Distribution Of Gas Bubbles Research Articles

The application of GIS to analysing 2-D models of porous systems in the context of gas mobility

The mobility of gas bubbles within the pore fluid of sediments, represented by changes in the spatial distribution of the gas phase, has been studied using a physical analogue model constructed in glass and analysed using a Geographical Information System (GIS). Such glass models have the appearance of petrographical thin sections in which the gas phase can be identified, but the mobility is difficult to quantify. To improve the quantification, images showing the position and size of individual gas bubbles, and images of the glass micro-model (2-D model) have been digitized for analysis in the GIS. The digitization of the 2-D models produces separate overlays outlining the grains and pores. Each individual grain or pore is given a separate label. The area of each pore space, grain and gas bubble can then be automatically calculated in two dimensions and from these measurements the corresponding cumulative frequency distribution curves can be obtained. The results show that the size of gas bubbles within a porous system of specified grain and pore size cannot easily be predicted using standard petrophysical parameters. The shapes of the gas bubble distribution curves appear to be unrelated to the shapes of either the pore or the grain size distribution curves. The results further show that the mobility of a gas phase in a porous medium seems to depend strongly on whether it has been subjected to pressure changes before, rather than on the magnitude of the pressure changes.

Predictions of the acoustic scattering response of free-methane bubbles in muddy sediments

The response of the sediments of Eckernfoerde Bay, Germany to acoustic remote sensing previously has been attributed qualitatively to gas features which were postulated to exist in situ within the sediment. The existence of features as small as 0.5-mm equivalent spherical radius has now been confirmed by x-ray computed tomography of cores taken and scanned at in situ pressures. The interaction of an acoustic pulse from the acoustic sediment classification system (ASCS) with this type of gassy sediment was modeled and the results are presented here. The bubble scattering response model includes both the effects of nonspherical bubbles and of sediment resistance to shear deformation (as expressed by the dynamic shear modulus). Model predictions made using the observed gas bubble distribution agree with normal incidence ASCS data, exhibiting extended returns (i.e., greater than the source pulse length) from the seafloor bubble layers as well as high attenuation within the bubble layers. Spectrograms of ASCS and modeled return pulses were also similar. These results suggest that the acoustic return characteristics of the near surface sediments of Eckernfoerde Bay are dominated by scattering from a distribution of gas bubbles with depth.

Biogeochemical processes controlling gas bubble production and distribution in organic-rich sediments

Biogeochemical processes in organic-rich, muddy sediments often result in the net production of biogenic gases including methane. In coastal sediments, methane production ultimately leads to near saturation gas concentrations and bubble formation. Rates of production, oxidation, and transport processes, together with insitu temperature and pressure (depth), combine to determine the actual sediment column depth of methane bubble occurrence. Recent studies along North Carolina’s Outer Banks and Eckernfoerde Bay in the Baltic Sea reveal how these processes combine to control saturation gas concentrations and bubble distributions in the upper few meters of coastal sediments. At the North Carolina site, gas production depths vary seasonally, resulting in a bubble layer whose shallowest depth oscillates between 10- and 30-cm depth from summer to winter, respectively. Large quantities of gas escape the sediments via diffusion and bubble ebullition during the warm months. Similar oscillations in the depth of the bubble (acoustic absorption) layer appear to occur in the sediments of Eckernfoerde Bay; however, competing microbial processes prevent saturation methane concentrations at depths above approximately 50 cm. Stable isotope measurements reveal that microbial methane oxidation consumes methane transported above the bubble layer, resulting in little release of gas into the water column.

Concentrated Emulsions: 4. Freeze Fracture SEM Studies of Chemically Generated Voids

Freeze fracture scanning electron microscopy (FFSEM) is shown to be a reliable technique for the study of chemically generated voids in concentrated emulsions. The gassing of such emulsions involves the reaction of ammonium nitrate and sodium nitrite to produce dinitrogen, the reaction being strongly dependent on pH and temperature. The changes in the size and distribution of voids were monitored from their inception by arresting the gassing reaction at various stages. The gassing temperature and the emulsion viscosity are both shown to bring about dramatic differences in the size and distribution of gas bubbles entrapped in an emulsion matrix.

