CFD simulation of gas—solid bubbling fluidized bed: an extensive assessment of drag models

Mahinpey, Nader; Vejahati, Farshid; Ellis, Naoko

doi:10.2495/mpf070061

Cited by 8 publications

(9 citation statements)

References 9 publications

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“…Although differences in the predictions have been noted previously (e.g. [43][44][45][46]), there has been no study extensively investigating the suitability of these models with varying bed geometries, particle properties and fluidization regimes. Through simulations conducted as part of this study, it is suggested that the Gidaspow model is more applicable to homogeneous bubbling fluidization (U/U mf <4) while the Syamlal-O'Brien model is more suited to faster fluidization and slugging (U/U mf >4).…”

Section: Governing Equationsmentioning

confidence: 88%

Eulerian–Eulerian simulation of dense solid–gas cylindrical fluidized beds: Impact of wall boundary condition and drag model on fluidization

et al. 2015

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Modeling the hydrodynamics of dense-solid gas flows is strongly affected by the wall boundary condition and in particular, the specularity coefficient φ which characterizes the tangential momentum transfer from the particles to the wall. The focus of this study is to investigate the impact of φ on the fluidization hydrodynamics using a fully Eulerian description of the solid and gas phases in 3D cylindrical coordinates. In order to quantify this impact, tools for characterizing the bubbling dynamics and solids circulation are developed and applied to both lab-scale (diameters 10 cm and 14.5 cm) and pilot-scale (diameter 30 cm) cylindrical beds. Comparison of simulation predictions with experimental data for different fluidization regimes and particle properties suggests that values of φ in the range [0.01,0.3] are suitable for simulating most dense solid-gas flows of practical interest. It is also shown that for this range of φ, the fluidization hydrodynamics are not significantly dependent on the choice of φ especially as the bed diameter is increased. Additionally, 3D validation of the variable φ model by Li and Benyahia [1] shows the bubble diameter predictions to be in excellent agreement with experiment and the average value of φ predicted within the range [0.01,0.3]. Quantifying the impact of φ and establishing an appropriate range is not only important for accurate simulations at both lab and pilot scales but also validation of models and sub-models for a better understanding of the fluidization phenomenon. Finally, a comparison of the Gidaspow and Syamlal-O'Brien gas-solids drag model shows that the former is more applicable to homogeneous bubbling fluidization (U/U mf <4) while the latter is only suitable for high velocities (U/U mf >4) associated with larger bubbles and slugs.

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Section: Governing Equationsmentioning

confidence: 88%

Eulerian–Eulerian simulation of dense solid–gas cylindrical fluidized beds: Impact of wall boundary condition and drag model on fluidization

et al. 2015

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“…The literature on this topic is abundant; from the earlier works of Boemer et al (1998), and Van Wachem et al (1998), to the more recent studies comprising image analysis (Busciglio et al, 2009), particle drag optimisation procedures (Mahinpey et al, 2007;Vejahati et al, 2009), and time averaged volume fraction (Deza et al, 2009;Min et al, 2010;. Particularly, the works of Deza et al (2009) and Min et al (2010) show a reasonable agreement between two dimensional (2D) and three dimensional (3D) simulations and X ray imaging experiments of cylindrical fluidized beds of internal diameter of 0.095 and 0.152 m, respectively.…”

