The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
M.p. Dudukovic - One of the best experts on this subject based on the ideXlab platform.
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hydrodynamics of pilot scale Bubble Columns effect of internals
Industrial & Engineering Chemistry Research, 2013Co-Authors: Ahmed Youssef, Muthanna H Aldahhan, Mohamed E Hamed, Joshua T Grimes, M.p. DudukovicAbstract:The gas holdup and Bubble characteristics are key parameters that affect the performance of Bubble Columns. An experimental study of the effect of heat exchanging internals on the gas holdup, Bubble dynamics, and their radial profiles is performed. An air–water system is used in a Plexiglas column 45 cm (18 in.) in diameter. Internals configurations mimicking those typical for the liquid-phase methanol synthesis and Fischer–Tropsch process and covering 5% and 25%, respectively, of the total cross-sectional area of the column, are investigated. High superficial gas velocities that fall within the churn turbulent flow regime, which are of interest for most industrial applications, are applied. An increase in the gas holdup is observed for the dense internals structure. A decrease in the Bubble chord length and a vigorous recirculation behavior are also obtained as a result of the insertion of the internals.
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flow regime diagnosis in Bubble Columns via pressure fluctuations and computer assisted radioactive particle tracking measurements
Industrial & Engineering Chemistry Research, 2009Co-Authors: Maria Sol Fraguio, Miryan Cassanello, Sujatha Degaleesan, M.p. DudukovicAbstract:The importance of diagnosing the flow regime in Bubble Columns by noninvasive and easy-to-implement methods is well-known. Hence, the aim of this work is to diagnose the flow regime in a pilot scal...
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cfd modeling of Bubble Columns flows implementation of population balance
Chemical Engineering Science, 2004Co-Authors: P Chen, J Sanyal, M.p. DudukovicAbstract:Abstract The Bubble Population Balance Equation is implemented both in the two-fluid model and in the Algebraic Slip Mixture Model. Two and three-dimensional numerical simulations of two-phase (air–water) and pseudo-two-phase (air–Therminol-Glass beads) transient flows are performed for laboratory scale Bubble Columns of two different diameters operated over a range of superficial gas velocities (8 to 20 cm/s) in the churn turbulent regime. The ability of the simulations to predict liquid recirculation and gas radial holdup profile, which drives the recirculation, is illustrated. The simulations also capture the effects of increased superficial gas velocity and of surface tension on Bubble size distribution in agreement with observations. At all conditions a uni-modal Bubble size distribution is predicted.
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experimental study of gas induced liquid flow structures in Bubble Columns
Aiche Journal, 2001Co-Authors: Sujatha Degaleesan, M.p. Dudukovic, Y. PanAbstract:The computer-automated radioactive-particle tracking (CARPT) technique is used to investigate liquid recirculation and turbulence in Bubble Columns. Experiments are conducted in air-water Bubble Columns of different sizes, with various gas distributors, and operated over a range of superficial gas velocities. This study covers gas-liquid flows from the bubbly regime to the churn turbulent regime. The time-averaged spatial flow structure, axial liquid velocity profiles, Reynolds shear stress, and turbulence intensities profiles are analyzed for different Columns and flow conditions. Supplementary experiments, using the hot-probe anemometry technique, are performed at selected flow conditions, and the results are compared with the corresponding ones from CARPT measurements. The Reynolds stress determined by CARPT was compared with that obtained by hot-film anemometry in an independent investigation by Menzel et al. (1990).
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dynamic simulation of bubbly flow in Bubble Columns
Chemical Engineering Science, 1999Co-Authors: Y. Pan, M.p. Dudukovic, M ChangAbstract:Gas–liquid bubbly flow in two-dimensional Bubble Columns is studied by numerical simulation. An Eulerian–Eulerian two-fluid model is used to describe the time-dependent motion of the liquid driven by small, spherical gas Bubbles injected at the bottom of the Columns. The simulations are able to capture the large scale structures as observed experimentally in the laboratory. The numerical results, which include the characteristics of large scale structures such as wave length and frequency, mean velocities, turbulence intensities and turbulence shear stress, are analized and compared with the experimental data of Lin et al. (1996) [A.I.Ch.E. J., 42, 301–318] and Mudde et al. (1997) [A.I.Ch.E. J., 43, 913–926] and show good agreement.
Liangshih Fan - One of the best experts on this subject based on the ideXlab platform.
