Growth Of Gas Bubbles Research Articles

A model to evaluate unstable ductile crack arrestability of offshore pipeline

We developed the first model to evaluate unstable ductile crack arrestability in offshore pipelines. The proposed model is an integrated one-dimensional model with four sub-models to calculate (a) pipe deformation, (b) gas flow inside pipe, (c) bubble growth, and (d) crack propagation. We validated the proposed model by applying it to two types of tests: laboratory scale underwater rupture tests and existing data of a full-scale burst test of an offshore pipeline. In addition, the calculation results of the proposed model showed that a deep water depth results in increased unstable crack arrestability of the pipeline.

Continuous manufacture of polymeric cellular dosage forms

The most prevalent pharmaceutical dosage forms at present are granular solids in the form of oral tablets and capsules. While effective in releasing drug rapidly upon contact with gastrointestinal fluid, their manufacture, which relies on particulate processing, is fraught with difficulties associated with the unpredictable inter-particle interactions. Such difficulties, however, could be easily overcome by transitioning to a liquid-based process. Therefore, we have recently introduced melt‐processed polymeric cellular dosage forms. The drug release behavior of the cellular forms was tailored by altering the microstructure; yet their preparation relied on an inefficient batch method comprising gas dissolution, and nucleation and growth of microscopic gas bubbles in the melt. In this study, therefore, we present a continuous microfluidic melt extrusion and molding process. The cellular dosage forms are produced by injecting gas bubbles directly into the melt stream in a micro‐ or milli-fluidic channel, followed by molding and solidification of the cellular structure. A model is developed to illustrate the effects of the width, frequency, and pressure of the gas injection pulses, and the flow rate and viscosity of the melt, on the microstructural parameters of the dosage forms produced. Experimental results show that the size and volume fraction of gas-filled cells (or voids) are predictable. They also confirm that the dosage form disintegration rate and density can be tailored by altering the volume fraction of voids. It is thus demonstrated that polymeric cellular dosage forms with predictable drug release properties, and density, can be readily manufactured by a continuous process.

Vapor and Gas-Bubble Growth Dynamics around Laser-Irradiated, Water-Immersed Plasmonic Nanoparticles.

Microbubbles produced by exposing water-immersed metallic nanoparticles to resonant light play an important role in emerging and efficient plasmonic-enhanced processes for catalytic conversion, solar energy harvesting, biomedical imaging, and cancer therapy. How do these bubbles form, and what is their gas composition? In this paper, the growth dynamics of nucleating bubbles around laser-irradiated, water-immersed Au plasmonic nanoparticles are studied to determine the exact origin of the occurrence and growth of these bubbles. The microbubbles' contact angle, footprint diameter, and radius of curvature were measured in air-equilibrated water (AEW) and degassed water (DGW) with fast imaging. Our experimental data reveals that the growth dynamics can be divided into two regimes: an initial bubble nucleation phase (regime I, < 10 ms) and, subsequently a bubble growth phase (regime II). The explosive growth in regime I is identical for AEW and DGW due to the vaporization of water. However, the slower growth in regime II is distinctly different for AEW and DGW, which is attributed to the uptake of dissolved gas expelled from the water around the hot nanoparticle. Our scaling analysis reveals that the bubble radius scales with time as R(t) ∝ t1/6 for both AEW and DGW in the initial regime I, whereas in the later regime II it scales as R(t) ∝ t1/3 for AEW and is constant for perfectly degassed water. These scaling relations are consistent with the experiments.

