Experimental Study of Bubble Behavior in a Two-Dimensional Gas–Solid Tapered Fluidized Bed

The two-dimensional two-fluid model (TFM) incorporating the kinetic theory of granular flow was used to simulate the hydrodynamic behavior of gas bubbles in tapered fluidized beds. Because numerous previous works conducted were mainly focused on the hydrodynamic behavior of the beds such as pressure drop, minimum fluidization velocity, and bed expansion ratio, it is required to investigate one of the most significant parameters in tapered fluidized beds (i.e., gas bubble diameter and rising velocity). The experimental data obtained in our laboratory were compared with the simulation results, and good agreement was found. Effects of the superficial gas velocity, apex angle, particle size, particle density, Geldart groups, initial bed height, operating pressure, and performances of various drag models were investigated carefully. It was found that Syamlal−O'Brien's drag model provides the best predictions for the gas bubble behavior with an RMSE of 11.4% (Syamlal, M.; O'Brien, T. J. Computer simulation of bubbles in a fluidized bed. AIChE Symp. Ser., 1989, 85, 22−31). In addition, with an increase in the particle density and size, operating pressure, and initial bed height, the gas bubble diameter and rising velocity decrease. Moreover, the gas bubble diameter decreases with an increase in the apex angle; however, no significant changes were observed in the gas bubble rising velocity. Furthermore, the gas bubble diameter and rising velocity were much larger for Geldart A particles.

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“…(1 e ) s s s s 0,ss ss s 1/2 (12) where the radial distribution function can be given as follows: 29…”

Section: Momentum Equationsmentioning

confidence: 99%

“…Sahoo and Sarkar studied the gas bubble diameter and rising velocity using an image analysis technique. They investigated the influences of apex angle and superficial gas velocity on the gas bubble diameter, fraction, shape, and rising velocity.…”

Section: Introductionmentioning

confidence: 99%

Gas Bubble Diameter and Rise Velocities in Tapered Fluidized Beds: Experiment and Computational Fluid Dynamics Simulation

Arabi

Sarafan

Dehkordi

2023

Ind. Eng. Chem. Res.

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“…Bubble characteristics can be quantified by photographing/imaging technologies − or analyzing signals from intrusive probes , and nonintrusive pressure transducers . Combining high speed video photography with digital image analysis can enable the measurement of bubble distribution in two-dimensional reactors. − Adopting a threshold determined by either empiricism ,, or the Otsu algorithm, the bubbles can be distinguished from the emulsion phase based on solids concentration distribution, so their properties can be further obtained by using the mathematical morphology algorithm and the connected component labeling algorithm. However, using a global threshold neglects the evident diversity of the flow hydrodynamics throughout the bed, thus is deficient in segregating the contiguous bubbles with blurred boundaries and is incapable of detecting the tiny bubbles .…”

Section: Introductionmentioning

confidence: 99%

“…However, using a global threshold neglects the evident diversity of the flow hydrodynamics throughout the bed, thus is deficient in segregating the contiguous bubbles with blurred boundaries and is incapable of detecting the tiny bubbles. 10 More importantly, it is difficult to obtain bubble information and local detailed flow hydrodynamics synchronously in experiments.…”

Section: Introductionmentioning

confidence: 99%

Machine Learning Assisted Characterization of Local Bubble Properties and Its Coupling with the EMMS Bubbling Drag

Jin,

Hu,

Liu

et al. 2024

Ind. Eng. Chem. Res.

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Empirical correlations for bubble diameter and velocity are incapable of predicting the local bubble behaviors fairly because the impact of local hydrodynamics on bubbles in fluidized beds. Based on image processing, a novel bubble identification method with an adaptive threshold was proposed to distinguish and characterize bubbles in fluidized beds. The information regarding bubble properties and local hydrodynamics can thus be extracted using the big data from highly resolved simulations. Accordingly, the deep neural network was trained to accurately predict local bubble properties, where the inputs were determined by performing correlation analysis and a random forest algorithm. We found Reynolds number, voidage, and relative coordinates are the dominant factors, and a four-variable choice was demonstrated to output satisfactory performance for predicting local bubble diameter and velocity. The model was preliminarily validated by coupling with the EMMS drag into CFD codes, which showed that the accuracy of coarse-grid simulations can be significantly improved.

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A Simplified Bubble Size Relation Compatible with the Energy Minimization Multiscale Drag Model for Studying Hydrodynamics in a 2D Gas–Solid Tapered Fluidized Bed

Sahoo,

Sarkar

2024

steel research int.

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Gas–solid fluidized bed reactors are extensively utilized in direct reduced iron production. In practice, these reactors will have a wide particle size distribution, which is better handled by tapered fluidized beds due to their vertical velocity gradient. Herein, a simplified bubble size relation is proposed to remove implicit interdependency between the bubble size and its drag coefficient in the bubble‐based energy minimization multiscale (EMMS) heterogeneous drag model. Further, the proposed drag model is coupled with the two‐fluid kinetic theory of granular flow model to investigate hydrodynamics. The heterogeneous flow structure predicted by the model is similar to experiments. Further, the bulk parameters such as bed expansion ratio and bubble fraction obtained from the simulations using a simplified EMMS drag model are compared and are found to be in good agreement with the experimental findings, with mean relative deviations of 3.95% and 14.64%, respectively. The time‐averaged bubble fraction and bed expansion ratio are found to increase with air velocity and decrease with taper angle, whereas a reverse trend is observed for the mean particulate fluidized area fraction. Based on the current study, the taper angle between 5° and 10° is found to be most suitable.

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Experimental Study of Bubble Behavior in a Two-Dimensional Gas–Solid Tapered Fluidized Bed

Cited by 9 publications

References 60 publications

Gas Bubble Diameter and Rise Velocities in Tapered Fluidized Beds: Experiment and Computational Fluid Dynamics Simulation

Gas Bubble Diameter and Rise Velocities in Tapered Fluidized Beds: Experiment and Computational Fluid Dynamics Simulation

Machine Learning Assisted Characterization of Local Bubble Properties and Its Coupling with the EMMS Bubbling Drag

A Simplified Bubble Size Relation Compatible with the Energy Minimization Multiscale Drag Model for Studying Hydrodynamics in a 2D Gas–Solid Tapered Fluidized Bed

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