Bubble Flow Characteristics Research Articles

Flow and heat transfer characteristics of high temperature continuous rising bubbles

In the movement process of continuous bubbles, different liquid-flow state and initial temperature of bubbles have important influence on bubble movement and heat transfer. In this study, the flow and heat transfer characteristics of high temperature bubbles in normal temperature liquid are investigated. The rising process of and temperature of bubbles are studied by numerical simulation and compared with experimental results for verification. The results show that the shape, velocity and temperature of the bubble are affected by the initial position of the bubble. Because the closer the initial position of the bubble is to the bottom of the cylinder, the greater decrease of the bubble aspect ratio, w*, the faster decrease of bubble temperature, and the larger bubble velocity would be. The increase of the bubble diameter would mitigate the influence of liquid jet on the bubble motion. Finally, as the bubble surface tension increases, the liquid jet would have less influence on the bubble movement.

BUBBLE FLOW CHARACTERISTICS OF SUBCOOLED FLOW BOILING IN HEAT SINKS WITH STRAIGHT AND WAVY MICROCHANNELS

BUBBLE FLOW CHARACTERISTICS OF SUBCOOLED FLOW BOILING IN HEAT SINKS WITH STRAIGHT AND WAVY MICROCHANNELS

An investigation on the bubbly flow of a Venturi channel based on the population balance model

AbstractIn this paper, the bubbly flow characteristics of a Venturi channel was revealed by using the population balance model (PBM) within the framework of computational fluid dynamics (CFD) numerical simulation and focused on the bubble size distribution and pressure drop △P of different regions. The simulation results indicated that bubble breakup mainly occurred in the diverging section of the Venturi channel, and the average diameter of the daughter bubbles davg in the sidewall region was much smaller than that in the central region. Through the correlational analysis between the bubble size distribution and turbulent flow field, the bubble breakup in the diverging section was positively related to the turbulent flow. Considering the influence of geometric parameters on davg and △P, the davg decreased and △P increased with the increasing of the diverging angle β. As the throat diameter D increased, the davg increased and △P decreased gradually. In order to quantify the bubble breakup characteristics, the concept of bubble breakup ratio τ is introduced and defined as the ratio of inlet average bubble diameter di to the outlet average bubble diameter do. Through dimensionless transformation, the fitting relationship between τ or △P and angle ratio a was Sinusoidal function (SINE), respectively, and was Boltzmann with the throat length‐diameter ratio b. Due to the relationship of first‐order linear function between τ and △P, the bubble breakup ratio can be obtained by measuring the pressure drop of the Venturi tube, which was significant to the practical engineering application.

Numerical simulation of two-phase hydrodynamics and mass transfer inside a serpentine tubular gas–liquid reactor

The multiphase behavior in gas–liquid reactors is a focused topic in chemical engineering. In this paper, the TFM-PBM method is implemented to study hydrodynamics and interfacial mass transfer characteristics of bubbly flow in a novel serpentine tubular reactor. The calculated evolution of bubble diameter and the gas phase distribution which converts between the ‘wall-peak’ and ‘core-peak’ pattern while flowing across the serpentine tube are in reasonable agreement with experiment results. Both the slip penetration model and the eddy cell model are employed to investigate the local mass transfer process, and the overall kla predicted by the two distinct models coincides with the measured data under various operating conditions. It was found that the deviation between the two distinct models becomes more pronounced as the turbulent dissipation rate increases, which is opposite to the results in the numerical study of bubble columns.

Gas holdup and bubble flow transition characteristics in column flotation process determined by capacitive signals measurement

A non-invasive and non-intrusive monitoring techniques are developed based on the signal capacitance method to observe column flotation performance. In general, gas holdup and bubble flow characteristics are the essential parameters that affect flotation performance. This study investigates and verifies the effects of frother dosage and solid percent on the gas holdup and bubble flow transition characteristic by analyzing the capacitance signals. Experiments were conducted in two- and three-phase systems with a variation of frother addition and solid concentration in the range of 1–5 cm/s of superficial gas velocities. The results showed that the capacitance signals method could characterize the bubble flow and its transition in column flotation, which consists of discrete bubbly, cap-discrete bubbly, and slug flow. The bubble flow transition in the three-phase system occurred at slightly lower superficial gas velocity and gas holdup than in the two-phase system, as measured by the deviation of gas holdup analysis. Higher frother addition and the higher solid concentration will decrease the gas holdup of bubble flow transition. In this study, the flow transition occurred between the superficial gas velocity of 2.5–3.3 cm/s for 2 phase and 2.5–3 cm/s for 3 phase systems.

