Bubble Shrinkage Research Articles

Shrinkage of an oxygen bubble rising in a molten glass

Abstract The mechanisms controlling the evolution of a bubble surrounded by molten glass are important to understand in order to improve melting in glass furnaces, particularly during a change in composition. In order to provide insight into this phenomenon, the behavior of an isolated bubble rising in molten glass is examined both experimentally and numerically. An experimental procedure developed specifically to observe, in situ, a rising bubble is described. Two soda-lime-silica compositions are tested, with low and high iron content, respectively. The numerical model used to describe bubble shrinkage is based on the results recently proposed in Pigeonneau (2009) . A specific mass transfer coefficient is used for oxygen where the oxidation–reduction reaction of iron oxides is taken into account. A comparison between the experimental and numerical results shows the importance of the oxidation–reduction reaction of iron in the mass transfer of oxygen. The shrinkage rate of a pure O2 bubble is enhanced with reduced molten glass iron content.

J0201-1-4 界面活性剤で覆われたマイクロバブルの成長・収縮に及ぼす気体拡散の影響(ドラッグデリバリーシステムとその周辺技術の基礎と展開(1))

The growth and shrinkage of surfactant-coated microbubbles are observed with a high-speed video camera. The observed bubble motion is compared with the simulation in which the dynamic surface tension and the variation of gas permeation resistance of surfactant layers are considered. The simulation is in good agreement with the experiment. It is shown that when the microbubble grows under pressure reduction, the gas diffusion from the surrounding liquid to bubble inside is suppressed by the increase of the surface tension, while it is promoted by the decrease of the gas permeation resistance. On the other hand, the bubble shrinkage due to gas diffusion after pressure increase is strongly affected by the increase of the gas permeation resistance. The variations of both the surface tension and the gas permeation resistance determine the diffusion process of microbubbles.

Threshold curves obtained under various gaseous conditions for free radical generation by burst ultrasound – Effects of dissolved gas, microbubbles and gas transport from the air

To understand the underlying concepts required for the determination of thresholds for free radical generation, effects of gas dissolution in and microbubble addition to sonicated solutions were investigated. Four solutions with different gaseous conditions, air-saturated and degassed solutions with and without microbubbles of 20 μm in diameter with shells, were studied in the presence of an air–liquid interface. These test solutions were exposed to 1 MHz ultrasound of 0.06 MPa p-p at various pulse durations (PDs) from 0.1 to 5 ms and pulse repetition frequencies from 0.1 to 2 kHz. Generation of free radicals was evaluated using the electron spin resonance (ESR) spin trapping method and starch–iodine method. Thresholds of duty ratio (DR) corresponding to temporal average intensity of ultrasound for free radical generation were significantly greater in degassed solutions than in air-saturated solutions. Microbubbles had no significant effects in air-saturated solutions but caused a slight decrease in the threshold in degassed solutions. In all of these results, the DR of a threshold curve against pulse repetition period (PRP) was not constant but linearly decreased with it, suggesting that a balance between bubble growth and shrinkage during the ON and OFF times of burst ultrasound is the primary parameter for the interpretation of thresholds. The effect of an air–liquid interface of the solution was also examined, and it was revealed that gas transport from the air is a predominant factor determining the amount of free radicals.

Quick Cavity Filling in UV Nanoimprint Using Pentafluoropropane

In the course of solving the bubble defect problem of UV Nanoimprint, it was found that filling of mold cavities during UV-nanoimprint can be completed within 5 s if pentafluoropropane is used as ambience. In this work, by employing a real-time monitoring system, bubble shrinkage in the recess of a mold for UV nanoimprint in air and in pentafluoropropane was observed. Then, the bubble elimination times for various pentafluoropropane flows were measured and the condition for the rapid elimination of bubbles was determined. The consumption of pentafluoropropane was considered and the cost of the rapid elimination of bubbles was roughly estimated. By measuring the bubble sizes at intervals of 0.1 s, the time evolution of bubble shrinkage was monitored and the results were converted into time evolution of mold sinking. The mold sinking for the UV nanoimprint in vacuum was also estimated by simulations based on Stefan's equation. It was found that the process speed in pentafluoropropane was equivalent to that in vacuum, while the process speed in air was found to be much slower than that in vacuum.

