Water Superficial Velocities Research Articles

Bubble Size Characterization in the HydroFloat® Fluidized-Bed Flotation Cell Using Tap Water and Seawater

This research aims to analyze the behavior of bubble size distribution in the HydroFloat® with seawater and tap water. The study characterized bubble size in a two-phase gas–water system in a fluidized-bed flotation cell. The impact of seawater was compared to tap water using two frothers, MIBC and polyglycol F507. The experimental design was used to investigate the influence of various parameters such as superficial air velocity, superficial liquid velocity, frother concentration, and seawater concentration on bubble size. The results indicate that the critical coalescence concentration followed the order of MIBC > F507. Bubble size decreases with increasing superficial liquid velocity, while the superficial gas velocity and frother/seawater concentration have the opposite effect. ANOVA results reveal that all linear factors are significant, the quadratic terms of the frother and seawater concentrations are significant, and the interaction term for the superficial air velocity–superficial liquid velocity is nonsignificant for bubble size. Global sensitivity analysis demonstrates that the variables significantly affecting bubble size are frother concentration and seawater concentration, followed by superficial water velocity. The superficial gas velocity has minimal impact on bubble size under the conditions studied.

Bubble Separation in a Gas–Liquid Swirling Pipe Flow

Gas–liquid swirling pipe flow plays an essential role in phase separators. Bubble motions and flow patterns transitions in the flow are crucial for further investigation of this flow. However, much attention has been paid to these in non-swirl flow instead of swirl flow. In this work, bubble separation generated by a vane-typed swirler in a vertical pipe with an inner diameter of 62 mm was experimentally studied. Superficial air velocities (0.036 − 1.41 m/s) and superficial water velocities (0.02 − 0.95 m/s). The results show that dispersed bubbles gradually transform to gas column flow with increasing superficial water velocities (0.093 − 0.640 m/s) in the swirl flow; gas column flow gradually transforms to swirling intermittent flow with increasing superficial air velocities (0.05 − 0.40 m/s), and one peak increases to two peaks in the probability density function curve of pressure drop; slug flow can transform to swirling intermittent flow. Finally, transition criteria for bubble separation were proposed: when the turbulent fluctuations are strong enough to overcome centrifugal force, then the bubbles move to the pipe center and coalescence with each other, lead to the transition of gas column flow/swirling intermittent flow.

Measurement of air-water counter-current flow rates in vertical annulus using multiple differential pressure signals and machine learning

Abstract Gas–liquid counter-current flow in vertical annulus is involved in several industrial fields such as petroleum engineering. For example, in coalbed methane wells with liquid pump drainage, obtaining the real-time flow rate of gas–liquid two-phase in the annulus is crucial for the development management of coalbed methane wells. However, due to complex flow conditions, this demand is difficult to achieve through traditional flow metering means. Therefore, this paper proposes a flow prediction method based on multi-group differential pressure signals and machine learning technology. Air-water two-phase flow experiments were carried out on a vertical annulus pipeline with inner and outer diameters of 75 mm/125 mm and adjustable eccentricity. The probability density function and power spectrum density of 3 groups of differential pressure signals collected at different height intervals in the annulus were used as model inputs. A gas–liquid two-phase flow prediction model was constructed based on the artificial neural network model, and the model hyper-parameters were optimized using Bayesian optimization. The results show that on the 440-group test dataset under the combined conditions of air superficial velocity of 0.06–5.04 m s−1, water superficial velocity of 0.03–0.25 m s−1, and pipeline eccentricity of 0, 0.25, 0.5, 0.75, 1, etc. This model can achieve average prediction errors of 9.12% and 29.34% for gas and water flow rates respectively. This method can be applied to the non-throttling, non-invasive measurement of phase flow rate under the condition of annulus air-liquid counter-current flow.

Study on the Flow Characteristics of Heavy Oil-Water Two-Phase Flow in the Horizontal Pipeline.

