Growth Of Gas Bubbles Research Articles

The Effect of Gas Properties on Bubble Formation, Growth, and Detachment

Bubble formation and growth play an important role in various processes and industries, where the dispersion of gas bubbles in a liquid medium occurs frequently. In this paper, the formation, growth, and detachment of gas bubbles produced from a submerged needle in water are numerically and experimentally investigated. The effect of injected gas properties on bubble characteristics, including bubble diameter, contact angle, and the frequency of bubble formation, is evaluated. In particular, the changes in bubble characteristics during the injection process are investigated for three different gases to evaluate the effect of density and surface tension on the bubble detachment criteria. The present numerical results show an acceptable agreement with experiments under different operating conditions. The results show that the increase in surface tension, and the decrease in gas density result in larger bubble sizes before detachment occurs. Moreover, the bubble generation frequency is found to strongly depend on the contact angle and the surface tension.

Multiscale simulation of xenon diffusion and grain boundary segregation in UO2

In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO2 have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO2 (Σ5 tilt, Σ5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.

Growth and setting of gas bubbles in a viscoelastic matrix imaged by X-ray microtomography: the evolution of cellular structures in fermenting wheat flour dough.

X-ray tomography is a relevant technique for the dynamic follow-up of gas bubbles in an opaque viscoelastic matrix, especially using image analysis. It has been applied here to pieces of fermenting wheat flour dough of various compositions, at two different voxel sizes (15 and 5 μm). The resulting evolution of the main cellular features shows that the creation of cellular structures follows two regimes that are defined by a characteristic time of connectivity, tc [30 and 80 min]: first (t ≤ tc), bubbles grow freely and then (t ≥ tc) they become connected since the percolation of the gas phase is limited by liquid films. During the first regime, bubbles can be tracked and the local strain rate can be measured. Its values (10(-4)-5 × 10(-4) s(-1)) are in agreement with those computed from dough viscosity and internal gas pressure, both of which depend on the composition. For higher porosity, P = 0.64 in our case, and thus occurring in the second regime, different cellular structures are obtained and XRT images show deformed gas cells that display complex shapes. The comparison of these images with confocal laser scanning microscopy images suggests the presence of liquid films that separate these cells. The dough can therefore be seen as a three-phase medium: viscoelastic matrix/gas cell/liquid phase. The contributions of the different levels of matter organization can be integrated by defining a capillary number (C = 0.1-1) that makes it possible to predict the macroscopic dough behavior.

Using cavity microelectrodes for electrochemical noise studies of oxygen-evolving catalysts.

Cavity microelectrodes were used as a binder-free platform to evaluate oxygen evolution reaction (OER) electrocatalysts with respect to gas bubble formation and departure. Electrochemical noise measurements were performed by using RuO2 as a benchmark catalyst and the perovskite La0.58 Sr0.4 Fe0.8 Co0.2 O3 as a non-noble metal OER catalyst with lower intrinsic conductivity. Changes in the current during the OER originate from variations in electrolyte resistance during the formation of the gas phase and partial coverage of the active area. Fluctuations observed in current and conductance transients were used to establish the contribution from the ohmic overpotential and to determine the characteristic frequency of oxygen evolution. The proposed quantitative determination of gas bubble growth and departure opens up the route for a rational interface design by considering gas bubble growth and departure as a main contributing factor to the overall electrocatalytic activity at high current densities.

Growth of gas bubbles in the biotissues with convective acceleration

This paper presents formulae and explanation about the growth of a convective gas bubble in the blood and other tissues of divers who surface too quickly, concentration distribution around the growing bubble is also presented. The formulae are valid all over the growth stages, i.e. under variable ambient pressure while the diver is ascending, and under constant ambient pressure at diving stops or at sea level. The mathematical model is solved analytically by using the method of combined variables. The growth process is affected by tissue diffusivity, concentration constant and the initial void fraction, which is the dominant parameter. Results show that, the time of the complete growth, in the convective growth model, is shorter than those earlier presented by Mohammadein and Mohamed [Concentration distribution around a growing gas bubble in tissue, Math. Biosci.225(1) (2010) 11–17] and Srinivasan et al. [Mathematical models of diffusion-limited gas bubble dynamics in tissue, J. Appl. Physiol.86 (1999) 732–741] for the growth of a stationary gas bubble, this explains the effect of bubble motion on consuming the oversaturated dissolved gas from the tissue into growing bubble which leads to increment in the growth rate to be more than those presented in the previous stationary models.

