Abstract: Single bubble rise characteristics wake structure wake instability - formation and shedding wake sizes wake solids concentration wake flow and pressure wake effects in various flow systems wake effects on mass and heat transfer and chemical reactions.

Abstract: The impact of a drop on the plane surface of the same liquid is studied numerically. The accuracy of the calculation is substantiated by its good agreement with available experimental data. An attempt is made to explain the recent observation that, in a restricted range of drop radii and impact velocities, small air bubbles remain entrained in the liquid. The implications of this process for the underwater sound due to rain are considered. The numerical approach consists of a new formulation of the boundary-element method which is explained in detail. Techniques to stabilize the calculation in the presence of strong surface-tension effects are also described.

Abstract: We show that when freely suspended hybridoma cells are cultured in an agitated bioreactor, two fluid-mechanical mechanisms can cause cell damage and growth retardation. The first is present only when there is a gas phase, and is associated with vortex formation accompanied by bubble entrainment and breakup. In the absence of a vortex and bubble entrainment, cells can be damaged only at very high agitation rates, above approximately 700 rpm, by stresses in the bulk turbulent liquid. Cell damage then correlates with Kolmogorov eddy sizes similar to or smaller than the cell size. In the absence of a vortex, the entrainment and motion of very fine bubbles cause no growth retardation even at agitation rates as high as 600 rpm.

Abstract: A detailed physical model of the life history of a typical bubble plume, from its formation by a breaking wave to its dissipation into the background bubble population, is given, and the relationship between the early, acoustically relevant stages in bubble-plume development and the associated, remotely detectable whitecap is described. The manner in which the fraction of the sea surface covered by stage A spilling crests and by stage B mature whitecaps depends upon wind speed and upon wind stress or friction velocity is investigated. Formal expressions are given whereby near-surface bubble concentrations can be estimated from observations of fractional whitecap coverage or from measurements of the 10-m elevation wind speed. >

Abstract: A general model for the design and scale-up of bubble columns and airlift loop reactors requires the exact prediction of their flow structure. The deterministic and stochastic components of the liquid flow in these gas-liquid contactors have therefore been measured. With the aid of a newly developed measuring technique, the hot-film anemometry with triple split probes, the local mean velocities, the turbulence intensities and, for the first time in bubble-column reactors, Reynolds shear stresses were determined. On the basis of a large amount of experimental data, a hydrodynamic model for the radial profile of the mean axial liquid velocity and an empiricial correlation for the prediction of the turbulence intensities have been developed. The hydrodynamic model and the correlation are valid for various reactor geometries, gas an liquid flow rates, and various properties of the liquid

Abstract: The late nonlinear and chaotic stage of Rayleigh–Taylor instability is characterized by the evolution of bubbles of the light fluid and spikes of the heavy fluid, each penetrating into the other phase. This paper is focused on the numerical study of bubble interactions and their effect on the statistical behavior and evolution of the bubble envelope. Compressible fluids described by the two‐fluid Euler equations are considered and the front tracking method for numerical simulation of these equations is used. Two major phenomena are studied. One is the dynamics of the bubbles in a chaotic environment and the interaction among neighboring bubbles. Another one is the acceleration of the overall bubble envelope, which is a statistical consequence of the interactions of bubbles. The main result is a consistent analysis, at least in the approximately incompressible case of these two phenomena. The consistency encompasses the analysis of experiments, numerical simulation, simple theoretical models, and variation of parameters. Numerical simulation results that are in quantitative agreement with laboratory experiment for one‐and‐one‐half (1 (1)/(2) ) generations of bubble merger are presented. To the authors’ knowledge, computations of this accuracy have not previously been obtained.

