Behavior Of Single Bubble Research Articles

Insight into the behavior of colloidal gas aphron (CGA) fluids at elevated pressures: An experimental study

Recently, colloidal gas aphron (CGA) fluids technology has been employed to drill depleted oil and gas reservoirs. Almost all reported experience on CGA fluids were conducted at ambient conditions, and little attention has been paid on the behavior of CGAs at high pressures which is more close to real conditions. In this study, high pressure experiments were conducted by using High Pressure Microscope cell to visualize/monitor the behavior of CGAs at elevated pressures. Single bubble behavior and bubble size distribution (BSD) of CGAs were investigated under different scenarios of pressure change. Results of experiments revealed that BSD of CGAs is controlled by the path of pressure changes, and sudden pressure change affects BSD less than stepwise changes in pressure. The pressure-volume product of bubbles, as a new criterion for analysis of single bubble behavior was introduced. The behavior of pressure-volume product for a single bubble shows significant loss of air via diffusion through tri-layer film into the bulk phase during compression as well as a hysteretic behavior during compression and decompression processes. Monitoring single bubble behavior at elevated pressures revealed that CGAs meet three distinct regions with time: first, they exhibited a sharp reduction in bubble size (region I), then became stable with minimum change in bubble diameter (region II), and finally, the size of bubbles decreased suddenly and after a short time they were collapsed (region III). Observations which showed aphrons were survived at pressures as high as 2000psig may support the idea for field applications of CGAs as drilling fluids. Results of this work may provide thorough insight into behavior of CGA fluids at elevated pressures.

Rising behavior of single bubble in infinite stagnant non-Newtonian liquids

This work is an experimental study of the rising behavior of single air bubbles in infinite stagnant non-Newtonian liquids. Aqueous solutions of carboxymethyl cellulose (CMC) are selected to study the effect of rheological properties. The high speed photography is employed to record the bubble motion in CMC solutions. The bubble size, rising trajectory, bubble shape and velocities are determined by digital image processing technique. As expected, the rheological properties have great influence on the rising behavior of single bubble. In the less concentrated CMC solutions, the bubble rising process can be divided into three stages according to spatial evolution of bubble shape. The deformation changes the trajectories of rising bubbles and bubble hydrodynamics. As the solution concentration increases, the transitional stage gradually disappears. In the most concentrated CMC solution, the first continuous shape flattening stage is directly followed by a rising process with bubble shape basically constant, the rectilinear path and constant rising velocity. Dimensional analysis is performed to formulate a general dimensionless correlation for the deformation and motion of bubbles in infinite liquids by considering the rheological properties.

In situ observation and numerical simulation of bubble behavior in CaO-SiO2 based slag during isothermal and nonisothermal processes

The hot thermocouple technique was used to observe the variation of bubble size in CaO-SiO2 based molten slag at above 1273K. Considering that the physical properties of gases change with temperature, the effect of cooling rate on the single bubble behavior was studied according to the heat and mass transfer equations. In order to investigate the distribution of pore size in solidified layer, solidification of slag was conducted in laboratory by using a water-cooled detector, and the pore size in the solidified layer was counted under the scanning electron microscope. The heat flux measured by the water-cooled detector was used as boundary conditions to establish a mathematical model that is capable of describing the characteristics of bubble size distribution. Both the calculation and the observations indicate that the time-temperature history is an important factor that could affect the bubble behavior in molten slag. For slag with no Na2SO4, bubbles with large size concentrate on the detector side with high cooling rate, while bubbles with small size are likely to appear on the liquid side with low cooling rate. For slags containing Na2SO4, bubbles with large size mainly distribute on the middle layer of the solid slag film.

The Investigation of the Effect of Reduced and Microgravity Conditions on Single Bubble (Drop) Behavior Fixed on a Solid Surface in a Liquid