Stability of Microbubbles under Variation of a Pressure Field

The shrinkage and growth of microbubbles coated by palmitic acid under variation of a pressure field are observed with a CCD camera. We investigate the influence of gas diffusion on the stability of microbubbles. It is shown that when the ambient liquid pressure increases, a tiny microbubble with a radius of about 5 μm shrinks accompanied with large surface depression, and does not return to the initial size even after the pressure is reduced. The depression suggests the formation of multilayers of surfactant on the bubble surface. A bubble model is constructed by taking the dynamic surface tension and the gas permeation resistance of surfactant layers into account. The simulations show that the hysteresis of the surface tension is an important factor in determining the bubble response to the pressure change; the bubble profiles in the experiments are simulated qualitatively by considering the hysteresis of the surface tension. Also, the simulations considering the variable permeation resistance are in good agreement with the experimental results. The results also show that the permeation resistance increases during bubble shrinkage and stabilizes the microbubble. The smaller the initial bubble radius becomes, the larger the permeation resistance becomes during bubble shrinkage. The present simulations support the experimental results that the surfactant multilayers are formed when the bubble is compressed under the pressure increase.

Observed bubble dynamics in oxygen or heliox breathing and altitude decompression sickness

altitude decompression sickness (DCS) is a common risk in aviation and has been extensively studied over the past two decades ([2][1], [3][2], [9][3]). Attempts have been made to find a correlation between ultrasonic bubble detection and symptoms of altitude DCS ([1][4], [8][5]). Models

Effect of bubble contamination on gas–liquid mass transfer coefficient on CO2 absorption in amine solutions

Abstract An electrochemical method was used to follow CO 2 absorption both in water and in alkanolamine solutions in a bubble column (∼1 m tall). This method allows the determination of local mass transfer coefficients along the column. No special care was taken in avoiding trace contaminants. It was found that bubbles contaminate mostly at the gas distributor. Gas–liquid mass transfer coefficient decreases as bubbles rise along the column, taking values closer to those expected for clean bubbles with a mobile surface at the bottom of the column, and values closer to those expected for rigid bubbles, at the top of the column. If this is quantitatively interpreted within the framework of the stagnant cap model, it may be concluded that this decrease is mainly due to bubble shrinkage, which leads to a greater fraction of bubble area being covered by the stagnant cap. Compared with this effect, the effect of further acquisition of contaminant molecules by the bubbles is negligible. The above conclusions can be drawn both for absorption with chemical reaction in amine solutions and for pure absorption of CO 2 in tap water, although in this case the shrinkage effect is less pronounced.

1434 動的表面張力と気体の拡散抵抗を考慮したマイクロバブルの安定性解析(S38-2 気泡・粒子,S38 マイクロ・ナノフルイズ)

The influence of gas diffusion is investigated for two kinds of microbubbles. It is shown that a tiny microbubble shrinks accompanied with large surface depression, and does not return to the initial size even after the pressure is reduced. On the other hand, a large microbubble shrinks nearly spherically. The depression of bubble surface suggests the formation of multilayers of surfactant or lipid on bubble surface. A bubble model is also constructed by considering the dynamic surface tension and gas permeation resistance of surfactant or lipid layers. The experimental results are compared with simulations based on the model. The results show that the dynamic surface tension is a significant factor to determine the bubble profile. The results also show that the increase of the permeation resistance during bubble shrinkage stabilizes microbubbles.

Cavitation Induced Breakup Model for Multicomponent Fuel Spray

Authors have developed a spray model for multicomponent fuel and reported the successful model which represents batch-distillation in multicomponent fuel by employing chemical thermo dynamics analysis including liquid-vapor equilibrium. However, the model considers the aerodynamic interaction as a breakup force by employing Taylor Analogy Breakup but ignored internal nozzle flow characteristics inspite of their importance. Nozzle flow is one of the major mechanisms for atomization of liquid jet. Therefore, this paper deals with a new breakup model for multicomponent fuel spray. The model takes account of the energy induced by cavitation bubble collapse or shrinkage. In addition, the model is implemented into KIVA-3 V code in order to validate the effect of energy generated by cavitation on the primary breakup of the discharging jet.

