Bubble Compression Research Articles

Motion of Gas Bubbles and Rigid Particles in Vibrating Fluid-Filled Volumes

Motion of gas bubbles and rigid particles in an oscillating fluid is of fundamental interest for the theory of various widely used technological processes, in particular, for the flotation process. Therefore, many studies have been concerned with this problem, some of those being undertaken by eminent scientists. The main remarkable effects are heavy particles rising and light particles (gas bubbles) sinking in vibrating fluid's volume, and asynchronous self-induced vibration of emerging air cushion.In the authors’ recent papers, the problem has been solved by means of the concept of vibrational mechanics and the method of direct separation of motions; experimental studies have been also conducted. The present paper generalizes and supplements these studies. A special attention is given to the analysis of motion of bubbles and light rigid particles, whose sizes are small in comparison with the amplitude of external excitation; motion of larger (compressible) bubbles is also considered in the paper. It is shown that at certain parameters of external excitation such particles and bubbles will sink in the fluid, corresponding conditions are formulated.

High frequency microbubble-switched oscillations modulated by microfluidic transistors

Creating high frequency two-phase oscillations (HF-TPOs) remains an important goal in advancing microscale fluidic logic devices, micro-mixers, micro-actuators, and flow controls. However, thermally driven TPO frequency has been hindered by confinements of compressible vapor bubbles and low thermal diffusivity in microfluidic systems. In this study, a mechanism creating high frequency microbubbles growth/collapse cycle has been developed to achieve HF-TPOs. A “microfluidic transistor” was conceptualized and fabricated to passively sustain and modulate HF-TPOs. Three orders of magnitude higher TPO frequency has been achieved compared to TPOs reported in literatures under similar working conditions.

Damping of intraocular pressure fluctuations

There is increasing evidence that relatively rapid spikes in intraocular pressure may contribute to axonal damage in glaucoma. The present study seeks to quantify the ability of a compressible damping element (a simple air bubble) to reduce intraocular pressure fluctuations induced by a known change in intraocular fluid volume. A mathematical model describing the damping of intraocular pressure increases for a given infusion volume was developed and compared with experimental data obtained from isolated pig eyes. A damping element (100 µL to 2 mL of air) was added to the system, and the effect on the induced intraocular pressure change for a given infusion volume was assessed. The introduction of the damping element reduced the intraocular pressure change in a volume-dependent manner consistent with the mathematical modelling. The maximum bubble size tested (2 mL) dampened the intraocular pressure change by an average of 63.5 ± 8.7% at a baseline pressure close to 20 mmHg. Close agreement was seen between the mathematical model and the experimental data. Mathematical modelling and experiments in isolated pig eyes demonstrated that the addition of a damping element in the form of a compressible air bubble is capable of significantly reducing induced intraocular pressure spikes.

Evolution of a small sphericity distortion of a vapor bubble during its supercompression

The possibility of using two models to study the evolution and maximum increase in amplitude of small distortions of sphericity of a bubble during its strong compression in a liquid is investigated. The investigation is performed in the conditions of experiments on acoustic cavitation of deuterated acetone. The first (fully hydrodynamic) model is based on the two-dimensional equations of gas dynamics. It is valid in every stage of the bubble compression. But its use takes up a lot of computational time. The second (simplified) model is derived by splitting the liquid and vapor motion into a spherical part and its small nonspherical perturbation. To describe the spherical component, a onedimensional version of the two-dimensional model is used in this model. The advantage of the simplified model over the full one is its much lower consumption of computational time. At the same time, the evolution of the nonspherical perturbation in this model is described by utilizing a number of assumptions, validity of which is justified only at the initial stage of the bubble compression. It is therefore logical to apply the simplified model at the initial low-speed stage of the bubble compression, while the full hydrodynamic one is applied at its final high-speed stage. It has been shown that such a combination allows one to significantly reduce the computational time. It has been found that the simplified model alone can be used to evaluate the maximum increase of the amplitude of small sphericity distortions of a bubble during its compression.