Abstract: A method of forming a polymer dispersed liquid crystal (PDLC) film is disclosed which consists of forming a solution of LC dissolved in a monomer, photopolymerizing the solution to form a film having a dispersion of LC bubbles therein, establishing a correlation between the LC bubble size and selected characteristics of the film, selecting a LC bubble size corresponding to desired film characteristics, and controlling the conditions of photopolymerization to achieve said LC bubble size. The LC bubble size is controlled by means of the UV exposure intensity, exposure temperature, exposure wavelength, LC concentration and/or concentration of polymerization initiator. Correlations are noted between LC bubble size and the resulting film's threshold and operating voltages for optical transmission, contrast ratio, absolute transmissivity and electro-optical response times. Special types of films, including in situ gratings and holograms, are obtained by periodically varying the conditions of polymerization over the film to produce a corresponding periodic spatial variation in the LC bubble size; different processes used to achieve this result are noted. Films with LC bubbles in a new size regime that significantly decreases the operating voltage threshold, and with gradients in the bubble size, are also disclosed.

Abstract: Foam fractionation of bovine serum albumin (BSA) was studied as a model system for potato wastewater The effects of feed concentration, superficial gas velocity, feed flow rate, bubble size, pH, and ionic strength on the enrichment and recovery of BSA were investigated in a single-stage continuous foam fractionation column Enrichments ranged from 15 to 60 and recoveries from 5 to 85% The feed concentrations were varied from 001 to 02 wt %, and enrichments were found to increase with lower feed concentrations Enrichments also increased with lower superficial gas velocities and larger bubble sizes At sufficiently low feed flow rates, enrichment was found to increase with an increase in the flow rate, eventually becoming insensitive to the feed flow rate at higher values The pH was varied from 35 to 70 and ionic strength from 0001M to 02M The effects of pH and ionic strength were found to be coupled with bubble size A minimum bubble size was found at pH 48, the isoelectric point of BSA, resulting in a minimum in the enrichment Bubble size, and thus enrichment, was found to increase as the ionic strength decreased from 02M to 001M Previous models(1,2) for the hydrodynamics of foam column were extended for a singlestage continuous foam fractionation column for the prediction of enrichment and recovery The model assumed adsorption equilibrium, infinite surface viscosity, and bubbles of the same size Though coalescence was formally accounted for in the model by considering bubble size as a function of foam height, calculations for the experimental runs were performed only for the case of no coalescence Quantitative predictions of enrichment and recovery could not be made with a single representative bubble size because of the broad inlet bubble size distribution as well as broadening of the distribution as a result of coalescence The experimental enrichments were higher and recoveries were lower than the model predictions, the discrepancy being more pronounced at lower feed concentrations because of increased coalescence The higher enrichments are due to the predominant effect of internal reflux as a result of coalescence whereas the lower recoveries are a result of detrimental effects of broadening bubble size distributions

Abstract: Laser light scattering, with the aid of Mie's scattering theory, was used to investigate bubble nucleation in concentrated polymer solutions. Solutions with 40, 50 and 60 wt % polystyrene in toluene were used. A test solution in a high-pressure optical cell made of strain-free quartz was heated to a predetermined temperature under pressure. Upon release of the pressure in the cell, both scattered and transmitted light fluxes were measured with photomultipliers, and the variation of system pressure with time was measured using a piezoelectric pressure transducer. The measurement of the light scattering flux and control of the experiment were performed by means of a microcomputer with a general-purpose data acquisition interface. Data reduction was done using the same microcomputer. The critical bubble size was determined by obtaining a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. While the Mie scattering theory is for monodisperse particles, the experimental scattering curves indicated that the bubbles had a distribution of sizes. Therefore, the log-normal distribution function was used to represent the size distribution; and theoretical scattering curves were computed by varying the breadth parameter in the log-normal distribution function, until we had a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. In this way, we were able to determine (a) the size distribution of bubbles in the optical cell, (b) the critical bubble size, (c) the total number of bubbles nucleated, and (d) the critical pressure for bubble nucleation, as functions of temperature, the initial equilibrium pressure in the optical cell, and the concentration of the polymer solution.

