Showing papers on "Bubble published in 1983"
TL;DR: In this paper, the cross-correlations between surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the separation bubble formed along the sides of a blunt flat plate with right-angled corners.
Abstract: Flow in the separation bubble formed along the sides of a blunt flat plate with right-angled corners has been studied in terms of extensive single- and two-point measurements of velocity and surface-pressure fluctuations. The cross-correlations between the surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the bubble. Large-scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xR, where U∞ is the approaching velocity and xR is the time-mean length of the bubble. On top of this regular vortex shedding, there exists a large-scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large-scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross-correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7–0.8) xR and their convection velocity is about 0.5U∞ near the reattachment line. The cross-correlations also suggest the existence of a longitudinal counter-rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.
491 citations
TL;DR: In this article, a theoretical model is developed to compute the contribution of bubbles to gas exchange in a wind-water tunnel filled with fresh water or seawater, and the transfer velocity kB is shown to be independent of the concentration gradient.
Abstract: Gas exchange experiments have been performed in a wind-water tunnel filled with fresh water or seawater. Transfer velocities have been measured for nitrous oxide and argon in a range of wind speeds extending from 3 m/s to 14 m/s. The air-liquid interface was covered either with only normally developed wind waves or with mechanically generated waves in addition. For u 9 m/s), a jump of the values of kL up to a factor of 3 is observed first for Ar and then for N2O, the ratio kL Ar/kL being highly variable. This observation is interpreted as being the result of the onset of breaking waves which create bubbles through which mass transfer takes place. No difference for gas exchange either in fresh water or in seawater has been identified from the whole set of experiments. A theoretical model is developed to compute the contribution of bubbles to gas exchange. The transport equations, derived for a single bubble, take into account the diffusive mass flux exchanged between the bubble and the liquid, the hydrodynamic pressure, and the presence of two gaseous components inside the bubble. The equations used to represent the dynamics take care of the orbital motion of water associated with waves. A relation to link sources and spectra of bubble populations is derived. Numerical values for spectral parameters are taken from the literature. It is found that the results of experiments run at 9 m/s and 10 m/s are well explained for N2O and for Ar. A unique distribution of bubbles explains the excess of gas transfer associated with the presence of breaking waves. In a further step the theoretical treatment is extended to compute the transfer velocity kB for gas exchange through bubbles as a function of the concentration gradient in atmosphere and water for three gases, helium, argon, and nitrous oxide. It is shown that in wind tunnel conditions, kB is independent of the concentration gradient. This does not hold at the atmosphere-ocean interface. The transfer velocity kB is highly dependent on the gas concentrations in air and water when they are close to solubility equilibrium. It is demonstrated that equilibrium must occur at the ocean surface for supersaturation conditions. The higher saturation anomalies and the larger transfer velocities are computed for the less soluble gas. This conclusion is in good agreement with observations made at sea.
226 citations
TL;DR: In this paper, the effect of physical properties of the fluid (surface tension, ionic strength, liquid viscosity) and that of the non-Newtonian behavior on mixing time was studied.
150 citations
TL;DR: Bubble departure diameters have been correlated for water over a wide range of pressures and the averaged deviation of the experimental data from the proposed correlation is approximately ±33% and is typical of most boiling correlations as discussed by the authors.
135 citations
TL;DR: The determination of foam bubble size by planimetric measurement of the area of the contact face a the glass wall of a column containing essentially homogeneous new foam yielded excellent agreement with the bubble size as known a priori as mentioned in this paper.
Abstract: The determination of foam bubble size by planimetric measurement of the area of the contact face a the glass wall of a column containing essentially homogeneous new foam yielded excellent agreement with the bubble size as known a priori. Furthermore, the said determination proved to be more reliable than measurement based on either the longest chord or the commonly employed longest median of the contact face. However, for highly heterogeneous new foam, all three measures of foam bubble size underestimated the true mean. Apparently, small bubbles wedge large bubbles away from the wall. The effects are presented quantitatively, along with correlations for their approximate prediction.
133 citations
TL;DR: In this article, a model for premature intergranular fracture of metals in creep tests during He injection and after room temperature He implantation is critically assessed, and the differences in the stress and temperature dependences of the lifetimes observed in the two cases are attributed to differences in bubble nucleation and growth kinetics.
