Showing papers on "Bubble published in 1998"
TL;DR: In this article, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail with high-speed photography with framing rates of up to one million frames/s.
Abstract: In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary (γ=2, where γ=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances (γ[les ]0.7). In this region, the impact velocity rises to 83 m s−1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at γ>1, the impact velocity is smaller than 25 m s−1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when γ<2 and at the moment of first collapse when γ<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range γ=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At γ[les ]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the circumference of the torus, the observed damage is circular as well. Bubbles in the ranges γ[les ]0.3 and γ=1.2 to 1.4 caused the greatest damage. The overall diameter of the damaged area is found to scale with the maximum bubble radius. Owing to the possibility of generating thousands of nearly identical bubbles, the cavitation resistance of even hard steel specimens can be tested.
860 citations
TL;DR: In this article, a simple but reliable correlation for a drag coefficient, CD, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubble.
Abstract: Simple but reliable correlations for a drag coefficient, CD, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubbles. The proposed CD consists of three equations, each of which corresponds to pure, slightly contaminated and contaminated systems. The effect of a frictional pressure gradient due to a liquid flow is also taken into account by introducing a concept of an effective body acceleration. Terminal rising velocities of single bubbles were calculated using the proposed CD, and compared with measured data under the condition of 10-2
644 citations
TL;DR: In this paper, the authors studied the mechanism of the transition in bubble release pattern through complete numerical simulation of the evolution of the vapor-liquid interface and found that at low wall superheats, bubbles break off, and the interface drops down alternatively at the nodes and antinodes.
Abstract: Attempts have recently been made to numerically simulate film boiling on a horizontal surface. It has been observed from experiments and numerical simulations that during film boiling the bubbles are released alternatively at the nodes and antinodes of a Taylor wave. Near the critical state, however, hydrodynamic transition in bubble release pattern has been reported in the literature. The purpose of this work is to understand the mechanism of the transition in bubble release pattern through complete numerical simulation of the evolution of the vapor-liquid interface. The interface is captured by a level set method which is modified to include the liquid-vapor phase change effect. It is found from the numerical simulation that at low wall superheats the interface moves upwards, bubbles break off, and the interface drops down alternatively at the nodes and antinodes. However, with an increase in wall superheat, stable vapor jets are formed on both the nodes and antinodes and bubbles are released from the top of the vapor columns. The numerical results are compared with the experimental data, and visual observations reported in the literature are found to be in good agreement with the data.
335 citations
TL;DR: In this article, the influence of surfactant on particle−bubble interaction was investigated and an experimental setup with which the interaction between colloidal particles and colloidal bubbles was investigated.
Abstract: The aim of this study was to determine the influence of surfactant on the particle−bubble interaction. Therefore we constructed an experimental setup with which the interaction between colloidal pa...
252 citations
TL;DR: In this article, a visual study of vapor bubble growth and departure in vertical upflow and downflow forced convection boiling is presented, where high-speed digital images of flow boiling phenomena were obtained, which were used to measure bubble growth, departure diameters, and lift-off diameters.
236 citations
TL;DR: In order to prolong the lifetime of 5-micron bubbles in the bloodstream from < 1 s (as found with pure air), the osmotic agent must have a low Ostwald coefficient and a relatively high saturated vapor pressure at body temperature.
Abstract: The problem of dissolution of a bubble in the bloodstream is examined. The bubble is assumed to be filled with a mixture of a sparingly water-soluble gas (osmotic agent) and air. The dissolution of the bubble has three definite stages. In Stage 1, the bubble quickly swells in air. The swelling ratio depends on the surface tension, blood pressure, level of oxygen metabolism and initial mole fraction of osmotic agent in the bubble. In Stage 2, the osmotic agent slowly diffuses out of the bubble. The squared radius decreases nearly linearly with time, at a rate proportional to the Ostwald coefficient and diffusivity of the osmotic agent. In Stage 3, the partial pressure of the osmotic agent becomes so high that it condenses into a liquid. In order to prolong the lifetime of 5-micron bubbles in the bloodstream from or = 0.3 atm = 3 x 10(4) Pa).