Influence of process parameters on microstructure of food foam whipped in a rotor–stator device within a wide static pressure range

Whipped foods like ice cream, chocolate mousse, fresh cheese or bakery products are increasingly popular. Related research in the field of foam process engineering is concerned with design and characterization of new aeration processes, generating foams with a well defined microstructure. The perception properties, stability and flow behavior of food foams strongly depend on their gas fraction and bubble size distribution. Ideally, foams contain smallest possible gas bubbles of equal size. Within this study, experiments on a rotor–stator whipping device were conducted and the influence of several process parameters on the resulting foam microstructure determined. All foams were produced from a model system containing a total milk protein and guar gum and were characterized by their overrun and bubble size distribution. The impacts of residence time in the dispersing flow field, rotational velocity of the whipping tool, overrun and pressure on the bubble size distribution were quantified. The traditional application of back-pressure during continuous foaming leads to bubble expansion when the back-pressure is released whereas a new way of foaming under partial vacuum conditions, developed within this work, allows for subsequent bubble shrinkage.

Bubble transport in three-dimensional laminar gravity-driven flow – mathematical formulation

This paper presents a complete set of coupled equations that govern the bubble transport in three-dimensional gravity-driven flow. The model accounts for bubble growth or shrinkage due to pressure and temperature changes as well as for multiple gas diffusion in and out of the bubbles but neglects bubble coalescence, break-up, and nucleation. The model applies to glass melting furnaces but it could be extended to other two-phase flow applications such as metal and polymer processing, passive cooling systems, and two-phase flow around naval surface ships. Governing equations are given for the key variables which are, in the present case, (1) the refining agent concentration, (2) the gas species dissolved in the liquid phase, and (3) the bubble radius, gas molar fraction, and density function. The method of solution based on the backward method of characteristics is briefly discussed.

Bubble transport in three-dimensional laminar gravity-driven flow – numerical results

This paper is the second part of a study on bubble transport, growth and shrinkage in three-dimensional gravity driven flow. Sample calculations with applications to glass melting furnaces are presented. First, a consistent set of thermophysical properties of the most common composition (74SiO 2–16Na 2O–10CaO (mol%)) of soda-lime silicate glass or similar compositions over the temperature range of 1000–2000 K is reported. The population balance equation is solved for the bubble density function using the backward method of characteristics. The zeroth to third order moments, i.e., number of bubbles, average radius, molar gas fraction, interfacial area, and void fraction are computed by numerical integration. Results for both transient and steady state operations are presented and analysed. Two cases are considered (1) bubbles containing only CO 2 and (2) bubbles containing a diffusing gas (O 2) and a non-diffusing gas (CO 2). The feasibility of such complex calculation is demonstrated and is in qualitative agreement with reported results.

Bubble removal in rotational molding

AbstractClosed form solutions have been obtained for bubble dissolution in typical polymer melts encountered in rotational molding. The solutions are in excellent agreement with experimental data available in the literature. Using these solutions, it is shown that under typical rotational molding conditions the polymer melts may be almost saturated. As a result, bubble shrinkage occurs over long periods. Depending on the degree of saturation, surface tension may contribute substantially to the concentration gradient that drives bubble shrinkage. It is also shown that a pressure increase imposed on a nearly saturated polymer melt leads to a steep concentration gradient at the bubble/melt interface that can cause extremely fast bubble shrinkage. Applied to the rotational molding process, such a pressure increase can result in substantial cycle‐time shortening through elimination (or reduction) of the currently used excessive heating. A further benefit may be that additional resins, which at present cannot be used because of oxidation at sustained high‐temperatures, can become available to the rotational molding industry. Under the under‐saturated conditions created by a pressure increase, the effect of surface tension on the rate of bubble shrinkage is negligible.