The study of the gas bubble (drop) behavior under reduced gravity and microgravity conditions may be used in the conceptual design of aircraft’s and space based gas-liquid management system. It is very important to consider the changed gravity and microgravity conditions influence on the gas bubble (drop) behavior fixed on the solid surface, as this influence can be more strongly than other external forces action. The main purpose of the present research to investigate the effect of reduced and microgravity conditions on single bubble (drop) behavior, fixed on the solid surface in the liquid. It has been developed a new mathematical techniques to model the behavior of the gas bubbles (drops), fixed on the solid surface in the liquid under reduced and microgravity conditions. These techniques have been used to modelling of the gas bubbles (drops) profiles behavior and to calculation of their common surface energy change under decreased, increased and microgravity conditions. The model has been used also to estimate conditions of bubbles (drops) tear from and fixation on the solid surface in these conditions. The numerical calculations of the developed model permitted to establish that under decreased gravity the gas bubble (drop) is ‘raised’ on the solid surface in the liquid and its common surface energy is free. The gas bubbles with volumes (as example) from 1.9-2.2 cm3 are tore from solid surface and their free energy is transformed to the kinetic energy of bubble jumping from top to the liquid bottom. The gas bubbles with volumes from 2.3-2.8 cm3 were fixed on the solid surface and their free energy was expensed on the gas bubbles oscillations at the solid surface. Under increased gravity conditions the gas bubble (drop) is ‘laid’ on the solid surface in the liquid and the common surface energy is not a free and it is expensed on the bubbles (drops) oscillations at the solid surface. The theoretical conclusions and numerical calculations of the developed model have been proved on the conducted parabolic aircraft's tests. The tests have proved that the developed model can correctly simulate the gas bubbles and drops profiles behavior, their common surface energy change and estimate conditions of their tear from and fixation on the solid surface in reduced and microgravity conditions. The computer techniques of the model can simulate the bubbles and drops behavior under different external forces influences in microgravity conditions (g=0) when they are considered. Besides, using of the developed model permits to control of the gas bubbles and drops behavior in microgravity by controlled changing of surface tension and cohesive angle (apolar reactives action).

Visualization of behavior of single bubble in horizontal turbulent channel flow

Visualization of behavior of single bubble in horizontal turbulent channel flow

非牛顿流体中单气泡运动行为研究

利用高速摄像机及数字图像处理技术对单气泡在不同质量分数的羧甲基纤维素钠(CMC)水溶液中的运动行为进行实验测试，得到气泡运动轨迹及上升速度。同时，采用VOF (volume of fluid)模型，模拟计算单气泡在不同质量分数CMC水溶液中的上升过程，考察上升气泡对周围液相场的影响规律。实验结果表明，流变特性对单气泡在CMC水溶液中的运动行为有较大影响。气泡在不同质量分数CMC水溶液中的上升速度沿水深变化规律不同。上升速度的稳定值随CMC水溶液的质量分数增加而减小。摆动运动的强度随CMC水溶液质量分数的增加而减弱，最终气泡趋于直线上升。模拟结果较好再现了单气泡在不同质量分数CMC水溶液中的上升过程。同时还发现，在低质量分数的CMC水溶液中，气泡摆动上升会在尾迹区形成交替漩涡；而在高质量分数的溶液中，尾迹区的液相流场基本按照对称分布。气泡对尾部液相流场的影响范围随着CMC水溶液质量分数的增加而减小。 The high speed photography and digital image processing technique have been employed to measure the rising behavior of the single bubble in carboxymethyl cellulose (CMC) solution to obtain the trajectory and the rising velocity of the bubble. Meanwhile, based on the volume of fluid (VOF) model, numerical simulation has been conducted to study the rising process of the single bubble in CMC solution, and the influence of the rising bubble on the velocity field of the surrounding liquid phase has been investigated. According to the experimental results, the rheological property has great influence on the rising behavior of single bubble in CMC solution. It is shown that the rising velocity of the bubble in the CMC solutions with different weight percentage has different variation patterns. The value of the steady rising velocity decreases with the increase of the weight percentage of the CMC solution. The strength of the oscillation grows weaker with the increase of the weight percentage of CMC solution and eventually tends to ascend along a straight line. The simulation results well predict the bubble’s rising process in CMC solution with different weight percentage. Furthermore, the simulated results show that the bubble generates alternate vortex in CMC solution with lower weight percentage as bubble swings up, while in the CMC solution with higher weight percentage, the flow field of liquid phase distributes symmetrically. The influence domain of the rising bubble on the wake field decreases with the increase of the weight percentage of the CMC solution.

Modeling of spout-fluidized beds and investigation of drag closures using OpenFOAM

The present work employs the open source package, OpenFOAM, for dynamic simulations of the intrinsically unsteady and nonhomogeneous gas-particle flows in spout fluidized beds using the discrete particle model (DPM) coupled with the computational fluid dynamics (CFD). Firstly, the effect of grid size on particle motion is investigated and a minimum ratio of grid size to particle diameter is suggested for gas-particle flow simulations. Secondly, the porosity calculation procedure is tested by the simulation of particle packing process. Finally, two cases of the single bubble behavior and the spout-fluidization regime in spout-fluidized beds are simulated and the effect of drag closures are investigated. The results show that the Plessis & Masliyah drag relation predicts an inappropriate gas-particle interaction especially in condition of low particulate volume fraction. The embedded drag relations from lattice-Boltzmann (LBM) simulations perform better than the Gidaspow relation especially for the spout-fluidization regime. The van der Hoef et al. drag relation is found more suitable for modeling spout-fluidized beds than the others in the present work.

