Behavior Of Gas Bubbles Research Articles

Volatile fission product bubble behaviour in uranium dioxide

The role of volatile fission products in the formation and migration of gas bubbles in the nuclear fuel UO 2 has been investigated. The theoretical model used previously to study the behaviour of inert fission gas bubbles in oxide fuel has been applied in the interpretation of annealing experiments of uranium dioxide implanted with other volatile fission products (Cs, Rb, I, and Te). The coalescence of the randomly migrating equilibrium bubbles was considered as a main mechanism defining the development of fission product porosity and swelling. The model predictions are compared with measured bubble size distributions and differences in the behaviour of different fission products are highlighted. The calculational results are applied to discuss important aspects of the formation and the behaviour of fission product filled bubbles in oxide nuclear fuel.

Behavior of helium gas atoms and bubbles in low activation 9Cr martensitic steels

The behavior of helium-gas release from helium-implanted 9Cr martensitic steels (500 appm implanted at 873 K) during tensile testing at 873 K was studied. Modified 9Cr-1Mo, low-activation 9Cr-2W and 9Cr-0.5V were investigated. Cold-worked AISI 316 austenitic stainless steel was also investigated as a reference which was susceptible helium embrittlement at high temperature. A helium release peak was observed at the moment of rupture in all the specimens. The total quantity of helium released from these 9Cr steels was in the same range but smaller than that of 316CW steel. Helium gas in the 9Cr steels should be considered to remain in the matrix at their lath-packets even if deformed at 873 K. This is the reason why the martensitic steels have high resistance to helium embrittlement.

Aerated mixing of viscoelastic fluids with helical ribbons impellers

Aerated mixing of shear thinning and elastic fluids with helical ribbon impellers in the laminar and transition flow regimes has been investigated. Various Newtonian, shear-thinning inelastic, viscoelastic and non-shear-thinning elastic fluids have been chosen to assess the influence of complex rheological properties on the power requirement. For the first time, the power requirement in non-shear-thinning elastic fluids is shown to be larger in gassed systems than in ungassed fluids, while a decrease of power is observed for the shear-thinning inelastic fluids. The gassed power is also dependent on the gas flow rate and Reynolds number. Two correlations are proposed in the laminar and transition flow regimes, respectively, to predict the power consumption as function of the Reynolds number defined for aerated non-Newtonian fluids, the aeration and Weissenberg numbers. Gas hold-up, bubble size and bubble behaviour have also been studied.

Reversal of bubble charge in multivalent inorganic salt solutions—effect of lanthanum

It was discovered recently that the charge of gas bubbles in aqueous solution can be reduced and even reversed by the addition of multivalent inorganic salts. In this work, the effect of LaCl 3 on the charge of bubbles was investigated and found to have an effect similar to that previously observed with AlCl 3 and MgCl 2. The electrokinetic behavior of gas bubbles was affected slightly by LaCl 3 additions at low concentrations but changed markedly at high concentration (1 × 10 −3 mol dm −3) of LaCl 3. A reversal of bubble charge was observed and this is attributed to the specific adsorption of La 3+ in the lower pH region and to the formation of La(OH) 3(s) precipitate at the gas—liquid interface in the alkaline pH region.

Temperature distribution and heat transfer from the pulsating bubble in ultrasonic field

Gas bubble behavior immersed in liquid under a high-intensity ultrasonic field was studied by using a self-consistent model. In this model, the temperature distribution of the gas inside the bubble was obtained by solving analytically the continuity and energy equations for the gas. Also heat transfer between the gas inside the bubble and the surrounding liquid was considered by solving the mass, momentum, and energy equation for the liquid. With this model, the polytropic approximation is no longer required to calculate the internal pressure of the oscillating bubble under ultrasonic field. Under the periodic ultrasonic field with an amplitude of 110 kPa and a frequency of 20 kHz, the temperature of air at the bubble center with equilibrium radius of 20 μm reached as high as 5000 K at the time of bubble collapse. The heat flux from the bubble to the surrounding fluid by conduction is above 10 MW/m2 at this stage. The pressure inside the bubble at this stage is about 10 bar, which is much less than that obtained by a previous model. Calculation results support the hot spot theory, which states that the phenomenon of sonoluminescence is due to chemiluminescence by the high temperature of gas inside the bubble.

