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Muthanna H Aldahhan - One of the best experts on this subject based on the ideXlab platform.
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influence of heat exchanging tubes diameter on the Gas Holdup and bubble dynamics in a bubble column
Fuel, 2019Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Ahmed A. JasimAbstract:Abstract The effects of the presence of vertical internal tubes and their diameters on the local Gas Holdup and bubble dynamics, including the specific interfacial area, bubble chord length, and bubble velocity were investigated in a 6 in. bubble column for the air-water system by using a four-point optical fiber probe technique. Two different diameters, 0.5-inch, and 1-inch, of vertical internals equally covering 25% of the column's cross-sectional area (CSA) were used to represent the heat-exchanging tubes utilized in the Fischer Tropsch (FT) process. For both sizes, the vertical internals were uniformly distributed over column CSA. The experiments were performed using the air-water system, in a 6-inch bubble column at superficial Gas velocities of 20, 30, and 45 cm/s. The experimental results indicated that the presence of vertical internals and their diameters have a significant effect on the hydrodynamic properties of the bubble column reactor at high superficial Gas velocities. The local Gas Holdup significantly increased in the core region and decreased at the wall regions when the 0.5-inch vertical internals were used. Contrarily, the 1-inch vertical internals enhanced the Gas Holdup near to the wall regions. Additionally, the bubble chord length and the bubble rise velocity were found to be larger in the presence of vertical internals, especially at high superficial Gas velocities. The specific interfacial area with the 0.5-inch internal was much lower than bubble column without vertical internals, but while using 1-inch internals, it was enhanced in the wall regions.
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investigating the influence of the configuration of the bundle of heat exchanging tubes and column size on the Gas Holdup distributions in bubble columns via gamma ray computed tomography
Experimental Thermal and Fluid Science, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract The impact of dense vertical internal tubes and their configurations on the Gas Holdup distributions and their diametrical profiles in pilot-scale bubble column is visualized and quantified for the first time ever using an advanced gamma-ray computed tomography (CT) technique. Two arrangements of vertical internals (circular and hexagonal configurations) occupying the same cross-sectional area (CSA) of the column (about 25% of the total cross-sectional area to represent the heat exchanging tubes that are used in the Fischer-Tropsch synthesis), were examined in addition to the measurement in the bubble column without vertical internals. Moreover, the Gas Holdup distribution results of the 18-inch (0.46 m in outer diameter, O.D.) bubble column are compared with an available data of 6-inch (0.15 m in O.D.) bubble columns with and without vertical internals. CT scans have been conducted for 18-inch bubble columns with and without vertical internals for the air-water system under a wide range of superficial Gas velocity (0.05–0.45 m/s). The experimental results indicate that an improvement in the Gas Holdup distribution over the column's cross-sectional area is obtained when the vertical internal tubes (arranged in either a circular or a hexagonal configuration) were used. However, better cross-sectional Gas Holdup distribution was achieved in the bubble column with vertical internals arranged in a hexagonal configuration as compared to the bubble column without and with vertical internals arranged in a circular arrangement. Additionally, the averages of the cross-sectional Gas Holdup and their profiles for bubble column with and without vertical internals are close to each other when the bubble column with vertical internals is operating at a high superficial Gas velocity, which is calculated based on the free cross-sectional area for the flow. Furthermore, the Gas Holdup distributions are further improved when the larger bubble column with vertical internals was used as compared to the 6-inch bubble columns with and without vertical internals.
