulation of commercial scale fluidized beds has been computationally impractical due to the required memory and processor speeds. In this study, 3D Computational Fluid Dynamics simulation of a gas–solid bubbling fluidized bed is performed to investigate the effect of using different inter-phase drag

Ehsan Esmaili; Nader Mahinpey

2011-01-01

346

Small Gas Bubble Experiment for Mitigation of Cavitation Damage and Pressure Waves in Short-pulse Mercury Spallation Targets  

SciTech Connect

Populations of small helium gas bubbles were introduced into a flowing mercury experiment test loop to evaluate mitigation of beam-pulse induced cavitation damage and pressure waves. The test loop was developed and thoroughly tested at the Spallation Neutron Source (SNS) prior to irradiations at the Los Alamos Neutron Science Center - Weapons Neutron Research Center (LANSCE-WNR) facility. Twelve candidate bubblers were evaluated over a range of mercury flow and gas injection rates by use of a novel optical measurement technique that accurately assessed the generated bubble size distributions. Final selection for irradiation testing included two variations of a swirl bubbler provided by Japan Proton Accelerator Research Complex (J-PARC) collaborators and one orifice bubbler developed at SNS. Bubble populations of interest consisted of sizes up to 150 m in radius with achieved gas void fractions in the 10^-5 to 10^-4 range. The nominal WNR beam pulse used for the experiment created energy deposition in the mercury comparable to SNS pulses operating at 2.5 MW. Nineteen test conditions were completed each with 100 pulses, including variations on mercury flow, gas injection and protons per pulse. The principal measure of cavitation damage mitigation was surface damage assessment on test specimens that were manually replaced for each test condition. Damage assessment was done after radiation decay and decontamination by optical and laser profiling microscopy with damaged area fraction and maximum pit depth being the more valued results. Damage was reduced by flow alone; the best mitigation from bubble injection was between half and a quarter that of flow alone. Other data collected included surface motion tracking by three laser Doppler vibrometers (LDV), loop wall dynamic strain, beam diagnostics for charge and beam profile assessment, embedded hydrophones and pressure sensors, and sound measurement by a suite of conventional and contact microphones.

Wendel, Mark W [ORNL] [ORNL; Felde, David K [ORNL] [ORNL; Sangrey, Robert L [ORNL] [ORNL; Abdou, Ashraf A [ORNL] [ORNL; West, David L [ORNL] [ORNL; Shea, Thomas J [ORNL] [ORNL; Hasegawa, Shoichi [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Kogawa, Hiroyuki [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Naoe, Dr. Takashi [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Farny, Dr. Caleb H. [Boston University] [Boston University; Kaminsky, Andrew L [ORNL] [ORNL

2014-01-01

347

Proteomics of juvenile senegal sole (Solea senegalensis) affected by gas bubble disease in hyperoxygenated ponds.  

PubMed

Solea senegalensis is a commercial flat fish traditionally farmed in earth ponds in coastal wetlands that might also become important to more intensive aquaculture. Gas bubble disease (GBD) is a potential risk for outdoor fish farming, particularly in certain periods of the year, related to improper management leading to macroalgae blooms. Physical-chemical conditions inducing hyperoxia, including radiation, temperature, and high levels of dissolved oxygen, have been monitored in fish affected by GBD together with observed symptoms. Exophthalmia, subcutaneous emphysemas, obstruction of gill lamellae, hemorrhages, and anomalous swimming were the main effects of oxygen supersaturation. A proteomic study was carried out for the first time under aquaculture conditions and protein expression changes are described for fish that were subject to hyperoxic conditions. Proteins identified in gill of GBD-affected fish are related to oxidative alteration of cytoskeleton structure/function (beta-tubulin, beta-actin), motility (light myosin chain, alpha-tropomyosin), or regulatory pathways (calmodulin, Raf kinase inhibitor protein), reflecting the central role of gill in oxygen exchange. Hepatic proteins identified are related to protein oxidative damages (beta-globin, FABPs), protection from oxidative stress (DCXR, GNMT), and inflammatory response (C3), in agreement with the predominant metabolic role of liver. Comparison of protein expression patterns and protein identification are suggested as potentially specific hyperoxia biomarkers that would facilitate prevention of GBD outbreaks. PMID:19101763

Salas-Leiton, E; Cánovas-Conesa, B; Zerolo, R; López-Barea, J; Cañavate, J P; Alhama, J

2009-01-01

348

Hydroacoustic methodology for detection, localization, and quantification of gas bubbles rising from the seafloor at gas seeps from the eastern Black Sea  

NASA Astrophysics Data System (ADS)

Detailed acoustic investigation of bubble streams rising from the seafloor were conducted during R/V Meteor cruise M72/3a at a deep submarine hydrocarbon seep environment. The area is located offshore Georgia (eastern part of the Black Sea) at a water depth between 840 m and 870 m. The sediment echosounder Parasound DS-3/P70 was used for detecting bubbles in the water column that causes strong backscatter in the echographs ("flares"). Employing the swath echsounder Kongsberg EM710 flares in the water column were mapped along the entire swath width of approximately 1000 m at high spatial resolution. The exact location of the flares could be extracted manually. Subsequently, the horizontally looking sonar Kongsberg digital telemetry MS1000 mounted on a remotely operated vehicle (ROV) was utilized to quantify the flux of bubbles. A model was developed that is based on the principle of finding the "acoustic mass" in order to quantify the bubble flux at various seeps. The acoustic approach from the backscatter data of the ROV sonar resulted in bubble fluxes in the range of 0.01 to 5.5 L/min (corresponding to 0.037 to 20.5 mol CH4/min) at in situ conditions (˜850 m water depth, ˜9°C). Independent flux estimations using a funnel-shaped device showed that the acoustic model consistently produced lower values but the offset is less than 12%. Furthermore, the deviation decreased with increasing flux rates. A field of bubble streams was scanned three times from different directions in order to reveal the reproducibility of the method. Flux estimations yielded consistent fluxes of about 2 l/min (7.4 mol CH4/min) with variations of less than 10%. Although gas emissions have been found at many sites at the seafloor in a range of geological settings, the amount of escaping gas is still largely unknown. With this study presenting a novel method of quantifying bubble fluxes employing a horizontally looking sonar system, it is intended to contribute to the global effort of better constraining bubble fluxes at deep-sea settings.

Nikolovska, Aneta; Sahling, Heiko; Bohrmann, Gerhard

2008-10-01

349

Gas-solid fluidized bed reactors: Scale-up, flow regimes identification and hydrodynamics  

NASA Astrophysics Data System (ADS)

This research studied the scale-up, flow regimes identification and hydrodynamics of fluidized beds using 6-inch and 18- inch diameter columns and different particles. One of the objectives was to advance the scale-up of gas-solid fluidized bed reactors by developing a new mechanistic methodology for hydrodynamic similarity based on matching the radial or diameter profile of gas phase holdup, since gas dynamics dictate the hydrodynamics of these reactors. This has been successfully achieved. However, the literature reported scale-up methodology based on matching selected dimensionless groups was examined and it was found that it was not easy to match the dimensionless groups and hence, there was some deviation in the hydrodynamics of the studied two different fluidized beds. A new technique based on gamma ray densitometry (GRD) was successfully developed and utilized to on-line monitor the implementation of scale-up, to identify the flow regime, and to measure the radial or diameter profiles of gas and solids holdups. CFD has been demonstrated as a valuable tool to enable the implementation of the newly developed scale-up methodology based on finding the conditions that provide similar or closer radial profile or cross sectional distribution of the gas holdup. As gas velocity increases, solids holdup in the center region of the column decreases in the fully developed region of both 6 inch and 18 inch diameter columns. Solids holdup increased with the increase in the particles size and density. Upflowing particles velocity increased with the gas velocity and became steeper at high superficial gas velocity at all axial heights where the center line velocity became higher than that in the wall region. Smaller particles size and lower density gave larger upflowing particles velocity. Minimum fluidization velocity and transition velocity from bubbly to churn turbulent flow regimes were found to be lower in 18 inch diameter column compared to those obtained in 6 inch diameter column. Also the absolute fluctuation of upflowing particles velocity multiplied by solids holdups v? 3? as one of the terms for solids mass flux estimation was found to be larger in 18-inch diameter column than that in 6-inch diameter column using same particles size and density.

Zaid, Faraj Muftah

350

Gas-bubbled nano zero-valent iron process for high concentration arsenate removal.  

PubMed

In this study, batch experiments were performed to investigate a novel process for high concentration arsenate removal in the presence of air and/or CO(2) bubbling. The pretreatment step, CO(2) bubbling at 300 mL/min for 5 min, was taken to adjust the solution pH to an acidic environment, followed by air bubbling at 300 mL/min for 10 min to increase dissolved oxygen in the solution. In the treatment period, the nano-scale zero-valent iron was applied to remove aqueous arsenate of 3000 ?g/L, while the treatment system was continuously bubbled by 300 mL/min of air. Such a process resulted in outstanding performance in arsenate removal. Furthermore, in the field groundwater application, the arsenate removal rate for the proposed process was 5 times faster than the rate measured when the system was pretreated by acidic chemical species only. PMID:21256674

Tanboonchuy, Visanu; Hsu, Jia-Chin; Grisdanurak, Nurak; Liao, Chih-Hsiang

2011-02-28

351

A Refined Approach to Bubble Nucleation and Polymer Foaming Process: Dissolved Gas and Cluster Size Effects  

Microsoft Academic Search

A refined approach to bubble nucleation is presented and applied to polymer foaming process. The integral overall energy balance and the integral Clausius-Duhem inequality are used to analyze a bubble nucleation experiment. The computation of long-range intermolecular potential results in expressions for surface tension, work, and critical work for cluster formation, as functions of the Hamaker constant, molecular and\\/or repeat

James G. Lee; Raymond W. Flumerfelt

1996-01-01

352

Hold-up power supply for flash memory  

NASA Technical Reports Server (NTRS)

A hold-up power supply for flash memory systems is provided. The hold-up power supply provides the flash memory with the power needed to temporarily operate when a power loss exists. This allows the flash memory system to complete any erasures and writes, and thus allows it to shut down gracefully. The hold-up power supply detects when a power loss on a power supply bus is occurring and supplies the power needed for the flash memory system to temporally operate. The hold-up power supply stores power in at least one capacitor. During normal operation, power from a high voltage supply bus is used to charge the storage capacitors. When a power supply loss is detected, the power supply bus is disconnected from the flash memory system. A hold-up controller controls the power flow from the storage capacitors to the flash memory system. The hold-up controller uses feedback to assure that the proper voltage is provided from the storage capacitors to the flash memory system. This power supplied by the storage capacitors allows the flash memory system to complete any erasures and writes, and thus allows the flash memory system to shut down gracefully.