Effects of compressibility on the flow of lava

Lava contains gas bubbles and hence is a compressible liquid whose density increases as a function of pressure. After eruption at the Earth's surface, it spreads at a rate which is a function of its thickness and it is compressed under its own weight. Therefore, both thickness and spreading rate are determined by a balance between viscous and compressible effects. Theoretical equations are derived for the shape and velocity of a compressible liquid spreading on a horizontal surface. Solutions are obtained for a fixed eruption rate Q. The radial extent of the flow increases proportional to t1/2. A dimensionless number C is defined which characterizes the importance of flow compression: \(C = \rho _0 \beta g\left( {\frac{{\mu Q}}{{\rho _0^2 g}}} \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}}\), where ρ0 is bubbly lava density at atmospheric pressure, β compressibility, μ viscosity and g the acceleration of gravity. C can be thought of as the ratio of two characteristic length-scales, one for compression effects and one for viscous effects. The larger C is, the more important compressibility effects are. As C is increased, the flow becomes thinner because the liquid is compressed more and more efficiently. Compressibility acts to smooth out variations of flow thickness, which provide the driving force. Thus, all else being equal, a compressible liquid flows less rapidly than an incompressible one. When trying to infer the effective viscosity of a flow from its spreading rate, the neglect of compressibility leads to an overestimate. The various factors which act to determine the distribution of gas bubbles in lava flows are reviewed and discussed quantitatively. Comparison with data from Obsidian Dome (Eastern California) shows that disequilibrium effects are important and that bubble resorption during burial in a thick flow is not a pervasive phenomenon. The analysis is applied to the 1979 dome of Soufriere de Saint Vincent (W.I.). An effective value of compressibility for this 100-m-thick dome is 1.5x10−6 Pa−1. This implies that, all else being equal, the viscosity of this lava may be overestimated by a factor of 5 if no account is taken of the compressible nature of the flow.

Behaviour of offshore soils containing gas bubbles

An extensive programme of research into the influence of undissolved gas bubbles on the behaviour of fine-grained onshore soils is reviewed. The programme has been based on the development of a laboratory technique for the preparation of reconstituted soil samples containing a uniform distribution of gas bubbles. The structure of these samples is similar to that observed in sediment recovered from the sea bed, and consists of large gas-filled cavities surrounded by a matrix of saturated soil. It is found that surface tension effects limit the difference between gas pressure and pore water pressure, and that the overall void size is effectively a function of the strength of the matrix, so that changes in void volume may be modelled by cavity expansion and contraction in an ideal plastic medium, leading to limits on the difference between gas pressure and mean total stress. A new parameter, operative stress, is shown to influence both the consolidation and the strength of these gassy soils. Thus, during consolidation, the gas volume is controlled by the total stress and the water volume by the operative stress; the undrained shear strength may be increased or decreased by the presence of the gas, depending on the specific values of total stress and operative stress. The operative stress for a gassy soil may therefore be seen as being analogous in its definition (total stress minus pore water pressure) to the effective stress for a saturated soil, but different from the effective stress in that it does not, on its own, control the strains and strength. Gas bubbles are shown to have a major influence on the acoustic behaviour of fine-grained offshore soils. L'article passe en revue un programme de grande envergure pour étudier l'influence exercée par des bulles de gaz non-dissoutes sur le comportement des sols à grains fins en mer. Le programme a été basé sur le développement d'une technique de laboratoire pour la préparation d'échantillons de sols reconstitués comprenant une distribution uniforme de bulles de gaz. La structure de ces échantillons ressemble à celle observée dans des sédiments obtenus au fond de la mer, comprenant de grandes cavités remplies de gaz entourées d'une matrice de sol saturé. Il a été trouvé que des effets de tension superficielle limitent la différence entre la pression du gaz et la pression de l'eau interstitielle et aussi que la valeur totale des vides dépend effectivement de la résistance de la matrice, de sorte que des changements dans le volume des vides peuvent être modelesés par l'expansion et la contraction des cavités dans un milieu idéal plastique, conduisant à des limites sur la différence entre la pression du gaz et la contrainte totale moyenne. On démontre la façon dont cette différence représente un nouveau paramètre (contrainte effective) qui influence à la fois la consolidation et la résistance de ces sols gazeux. Par exemple, pendant la consolidation le volume de gaz est contrôlé par la contrainte totale, tandis que le volume d'eau est contrôlé par cette contrainte effective. Selon les valeurs spécifiques de la contrainte totale et de la contrainte effective la résistance au cisaillement non-drainé peut être augmentée ou diminuée par la présence du gaz. On peut alors considérer que cette définition de la contrainte effective dans le cas d'un sol gazeux (contrainte totale moins pression d'eau interstitielle) est analogue à la contrainte effective pour un sol saturé mais diffère de celle-ci en ce qu'elle seul ne contrôle pas les déformations ni la résistance. On démontre que les bulles de gaz exercent une influence très importante sur le comportement acoustique des sols à grains fins en mer.

