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Fluidization Regime (fluidization + regime)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Investigation of Drying Geldart D and B Particles in Different Fluidization Regimes

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006
Wai 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]

Numerical investigation of gas mixing in gas-solid fluidized beds

AICHE JOURNAL, Issue 9 2010
Tingwen Li
Abstract Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is simulated with the aid of computational fluid dynamics. In the first part, a parametric study is conducted to investigate the influence of various parameters on the gas mixing. Among the parameters studied, the specularity coefficient for the partial-slip solid-phase wall boundary condition had the most significant effect on gas mixing. It was found that the solid-phase wall boundary condition needs to be specified with great care when gas mixing is modeled, with free slip, partial slip and no-slip wall boundary conditions giving substantial differences in the extent of gas back mixing. Axial and radial tracer concentration profiles for different operating conditions are generally in good agreement with experimental data from the literature. Detailed analyses of tracer back mixing are carried out in the second part. Two parameters, the tracer backflow fraction and overall gas backflow fraction, in addition to axial profiles of cross-sectional averaged tracer concentrations, are evaluated for different flow conditions. Qualitative trends are consistent with reported experimental findings. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Demarcation of a new circulating turbulent fluidization regime

AICHE JOURNAL, Issue 3 2009
Xiaobo Qi
Abstract Transient flow behaviors in a novel circulating-turbulent fluidized bed (C-TFB) were investigated by a multifunctional optical fiber probe, that is capable of simultaneously measuring instantaneous local solids-volume concentration, velocity and flux in gas-solid two-phase suspensions. Microflow behavior distinctions between the gas-solid suspensions in a turbulent fluidized bed (TFB), conventional circulating fluidized bed (CFB), the bottom region of high-density circulating fluidized bed (HDCFB), and the newly designed C-TFB were also intensively studied. The experimental results show that particle-particle interactions (collisions) dominate the motion of particles in the C-TFB and TFB, totally different from the interaction mechanism between the gas and solid phases in the conventional CFB and the HDCFB, where the movements of particles are mainly controlled by the gas-particle interactions (drag forces). In addition, turbulence intensity and frequency in the C-TFB are significantly greater than those in the TFB at the same superficial gas velocity. As a result, the circulating-turbulent fluidization is identified as a new flow regime, independent of turbulent fluidization, fast fluidization and dense suspension upflow. The gas-solid flow in the C-TFB has its inherent hydrodynamic characteristics, different from those in TFB, CFB and HDCFB reactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Spanning the flow regimes: Generic fluidized-bed reactor model

AICHE JOURNAL, Issue 7 2003
I. 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]

Investigation of Drying Geldart D and B Particles in Different Fluidization Regimes

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006
Wai 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]