Analysis of Solid Structures and Stresses in a Gas Fluidized Bed

2007 ◽  
Author(s):  
Jin Sun ◽  
Francine Battaglia
Keyword(s):  
Kinetic Theory ◽  
Normal Stress ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Coarse Graining ◽  
Contact Forces ◽  
Normal Contact ◽  
Stress Components ◽  
Force Network

Structures and stresses for the solid phase in a gas-solid fluidized bed are analyzed using results from hybrid simulations. The hybrid method couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) equations for the gas phase. The coupling between the two phases is modeled using an interphase momentum transfer term. Structure information is characterized using force network size distribution, which shows no large force network existing in the fluidized bed. The normal contact forces have an exponentially decaying distribution. Solid phase continuum fields (local volume fraction, strain rate, stress tensor, and granular temperature) are computed using a coarse-graining process. The results show that the stress has difference in normal stress components. The collisional contribution is larger than the kinetic contribution and spatially correlated to force networks. Stresses are also computed using a kinetic theory stress model. It is demonstrated that the kinetic theory model predicts no difference in normal stress components and larger normal stresses than those computed from the coarse-graining process.

CFD Modelling of a Fluidized Bed Gasifier; Effects of Drag Model and Bed Heights

2014 ◽  
Vol 699 ◽  
pp. 730-735
Author(s):  
Kamariah Md Isa ◽  
Kahar Osman ◽  
Nik Rosli Abdullah ◽  
Azfarizal Mukhtar ◽  
Nor Fadzilah Othman
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Multiphase Model ◽  
Cfd Modelling ◽  
Drag Model ◽  
Bed Height ◽  
Representative Unit Cell ◽  
Fluidized Bed Gasifier ◽  
Drag Models

One of the unresolved issues in using the gasifier is the inability to determine the occurrence of the transition regime of fluidized bed. In modeling gas-solid phase, drag force is one of the main mechanisms for inter-phase momentum transfer. Thus, a simulation of fluidized bed was developed to study the effect of using various drag models over different bed height of H/D ratio such as 0.5, 1 and 2. A two dimensional model using Eulerian-Granular Multiphase Model (EGM) based on two fluid models have been used to simulate hydrodynamics of a bubbling fluidized beds. Gas-solid interactions are modeled via inter-phase of a drag model. The drag correlations of Gidaspow, Wen Yu, Syamlal-O'Brien, Hill Koch Ladd (HKL) and Representative Unit Cell (RUC) were implemented to simulate the interaction between phases. From this study, we found that different H/D ratio such as 0.5, 1 and 2 yields different volume fraction as increasing bed height slows kinetic transport of particle sand to the upper side of the bed. Besides that, different H/D ratio also resulted in different velocity vector. The results also show that Wen Yu and Syamlal-O'Brien are sufficient enough in detecting the change from one regime to another regardless of the bed height.

scholarly journals Normal stress differences in dense suspensions

2018 ◽  
Vol 857 ◽  
pp. 200-215 ◽  
Author(s):  
Ryohei Seto ◽  
Giulio G. Giusteri
Keyword(s):  
Normal Stress ◽  
Simple Shear ◽  
Volume Fraction ◽  
Hydrodynamic Lubrication ◽  
Contact Forces ◽  
Simple Shear Flow ◽  
First Normal Stress Difference ◽  
Dense Suspensions ◽  
Normal Stress Differences ◽  
Dynamics Simulations

The presence and the microscopic origin of normal stress differences in dense suspensions under simple shear flows are investigated by means of inertialess particle dynamics simulations, taking into account hydrodynamic lubrication and frictional contact forces. The synergic action of hydrodynamic and contact forces between the suspended particles is found to be the origin of negative contributions to the first normal stress difference $N_{1}$ , whereas positive values of $N_{1}$ observed at higher volume fractions near jamming are due to effects that cannot be accounted for in the hard-sphere limit. Furthermore, we found that the stress anisotropy induced by the planarity of the simple shear flow vanishes as the volume fraction approaches the jamming point for frictionless particles, while it remains finite for the case of frictional particles.

