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In this study, the dissolution of a single oxygen bubble on a solid surface, here Titanium alloy Ti64, in ultrapure water with different oxygen undersaturation levels is investigated. For that purpose, a combination of shadowgraph technique and planar laser-induced fluorescence is used to measure simultaneously the changes in bubble geometry and in the dissolved oxygen concentration around the bubble. Two different wettabilities of the Ti64 surface are adjusted by using plasma-enhanced chemical vapor deposition. The dissolution process on the solid surface involves two distinct phases, namely bouncing of the oxygen bubble at the Ti64 surface and the subsequent dissolution of the bubble, primarily by diffusion. By investigating the features of oxygen bubbles bouncing, it was found that the boundary layer of dissolved oxygen surrounding the bubble surface is redistributed by the vortices emerging during bouncing. This establishes the initial conditions for the subsequent second dissolution phase of the oxygen bubbles on the Ti64 surfaces. In this phase, the mass transfer of O2 proceeds non-homogeneously across the bubble surface, leading to an oxygen accumulation close to the Ti64 surface. We further show that the main factor influencing the differences in the dynamics of O2 bubble dissolution is the variation in the surface area of the bubbles available for mass transfer, which is determined by the substrate wettability. As a result, dissolution proceeds faster at the hydrophilic Ti64 surface due to the smaller contact angle, which provokes a larger surface area.

The bubble shape affects the gas-liquid interface momentum, heat and mass transfer, as well as the flow field around the bubble. Correctly predicting the bubble shape is challenging but indispensable under bubble swarm conditions. In this work, the bubble aspect ratio, which is adopted for the characterization of the bubble shape, is obtained through high-speed photography combined with an image processing algorithm from several experiments with an oscillating bubble plume. The results show that the bubble aspect ratio tends to be a constant value with increasing the bubble diameter, rather than decreasing as predicted by various empirical correlations developed in single bubble experiments. None of the available empirical correlations can accurately correlate the bubble aspect ratio with Weber number or Tadaki number. Among the available correlations in literature, Eo based correlation proposed by Besagni and Inzoli (2016) and Eo-Re based correlation proposed by Besagni and Deen (2019) show a better performance. The predicted values of Eo-Re based correlation developed in this work are the closest to the experimental data compared with others.

Two-phase liquid-gas injection constitutes an important industrial process that is used in most separators. At the early step of injection, a cylindrical bubble is formed. As time elapses, the bubble shape becomes more complex and very difficult to analyze. In this study, a simple analytical model is developed to explain bubble shape changes. The analytical model was developed based on water flow inertia that continually pushes the bubble while the drag force resists it so that the frontal area of the bubble increases. The bubble size and frontal area were estimated using the assumption of the equilibrium between inertia force and drag force neglecting viscous force. From the estimation, the role of the vortex ring from the difference between theoretical and experimental results can be identified. The analytical model was verified through experimental data collected on the shape deformation induced by bubble motion at the beginning of injection. The experimental data used as verification were measured from the bubble nose image with ten times repetition having the uncertainty of ±6 %. The experimental method is conducted by injecting a bubble along the horizontal direction into a water pool. The inertial force of the water flow in front of the bubble nose generates the bubble. The bubble suddenly changes its shape, moves in the form of a bubble jet, and undergoes gradual shape changes. The frontal area of the bubble increases and reaches a maximum at the terminal velocity point. The bubble shape deformation is affected by the inertial force of the water flow that pushes the bubble forward. Accordingly, the bubble changes its shape from cylindrical to spherical, and then to an ellipsoidal disk. When the bubble attains terminal velocity, the inertial force becomes equal to the drag force. The edge of the ellipsoidal disk bubble exhibits increased surface tension. The difference between experimental data and the analytical model is due to the complex fluid and dynamic

The bubble shape is a required parameter in the modeling and design of multiphase reactors. This communication contributes to the broader discussion and closes the knowledge gap by providing a practical correlation for the bubble shape. The correlation is based on a very large experimental dataset, encompassing a wide range of Morton numbers (Log10(Mo) in the range of −10.8 and 2.3), flow conditions (single bubbles and dense bubbly flows) and considering both gravity-driven flows and flows with an extra-external pressure gradient (counter-current flows). The experimental data were post-processed to derive a simple and physics-based correlation, relating the bubble aspect ratio to the bubble Reynolds and Eötvös numbers. This correlation provides a more accurate description and covers a wider range of applicability compared with literature correlations. As such, it can be helpful in the estimation of the interfacial area and velocity of a dispersed phase rising in a continuous phase.

