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Gas Velocity (gas + velocity)
Kinds of Gas Velocity Selected AbstractsGas-Liquid Mass Transfer in a Slurry Bubble Column at High Slurry Concentrations and High Gas VelocitiesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2005C. O. Vandu Abstract The volumetric mass transfer coefficient kLa in a 0.1,m-diameter bubble column was studied for an air-slurry system. A C9 -C11n -paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n -paraffin oil had properties similar to those of the liquid phase in a commercial Fischer-Tropsch reactor under reaction conditions. The superficial gas velocity UG was varied in the range of 0.01 to 0.8,m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration ,S ranged from 0 to 0.5. The experimental results obtained show that the gas hold-up ,G decreases with an increase in slurry concentration, with this decrease being most significant when ,S < 0.2. kLa/,G was found to be practically independent of the superficial gas velocity when UG > 0.1,m/s is taking on values predominantly between 0.4 and 0.6,s,1 when ,S = 0.1 to 0.4, and 0.29,s,1, when ,S = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient kLa in an industrial-size bubble column slurry reactor, with a particular focus on the Fischer-Tropsch process as well as high gas velocities and high slurry concentrations. [source] Nonintrusive characterization of fluidized bed hydrodynamics using vibration signature analysisAICHE JOURNAL, Issue 3 2010M. Abbasi Abstract There are many techniques to characterize the hydrodynamics of fluidized beds, but new techniques are still needed for more reliable measurement. Bed vibrations were measured by an accelerometer in a gas,solid fluidized bed to characterize the hydrodynamics of the fluidized bed in a nonintrusive manner. Measurements were carried out at different superficial gas velocities and particle sizes. Pressure fluctuations were measured simultaneously. Vibration signals were processed using statistical analysis. For the sake of the evaluation, the vibration technique was used to calculate minimum fluidization velocity. It was shown that minimum fluidization velocity can be determined from the variation of standard deviation, skewness, and kurtosis of vibration signals against superficial gas velocity of the bed. Kurtosis was proved to be a new method of analyzing vibration signals. Results indicate that analyzing the vibration signals can be an effective nonintrusive technique to characterize the hydrodynamics of fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] The influence of the particle size distribution on fluidized bed hydrodynamics using high-throughput experimentationAICHE JOURNAL, Issue 8 2009Renske Beetstra Abstract The goal of the described project is to design mixtures of particles with optimal fluidization properties. Using high-throughput experimentation, a novel approach to study hydrodynamics in fluidized beds, the relevant properties can be obtained in a limited period of time. This approach is demonstrated by assessing the influence of particle size distribution on fluidized bed hydrodynamics of Geldart A powders. By manipulating the width of the particle size distribution of alumina powder, the bubble diameter is reduced up to 40%. The addition of fines to a given particle size distribution also decreases the bubble diameter up to 40%, whereas the addition of coarse particles hardly influences the bubble size. At low gas velocities, the bubble size was found to increase with fines addition or increasing standard deviation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid systemAICHE JOURNAL, Issue 7 2006Izumi Taniguchi Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Detecting regime transitions in slurry bubble columns using pressure time seriesAICHE JOURNAL, Issue 7 2005Keshav C. Ruthiya Abstract Changes in the coherent standard deviation and in the average frequency of measured pressure time series with gas velocity, are proposed, as unique and unambiguous criteria to mark flow regime transitions in slurry bubble columns. In a 2-dimensional (2-D) slurry bubble column, pressure time series are measured at different gas velocities simultaneously with high-speed video recording of the gas-liquid flow. The frequency of occurrence and the average diameter of the large bubbles are determined from video image analysis. The gas velocity where the first large bubbles are detected, with an average diameter of 1.5 cm, and with a frequency of occurrence of one bubble per s, is designated as the first regime transition point (transition from the homogeneous regime to the transition regime). At this point, the coherent standard deviation of the measured pressure fluctuations clearly increases from zero. The gas velocity where the average diameter and the frequency of occurrence of the large bubbles become constant, is designated as the second regime transition point (transition from the transition regime to the heterogeneous regime). From this point onward, the slope of the coherent standard deviation of the measured pressure fluctuations clearly decreases with gas velocity, while the average frequency becomes constant. These clear changes with gas velocity in the coherent standard deviation, and in the average frequency are also demonstrated in a 3-D slurry bubble column. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Kinetic modeling of the photocatalytic degradation of air-borne pollutantsAICHE JOURNAL, Issue 5 2004H. Ibrahim Abstract The photocatalytic conversion of organic model pollutants (acetone, acetaldehyde, and isopropanol) in a novel Photo-CREC-Air unit is considered. This photocatalytic unit features: (1) external near-UV lamps placed in parabolic reflectors, (2) a basket supporting the irradiated glass mesh holding TiO2 loadings to achieve high photoconversion rates, and (3) a fluid flow pattern securing high gas velocities in the near-mesh region. Given the high quantum efficiencies observed in Photo-CREC-Air and, as a result, the high prospects for this novel design, rate equations and associated mechanistic formulations are investigated. With this goal, a Langmuir,Hinshelwood model, involving a one-site model pollutant mechanism, is considered. The associated kinetic parameters with the related statistical indicators are established, using least-square nonlinear regression. It is found that this model is adequate for describing the photodegradation of acetone on both Degussa P25 and Hombikat UV-100. It is also observed that the same type of reaction rate model is less adequate for the photodegradation of acetaldehyde and isopropanol, in particular, for predicting the formation of carbon dioxide. © 2004 American Institute of Chemical Engineers AIChE J 50: 1017,1027, 2004 [source] Spanning the flow regimes: Generic fluidized-bed reactor modelAICHE JOURNAL, Issue 7 2003I. A. Abba Probabilistic averaging is used to model fluidized-bed reactors across the three fluidlization flow regimes most commonly encountered in industry (bubbling, turbulent, and fast fluidization), extending earlier work, which introduced this approach to bridge the bubbling and turbulent regimes of fluidization. In extending this concept to the fast fluidization regime, the probabilities of being in each of the three regimes are represented as probability density functions derived from regime boundary transition data. The three regime-specific models,a generalized version of a two-phase bubbling bed model at low gas velocities, a dispersed flow model for turbulent beds at intermediate velocities, and a generalized version of a core-annulus model at higher velocities,are employed, leading to improved predictions compared with any of the individual models, while avoiding discontinuities at the regime boundaries. Predictions from the new integrated model are in good agreement with available ozone decomposition data over the full range of applicability covered elsewhere. [source] Fluid dynamics in coal liquefaction reactors using neutron absorption tracer techniqueAICHE JOURNAL, Issue 8 2000Naohide Sakai Hydrodynamic properties in the coal liquefaction reactors at the Kashima pilot plant, which was constructed based on the NEDOL process, were investigated using the neutron absorption tracer technique. The reactor system is composed of three vessels, each with 1.0 m ID and 11.8 m in height. The gas velocity in the reactors under coal liquefaction conditions was estimated using a reaction simulator that contained reaction rates and vapor,liquid equilibrium. The axial dispersion coefficients in the first and third reactors at superficial gas velocities of 0.06,0.07 m/s were much smaller than those reported for air,water systems under ambient conditions. This suggests that the pilot-plant reactors operated fundamentally in the homogeneous bubble flow regime. [source] Alumina Volatility in Water Vapor at Elevated TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Elizabeth J. Opila The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250° and 1500°C, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 ± 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process. [source] Hydrodynamic characteristics of gas,solid fluidization at high temperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Shabnam Sanaei Abstract Effect of temperature on the hydrodynamics of bubbling gas,solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25,600°C and different superficial gas velocities in the range of 0.17,0.78,m/s with sand particles. The time-position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward-moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward-moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely. L'effet de la température sur l'hydrodynamique de lits fluidisés de gaz-solide bouillonnants a fait l'objet de l'étude de cet ouvrage. Des expériences ont été faites à différentes températures se situant entre 25 et 600°C et différentes vélocités de gaz superficiels sur une plage de 0,17 à 0,78,m/s avec particules de sable. La trajectoire