Prediction of the Flotsam Component in a Gas-Fluidized Bed of Two Dissimilar Solids

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Alberto Di Renzo ◽  
Francesco P. Di Maio ◽  
Vincenzino Vivacqua
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Simple Model ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Computational Simulations ◽  
The Difference ◽  
Gas Fluidized Beds

In the present paper the segregating behaviour of solids of different size and density in gas-fluidized beds is studied. In particular, the attention is focussed on pairs composed of a bigger/less dense species and a smaller/denser species. Typical industrial examples of such combinations are encountered in fluidized beds of biomass/sand mixtures. Their behaviour is not easily predictable, as the segregation tendency promoted by the difference in density is counteracted by the difference in size. While typically the denser component is expected to appear predominantly at the bottom of the fluidized bed, experiments on mixtures exhibiting the reverse behaviour have been reported (e.g. Chiba et al., 1980).A simple model to predict the segregation direction of the components, i.e. which species will segregate to the top of the bed (the flotsam), depending upon their difference in properties (size, density) and the mixture composition, is discussed. The predicted behaviour is compared with experimental data available in the literature and agreement is found for the majority of them. For one mixture, experiments are conducted as well as computational simulations based on the combined Discrete Element Method and Computational Fluid Dynamics (DEM-CFD) approach. This allows investigating how an initially mixed bed upon suspension evolves as a result of the segregation prevalence in the bed.

Modeling a Fluidized Bed Dryer through Computational Fluid Dynamics and Discrete Element Method

2021 ◽  
Author(s):  
Sebastian Alexander Pérez Cortés ◽  
Yerko Rafael Aguilera Carvajal ◽  
Juan Pablo Vargas Norambuena ◽  
Javier Antonio Norambuena Vásquez ◽  
Juan Andrés Jarufe Troncoso ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
Discrete Element ◽  
Fluidized Bed Dryer ◽  
Element Method

Transient Computational Fluid Dynamics/Discrete Element Method Simulation of Gas–Solid Flow in a Spouted Bed and Its Validation by High-Speed Imaging Experiment

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Ling Zhou ◽  
Lingjie Zhang ◽  
Weidong Shi ◽  
Ramesh Agarwal ◽  
Wei Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
High Speed ◽  
Discrete Element ◽  
Bubble Shape ◽  
High Speed Imaging ◽  
Bed Height ◽  
Simulation Results

A coupled computational fluid dynamics (CFD)/discrete element method (DEM) is used to simulate the gas–solid two-phase flow in a laboratory-scale spouted fluidized bed. Transient experimental results in the spouted fluidized bed are obtained in a special test rig using the high-speed imaging technique. The computational domain of the quasi-three-dimensional (3D) spouted fluidized bed is simulated using the commercial CFD flow solver ANSYS-fluent. Hydrodynamic flow field is computed by solving the incompressible continuity and Navier–Stokes equations, while the motion of the solid particles is modeled by the Newtonian equations of motion. Thus, an Eulerian–Lagrangian approach is used to couple the hydrodynamics with the particle dynamics. The bed height, bubble shape, and static pressure are compared between the simulation and the experiment. At the initial stage of fluidization, the simulation results are in a very good agreement with the experimental results; the bed height and the bubble shape are almost identical. However, the bubble diameter and the height of the bed are slightly smaller than in the experimental measurements near the stage of bubble breakup. The simulation results with their experimental validation demonstrate that the CFD/DEM coupled method can be successfully used to simulate the transient gas–solid flow behavior in a fluidized bed which is not possible to simulate accurately using the granular approach of purely Euler simulation. This work should help in gaining deeper insight into the spouted fluidized bed behavior to determine best practices for further modeling and design of the industrial scale fluidized beds.

scholarly journals Simulation of different gas–solid flow regimes using a drag law derived from lattice Boltzmann simulations

2018 ◽  
Vol 10 (4) ◽  
pp. 202-214
Author(s):  
Yeping Xie ◽  
Yongquan Liu ◽  
Linmin Li ◽  
Chang Xu ◽  
Baokuan Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
Lattice Boltzmann ◽  
Flow Regimes ◽  
Discrete Element ◽  
Solid Flow ◽  
Lattice Boltzmann Simulations ◽  
Drag Law