A Computer Model for Predicting Transient Fission Gas Release from UO2Fuel

The KFGR-T computer model has been developed to predict transient fission gas release from UO2fuel with an emphasis on the nonequilibrium behavior of fission gas bubbles. It takes into account the ...

Flow regimes and liquid mixing in a draft tube gas-liquid-solid fluidized bed

Flow behavior of gas bubbles, liquid and particles, and mixing in the liquid phase were studied in draft and annulus of a draft tube gas-liquid-solid fluidized bed. The experimental unit was a 80mm ID × 1.5 m column with an 50mm ID internal draft tube. A 2-D unit of the same size and geometry was used to assess the local concentrations and velocities of liquid, particles and air bubbles. Fluid and particle dynamics in the draft and annular regions were analyzed using the drift-flux model extended to the 3- phase flow, and in terms of the effective buoyancy of solid particles. Liquid mixing was studied based on the tracer-response technique, using the model of axial dispersion.

Modelling of inert gas bubble behaviour during annealing of irradiated molybdenum

By theoretically studying the gas bubble evolution in molybdenum doped with heavy inert gas (Xe) a bimodal size distribution in a broad temperature region (1473–1973 K) is predicted. For molybdenum implanted with helium the size distribution is typical and has only a single peak. A modelling of gas porosity development was carried out using the assumption, that the basic mechanism of bubble nucleation and growth is the collision and coalescence of randomly migrating bubbles. An analysis of the calculation results leads to a conclusion, that the major cause of the formation of the bimodal size distribution is the existence of a deep bubble mobility minimum for molybdenum doped with heavy inert gas. The proposed mechanism of bimodal size distribution formation is supported by results obtained recently by Rest and Birtcher for nickel implanted with heavy inert gases.

Behavior of gas bubbles in a concentric cylindrical airlift column

Using a light transmission optical probe, the effect of superficial gas velocity on bubble properties(bubble size, bubble rising velocity, bubble frequency and local gas holdup) at axial and radial positions was determined in the riser and the downcomer of a concentric cylindrical airlift reactor. The vertical bubble length, the bubble rising velocity and the bubble frequency at axis in the riser increased with increasing superficial gas velocity and the bed height. The radial distribution of the local gas holdup, vertical bubble length and bubble frequency in the riser and the downcomer were found to be non-uniform. The profiles of the local gas holdup, vertical bubble length and bubble rising velocity in the riser were shown as parabolic shapes. The local gas holdup, the vertical bubble length and the bubble frequency in the downcomer changed with superficial gas velocity and the distance from the top of the draft tube.

The behaviour of large gas bubbles at a liquid-liquid interface. Part 2: Liquid entrainment

On a elucide le role que jouent les grosses bulles de gaz dans la production et la coalescence des gouttes liquides a une interface liquide-liquide. La quantite de liquide de la phase inferieure entraine par les bulles separement et les distributions de taille des gouttes qui en resultent dans la phase superieure, est estimee pour le systeme triphasique: huile de tournesol + 50% en poids de decane, eau + 50% en poids de sucre, air, et des modeles theoriques qualitatifs sont presentes. On a trouve que les gouttes se formant a l'interface se combinaient rapidement et le flux de bulles ne montre aucun effet apparent sur la vitesse de coalescence des gouttes a l'interface liquide-liquide

Flow Characteristics of Bubbles in a Single-Layer Gas-SolidFluidized Bed.

A single-layer gas-solid fluidized bed is developed by setting two glass plates vertically with a spacing space of which is slightly greater than the diameter of the particles. The behavior of gas bubbles is observed in detail by introducing high shutter-speed video cameras with 1/2000 s exposure time and an image analyzer.It is found that the rising velocity of bubbles in the single-layer fluidized bed is almost the same as that in the ordinary two-dimensional fluidized bed. The effect of gas velocity and height from the distributor on bubble growth is almost the same as in the three-dimensional fluidized bed despite its extremely small bed width.

