scholarly journals Homogeneous swarm of high-Reynolds-number bubbles rising within a thin gap. Part 1. Bubble dynamics

2012 ◽  
Vol 704 ◽  
pp. 211-231 ◽  
Author(s):  
Emmanuella Bouche ◽  
Véronique Roig ◽  
Frédéric Risso ◽  
Anne-Marie Billet
Keyword(s):  
Bubble Dynamics ◽  
Volume Fraction ◽  
Vertical Direction ◽  
Wall Friction ◽  
Bubble Velocity ◽  
Velocity Statistics ◽  
Velocity Variance ◽  
Gas Volume Fraction ◽  
Gas Volume ◽  
Bubble Agitation

AbstractThe spatial distribution, the velocity statistics and the dispersion of the gas phase have been investigated experimentally in a homogeneous swarm of bubbles confined within a thin gap. In the considered flow regime, the bubbles rise on oscillatory paths while keeping a constant shape. They are followed by unstable wakes which are strongly attenuated due to wall friction. According to the direction that is considered, the physical mechanisms are totally different. In the vertical direction, the entrainment by the wakes controls the bubble agitation, causing the velocity variance and the dispersion coefficient to increase almost linearly with the gas volume fraction. In the horizontal direction, path oscillations are the major cause of bubble agitation, leading to a constant velocity variance. The horizontal dispersion, which is lower than that in the vertical direction, is again observed to increase almost linearly with the gas volume fraction. It is however not directly due to regular path oscillations, which are unable to generate a net deviation over a whole period, but results from bubble interactions which cause a loss of the bubble velocity time correlation.

scholarly journals Dynamics and mass transfer of rising bubbles in a homogenous swarm at large gas volume fraction

2014 ◽  
Vol 763 ◽  
pp. 254-285 ◽  
Author(s):  
Damien Colombet ◽  
Dominique Legendre ◽  
Frédéric Risso ◽  
Arnaud Cockx ◽  
Pascal Guiraud
Keyword(s):  
Mass Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Volume Fraction ◽  
Interfacial Area ◽  
Optical Probe ◽  
Bubble Velocity ◽  
Gas Volume Fraction ◽  
Bubble Rising ◽  
Gas Volume

AbstractThe present work focuses on the collective effect on both bubble dynamics and mass transfer in a dense homogeneous bubble swarm for gas volume fractions${\it\alpha}$up to 30 %. The experimental investigation is carried out with air bubbles rising in a square column filled with water. Bubble size and shape are determined by means of a high-speed camera equipped with a telecentric lens. Gas volume fraction and bubble velocity are measured by using a dual-tip optical probe. The combination of these two techniques allows us to determine the interfacial area between the gas and the liquid. The transfer of oxygen from the bubbles to the water is measured from the time evolution of the concentration of oxygen dissolved in water, which is obtained by means of the gassing-out method. Concerning the bubble dynamics, the average vertical velocity is observed to decrease with${\it\alpha}$in agreement with previous experimental and numerical investigations, while the bubble agitation turns out to be weakly dependent on ${\it\alpha}$. Concerning mass transfer, the Sherwood number is found to be very close to that of a single bubble rising at the same Reynolds number, provided the latter is based on the average vertical bubble velocity, which accounts for the effect of the gas volume fraction on the bubble rise velocity. This conclusion is valid for situations where the diffusion coefficient of the gas in the liquid is very low (high Péclet number) and the dissolved gas is well mixed at the scale of the bubble. It is understood by considering that the transfer occurs at the front part of the bubbles through a diffusion layer which is very thin compared with all flow length scales and where the flow remains similar to that of a single rising bubble.

scholarly journals Gas Distribution Law for the Fully Mechanized Top-Coal Caving Face in a Gassy Extra-Thick Coal Seam

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Wenlin Wang ◽  
Fangtian Wang ◽  
Bin Zhao ◽  
Gang Li
Keyword(s):  
Longwall Mining ◽  
Volume Fraction ◽  
Vertical Direction ◽  
Thick Coal Seam ◽  
Working Face ◽  
Coal Wall ◽  
The Face ◽  
Fraction Distribution ◽  
Gas Volume Fraction ◽  
Gas Volume

Mine gas overflow is a serious threat to the safe and efficient longwall mining of gassy coal seams. Based on the field mining conditions and gas extraction of the fully mechanized top-coal caving face of a gassy coal mine, the space volume fraction distribution and emission (extraction rate) of gas in the face were tested by an arrangement of measuring points in the stereo grid. The isograms of gas volume fraction distribution for each measurement section and air direction in the face are drawn. The research shows that each measurement section gas volume fraction distribution is presented for an asymmetric concave curve along the vertical direction of the coal wall in the air-inlet side and the air-return side of the face; on the working face air-return side, the determination of gas volume fraction distribution of the section appears as falling straight line along the vertical direction of the coal wall. Before the first weighting, the absolute quantity of gas emission in the working face increased with the advancing of the working face, reached the maximum at the time of the first weighting, and then remained stable.

