scholarly journals A Combined Numerical and Experimental Study of Hydrodynamics for an Air-Water External Loop Airlift Reactor

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Deify Law ◽  
Samuel T. Jones ◽  
Theodore J. Heindel ◽  
Francine Battaglia
Keyword(s):  
Liquid Velocity ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Airlift Reactor ◽  
Cfd Modeling ◽  
Bubble Column Reactor ◽  
Ensemble Averaging ◽  
3D Simulations ◽  
External Loop

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because they can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR was simulated using an Eulerian–Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. The computational fluid dynamics (CFD) simulations were compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 cm/s to 20 cm/s. The effect of specifying a mean bubble diameter to represent the gas phase in the CFD modeling was investigated, and 2D and 3D simulations were found to be in good agreement with the experimental data. The ELALR flow regimes were compared for the reactor operating in bubble column, closed vent, and open vent modes, and the 2D simulations qualitatively predicted the behavior of bubble growth in the downcomer. However, it was found that 3D simulations were necessary to capture the physics of the ELALR for gas holdup, bulk density differences, and riser superficial liquid velocity.

scholarly journals Simulating Gas-Liquid Flows in an External Loop Airlift Reactor

2008 ◽  
Author(s):  
Deify Law ◽  
Francine Battaglia ◽  
Theodore J. Heindel
Keyword(s):  
Bubble Column ◽  
Bubble Diameter ◽  
Scale Up ◽  
Three Dimensional ◽  
Airlift Reactor ◽  
Cfd Modeling ◽  
Bubble Column Reactor ◽  
Ensemble Averaging ◽  
Cfd Simulations ◽  
External Loop

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are connected with two horizontal connectors. Airlift reactors are utilized in fermentation processes and are preferred over traditional bubble column reactors because they can operate over a wider range of conditions. Computational fluid dynamics (CFD) simulations can be used to enhance our understanding of the hydrodynamics within these reactors. In the present work, the gas-liquid flow dynamics in an external loop airlift reactor are simulated using CFDLib with an Eulerian-Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. In addition, models are employed for the interphase momentum transfer drag coefficient and turbulence behavior. The CFD simulations for temporal and spatial averaged gas holdup are compared to the experimental measurements of Jones and Heindel [1] who used a 10.2 cm diameter ELALR over a range of superficial gas velocities from 0.5 to 20 cm/s. The effect of specifying a mean bubble diameter size for the CFD modeling is examined. The objectives are to validate 2D and 3D CFD simulations with experimental data in order to predict the hydrodynamics in an airlift reactor for future studies on scale-up and design.

Numerical Simulations for Hydrodynamics of Air-Water External Loop Airlift Reactor Flows With Bubble Break-Up and Coalescence Effects

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Deify Law ◽  
Francine Battaglia
Keyword(s):  
Bubble Size ◽  
Bubble Column ◽  
National Laboratory ◽  
Airlift Reactor ◽  
Single Bubble ◽  
Bubble Column Reactor ◽  
Dimensional System ◽  
Ensemble Averaging ◽  
External Loop ◽  
Bubble Breakup

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because it can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR were simulated using an Eulerian–Eulerian ensemble-averaging method with bubble breakup and coalescence effects in a three-dimensional system. The population balance models (PBM) of Luo and Svendsen (1996, “Theoretical Model for Drop and Bubble Breakup in Turbulent Dispersions,” AIChE J., 42, pp. 1225–1233) and Prince and Blanch (1990, “Bubble Coalescence and Breakup in Air-Sparged Bubble Columns,” AIChE J., 36, pp. 1485–1499) were used to simulate the bubble breakup and coalescence effects, respectively. The bubble breakup and coalescence closure models were implemented into CFDLib, a multiphase flow source code developed by Los Alamos National Laboratory, and validated with experiments. The computational fluid dynamics (CFD) simulations were then compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 to 20 cm/s. From this work, the 3D PBM simulations of an external loop airlift reactor were generally comparable with the 3D single bubble size simulations. However, the 3D PBM simulations have closer agreement with experimental findings than the single bubble size simulations especially regarding the length of gas bubbles in the downcomer.