Reversal of bubble charge in multivalent inorganic salt solutions—Effect of magnesium

An experimental technique has been developed to study the electrokinetic behavior of gas bubbles in aqueous electrolyte solutions. It was found that bubbles are negatively charged in NaCl solutions whereas, under certain conditions, they become positively charged in MgCl 2 solutions. The observed charge reversal in the pH range of 9 to 11 is attributed to the precipitation of Mg(OH) 2(s) at the gas-liquid interface while the reduction in the magnitude of the zeta potential of the bubble observed in the acidic pH range is considered to be due to the specific adsorption of Mg +2.

Principles and recent developments in ultrasound contrast agents

The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications.

Simulation of the mass transfer behaviour of individual gas bubbles undergoing fast chemical stripping using the jet stream model

The mass transfer of solute from a dilute gaseous mixture during bubble formation at the tip of a submerged nozzle in the presence of an instantaneous chemical reaction on the liquid side is simulated via a two-parameter model. This mechanistic model is developed from the general mass balance of solute by introducing a number of physically reasonable assumptions coupled with carefully checked mathematical approximations. Using data reported elsewhere, parameter estimates are found and a statistical analysis of their significance is presented. Experimental evidence is predicted much better than via other theoretical models. The analysis reported is useful for the preliminary design of industrial sparging vessels because most of the solute removal occurs during bubble growth.

A Study of the Solubility of Blowing Agents in Foam Extrusion Systems

The solubility of fluorocarbon blowing agents in foam extrusion of thermoplastic resin was investigated by both experimental and theoretical approaches. The thermoplastic resin used was polystyrene, while CFC-12 and HFC-134 a were the selected fluorocarbon blowing agents.First of all, in our experimental approach, we developed a direct observation system using a fiberscope, and observed the shape and behavior of gas bubble in the extrusion system. In this experiment, we used CFC-12 as the blowing agent. It was noted that (1) the phenomena called gas dispersion in this field is the same as gas solubility in the resin, (2) huge voids generated in the plastic foam was mainly caused by poor solubility of the blowing agent. We considered the effects of pressure, temperature, and residence time in additional experiments.Next, we constructed a quantitative theoretical model by applying the concept of absorption velocity that is defined for gas-liquid equilibrium for this phenomena. In a numerical simulation based on this model, the results showed good agreement with experimental results.Finally experimental production parameters (pressure, temperature and residence time) were caluclated for HFC-134 a and polystyrene.

Bubble Dynamics in Polymer Melts

AbstractA system has been developed for studying the dynamic behaviour of gas bubbles in liquid media and is currently being used to investigate the behaviour of a single nitrogen bubble in molten LDPE. It involves the formation of an initial gas-liquid interface from a capillary by direct injection of the gas into the melt, subsequent growth until an equilibrium state is reached and the application of ambient pressure ramps which result in bubble expansion or contraction. The response depends on the rate of change of the ambient pressure. Experiments have been conducted at various temperatures above the crystalline melting temperature, Tm, of LDPE in the range 120°C-150°C. The numerical data acquired are in the form of pressure and temperature values, and these data are superimposed on stored video images of the bubbles for further processing on an image analyser whereby bubble sizes and shapes are determined.The results obtained reveal the effect of melt viscoelasticity on the dynamics of bubbles in highly viscous fluid media. Furthermore, the changes in bubble shapes with time due to buoyancy effects are also shown. Clearly, the bubble response in the melt is governed by a combination of viscous and elastic effects. However, in the absence of suitable viscous solutions to the problem, we have attributed the behaviour to a time-dependent elastic response, but only as a first order approximation.