Aiming at the problem of transportation for heavy oil during the middle-later development stages of the Lvda oilfield, based on the self-developed design of a visual circulating flow experimental apparatus for heavy oil-water two-phase flow-the flow regime characteristics and corresponding drag properties of the two-phase flow of Lvda viscous oil, which is simulated by 500# industrial white oil and water in a horizontal pipeline are investigated experimentally. According to the Kelvin-Helmholtz instability theory, the flow pattern transition criteria from stratified flow to annular flow (AF) are proposed. The effects of 0.11-0.90 m/s oil superficial velocities, 0.06-1.49 m/s water superficial velocities, and 0.09-0.93 input water cuts on the drag reduction effect of different flow regimes are analyzed. The experimental results indicated that with the increase of mixing velocity and water volume fraction, stratified flow, AF, oil plug flow, and dispersed oil lump flow are successively observed in the horizontal heavy oil-water two-phase flow, in which AF is the main flow pattern. As the Froude number increases to 4.0, the input water volume fraction does not change any more and remains at about 10% of the total flow rate in the process of converting from stratified flow to AF. The four delivery approaches can archive the reduction of transportation resistance for heavy oil at different degrees, in which the transportation of heavy oil surrounded by a water ring has the best effect of drag reduction. At the optimal working conditions of 0.61 m/s oil superficial velocity, 0.07 m/s water superficial velocity, and 0.10 input water cut, the pressure drop of water annulus conveying for heavy oil is only 1/62.54 of that of separate transport for pure heavy oil under the same oil flow rate.

Investigation of the Static Pressure Drop and Production that Occurs due to Flow Patterns in a Perforated Horizontal Wellbore

This study examined the intricate interaction between flow patterns and production within a perforated horizontal wellbore. The study precisely assessed the behavior of static pressure drop by utilizing an array of flow regimes encompassing bubble, dispersed bubble, transitional bubble/slug, slug, stratified, transitional slug/stratified wave, and stratified wave. Remarkably, an upward trend in static pressure drop was observed with increasing water phase presence, while the converse was true for the air phase. Besides, the air phase superficial velocity exhibited a direct correlation with the magnitude of pressure drop fluctuations. The liquid production demonstrated a peak during bubble and slug flow regimes, followed by a descent during the transition to stratified and stratified wave flow. This decline can be attributed to mixing pressure drops localized during the perforations. Furthermore, an upward trend in average liquid production was observed with increasing mixture superficial velocity, primarily due to the dominant presence of the water phase. Additionally, the percentage of liquid production was positively associated with the water's superficial velocity when the air's superficial velocity was held constant. While the experimental and numerical results were in agreement for slugs and structured flows, there were discrepancies in the behavior of static pressure for bubbles, small bubbles, and structured waves.

Characteristics of turbulent core–annular flow with water-lubricated high viscosity oil in a horizontal pipe

Direct numerical simulations are performed to investigate the characteristics of a turbulent core–annular flow with water-lubricated high viscosity oil in a horizontal pipe. Six different superficial velocity ratios ( $\,j_w/j_o = 0.057\unicode{x2013}0.41$ ) are examined by changing the water superficial velocity $j_w$ for a fixed oil superficial velocity $j_o$ . The pressure drops in the pipe and the shapes of the phase interface agree well with those from previous experiments. The oil core flow is almost a plug flow, and the gaps between the phase interface and pipe wall are narrow and wide near the upper and lower surfaces of the pipe, respectively, due to the buoyancy. Within a narrow gap, water is confined mostly in a valley region of the wavy phase interface and hardly goes through its crest. On the other hand, water near the phase interface at a wide gap convects downstream almost at the core speed and the flow near the wall is similar to that of single-phase wall-bounded turbulent flow. The annular flow is characterized by three different regimes depending on the clearance Reynolds number ( $Re_c$ ) based on the core velocity and local gap size: laminar Couette flow driven by the core for $Re_c \le 600$ , transitional flow for $600 < Re_c < 2500$ and turbulent flow for $Re_c \ge 2500$ . The minimum pressure drop occurs at $j_w/j_o = 0.11$ in the early transition regime. For all $j_w/j_o$ considered, the negative lift force acting on the core comes from the pressure force which balances the buoyancy.