Gas–solid flows are widely found in various industrial processes, e.g. chemical engineering and sand ingestion test for aero-engine; the interaction between continuum and discrete particles in such systems always leads to complex phase structures of which fundamental understandings are needed. Within the OpenFOAM, the present work uses the discrete element method combined with the computational fluid dynamics to investigate the gas–solid flow behaviors in a dense fluidized bed under various conditions. A drag law which is for polydisperse systems derived from lattice Boltzmann simulations is incorporated into the computational fluid dynamics-discrete element method framework and its suitability for different flow regimes is investigated. The regimes including, namely slugging bed, jet-in-fluidized bed, spout fluidization, and intermediate, are simulated and validated against experiments. The results show that the lattice Boltzmann drag relation performs well in capturing characteristics of different gas–solid flow regimes. Good agreements are also obtained quantitatively by comparisons of pressure drop fluctuation, and time-averaged gas velocity and particle flux.

scholarly journals A Validation Study for the Hydrodynamics of Biomass in a Fluidized Bed

2008 ◽  
Author(s):  
Mirka Deza ◽  
Francine Battaglia ◽  
Theodore J. Heindel
Keyword(s):  
Experimental Data ◽  
Fluidized Bed ◽  
Validation Study ◽  
Fluidized Beds ◽  
Coefficient Of Restitution ◽  
Computational Simulations ◽  
Eulerian Model ◽  
X Ray ◽  
Solid Phases ◽  
Interpenetrating Continua

Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work focused on computational simulations of a fluidized bed using a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. Hydrodynamic results from the simulations were quantitatively compared with X-ray flow visualization studies of a similar bed. It was found that the Gidaspow model can accurately predict the hydrodynamics of the biomass in a fluidized bed. The coefficient of restitution of biomass was fairly high and did not affect the hydrodynamics of the bed; however, the model was more sensitive to particle sphericity variation.

Discrete element method–computational fluid dynamics analyses of flexible fibre fluidization

2021 ◽  
Vol 910 ◽  
Author(s):  
Yiyang Jiang ◽  
Yu Guo ◽  
Zhaosheng Yu ◽  
Xia Hua ◽  
Jianzhong Lin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Discrete Element Method ◽  
Discrete Element ◽  
Dynamics Analyses ◽  
Element Method

Abstract

Expulsion of particles from a buoyant blob in a fluidized bed

1994 ◽  
Vol 278 ◽  
pp. 63-81 ◽  
Author(s):  
G. K. Batchelor ◽  
J. M. Nitsche
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Particle Concentration ◽  
Small Concentration ◽  
Numerical Calculations ◽  
Significant Feature ◽  
Average Particle ◽  
Remarkable Property ◽  
Gas Fluidized Beds ◽  
Secondary Instabilities

It is a significant feature of most gas-fluidized beds that they contain rising ‘bubbles’ of almost clear gas. The purpose of this paper is to account plausibly for this remarkable property first by supposing that primary and secondary instabilities of the fluidized bed generate compact regions of above-average or below-average particle concentration, and second by invoking a mechanism for the expulsion of particles from a buoyant compact blob of smaller particle concentration. We postulate that the rising of such an incipient bubble generates a toroidal circulation of the gas in the bubble, roughly like that in a drop of liquid rising through a second liquid of larger density, and that particles in the blob carried round by the fluid move on trajectories which ultimately cross the bubble boundary. Numerical calculations of particle trajectories for practical values of the relevant parameters show that a large percentage of particles, of such small concentration that they move independently, are expelled from a bubble in the time taken by it to rise through a distance of several bubble diameters.Similar calculations for a liquid-fluidized bed show that the expulsion mechanism is much weaker, as a consequence of the larger density and viscosity of a liquid, which is consistent with the absence of observations of relatively empty bubbles in liquid-fluidized beds.It is found to be possible, with the help of the Richardson-Zaki correlation, to adjust the results of these calculations so as to allow approximately for the effect of interaction of particles in a bubble in either a gas- or a liquid-fluidized bed. The interaction of particles at volume fractions of 20 or 30 % lengthens the expulsion times, although without changing the qualitative conclusions.

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