Bubble Formation Process Research Articles

Generation, growth and collapse of bubbles on collision of particle with electrode in DC electrically stressed liquid helium

The paper deals with the bubble formation process in the presence of a free conducting particle in liquid helium to understand the electrical insulation environment in pool cooled superconducting devices under particle contaminated conditions. Experiments were conducted with DC stressed parallel plane electrodes containing a free spherical metallic particle of 1 mm radius in saturated normal and saturated superfluid helium. Experimental results show that a single bubble is always generated at the moment of particle collision with the electrode and the bubble behavior depends strongly on the state of the liquid helium. The bubble expanding and shrinking processes were analyzed on the basis of energy balance among released electrostatic and kinetic energies of the particle at the moment of particle collision with the electrode, kinetic energy of liquid driven by bubble growth, work done on environmental pressure and internal energy of the bubble gas. The analysis shows a fairly good agreement with experiments.

Monitoring air entrainment with breaking wave noise

It is now known that the dominant component of wind-driven oceanic noise comes from breaking waves. Bubbles ranging in size from tens of microns to centimeters are forced into the water column during the first second or so of whitecap formation. At the moment of creation, each bubble emits a pulse of sound at a center frequency inversely proportional to its radius. The ensemble of such events amounts to a burst of noise that continues throughout the active phase of bubble creation within the whitecap. As the noise spectrum is related to the bubble size distribution within the whitecap, it is natural to explore the possibility that underwater oceanic ambient noise could be used as tool to remotely monitor air entrainment rates across the ocean surface. One of the problems with developing such a tool is understanding the relationship between bubble formation processes occurring within whitecaps and the concurrent noise emission. Here we will report recent progress in our understanding of bubble formation mechanisms in whitecaps, their role in ambient noise generation, and the implications for monitoring air entrainment rates.

Juggling with bubbles in cylindrical ferrofluid foams

Monodisperse foams in long cylinders exhibit ordered spiral structures. We have made ferrofluid foams of this kind and find that they can be manipulated in a variety of ways by an external magnetic field. Effects include morphological changes, twisting of structures and size control in the bubble formation process. This offers a promising technique for the efficient transport, switching and combining of samples in fluidic networks, possibly on the microfluidic scale.

Implantation temperature dependence of He bubble formation in Si

We report experimental results on the formation of He bubbles in Cz grown (1 0 0) Si crystals implanted with 40 keV He + ions to a fluence of 1×10 16 cm −2 at distinct implantation temperatures within the 373⩽ T i⩽573 K range, and upon 600 s post-implantation thermal annealings at temperatures from 673 to 1073 K. The samples were analyzed by Rutherford backscattering/channeling spectrometry, elastic recoil detection analysis and transmission electron microscopy. The results obtained show that the microstructure characteristics of the bubble systems, as well as their thermal evolution behavior, depend significantly on the implantation temperature. A correlation between the dynamic annealing behavior and the bubble formation process is proposed.

Dissolved gas method of generating bubbles for potential use in ore flotation

Production and use of dissolved air bubbles were investigated with the purpose of improving the recovery of fine particles in ore flotation processes.The rate and extent of air dissolution were studied under different conditions of pressure, temperature, liquid volume, and gas-solid contact. The process of bubble formation by pressure release was also examined. Assessments made through dissolved oxygen measurements indicated that dissolution of air and the release of dissolved air could be achieved within a 1-minute period. Flotation tests carried out on a −37 μm magnetite ore sample demonstrated superior results with dissolved gas bubbles compared to conventional bubbles.

Control of Bubble Formation. Effect of Additional Oscillation to Gas Velocity on Bubble Formation.

A technique to control the bubble size and frequency about small or micro bubble was examined experimentally. A feature of this technique is to adopt an audio speaker for the addition of the pressure or flow oscillation to the gas flow in the nozzle. In this paper, the bubble detaching process from a nozzle and the effectiveness for the both systems of single nozzle and multi nozzles were described. As a result, it was made clear that the gas flow oscillation was the dominant factor in the bubble formation process, and the present technique could control with high accuracy the bubble frequency, bubble detaching time and bubble size over the wide range of condition. It was also clear that this technique could apply to the simultaneous bubble formation from nozzles submerged in different depth.

Effect of Operating Conditions on Two-Phase Bubble Formation Behavior at Single Nozzle Submerged in Water.

