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Liquid Velocity (liquid + velocity)

Distribution by Scientific Domains

Chemistry	90%
Engineering	6%

Kinds of Liquid Velocity

superficial liquid velocity

Selected Abstracts

Measurement and Correlation of Critical Gas and Liquid Velocities for Complete Circulation of Solid Particles in External Loop Airlift Bubble Columns

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Katsumi Nakao
Abstract The external loop airlift bubble column provides an easy way of good contacting among gas, liquid and solid phases due to a relatively high recirculating liquid velocity UL. The critical gas and liquid velocities for complete circulation of solid particles, UG,C and UL,C, were measured in two different scales of columns with air, tap water and aqueous CMC solutions, and ion exchange resin and glass beads (155,3834 µm) were employed. The UG,C was determined as the inflection point on the plot of the pressure drop due to the suspended solid particles in the downcomer as a function of the gas velocity UG. The critical liquid velocity UL,C corresponding to the UG,C was obtained from the measured relationship between UL and UG. As a result, a unified dimensionless empirical correlation of UL,C was obtained within an error of ±20% and a dimensionless empirical relationship between UL and UG was developed within an error of ±15%. La colonne à bulles de type airlift à boucle externe offre un moyen facile pour le contact entre les phases gazeuse, liquide et solide grâce à la vitesse de liquide en recirculation UL relativement élevée. Les vitesses de gaz et de liquide critiques pour la circulation complète des particules solides, UG,C et UL,C, ont été mesurées dans deux colonnes d'échelle différente avec de l'air, de l'eau du robinet et des solutions aqueuses de CMC, et des billes de verre et de résine échandeuse d'ions (155,3834 µm) ont été employées. La vitesse UG,C est déterminée comme étant le point d'inflexion sur la courbe de la perte de chgarge causée par les particules solides suspendues dans le déversoir en fonction de la vitesse de gaz UG. La vitesse de liquide critique UL.C correspondant à la vitesse UG.C est obtenue à partir de la relation mesurée entre UL et UG. Ainsi, on obtient une corrélation empirique adimensionnelle unifiée de UL.C avec une erreur de ± 20% et une relation empirique adimensionnelle entre UL et UG est établie avec une erreur de ±15%. [source]

A hollow fiber membrane photo-bioreactor for CO2 sequestration from combustion gas coupled with wastewater treatment: a process engineering approach

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2010
Amit Kumar
Abstract BACKGROUND: In the presence of light, micro-algae convert CO2 and nutrients to biomass that can be used as a biofuel. In closed photo-bioreactors, however, light and CO2 availability often limit algae production and can be difficult to control using traditional diffuser systems. In this research, a hollow fiber membrane photo-bioreactor (HFMPB) was investigated to: (1) increase the interfacial contact area available for gas transfer, (2) treat high nutrient strength (412 mg NO3, -N L,1) wastewater, and (3) produce algal biomass that can be used as a biofuel. RESULTS: A bench scale HFMPB was inoculated with Spirulina platensis and operated with a 2-15% CO2 supply. A mass transfer model was developed and found to be a good tool to estimate CO2 mass transfer coefficients at varying liquid velocities. Overall mass transfer coefficients were 1.8 × 10,6, 2.8 × 10,6, 5.6 × 10,6m s,1 at Reynolds numbers of 38, 63, and 138, respectively. A maximum CO2 removal efficiency of 85% was observed at an inlet CO2 concentration of 2% and a gas residence time (membrane-lumen) of 8.6 s. The corresponding algal biomass concentrations and NO3 removal efficiencies were 2131 mg L,1 and 68%, respectively. CONCLUSION: The results show that the combination of CO2 sequestration, wastewater treatment and biofuel production in an HFMPB is a promising alternative for greenhouse gas mitigation. Copyright © 2010 Society of Chemical Industry [source]