Modeling of the Anode Crater Formation in Electrical Discharge Machining

This research presents a numerical model and the experimental validation of the anode crater formation in electrical discharge machining (EDM) process. The modeling is based on the theory that the material removal process in EDM is composed of two consecutive phases: the plasma heating phase in which intensive thermal energy density is applied locally to melt the work-material and the bubble collapsing phase in which the fluidic impact expels the molten material. A mathematical heat source model with Gaussian distributed heat flux and time variant heating area is applied in the plasma heating phase. Standard modules of a commercial computational fluid dynamics software, fluent, are adapted to model the crater formation in EDM. The material melting is simulated using transient heat transfer analysis and an enthalpy balance method. The volume of fraction (VOF) method is used to tackle the multiphase interactions in the processes of bubble compression and collapsing and molten material splashing and resolidification. Crater and debris geometries are attained from the model simulation and validation experiments are conducted to compare the crater morphology. The simulation and experiment results at different discharge conditions show good agreement on crater diameter suggest that the model is able to describe the mechanism of EDM crater formation.

Cumulation during compression of cavitation bubbles in liquid

Cumulative effects under strong compression of cavitation bubbles in liquid are considered. The dependence of cumulation on small initial nonsphericity of bubbles is discussed in three cases. In the first case, the compression of the bubble in liquid is realized at a great distance from the liquid boundaries (free surface, rigid walls). In the second case, the influence of a nearby wall is considered. In the third case, the bubble is compressed in the presence of other bubbles in its vicinity.

Wavy Motion of Viscous Bubbly Liquid in Tubes of Orthotropic Material

This article investigates the pulsating flow of a compressible two-phase bubble of viscous fluid contained in an elastic orthotropicle direct axis tube. In this work, one-dimensional linear equations have been used. It is assumed that the tube is rigidly attached to the certain environment. In the case of finite length the pressure is applied at the end of its faces. In the limited process, relations obtained for a very long tube. Such a description, in a sense generalizes and strengthens the work of this type. In the numerical experiment a semi-infinite tube with flowing water containing small amount of air bubbles is considered. The influence of volume fraction of bubbles on wave characteristics is determined.

Bubble dynamics atop an oscillating substrate: Interplay of compressibility and contact angle hysteresis

We consider a sessile hemispherical bubble sitting on the transversally oscillating bottom of a deep liquid layer and focus on the interplay of the compressibility of the bubble and the contact angle hysteresis. In the presence of contact angle hysteresis, the compressible bubble exhibits two kinds of terminal oscillations: either with the stick-slip motion of the contact line or with the completely immobile contact line. For the stick-slip oscillations, we detect a double resonance, when the external frequency is close to eigenfrequencies of both the breathing mode and shape oscillations. For the regimes evolving to terminal oscillations with the fixed contact line, we find an unusual transient resembling modulated oscillations.

Dynamic manipulation of the subharmonic scattering of phospholipid-coated microbubbles

In this paper, the influence of a dynamic variation in the ambient pressure on the subharmonic response of phospholipid-coated microbubbles was investigated. The ambient pressure in water was modulated by a 2.5 kHz acoustic wave with a peak amplitude of 15 kPa. We investigated the fundamental and subharmonic emissions at two driving frequencies: 5 and 10 MHz. The modulation of the bubble radius induced by the dynamic variation in the liquid ambient pressure subsequently causes modulations of the scattered acoustic pressure at the fundamental and subharmonic frequencies (half the fundamental frequency). As a first result, we measured that the variation in the ambient pressure of 15 kPa can modulate the subharmonic amplitude up to 10 dB as compared to the static atmospheric pressure condition. As a second result, we noticed that the relative subharmonic amplitude modulation as a function of the LF acoustic pressure was symmetrical for the 5 MHz driving frequency but asymmetric for 10 MHz. In the latter case, the subharmonic amplitude was more enhanced for an ambient overpressure than reduced for an ambient depression of the same amplitude likely due to the buckling of the lipid shell. However, the fundamental amplitude was symmetrically modulated during bubble compression and expansion. Moreover, subharmonic and fundamental amplitude modulations were found to be either in phase or out of phase with the low-frequency acoustic pressure. Numerical simulations showed that this behavior can be obtained depending on the bubbles' diameter. The highest subharmonic amplitude was measured when microbubbles were insonified at 10 MHz. This fact together with the asymmetry observed in the subharmonic modulation suggests that smaller bubbles with a buckling shell are excited at 10 MHz compared to 5 MHz. These results present new potentials for in vitro characterization of contrast agent microbubbles and possibly a new imaging modality.