The effects of operating parameters and physical properties of a dispersed phase on the volume change of a two-phase bubble formed in water as an immiscible continuous phase were experimentally investigated. The operating parameters are inner diameter of nozzle, vapor flow rate and temperature difference between water and vapor in the bubble. A larger two-phase bubble volume can be obtained by a larger nozzle inner diameter, higher flow rate, and lower temperature difference, and vice versa. The present mathematical model estimates well the two-phase bubble formation process.

A non-spherical model for bubble formation with liquid cross-flow

A non-spherical model for bubble formation at an orifice with liquid cross-flow has been developed. The interface element approach is applied to describe the dynamics of bubble formation. The effect of liquid cross-flow on the bubble formation process is modelled by a combination of tilting of the bubble axis and liquid pressure analysis of each element on the bubble interface. Model predictions compare well with the experimental results available in the literature for different conditions of gas flow rate, orifice diameter and liquid cross-flow velocity. Simulated bubble shapes are highly non-spherical, especially at high liquid velocities, and bear a striking resemblance with the experimental high-speed video sequences.

Formation and migration of helium bubbles in Fe–16Cr–17Ni austenitic alloy at high temperature

The formation and migration of helium bubbles in Fe–16Cr–17Ni austenitic model alloy at temperatures 400–1250°C have been studied by in situ electron microscopy, energy dispersive spectrometry (EDS) and EELS analysis. The nucleation of bubbles under 10 keV He+ ion irradiation was dominant at 400°C, while the growth was dominant above 600°C. It was revealed that the mean square of the migration distance was proportional to time, which is quantitative evidence of Brownian type motion and yielded diffusivities from 10−18 to 10−20 m2/s at 1185°C, depending on the diameter from 1 to 3 nm. These facts suggest that the mobility of helium–vacancy complexes or bubbles is an important factor governing the formation process of helium bubbles. The analysis by scanning transmission electron microscope-electron energy loss spectrometry (STEM-EELS) elucidated Ni precipitation even around small helium bubbles.

Bubble formation from wall orifice in liquid cross-flow under low gravity

Two-phase flows present a wide variety of applications for spacecraft thermal control systems design. Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to experimentally investigate the effects of liquid cross-flow velocity, gas flow rate, and orifice diameter on bubble formation in a wall–bubble injection configuration. Data were taken mainly under reduced gravity conditions but some data were taken in normal gravity for comparison. The reduced gravity experiment was conducted aboard the NASA DC-9 Reduced Gravity Aircraft. The results show that the process of bubble formation and detachment depends on gravity, the orifice diameter, the gas flow rate, and the liquid cross-flow velocity. The data are analyzed based on a force balance, and two different detachment mechanisms are identified. When the gas momentum is large, the bubble detaches from the injection orifice as the gas momentum overcomes the attaching effects of liquid drag and inertia. The surface tension force is much reduced because a large part of the bubble pinning edge at the orifice is lost as the bubble axis is tilted by the liquid flow. When the gas momentum is small, the force balance in the liquid flow direction is important, and the bubble detaches when the bubble axis inclination exceeds a certain angle.

Effects of helium on radiation-induced defect microstructure in austenitic stainless steel

In the construction materials surrounding the spallation neutron source (SNS) mercury target, considerable quantities of transmutation products, particularly hydrogen and helium, will be generated due to the exposure to a high flux of 1 GeV protons and associated neutrons. In an effort to investigate the effects of high helium, therefore, bubble formation and defect clustering processes in AISI 316 LN austenitic steel were studied as a function of helium concentration and displacement damage dose with 360 keV He + and 3500 keV Fe + ion beams at 200°C. Helium irradiation was less effective in producing defects such as black dots and dislocation loops than Fe + ion irradiation at equivalent displacement dose. On the other hand, the formation of helium bubbles produced a strong depressive effect on the growth of loops and the evolution of line dislocations. The results indicated that the effect of helium bubbles was augmented as the bubble number density and size increased with increasing helium beyond 1 atomic percent (at.%). In such a case, the effect of helium bubbles can be more important than that of radiation-induced defects on the evolution of microstructure and the change in mechanical properties.