temps-position des particules a été obtenue à l'aide d'une technique de repérage par particules radioactives à haute température. Ces données ont été utilisées pour déterminer certains des paramètres hydrodynamiques (vélocité moyenne des particules ascendantes et descendantes, la fréquence de sauts bonds, la fréquence de cycles et les diffusivités axiales et radiales), lesquels sont représentatifs de solides se mélangeant dans le lit. Il a été démontré que le mélange de solides et la diffusivité des particules augmentent en haussant la température à environ 300°C. Cependant, ces paramètres diminuent en accroissant davantage la température au-delà de 300°C. Cela pourrait être attribué aux propriétés des phases de bouillonnement et d'émulsion. Les résultats de cette étude indiquent que les bulles croissent pour atteindre un diamètre maximum en augmentant la température jusqu'à 300°C. Au-delà de cette température, les bulles deviennent plus petites. Les résultats démontrent qu'en raison de l'effet de paroi, il n'y a pas de changement significatif à la vélocité moyenne des grappes descendantes. Afin d'expliquer ces tendances, la tension de surface de l'émulsion entre la bulle ascendante et la phase émulsion a été introduite et évaluée dans le lit fluidisé bouillonnant. Les résultats ont démontré que la tension de surface entre la bulle et l'émulsion augmente en haussant à température jusqu'à 300°C; cependant, après cette température, elle agit inversement. [source] Investigation into the hydrodynamics of gas,solid fluidized beds using particle image velocimetry coupled with digital image analysisTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Jan Albert Laverman Abstract The hydrodynamics of a freely bubbling, pseudo 2-D fluidized bed has been investigated experimentally for different bed aspect ratios at different superficial gas velocities by using Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA). Coupling of both non-invasive measuring techniques allows us to obtain information on both the bubble behaviour and emulsion phase circulation patterns simultaneously. In particular, the combination of DIA with PIV allows to correct for the influence of particle raining through the roof of the bubbles on the time-averaged emulsion phase velocity profiles. On a étudié de façon expérimentale l'hydrodynamique d'un lit fluidisé pseudo 2-D en bouillonnement libre, pour différents rapports de forme de lits à différentes vitesses de gaz superficielles par vélocimétrie à images de particules (PIV) combinée à l'analyse d'images numériques (DIA). Le couplage de deux techniques de mesure non invasives nous permet d'obtenir de l'information sur le comportement des bulles et les schémas de circulation de la phase d'émulsion, simultanément. En particulier, la combinaison de DIA et de PIV permet de corriger l'influence de la pluie de particules s'écoulant du toit de bulles sur les profils de vitesse de la phase d'émulsion moyennés dans le temps. [source] Entrainment Rate of Coarse Particles at Different Temperatures in Gas Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2007Jeong-Hoo Choi Abstract Based on available experimental data, an empirical relationship is developed for the entrainment rate of coarse particles at the exit of gas-fluidized beds, including the effects of fine particles in the bed, temperature, gas velocity, particle size and density, and column size. It predicts well the influence of fine particles on the entrainment rate of coarse particles, taking into account the momentum of the fine particles and the effect of superficial gas velocity. It also accounts well for the influence of temperature at different solid densities and gas velocities. À partir de données expérimentales disponibles, on a mis au point une relation empirique pour la vitesse d'entraînement des grosses particules à la sortie des lits fluidisés de gaz, incluant les effets des particules fines dans le lit, la température, la vitesse de gaz, la taille et la masse volumique des particules ainsi que la dimension de la colonne. Cette relation prédit bien l'influence des particules fines sur la vitesse d'entraînement des grosses particules, en tenant compte de la quantité de mouvement des particules fines et de l'effet de la vitesse de gaz superficielle. Elle prend bien en compte également l'influence de la température à différentes masses volumiques de solides et vitesses de gaz. [source] Investigation of Drying Geldart D and B Particles in Different Fluidization RegimesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006Wai Kiong Ng Abstract Drying of nylon (Geldart D) and expanded polystyrene (Geldart B) particles in fixed and fluidized beds were studied experimentally and theoretically. Fluidized bed dryers are sometimes operated at velocities beyond bubbling fluidization to mitigate against de-fluidization of surface wet particles. It was found that theoretical analysis using three different drying methods could predict the constant-drying rate at such velocities and also across the entire fluidization