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impact of heat exchanging tube configurations on the Gas Holdup distribution in bubble columns using gamma ray computed tomography
International Journal of Multiphase Flow, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract An advanced gamma-ray computed tomography (CT) technique was used for the first time to visualize and quantify the impacts of the presence of heat-exchanging tubes and their configurations on the Gas-liquid distributions and their profiles in a 6-inch (0.1524 m O.D.) Plexiglas® bubble column in an air-water reactor. Two superficial Gas velocities (i.e., 0.2 and 0.45 m/s) were employed to simulate the churn turbulent flow regime. To investigate the impact of vertical internals configurations, three arrangements (i.e., hexagonal, circular without a central internal, and circular with a central internal) were employed in addition to the column with no internals. Using the same sized vertical internals and the same occluded cross-sectional area (CSA), it was found that the configuration of the vertical internals significantly impacted the Gas Holdup distribution over the CSA of the column. All studied superficial Gas velocities resulted in symmetrical Gas Holdup distributions over the CSA of the bubble columns without vertical internals; however, the columns equipped densely with vertical internals did not have symmetrical Gas Holdup distributions. The presence of an extra central tube in the circular configuration played a key role in the Gas-liquid distribution over the CSA of the bubble column. The hexagonal configuration had the advantage of providing the best spread of the Gas phase over the entire CSA of the column. Gas Holdup values at the wall region of the bubble column increased with the addition of vertical tubes in all investigated configurations. However, a remarkable increase in the Gas Holdup values was obtained with the hexagonal configuration. The experimental data (i.e., Gas Holdup distributions and their diametrical profiles) can help to evaluate and validate three-dimensional (3-D) computational fluid dynamics (CFD) simulations to better predict the hydrodynamic parameters involved in these types of reactors.
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influence of the size of heat exchanging internals on the Gas Holdup distribution in a bubble column using gamma ray computed tomography
Chemical Engineering Science, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract The effects of the presence of the vertical internals of different sizes at a wide range of superficial Gas velocity on the overall, local Gas Holdup distributions and their profiles have been studied and quantified in a 6-in. (0.14 m) Plexiglas® bubble column with air-water system using a non-invasive advanced gamma-ray computed tomography (CT) technique. In this study, two sizes of Plexiglas® vertical internals, having the same occupying area (∼25%) of the column's cross-sectional area (CSA) that represents those used in Fischer-Tropsch synthesis, have been used within a range of superficial Gas velocities that cover bubbly and churn turbulent flow regimes (0.05–0.45 m/s). The reconstructed CT scan images revealed that the bubble columns equipped with or without internals displayed a uniform cross-sectional Gas Holdup distribution (symmetric) for all studied superficial Gas velocities. However, the bubble column equipped with 1-in. vertical internals exhibited more uniform Gas Holdup distribution than the column with 0.5-in. internals. Also, the visualization of the Gas-liquid distributions for bubble columns with and without internals reveal that the well-known phenomenon of the core-annular liquid circulation pattern that observed in the bubble column without internals still exists in bubble column packed densely with vertical internals. Moreover, a remarkable increase in the Gas Holdup values at the wall region was achieved in the churn turbulent flow regime based on the insertion of the vertical internals inside the column as compared with using a bubble column without obstacles. Furthermore, the values of the Gas Holdup in the core region of the bubble column with vertical internals are similar to those of the bubble column without vertical internals when they are operated at high superficial Gas velocity (churn turbulent flow regime), based on the free cross-sectional area (CSA) for the flow. In general, the magnitude of the Gas Holdup increased significantly with increasing superficial Gas velocity for the bubble columns with and without internals. However, the Gas Holdup profile was shaped like a wavy line in the bubble column with vertical internals, whereas it exhibited a parabolic Gas Holdup profile in the bubble column without obstacles.
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impacts of dense heat exchanging internals on Gas Holdup cross sectional distributions and profiles of bubble column using gamma ray computed tomography ct for ft synthesis
Chemical Engineering Journal, 2016Co-Authors: Mohammed Al K Mesfer, Abbas Jawad Sultan, Muthanna H AldahhanAbstract:Abstract The effect of heat exchanging internals that represent Fischer–Tropsch (FT) synthesis in bubble column has been investigated for the first time using gamma ray Computed Tomography (CT) in a 5.5″ (0.14 m) inner diameter Plexiglas bubble column operated at atmospheric condition with air water system. Thirty vertical Plexiglas rods of 0.5″ outer diameter were used which covered ∼25% of the total cross-sectional area and were arranged in a triangular pitch of 0.84″ (2.14 cm). The superficial Gas velocities applied were based on both total cross-sectional area as well as free cross-sectional area available for the flow and were in the range of 5–45 cm/s covering the bubbly through churn-turbulent flow regimes. New knowledge and findings have been obtained which have not been reported in previous studies. In churn turbulent flow regime, the overall Gas Holdup and the profiles of Gas Holdup obtained in bubble columns without internals can be extrapolated to those with internals in the central region of the column if the superficial Gas velocity is based on the free cross-sectional area (CSA) available for the flow of the phases provide that symmetric time averaged Gas Holdup cross-sectional distributions are achieved. The results show that a significant increment in overall and local Gas Holdup are obtained upon inserted of the internals when the velocity measured based on the total cross sectional area of the column. The Gas Holdup distribution over the cross-sectional area (CSA) of the column in the presence of internals has a symmetrical shape at low Gas velocities and asymmetry at higher ones for the honeycomb configuration and its installation used in this study. At a high superficial Gas velocity that is based on free CSA for the flow, the influence of dense internal becomes insignificant at the central region of the column. However, the profiles of the Gas Holdup in the column with internals become less steeper compared to those that are like parabolic shape at high Gas velocity in the column without internals due to higher Gas Holdup was obtained in the region near the wall with internals.
