The critical bubble diameter of the lift force in technical and environmental, buoyancy-driven bubbly flows

2019 ◽  
Vol 116 ◽  
pp. 26-38 ◽  
Author(s):  
T. Ziegenhein ◽  
D. Lucas
Keyword(s):  
Lift Force ◽  
Bubble Diameter ◽  
Bubbly Flows ◽  
Critical Bubble

scholarly journals Modeling of Multisize Bubbly Flow and Application to the Simulation of Boiling Flows with the Neptune_CFD Code

2009 ◽  
Vol 2009 ◽  
pp. 1-8 ◽  
Author(s):  
Christophe Morel ◽  
Jérôme M. Laviéville
Keyword(s):  
Heat Transfer ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Mathematical Expression ◽  
Original Model ◽  
Bubbly Flows ◽  
Condensation Rate ◽  
Interface Heat Transfer ◽  
Interface Heat ◽  
Transfer Term

This paper describes the modeling of boiling multisize bubbly flows and its application to the simulation of the DEBORA experiment. We follow the method proposed originally by Kamp, assuming a given mathematical expression for the bubble diameter pdf. The original model is completed by the addition of some new terms for vapor compressibility and phase change. The liquid-to-interface heat transfer term, which essentially determines the bubbles condensation rate in the DEBORA experiment, is also modeled with care. First numerical results realized with the Neptune_CFD code are presented and discussed.

scholarly journals Turbulence modulation in buoyancy-driven bubbly flows

2021 ◽  
Vol 932 ◽  
Author(s):  
Vikash Pandey ◽  
Dhrubaditya Mitra ◽  
Prasad Perlekar
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Bubble Diameter ◽  
Bubbly Flows ◽  
Air Bubbles ◽  
Rise Velocity ◽  
Turbulence Modulation ◽  
Budget Analysis ◽  
Average Rise ◽  
Turbulence Scaling

We present a direct numerical simulation (DNS) study of buoyancy-driven bubbly flows in the presence of large-scale driving that generates turbulence. On increasing the turbulence intensity: (a) the bubble trajectories become more curved and (b) the average rise velocity of the bubbles decreases. We find that the energy spectrum of the flow shows a pseudo-turbulence scaling for length scales smaller than the bubble diameter and a Kolmogorov scaling for scales larger than the bubble diameter. We conduct a scale-by-scale energy budget analysis to understand the scaling behaviour observed in the spectrum. Although our bubbles are weakly buoyant, the statistical properties of our DNS are consistent with the experiments that investigate turbulence modulation by air bubbles in water.

Experiments and Modeling in Bubbly Flows at Elevated Pressures

2003 ◽  
Author(s):  
R. Kumar ◽  
T. A. Trabold ◽  
C. C. Maneri
Keyword(s):  
Void Fraction ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Bubbly Flows ◽  
Rise Velocity ◽  
Two Phase ◽  
Flow Models ◽  
Gamma Densitometer ◽  
Visualization Techniques

Measurements of local void fraction, rise velocity and bubble diameter have been obtained for cocurrent, wall-heated, upward bubbly flows in a pressurized refrigerant. The instrumentation used was the gamma densitometer and the hot-film anemometer. Departure bubble size and bulk size measurements were also made and correlated with appropriate parameters. Flow visualization techniques have also been used to understand the two-phase flow structure and the behavior of the bubbly flow for different bubble shapes and sizes, and to obtain the rise velocity. Such insight, coupled with quantitative local and averaged data on void fraction and bubble size at different pressures, has aided in developing bubbly flow models applicable to heated two-phase flows at high pressure.

Experiments and Modeling in Bubbly Flows at Elevated Pressures

2003 ◽  
Vol 125 (3) ◽  
pp. 469-478 ◽  
Author(s):  
Ranganathan Kumar ◽  
Thomas A. Trabold ◽  
Charles C. Maneri
Keyword(s):  
Void Fraction ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Bubbly Flows ◽  
Rise Velocity ◽  
Two Phase ◽  
Flow Models ◽  
System Pressure ◽  
Eotvos Number

Measurements of local void fraction, rise velocity, and bubble diameter have been obtained for cocurrent, wall-heated, upward bubbly flows in a pressurized refrigerant. The instrumentation used are the gamma densitometer and the hot-film anemometer. Departure bubble size is correlated in terms of liquid subcooling and bulk bubble size in terms of void fraction. Flow visualization techniques have also been used to understand the two-phase flow structure and the behavior of the bubbly flow for different bubble shapes and sizes, and to obtain the bubble diameter and rise velocity. The lift model is provided explicitly in terms of Eotvos number which is changed by changing the system pressure. In general, Eotvos number plays a strong role in determining both bubbly lift and drag. Such insight coupled with quantitative local and averaged data on void fraction and bubble size at different pressures has aided in developing bubbly flow models applicable to heated two-phase flows at high pressure.

scholarly journals CFD Modeling of Gas-Liquid Bubbly Flow in Horizontal Pipes: Influence of Bubble Coalescence and Breakup

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
K. Ekambara ◽  
R. Sean Sanders ◽  
K. Nandakumar ◽  
J. H. Masliyah
Keyword(s):  
Volume Fraction ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Gas Bubbles ◽  
Bubbly Flows ◽  
Cfd Modeling ◽  
Horizontal Pipe ◽  
The Impact