Analysis of Bubble Flow Mechanism and Characteristics in Gas–Liquid Cyclone Separator

The separation of bubbles in a gas–liquid cyclone is complicated. A combination of numerical simulation and visual experimentation was considered apt to reveal the microscopic mechanisms of bubble flow. First of all, cyclones with different structures were numerically simulated. The calculation results show that the larger the diameter of the exhaust port, the better the bubble flow effect. When the exhaust port diameter was 24 mm, the gas discharge efficiency was 8% higher than that with an exhaust port diameter of 16 mm. The sequence of the bubble flow effect of a four-structure cyclone was obtained, and the gas discharge efficiency of the cyclone with a rectangular inlet was 7% higher than that of the trapezoidal inlet. Finally, a visual experimental platform was built to compare the rectangular inlet cyclone and spiral inlet cyclone with the best bubble flow effect. In accordance with the simulation numerical calculations, the bubble flow effect of the rectangular inlet cyclone was better than that of the spiral and trapezoid inlet cyclones, and the rectangular inlet in the middle was better. This article provides a specific theory and experience to guide further research on the separation mechanism, flow field characteristics and structurally optimal design of gas–liquid cyclones.

Experimental study of gas-liquid two-phase bubbly flow characteristics in a static mixer with three twisted leaves

Under the conditions of liquid phase inlet Re ranging from 9,836 to 56,206 and gas fraction a from 4.76% to 66.67%, gas-liquid two-phase bubbly flow was investigated in a static mixer with three twisted leaves (TKSM) with a diameter of 100 mm and an aspect ratio of 1.5. A high-speed camera Revealer-2F04M with a resolution of 1,920×1,080 pixels was used to capture the evolution of bubble groups at the different axial windows of mixer elements. The results show that the flow pattern in the TKSM is still in bubbly flow at the flow rate of continuous phase QL no more than 1.0 m3/h and gas fraction α higher up to 54.55%–66.67%. The Sauter mean diameter d32 of bubble groups gradually decreased with the increase of the mixing elements number. With the given liquid flow rate Ql≤1.0 m3/h, the Sauter mean diameter d32 firstly decreased and then increased with the increase of gas flow rate. The local minimum of d32 was obtained at QG=0.72m3/h and 84.5% of the dB/D0 is in the range of 0.02–0.05. The relationship among Sauter mean diameter, the inner diameter and the non-dimensional residence time τ satisfies the correlation We0.35·d32/D0=0.026τ−0.17.

Cavitation bubble collapse between parallel rigid walls with the three-dimensional multi-relaxation time pseudopotential lattice Boltzmann method

Studying the flow characteristics of bubbles in a narrow gap is an important problem related to bearing cavitation and gas–liquid two-phase flow. In this paper, we present a modified three-dimensional multi-relaxation-time pseudo-potential model for large density ratio multiphase phenomena. The accuracy of the model is verified by the Maxwell construction, Laplace law, and Rayleigh–Plesset equation. The influence of the force scheme parameter and the dimensionless relaxation time on the thermodynamic consistency of the model is analyzed. The results show that the three-dimensional lattice Boltzmann pseudo-potential model proposed in this paper has good numerical stability in simulating multiphase phenomena. Furthermore, the cavitation bubble collapse process between parallel rigid walls is simulated by the proposed model. The collapse process obtained by the present method agrees well with the experimental result. The different orientations for the bubble to the wall exert a significant influence on the variation of the pressure field, velocity field, and evolution of maximum pressure and micro-jet velocity. During the cavitation bubble collapse process, the pressure and the velocity at the collapse point will increase instantaneously, and the orientation for the bubble to the wall is a key factor to determine the collapsed form of the cavitation bubble. The results verified the practicability of the addressed model to study the collapse of three-dimensional cavitation bubbles in the presence of parallel rigid walls.

