Abstract: In an experimental investigation of the transient processes that occur when a single droplet of butane at the superheat limit vaporizes explosively, short-exposure photographs and fast-response pressure measurements have been used to construct a description of the complete explosion process. It is observed that only a single bubble forms within the drop during each explosion, and that the growth proceeds on a microsecond time scale. An interfacial instability driven by rapid evaporation has been observed on the surface of the bubbles. It is suggested that the Landau mechanism of instability, originally described in connection with the instability of laminar flames, also applies to rapid evaporation at the superheat limit. The photographic evidence and the pressure data are used to estimate the evaporative mass flux across the liquid-vapour interface after the onset of instability. The ;ate of evaporation is shown to be two orders of magnitude greater than would be predicted by conventional bubble-growth theories that do not account for the effects of instability. An estimate of the mean density within the bubbles during the evaporative stage indicates that it is more than one half of the critical density of butane. Additional interesting dynamical effects that are observed include a series of toroidal waves that form on the interface between the butane vapour and the external host liquid in the bubble column apparatus after the bubble has grown large enough to contact the outer edge of the drop, and violent oscillations of the bubble that occur on a millisecond time scale, after evaporation of the liquid butane is complete, that cause the disintegration of the bubble into a cloud of tiny bubbles by Rayleigh-Taylor instability.

Abstract: The classical Rayleigh‐Plesset equation of spherical bubble dynamics in an incompressible liquid is generalized to include the non‐Newtonian behavior of the liquid and mass exchange processes at the bubble interface.

Abstract: With the help of laser produced bubbles in water and high speed photography and holography sophisticated experiments on cavitation bubble dynamics can be conducted. The observation of a bubble vortex ring after jet formation upon collapse of a spherical bubble in front of a plane solid boundary is reported. The vortex ring may expand and contract several times until it disintegrates into a ring of bubbles by some instability finally taking over. A critical discussion of our qualitative understanding of jet formation is included. In a second part the problem of the acoustic cavitation noise spectrum is discussed. Numerically obtained ‘visible cavitation noise’ plots from a single bubble already resemble those obtained experimentally from acoustic cavitation. A discussion shows that the theory should be extended to self-consistency.

Abstract: Gas holdup structures in highly viscous glycerine and CMC solutions are studied in a 0.305 m diameter batch bubble column. The fractional gas holdups are determined using the dynamic gas disengagement method. Empirical correlations for the gas holdup based on data covering wide ranges of viscosities in Newtonian and pseudoplastic non-Newtonian solutions are presented. For highly viscous pseudoplastic solutions in small diameter columns, the gas holdup has a square root dependence on the diameter of the column. The absence of small bubbles is suggested to be a reason for the very low volumetric mass transfer coefficients in highly viscous solutions, reported in the literature.

Abstract: Observations of the behavior of spark-generated bubbles in the vicinity of solid and free boundaries are described. In all cases, the formation of a reentering region (microjet or constriction) occurs on the part of the bubble which has the most freedom of motion. Drag-reducing polymer additives are seen to significantly affect bubble departure from sphericity. Their presence weakens the influence of nearby solid boundaries, and seems to enhance that of a free surface. The relative importance of the acoustic pulses emitted during successive implosions and rebounds of the bubble is seen to be modified by the proximity of a solid wall. When the radius of the bubble is small compared to its distance from the closest boundary, a theoretical approach, using matched asymptotic expansion, is applied successfully to describe the nonspherical bubble behavior and the pressure field. This method is extended to the case of a multi-bubble system. It is very useful in determining the limiting distances of interaction. In the case of a free surface this distance is less than two bubble diameters. When applied to a solid wall covered with an elastic coating of finite thickness, or to a two-liquid interface this technique shows a selection process: bubbles closer than a limiting distance to the boundary are repelled during their collapse. The collapse is toward the boundary only for bubbles beyond this distance and is therefore less damaging.