Stability Criteria of the Steady Flow of a Liquid Containing Bubbles Along a Nozzle

2001 ◽  
Vol 123 (4) ◽  
pp. 836-840 ◽  
Author(s):  
A. Crespo ◽  
J. Garcı´a ◽  
J. Jime´nez-Ferna´ndez
Keyword(s):  
Bubble Dynamics ◽  
Volume Fraction ◽  
Flow Instability ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Critical Value ◽  
Stability Criteria ◽  
Flow Through ◽  
Gas Volume Fraction ◽  
Gas Volume

The steady cavitating flow through a converging-diverging nozzle is considered. A continuum model is assumed with the Rayleigh-Plesset equation to account for the bubble dynamics. A similar problem has been studied previously by Wang and Brennen, and they found that if the upstream gas volume fraction of the bubbles exceeds a critical value there is flashing flow instability. In the present work, a perturbation analysis is made introducing a small parameter, ε, that is the ratio of the initial bubble diameter to the length scale of the nozzle. As a result of this analysis, the critical value of the upstream void fraction is calculated as a function of the several parameters appearing in the problem, and turns out to be very small and proportional to ε3. A correlation is proposed giving explicitly the functional dependence of this critical value.

scholarly journals Homogeneous swarm of high-Reynolds-number bubbles rising within a thin gap. Part 2. Liquid dynamics

2014 ◽  
Vol 758 ◽  
pp. 508-521 ◽  
Author(s):  
Emmanuella Bouche ◽  
Véronique Roig ◽  
Frédéric Risso ◽  
Anne-Marie Billet
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Volume Fraction ◽  
Vertical Direction ◽  
Spatial Spectrum ◽  
Wall Friction ◽  
Flow Disturbances ◽  
High Reynolds ◽  
Confined Flows ◽  
Gas Volume

AbstractThe agitation of the liquid phase has been investigated experimentally in a homogeneous swarm of bubbles rising at high Reynolds number within a thin gap. Owing to the wall friction, the bubble wakes are strongly attenuated. Consequently, liquid fluctuations result from disturbances localized near the bubbles and direct interactions between them. The signature of the average wake rapidly fades and the probability density function of the fluctuations becomes Gaussian as the gas volume fraction $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\alpha $ increases. The energy of the fluctuations scales differently with $\alpha $ depending on the direction, indicating that hydrodynamic interactions are different in the horizontal and vertical directions. The spatial spectrum shows that the length scales of the fluctuations are independent of $\alpha $ and exhibits a $k^{-3}$ subrange, which results from localized random flow disturbances of various sizes. Comparisons with the dynamics of the gas phase show that liquid and bubble agitations are driven by the same mechanism in the vertical direction, whereas they turn out to be almost uncoupled in the horizontal direction. Comparisons with unconfined flows show that the generation of liquid fluctuations is very different. However, the cause of the $k^{-3}$ spectral subrange is the same for confined flows as for the spatial fluctuation of unconfined flows.

scholarly journals Mixing by bubble-induced turbulence

2015 ◽  
Vol 776 ◽  
pp. 458-474 ◽  
Author(s):  
Elise Alméras ◽  
Frédéric Risso ◽  
Véronique Roig ◽  
Sébastien Cazin ◽  
Cécile Plais ◽  
...  
Keyword(s):  
Diffusion Coefficients ◽  
Time Scale ◽  
Volume Fraction ◽  
Vertical Direction ◽  
Diffusion Time ◽  
Physical Models ◽  
Horizontal Direction ◽  
Time Interval ◽  
Gas Volume Fraction ◽  
Gas Volume

This work reports an experimental investigation of the dispersion of a low-diffusive dye within a homogeneous swarm of high-Reynolds-number rising bubbles at gas volume fractions ${\it\alpha}$ ranging from 1 % to 13 %. The capture and transport of dye within bubble wakes is found to be negligible and the mixing turns out to result from the bubble-induced turbulence. It is described well by a regular diffusion process. The diffusion coefficient corresponding to the vertical direction is larger than that corresponding to the horizontal direction, owing to the larger intensity of the liquid fluctuations in the vertical direction. Two regimes of diffusion have been identified. At low gas volume fraction, the diffusion time scale is given by the correlation time of the bubble-induced turbulence and the diffusion coefficients increase roughly as ${\it\alpha}^{0.4}$. At large gas volume fraction, the diffusion time scale is imposed by the time interval between two bubbles and the diffusion coefficients become almost independent of ${\it\alpha}$. The transition between the two regimes occurs sooner in the horizontal direction ($1\,\%\leqslant {\it\alpha}\leqslant 3\,\%$) than in the vertical direction ($3\,\%\leqslant {\it\alpha}\leqslant 6\,\%$). Physical models based on the hydrodynamic properties of the bubble swarm are introduced and guidelines for practical applications are suggested.