The lift force is known to strongly influence the lateral bubble distribution in bubbly flows and is therefore an important force that has to be modeled in corresponding CFD simulations. For ellipsoidal bubbles, which are mostly present in industrial cases, the strength as well as the direction in which the lift force acts is determined by the bubble deformation. The bubble deformation however, can strongly be reduced when surface-active contaminations like salts are present in the liquid bulk, which implies a change of the lift force by contaminations too. In the present work, lift coefficients for single bubbles rising in aqueous NaCl solutions were determined to investigate the influence of such an inorganic surfactant on the lift force. For this purpose, a recently developed method by Ziegenhein et al. [Int. J. Multiphase Flow, Vol. 108, 11-24 (2018)] is used, which is capable to measure the lift force in low viscous liquids. Besides the lift force, the bubble shape and slip velocity were studied in detail to connect the results to known contamination effects, which showed different behavior in dependence on the salt concentration. The results reveal that the contamination level plays an important role on changes of the lift force in comparison to clean bubbles. Up to a concentration of 1.0 mol/l the salt has only a weak effect on the lift force of larger bubbles. The lift coefficients of smaller bubbles however, clearly show significant changes, which were also reflected in a change of the bubble shape. However, some findings could only be connected to the slip velocity, which implies a connection of the lift force to more than just the shape.

The lift force is known to strongly influence the lateral bubble distribution in bubbly flows and is therefore an important force that has to be modeled in corresponding CFD simulations. For ellipsoidal bubbles, which are mostly present in industrial cases, the strength as well as the direction in which the lift force acts is determined by the bubble deformation. The bubble deformation however, can strongly be reduced when surface-active contaminations like salts are present in the liquid bulk, which implies a change of the lift force by contaminations too. In the present work, lift coefficients for single bubbles rising in aqueous NaCl solutions were determined to investigate the influence of such an inorganic surfactant on the lift force. For this purpose, a recently developed method by Ziegenhein et al. [Int. J. Multiphase Flow, Vol. 108, 11-24 (2018)] is used, which is capable to measure the lift force in low viscous liquids. Besides the lift force, the bubble shape and slip velocity were studied in detail to connect the results to known contamination effects, which showed different behavior in dependence on the salt concentration. The results reveal that the contamination level plays an important role on changes of the lift force in comparison to clean bubbles. Up to a concentration of 1.0 mol/l the salt has only a weak effect on the lift force of larger bubbles. The lift coefficients of smaller bubbles however, clearly show significant changes, which were also reflected in a change of the bubble shape. However, some findings could only be connected to the slip velocity, which implies a connection of the lift force to more than just the shape.

The bubble shape is a required parameter in the modeling and design of multiphase reactors. This communication contributes to the broader discussion and closes the knowledge gap by providing a practical correlation for the bubble shape. The correlation is based on a very large experimental dataset, encompassing a wide range of Morton numbers (Log10(Mo) in the range of −10.8 and 2.3), flow conditions (single bubbles and dense bubbly flows) and considering both gravity-driven flows and flows with an extra-external pressure gradient (counter-current flows). The experimental data were post-processed to derive a simple and physics-based correlation, relating the bubble aspect ratio to the bubble Reynolds and Eötvös numbers. This correlation provides a more accurate description and covers a wider range of applicability compared with literature correlations. As such, it can be helpful in the estimation of the interfacial area and velocity of a dispersed phase rising in a continuous phase.

Bubble detachment, rise, and bouncing upon impact with a free surface is studied experimentally in variable gravity conditions. Previous investigations focused on the effects of fluid properties such as viscosity or surface tension on the rise and bouncing dynamics. Gravity force is a crucial factor in the detachment, rise and bouncing processes. However, the effect of different gravity levels has never been studied experimentally. In this paper we analyze the role of gravity in the detachment, rise velocity and bouncing motion of millimetric bubbles colliding with a free surface. Single air bubbles in ethanol are detached from a nozzle by the buoyancy force. After reaching a terminal velocity, the rising bubble interacts with the free surface in a bouncing process prior to coalescence. The equivalent bubble diameter at detachment decreases as the gravity level increases, in agreement with the theoretical prediction. An expression for the terminal velocity as a function of gravity is proposed. The terminal velocity is found to increase with the gravity level, although bubbles are smaller at higher values of gravity. The bouncing process has been modelled by a damped oscillator, in which the free surface acts as an elastic membrane. An expression for the frequency of bouncing as a function of gravity has been obtained, showing a good agreement with the experimental results. The motion of the bubble during the bouncing process can be approximated by an underdamped oscillator even if viscosity is negligible. Therefore, viscosity is not the main responsible for damping, which is probably due to energy transfer from the bubble to the fluid in the form of vortex and surface waves generation., Peer Reviewed, Postprint (author's final draft)