Ott, William E. (Inventor)

2004-01-01

353

Unsteady Thermocapillary Migration of Bubbles.  

National Technical Information Service (NTIS)

Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubb...

L. H. Dill R. Balasubramaniam

1988-01-01

354

Novel techniques for slurry bubble column hydrodynamics  

SciTech Connect

The objective of this cooperative research effort between Washington University, Ohio State University and Exxon Research Engineering Company was to improve the knowledge base for scale-up and operation of slurry bubble column reactors for syngas conversion and other coal conversion processes by increased reliance on experimentally verified hydrodynamic models. During the first year (July 1, 1995--June 30, 1996) of this three year program novel experimental tools (computer aided radioactive particle tracking (CARPT), particle image velocimetry (PIV), heat probe, optical fiber probe and gamma ray tomography) were developed and tuned for measurement of pertinent hydrodynamic quantities, such as velocity field, holdup distribution, heat transfer and bubble size. The accomplishments were delineated in the First Technical Annual Report. The second year (July, 1996--June 30, 1997) was spent on further development and tuning of the novel experimental tools (e.g., development of Monte Carlo calibration for CARPT, optical probe development), building up the hydrodynamic data base using these tools and comparison of the two techniques (PIV and CARPT) for determination of liquid velocities. A phenomenological model for gas and liquid backmixing was also developed. All accomplishments were summarized in the Second Annual Technical Report. During the third and final year of the program (July 1, 1997--June 30, 1998) and during the nine months no cost extension, the high pressure facility was completed and a set of data was taken at high pressure conditions. Both PIV, CT and CARPT were used. More fundamental hydrodynamic modeling was also undertaken and model predictions were compared to data. The accomplishments for this period are summarized in this report.

Dudukovic, M.P.

1999-05-14

355

Evaluation of the Integrated Holdup Measurement System with the M3(superscript 3)CA for Assay of Uranium and Plutonium Holdup  

SciTech Connect

Uranium and plutonium holdup that has been simulated by insertion of a variety of sealed, reference samples into pipes, ducts, and other hardware has been measured over a period of six years with an integrated holdup measurement system. The result is a systematic evaluation of the generalized-geometry holdup (GGH) formalism applied to portable gamma-ray holdup measurements with low-resolution detectors. The extended exercise was carried out both with and without automation of the measurements, data reduction/analysis, and holdup evaluation. Automation was accomplished by the software Version 2 for the Holdup Measurement System (HMS2). The purpose of the exercise was to establish reliable benchmarks for GGH measurements and to document the advantages of the automation with actual measurement results. The results presented below demonstrate a factor of 2 improvement in the quantitative reliability of the holdup assay automated by HMS2. The automated results are otherwise identical to the manual measurements. These and similar exercises also show that automation can decrease by a factor of 20 or more the time required to execute a holdup measurement campaign and obtain the holdup quantities for the facility using an integrated holdup measurement system, and that only one person, rather than two, is required to perform the measurements. Enhanced implementation of the integrated holdup measurement system with new software, corrections for systematic effects, and improved room-temperature gamma-ray detectors is planned.

P. A. Russo; J. K. Sprinkle, Jr.; C. W. Bjork; T. O. McKown; G. A. Sheppard; S. E. Smith; J. F. Harris

1999-08-01

356

Evolution of the two-phase flow in a vertical tube—decomposition of gas fraction profiles according to bubble size classes using wire-mesh sensors  

Microsoft Academic Search

The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2–3 mm. At moderate flow velocities (up to 1–2 m·s?1), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions.

Horst-Michael Prasser; Eckhard Krepper; Dirk Lucas

2002-01-01

357

The North Sea Blowout: A gas bubble megaplume with spiral vortex motion and why it might, or might not, contribute much to the atmospheric methane  

NASA Astrophysics Data System (ADS)

In the Central North Sea, during drilling operations, a gas blowout accident happened in 1990. Thereafter, natural gas has leaked prodigiously from a 60 m diameter and 20 m deep crater located at 95 m depth into the water column and to the sea surface. A series of field studies was carried out at this site since 2005 evidencing ongoing intense seepage activity. Three gas bubble megaplumes and dozens of minor to major bubble seeps were observed in the crater during a manned submersible dive, ROV mapped hundreds. Analysis of gas bubbles captured at 118 m water depth revealed concentrations between 88-90%Vol CH4 with ? 13C-CH4 values around -74‰ VPDB, consistent with a biogenic origin. Blowout site flux estimates derived from ROV video show the site's emissions are the strongest and most intense marine methane seepage quantified to date with seabed emissions of ~32.6 kt/y. Based on previous research suggesting greater flux correlates with greater transport efficiency, the direct bubble-mediated atmospheric flux to the atmosphere was estimated at a surprisingly low 0.7kt/y. This is orders of magnitude smaller compared to the seabed flux, thus the bulk methane dissolves before reaching the atmosphere, suggesting enhanced bubble dissolution rates for megaplumes. Analysis of more than 120 water samples from near the blowout plume showed dissolved methane concentration distributions consistent with enhanced bubble dissolution at depth. CH4 concentrations ranged from 0.2 µmol/L at 20 m depth to a peak in the crater of an extraordinary 400 µmol/L. To evaluate further the controlling factors on the rising bubble plume, multibeam water column data were analyzed. The bubble plume spatial distribution revealed a horizontal intrusion of gas bubbles just below the thermocline. This pronounced pattern was traced 200 m horizontally with a downflow plume orientation suggesting trapping of methane-enriched fluids at depth. A numerical bubble propagation model was used to simulate the extraordinarily intense Blowout site plume. Simulations that used normal bubble dissolution rates were unable to explain the observed trapping of almost all methane at depth, even when neglecting the observed very strong upwelling flows at the site. Incorporating a hypothesized enhanced bubble gas exchange rate allowed reproduction of observations. Video and multibeam water column analyses revealed significant turbulence in and around the bubble plume on decimeter and meter scale. Moreover 3D water column assessments by multibeam reveal that the gas ebullitions merge into a 20 m wide spiral vortex extending throughout the water column. Spiral vortex formation never has been reported for gas seepage and may be an important process enhancing plume methane dissolution. Numerical simulations incorporating vortical bubble trapping (slow rise) and enhanced bubble gas exchange were able to reproduce observations. Thus, megaplume processes could explain the surprising low surface methane observations, with important implications for understanding the fate of methane from intense seepage and for blowout response.

Schneider von Deimling, Jens; Leifer, Ira; Schmidt, Mark; Rehder, Gregor; Linke, Peter

2014-05-01

358

Production of Radiolytic Gas Bubbles and Their Influence on the Dynamic Behavior of Water Boiler Reactors (thesis); BILDUNG VON RADIOLYTISCHEN BLASEN UND IHR EINFLUSS AUF DAS DYNAMISCHE VERHALTEN VON WASSERKOCHER-REAKTOREN (THESE)  

Microsoft Academic Search

Experiments performed in the normal operation range of the Water Boiler Reactor FRF (L-54-F) show that radiolytic gas bubbles are formed only after a critical energy input, when the fuel solution has become highly supersaturated with dissolved gas. The supersaturation observed can be shown to be high enough to allow a nucleation of gas bubbles by the recoil of fission

Stelzer

1963-01-01

359

Bubble Mania  

NSDL National Science Digital Library

In this math lesson, learners practice measurement skills as they examine a soap bubble print. Learners follow a recipe to make a soap bubble solution. They use the soapy solution to blow large bubbles with a plastic drinking straw until the bubbles pop, leaving behind circular prints. Learners find the diameter, circumference, and area of the bubble print.

Pbs

2012-01-01

360

Implementation and verification of numerical model for gas bubble dynamics in electroconductive fluid  

NASA Astrophysics Data System (ADS)

Apart from common steam reforming process the thermal decomposition of methane is regarded as an alternate route to producing hydrogen and elemental carbon with out of CO2 emissions. Chemical reaction of decarburation can be ensured by means of methane bubbly flow through a molten metal bath and additionally controlled by external electromagnetic field. This is the initial stage of research and preliminary calculation results for the single bubble rise dynamics in 2D axisymmetric consideration at different flow conditions and 2D planar consideration in the presence of external DC EM field are obtained and compared to experimental and simulation data from literature.

Tucs, A.; Spitans, S.; Jakovics, A.; Baake, E.

