Two-Fluid-Model-Based Full Physics Simulations of Mixing in Noncohesive Wet Fluidized Beds

Askarishahi, Maryam; Salehi, Mohammadsadegh; Radl, Stefan

doi:10.1021/acs.iecr.9b01344

Cited by 18 publications

(8 citation statements)

References 51 publications

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“…The only exception is when the bed falls into the bubble-less expansion regime. This finding is in accordance with our previous study and the study of Luding and Radl et al . This revealed that particle cohesiveness increases the velocity fluctuation at the particle level.…”

Section: Resultssupporting

confidence: 94%

Capability of the TFM Approach to Predict Fluidization of Cohesive Powders

Askarishahi

Salehi

Radl

2022

Ind. Eng. Chem. Res.

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The fluidization behavior of cohesive particles was investigated using an Euler–Euler approach. To do so, a two-fluid model (TFM) platform was developed to account for the cohesivity of particles. Specifically, the kinetic theory of granular flow (KTGF) was modified based on the solid rheology developed by Gu et al. J. Fluid Mech. 2019 . The results of our simulations demonstrated that the modified TFM approach can successfully predict the formation of particle agglomerates and clusters in the fluidized bed, induced by the negative (tensile-dominant) pressure. The formation of such granules and clusters highly depended on the particle Bond number and the tensile pressure prefactor. To evaluate fluidization regimes, a set of simulations was conducted for a wide range of particle cohesivity (e.g., Bond number and tensile pressure prefactor) at two different fluidization numbers of 2 and 5. Our simulation results reveal the formation of four different regimes of fluidization for cohesive particles: (i) bubbling, (ii) bubbling–clustering, (iii) bubble-less fluidization, and (iv) stagnant bed. Comprehensive analysis of the shear-to-yield ratio reveals that the observed regime map is attributed to the competition between the shear stress and yield stress acting on the particles. The obtained regime map can be extended to incorporate the effect of dimensionless velocity and dimensionless diameter as a comprehensive fluidization chart for cohesive particles. Such fluidization charts can facilitate the design of fluidized beds by predicting the conditions under which the formation of particle agglomeration and clustering is likely in fluidized beds.

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Section: Resultssupporting

confidence: 94%

Capability of the TFM Approach to Predict Fluidization of Cohesive Powders

Askarishahi

Salehi

Radl

2022

Ind. Eng. Chem. Res.

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“…Using the least squares method, α coh, 1 for the best fitting is shown to decrease (from 785 to 682) with the increase of B o (see the legend of Figure ). This may be ascribed to the decreased particle velocity for the increase of B o in fluidization of particles; for the particles with decreased velocity and increased B o , they may have more enduring contacts with their neighbors, which may more easily lead to the negative tensile pressure and result in a smaller α coh, 1 .…”

Section: Resultsmentioning

confidence: 99%

Linking discrete particle simulation to continuum properties of the gas fluidization of cohesive particles

Hou

2020

AIChE Journal

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Discrete particle simulation can explicitly consider interparticle forces and obtain microscopic properties of the fluidized cohesive particles, but it is computationally expensive. It is thus pivotal to link the microscopic discrete properties to the macroscopic continuum description of the system for large scale applications. This work studies the fluidization of cohesive particles through the coupled computational fluid dynamics and discrete element method (CFD‐DEM). First, discrete CFD‐DEM results show the increased particle cohesion leads to the severe particle agglomeration which affects the fluidization quality significantly. Then, continuum properties are attained by a weighted time‐volume averaging method, showing that tensile pressure becomes significant as particle cohesion increases. By incorporating Rumpf correlation into the solid pressure equation, the tensile pressure could be predicted consistently with the averaged CFD‐DEM results for different particle cohesion. Finally, those overall steady averaged properties of the bed are obtained for understanding the general macroscopic properties of the system.

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“…These facts motivated our study in rectangular beds that are significantly easier to analyze both experiments and simulations. Besides, the validation study conducted in our previous work 41 demonstrated the reliability of 2D TFM for cylindrical FB in the range of u < 4 u mf .…”

Section: Mathematical Modelmentioning

confidence: 78%

“…To calculate the sample means, the mass fraction x s in each cell was weighted with the cell's solid volume fraction. Readers are referred to our previous work 41 for more information about the encoded modules for sampling procedure. The resulting time history of scalar variance is stored in the disk.…”

Section: Resultsmentioning

confidence: 99%

Quantification of Solid Mixing in Bubbling Fluidized Beds via Two-Fluid Model Simulations

Salehi

Askarishahi

Radl

2020

Ind. Eng. Chem. Res.

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The influence of particle density and fluidization velocity on the mixing behavior of Geldart B particles was investigated in bubbling fluidized beds for various operating conditions using a two-fluid model approach. The simulation results proved that the predicted solid flow pattern for a wide range of Geldart B particles differs from particles of Geldart B/D classification at identical fluidization numbers. Quantitative analysis of the predicted solid velocity variances revealed that the solid axial dispersion rate is higher than the lateral one. In detail, a Peclet number of 1.54 and 3.92 was predicted for axial and lateral mixings, respectively. Also, the solid dispersion and diffusion coefficients were linearly correlated with the excess gas velocity for a range of particle properties. Finally, the characteristic global particle mixing times were computed. Thereby, the characteristic mixing time can be correlated with the particle Froude number, expanded bed height, and solid dispersion coefficient with high accuracy.

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Two-Fluid-Model-Based Full Physics Simulations of Mixing in Noncohesive Wet Fluidized Beds

Cited by 18 publications

References 51 publications

Capability of the TFM Approach to Predict Fluidization of Cohesive Powders

Capability of the TFM Approach to Predict Fluidization of Cohesive Powders

Linking discrete particle simulation to continuum properties of the gas fluidization of cohesive particles

Quantification of Solid Mixing in Bubbling Fluidized Beds via Two-Fluid Model Simulations

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