236 citations
TL;DR: In this article, a model of diffusive and decompressive growth of a bubble in a finite region of melt was developed, which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between viscosity, volatile concentration and diffusivity.
Abstract: We have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity, volatile concentration, and diffusivity. On the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems. We conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined. Variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2–4 orders of magnitude. Our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions. An analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics R∼t1/2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship R∼log(t) is more appropriate during active bubble growth under certain conditions. A second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression. Model results for degassing of initially water-saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent. On the basis of decompression history, explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates >1–5 m s−1.
227 citations
15 Jan 1998
TL;DR: A collision theory has been developed which accounts for the influence of positive and negative inertial forces in the case of bubbles with mobile surfaces, and the analytical equation developed is termed the generalized Sutherland equation (GSE).
Abstract: The collection efficiency of single bubbles rising through a very dilute pulp of hydrophobized quartz particles has been determined. Measurements have been performed under conditions in which the bubble surface is mobile, as a function of electrolyte concentration, particle diameter (7 to 70 μm), bubble diameter (0.77 × 10−3to 1.52 × 10−3m), and particle advancing water contact angle. Situations in which the product of attachment and stability efficiency is at its maximum value have been identified, permitting a stringent, critical test of collision theory to be performed. A collision theory has been developed which accounts for the influence of positive and negative inertial forces in the case of bubbles with mobile surfaces. The approach considers only long-range hydrodynamic interactions under conditions where short-range interactions are strongly suppressed (i.e., high particle contact angle and high electrolyte concentrations) and attachment occurs at first collision. In this instance, good agreement between theory and experiment is achieved for particle diameters between 7 and 60 μm and Stokes numbers up to 0.27. The analytical equation developed is termed the generalized Sutherland equation (GSE).
192 citations
TL;DR: In this article, a two-dimensional Boussinesq convection is studied numerically using two different methods: a filtered pseudospectral method and a high-order accurate eno scheme.
Abstract: Two‐dimensional Boussinesq convection is studied numerically using two different methods: a filtered pseudospectral method and a high‐order accurate eno scheme. The issue whether finite time singularity occurs for initially smooth flows is investigated. In contrast to the findings of Pumir and Siggia who reported finite time collapse of the bubble cap, the present numerical results suggest that the strain rate corresponding to the intensification of the density gradient across the front saturates at the bubble cap. Consequently, the thickness of the bubble decreases exponentially. On the other hand, the bubble experiences much stronger straining and intensification of gradients at its side. As the bubble rises, a secondary front also forms from its tail. Together with the primary front, they constitute a pair of tightly bound plus and minus double vortex sheet structure which is highly unstable and vulnerable to viscous dissipation.
191 citations
TL;DR: In this paper, an experimental study of the deformation and breakup of a bubble in a turbulent flow was performed under microgravity conditions to ensure that turbulence was not the only cause of bubble deformation.
Abstract: This work is an experimental study of the deformation and breakup of a bubble in a turbulent flow. A special facility was designed to obtain intense turbulence without significant mean flow. The experiments were performed under microgravity conditions to ensure that turbulence was the only cause of bubble deformation. A scalar parameter, characteristic of this deformation, was obtained by video processing of high-speed movies. The time evolution and spectral representation of this scalar parameter showed the dynamical characteristics of bubble deformation. The signatures of the eigenmodes of oscillation predicted by the linear theory were clearly observed and the predominance of the second mode was proved. In addition, numerical simulations were performed by computing the response of a damped oscillator to the measured turbulence forcing. Simulations and experiments were found to be in good agreement both qualitatively, from visual inspections of the signals, and quantitatively, from a statistical analysis. The role of bubble dynamics in the deformation process has been clarified. On the one hand, the time response of the bubble controls the maximum amount of energy which can be extracted from each turbulent eddy. On the other hand, the viscous damping limits the energy that the bubble can accumulate during its fluctuating deformation. Moreover, two breakup mechanisms have been identified. One mechanism results from the balance between two opposing dominant forces, and the other from a resonance oscillation. A new parameter, the mean efficiency coefficient, has been introduced to take into account the various aspects of bubble dynamics. Used together with the Weber number, this parameter allows the prediction of the occurrence of these two mechanisms. Finally, the influence of the residence time of the bubble on the statistics of the deformation has been analysed and quantified.