Layer Inversion and Bed Contraction in Down-Flow Binary-Solid Liquid-Fluidized Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2007
R. Escudié
Abstract Experiments were carried out on downward-flow water-fluidized binary mixture of spheres selected for possible layer inversion. With the two binaries tested (relatively high-density large particles mixed with lower-density smaller particles), only one of the five possible steps of the layer inversion progression was clearly identified for the higher liquid velocities, a mixed layer being observed at the top of the column close to the distributor. This layer manifested a bed contraction so large that its bulk density was lower than those of its constituent mono-components at the same liquid velocity, which determined its location within the column. The voidage of the mixed layer could be predicted with good accuracy (<0.7%) by regression of the Westman packed bed equation with one adjustable parameter. Des expériences ont été menées sur un mélange binaire fluidisé par de l'eau et à écoulement descendant, comprenant des sphères sélectionnées pour une inversion possible des couches. Avec les deux binaires testées (de grosses particules de masse volumique relativement élevée mélangées à de petites particules de faible masse volumique), seulement une des cinq étapes possibles menant à l'inversion des couches est clairement identifiée pour les vitesses de liquide les plus élevées, une couche mixte étant observée dans la partie supérieure de la colonne près du distributeur. Cette couche montre une contraction du lit si grande que sa masse volumique globale est plus faible que celle de ses composants individuels constitutifs à la même vitesse de liquide, ce qui détermine sa position dans la colonne. Le degré de vide de la couche mixte a pu être prédit avec une bonne précision (<0,7%) en effectuant une régression sur l'équation de lit garni de Westman avec un paramètre ajustable. [source]

Radial Liquid Dispersion and Bubble Distribution in Three-Phase Circulating Fluidized Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003
Yong Kang
Abstract The liquid dispersion and bubble distribution in the radial direction have been investigated in the riser of a three-phase circulating fluidized bed whose diameter is 0.102m and 3.5m in height. Effects of gas and liquid velocities and solid circulation rate have been determined. It has been found that the radial distribution of bubbles is related closely to the liquid dispersion in the radial direction. The size and rising velocity of bubbles tend to increase as the radial position approaches to the center of the riser. The bubble size increases with increasing UG, but it decreases with increasing UL or GS in all radial positions. The radial dispersion coefficient of the liquid phase increases with increasing UG or GS, however, it tends to decrease with increasing UL. The value of Dr has been well correlated in terms of dimensionless groups based on the isotropic turbulence model. La dispersion liquide et la distribution de bulles dans la direction radiale ont été étudiées dans la colonne montante d'un lit fluidisé circulant triphasique de 0,102 m de diamètre et 3,5 m de hauteur. On a déterminé les effets des vitesses de gaz et de liquide et la vitesse de circulation des solides. On a trouvé que la distribution radiale des bulles était étroitement liée à la dispersion liquide dans la direction radiale. La taille des bulles et leur vitesse de montée tendent à augmenter lorsque la position radiale se rapproche du centre de la colonne. La taille des bulles augmente avec l'augmentation de UG, mais elle diminue avec l'augmentation de UL ou de GS dans toutes les positions radiales. Le coefficient de dispersion radiale de la phase liquide augmente avec l'augmentation de UG ou de Gs, mais celui-ci tend à diminuer avec l'augmentation de UL. La valeur de Dr est bien corrélée par des nombres adimensionnels basés sur le modèle de turbulence isotrope. [source]

Measurement and Correlation of Critical Gas and Liquid Velocities for Complete Circulation of Solid Particles in External Loop Airlift Bubble Columns

Measurement of Solid Circulation Patterns in Liquid,Solid and Gas,Liquid,Solid Fluidized Beds

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003
Shahzad Barghi
Abstract Solid circulation patterns were determined by measuring collisions between tracer particles and cylindrical probes in liquid,solid and gas,liquid,solid fluidized beds. Special probes were used to obtain two- and three-dimensional views of particle motion. Circulation patterns for 3 and 5 mm glass beads were studied. Mixing cells, which had been formed at low liquid velocities, grew in size and eventually merged as the liquid velocity increased. The flow patterns of smaller particles having the same density as bed particles and particles lighter than bed particles (graphite particles) with the same size were also measured. On a déterminé des profils de circulation des solides en mesurant les collisions entre des traceurs particulaires et des sondes cylindriques dans des lits fluidisés liquide, solide et gaz,liquide,solide. Des sondes spéciales ont été employées pour obtenir des images bidimensionnelle et tridimensionnelle du déplacement des particules. Les profils de circulation pour des billes de verre de 3 mm et 5 mm ont été étudiés. Les cellules de mélange, qui se forment à de faibles vitesses de liquide, augmentent en taille et finissent par fusionner à mesure que la vitesse du liquide augmente. On a également mesuré les profils d'écoulement des particules plus petites ayant la même masse volumique que les particules de lit et des particules plus légères que les particules de lit (particules de graphite) ayant la même taille. [source]