regimes (fixed bed, bubbling, slugging and turbulent fluidization) as long as the bed remains completely fluidized. Results also showed that the theoretical predictions were accurate beyond previously reported velocity limits in a laboratory scale dryer. During bubbling fluidization, the cross flow factor method was used effectively to predict the influence of bubble phase on drying rates. In the falling-rate period, it is demonstrated that the drying behaviour of nylon at different gas velocities can be characterised by a single normalized drying curve. On a étudié de manière expérimentale et théorique le séchage de particules de nylon (Geldart D) et de polystyrène expansé (Geldart B) dans des lits fixes et fluidisés. Les séchoirs à lits fluidisés fonctionnent parfois à des vitesses qui vont au-delà de la fluidisation bullante pour atténuer la dé-fluidisation des particules mouillées en surface. On a trouvé que l'analyse théorique à l'aide de trois méthodes de séchage différentes pouvait prédire le taux de séchage constant à de telles vitesses et également dans tous les régimes de fluidisation (fluidisation à lit fixe, bullante, pistonnante et turbulente) tant que le lit demeure entièrement fluidisé. Les résultats montrent également que les prédictions théoriques sont précises au-delà des limites de vitesse mentionnées précédemment dans un séchoir à l'échelle de laboratoire. Lors de la fluidisation bullante, on a utilisé avec efficacité la méthode du facteur d'écoulement transversal afin de prédire l'influence de la phase bullante sur les vitesses de séchage. Dans la période de vitesse descendante, on démontre que le comportement de séchage du nylon à différentes vitesses de gaz peut être caractérisé par une courbe de séchage normalisée unique. [source] Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different ScalesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003Wei Chen Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source] Intensification of Slurry Bubble Columns by Vibration ExcitementTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Jürg Ellenberger Abstract We show that application of low-frequency vibrations, in the 30 to 60 Hz range, to the liquid phase of an air , water , silica catalyst slurry bubble column causes significant enhancement of both gas holdup and volumetric mass transfer coefficient over a wide range of superficial gas velocities. The increase in the gas holdup is attributed mainly to a significant reduction in the rise velocity of the bubble swarm due to the generation of standing waves in the column. Furthermore, application of vibrations to the liquid phase serves to stabilize the homogenous bubbly flow regime and delay the onset of the churn-turbulent flow regime. On montre que l'application de vibrations de faibles fréquences (entre 30 et 60 Hz) à la phase liquide d'une colonne à bulles à suspensions de catalyseur air-eau-silice, permet une amélioration significative à la fois du coefficient de rétention de gaz et du coefficient du transfert de matière volumétrique pour une vaste gamme de vitesses de gaz superficielles. L'augmentation de la rétention de gaz est imputée principalement à une réduction importante de la vitesse de montée de l'essaim de bulles qui est due à la création de vagues stationnaires dans la colonne. En outre, l'application des vibrations à la phase liquide sert à stabiliser le régime d'écoulement à bulles homogène et retarde l'apparition du régime d'écoulement agité-pistonnant. [source] Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) ReactorTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Mike Winterbottoma Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source] Effect of Gas Density on the Hydrodynamics of Bubble Columns and Three-Phase Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Arturo Macchi Abstract Experiments were performed at ambient temperature and pressure in a 127 mm inner diameter column with a 55% wt. aqueous glycerol solution, 6-mm spherical borosilicate beads and four gases , helium, air, carbon dioxide and sulphur hexafluoride , giving a 35-fold gas density range. The dispersed bubble flow regime was sustained to higher gas velocities and gas holdups for denser gases. This finding appears to be due to the reduction of the maximum stable bubble size (i.e. enhanced bubble break-up), rather than to formation of smaller bubbles at the distributor with increasing gas density. The effect of gas density was significant both with and without the particles present, with gas holdup increasing, bed voidage increasing and liquid holdup decreasing with increasing gas density. The holdup correlations of Han et al. (1990) have been modified to incorporate the effect of gas density. On a mené des expériences à la température et à la pression ambiante dans une colonne de 127 mm de diamètre intérieur avec une solution de glycérol aqueux de 55 % en poids, des billes de verre de borosilicate sphériques de 6 mm et quatre gaz , hélium, air, gaz carbonique et hexafluorure de soufre , donnant une gamme de densité gazeuse multipliée par 35. Le régime d'écoulement bouillonnant dispersé est maintenu jusqu'à des vitesses et des rétentions de gaz supérieures pour les gaz plus denses. Ce résultat semble être dû à la réduction de la taille de bulle stable maximum (c.