Numerical simulation of single bubble rising in shear-thinning fluids by level set method

The behavior of single bubble rising in quiescent shear-thinning fluids was investigated numerically by level set method. A number of bubbles in a large range of Reynolds number and Eotvos number were investigated including spherical, oblate and spherical. The bubble shape and drag coefficient were compared with experimental results. It is observed that the simulated results show good conformity to experimental results over a wide range of Reynolds number. In addition, the detailed flow field based on the reference coordinate system moving with the bubble is obtained, and the relationship among flow field, bubble shape and velocity is discussed.

Analysis of the nonlinear dynamic characteristics of two-phase flow based on an improved matrix pencil method

Gas–liquid two-phase flow is complex and has uncertainty in phase interfaces, which make the two-phase flow look very complicated. Even though the flow behavior (e.g. coalescence, crushing and separation) of single bubble or bubble groups in the liquid phase looks random, combining some established characteristics and methodologies can find regularities among the randomness. In order to excavate the nonlinear dynamic characteristics of gas–liquid two-phase flow, the authors developed an improved matrix pencil (IMP) method to analyze the pressure difference signals of the two-phase flow. This paper elucidates the influence of signal length on MP calculation results and the anti-noise-interference ability of the MP method. An IMP algorithm was applied to the fluctuation signals of gas–liquid two-phase flow to extract the mode frequency and damping ratio, which were combined with the component energy index (CEI) entropy to identify the different flow patterns. It is also found that frequency, damping ratio, CEI entropy and stability diagram together not only identify flow patterns, but also provide a new way to examine and understand the evolution mechanism of physical dynamics embedded in flow patterns. Combining these characteristics and methods, the evolution of the nonlinear dynamic physical behavior of gas bubbles is revealed.

Bubble nonlinear dynamics and stimulated scattering process**Project supported by the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT1228) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant Nos. 11204050 and 11204049).

A complete understanding of the bubble dynamics is deemed necessary in order to achieve their full potential applications in industry and medicine. For this purpose it is first needed to expand our knowledge of a single bubble behavior under different possible conditions including the frequency and pressure variations of the sound field. In addition, stimulated scattering of sound on a bubble is a special effect in sound field, and its characteristics are associated with bubble oscillation mode. A bubble in liquid can be considered as a representative example of nonlinear dynamical system theory with its resonance, and its dynamics characteristics can be described by the Keller–Miksis equation. The nonlinear dynamics of an acoustically excited gas bubble in water is investigated by using theoretical and numerical analysis methods. Our results show its strongly nonlinear behavior with respect to the pressure amplitude and excitation frequency as the control parameters, and give an intuitive insight into stimulated sound scattering on a bubble. It is seen that the stimulated sound scattering is different from common dynamical behaviors, such as bifurcation and chaos, which is the result of the nonlinear resonance of a bubble under the excitation of a high amplitude acoustic sound wave essentially. The numerical analysis results show that the threshold of stimulated sound scattering is smaller than those of bifurcation and chaos in the common condition.

Research Progress of Bubble Behavior in Ionic Liquid Systems

As a new class of green solvents, ionic liquids (ILs) are very promising for gas separation due to their high capacity and selectivity of gases. Among the research on ILs, the hydrodynamics in IL systems is essential for industrial application. This paper reviews the bubble behavior in IL systems, which is common in reactors for gas separation. The single bubble behavior, multi-bubble behavior and bubble behavior in microchannels are discussed in the aspects of experiment and numerical simulation respectively. Furthermore, the tendency and challenges of research on bubble behavior in IL systems are proposed.

Numerical simulation on single bubble behavior during Al2O3/H2O nanofluids flow boiling using Moving Particle Simi-implicit method