Exploring the correlation between inclination angle and flow pattern transition in oil-water flow

The impact of pipe inclination angle on oil-water flow regimes transition boundaries is vital in various engineering applications, including pipeline and separator inlet design. Understanding this influence is crucial for identifying alternative and optimal designs. The standard way of presenting oil and water superficial velocities on 2D flow pattern maps doesn't consider how the flow pattern varies with pipe tilt angle. This article aims to clarify how the angle of pipe inclination affects oil-water flow regime transitions. This method uses pipe inclination angle as a direct representation, with the angle shown on the x-axis of a 2D flow pattern map, which has not been done before in literature. The y-axis, or ordinate, is a dimensionless number that accounts for mixture velocity, fluid densities, and pipe diameter. Two dimensionless numbers were utilized. The Froude number based on mixture velocity, FrM, and the Reynolds number (ReOM) based on mixture velocity and oil properties, are plotted against pipe inclination angle. The evaluation and validation of the proposed methods for the effect of the inclination angle were performed using a database of more than 10,000 points established from studies reported in the literature. The findings show that both the Dispersed (DF) and Semi-Dispersed flow regimes (SDF) exhibit higher FrM values than smooth stratified regardless of the pipe's incline. Moreover, the spreading area is symmetric around the horizontal line which means that the DF and SDF can be observed at similar FrM for both positive and negative inclinations. Focusing horizontally, FrM is highest for ST-MI, lower for SW, and lowest for ST. This paper also presents and demonestrates a case study showcasing a new application for flow pattern maps, illustrating their potential in design purposes.

The impact of 180° return bend inclination on pressure drop characteristics and phase distribution during oil-water flow

The present work aims to capture the influence of the inclination of the return bend on flow patterns and pressure drop during oil-water flow. The experiments were carried out for different inclinations (0°, 15°, 30°, and 45°) of return bend for various superficial velocity combinations of oil (kerosene) and water ranging from 0.07 to 0.66 m/s. The experiments showed that pressure drop increases with the increase in inclination. However, the pressure drop at a fixed inclination (say 15°) decreases with the increase in the superficial velocity of the water. Distinct flow patterns observed in the return bend were droplet flow, film inversion, slug flow, plug flow and large slug flow. Droplet flow dominates at the lower range of kerosene (i.e., Usk = 0.07–0.2 m/s) and higher range of water superficial velocity (i.e., Usw = 0.40–0.66 m/s) at all the inclinations considered in this study. Additionally, comparisons between the experimental and numerical simulation results were made. The numerical solution utilized the Euler-Euler approach, considering the different phases as interpenetrating continua. The Volume of Fluid (VOF) model was used within this approach, monitoring the volume fraction of each phase over the domain while calculating one set of momentum equations for each phase. To capture the turbulent effects accurately, the k-ε turbulence model was incorporated. It happened to be found that the numerical findings showed remarkable agreement with the experimental data.

Numerical Studies On the Oil Film Thickness in the Case of Stratified Flow with Different Oil-Water Flow Combinations Through Sudden Contraction Tube

Abstract Most of the oil transportation industries deal with liquid-liquid flow considering the adiabatic situation. In such applications, film thickness measurement plays a very significant role in understanding the flow characteristics. The distribution of phases for efficient wall treatment and to understand the phase distribution, measurement of film thickness is very important. Among different flow patterns, stratified flow is most common for low and medium viscous oil-water flow. At lower oil velocities, stratified flow is observed downstream of singularity whereas in the upstream section, stratified flow is observed for low to medium oil velocities and high-water superficial velocity. Variation of oil film thickness for stratified flow has been analyzed in the present study. Results show that oil film thickness decreases with the increase in the superficial velocity of water (Us-Water) for a constant oil superficial velocity (Us-Oil). With the increase in the volume fraction of one phase, the film thickness of that phase increases. As Us-Oil increases, the film thickness of oil also increases for a constant Us-Water. Oil film thickness is directly proportional to the viscosity of oils. This means, the more the viscosity of the oil, the more will be the oil film thickness.

Evaluation of airlift pump performance for vertical conveying of coal particles

AbstractOne of the crucial aspects of reducing air consumption when conveying particles with an airlift pump is to know the factors that affect the process of particle motion at an initial velocity of zero. To determine the influence of submergence ratio and physical properties of particles (such as size, shape, and mass) on the onset of vertical particle motion, the airlift pump was taken as the research object, and spherical glass together with irregular shaped coal were used as experimental test particles. The results show that unlike the water-solid environment, the start of particle motion in the water-air mixture does not always occur at a certain value of superficial water velocity and this value also increases with increasing submergence level. Among the parameters considered, the role of submergence ratio is much more effective than the dimensions and the shape of the particle, because by increasing submergence from 0.3 to 0.8, it is possible to reduce air consumption by up to 8 times. Based on this study the corresponding theoretical model derived by Fujimoto et al. is optimized, wherein the overall agreement between the modified theory and present experimental data is particularly good. Contrary to Fujimoto, the minimum superficial water velocity for lifting solids in the air-water mixture is not always smaller than water ambient which indicates on optimum submergence ratio higher than 0.7. Finally, a new criterion was introduced to describe the moment of onset of the particle motion as a function of the superficial fluid velocity ratio for each submergence value.