Mechanical behaviour of gas-charged fine sediments: model formulation and calibration

Multi-phase fluid conditions encountered in geotechnical and geo-environmental problems have led to the development of models that account for the influence of gas solubility and compressibility on the behaviour of soils of various grain sizes. Yet, no consideration has been given to damages related to the nucleation and growth of gas bubbles in fine-grained soils. The purpose of this paper is to present a Cam Clay based constitutive model extended to incorporate such detrimental effects on gassy soils. This is achieved by deriving an analytical expression relating the preconsolidation pressure to a damage parameter dependent on the gas content. That expression is coupled to a deviatoric yield surface accounting for inherent and stress-induced anisotropy. Comparisons of simulations and experimental results attest that introducing a single additional parameter to a conventional Cam Clay type model allows key behavioural features of gas-charged fine sediments to be reproduced.

Kinetics of gas bubble nucleation and growth in magmatic melt at its rapid decompression

The model of gas bubble growth in high-viscous gas-saturated magmatic melt, subjected to rapid decompression, is presented in the current study. It is shown that consideration of unsteady character of the process is extremely important in a wide range of supersaturation. The analytical solution is found for the profile of dissolved gas concentration and the rate of bubble growth. The model of kinetics of overall degassing is developed. This model is based on distinguishing the so-called “forbidden” zone in the melt volume with suppressed formation of the new nucleation sites. The simple analytical dependences of the number of nucleating bubbles and typical nucleation time on the value of initial decompression were derived together with time dependence of volumetric concentration of the gas phase. Our results match the available experimental data.

Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity

AbstractChanges in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1–1.0 MPa, 0.01–0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ± 15 cm and 23 ± 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.

Distribution of dissolved water in magmatic glass records growth and resorption of bubbles

Volcanic eruptions are driven by the growth of gas bubbles in magma. Bubbles grow when dissolved volatile species, principally water, diffuse through the silicate melt and exsolve at the bubble wall. On rapid cooling, the melt quenches to glass, preserving the spatial distribution of water concentration around the bubbles (now vesicles), offering a window into pre-eruptive conditions. We measure the water distribution around vesicles in experimentally-vesiculated samples, with high spatial resolution. We find that, contrary to expectation, water concentration increases towards vesicles, indicating that water is resorbed from bubbles during cooling; textural evidence suggests that resorption occurs largely before the melt solidifies. Speciation data indicate that the molecular water distribution records resorption, whilst the hydroxyl distribution records earlier decompressive growth. Our results challenge the emerging paradigm that resorption indicates fluctuating pressure conditions, and lay the foundations for a new tool for reconstructing the eruptive history of natural volcanic products.

Transient pore pressure response to confining stress excursions in Berea sandstone flooded with an aqueous solution of CO2

AbstractWe measured the pore pressure response due to carbon dioxide (CO2) gas bubble nucleation and growth in a Berea sandstone core flooded with an initially subsaturated aqueous solution of CO2, in response to a rapid drop in confining stress, under conditions representative of a confined aquifer. A portion of the CO2 in the Earth's crust, derived from volcanic, magmatic, and biogenic sources, dissolves in groundwater. Sudden reductions in confining stress in the Earth's crust occur due to dilational strain generated by the propagation of seismic Rayleigh and P waves, or aseismic slip in the near field of earthquakes. A drop in confining stress produces a proportional drop in pore fluid pressure. When the pore fluid contains dissolved CO2, the pore pressure responds to a drop in confining stress like it does in the dissolved gas‐free case, until the pore pressure falls below the bubble pressure. Gas bubble nucleation and diffusive growth in the pore space trigger spontaneous, transient buildup of the pore fluid pressure, and reduction of effective stress. We measured the rate of pore fluid pressure buildup in the 100 s immediately following the confining stress drop, as a function of the saturation with respect to CO2 at the lowest pore pressure realized during the confining stress drop, using five different CO2 partial pressures. The rate scales with the saturation with respect to dissolved CO2, from 10 kPa/min at 1.25 to 166 kPa/min at 1.8. The net pore pressure rise was as large as 0.7 MPa (100 psi) over 5 h.

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

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).

Nucleation and growth of electrolytic gas bubbles under microgravity

The evolution of oxygen gas bubbles in potassium hydroxide solution is observed in situ under microgravity by a charge-coupled device camera, focusing on the wettability of a platinum electrode modified by thiol self-assembled monolayers. Single bubble measurements on the microwire electrode reveal a three-step growth process involving (1) the nucleation and formation of a supersaturated layer of dissolved gas followed by (2) a rapid growth phase depending on the gas diffusion process, and finally, (3) a stable growth phase where the growth rate is dominated by the bubble configuration depending on the contact angle. Moreover, correlation of multiple gas bubble observations with electrochemical data and surface coverage on the plate electrode reinforce the important role of wettability in determining bubble motion and energy consumption during electrolysis under microgravity.