122 citations
TL;DR: In this paper, an analytical model of vapor-bubble growth was applied to enhance understanding of the flash-injection process and calculated time scales for bubble growth and delay times were found to be consistent with the above two flashing regimes at both low and high fuel preheat temperatures.
Abstract: Flash-boiling fuel injection is obtained by preheating liquid fuel within the injector so that the sudden decrease of pressure during injection causes rapid boiling of the fuel. Rapid expansion of the vapor phase may then atomize the liquid jet. Two distinct types of flash atomization were observed experimentally. First, at relatively low fuel temperatures the liquid jet remains intact for a short period after leaving the nozzle, then suddenly breaks up when rapid bubble growth begins. Second, at higher fuel temperatures, flash boiling within the injector orifice produces an underexpanded, compressible, two-phase flow. Sudden expansion immediately upon leaving the orifice yields large spray cone angles. An analytical model of vapor-bubble growth was applied to enhance understanding of the flash-injection process. Calculated time scales for bubble growth and delay times were found to be consistent with the above two flashing regimes at both low and high fuel preheat temperatures. Also an unfavorable trend toward suppressed bubble growth with increasing injection pressure was calculated.
117 citations
TL;DR: In this article, gas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schugerl et al. are presented.
Abstract: Gas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schugerl et al. (1977) are presented. Data for cocurrent and batch systems are qualitatively explained using Zuber and Findlay's theory (1965) and bubble structure, and quantified further using a dynamic gas disengagement technique. Unified empirical correlations for the gas holdup and axial dispersion coefficients are presented.
103 citations
TL;DR: In this article, a two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume.
Abstract: The phenomena of the bubble formation from an orifice submerged in a liquid is classified according to their formation mechanisms and the estimation expressions of the bubble volume are reviewed The revised two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume. Effects of some factors on the bubble volume, such as, gas chamber volume, orifice diameter, physical properties of gas and velocity of surrounding liquid are discussed
102 citations
TL;DR: In this paper, a single spark-generated bubble near a solid wall and the mechanism of its induced impact pressure generation were investigated by changing L/?max from 0.14 to 17.1, where L is the distance between the electrodes and the solid wall, and /?max a maximum bubble radius.
Abstract: This paper deals with a detailed experimental investigation on the collapse of a single spark-generated bubble near a solid wall and the mechanism of its induced impact pressure generation. By changing L//?max from 0.14 to 17.1, where L is the distance between the electrodes and the solid wall and /?max a maximum bubble radius, the collapse of the bubble was observed with an Ima-Con high speed camera and, simultaneously, the induced impact wall pressure was measured. Consequently, the induced impact wall pressure history revealed that three types of the bubble collapse modes exist depending on L//?max; i.e., the region where a shock wave is dominant to the impact wall pressure at L//?max 1.5, a liquid jet at 0.6
98 citations
TL;DR: Theoretical approaches to the solution of the motion of the radius of the bubble normally involve the polytropic exponent of the gas as discussed by the authors, which is the exponent of a gas bubble that is driven into oscillation within a liquid pulsate with amplitudes that are determined largely by the thermodynamic behavior of gas contained within the bubble.
Abstract: Gas bubbles that are driven into oscillation within a liquid pulsate with amplitudes that are determined largely by the thermodynamic behavior of the gas contained within the bubble. Theoretical approaches to the solution of the motion of the radius of the bubble normally involve the polytropic exponent of the gas. Measurements are presented of this exponent for three different gases and for a wide range of values of the exponent. Comparison with available theories indicates good agreeement between measurements and predictions provided the gas bubble is not driven near one of its harmonic resonances.
TL;DR: In this paper, the effects of free-stream turbulence on a separation bubble formed along a side of a blunt plate with right-angled corners are studied and the surface pressure is estimated in terms of the longitudinal gradient of the time-mean pressure and the length scale of vortices in the reattaching zone.
TL;DR: In this paper, the motion of two bubbles along their line of centers in an imposed thermal gradient is considered, and the governing equations are solved in the quasistatic limit using bipolar coordinates.
TL;DR: In this article, the authors used a batch flotation cell to determine the bubble size distributions and flotation rates as a function of air flow rate and frother concentration using a specially designed batch-flotation cell, which allowed the unambiguous determination of the flotation rate from the slurry to the froth.
TL;DR: In this article, the pulsation amplitude of an individual air bubble that is levitated in a glycerine-water mixture by a stationary acoustic wave operating at a frequency of 22.2 kHz was measured.