Effect of packed structure on flow behaviour in a trickle bed biofilter

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001
Meisen Li
Abstract The effects of operation conditions on the flow behaviour in gas,liquid countercurrent trickle bed biofilter were experimentally examined. In order to prevent gas channelling in the biofilter, packings with a relatively large void fraction, which have a role to maintain a high void fraction in the bed, were added. The gas and liquid velocities of the packed structure and the packings were changed, and the residence time distributions (RTDs) of the gas and liquid were measured. It was found that the addition of void supporters was very effective in the suppression of gas channelling. On a examiné de manière expérimental les effets des conditions opératoires sur les comportements d'écoulement dans un biofiltre à lit ruisselant à contre-courant gaz-liquide. Afin d'emp,cher le renardage dans le biofiltre, des garnissages ayant une fraction de vide relativement grande, qui joue un r,le pour maintenir un haut degré de vide, ont été ajoutés. Les vitesses de gaz et de liquide, la structure garnie et les garnissages ont été modifiés, et les distributions de temps de séjour (RTD) du gaz et du liquide ont été mesurées. On a trouvé que l'ajout de supports de vide était très efficace pour la suppression du renardage. [source]

Effect of Volume Fraction of Material on Separation by Density Difference in a Liquid-Fluidized Bed of Inert Particles

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2010
Y. Tatemoto
Abstract A liquid-fluidized bed was used to separate a pure material from a mixture. A quantity of relatively large sized material was immersed in an inert-particle fluidized bed and the behavior of materials was examined for different liquid velocities. In particular, the volume fraction of the material was varied and its effect on the separation characteristics was examined. The material floats on the inert-particle fluidized bed when the density of the material is lower than the apparent density of the bed, regardless of the volume fraction of the material. The apparent density of the bed can be adjusted by changing the liquid velocity. The materials in the upper portion of the bed affect the properties of the bed below them, i.e., the void fraction decreases and the apparent density increases in the inert-particle suspension when materials are present in the upper portion of the bed. Therefore, the materials float on the bed although the apparent density of the inert-particle suspension obtained from the case without material is less than the density of the material at a relatively high volume fraction of material. This phenomenon occurs more easily for lighter and smaller materials. This means that small inert particles and low liquid velocities are the optimum operating conditions for the separation. [source]

Hydrodynamics and Mass Transfer in Gas-Liquid-Solid Circulating Fluidized Beds

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2003
Z. Liu
Abstract Although extensive work has been performed on the hydrodynamics and gas-liquid mass transfer in conventional three-phase fluidized beds, relevant documented reports on gas-liquid-solid circulating fluidized beds (GLSCFBs) are scarce. In this work, the radial distribution of gas and solid holdups were investigated at two axial positions in a GLSCFB. The results show that gas bubbles and solid particles distribute uniformly in the axial direction but non-uniformly in the radial direction. The radial non-uniformity demonstrates a strong factor on the gas-liquid mass transfer coefficients. A local mass transfer model is proposed to describe the gas-liquid mass transfer at various radial positions. The local mass transfer coefficients appear to be symmetric about the central line of the riser with a lower value in the wall region. The effects of gas flow rates, particle circulating rates and liquid velocities on gas-liquid mass transfer have also been investigated. [source]

Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bed: 2nd report: On tube bundles of fundamental layouts including in-line layouts

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009
Kenichi Hashizume
Abstract Heat transfer coefficients were measured on tube bundles of fundamental layouts including in-line layouts embedded horizontally in a liquid-fluidized bed. Tested tube layouts were single tubes, transverse single tube rows, longitudinal single tube rows, and in-line arranged tube bundles. A total of 7 kinds of particles were used. Comparisons of the experimental data showed a good agreement with the heat transfer correlation developed for staggered layouts, when the average liquid velocity through each tube bundle was used as the reference velocity for the particle Reynolds number. Distribution of the local heat transfer coefficient was also investigated around tubes. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20245 [source]