scholarly journals Functional input and membership characteristics in the accuracy of machine learning approach for estimation of multiphase flow

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Meisam Babanezhad ◽  
Ali Taghvaie Nakhjiri ◽  
Mashallah Rezakazemi ◽  
Azam Marjani ◽  
Saeed Shirazian
Keyword(s):  
Learning Process ◽  
Liquid Velocity ◽  
Bubble Column ◽  
Three Dimensional ◽  
Bubble Column Reactor ◽  
Membership Functions ◽  
Turbulence Flow ◽  
Machine Learning Approach ◽  
Anfis Method ◽  
Prediction Capability

Abstract In the current study, Artificial Intelligence (AI) approach was used for the learning of a physical system. We applied four inputs and one output in the learning process of AI. In the learning process, the inputs are space locations of a BCR (bubble column reactor), which are x, y, and z coordinate as well as the amount of gas fraction in BCR. The liquid velocity is also considered as output. A variety of functions were used in learning, such as gbellmf and gaussmf functions, to examine which functions can give the best learning. At the end of the study, all of the results were compared to CFD (computational fluid dynamics). A three-dimensional (3D) BCR was used in this research, and we studied simulation by CFD as well as AI. The data from CFD in a 3D BCR was studied in the AI domain. In AI, we tuned for various parameters to achieve the best intelligence in the system. For instance, different inputs, different membership functions, different numbers of membership functions were used in the learning process. Moreover, the meshless prediction was used, meaning that some data in the BCR have not participated in the learning, and they were predicted in the prediction process, which gives us a special capability to compare the results with the CFD outcomes. The findings showed us that AI can predict the CFD results, and a great agreement was achieved between CFD computing nodes and AI elements. This novel methodology can suggest a meshless and multifunctional AI model to simulate the turbulence flow in the BCR. For further evaluation, the ANFIS method is compared with ACOFIS and PSOFIS methods with regards to model’s accuracy. The results show that ANFIS method contains higher accuracy and prediction capability compared with ACOFIS and PSOFIS methods.

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.

scholarly journals CFD Modeling of Gas-Liquid Bubbly Flow in Horizontal Pipes: Influence of Bubble Coalescence and Breakup

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
K. Ekambara ◽  
R. Sean Sanders ◽  
K. Nandakumar ◽  
J. H. Masliyah
Keyword(s):  
Volume Fraction ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Gas Bubbles ◽  
Bubbly Flows ◽  
Cfd Modeling ◽  
Horizontal Pipe ◽  
The Impact

Modelling of gas-liquid bubbly flows is achieved by coupling a population balance equation with the three-dimensional, two-fluid, hydrodynamic model. For gas-liquid bubbly flows, an average bubble number density transport equation has been incorporated in the CFD code CFX 5.7 to describe the temporal and spatial evolution of the gas bubbles population. The coalescence and breakage effects of the gas bubbles are modeled. The coalescence by the random collision driven by turbulence and wake entrainment is considered, while for bubble breakage, the impact of turbulent eddies is considered. Local spatial variations of the gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, and liquid velocity are compared against experimental data in a horizontal pipe, covering a range of gas (0.25 to 1.34 m/s) and liquid (3.74 to 5.1 m/s) superficial velocities and average volume fractions (4% to 21%). The predicted local variations are in good agreement with the experimental measurements reported in the literature. Furthermore, the development of the flow pattern was examined at three different axial locations ofL/D= 25, 148, and 253. The first location is close to the entrance region where the flow is still developing, while the second and the third represent nearly fully developed bubbly flow patterns.

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

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 ◽  
Superficial Gas Velocity ◽  
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.