Quantification of a Single Gas Bubble Growth in Solvent(s)–CO2–Heavy Oil Systems With Consideration of Multicomponent Diffusion Under Nonequilibrium Conditions

A mechanistic model has been developed and validated to quantify a single gas bubble growth with considering multicomponent gas diffusion in solvent(s)–CO2–heavy oil systems under nonequilibrium conditions. Experimentally, constant-composition expansion (CCE) experiments are conducted for C3H8–CO2–heavy oil systems under equilibrium and nonequilibrium conditions, respectively. Theoretically, the classic continuity equation, motion equation, diffusion–convection equation, real gas equation, and Peng–Robinson equation of state (PR EOS) are integrated into an equation matrix to dynamically predict gas bubble growth. Also, the viscous term of motion equation on the gas phase pressure is included due mainly to the viscous nature of heavy oil. The newly proposed model has been validated by using the experimentally measured gas bubble radius as a function of time with good accuracy. Combining with the experimental measurements, the critical nucleus radius and gas bubble growth are quantitatively predicted with the newly proposed model. Effects of mass transfer, supersaturation pressure, mole concentration of each component, liquid cell radius, and pressure decline rate on the gas bubble growth are examined and analyzed. In general, gas bubble growth rate is found to increase with an increase of each of the aforementioned five parameters though the contribution of individual component in a gas mixture to the bubble growth rate is different. A one-step pressure drop and the unlimited liquid volume surrounding a gas bubble are considered to be the necessary conditions to generate the linear relationship between gas bubble radius and the square root of time.

GROWTH OF A GAS BUBBLE IN A STEADY DIFFUSION FIELD IN A TISSUE UNDERGOING DECOMPRESSION

This paper presents parameterized study on the growth of a convective gas bubble in tissues of a steady diffusion field. Resulting formulae are obtained analytically, which are valid for constant ambient pressure. It’s found that the growing bubble radius is proportional to initial bubble radius, initial concentration difference, diver’s average temperature and initial void fraction which is the dominant parameter, while it’s inversely proportional to surface tension, viscosity, density ratio and ambient pressure. Comparison to some previous work is performed.

An alternative explanation for cyanobacterial scum formation and persistence by oxygenic photosynthesis

The cause of persistent cyanobacteria scum formation in lakes is an unresolved subject. Scum refers to the event in which cyanobacteria are at the water surface of a lake. Factors like low turbulence levels, long day-light, high water temperatures and the buoyant capacity of cyanobacterial cells play a role in the occurrence of scums. However, they do not explain why scums are observed at periods during the day when according to theory they should have disappeared into the deeper water layers. In this study, we present an alternative explanation. The hypothesis we present here is that irreversible buoyancy of cyanobacteria colonies is created by the growth of gas bubbles on or within the mucilage of the colonies. These bubbles grow under oxygen super-saturated conditions. At low wind speed and high chlorophyll levels, the dissolved oxygen (DO) produced during photosynthesis by cyanobacteria, cannot escape sufficiently fast to the atmosphere hence a DO supersaturated condition arises in the water. At this stage, growth of oxygen bubbles may occur inside or attached to the mucilage. We present results of compression experiments to support our hypothesis. In a chamber, the pressure on lake water containing a natural cyanobacteria population is increased. At 3×105 and 4×105Pa the cyanobacteria colonies were not able to float anymore and sank. This pressure is lower than the 106Pa needed to collapse all gas vacuoles inside the cyanobacteria cells (Walsby, 1994). The observed change from floating to sinking colonies due to increased water pressure suggests that gas bubbles were present inside the colonies. In lakes, these gas bubbles may lead to permanent buoyancy, i.e. a persistent scum.

Influence of limiting throat and flow regime on oxygen bubble saturation of polymer electrolyte membrane electrolyzer porous transport layers

In this work, the effect of porous transport layer (PTL) microstructure on the growth of oxygen gas bubbles was investigated using a microfluidic platform, termed PTL-on-Chip. The microfluidic chip was designed through stochastic pore network generation and height calibration, and was fabricated using soft-lithography. It was found that PTL throats have the dominating threshold capillary pressures compared to PTL pores; therefore, the size distribution of PTL throats ultimately govern the distribution of bubbles within the water saturated PTL. A unique throat is herein termed the limiting throat, whereby once it has been penetrated by the bubble, breakthrough instantly follows. This limiting throat is also the location of snap-off for subsequent bubble detachment. Within the porous media, oxygen bubble saturation increased as the distance of the limiting throat from the inlet increased. Lastly, it was observed that the heterogeneity of the PTL structure can enable the simultaneous co-existence of two flow regimes (capillary fingering and viscous fingering) at distinct regions within the bulk.

