Arrangement Of Bubbles Research Articles

Dynamics of cavitation bubbles in acoustic field near the rigid wall

Dynamics of multiple cavitation bubbles near the rigid wall subjected to the incident acoustic wave with different arrangements is researched in this paper. Wave equation is used to approximate the prophase and anaphase motion of cavitation bubble to consider the compressibility of fluid. The modified Bernoulli equation is deduced as the boundary condition for cavitation bubble in acoustic field. Influences of compressibility, acoustic wave frequency and amplitude, incident angle, and the bubble arrangements on the dynamics of cavitation bubbles are presented. Numerical results show that the compressibility of fluid will impact the intensity of motion. The dynamics of bubbles is affected by the incident amplitude and frequency, and limited by the rigid wall. The different incident angles and arrangements of bubbles will change the acting pressure phase and interaction between bubbles and rigid wall, which will lead to the motion advancement or delay. The radius difference will increase with the large phase difference and the strong rejection. The jet will be oblique to the incident direction, as well as the rigid wall and bubbles around.

Dynamics of Two-Phase Flow through a Minichannel: Fourier and Multiscale Entropy Analyses

By changing a air flow rate of the two-phase (air-water) flow through a minichannel weidentified aggregation and partitioning of air bubbles and slugs of different sizes and air bubble arrangement into periodic patterns. The identification of these spatio-temporal behaviour was doneby digital camera. Simultaneously, we provide the detailed studies of these phenomena by using thecorresponding sequences of light transmission time series recorded by a laser-phototransistor sensor.To distinguish the instabilities in air slags and their breakups and aggregations we used the Fourierand multiscale entropy analysis.

Growth-and-collapse dynamics of small bubble clusters near a wall

The violent collapse of bubble clusters is thought to damage adjacent material in both engineering and biomedical applications. Yet the complexities of the root mechanisms have restricted theoretical descriptions to significantly simplified configurations. Reduced-physics models based upon either homogenization or arrays of idealized spherical bubbles do reproduce important gross cluster-scale features. However, these models neglect detailed local bubble–bubble interactions, which are expected to mediate damage mechanisms. To describe these bubble-scale interactions, we simulate the expansion and subsequent collapse of a hemispherical cluster of 50 bubbles adjacent to a plane rigid wall, explicitly representing both the asymmetric dynamics of each bubble within the cluster and the compressible-fluid mechanics of bubble–bubble interactions. Results show that the collapse propagates inward, as visualized in experiments, and that geometric focusing generates high impulsive pressures. This gross behaviour is nearly independent of the specific arrangement of bubbles within the cluster and matches predictions from the corresponding particle and homogenized models we consider. The peak pressure in the detailed simulations is associated with the centremost bubble, which causes a corresponding peak pressure on the nearby wall. However, the peak pressures in all cases are a small fraction – over a factor of ten times smaller in many cases – of those predicted in the corresponding reduced models. This is due to the enhanced focusing in the homogeneous model and the spherical constraint on each bubble in the particle models assessed. These would be important factors to consider in any subsequent predictions of wall damage based upon reduced models.

Computational modelling of the interaction of shock waves with multiple gas-filled bubbles in a liquid

This study presents a computational investigation of the interactions of a single shock wave with multiple gas-filled bubbles in a liquid medium. This work illustrates how multiple bubbles may be used in shock-bubble interactions to intensify the process on a local level. A high resolution front-tracking approach is used, which enables explicit tracking of the gas-liquid interface. The collapse of two identical bubbles, one placed behind the other is investigated in detail, demonstrating that peak pressures in a two bubble arrangement can exceed those seen in single bubble collapse. Additionally, a parametric investigation into the effect of bubble separation is presented. It is found that the separation distance has a significant effect on both the shape and velocity of the main transverse jet of the second bubble. Extending this analysis to effects of relative bubble size, we show that if the first bubble is sufficiently small relative to the second, it may become entirely entrained in the second bubble main transverse jet. In contrast, if the first bubble is substantially larger than the second, it may offer it significant protection from the incident shock. This protection is utilised in the study of a triangular array of three bubbles, with the central bubble being significantly smaller than the outer bubbles. It is demonstrated that, through shielding of bubbles until later in the collapse process, pressures over five times higher than the maximum pressure observed in the single bubble case may be achieved. This corresponds to a peak pressure that is approximately 40 times more intense than the incident shock wave. This work has applications in a number of different fields, including cavitation erosion, explosives, targeted drug delivery/intensification, and shock wave lithotripsy.