Modelling of paste flows subject to liquid phase migration

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2007
M. J. Patel
Abstract Particulate pastes undergoing extrusion can exhibit differential velocities between the solid and liquid phases, termed liquid phase migration (LPM). This is observed experimentally but understanding and predictive capacity for paste and extruder design is limited. Most models for LPM feature one-dimensional analyses. Here, a two-dimensional finite element model based on soil mechanics approaches (modified Cam-Clay) was developed where the liquid and the solids skeleton are treated separately. Adaptive remeshing routines were developed to overcome the significant mesh distortion arising from the large strains inherent in extrusion. Material data to evaluate the model's behaviour were taken from the literature. The predictive capacity of the model is evaluated for different ram velocities and die entry angles (smooth walls). Results are compared with experimental findings in the literature and good qualitative agreement is found. Key results are plots of pressure contributions and extrudate liquid fraction against ram displacement, and maps of permeability, liquid velocity and voids ratio. Pore liquid pressure always dominates extrusion pressure. The relationship between extrusion geometry, ram speed and LPM is complex. Overall, for a given geometry, higher ram speeds give less migration. Pastes flowing into conical entry dies give different voids ratio distributions and do not feature static zones. Copyright © 2007 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 2010
Haibo 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]

Effect of a gas,liquid separator on the hydrodynamics and circulation flow regimes in internal-loop airlift reactors

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2001
Jaroslav Klein
Abstract The role of the gas,liquid separator on hydrodynamic characteristics in an internal-loop airlift reactor (ALR) was investigated. Both gas holdup and liquid velocity were measured in a 30,dm3 airlift reactor with two different head configurations: with and without an enlarged separator. A magnetic tracer method using a neutrally buoyant magnetic particle as flowfollower was used to measure the liquid velocity in all sections of the internal-loop airlift reactor. Average liquid circulation velocities in the main parts of the ALR were compared for both reactor configurations. At low air flow rates the separator had no influence on gas holdup, circulation velocity and intensity of turbulence in the downcomer and separator. At higher superficial air velocities, however, the separator design had a decisive effect on the hydrodynamic parameters in the downcomer and the separator. On the other hand, the gas holdup in the riser was only slightly influenced by the separator configuration in the whole range of air flow. Circulation flow regimes, characterising the behaviour of bubbles in the downcomer, were identified and the effect of the separator on these regimes was assessed. © 2001 Society of Chemical Industry [source]

Influence of elevated pressure and particle lyophobicity on hydrodynamics and gas,liquid mass transfer in slurry bubble columns

AICHE JOURNAL, Issue 3 2010
Vinit P. Chilekar
Abstract This article reports on the influence of elevated pressure and catalyst particle lyophobicity at particle concentrations up to 3 vol % on the hydrodynamics and the gas-to-liquid mass transfer in a slurry bubble column. The study was done with demineralized water (aqueous phase) and Isopar-M oil (organic phase) slurries in a 0.15 m internal diameter bubble column operated at pressures ranging from 0.1 to 1.3 MPa. The overall gas hold-up, the flow regime transition point, the average large bubble diameter, and the centerline liquid velocity were measured along with the gas,liquid mass transfer coefficient. The gas hold-up and the flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. Increasing operating pressure significantly increases the gas hold-up and the regime transition velocity, irrespective of the particle lyophobicity. The gas,liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity, the particle concentration, and the operating pressure. A correlation is presented to estimate the gas,liquid mass transfer coefficient as a function of the measured gas hold-up: . © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Investigation of nonuniformity in a liquid,solid fluidized bed with identical parallel channels

AICHE JOURNAL, Issue 1 2010
Long Fan
Abstract Previous work has demonstrated that multiphase flow through identical parallel channels and multiple cyclones can give rise to significant nonuniformity among the flow paths. This article presents results from a study where the distribution of voidage and flux through parallel channels in liquid,solid fluidized beds is investigated. Experiments and computational fluid dynamics simulations were performed with 1.2 mm glass beads fluidized by water where a cross baffle divided a 191 mm diameter column into four identical parallel channels. Voidages were measured by optical fiber probes. Simulations from a three-dimensional unsteady-state Eulerian,Eulerian model based on FLUENT software showed good agreement with the experimental results. Despite the symmetrical geometry of the system, the average voidage and particle velocities in one channel differed somewhat from those in the others. Increasing the superficial liquid velocity could increase voidage greatly and affect the degree of nonuniformity in the four channels. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Volume-of-fluid-based model for multiphase flow in high-pressure trickle-bed reactor: Optimization of numerical parameters

