An Analytical Study of Turbulent Dispersion of Bubbles

2001 ◽  
Author(s):  
Anthony L. Lawson ◽  
Ramkumar N. Parthasarathy
Keyword(s):  
Root Mean Square ◽  
Time Scale ◽  
Liquid Velocity ◽  
Added Mass ◽  
Mean Square ◽  
Rise Velocity ◽  
Velocity Fluctuations ◽  
Bubble Rise ◽  
Integral Time Scale ◽  
Bubble Rise Velocity

Abstract An analysis of the dispersion of bubbles in homogenous and isotropic turbulent liquid flows was performed to study the effects of bubble and flow characteristics on their dispersion. Bubbles were assumed to be spherical and to follow the fluid motion in the mean. No mass transfer occurred between the bubble and liquid; also, there was no interaction between individual bubbles. It was found that for accurate prediction of bubble dispersion requires a simultaneous consideration of the inertia of the added mass of liquid (because the inertia of the bubble itself is small) and the bubble rise velocity. Normalized bubble diffusivity, root-mean-square fluctuating velocity, and Lagrangian integral time scale were related to two non-dimensional parameters: ratio of the added mass response time to the liquid flow integral time scale, and the ratio of the bubble rise velocity to the root-mean-square liquid velocity fluctuation. In general, the bubble Lagrangian velocity auto-correlations decreased as the rise velocity ratio increased. The dependence of the autocorrelations on the time-scale ratio was complex. A surprising result was that the bubble velocity fluctuations could exceed the liquid velocity fluctuations for certain conditions because of their low inertia.

Measurements of Bubble Rise Characteristics in Various Temperatures and Liquid Velocities

2002 ◽  
Author(s):  
Kazuhiro Torimoto ◽  
Masanori Nishiura ◽  
Tomoe Tanaka ◽  
Tomio Okawa ◽  
Isao Kataoka
Keyword(s):  
Turbulent Flow ◽  
Nuclear Reactor ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Measured Data ◽  
Rise Velocity ◽  
Reactor Safety ◽  
Bubble Rise ◽  
Bubble Rise Velocity ◽  
Nuclear Reactor Safety

Single bubble rise characteristics in turbulent flow in a vertical circular pipe were experimentally observed. As a result, it was found that bubble rise velocity relative to the time averaged local liquid velocity decreases with the increase of liquid flowrate and that it also decreases with the decrease of the distance between a bubble and wall. Investigating the mechanisms of the reductions of relative velocity, new correlations were developed for accurately evaluating the bubble rise velocities in turbulent flow. Since the predicted bubble rise velocities reasonably agreed with the measured data, the new correlations could contribute to the improvement of bubbly flow calculations in nuclear reactor safety analysis.

Numerical Simulation of Single Bubble Moving in Stagnant Solid-Liquid Mixture Pool Using Finite Volume Particle Method

2013 ◽  
Author(s):  
Yuki Aramaki ◽  
Takahito Suzuki ◽  
Ichiro Miya ◽  
Liancheng Guo ◽  
Koji Morita
Keyword(s):  
Liquid Mixture ◽  
Single Bubble ◽  
Phase Flow ◽  
Bubble Shape ◽  
Rise Velocity ◽  
Bubble Rise ◽  
Bubble Rise Velocity ◽  
Three Phase ◽  
Three Phase Flow ◽  
Fluid Interactions

Three-phase flow formed in a disrupted core of nuclear reactors is one of the key phenomena to be simulated in reactor safety analysis. Particle-based simulation could be a powerful CFD tool to understand and clarify local thermal-hydraulic behaviors involved in such three-phase flows. In the present study, to develop a computational framework for three-phase flow simulations, a single bubble moving in a stagnant solid particle-liquid mixture pool was simulated using the finite volume particle (FVP) method. The simulations were carried out in a two dimensional system. The bubble shape change and the bubble rise velocity were compared with the newly performed experiments, which used solid particulate glasses of 0.9 mm in diameter, liquid silicone and air. The two-phase flow simulation of a single bubble rising in a stagnant liquid pool reproduced measured bubble shape and bubble rise velocity reasonably. On the other hand, the bubble rise velocity in a stagnant particle-liquid mixture pool was overestimated in comparison with the measurement. This result suggests that particle-particle and particle-fluid interactions would have dominant influence on bubble motion behavior in the particle-liquid mixture pool under the present multiphase conditions. To evaluate such interactions in the simulations, the particle-particle interactions were modeled by the distinct element method (DEM), while two models were applied to represent particle-fluid interactions. One is the theoretical model for apparent viscosity of particle-liquid mixture, which describes the viscosity increase of liquid mixed with solids based on the Frankel-Acrivos equation. The other is the drag force model for solid-fluid interactions. In the present study, we took the Gidaspow drag correlation, which is a combination of the Ergun equation and Wen-Yu equation. A comparison of both the transient bubble shape and bubble rise velocity between the results of experiment and simulation demonstrates that the present computational framework based on the FVP method and solid-phase interaction models is useful for numerical simulations of a single bubble moving in a stagnant solid particle-liquid mixture pool.