Three-circle method in the investigations of shapes of gas bubble clusters in two-phase flow

We present an attempt of formulating a quantitative criterion for division into homogeneous and heterogeneous flow patterns basing on the probabilistic analysis of gas bubble distribution in the liquid

Bubble coalescence in basalt flows: comparison of a numerical model with natural examples

Gas accumulation in magma may be aided by coalescence of bubbles because large coalesced bubbles rise faster than small bubbles. The observed size distribution of gas bubbles (vesicles) in lava flows supports the concept of post-eruptive coalescence. A numerical model predicts the effects of rise and coalescence consistent with observed features. The model uses given values for flow thickness, viscosity, volume percentage of gas bubbles, and an initial size distribution of bubbles together with a gravitational collection kernel to numerically integrate the stochastic collection equation and thereby compute a new size spectrum of bubbles after each time increment of conductive cooling of the flow. Bubbles rise and coalesce within a fluid interior sandwiched between fronts of solidification that advance inward with time from top and bottom. Bubbles that are overtaken by the solidification fronts cease to migrate. The model predicts the formation of upper and lower vesicle-rich zones separated by a vesicle-poor interior. The upper zone is broader, more vesicular, and has larger bubbles than the lower zone. Basaltic lava flows in northern California exhibit the predicted zonation of vesicularity and size distribution of vesicles as determined by an impregnation technique. In particular, the size distribution at the tops and bottoms of flows is essentially the same as the initial distribution, reflecting the rapid initial solidification at the bases and tops of the flows. Many large vesicles are present in the upper vesicular zones, consistent with expected formation as a result of bubble coalescence during solidification of the lava flows. Both the rocks and model show a bimodal or trimodal size distribution for the upper vesicular zone. This polymodality is explained by preferential coalescence of larger bubbles with subequal sizes. Vesicularity and vesicle size distribution are sensitive to atmospheric pressure because bubbles expand as they decompress during rise through the flow. The ratio of vesicularity in the upper to that in the lower part of a flow therefore depends not only on bubble rise and coalescence, but also on flow thickness and atmospheric pressure. Application of simple theory to the natural basalts suggests solidification of the basalts at 1.0±0.2 atm, consistent with the present atmospheric pressure. Paleobathymetry and paleoaltimetry are possible in view of the sensitivity of vesicle size distributions to atmospheric pressure. Thus, vesicular lava flows can be used to crudely estimate ancient elevations and/or sea level air pressure.

Structural modification to glass-like materials under laser irradiation

Laser-induced changes in glasslike materials may involve the expansion of gas trapped in materials that contain voids, with the resultant growth of bubbles around the voids, which serve as nucleation sites. If the trapped gas is initially frozen in out of equilibrium, this process will lead to irreversible changes in the material. This paper examines theoretically the process of laser-induced bubble growth in a glasslike material and the concomitant changes in the bulk properties of the material. It is pointed out that the theoretical treatment of this laser material interaction can be tested by measuring the gas-bubble distribution function and porosity in a sample of quartz-fiber material after laser irradiation. The foaming of the surface of the material can be measured and used to deduce the frozen-in pressure in the bubbles. 5 refs.