Modelling of gas-liquid bubbly flows is achieved by coupling a population balance equation with the three-dimensional, two-fluid, hydrodynamic model. For gas-liquid bubbly flows, an average bubble number density transport equation has been incorporated in the CFD code CFX 5.7 to describe the temporal and spatial evolution of the gas bubbles population. The coalescence and breakage effects of the gas bubbles are modeled. The coalescence by the random collision driven by turbulence and wake entrainment is considered, while for bubble breakage, the impact of turbulent eddies is considered. Local spatial variations of the gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, and liquid velocity are compared against experimental data in a horizontal pipe, covering a range of gas (0.25 to 1.34 m/s) and liquid (3.74 to 5.1 m/s) superficial velocities and average volume fractions (4% to 21%). The predicted local variations are in good agreement with the experimental measurements reported in the literature. Furthermore, the development of the flow pattern was examined at three different axial locations ofL/D= 25, 148, and 253. The first location is close to the entrance region where the flow is still developing, while the second and the third represent nearly fully developed bubbly flow patterns.

Freestream Nuclei and Traveling-Bubble Cavitation

1992 ◽  
Vol 114 (4) ◽  
pp. 672-679 ◽  
Author(s):  
R. S. Meyer ◽  
M. L. Billet ◽  
J. W. Holl
Keyword(s):  
Bubble Diameter ◽  
Pressure Coefficient ◽  
Critical Diameter ◽  
Computer Code ◽  
The Body ◽  
Water Tunnel ◽  
Cavitation Inception ◽  
Bubble Cavitation ◽  
Definition Of ◽  
Critical Bubble

Traveling-bubble cavitation inception tests were conducted in a 30.48 cm water tunnel with a Schiebe headform. A computer code was developed to statistically model cavitation inception on a Schiebe headform, consisting of a numerical solution to the Rayleigh-Plesset equation coupled to a set of trajectory equations. Using this code, trajectories and growths were computed for bubbles of varying initial sizes. An initial off-body distance was specified and the bubble was free to follow an off-body trajectory. A Monte Carlo cavitation simulation was performed in which a variety of random processes were modeled. Three different nuclei distributions were specified including one similar to that measured in the water tunnel experiment. The results compared favorably to the experiment. Cavitation inception was shown to be sensitive to nuclei distribution. Off-body effect was also found to be a significant factor in determining whether or not a bubble would cavitate. The effect of off-body trajectories on the critical bubble diameter was examined. The traditional definition of critical diameter based on the minimum pressure coefficient of the body or the measurement of liquid tension was found to be inadequate in defining cavitation inception.

scholarly journals Simulation Study on Gas Holdup of Large and Small Bubbles in a High Pressure Gas–Liquid Bubble Column

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 594 ◽  
Author(s):  
Fangfang Tao ◽  
Shanglei Ning ◽  
Bo Zhang ◽  
Haibo Jin ◽  
Guangxiang He
Keyword(s):  
Surface Tension ◽  
High Pressure ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Gas Holdup ◽  
Operating Pressure ◽  
Gas Velocity ◽  
Superficial Gas Velocity ◽  
Critical Bubble ◽  
Small Bubbles

The computational fluid dynamics-population balance model (CFD-PBM) has been presented and used to evaluate the bubble behavior in a large-scale high pressure bubble column with an inner diameter of 300 mm and a height of 6600 mm. In the heterogeneous flow regime, bubbles can be divided into “large bubbles” and “small bubbles” by a critical bubble diameter dc. In this study, large and small bubbles were classified according to different slopes in the experiment only by the method of dynamic gas disengagement, the critical bubble diameter was determined to be 7 mm by the experimental results and the simulation values. In addition, the effects of superficial gas velocity, operating pressure, surface tension and viscosity on gas holdup of large and small bubbles in gas–liquid two-phase flow were investigated using a CFD-PBM coupling model. The results show that the gas holdup of small and large bubbles increases rapidly with the increase of superficial gas velocity. With the increase of pressure, the gas holdup of small bubbles increases significantly, and the gas holdup of large bubbles increase slightly. Under the same superficial gas velocity, the gas holdup of large bubbles increases with the decrease of viscosity and the decrease of surface tension, but the gas holdup of small bubbles increases significantly. The simulated values of the coupled model have a good agreement with the experimental values, which can be applied to the parameter estimation of the high pressure bubble column system.

Effect of Gravity on Axial Development of Phase Distribution Patterns in Bubbly Two-Phase Flow

2009 ◽  
Author(s):  
Takashi Nishioji ◽  
Taichi Kato ◽  
Yutaka Fukuhara ◽  
Tatsuya Hazuku ◽  
Tomoji Takamasa ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Phase Distribution ◽  
Bubble Diameter ◽  
Distribution Patterns ◽  
Stereo Image ◽  
Bubbly Flows ◽  
Phase Flow ◽  
Two Phase ◽  
Microgravity Conditions ◽  
Axial Development

The axial development of the void fraction profile, interfacial area concentration and Sauter mean bubble diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured using stereo image processing in normal and microgravity conditions. The effect of gravity and flow conditions on the radial distribution of bubbles and the axial development of the two-phase flow parameter is discussed in detail based on the obtained data. By taking into account normalized parameters based on void peak fraction and void peak intensity in the pipe cross-section, the phase distribution patterns were classified into three types: a wall peak, a core peak and an intermediate peak. Phase distribution pattern maps are presented for vertical upward bubbly flows in normal and microgravity conditions.

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