M.p. Dudukovic - One of the best experts on this subject based on the ideXlab platform.
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on the measurement of Gas Holdup distribution near the region of impeller in a Gas liquid stirred rushton tank by means of γ ct
Chemical Engineering Journal, 2012Co-Authors: Lina Kong, Muthanna H Aldahhan, Luchang Han, Yuejin Liu, Hean Luo, M.p. DudukovicAbstract:Abstract Three flow patterns of flooding, loading and complete recirculation in a Gas–liquid stirred Rushton tank were identified based on experimental observation. The Gas–liquid system was composed of air and water. Under different operating conditions of Gas flow rate and impeller rotating speed, the distribution of Gas Holdup near the region of impeller was measured using a γ-CT scan method. Both quantitative digital distribution curves of Gas Holdup and their qualitative color CT images were obtained. At the region of impeller, there was a convex characteristic peak of Gas Holdup distribution both in radial and in axial directions, and with the region being gradually away from the impeller, the distribution of Gas Holdup became flatter. The values of Gas Holdup in S33 regime were a little higher than those in L33 regime. Higher impeller rotating speed had some effect on the increasing of Gas Holdup at the region of higher axial height. The experimental measurement results were basically consistent with those previously published by Bombac. The hole number and diameter of sparger had little influence on the distribution of Gas Holdup, while the sparger's installed height had significant influence on them. When the sparger was installed close to the bottom of Rushton tank, a comparatively smoother distribution of Gas Holdup above the space of impeller could be obtained. The research results in this paper were useful for better understanding of Gas Holdup distribution near the region of impeller of Rushton tank, and could also provide experimental data for CFD simulation.
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γ ct measurement and cfd simulation of cross section Gas Holdup distribution in a Gas liquid stirred standard rushton tank
Chemical Engineering Science, 2011Co-Authors: Yueji Liu, Yang Cao, Hea Luo, Muthanna H Aldahha, M.p. DudukovicAbstract:Abstract Cross section Gas Holdup distributions at 3/4 dimensionless static liquid height in a Gas–liquid stirred standard Rushton tank were measured using 137 Cs γ-CT scan measuring technology at larger Gas flow rates and higher impeller rotating speeds. The obtained CT scan images and digital distribution curves of Gas Holdup with dimensionless radius based on the CT images could explain the fluctuation changes of Gas Holdup distribution. The dense area of Gas Holdup distribution appeared in the upper space of impeller blades. Gas Holdup increased both with Gas flow rate and impeller rotating speed, but Gas flow rate had more influence on Gas Holdup than impeller rotating speed. The Eulerian–Eulerian two-fluid model coupling with the bubbles' coalescence and break-up models, and the drag coefficient model were established to make CFD simulation of Gas Holdup distributions for the Gas–liquid stirred Rushton tank under different Gas flow rates and impeller rotating speeds.
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Gas Holdup in Gas liquid stirred tanks
Industrial & Engineering Chemistry Research, 2010Co-Authors: Sean G Mueller, M.p. DudukovicAbstract:A single-point optical probe is developed that can accurately obtain local Gas Holdup in a Gas-liquid stirred tank across a wide range of operating pressures, temperatures, and fluids. It is found that the probe orientation to the flow in a stirred tank can cause underestimations in Gas Holdup if only a single probe orientation is used. The probe is also able to capture the complex flow pattern in the vessel. This allows improved understanding of optical probes and stirred tanks and generation of data at elevated pressure and temperature conditions needed for development of new fundamental models.