Three-dimensional computational fluid dynamics investigation of hydrodynamics behaviour of gas–solid flow in fluidized bed of Geldart D particles

2021 ◽  
pp. 095440892098769
Author(s):  
Fazia Aiche ◽  
Salah Belaadi ◽  
Adel Lalaoua ◽  
Abdallah Sofiane Berrouk ◽  
Abdelwahid Azzi
Keyword(s):  
Fluidized Bed ◽  
Gas Flow ◽  
Turbulence Modeling ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Model ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Industrial Processes ◽  
Cyclic Process

Fluidized beds are widely used in many industrial processes as they ensure the desirable high-intensity heat and mass transfers between gas and particles and offer the possibility to perform operations in a continuous mode and powders recycling. Some of these industrial processes use Geldart D type of powders and operate in the slugging mode. This paper presents a 3 D numerical model of gas-solid flows in a fluidized bed based on the Two-Fluid Model (TFM). Turbulence modeling (k- ε) was used to predict flow behavior in fluidized bed of Geldart D particles. The solid phase consists of Geldart D powders and the gas flow is in a slug regime. The numerical results are validated against the experimental work of Azzi et al. Model predictions on flow patterns, bed expansion, volume fraction time series and pressure drop fluctuations are presented and discussed in details in order to demonstrate the cyclic process of slug formation (onset, growth, rising and bursting of slugs) and its effects on the overall performance of beds fluidizing Geldart D type of powders.

Numerical Analysis on the Dynamic Behaviour of Fluidized Bed Reactor

2015 ◽  
Vol 813-814 ◽  
pp. 718-722
Author(s):  
P.M. Suhaile ◽  
S. Rupesh ◽  
C. Muraleedharan ◽  
P. Arun
Keyword(s):  
Fluid Dynamics ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Model ◽  
Turbulence Models ◽  
Fluidized Bed Reactor ◽  
Two Fluid Model ◽  
Bed Expansion ◽  
Phase Transport

A gas-solid multiphase flow is simulated using CFD to investigate the fluid dynamics of a fluidized bed reactor. The simulation is based on Euler-Euler two fluid model where Kinetic Theory of Granular Flow is used for predicting the solid phase transport properties. The simulation procedure is validated by reproducing and comparing hydrodynamic parameters with those available in the literature. The effect of different turbulence models on bed fluid dynamics is analyzed and k-ε RNG per-phase model is found to have better prediction accuracy compared to other models. The minimum fluidization velocity, granular temperature, bed expansion, particle velocity and volume fraction are determined by the model.

scholarly journals Coarse-Grain DEM Modelling in Fluidized Bed Simulation: A Review

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 279
Author(s):  
Alberto Di Renzo ◽  
Erasmo Napolitano ◽  
Francesco Di Maio
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Circulating Fluidized Bed ◽  
Coarse Graining ◽  
Pilot Scale ◽  
Contact Forces ◽  
Coarse Grain ◽  
Fluidized Bed Reactors ◽  
Future Directions ◽  
Spouted Beds

In the last decade, a few of the early attempts to bring CFD-DEM of fluidized beds beyond the limits of small, lab-scale units to larger scale systems have become popular. The simulation capabilities of the Discrete Element Method in multiphase flow and fluidized beds have largely benefitted by the improvements offered by coarse graining approaches. In fact, the number of real particles that can be simulated increases to the point that pilot-scale and some industrially relevant systems become approachable. Methodologically, coarse graining procedures have been introduced by various groups, resting on different physical backgrounds. The present review collects the most relevant contributions, critically proposing them within a unique, consistent framework for the derivations and nomenclature. Scaling for the contact forces, with the linear and Hertz-based approaches, for the hydrodynamic and cohesive forces is illustrated and discussed. The orders of magnitude computational savings are quantified as a function of the coarse graining degree. An overview of the recent applications in bubbling, spouted beds and circulating fluidized bed reactors is presented. Finally, new scaling, recent extensions and promising future directions are discussed in perspective. In addition to providing a compact compendium of the essential aspects, the review aims at stimulating further efforts in this promising field.

scholarly journals Effect of confinement in wall-bounded non-colloidal suspensions

2016 ◽  
Vol 799 ◽  
pp. 100-127 ◽  
Author(s):  
Stany Gallier ◽  
Elisabeth Lemaire ◽  
Laurent Lobry ◽  
Francois Peters
Keyword(s):  
Normal Stress ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Colloidal Suspensions ◽  
Wall Slip ◽  
Hexagonal Structure ◽  
Normal Stress Difference ◽  
Contact Forces ◽  
Wall Region ◽  
Stress Difference