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ecvt imaging of 3d spiral Bubble plume structures in gas liquid Bubble Columns
Canadian Journal of Chemical Engineering, 2014Co-Authors: Aining Wang, Qussai M. Marashdeh, Liangshih FanAbstract:Electrical Capacitance Volume Tomography (ECVT) is a 3D, real-time imaging technique that is recently developed to image the multiphase flow behaviour in Columns of regular or irregular geometries. In this study, the ECVT measurements are conducted to obtain phase holdups and flow structures in Bubble Columns of a straight-cylinder shape and a tapered-cylinder shape with porous and orifice gas distributors. The phase holdups obtained by the ECVT in a straight-cylinder Bubble column with porous gas distributor are verified by other measurement techniques and correlation equations reported in the literature. The flow regimes of the Bubble Columns are also characterized by the ECVT. Particularly, a dynamic 3D flow structure, which is uniquely represented by the spiral motion of the Bubble plumes occurring within the heterogeneous regime of the gas-liquid flow in a straight-cylinder shape Bubble column with perforated distributor, is captured for the first time instantaneously over the entire flow field with the ECVT. Other flow behaviour such as the converging flow pattern of the gas Bubbles in a tapered-cylinder shape Bubble column is also revealed by the ECVT.
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gas liquid mass transfer in high pressure Bubble Columns
Industrial & Engineering Chemistry Research, 2004Co-Authors: Raymond Lau, W Peng, Luis G Velazquezvargas, And G Q Yang, Liangshih FanAbstract:Volumetric gas−liquid mass-transfer coefficients are investigated in Bubble Columns under high-pressure and moderate-temperature conditions by utilizing an oxygen desorption method. The oxygen concentration in the liquid phase, water or Paratherm NF heat-transfer fluid, is monitored with a high-pressure optical fiber oxygen probe. The study covers operating conditions up to pressures of 4.24 MPa and up to temperatures of 92 °C. The superficial gas and liquid velocities vary up to 40 and 0.89 cm/s, respectively. Experimental results show that system pressure, temperature, gas and liquid velocities, liquid properties, and column dimensions are major factors affecting mass transfer. The mass-transfer coefficient increases with both pressure and temperature. Both gas and liquid velocities improve mass transfer due to higher turbulence at high-velocity conditions. Liquid properties and column dimensions also have significant effects on mass transfer. The effect of liquid velocity on kla is mainly due to the ch...
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maximum stable Bubble size and gas holdup in high pressure slurry Bubble Columns
Aiche Journal, 1999Co-Authors: Xukun Luo, D J Lee, Raymond Lau, G Q Yang, Liangshih FanAbstract:Experiments of pressure effects on gas holdup and Bubble size in slurry Bubble Columns at 5.6 MPa and at gas velocities up to 45 cm/s indicate that the gas holdup increases with an increase in pressure, especially at high slurry concentration. At ambient pressure, a higher solids concentration significantly lowers gas holdup over the entire gas-velocity range, while at 5.6 MPa, the effect of solids concentration on gas holdup is relatively small at gas velocities above 25 cm/s. An empirical correlation was developed based on these data and those in the literature to predict gas holdup in Bubble and slurry Bubble Columns over a wide range of operating conditions. An analysis of Bubble flow characteristics during dynamic gas disengagement indicates that large Bubbles play a key role in determining gas holdup due to the large Bubble and wake volumes that induce the acceleration of small Bubbles. Direct measurement of Bubble size shows that elevated pressures lead to smaller Bubble size and narrower Bubble-size distributions. Bubble size increases significantly with increasing solids concentration at ambient pressure, while at high pressures this effect is less pronounced. A theoretical analysis of circulation of gas inside the Bubble yields an analytical expression for maximum stable Bubble size in high-pressure slurry Bubble Columns. Based on this internal circulation model, the maximum stable Bubble size at high pressures is significantly smaller due to the high gas inertia and low gas-liquid surface tension. The smaller Bubble size and its reduced Bubble rise velocity account for the observed pressure effect on gas holdup.
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quantitative analysis and computation of two dimensional Bubble Columns
Aiche Journal, 1996Co-Authors: Tsaojen Lin, J Reese, T Hong, Liangshih FanAbstract:Experiments conducted quantify the macroscopic hydrodynamic characteristics of various scale 2-D Bubble Columns, which include dispersed and coalesced Bubble regimes characterized by two flow conditions (4- and 3-region flow) with coherent flow structures. Hydrodynamic behavior is analyzed based on flow visualization and a particle image velocimetry (PIV) system. Columns operated in the 4-region flow condition comprise descending, vortical, fast Bubble and central plume regions. The fast Bubble flow region moves in a wavelike manner, and thus the flow in the vicinity of this region is characterized macroscopically in terms of wave properties. In Columns greater than 20 cm in width, the transition from the dispersed Bubble flow regime to the 4- and then to 3-region flow in the coalesced Bubble regime occurs progressively with gas velocities at 1 and 3 cm/s, respectively. The demarcation of flow regimes is directly related to measurable coherent flow structures. The instantaneous and time-averaged liquid velocity and holdup profiles provided by the PIV system are presented in light of the macroscopic flow structure in various 2-D Bubble Columns. Numerical simulations demonstrate that the volume of fluid method can provide the time-dependent behavior of dispersed bubbling flows and account for the coupling effects of pressure field and the liquid velocity on the Bubble motion. Comparison of computational results with PIV results for two different Bubble injector arrangements is satisfactory.
