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Hydrodynamic Phenomena (hydrodynamic + phenomenon)

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Chemistry	100%

Selected Abstracts

2D Slurry Bubble Column Hydrodynamic Phenomena Clarified with a 3D Gas,Liquid Model

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Jeroen H. J. Kluytmans
Abstract The gas hold-up in a 2D bubble column is modelled using a 3D gas hold-up model. The influence of the scale of 2D bubble columns on several parameters, for instance, transition gas hold-up, transition gas velocity, and bubble rise velocities, is investigated and related to 3D bubble columns. By adapting the rise velocity of the large bubbles of an existing 3D bubble column model (Krishna et al., 2001a), the gas hold-up in both the homogeneous and the heterogeneous regime can be described satisfactorily. By adjusting the transition points only, it is also possible to describe the gas hold-up in systems containing small amounts of carbon particles and electrolyte. The smallest dimension of the 2D slurry bubble column, the column thickness, influences the location of the regime transition point. In the heterogeneous regime, however, it is only the largest column dimension, the column width, that influences the gas hold-up. These observations together enable proper 2D/3D bubble column comparison in future studies. Dans cette étude, la rétention de gaz dans une colonne à bulles en 2D est modélisée à l'aide d'un modèle de rétention de gaz en 3D. L'influence de l'échelle des colonnes à bulles 2D sur plusieurs paramètres, comme la rétention de gaz de transition, la vitesse de gaz de transition et les vitesses de montée des bulles, est étudiée et reliée aux colonnes à bulles 3D. On montre qu'en adaptant la vitesse de montée des bulles larges fournie par un modèle de colonnes à bulles 3D existant (Krishna et al., 2001a), la rétention de gaz tant en régime homogène qu'hétérogène peut être décrite de manière satisfaisante. En ajustant seulement les points de transition, il est également possible de décrire la rétention de gaz dans des systèmes contenant de petites quantités de particules de carbone et d'électrolyte. On a trouvé que la plus petite dimension de la colonne à bulles à suspensions 2D, soit l'épaisseur de la colonne, influence la position du point de transition de régime. Cependant, dans le régime hétérogène, c'est seulement la plus grande dimension de la colonne, soit la largeur de la colonne, qui influence la rétention de gaz. Toutes ces observations vont permettre des comparaisons adéquates des colonnes 2D et 3D dans les prochaines études. [source]

Magnetic emulation of microgravity for earth-bound multiphase catalytic reactor studies,Potentialities and limitations

AICHE JOURNAL, Issue 5 2009
Faïçal Larachi
Abstract A method is proposed to generate Earth-bound artificial microgravity in a controlled facility capable of emulating lunar/Martian gravity or microgravity for experiments on passive/reactive catalytic multiphase flows. Its applicability was illustrated for trickle beds where flowing gas and liquid experience artificial microgravity inside the bore of a superconducting magnet generating large gradient magnetic fields to compensate for gravity. Artificial gravity is realized by commuting into apparent gravity acceleration the magnetization force at work on common "chemical engineering" non-magnetic fluids. The scaling property to be matched and maintained invariant in multiphase systems to achieve magnetic mimicry is phasic mass magnetic susceptibility. Hydrodynamic (liquid holdup, wetting efficiency, pressure drop) as well as catalytic reaction (conversion and selectivity) measurements were obtained. The main finding is a proof that magnetic fields affect reactor outcomes exclusively via hydrodynamic phenomena making them appealing proxies for emulating non-terrene reactor applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Rate-based nonisothermal LLX model and its experimental validation

AICHE JOURNAL, Issue 2 2004
Debjit Sanpui
Abstract Most of the current open literature handles liquid,liquid extraction (LLX) using equilibrium and/or isothermal models. However, in most industrial applications, the assumption of equilibrium and isothermal operation is not reasonable. A rate-based nonequilibrium model for both the mass and energy transfer in LLX during the three distinct stages of drop formation,drop, fall or rise, and drop coalescence,has been developed. These three hydrodynamic phenomena affect the mass transfer between dispersed and continuous phases for which a parallel,parallel mass-transfer resistance model has been incorporated. Because of the very large number of computations associated with repeated calculations of mass-transfer coefficients a local model has been proposed. We have compared our rate-based simulator with two other commercial simulators and our bench-scale experiments have been done for toluene,acetone,water and methyl isobutyl ketone,acetic acid,water systems. Stagewise mass and energy transfer and the hydrodynamics features have been compared between the experimental and the simulation runs. Relative-error square analysis (for the concentration profiles) shows that our simulation results are two orders of magnitude better in comparison to other commercial simulators. © 2004 American Institute of Chemical Engineers AIChE J, 50: 368,381, 2004 [source]

Hydrodynamic modelling of the axial density profile in the riser of a low-density circulating fluidized bed

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2001
Kathleen Smolders
Abstract The axial density profile is an important characteristic of the CFB riser and a key parameter in the CFB design. A simple, but reliable model is needed to predict the density profiles. Elutriation-based models treat the dense phase at the bottom of the riser as a dense bubbling bed whereas the dilute phase higher up can be looked upon as the entrainment zone above the dense bed. The elutriation model, as originally presented by Rhodes et al. (1986) and based on Wen et al. (1982) is extensively studied and modified. In spite of the modifications, the use of entrainment models has certain clear limitations due to a wide range of predictions as evident from Table 1. Elutriation rates are calculated based on the hydrodynamic phenomena in the dense bed and a fitting procedure for the entrainment decay constant (,) was performed. Le profil de masse volumique axiale est une caractéristique importante de la colonne montante d'un lit fluidisé circulant (CFB) et un paramètre clé dans la conception du CFB. Un modèle simple mais fiable est nécessaire pour prédire les profils de masse volumique. Les modèles basés sur I'élutriation traitent la phase dense dans la partie inférieure de la colonne comme un lit bouillonnant dense, alors que la phase diluée dans la partie supéieure peut ,tre vue comme la zone d'entra,nement au-dessus du lit dense. Le modèle d'élutriation, tel qu'il fut présenté à l'origine par Rhodes et al. (1986) et basé sur Wen et al. (1982), est largement étudié et modifié. Malgré ces modifications, le recours aux modèles d'entra,nement présente des limites évidentes à cause d'une vaste gamme de prédictions comme le montre clairement le tableau 1. Les vitesses d'élutriation sont calculées d'après les phénomènes hydrodynamiques dans le lit dense et une procédure de calage est utilisée pour la constante de diminution d'entra,nement (,). [source]