Home About us Contact
|
Home About us Contact | ||
|
|
||
Radial Distribution (radial + distribution)
Terms modified by Radial Distribution Selected AbstractsRadial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution ,CDM hydrodynamical simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Andrea V. Macciò ABSTRACT We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N -body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray-shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N -body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars. [source] Turbulent Dynamics of Beryllium Seeded Plasmas at the Edge of TokamaksCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010R.V. Shurygin Abstract Numerical simulation of turbulent MHD dynamics of beryllium seeded plasmas at the edge of tokamaks is performed. The model is based on the 4-fluid {,, n, pe, pi } reduced nonlinear Braginsky's MHD equations. Neutral hydrogen flow from the wall is described with a diffusion model. Beryllium line radiation is taken into consideration. The Be ion distribution over ionization states is calculated using the reduced model. Electron impact ionization, three body, photo- and dielectronic recombination and charge-exchange with neutral hydrogen are taken into account. Coronal equilibrium is not supposed. Simulations are performed for T-10 parameters. Radial distributions of averaged temperatures and their fluctuation levels, species flows, impurity radiation power, and impurity ions concentrations are obtained as functions of the Be concentration at the wall. The impurity radiation is shown to act on the turbulent oscillation level significantly if the total Be concentration at the wall exceeds 3 · 1011cm,3. The impurity turbulent transversal flow is directed inward and exceeds neoclassical flow significantly. The parallel conductivity and, as a consequence, turbulent transport are increased significantly by impurity radiation. The radiation loss dependence on the neutral Hydrogen concentration at the wall is also examined. The hydrogen concentration increasing the plasma density also rises. The relative beryllium concentration decreases. In total, these two effects are compensated, and the level of radiation losses is changed insignificantly (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of charged ultrafiltration poly(styrene- co -divinyl benzene) composite membraneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Sonny Sachdeva Abstract A ceramic supported crosslinked polystyrene composite membrane has been prepared from its monomers using a dual initiator system. The nonionic hydrophobic membrane so prepared has been chemically modified by a low temperature (50°C), single step reaction with chloroacetic acid. The carboxylated membrane has acid functional groups on its surface making it negatively charged and highly hydrophilic in nature. The membranes (unmodified and carboxylated) have been used for the separation of hazardous chromium (VI) salt solution where observed and intrinsic rejection has been studied as a function of pressure and concentration of the feed solution. The intrinsic rejection has been determined by calculating the concentration at the membrane surface (Cm) using Speigler-Kedam model and osmotic pressure model. The observed rejection for the chemically modified membrane decreases with increasing pressure but the intrinsic rejection is found to be more than 80% for all concentrations in the range of study. The experimental results have been fitted using Space-Charge model to obtain the membrane wall potential and the membrane surface concentration which are difficult to measure directly. The transport through the membrane capillaries has been described by the two dimensional model using Nernst-Planck equation for ion transport, Navier-Stokes equation and Poisson-Boltzmann equation for the radial distribution of potential. We have then presented a semianalytical series solution to the highly nonlinear Poisson-Boltzmann equation to reduce the computational time required to solve the set of coupled differential equations. The effective wall potential of the carboxylated membrane was found to be ,28.07 mV. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Design of granule structure: Computational methods and experimental realizationAICHE JOURNAL, Issue 11 2006Mansoor A. Ansari Abstract The spatial distribution of solid components and porosity within a composite granule,its microstructure,is an important attribute as it carries information about the processing history of the granule and determines its end-use application properties, particularly the dissolution rate. In this work, the problem of rational design of granule structure is formulated, and two methods for its solution are proposed,stochastic design, which is based on random permutation of points within the structure using the simulated annealing algorithm, and variational design, which is based on direct simulation of granule formation from its constituent primary particles, followed by direct simulation of granule dissolution. The variational design method is demonstrated in a case study of the effect of primary particle size, radial distribution of components, and composition of a two-component granule (active, excipient) on the dissolution profile. Selected granule structures designed computationally were also physically made by fluid-bed granulation, their structure analyzed by X-ray micro-tomography, and dissolution curves measured. It was confirmed that the designed structures are feasible to manufacture and that they meet the required dissolution profiles. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] The stellar content of the isolated transition dwarf galaxy DDO210,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006Alan W. McConnachie ABSTRACT We use Subaru Suprime-Cam and VLT FORS1 photometry of the dwarf galaxy DDO210 to study the global stellar content and structural properties of a transition-type galaxy (with properties intermediate between dwarf irregular and dwarf spheroidal systems). This galaxy is sufficiently isolated that tidal interactions are not likely to have affected its evolution in any way. The colour,magnitude diagrams of DDO210 show a red giant branch (RGB) population (with an RGB bump), a bright asymptotic giant branch population, a red clump, young main-sequence stars and blue-loop stars. The youngest stars formed within the last 60 Myr and have a distinct radial distribution compared to the main population. Whereas the overall stellar spatial distribution and H i spatial distribution are concentric, the young stars are offset from the centre of DDO210 and are coincident with a ,dent' in the H i distribution. The implied recent star formation rate required to form the young population is significantly higher than the derived current star formation rate, by a factor of >10. Most of the stars in DDO210 are found in a red clump, and its mean I -band magnitude suggests that the majority of stars in DDO210 have an average age of 4+2,1 Gyr. Given this age, the colour of the RGB implies a mean metallicity of [Fe/H],,1.3. By comparing the shape of the red clump with models for a variety of star formation histories, we estimate that an old (>10 Gyr) stellar population can contribute ,20,30 per cent of the stars in DDO210 at most. The unusual star formation history of DDO210, its low-mass estimate and its isolated nature, provide insight into how star formation proceeds in the lowest mass, unperturbed, dwarf galaxy haloes. [source] Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution ,CDM hydrodynamical simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Andrea V. Macciò ABSTRACT We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N -body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray-shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N -body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars. [source] The abundance and radial distribution of satellite galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2005Frank C. Van Den Bosch ABSTRACT Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ,CDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of ,8, 0.7. The same cosmology but with ,8= 0.9 is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity function. [source] Radial Liquid Dispersion and Bubble Distribution in Three-Phase Circulating Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003Yong 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] Fluid Dynamic Studies in Support of an Industrial Three-Phase Fluidized Bed HydroprocessorTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Craig A. McKnight Abstract Reducing gas hold-up has been identified as a key objective to improve the performance of Syncrude's LC-FinerSM unit. Redesign of the liquid recycle pan in the freeboard region, aided by multiphase CFD simulation and tests in a kerosene cold model experimental system, led to reduced gas hold-ups. The addition of an anti-foam agent did not provide any improvement. Cold-flow dimensional similitude tests demonstrated the importance of gas density, distributor geometry, and interfacial phenomena. Grid redesign was undertaken to diminish swirl and provide improved radial distribution of gas. Dispersion tests indicate favourable catalyst mixing in the reactors. La réduction de la rétention de gaz a été déterminée comme étant un objectif clé dans l'amélioration de la performance de l'unité LC-FinerMD de Syncrude. Une nouvelle conception de la cuve de recyclage de liquide dans la région d'espace libre, aidée par une simulation CFD polyphasique et des tests dans une maquette de laboratoire utilisant du kérosène, mène à une réduction des rétentions de gaz. L'ajout d'un agent anti-mousse n'apporte aucune amélioration. Des tests de similitude dimensionnelle de l'écoulement démontrent l'importance de la masse volumique du gaz, de la géométrie du distributeur et des phénomènes interfaciaux. On a revu la conception de la grille afin de diminuer le tourbillon et d'améliorer la distribution radiale de gaz. Les tests de dispersion indiquent un mélange de catalyseur favorable dans les réacteurs. [source] Packed bed structure: Evaluation of radial particle distributionTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2002Néstor J. Mariani Abstract A model describing the radial distribution of monosized spheres in randomly packed beds up to distances of about two particle diameters from the vessel wall is presented here. The model is based on the existence of a highly ordered layer of particles adjacent to the wall followed by a more diffuse, but still identifiable, second layer. Expressions generated from simple geometrical concepts (intersection between a cylindrical surface and a sphere) straightforwardly allow calculating the radial voidage profile given the radial distribution of particle centers and vice versa. These expressions are employed to fit the model to measures of voidage profiles within a wide range of aspect ratios, a = (RT/RP). The model can be used to accurately predict radial voidage profiles, but it is stressed that the identification of particle distribution constitutes more valuable information than an empirical expression for describing voidage variations. On présente ici un modèle décrivant la distribution radiale de sphères monodisperses dans des lits garnis aléatoires jusqu'à des distances d'environ deux diamètres de particules de la paroi du réservoir. Le modèle s'appuie sur l'existence d'une couche très ordonnée de particules adjacentes à la paroi, suivie d'une seconde couche, plus diffuse mais cependant identifiable. Les expressions provenant de concepts géométriques simples (intersection entre une surface cylindrique et une sphère) permettent de calculer directement le profil de vide radial lorsque la distribution radiale des centres de particules est donnée et vice versa. Ces expressions servent à