-à-d. une rupture de bulles améliorée), plutôt qu'à la formation de bulles plus petites au distributeur avec l'augmentation de la densité gazeuse. L'effet de la densité gazeuse est significatif avec ou sans la présence des particules, avec l'augmentation de la rétention de gaz, l'augmentation du vide du lit et la diminution de la rétention de liquide avec l'augmentation de la densité gazeuse. Les corrélations de rétention de Han et al. (1990) sont modifiées de sorte à introduire l'effet de la densité gazeuse. [source] Close-to-streamline numerical study on gas velocity distribution in industrial scale electrostatic precipitator gas inlet hoodASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Jie Zhang Abstract The uniformity of gas velocity distribution in gas inlet hoods is important to guarantee high dedust efficiency in electrostatic precipitators (ESPs), especially for high solid concentration applications. The close-to-streamline numerical method was developed to geometrically 1:1 simulate an industrial scale ESP gas inlet hood, which had complicated internal structures, such as dedust angle irons and gas distribution perforated plates with up to 10 000 holes. The realizable k-, model was used for the gas flow simulation. The numerical results of the gas velocity distribution show reasonable agreement with the field measurements. The outlet gas velocity distribution was non-uniform, which was lower in the central region and higher in the near-wall regions. The gas flow characteristics were analysed to reveal the main influence factors on gas velocity distribution and put forward corresponding modification methods. After the retrofit, the field measurements of the outlet gas velocities showed that the gas velocity distribution improved. The non-uniform index of outlet gas velocity distribution decreased greatly from 0.355 to 0.244. The visible dust emissions from the chimney disappeared which indicated increased dedust efficiency. Therefore, the close-to-streamline method can simulate gas velocity distribution in complicated structures of ESP gas inlet hoods. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Gas,liquid mass transfer in three-phase inverse fluidized bed reactor with Newtonian and non-Newtonian fluidsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010V. Sivasubramanian Abstract Liquid-phase volumetric mass transfer coefficients, kLa were determined in three-phase inverse fluidized beds of low-density polyethylene (LDPE) and polypropylene (PP) spheres fluidized by a countercurrent flow of air and Newtonian (water and glycerol solutions) or non-Newtonian liquids [carboxy methyl cellulose (CMC) solutions]. The effects of liquid and gas velocities, particle size, solid loading and addition of organic additives (glycerol and CMC) on the volumetric mass transfer coefficient, kLa were determined. The superficial liquid velocity had a weak effect on the mass transfer whereas the gas flow rate affected the mass transfer positively. kLa increased with increase in particle diameter and decreased with increase in initial bed height (solid loading). kLa decreased as the concentration of glycerol (viscosity) and CMC increased. Empirical correlations are presented to predict the gas,liquid volumetric mass transfer coefficient in terms of operating variables. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Re-entrainment of wall deposits from a laboratory-scale spray dryerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2007M. J. Hanus Abstract This work has determined the magnitude of re-entrainment and established the operational parameters that may be manipulated to influence re-entrainment of salt particles for a small-scale spray dryer (Buchi B-290). The wetness of the spray dryer wall deposits was found to significantly influence the magnitude of re-entrainment. It was shown both experimentally and numerically that wet deposits form at low nozzle air-to-liquid ratios (<2000), which form large droplets that dry slowly, while the initial droplet velocity did not have a large influence on wet deposition. Wet deposits form strong liquid and solid bridges, and thus deposits formed from wet particles were difficult to re-entrain. Less than 2% of deposits formed at nozzle air-to-liquid ratios less than 2000 were re-entrained, while 15.4 to 21.2% of dry deposited particles (formed at nozzle air-to-liquid ratios ranging from 2308 to 3409) were re-entrained. The threshold re-entrainment velocity of sodium chloride particles in the Buchi B-290 spray dryer was found to be between 4 and 7.7 ms,1, which is consistent with the lower-end threshold velocities presented in the literature. No significant trend relating relative humidity to the magnitude of re-entrainment was found in the 0.2,7.4% average relative humidity range, suggesting that the adhesive forces in spray dryer wall deposits are fairly constant across this relative humidity range. Decreasing wall deposit wetness through use of high (>2000) nozzle air-to-liquid ratios and use of high main gas velocities increased the re-entrainment of wall deposits in this spray dryer. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Holdup and Pressure Drop in Vertical and Near-Vertical Three-Phase Up-Flow: A Collection of Flow RegimesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2002P.L. Spedding Three-phase oil, water and air data are reported for vertical and near vertical +86 5° upflow in a 0 026 m i d pipe In general, the liquid holdup for near vertical flow was greater than for the corresponding vertical upflow, the exception being at low liquid and superficial velocities under 0 6 m/s and high superficial gas velocities over 20 m/s Here the liquid holdup varied being sometimes below and other times above the corresponding vertical value These variations of liquid holdup were shown to depend on the fine structure of the flow patterns present The total pressure drop and its component parts showed significantly different patterns of behaviour depending on whether the superficial gas velocity was above or below the rise velocity of a Taylor bubble The total pressure drop generally was greater for near vertical flow compared to the vertical upflow case but reflected changes in the fine structure of the flow patterns A comprehensive collection of flow regimes is included in this paper [source] NS0 cell damage by high gas velocity sparging in protein-free and cholesterol-free culturesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2008Ying Zhu Abstract Recent developments in high cell density and high productivity fed-batch animal cell cultures have placed a high demand on oxygenation and carbon dioxide removal in bioreactors. The high oxygen demand is often met by increasing agitation and sparging rates of air/O2 in the bioreactors. However, as we demonstrate in this study, an increase of gas sparging can result in cell damage at the sparger site due to high gas entrance velocities. Previous studies have showed that gas bubble breakup at the culture surface was primarily responsible for cell damage in sparged bioreactors. Such cell damage can be reduced by use of surfactants such as Pluronic F-68 in the culture. In our results, where NS0 cells were grown in a protein-free and cholesterol-free medium containing 0.5 g/L Pluronic F-68, high gas entrance velocity at the sparger site was observed as the second mechanism for cell damage. Experiments were performed in scaled-down spinners to model the effect of hydrodynamic force resulting from high gas velocities on antibody-producing NS0 cells. Cell growth and cell death were described by first-order kinetics. Cell death rate constant increased significantly from 0.04 to 0.18 day,1 with increasing gas entrance velocity from 2.3 to 82.9 m/s at the sparger site. The critical gas entrance velocity for the NS0 cell line studied was found to be ,30 m/s; velocities greater than 30 m/s caused cell damage which resulted in reduced viability and consequently reduced antibody production. Observations from a second cholesterol-independent NS0 cell line confirmed the occurrence of cell damage due to high gas velocities. Increasing the concentration of Pluronic F-68 from 0.5 to 2 g/L had no additional protective effect on cell damage associated with high gas velocity at the sparger. The results of gas velocity analysis for cell damage have been applied in two case studies of large-scale antibody manufacturing. The first is a troubleshooting study for antibody production carried out in a 600 L bioreactor, and the second is the development of a gas sparger design for a large bioreactor scale (e.g., 10,000 L) for antibody manufacturing. Biotechnol. Bioeng. 2008;101: 751,760. © 2008 Wiley Periodicals, Inc. [source] Bubble Size Distribution in Oil-Based Bubble ColumnsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2008S.-S. Homayouni Abstract A practical population balance model was used to evaluate the bubble size distribution in a bubble column. In addition, the bubble size distribution in the bubble column was measured at different gas velocities by photography and analysis of the pictures. Four types of liquid, i.e., water and three petroleum-based liquids, were used in the experiments. The gas phase was air. It was found that the existing models in the literature are not able to satisfactorily predict the experimentally measured bubble size distribution. The model can be corrected by applying a correction factor to the energy dissipation rate. The corrected model fits the experimental bubble size distribution considerably better than the existing models. The variation of this correction factor is reported for different systems at different gas velocities. [source] Gas-Liquid Mass Transfer in a Slurry Bubble Column at High Slurry Concentrations and High Gas VelocitiesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2005C. O. Vandu Abstract The volumetric mass transfer coefficient kLa in a 0.1,m-diameter bubble column was studied for an air-slurry system. A C9 -C11n -paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n -paraffin oil had properties similar to those of the liquid phase in a commercial Fischer-Tropsch reactor under reaction conditions. The superficial gas velocity UG was varied in the range of 0.01 to 0.8,m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration ,S ranged from 0 to 0.5. The experimental results obtained show that the gas hold-up ,G decreases with an increase in slurry concentration, with this decrease being most significant when ,S < 0.2. kLa/,G was found to be practically independent of the superficial gas velocity when UG > 0.1,m/s is taking on values predominantly between 0.4 and 0.6,s,1 when ,S = 0.1 to 0.4, and 0.29,s,1, when ,S = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient kLa in an industrial-size bubble column slurry reactor, with a particular focus on the Fischer-Tropsch process as well as high gas velocities and high slurry concentrations. [source] Polarization characteristics and property distributions of a proton exchange membrane fuel cell under cathode starvation conditionsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2010Dongsoo Ko Abstract Property distribution and polarization characteristics of a proton exchange membrane fuel cell (PEMFC) under cathode starvation conditions were investigated numerically and experimentally for a unit cell. The polarization curves of a lab-scale PEMFC were measured with increasing current density for different cell temperatures (40°C, 50°C, and 60°C) at a relative humidity of 100%. To investigate the local temperature, water content and current density on the membrane, and gas velocity in the channel of the PEMFC, numerical studies using the es-pemfc module of the commercial flow solver STAR-CD, which were matched with experimental data, were conducted. Temperature, current density on the membrane, and water content in the MEA were examined to investigate the effect of cell temperature on performance under the cathode starvation condition. At cathode starvation conditions, the performance of a higher cell temperature condition might drop significantly and the mean temperature on the membrane increase abruptly with increasing cell temperature or current density. Copyright © 2009 John Wiley & Sons, Ltd. [source] Energy analysis in fluidized-bed drying of large wet particlesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2002S. Syahrul Abstract Energy analysis of a fluidized-bed drying system is undertaken to optimize the fluidized-bed drying conditions for large wet particles (Group D) using energy models. Three critical factors; the inlet air temperature, the fluidization velocity, and the initial moisture contents of the material (e.g., wheat) are studied to determine their effects on the overall energy efficiency to optimize the fluidized bed drying process. In order to verify the model, different experimental data sets for wheat material taken from the literature are used. The results show that the energy efficiencies of the fluidized-bed dryer decrease with increasing drying time and become the lowest at the end of the drying process. It is observed that the inlet air temperature has an important effect on energy efficiency for the material where the diffusion coefficient depends on both the temperature and the moisture content of the particle. Furthermore, the energy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the material properties. A good agreement is achieved between the model predictions and the available experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source] Modelling of the fluid dynamic processes in a high-recirculation airlift reactorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2001David A. Sanders Abstract This paper describes the creation of two models of the steady-state fluid dynamic processes occurring in a high-recirculation airlift reactor. The new models were created to provide information to assist in the design of a reactor, in particular considering the selection of parameters to adjust in order to achieve a steady state solution. The modelling of two-phase flow of air and water in small-scale airlift bioreactors is considered. This modelling was applied to the high-recirculation airlift reactor process. New computer simulations were created and tests performed to evaluate the new models. The results of this evaluation are presented. The evaluation showed that variation of the superficial gas velocity or the simultaneous variation of the downcomer and riser diameters could be used to produce a steady-state design solution. Copyright © 2001 John Wiley & Sons, Ltd. [source] The effect of gas-liquid counter-current operation on gas hold-up in bubble columns using electrical resistance tomography,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2010Haibo Jin Abstract BACKGROUND: In order to improve the