Evaluation of boundary conditions used to model dilute, turbulent gas/solids flows in a pipe

Benyahia, Sofiane; Syamlal, Madhava; O’Brien, Thomas J.

doi:10.1016/j.powtec.2005.04.002

Cited by 158 publications

(98 citation statements)

References 17 publications

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“…Later, Almuttahar et al [9] confirmed the predictions of [8] in 2D simulations of a circulating fluidized bed (CFB) by showing that using a free slip boundary condition, the near-wall solids volume fraction was in better agreement with experimental data. In their parametric study, they used only four values for φ, namely 0, 0.1, 0.5 and 1.…”

Section: Introductionmentioning

confidence: 91%

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3D Eulerian modeling of thin rectangular gas–solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

2015

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This study aims at investigating the influence of the wall boundary conditions and specifically the specularity coefficient on the fluidization behavior of a thin rectangular fluidized bed by means of 3D numerical simulation employing an Eulerian description of the gas and the solid phases. Thin rectangular fluidized beds have been extensively used in the research literature since it is assumed that the flow behaves like a simpler twodimensional flow and hence they offer validation data for 2D simulations. However, the effects of the front and the back walls are significant, influencing the sensitivity of the fluidization hydrodynamics to the third dimension whose consideration is thus necessary. In order to investigate the influence of the specularity coefficient, φ (a parameter controlling the momentum transfer from the particles to the wall), on the fluidization hydrodynamics, a parametric analysis is conducted and the response of the bubble dynamics, reflecting the gas motion, and the circulation fluxes, displaying the solids motion, are examined in detail. The computational results are compared with available experimental data in order to determine the values of φ that lead to the accurate description of the fluidization hydrodynamics via a two-fold validation strategy which involves the calculation of the circulation time and the solids concentration maps. It is observed that the appropriate value of the specularity coefficient depends rather strongly on the superficial gas velocity of the bed.

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Section: Introductionmentioning

confidence: 91%

“…Benyahia et al [8] conducted 2D axisymmetric simulations of dilute turbulent gas-solid flow in a cylinder and showed that values of φ close to 0 were preferred.…”

Section: Introductionmentioning

confidence: 99%

3D Eulerian modeling of thin rectangular gas–solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

2015

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“…In fact, Altantzis et al [31] recently showed that for a thin rectangular bed, the choice of φ may even alter the fluidization regime; slug formation being characteristic to lower values of φ. In general, it has been determined that low values (∼ 10 −4 − 10 −3 ) are suitable for circulating beds [32,33] while higher values (∼ 0.05-0.5) are appropriate for bubbling beds [15][16][17]30]. This suggests that the choice of φ is dependent on the flow and particle-wall collision properties and may not be universally applicable [1,15,31].…”

Section: Introductionmentioning

confidence: 99%

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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“…The specularity coefficient is an empirical parameter describing the particle-wall collisions. Its value has a range from zero for perfect specular collision to unity for perfect diffuse collision [42] . A smaller value generally represents a smooth wall with less friction.…”

Section: Simulation Systemmentioning

confidence: 99%

CFD investigation of gas-solids flow in a new fluidized catalyst cooler

Yao

Zhang

et al. 2016

Powder Technology

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In our previous work, a new concept of annular catalyst cooler (ACC) was recently proposed and validated experimentally, which showed that an internal circulation of solids can be formed by using two gas distributors and both hydrodynamics and heat transfer can be largely improved. The current work simulated the detailed hydrodynamics of gas-solids flow to advance our understanding of the ACC by using the two-fluid model.. The influence of effective particle diameter dp * and specularity coefficient in solids wall boundary condition are examined and compared with experimental data. Optimum values of dp * =170 m and =0.3 are determined and used in the simulations. The results show that by properly selecting the gas velocities and the position of heat transfer tube, internal solids circulation can be formed. TheACC has a combined hydrodynamic feature of up-and down-flow catalyst coolers with bigger solids volume fraction and smaller particle resident time, which are beneficial for improving heat transfer coefficients. Detailed hydrodynamics of gas-solids flow are obtained, and the influential parameters are examined, which provides valuable information on the design and optimization of such new ACCs.

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Evaluation of boundary conditions used to model dilute, turbulent gas/solids flows in a pipe

Cited by 158 publications

References 17 publications

3D Eulerian modeling of thin rectangular gas–solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

3D Eulerian modeling of thin rectangular gas–solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

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

CFD investigation of gas-solids flow in a new fluidized catalyst cooler

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