Gas Holdup in a Cocurrent Air-Water-Fiber Bubble Column

Effects of superficial liquid velocity (Ul), superficial gas velocity (Ug), and fiber mass fraction (C) on gas holdup (ε) and flow regime transition are studied experimentally in well-mixed water-cellulose fiber suspensions in a cocurrent bubble column. Experimental results show that the gas holdup decreases with increasing Ul when C and Ug are constant. The gas holdup is not significantly affected by C in the range of C < 0.4%, but decreases with increasing C in the range of 0.4% ≤ C ≤ 1.5%. When C > 1.5%, a significant amount of gas is trapped in the fiber network and recirculates with the water-fiber slurry in the system; as a result, the measured gas holdup is higher than that at C = 1.5%. The axial gas holdup distribution is shown to be a complex function of superficial gas and liquid velocities and fiber mass fraction. The drift-flux model is used to analyze the flow regime transitions at different conditions. Three distinct flow regimes are observed when C ≤ 0.4%, but only two are identified when 0.6% ≤ C ≤ 1.5%. The superficial gas velocities at which flow transition occurs from one regime to another are not significantly affected by Ul and slightly decrease with increasing C.

Gas Holdup in Opaque Cellulose Fiber Slurries

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2005-77043 ◽

2005 ◽

Cited By ~ 1

Author(s):

Sarah M. Talcott ◽

Theodore J. Heindel

Keyword(s):

Flow Regime ◽

Mass Fraction ◽

Cellulose Fiber ◽

Gas Holdup ◽

Fiber Types ◽

Homogeneous Flow ◽

Heterogeneous Flow ◽

Drift Flux Model ◽

Mass Fractions ◽

Three different cellulose fiber types are used to study their effect on gas holdup and flow regime transition in a 10.2 cm semi-batch bubble column. The three natural fiber types include bleached softwood chemical pulp (softwood), bleached hardwood chemical pulp (hardwood), and bleached softwood chemithermomechanical pulp (BCTMP). Gas holdup is recorded over a range of fiber mass fractions (0 ≤ C ≤ 1.6%) and superficial gas velocities (Ug ≤ 23 cm/s). Experimental results show that gas holdup decreases with increasing fiber mass fraction. Homogeneous, transitional, and heterogeneous flow is observed for all three fiber types at low fiber mass fractions. All three fiber types produce similar results in the homogeneous flow regime while significant differences are recorded in the heterogeneous flow regime; those being low mass fraction hardwood (softwood) fiber slurries produce the highest (lowest) gas holdup. At higher fiber mass fractions, only pure heterogeneous flow is observed and softwood fiber slurries still produce the lowest gas holdup, although the differences in gas holdup between fiber types are small. The Zuber-Findlay drift flux model is used to describe the gas holdup results in cellulose fiber slurries when the flow conditions are heterogeneous. The Zuber-Findlay drift flux model is also used to identify the superficial gas velocity at which homogeneous flow is no longer observed with some success. Generally, the superficial gas velocity at which the flow deviates from homogeneous flow decreases with increasing fiber mass fraction.

CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2020-0172 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Xi Zhang ◽

Ping Zhu ◽

Shuaichao Li ◽

Wenyuan Fan ◽

Jingyan Lian

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Radial Direction ◽

Liquid Velocity ◽

Bubble Column ◽

Gas Holdup ◽

Gas Velocity ◽

Gas Distributor ◽

The Right

Abstract A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

Statistical Analysis of Experimental Variables on Gas Holdup in Novel Bubble Column Using Box-Behnken Design

International Journal of Chemical Reactor Engineering ◽

10.1515/1542-6580.2908 ◽

2012 ◽

Vol 10 (1) ◽

Author(s):

S Dhanasekaran ◽

T Karunanithi

Keyword(s):

Liquid Velocity ◽

Bubble Column ◽

Perforated Plate ◽

Water System ◽

Gas Holdup ◽

Bubble Columns ◽

Interactive Effects ◽

Stirred Tank Reactors ◽

Plate Spacing ◽

A novel hybrid rotating and reciprocating perforated plate bubble column is designed indigenously. The novelty lies in combining the effects of stirred tank reactors, bubble columns and reciprocating plate columns using bevel gear arrangement. Box-Behnken experimental design in response surface methodology is chosen to predict the relationship between experimental variables and desired response of gas holdup. Agitation level, superficial gas velocity, superficial liquid velocity, perforation diameter and plate spacing are used as experimental variables. Air-water system is used in this investigation. The linear, square and interactive effects of experimental variables on gas holdup are studied. The F-test and P values were used to identify the experimental variables that significantly impact gas holdup.