Controlled permeation of cell membrane by single bubble acoustic cavitation

Sonoporation is the membrane disruption generated by ultrasound and has been exploited as a non-viral strategy for drug and gene delivery. Acoustic cavitation of microbubbles has been recognized to play an important role in sonoporation. However, due to the lack of adequate techniques for precise control of cavitation activities and real-time assessment of the resulting sub-micron process of sonoporation, limited knowledge has been available regarding the detail processes and correlation of cavitation with membrane disruption at the single cell level. In the current study, we developed a combined approach including optical, acoustical, and electrophysiological techniques to enable synchronized manipulation, imaging, and measurement of cavitation of single bubbles and the resulting cell membrane disruption in real-time. Using a self-focused femtosecond laser and high frequency ultrasound (7.44 MHz) pulses, a single microbubble was generated and positioned at a desired distance from the membrane of a Xenopus oocyte. Cavitation of the bubble was achieved by applying a low frequency (1.5 MHz) ultrasound pulse (duration 13.3 or 40 μs) to induce bubble collapse. Disruption of the cell membrane was assessed by the increase in the transmembrane current (TMC) of the cell under voltage clamp. Simultaneous high-speed bright field imaging of cavitation and measurements of the TMC were obtained to correlate the ultrasound-generated bubble activities with the cell membrane poration. The change in membrane permeability was directly associated with the formation of a sub-micrometer pore from a local membrane rupture generated by bubble collapse or bubble compression depending on ultrasound amplitude and duration. The impact of the bubble collapse on membrane permeation decreased rapidly with increasing distance (D) between the bubble (diameter d) and the cell membrane. The effective range of cavitation impact on membrane poration was determined to be D/d = 0.75. The maximum mean radius of the pores was estimated from the measured TMC to be 0.106 ± 0.032 μm (n = 70) for acoustic pressure of 1.5 MPa (duration 13.3 μs), and increased to 0.171 ± 0.030 μm (n = 125) for acoustic pressure of 1.7 MPa and to 0.182 ± 0.052 μm (n = 112) for a pulse duration of 40 μs (1.5 MPa). These results from controlled cell membrane permeation by cavitation of single bubbles revealed insights and key factors affecting sonoporation at the single cell level.

Modeling void formation and unsaturated flow in liquid composite molding processes: a survey and review

In this study, we present a review of the modeling of void formation and unsaturated flow in liquid composite molding processes. We examine modeling efforts considering all the mechanisms involved such as void formation and transport, bubble compression, and gas dissolution. In particular, the capillary number is identified as a key parameter for void formation and transport. Numerical simulation studies are reviewed, and a state-of-the-art is presented. The influence of microvoids on the global resin flow is also investigated. To model the unsaturated flow more accurately, we suggest considering the surface tension or capillary pressure, variation in permeability in terms of saturation and fiber displacement, as well as tow saturation. From this investigation, the apparent permeability and pressure profile in saturated and unsaturated flows are compared.

Enhancement of the photoacoustic effect and sonoluminescence in carbon suspensions through exothermic chemical reaction.

Generation of the photoacoustic effect through chemical reaction of particulate carbon in chemically reactive solutions is presented. Experiments are carried out using a Q-switched Nd:YAG laser to heat carbon nanoparticles, initiating chemical reaction which results in sound production. The amplitude of the photoacoustic signal from a carbon suspension in H2O2–H2O mixtures is shown to increase dramatically as the percentage of H2O2 in solution increases. Laser induced chemical generation of sonoluminescence in aqueous carbon suspensions is also reported. Following irradiation and chemical reaction, highly compressed gas bubbles are formed. The expansion of the gas bubble past its equilibrium diameter results in oscillation of the bubble diameter. Tens of μs after the initial formation of the bubble, sonoluminescence is found to take place on collapse of the bubble. Experiments show that the sonoluminescent intensity is increased by a factor of more than 10 as the external pressure is increased from 1 to 6 atm. The time of appearance of optical radiation following the initial firing of the laser is found to decrease with increasing external pressure as well.

Modeling and simulation of voids and saturation in liquid composite molding processes

We propose modeling and simulation of the void formation and the tow saturation in liquid composite molding processes. The present model addresses the void formations in the macropore between fiber tows as well as in the micropore inside fiber tows. We also consider the bubble compression and tow saturation after voids are formed at the flow front. Finally, a void migration model is considered. The present models are validated by a comparison between simulation results and experimental data. The simulation results successfully represent important features of the void physics: the correlation of void formation at the flow front with capillary number, the advantage of vacuum application at air vents to reduce the void content inside tows, and the existence of partially saturated zone behind the global flow front. The representation of mold filling patterns by a degree of saturation shows the presence of a bubbly zone behind the flow front.