Abstract: Measurements are presented in this paper of the pulsation amplitude of an individual air bubble that is levitated in a glycerine–water mixture by a stationary acoustic wave operating at a frequency of 22.2 kHz. Observations of the bubble pulsation for a wide range of bubble sizes demonstrate the existence of the n=2 harmonic resonance (ω≊ω0/2). The available theoretical information on linear and nonlinear bubble oscillations is adapted to apply to the specific experimental conditions. Comparisons made with the theory show excellent agreement between measurements and predictions.
TL;DR: Bubble dynamics for saturated nucleate boiling of water on an electrically heated platinum wire at atmospheric pressure have been photographed using a high-speed movie camera as mentioned in this paper, and the average number density of active nucleation sites has been found to increase linearly with the boiling heat flux.
TL;DR: In this paper, the applicability of axial dispersion model (ADM) for the measurement of the gas-liquid mass transfer coefficient (kLa) in bubble columns is discussed.
Abstract: The applicability of axial dispersion model (ADM) for the measurement of the gas-liquid mass transfer coefficient (kLa) in bubble columns is discussed. It is shown that the misinterpretation of the concentration jump near the column inlet can lead to wrong conclusions regarding the mass transfer rates. It is further illustrated that some reported kLa dependencies on the superficial liquid velocity and the axial distance are resulted from the use of an incorrect model and can be rectified by an application of ADM. Finally, it is shown that ADM can be effectively used to calculate kLa a for: (a) highly viscous liquids, (b) in the presence of chemical reaction, (c) slurry reactors, and (d) the columns with different liquid inlet locations.
TL;DR: In this article, the authors measured liquid velocity profiles in a bubble column with the aid of a hot-film anemometer, and two different types of profiles were detected that were characterized by the formation of a boundary layer at the column wall.
Abstract: Liquid velocity profiles in a bubble column were measured with the aid of a hot-film anemometer. Two different types of profiles were detected that were characterized by the formation of a boundary layer at the column wall. Under slow flow conditions, the boundary layer is large and controls the liquid velocity profile, but in turbulent flow the boundary layer is very small and has no significant effect on the velocity profile. Microscopic and macroscopic balances were used to predict both the liquid velocity profile and the average liquid velocity. The effect of the liquid velocity profile and average velocity on axial dispersion and gas-hold-up are analyzed and design procedures are recommended.
TL;DR: In this article, the conditions under which heterogeneous bubble nucleation takes place in a conical pit in the boundary of a constant size volume containing a liquid-gas solution, and the size to which the nucleate bubble grows is predicted.
Abstract: The conditions are considered under which heterogeneous bubble nucleation takes place in a conical pit in the boundary of a constant size volume containing a liquid–gas solution, and the size to which the nucleate bubble grows is predicted. Four possible equilibrium states are found for the nucleate bubble: two unstable, one metastable, and one stable. The unstable state corresponding to the smallest equilibrium size is the one that acts as the threshold size that must be exceeded in the nucleation event. The metastable and second unstable state are encountered as the nucleate bubble emerges from the conical pit and the stable state corresponds to the largest equilibrium size. It arises from the bubble being in a finite volume with fixed mass. The pressure produced in the volume by the growth of the bubble depends on the final state it attains (i.e., either the metastable or stable state). The theoretical expressions obtained from the analysis are applied to predict the conditions under which bubble nucleation and growth take place within a type of bone cell, and the results are used to explain certain types of damage to the bone of animals undergoing decompression from high pressures that have been previously reported in the literature. The expressions are also applied to predict the superheat necessary to produce bubble emergence from a conical pit and are shown to be in agreement with results previously reported.
TL;DR: In this article, the authors developed a tentative cold bed hydrodynamic model for an idealized fluidized bed gasifier and showed that the model can predict bubbles forming in the fluidized beds.
Abstract: During the past three years we have developed a tentative cold bed hydrodynamic model for an idealized fluidized bed gasifier. The computer program calculates the pressure, the void fraction and the velocities for a single size solid and for a gas. The fluid bed never reaches a steady slate, but continually oscillates, as bubbles form, rise through the bed and collapse on top of the bed. In this paper we show that the hydrodynamic model can predict bubbles forming in the fluidized bed. Photographically determined bubble sizes agree with the predicted bubble sizes. They increase with height of bed and with jet velocity. The model produces bubble splitting which agrees with observations at higher jet velocities.