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computed tomographic investigation of the influence of Gas sparger design on Gas Holdup distribution in a bubble column
Industrial & Engineering Chemistry Research, 2009Co-Authors: Boon Cheng Ong, Muthanna H Aldahhan, Puneet Gupta, Ahmed Youssef, M.p. DudukovicAbstract:The effect of Gas sparger design on the Gas Holdup radial profile in a bubble column (with a diameter of 0.162 m) has been studied using γ-ray computed tomography (CT). Six different configurations of Gas spargers were examined, using an air−water system for selected superficial Gas velocities from 2 cm/s to 30 cm/s, covering the homogeneous and heterogeneous (churn-turbulent) flow regimes. Two operating pressures were used: 1 and 4 atm. Differences were found between the Gas Holdup distributions produced by different spargers at dimensionless radii of r/R < 0.8 in the central region of the column. The cross and single nozzle spargers produced closely similar Gas Holdup distributions, while the perforated plate sparger produced a higher Gas Holdup when compared to other spargers with the same percentage open area (POA). At 4 atm, the sparger design did not have a significant effect on the Gas Holdup profiles, compared to atmospheric pressure, except for the case of the single-hole sparger, which was found...
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Gas Holdup in bubble columns at elevated pressure via computed tomography
International Journal of Multiphase Flow, 2001Co-Authors: A Kemoun, Boon Cheng Ong, Muthanna H Aldahhan, Puneet Gupta, M.p. DudukovicAbstract:Abstract Gas Holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a laboratory scale vessel (diameter 0.162 m) with air–water system over a range of superficial Gas velocities (0.02–0.18 m/s) using non-invasive γ-ray based Computed Tomography (CT). It was found that the cross-sectional average Gas Holdup increases with pressure, as well as with superficial Gas velocity. At all operating conditions, the azimuthally averaged radial Gas Holdup profiles exhibit a characteristic shape with greater Gas Holdup in the column center than by the walls. It is also observed that with an increase in pressure, the transition to churn-turbulent regime characterized by the change of the radial Gas Holdup profile from relatively flat to almost parabolic, is delayed to higher superficial Gas velocities. The average cross-sectional Gas Holdup at each operating condition was compared with predictions of existing correlations and large discrepancies in predictions (as high as 300%) were found.
Theodore J. Heindel - One of the best experts on this subject based on the ideXlab platform.
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local time average Gas Holdup comparisons in cold flow fluidized beds with side air injection
Chemical Engineering Science, 2012Co-Authors: Joshua B Drake, Theodore J. HeindelAbstract:Abstract Fluidized beds are interesting and useful processing systems that are employed in many industries such as processing biomass into biofuels or the coating of pharmaceuticals. Knowledge of fluidized bed hydrodynamics is necessary for the design and scale-up of such devices. This paper describes the local time-average differences of Gas Holdup in a 10.2 cm and 15.2 cm diameter cold flow fluidized bed that were recorded using 3D X-ray computed tomography. Three different Geldart type B bed materials are studied at various superficial Gas velocities and side-air injection flow rates, where the side-air injection simulated the immediate volatilization of a fuel like coal or biomass particles. Variations in side-air injection flow rate have little influence on global bed hydrodynamics, but significantly affects local Gas Holdup. Axial annular flow dominates over all flow conditions for each material and bed diameter. Wall effects increasingly influence hydrodynamics as bed diameter decreases for all materials.
