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

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.

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

Volume 3 ◽  
2004 ◽  
Author(s):  
Chengzhi Tang ◽  
Theodore J. Heindel
Keyword(s):  
Flow Regime ◽  
Mass Fraction ◽  
Liquid Velocity ◽  
Bubble Column ◽  
Complex Function ◽  
Cellulose Fiber ◽  
Gas Holdup ◽  
Fiber Network ◽  
Drift Flux Model ◽  
Superficial Gas Velocity

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.

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

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 ◽  
Superficial Gas Velocity ◽  
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.

A review on empirical correlations estimating gas holdup for shear-thinning non-Newtonian fluids in bubble column systems with future perspectives

2018 ◽  
Vol 34 (6) ◽  
pp. 887-928 ◽  
Author(s):  
Ajay Sujan ◽  
Raj K. Vyas
Keyword(s):  
Rheological Properties ◽  
Gas Flow ◽  
Bubble Column ◽  
Flow Behavior ◽  
Gas Holdup ◽  
Operating Conditions ◽  
Bubble Columns ◽  
Empirical Correlations ◽  
Flow Behavior Index ◽  
Data Set

Abstract Gas holdup is one of the most important parameters for characterizing the hydrodynamics of bubble columns. Modeling and design of bubble columns require empirical correlations for precise estimation of gas holdup. Empirical correlations available for prediction of gas holdup (εG) in various non-Newtonian systems for both gas-liquid and gas-liquid-solid bubble columns have been presented in this review. Critical analysis of correlations presented by different researchers has been made considering the findings and pitfalls. As the magnitude of gas holdup depends on many factors, such as physicochemical properties of gas and/or liquid, column geometry, type and design of gas distributors, operating conditions, phase properties, and rheological properties, etc., all of these have been discussed and examined. In order to emphasize the significance, relative importance of parameters such as flow behavior index, consistency index, column diameter, gas flow rate, and density of aqueous carboxymethylcellulose (CMC) solution on gas holdup has been quantified using artificial neural network and Garson’s algorithm for an experimental data set of air-CMC solution from the literature. Besides, potential areas for research encompassing operating conditions, column geometry, physical properties, modeling and simulation, rheological properties, flow regime, etc., have been underlined, and the need for developing newer correlations for gas holdup has been outlined. The review may be useful for the modeling and design of bubble columns.

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

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 ◽  
Superficial Gas Velocity

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.

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

2006 ◽  
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 Gas Velocity ◽  
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.

Experimental Investigation of Flow Behavior in a Bend and Sand Erosion Pattern Under Single-Phase and Multiphase Flow Conditions

2018 ◽  
Author(s):  
Peyman Zahedi ◽  
Alireza Asgharpour ◽  
Hadi Arabnejad Khanouki ◽  
Brenton S. McLaury ◽  
Siamack A. Shirazi
Keyword(s):  
Multiphase Flow ◽  
Liquid Film ◽  
Liquid Velocity ◽  
Flow Behavior ◽  
Thickness Measurement ◽  
Transportation Systems ◽  
Gas Production ◽  
Flow Conditions ◽  
Pipe Failure ◽  
Experimental Apparatus

Solid particle erosion in pipe fittings may cause pipe failure and major safety and environmental issues. Elbows are widely used in oil and gas production and transportation systems, and they are one of the most vulnerable fittings when presence of sand particles is anticipated in the system. An experimental apparatus was created to investigate the flow behavior in a 4-inch 90 degree bend under multiphase flow conditions in both horizontal-horizontal and vertical-horizontal elbow orientations. It was observed that in vertical annular flows, entrained droplets and liquid film are focused at the center of the outer bend, and as liquid velocity increases, the liquid film inside the elbow outer radius becomes thicker and it decreases the measured erosion. Observations were verified by comparison of erosion magnitudes in bends for different liquid velocities obtained utilizing a state-of-the-art ultrasonic thickness measurement technique. Erosion patterns and location of maximum erosion results were also examined through paint erosion experiments. It was concluded that regardless of particle size and gas and liquid flow rates, maximum erosion occurs in the range between 40° to 50° on the bend for gas dominant flows in low pressure gas environment studied here. A secondary erosion pattern caused by particle rebounds was observed to occur in the range between 60° to 90° in the bend. Erosion experimental results in the 4-inch elbow were compared with Computational Fluid Dynamics (CFD) predictions of erosion, and agreement was observed in terms of erosion pattern and 40% agreement in magnitude.