Abstract: An experimental investigation was conducted to measure the reverse flow within the transitional separation bubble that forms on an airfoil at low Reynolds numbers. Measurements were used to determine the effect of the reverse flow on integrated boundary-layer parameters often used to model the bubble. Velocity profile data were obtained on an NACA 663-018 airfoil at angle of attack of 12 deg and a chord Reynolds number of 140,000 using laser Doppler and single-sensor hot-wire anemometry. A new correlation is proposed based on zero velocity position, since the Schmidt (1986) correlations fail in the turbulent portion of the bubble.

Abstract: Various forms of plumes have been identified following the injection of air at different rates through a porous plug into water contained in a ladle-shaped vessel. Discrete bubbles form at the plug and rise uniformly through the column of liquid at gas flow rates up to 14 cm3/s cm2 of plug surface; at higher flow rates, groups of bubbles increasingly coalesce into larger gas pockets, and beyond about 40 cm3/s cm2, the gas globes are large enough to cover the entire plug surface before detachment and gradual disintegration as they rise through the body of liquid. The gas fraction, as well as bubble frequency, bubble velocity, and bubble size, have been measured in the various dispersion regimes by means of an electroresistivity probe. The radial distributions of gas fraction and bubble frequency are approximately bell-shaped about the axis of flow, and the reduced values are close to Gaussian functions of the reduced radial distance from the axis. The gas fraction along the axis has been correlated to the reduced height of the plume; it increases with decreasing distance above the plug and with increasing gas flow rate. The axial bubble frequency shows a decrease in the vicinity of the plug with the onset of bubble coalescence, but the values of the frequencies at all gas injection rates converge to about 12 s−1 toward the surface of the bath. The mean bubble velocity increases with increasing flow rate but drops once coalescence is fully established. Conversely, there is a sudden increase in the mean bubble diameter with the onset of coalescence. The axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime. The axial flow which is upward in the vicinity of the plume decreases in magnitude with increasing radial distance, ultimately reversing to an in-creasing downward flow beyond a certain distance from the plug axis. Similarly, the radial flow which is outward from the plume near the liquid surface decreases steadily with depth and eventually reverses to an inward flow at a depth independent of the gas injection rate. The profiles of the axial velocities are almost sigmoidal, except in the coalescence regime, where the effect of turbulence is profound at the upper liquid layers. The radial liquid velocities are generally small relative to the axial components, only about one-fifth as large, considering the maximum average values.

Abstract: In this paper we consider a uniform gas bubble-liquid mixture rising under buoyancy When the gas volume flux is decreased, while keeping bubble size constant, a smooth transition is formed between the region of lower concentration by volume and the region of initial concentration This transition travels through the mixture as a permanent wave We start by discussing the mechanisms which make possible such a permanent wave The first is its tendency to steepen at the low concentration side At the root of this is the decrease of the uniform rise velocity, under buoyancy, with increasing concentration Associated with the motion of the bubbles is the liquid impulse It is shown that this increases with increasing concentration, producing a reactive force on the bubbles which counteracts buoyancy and reduces the force available to overcome friction In the transition a balance between these two effects occurs The internal structure following from this balance is analysed in detail and it is shown that under certain conditions all its properties can be derived from knowledge of the average rise velocities of bubbles in uniform mixtures as a function of concentration Measurements on these are reported subsequently, followed by a discussion of our experiments on transitions of the kind mentioned in which velocity, thickness etc of the waves have been measured The data are compared with the results of the analysis Order-of-magnitude agreement is found but there are differences as well, requiring further research

Abstract: In this paper, we report new results of an experimental study concerning the motion and coalescense of bubbles in viscoelastic polymer solutions. In particular, the shapes and velocity-volume characteristics of air nitrogen and carbon dioxide bubbles have been examined in solutions of polyacrylamide in 50/50 glycerine/water mixtures under a wide range of conditions. Furthermore, the possible effects of surface-active agents and of the aging characteristics of polymer solutions were also explored. Under no conditions did we observe an abrupt discontinuity in bubble velocity-volume data, and the fluid viscoelasticity is known to exert a significant influence in governing the shapes of bubbles moving in viscoelastic media. Finally, the coalescence of two bubbles simultaneously released from different orifices was studied in terms of the volume of one bubble required to achieve coalescence with a second bubble of fixed volume at predetermined heights above the orifices. Coalescence was studied with different polymer solutions for air, N 2 and CO 2 for a range of (initial) orifice separations. It is shown that the fluid viscoelasticity influences the coalescence via the shapes and wake characteristics of bubbles.