Evaluation of a Cleaning Procedure for Micro-Structured Devices by Optical Inspection

Fouling and cleaning evaluations are commonly performed integrally, for instance, via pressure drop measurements of selected devices. For micro-structured devices, local fouling and cleaning behavior is of great interest due to the reduced dimensions and characteristic lengths of some hundred micrometers, which can lead to totally blocked microchannels. In this work, a method for local visual cleaning evaluations in microchannels was investigated. It is based on a visually accessible micro heat exchanger with a digital microscope that can be moved to different observation points within one experiment. Captured images are converted via a MATLAB® (The MathWorks, Natick, Massachusetts, USA) algorithm into black-and-white images containing only one descriptor for each pixel: soiled (black) or clean (white). The soil coverage is then calculated through the ratio of black pixels to the number of all pixels in the regarded images. It is shown that the method is suitable for on-line monitoring of cleaning progress in microchannels. Different developments in the calculated soil coverage are discussed. Decreasing soil coverage is found for successful cleaning methods; increasing soil coverage is found for blocked sections, which act like a filter for upstream detached particles or agglomerates; and constant soil coverage is found for sections with no change in soiled surface area. Gas bubble growth at attached particles for nucleation are found in sudden and short increases of the soil coverage.

A General Approach for Rectified Mass Diffusion of Gas Bubbles in Liquids Under Acoustic Excitation

Rectified mass diffusion serves as an important mechanism for dissolution or growth of gas bubbles under acoustic excitation with many applications in acoustical, chemical and biomedical engineering. In this paper, a general approach for predicting rectified mass diffusion phenomenon is proposed based on the equation of bubble motion with liquid compressibility. Nonuniform pressure inside gas bubbles is considered in the approach through employing a well-established framework relating with thermal effects during gas bubble oscillations. Energy dissipation mechanisms (i.e., viscous, thermal, and acoustic dissipation) and surface tension are also included in the approach. Comparing with previous analytical investigations, present approach mainly improves the predictions of rectified mass diffusion in the regions far above resonance and regions with frequencies megahertz and above. Mechanisms for the improvements are shown and discussed together with valid regions and limitations of present approach.

Volcano inflation prior to an eruption: Numerical simulations based on a 1-D magma flow model in an open conduit

We numerically simulate volcanic inflation caused by magma ascent in a shallow conduit at volcanoes which repeatedly erupt, in order to understand the effect of volatile behavior on magma from geodetic data. Considering magma in which the relative velocities between melt and gas bubbles are negligible, we model magma flow in a one-dimensional open conduit with diffusive gas bubble growth. We calculate the ground displacements and tilts caused by spatio-temporal changes of magma pressure in the conduit. Our simulations show that magma without volatiles causes decelerated changes in volcanic inflation. Magma with gas bubble growth inflates the volcano with a constant, or accelerated, rate. Temporal changes of volcanic deformation are also affected by the magma pressure at the bottom of the conduit. When the pressure is small, the displacements and tilts increase in proportion to the 1.5th power of time. This time rate is similar to that predicted from a basic gas bubble growth model. When the pressure equals the lithostatic pressure, the effects of gas bubble growth relatively decrease and the displacements and tilts increase linearly with time.

Simulation of Gas Bubble Growth and Dissolution in Human Tissues During Dives and Recompression

As is known, there are many cases when symptoms of decompression sickness (DCS) in divers appear extremely late (> 15 h after completion of diving) and there is much evidence for unsuccessful treatment of DCS by means of recompression. In this study, we have tried to gain insight into the roots of these phenomena. Using the mathematical model of extravascular gas bubble dynamics, we have analyzed the time history of such bubbles under typical air dives and recompression procedures used for DCS treatment. If the parameters defining the bubble dynamics remained invariable, the bubbles formed in different body tissues would reach their maximal sizes within the well-known latency time range for DCS onset, and later these bubbles would dissolve completely during standard recompression procedures. Actually, the parameters defining the processes of bubble growth and dissolution vary with time. The symptoms of DCS that arise with abnormal latency may be induced by bubbles that grow a very long time in some tissues when the rate of nitrogen washout from them is reduced significantly due to vascular bubbles blocking the microcirculation. An abnormal latency of DCS onset may also appear when the negative effects of the initially asymptomatic bubbles are detected during the very slow process of their dissolution. The failure of recompression to resolve this DCS probably happens when the previously formed bubbles are large and located in tissues with less permeability so that they dissolve very slowly.

