A DEM study of bubble formation in Group B fluidized beds with and without cohesive inter-particle forces

2007 ◽  
Vol 62 (1-2) ◽  
pp. 159-166 ◽  
Author(s):  
Jai Kant Pandit ◽  
X.S. Wang ◽  
M.J. Rhodes
Keyword(s):  
Fluidized Beds ◽  
Bubble Formation ◽  
Group B

Fully developed travelling wave solutions and bubble formation in fluidized beds

1997 ◽  
Vol 334 ◽  
pp. 157-188 ◽  
Author(s):  
B. J. GLASSER ◽  
I. G. KEVREKIDIS ◽  
S. SUNDARESAN
Keyword(s):  
Numerical Integration ◽  
Fluidized Beds ◽  
Bubble Formation ◽  
Travelling Wave ◽  
Numerical Continuation ◽  
Travelling Wave Solutions ◽  
Wave Solutions ◽  
Averaged Equations ◽  
Wide Range ◽  
Direct Numerical Integration

It is well known that most gas fluidized beds of particles bubble, while most liquid fluidized beds do not. It was shown by Anderson, Sundaresan & Jackson (1995), through direct numerical integration of the volume-averaged equations of motion for the fluid and particles, that this distinction is indeed accounted for by these equations, coupled with simple, physically credible closure relations for the stresses and interphase drag. The aim of the present study is to investigate how the model equations afford this distinction and deduce an approximate criterion for separating bubbling and non-bubbling systems. To this end, we have computed, making use of numerical continuation techniques as well as bifurcation theory, the one- and two-dimensional travelling wave solutions of the volume-averaged equations for a wide range of parameter values, and examined the evolution of these travelling wave solutions through direct numerical integration. It is demonstrated that whether bubbles form or not is dictated by the value of Ω = (ρsv3t/Ag) 1/2, where ρs is the density of particles, vt is the terminal settling velocity of an isolated particle, g is acceleration due to gravity and A is a measure of the particle phase viscosity. When Ω is large (> ∼ 30), bubbles develop easily. It is then suggested that a natural scale for A is ρsvtdp so that Ω2 is simply a Froude number.

scholarly journals Bubble Properties in Bubbling and Turbulent Fluidized Beds for Particles of Geldart’s Group B

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1098
Author(s):  
Tom Wytrwat ◽  
Mahdi Yazdanpanah ◽  
Stefan Heinrich
Keyword(s):  
Fluidized Beds ◽  
Pressure Fluctuations ◽  
Bubble Velocity ◽  
Turbulent Regime ◽  
Bubble Behavior ◽  
Low Velocity ◽  
Group B ◽  
Superficial Gas Velocity ◽  
Bubble Properties

Predicting bubble properties in fluidized beds is of high interest for reactor design and modeling. While bubble sizes and velocities for low velocity bubbling fluidized beds have been examined in several studies, there have been only few studies about bubble behavior at superficial gas velocities up into the turbulent regime. For this reason, we performed a thorough investigation of the size, shape and velocity of bubbles at superficial gas velocities ranging from 0.18 m/s up to 1.6 m/s. Capacitance probes were used for the determination of the bubble properties in three different fluidized bed facilities sized of 0.1 m, 0.4 m and 1 m in diameter. Particles belonging to Geldart’s group B (Sauter mean diameter: 188 µm, solid density: ρs = 2600 kg/m3) were used. Correlations for the determination of bubble phase holdup, vertical bubble length and bubble velocity are introduced in this work. The shape of bubbles was found to depend on superficial gas velocity. This implies that at large superficial gas velocities the horizontal size of a bubble must be much smaller in comparison to its vertical size. This leads to a decrease of pressure fluctuations, which is observed in the literature as a characteristic of transitioning into a turbulent regime.