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local time averaged Gas Holdup in a fluidized bed with side air injection using x ray computed tomography
Powder Technology, 2009Co-Authors: Nathan P Franka, Theodore J. HeindelAbstract:Abstract Local time-averaged Gas Holdup in a 10.2 cm diameter fluidized bed is determined using X-ray computed tomography (CT) over a range of superficial Gas velocities (Ug), side air injection flow rates (Qside), and fluidized bed material. Without side air injection, only small variations in the local time-averaged Gas Holdup are observed for beds composed of glass beads, ground walnut shell, or ground corncob. With the introduction of side air injection, which simulates the immediate volatilization of biomass in a fluidized bed Gasifier, a distinctive plume is observed along the reactor wall above the side injection port. The plume gradually expands toward the center of the bed as height increases; the expansion is found to increase with increasing Qside. As Ug increases, fluidization becomes more uniform and the effect of the side air injection on the fluidization hydrodynamics is less pronounced. Additionally, increasing Ug increases overall Gas Holdup and bed expansion. Of the three bed materials examined, ground corncob fluidization is the least affected by side air injection and shows the highest overall Gas Holdup while glass bead fluidization is much more affected by side air injection and has the lowest overall Gas Holdup. This study demonstrates the usefulness of X-ray CT in noninvasively visualizing detailed internal features of fluidized beds. These results will be used in future studies to validate computational fluid dynamics (CFD) models of fluidized beds.
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minimum fluidization velocity and Gas Holdup in fluidized beds with side port air injection
ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer Energy Sustainability and 3rd Energy Nanotechnology Conferences, 2008Co-Authors: Nathan P Franka, Joshua B Drake, Theodore J. HeindelAbstract:Fluidized beds can be used to Gasify biomass in the production of producer Gas, a flammable Gas that can replace natural Gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 cm and 15.2 cm diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Time-averaged local and global Gas Holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local Gas Holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.© 2008 ASME
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estimating Gas Holdup via pressure difference measurements in a cocurrent bubble column
International Journal of Multiphase Flow, 2006Co-Authors: Chengzhi Tang, Theodore J. HeindelAbstract:Abstract Estimating Gas Holdup via pressure difference measurements is a simple and low-cost non-invasive technique to study Gas Holdup in bubble columns. It is usually used in a manner where the wall shear stress effect is neglected, termed Method II in this paper. In cocurrent bubble columns, when the liquid velocity is high or the fluid is highly viscous, wall shear stress may be significant and Method II may result in substantial error. Directly including the wall shear stress term in the determination of Gas Holdup (Method I) requires knowledge of two-phase wall shear stress models and usually requires the solution of non-linear equations. A new Gas Holdup estimation method (Method III) via differential pressure measurements for cocurrent bubble columns is proposed in this paper. This method considers the wall shear stress influences on Gas Holdup values without calculating the wall shear stress. A detailed analysis shows that Method III always results in a smaller Gas Holdup error than Method II, and in many cases, the error is significantly smaller than that of Method II. The applicability of Method III in measuring Gas Holdup in a cocurrent air–water–fiber bubble column is examined. Analysis based on experimental data shows that with Method III, accurate Gas Holdup measurements can be obtained, while measurement error is significant when Method II is used for some operational conditions.
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The effect of bubble column diameter on Gas Holdup in fiber suspensions
Chemical Engineering Science, 2006Co-Authors: Philip D. Hol, Sarah M. Talcott, Ann K. Staudt, Theodore J. HeindelAbstract:Abstract Three bubble column diameters ( D = 10.2 , 15.2, and 32.1 cm) are employed to study the scale-up effect on Gas Holdup in air–water and air–water–cellulose fiber (hardwood, softwood, and BCTMP) systems. The effect of column diameter depends on flow regime and fiber mass fraction. When D ⩽ 15.2 cm , Gas Holdup decreases with increasing column diameter for the transitional and heterogeneous flow regime, and column diameter effects are negligible in the homogeneous flow regime. When D ⩾ 15.2 cm , Gas Holdup is only affected by column diameter in the transitional flow regime for an air–water system and low fiber mass fraction suspensions ( C ⩽ 0.25 % ); column diameter effects disappear at medium fiber mass fractions (e.g., C = 0.8 % ) but are significant at high fiber mass fractions (e.g., C = 1.4 % ).
Rajamani Krishna - One of the best experts on this subject based on the ideXlab platform.
