Bubble Characteristics in a Developing Vertical Gas–Liquid Upflow Using a Conductivity Probe

1999 ◽  
Vol 122 (1) ◽  
pp. 138-145 ◽  
Author(s):  
Junping Zhang ◽  
Norman Epstein ◽  
John R. Grace ◽  
Kokseng Lim
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Flow Region ◽  
Flow Regimes ◽  
Chord Length ◽  
Bubble Velocity ◽  
Gas Velocity ◽  
Bubble Frequency ◽  
Local Bubble ◽  
Bubble Characteristics

Experiments were carried out in an 82.6-mm-dia column with a perforated distributor plate. Conductivity probes on the axis of the column were used to measure local bubble properties in the developing flow region for superficial air velocities from 0.0018 to 6.8 m/s and superficial water velocities from 0 to 0.4 m/s, corresponding to the discrete bubble, dispersed bubble, coalesced bubble, slug, churn, bridging, and annular flow regimes. Bubble frequency increased linearly with gas velocity in the discrete and dispersed bubble regimes. Bubble frequency also increased with gas velocity in the slug flow regime, but decreased in the churn and bridging regimes. Bubble chord length and its distribution were smaller and narrower in the dispersed than in the discrete bubble regime. Both the average and standard deviation of the bubble chord length increased with gas velocity in the discrete, dispersed, and churn flow regimes. However, the average bubble chord length did not change significantly in the slug flow regime due to the high population of small bubbles in the liquid plugs separating Taylor bubbles. The bubble travel length, defined as the product of local gas holdup and local bubble velocity divided by local bubble/void frequency, is used to correlate bubble characteristics and to characterize the flow regimes. [S0098-2202(00)00101-2]

scholarly journals On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

2010 ◽  
Vol 49 (5) ◽  
pp. 1147-1160
Author(s):  
Leonor Hernández ◽  
J. Enrique Juliá ◽  
Sidharth Paranjape ◽  
Takashi Hibiki ◽  
Mamoru Ishii
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Chord Length ◽  
Phase Flow ◽  
Two Phase ◽  
Local Bubble

scholarly journals Experimental investigation of multiphase separation in different flow regimes through T-junction with an expander section

2019 ◽  
Vol 13 (2) ◽  
pp. 5163-5181
Author(s):  
Z. Q. Memon ◽  
W. Pao ◽  
F. Hashim ◽  
S. Ahmed
Keyword(s):  
Experimental Data ◽  
Phase Separation ◽  
Slug Flow ◽  
Vertical Plane ◽  
Flow Regimes ◽  
Diameter Ratio ◽  
Superficial Velocity ◽  
Inlet Section ◽  
Water Mixture ◽  
Gas Velocity

The experimental data for phase separation of the air-water mixture in a T-Junction with the expander section after the branch arm is presented in this work. The main and run arms of the T-junction are directed along the horizontal plane with the branch arm positioned in the vertical plane. The diameter of the main arm is 74 mm, with diameter ratio(s) of, 0.67, and 0.33 in relation to branch arm. At the inlet section of the T-junction, the flow regimes generated were stratified, stratified wavy and slug flow. At the inlet, the air and water superficial velocities are in the range of 0.25 - 0.140 m/s and 0.14-0.78 m/s respectively. The effect of the expander section after the branch arm, the air superficial velocity USA and water superficial velocity USw on liquid carryover (WL3/WL1)max in branch arm have been studied. Based on the experimental data obtained for T-junction with expander section, complete phase separation of air and water was observed in stratified and stratified wavy flow for all superficial velocities and improved phase separation for slug flow. In slug flow, increasing the liquid superficial velocity improves the phase separation but increasing the gas velocity decreases the phase separation. Finally, the volume weighted phase in this new T-junction design is compared with the phase separation data of a simple T-junction.

The Mapping of Flow Regimes for a Light Material: Cork

2003 ◽  
Author(s):  
Joseph S. Mei ◽  
Esmail R. Monazam ◽  
Lawerence J. Shadle
Keyword(s):  
Mathematical Models ◽  
Flow Regime ◽  
Fluidized Bed ◽  
Density Ratio ◽  
Flow Regimes ◽  
Ambient Air ◽  
Gas Velocity ◽  
Dense Phase ◽  
Empirical Correlations ◽  
Light Material