Generation and maintenance of bubbles in small tubes by low-frequency ultrasound

A system has been developed to generate and maintain a bubble population in nonscattering fluid media within a small 1.3-mm (i.d.) transparent silicone tube by use of low-frequency ultrasound at 28.8 kHz. The system uses a sequence of three different kinds of acoustic cavitation processes: transient, stable and cyclic. In the final step of the sequence, low-duty cycle (∼10%) and low-pressure (∼30 kPa) ultrasound is used to maintain a microbubble population whose mean diameter is ∼12 μm, which can be used as Doppler ultrasound scatterers. To understand and measure the behavior of bubbles for three different kinds of cavitation processes in the tube, a CCD imaging system and a synchronized short duration flash were used to capture movie frame sequences. Subsequent analysis of the frames enabled the following bubble parameters to be measured: size distributions, fractional volume concentration, flow characteristics, rise velocity, dissolution time, growth rate and various bubble formation processes. In addition, the cavitation threshold of distilled water inside the tube was found to be ∼292±99 kPa. Techniques were also developed to identify successful bubble initiation and excitation by either detecting the harmonic components of the bubble emission power spectra or by detecting the power level of the Doppler spectrum.

Bubble dissolution in molten polymers and its role in rotational molding

AbstractThe presence of bubbles is inherent in the rotational molding process and can often cause poor quality in rotomolded parts. In an effort to gain a fundamental understanding of bubble removal in polymer melts, a model that includes diffusion, surface tension, and viscosity effects has been implemented. This work has been complemented with experiments performed in a heated chamber, which enabled the visualization of the bubble formation and removal process. It was concluded that bubble removal is mainly diffusion controlled and is not influenced significantly by melt viscosity when the latter lies within ranges typical for rotational molding resins. Air concentration in the bulk of the polymer melt and initial bubble size were found to be of great importance. The application of pressure after the polymer has melted accelerates the dissolution rate, owing to an increased driving force for diffusion.

Computer simulation of fluid phase change: vapor nucleation and bubble formation dynamics

Using large scale molecular dynamics (MD) simulation techniques, two types of fluid–fluid phase changes were investigated. One is a homogeneous nucleation process from supersaturated vapor, in which we compare a Lennard–Jones system and water system. Another is a bubble formation (cavitation) process in stretched liquid, in which we compare one-component and two-component systems.

Starting mechanisms and dynamics of bubble formation induced by a Ho:Yttrium aluminum garnet laser in water

The starting mechanisms and dynamics of laser-induced bubble formation at a submerged fiber tip in distilled water were experimentally investigated using pressure measurements and fast flash videography. A fiber guided Ho:YAG laser operating in the free running (τ=200 μs) and Q-switched (τ=45 ns) mode at a wavelength of λ=2.12 μm was used as a light source. It is shown that the beam profile at the distal fiber tip (multimode fiber d=300 μm) exhibits hot spots that result in an inhomogeneous temperature distribution in the heated water volume. Depending on the laser irradiance, three different bubble formation processes are distinguished: bubble formation by heating, by rarefraction (cavitation), and by a combination of these two processes. For laser irradiances of less than 0.5 MW/ cm2 bubble formation takes place at temperatures near the critical point of water (T=280 °C). A rapid decrease in the threshold temperature for bubble formation was found for laser irradiances between 0.5 and 1 MW/cm 2. At laser irradiances higher than 3 MW/cm2, microbubbles with radii of up to 20 μm were formed at the front of the laser pulse even though the average water temperature was far below 100 °C. The water temperature distribution during the laser pulse was determined by numerical simulation. Simultaneous pressure measurements revealed that each subablative laser spike induces a bipolar pressure transient. The onset of the bubble expansion was found to be correlated with a characteristic pressure increase that can be used for on-line monitoring of the ablation process. The distortion of the temporal profile of the pressure wave is shown to be an effect of diffraction. The reduction of pressure by the negative part of the bipolar pressure transients leads to a lowering of the evaporation pressure and therefore to the initiation of bubbles by cavitation. With increasing irradiance this mechanism becomes more efficient.

Bubble formation in a coflow configuration in normal and reduced gravity

AbstractA study of bubble generation for constant gas‐flux condition by single‐nozzle injection in a coflowing liquid is reported. Focusing on single‐bubble generation in the dynamic and bubbly flow regime, the onset condition for bubble coalescence is investigated. The role of various forces involved in the bubble formation process is studied, and an overall force balance describing bubble dynamics is developed. Gas‐momentum flux and buoyancy in normal gravity enhance, while the surface‐tension force at the nozzle rim inhibits bubble detachment. On the other hand, liquid drag and inertia can act both as attaching or detaching forces, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with the present reduced‐gravity experiment and available normal‐gravity experiments. Effects of the fluid properties, injection geometry, and flow conditions on bubble size are investigated.

