The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Muthanna H Aldahhan - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
-
gas liquid mass transfer in a high pressure Bubble Column reactor with different sparger designs
Chemical Engineering Science, 2007Co-Authors: Lu Han, Muthanna H AldahhanAbstract:Abstract The gas–liquid mass transfer in a 0.162 m high pressure stainless steel Bubble Column was investigated using three different gas sparger designs. An oxygen-enriched-air dynamic method and an optical oxygen probe technique were implemented to measure k 1 a values in the Bubble Column reactor. Using the interfacial area ( a ) values measured by a four-point optical probe technique at similar conditions ( Xue, 2004 ), the k 1 values were estimated. Axial dispersion model (ADM) and continuous stirred tank reactor (CSTR) model were used to calculate k 1 a as a fitted parameter with the measured data. The ADM gave better fits to the experimental data than the CSTR model, especially at high axial locations for the Bubble Column used with a large L / d c ratio. The sparger design was found to have a noticeable effect on k 1 a in the low gas velocity range ( u g 0.15 m / s ) but only a slight effect in the high gas velocity range ( u g > 0.20 m / s ) . The sparger design showed almost no effect on the liquid side mass transfer coefficient, k 1 , at high gas velocity ( u g = 0.30 m / s ) , where no significant variations of the Bubble size distribution and hydrodynamics were obtained using different sparger designs. Although the k 1 a values increased with the operating pressure, the pressure change from 0.1 to 0.4 MPa yielded lower k 1 values, as a result of the reduced Bubble size. However, as the pressure further increased to 1.0 MPa, the a and k 1 a values increased, while the k 1 values negligibly decreased. In addition to the pressure and sparger design effects, the superficial gas velocity had effect of increasing the k 1 values, while such effect became small and flattened out at high superficial gas velocities.
-
predictions of radial gas holdup profiles in Bubble Column reactors
Chemical Engineering Science, 2001Co-Authors: Boon Cheng Ong, Muthanna H AldahhanAbstract:Gas holdup and its profile are important parameters to be characterized in Bubble Column reactors. Proper prediction of the radial gas holdup profiles is necessary for determining liquid mixing, flow regime transition, heat and mass transfer. In this study, the following gas holdup profile form, which can be fitted to the observed holdup profiles, is proposed: e G =e G ((n+2)/(n+2-2c))[1-c(r/R) n ]. The parameters n and c needed to describe the gas holdup profile are correlated with appropriate dimensionless groups. n=2.188x10 3 Re G -0.598 Fr g 0.146 Mo L -0.004 , c=4.32x10 -2 Re G 0.2492 . However, the cross-sectional average gas holdup, e G , can be estimated using the available correlations for overall gas holdup. The agreement between the correlation predictions and experimental data is reasonable over wide range of operating conditions.
M. W. Abdulrahman - One of the best experts on this subject based on the ideXlab platform.
-
CFD simulations of direct contact volumetric heat transfer coefficient in a slurry Bubble Column at a high gas temperature of a helium-water-alumina system
Applied Thermal Engineering, 2016Co-Authors: M. W. AbdulrahmanAbstract:In this paper, computational fluid dynamics (CFD) simulations are used to investigate the volumetric heat transfer coefficient in a direct contact heat transfer for a helium-water-alumina slurry Bubble Column reactor, where helium gas is injected at 90 °C through a slurry of water at 22 °C and alumina solid particles. This paper studies the effects of superficial gas velocity, static liquid height, and solid particle concentration on the volumetric heat transfer coefficient of the slurry Bubble Column reactor. In this study, it is assumed that the slurry inside the slurry Bubble Column is perfectly mixed, and the approach used to model the slurry Bubble Column by CFD is 2D plane. From the CFD results, it is found that the volumetric heat transfer coefficient increases by increasing the superficial gas velocity and decreases by increasing the static liquid height and/or the solid concentration at any given superficial gas velocity. Also, it is found that the rate of decrease of the volumetric heat transfer coefficient with the solid concentration is approximately the same for different superficial gas velocities. The results of CFD simulations were compared with experimental data from previous literature and show that the profiles of the volumetric heat transfer coefficient calculated from CFD models generally under-predict the experimental data. The CFD model correctly predicts the experimental effects of static liquid height and solid concentration on volumetric heat transfer coefficient.