Study on rising flow characteristics of triple bubbles

In order to study the influence of bubble size and distance on the interaction between bubbles, this paper discussed the rising movement characteristics of triple bubbles in static water based on Fluent software. By analyzing the rising track, flow fields and velocity of bubbles, the results show that, when bubble diameters are 4mm, 4mm, 4mm, the distance between the left bubble and the middle bubble is smaller than the minimum coalescence distance, and they coalesce. When bubble diameters are 6mm, 4mm, 4mm, the velocity and track of the small bubble at the bottom will be affected by the wake of the big bubble as the big bubble rises, but they do not coalesce. When bubble diameters are 2mm, 6mm, 2mm, the smaller bubbles on both sides are attracted by the middle bubble and they coalesce; there is almost no vertical rise or deviation process.

Partial discharge characteristics of bubble flow under AC non-uniform electric field in FC-72

In the present study, a test chamber filled with perfluorohexane (FC-72) is set up to investigate partial discharge (PD) in phase-cooling bubbles. Under the non-uniform electric field with needle point-to-hemisphere electrodes, thermal bubbles are generated from the needle point. The difference between PD with and without the bubbles is analyzed to identify features of the discharge in the bubbles. It is observed that the bubbles reduce the PD inception and intensify the discharge. A model of bubble motion is established to investigate bubble behavior in an electric field. Based on the observation of the flow and streamer patterns, a mechanism of PD in bubble flow is established and confirmed by phase-distribution of PDs with bubble transit time.

3D 프린터로 제작한 마이크로 믹서의 액체 슬러그 길이 및 속도와 기포의 상관성에 관한 실험적 연구

3D 프린터로 제작한 마이크로 믹서의 액체 슬러그 길이 및 속도와 기포의 상관성에 관한 실험적 연구

Gas–Liquid Two-Phase Performance of Centrifugal Pump Under Bubble Inflow Based on Computational Fluid Dynamics–Population Balance Model Coupling Model

Abstract In this study, a numerical simulation method based on Eulerian–Eulerian model and population balance model (PBM) (i.e., computational fluid dynamics (CFD)–PBM coupling model) was developed to investigate the gas–liquid two-phase performance of centrifugal pump under bubble inflow. The realizable k–ε model turbulence model was implemented in ansysfluent solver. The air and water were employed as the working fluids, which was consistent with the experiment. The water head and pressure increment obtained by the experiment were used to validate the numerical method. The results show that the CFD–PBM coupling model is superior to the Eulerian–Eulerian model, particularly in the “surging” conditions. Using the CFD–PBM coupling model, the influences of parameters, such as inlet gas volume fraction, liquid phase flowrate, and rotational speed, on the head and efficiency of the centrifugal pump were investigated. Under the design condition, when the inlet gas volume fraction increases from 3% to 5%, the bubbles form air mass and stagnate in the impeller channel. The stagnated air mass can hardly be discharged with the liquid phase. Thus, the pump head drops suddenly, i.e., the surging occurs. The two-phase performance of centrifugal pump can be improved under the surging condition by increasing the liquid flowrate and the rotational speed to a certain value. The results contribute to an alternative simulation method to investigate the characteristics of bubble flow in pump and shed new lights on the understanding of the performance of centrifugal pumps under two-phase flow conditions.