A series of experiments was conducted in the 0.3-meter diameter circulating fluidized bed test facility at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). Cork, the bed material used in this study, is a coarse, light material, with a particle density of 189 kg/m3 and a mean diameter of 1007 μm. Fluidizing this material in ambient air provides approximately the same gas to solids density ratio as coal and coal char in a pressurized gasifier. Furthermore, the density ratio of cork to air under ambient conditions is similar to the density ratio of coal to gas at the gasification and pressurized fluidized bed combustion environment. The purpose of this study is to generate reliable data to validate the mathematical models currently under development at NETL. Using such coarse, light material can greatly facilitate the computation of these mathematical models. This paper presents and discusses data for the operating flow regimes of dilute-phase, fast-fluidization, and dense-phase transport by varying the solid flux (Gs) at a constant gas velocity (Ug). Data are presented by mapping the flow regime for coarse cork particles in a ΔP/ ΔL-Gs-Ug plot. The coarse cork particles exhibited different behavior than the measurements on heavier materials found in published literature, such as alumina, sand, FCC, and silica gel. Stable operation can be obtained at a fixed riser gas velocity that is higher than the transport velocity (e.g. at Ug = 3.2 m/sec), even though the riser is operating within the fast fluidization flow regime. Depending upon the solid influx, the riser can also be operated at dilute-phase or dense-phase flow regimes. Experimental data were compared to empirical correlations in published literature for flow regime boundaries, and solid fractions in the upper-dilute and the lower-dense regions of a fast fluidization flow regime. Comparisons of measured data show rather poor agreement with these empirical correlations. Xu et al. (2000) have observed this lack of agreement in their study of the effect of bed diameter on the saturation carrying capacity. The basis of empirical correlations depends on bed diameter and particle type, and are generally not well understood.

scholarly journals Three-Dimensional Aerators: Characteristics of the Air Bubbles

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1430
Author(s):  
Shuai Li ◽  
Jianmin Zhang ◽  
Xiaoqing Chen ◽  
Jiangang Chen
Keyword(s):  
Three Dimensional ◽  
Flow Region ◽  
Air Entrainment ◽  
Chord Length ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Cross Sectional ◽  
Frequency Distributions ◽  
Air Bubble ◽  
Flow Features

Three-dimensional aerators are often used in hydraulic structures to prevent cavitation damage via enhanced air entrainment. However, the mechanisms of aeration and bubble dispersion along the developing shear flow region on such aerators remain unclear. A double-tip conductivity probe is employed in present experimental study to investigate the air concentration, bubble count rate, and bubble size downstream of a three-dimensional aerator involving various approach-flow features and geometric parameters. The results show that the cross-sectional distribution of the air bubble frequency is in accordance with the Gaussian distribution, and the relationship between the air concentration and bubble frequency obeys a quasi-parabolic law. The air bubble frequency reaches an apex at an air concentration (C) of approximately 50% and decreases to zero as C = 0% and C = 100%. The relative location of the air-bubble frequency apex is 0.210, 0.326 and 0.283 times the thickness of the layers at the upper, lower and side nappes, respectively. The air bubble chord length decreases gradually from the air water interface to the core area. The air concentration increases exponentially with the bubble chord length. The air bubble frequency distributions can be fit well using a “modified” gamma distribution function.

Two-Phase Flow Induced Force Fluctuations on Pipe Bend

2014 ◽  
Author(s):  
Shuichiro Miwa ◽  
Yang Liu ◽  
Takashi Hibiki ◽  
Mamoru Ishii ◽  
Yoshiyuki Kondo ◽  
...  
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Pressure Fluctuations ◽  
Flow Regimes ◽  
Phase Flow ◽  
Liquid Slug ◽  
Two Phase ◽  
Pipe Bend ◽  
Force Fluctuation

In this study, fluctuating force induced by both upward and horizontal gas-liquid two-phase flow on 90 degree pipe bend at atmospheric condition was investigated. First, the database comprised of dynamic force signals and two-phase flow parameters such as volumetric fluxes, area averaged void fraction and pressure fluctuations covering entire two-phase flow regimes was developed for both flow orientations. Then, study was conducted to develop a model which is capable of predicting the force fluctuation frequency and magnitudes particularly for the slug flow regime. The model was fundamentally developed from the local instantaneous two-fluid model which was applied to the control volume around the elbow test section. Main contribution of the force fluctuation of two-phase flow is from the momentum and pressure fluctuations for most of the flow regimes. For slug flow regime, however, water-hammer like impact was produced by the collision of liquid slug against the structure surface. In order to consider that effect, the liquid slug impact force model was developed. The model utilizes two-group interfacial area concentration correlation to treat the flow regime transition without an abrupt discontinuity. It was found that the newly developed model is capable of predicting two-phase flow induced force fluctuation and dominant frequency range with satisfactory accuracy for flow regimes up to churn-turbulent.