Effect of bubble’s arrangement on the viscous torque in bubbly Taylor-Couette flow

An experimental investigation of the interactions between bubbles, coherent motion, and viscous drag in a Taylor-Couette flow with the outer cylinder at rest is presented. The cylinder radii ratio η is 0.91. Bubbles are injected inside the gap through a needle at the bottom of the apparatus. Different bubbles sizes are investigated (ratio between the bubble diameter and the gap width ranges from 0.05 to 0.125) for very small void fraction (α ≤ 0.23%). Different flow regimes are studied corresponding to Reynolds number Re based on the gap width and velocity of the inner cylinder, ranging from 6 × 102 to 2 × 104. Regarding these Re values, Taylor vortices are persistent leading to an axial periodicity of the flow. A detailed characterization of the vortices is performed for the single-phase flow. The experiment also develops bubbles tracking in a meridian plane and viscous torque of the inner cylinder measurements. The findings of this study show evidence of the link between bubbles localisation, Taylor vortices, and viscous torque modifications. We also highlight two regimes of viscous torque modification and various types of bubbles arrangements, depending on their size and on the Reynolds number. Bubbles can have a sliding and wavering motion near the inner cylinder and be either captured by the Taylor vortices or by the outflow areas near the inner cylinder. For small buoyancy effect, bubbles are trapped, leading to an increase of the viscous torque. When buoyancy induced bubbles motion is increased by comparison to the coherent motion of the liquid, a decrease in the viscous torque is rather observed. The type of bubble arrangement is parameterized by the two dimensionless parameters C and H introduced by Climent et al. [“Preferential accumulation of bubbles in Couette-Taylor flow patterns,” Phys. Fluids 19, 083301 (2007)]. Phase diagrams summarizing the various types of bubbles arrangements, viscous torque modifications, and axial wavelength evolution are built.

Chancelloriid sclerites from theLowerCambrian (Meishucunian) of easternYunnan,China, and the early history of the group

AbstractChancelloriids are a group of enigmatic sessile animals that are covered with sclerites shaped as rosettes of spines, producing an appearance like that of a barrel cactus. They are known only fromCambrian rocks. Isolated sclerites of chancelloriids are widespread in small shelly faunas, but they have proven difficult to treat taxonomically due to the variation within and between individual animals. We report on large samples of chancelloriid sclerites from theMeishucunian (pre‐trilobiticLowerCambrian) of easternYunnanProvince,China, including material from theDahaiMember of theZhujiaqingFormation (theZhujiaqing section,Dahai,HuizeCounty) and theShiyantouFormation (theXiaotan section,YongshanCounty). The material from theDahaiMember appears to come from a single species,Chancelloriella irregularis. Statistical analysis of morphotype co‐occurrences in different samples suggests that several species are represented in the material from theShiyantouFormation, which we herein tentatively place in four species,Allonnia erromenosa,Allonnia tetrathallis,Archiasterella charmasp. nov. andArchiasterellacf.pentactina. We suggest therefore that careful study of large collections of isolated chancelloriid sclerites permits the identification of different species, opening the possibility of their use in evolutionary or stratigraphical studies. In particular, inSouthChina, it seems thatChancelloriella irregularisis characteristic of rocks of theParagloborilus subglobosus–Purella squamulosaAssemblageZone and theWatsonella crosbyiAssemblageZone, whilstArchiasterellaandAllonniafirst appear in the overlyingSinosachites flabelliformis–Tannuolina zhangwentangiAssemblageZone.C. irregularisis thus amongst the oldest well‐characterized chancelloriids, and the irregularity and poor organization of its sclerites relative to those of younger forms support the hypothesis that chancelloriid sclerites are compound structures arising from the fusion of originally separate elements, perhaps homologous with sclerites of halkieriids and other coeloscleritophorans. The similarity between the arrangement of rays in a chancelloriid sclerite and the arrangement of bubbles in small bubble clusters suggests that in many cases, aspects of the form of chancelloriid sclerites are the result of simple physical processes.

0215 水平チャネル内気泡流における単分散気泡のクラスター形成

Bubble cluster is naturally formed during the bubbles' advection in horizontal turbulent channel flows. The phenomenon cannot be mathematically modeled by the linear sum of bubble-liquid interaction, but it should be assessed with multi-scale modeling in densely dispersed bubbly flow. A series of original geometrical definitions have been proposed to characterize the bubble cluster behavior, such as statistical uniformity of spatial bubble arrangement and bubbles' radial distribution function. From the data analysis, we have found that bubble clustering remains potentially in any flow conditions including the case of large bubble-size deviation

Microfluidics with foams

Lab-on-a-chip devices can handle very tiny amounts of fluids, as small as a picolitre. Samples of gas are conveniently encapsulated and transported within bubbles. The generation of these calibrated bubbles involves specific microfluidic devices that we describe. When the bubble concentration is high enough in a channel, they come into contact, and they flow as a crystalline foam. The flow of the foams depends strongly on the arrangement of bubbles within the channel, which entails original dynamical behaviours such as super-stability of the flow, or on the contrary spontaneous oscillations.