Self-cleansing velocity in upward three-phase steady pipe-flow

The solids transport and the conditions required to begin the transport of granular particles, or to avoid their deposition, in three-phase turbulent flows of mixtures of gas–liquid–solids, in upward inclined pipes, are complex phenomena whose governing equations and corresponding solutions can be approximated via experimental investigation and numerical computation. An experimental installation for establishing steady flow conditions of air–water-solids in an upward transparent acrylic pipe of 84 mm was built and prepared to allow the measurement of the transported flow rates of air, water, sand and fine gravel, with particle diameters between 0.425 and 7.20 mm. Two full set of experiments with water-solids, and air–water-solids, under comparable conditions, were performed in Laboratory, in order to analyse the influence of the gas phase. Three pipe angles between 30° and 58°, and four solid particle ranges with intermediate sizes forming a bed were tested. The average water superficial velocity demonstrates to be the most relevant variable for the solids transport beginning, and the presence of air has a positive influence, even without the mobilisation of the water flow rate increase due to air-lift pumping. A model relating a modified Shields parameter (Shmixc) with a modified Reynolds number of the particles (Remixc), both defined for the critical average flow rates of three-phase mixtures under steady flow, for which a residual mass of solid particles begins to be transported, is proposed. The resulting equation follows a power law of the generic type Shmixc = a Remixc−b, where a and b are positive constants experimentally obtained for the different angles of inclination of the upward pipe, with coefficients of determination well above 90%. The mathematical model proposed in this work allows the explicit computation of the self-cleansing velocity required for two-phase flows. The critical average air superficial velocity and subsequent average velocity of the mixture required for the solids transport in steady three-phase flows, when the average water superficial velocity is below the two-phase self-cleansing velocity, are computed using the proposed model by numerical iterative processes.

Investigation of flow regimes, pressure drop, void fraction, film thickness, friction factor and production of two-phase flow in a perforated horizontal wellbore

This study focuses on investigating the impact of flow patterns on production in perforated horizontal wellbores. According to experimental and numerical results, this paper discussion the behaviour of total pressure drop, mixture superficial velocity, void fraction, liquid film thickness, and production that occur with various flow patterns in a perforated horizontal pipe. The flow patterns were predicted experimentally and numerically using a pipe with a length of 3 m and an internal diameter of 0.0381 m, with two perforations of inside diameter 0.004 m with a phasing angle of °180, to simulate the complex flow in horizontal wellbores. Total pressure drop and liquid film thickness were reduced by increasing the radial air flow of the perforations. At the same time, void fraction and mixture superficial velocity were observed to increase. Additionally, the film thickness increased with the holdup fraction but decreased with the void fraction. The local friction factor reflected the behaviour of the mixture's superficial velocity during the region of the perforations. The friction factor with the perforated horizontal pipe was greater than that in the unperforated horizontal pipe. The liquid product increased with an increase in the mixture's superficial velocity, and the percentage amounts of production shown were 10%, 40%, and 75%, depending on the water's superficial velocity. The convergence between experimental and numerical results was good during the flow patterns (slug flow and stratified flow). In contrast, some differences in the static pressure drop behaviour occur during flow patterns (bubble flow, dispersed bubble flow, and stratified wave flow).

Effect of nanobubbles on flotation of El-Maghara coal

ABSTRACT To extensively explore the advantage of using nanobubbles in the El-Maghara coal flotation process, the effect of nanobubbles on both column and mechanical flotation was investigated under different operating parameters such as diesel oil collector dosage, MIBC frother concentration, superficial feed velocity, superficial air velocity, and superficial wash water velocity in column flotation; besides the slurry flow rate through nanobubbles generator into a 25-liter mechanical flotation cell. The representative coal flotation feed acquired from the El-Maghara deposit located in Sinai, Egypt with chemical characterization using proximate analysis containing 25.27% mineral matter forming ash during coal combustion and with particle size distribution measurement using laser particle size analyzer is 57 µm d90. Also, the flotation kinetic experiments were done to show the influence of nanobubbles on the flotation time required to obtain high-quality coal products with high combustible recovery. Nanobubbles enhanced the flotation performance and kinetics by up to 24% combustible recovery based on the operation parameters reducing flotation time from 4 to 2.25 min for 80% combustible recovery.