Effect of the Trendelenburg Position on the Distribution of Arterial Air Emboli in Dogs

We examined the effects of buoyancy on the distribution of arterial gas bubbles using in vitro and in vivo techniques in dogs. A simulated carotid artery preparation was used to determine the effects of bubble size and vessel angle on the velocity and direction of bubble movement in flowing blood. Because buoyancy tends to float bubbles away from dependent areas, bubble velocity would be expected to decrease as the vessel angle increased. We found that larger bubbles increased in velocity in the same direction as the blood flow at 0-, 10-, and 30-degree vessel angles and decreased when the vessel was positioned at 90 degrees. Smaller bubbles did not change velocity from 0 to 30 degrees and increased in velocity in the same direction as blood flow at 90 degrees. In 10 anesthetized dogs, we studied the effects of 0-, 10-, 15-, and 30-degree Trendelenburg's position on carotid artery distribution of gas bubbles injected into the left ventricle or ascending aorta. Regardless of the degree of the Trendelenburg position, the bubbles passed into the carotid artery simultaneously with passage into the abdominal aorta. We conclude that the forces of buoyancy do not overcome the force of arterial blood flow and that the Trendelenburg position does not prevent arterial bubbles from reaching the brain.

Radiation re-solution of fission gas in uranium dioxide and carbide

Abstract Calculations have been performed to estimate the removal rate of fission gas atoms from bubbles due to collisions with energetic fission fragments and recoil cascades. The efficiency of this process was found to be higher than estimated earlier, but is still too low to be responsible for the experimental observations of fission gas bubble destruction during irradiation of oxide fuel. An irradiation experiment to investigate the interaction of fission spikes with free surfaces has enabled a simple theory to be developed which can explain the shrinkage of bubbles and pores by the surface relaxation of a shock wave produced by the passage of a fission fragment. This mechanism occurs in oxides but not carbides because of the faster dispersion of the fission fragment energy and provides the major reason for the difference in gas bubble distributions in oxide and carbide fuel. This process, however, does not remove gas atoms from the bubbles. Since high levels of apparently diffusive fission gas release are observed in oxides, the “effective solubility” of the fission gases required for this release must be sought in phenomena other than the fission spike.

A new method for measuring the size distribution of gas bubbles in aqueous media

A simple and rapid method for the determination of the size distribution of gas bubbles in aqueous media is described which is, in principle, analogous to the size analysis of solid particles in a liquid by sedimentation. The procedure involves the measurement of the liquid column height as a function of time that elapses after the bubbling of gas has been discontinued. A pressure transducer, placed at a fixed position below the meniscus of the liquid, is used in these experiments. The size distribution of argon bubbles (0.1–1.5 mm in diameter) in aqueous solution of sodium hexadecyl sulfate (1 × 10−6 and 1 × 10−5 mole dm−3) was evaluated and the results compared with those obtained by the photographic method.

Kinetics of the growth of helium bubbles at the grain boundaries. formation of the spatially inhomogeneous distribution of helium bubbles near the grain boundaries

In the present paper the kinetics of nucleation and development of gas bubbles near and at the grain boundaries have been investigated. A self-consistent theoretical calculation of the diffusion growth of three ensembles of gas bubbles has been made: bubbles at the grain boundaries, bubbles on dislocations and bubbles in the grain interior. Emphasis is placed on investigating the influence of the spatially inhomogeneous distribution of the dislocation density on the kinetics of growth of ensembles of gas bubbles. The theory formulated makes it possible to explain the more rapid growth of bubbles at the grain boundaries in comparison with the growth of bubbles on dislocations and in the grain interior. We have obtained a spatially inhomogeneous distribution of gas bubbles near the grain boundaries. The basic results of the theory are compared with the results of an experiment on the kinetics of nucleation of helium bubbles under the conditions of annealing near and at the grain boundaries in polycrystal nickel irradiated with alpha particles.

Control over gas bubble distribution in shaped sapphire crystals

AbstractBubble distribution in shaped sapphire crystals grown by Stepanov technique is found to depend on the field of velocities of the melt flows between the top surface of a die and the crystallization front. A die design defining the flows in the meniscus is a tool for control over the bubble distribution.