2013-10-01

361

A Refined Approach to Bubble Nucleation and Polymer Foaming Process: Dissolved Gas and Cluster Size Effects  

PubMed

A refined approach to bubble nucleation is presented and applied to polymer foaming process. The integral overall energy balance and the integral Clausius-Duhem inequality are used to analyze a bubble nucleation experiment. The computation of long-range intermolecular potential results in expressions for surface tension, work, and critical work for cluster formation, as functions of the Hamaker constant, molecular and/or repeat unit interaction distance, molar fractions of each component, and cluster radius. The variation of surface tension with cluster size, temperature, and pressure is determined in terms of well-known macroscopic properties and compared with available experimental data. PMID:8978536

Lee; Flumerfelt

1996-12-25

362

Upper ocean bubble measurements from the NE Pacific and estimates of their role in air-sea gas transfer of the weakly soluble gases nitrogen and oxygen  

NASA Astrophysics Data System (ADS)

Simultaneous observations of upper-ocean bubble clouds, and dissolved gaseous nitrogen (N2) and oxygen (O2) from three winter storms are presented and analyzed. The data were collected on the Canadian Surface Ocean Lower Atmosphere Study (C-SOLAS) mooring located near Ocean Station Papa (OSP) at 50°N, 145°W in the NE Pacific during winter of 2003/2004. The bubble field was measured using an upward looking 200 kHz echosounder. Direct estimates of bubble mediated gas fluxes were made using assumed bubble size spectra and the upward looking echosounder data. A one-dimensional biogeochemical model was used to help compare data and various existing models of bubble mediated air-sea gas exchange. The direct bubble flux calculations show an approximate quadratic/cubic dependence on mean bubble penetration depth. After scaling from N2/O2 to carbon dioxide, near surface, nonsupersaturating, air-sea transfer rates, KT, for U10 > 12 m s-1 fall between quadratic and cubic relationships. Estimates of the subsurface bubble induced air injection flux, VT, show an approximate quadratic/cubic dependence on mean bubble penetration depth. Both KT and VT are much higher than those measured during Hurricane Frances over the wind speed range 12 < U10 < 23 m s-1. This result implies that over the open ocean and this wind speed range, older and more developed seas which occur during winter storms are more effective in exchanging gases between the atmosphere and ocean than younger less developed seas which occur during the rapid passage of a hurricane.

Vagle, Svein; McNeil, Craig; Steiner, Nadja

2010-12-01

363

What can be Learned from X-ray Spectroscopy Concerning Hot Gas in Local Bubble and Charge Exchange Processes?  

NASA Technical Reports Server (NTRS)

What can be learned from x-ray spectroscopy in observing hot gas in local bubble and charge exchange processes depends on spectral resolution, instrumental grasp, instrumental energy band, signal-to-nose, field of view, angular resolution and observatory location. Early attempts at x-ray spectroscopy include ROSAT; more recently, astronomers have used diffuse x-ray spectrometers, XMM Newton, sounding rocket calorimeters, and Suzaku. Future observations are expected with calorimeters on the Spectrum Roentgen Gamma mission, and the Solar Wind Charge Exchange (SWCX). The Geospheric SWCX may provide remote sensing of the solar wind and magnetosheath and remote observations of solar CMEs moving outward from the sun.

Snowden, Steve

2007-01-01

364

Gas Bubble Detection and Decompression Sickness Prevention by Noninvasive Bioelectrical Impedance Spectroscopy.  

National Technical Information Service (NTIS)

Excessively rapid decompression causes bubble formation in the blood and tissues which can in turn cause Decompreesion SicKness (DcS) through a variety of mecheniams that inc1ude direct mechanical damage to tissue and perfusion impairment. Noninvasive com...

W. A. Gerth

1991-01-01

365

On the theory of fission gas bubble evolution in irradiated UO 2 fuel  

Microsoft Academic Search

The standard approaches for modelling of the intra- and intergranular bubbles evolution in the UO2 fuel are critically analysed on the basis of available experimental data. It is demonstrated that the main disadvantage of the simplified treatment of the problem by the standard models can be associated with underestimation of the radiation effects at low temperatures (below 1500°C) and thermal

M. S. Veshchunov

2000-01-01

366

Gravity effects in the problem of gas bubble formation and dynamics in liquid phase  

Microsoft Academic Search

Gravity effects in the problem of nucleation, development, and dynamics of gaseous inclusions in liquid phase are considered under gravity and microgravity conditions. It is shown that gravity has an impact on nucleation due to both the hydrostatic pressure in liquid and the capillary pressure. For poor wetting the latter effect suppresses the bubble nucleation with the evaporation of volatile

V. P. Shalimov

1991-01-01

367

Water holdup measurement in kerosene water two-phase flows  

NASA Astrophysics Data System (ADS)

This paper proposes an intrusive method for measurement of water holdup based on water layer thickness in horizontal pipes. Water layer thickness is measured by a capacitance probe, which is made of a metal wire with an insulating film. The capacitance is linearly proportional to the water layer thickness and is independent of water salinity and its distribution. Seven thicknesses over the cross section of the pipe are measured simultaneously to compute water holdup. A curve of water layer thickness as a function of time is compared with a flow structure photo and the measured time-averaged water holdup is compared with that of a quick-closing valve (QCV) system. The experiments were carried out in kerosene-oil two-phase flows with high water fraction in horizontal pipes of 29 mm diameter. Four flow patterns with continuous water are reported, namely wavy stratified flow (WS), three-layer flow (3 L), water and dispersed oil in water flow (W&DO/W) and dispersed oil in water flow (DO/W). The results show that the layer thickness curves are in reasonable agreement with the flow structures to different extents under different flow patterns and that the accuracies of the measured water holdup mainly depend on flow patterns. The relative error limits of water holdup are -15.2% for WS, 12.9% and -14.5% (positive and negative) for 3 L, 34.9% for W&DO/W and 15.8% for DO/W.

Huang, S.-F.; Zhang, X.-G.; Wang, D.; Lin, Z.-H.

2007-12-01

368

Cohesion of Bubbles in Foam  

ERIC Educational Resources Information Center

The free-energy change, or binding energy, of an idealized bubble cluster is calculated on the basis of one mole of gas, and on the basis of a single bubble going from sphere to polyhedron. Some new relations of bubble geometry are developed in the course of the calculation. (BB)

Ross, Sydney

1978-01-01

369

The effect of lattice and grain boundary diffusion on the redistribution of Xe in metallic nuclear fuels: Implications for the use of ion implantation to study fission-gas-bubble nucleation mechanisms  

Microsoft Academic Search

A multi-atom gas bubble-nucleation mechanism has been proposed as part of a predictive fission-gas release model for metallic nuclear fuels. Validation of this mechanism requires experimental measurement of fission-gas bubble-size distributions at well-controlled gas concentrations and temperatures. There are advantages to carrying out such a study using ion implantation as the source of gas atoms compared with neutron irradiations. In

Wayne E. King; Scott J. Tumey; Jeffrey Rest; George H. Gilmer

2011-01-01

370

Binary coalescence of gas bubbles in the presence of a non-ionic surfactant.  

PubMed

The coalescence behavior of air bubbles in a dilute aqueous surfactant solution of a polyglycerol fatty acid ester (PGE), a commercial non-ionic surfactant, is investigated in a binary coalescence experiment. The focus is on the influence of the ionic strength of the solution on the rate of coalescence. Results are compared with the adsorption kinetics and surface shear/dilatational rheological properties of the surfactant. Experiments show that the coalescence frequency is significantly lower at low ionic strength, and that bubble stability increases with increasing aging time. Stabilization occurs via surfactant adsorption and a resulting electrostatic and/or steric repulsive force. The electrostatic force presumably originates from small amounts of anionic fatty acid soaps, which are residues from the industrial synthesis. The steric force can be related to the adsorption of visco-elastic layers of PGE at the air-water interface. PMID:19200557

Duerr-Auster, N; Gunde, R; Mäder, R; Windhab, Erich J

2009-05-15

371

Cluster finds giant gas vortices at the edge of Earth's magnetic bubble  

NASA Astrophysics Data System (ADS)

12 August 2004 ESA’s quartet of space-weather watchers, Cluster, has discovered vortices of ejected solar material high above the Earth. The superheated gases trapped in these structures are probably tunnelling their way into the Earth’s magnetic ‘bubble’, the magnetosphere. This discovery possibly solves a 17-year-mystery of how the magnetosphere is constantly topped up with electrified gases when it should be acting as a barrier. hi-res Size hi-res: 1446 Kb Credits: H. Hasegawa (Dartmouth College) Three-dimensional cut-away view of Earth's magnetosphere This figure shows a three-dimensional cut-away view of Earth' s magnetosphere. The curly features sketched on the boundary layer are the Kelvin-Helmholtz vortices discovered by Cluster. They originate where two adjacent flows travel with different speed. In this case, one of the flows is the heated gas inside the boundary layer of the magnetosphere, the other the solar wind just outside it. The arrows show the direction of the magnetic field, in red that associated with the solar wind and in green the one inside Earth’s magnetosphere. The white dashed arrow shows the trajectory followed by Cluster. High resolution version (JPG format) 1446 Kb High resolution version (TIFF format) 15 365 Kb hi-res Size hi-res: 22 Kb Credits: H. Hasegawa (Dartmouth College) Electrified gas varies across the vortices along Cluster’s trajectory This computer simulation shows how the density of the electrified gas is expected to vary across the vortices along Cluster’s trajectory (white dashed line). The density is lower inside the boundary layer (blue region) and higher outside, in the region dominated by the solar wind (shown in red). The density variations measured by the instruments on board Cluster match those predicted by this model. Low resolution version (JPG format) 22 Kb High resolution version (TIFF format) 3438 Kb The Earth’s magnetic field is our planet’s first line of defence against the bombardment of the solar wind. The solar wind itself is launched from the Sun and carries the Sun’s magnetic field throughout the Solar System. Sometimes this magnetic field is aligned with Earth’s and sometimes it points in the opposite direction. When the two fields point in opposite directions, scientists understand how ‘doors’ in Earth’s field can open. This phenomenon, called ‘magnetic reconnection’, allows the solar wind to flow in and collect in the reservoir known as the boundary layer. On the contrary, when the fields are aligned they should present an impenetrable barrier to the flow. However, spacecraft measurements of the boundary layer, dating back to 1987, present a puzzle because they clearly show that the boundary layer is fuller when the fields are aligned than when they are not. So how is the solar wind getting in? Thanks to the data from the four formation-flying spacecraft of ESA’s Cluster mission, scientists have made a breakthrough. On 20 November 2001, the Cluster flotilla was heading around from behind Earth and had just arrived at the dusk side of the planet, where the solar wind slides past Earth’s magnetosphere. There it began to encounter gigantic vortices of gas at the magnetopause, the outer ‘edge’ of the magnetosphere. “These vortices were really huge structures, about six Earth radii across,” says Hiroshi Hasegawa, Dartmouth College, New Hampshire who has been analysing the data with help from an international team of colleagues. Their results place the size of the vortices at almost 40 000 kilometres each, and this is the first time such structures have been detected. These vortices are known as products of Kelvin-Helmholtz instabilities (KHI). They can occur when two adjacent flows are travelling with different speeds, so one is slipping past the other. Good examples of such instabilities are the waves whipped up by the wind slipping across the surface of the ocean. Although KHI-waves had been observed before, this is the first time that vortices are actually detected. When a KHI-wave rolls up into a vortex, it become