Investigation of Bubble Frequency for Slug Flow Regime in a Uniformly Heated Horizontal Microchannel

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Amen Younes ◽  
Ibrahim Hassan ◽  
Lyes Kadem
Keyword(s):  
Flow Pattern ◽  
Flow Regime ◽  
Slug Flow ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Bubble Frequency ◽  
Drift Flux Model ◽  
Wide Range ◽  
Bubble Length ◽  
Bubble Zone

Slug flow is an essential flow pattern observed in microchannels where its transition boundaries in microchannels are characterized by two complex hydrodynamic phenomena, the bubble confinement and the bubble coalescence. Slug flow may be classified in terms of bubble size into two major zones: isolated bubble zone and coalescence bubble zone. In this paper, a semi-analytical model is developed for predicting the main characteristics of isolated bubble zone for flow boiling in a horizontal microchannel. The influences of surface tension, shear, and inertial forces have been taken into account. The model is developed on the basis of drift flux model, and a fully developed slug unit is chosen as a control volume for deriving the equations of motion. The effects of main operating conditions, mass and heat fluxes, on bubble length and bubble frequency have been investigated. The boundaries of slug flow regime have been identified based on the most proper diabatic flow pattern maps available in the literature for the chosen database. The model has been validated using the database available in the literature for flow boiling of R134a and R245fa in 0.509 mm and 3.0 mm inner diameter horizontal mini-tubes, respectively, and over wide range of mass fluxes (300≤G≤1000 kg/m2 s). This study has shown that the mass flux has a significant effect on the slug length and the bubble frequency. The model gave a good agreement with the experimental data of bubble length and bubble frequency with a mean absolute error (MAE) of 18.0% and 27.34%, respectively.

Flow Regime Classification and Transition of Flow Boiling Through Porous Channel

2009 ◽  
Author(s):  
Bofeng Bai ◽  
Xiaojie Zhang ◽  
Maolong Liu ◽  
Wang Su
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Mass Flux ◽  
Slug Flow ◽  
Flow Boiling ◽  
Particle Diameter ◽  
Experimental Parameter ◽  
Flow Regimes ◽  
Two Phase ◽  
Porous Channels

In the present research, a visual experiment was carried out on the flow regimes of the porous channels in the spherical fuel element nuclear reactor. Boiling two-phase flow in different porous channels composed of particles with diameters of 4mm, 6mm and 8mm were studied respectively, and four different flow regimes occur within the experimental parameter range: bubbly flow, bubbly-slug flow, slug flow and slug-annular flow. The effects of heat flux, mass flux and particle diameter on the flow regimes were obtained. Bubbles and slugs deform, coalesce and break up more frequently, and increase in both number and size with the increase of the heat flux; bubbles and slugs tend to decrease in number and size with higher mass flux and particles of smaller diameters. At higher mass flux, a higher heat flux is needed to get the same flow regime that occurs at lower mass flux; with particles of smaller diameter, a higher heat flux is needed to get the same flow regime as that of particles of larger diameter. The flow regime map and flow regime transition have been proposed by modifying the void fractions of Tung/Dhir model.

On Instabilities in Horizontal Two-Phase Flow

1994 ◽  
Vol 59 (12) ◽  
pp. 2595-2603
Author(s):  
Lothar Ebner ◽  
Marie Fialová
Keyword(s):  
Differential Equation ◽  
Flow Regime ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Annular Flows ◽  
Flow Regime Maps

Two regions of instabilities in horizontal two-phase flow were detected. The first was found in the transition from slug to annular flow, the second between stratified and slug flow. The existence of oscillations between the slug and annular flows can explain the differences in the limitation of the slug flow in flow regime maps proposed by different authors. Coexistence of these two regimes is similar to bistable behaviour of some differential equation solutions.

The influences of bathymetry and flow regime upon the morphology of sublittoral sponge communities

2000 ◽  
Vol 80 (4) ◽  
pp. 707-718 ◽  
Author(s):  
James J. Bell ◽  
David K.A. Barnes
Keyword(s):  
Turbulent Flow ◽  
Flow Regime ◽  
Current Flow ◽  
Volume Ratio ◽  
Basal Area ◽  
Morphological Diversity ◽  
Flow Regimes ◽  
High Energy ◽  
Similarity Analysis ◽  
Lough Hyne

Sponge communities were sampled at 3 m depth intervals at six sites experiencing different flow regimes at Lough Hyne, Ireland. Sponges were identified and classified within the following morphological groups: encrusting, massive, globular, pedunculate, tubular, flabellate, arborescent, repent and papillate morphological types on both vertical (≈90°) and inclined (≈45°) surfaces.Differences in the proportional abundance of the sponge body forms and density (sponge m−2) were observed between sites and depths. The density of sponges increased with depth at sites of slight to moderate current flow, but not at the site where current flow was turbulent. Morphological diversity of sponge communities decreased with increasing current flow due to the removal of delicate forms such as pedunculate and arborescent shaped sponges. Massive and encrusting morphologies dominated at the high-energy sites (fast and turbulent flow regimes) due to a high basal area to volume ratio, which prevents removal from cliff surfaces. However, pedunculate, papillate and arborescent types dominated at the low current sites as these shapes may help to prevent the settlement of sediment on sponge surfaces. Bray–Curtis Similarity analysis and Correspondence Analysis were used to distinguish between five different morphological communities.

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