TL;DR: In this article, a one-dimensional mechanistic model is developed to calculate the critical mass flux of an initially two-phase, saturated or subcooled fluid, which allows for thermal non-equilibrium vapor drift velocity and non-uniform bubble distribution.
TL;DR: In this article, the critical gas velocity required for complete suspension of solid particles has been studied experimentally in solid-suspended bubble columns with diameters of 0.1-0.3 m.
Abstract: The critical gas velocity required for complete suspension of solid particles has been studied experimentally in solid-suspended bubble columns. It was shown that the critical gas velocity increases with increasing terminal velocity of a single particle, column diameter and the density difference between solid and liquid, and decreases with increasing liquid viscosity and liquid surface tension. It was also shown that the critical gas velocity decreases when a conical bottom is used instead of a flat one. Based on these observations, an empirical correlation for critical gas velocity has been proposed that is applicable to columns with diameters of 0.1-0.3 m.
TL;DR: In this paper, the division of gas flow between the bubble and dense phases of fluidized beds of six different types of Group A powders was studied at pressures of up to 20 bar using surface collapse and X-ray absorption measurements.
TL;DR: In this article, gas holdup and axial heat dispersion coefficient measurements in the presence of an electrolyte solution were performed in order to investigate the effect of the electrolyte on the axial temperature.
Patent•
20 Jun 1983
TL;DR: In this paper, an apparatus and method for determining the size and velocity of particles, droplets, bubbles, or the like employing laser light scattering is disclosed and a laser generation means is provided for generating a pair of coherent laser beams.
Abstract: An apparatus and method for determining the size and velocity of particles, droplets, bubbles, or the like employing laser light scattering is disclosed. A laser generation means is provided for generating a pair of coherent laser beams. These beams are directed along an axis and are caused to cross the axis at an angle to establish a sample volume. A collection means for sensing the scattering caused by particles, droplets, bubbles or the like within the sample volume is provided. The collected scattered signals are directed onto photo-detectors which are coupled to a signal phase determining means for determining the phase of the scattered signals as the particle, droplet, bubble or the like passes through the sample volume. Sizing means are coupled to the signal phase determining means for determining the size of the particle, droplet, bubble or the like from phase changes and the scattered signal. The velocity of the particle, droplet, bubble or the like is determined using well known laser Doppler anemometry techniques. In addition, the present invention discloses a method to determine the direction of motion of a particle, droplet, bubble or the like passing through the sample volume.
TL;DR: In this article, the authors calculated the energies of the double layer forces between the particle and the bubble using data for the zeta potential of the mineral, the surface tension of the solutions and the surfactant adsorption density for the alumina-dodecylsulfonate system.
TL;DR: In this article, it was shown that bubble growth in nickel during 5 keV He+-implantation in the temperature range 200 K-600 K and dose range 5 × 1020He+/m2-1022He+ /m2 can fairly well be described by a loop-punching mechanism.
TL;DR: Etude experimentale du processus d'effondrement de la bulle et de la pression parietale induite par le choc as discussed by the authors, et.
Abstract: Etude experimentale du processus d'effondrement de la bulle et de la pression parietale induite par le choc
TL;DR: In this paper, the authors developed relationships for determining interfacial areas as a function of bubble coalescence and for predicting liquid-film-controlled mass transfer in deep seal bubble column reactors.
Abstract: Relationships are developed for determining interfacial areas as a function of bubble coalescence and for predicting liquid-film-controlled mass transfer in deep seal bubble column reactors. Interfacial area is inversely dependent on mean bubble size; the mass transfer constant is directly dependent on bubble size. A correction for enhancement due to liquid-phase reaction must be applied, and enhancement is shown to decrease with increasing bubble size.
Experimental measurements on the catalyzed rate of oxygen absorption from air in aqueous sodium sulfite solutions were made in a 0.299 m diameter × 9.14 m high glass column. Water and aqueous solutions of a surfactant and corn syrup were used to simulate ranges of surface tensions, densities, and viscosities. Perforated plates with 0.00635-m holes and 2.85% open area were inserted at 1.524-m spacing on half of the experimental runs to show the effects of gas redispersion. Two-phase flow velocities were adjusted to cover ranges of interest in full-scale, commercial bubble column reactor design.