Gas Evolution at Porous Electrodes

Porous electrodes for PEM electrolyser and fuel cell technologies are optimized primarily to provide a high specific surface area for the desired electrochemical reactions. However, the increase in surface area comes at the cost of increased voltage losses due to the transport of reactant and product species through the porous medium. In gas evolving electrolyzer electrodes, the formation and transport of gas bubbles plays an important role: on the one hand, gas in the pores replaces the electrolyte phase, thus hindering ion transport and reducing the effective ionic conductivity in the porous electrode; on the other hand, gas bubbles cover and deactivate a portion of the internal surface area. The impacts of gas formation and removal must be accounted for in the design of electrolyzer electrodes. The focus of the presented work is on the fundamental understanding of the relationships between structure, properties and performance of porous gas-evolving electrodes. The approach combines a macro-scale performance model of the electrode with a micro-scale model of gas evolution. At the macro-scale, a classic porous electrode model describes the transport of ions, electrons and produced oxygen using effective medium theory and accounting for the gas phase volume and distribution. The micro-scale model describes the formation and growth of gas bubbles based on chemical energy considerations. It can explain the experimentally found high oversaturation that is necessary to nucleate bubbles [1]. Additionally, the size of the bubble nucleus in the experiment was estimated. The model was used to study the influence of structural parameters on the operation of porous electrodes and to establish guidelines for an enhanced electrode design. It was found that the transport regime of the dissolved gas, viz. diffusion control vs. transfer control at the liquid-gas interface, determines the bubble growth law. Applications of the model to gas evolving porous electrodes in electrolyzers with liquid electrolyte as well as polymer electrolyte electrolyzers (PEEC) will be discussed. [1] Chen, Q., Luo, L. and White, H. S. Electrochemical generation of a hydrogen bubble at a recessed platinum nanopore electrode. Langmuir 31, 4573–4581 (2015). Figure 1: Bubble growth on an artificial nucleation site at 20 mA/cm2. Comparison of model results with experimental data from C. Brussieux et al., Electrochimica Acta 56 (2011) 7194-7201. Deviation at large bubble radii due to deformation of the bubbles before detachment, which is neglected in the model. Figure 1

Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the formation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was developed. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials along 〈110〉 directions in the body-centered cubic U matrix causes the gas bubble alignment along 〈110〉 directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.

Erratum to: Modeling the diffusion-driven growth of a pre-existing gas bubble in molten tin

Erratum to: Modeling the diffusion-driven growth of a pre-existing gas bubble in molten tin

Microstructure of α-U and δ-UZr2 phase uranium–zirconium alloys irradiated with 140-keV He+ ion-beam

Ion-beam irradiation has been conducted to demonstrate and assess solid phase dependence of fission gas bubble nucleation and growth in metallic nuclear fuels. Differential formation and growth of irradiation-induced voids and bubbles were observed from as-cast uranium-zirconium (U–Zr) alloys including 0.1 and 40 wt% zirconium. The U–Zr alloys were irradiated with 140-keV He+ ions with fluences ranged from 1 × 1014 ions/cm2 to 5 × 1016 ions/cm2. Several larger spherical bubbles (<∼70 nm) were revealed from an irradiated single α-U phase alloy (U–0.1Zr) in which observed bubbles were mobile under 200-keV electron beam of transmission electron microscope (TEM). In-situ mergence and leakage of the bubbles in the uranium-rich alloy was also evident during the observation. In contrast, numerous number of small (∼6 nm) angular voids, or low pressure bubbles, were found in an irradiated δ-UZr2 phase alloy (U–40Zr), in which the radiation-induced nanostructure was stationary throughout the observation. This study may reaffirm higher radiation-susceptibility of the α-U phase than the δ-UZr2 phase, which could strengthen the needs of separate accounting of solid phase effects for metallic fuel performance modeling particularly regarding the fuel restructuring phenomena, such as fission gas swelling and constituent redistribution, since conventional models are commonly adopted homogeneous medium assumption, not in accordance with the results of post-irradiation examinations of used metallic nuclear fuel in which the formation of several concentric phase zone was distinct corresponding to a steep radial temperature gradient in the fuel pin and multiple isotherm lines in the binary phase diagram of U–Zr alloy system.