Growing bubbles in a slightly supersaturated liquid solution

We have designed and constructed an experimental system to study gas bubble growth in slightly supersaturated liquids. This is achieved by working with carbon dioxide dissolved in water, pressurized at a maximum of 1 MPa and applying a small pressure drop from saturation conditions. Bubbles grow from hydrophobic cavities etched on silicon wafers, which allows us to control their number and position. Hence, the experiment can be used to investigate the interaction among bubbles growing in close proximity when the main mass transfer mechanism is diffusion and there is a limited availability of the dissolved species.

A numerical study of quasi-static gas injected bubble growth: Some aspects of gravity

In the present investigation, adiabatic gas bubble growth from a submerged orifice has been numerically simulated. The growth of the bubble is described by the full Navier–Stokes equations which have been solved by the finite-volume method using the commercial software package TransAT. The numerical simulations have been validated against detailed experimental measurements including the position of the centre of gravity, the curvature profiles and the departure volume. Subsequent to this the CFD platform was used to study some aspects of the influence of gravity level on bubble growth dynamics. In particular, the influence of gravity in the range of 0.1⩽g/g∗⩽1.5 is investigated and the subsequent influence on the bubble formation and departure characteristics are discussed.

Extended fuel swelling models and ultra high burn-up fuel behavior of U–Pu–Zr metallic fuel using FEAST-METAL

Computational models in FEAST-METAL U–Pu–Zr metallic fuel behavior code have been upgraded to improve fission gas, solid fission product swelling, and pore sintering behavior in a microstructure dependent form. First, fission gas bubble growth is modeled by selecting small and large bubble groups according to a fixed number of gas atoms per bubble group. Small bubbles nucleated at phase boundaries grow via gas migration and turn into large bubbles. Furthermore, bubble morphology for each phase structure is captured by selecting the number of atoms per bubble and the shape of the bubbles in a phase dependent form. The gas diffusion coefficients for the single gamma phase and effective dual (α+δ) and (β+γ) phase structures are modeled separately, using the activation energy of the corresponding phase structure. In this study, it is found that pressure sintering of the interconnected porosity in dual phases should be less effective than the reference model in order to match clad strain and fission gas release behavior. In addition to these improvements, a probabilistic approach is taken to verify the fission gas-swelling threshold at which interconnected porosity begins. This fracture problem is treated as a function of critical crack length formed via bubble coalescence. It was found that a 10% gas-swelling threshold is appropriate for a wide range of gas bubble sizes. The new version of FEAST-METAL predicts the burn-up, smear density, and axial variation of the clad hoop strain and fission gas release behavior satisfactorily for selected test pins under EBR-II conditions. The code is used to predict ultra-high burn-up U–Pu–6Zr vented metallic fuel behavior with HT9 cladding for fast breeder reactor applications for 20 years of irradiation. It is assumed that HT9 clad will retain its fracture toughness and creep properties for this simulation. It appears that the increased dose on the cladding, increased solid fission product swelling, and low operating fuel temperature requires lower fuel smear density (∼60%) in order to ensure acceptable clad hoop strain at high burn-up (∼35at.%). Furthermore, keeping the peak clad temperature below 550°C seems to control lanthanide migration and clad inner wastage at a reasonable level. Possible design concerns and improvements are discussed.

In situ TEM investigation of Xe ion irradiation induced defects and bubbles in pure molybdenum single crystal

In order to study irradiation damage and inert gas bubble formation and growth behaviors, and to provide results and insights useful towards the validation of a multi-scale simulation approach based on a newly developed Xe–Mo inter-atomic potential, in situ Transmission Electron Microscopy (TEM) studies of Xe implantations in pure single crystal Molybdenum (Mo) have been conducted. 300keV and 400keV Xe+ ion beams were used to implant Xe in pre-thinned TEM Mo specimens. The irradiations were conducted at 300°C and 600°C to ion fluence up to 4×1016ions/cm2.In situ TEM characterization allows detailed behaviors of defect clusters to be observed and is very useful in illustrating defect interaction mechanisms and processes. Dislocation loops were found to form at relatively low irradiation fluence levels. The characterization results showed that the free surfaces, formed in the process of producing pre-thinned specimens, play an important role in influencing the behaviors of dislocation loops. Similar characterizations were conducted at high fluence levels where Xe gas bubbles can be clearly observed. Xe gas bubbles were observed to form by a multi-atom nucleation process and they were immobile throughout the irradiation process at both temperatures. Measurements on both the number density and the size of dislocation loops and gas bubbles were taken. The results and implications of the measurements are discussed in this paper.