caler le modèle de mesures de profils de vide dans une vaste gamme de paramètres d'élancement, a = (RT/RP. Le modèle peut être utile pour prédire de manière précise les profils de vide radiaux, mais il faut dire que la détermination de la distribution des particules constitue une information plus valable qu'une expression empirique pour décrire les variations de vide. [source] Evaluation of radial voidage profiles in packed beds of low-aspect ratiosTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2000Nestor J. Mariani Abstract The relationship between the radial voidage profile, ,(r), and the radial distribution of centres of mono-sized spherical particles, f(r), is revised. A close expression is given for the section S(r1, rc), the area of the segment of a cylindrical surface of radius r intersected by a particle centred at rC. From this expression, ,(r) can be evaluated straightforwardly from the knowledge of f(r). The range 1, a , 2 of aspect ratios (a = dT/dp is then analysed specifically. For this range, the distribution of spherical particles has been characterized theoretically (Govindarao et al., 1992) and a simple expression allows the evaluation of ,(r). The use of this expression for actual catalyst particles, imperfect spheres showing a distribution of sizes, in finally analyzed. La relation entre le profil de vide radial,,(r), et la distribution radiale des centres de particules sphériques de taille unique, f(r), est examinée. Une expression analytique est donnée pour la section S(r,rc), la région du segment d'une surface cylindrique de rayon r intersectée par une particule centrée en rc. À partir de cette expression, il est possible d'évaluer ,(r) directement à partir de f(r). La gamme des élance-ments 1 , a , 2 (a =d, / dp est ensuite évaluée spéci-fiquement. Pour cette gamme, la distribution des particules sphériques a été caractérisée de manière thérique (Govindarao et al., 1992) et une expression simple permet l'évaluation de ,(r). Enfin, on analyse l'emploi de cette expression pour des particules de catalyseurs réelles, des sphères imparfaites présentant une distribution des tailles. [source] Dynamical evolution of the mass function and radial profile of the Globular Cluster systems of the Milky Way and M87ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008J. Shin Abstract Evolution of the mass function (MF) and radial distribution (RD) of the globular cluster (GC) systems of the Milky Way and M87 are calculated using an advanced and realistic Fokker-Planck (FP) model that considers dynamical friction, disk/bulge shocks, and eccentric cluster orbits. We perform hundreds of FP calculations with different initial cluster conditions, and then search a wide parameter space for the best-fit initial GC MF and RD that evolves into the observed present-day GC MF and RD. By allowing both MF and RD of the initial GC system to vary, we find that in case of the Milky Way, our best-fit models have a higher peak mass for a log-normal initial MF and a higher cutoff mass for a powerlaw initial MF than previous estimates. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Direct Measurements of Instantaneous Solid Flux in a CFB Riser using a Novel Multifunctional Optical Fiber ProbeCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2009S. Ye Abstract With a novel optical fiber probe that can measure instantaneous local particle velocity and solid concentration simultaneously, extensive experiments were conducted to study transient flow structures in a 15.1-m long circulating fluidized bed (CFB) riser of 100,mm in diameter. This study analyzed the radial and axial distributions of solid concentration, particle velocity, and their variations with nine operating conditions and at six axial levels. Instantaneous local solid concentration and particle velocity were found to be well correlated at most of the radial positions. The detailed time evolution, axial and radial distribution of instantaneous solid flux, and the variation of solid flux with operating conditions were also investigated. The radial solid flux profile showed a flat shape with a maximum at near wall area under most operating conditions. The instantaneous solid flux was found to have a strong fluctuation at a radial position of r/R,=,0.8 ~ 0.9. [source] Experimental and Numerical Simulation Study of Heat Transfer Due to Confined Impinging Circular JetCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007L. Chang-geng Abstract An experimental and numerical simulation study of heat transfer due to a confined impinging circular jet is presented. In this research, a stainless steel foil heated disk was used as the heat transfer surface of a simulated chip, and the thermocouples were mounted symmetrically along the diameter of the foil to measure the temperature distribution on the surface. Driven by a small pump, a circular air jet (1.5,mm and 1,mm in diameter) impinged on the heat-transfer surface with middle and low Reynolds numbers. The parameters, such as Reynolds number and ratio of height-to-diameter, were changed to investigate the radial distribution of the Nusselt number and the characteristics of heat transfer in the stagnation region. Numerical computations were performed by using several different turbulence models. In wall bounded turbulent flows, near-wall modeling is crucial. Therefore, the turbulence models enhanced wall treatment, such as the RNG ,-, model, may be superior for modeling impingement flows. The numerical results showed reasonable agreement with the experimental data for local heat transfer coefficient distributions. The impinging jet may be an effective method to solve the cooling problem of high power density electronic packaging. [source] Overview of Multiphase Flow Phenomena in Moving Time-Averaged SpaceCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006K. Ueyama Abstract An overview of multiphase flow phenomena is described on the basis of three relations; a relation between an interaction force and time-averaged physical quantities, a relation between an interaction force and the surrounding flow field, and a relation between time-averaged physical quantities and multiphase flow. The three relations used to theoretically derive the parabolic radial distribution of gas holdup for recirculating turbulent flow in a bubble column are in good agreement with experimental data. General applicability of the three relations for a variety of multiphase flows is also discussed. [source] Hydrodynamics and Mass Transfer in Gas-Liquid-Solid Circulating Fluidized BedsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2003Z. 