191 citations
TL;DR: In this paper, the Rayleigh-Plesset equation was used to derive analytical approximations for RP dynamics and subsequent analytical laws for parameter dependences for single-bubble sonoluminescence (SBSL).
Abstract: Recent work on single-bubble sonoluminescence (SBSL) has shown that many features of this phenomenon, especially the dependence of SBSL intensity and stability on experimental parameters, can be explained within a hydrodynamic approach. More specifically, many important properties can be derived from an analysis of bubble wall dynamics. This dynamics is conveniently described by the Rayleigh-Plesset (RP) equation. Here we derive analytical approximations for RP dynamics and subsequent analytical laws for parameter dependences. These results include (i) an expression for the onset threshold of SL, (ii) an analytical explanation of the transition from diffusively unstable to stable equilibria for the bubble ambient radius (unstable and stable sonoluminescence), and (iii) a detailed understanding of the resonance structure of the RP equation. It is found that the threshold for SL emission is shifted to larger bubble radii and larger driving pressures if surface tension is increased, whereas even a considerable change in liquid viscosity leaves this threshold virtually unaltered. As an enhanced viscosity stabilizes the bubbles to surface oscillations, we conclude that the ideal liquid for violently collapsing, surface-stable SL bubbles should have small surface tension and large viscosity, although too large viscosity ([eta]l[gt-or-equal, slanted]40[eta]water) will again preclude collapses.
TL;DR: In this article, the collapse of a bubble is modeled by taking into account all the energy forms involved (i.e., mechanical, thermal, chemical, and radiative) and compared the calculated radical yields with sonochemical data in H2O.
Abstract: We model the collapse of a bubble by taking into account all the energy forms involved (i.e., mechanical, thermal, chemical, and radiative) and compare the calculated radical yields with sonochemical data in H2O. Water decomposition plays a critical role in the energy balance, but trails equilibrium even in bubbles collapsing at subsonic speeds. Integration of the equation of bubble motion coupled with a full chemical mechanism reveals that (1) terminal gas temperatures and Mach numbers ML increase in cooler water, (2) ΓOH, the number of OH-radicals produced per unit applied work at maximum MLwhen bubbles become unstable and disperse into the liquiddecreases at small and very large sound intensities. We show that available data on the sonochemical decomposition of volatile solutessuch as CCl4, which is pyrolyzed within collapsing bubblesare compatible with the efficient conversion of ultrasonic energy into transient cavitation. On this basis we calculate ΓOH = (1 ± 0.5) × 1017 molecules/J for R0 = 2 μm bu...
TL;DR: The scattering and backscattering properties of bubble populations in the upper ocean are estimated with Mie theory and a generalized bubble size spectrum based on in situ observations and results are compared with the corresponding optical properties of micro-organisms of similar size.
Abstract: The scattering and backscattering properties of bubble populations in the upper ocean are estimated with Mie theory and a generalized bubble size spectrum based on in situ observations. Optical properties of both clean bubbles and bubbles coated with an organic film are analyzed; the results are compared with the corresponding optical properties of micro-organisms of similar size. Given a bubble number density (from ~10(5) to ~10(7) m(-3)) frequently found at sea, the bubble populations significantly influence the scattering process in the ocean, especially in oligotrophic waters. Bubbles appear to make a large contribution to the missing terms in constructing the observed total backscattering coefficient of the ocean. This contribution to backscattering is strongly enhanced if the bubbles are coated with organic film. The injection of bubbles will shift ocean color toward the green, resembling phytoplankton blooms, and hence introducing error in ocean color remote sensing if its effect is not corrected.
TL;DR: In this article, it was shown that the measured pressure fluctuations are a result of slow and fast propagating pressure waves, which are unambiguously identified as compression waves, and the amplitude of upward moving pressure waves is linearly dependent on the distance to the bed surface.
TL;DR: In this paper, the Rayleigh-Plesset equation was used to derive analytical approximations for RP dynamics and subsequent analytical laws for parameter dependences for single bubble sonoluminescence (SBSL).