Rajamani Krishna - One of the best experts on this subject based on the ideXlab platform.
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liquid dispersion in large diameter Bubble Columns with and without internals
Canadian Journal of Chemical Engineering, 2008Co-Authors: Ann Forret, Rajamani Krishna, Jeanmarc Schweitzer, Thierry Gauthier, D. SchweichAbstract:Liquid mixing has been studied in a 1 m diameter Bubble column, with and without internals (vertical cooling tubes). The presence of internals significantly affects both large scale recirculation and local dispersion. The most common approach to model liquid mixing is the one-dimensional axial dispersion model, validated many times in small Bubble Columns without internals. This paper shows that this model is still appropriate to large Columns, but without internals. A two-dimensional model, taking into account a radially dependent axial velocity profile, and both axial and radial dispersion, is required to account for the internals on liquid mixing.
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influence of scale on the volumetric mass transfer coefficients in Bubble Columns
Chemical Engineering and Processing, 2004Co-Authors: C O Vandu, Rajamani KrishnaAbstract:Abstract The gas holdup, e , and volumetric mass transfer coefficient, k L a , were measured for the air–water system in Bubble Columns of three different diameters, 0.1, 0.15 and 0.38 m. The superficial gas velocity U was varied in the range 0–0.35 m s −1 , spanning both the homogeneous and heterogeneous flow regimes. The gas holdup e shows a small decrease with increased column diameter; this effect is due to increased liquid recirculations with increasing scale. The volumetric mass-transfer coefficient, k L a , closely follows the trend in gas holdup. For U >0.08 m s −1 , the value of k L a / e was found to be practically independent of column diameter and superficial gas velocity; the value of this parameter is found to be about 0.48 s −1 . Our studies provide a simple method for estimation of k L a in industrial size Bubble Columns operated at high superficial gas velocities.
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Mass transfer in Bubble Columns
Catalysis Today, 2003Co-Authors: Rajamani Krishna, J.m. Van BatenAbstract:Abstract Bubble Columns are operated either in the homogeneous or heterogeneous flow regime. In the homogeneous flow regime, the Bubbles are nearly uniform in size and shape. In the heterogeneous flow regime, a distribution of Bubble sizes exists. In this paper, a computational fluid dynamics (CFD) model is developed to describe the hydrodynamics, and mass transfer, of Bubble Columns operating in either of the two flow regimes. The heterogeneous flow regime is assumed to consist of two Bubble classes: “small” and “large” Bubbles. For the air–water system, appropriate drag relations are suggested for these two Bubble classes. Interactions between both Bubble populations and the liquid are taken into account in terms of momentum exchange, or drag, coefficients, which differ for the “small” and “large” Bubbles. The turbulence in the liquid phase is described using the k – e model. For Bubble Columns operating with the air–water system, CFD simulations have been carried out for superficial gas velocities, U , in the range 0–0.08 m/s, spanning both regimes. These simulations reveal some of the characteristic features of homogeneous and heterogeneous flow regimes, and of regime transition on the gas holdup and mass transfer. By comparing the simulations with measured experimental data, it is concluded that mass transfer from the large Bubble population is significantly enhanced due to frequent coalescence and break-up into smaller Bubbles. The CFD simulations also underline the strong influence of column diameter on hydrodynamics and mass transfer.
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Improving gas-liquid mass transfer in Bubble Columns by applying low-frequency vibrations
Chemical Engineering & Technology, 2002Co-Authors: Rajamani Krishna, J. EllenbergerAbstract:We show that application of low-frequency vibrations, in the 50-200 Hz range, to the liquid phase of an air-water Bubble column causes significantly smaller Bubbles to be generated at the distributor plate. For Bubble column operation in the homogeneous flow regime, measurements of the volumetric mass transfer coefficient using the oxygen absorption technique show that the increase in the k L a values ranges from 50-100 % depending on the flow rate. It is concluded that application of low-frequency vibration has the potential of improving the performance of Bubble Columns.
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Flow regime transition in Bubble Columns
International Communications in Heat and Mass Transfer, 1999Co-Authors: Rajamani Krishna, J. Ellenberger, C. MarettoAbstract:The various factors influencing the regime transition point in gas-liquid Bubble Columns are examined. Increasing gas density delays regime transition. This phenomenon is described in a qualitative way by the correlations of Reilly [1] and Wilkinson [2] of which the Reilly correlation is found to be more accurate. However, both correlations are unable to account for the influence of the addition of small quantities of surface tension reducing agents. The Reilly and Wilkinson correlations are also not adequate to describe the influence of the addition of catalyst particles on the transition point for a Bubble column slurry reactor.