In this study, regression analysis on the thermal properties of Al2O3/H2O nanofluids was made firstly. The growth and departure of a single bubble behavior in Al2O3/H2O nanofluid and pure water flow boiling process were then numerically simulated by an improved Moving Particle Semi-implicit method in different flow boiling conditions. The results indicate that the bubble in Al2O3/H2O nanofluids grows faster and the bubble departure frequency of Al2O3/H2O nanofluids is greater than that in pure water. The flow boiling heat flux is also improved by dispersing nanoparticles of Al2O3/H2O in pure water. This work initially reveals that nanofluids can enhance flow boiling heat transfer from the point of view of bubble dynamics behavior. The effects of nanoparticle concentrations and diameters of Al2O3/H2O nanofluids on the bubble behavior were also investigated and compared under the same flow conditions. It is found that the increasing of nanoparticle volume concentration may increase the bubble departure frequency and departure diameter, while the increasing rates of departure frequency and departure diameter are lessened with the increasing of nanoparticle volume concentration. It is suggested that the suitable nanoparticle volume concentration of nanofluid for flow boiling heat transfer enhancement should not be too large, especially regarding the negative effect of flow resistance increase due to the increasing of nanoparticle volume concentration. The interesting finding is that in the same nanoparticle volume concentration condition, the bubble departure frequency for the nanofluid with nanoparticle diameter of 29 nm shows a maximum value. The increasing of nanoparticle diameter leads to the decreasing of bubble departure diameter. It is boldly to predict that an optimal nanoparticle diameter range between 20 and 38 nm should be beneficial to flow boiling heat transfer enhancement of Al2O3/H2O nanofluids.

Modeling of micro-bubble surfactant multi-layer drilling fluid stability based on single bubble behavior under pressure and temperature in a deviated gas well

Micro-bubble surfactant multi-layer (MBSML) drilling fluids are included in the drilling operation of low pressure reservoirs. These fluids contain tiny dispersed micro-bubbles coated with two surfactant layers. For the stability evaluation of these fluids in operational conditions, surfactant type, concentration, pressure and temperature effects on the size of micro-bubble fluid, should be scrutinized. For investigating these variables, a diffusion model for solute transport in micro-bubble fluids was proposed with the mass transfer concept. The model included mass transfer resistance of fluid phases and interfaces. It was observed that the bubble sizes decrease as a result of adding surfactant to the fluid. However, there were pressure, temperature and surfactant concentration thresholds for the bubble stability.

Numerical simulation of vapor bubble condensation in turbulent subcooled flow boiling

Subcooled flow boiling is a significant heat transfer regime in pressurized water reactors (PWRs) and also occurs in boiling water reactors (BWRs) prior to the onset of saturated nucleate boiling. In subcooled boiling, individual bubbles experience a life-cycle of nucleation from the wall, (possible) departure from the wall, and transport along the channel during condensation/collapse. The present paper focuses on the last stage of this life cycle. CFD analysis of a single bubble behavior in upward subcooled flow boiling was performed using volume-of-fluid (VOF) interface tracking method and large eddy simulation (LES) turbulence model. High pressure steam-water conditions at high flow velocity were simulated due to their relevance to the nuclear application. The numerical solutions were compared with terminal velocity correlations. Bubble behavior was investigated at different system pressure, subcooling temperature, bubble diameter, pipe diameter, and bulk fluid velocity, corresponding to bulk Reynolds number range of 0–410,000. The effects of these parametric variations on bubble rise velocity, deformation rate, trajectory, and distortion are presented. Results show that bubble rise velocity increases with bulk velocity, and bubble size, but decreases with increasing pipe diameter. A reverse bubble velocity trend with varying system pressure is observed with and without bulk velocity. Bubble condensation rate decreased with increasing system pressure, bubble size and pipe diameter, but increased with increasing subcooling temperature and bulk fluid velocity.

Rising behaviour of single bubbles in narrow rectangular channels in Newtonian and non-Newtonian liquids

A phenomenological investigation of single bubbles ascending in a confined geometry with a rectangular cross section was done. Motivated by the goal to get a deeper understanding of the bubble behaviour in flat sheet membrane modules used in membrane bioreactors, the parameters channel depth (=spacing, 5–7mm), bubble size (3–9mm), superimposed liquid velocity (0–23.5cm/s) and rheology of the continuous phase (Newtonian, shear-thinning) were varied. The shear-thinning liquid was used to simulate the rheological behaviour of activated sludge apparent in membrane bioreactors. The analysed properties included the rising paths, bubble shape, absolute and relative terminal rise velocities, friction factors and oscillation frequencies and amplitudes of the bubble.As expected, a significant influence of the rheology of the continuous phase was found on the rising behaviour. In the shear-thinning liquid, the bubbles followed mostly a straight rising path with negligible oscillations. The variation of the channel depth mainly had an influence on the terminal rise velocity of the bubbles ascending in the shear-thinning liquid with higher values in the channel with the larger channel depth. Increasing the bubble size led to higher rising velocities and to enhanced oscillations.