Helium implanted gallium nitride evidence of gas-filled rod-shaped cavity formation along the c-axis

The structural defects induced by He implantation in GaN epilayer at high fluence (1×1017He/cm2) and elevated temperature (750 °C) have been studied by conventional and high resolution transmission electron microscopy. In addition to the planar interstitial-type defects lying in the basal plane usually observed after high fluence implantation into GaN, a continuous layer of bubbles arranged in rows parallel to the implanted surface is observed in the region of maximum He concentration. This arrangement of bubbles is ascribed to interactions with dislocations. Beyond, one dimensional rod-shaped defects appear perpendicular to the implanted surface. Contrast analysis of high resolution images and atomistic simulations gives converging results in the determination of the nature and structure of these defects, i.e., gas-filled rod-shaped cavities in an overpressurized state.

Calculation of the wave structure of bubble detonation taking into account the discrete arrangement of bubbles

The dynamics of inert and chemically reactive single bubbles in solitary waves of various intensities were calculated. Calculations of the dynamics of layers of reactive bubbles in the pressure field of solitary waves allows a description of the wave structure of bubble detonation. In the model proposed, the detonation wave is formed from the pressure pulsations resulting from the action of the averaged pressure field of the entire ensemble of bubbles on each individual bubble layer. Each bubble performs two to three oscillations, producing pressure pulsations in the liquid that exceed several times the amplitude of the averaged wave. The model with the discrete arrangement of bubbles has for the first time provided agreement between calculated and experimental profiles of the bubble detonation wave pressure.

Constrained sessile drop as a new configuration to measure low surface tension in lung surfactant systems

Existing methodology for surface tension measurements based on drop shapes suffers from the shortcoming that it is not capable to function at very low surface tension if the liquid dispersion is opaque, such as therapeutic lung surfactants at clinically relevant concentrations. The novel configuration proposed here removes the two big restrictions, i.e., the film leakage problem that is encountered with such methods as the pulsating bubble surfactometer as well as the pendant drop arrangement, and the problem of the opaqueness of the liquid, as in the original captive bubble arrangement. A sharp knife edge is the key design feature in the constrained sessile drop that avoids film leakage at low surface tension. The use of the constrained sessile drop configuration in conjunction with axisymmetric drop shape analysis to measure surface tension allows complete automation of the setup. Dynamic studies with lung surfactant can be performed readily by changing the volume of a sessile drop, and thus the surface area, by means of a motor-driven syringe. To illustrate the validity of using this configuration, experiments were performed using an exogenous lung surfactant preparation, bovine lipid extract surfactant (BLES) at 5.0 mg/ml. A comparison of results obtained for BLES at low concentration between the constrained sessile drop and captive bubble arrangement shows excellent agreement between the two approaches. When the surface area of the BLES film (0.5 mg/ml) was compressed by about the same amount in both systems, the minimum surface tensions attained were identical within the 95% confidence limits.

Experimental study of water degassing from phonolite melts: implications for volatile oversaturation during magmatic ascent

We have experimentally studied degassing of phonolite melts between 50 and 200 MPa and 825 and 850 °C. Our results indicate that decompressed phonolite melts contain equilibrium water contents regardless of decompression rate or final pressure. In addition, the total porosities of our experiments agree with predicted equilibrium values, regardless of final pressure or decompression rate. Combined observations of mean bubble diameters, porosities, and arrangement of bubbles in our experiments indicate that degassing occurs preferentially in the large bubble fraction of the population. Because of this, retardation of growth in the small bubble population occurs. This may lead to bimodal bubble size distributions in completely degassed phonolites. Our results indicate that water saturated phonolites at temperatures >800 °C can degas in equilibrium, while rhyolites follow a disequilibrium trend, at decompression rates of ∼0.5–1.0 MPa/s. Thus, hotter, water-saturated phonolitic magmas are likely to maintain equilibrium magma water contents during ascent at rates up to 20 m/s, which are typical of highly explosive eruptions. These results may apply to eruptions such as the 79 AD eruption of Vesuvius, which is the type location for Plinian-style, explosive eruptions. However, caution must be used when applying these results to lower temperature, more differentiated, and water-undersaturated phonolite magmas. If fragmentation can occur at depths of ∼2 km or greater in the conduit, our results indicate that highly explosive eruptions of phonolitic magma may occur in the absence of water oversaturation in the magma during ascent. Fast ascent rates and high shear stresses in the conduit may provide a better explanation for fragmentation in this case.

SPACETIME FOAM

Spacetime is composed of a fluctuating arrangement of bubbles or loops called spacetime foam, or quantum foam. We use the holographic principle to deduce its structure, and show that the result is consistent with gedanken experiments involving spacetime measurements. We propose to use laser-based atom interferometry techniques to look for spacetime fluctuations. Our analysis makes it clear that the physics of quantum foam is inextricably linked to that of black holes. A negative experimental result, therefore, might have non-trivial ramifications for semiclassical gravity and black hole physics.