The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2006-98011 ◽

2006 ◽

Cited By ~ 1

Author(s):

Samuel T. Jones ◽

Theodore J. Heindel

Keyword(s):

Liquid Velocity ◽

Bubble Column ◽

Gas Holdup ◽

Area Ratio ◽

Airlift Reactor ◽

Open Area ◽

Gas Velocity ◽

External Loop ◽

Superficial Liquid Velocity

Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with an area ratio of 1:16. Two downcomer configurations are investigated consisting of the downcomer open or closed to the atmosphere. Experiments for these two configurations are carried out over a range of superficial gas velocities from UG = 0.5 to 20 cm/s using three aeration plates with open area ratios of 0.62, 0.99 and 2.22%. These results are compared to a bubble column operated with similar operating conditions. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different. The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a function of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio. When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to increase with increasing superficial gas velocity until the onset of choking occurs in the downcomer. Increasing the superficial gas velocity beyond the onset of choking increases the effect of choking and decreases the superficial liquid velocity. Once maximum choking is reached, the superficial liquid velocity becomes independent of the superficial gas velocity. When the downcomer vent is closed to the atmosphere, the superficial liquid velocity is initially observed to decrease with increasing superficial gas velocity as choking in the downcomer is immediately present. Once maximum choking occurs, the superficial liquid velocity once again becomes independent of the superficial gas velocity.

Impact of Dense Internals on Fluid Dynamic Parameters in Bubble Column

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2018-0012 ◽

2018 ◽

Vol 16 (12) ◽

Author(s):

Dinesh V. Kalaga ◽

Vishal Bhusare ◽

H.J. Pant ◽

Jyeshtharaj B. Joshi ◽

Shantanu Roy

Keyword(s):

Liquid Phase ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Liquid Velocity ◽

Bubble Column ◽

Vertical Tube ◽

Gas Holdup ◽

Gas Velocity ◽

Cross Sectional ◽

Abstract Industrial gas-liquid processes such as oxidation, hydrogenation, Fischer-Trospch synthesis, liquid-phase methanol synthesis, and nuclear fission are exothermic in nature; the reactor of choice for such processes is, therefore, a bubble column equipped with heat exchanging internals. In addition to maintaining the desired process temperature, the heat exchanging vertical tube internals are used to control flow structures and liquid back mixing. The present work reports the experimentally measured gas hold-up, mean liquid velocity and liquid phase turbulent kinetic energy, using the Radioactive Particle Tracking (RPT) technique, in a 120 mm diameter bubble column equipped with dense vertical tube internals covering 23 % of the total cross-sectional area of the column. The effect of superficial gas velocity (44–265 mm/s) on gas hold-up, mean liquid velocity and turbulent kinetic energy is presented and discussed. It has been inferred from the experimental results that the vertical tube internal located at the center of the column plays a vital role in affecting the hydrodynamics when compared to the conventional internal configurations reported in the literature. For the chosen dense internal configuration, the cross-sectional distribution of the gas holdup, mean liquid velocity and turbulent kinetic energy show asymmetry for all the superficial gas velocities investigated. The overall gas holdup and the liquid turbulence increases with an increase in the superficial gas velocity. The strong liquid circulation velocities have been seen upon the insertion of the dense internals.

Influence of Operating Pressure on Gas Holdup and Flow Regime Transition in a Bubble Column

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN ◽

10.1252/jcej.10we157 ◽

2010 ◽

Vol 43 (10) ◽

pp. 829-832 ◽

Author(s):

Hiroaki Matsubara ◽

Kiyoshi Naito ◽

Hideharu Kuwamoto ◽

Toshiyuki Sakaguchi

Keyword(s):

Flow Regime ◽

Bubble Column ◽

Gas Holdup ◽

Operating Pressure ◽

Regime Transition ◽

Flow Regime Transition

Mass Transfer Studies in a Novel Perforated Plate Bubble Column

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2340 ◽

2010 ◽

Vol 8 (1) ◽

Author(s):

S. Dhanasekaran ◽

T. Karunanithi

Keyword(s):

Mass Transfer ◽

Liquid Velocity ◽

Bubble Column ◽

Perforated Plate ◽

Gas Velocity ◽

Plate Spacing ◽

Mass Transfer Studies ◽

Superficial Liquid Velocity

This investigation reports the experimental and theoretical results carried out to evaluate the volumetric mass transfer coefficient (kLa) in a novel hybrid rotating and reciprocating perforated plate bubble column. Countercurrent condition is performed. kLa is studied by the absorption of oxygen from air into deoxygenated water at room temperature (27 ± 1°C). Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate spacing on kLa were analyzed and found to be significant. With an increase in agitation level at a constant superficial gas and liquid velocities, the breakage process of gas bubbles starts to be more pronounced and intensive oxygen mass transfer occurs. Hence, kLa increases sharply. kLa increases with an increase in superficial gas velocity, due to higher gas holdup and the enhanced breakup of bubbles. Similarly, kLa increases with an increase in superficial liquid velocity and the effect is found to be significant. When plate spacing is decreased (by increasing the number of plates), it is observed that the kLa increases at higher superficial gas velocity and agitation level. Correlation is developed for the determination of kLa and found to concur with experimental results. This correlation can be used for the determination of kLa for this hybrid column with 95% accuracy within the range of variables investigated in this present study.