AICHE JOURNAL, Issue 11 2009
Rodrigo J. G. Lopes
Abstract Aiming to understand the effect of various parameters such as liquid velocity, surface tension, and wetting phenomena, a Volume-of-Fluid (VOF) model was developed to simulate the multiphase flow in high-pressure trickle-bed reactor (TBR). As the accuracy of the simulation is largely dependent on mesh density, different mesh sizes were compared for the hydrodynamic validation of the multiphase flow model. Several model solution parameters comprising different time steps, convergence criteria and discretization schemes were examined to establish model parametric independency results. High-order differencing schemes were found to agree better with the experimental data from the literature given that its formulation includes inherently the minimization of artificial numerical dissipation. The optimum values for the numerical solution parameters were then used to evaluate the hydrodynamic predictions at high-pressure demonstrating the significant influence of the gas flow rate mainly on liquid holdup rather than on two-phase pressure drop and exhibiting hysteresis in both hydrodynamic parameters. Afterwards, the VOF model was applied to evaluate successive radial planes of liquid volume fraction at different packed bed cross-sections. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Hydrogenation of 2-ethylanthraquinone under Taylor flow in single square channel monolith reactors

AICHE JOURNAL, Issue 3 2009
Dingsheng Liu
Abstract The hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz-glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas-liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two-phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi-empirical formula were used to predict gas-solid, gas-liquid, and liquid-solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

A CFD,PBM coupled model for gas,liquid flows

AICHE JOURNAL, Issue 1 2006
Tiefeng Wang
Abstract A computational fluid dynamics,population balance model (CFD-PBM) coupled model was developed that combines the advantages of CFD to calculate the entire flow field and of the PBM to calculate the local bubble size distribution. Bubble coalescence and breakup were taken into account to determine the evolution of the bubble size. Different bubble breakup and coalescence models were compared. An algorithm was proposed for computing the parameters based on the bubble size distribution, including the drag force, transverse lift force, wall lubrication force, turbulent dispersion force, and bubble-induced turbulence. With the bubble breakup and coalescence models and the interphase force formulations in this work, the CFD-PBM coupled model can give a unified description for both the homogeneous and the heterogeneous regimes. Good agreement was obtained with the experimental results for the gas holdup, liquid velocity, and bubble size distribution. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

Axial liquid mixing in high-pressure bubble columns

AICHE JOURNAL, Issue 8 2003
G. Q. Yang
Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn-turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid-phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid-phase turbulence. The scale-up effect on liquid mixing reduces as the pressure increases. [source]