Nonequilibrium Phase Behavior of Alkane Solvent(s)–CO2–Heavy Oil Systems under Reservoir Conditions

A pragmatic technique has been developed to experimentally and theoretically quantify the nonequilibrium phase behavior of alkane solvent(s)–CO2–heavy oil systems under reservoir conditions. Experimentally, constant-composition expansion tests have been conducted for alkane solvents–CO2–heavy oil systems at constant-volume expansion rates with a PVT setup to simultaneously measure volume and pressure change of the aforementioned systems. Theoretically, mathematical formulations have been developed to quantify the amount of the evolved gas as a function of time based on the real gas equation, while mathematical models on compressibility and density of the oleic phase mixed with the entrained gas (i.e., foamy oil) are respectively formulated. The required equilibrium time and exponential coefficients associated with gas-bubble growth are determined once the deviation between the experimentally measured pressure–volume profile and the theoretically calculated one has been minimized. In addition to effectivel...

Analysis of Flame Retardancy in Polymer Blends by Synchrotron X-ray K-edge Tomography and Interferometric Phase Contrast Movies.

Underwriters Laboratories 94 test bars have been imaged with X-ray K-edge tomography between 12 and 32 keV to assess the bromine and antimony concentration gradient across char layers of partially burnt samples. Phase contrast tomography on partially burnt samples showed gas bubbles and dark-field scattering ascribed to residual blend inhomogeneity. In addition, single-shot grating interferometry was used to record X-ray movies of test samples during heating (IR and flame) intended to mimic the UL 94 plastics flammability test. The UL 94 test bars were formulated with varying concentrations of a brominated flame retardant, Saytex 8010, and a synergist, Sb2O3, blended into high-impact polystyrene (HIPS). Depending on the sample composition, samples will pass or fail the UL 94 plastics flammability test. Tomography and interferometry imaging show differences that correlate with UL 94 performance. Key features such as char layer, gas bubble formation, microcracks, and dissolution of the flame retardant in the char layer regions are used in understanding the efficiency of the flame retardant and synergist. The samples that pass the UL 94 test have a thick, highly visible char layer as well as an interior rich in gas bubbles. Growth of gas bubbles from flame-retardant thermal decomposition is noted in the X-ray phase contrast movies. Also noteworthy is an absence of bubbles near the burning surface of the polymer; dark-field images after burning suggest a microcrack structure between interior bubbles and the surface. The accepted mechanism for flame retardant activity includes free radical quenching in the flame by bromine and antimony species. The imaging supports this as well as provides a fast inspection of other parameters, such as viscosity and surface tension.

海底パイプラインを模擬した水中ラプチャーディスク試験及びガス減圧の数値モデル開発

In this research, atmospheric and underwater small-scale pipe rupture disk tests were conducted. Tested pipes with rupture disk were pressurized by pure nitrogen, in which internal pressure changes and external pressure changes were measured by pressure transducers. By comparing results of the underwater tests with results of the atmospheric tests, water effects were clarified: (1) gas decompression in the underwater tests delays due to constrained gas leak by bubble generation and growth as compared to gas decompression in the atmospheric tests, and (2) larger external pressure changes were measured in the underwater tests. In addition, 1D finite-difference based coupled model for gas decompression, in which gas flow inside a pipe and bubble growth are considered, was developed. In the model, governing equations for gas flow inside a pipe and a bubble are derived from mass conservation law and momentum conservation law assuming isentropic changes of gas. Bubble growth is formulated based on Rayleigh-Plesset equation. The calculated results for the rupture disk tests using the model showed good agreements with the experimental results, which analytically clarified the above stated water effects. This research reveals an importance of considering the water effects in evaluating fractures in offshore pipelines. In the future, it is expected that the model is extended to incorporate crack propagation and pipe deformation together with gas decompression and bubble growth.