The research on the interfacial area transport equation in rectangular channels: Interfacial characteristics distribution and bubbles interaction mechanism

The interfacial area transport equation (IATE) is employed to describe the evolution of interfacial structure and evaluate the interfacial area concentration of two-phase flow. However, the interaction mechanisms among bubbles change in different rectangular channels, significantly impacting interfacial characteristics and source terms in IATE. In order to study the interface characteristics and mechanism of bubble interaction in rectangular channels with different gap sizes, an experimental study was conducted on the upward mixture flow of air and water in an adiabatic vertical channel under atmospheric pressure. Two channels with cross-sections of 4 × 66 mm and 8 × 66 mm were selected. The superficial velocities of water and air were 0.5–3 and 0–1.12 m/s, respectively, almost at the transitional region of bubbly to slug flow. Flat electrodes and the four-sensor probes measured the interfacial characteristics. This study analyzes the development of interface and mechanism of interaction among bubbles. The result shows that the evolution in the distribution of void fraction and interfacial area concentration significantly depends on the flow regime, flow rate, and cross-sectional geometric size of channels. Under the condition of a lower liquid flow rate, the gap size of the channel plays a vital role in the efficiency of bubble coalescence, influencing the mechanisms of the random collision and wake entrainment among bubbles. However, the interfacial parameter distribution under higher liquid rate conditions is dominated by turbulence intensity and flow regime, and the mechanisms of bubble interaction become identical. Finally, the mechanisms of interaction among bubbles (random collision and wake entrainment) are analyzed based on the development of interfacial characteristics. In a word, based on the conclusions specified in this research, the new models of source terms of ITAE in rectangular channels will be predictably established in the future.

Study on the Hydrodynamic Performance and Stability Characteristics of Oil-Water Annular Flow through a 90° Elbow Pipe

The transportation of highly viscous oil surrounded by water annulus has been recognized as a feasible option in terms of low-energy consumption and high efficiency. During the process of heavy oil delivery, the problem of pipe fittings is inevitably encountered, and the most common one is elbow assembly. In this present study, simulations for oil-water core annular flow (CAF) through a 90° elbow pipe were performed by computational fluid dynamics (CFD) based on VOF, standard k-ε, and CSF models. Simulation results were consistent with experimental data, which verifies the validity and practicability of the proposed model. The effects of inlet water fraction, superficial velocities of oil and water, oil properties (density and viscosity), and pipe geometry-related parameters (diameter ratio, wall roughness, and surface wettability) on the hydrodynamic performance and stability characteristics were explored. It is revealed that inlet water fraction, superficial velocities of oil and water, oil properties, and pipe geometric parameters do influence the volume fraction of oil and the stability of the water ring. Furthermore, the oil core may adhere to the downstream of the 90° elbow pipe under certain operational conditions. The results could provide a reference for the design of 90° elbow pipe structures and the optimization of operation parameters.

Effect of the down-slope on the structure and the pressure loss of an oil-water stream

The methodology and the results of an experimental campaign aimed at characterizing a two-phase flow of an oil-water-mixture in downward inclined pipes are here described. The goal was to assess the effects of the downslope on an oil-water stream in terms of flow patterns, pressure gradients and phase holdup inside a 40 mm I.D. pipe. The experiments ranged within (0.56−1.06ms) and (0.66−1.33ms) oil and water superficial velocities, respectively. The transition from annular to stratified-wavy flow pattern was analyzed and showed to occur at lower oil velocities with respect to the horizontal configuration. The frictional pressure gradients were measured, the results compared to mechanistic and empirical models showed to be in good agreement. The phase holdups were measured by quick-closing valves and compared to horizontal configuration results and literature models. Eventually, the drift-flux model was implemented confirming its applicability and a relationship for the of oil holdup was derived.