Abstract: When a small drop or bubble approaches a solid surface, a thin liquid film forms between them, drains, until an instability forms and coalescence occurs. A hydrodynamic theory is developed for the first portion of this coalescence process: the drainage of the thin liquid film while it is still sufficiently thick that the effects of London-van der Waals forces and electrostatic forces can be ignored. This theory describes the time rate of change of the film profile, given only the drop radius and the required physical properties. Predictions are compared with profiles measured by Platikanov (1964) for gas bubbles. It is concluded that, even with only a trace of surfactant present, the liquid-gas interface may be nearly immobile (tangential components of velocity are zero) and the surface viscosities will have little effect upon the drainage rate.

Abstract: The conditions are examined under which a single bubble and a number of bubbles are in equilibrium within a closed volume of liquid that is maintained at constant temperature and pressure. It is predicted that depending on the amount of gas present in the volume, there may be no equilibrium state for the bubble or bubbles, one equilibrium size, or two possible equilibrium sizes. In the latter case, it is also predicted that the equilibrium state corresponding to the larger bubble size is a stable equilibrium state. This is in contrast to the case of an unbounded volume of liquid where there is the possibility of only one equilibrium state for a bubble, and this state is unstable. The predicted stability for a bubble in a closed volume was examined experimentally, and agreement was found between the measurement and the prediction. A striking result is the reduction in the stable equilibrium size with the number of bubbles present. In particular, micron‐sized bubbles can be shown to be in stable equilibrium under the constraint of a closed volume, and for reasonable conditions of liquid temperature and pressure.

Abstract: The statistical rate theory approach is used to derive the expression for the rate of gas absorption by a liquid. This process involves two sequential rates−the rate of transport from the gas to the surface and the rate of transport from the surface to the bulk liquid. According to the statistical rate theory, the rate limiting step is the rate of transport from the surface. After deriving the rate expression for the rate limiting step, it is incorporated in an integral equation approach for predicting the rate of evolution of a bubble evolving isothermally in a liquid–gas solution. This approach accounts for the movement of the bubble boundary in the diffusion problem. Statistical rate theory leads to a complete expression for the rate of gas absorption; thus by comparing the predicted rate of bubble evolution with a set of measurements, one can investigate the validity of the statistical rate theory. This comparison is carried out and the predictions are found to be in close agreement with the experiments throughout the experimental period.

Abstract: Processes of bubble formation and spreading in breaking wind waves are experimentally investigated in a wind-wave tank. The distribution and movement of bubbles relative to the wave form are measured using photographic techniques. The main mechanism of bubble formation in these waves is intermittent bubble entrainment by an ordered convergent flow on the leading slope near the crest. This conclusion is supported by a simple experiment for modeling the bubble entrainment, where a small jet of water is injected into water whose surface is at rest: bubbles are entrained by the water jet. In the oceans, the mechanism under consideration will be important in understanding the breaking process of smaller scale waves superposed on dominant waves. A model experiment also shows that the existence of a stagnation point on a water surface (convergent flow) is not a sufficient condition for bubble entrainment. The downward force of the convergent flow must be greater than the restoring force of the surface tension at the stagnation point for bubble entrainment to occur. DOI: 10.1111/j.2153-3490.1982.tb01836.x

Abstract: When a small drop or bubble approaches a fluid–fluid interface, a thin liquid film forms between them, drains, until an instability forms and coalescence occurs. A hydrodynamic theory is developed for the first portion of this coalescence process: the drainage of the thin liquid film while it is still sufficiently thick that the effects of London-van der Waals forces and electrostatic forces can be ignored. The time rate of change of the film profile is predicted, given only the drop radius and the required physical properties. Comparisons are offered with the limited experimental data available.

Abstract: Mixtures of propane and air have been used to fluidise a bed of silica sand at atmospheric pressure. Both the ignition and combustion of these gas mixtures have been studied in this situation. It is noteworthy that high temperatures (ca. 800°C) have to be reached before bubbles of propane and air ignite within the bed. The indications are that combustion occurs only in the bubble phase and not to any significant extent in the particulate phase. Moreover, it appears that a bubble of fuel and air has to reach a critical size (about 30 mm, depending on bed conditions) before it ignites. This is because ignition is controlled by a balance between near-isothermal chain branching and rapid removal of radicals from a bubble by gas circulating to the surrounding sand particles where radical recombination occurs. Analysis of the size of bubbles igniting at various temperatures indicates an activation energy for the chain branching step of around 254 kJ/mol. In addition, a correlation due to Darton appears preferable to an alternative one for predicting the sizes of gas bubbles in hot fluidised beds.