Bubble Migration and Coalescence during the Solidification of Basaltic Lava Flows

The initial size distribution of gas bubbles in lava flows is modified by bubble rise and coalescence during post eruptive cooling and crystallization. A simple model which computes the effects of rise and coalescence accounts for observed features and may provide a means whereby the initial bubble size distribution can be inferred. A model lava flow of assumed thickness, viscosity, and volume percentage of gas bubbles is given an initial bubble size distribution. Bubbles coalesce due to differences in their relative rise velocities. Using a gravitational collection kernel, the process may be modeled by numerical integration of the stochastic collection equation, which yields the change in the number density spectrum of the population from the number densities of all pairs of bubbles and their probabilities of collision. Bubbles rise and coalesce within a fluid interior sandwiched between fronts of crystallization that advance inward from top and bottom. Bubbles that are overtaken by the crystallization fronts cease to migrate. The model predicts the formation of upper and lower vesicle-rich zones separated by a vesicle-free interior. The upper zone is broader, more vesicular, and has larger bubbles than the lower zone. Increasing the initial average bubble size in the model results in a stratigraphically lower and thinner lower vesicular zone, a thicker vesicle-free central region, and a higher and more vesicular upper zone.

Virtual mass in two-phase bubbly flow

The two-phase flow equations in their usual form are unstable. It is known that the inclusion of the virtual mass of the gas bubbles greatly improves the stability of numerical computations. Since there is some confusion concerning the proper form of the virtual-mass terms, we first present a systematic derivation of the two-fluid equations for a liquid/gas mixture from a generalised form of Hamilton's variational principle. The two-fluid theory of superfluid 4He has been derived in a similar way. The resulting equations do not seem to have been presented before in the literature on two-phase flow. The derivation demonstrates how the pressure of the liquid/gas mixture can be defined in a natural way. Two independent vorticities can be distinguished, each having its own law of transportation (Kelvin theorem). A subsequent stability analysis shows that at neutral stability the virtual-mass coefficient m(α) takes the form m(α)= 1 2 α(1−α)(1−3α) in the case of spherical gas bubbles with void fraction α. The corresponding local distribution of gas bubbles is anisotropic. The vanishing of the virtual mass at α= 1 3 is interpreted as the breakdown of bubbly flow. Dissipative terms are introduced and analysed in an appendix.

Fluid motion and mixing in a gas-liquid contactor with turbine agitators

Gas bubble distributions, estimated from local holdup measurements, and flow profiles near the vessel wall, deduced from wall pressure measurements, we Typical findings were that (1) the flow field under the impeller was quite similar to that for unaerated agitation, (2) the circulation flow of liquid Mixing measurements under aeration for comparison with single-phase measurements obtained at lower speeds to maintain the same total power input confir

A New Instrument in Cavitation Research: The Cavitation Susceptibility Meter

The rate of cavitation in liquid flow appears to be linked to the concentration and size distribution of gas bubbles and “weak” nuclei in the liquid used, as well as to the dissolved gas content. Consequently, the onset of cavitation is related to the tensile strength of the liquid, rather than the vapor pressure. The tensile strength of the liquid depends on the amount of gas in gas pockets (i.e., gas bubbles and gas absorbed at solid particles) suspended in the liquid and the shape of these gas pockets. An instrument will be described, which measures the tensile strength in a direct way. In this method a sample of liquid is made to pass through a pressure well, the minimum pressure of which can be adjusted.

An analysis of observations of fission gas bubble distributions in fuel

Models of the behaviour of the fission gas in fast reactor fuel are used to analyse recent transmission electron microscope observations of gas bubble distributions. The single knock-on and complete bubble destruction mechanisms of re-solution are considered and compared. The complete bubble destruction model is found to provide a better description of the experimental observations, and the effectiveness of the re-solution process is estimated. Information about bubble nucleation kinetics is also derived.

The fission gas bubble distribution in a mixed oxide fast reactor fuel pin

The fission gas bubble distribution has been studied in a mixed oxide fast reactor fuel pin irradiated in DIDO MTR to 2.8% burn-up at centre and surface temperatures of 2000 and 1000°C. The intragranular fission gas bubbles are very small (<6 nm diameter) and this is a consequence of the high re-solution rate at fast reactor ratings. The bubbles nucleate heterogeneously and linear arrays of bubbles, due to nucleation on fission tracks, are observed up to irradiation temperatures of 1900°C. At 1980°C ~4% of the fission gas produced is present in intragranular bubbles. There is no definite evidence for gas bubble mobility or coalescence. Apart from any effects of columnar grain growth fission gas release in fast reactor fuel pins seems to occur predominantly by the diffusion of single gas atoms, at least up to irradiation temperatures of 2000°C.