Section: Introductionmentioning

confidence: 99%

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Hernández-Jiménez

Sánchez-Delgado

Gómez-García

et al. 2011

Chemical Engineering Science

108

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a b s t r a c tThis work compares simulation and experimental results of the hydrodynamics of a two dimensional, bubbling air fluidized bed. The simulation in this study has been conducted using an Eulerian Eulerian two fluid approach based on two different and well known closure models for the gas particle interaction: the drag models due to Gidaspow and Syamlal & O'Brien. The experimental results have been obtained by means of Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV) techniques applied on a real bubbling fluidized bed of 0.005 m thickness to ensure its two dimensional behaviour. Several results have been obtained in this work from both simulation and experiments and mutually compared. Previous studies in literature devoted to the comparison between two fluid models and experiments are usually focused on bubble behaviour (i.e. bubble velocity and diameter) and dense phase distribution. However, the present work examines and compares not only the bubble hydrodynamics and dense phase probability within the bed, but also the time averaged vertical and horizontal component of the dense phase velocity, the air throughflow and the instantaneous interaction between bubbles and dense phase. Besides, quantitative comparison of the time averaged dense phase probability as well as the velocity profiles at various distances from the distributor has been undertaken in this study by means of the definition of a discrepancy factor, which accounts for the quadratic difference between simulation and experiments The resulting comparison shows and acceptable resemblance between simulation and experiments for dense phase probability, and good agreement for bubble diameter and velocity in two dimensional beds, which is in harmony with other previous studies. However, regarding the time averaged velocity of the dense phase, the present study clearly reveals that simulation and experiments only agree qualitatively in the two dimensional bed tested, the vertical component of the simulated dense phase velocity being nearly an order of magnitude larger than the one obtained from the PIV experiments. This discrepancy increases with the height above the distributor of the two dimensional bed, and it is even larger for the horizontal component of the time averaged dense phase velocity. In other words, the results presented in this work indicate that the fine agreement commonly encountered between simulated and real beds on bubble hydrodynamics is not a sufficient condition to ensure that the dense phase velocity obtained with two fluid models is similar to that from experimental measurements on two dimensional beds.

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“…= -€ 9 \lP 9 + v · a 11 + ly + fgp 9 g (3) :t (c,.psUs) + "il· (EsPsU5 Us) = -t 8 v P 9 + v · as -1 9 + t:sp.,g (4) The expressions on the left side are the net rate of momentum increase and the net rate of momentum transfer by convection. The right side includes contributions for buoyancy caused by the fluid pressure gradient, the stress tensors (a).…”

Section: Numerical Modelmentioning

confidence: 99%

“…Further details related to the constitutive relations in Eqns. (3)(4)(5) can be found in the MFIX theory guide f6].…”

Section: Numerical Modelmentioning

confidence: 99%

“…Taghipour eta!. [31 compared the Syamlal-O'Brien, Gidaspow, and Wen-Yu models with experimental data and found that for relatively large Geldart B particles, the models predicted the hydrodynamics of the bed reasonably well. Another extensive model comparison in fluidized beds was made by Mahinpey et al [4], comparing bed expansion and pressure drop with different superficial velocities in a fluidized bed using the Di Felice, Gibilaro, Koch, Syamlal-O'Brien, Arastoopur, Syamlal-0' Brien (adjusted), Di Felice (adjusted), Gidaspow, ZhangReese, and Wen-Yu drag models. All of the models gave acceptable qualitative agreement with experimental data; however results for the adjusted models of Syamlal-O'Brien and Di Fe-lice showed an improvement in quantitative predictions of the bed hydrodynamics.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modeling a Biomass Fluidizing Bed With Side Port Air Injection

Deza

Battaglia

Heindel

2009

Volume 1: Symposia, Parts A, B and C

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Fluidized beds are used to gasify materials such as coal or biomass in the production of producer gas. Modeling these reactors using computational fluid dynamics is advantageous when performing parametric studies for design and scale-up. While two-dimensional simulations are easier to perform than threedimensional simulations, they may not capture the proper physics. This paper compares two-and threedimensional simulations with experiments for a reactor geometry with side port air injection. The side port is located within the bed region so that the injected air can help promote mixing. Of interest in this study is validating the hydrodynamics of fluidizing biomass. Two operating conditions of the fluidized bed are studied for superficial gas velocities of 1.5Umf and 3.0Umf , where Umf is the minimum fluidization velocity. The material used to represent biomass is ground walnut shell because it tends to fluidize uniformly and falls within the Geldart type B classification. The simulations are compared to experimental data of time-averaged local gas holdup values using X-ray computed tomography. Results indicate that for the conditions of this study, two-dimensional simulations overpredict the gas holdup trends when compared to the experiments. However, the three-dimensional simulations compare exceptionally well with the experiments, thus predicting the fluidization hydrodynamics, irrespective of flowrate or complexity due to the side air port. Furthermore, the study demonstrates the importance of using a three-dimensional model for bubbling fluidized beds with complex physics.

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CFD simulation of gas—solid bubbling fluidized bed: an extensive assessment of drag models

Cited by 8 publications

References 9 publications

Eulerian–Eulerian simulation of dense solid–gas cylindrical fluidized beds: Impact of wall boundary condition and drag model on fluidization

Eulerian–Eulerian simulation of dense solid–gas cylindrical fluidized beds: Impact of wall boundary condition and drag model on fluidization

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Modeling a Biomass Fluidizing Bed With Side Port Air Injection

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