Phase-field modeling of microstructure evolution during solidification in presence of gas bubble

The microstructure evolution during solidification of pure Aluminum metal with gas bubble nucleation and growth is modeled and simulated by the phase-field method. Interface microstructure formation in the presence of gas bubble is simulated to investigate the interaction between gas bubble and microstructural evolution, and also a pressure correction equation is implemented to study the effect of pressure difference between the bubbles and melts. Results indicate that pressure difference between gas bubble and the liquid melt can significantly affect the gas atoms diffusion near the gas–liquid interface, which will lead to the bubble growth velocity change. These simulation results are in agreement with experimental observations.

Melt-processed polymeric cellular dosage forms for immediate drug release

The present immediate-release solid dosage forms, such as the oral tablets and capsules, comprise granular matrices. While effective in releasing the drug rapidly, they are fraught with difficulties inherent in processing particulate matter. By contrast, liquid-based processes would be far more predictable; but the standard cast microstructures are unsuited for immediate-release because they resist fluid percolation and penetration. In this article, we introduce cellular dosage forms that can be readily prepared from polymeric melts by incorporating the nucleation, growth, and coalescence of microscopic gas bubbles in a molding process. We show that the cell topology and formulation of such cellular structures can be engineered to reduce the length-scale of the mass-transfer step, which determines the time of drug release, from as large as the dosage form itself to as small as the thickness of the cell wall. This allows the cellular dosage forms to achieve drug release rates over an order of magnitude faster compared with those of cast matrices, spanning the entire spectrum of immediate-release and beyond. The melt-processed polymeric cellular dosage forms enable predictive design of immediate-release solid dosage forms by tailoring microstructures, and could be manufactured efficiently in a single step.

Modeling the diffusion-driven growth of a pre-existing gas bubble in molten tin

Finite element method is utilized to solve the diffusion equation and model the diffusion driven growth of a pre-existing spherical gas bubble in molten tin at the solder/substrate interface for reflow time of 120 s and temperature of 250 °C. The gibbs free energy change required for determining the equilibrium concentration at liquid solder/gas bubble boundary was calculated using the thermodynamic polynomial coefficients. The rate of change of radius, as function of concentration flux, is calculated using the lagrangian mesh update methodology. With an initial diameter of 20 μm, the bubble growth is calculated as a function of contact angle. When the wetting angle is varied from a value of 30° to 135°, the numerical calculation has yielded the final sizes for the bubble to change from 62.87 μm to 82.8 μm respectively. The effect of wetting transition in the growth of bubble was studied by the in-situ observation of bubble dynamics through synchrotron radiation imaging technique. The scanning electron microscopy images of the morphologies of intermetallic compounds influenced by growing bubble in Sn/Cu solder joint and bubble pictures obtained through synchrotron radiation are utilized to get the experimental size of the bubble. The mean experimental bubble diameter has been obtained as 76.39 μm. The growing bubble inhibits the growth of intermetallic compound at its vicinity and thereby reduces the strength of solder joints.