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Gas Holdup and volumetric mass transfer coefficient in a slurry bubble column
Chemical Engineering & Technology, 2003Co-Authors: C O Vandu, Rajamani KrishnaAbstract:The Gas Holdup, e, and volumetric mass transfer coefficient, k L a, were measured in a 0.051 m diameter glass column with ethanol as the liquid phase and cobalt catalyst as the solid phase in concentrations of 1.0 and 3.8 vol%. The superficial Gas velocity U was varied in the range from 0 to 0.11 m/s, spanning both the homogeneous and heterogeneous flow regimes. Experimental results show that increasing catalyst concentration decreases the Gas Holdup to a significant extent. The volumetric mass transfer coefficient, k L a, closely follows the trend in Gas Holdup. Above a superficial Gas velocity of 0.04 m/s the value of k L a/e was found to be practically independent of slurry concentration and the Gas velocity U; the value of this parameter is found to be about 0.45 s -1 . The studies provide a simple method for the estimation of k L a in industrial-size bubble column slurry reactors.
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Gas Holdup and mass transfer in bubble column reactors operated at elevated pressure
Chemical Engineering Science, 1999Co-Authors: Rajamani Krishna, J Jaap C Schouten, H M Letzel, C M Van Den BleekAbstract:Abstract Measurements of the total Gas Holdup, e , have been made in a 0.15 m diameter bubble column operated at pressures ranging from 0.1 up to 1.3 MPa. The influence of the increasing system pressure is twofold: (1) a shift of the flow regime transition point to higher Gas fractions, and (2) a decrease of the rise velocity of “large” bubbles in the heterogeneous regime. The large bubble rise velocity is seen to decrease with the square root of the Gas density, ρ G . This square root dependence can be rationalized by means of a Kelvin–Helmholtz stability analysis. The total Gas Holdup model of Krishna and Ellenberger (1996, A.I.Ch.E. J. 42, 2627–2634), when modified to incorporate the ρ G correction for the large bubble rise velocity, is found to be in good agreement with the experimental results. The influence of system pressure on the volumetric mass transfer coefficient, k L a , is determined using the dynamic pressure-step method of Linek et al. (1993, Chem. Engng Sci. 48, 1593–1599). This pressure step method was adapted for application at higher system pressures. The ratio ( k L a/e ) is found to be practically independent of superficial Gas velocity and system pressure up to 1.0 MPa; the value of this ratio is approximately equal to one half. This result provides a simple method for predicting k L a using the model developed for estimation of e .
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Gas Holdup in Slurry Bubble Columns: Effect of Column Diameter and Slurry Concentrations
AIChE Journal, 1997Co-Authors: Rajamani Krishna, Gilbert B. Martina, Jeroen W.a. De Swart, Jürg Ellenberger, Cristina MarettoAbstract:To study the influence of particle concentration on the hydrodynamics of bubble-column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38-m-dia. columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the two-phase model for Gas-solid fluid beds was used to describe bubble hydrodynamics. The two phases identified are: a dilute phase consisting of fast-rising large bubbles that traverse the column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic Gas disengagement was experimented in the heterogeneous flow regime to determine the Gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total Gas Holdup significantly, but the influence on the dilute-phase Gas Holdup is small. The dense-phase Gas voidage significantly decreases Gas Holdup due to enhanced coalescence of small bubbles resulting from introduction of particles. The dense-phase Gas voidage is practically independent of the column diameter. The dilute-phase Gas Holdup, on the other hand, decreases with increasing column diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for Gas-liquid systems.
Abbas Jawad Sultan - One of the best experts on this subject based on the ideXlab platform.
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influence of heat exchanging tubes diameter on the Gas Holdup and bubble dynamics in a bubble column
Fuel, 2019Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Ahmed A. JasimAbstract:Abstract The effects of the presence of vertical internal tubes and their diameters on the local Gas Holdup and bubble dynamics, including the specific interfacial area, bubble chord length, and bubble velocity were investigated in a 6 in. bubble column for the air-water system by using a four-point optical fiber probe technique. Two different diameters, 0.5-inch, and 1-inch, of vertical internals equally covering 25% of the column's cross-sectional area (CSA) were used to represent the heat-exchanging tubes utilized in the Fischer Tropsch (FT) process. For both sizes, the vertical internals were uniformly distributed over column CSA. The experiments were performed using the air-water system, in a 6-inch bubble column at superficial Gas velocities of 20, 30, and 45 cm/s. The experimental results indicated that the presence of vertical internals and their diameters have a significant effect on the hydrodynamic properties of the bubble column reactor at high superficial Gas velocities. The local Gas Holdup significantly increased in the core region and decreased at the wall regions when the 0.5-inch vertical internals were used. Contrarily, the 1-inch vertical internals enhanced the Gas Holdup near to the wall regions. Additionally, the bubble chord length and the bubble rise velocity were found to be larger in the presence of vertical internals, especially at high superficial Gas velocities. The specific interfacial area with the 0.5-inch internal was much lower than bubble column without vertical internals, but while using 1-inch internals, it was enhanced in the wall regions.
