Numerical Study of Bubbling Gas-Solid Fluidized Beds Hydrodynamics: Influence of Immersed Horizontal Tubes and Data Analysis

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Teklay W. Asegehegn ◽  
Matthias Schreiber ◽  
Hans J. Krautz
Keyword(s):  
Fluidized Beds ◽  
Numerical Study ◽  
Fluid Model ◽  
Vertical Direction ◽  
Expansion Ratio ◽  
Solid Particles ◽  
Superficial Velocity ◽  
Tube Bank ◽  
Horizontal Tubes ◽  
Two Fluid Model

Numerical simulations of two dimensional gas-solid bubbling fluidized beds with and without immersed horizontal tubes were performed using Eulerian - Eulerian Two Fluid Model (TFM). The influences of immersed horizontal tubes and different data analyses techniques on the bed and bubble hydrodynamics were investigated. The results were compared with experimental data and correlations available in the literature.Different ways for extracting and defining hydrodynamic properties, such as bed expansion ratio and bubble properties, were found to influence the simulation results. Furthermore, the time-averaged values showed greater sensitivity to the length of averaging time in the first few seconds. With regard to tube influence, immersed tubes were found to be the main source of bubble breakup. Thus, the calculated mean bubble diameters and rise velocities were found to be lower with tubes than without for the same bed geometry and superficial velocity. The bubble shapes were observed to elongate in the vertical direction in the tube bank region compared to the bed region below and above the tube bank. In addition, the TFM was found to successfully predict the overall time-averaged solid motion and distribution. For beds with immersed tubes, defluidized regions were observed at the upper part of the tubes where solid particles rested without moving. On the other hand, the lower parts of the tubes were usually covered with gas pockets. These effects were seen to reduce with increasing superficial velocity.

scholarly journals Numerical Study of Shear Banding in Flows of Fluids Governed by the Rolie-Poly Two-Fluid Model via Stabilized Finite Volume Methods

Processes ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 810
Author(s):  
Jade Gesare Abuga ◽  
Tiri Chinyoka
Keyword(s):  
Finite Volume ◽  
Numerical Algorithm ◽  
Numerical Study ◽  
Fluid Model ◽  
Shear Banding ◽  
Numerical Algorithms ◽  
Viscoelastic Fluids ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Good Agreement

The flow of viscoelastic fluids may, under certain conditions, exhibit shear-banding characteristics that result from their susceptibility to unusual flow instabilities. In this work, we explore both the existing shear banding mechanisms in the literature, namely; constitutive instabilities and flow-induced inhomogeneities. Shear banding due to constitutive instabilities is modelled via either the Johnson–Segalman or the Giesekus constitutive models. Shear banding due to flow-induced inhomogeneities is modelled via the Rolie–Poly constitutive model. The Rolie–Poly constitutive equation is especially chosen because it expresses, precisely, the shear rheometry of polymer solutions for a large number of strain rates. For the Rolie–Poly approach, we use the two-fluid model wherein the stress dynamics are coupled with concentration equations. We follow a computational analysis approach via an efficient and versatile numerical algorithm. The numerical algorithm is based on the Finite Volume Method (FVM) and it is implemented in the open-source software package, OpenFOAM. The efficiency of our numerical algorithms is enhanced via two possible stabilization techniques, namely; the Log-Conformation Reformulation (LCR) and the Discrete Elastic Viscous Stress Splitting (DEVSS) methodologies. We demonstrate that our stabilized numerical algorithms accurately simulate these complex (shear banded) flows of complex (viscoelastic) fluids. Verification of the shear-banding results via both the Giesekus and Johnson-Segalman models show good agreement with existing literature using the DEVSS technique. A comparison of the Rolie–Poly two-fluid model results with existing literature for the concentration and velocity profiles is also in good agreement.

scholarly journals Computational investigation of liquid-solid slurry flow through an expansion in a rectangular duct