Vesiculation processes in silicic magmas

Abstract The physics of vesiculation, i.e. the process of bubble formation and evolution, controls the manner of volcanic eruptions. Vesiculation may lead to extreme rates of magma expansion and to explosive eruptions or, at the other extreme, to low rates and calm effusion of lava domes and flows. In this paper, we discuss the theory of the different stages of vesiculation and examine the results of relevant experimental studies. The following stages are discussed: (1) The development of supersaturation of volatiles in melts. Supersaturation may develop due to a decrease in equilibrium solubility following changes in ambient pressure or temperature or due to an increase in the magma volatile content (e.g. in response to crystallization of water-free or waterpoor mineral assemblages). (2) Bubble nucleation. The classical theory of homogeneous nucleation and some modern modifications, heterogeneous nucleation with emphasis on the nucleation of water bubbles in rhyolitic melts and the role of specific crystals as heterogeneous sites. (3) Bubble growth. The effect of diffusion, viscosity, surface tension, ambient pressure and inter-bubble separation on the dynamics of growth. (4) Bubble coalescence. The theory of coalescence of static foams. factors that may effect coalescence in expanding foams and shape relaxation following bubble coalescence.

The Solubility of Ar in Liquid Succinonitrile.

Since a gas bubble formation process ahead of a growing dendritic solid/liquid interface is quite complex, the direct observation of gas bubble formation by using the transparent materials is very useful method to study. For works on the gas bubble formation during the solidification, the information of solubility of gas in the melt was required. The first attempt to measure the solubility of Ar in molten succinonitrile was carried out by using a newly developed method which consists of the injection of He into molten salts through a nozzle, collection of ascending bubbles of He–Ar gas mixture, determination of concentration of Ar in the He-Ar gas mixture using a high sensitive mass spectrometer. The solubilities of Ar in molten succinonitrile have been determined as a function of temperature from 333 to 348 K and were best expressed byln[Ar]=–7.64–1630/Twhere the unit of solubility is expressed by mol-Ar/cm3-succinonitrile. From the temperature dependency of Ar solubility, the enthalpy of solution was found to be about 13.5 kJ/mol.

The effect of gas-phase density on bubble formation at a single orifice in a two-dimensional gas-fluidized bed

In this study the effect of the gas-phase density on the process of bubble formation at a single orifice in a two-dimensional gas-fluidized bed has been studied experimentally and theoretically. Specifically, a detailed comparison between experimentally observed and theoretically calculated bubble growth curves has been made in the case where the density of the gas injected through the orifice (He and SF 6) differs significantly from the density of the primary fluidizing agent (air). The calculations have been carried out using an earlier developed, first principles hydrodynamic model of gas-fluidized beds which has been extended with a species conservation equation to calculate the composition of the fluidizing gas in the vicinity of the evolving bubbles. Besides, the present experimental and theoretical results were compared with predictions obtained from adapted versions of approximate bubble formation models previously reported in the literature. The advanced hydrodynamic model appears to predict the experimentally observed diameters satisfactorily. In addition, the model correctly predicts the effect of the gas-phase density on the experimentally observed bubble growth. This effect can be explained satisfactorily in terms of the dependence of the interphase momentum transfer coefficient on gas-phase density. Finally, calculations with a three-dimensional version of our hydrodynamic model have been carried out to account for the effect of the front and back wall of the pseudo two-dimensional gas-fluidized bed used in our experiments. Our preliminary computational results indicate that the magnitude of the wall effect strongly depends on the boundary condition enforced for the gas-solid dispersion at these walls. In the case that the no-slip boundary condition was enforced in the calculations for the solid phase, the wall effect was significant and a considerable deviation between computed and experimentally observed bubble growth curves was found. However, when a more realistic partial slip boundary condition for the solid phase was implemented the agreement between theory and experiment could be improved by altering the slip parameter in the partial slip boundary condition expression.

Tomographic Imaging of Phase Distribution and Spatial Correlation of the fluidization dynamics in a fluidized bed

AbstractThis paper describes the use of a capacitance tomography system for imaging gas bubbles in a fluidized bed in the vicinity of an air distributor plate. The results show how the solid concentration distribution varies as a function of time for three different flow regimes: bubbling, slugging and the transition to turbulent. Bubble shape, Length and coalesence can be observed. A method of spatial correlation to elucidate the bubble formation process is described.