Modeling and Optimization of Porous Electrodes for Alkaline Oxygen Evolution

The oxygen evolution reaction (OER) plays an important role in many industrial applications like electrolytic water splitting or regenerative fuel cell systems. So far, IrO2 and RuO2 are the benchmark OER catalysts, owing to their high catalytic activity. However, these precious metals are costly and their supply is not sustainable, which makes them unsuitable for large-scale applications. Hence, research efforts have been devoted to the development of low-cost OER catalysts on the basis of first-row transition metals and their oxides. Especially nickel- and cobalt based composites show promising OER catalytic activity. Strategies to further enhance OER activity of the transition metal-based catalysts to levels comparable to the benchmark IrO2 and RuO2 catalysts pursue the design and fabrication of nanoporous catalyst structures and the use of catalyst nanoparticles immobilized on carbon nanomaterial substrates. Porous electrode structures offer high specific surface area available for reaction. However, this increase in surface area comes at the cost of additional transport losses of reactants and products through the porous medium. In this context, gas evolution plays an important role: on the one hand, gas in the pores replaces the electrolyte phase, thus hindering ion transport and reducing the effective ionic conductivity in the porous electrode. Limited ion transport leads to transport losses and defines a reaction penetration depth, beyond which the porous electrode becomes inactive. On the other hand, the gas covers part of the internal surface area, rendering it inactive. In order to maximize the activity of a porous gas evolution electrode, its structure needs to be optimized. To do so, the current work attempts to gain a fundamental understanding of the relationships between structure, properties and performance of the porous electrode. Our approach combines a macro-scale performance model of the electrode with a micro-scale model of gas evolution. At the macro-scale, a classic porous electrode model describes the transport of ions, electrons and produced oxygen using effective medium theory and accounting for the gas phase volume and distribution. The gas phase is modeled by a micro-scale model describing the formation, growth and transport of gas bubbles in the porous medium. The model is applied in practice to a regenerative zinc fuel cell system for energy storage. In this system, energy is released in an alkaline zinc air fuel cell by oxidizing zinc suspended in alkaline solution. The system can be recharged by regenerating the zinc on the cathode of the regenerator unit, as shown in Fig. 1. On the anode of this regenerator unit, the OER takes place, which imposes one of the major losses in the system. The presented work uses this system as a concrete example for the development of a general theory for gas evolving porous electrodes and aims at verifying this theory by targeted experiments on this practical system. The model can then be used to optimize the structure of the electrode in order to optimize the performance of the regenerator. Figure 1

Bubble Nucleation and Growth of Dissolved Gas in Solution Flowing across a Cavitating Nozzle

Computational modelling of dissolved gas bubble formation and growth in supersaturated solution is essential for various engineering applications, including flash vaporisation of petroleum crude oil. The common mathematical modelling of bubbly flow only caters for single liquid and its vapour, which is known as cavitation. This work aims to simulate the bubble nucleation and growth of dissolved CO2 in water across a cavitating nozzle. The dynamics of bubble nucleation and growth phenomenon will be predicted based on the hydrodynamics in the computational domain. The complex interrelated bubble dynamics, mass transfer and hydrodynamics was coupled by using Computational Fluid Dynamics (CFD) and bubble nucleation and growth model. Generally, the bubbles nucleate at the throat of the nozzle and grow along with the flow. Therefore, only the region after the throat of the nozzle has bubbles. This approach is expected to be useful for various types of bubbly flow modelling in supersaturated condition.

Uranium vacancy mobility at the Σ5 symmetric tilt and Σ5 twist grain boundaries in UO2

Ionic transport at grain boundaries in oxides dictates a number of important phenomena, from ionic conductivity to sintering to creep. For nuclear fuels, it also influences fission gas bubble nucleation and growth. Here, using a combination of atomistic calculations and object kinetic Monte Carlo (okMC) simulations, we examine the kinetic pathways associated with uranium vacancies at two model grain boundaries in UO2. The barriers for vacancy motion were calculated using the nudged elastic band method at all uranium sites at each grain boundary and were used as the basis of the okMC simulations. For both boundaries considered – a simple tilt and a simple twist boundary – the mobility of uranium vacancies is significantly higher than in the bulk. For the tilt boundary, there is clearly preferred migration along the tilt axis as opposed to in the perpendicular direction while, for the twist boundary, migration is essentially isotropic within the boundary plane. These results show that cation defect mobility in fluorite-structured materials is enhanced at certain types of grain boundaries and is dependent on the boundary structure with the tilt boundary exhibiting higher rates of migration than the twist boundary.