The lift force, which strongly influences the spatial bubble distribution, is one of the most important non-drag forces. However, measurements in systems with a low Morton number are limited. In the present work, a time-averaging measurement method with which this gap can be closed is discussed. The experimental setup is kept as simple as possible, avoiding any moving parts. The single bubble movement through a linear shear field was observed three-dimensional over 75 minutes. In total, 85 measurement points cover 13 bubble sizes at 7 different shear rates. The results reveal that former empirical correlations obtained from experiments and simulations in predominantly high Morton number systems are applicable. In this context, the characteristic length scale that is used to describe the lift force needs to be carefully defined. From the present results, the major axis seems to be the most reasonable choice for wobbling bubbles. However, the major axis might be dependent on the flow properties, which leads to a flow dependent lift force formulation.

The lift force, which strongly influences the spatial bubble distribution, is one of the most important non-drag forces. However, measurements in systems with a low Morton number are limited. In the present work, a time-averaging measurement method with which this gap can be closed is discussed. The experimental setup is kept as simple as possible, avoiding any moving parts. The single bubble movement through a linear shear field was observed three-dimensional over 75 minutes. In total, 85 measurement points cover 13 bubble sizes at 7 different shear rates. The results reveal that former empirical correlations obtained from experiments and simulations in predominantly high Morton number systems are applicable. In this context, the characteristic length scale that is used to describe the lift force needs to be carefully defined. From the present results, the major axis seems to be the most reasonable choice for wobbling bubbles. However, the major axis might be dependent on the flow properties, which leads to a flow dependent lift force formulation.

A precise estimation of bubble size distributions is of fundamental and practical importance to understand the fluid dynamics and to estimate the mass transfer in bubble columns. Multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions from the fluid flow conditions by using coalescence and breakage kernels. In particular, this study concerns the prediction of the bubble size distributions in the “pseudo-homogeneous” flow regime, which is characterized by a wide spectrum of bubble sizes and is generally observed in industrial applications. Reliable predictions of the “pseudo-homogeneous” flow regime are, however, limited up to now: one important drawback concerns the selection of appropriate models for the coalescence and break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been further extended to the “pseudo-homogeneous” flow regime by comparing experimental and numerical bubble size distributions at different axial positions in a large-diameter and large-scale bubble column. The results have been critically analysed and may serve as basis to improve the coalescence and break-up closures.

Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flow, which is far away from the flow field observed in multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape, at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. The results reveal that in the bubble column experiments almost the same shape is found whereas the shape in the pipe flows distinctly depends on the flow conditions. The conclusion may be drawn that in bubble columns the assumption of a constant shape regarding the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform the bubble distinctly.

Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flow, which is far away from the flow field observed in multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape, at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. The results reveal that in the bubble column experiments almost the same shape is found whereas the shape in the pipe flows distinctly depends on the flow conditions. The conclusion may be drawn that in bubble columns the assumption of a constant shape regarding the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform the bubble distinctly.

A precise estimation of bubble size distributions is of fundamental and practical importance to understand the fluid dynamics and to estimate the mass transfer in bubble columns. Multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions from the fluid flow conditions by using coalescence and breakage kernels. In particular, this study concerns the prediction of the bubble size distributions in the “pseudo-homogeneous” flow regime, which is characterized by a wide spectrum of bubble sizes and is generally observed in industrial applications. Reliable predictions of the “pseudo-homogeneous” flow regime are, however, limited up to now: one important drawback concerns the selection of appropriate models for the coalescence and break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been further extended to the “pseudo-homogeneous” flow regime by comparing experimental and numerical bubble size distributions at different axial positions in a large-diameter and large-scale bubble column. The results have been critically analysed and may serve as basis to improve the coalescence and break-up closures.

Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flow, which is far away from the flow field observed in multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape, at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. The results reveal that in the bubble column experiments almost the same shape is found whereas the shape in the pipe flows distinctly depends on the flow conditions. The conclusion may be drawn that in bubble columns the assumption of a constant shape regarding the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform the bubble distinctly.

Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flows, which is far away from the flow field observed in large-scale multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape (in terms of aspect ratio), at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. In the bubble column experiments almost the same shape is observed; conversely, the shape in the pipe flows distinctly depends on the flow conditions. In conclusion, in bubble columns the assumption of a constant shape regardless of the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform distinctly the bubbles.

The bubble shape is fundamental for every aspect of modelling bubbly flows. The interface is usually highly deformable so that the bubble shape is in general dependent on the surrounding flow field. Since recent work on this topic addressed almost entirely single-bubbles rising in quiescent flow, the extent of such flow field dependencies is rather unknown. This study examines the effect on the bubble shape when flow properties, i.e. the gas flow rate, sparger setup, and column geometry, are changed by evaluating six different bubble column experiments. The results of this integral approach reveal that the bubble shape of small bubbles is distinctly influenced whereas the shape of large bubbles is unchanged. Averaged over all flow rates, we find that the size-dependent bubble shapes are quite similar for all six experiments. Further studies focusing on single local effects like the shear rate or wake effects are highly desirable to obtain a deeper understanding of the underlying processes; for this purpose, the given results can help to assess the most important effect and in which extend it should be studied.

The bubble shape is fundamental for every aspect of modelling bubbly flows. The interface is usually highly deformable so that the bubble shape is in general dependent on the surrounding flow field. Since recent work on this topic addressed almost entirely single-bubbles rising in quiescent flow, the extent of such flow field dependencies is rather unknown. This study examines the effect on the bubble shape when flow properties, i.e. the gas flow rate, sparger setup, and column geometry, are changed by evaluating six different bubble column experiments. The results of this integral approach reveal that the bubble shape of small bubbles is distinctly influenced whereas the shape of large bubbles is unchanged. Averaged over all flow rates, we find that the size-dependent bubble shapes are quite similar for all six experiments. Further studies focusing on single local effects like the shear rate or wake effects are highly desirable to obtain a deeper understanding of the underlying processes; for this purpose, the given results can help to assess the most important effect and in which extend it should be studied.

Lift coefficients, CL, of single bubbles in linear shear flows are measured to investigate effects of the bubble shape, the liquid velocity gradient and the fluid property on CL. The range of the Morton number, M, tested are from logM = −6.6 to −3.2. The shapes of bubbles are spherical and ellipsoidal. A correlation of bubble aspect ratio for single bubbles in infinite stagnant liquids proposed in our previous study can give good evaluations for bubbles in the linear shear flows. The CL of spherical bubbles at low bubble Reynolds numbers, Re, depend on the dimensionless shear rate Sr and Re and decrease with increasing Re. These characteristics agree with the Legendre-Magnaudet correlation. The use of a single dimensionless group such as Re, the Eötvös number, the Weber number and the Capillary number cannot correlate CL of non-spherical bubbles. The trend of the critical Re for the reversal of the sign of CL is the same as that for the onset of oscillation of bubble motion, which supports the mechanism proposed by Adoua et al., at least within the range of -6.6 < logM < -3.2. An experimental database of CL is provided for validation of available CL models and CFD.

Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flow, which is far away from the flow field observed in multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape, at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. The results reveal that in the bubble column experiments almost the same shape is found whereas the shape in the pipe flows distinctly depends on the flow conditions. The conclusion may be drawn that in bubble columns the assumption of a constant shape regarding the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform the bubble distinctly.

This work deals with the study of bubble-liquid mass transfer coupled with chemical reactions. The absorption of carbon dioxide in aqueous solu- tion of sodium carbonate and bicarbonate is used as a reference case. The influences of the interface contamination state and of the ellipsoidal shape of the bubble on the mass transfer rate are studied using a two-dimensional (2-D) axisymmetric model. On the one hand, the case of a spherical bubble with a partially contaminated interface is investigated. It is assumed that a fixed stagnant cap lies on a part of the bubble surface in the rear. On the other hand, the case of an ellipsoidal bubble with a clean interface is investigated. In a first stage, correlations to estimate the transfer rate without reaction are presented and compared to the 2-D model results. In a second stage, the mass transfer rate is computed with chemical reactions for several reaction rates. The influences of the coupling reactions - contamination state and the coupling reactions - ellipsoidal shape are then presented and discussed. These 2-D model results are also compared to mass transfer rate estimations based on classical one-dimensional (1-D) models. It is shown that 1-D approaches are useful to provide a rough estimation of the mass transfer rate but 2-D models have to be used when an accurate estimation of the mass transfer rate is required., SCOPUS: ar.j, info:eu-repo/semantics/published