Abstract: Recent work on single bubble sonoluminescence (SBSL) has shown that many features of this phenomenon, especially the dependence of SBSL intensity and stability on experimental parameters, can be explained within a hydrodynamic approach. More specifically, many important properties can already be derived from an analysis of bubble wall dynamics. This dynamics is conveniently described by the Rayleigh-Plesset (RP) equation. In this work we derive analytical approximations for RP dynamics and subsequent analytical laws for parameter dependences. These results include (i) an expression for the onset threshold of SL, (ii) an analytical explanation of the transition from diffusively unstable to stable equilibria for the bubble ambient radius (unstable and stable sonoluminescence), and (iii) a detailed understanding of the resonance structure of the RP equation. It is found that the threshold for SL emission is shifted to larger bubble radii and larger driving pressures if surface tension is enlarged, whereas even a considerable change in liquid viscosity leaves this threshold virtually unaltered. As an enhanced viscosity stabilizes the bubbles against surface oscillations, we conclude that the ideal liquid for violently collapsing, surface stable SL bubbles should have small surface tension and large viscosity, although too large viscosity (>40 times the viscosity of water) will again preclude collapses.
TL;DR: In this article, a CFD model for a free bubbling fluidised bed was implemented in the commercial code CFX of AEA Technology, which is based on a two fluid model including the kinetic theory of granular flow.
TL;DR: In this article, the authors extended the Layzer-type approach to unstable interfacial fluid mixing, applied up to now only to vacuum bubbles, to spikes and derive the analytical solutions of the model for the positions, velocities, accelerations, and curvatures at the tips of the bubble and spike over all times.
Abstract: We extend the Layzer-type approach to unstable interfacial fluid mixing, applied up to now only to vacuum bubbles, to spikes and derive the analytical solutions of the model for the positions, velocities, accelerations, and curvatures at the tips of the bubble and spike over all times. The analytical predictions are in good agreement with the results from numerical simulations for both spikes and bubbles. We give the first analytical prediction for the asymptotic growth rate of a spike at the Richtmyer-Meshkov unstable interface. We predict that, in contrast to the asymptotic bubble growth rate, the asymptotic growth rate of a spike at the Richtmyer-Meshkov unstable interface is a constant and depends on the initial condition.
Patent•
14 Jul 1998TL;DR: A bubble valve that comprises a liquid delivery channel and a localized heating arrangement is presented in this article, where the localized heating is used to nucleate and enlarge a bubble in the liquid.
Abstract: A bubble valve that comprises a liquid delivery channel and a localized heating arrangement The liquid delivery channel includes an upstream portion and a constriction downstream of the upstream portion The constriction has a smaller cross-sectional area than the upstream portion The localized heating arrangement is located in the liquid delivery channel and generates heat to nucleate and enlarge a bubble in the liquid The constriction is shaped to form a seal with the bubble The localized heating arrangement additionally generates heat to move the bubble relative to the constriction to control the flow of the liquid A pressure regulator that comprises a liquid delivery channel connected to a liquid outlet, a sensor located adjacent the liquid outlet, a controller that operates in response to the sensor and a localized heating arrangement The liquid delivery channel includes an upstream portion, and a constriction located between the upstream portion and the liquid outlet The constriction has a smaller cross-sectional area than the upstream portion The localized heating arrangement is located in the liquid delivery channel and generates heat in response to the controller to nucleate and enlarge a bubble in the liquid The constriction is shaped to form a seal with the bubble The localized heating arrangement additionally generates heat to move the bubble relative to the constriction to control the flow of the liquid to the liquid outlet
TL;DR: In this paper, the authors used a CCD camera coupled with a microscope to follow a spherical rising gas bubble and estimate the drag coefficients and Sherwood number for the dissolution of gas bubbles at Reynolds numbers below 100.
TL;DR: In this paper, a numerical study of the natural frequency of the volume oscillations of gas bubbles in a liquid contained in a finite-length tube, when the bubble is not small with respect to the tube diameter, is presented.