Phase distributions in a gas,liquid,solid circulating fluidized bed riser

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
S. A. Razzak
Abstract The distributions of the three phases in gas,liquid,solid circulating fluidized beds (GLSCFB) were studied using a novel measurement technique that combines electrical resistance tomography (ERT) and optical fibre probe. The introduction of gas into a liquid,solid circulating fluidized bed (LSCFB), thus forming a GLSCFB, caused the increase of solids holdup due to the significantly decreased available buoyancy with the lower density of the gas, even with a somewhat increased liquid velocity due to the decreased liquid holdup giving space for the gas holdup. The gas passed through the riser in the form of bubbles, which tended to flow more through the central region of the riser, leading to more radial non-uniformity in radial holdup of the phases. The gas velocity has the most significant effect on the gas phase holdup. While the gas velocity also has an obvious effect to the solids holdups, the liquid flow rate had a much more considerable effect on the phase holdups. The solids circulation rate also had a significant effect on the phase holdups, with increasing solids circulation rate causing much more increased solids holdup in the central region than close to the wall. A correlation was developed for the relative radial distributions of solids holdup in GLSCFB, as such radial profiles were found similar over a wide range of operating conditions, like those in a typical gas,solid circulating fluidized beds (GSCFB). Finally, the axial solids profiles in a GLSCFB was found to be much closer to those in an LSCFB which are very uniform, than those found in a GSCFB which are less uniform and sometime having a S shape. Water was used as the continuous and conductive phase, air was the gas phase and glass bead and lava rock particles were used as the solid and non-conductive phase. Les distributions des trois phases des lits fluidisés circulants gaz-liquide-solide (LFCGLS) ont été étudiées à l'aide d'une technique de mesure originale qui combine la tomographie à résistance électrique (ERT) et la sonde à fibre optique. L'introduction de gaz dans un lit fluidisé circulant liquide-solide, formant par conséquent un lit fluidisé circulant gaz-liquide-solide, a provoqué une retenue de solides en raison de la diminution importante de la flottabilité disponible avec la densité moindre du gaz, même avec une vitesse de liquide quelque peu accrue causée par la retenue de liquide diminuée qui donne de l'espace pour la retenue de gaz. Le gaz passé dans la colonne de montée sous forme de bulles, qui avaient tendance à circuler davantage dans la région centrale de la colonne, donne une non-uniformité plus radiale dans la retenue radiale des phases. La vitesse du gaz a aussi un effet évident sur les retenues des solides; le débit du liquide a un effet beaucoup plus considérable sur les retenues des phases. Le taux de circulation des solides avait également un effet important sur les retenues des phases, le taux de circulation des solides croissant causant beaucoup plus de retenues de solides accrues dans la région centrale que près du mur. Une corrélation a été créée pour les distributions radiales relatives de la retenue des solides dans le LFCGLS, puisque de tels profils radiaux ont été trouvés semblables sur une vaste gamme de conditions d'utilisation, comme celles dans un LFCGS typique. Enfin, on a découvert que les profils des solides axiaux dans un LFCGLS sont beaucoup plus près que ceux d'un LFCLS qui sont très uniformes, que ceux découverts dans un LFCGS, qui sont moins uniformes et qui ont à peu près la forme d'un « S ». [source]

Clustering behaviour in gas,liquid,solid circulating fluidized beds with low solid holdups of resin particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
Jianhua Liu
Abstract The flow in a gas,liquid,solid circulating fluidized bed is self-organised and manifests itself with clustering of particles and bubbles. The clustering behaviour in the fluidized bed at low solid holdups of resin particles was experimentally investigated with a high-speed image measurement and treatment technique of complementary metal oxide semiconductor to enhance the fundamental understanding on such a flow. Several new physical quantities were suggested to characterise such ordered flow structures. The main findings are as follows. The clusters of solid particles largely exist as doublets and triplets, the mixed groups of particles and bubbles mostly exist as one bubble carrying two to four particles. Increasing superficial liquid velocity, particle diameter or density weakens the aggregation degrees of both particle and mixed clusters in the riser and downer, except that the increase of superficial liquid velocity enhances the mixed clustering behaviour in the riser. The climbing of the auxiliary liquid velocity or liquid phase viscosity intensifies the aggregation behaviour, except that the increase of liquid phase viscosity reduces the mixed clustering degree in the riser. The influences of superficial gas velocity and surface tension of liquid phase on the clustering behaviour seem to be a little complex and the trends are not simply increasing or decreasing. The life cycle of solid particle clusters in the GLS riser is not sensitive to the operation conditions, being around 0.07,s. The mixed clusters' life cycle is more sensitive to the conditions and physical properties of phases, changing from 0.02 to 0.07,s. L'écoulement dans un lit fluidisé de circulation gaz-liquide-solide s'organise souvent de lui même et se manifeste avec l'agrégation des particules et des bulles. Le comportement de l'agrégation dans le lit fluidisé à faible retenue de particules de résine solide a été étudié expérimentalement en utilisant une technique d'imagerie ultra-rapide de mesure et de traitement à base de semi-conducteur complémentaire à l'oxyde de métal afin d'approfondir la compréhension fondamentale d'un tel écoulement. Plusieurs nouvelles quantités physiques ont été suggérées pour caractériser une telle structure d'écoulement auto-organisé. Les principaux résultats sont comme suit. Les agrégations de particules solides existent principalement en tant que doublets et triplets, les groupes mixtes de particules et de bulles existent pour la plupart sous la forme d'une bulle comportant deux à quatre particules. Une augmentation de la vitesse superficielle du liquide, du diamètre des particules ou de la densité affaiblit à la fois les degrés d'agrégation des particules et des agrégats mixtes dans la colonne montante et dans la colonne descendante, sauf que l'augmentation de la vitesse superficielle du liquide intensifie le comportement d'agrégation mixte dans la colonne montante. L'accroissement de la vitesse auxiliaire du liquide ou de la viscosité de la phase liquide intensifie le comportement d'agrégation, sauf que l'augmentation de la viscosité de la phase liquide réduit le degré d'agrégation mixte dans la colonne montante. Les influences de la vitesse superficielle du gaz et de la tension de surface de la phase liquide sur le comportement de l'agrégation semblent être quelque peu complexes et les tendances ne sont pas simplement croissantes ou décroissantes. Le cycle de vie des agrégats de particules solides dans la colonne gaz-liquide-solide montante n'est pas sensible aux facteurs, tournant autour de 0.07,s. Le cycle de vie des agrégats mixtes est plus sensible aux conditions de fonctionnement et aux caractéristiques physiques des phases, évoluant de 0.02 à 0.07,s. [source]

