Computational approach for a pair of bubble coalescence process (original) (raw)
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Numerical investigation on coalescence of bubble pairs
2011
In the present study, we preformed a two-dimensional numerical simulation of the motion and coalescence of bubble pairs rising in the stationary liquid pool, using the moving particle semi-implicit (MPS) method. Moving particles were used to describe the liquid phase and the vapor phase was evaluated using real vapor sate equation. The bubble-liquid interface was set to be a free surface boundary which could be captured according to the motion and location of interfacial particles. The behaviors of coalescence between two identical bubbles predicted by the MPS method were in good agreement with the experimental results reported in the literature. Numerical results indicated that the rising velocity of the trailing bubble was larger than that of the leading bubble. Both of the leading bubble and the trailing bubble rose faster than the isolated bubble. After coalescence, the coalesced bubble showed velocity and volume oscillations. The time of the volume oscillations increased with increasing initial bubble diameter. The wake flow and vortex would form behind the coalesced bubble.
Numerical investigation on coalescence of bubble pairs rising in a stagnant liquid
Chemical Engineering Science, 2011
In the present study, we preformed a two-dimensional numerical simulation of the motion and coalescence of bubble pairs rising in the stationary liquid pool, using the moving particle semi-implicit (MPS) method. Moving particles were used to describe the liquid phase and the vapor phase was evaluated using real vapor sate equation. The bubble-liquid interface was set to be a free surface boundary which could be captured according to the motion and location of interfacial particles. The behaviors of coalescence between two identical bubbles predicted by the MPS method were in good agreement with the experimental results reported in the literature. Numerical results indicated that the rising velocity of the trailing bubble was larger than that of the leading bubble. Both of the leading bubble and the trailing bubble rose faster than the isolated bubble. After coalescence, the coalesced bubble showed velocity and volume oscillations. The time of the volume oscillations increased with increasing initial bubble diameter. The wake flow and vortex would form behind the coalesced bubble.
Coalescence and rising behavior of co-axial and lateral bubbles in viscous fluid: a CFD study
Asia-Pacific Journal of Chemical Engineering, 2017
The coalescence and rising behavior of co-axial and lateral bubbles in viscous fluid is reported for nonambient conditions in line with actual operating conditions of industrial bubble column. The volume of fluid with the continuum surface force (VOF-CSF) model embedded in FLUENT CFD package is used. Three main case studies, namely under ambient and aqueous condition (μ* = σ* = 1), under reduced viscosity (μ* = 0.1) and surface tension (σ* = 0.1) are investigated and compared using two co-axial bubble and three lateral bubble rise configuration models. The latter two cases represent operating conditions at high temperature or pressure. Details of co-axial bubble (or a pair of bubbles rising in a vertical line) and three lateral bubble rise and coalescence characteristics are presented.
Coalescence of Co-Axial Bubbles in a Stagnant Water Column
Academia Letters, 2021
The bubble formation and dynamics in the liquid phase affect the heat and mass transfer mechanism between phases, which is crucial in determining the equipment's performance. The commercial applications include floatation, absorbers, reactors, and distillers [1,2]. Thus, it is vital to understand the bubble hydrodynamics such as bubble rise velocity, residence time, shape formation, coalescence and break-up, better equipment design, and enhanced process optimization. The specifics of the bubble hydrodynamics and the coalescent combination of the co-axial and lateral engagements of individual bubbles are essential factors to analyze the bubbles flow in the column [3,4]. Several researchers have experimentally, numerically, and analytically studied and discussed the bubble dynamics. Lin et al. [5] experimentally examined the co-axial bubble coalescence process in the non-Newtonian fluid. They also observed that in bubble coalescence, the shear-thinning and viscoelastic effects play a crucial role. Ganesan et al. [6] numerically analyzed the coalescence of axial and lateral bubbles having diameters ranging from 4-10 mm for small Weber numbers. They validated their model with the experimental data available in the literature. They concluded that the profile of trailing bubble changes significantly for non-Newtonian fluid as compared to Newtonian fluids. Faik and Mohammed [7] performed experiments to investigate the effect of temperature on the bubble rise and shape. They found that the bubble stability along the vertical path decreases and bubble rise velocity increases with the rise in temperature, respectively.