A multislope MUSCL method on unstructured meshes applied to compressible Euler equations for axisymmetric swirling flows

A finite volume method for the numerical solution of axisymmetric inviscid swirling flows is presented. The governing equations of the flow are the axisymmetric compressible Euler equations including swirl (or tangential) velocity. A first-order scheme is introduced where the convective fluxes at cell interfaces are evaluated by the Rusanov or the HLLC numerical flux while the geometric source terms are discretizated to provide a well-balanced scheme i.e. the steady-state solutions with null velocity are preserved. Extension to the second-order space approximation using a multislope MUSCL method is then derived. To test the numerical scheme, a stationary solution of the fluid flow following the radial direction has been established with a zero and nonzero tangential velocity. Numerical and exact solutions are compared for classical Riemann problems where we employ different limiters and effectiveness of the multislope MUSCL scheme is demonstrated for strongly shocked axially symmetric flows like in spherical bubble compression problem. Two other tests with axisymmetric geometries are performed: the supersonic flow in a tube with a cone and the axisymmetric blunt body with a free stream.

Adsorption of Egg Phosphatidylcholine to an Air/Water and Triolein/Water Bubble Interface: Use of the 2-Dimensional Phase Rule To Estimate the Surface Composition of a Phospholipid/Triolein/Water Surface as a Function of Surface Pressure

Phospholipid monolayers play a critical role in the structure and stabilization of biological interfaces, including all membranes, the alveoli of the lungs, fat droplets in adipose tissue, and lipoproteins. The behavior of phospholipids in bilayers and at an air-water interface is well understood. However, the study of phospholipids at oil-water interfaces is limited due to technical challenges. In this study, egg phosphatidylcholine (EPC) was deposited from small unilamellar vesicles onto a bubble of either air or triolein (TO) formed in a low-salt buffer. The surface tension (gamma) was measured using a drop tensiometer. We observed that EPC binds irreversibly to both interfaces and at equilibrium exerts approximately 12 and 15 mN/m of pressure (Pi) at an air and TO interface, respectively. After EPC was bound to the interface, the unbound EPC was washed out of the cuvette, and the surface was compressed to study the Pi/area relationship. To determine the surface concentration (Gamma), which cannot be measured directly, compression isotherms from a Langmuir trough and drop tensiometer were compared. The air-water interfaces had identical characteristics using both techniques; thus, Gamma on the bubble can be determined by overlaying the two isotherms. Both TO and EPC are surface-active, so in a mixed TO/EPC monolayer, both molecules will be exposed to water. Since TO is less surface-active than EPC, as Pi increases, the TO is progressively ejected. To understand the Pi/area isotherm of EPC on a TO bubble, a variety of TO-EPC mixtures were spread at the air-water interface. The isotherms show an abrupt break in the curve caused by the ejection of TO from the monolayer into a new bulk phase. By overlaying the compression isotherm above the ejection point with a TO bubble compression isotherm, Gamma can be estimated. This allows determination of Gamma of EPC on a TO bubble as a function of Pi.

The problem of stability of the spherical shape of a bubble during its supercompression

Deviation of the bubble shape from the spherical one during supercompression of a bubble in liquid is considered. The main attention is focused on determining the law of the initial bubble nonsphericity distribution in the spherical harmonics. The most probable one is that with the amplitude reducing as the harmonics number increases. Such distribution is confirmed by the analysis of the bubble sphericity perturbation evolution at the bubble collapse near a solid wall and at coalesce of two identical bubbles. The influence of the bubble sphericity distortion during bubble compression on the deformation of a shock wave arising in the bubble and the dependence of the bubble nonsphericity evolution on the nonlinear interaction between the distortions in the form of different harmonics are also discussed.