This work deals with the study of bubble-liquid mass transfer coupled with chemical reactions. The absorption of carbon dioxide in aqueous solu- tion of sodium carbonate and bicarbonate is used as a reference case. The influences of the interface contamination state and of the ellipsoidal shape of the bubble on the mass transfer rate are studied using a two-dimensional (2-D) axisymmetric model. On the one hand, the case of a spherical bubble with a partially contaminated interface is investigated. It is assumed that a fixed stagnant cap lies on a part of the bubble surface in the rear. On the other hand, the case of an ellipsoidal bubble with a clean interface is investigated. In a first stage, correlations to estimate the transfer rate without reaction are presented and compared to the 2-D model results. In a second stage, the mass transfer rate is computed with chemical reactions for several reaction rates. The influences of the coupling reactions - contamination state and the coupling reactions - ellipsoidal shape are then presented and discussed. These 2-D model results are also compared to mass transfer rate estimations based on classical one-dimensional (1-D) models. It is shown that 1-D approaches are useful to provide a rough estimation of the mass transfer rate but 2-D models have to be used when an accurate estimation of the mass transfer rate is required., SCOPUS: ar.j, info:eu-repo/semantics/published

Dynamic behavior of a two-phase bubble, i.e. a steam bubble containing a droplet evaporating in the bubble, in the molten alloy was clearly visualized using high-frame-rate neutron radiography. In relation to some direct contact heat exchanger design with molten lead-bismuth (Pb-Bi), experiments have been done at JRR-3M of JAEA (Japan Atomic Energy Agency) with water droplets evaporating in a stable thermally stratified Newton's alloy pool. The instantaneous shape and size of the bubble has been iteratively estimated from the void fraction distributions and total void volume by assuming a symmetrical bubble shape.

A simple equation with only a few physical parameters for the description of the high stalk bubbles has been derived from variational principles. The proposed equation was used in modeling of the film blowing process and a very good agreement between measured and simulated data was found.

A simple equation with only a few physical parameters for the description of the high stalk bubbles has been derived from variational principles. The proposed equation was used in modeling of the film blowing process and a very good agreement between measured and simulated data was found.

A simple equation with only four physical parameters for the description of the bubble shape (including HDPE wine-glass shape) has been derived from variational principles. The proposed equation was used in modeling of the film blowing process for a variety of process conditions and polymer melts, and a very good agreement between measured and simulated data was found.

A simple equation with only four physical parameters for the description of the bubble shape (including HDPE wine-glass shape) has been derived from variational principles. The proposed equation was used in modeling of the film blowing process for a variety of process conditions and polymer melts, and a very good agreement between measured and simulated data was found.

NR 20140805

The wide range of applications of bubbly flows in the industry makes its accurate modelling strongly demanded. The modelling of bubbly flow, however, is not straightforward because it consists of multi-scale structures in both time and space. Furthermore, the experimental verifications of the theoretical and the Direct Numerical Simulations, DNS, available are noticeably scarce especially for bubbles at high Reynolds numbers. Hence, this research aims to make its contribution to addressing the basic roots that make the modelling process difficult. These roots are represented, but not limited, by the bubble dynamics and bubble-bubble interaction. Tracking of single and dual air bubbles in quiescent water is experimentally carried out using a high-speed camera. For the numerical simulations, using ANSYS-FLUENT software with the VOF model, a structured adaptive mesh technique was developed here that is used to achieve a desirable level of refinement of the mesh around the rising bubbles. It has been found that there is a relationship between the lateral migration of an ellipsoidal bubble and the shape oscillation. This relationship, however, has not been observed for the numerical approach. It also overestimated the experimental findings of bubble kinetics and shape oscillation by 30%. Interestingly, this research contributes to awakening the small details in the underlying physics of the interaction between a pair of rising bubbles. It has been found that a slight deviation in the size of a trailing bubble plays an important role in the state of the trailing bubble whether it approaches the leading bubble or separates from at large separation distances. This is considered due to the greater rise velocity that a smaller bubble has in the ellipsoidal regime compared to the larger bubble. Furthermore, when the separation distance between the rising bubbles is decreased, the appreciable acceleration that the trailing bubble owns has led it to approach the leading bubble a