CFD Simulations of Gas Fluidized Beds Using Alternative Eulerian-Eulerian Modelling Approaches

2002 ◽  
Vol 1 (1) ◽  
Author(s):  
Paola Lettieri ◽  
Luca Cammarata ◽  
Giorgio D. M. Micale ◽  
John Yates
Keyword(s):  
Kinetic Model ◽  
Fluidized Beds ◽  
Numerical Procedure ◽  
Commercial Code ◽  
Fluid Bed ◽  
Group A ◽  
Gas Fluidized Beds ◽  
Group B ◽  
Particle Bed ◽  
First Time

A commercially available Computational Fluid-Dynamics code, CFX-4, has been chosen to carry out computer simulations of gas fluidized beds. In this study, the Eulerian-Eulerian granular kinetic model, which is a standard option of the code, has been used. Fluid-bed simulations of Geldart Group B materials have been performed using the granular kinetic model, spanning three hydrodynamic regimes: bubbling, slugging and turbulent fluidization. Furthermore, an alternative Eulerian-Eulerian model, the so-called "particle-bed model", has been implemented for the first time within a commercial code, and results are presented from simulations of the bubbling and slugging fluidization of a Geldart Group B material, and for the homogeneous fluidization of a Group A material. A numerical procedure has been developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations with the particle-bed model. Results show that both the granular kinetic model approach and the particle-bed model are able to describe significant aspects of the investigated fluidization regimes.

2D and 3D CFD Simulations of Bubbling Fluidized Beds Using Eulerian-Eulerian Models

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Luca Cammarata ◽  
Paola Lettieri ◽  
Giorgio D. M. Micale ◽  
Derek Colman
Keyword(s):  
Kinetic Model ◽  
Bubble Size ◽  
Fluidized Beds ◽  
Numerical Procedure ◽  
Cfd Simulations ◽  
3D Simulations ◽  
Gas Fluidized Beds ◽  
Group B ◽  
Particle Bed ◽  
2D And 3D

This paper reports on CFD simulations of freely bubbling gas fluidized beds using CFX-4, a commercial code developed by CFX Ltd. (formerly AEA Technology). Two Eulerian-Eulerian modelling approaches, the granular kinetic model and the particle-bed model (Gibilaro, 2001), have been investigated. The particle bed model has been recently implemented in CFX-4 for 2D simulations and a numerical procedure was developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations, see Lettieri et al. (2003). The work has now been extended to 3D simulations and qualitative and quantitative results are presented in this paper for both the 2D and 3D simulations of the bubbling fluidization of a Geldart Group B material. Results on bed expansion, bubble size and bubble hold-up are reported. In particular, simulated bubble size is compared with predictions given by the Darton et al. (1977) equation at different bed heights. The paper shows that the bubble size predicted by both the granular kinetic model and the particle-bed model is in good agreement with the Darton's equation.

On the formation of bubbles in gas-particulate fluidized beds

1979 ◽  
Vol 94 (2) ◽  
pp. 353-367 ◽  
Author(s):  
Jerome B. Fanucci ◽  
Nathan Ness ◽  
Ruey-Hor Yen
Keyword(s):  
Fluidized Beds ◽  
Method Of Characteristics ◽  
Bubble Formation ◽  
Shock Formation ◽  
Fluid Viscosity ◽  
Phase Flow ◽  
Fluid Density ◽  
Pressure Function ◽  
Two Phase ◽  
Particulate Size

The method of characteristics is applied to the nonlinear equations describing two-phase flow in a fluidized bed. The method shows how a small disturbance changes with time and distance and can, eventually, produce a flow discontinuity similar to a shock wave in gases. The parameters entering the analysis are the amplitude of the initial disturbance, the wavelength of the original disturbance, the particulate pressure function, the particulate size, the uniform fluidization voidage, the uniform fluidization velocity, the fluid viscosity, the particulate density, and the fluid density. A parametric study shows that the following factors delay shock formation: a decrease in particulate size, an increase in bed density, an increase in fluid viscosity, and a decrease in particulate density. Experimental data on bubble formation in gas-particulate fluidized beds show that these same factors delay bubble formation. It is concluded, therefore, that the shock front and the bubble front are one and the same thing.

Sign in / Sign up

Export Citation Format

Share Document