2004-08-01

372

Velocity of a freely rising gas bubble in a soda-lime silicate glass melt  

NASA Technical Reports Server (NTRS)

A comparison is conducted between measured velocities for the buoyant rise of single bubbles of varying size and composition, in a soda-lime silicate glass melt, with the steady state velocities predicted by the Stokes and Hadamard-Rybczynski formulas. In all cases, the data are noted to fit the Hadamard-Rybczynski expression for steady state rise speed considerably better than the Stokes formula.

Hornyak, E. J.; Weinberg, M. C.

1984-01-01

373

In situ visualization study of CO 2 gas bubble behavior in DMFC anode flow fields  

Microsoft Academic Search

This paper reports on a visual study of the CO2 bubble behavior in the anode flow field of an in-house fabricated transparent Direct Methanol Fuel Cell (DMFC), which consisted of a membrane electrode assembly (MEA) with an active area of 4.0 × 4.0cm2, two bipolar plates with a single serpentine channel, and a transparent enclosure. The study reveals that at

H. Yang; T. S. Zhao; Q. Ye

2005-01-01

374

Use of tracers in materials-holdup study  

SciTech Connect

Holdup measurements of special nuclear materials in large processing facilities offer considerable challenges to conventional nondestructive-assay techniques. The use of judiciously chosen radioactive tracers offer a unique method of overcoming this difficulty. Three examples involving the use of /sup 46/Sc and fission products from activated uranium in large-scale experimental studies of uranium holdup are discussed. A justification for the method and its advantages along with examples of successful applications of this technique for large-sale experimental studies are presented.

Pillay, K.K.S.

1983-01-01

375

Bubble dielectrophoresis  

Microsoft Academic Search

The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements,

T. B. Jones; G. W. Bliss

1977-01-01

376

Investigation of the influence of an inner gas bubble on the response of a liquid scintillation detector to ?-rays and neutrons  

NASA Astrophysics Data System (ADS)

The influence of an inert gas bubble inside EJ301 cylindrical cell on the response of the liquid scintillation detector to ?-rays and neutrons has been investigated. It is found experimentally that the response of the detector to radiation varies with the detector placement styles. The explanation proposed in this article is that this variation arises from the change of the light transmission process induced by the motion of the inner gas bubble. This assertion has been supported by the simulations of both radiation energy deposition and light transmission process inside the detector with the GEANT4 code. For the recommended detector placement style when the detector is placed horizontally, the variation of the response is smaller than 1.56%, which will increase to about 22% when the detector is placed facing down and the bubble lies between the scintillator and photomultiplier tube.

Xufei, Xie; Xing, Zhang; Xi, Yuan; Tieshuan, Fan; Jinxiang, Chen; Xiangqing, Li

2013-09-01

377

Influence of infection with Renibacterium salmoninarum on susceptibility of juvenile spring chinook salmon to gas bubble trauma  

USGS Publications Warehouse

During experiments in our laboratory to assess the progression and severity of gas bubble trauma (GBT) in juvenile spring chinook salmon Oncorhynchus tshawytscha, we had the opportunity to assess the influence of Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease, on the susceptibility of salmon to GBT. We exposed fish with an established infection of Rs to 120% total dissolved gas (TDG) for 96 h and monitored severity of GBT signs in the fins and gills, Rs infection level in kidneys by using an enzyme-linked immunosorbent assay (ELISA), and mortality. Mortality occurred rapidly after exposure to 120% TDG, with a LT20 (time necessary to kill 20% of the population) of about 37 h, which is at a minimum about 16% earlier than other bioassays we have conducted using fish that had no apparent signs of disease. Fish that died early (from 31 to 36 h and from 49 to 52 h) had significantly higher infection levels (mean ?? SE ELISA absorbance = 1.532 ?? 0.108) than fish that survived for 96h (mean ?? SE ELISA absorbance = 0.828 ?? 0.137). Fish that died early also had a significantly greater number of gill filaments occluded with bubbles than those that survived 96 h. Conversely, fish that survived for 96 h had a significantly higher median fin severity ranking than those that died early. Our results indicate that fish with moderate to high levels of Rs infection are more vulnerable to the effects of dissolved gas supersaturation (DGS) and die sooner than fish with lower levels of Rs infection. However, there is a substantial amount of individual variation in susceptibility to the apparent cumulative effects of DGS and Rs infection. Collectively, our findings have important implications to programs designed to monitor the prevalence and severity of GBT in juvenile salmonids in areas like the Columbia River basin and perhaps elsewhere.

Weiland, L. K.; Mesa, M. G.; Maule, A. G.

1999-01-01

378

Dynamic simulation of bubbly flow in bubble columns  

Microsoft Academic Search

Gas–liquid bubbly flow in two-dimensional bubble columns is studied by numerical simulation. An Eulerian–Eulerian two-fluid model is used to describe the time-dependent motion of the liquid driven by small, spherical gas bubbles injected at the bottom of the columns. The simulations are able to capture the large scale structures as observed experimentally in the laboratory. The numerical results, which include

Y. Pan; M. P. Dudukovic; M. Chang

1999-01-01

379

Tribonucleation of bubbles.  

PubMed

We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rubbing force and velocity exceed a certain threshold. Direct observation through a transparent solid shows that each bubble in the trail results from the early coalescence of several microscopic bubbles, themselves detaching from microscopic gas pockets forming between the solids. From a detailed study of the wear tracks, with atomic force and scanning electron microscopy imaging, we conclude that these microscopic gas pockets originate from a local fracturing of the surface asperities, possibly enhanced by chemical reactions at the freshly created surfaces. Our findings will be useful either for preventing undesired bubble formation or, on the contrary, for "writing with bubbles," i.e., creating controlled patterns of microscopic bubbles. PMID:24982169

Wildeman, Sander; Lhuissier, Henri; Sun, Chao; Lohse, Detlef; Prosperetti, Andrea

2014-07-15

380

Soluble surfactants favorably modify fluid structure and wall shear stress profiles during near-occluding bubble motion in a computational model of intravascular gas embolism  

NASA Astrophysics Data System (ADS)

Finite sized gas bubble motion in a blood vessel causes temporal and spatial gradients of shear stress at the endothelial cell surface lining the vessel wall as the bubble approaches the cell, moves over it and passes it by. Rapid reversals occur in the sign of the shear stress imparted to the cell surface during this motion. The sign-reversing shear is a potently coupled source of cell surface mechanical stretch, potentiating cell injury. The presence of a suitable soluble surfactant in the bulk medium considerably reduces the level of the shear stress gradients imparted to the cell surface as compared to an equivalent surfactant-free system. The bubble shape and the film thickness between the bubble and the vessel wall are also different. Furthermore, the bubble residence time near the proximity of a cell surface changes in comparison. These results based on our modeling may help explain several phenomena observed in experimental studies related to gas embolism, a significant problem in cardiac surgery and decompression sickness.

Swaminathan, T. N.; Ayyaswamy, P. S.; Eckmann, D. M.

2009-11-01

381

The influence of the wall contact angle on gas bubble behaviour in xylem conduits under tension and possible consequences for embolism  

Microsoft Academic Search

Gas-filling of conduits decreases hydraulic conductance of the xylem vessels. Therefo re, embolism formation and reversal is one of the crucial topics in plant water transport. The negative pressure (=tension) in xylem water during plant transpiration may cause embolism in tw o ways: (i) Homogeneous nucleation, the spontaneous formation of a water vapour bubble within the water column due to

Wilfried Konrad; Anita Roth-Nebelsick

2009-01-01

382

Energy effects in bubble nucleation  

SciTech Connect

Bubble size and number produced by desorption are important considerations for certain industrial processes such as flotation, gas stripping, and some types of chemical reactions and mass transfer. The size and number of bubbles produced by the desorption of supersaturated gases from water are shown to be a primary function of the energy available for bubble formation in a flowing system; this energy is that not dissipated in turbulence and friction. The number of nucleation sites is greatly increased when certain impurities are present, particularly surface-active agents. Low saturation pressures can produce very large numbers of very small bubbles when added energy is provided for discharge. High gas concentrations produce excess large bubbles which pass up rapidly through the much slower rising bubble mass. A combination of low saturation pressure followed by higher pressure for flow, such as by liquid pumping, results in bubble characteristics which can be controlled for applications.