Temporal Gas Volume Fraction and Bubble Velocity Measurement Using an Impedance Needle Probe

2013 ◽  
Author(s):  
Sahand Pirouzpanah ◽  
Gerald L. Morrison
Keyword(s):  
Oil And Gas ◽  
Volume Fraction ◽  
Flow Behavior ◽  
Oil And Gas Industry ◽  
Bubble Velocity ◽  
Time Interval ◽  
Needle Probe ◽  
Measured Time ◽  
Gas Volume Fraction ◽  
Gas Volume

Impedance probes are used by the oil and gas industry to investigate multiphase flow behavior. In this study, an impedance needle probe has been developed to measure the local and temporal gas volume fraction in conductive and non-conductive process fluid. Measuring both resistance and capacitance enables this probe to be functional in both types of fluids and facilitates the measurement of local bubble velocity. Two 1/32″ insulated brass (alloy 260) rods with bare tips protrude into the flow. The gap between the electrodes is designed to be 0.085″. The probe can measure directional bubble velocity by measuring duration of signal gradient from liquid to gas transition. For a known distance between electrodes and by the measured time, directional bubble velocity in the direction of the connecting line between electrodes can be measured. The ratio between the time interval when signal is non-zero to the total time represents the temporal gas volume fraction.

scholarly journals Effect of the Gas Volume Fraction on the Pressure Load of the Multiphase Pump Blade

Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 650
Author(s):  
Guangtai Shi ◽  
Dandan Yan ◽  
Xiaobing Liu ◽  
Yexiang Xiao ◽  
Zekui Shu
Keyword(s):  
Flow Rate ◽  
Static Pressure ◽  
Volume Fraction ◽  
Pump Impeller ◽  
Impeller Blade ◽  
Multiphase Pump ◽  
Pressure Load ◽  
Gas Volume Fraction ◽  
Power Capability ◽  
Gas Volume

The gas volume fraction (GVF) often changes from time to time in a multiphase pump, causing the power capability of the pump to be increasingly affected. In the purpose of revealing the pressure load characteristics of the multiphase pump impeller blade with the gas-liquid two-phase case, firstly, a numerical simulation which uses the SST k-ω turbulence model is verified with an experiment. Then, the computational fluid dynamics (CFD) software is employed to investigate the variation characteristics of static pressure and pressure load of the multiphase pump impeller blade under the diverse inlet gas volume fractions (IGVFs) and flow rates. The results show that the effect of IGVF on the head and hydraulic efficiency at a small flow rate is obviously less than that at design and large flow rates. The static pressure on the blade pressure side (PS) is scarcely affected by the IGVF. However, the IGVF has an evident effect on the static pressure on the impeller blade suction side (SS). Moreover, the pump power capability is descended by degrees as the IGVF increases, and it is also descended with the increase of the flow rate at the impeller inlet. Simultaneously, under the same IGVF, with the increase of the flow rate, the peak value of the pressure load begins to gradually move toward the outlet and its value from hub to shroud is increased. The research results have important theoretical significance for improving the power capability of the multiphase pump impeller.

scholarly journals Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting Nozzle With a Throat

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Sowmitra Singh ◽  
Tiffany Fourmeau ◽  
Jin-Keun Choi ◽  
Georges L. Chahine
Keyword(s):  
Volume Fraction ◽  
Bubbly Flow ◽  
Design Tool ◽  
Nozzle Geometry ◽  
Mixture Flow ◽  
Subsonic Flows ◽  
Choked Flow ◽  
Optimum Geometry ◽  
Gas Volume Fraction ◽  
Gas Volume

This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the injected gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study provides analytical and numerical support to analytical observations and serves as a design tool for nozzle geometries that can achieve efficient choked bubbly flows through nozzles. Starting from the 1D mixture continuity and momentum equations, along with an equation of state for the bubbly mixture, expressions for mixture velocity and gas volume fraction were derived. Starting with a fixed geometry and an imposed upstream pressure for a choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different injected gas volume fractions. The variation of thrust enhancement with the injected gas volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor, which can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the injected gas volume fraction. Furthermore, for the same injected gas volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.

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