Abstract: The surface bubble spectral density of newly created bubbles has been measured under spilling breakers in a laboratory facility. This has been accomplished acoustically by passively identifying the radius, position, and time of creation of several hundred individual bubbles as their shock‐excited pulsations radiate damped spherical waves of sound. The measured bubble spectrum ranges from radius 50 μm to 7.4 mm with a peak of 6 bubbles per square meter in a 1‐μs‐radius increment at radius 150 μs. The rate of bubble production has an exponential fall‐off with time and 97% of the bubbles are produced in the first 500 ms after the breaker passes. The results supplement recent ocean data for low sea states.

Abstract: The mechanism of Er:YAG laser-induced long-range damage in intraocular surgery was investigated using high-speed photography. A short pulse of 2.94-microns radiation delivered by an optical fiber into an aqueous medium causes rapid localized heating and vaporization and creates a bubble at the tip of the fiber. The size of the bubble depends on the pulse energy and is about 1 mm at 1 mJ. The shape of the bubble has multiple lobes, which can be attributed to the spiky output of the laser pulse. The expanding bubble can cause thermal and mechanical damage to tissues. In addition, laser spikes propagating through the bubble can strike and damage tissue on the distal side of the bubble. In both mechanisms the damage zone approximates the bubble size and can be greater than 1 mm, ie, 1000 times the steady-state absorption length of water at 2.94 microns. The authors discuss ways to reduce the damage zone by bubble confinement.

Abstract: The electrical conduction of purified nonpolar liquids with point-plane electrode geometry was studied as a function of various parameters. For negative polarity of the point, a pulse regime has been observed which bears a great similarity to the TRICHEL pulses occurring in air, with the exception of a lack of pressure dependence. At atmospheric pressure, bubble formation was correlated with current pulse. The generation and dynamics of the bubble are studied as a function of various parameters: injected energy, hydrostatic pressure (up to 12 MPa), and the nature of the liquid (cyclohexane, n-pentane, n-decane, iso-octane, and tetramethylsilane). >

Abstract: Transient wave phenomena in two‐phase mixtures with a liquid as the matrix and gas bubbles as the dispersed phase have been studied in a shock tube using glycerine as the liquid and He, N2, and SF6 as gases having a large variation in the ratio of specific heats and the thermal diffusivity. Two different sizes of bubble radii have been produced , R0=1.15 and 1.6 mm, with a dispersion in size of less than 5%. The void fraction was varied over one order of magnitude, φ0=0.2%–2%. The measured pressure profiles were averaged by superimposing many shots, typically 20. Speeds and profiles were measured for shock waves and for wave packets. Investigation of the wave structure allows one to approach the fundamental question of how the physics on the level of the microstructure influences the behavior on the macroscale. In the theoretical work, modeling on the basis of a hierarchy of characteristic length scales is developed. Bubble interactions, transient heat transfer, and dissipation due to molecular and bulk v...

Abstract: A new theory to predict liquid circulation was derived and compared with applicable literature data. A single dimensionless group, e(gRd2/v2c), is shown to control mixing intensity under low-viscosity conditions, but two separate groups (e and gRd2/v2c) are necessary for viscous systems. Closure was accomplished using the Prandtl model for Reynolds stress. Locally varying mixing length was taken to be proportional to bubble size and bubble concentration. The model was constructed based on the premise that two distinct zones exist: a mainly turbulent core joined to a thin viscous wall layer.