On accelerated random vibration testing of product based on component acceleration RMS–life curve

2017 ◽  
Vol 24 (15) ◽  
pp. 3384-3399 ◽  
Author(s):  
Zhi-Wei Wang ◽  
Li-Jun Wang
Keyword(s):  
Root Mean Square ◽  
Time Scale ◽  
Random Vibration ◽  
Response Spectrum ◽  
Equivalent Stress ◽  
Practical Method ◽  
Mean Square ◽  
Vibration Testing ◽  
Validation Experiment ◽  
Von Mises

Accelerated random vibration testing is usually used to certify a product in random vibration environments. The current certification method is based on the inverse power law and is strictly valid only for Basquin’s type of damage and fatigue of materials. Based on the response spectrum analysis of the product in “the simply scaled accelerated vibrations” and taking the size of acceleration power spectral densities (PSD) the component is undergoing as an index to characterize and compare the damage of the component in different experiments, this paper develops a more practical method in engineering for accelerated random vibration testing of the product in the framework of linear random vibration theory and the rule of acceleration root mean square (RMS)–life curve of the component. The suggested method shows that the time scale is determined by the zero-th and second-order response acceleration spectral moments of the component in real vibration and that simulated in the laboratory, which demonstrates its potential value and advantage in practical application when compared with that based on the von Mises equivalent stress. Simplifications of the method are discussed in detail. In “the simply scaled accelerated vibrations”, the time scale is determined by the acceleration root mean square of the component in real or simulated vibration. It is coincident with the form reported by Allegri but having different physical significance in the case of Basquin’s type of damage and fatigue of the component. The validation experiment with a desk computer was carried out, leading to the verification of the present method.

Bubble rise velocity in two-dimensional fluidized beds

1995 ◽  
Vol 84 (3) ◽  
pp. 283-285 ◽  
Author(s):  
Dinesh Gera ◽  
Mridul Gautam
Keyword(s):  
Fluidized Beds ◽  
Two Dimensional ◽  
Rise Velocity ◽  
Bubble Rise ◽  
Bubble Rise Velocity

scholarly journals COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF TAYLOR BUBBLE RISE IN FLOWING LIQUIDS

2021 ◽  
Vol 36 (2) ◽  
pp. 35-42
Author(s):  
H.A Abubakar
Keyword(s):  
Finite Element ◽  
Fluid Dynamic ◽  
Total Curvature ◽  
Rise Velocity ◽  
Systematic Analysis ◽  
Taylor Bubble ◽  
Bubble Rise ◽  
Bubble Rise Velocity ◽  
Bubble Rising ◽  
Dynamics Simulations

Systematic analysis of the effect of gravitational, interfacial, viscous and inertia forces acting on a Taylor bubble rising in flowing liquids characterised by the dimensionless Froude (Uc), inverse viscosity (Nf ) and Eötvös numbers (Eo) is carried out using computational fluid dynamic finite element method. Particular attention is paid to cocurrent (i.e upward) liquid flow and the influence of the characterising dimensionless parameters on the bubble rise velocity and morphology analysed for Nf, Eo and Uc ranging between [40, 100], [20, 300] and [−0.20, 0.20], respectively. Analysis of the results of the numerical simulations showed that the existing theoretical model for the prediction of Taylor bubble rise velocity in upward flowing liquids could be modified to accurately predict the rise velocity in liquids with high viscous and surface tension effects. Furthermore, the mechanism governing the change in morphology of the bubble in flowing liquids was shown to be the interplay between the viscous stress and total curvature stress at the interface. Keywords: Taylor bubble, finite element, slug flow, CFD, rise velocity

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