Computers & Fluids, 2018
The dynamics of a single air bubble, the wake structure, the instantaneous liquid velocity field around it and the coaxial coalescence of two successive bubbles have been widely studied in this work by using the VOF method on the software platform of Fluent. It is observed that the bubble rising trajectory changes from one dimension to three dimensions by decreasing the viscosity of the liquid phase. The different behaviors of air bubbles introduce various instantaneous bubbles wake structures which strongly depend on their shape and on the physical properties of the liquid phase. Indeed, as the solution viscosity decreases, the bubbles' shape changes from non-deformed (ellipsoidal) to the deformed shape. In the case of bubbles chain, the wake of the leading bubble significantly affects the shape, trajectory and velocity of the trailing bubble, as well as the velocity field of the liquid phase surrounding it. For high orifice air velocities and due to the wake of the leading bubble, the trailing bubble accelerates and approaches to the leading bubble and finally coalescence phenomenon occurs. During this process, the shape of the leading bubble becomes oblate while the shape of the trailing bubble is stretched in a vertical direction. Thus, the coalescence time and position of two successive bubbles generally increase with increasing the surface tension of the liquid and reducing its viscosity.
Numerical Simulation of Bubble Breakup and Coalescence in Bubbling Two-Phase Flow
2018
The aim of the present work is to study the behavior of gas-liquid bubbly flow by means of Computational Fluid Dynamics (CFX ANSYS). The population balance approach taking into account the bubble coalescence and breakup in turbulent gas-liquid dispersion is included.The Euler-Euler approach and the standard k-ε mixture turbulence model in three-dimensional computational domains accounting the effect of turbulence are used to simulate the two phase flows of the bubble column.The bubble size distribution along the column height, the gas volume fraction and liquid velocity have been predicted for the two-phase systems and for liquids different from water(ethanol, glycerol). The results of nonuniform bubbles size distribution in dispersed flow are presented grouped into individual size fractions at varying initial conditions and density of the elementary mesh.
The Study of Bubble Coalescence in Coaxial and Side-by-Side Motions
20th Annual International …, 2012
The bubble coalescence is discussed in many chemical and metallurgical phenomena. In this paper, the coalescence process of two bubbles moving in a cylindrical tube is studied using both 2D and 3D numerical simulations. The Navier-Stokes equations along with an equation for the interface advection by the Volume-of-Fluid (VOF) method are solved. The results are compared with experimental data reported in the literatures. Simulations are performed for various cases with different configurations of the two bubbles. First, the coaxial bubble motion is studied. The Reynolds number, the density ratio and the viscosity ratio are held constant. The results show that by increasing the Bond number the coalescence time decreases and the leading bubble reveals a more concave interface. Both of these effects make the two bubbles to coalesce faster. Next, the motion of the two bubbles rising side-by-side is studied. On the basis of different Weber numbers based on the approach velocity of the bubbles and the rise velocity, either coalescence or separation will occur.
Development and validation of models for bubble coalescence and breakup
2014
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model. Besides, I would like to extend my gratitude to all support staff at the Institute of Safety Research for their assistance, especially the secretaries, Claudia Losinski, Petra Vetter, Annett Richter and special thanks to the computer administrator Torsten Berger. I am most thankful to the German Federal Ministry of Economics and Technology for funding my research work through the program of competence maintenance in nuclear technology. Finally, a great thanks to my husband Wenxing, for his love and continuous support, and my children Ye and Lei.
COALESCENCE OF BUBBLES – A CASE STUDY
Multiphase contactors have broad application in chemical industry. This type of devices may be used as reactors in chemical and biochemical processes, as well as in separations processes, e.g. absorption and distillation and its performance depends usually on the mass transfer rate. The present work focus on one of the less understood problems controlling the bubble size distribution in such devices and, as a result, the contact area between phases and the mass transfer rate: the coalescence. For the study of coalescence, a new coalescence cell was built allowing the control of the production of pairs of bubbles with the following parameters: bubble growth velocity, bubble size at contact moment and angle of the bubble production. This new coalescence cell was used for the study of the effect of the mentioned geometric parameters on coalescence of pairs of bubbles, contacted in liquids known to be either coalescent (pure water) or non-coalescent (surfactant solutions).
Coalescence efficiency of bubbles in bubble columns
The Canadian Journal of Chemical Engineering, 2012
Bubble size distribution was modelled by employing the population balance equation (PBE). All three bubble coalescence mechanisms (turbulence, buoyancy and laminar shear) and the main bubble breakup mechanism (breakup due to turbulent eddies) were considered in the model. Local bubble size distributions at the top and bottom of the column were obtained by solving this PBE. The results were compared with the experimental data for seven independent multiphase systems (water/air, isomax diesel/air, kerosene/air and four other liquid mixture/air) at two diverse gas velocities. The experimental adjustable constant in the coalescence efficiency function was determined by fitting the population balance to the experimental bubble size distributions. An empirical correlation was proposed for the coalescence efficiency by the dimensional analysis, which includes Reynolds and Weber numbers.