Jackson, M.L. (Univ. of Idaho, Moscow, ID (United States). Dept. of Chemical Engineering)

1994-04-01

383

Buoyant Bubbles  

NSDL National Science Digital Library

What keeps bubbles and other things, like airplanes, floating or flying in the air? In this activity, learners blow bubbles and wave 3x5 cards above, below and on different sides of the bubbles to keep them afloat as long as possible. The Did You Know section explains the Bernoulli principle: how waving cards above the bubbles helps keep them afloat because faster moving air exerts less pressure to push the bubbles down. The activity can be extended by having learners wave their bubbles through an obstacle course they design themselves.

Science, Lawrence H.

2009-01-01

384

Fluid Dynamics of Bubbly Liquids  

NASA Technical Reports Server (NTRS)

Experiments have been performed to study the average flow properties of inertially dominated bubbly liquids which may be described by a novel analysis. Bubbles with high Reynolds number and low Weber number may produce a fluid velocity disturbance that can be approximated by a potential flow. We studied the behavior of suspensions of bubbles of about 1.5 mm diameter in vertical and inclined channels. The suspension was produced using a bank of 900 glass capillaries with inner diameter of about 100 microns in a quasi-steady fashion. In addition, salt was added to the suspension to prevent bubble-bubble coalescence. As a result, a nearly monodisperse suspension of bubble was produced. By increasing the inclination angle, we were able to explore an increasing amount of shear to buoyancy motion. A pipe flow experiment with the liquid being recirculated is under construction. This will provide an even larger range of shear to buoyancy motion. We are planning a microgravity experiment in which a bubble suspension is subjected to shearing in a couette cell in the absence of a buoyancy-driven relative motion of the two phases. By employing a single-wire, hot film anemometer, we were able to obtain the liquid velocity fluctuations. The shear stress at the wall was measured using a hot film probe flush mounted on the wall. The gas volume fraction, bubble velocity, and bubble velocity fluctuations were measured using a homemade, dual impedance probe. In addition, we also employed a high-speed camera to obtain the bubble size distribution and bubble shape in a dilute suspension. A rapid decrease in bubble velocity for a dilute bubble suspension is attributed to the effects of bubble-wall collisions. The more gradual decrease of bubble velocity as gas volume fraction increases, due to subsequent hindering of bubble motion, is in qualitative agreement with the predictions of Spelt and Sangani for the effects of potential-flow bubble-bubble interactions on the mean velocity. The ratio of the bubble velocity variance to the square of the mean is 0(0.1). For these conditions Spelt and Sangani predicted that the homogeneous suspension would be unstable and clustering into horizontal rafts will take place. Evidence for bubble clustering is obtained by analysis of video images. The liquid velocity variance is larger than would be expected for a homogeneous suspension and the liquid velocity frequency spectrum indicates the presence of velocity fluctuations that are slow compared with the time for the passage of an individual bubble. These observations provide further evidence for bubble clustering.

Tsang, Y. H.; Koch, D. L.; Zenit, R.; Sangani, A.; Kushch, V. I.; Spelt, P. D. M.; Hoffman, M.; Nahra, H.; Fritz, C.; Dolesh, R.

2002-01-01

385

EFFECT OF STATIC LIQUID HEIGHT ON GAS-LIQUID MASS TRANSFER IN A DRAFT-TUBE BUBBLE COLUMN AND THREE-PHASE FLUIDIZED BED  

Microsoft Academic Search

Experiments are performed under batch-liquid operating conditions to investigate the effect of static liquid height on the gas-liquid mass transfer coefficient (KLa) in a draft-tube bubble column (DTBC) and a draft-tube three-phase fluidized bed (DTFB). In addition, the effects of column diameter, gas-distributor, and draft-tube diameter are studied. The results indicate that for a given system with a porous plate

FARSHAD BAVARIAN; CHIA-JUI LINN; T. S. RAMESH; LIANG-SHIH FAN

1991-01-01

386

Gas flow induced by ultrasonic cavitation bubble clouds and surface capillary wave.  

PubMed

In this paper, we report a gas flow phenomenon induced by ultrasonic water cavitation and capillary wave in a vibrating hollow tip and reflector system. The cavitation clouds generated a gas suction force and the capillary wave created tunnels through which the gas could go into the liquid. The gas flow rate was measured and compared under different conditions, including applied power, type of reflector, and tip-to-reflector distance. A model was proposed to explain the mechanisms of the gas flow and analyze the results in the experiments. PMID:24859668

Wang, Ying; Li, Tao; Kong, Ling; Hng, Huey; Lee, Pooi

2014-06-01

387

Observations of solute effects on bubble formation  

SciTech Connect

The authors have studied the effects of solute, in particular aqueous electrolyte, on bubble formation at capillary orifices and frits at varying gas flow rates. Using a stroboscope, video microscope, and rotating mirror, they have obtained pictures which show how bubble formation involves the interaction of bubbles at the orifice. These interactions depend on the value of the surface elasticity E due to positively (ethanol) or negatively (NaCl) adsorbed solute. At low flow rates consecutive bubbles do not interact. Each bubble detaches and leaves the orifice region before the next one starts forming. A intermediate flow rates the more closely spaced, consecutive bubbles begin to interact. In pure liquids there is no barrier to bubble coalescence and the detached bubble is fed by the subsequent bubble as this starts to grow. The process may be repeated several times before the original bubble has risen out of range. In solutions where E is large enough bubble coalescence is inhibited. Instead of feeding into the detached bubble the following bubble pushes it aside, and the bubbles appear to bounce off each other. Bouncing may give rise to a characteristic sequence of larger and smaller bubbles if the emerging bubbles break off prematurely from the orifice due to the inertia of the original bubble. The transition from feeding to bouncing depends critically on E of the solution and leads to a smaller average bubble size for large E values. At high flow rates detached bubbles are invariably fed by several subsequent ones. At very high flow rates the bubbling becomes chaotic, but the interaction of bubbles after leaving the orifice area produces smaller bubbles in solutions. Bouncing is more likely to occur with narrow and irregular capillaries. The dramatically different appearance of gas-sparged columns in salt water and freshwater has its origin in the difference between assemblies of pores showing mainly feeding (freshwater) or bouncing (salt water).

Hofmeier, U.; Yaminsky, V.V.; Christenson, H.K. [Australian National Univ., Canberra (Australia)] [Australian National Univ., Canberra (Australia)

1995-09-01

388

Bubble dielectrophoresis  

NASA Technical Reports Server (NTRS)

The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements, static-levitation experiments, and dynamic-force measurements.

Jones, T. B.; Bliss, G. W.

1977-01-01

389

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

PubMed

The efficacy of large tethered encapsulated gas bubbles for the mitigation of low frequency underwater noise was investigated with an acoustic resonator technique. Tethered latex balloons were used as the bubbles, which had radii of approximately 5 cm. Phase speeds were inferred from the resonances of a water and balloon-filled waveguide approximately 1.8 m in length. The Commander and Prosperetti effective-medium model [J. Acoust. Soc. Am. 85, 732-746 (1989)] quantitatively described the observed dispersion from well below to just below the individual bubble resonance frequency, and it qualitatively predicted the frequency range of high attenuation for void fractions between 2% and 5% for collections of stationary balloons within the waveguide. A finite-element model was used to investigate the sensitivity of the waveguide resonance frequencies, and hence the inferred phase speeds, to changes in individual bubble size and position. The results indicate that large tethered encapsulated bubbles could be used mitigate low frequency underwater noise and that the Commander and Prosperetti model would be useful in the design of such a system. PMID:22088005

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

2011-11-01

390

Study on bubbly flow behavior in natural circulation reactor by thermal-hydraulic simulation tests with SF6-Gas and ethanol liquid  

NASA Astrophysics Data System (ADS)

An advanced experimental technique has been developed to simulate two-phase flow behavior in a light water reactor (LWR). The technique applies three kinds of methods; (1) use of sulfur-hexafluoride (SF6) gas and ethanol (C2H5OH) liquid at atmospheric temperature and a pressure less than 1.0MPa, where the fluid properties are similar to steam-water ones in the LWR, (2) generation of bubble with a sintering tube, which simulates bubble generation on heated surface in the LWR, (3) measurement of detailed bubble distribution data with a bi-optical probe (BOP), (4) and measurement of liquid velocities with the tracer liquid. This experimental technique provides easy visualization of flows by using a large scale experimental apparatus, which gives three-dimensional flows, and measurement of detailed spatial distributions of two-phase flow. With this technique, we have carried out experiments simulating two-phase flow behavior in a single-channel geometry, a multi-rod-bundle one, and a horizontal-tube-bundle one on a typical natural circulation reactor system. Those experiments have clarified a) a flow regime map in a rod bundle on the transient region between bubbly and churn flow, b) three-dimensional flow behaviour in rod-bundles where inter-subassembly cross-flow occurs, c) bubble-separation behavior with consideration of reactor internal structures. The data have given analysis models for the natural circulation reactor design with good extrapolation.

Kondo, Yoshiyuki; Suga, Keishi; Hibi, Koki; Okazaki, Toshihiko; Komeno, Toshihiro; Kunugi, Tomoaki; Serizawa, Akimi; Yoneda, Kimitoshi; Arai, Takahiro

2009-02-01

391

Gas Bubbles and Gas Pancakes at Liquid\\/Solid Interface: A Continuum Theory Incorporated with Molecular Interactions  

Microsoft Academic Search

The states of gas accumulated at the liquid-solid interface are analyzed based on the continuum theory where the Hamaker constant is used to describe the long-range interaction at the microscopic scale. The Hamaker constant is always negative, whereas the gas spreading coefficient can be either sign. Despite the complexity of gas, including that the density profile may not be uniform

Zhaoxia Li; Xuehua Zhang; Lijuan Zhang; Xiaocheng Zeng; Jun Hu; Haiping Fang

2006-01-01

392

Soap Bubbles  

NSDL National Science Digital Library

Learners explore three-dimensional geometric frames including cubes and tetrahedrons, as they create bubble wands with pipe cleaners and drinking straws. Then they investigate how soap film flows into a state of minimum energy when they lift the wand up from the bubble solution. Learners also see how light reflection and interference create shimmering colors in the bubbles.