Impact of Dense Internals on Fluid Dynamic Parameters in Bubble Column

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 ◽  
Superficial Gas Velocity

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.

Investigation on the control of multiphase flow behavior in a continuous casting tundish during ladle change

2020 ◽  
Vol 117 (6) ◽  
pp. 619
Author(s):  
Rui Xu ◽  
Haitao Ling ◽  
Haijun Wang ◽  
Lizhong Chang ◽  
Shengtao Qiu
Keyword(s):  
Multiphase Flow ◽  
Flow Behavior ◽  
Rolled Strip ◽  
Impact Zone ◽  
Steel Cleanliness ◽  
Carry Over ◽  
Slag Carry Over ◽  
Hot Rolled ◽  
Turbulence Inhibitor ◽  
The Impact

The transient multiphase flow behavior in a single-strand tundish during ladle change was studied using physical modeling. The water and silicon oil were employed to simulate the liquid steel and slag. The effect of the turbulence inhibitor on the slag entrainment and the steel exposure during ladle change were evaluated and discussed. The effect of the slag carry-over on the water-oil-air flow was also analyzed. For the original tundish, the top oil phase in the impact zone was continuously dragged into the tundish bath and opened during ladle change, forming an emulsification phenomenon. By decreasing the liquid velocities in the upper part of the impact zone, the turbulence inhibitor decreased considerably the amount of entrained slag and the steel exposure during ladle change, thereby eliminating the emulsification phenomenon. Furthermore, the use of the TI-2 effectively lowered the effect of the slag carry-over on the steel cleanliness by controlling the movement of slag droplets. The results from industrial trials indicated that the application of the TI-2 reduced considerably the number of linear inclusions caused by ladle change in hot-rolled strip coils.

Dynamical Behavior and Flow Mechanism of Fluid in Nanochannel by Molecular Dynamics Simulation

2009 ◽  
Author(s):  
Juanfang Liu ◽  
Chao Liu ◽  
Qin Li
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Dynamical Behavior ◽  
Velocity Profiles ◽  
The Other ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Interfacial Region ◽  
Flow Mechanism ◽  
Bulk Fluid

The flow properties and dynamical behavior of fluid in a nanochannel were investigated by nonequilibrium molecular dynamics simulation. First of all, the locale distribution of molecules in the channel is found to be strongly inhomogeneous compared to the bulk fluid. In the vicinity of the wall, portion of the fluid molecules are absorbed on the surface of wall due to the strong interaction of the atoms between the wall and liquid, so that the fluid density in the contact region would be much larger than one of the bulk fluid. But in the other region, the local density value approaches one of the bulk fluids with the increasing distance from the wall. This oscillatory behavior of density resulted in different motion behavior of molecules in the different region of nanochannel. The molecular behavior in the interfacial region is remarkably different from those of fluid atoms in the center of channel and wall atoms, which posses both the motion properties of bulk liquids and a solid atom. At the molecular level, macroscopic continuum hypothesis failed, that is, the results predicted by the Navier-Stoke equations deviate from the simulation data adopted by molecular dynamics simulation. In the paper, the velocity profiles for the channels with different width were plotted, which demonstrated that the time-averaged velocity profiles was not quadratic when the channel width was less than 10 molecular diameters. But on the other cases, the velocity profiles will agree well with the analytical solution based on the NS theory. The molecular dynamics simulation method can withdraw the important microscopical information from the simulation process, which benefit to analyze the flow mechanism at such length scale channel.

Sign in / Sign up

Export Citation Format

Share Document