Formation, growth and dissociation of He bubbles in Al 2O 3

The formation and dissociation of helium bubbles and helium desorption are investigated in sapphire Al 2O 3(0 0 0 1) implanted with 30 keV He ions to four different doses of 0.1, 0.3, 1.0 and 2.0 × 10 16 ions cm −2. The samples were annealed isochronally up to 1850 K in steps of 100 K. The techniques of Doppler broadening positron beam analysis (PBA) and neutron depth profiling (NDP) were used to investigate defect evolution and helium retention, respectively, during the annealing procedure. It was observed that the maximum bubble volume is found after 1250 K annealing, after which a process of bubble shrinkage sets in. Cross-sectional transmission electron microscopy (XTEM) was performed on the sample that was implanted with the highest-dose (2.0 × 10 16 He ions cm −2) after annealing at 1250 K. It was found that the bubbles are shaped as discs lying parallel with the surface and that the average bubble size is 5.5 nm. In all samples, helium is released mainly at a temperature of 1750 K. The desorption curves were analyzed by means of a permeation model. The activation energy for permeation was found as 4.0 eV.

Mechanism of action of benzoin as a degassing agent in powder coatings

The mechanism of action of benzoin as a degassing agent in powder coatings has been analyzed. The gas bubble shrinkage was monitored using a light microscope equipped with a hot stage. In the absence of benzoin, the air bubbles start to shrink very slowly as a result of a diffusion-controlled process. Because of the continuing cross-linking reaction and increase in the viscosity, the bubble shrinkage halts at elevated temperatures. Quite remarkably, we observed that in the presence of benzoin the process of bubble shrinkage is accelerated to such an extent that most air bubbles disappear before any significant increase in the viscosity occurs. This suggests that benzoin functions by accelerating the rate of bubble shrinkage. To analyze the mechanism of action of benzoin in detail, we studied the coating formulations using various techniques. X-ray diffraction in combination with deuterium NMR using labeled benzoin indicated that benzoin dissolves on a molecular level in polyester resin and becomes mobile above the glass transition temperature of the matrix. Mass spectroscopy experiments revealed that benzoin, in its oxidized form (benzil), starts to evaporate above 100 °C. At 200 °C more than 90% of the initial concentration of benzoin has evaporated from the coating. As was to be expected, the conversion of benzoin to benzil halted when the experiments were carried out in nitrogen. We postulated that the action of benzoin as a degassing agent is somehow related to its ability to oxidize in situ. This claim is substantiated by the results of bubble dissolution experiments using different gases such as oxygen and nitrogen. It is shown that in the presence of benzoin oxygen bubbles shrink much faster than air bubbles. On the other hand, the shrinkage of nitrogen bubbles is not affected by benzoin. Based on the above results, a two-step mechanism is proposed for the action of benzoin as a degassing agent. This mechanism has been successfully used as a guideline to identify alternative degassing agents with higher efficiency and fewer side-effects, such as less severe yellowing.

The effect of irradiation-induced gas-atom re-solution on grain-boundary bubble growth

The rim region of high-burnup fuels is characterized by an exponential growth of intergranular porosity. In particular, the understanding of the dynamics of irradiation-induced recrystallization and subsequent gas-bubble swelling requires a quantitative assessment of the nucleation and growth of grain-boundary bubbles. Calculations of bubble growth on the grain boundaries of irradiated nuclear fuels at relatively low temperatures have, in general, been performed under the assumption that these bubbles are not appreciably affected by irradiation-induced gas-atom re-solution. In contrast, matrix bubbles are strongly affected by this bubble shrinkage mechanism and as a consequence are generally two to three orders or more of magnitude smaller than the grain-boundary bubbles. A variational method is used to calculate diffusion from a spherical fuel grain. The junction position of two trial functions is set equal to the bubble gas-atom knock out distance. The effect of grain size, gas-atom re-solution rate and diffusivity, gas-atom knock out distance, and grain-boundary bubble density on the growth of intergranular bubbles is studied, and the conditions under which intergranular bubble growth occurs are elucidated.