2014 ◽  
Vol 62 (3) ◽  
pp. 234-240 ◽  
Author(s):  
Gianandrea Vittorio Messa ◽  
Stefano Malavasi
Keyword(s):  
Volume Fraction ◽  
Particle Density ◽  
Fluid Model ◽  
Solid Volume Fraction ◽  
Solid Particles ◽  
Rectangular Duct ◽  
Two Phase ◽  
Horizontal Pipe ◽  
Two Fluid Model ◽  
Two Fluid

Abstract The flow of a mixture of liquid and solid particles at medium and high volume fraction through an expansion in a rectangular duct is considered. In order to improve the modelling of the phenomenon with respect to a previous investigation (Messa and Malavasi, 2013), use is made of a two-fluid model specifically derived for dense flows that we developed and implemented in the PHOENICS code via user-defined subroutines. Due to the lack of experimental data, the two-fluid model was validated in the horizontal pipe case, reporting good agreement with measurements from different authors for fully-suspended flows. A 3D system is simulated in order to account for the effect of side walls. A wider range of the parameters characterizing the mixture (particle size, particle density, and delivered solid volume fraction) is considered. A parametric analysis is performed to investigate the role played by the key physical mechanisms on the development of the two-phase flow for different compositions of the mixture. The main focuses are the distribution of the particles in the system and the pressure recovery

A NUMERICAL STUDY OF TWO-PHASE FLOW USING A TWO-DIMENSIONAL TWO-FLUID MODEL

2004 ◽  
Vol 45 (10) ◽  
pp. 1049-1066 ◽  
Author(s):  
Moon-Sun Chung ◽  
Seung-Kyung Pak ◽  
Keun-Shik Chang
Keyword(s):  
Two Phase Flow ◽  
Numerical Study ◽  
Fluid Model ◽  
Phase Flow ◽  
Two Dimensional ◽  
Two Phase ◽  
Two Fluid Model ◽  
Two Fluid

Numerical Simulation of Effect of Internals on Slugging Fluidization and Analysis of Nonuniformity Index

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiaoling Wang ◽  
Liang Yu ◽  
Jun Wang
Keyword(s):  
Experimental Data ◽  
Granular Flow ◽  
Fluidized Beds ◽  
Fluid Model ◽  
Two Fluid Model ◽  
Reasonable Prediction ◽  
Two Fluid ◽  
Radial Nonuniformity ◽  
Flow Nonuniformity

Abstract The Two-Fluid Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) was applied to simulate 3-D dense fluidized beds with different complex internals. The slugging fluidization was found in the simulated results. When the internals were placed into the reactors, the simulated results showed that the slugs were broken up and bubbling fluidization was formed instead of slugging fluidization. The formation, growth, size, and shape of bubbles were validated to ensure a reasonable prediction. Furthermore, the simulated pressure drop was compared with the corresponding experimental data from the dense fluidized beds with different complex internals, and good agreements were observed. Finally, the flow nonuniformity in the dense fluidized beds was evaluated by a developed method. This method extended Radial Nonuniformity Index (RNI) to Face Nonuniformity Index (FNI) and Volume Nonuniformity Index (VNI). From the calculated FNI and VNI, the fluidization quality of the fluidized beds was quantitatively judged as follows: No.3 > No.1> No.2 > No.4 > Without Internal.

scholarly journals Hybrid Two-Fluid DEM Simulation of Gas-Solid Fluidized Beds

2006 ◽  
Author(s):  
Jin Sun ◽  
Francine Battaglia ◽  
S. Subramaniam
Keyword(s):  
Momentum Transfer ◽  
Fluidized Beds ◽  
Structural Information ◽  
Fluid Model ◽  
Fluid Phase ◽  
Transfer Model ◽  
Dem Simulation ◽  
Dem Simulations ◽  
Two Fluid Model ◽  
Two Fluid