The particle hydrodynamic effect on the mass transfer in a buoyant CO2-bubble through the experimental and computational studies

In this paper, we present the mass transfer during the buoyant CO2 bubble absorption in a particle suspension by the experimental and computational studies. In the experimental study, the transient evolution of a single bubble behavior is visualized for the CO2 absorption in Al2O3-nanofluids. In the computational study, the finite element approximated Navier–Stokes equations are employed integrating with a level set method for tracking the interface on the convective diffused mass transfer in a CO2 bubble with the multi-freely suspended non-Brownian Al2O3-particles. In both approached studies, the particle hydrodynamic effect to the bubble motion takes effect on increasing the mass transfer area followed by inducing the mass transfer enhancement (MTE) by a term of the larger mass transfer coefficient (MTC) at the gas–liquid phase. From computational study, this is also supported that the enhanced mass flux is highly influenced by the particle hydrodynamics on the bubble surface in a buoyant bubble. Consequently, it can lead to find an existence as one of possible mechanisms for MTE on a gas-absorption in a suspension.

Numerical Analysis of Single Bubble Behavior in a Megasonic Field by Non-Spherical Eulerian Simulation

The mechanism of particle removal in megasonic cleaning needs to be clarified so that it can be controlled and used to clean nanodevices without causing pattern damage. Single bubble behavior in a standing megasonic wave was analyzed using a compressible locally homogeneous model of a gas-liquid two-phase medium. This simulation is the first step toward understanding the particle removal mechanism in megasonic cleaning. We confirmed that our numerical method simulated the characteristics of bubble translational motion in a standing wave, in which the direction of the movement due to the primary Bjerknes force changed at the resonant radius. When the initial position of the bubble was near a moving wall, even a bubble with a radius smaller than the resonant radius moved toward the pressure node. In the three-dimensional calculations, bubble collapse near a side wall induced a higher pressure on the side wall than the maximum pressure of the megasonic wave. The bubble dynamics calculation with gas diffusion indicated that the effect of the rectified diffusion was small because the effect of the dynamic bubble motion was dominant on a timescale of several milliseconds.

Study of a single coarse bubble behavior in the presence of D.C. electric field

An experimental study was carried out to investigate the effects of both uniform and non uniform D.C. electric fields on the motion and deformation of a single coarse bubble rising in dielectric liquid media. Bubble shape, aspect ratio, rising path, rise velocity and maximum inclination angle were determined by digital processing of high speed video images (600 fps). Three different viscosities of silicone oil were utilized as a base of quiescence media. Results show that the bubble deformation under the influence of electric field increases at low Re number. Moreover bubble deviation from its rising path increases by adding to electric field strength as well as reduction in liquid viscosity and subsequently the more inclination angle is observed. Bubble velocity in the region of steady and unsteady motion is not affected by applied electric field due to high hydrodynamic forces associated with relatively large bubble; though, its detachment is improved by the applied electric field. Our observations revealed that in the case of coarse bubbles, where electric forces are negligible in comparison with high hydrodynamic instability, EHD flow plays an important role in controlling the motion. This investigation can be helpful in giving a better insight of coarse bubble's behavior under the influence of electric fields and also provides a means for its manipulation in scientific problems as well as engineering applications

Modeling of non-isothermal CO2particle leaked from pressurized source: I. Behavior of single bubble

This study revealed the behavior of droplets formed through leak process in deep water. There was a threshold depth named the universal attraction depth (UAD). Droplets rose upward in the zone below the UAD called the rising zone, and settled down in the zone above the UAD called the settling zone. Three mass loss modes were identified and formulated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. The first two were active for the settling zone, and all the three were effective for the rising zone. In consequence, the life time of the droplets in the rising zone was far shorter than that of the droplets in the settling zone.

Two-dimensional volume of fluid simulation studies on single bubble formation and dynamics in bubble columns

In this paper, the volume of fluid (VOF) model in conjunction with continuum surface force (CSF) model was used to numerically investigate the single bubble formation and dynamics in the bubble columns on the software platform of Fluent 6.3. A set of transient conservation equations of mass and momentum taking surface tension and gravitational force effects into consideration were solved by pressure implicit splitting operator (PISO) algorithm and a piecewise linear interface calculation (PLIC) was applied to characterize the behavior of gas–liquid interface movement in the VOF method. The simulation results of bubble formation and dynamics compare well with available literature results. The effects of physical properties including surface tension, liquid viscosity and density, gas or liquid operation conditions and orifice size on the single bubble generation, detachment, rising and coaxial bubble coalescence were systematically analyzed, and the effect of superficial liquid velocity on single bubble behavior was especially discussed. It is found that non-zero superficial liquid velocity enhances the bubble detachment, decreases the bubble size, and delays the coaxial bubble coalescence obviously. Increasing superficial liquid velocity largely raises the velocity of the leading bubble and enlarging orifice gas velocity mainly accelerates the second bubble of two coalescence bubbles.