Layer Inversion and Bed Contraction in Down-Flow Binary-Solid Liquid-Fluidized Beds

Important Factors in Bubble Coalescence Modeling in Stirred Tank Reactors

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Rahman Sudiyo
Abstract Bubble coalescence has been studied in a 2.6 L stirred tank. Instantaneous velocity fields were measured using PIV and corresponding turbulent kinetic energy, dissipation rate, various length and timescales were estimated. All of these data, combined with data of local gas hold-up, bubble size and coalescence rate obtained with shadowgraph were used to assess bubble coalescence at different positions. Results show that bubble coalescence takes place mostly near the tank wall, especially on the leeward side of baffles. The most important factors affecting coalescence are gas hold-up, fluctuation of liquid velocity, different rise velocities of bubbles, and trapping of bubbles in stationary and turbulent eddies. On a étudié la coalescence des bulles dans un réservoir agité de 2,6 L. Les champs de vitesse instantanée ont été mesurés par vélocimétrie à imagerie de particules (PIV), et l'énergie cinétique turbulente correspondante, la vitesse de dissipation et diverses échelles de longueur et de temps ont été estimés. Toutes ces données, combinées à des données de rétention de gaz locale, de taille des bulles et de vitesse de coalescence obtenues avec le projecteur de profils, ont permis d'évaluer la coalescence des bulles à différentes positions. Les résultats montrent que la coalescence des bulles se produit principalement près de la paroi du réservoir, spécialement sur la face aval des chicanes. Les principaux facteurs qui influent la coalescence sont la rétention de gaz, la fluctuation de la vitesse de liquide, les différentes vitesses d'ascension des bulles et le piégeage des bulles dans des tourbillons stationnaires et turbulents. [source]

Comparison, Combination and Validation of Measuring Techniques for Local Flow and Turbulence Analysis in Bubble Columns and Airlift Reactors

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Christophe Vial
Abstract The applicability of velocimetry techniques based on the Doppler effect , such as laser and ultrasound Doppler velocimetry , for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non-coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes. L'applicabilité des techniques de vélocimétrie laser Doppler et de vélocimétrie ultrasonore pour décrire l'hydrodynamique locale dans les colonnes à bulles et les airlifts est étendue aux milieux non-coalescents. On étudie leurs limitations, notamment en fonction du type de distributeur et de réacteur. On montre que la technique ultrasonore permet à la fois la mesure de la vitesse locale des bulles et du liquide. Les différences dues à l'aptitude à la coalescence du milieu sont démontrées. Les résultats sont validés par des bilans et par la comparaison avec d'autres techniques (sonde électrochimique, tube de Pavlov et sonde optique). [source]

Combined PIV/PTV-Measurements for the Analysis of Bubble Interactions and Coalescence in a Turbulent Flow