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] Gas-solids flow behavior: CFB riser vs. downerAICHE JOURNAL, Issue 9 2001H. Zhang Comparisons are made in a circulating fluidized-bed riser/downer system between a 15.1 m high, 0.10 m ID riser and a 9.3 m high, 0.10 m ID downer, based on the measurements of the radial distributions of the local solids holdups and local particle velocities along the two columns. Although the core-annulus flow structures exist in both the riser and downer, the radial flow structure in the downer differs largely from that in the riser. The radial distributions of solids holdup and particle velocity in the downer are much more uniform than those in the riser, thus ensuring the low back mixing and the narrow particle residence time distribution in the downer. The axial flow structure in the downer is also more uniform than that in the riser. Due to the high particle acceleration and the high particle velocity in the downer, the overall solids holdup is significantly lower than that in the riser. The microflow structure in the downer, characterized by the low intermittency indices, is also more uniform than that in the riser. These key properties of the downer make it a very promising candidate for industrial applications where short reaction times and high product selectivity are required. [source] Gas-solid Two-phase Mixtures Flowing Upward through a Confined Packed Bed,PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3-4 2006Yurong He Abstract This paper deals with flows of a gas-solid two-phase mixture through a confined packed bed. Both experimental work and numerical modelling are performed on the behaviour of suspended particles within the packed bed. The experimental work is carried out with a non-intrusive Positron Emission Particle Tracking (PEPT) technique, which tracks particle motion at the single particle level for a prolonged period thus allows both the microscopic and macroscopic solids behaviour to be analysed under the steady-state conditions. A continuous based model is used to simulate the flow behaviour. The model uses a newly proposed porosity model and treats the suspended and packed particles as a binary mixture with the packed particles being at zero velocity. The results show that the model captures the main features of solids behaviour in terms of the radial distributions of the suspended particle concentration and the axial solids velocity. Both the experiments and modelling suggest that the wall effect on the motion of suspended particles be limited to a small region close to the wall (,0.5,1 packed particle diameter). However, deviations exist between the model predictions and experiments; more work is therefore proposed to improve the interaction terms in the model between the suspended and packed particles. [source] Phase distributions in a gas,liquid,solid circulating fluidized bed riserTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010S. 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] Radial nonuniformity index (RNI) in fluidized beds and other multiphase flow systemsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2001Jing-Xu (Jesse) Zhu Abstract The radial nonuniformity index (RNI) is a new non-dimensional index recently devised to quantify the extent of radial variations of flow parameters in fluidized beds and other multiphase flow systems. The index, defined as the ratio of the standard deviation of the given flow parameter in the radial direction to the maximum practically possible standard deviation of that particular parameter, is shown to be an excellent measure of the radial flow structure. This index allows the use of a single value to summarize the radial variation of a given flow parameter. The higher the value of the RNI the less uniform is the flow, and vice versa. Using this technique, radial distributions of local solids concentration and particle velocities from different circulating fluidized bed systems (gas-solid and liquid-solid, upflow and downflow) were examined. It has been found that the RNI can be confidently related to the flow conditions in the circulating fluidized beds, and more insight understanding has been achieved. L'indice de non-uniformité radiale (RNI) est un nouvel indice adimensionnel introduit récemment pour quantifier l'étendue des variations radiales des paramètres d'écoulement dans les lits fluidisés et autres systèmes d'écoulement multiphasiques. On montre que cet indice, défini comme le rapport entre I'écart type du paramètre d'écoulement donné dans la direction radiale et I'écart type maximum pratiquement possible de ce paramètre particulier, est une excellente mesure de la structure d'écoulement radial. Il permet I'utilisation d'une valeur unique pour décrire la variation radiale d'un paramètre d'écoulement donné. Plus la valeur de RNI est élevée, moins I'écoulement est uniforme, et vice-versa. À I'aide de cette technique, on a examiné les distributions radiales des concentrations de solides locales et des vitesses de particules pour différents systèmes de lits fluidisés circulants (gaz-solide et liquide-solide, ascendant et descendant). On a trouvé que le RNI pouvait ,tre relié en toute confiance aux conditions d'écoulement dans les lits fluidisés circulants, ce qui permet de mieux comprendre ce problème. [source] | ||||||||||||||||