Jyeshtharaj B. Joshi - One of the best experts on this subject based on the ideXlab platform.
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Stability analysis of Bubble Columns: Predictions for regime transition
Chemical Engineering Science, 2005Co-Authors: Manish R Bhole, Jyeshtharaj B. JoshiAbstract:A criterion for the transition from the homogeneous to the heterogeneous regime in a Bubble column is developed based on the theory of linear stability. Hydrodynamics of Bubble column is described by two-fluid model incorporating the interphase forces like drag force and added mass force. Added mass force affects the hydrodynamics of gas-liquid flows significantly and is formulated by taking into account the Bubble deformation. A proper understanding of the nature of gas-liquid interface (clean or contaminated) is desired for the reliable predictions of the added mass coefficient. Data from the literature on the transition in Bubble Columns is critically analyzed. A good agreement has been obtained between the experimental transition gas hold-up and the predictions of the same obtained by the theory developed in this work.
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Simultaneous measurement of flow pattern and mass transfer coefficient in Bubble Columns
Chemical Engineering Science, 2004Co-Authors: Amol A. Kulkarni, Jyeshtharaj B. JoshiAbstract:Mass transfer studies were carried out in a Bubble column using the chemical method. Catalytic oxidation of sodium sulfite was chosen for the studies and the corresponding specific rates of oxidation were obtained using a stirred cell. Laser Doppler anemometer (LDA) was used to measure the instantaneous velocities in the same stirred cell as well as in Bubble Columns (100 and 150 mm i.d.). An efficient algorithm based on the multiresolution analysis of the velocity-time data using wavelets was used for the isolation of data belonging to the gas and liquid phases. Eddy isolation model was used for the characterization of the eddy motion including the estimation of the energy dissipation rate. Using the knowledge of eddy motion, a methodology was developed for the prediction of true mass transfer coefficient (k L ) in a stirred cell as well as in Bubble Columns. The predicted values of k L have been compared with the experimental values obtained by the chemical method.
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Disengagement of the gas phase in Bubble Columns
International Journal of Multiphase Flow, 1995Co-Authors: N. S. Deshpande, M. Dinkar, Jyeshtharaj B. JoshiAbstract:The technique of gas disengagement is popularly used to assess the Bubble size distribution in Bubble Columns. The technique involves the dynamic measurement of dispersion height when the gas supply is stopped. In this paper a mathematical model has been proposed for the process of dynamic gas disengagement. It has been shown that the initial faster disengagement is due to the presence of internal liquid circulation and not due to the presence of very large Bubbles. Further, slower disengagement has been attributed to the transition from heterogeneous dispersion to homogeneous dispersion. The new model also explains the effects of superficial gas velocity, column diameter, column height and liquid phase physical properties on the gas disengagement.
Y. Pan - One of the best experts on this subject based on the ideXlab platform.
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experimental study of gas induced liquid flow structures in Bubble Columns
Aiche Journal, 2001Co-Authors: Sujatha Degaleesan, M.p. Dudukovic, Y. PanAbstract:The computer-automated radioactive-particle tracking (CARPT) technique is used to investigate liquid recirculation and turbulence in Bubble Columns. Experiments are conducted in air-water Bubble Columns of different sizes, with various gas distributors, and operated over a range of superficial gas velocities. This study covers gas-liquid flows from the bubbly regime to the churn turbulent regime. The time-averaged spatial flow structure, axial liquid velocity profiles, Reynolds shear stress, and turbulence intensities profiles are analyzed for different Columns and flow conditions. Supplementary experiments, using the hot-probe anemometry technique, are performed at selected flow conditions, and the results are compared with the corresponding ones from CARPT measurements. The Reynolds stress determined by CARPT was compared with that obtained by hot-film anemometry in an independent investigation by Menzel et al. (1990).
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dynamic simulation of bubbly flow in Bubble Columns
Chemical Engineering Science, 1999Co-Authors: Y. Pan, M.p. Dudukovic, M ChangAbstract:Gas–liquid bubbly flow in two-dimensional Bubble Columns is studied by numerical simulation. An Eulerian–Eulerian two-fluid model is used to describe the time-dependent motion of the liquid driven by small, spherical gas Bubbles injected at the bottom of the Columns. The simulations are able to capture the large scale structures as observed experimentally in the laboratory. The numerical results, which include the characteristics of large scale structures such as wave length and frequency, mean velocities, turbulence intensities and turbulence shear stress, are analized and compared with the experimental data of Lin et al. (1996) [A.I.Ch.E. J., 42, 301–318] and Mudde et al. (1997) [A.I.Ch.E. J., 43, 913–926] and show good agreement.