Experimental Investigations of Single Bubble Rising in Static Newtonian Fluids as a Function of Temperature Using a Modified Drag Coefficient

In the oil production industry, it is of significance to measure and predict the form of multi-phase flow and gas flow that are present within petroleum production and processing pipelines. One component which has received little attention is the characteristics of bubbly flow around production pipelines. Rising bubble behavior in a wellbore changes with various factors, of which temperature leading to variations of liquids properties is one of the important factors. Herein, using an improved drag coefficient model to investigate bubble rising behavior at different temperatures is considered to calculate bubble flow velocities for drilling design, operation and wellbore pressure control. Firstly, a series of simulated laboratory experiments were conducted at 5–100 °C in four Newtonian fluids to obtain liquid properties and bubble parameters, such as bubbles shape, terminal velocity and trajectory. Then, compared with terminal velocities obtained by using the drag coefficients models CD = 0.95, which was considered to be constant by many literature at high Reynolds region (Re > 135), the modified drag coefficient model CD = 1.227 yielded better satisfactory prediction results for bubbles terminal rising velocity. Additionally, a new correlation using Reynolds number, Eotvos number, Weber number is proposed to predict bubble terminal velocity at low Reynolds number (Re < 135) based on experimental data and the Schiller–Naumann model. The results showed excellent agreement with the experimental data, with standard error of 5.32%.

Experimental study of single-bubble behavior containing aerosol during pool scrubbing

During a severe accident (SA) in a nuclear power plant, the damaged core releases fission products (FPs). Pool scrubbing is a filtering process to avoid the release of radioactive aerosols into the environment, and its effects have already been modeled and implemented in some SA codes such as MELCOR. However, the effect of aerosols on bubble motion is not defined in this code's model. Therefore, in this study, we visualized the effect of aerosol on the bubble interface via the measurement of the bubble aspect ratio and rising velocity. High-speed videography enabled us to clearly record the effect of aerosol solubility on bubble shape. We found that the solubility of the aerosol inside the bubble – a factor not considered in the MELCOR code – affected the bubble shape and rising velocity. Moreover, soluble aerosols tended to affect bubbles in a manner similar to surfactants. The internal velocity of an oil droplet – a simulated air bubble – was measured using a PIV method. Using image processing, we obtained the interface velocity from the PIV data. The comparison of the experimentally obtained interface velocity and the theoretical value calculated from the equation in MELCOR suggests that MELCOR's internal flow can qualitatively predict the characteristics of internal bubble flow. Additionally, we combined the bubble visualization data and the MELCOR internal bubble flow model and calculated the decontamination factor (DF) for a single-bubble. The results show that the difference in the DF is due to solubility of aerosol, which is caused by the bubble shape and rising velocity.

An improved image procession algorithm for bubble flow characteristics in gas–liquid reactor

AbstractBubble size distributions in bubble‐liquid reactors are essentially determined by the multiphase turbulent hydrodynamic behaviors, which take greatly effects on the heat and mass transfer. An improved image procession algorithm, effectively combined for the first time, color space transformation, shadow detection and removal, and watershed segmentation to handle the raw pictures captured by high‐speed camera was proposed to characterize the distributions of bubble sizes. The hue–saturation–intensity color space approach to detect bubble edges and shadow regions for their intensity was set to as input value for processing background subtraction. Furthermore, the removal of bubble shadow was successfully performed by means of extracting shadow regions to attain the satisfied compensation images, a watershed transformation function was also developed to segment the overlapping bubbles into the individual bubble objects after shadow removed as well. Bubble parameters, that is, bubble areas and bubble perimeters are obtained details, and results showed that the maximum errors between calculated results and measurement without considering shadow effects are approximately 25%. Thus, it indicated that the effects of shadow are seriously, and it must be optimized for better prediction regarding the ability and the capacity of reactor design.

Bubble Collapse and Flow Characteristics in Bubble Flow in a Venturi Tube

This paper shows bubbly flow characteristics measured of standing flow and unsteady flow in a Venturi tube. As for the standing flow characteristics, the distribution of pressure and void fraction are measured. Using the equation of sound velocity in adiabatic isentropic, the shock waves occurs at the point of transition from supersonic flow to subsonic flow, and the bubbles are collapsed at the same area. As a non-steady phenomena, by performing visualization and synchronous measurement of pressure, the presence of propagating pressure wave caused by bubble collapse. The bubble diameters generated by using this device showed a tendency to be further miniaturized under both condition that a shock wave is generated and a pressure wave is generated.