Abstract: A numerical study is presented of the natural frequency of the volume oscillations of gas bubbles in a liquid contained in a finite-length tube, when the bubble is not small with respect to the tube diameter. Tubes rigidly terminated at one end, or open at both ends, are considered. The open ends may be open to the atmosphere or in contact with a large mass of liquid. The numerical results are compared with a simple approximation in which the bubble consists of a cylindrical mass of gas filling up the cross section of the tube. It is found that this approximation is very good except when the bubble radius is much smaller than that of the tube. An alternative approximate solution is developed for this case. The viscous energy dissipation in the tube is also estimated and found generally small compared with the thermal damping of the bubble. This work is motivated by the possibility of using gas bubbles as actuators in fluid-handling microdevices.
TL;DR: In this article, the Newton/Reynolds characteristics of a continuous rotor/ stator mixer for foam production were determined with special geometrically adapted Newton and Reynolds numbers.
TL;DR: In this paper, a semi-analytical model for nucleate boiling is proposed, which assumes the tunnel is vapor filled, except liquid menisci in the corners, and analyzes meniscus thickness, bubble departure diameter, and bubble growth.
TL;DR: In this paper, a method based on a dispersion relation for propagation of sound waves through a bubbly liquid is developed, which is used to relate the attenuation and phase velocity of a sound wave to the bubble population.
Abstract: A nuclei size measurement technique is developed, based on a dispersion relation for propagation of sound waves through a bubbly liquid. This is used to relate the attenuation and phase velocity of a sound wave to the bubble population, leading to two integral equations. These equations are ill posed, and require special treatment for solution. Algorithms based on a minimization method that imposes a number of physical constraints on the solution, rendering the equation well posed, are developed. The procedure is first tested on analytical data with varying artificial noise added, and found to be successful in recovering the bubble density function, and to perform much better than other published solution techniques. Then, bubbles were generated using electrolysis and air injection through porous tubes, and bubble populations measured. Short monochromatic bursts of sound at different frequencies were emitted and received using hydrophones. The received signals were then processed and analyzed to obtain the attenuation and phase velocity. The void fraction and known experimental errors were also obtained and were fed as constraints to the inverse problem solution procedure. This resulted in bubble populations which compare favorably to those obtained by microphotography.
TL;DR: In this article, an experimental investigation on flow around an oscillating bubble and a solid ellipsoid with a flat bottom was conducted, where a single air bubble (equivalent diameter D e = 9.12mm) was attached to a small disk (∼1mm) at the end of a needle and suspended across a vertical square channel (100mm) by wire wherein water flowed downward at a constant flowrate.
TL;DR: In this article, Wang et al. investigated the nonlinear dynamics of a gas bubble close to an inclined wall, where the fluid is assumed to be inviscid and incompressible and the flow irrotational.
Abstract: The nonlinear dynamics of a gas bubble close to an inclined wall is investigated numerically. The fluid is assumed to be inviscid and incompressible and the flow irrotational. A time-integration boundary integral method is used to solve the Laplace equation for the velocity potential to calculate the shape and position of the bubble. Improvements to the previous research on this subject have been made in the surface triangulation of the initial spherical bubble, the integration of the influence coefficients, the calculations of the normal vector and tangential velocity vector at a node, the time integration scheme, etc. Comparisons have been carried out between the results of the present three-dimensional model and the results of a validated axis-symmetrical bubble code (Wang et al., 1996a,b, 1998) for axis-symmetrical cases. The comparisons demonstrate the robustness and accuracy of the present method. Simulations have been carried out for a gas bubble initiated at 3.0R
m, 2.0R
m, and 1.0R
m (R
m being defined as the maximum radius of the bubble) from an inclined wall with various buoyancy parameters and wall angles. All the simulations are performed at high resolution and without numerical instabilities occurring nearly up until the re-entrant jet impacts on the opposite bubble surface. The following qualitative features have been observed. When a bubble is initiated at $3.0R_{\rm m}$ or more away from an inclined wall, the jet is roughly symmetric; the jet direction is roughly the same as that of the motion of the bubble centroid, which can be approximately predicted by the Kelvin impulse theory. When a bubble is initiated around 2.0R
m from a wall, the jet is obviously asymmetric and inclined upwards; the Kelvin impulse theory can only be used to predict the location where the jetting occurs, but it can no longer be used to predict the jet direction. When a bubble is initiated at 1.0R
m or less near an inclined wall and the buoyancy and Bjerknes attraction are comparable, the jet is roughly in the upward direction.