Erratum: transient pulsations of small gas bubbles in water [J. Acoust. Soc. Am. 84, 985-998 (1988)] [corrected and republished

Transient behavior of small gas bubbles in a liquid set into violent motion by ultrasonic pressure waves is of interest because of widespread use of microsecond pulses in diagnostic ultrasound. Such pulses contain only a few pressure cycles and the transient pulsations of bubbles set in motion by such pulses would determine the bubble-ultrasound interaction. A computer study has been made to obtain a global representation of the pulsation amplitudes R (t) of small gas bubbles (nuclei) in water during the first few cycles of a cw ultrasonic pressure. One objective was to obtain a better understanding of cavitation phenomena where many nuclei with initial radii Rn from 0.1-20 microns are set in motion at pressures ranging from 0.5-5 bars and at frequencies from 0.5-10 MHz. Results allowed construction of surfaces showing the relative bubble amplitude R/Rn as a function of Rn and of the time t/TA, where TA is the acoustic period. One finding is that, in the range of peak pressures found in diagnostic pulses, transient cavities would be generated during the first pressure cycle from nuclei with initial radii as small as a few microns (micron). Nuclei that grow into transient cavities in the first pressure cycle are here called "prompt" nuclei. At a specified pressure, the size range of radii Rn in which they occur decreases with increasing frequency. At 5 bars, the range of Rn for prompt nuclei is 0.166-11.35 microns at 0.5 MHz and vanishes at 10 MHz.

Transient pulsations of small gas bubbles in water

Transient behavior of small gas bubbles in a liquid set into violent motion by ultrasonic pressure waves is of interest because of widespread use of microsecond pulses in diagnostic ultrasound. Such pulses contain only a few pressure cycles and the transient pulsations of bubbles set in motion by such pulses would determine the bubble–ultrasound interaction. A computer study has been made to obtain a global representation of the pulsation amplitudes R(t) of small gas bubbles (nuclei) in water during the first few cycles of a cw ultrasonic pressure. One objective was to obtain a better understanding of cavitation phenomena where many nuclei with initial radii Rn from 0.1–20 μm are set in motion at pressures ranging from 0.5–5 bars and at frequencies from 0.1–10 MHz. Results allowed construction of surfaces showing the relative bubble amplitude R/Rn as a function of Rn and of the time t/TA, where TA is the acoustic period. One finding is that, in the range of peak pressures found in diagnostic pulses, transient cavities would be generated during the first pressure cycle from nuclei with initial radii as small as a few microns (μm). Nuclei that grow into transient cavities in the first pressure cycle are here called ‘‘prompt’’ nuclei. At a specified pressure, the size range of radii Rn in which they occur decreases with increasing frequency. At 5 bars, the range of Rn for prompt nuclei is 0.166–11.35 μm at 0.5 MHz and vanishes at 10 MHz.

Enhanced nonlinearity in a bubbly liquid considered as a mixture

During the past decade there has been an increasing interest in the nonlinear behavior of gas bubbles in liquids. Recent papers by Soviet investigators [e.g., Kustov et al., Sov. Phys. Acoust. 32(6), 500–503 (1986)] have concentrated on phenomena observed when sound interacts with a bubbly layer. These phenomena can include acoustic solitons, parametric radiation, self‐focusing, phase conjugation, and other effects that occur because the system is highly nonlinear. An investigation of the acoustic nonlinear parameter of mixtures was conducted to help infer the volume fractions of the mixture components. When a bubbly medium of known air volume fraction is considered as a two‐component mixture, its effective nonlinear parameter may be calculated using mixture methodologies [R. Apfel, J. Acoust. Soc. Am. 74, 1866–1869 (1983)]. The mixture analysis in this work, which is independent of any assumptions regarding bubble oscillation, yields nonlinear parameter values comparable to those of the Soviet investigators. For certain volume fractions, values of the nonlinear parameter of a bubbly liquid may be hundreds of times that of either the gas or the liquid host. Both experimental and theoretical work will be presented and the implications of this enhanced nonlinearity will be discussed. [Work supported by NIH through Grant 5‐R01‐GM30419.]

Fundamentals of Gas Fluidization Technology

The fluidization technology for gas-solid systems was overviewed. The stress was put on behavior of gas bubbles, properties of emulsion phase, description of powder groups, axial mixing of solids, and modeling of fluidized-bed contactors. The fluidization of ultrafine particles was also mentioned.