Abstract: Results are presented on the discovery of plasma bubble domains (PBD’s), which occur as regular patterns of localized glow discharges formed under ac excitation in an atmospheric pressure inert gas based mixture confined between large‐area, closely spaced, plane‐parallel, dielectric‐covered electrodes. These plasma bubble domains have many characteristics analogous to those of magnetic bubble domains (MBD’s): (1) Changing the applied field changes the size and the shape of the domain that forms (bubble, stripe, etc.). (2) There is a range of applied fields over which a bubble domain exhibits a corresponding range of stable diameters. (3) Bubble domains are bistable. Whereas MBD’s are used in computer memory devices, PBD’s are most likely to be used in computer display devices. ials; electrodes; surface coatings; electric fields; configuration;

Abstract: A theoretical study was carried out to achieve a better understanding of the oscillatory behavior of a gas bubble growing (or collapsing) in a viscoelastic liquid, by taking into account both the hydrodynamic and diffusion effects. The Zaremba-DeWitt model was chosen to represent the rheological properties of the suspending medium. The finite difference method was employed to solve the governing system equations. The computational results show that, in the case of very fast diffusion (i.e., constant bubble pressure), the oscillatory behavior of a bubble takes place only when the ratio of the initial pressure difference between the gas bubble and the liquid phase to the elastic modulus of the suspending medium is below a certain critical value. On the other hand, in the case of very slow diffusion, the oscillatory behavior of a bubble persists, regardless of the magnitude of the rheological properties of the suspending medium. Our study indicates further that the diffusivity of a gas has a profound influence on the occurrence of oscillatory behavior, that the elastic property of the suspending medium enhances oscillatory behavior while its viscosity plays the opposite role, and that even a Newtonian medium can give rise to an oscillatory pattern of bubble growth (or collapse), although it dampens out very quickly.

Abstract: Possibly the first practical application of the pronounced atI Air bubbles in water increase the compressibility several tenuating -property of-air bubbl& in water was one proposed and orders of magnitude above that in bubble-free water, thereby greatly reducing the velocity and increasing attenuation of acoustic waves. The effect of air bubbles in water on acoustic wave propagation was studied extensively during World War II as part of an overall effort to apply underwater sound in submarine warfare. Currently, air bubble curtains are used to prevent damage of submerged structures (e.g., dams) by shock waves from submarine explosives. Also, air-bubble curtains are used to reduce damage to waterfilled tanks in which metals are formed by explosives. Since World War II, research has progressed less feverishly in government and university laboratories. Published results of laboratory experiments generally confirm theoretical velocity and attenuation functions and demonstrate that these quantities are dependent principally upon frequency, bubble size, and fractional volume of air. Below the bubble resonant frequency and in the frequency range of marine energy sources, acoustic wave velocity is essentially independent of frequency and bubble radius, being well below the velocity in bubble-free water. In this frequency range, attenuation increases with increasing frequency, decreasing bubble radius, and increasing fractional air volume.

Abstract: Several aspects of small-amplitude oscillations of bubbles containing gas, vapor, or a gas-vapor mixture are discussed. An application to pressure-wave propagation in a bubbly liquid is described. Nonlinear forced oscillations are considered in the light of recent research on forced oscillations of nonlinear systems. The growth of vapor bubbles, an extension of the Rayleigh-Plesset equation to non-Newtonian liquids and appreciable mass transfer at the interface, and a boundary integral numerical method for non-spherical cavitation bubble dynamics are also briefly discussed.