Microstructural evolution of helium-implanted α-SiC

Helium has a decisive effect on the microstructure of silicon carbide materials after implantation and subsequent annealing. A dense population of bubbles and dislocation loops is already observed at relatively low displacement doses after annealing of helium-implanted \ensuremath{\alpha}-SiC, while no visible damage appears after irradiation without helium implantation under otherwise equal conditions. The defects are separated from grain boundaries by defect-free zones of approximately 0.5 \ensuremath{\mu}m width. The most intriguing features of the evolving microstructure are lenticular cavities (platelets), which transform to disk-shaped arrangements of bubbles with associated dislocation loops or even stacks of loops. The observed microstructural evolution and its dependence on implantation dose, annealing temperature, and time are quantitatively explained and discussed in terms of diffusion of interstitial He atoms and their clustering between adjacent lattice planes, thus forming nanocracks during implantation. The relaxation of the high gas pressure by matrix atom transfer from bubbles to loops during annealing and the coarsening of bubble-loop complexes are described by a coupled two-component Ostwald ripening process.

気泡流の初期挙動に関する数値シミュレーション

This papar is concerned with numerical simulation of a bubbly flow which is generated by continuous release of bubbles with various arrangements from the bottom of a vessel in gravitational field. The flow was analyzed as a continuum in which density and viscosity changed owing to existence of the bubbles. The availability of the exact solution of B. B. O.'s equation with constant acceleration during small time interval made it easy to analyze the motion of the bubbles in the flow. The velocity and pressure fields based on one fluid model were calculated using the SIMPLE method. For initially asymmetric arrangement of bubbles or asymmetric release position, the flow tends to be unstable, even if asymmetry is slight. For initially symmetric arrangement, small bubbles, released from symmetric bottom position of a vessel, are caught in vortices generated by rising bubbles and the flow. tends also to be unstable because of the slight difference of number density of the bubbles in the vortices. This tendency becomes to be weak when large bubbles are mixed with the small bubbles.

Thermal Effects of Internal Gas on the Oscillations of a Cluster of Bubbles.

The governing equations of a cluster of bubbles are derived by taking account of the thermal effects of the internal gas and the three-dimensional translational motion and deformation of each bubble. The equations are applied to the nonlinear oscillations of multiple interacting bubbles. The frequency response curves are obtained for two typical arrangements of bubbles with the same radii. The present results are compared with the results of polytropic analysis in which the thermal effects are evaluated using the effective polytropic index and the effective viscosity. It is shown that the heat transfer inside the bubble is important in investigating the nonlinear bubble oscillations. The polytropic relation for the internal gas does not hold when the nonlinearity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. It is also shown that the subharmonic oscillation of interacting bubbles occurs more easily than that of an isolated bubble due to the bubble-bubble interaction.

Further remarks on the drag of a swarm of bubbles

In this note, the influence of the geometrical arrangement of bubbles on the drag of bubble swarms has been ascertained by carrying out detailed comparisons between various estimates of drag available in the literature. Likewise, the predictions based on the two commonly used cell (free surface and zero vorticity) models have been contrasted with each other. A simple method for estimating the free rise velocity of bubble swarms is outlined.

Thermal Effects of the Internal Gas on the Oscillations of a Cluster of Bubbles.

The governing equations of a cluster of bubbles are derived by taking account of the thermal effects of the internal gas and the three-dimensional translational motion and deformation of each bubble. The equations are applied to the nonlinear oscillations of multiple interacting bubbles. The frequency response curves are obtained for two typical arrangements of bubbles with the same radii. The present results are compared with the results of polytropic analysis in which the thermal effects are evaluated using the effective polytropic index and the effective viscosity. It is shown that the heat transfer inside the bubble is important in investigating the nonlinear bubble oscillations : The polytropic relation for the internal gas does not hold when the nonlinearity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. It is also shown that the subharmonic oscillation of interacting bubbles occurs more easily than that of an isolated bubble due to the bubble-bubble interaction.

Film Boiling on a Horizontal Plate

>Film boiling is studied for water and Freon-11 (CCl₃F) at atmospheric pressure on a flat horizontal aluminum heating surface 8 in. square. High speed motion pictures were taken from which interbubble distances, bubble periods, breakoff diameters, and geometric arrangement of bubbles were determined. The results show that the minimum heat flux in film boiling from a horizontal surface is definitely a type of Taylor hydrodynamic instability. A new experimental technique was developed for obtaining film boiling on a large area without the necessity of using huge heat fluxes to go over the peak of the boiling curve. Once film boiling was established, the film boiling region could be traversed by changing the heat output from the gas burner beneath the slab. (auth)