Bubble Diameter and Effective Interfacial Area in a Novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column

International Journal of Chemical Reactor Engineering ◽

10.1515/1542-6580.2914 ◽

2012 ◽

Vol 10 (1) ◽

Author(s):

Dhanasekaran S ◽

Karunanithi T

Keyword(s):

Liquid Velocity ◽

Bubble Column ◽

Bubble Diameter ◽

Perforated Plate ◽

Interfacial Area ◽

Gas Velocity ◽

The Mean ◽

Plate Column

This investigation reports on the experimental and theoretical investigation carried out to evaluate the bubble diameter and effective interfacial area in a novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column. Air-water system is used in this investigation. Countercurrent mode is employed. The effects of agitation level, superficial gas velocity and superficial liquid velocity on the bubble size distribution are studied. The mean bubble diameter is predicted using photographic technique. A simple correlation is developed for the determination of mean bubble diameter. It is found that the mean bubble diameter values for hybrid column are 1.8 to 2.5 times smaller when compared with conventional reciprocating plate column. The interfacial area is calculated based on the experimental results of the gas holdup and bubble diameter. Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate free area on the interfacial area have been investigated. Correlations are developed for the determination of interfacial area for both mixer-settler and emulsion regions. It could be noted that the interfacial area for the hybrid column is 3 to 6 times higher in both mixer-settler region and emulsion region than that of conventional reciprocating plate column which is quite large.

Annular Gap Bubble Column: Experimental Investigation and Computational Fluid Dynamics Modeling

Journal of Fluids Engineering ◽

10.1115/1.4031002 ◽

2015 ◽

Vol 138 (1) ◽

Cited By ~ 27

Author(s):

Giorgio Besagni ◽

Gaël Raymond Guédon ◽

Fabio Inzoli

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Flow Regime ◽

Bubble Column ◽

Gas Holdup ◽

Operating Conditions ◽

Optical Probes ◽

Annular Gap ◽

Fiber Optical ◽

Flow Visualizations

This paper investigates the countercurrent gas–liquid flow in an annular gap bubble column with a 0.24 m inner diameter by using experimental and numerical investigations. The two-phase flow is studied experimentally using flow visualizations, gas holdup measurements, and double fiber optical probes in the following range of operating conditions: superficial air velocities up to 0.23 m/s and superficial water velocities up to −0.11 m/s, corresponding to gas holdups up to 29%. The flow visualizations were used to observe the flow patterns and to obtain the bubble size distribution (BSD). The gas holdup measurements were used for investigating the flow regime transitions, and the double fiber optical probes were used to study the local flow phenomena. A computational fluid dynamics (CFD) Eulerian two-fluid modeling of the column operating in the bubbly flow regime is proposed using the commercial software ansys fluent. The three-dimensional (3D) transient simulations have been performed considering a set of nondrag forces and polydispersity. It is shown that the errors in the global holdup and in the local properties are below 7% and 16%, respectively, in the range considered.

CFD Simulation of Multiphase Flow in an Airlift Column Photobioreactor for the Cultivation of Microalgae

ASME 2012 6th International Conference on Energy Sustainability, Parts A and B ◽

10.1115/es2012-91297 ◽

2012 ◽

Author(s):

Samira García ◽

Edgardo Paternina ◽

Oscar R. Pupo ◽

Antonio Bula ◽

Francisco Acuña

Keyword(s):

Multiphase Flow ◽

Liquid Velocity ◽

Bubble Column ◽

Flow Behavior ◽

Velocity Profiles ◽

Gas Holdup ◽

Superficial Velocity ◽

Dynamics Simulation ◽

High Mass ◽

Air Supply

Due to their better operational advantages, such as good scalability, operational flexibility, high mass and heat transfer characteristics, homogenous shear stress, good mixing and better control over fluid circulation, airlift column photobioreactors (PBR) have become a promising design alternative for microalgae culture, among bubble column and other types of photobioreactors. The good hydrodynamic environment for fragile microorganisms in airlift columns have led to numerous investigations in order to understand the hydrodynamic phenomena of multiphase flow, particularly gas-liquid, inside this type of PBR. In the present paper, a CFD (Computer Fluid Dynamics) simulation in CFX, ANSYS Inc. 11.0, is developed following a multiphase flow model with an Eulerian-Eulerian approach. For evaluating turbulence, the modified k–ε model is chosen. Gas holdup, gas superficial velocity and liquid velocity profiles for different heights column are obtained by varying air volumetric flow rates at 2, 5 and 8 L/min. Also gas holdup, gas superficial velocity and liquid velocity contours are obtained for a sequence of five step times. An experimental video validation to compare the multiphase flow behavior has been made with a high-resolution video camera. The experiments are carried out by using an airlift column photobioreactor with air supply by a porous sparger. The profiles of the hydrodynamic variables made for 5 different column heights show that the trends of gas holdup and gas superficial velocity are very similar and do not depend on the variation of inlet air flow. For the liquid velocity profiles, the trends don’t show the same behavior, the profiles at lower heights are off-centered and less symmetric and the maximum velocities are reached at h = 0.2 m. The time sequences with the variable contours are made to enhance the visualization and understanding of the hydrodynamic behavior, especially when air supply begins and the bubble plume starts to form.