Abstract: Bubble size distributions in a bubble column of 200 mm diameter were measured by means of a photoelectric probe. The gas-liquid dispersion was generated by distributing air with a porous plate into aqueous solutions of electrolytes and of organic compounds (alcohols, glycols, ketones, carboxylic acids, saccharose, carboxymethyl-cellulose, detergents). For all these solutes there exists a rather narrow concentration range in which the change from quick coalescence in pure water to coalescence suppression takes place. Though rough relationships between concentrations for coalescence suppression and molecular properties can be found (ionic strength for electrolytes, number of carbon atoms in a homologous series of organic compounds), exact equations based on a theory of coalescence cannot be given. The bubble size distributions obtained in the experiments have also been used to show the impact of coalescence phenomena on gas-liquid mass transfer. For this purpose, surface areas were calculated from measured ...

Abstract: When a small drop or bubble approaches a solid surface, a thin liquid film forms between them, drains, until an instability forms and coalescence occurs. Lin and Slattery (1982a) developed a hydrodynamic theory for the first portion of this coalescence process: the drainage of the thin liquid film while it is sufficiently thick that the effects of London-van der Waals forces and electrostatic forces can be ignored. Here the effects of the London-van der Waals forces are included. The resulting theory describes the evolution of the film profile, given only the bubble radius and the required physical properties. The inclusion of a positive disjoining pressure results in better descriptions of the film profiles measured by Platikanov (1964) for air bubbles pressed against glass plates. When the disjoining pressure is negative, an unstable draining film evolves and finally ruptures. Unfortunately, there are no experimental data with which to compare our predicted coalescence times.

Abstract: Evidence is reviewed, from theory and experiment, that biological systems can be affected by ultrasound at low levels, if resonant gas bodies are present. In a suspension of cells or other particles a pulsating gas bubble causes the particles to migrate toward its surface via radiation force. This motion, in addition to acoustic micro-streaming, transports particles into the bubble near-field where they are subjected to highly localized stress fields. In plant leaves containing gas-filled channels, the ultrasonic intensity required to produce cell death varies with frequency, showing minima in ranges corresponding roughly to calculated frequencies for resonance of the channels.

Abstract: Cavitation bubble dynamics is investigated by the method of ‘optic cavitation’, i.e. the formation of single cavities in liquids by light. From the sound waves radiated upon collapse the pressure-time curve is obtained. Maximum bubble size and shock wave amplitudes are evaluated and an energy balance is considered. Numerical calculations with a modified Gilmore model taking into account the mass loss of the cavity can explain the rapid damping of the bubble oscillation observed in the experiments.

Abstract: This paper reviews recent progress in the theories of the surface boundary conditions of adsorbed solutes in liquids, and of the effects of those solutes on the steady motion of a bubble or drop in the liquid. Both singular perturbation theory and numerical solutions have useful roles in this problem, and their relationship is explored. In addition, analytical solutions are given to two problems concerning a spherical bubble rising steadily at low Reynolds number in a viscous fluid. One of these is displacement of the internal vortex centre from its position in the absence of surface activity when there is a small stagnant cap of surfactant at the rear. The results agree with experimental data in the direction of that displacement but give only about half its amount. The other problem is the velocity perturbation all round the surface caused by a very dilute solution of a weak surfactant at high Peclet number. This compares quite well with the numerical solution for a Peclet number of 60, having relative errors of order (60)−1/2 as would be expected.

Abstract: Shock wave propagation in glycerin with 70% Ar+30% (2H 2 +O 2 ) bubbles and associated bubble behaviors were observed in a vertical shock tube where the pressure ratio between the high and low pressure sections was p 4 /p 1 =15. It was found that once a bubble explosion started in the glycerin, it continued propagating, the amplitude and the propagation velocity of the shock wave increased, and the pressure profile changed significantly. On the other hand, there was a limit of such a chain bubble explosion, depending on the initial bubble radius, shock strength, interbubble distance, and exothermicity. These results imply the existence of bubble detonation. A theoretical calculation of bubble dynamics containing realistic oxyhydrogen reaction kinetics was performed, and showed agreement with the observed results. Finally, a phenomenological model of bubble detonation was introduced to explain the mechanism of propagation. This theory leads to a qualitative interpretation of the measured velocity.

Abstract: Optical information recording and storage is investigated in hydrogenated amorphous semiconductor films. The recording mechanisms are based on the evolution of hydrogen within the active layer. Three different processes are observed: (1) bulge (or bubble) formation, (2) spongelike microswelling, and (3) ablation without melting.