Measuring the Taylor Bubble Length in a Two-Phase Flow using an Electrical Resistance Sensor and a High-Speed Camera

The present research aims to investigate the two-phase air/water flow in a vertical pipe using an electrical resistance sensor and a high-speed camera. An electrical resistance sensor is designed and embedded in the inner wall of the tube. A flow pattern map is drawn at the height of 270 cm from the testbed inlet for 320 different phase velocities using a high-speed camera. By measuring the output voltage of the electrical resistance sensor and using the Maxwell relation, the volume fraction in bubbly and slug flow regimes are calculated for different phase velocities. The volume fraction values detected from the output signal of the electrical resistance sensor are compared with the results obtained from the high-speed camera images. The width of the output signal from the electrical resistance sensor indicates the length of the Taylor bubble. The output signal width is compared to the obtained Taylor bubble length from high-speed camera images, for several different velocities of the phases. It is noticed that at a constant velocity of the phases, the output signal width from the sensor is linearly related to the length of the Taylor bubble. The variations of the output signal width are plotted in terms of the ratio of the Taylor bubble length to the summation of air and water superficial velocities. By linear fitting of the available data, a novel equation is presented to calculate the Taylor bubble length in terms of the signal output from the electrical resistance sensor and the total superficial velocity of the phases.

ANALISA KECEPATAN SLUG ALIRAN DUA FASE DI DOWNSTREAM T-JUNCTION MINICHANNEL HORIZONTAL DENGAN RADIUS BELOKAN (r/dh) 0.7

Uneven distribution of the phases between in the main channel when two-phase flow passes through the T-junction it can cause the formation of slug flow which affects performance in the downstream area. The slug is formed due to the acceleration of the gas phase moving towards an average or stable velocity. The bend radius of the T-junction affects the formation of slug because the radius can increase the velocity of the gas phase. Research on the slug velocity was carried out in the downstream region of the horizontal mini channel T-junction. The working fluid used is air as the gas phase and water. The flow pattern and velocity slug analysis were carried out by visualizing the flow at a distance of ±30 mm from the T-junction, that works as a mixer of the working fluid. High-speed camera is used to record video and processed in the form of image processing with the MATLAB program. Two-phase flow slug velocity analysis conducted in the downstream area of ​​the horizontal minichannel T-junction, it can be concluded that the slug velocity tends to increase linearly with increasing superficial velocity of air and water. Comparison of slug velocity experimentally with the results of calculations using the equations of Fukano and Kariyasaki (1993) and Sudarja et al (2018) shows conformity with less than 10% of error margin, while Nicklin et al (1962) is ±30%.

Measurement of Liquid–Liquid Flows Using Turbine Flowmeter and Conductance Sensor With Multiheight Electrodes in Vertical Pipes

Liquid–liquid two-phase flows are common industrial processes in chemical, petroleum, and other related fields. It is a great challenge for the flow measurement using the turbine flowmeter (TFM) in low-velocity liquid–liquid flows due to the serious slippage effect between the oil and water phases. The complex physical discrepancies between the two phases make the response of TFM vastly different from that in single-phase flow. This study proposes a system combining TFM and conductance sensors with multiheight electrodes (CSMHEs) to determine liquid–liquid two-phase flows. This study investigates the effects of phase distribution and slippage on the wheel hub drag torque. The model of wheel hub drag torque in different flow patterns is established, and a new variable meter factor model of TFM in liquid–liquid flows is constructed. Experiments in 20-mm simulated well reveal that the TFM can make accurate predictions of total flow rate and enable online measurements of individual phase superficial velocities. The absolute average percentage deviations (AAPDs) of superficial water and oil velocities are 2.01% and 7.24%, respectively.

Analysis of two-phase flow regimes and parameter distribution in 5 x 5 rod bundle using image processing techniques

With the recent developments in image processing and analysis, this paper presents bubble characteristics distribution in adiabatic air-water two-phase flow through a 5 × 5 rod bundle. The experiment covered water superficial velocities (Jl = 0.012 m/s – 0.421 m/s) and air superficial velocities (Jg = 0.042 m/s – 0.987 m/s) in which three distinct flow regimes were identified. The flow regime map was compared with existing flow regime transition criteria for vertical rod bundles. Distinct features from the two-phase flow images were extracted to train a classifier model to distinguish between regimes from a separate experiment. The model distinguishes between the bubbly flow regime and others accurately. The void fraction and velocity distributions were also extracted from the R–CCN masked images. Bubble-induced turbulence that was dominant in the subchannel at (Jl = 0.28 m/s) shifted to the outer subchannels and gaps when the flow rate increased (Jl = 0.42 m/s). These methods over-predicted the void faction around the surfaces of the inner rods.