ASYMPTOTIC POWER SPECTRUM ANALYSIS OF CHAOTIC BEHAVIOR IN FLUIDIZED BEDS

1994 ◽  
Vol 04 (02) ◽  
pp. 327-341 ◽  
Author(s):  
JIANMIN DING ◽  
SHIU-WING TAM
Keyword(s):  
Power Spectrum ◽  
Fluidized Bed ◽  
Power Law ◽  
Fluidized Beds ◽  
Chaotic Behavior ◽  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Asymptotic Power ◽  
Bubbling Fluidized Bed ◽  
Fluidization Condition

The nonlinear behavior of fluidized beds is analyzed quantitatively using an asymptotic power spectrum method. A model based on kinetic theory is used to compute the voidage signals in a two-dimensional bubbling fluidized bed with a fluidization condition of U/Umf=4, where U is the fluidizing velocity and Umf is the minimum fluidizing velocity. The data for power versus frequency in the asymptotic frequency regime are shown to obey a power-law falloff. This means that the bubbling fluidization under such a fluidization condition cannot be a low-dimensional strange attractor. Pressure fluctuation data, obtained from a three-dimensional bubbling fluidized bed, are also analyzed and clearly show the power-law falloff. This is consistent with previous findings in that the correlation dimension for these data cannot be small (i.e., 2 or 3). The differences between our findings and others are discussed.

Three dimensional multi fluid modeling of Geldart B bubbling fluidized bed with complex inlet geometries

2017 ◽  
Vol 312 ◽  
pp. 89-102 ◽  
Author(s):  
Peter Ostermeier ◽  
Annelies Vandersickel ◽  
Stephan Gleis ◽  
Hartmut Spliethoff
Keyword(s):  
Fluidized Bed ◽  
Three Dimensional ◽  
Fluid Modeling ◽  
Bubbling Fluidized Bed

scholarly journals Three-dimensional numerical simulation of upflow bubbling fluidized bed in opaque tube under high flux solar heating

AIChE Journal ◽  
2018 ◽  
Vol 64 (11) ◽  
pp. 3857-3867 ◽  
Author(s):  
Hadrien Benoit ◽  
Renaud Ansart ◽  
Hervé Neau ◽  
Pablo Garcia Triñanes ◽  
Gilles Flamant ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fluidized Bed ◽  
Three Dimensional ◽  
Solar Heating ◽  
High Flux ◽  
Bubbling Fluidized Bed

Particle-scale modeling of biomass gasification in the three-dimensional bubbling fluidized bed

2019 ◽  
Vol 196 ◽  
pp. 1-17 ◽  
Author(s):  
Shiliang Yang ◽  
Hua Wang ◽  
Yonggang Wei ◽  
Jianhang Hu ◽  
Jia Wei Chew
Keyword(s):  
Fluidized Bed ◽  
Three Dimensional ◽  
Biomass Gasification ◽  
Scale Modeling ◽  
Bubbling Fluidized Bed

Effect of the Shape of the Baffles on the Hydrodynamics of a Fluidized Bed

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Srinivasa Rao Venkata Naga Kaza
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Experimental Studies ◽  
Expansion Ratio ◽  
Blockage Ratio ◽  
Minimum Fluidization Velocity ◽  
Fluidization Velocity ◽  
Minimum Fluidization ◽  
Bubbling Fluidized Bed

Gas flow in a gas–solid fluidized bed is characterized by the predominance of bubbles. When gas flow is more than the minimum fluidization velocity, the top of the fluidized bed may fluctuate vigorously leading to unstable operation. Bed fluctuation and fluidization quality are interrelated. The quality of fluidization can largely be improved by introducing baffles in bubbling and turbulent fluidized beds. In the present work three baffle geometries, i.e., circular, triangular and square are used to determine different hydrodynamic parameters such as minimum fluidization velocity, bed expansion, pressure drop across the bed, fluctuation ratio, expansion ratio, etc. in a bubbling fluidized bed. A new parameter blockage ratio is introduced to analyze the behaviour of baffled fluidized beds. It is found from the current experimental studies that the blockage ratio mainly influences the hydrodynamics of the bed rather than the shape of the baffle.

Comparing ANSYS Fluent® and OpenFOAM® simulations of Geldart A, B and D bubbling fluidized bed hydrodynamics

2019 ◽  
Vol 30 (1) ◽  
pp. 93-118 ◽  
Author(s):  
Cesar Martin Venier ◽  
Andrés Reyes Urrutia ◽  
Juan Pablo Capossio ◽  
Jan Baeyens ◽  
Germán Mazza
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Internal Diameter ◽  
Ansys Fluent ◽  
Content Type ◽  
Current State ◽  
Bubbling Fluidized Bed ◽  
Bubble Sizes

Purpose The purpose of this study is to assess the performance of ANSYS Fluent® and OpenFOAM®, at their current state of development, to study the relevant bubbling fluidized bed (BFB) characteristics with Geldart A, B and D particles. Design/methodology/approach For typical Geldart B and D particles, both a three-dimensional cylindrical and a pseudo-two-dimensional arrangement were used to measure the bed pressure drop and solids volume fraction, the latter by digital image analysis techniques. For a typical Geldart A particle, specifically to examine bubbling and slugging phenomena, a 2 m high three-dimensional cylindrical arrangement of small internal diameter was used. The hydrodynamics of the experimentally investigated BFB cases were also simulated for identical geometries and operating conditions using OpenFOAM® v6.0 and ANSYS Fluent® v19.2 at identical mesh and numerical setups. Findings The comparison between experimental and simulated results showed that both ANSYS Fluent® and OpenFOAM® provide a fair qualitative prediction of the bubble sizes and solids fraction for freely-bubbling Geldart B and D particles. For Geldart A particles, operated in a slugging mode, the qualitative predictions are again quite fair, but numerical values of relevant slug characteristics (length, velocity and frequency) slightly favor the use of OpenFOAM®, despite some deviations of predicted slug velocities. Originality/value A useful comparison of computational fluid dynamics (CFD) software performance for different fluidized regimes is presented. The results are discussed and recommendations are formulated for the selection of the CFD software and models involved.

3-D Modeling of Liquid Injection into Fluidized Beds

2004 ◽  
Vol 2 (1) ◽  
Author(s):  
Joachim Werther ◽  
Stefan Bruhns
Keyword(s):  
Fluidized Bed ◽  
Flow Structure ◽  
Three Dimensional ◽  
Fluidized Bed Reactors ◽  
Three Dimensional Model ◽  
Liquid Injection ◽  
Bubbling Fluidized Bed ◽  
Solids Mixing ◽  
Semi Empirical ◽  
Bubble Splitting

A three-dimensional model has been developed to describe the injection of liquid reactants into fluidized bed reactors operating in the bubbling fluidized bed regime. The model considers the processes of liquid transport and evaporation in the vicinity of the point of injection. The underlying idea, which is supported by previous measurements, is that the particles in the dense suspension phase are wetted by the liquid or gas-liquid spray. The wetted particles are subsequently dried while they are following the gross solids circulation within the bed. The model considers the flow structure of the bubbling fluidized bed and the solids mixing with the aid of a hybrid model which combines semi-empirical models for bubble growth by coalescence and for bubble splitting with a CFD approach for the continuous emulsion phase surrounding the bubbles. Submodels for heat and mass transfer are used to describe the temperature and concentration fields in the vicinity of the injection nozzle and the drying process of the wetted particles with the resulting release of the vaporized injection liquid. The model was validated separately against flow structure measurements, solids tracer measurements and experiments with the injection of water and ethanol, respectively, into beds of FCC particles.

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