Simulations of gas-solid fluidized beds have been carried out using a hybrid simulation method, which couples the discrete element method (DEM) for particle dynamics with the ensemble-averaged two-fluid (TF) equations for the fluid phase. The coupling between the two phases is modeled using an interphase momentum transfer term. The results of the hybrid TF-DEM simulations are compared to experimental data and two-fluid model simulations. It is found that the TF-DEM simulation is capable of predicting general fluidized bed dynamics, i.e., pressure drop across the bed and bed expansion, which are in agreement with experimental measurements and two-fluid model predictions. In addition, the TF-DEM model demonstrates the capability to capture more heterogeneous structural information of the fluidized beds than the two-fluid model alone. The microstructures in fluidized beds are analyzed and the implications to kinetic theory for granular flows are discussed. However, the TF-DEM simulations depend on the form of the interphase momentum transfer model, which can be computed in terms of averaged or instantaneous particle quantities. Various forms of the interphase momentum transfer model are examined, and their suitability to the hybrid TF-DEM simulation approach is evaluated.

scholarly journals A Numerical Study of a Simple Stochastic/ Deterministic Model of Cycle-to-Cycle Combustion Fluctuations in Spark Ignition Engines

2005 ◽  
Vol 11 (3) ◽  
pp. 371-379 ◽  
Author(s):  
G. Litak ◽  
M. Wendeker ◽  
M. Krupa ◽  
J. Czarnigowski
Keyword(s):  
Deterministic Model ◽  
Numerical Study ◽  
Fluid Model ◽  
Combustion Process ◽  
Fuel Mixture ◽  
Spark Ignition ◽  
Spark Ignition Engines ◽  
Fuel Feed ◽  
Lean Combustion ◽  
Two Fluid Model

We examine a simple, fuel-air model of combustion in a spark ignition (SI) engine with indirect injection. In our two-fluid model, variations of fuel mass burned in cycle sequences appear due to stochastic fluctuations of a fuel feed amount. We have shown that a small amplitude of these fluctuations affects considerably the stability of a combustion process strongly depending on the quality of the air-fuel mixture. The largest influence was found in the limit of a lean combustion. The possible effect of nonlinearities in the combustion process has been also discussed.

Transverse instability of plane wavetrains in gas-fluidized beds

1995 ◽  
Vol 303 ◽  
pp. 55-81 ◽  
Author(s):  
M. F. Göz
Keyword(s):  
Plane Wave ◽  
Fluidized Beds ◽  
Fluid Model ◽  
Vertical Component ◽  
Dominant Mode ◽  
Secondary Instability ◽  
Transverse Modes ◽  
Mixed Modes ◽  
Two Fluid Model ◽  
Gas Fluidized Beds

Using a two-fluid model of gas-fluidized beds, it is shown that periodic plane voidage waves travelling against gravity are unstable to perturbations with large transverse wavelength. This secondary instability sets in at arbitrarily small amplitudes of the plane wave and correspondingly small transverse wavenumbers of the two-dimensional perturbation. More precisely, if the bed is wide enough to accommodate sufficiently long horizontal waves, then the plane wave becomes unstable as soon as its amplitude has grown to the order of the square of the transverse wavenumber. The instability can be stationary or oscillatory in nature and has its origin in the interaction between the plane wave and four least-stable modes with small transverse wavenumber. Two of them represent a pair of bubble-like ‘mixed modes‘; the other two are initially, i. e. at the onset of the primary wave, pure transverse modes, one consisting only of an initially pure vertical velocity perturbation of the state of uniform fluidization. Depending on a relation between the eigenvalues of the least-stable modes at the primary bifurcation point, either one of these can be the dominant mode, which becomes (most) unstable along the growing vertically travelling plane wave. While the transverse modes gain longitudinal structure during this process, the mixed modes obtain a vertical component of the vertically averaged velocity as well, so that it appears that the secondary instability described here is a variant of Batchelor & Nitsche's (1991) ‘overturning’ instability found recently for unbounded stratified fluids, see also Batchelor (1993).

Sign in / Sign up

Export Citation Format

Share Document