Numerical simulation of annular bubble plume by vortex in cell method

PurposeThis study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.Design/methodology/approachThe bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-L–L) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase.FindingsFirst, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-L–L approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation.Originality/valueThe semi-L–L approach is applied to the simulation of the gas–liquid two-phase flows.

Experimental Study of Foamy Oil Solution Gas Drive Process in an Etched Glass Micromodel

Foamy oil phenomenon is of great significance for the exploitation of some heavy oil reservoirs. Many researchers have conducted a lot of research on foamy oil, but there is still no systematic research on why foamy oil phenomenon only appears in some special heavy oil reservoirs. Therefore, it is of great significance to study the formation of foamy oil in depth. This paper simulates the process of three kinds of heavy oil solution gas drive processes with different types of heavy oil under the formation conditions in an etched glass micromodel, and the flow characteristics of gas bubbles in the micromodel were observed. The results show that the location of gas bubbles nucleation was mainly distributed in the main channel and the rock surface of the micromodel. Compared with gas bubbles in the foamy oil, the dispersed gas bubbles in the conventional heavy oil had a shorter existence time and no obvious foamy oil phenomenon, the size of gas bubbles in the conventional heavy oil was larger, and the migration, growth and coalescence rate were faster.

Phase distribution characteristics of bubbly flow in 5 × 5 vertical rod bundles with mixing vane spacer grids

In order to predict the thermal–hydraulic parameters in nuclear reactor accurately, it is essential to reveal the phase distribution characteristics, the mechanisms of phase interactions and the effects of the mixing vane spacer grid (MVSG) in rod bundles, based on which the drift-flux model and interfacial area transport equation could be developed further. The profiles of local two phase flow parameters could give an insight into these phenomena. Therefore, the adiabatic air–water upward two-phase flow experiments are performed to measure local parameters in 5 × 5 rod bundles with mixing vane spacer grids (MVSGs) under different bubbly flow conditions. The miniaturized four-sensor conductivity probe (MFSCP) has been developed to measure local two-phase flow parameters, such as void fraction, interfacial area concentration (IAC), bubble velocity and bubble chord length. The detail local parameters are measured and analyzed in the bubbly flow. Typical wall peaks for void fraction are identified and the bubble velocity profiles have a reverse phase position with void fraction profiles. The mixing vane spacer grid (MVSG) plays an important role in phase distribution in rod bundles: the skewed peaks of void fraction is associated with the direction of mixing vanes; a larger value of area-averaged void fraction is induced at the downstream of MVSG; compared with other factors, the MVSG plays a leading role in interfacial area transportation. Moreover, the dissipation length of MVSG is less than 19.4 L/D for current bubbly flow conditions.

Effect of the wall presence on the bubble interfacial forces in a shear flow field

Understanding the interactions between the bubbles and solid walls is important for predicting how the bubbly flow characteristics, such as void fraction and statistical distribution of bubble sizes, are affected by the presence of solid boundaries. In the present research, the numerical simulations with interface tracking method are performed to evaluate the interfacial forces’ closures in shear flow field under well-controlled conditions. The proportional-integral-derivative bubble controller is adopted to keep a single bubble at fixed position near the wall by balancing the forces in all three directions. This allows the extraction of the interfacial forces and the calculation of the corresponding coefficients. Validation tests have previously been conducted by the authors to compare the interfacial closures’ results against the experimental data. In this work, the influence of wall distance, relative velocity and bubble deformation on the interfacial forces are investigated. The results show that as the bubble approaches the wall, it experiences a transition from attractive force to repulsive force normal to the wall. The bubble Reynolds number also has significant impact on the interfacial forces: the net lateral force changes direction at Reb=35. The coupled phenomenon of bubble deformation and wall effect is investigated as well. The net lift sign change is observed at Eo=2.3 when the dimensionless wall distance (the ratio between the distance from the bubble center to the wall and the bubble diameter) is equal to 1. The presented studies complement the state-of-the-art knowledge and those are aimed to help improve the closure laws for interfacial forces and contribute to the multiphase computational fluid dynamics (M-CFD) closure model development.