-
Experimental studies of the transition velocity in a slurry Bubble Column at high gas temperature of a helium-water-alumina system
Experimental Thermal and Fluid Science, 2016Co-Authors: M. W. AbdulrahmanAbstract:In this paper, the transition velocity is investigated experimentally for a helium gas at 90. °C injected through a slurry of water at 22. °C and alumina solid particles in a slurry Bubble Column reactor. This paper examines the effects of superficial gas velocity, static liquid height and solid particles concentration, on the transition velocity of the SBCR. From the experimental work, it is found that the transition velocity between homogeneous and churn turbulent flow regimes, decreases by increasing the static liquid height and/or the solid concentration. It is also found that there is no slug flow regime in the industrial slurry Bubble Column reactors.
R Krishna - One of the best experts on this subject based on the ideXlab platform.
-
design and scale up of a Bubble Column slurry reactor for fischer tropsch synthesis
Chemical Engineering Science, 2001Co-Authors: R Krishna, J M Van Baten, M I Urseanu, J EllenbergerAbstract:Abstract We develop a strategy for scaling up a Bubble Column slurry reactor, which is used for example for carrying out the Fischer–Tropsch synthesis reaction. The strategy involves development of a proper description for the large Bubble swarm velocity in highly concentrated paraffin-oil slurries in Columns of varying diameters. The developed relationship is incorporated into an Eulerian simulation code which is then used to predict the hydrodynamic parameters (hold-up, velocity distribution, etc.) for reactors of commercial scale.
-
modelling of a Bubble Column slurry reactor for fischer tropsch synthesis
Catalysis Today, 1999Co-Authors: C Maretto, R KrishnaAbstract:Abstract This work deals with the simulation of a commercial size slurry Bubble Column reactor for catalytic conversion of syngas (CO+H 2 ) to liquid hydrocarbons (Fischer–Tropsch synthesis). The reactor was assumed to operate in the heterogeneous or churn-turbulent flow regime and the complex hydrodynamics of the slurry Bubble Column was described by means of a model, based on an extended experimental program, which takes into account the effect of Column diameter, slurry concentration, system properties and pressure on the gas holdup. The reactor model was developed adopting two different classes of Bubbles: large Bubbles (20–70 mm) which rise through the Column virtually in plug-flow, and small Bubbles (1–10 mm) which are entrained in the slurry phase (liquid+solid catalyst particles). The slurry phase, together with the entrained small Bubbles, was considered completely mixed due to the upward motion of the fast-rising large Bubbles. The reaction kinetics was chosen from the literature and referred to a cobalt based catalyst. Design calculations have been carried out for a plant with a 5000 t/day capacity for producing middle distillates. Operating conditions with respect to superficial gas velocity and slurry concentration are suggested so as to achieve the optimum reactor performance.
Badie I Morsi - One of the best experts on this subject based on the ideXlab platform.