performance of a counter-current bubble column, radial variations of the gas hold-ups and mean hold-ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s,1, and the liquid velocity varied from 0 to 0.01 m s,1. The effect of liquid velocity on the distribution of mean hold-ups and radial gas hold-ups is discussed. RESULTS: The gas hold-up profile in a gas,liquid counter-current bubble column was determined by electrical resistance tomography. The liquid velocity slightly influences the mean hold-up and radial hold-up distribution under the selected operating conditions and the liquid flow improves the transition gas velocity from a homogeneous regime to a heterogeneous regime. Meanwhile, the radial gas hold-up profiles are steeper at the central region of the column with increasing gas velocity. Moreover, the gas hold-up in the centre of the column becomes steeper with increasing liquid velocity. CONCLUSIONS: The value of mean gas hold-ups slightly increases with increasing downward liquid velocity, and more than mean gas hold-ups in batch and co-current operation. According to the experimental results, an empirical correlation for the centreline gas hold-up is obtained based on the effects of gas velocity, liquid velocity, and ratio of axial height to column diameter. The values calculated in this way are in close agreement with experimental data, and compare with literature data on gas hold-ups at the centre of the column. Copyright © 2010 Society of Chemical Industry [source] Multiparameter models for performance analysis of UASB reactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2008C M Narayanan Abstract BACKGROUND: UASB (upflow anaerobic sludge blanket) bioreactors have the distinct advantage that they do not demand support particles and provide a high rate of bioconversion even with high strength feedstocks. Although apparently simple in construction, the performance analysis of these reactors involves a high degree of mathematical complexity. Most simulation models reported in the literature are rudimentary in nature as they involve gross approximations. In the present paper, two multiparameter simulation packages are presented that make no simplifying assumptions and hence are more rigorous in nature. RESULTS: The first package assumes the sludge bed to be a plug-flow reactor (PFR) and the sludge blanket to be an ideal continuous stirred tank reactor (CSTR). The second package equates the reactor to a plug flow dispersion reactor (PFDR), the axial dispersion coefficient however being a function of axial distance. The three phase nature of the sludge blanket has been considered and the variation of gas velocity in the axial direction has been taken into account. Three different kinetic equations have been considered. Resistance to diffusion of substrate into sludge granules has been accounted for by incorporating appropriately defined effectiveness factors. The applicability of simulation packages developed has been ascertained by comparing with real-life data collected from industrial/pilot plant/laboratory UASB reactors. The maximum deviation observed is ± 15%. CONCLUSIONS: Although the software packages developed have high computational load, their applicability has been successfully ascertained and they may be recommended for design and installation of industrial UASB reactors and also for the rating of existing installations. Copyright © 2008 Society of Chemical Industry [source] Measurement of mass transfer coefficient in an airlift reactor with internal loop using coalescent and non-coalescent liquid mediaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2004M Bla Abstract In this work the sulfite oxidation (SOM), dynamic pressure-step (DPM) and gassing-out (GOM) methods were compared for volumetric mass transfer coefficient measurement in an airlift reactor with internal loop. As a liquid phase both, non-coalescent and coalescent media were used. Among the methods discussed here, the mass transfer coefficient (kLa) values obtained by the DPM appear as the most reliable as they were found to be independent of oxygen concentration in the inlet gas, which confirmed the physical correctness of this method. The difference between data measured using air and oxygen was not higher than 10%, which was comparable to the scatter of experimental data. It has been found that the sulfite oxidation method yielded kLa values only a little higher than those obtained by the DPM and the difference did not exceed 10%. Up to an inlet gas velocity (UGC) of ,0.03 m s,1 the GOM using oxygen as a gas medium gave kLa values in fact identical with those obtained by the DPM. At higher flows of the inlet gas, the GOM yielded kLa values as much as 15% lower. The enhancement in oxygen mass transfer rate determined in non-coalescent media was estimated to be up to +15%, when compared with a coalescent batch. The experimental dependence of kLa vs the overall gas hold-up was described by an empirical correlation.1 Copyright © 2004 Society of Chemical Industry [source] | |||||||||||||||||||