TL;DR: In this article, the axial dispersion coefficient, Ez, was shown to be dominated by bubble slip, and fits 78% of the measured data with less than 20% error.
TL;DR: In this article, a bubble generation system that creates individual, spherical vapor bubbles from 2 to 500 μm in diameter is presented, where polysilicon resistors with a typical size of 50 x 2 x 0.53 μm 3 are fabricated by means of micromachining.
Abstract: Thermal bubble formation in the microscale is of importance for both scientific research and practical applications. A bubble generation system that creates individual, spherical vapor bubbles from 2 to 500 μm in diameter is presented. Line shape, polysilicon resistors with a typical size of 50 x 2 x 0.53 μm 3 are fabricated by means of micromachining. They function as resistive heaters and generate thermal microbubbles in working liquids such as Fluorinert fluids (inert, dielectric fluids available from the 3M company), water, and methanol. Important experimental phenomena are reported, including Marangoni effects in the microscale; controllability of the size of microbubbles; and bubble nucleation hysteresis. A one-dimensional electrothermal model has been developed and simulated in order to investigate the bubble nucleation phenomena. It is concluded that homogeneous nucleation occurs on the microresistors according to the electrothermal model and experimental measurements.
TL;DR: In this article, the heat transfer rate and the hydrodynamic forces experienced by a single vapor bubble of variable radius moving in a superheated or subcooled liquid are studied by means of numerical simulation.
Abstract: The heat transfer rate and the hydrodynamic forces experienced by a single vapor bubble of variable radius moving in a superheated or subcooled liquid are studied by means of numerical simulation. For that purpose the full Navier–Stokes equations and the temperature equation are solved in a frame of reference where the bubble surface is steady. The time evolution of the bubble radius is determined by solving the energy balance at the bubble surface. The numerical method is first validated by comparing present predictions with previous asymptotic or numerical results in the case where no relative motion between the liquid and the bubble exists. Then the situation where a constant relative velocity exists is considered. Effects of the mean flow on the heat transfer rate and on the bubble radius evolution are first discussed. Two different stages are generally observed in the computations. First, the radial motion induced by the displacement of the bubble surface dominates and the bubble evolution is essenti...
TL;DR: In this article, a semi-empirical model of spherical bubble growth under constant flow conditions is presented to predict the bubble volume at the detachment stage and an expression for the net viscous force acting on the surrounding fluid.
Abstract: The continuous emission of gas bubbles from a single ejection orifice immersed in a viscous fluid is considered. We first present a semi empirical model of spherical bubble growth under constant flow conditions to predict the bubble volume at the detachment stage. In a second part, we propose a physical model to describe the rise velocity of in-line interacting bubbles and we derive an expression for the net viscous force acting on the surrounding fluid. Experimental results for air/water-glycerol systems are presented for a wide range of fluid viscosity and compared with theoretical predictions. An imagery technique was used to determine the bubble size and rise velocity. The effects of fluid viscosity, gas flow rate, orifice diameter and liquid depth on the bubble stream dynamic were analyzed. We have further studied the effect of large scale recirculation flow and the influence of a neighbouring bubble stream on the bubble growth and rising velocity.
TL;DR: In this article, the authors describe a number of experiments in which the effect of electrons on cavitation is studied and show that the circulation of the liquid around the electron bubble leads to a reduction in the magnitude of the negative pressure required to explode the bubble, and they have been able to measure this reduction.
Abstract: We describe a number of experiments in which the effect of electrons on cavitation is studied. Electrons in liquid helium become trapped in a bubble from which the liquid is almost completely excluded. By applying a negative pressure to the helium, we are able to make these bubbles explode. We have measured the variation of this pressure with temperature and the results are in very good agreement with theoretical expectations. At low temperatures the electron bubbles become attached to vortices. The circulation of the liquid around the electron bubble leads to a reduction in the magnitude of the negative pressure required to explode the bubble, and we have been able to measure this reduction. @S0163-1829~98!05806-8#