Exploratorium, The

2011-12-07

393

Best Bubbles  

NSDL National Science Digital Library

In this activity, learners experiment with creating various types of bubble solutions and testing which ingredients form longer-lasting bubbles. Learners investigate how surface tension works and the importance of using a surfactant to make bubbles. This activity includes a video about NASA astronaut Don Pettit, who used candy corn to conduct science experiments during his stint aboard the International Space Station.

Saltz, Austen

2010-01-01

394

Intense gas bubble emissions in the Kerch seep area - A newly discovered high-flux seep site in the Black Sea  

NASA Astrophysics Data System (ADS)

More than 500 bubble-induced hydroacoustic anomalies (flares) were found in the water column above the seafloor in the study area comprising about 430 km2 at the Don-Kuban paleo-fan (Eastern Black Sea) by using ship mounted single beam and multibeam echosounders. Almost all flares originated from the seafloor above the gas hydrate stability zone (GHSZ), which in that region is located below ~700 m water depth. This observation confirms the sealing mechanism of gas hydrate, which impedes migration of free gas through the GHSZ and subsequent bubble emission from the seafloor. However, an intense seep site, called the "Kerch seep area" was discovered as an exception at 890 m water depth well within the GHSZ. In situ temperature measurements in shallow sediments indicate locally elevated temperatures probably caused by enhanced upward fluid flow. The base of the GHSZ in this region is generally situated at about 150 m below the seafloor. However, the local thermal anomalies result in a thinning of the gas hydrate occurrence zone to only a few meters below the seafloor and allow free gas to reach the seafloor. At sites where gas migrated into near-surface deposits, shallow gas hydrate deposits evolved and up-doming of overlying sediments led to the formation of mounds rising several meters from the surrounding seafloor. Further gas bubbles ascending from greater depth are accumulated below the gas hydrate layer at the base of the mound structures and migrate horizontally to their rims. At the mound edges gas bubbles either might form fresh gas hydrates and increase the extent of the mound structures by pushing up overlying sediments or escape at several sites into the water column. Two mounds were mapped in ultra-high resolution during dives with the autonomous underwater vehicle 'AUV MARUM SEAL 5000'. Several individual flares were detected in the Kerch seep area using hydroacoustic systems. Repeated surveys in that area conducted during three cruises within four years suggested that gas discharge varied spatially and temporally while the total number of flares remained rather constant. During seafloor inspections with MARU?s remotely operated vehicle 'ROV QUEST 4000 m' gas bubble emission sites were investigated in detail. Gas bubbles collected during the ROV dives mainly consisted of methane predominantly of microbial origin. By analyzing the high-definition video material the gas flux from several bubble emission sites was calculated. In combination with the hydroacoustic results (flare distributions) it is estimated that about 2.2 - 87 × 106 mol CH4/yr are emitted from the seafloor at the Kerch seep area. Despite this high mass of methane injected into the hydrosphere, the peak of the highest flares at ~350 m water depth as revealed by echosounder recording suggest that the ascending methane completely dissolves in the water column and does not pass the sea-atmosphere boundary.

Römer, M.; Sahling, H.; Pape, T.; Bahr, A.; Feseker, T.; Wintersteller, P.; Bohrmann, G.

2012-04-01

395

Removal of NO from flue gas by aqueous chlorine-dioxide scrubbing solution in a lab-scale bubbling reactor.  

PubMed

The present study attempts to clean up nitric oxide from the simulated flue gas using aqueous chlorine-dioxide solution in the bubbling reactor. Chlorine-dioxide is generated by chloride-chlorate process. Experiments are carried out to examine the effect of various operating variables like input NO concentration, presence of SO(2), pH of the solution and NaCl feeding rate on the NO(x) removal efficiency at 45 degrees C. Complete oxidation of nitric oxide into nitrogen dioxide occurred on passing sufficient ClO(2) gas into the scrubbing solution. NO is finally converted into nitrate and ClO(2) is reduced into chloride ions. A plausible reaction mechanism concerning NO(x) removal by ClO(2) is suggested. DeNO(x) efficiency increased slightly with the increasing input NO concentration. The presence of SO(2) improved the NO(2) absorption but pH of solution showed marginal effect on NO(2) absorption. NO(x) removal mechanism changed when medium of solution changed from acidic to alkaline. A constant NO(x) removal efficiency of about 60% has been achieved in the wide pH range of 3-11 under optimized conditions. PMID:17583424

Deshwal, Bal Raj; Jin, Dong Seop; Lee, Si Hyun; Moon, Seung Hyun; Jung, Jong Hyeon; Lee, Hyung Keun

2008-02-11

396

TECHNOLOGY ASSESSMENT OF FINE BUBBLE AERATORS  

EPA Science Inventory

This technology assessment addresses design and evaluation of fine bubble aeration equipment. It discusses the associated gas transfer theory used as the basis for measuring water and wastewater oxygenation efficiency. Mixing requirements are also discussed. While bubble aeration...

397

Review of Current Literature and Research on Gas Supersaturation and Gas Bubble Trauma: Special Publication Number 1, 1986.  

SciTech Connect

This report presents recently published information and on-going research on the various areas of gas supersaturation. Growing interest in the effects of chronic gas supersaturation on aquatic animals has been due primarily to heavy mortality of salmonid species under hatchery conditions. Extensive examination of affected animals has failed to consistently identify pathogenic organisms. Water quality sampling has shown that chronic levels of gas supersaturation are commonly present during a significant period of the year. Small marine fish larvae are significantly more sensitive to gas supersaturation than salmonids. Present water quality criteria for gas supersaturation are not adequate for the protection of either salmonids under chronic exposure or marine fish larvae, especially in aquaria or hatcheries. To increase communication between interested parties in the field of gas supersaturation research and control, addresses and telephone numbers of all people responding to the questionnaire are included. 102 refs.

Colt, John; Bouck, Gerald R.; Fidler, Larry

1986-12-01

398

Laser diagnostics of hydrodynamics and gas-mixing induced by bubble bursting at the surface of gas-fluidized beds  

Microsoft Academic Search

Gas mixing in the splash zone of gas-fluidized bed reactors plays an important role in fluidized bed processes where fast homogeneous gas-phase reactions take place. An example is represented by the fluidized bed combustion of high-volatile solid fuels, where the large contribution to overall heat release due to homogeneous combustion of volatile matter and the “stratified” combustion pattern emphasize the

Roberto Solimene; Antonio Marzocchella; Raffaele Ragucci; Piero Salatino

2007-01-01

399

Recalcitrant bubbles  

PubMed Central

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles).

Shanahan, Martin E. R.; Sefiane, Khellil

2014-01-01

400

Recalcitrant bubbles  

NASA Astrophysics Data System (ADS)

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in `anomalous' mixtures. Unlike `ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just `downstream' of the minimum in surface tension. The exponential trend for bubbles in `anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles).

Shanahan, Martin E. R.; Sefiane, Khellil

2014-04-01

401

Holdup Measures on an SRNL Mossbauer Spectroscopy Instrument  

Microsoft Academic Search

Gamma-ray holdup measurements of a Mossbauer spectroscopy instrument are described and modeled. In the qualitative acquisitions obtained in a low background area of Savannah River National Laboratory, only Am-241 and Np-237 activity were observed. The Am-241 was known to be the instrumental activation source, while the Np-237 is clearly observed as a source of contamination internal to the instrument. The

R. Dewberry; T. Brown; S. Salaymeh

2010-01-01

402

Holdup measurements on an SRNL Mossbauer spectroscopy instrument  

Microsoft Academic Search

Gamma-ray holdup measurements of a Mossbauer spectroscopy instrument are described and modeled. In the qualitative acquisitions\\u000a obtained in a low background area of Savannah River National Laboratory, only Am-241 and Np-237 activity were observed. The\\u000a Am-241 was known to be the instrumental activation source, while the Np-237 is clearly observed as a source of contamination\\u000a internal to the instrument. The

R. A. Dewberry; T. B. Brown; S. R. Salaymeh

2011-01-01

403

A three dimensional model of an ultrasound contrast agent gas bubble and its mechanical effects on microvessels  

PubMed Central

Ultrasound contrast agents inside a microvessel, when driven by ultrasound, oscillate and induce mechanical stresses on the vessel wall. These mechanical stresses can produce beneficial therapeutic effects but also induce vessel rupture if the stresses are too high. Therefore, it is important to use sufficiently low pressure amplitudes to avoid rupturing the vessels while still inducing the desired therapeutic effects. In this work, we developed a comprehensive three dimensional model of a confined microbubble inside a vessel while considering the bubble shell properties, blood viscosity, vessel wall curvature and the mechanical properties of the vessel wall. Two bubble models with the assumption of a spherical symmetric bubble and a simple asymmetrical bubble were simulated. This work was validated with previous experimental results and enabled us to evaluate the microbubbles’ behaviour and the resulting mechanical stresses induced on the vessel walls. In this study the fluid shear and circumferential stresses were evaluated as indicators of the mechanical stresses. The effects of acoustical parameters, vessel viscoelasticity and rigidity, vessel/bubble size and off-center bubbles on bubble behaviour and stresses on the vessel were investigated. The fluid shear and circumferential stresses acting on the vessel varied with time and location. As the frequency changed, the microbubble oscillated with the highest amplitude at its resonance frequency which was different from the resonance frequency of an unbound bubble. The bubble resonance frequency increased as the rigidity of a flexible vessel increased. The fluid shear and circumferential stresses peaked at frequencies above the bubble’s resonance frequency. The more rigid the vessels were, the more damped the bubble oscillations. The synergistic effect of acoustic frequency and vessel elasticity had also been investigated, since the circumferential stress showed either an increasing trend or a decreasing one versus the vessel rigidity at difference acoustic frequencies. When the acoustic pressure was increased from 52 kPa to 680 kPa, the maximum bubble radius increase by 2.5 folds and the maximum shear and circumferential stress increased by 15.7 and 18.3 folds respectively. The shear stress was largest when the acoustic frequency was higher (3.25 MHz) and the ratio of the vessel radius to the bubble radius was lower. The circumferential stress was largest when the bubble wall was closer to the vessel wall. An oscillating off-center bubble forms a mushroom shape with the most damping on the points closest to the vessel wall.