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Impact of Heat Exchanging Internals Configurations on the Gas Holdup and Bubble Properties in a Bubble Column
International Journal of Multiphase Flow, 2019Co-Authors: Ahmed A. Jasim, Abbas Jawad Sultan, Muthanna H. Al-dahhanAbstract:Abstract The effect of the vertical heat-exchanging tube bundle configurations on local Gas Holdup and bubble dynamics, including specific Gas-liquid interfacial area, bubble chord length, bubble rise velocity, and bubble passage frequency have been studied using the 4-point optical fiber probe technique. Two different tube bundle configurations were investigated, circular tube bundle and hexagonal tube bundle. 30 internal tubes, each with a diameter of 0.5 inches (0.013 m), were used in each configuration occupying 25% of the column cross-section area to represent the heat exchanging tubes utilized in the Fischer–Tropsch process. The experimental work was performed in a 0.14 m inner diameter Plexiglas bubble column using an air-water system. The applied superficial Gas velocities were based on the free cross-sectional area of the column available for fluid flow and were in the range of 0.02 to 0.45 m/s covering bubbly, transition, and churn turbulent flow regimes. Although the size and the number of the tubes in both configurations were similar, their effects on the hydrodynamics were found to be different. When compared to bubble column without internals, the circular tube bundle showed a significant increase in the local Gas Holdup in the core region and a decrease in the wall regions. Simultaneously, a substantial increase in the bubble chord length and bubble velocity was seen. Another important observation was the decrease in the interfacial area while using circular tube bundle. A distinct asymmetrical effect on the radial profiles of Gas Holdup and the specific interfacial area was observed when the hexagonal configuration was used. The Gas Holdup and interfacial area significantly increased on one side of the column and decreased on the other side. The bubble chord length and bubble rise velocity decreased, exhibiting a narrower distribution with smaller values, in comparison to the bubble column without internals.
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investigating the influence of the configuration of the bundle of heat exchanging tubes and column size on the Gas Holdup distributions in bubble columns via gamma ray computed tomography
Experimental Thermal and Fluid Science, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract The impact of dense vertical internal tubes and their configurations on the Gas Holdup distributions and their diametrical profiles in pilot-scale bubble column is visualized and quantified for the first time ever using an advanced gamma-ray computed tomography (CT) technique. Two arrangements of vertical internals (circular and hexagonal configurations) occupying the same cross-sectional area (CSA) of the column (about 25% of the total cross-sectional area to represent the heat exchanging tubes that are used in the Fischer-Tropsch synthesis), were examined in addition to the measurement in the bubble column without vertical internals. Moreover, the Gas Holdup distribution results of the 18-inch (0.46 m in outer diameter, O.D.) bubble column are compared with an available data of 6-inch (0.15 m in O.D.) bubble columns with and without vertical internals. CT scans have been conducted for 18-inch bubble columns with and without vertical internals for the air-water system under a wide range of superficial Gas velocity (0.05–0.45 m/s). The experimental results indicate that an improvement in the Gas Holdup distribution over the column's cross-sectional area is obtained when the vertical internal tubes (arranged in either a circular or a hexagonal configuration) were used. However, better cross-sectional Gas Holdup distribution was achieved in the bubble column with vertical internals arranged in a hexagonal configuration as compared to the bubble column without and with vertical internals arranged in a circular arrangement. Additionally, the averages of the cross-sectional Gas Holdup and their profiles for bubble column with and without vertical internals are close to each other when the bubble column with vertical internals is operating at a high superficial Gas velocity, which is calculated based on the free cross-sectional area for the flow. Furthermore, the Gas Holdup distributions are further improved when the larger bubble column with vertical internals was used as compared to the 6-inch bubble columns with and without vertical internals.