-
an algorithm for predicting the hydrodynamic and mass transfer parameters in Bubble Column and slurry Bubble Column reactors
Fuel Processing Technology, 2008Co-Authors: Romain Lemoine, Arsam Behkish, Rachid Oukaci, Laurent Sehabiague, Yannick J Heintz, Badie I MorsiAbstract:Abstract A large number of experimental data points obtained in our laboratory as well as from the literature, covering wide ranges of reactor geometry (Column diameter, gas distributor type/open area), physicochemical properties (liquid and gas densities and molecular weights, liquid viscosity and surface tension, gas diffusivity, solid particles size/density), and operating variables (superficial gas velocity, temperature and pressure, solid loading, impurities concentration, mixtures) were used to develop empirical as well as Back-Propagation Neural Network (BPNN) correlations in order to predict the hydrodynamic and mass transfer parameters in Bubble Column reactors (BCRs) and slurry Bubble Column reactors (SBCRs). The empirical and BPNN correlations developed were incorporated in an algorithm for predicting gas holdups (eG, eG-Small, eG-Large); volumetric liquid-side mass transfer coefficients (kLa, kLa-Small, kLa-Large); Sauter mean Bubble diameters (dS, dS-Small, dS-Large); gas–liquid interfacial areas (a, aSmall, aLarge); and liquid-side mass transfer coefficients (kL, kL-Large, kL-Small) for total, small and large gas Bubbles in BCRs and SBCRs. The developed algorithm was used to predict the effects of reactor diameter and solid (alumina) loading on the hydrodynamic and mass transfer parameters in the Fisher–Tropsch (F–T) synthesis for the hydrogenation of carbon monoxide in a SBCR, and to predict the effects of presence of organic impurities (which decrease the liquid surface tension) and air superficial mass velocity in the Loprox process for the wet air oxidation of organic pollutants in a BCR. In the F–T process, the predictions showed that increasing the reactor diameter from 0.1 to 7.0 m and/or increasing the alumina loading from 25 to 50 wt.% significantly decreased eG, kLaH2 and kLaCO and increased dS. The decrease of the total gas holdup was found to be controlled by the holdup of small gas Bubbles. The increase of the Sauter mean Bubble diameter increased both kLH2 and kLCO, however, the decrease of the total gas holdup coupled with the increase of dS resulted in a dramatic decrease of the gas–liquid interfacial area, a, and subsequently kLaH2 and kLaCO. Thus, in the churn-turbulent flow regime, the hydrodynamic and mass transfer behaviors of the F–T SBCR were controlled by the holdup and the gas–liquid interfacial area of small Bubbles. In the Loprox process, the predictions showed that increasing the liquid surface tension (removal of organic impurities from water) significantly increased dS and decreased both eG and kLaO2. The decrease of the total gas holdup with increasing liquid-phase surface tension was due mainly to the decrease of the liquid-phase foamability which led to the decrease of the holdup of small gas Bubbles. The increase of the Sauter mean Bubble diameter and the decrease of the total gas holdup resulted in a strong decrease of the gas–liquid interfacial area, and subsequently kLaO2. Increasing the air superficial mass velocity increased eG, dS, a, kL-O2 and kLaO2. Within the conditions used in the Loprox BCR, the hydrodynamics and mass transfer parameter behaviors of the process appeared also to be controlled by the gas holdup of small gas Bubbles; and the gas–liquid interfacial area.
-
novel correlations for gas holdup in large scale slurry Bubble Column reactors operating under elevated pressures and temperatures
Chemical Engineering Journal, 2006Co-Authors: Arsam Behkish, Romain Lemoine, Rachid Oukaci, Badie I MorsiAbstract:Abstract A comprehensive literature search was conducted to obtain the holdup data for different gases in various liquids and slurries using Bubble and slurry Bubble Column reactors operating under wide ranges of conditions in different size reactors provided with a variety of gas spargers. The data were used to develop two novel correlations, one for the total gas holdup and the other for the holdup of large gas Bubbles. The total gas holdup correlation is capable of predicting the experimental data within an absolute average relative error (AARE) and standard deviation (σ) of 20%, whereas the correlation of the holdup of large Bubbles is capable of predicting the experimental values within AARE and σ of about 25 and 27%, respectively. The novel correlations were used to predict the effects of pressure, temperature, gas velocity, solid concentration, rector size, and distributor type on the holdup of syngas (H2/CO = 2) in various slurry Bubble Column reactors (SBCRs) operating under typical Fischer–Tropsch conditions.
Fabio Inzoli - One of the best experts on this subject based on the ideXlab platform.