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Dirk Bröder
Abstract In order to allow more reliable modeling of coalescence processes in turbulent bubbly flows, detailed experiments in a double loop reactor were performed. Narrow and essentially monomodal bubble size distributions in the range of 2 to 4 mm were created. For simultaneous measurements of bubble size, bubble velocity and liquid velocity a combined system of PIV and PTV was developed and applied. It was possible to determine bubble size distributions and mean, as well as fluctuating velocities for both phases. The spatial changes of the bubble size distribution, due to the influence of bubble coalescence, was analyzed and coalescence rates were calculated. Afin d'améliorer la fiabilité de la modélisation des procédés de coalescence dans les écoulements bouillonnants turbulents, des expériences poussées ont été menées dans un réacteur à double boucle. Des distributions de taille des bulles étroites, essentiellement monodisperses, dans la gamme de 2 à 4 mm, ont été créées. Pour les mesures simultanées de la taille des bulles, de la vitesse des bulles et de la vitesse du liquide, on a mis au point et appliqué un système combiné de PIV et PTV. Il a été possible de déterminer les distributions de taille des bulles et la moyenne mais également les vitesses fluctuantes pour les deux phases. Les changements spatiaux de la distribution de la taille des bulles dus à l'influence de la coalescence des bulles ont été analysés et les vitesses de coalescence ont été calculées. [source]

Measurement of Solid Circulation Patterns in Liquid,Solid and Gas,Liquid,Solid Fluidized Beds

Two-phase bifurcated dividing pipe flow

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009
A. Murphy
Abstract Data are reported on the pressure drop of co-current air,water two-phase flow through 0.0454 m i.d. bifurcations with included angles of 60°, 90°, 120° and 180°. The pressure changes on account of the angles at the junctions depended on the superficial phase velocities and the angle of bifurcation. For the 60° lowest angle of bifurcation the pressure drop was insensitive to flow rates if the superficial liquid velocity was in the lower range at and below 0.1 m s,1. For higher liquid flows the pressure loss increased dramatically, particularly in the annular-type regimes. When the angle at the junction was increased, negative values of pressure loss, i.e. an increase in pressure was recorded across the bifurcation in the gas velocity region under 10 m s,1 and liquid rates at and above 0.1 m s,1 in the slug and blow-through slug regimes. The effect coincided with liquid separation from the inner inlet pipe wall of the junction and its subsequent reformation on the downstream walls. A second less dramatic increase in junction pressure drop occurred at the lowest liquid flow rate of 0.05 m s,1 for the tee (180° bifurcation) that was due both to the smooth transition of liquid through the junction and the damping of surface waves in stratified-type flow. A flow regime map was presented for the tee junction. The inlet flow showed agreement with the map but the flow regimes found in the outlet arms of the junction tended to form earlier than expected being triggered by the pressure disturbances in the passage through the bifurcation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Effect of various parameters on the solid circulation rate in a liquid,solid circulating fluidized bed

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008
P. Natarajan
Abstract A liquid,solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant, and between the conventional liquid fluidized bed and the dilute-phase liquid transport regimes. In the present work, systematic experiments were carried out in a 0.094 m i.d. and 2.4 m height laboratory-scale LSCFB apparatus by using various solid particles and tap water as fluidizing medium to study the hydrodynamics. The effects of operating parameters, i.e. primary liquid flow rate in the riser (jf), auxiliary liquid flow rate (ja), total liquid flow rate (jl), particle density (,s), particle diameter (dp) and solid feed pipe diameter (do) on the solid circulation rate were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate solid velocity (solid circulation rate), and was compared with the present experimental and available data in the literature. They agree well with a maximum root mean-square (RMS) deviation of 12%. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Enzyme recovery during gas/liquid two-phase flow microfiltration of enzyme/yeast mixtures

BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2002
Muriel Mercier-Bonin
Abstract The effect of a gas/liquid two-phase flow on the recovery of an enzyme was evaluated and compared with standard crossflow operation when confronted with the microfiltration of a high-fouling yeast suspension. Ceramic tubular and flat sheet membranes were used. At constant feed concentration (permeate recycling) and transmembrane pressure, the results obtained with the tubular membrane were dependent on the two-phase flow pattern. In comparison with single-phase flow performances at the same liquid velocity, the enzyme transmission was maintained at a high level with a bubble flow pattern but it decreased by 70% with a slug flow, whatever the flow rate ratio. Identical results were obtained with flat sheet membranes: for the highest flow rate ratio, the enzyme transmission was reduced by 70% even though the permeate flux was improved by 240%. During diafiltration experiments with the tubular membrane, it was found that a bubble flow pattern led to a 13% higher enzyme recovery compared to single-phase flow conditions, whereas with a slug flow the enzyme recovery was strongly reduced. With bubble flow conditions, energy consumption was minimal, confirming that this flow pattern was the most suitable for enzyme recovery. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 610,621, 2002. [source]