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impact of heat exchanging tube configurations on the Gas Holdup distribution in bubble columns using gamma ray computed tomography
International Journal of Multiphase Flow, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract An advanced gamma-ray computed tomography (CT) technique was used for the first time to visualize and quantify the impacts of the presence of heat-exchanging tubes and their configurations on the Gas-liquid distributions and their profiles in a 6-inch (0.1524 m O.D.) Plexiglas® bubble column in an air-water reactor. Two superficial Gas velocities (i.e., 0.2 and 0.45 m/s) were employed to simulate the churn turbulent flow regime. To investigate the impact of vertical internals configurations, three arrangements (i.e., hexagonal, circular without a central internal, and circular with a central internal) were employed in addition to the column with no internals. Using the same sized vertical internals and the same occluded cross-sectional area (CSA), it was found that the configuration of the vertical internals significantly impacted the Gas Holdup distribution over the CSA of the column. All studied superficial Gas velocities resulted in symmetrical Gas Holdup distributions over the CSA of the bubble columns without vertical internals; however, the columns equipped densely with vertical internals did not have symmetrical Gas Holdup distributions. The presence of an extra central tube in the circular configuration played a key role in the Gas-liquid distribution over the CSA of the bubble column. The hexagonal configuration had the advantage of providing the best spread of the Gas phase over the entire CSA of the column. Gas Holdup values at the wall region of the bubble column increased with the addition of vertical tubes in all investigated configurations. However, a remarkable increase in the Gas Holdup values was obtained with the hexagonal configuration. The experimental data (i.e., Gas Holdup distributions and their diametrical profiles) can help to evaluate and validate three-dimensional (3-D) computational fluid dynamics (CFD) simulations to better predict the hydrodynamic parameters involved in these types of reactors.
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influence of the size of heat exchanging internals on the Gas Holdup distribution in a bubble column using gamma ray computed tomography
Chemical Engineering Science, 2018Co-Authors: Muthanna H Aldahhan, Abbas Jawad Sultan, Laith S SabriAbstract:Abstract The effects of the presence of the vertical internals of different sizes at a wide range of superficial Gas velocity on the overall, local Gas Holdup distributions and their profiles have been studied and quantified in a 6-in. (0.14 m) Plexiglas® bubble column with air-water system using a non-invasive advanced gamma-ray computed tomography (CT) technique. In this study, two sizes of Plexiglas® vertical internals, having the same occupying area (∼25%) of the column's cross-sectional area (CSA) that represents those used in Fischer-Tropsch synthesis, have been used within a range of superficial Gas velocities that cover bubbly and churn turbulent flow regimes (0.05–0.45 m/s). The reconstructed CT scan images revealed that the bubble columns equipped with or without internals displayed a uniform cross-sectional Gas Holdup distribution (symmetric) for all studied superficial Gas velocities. However, the bubble column equipped with 1-in. vertical internals exhibited more uniform Gas Holdup distribution than the column with 0.5-in. internals. Also, the visualization of the Gas-liquid distributions for bubble columns with and without internals reveal that the well-known phenomenon of the core-annular liquid circulation pattern that observed in the bubble column without internals still exists in bubble column packed densely with vertical internals. Moreover, a remarkable increase in the Gas Holdup values at the wall region was achieved in the churn turbulent flow regime based on the insertion of the vertical internals inside the column as compared with using a bubble column without obstacles. Furthermore, the values of the Gas Holdup in the core region of the bubble column with vertical internals are similar to those of the bubble column without vertical internals when they are operated at high superficial Gas velocity (churn turbulent flow regime), based on the free cross-sectional area (CSA) for the flow. In general, the magnitude of the Gas Holdup increased significantly with increasing superficial Gas velocity for the bubble columns with and without internals. However, the Gas Holdup profile was shaped like a wavy line in the bubble column with vertical internals, whereas it exhibited a parabolic Gas Holdup profile in the bubble column without obstacles.