Mechanism of Bubble Dissolution in Reactive Coatings: The Role of Benzoin

The process of bubble dissolution in reactive coatings and the role of benzoin as a degassing agent have been investigated. The gas bubble shrinkage was monitored using a light microscope equipped with a hot stage. In the absence of benzoin, the air bubbles started to shrink very slowly as a result of a diffusion-controlled process. Because of the continuing cross-linking reaction and increase in the viscosity, the bubble shrinkage halted at elevated temperatures. Quite remarkably, we observed that in the presence of benzoin the process of bubble shrinkage was accelerated to such an extent that most air bubbles dissolved before any significant increase in the viscosity occurred. This suggests that benzoin functions by accelerating the rate of bubble shrinkage. To elucidate the mechanism of the action of benzoin in detail, we studied the coating formulations using various techniques. X-ray diffraction in combination with deuterium NMR on labeled benzoin indicated that benzoin is distributed on a molecular ...

Densification and Swelling in UO2 Pellets under Hydrostatic Pressure Condition

The effect of hydrostatic pressure on the volume change in unirradiated UO2 pellets has been examined using an out-of-pile high pressure annealing technique. The pellet volume change was generated by annealing UO2 pellets at 1,500°C and at higher or lower ambient external pressures of 10–150 MPa Ar/0.2%H2 gas than the sintering pressures of 50 or 100MPa at 1,800°C. The pressure difference, Δ P, between bubble internal and external hydrostatic pressures during the annealing corresponded to a range of −101 to 82MPa. The volume change directly depended on the sign and magnitude of Δ P. More negative Δ P caused larger densification due to the shrinkage of the as-sintered bubbles. Almost no volume change was observed at nearly zero Δ P, and fuel swelling due to the bubble growth increased at more positive Δ P. The bubble shrinkage and growth data were analyzed by the rate equation of Hull and Rimmer. The fractional volume changes calculated by the model were in good accordance with the measured values in the wide range of—8 to +10%.

Calculations of interactions of gas bubbles with glass liquids containing sulphates

The behaviour of bubbles in commercial sulphate containing glasses is usually controlled by the diffusion of gases in the liquid glass; however, the bubble surface reaction of sulphate layer formation or decomposition can control the mass transfer of the SO 2 and O 2 at the highest concentrations of both gases in bubbles. The equations describing this mass transfer were numerically solved to reveal the typical features of size and composition development of bubbles in the soda-lime-silica liquid glass. Layer formation on the bubble surface was accompanied by bubble shrinkage. According to the model, the extent of the bubble size reduction and the sulphate layer thickness grow as the initial amount of SO 2 and O 2 in the bubble increases, as the volume ratio between the SO 2 and O 2 approaches the stoichiometry (2:1) and as temperature decreases. The development of the SO 2 and O 2 concentrations in the bubble shows the largest terminal SO 2/O 2 ratios if the initial SO 2/O 2 ratio is greater than 2, if the initial state of the glass is reduced and if the glass is slowly cooled. The results have importance for the mathematical modelling of the refining process in glass melting and for the identification of bubble sources in a furnace, using results of bubble composition analyses.

Mass-Transfer Properties of Microbubbles. 2. Analysis Using a Dynamic Model

Gas-to-liquid mass transfer is commonly the rate-limiting step in industrial fermentations. Microbubble sparging has been shown to give extremely high volumetric mass-transfer rates, even for low power-to-volume ratios. Microbubbles are surfactant-stabilized bubbles having a radius on the order of 25 μm. The extremely high surface-area-to-volume ratios of microbubbles can result in rapid changes in their size, internal pressure, and gas composition. Consequently, an unsteady-state modeling approach is needed to adequately describe microbubble mass transfer. A dynamic model of a single microbubble immersed in an infinite pool of stagnant liquid was developed and solved numerically. The model accounts for mass-transfer resistances of the surfactant shell and surrounding bulk liquid, bubble shrinkage, changes in the gas pressure and composition inside the bubble, and changes in the liquid-phase concentration profile of the transferred gas surrounding the bubble. The model was used to explore a variety of dynamic phenomena associated with microbubble mass transfer. The presence of a nontransferred gas in the microbubble was predicted to significantly reduce the mass-transfer rate, indicating that microbubble sparging is better suited to gases with a high consumable fraction. The instantaneous mass-transfer coefficient was predicted to change significantly with time, but the time-averaged coefficient was constant enough to justify the measurement of average mass-transfer coefficients for microbubbles. Average mass-transfer coefficients predicted by the model agreed well with values measured experimentally and calculated using literature correlations.