Hosseinkhah, N.; Hynynen, K.

2012-01-01

404

Application of the ultrasonic technique and high-speed filming for the study of the structure of air-water bubbly flows  

SciTech Connect

Multiphase flows are very common in industry, oftentimes involving very harsh environments and fluids. Accordingly, there is a need to determine the dispersed phase holdup using noninvasive fast responding techniques; besides, knowledge of the flow structure is essential for the assessment of the transport processes involved. The ultrasonic technique fulfills these requirements and could have the capability to provide the information required. In this paper, the potential of the ultrasonic technique for application to two-phase flows was investigated by checking acoustic attenuation data against experimental data on the void fraction and flow topology of vertical, upward, air-water bubbly flows in the zero to 15% void fraction range. The ultrasonic apparatus consisted of one emitter/receiver transducer and three other receivers at different positions along the pipe circumference; simultaneous high-speed motion pictures of the flow patterns were made at 250 and 1000 fps. The attenuation data for all sensors exhibited a systematic interrelated behavior with void fraction, thereby testifying to the capability of the ultrasonic technique to measure the dispersed phase holdup. From the motion pictures, basic gas phase structures and different flows patterns were identified that corroborated several features of the acoustic attenuation data. Finally, the acoustic wave transit time was also investigated as a function of void fraction. (author)

Carvalho, R.D.M.; Venturini, O.J.; Tanahashi, E.I. [Universidade Federal de Itajuba (UNIFEI), Itajuba (Brazil); Neves, F. Jr. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba (Brazil); Franca, F.A. [Universidade Estadual de Campinas (UNICAMP), Campinas (Brazil)

2009-10-15

405

Tritium Inventory Differences: 2. Molecular Sieve Holdup.  

National Technical Information Service (NTIS)

Aluminosilicate zeolite (molecular sieve) materials are employed widely to remove condensable gases from tritium-containing gas streams. By several mechanisms, the bound-tritium contents of zeolite columns can increase significantly over time, primarily a...

J. T. Gill R. E. Ellefson W. M. Rutherford

1986-01-01

406

Bubble formation at nozzles in pig iron  

Microsoft Academic Search

An experimental study was undertaken to determine how several variables affect the size of gas bubbles formed at nozzles in\\u000a liquid pig iron. The frequency of bubble formation was measured by an acoustic device, which could detect the vibrations produced\\u000a by the bubble release. Accurate knowledge of the gas flow rate then enabled the calculation of bubble volumes. The use

G. A. Irons; R. I. L. Guthrie

1978-01-01

407

Models for gamma-ray holdup measurements at duct contact  

SciTech Connect

The use of gamma-ray measurements to nondestructively assay special nuclear material holdup in DOE processing facilities has increased recently. A measurement approach that is relatively insensitive to deposit geometry involves withdrawing the detector from the holdup-bearing equipment far enough to validate an assumed point-, line-, or area-source deposit geometry. Because of facility constraints, these generalized geometry procedures are not always followed, and some ducts are measured at contact. Quantitative interpretation of contact measurements requires knowledge of the width of the deposit transverse to the duct axis. Rocky Flats personnel have introduced a method to obtain data from which this width can be deduced. It involves taking measurements in pairs, with the detector viewing the holdup deposit at contact from above and below the duct. The interpretation of the top and bottom measurements to give the deposit width at each location requires a model for the detector's response to radial source position and a model for the deposit geometry. We have derived a relationship between the top-to-bottom count rate ratio and the deposit width that approximates the detector response and models the deposit geometry as a uniform strip. The model was validated in controlled experiments that used thin foils of high-enriched uranium metal to simulate duct deposits. 4 refs., 5 figs., 1 tab.

Sheppard, G.A.; Russo, P.A.; Wenz, T.R.; Miller, M.C.; Piquette, E.C. (Los Alamos National Lab., NM (United States)); Haas, F.X.; Glick, J.B.; Garrett, A.G. (EG and G Rocky Flats, Inc., Golden, CO (United States))

1991-01-01

408

Reduced gradient bubble model.  

PubMed

An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent. PMID:2276850

Wienke, B R

1990-11-01

409

The role of vacancies and dislocations in the nucleation and growth of gas bubbles in irradiated fissile material  

Microsoft Academic Search

It is shown that fine-scale bubbles are to be expected in reasonably ; pure uranium, the bubbles nucleating either homogeneously with a spacing less ; than a micron or on any suitable nucleation sites that may exist on this or a ; finer scale. The precise value of the homogeneous nucleation spacing depends on ; the diffusion coefficient of the

G. W. Greenwood; A. J. E. Foreman; D. E. Rimmer

1959-01-01

410

Dynamics of the behavior of a gas-bubble nucleus in a heterophase medium  

Microsoft Academic Search

We consider the crystallization of a binary alloy containing dissolved gas. We assume that the volume occupied by the alloys is small enough for the internal thermal resistance of the substance to be neglected in comparison with the external thermal resistance and for the crystallization of the alloy to be regarded as a volume process. We neglect shrinkage effects in

V. N. Popov; A. N. Cherepanov

1986-01-01

411

Propagation of acoustic waves in a viscoelastic two-phase system: influence of gas bubble concentration  

Microsoft Academic Search

Volcanic explosions generate pressure perturbations in the atmosphere and a seismic wavefield in the ground. The source is therefore well coupled with the atmosphere and the ground. The acoustic and elastic wavefields reflect dynamical processes at the source and the viscoelastic properties of the magma–gas medium. At low pressure (<10 MPa), magma cannot be considered as a homogeneous medium, and

Emanuele Marchetti; Mie Ichihara; Maurizio Ripepe

2004-01-01

412

Tritium inventory differences: II. Molecular sieve holdup  

Microsoft Academic Search

Aluminosilicate zeolite (molecular sieve) materials are employed widely to remove condensable gases from tritium-containing gas streams. By several mechanisms, the bound-tritium contents of zeolite columns can increase significantly over time, primarily as tritiated water. Attempts have previously been made to assay the triatiated water by ''regeneration'' from the zeolite, but have encountered poor efficiency. More accurate assays have now been

J. T. Gill; R. E. Ellefson; W. M. Rutherford

1986-01-01

413

Tritium inventory differences: II. Molecular sieve holdup  

Microsoft Academic Search

Aluminosilicate zeolite (molecular sieve) materials are employed widely to remove condensable gases from tritium-containing gas streams. By several mechanisms, the bound-tritium contents of zeolite columns can increase significantly over time, primarily as tritiated water. Attempts have previously been made to assay the tritiated water by ''regeneration'' from the zeolite, but have encountered poor efficiency. More accurate assays have now been

J. T. Gill; R. E. Ellefson; W. M. Rutherford

1986-01-01

414

Residual-Impurity Effects in Directional Solidification: Long-Lasting Recoil of the Front and Nucleation-Growth of Gas Bubbles  

Microsoft Academic Search

Directional-solidification experiments are often perturbed by the nucleation of gas bubbles and other residual-impurity effects. We present a detailed experimental study of these phenomena in the system CBr{4}-C2Cl6 directionally solidified in thin films. As is usual in this type of experiments, we use zone-refined and outgased products, but do not fill and seal the samples under vacuum. We study the

Silvère Akamatsu; Gabriel Faivre

1996-01-01

415

Mesoporous hollow spheres from soap bubbling.  

PubMed

The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites. PMID:22078340

Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong

2012-02-01

416

Big Bubbles  

NSDL National Science Digital Library

How do you measure a bubble when it's floating? You can't really, but in this activity, learners can measure the diameter of the ring of suds a bubble leaves on a flat surface. The fun is blowing up the bubbles as big as possible with a straw. Then comes the measuring. This activity can be used to connect science and math, and makes a great rainy day or indoor lunch activity.

Science, Lawrence H.