Effects of Sparger and Internals Designs on the Local Hydrodynamics in Slurry Bubble Column Reactors Operating under Typical Fischer-Tropsch Process Conditions - I

2017 ◽  
Vol 16 (3) ◽  
Author(s):  
Omar M Basha ◽  
Badie I Morsi
Keyword(s):  
Large Scale ◽  
Bubble Column ◽  
Perforated Plate ◽  
Pilot Scale ◽  
Cfd Modeling ◽  
Bubble Column Reactor ◽  
Process Conditions ◽  
Bubble Column Reactors ◽  
Slurry Bubble Column ◽  
Slurry Bubble Column Reactors

AbstractOur rigorously validated Computational Fluid Dynamics (CFD) model (Basha Omar, M., L. Weng, Z. Men, and I. Morsi Badie. 2016. “CFD Modeling with Experimental Validation of the Internal Hydrodynamics in a Pilot-Scale Slurry Bubble Column Reactor.”International Journal of Chemical Reactor Engineering14(2):599–619), was used to predict the effects of spargers design and internals configuration on the local hydrodynamics and flow structure in a pilot-scale (0.3-m ID) and a large-scale (10-m ID) Slurry Bubble Column Reactors (SBCRs), operating under Fisher-Tropsch (F-T) process conditions. In the pilot-scale SBCR without internals, the 6-arms spider created small/fast liquid recirculations in the vicinity of the sparger and slow/large liquid recirculations at about 1.2 times reactor diameter, whereas, the 3-concentric-rings and perforated plate spargers created slow/large recirculations throughout the reactor. In the pilot-scale SBCR with internals, spargers with downward-pointing orifices created larger Sauter mean bubble diameters (ds), leading to more effective solids suspension when compared with those with upward-pointing orifices. Also, 3-concentric-rings spargers resulted in larger Sauter mean bubble diameter values when compared with those of 6-arms spiders. In the large-scale SBCR provided with a large 3-concentric-rings sparger, the effects of vertical parallel and bundled internals on the local hydrodynamics and flow structures were predicted. Bundled internals led to slower and smaller liquid recirculations, smoother radial gas holdup profiles, larger average gas bubbles size, and smaller local gas holdups, when compared those predicted when using parallel internals.

scholarly journals On bubble clustering and energy spectra in pseudo-turbulence

2010 ◽  
Vol 650 ◽  
pp. 287-306 ◽  
Author(s):  
JULIÁN MARTÍNEZ MERCADO ◽  
DANIEL CHEHATA GÓMEZ ◽  
DENNIS VAN GILS ◽  
CHAO SUN ◽  
DETLEF LOHSE
Keyword(s):  
Isotropic Turbulence ◽  
Liquid Velocity ◽  
Pair Correlation ◽  
Bubble Diameter ◽  
Three Dimensional ◽  
Radial Distance ◽  
Energy Spectra ◽  
Bubble Velocity ◽  
Vertical Orientation ◽  
Gaussian Form

Three-dimensional particle tracking velocimetry (PTV) and phase-sensitive constant temperature anemometry in pseudo-turbulence – i.e. flow solely driven by rising bubbles – were performed to investigate bubble clustering and to obtain the mean bubble rise velocity, distributions of bubble velocities and energy spectra at dilute gas concentrations (α ≤ 2.2 %). To characterize the clustering the pair correlation function G(r, θ) was calculated. The deformable bubbles with equivalent bubble diameter db = 4–5 mm were found to cluster within a radial distance of a few bubble radii with a preferred vertical orientation. This vertical alignment was present at both small and large scales. For small distances also some horizontal clustering was found. The large number of data points and the non-intrusiveness of PTV allowed well-converged probability density functions (PDFs) of the bubble velocity to be obtained. The PDFs had a non-Gaussian form for all velocity components and intermittency effects could be observed. The energy spectrum of the liquid velocity fluctuations decayed with a power law of −3.2, different from the ≈ −5/3 found for homogeneous isotropic turbulence, but close to the prediction −3 by Lance & Bataille (J. Fluid Mech., vol. 222, 1991, p. 95) for pseudo-turbulence.

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