Simulating compressible gas bubbles with a smooth volume tracking 1-Fluid method

The physical relevance of an improved front-capturing 1-Fluid method is investigated considering the behavior of either incompressible or compressible gas bubbles driven by buoyancy in a two-dimensional framework. Through the coupling of a VOF–PLIC technique and a smoothing function of adjustable thickness, the Smooth Volume of Fluid technique SVOF is intended to capture accurately strong interface distorsion with large density and viscosity contrasts between phases, combined with the front-capturing automatic treatment of interface rupture or reconnection. The fundamental idea lies in using the regular VOF–PLIC technique, while applying a smoothing procedure affecting both physical characteristics averaging and surface tension modeling. A thorough assessment procedure is achieved comparing the present method, front-tracking simulations and experiments from Bhaga and Weber that characterize the shape and velocity of single gas bubbles rising into liquid columns. A series of 200 SVOF simulations was necessary to provide a unique set of smoothing and averaging parameters available for any kind of bubble that is stable in an axisymmetric framework. The front-capturing strategy greatly eases the extension to gas injection applications as there is no micro-management required during interface coalescence or break-up, and no volume correction either. Finally the robustness of the 1-Fluid SVOF method is demonstrated in two-dimensions, in the case of compressible or incompressible gas injection into cold metal alloys where the density ratio between phases is greater than 3500.

Modeling strong compression of a gas bubble in fluid

A technique for calculating strong adiabatic compression of a gas bubble in fluid is proposed. The compression results from the pressure applied to the outer surface of the fluid. The motion of the fluid and gas is described by two-dimensional dynamic equations of compressed fluid and gas with realistic equations of its state. The effects of viscosity and thermal conductivity are not allowed for. The bubble surface is defined as a contact interface where there is a surface tension. Coupled Euler-Lagrange coordinates are used, with the bubble surface serving as a coordinate system. A spherical system of coordinates is used as a fixed reference. Equations of gas and fluid dynamics are solved by Godunov’s equations with second-order accuracy in space and time. The economic feasibility of the technique is illustrated by some model problems. The proposed method has been proven to be much more efficient than the classic first-order-approximation Godunov’s schemes traditionally used in solving problems of a highly compressed bubble. One of the scenarios is used to show the influence of slight spherical-shape distortions of the bubble on the evolution of the radially converged shock wave resulting from the strong compression.

Probing Luminescence from Conical Bubble Collapse

ABSTRACTA summary of experimental findings on the luminescence from conical bubble collapse, CBL is presented. Spatial, temporal, and spectral features of luminescence were investigated. In the experimental runs, two inert gases (Ar, Xe) and 1,2-Propanediol, PD, as work liquid were used. Single and multiple light emission events were recorded. Results show that there is a spectral evolution inside each pulse and through the whole experimental sequence. The average spectra consist of a broad continuum background, on which line emissions of OH°, CN, Na+, K+, and Swan lines are superimposed. An increase in continuum intensity from 300 to 860 nm was observed. The molecular and atomic lines as well as the continuum emission arise from different chemical pathways that take place during the bubble compression. Pathways come from the degradation of the liquid due to the repetition of the compression process, resulting in changes of the thermo-chemical conditions inside the cavity, such that each collapse was different. This becomes evident, by using low gas pressures, in which the luminescence was spatially and temporally non uniform. On the other hand if Xe instead of Ar is used the intensity of the luminescence increased one order of magnitude. These findings indicate that several components are presents in the bubble, besides the residual air and inert gas, vapor and liquid droplets, and within the latest water vapor, inert gas and alkali solutions are dissolved.

Continuous profiles of electromagnetic wave velocity and water content in glaciers: an example from Bench Glacier, Alaska, USA

AbstractWe conducted two-dimensional continuous multi-offset georadar surveys on Bench Glacier, south-central Alaska, USA, to measure the distribution of englacial water. We acquired data with a multichannel 25 MHz radar system using transmitter–receiver offsets ranging from 5 to 150 m. We towed the radar system at 5–10 kmh–1 with a snow machine with transmitter/receiver positions established by geodetic-grade kinematic differentially corrected GPS (nominal 0.5 m trace spacing). For radar velocity analyses, we employed reflection tomography in the pre-stack depth-migrated domain to attain an estimated 2% velocity uncertainty when averaged over three to five wavelengths. We estimated water content from the velocity structure using the complex refractive index method equation and use a three-phase model (ice, water, air) that accounts for compression of air bubbles as a function of depth. Our analysis produced laterally continuous profiles of glacier water content over several kilometers. These profiles show a laterally variable, stratified velocity structure with a low-water-content (~0–0.5%) shallow layer (~20–30 m) underlain by high-water-content (1–2.5%) ice.