2010-01-01

417

A second-order moment method of dense gas–solid flow for bubbling fluidization  

Microsoft Academic Search

A gas–solid two-fluid model with the second-order moment method is presented to close the set of equations applied to fluidization. With the kinetic theory of granular flow, transport equations for the velocity moments are derived for the particle phase. Closure equations for the third-order moments of velocity and for the fluid–particle velocity correlation are presented. The former is based on

Sun Dan; Wang Shuyan; Lu Huilin; Shen Zhiheng; Li Xiang; Wang Shuai; Zhao Yunhua; Wei Lixin

2009-01-01

418

Bubble nucleation in stout beers  

Microsoft Academic Search

Bubble nucleation in weakly supersaturated solutions of carbon dioxide---such as champagne, sparkling wines, and carbonated beers---is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology

W. T. Lee; J. S. McKechnie; M. G. Devereux

2011-01-01

419

Gas-bubble snap-off under pressure driven flow in constricted noncircular capillaries  

SciTech Connect

A model for snap-off of a gas thread in a constricted cornered pore is developed. The time for wetting liquid to accumulate at a pore throat into an unstable collar is examined, as for the resulting pore-spanning lens to be displaced from the pore so that snap-off is the time may repeat. A comer-flow hydrodynamic analysis for the accumulation rate of wetting liquid due to both gradients in interfacial curvature and in applied liquid-phase pressure reveals that wetting-phase pressure gradients significantly increase the frequency of liquid accumulation for snap-off as compared to liquid rearrangement driven only by differences in pore-wall curvature. For moderate and large pressure gradients, the frequency of accumulation increases linearly with pressure gradient because of the increased rate of wetting liquid flow along pore comers. Pore topology is important to the theory, for pores with relatively small throats connected to large bodies demonstrate excellent ability to snapoff gas threads even when the initial capillary pressure is high or equivalently when the liquid saturation is low. A macroscopic momentum balance across the lens resulting from snap-off reveals that lens displacement rates are not linear with the imposed pressure drop. Instead, the frequency of lens displacement scales with powers between 0.5 and 0.6 for pores with dimensionless constriction radii between 0.15 and 0.40. Statistical percolation arguments are employed to form a generation rate expression and connect pore-level foam generation events to macroscopic pressure gradients in porous media. The rate of foam generation by capillary snap-off increases linearly with the liquid-phase pressure gradient and according to a power-law relationship with respect to the imposed gas-phase pressure gradient.

Kovscek, A.R.; Radke, C.J.

1996-04-01

420

Mesoscale Benchmark Demonstration Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing  

SciTech Connect

A study was conducted to evaluate the capabilities of different numerical methods used to represent microstructure behavior at the mesoscale for irradiated material using an idealized benchmark problem. The purpose of the mesoscale benchmark problem was to provide a common basis to assess several mesoscale methods with the objective of identifying the strengths and areas of improvement in the predictive modeling of microstructure evolution. In this work, mesoscale models (phase-field, Potts, and kinetic Monte Carlo) developed by PNNL, INL, SNL, and ORNL were used to calculate the evolution kinetics of intra-granular fission gas bubbles in UO2 fuel under post-irradiation thermal annealing conditions. The benchmark problem was constructed to include important microstructural evolution mechanisms on the kinetics of intra-granular fission gas bubble behavior such as the atomic diffusion of Xe atoms, U vacancies, and O vacancies, the effect of vacancy capture and emission from defects, and the elastic interaction of non-equilibrium gas bubbles. An idealized set of assumptions was imposed on the benchmark problem to simplify the mechanisms considered. The capability and numerical efficiency of different models are compared against selected experimental and simulation results. These comparisons find that the phase-field methods, by the nature of the free energy formulation, are able to represent a larger subset of the mechanisms influencing the intra-granular bubble growth and coarsening mechanisms in the idealized benchmark problem as compared to the Potts and kinetic Monte Carlo methods. It is recognized that the mesoscale benchmark problem as formulated does not specifically highlight the strengths of the discrete particle modeling used in the Potts and kinetic Monte Carlo methods. Future efforts are recommended to construct increasingly more complex mesoscale benchmark problems to further verify and validate the predictive capabilities of the mesoscale modeling methods used in this study.

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert; Gao, Fei; Sun, Xin; Tonks, Michael; Biner, Bullent; Millet, Paul; Tikare, Veena; Radhakrishnan, Balasubramaniam; Andersson , David

2012-04-11

421

Magnetic Bubbles  

NASA Astrophysics Data System (ADS)

Bubbles in liquids driven by a sound field are used in many disciplines: for example bubbles clean surfaces in ultrasonic water bathes, they catalyze unique chemical reactions in sonochemistry, and under special conditions even create light. However, conventional bubbles have a major limitation when placed in an acoustic field: it is extremely hard to control their position. Here we present a new type of bubble that has permanent magnetization originating from a shell of self-assembled nanoparticles, so that magnetic fields can be used to control the bubble's position independently. We will report on the recipe and the experiment to study bubble oscillations in weak magnetic fields. The magnetic susceptibility of the bubbles is proportional to their surface area,?=(9±3x10-6m)r^2, where r is the radius. Also they are compressible in moderate acoustic fields and induce a microstreaming flow with a toroidal vortex at the upper pole of the bubble. Similar microstreaming flows have been used to transport and rupture cells at small scales. Thus we envision applications in manipulation of biological materials and in microfluidic devices using acoustic and magnetic forces.

Zhao, Xue; Quinto-Su, Pedro; Ohl, Claus-Dieter

2008-11-01

422

Bubble Tray  

NSDL National Science Digital Library

In this activity, learners use simple materials to create giant bubbles. Learners will explore what gives bubbles their shape, what makes them break or last, what causes the colors and patterns in the soap film, and why do they change? Use this activity to introduce the concepts of surface tension and interference.

Exploratorium, The

2012-06-26

423

Bubble Trouble  

NSDL National Science Digital Library

In this activity on page 15 of the PDF, learners measure the amount of bubbles that they make using a detergent. Learners investigate whether adding Epsom salt to the solution affects its "sudsiness"--an important attribute of soap, since sudsy bubbles help soap clean greasy dirt. Use this activity to explore how chemicals can change a material's properties and how substances dissolve.

Society, American C.

2011-01-01

424

A study of the bubble-to-slug transition in vertical gas-liquid flow in columns of different diameter  

Microsoft Academic Search

The aim of this study is to investigate the structure of upwards air-water flow and its variation as the bubble-to-slug transition is approached, with a view to understanding the mechanism of the transition. The development of bubble size with column height is measured with a double needle resistivity probe, and of void fraction waves with an Impedance Void Fraction Meter

H. Cheng; J. H. Hills; B. J. Azzorpardi

1998-01-01

425

Mechanisms for stable single bubble sonoluminescence  

SciTech Connect

A gas bubble trapped in water by an oscillating acoustic field is expected to either shrink or grow on a diffusive time scale, depending on the forcing strength and the bubble size. At high ambient gas concentration this has long been observed. However, recent sonoluminescence experiments show that when the ambient gas concentration is low the bubble can be stable for days. This paper discusses mechanisms leading to stability. {copyright} {ital 1996 The American Physical Society.}

Brenner, M.P. [Department of Mathematics, MIT, Cambridge, Massachusetts 02139 (United States)] [Department of Mathematics, MIT, Cambridge, Massachusetts 02139 (United States); Lohse, D. [Fachbereich Physik der Universitaet Marburg, Renthof 6, 35032 Marburg (Germany)] [Fachbereich Physik der Universitaet Marburg, Renthof 6, 35032 Marburg (Germany); [Department of Mathematics, The University of Chicago, Chicago, Illinois 60637 (United States); Oxtoby, D. [Department of Chemistry and James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Chemistry and James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States); Dupont, T.F. [Department of Mathematics, The University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Mathematics, The University of Chicago, Chicago, Illinois 60637 (United States)

1996-02-01

426

Methane discharge from a deep-sea submarine mud volcano into the upper water column by gas hydrate-coated methane bubbles  

NASA Astrophysics Data System (ADS)

The assessment of climate change factors includes a constraint of methane sources and sinks. Although marine geological sources are recognized as significant, unfortunately, most submarine sources remain poorly quantified. Beside cold vents and coastal anoxic sediments, the large number of submarine mud volcanoes (SMV) may contribute significantly to the oceanic methane pool. Recent research suggests that methane primarily released diffusively from deep-sea SMVs is immediately oxidized and, thus, has little climatic impact. New hydro-acoustic, visual, and geochemical observations performed at the deep-sea mud volcano Håkon Mosby reveal the discharge of gas hydrate-coated methane bubbles and gas hydrate flakes forming huge methane plumes extending from the seabed in 1250 m depth up to 750 m high into the water column. This depth coincides with the upper limit of the temperature-pressure field of gas hydrate stability. Hydrographic evidence suggests bubble-induced upwelling within the plume and extending above the hydrate stability zone. Thus, we propose that a significant portion of the methane from discharged methane bubbles can reach the upper water column, which may be explained due to the formation of hydrate skins. As the water mass of the plume rises to shallow water depths, methane dissolved from hydrated bubbles may be transported towards the surface and released to the atmosphere. Repeated acoustic surveys performed in 2002 and 2003 suggest continuous methane emission to the ocean. From seafloor visual observations we estimated a gas flux of 0.2 (0.08-0.36) mol s -1 which translates to several hundred tons yr -1 under the assumption of a steady discharge. Besides, methane was observed to be released by diffusion from sediments as well as by focused outflow of methane-rich water. In contrast to the bubble discharge, emission rates of these two pathways are estimated to be in the range of several tons yr -1 and, thus, to be of minor importance. Very low water column methane oxidation rates derived from incubation experiments with tritiated methane suggest that methane is distributed by currents rather than oxidized rapidly.

Sauter, Eberhard J.; Muyakshin, Sergey I.; Charlou, Jean-Luc; Schlüter, Michael; Boetius, Antje; Jerosch, Kerstin; Damm, Ellen; Foucher, Jean-Paul; Klages, Michael

2006-03-01

427

Enhancing gas-liquid mass transfer rates in non-newtonian fermentations by confining mycelial growth to microbeads in a bubble column  

SciTech Connect

The performance of a penicillin fermentation was assessed in a laboratory-scale bubble column fermentor, with mycelial growth confined to the pore matrix of celite beads. Final cell densities of 29 g/L and penicillin titres of 5.5 g/L were obtained in the confined cell cultures. In comparison, cultures of free mycelial cells grown in the absence of beads experienced disso