-
the dual effect of viscosity on Bubble Column hydrodynamics
Chemical Engineering Science, 2017Co-Authors: Giorgio Besagni, Fabio Inzoli, Giorgia De Guido, Laura A PellegriniAbstract:Abstract Some authors, in the last decades, have observed the dual effect of viscosity on gas holdup and flow regime transition in small-diameter and small-scale Bubble Columns. This work concerns the experimental investigation of the dual effect of viscosity on gas holdup and flow regime transition as well as Bubble size distributions in a large-diameter and large-scale Bubble Column. The Bubble Column is 5.3 m in height, has an inner diameter of 0.24 m, and can be operated with gas superficial velocities in the range of 0.004–0.20 m/s. Air was used as the dispersed phase, and various water-monoethylene glycol solutions were employed as the liquid phase. The water-monoethylene glycol solutions that were tested correspond to a viscosity between 0.9 mPa s and 7.97 mPa s, a density between 997.086 kg/m3 and 1094.801 kg/m3, a surface tension between 0.0715 N/m and 0.0502 N/m, and log10(Mo) between −10.77 and −6.55 (where Mo is the Morton number). Gas holdup measurements were used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. An image analysis method was used to investigate the Bubble size distributions and shapes for different gas superficial velocities, for different solutions of water-monoethylene glycol. In addition, based on the experimental data from the image analysis, a correlation between the Bubble equivalent diameter and the Bubble aspect ratio was proposed. The dual effect of viscosity, previously verified in smaller Bubble Columns, was confirmed not only with respect to the gas holdup and flow regime transition, but also for the Bubble size distributions. Low viscosities stabilize the homogeneous flow regime and increase the gas holdup, and are characterized by a larger number of small Bubbles. Conversely, higher viscosities destabilize the homogeneous flow regime and decrease the gas holdup, and the Bubble size distribution moves toward large Bubbles. The experimental results suggest that the stabilization/destabilization of the homogeneous regime is related to the changes in the Bubble size distributions and a simple approach, based on the lift force, was proposed to explain this relationship. Finally, the experimental results were compared to the dual effect of organic compounds and inorganic compounds: future studies should propose a comprehensive theory to explain all the dual effects observed.
-
Bubble size distributions and shapes in annular gap Bubble Column
Experimental Thermal and Fluid Science, 2016Co-Authors: Giorgio Besagni, Fabio InzoliAbstract:Abstract An understanding of the Bubble properties, size distributions and shapes is of fundamental importance for comprehending flow dynamics and mass transfer phenomena in Bubble Column reactors. A large number of studies have focused on open tube Bubble Columns, and the knowledge concerning Bubble Columns with internals is still limited. This paper contributes to the existing discussion experimentally investigating a counter-current annular Bubble Column with 0.24 m inner diameter and two internal pipes. The experimental investigation consists in holdup measurements and image analysis. The former is used for identifying the flow regime transition and studying the Bubble Column hydrodynamics, whereas the latter is used for investigating the Bubble shapes and size distributions. The definition of the transition point is important because the size distribution and Bubble shapes depend on the operating conditions and a change of the Bubble properties is expected near the transition. The image analysis is applied at different superficial gas and liquid velocities, corresponding to a gas holdup between 2.9% and 9.6%. It is difficult to measure Bubble size distribution accurately in large-diameter Bubble Columns owing to the overlapping of Bubbles, even at low void fractions, and—in an annular gap Bubble Column—the fact that cap Bubbles have also been reported in the homogeneous flow regime. The use of a Bubble image analysis method to study the bubbly flows in a large-diameter annular gap Bubble Column is described. In the proposed method, each Bubble is approximated and reconstructed using an ellipse. The proposed approach is used to quantify the Bubble size distribution, as well as to study the Bubble shape and orientation as function of the superficial gas and liquid velocities. The experimental data obtained are used to develop a correlation between non-dimensional parameters and aspect ratios. Also, the experimental data are compared with non-dimensional diagrams from the literature, revealing good agreement. Finally, the image analysis is used for supporting the flow regime transition prediction in the stability analysis method: the virtual mass formulation is obtained by using the aspect ratio correlation provided by the image analysis. The stability analysis—supported by the image analysis—was able to predict the transition point in very good agreement with experimental data and performed better than literature correlations.