This paper presents three-dimensional numerical simulations of non-colloidal dense suspensions in a wall-bounded shear flow at zero Reynolds number. Simulations rely on a fictitious domain method with a detailed modelling of particle–particle and wall–particle lubrication forces, as well as contact forces including particle roughness and friction. This study emphasizes the effect of walls on the structure, velocity and rheology of a moderately confined suspension (channel gap to particle radius ratio of 20) for a volume fraction range $0.1\leqslant {\it\phi}\leqslant 0.5$. The wall region shows particle layers with a hexagonal structure. The size of this layered zone depends on volume fraction and is only weakly affected by friction. This structure implies a wall slip which is in good accordance with empirical models. Simulations show that this wall slip can be mitigated by reducing particle roughness. For ${\it\phi}\lessapprox 0.4$, wall-induced layering has a moderate impact on the viscosity and second normal stress difference $N_{2}$. Conversely, it significantly alters the first normal stress difference $N_{1}$ and can result in positive $N_{1}$, in better agreement with some experiments. Friction enhances this effect, which is shown to be due to a substantial decrease in the contact normal stress $|{\it\Sigma}_{xx}^{c}|$ (where $x$ is the velocity direction) because of particle layering in the wall region.

scholarly journals Simulation of Coal and Biomass Cofiring with Different Particle Density and Diameter in Bubbling Fluidized Bed under O2/CO2 Atmospheres

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Chao Chen ◽  
Xuan Wu ◽  
Lingling Zhao
Keyword(s):  
Fluidized Bed ◽  
Mass Fraction ◽  
Volume Fraction ◽  
Solid Phase ◽  
Particle Density ◽  
Reaction Rates ◽  
High Mass ◽  
Species Concentration ◽  
Bubbling Fluidized Bed ◽  
Biomass Cofiring

A 2D dynamic model for a bubbling fluidized bed (BFB) combustor has been developed for simulating the coal and biomass cofiring process under 21% O2/79% CO2 atmosphere in a 6 kWth bubbling fluidized bed, coupled with the Euler-Euler two-phase flow model. The kinetic theory of binary granular mixtures is employed for the solid phase in order to map the effect of particle size and density. The distribution of temperature, volume fraction, velocity, gas species concentration, and reaction rates are studied with numerical calculations. The simulated temperature distribution along the height of the combustor and outlet gas concentrations show good agreement with experimental data, validating the accuracy and reliability of the developed cofiring simulation model. As indicated in the results, there are two high temperature zones in the combustor, which separately exist at the fuel inlet and dilute phase. The reaction rates are related to the species concentration and temperature. The higher concentration and temperature lead to the larger reaction rates. It can be seen that all of the homogeneous reaction rates are larger at the fuel inlet region because of rich O2 and volatiles. High mass fraction of volatile gas is found at the fuel inlet, and the main reburning gas at the dilute phase is CH4. The mass fraction distribution of CO is related to the volume fraction of fuel which is due to the fact that the source of CO is not only from the devolatilization but also from the gasification. On the basis of this theoretical study, a better understanding of flow and combustion characteristics in biomass and coal cofiring under oxy-fuel atmospheres could be achieved.

scholarly journals Experimental Preliminary  Analysis of the Fluid Drag Effect in Rapid and Long-runout Flowlike Landslides

2021 ◽  
Author(s):  
Yang Gao ◽  
Haoyuan Gao ◽  
Bin Li ◽  
Tongyao Wei ◽  
Zhuang Li
Keyword(s):  
Liquid Phase ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Liquid Velocity ◽  
Solid Phase ◽  
Contact Forces ◽  
Phase Flow ◽  
Long Runout ◽  
Two Phase ◽  
Frictional Forces

Abstract During a landslide, the multi-phase nature of landslide debris defines its mobility. Eventually, frictional forces cause the slide energy to dissipate, and contact forces transmit the energy into nearby material. To analyze the dynamic characteristics of high-velocity long-runout landslides, we conducted flume model tests to empirically determine the mobility characteristics of flow-like landslides with various slide materials. Our conclusions are as follows: (1) Liquid-phase flow-like landslides are highly mobility and have long runout; solid-phase flow-like landslides are highly destructive because of their higher kinetic energy; and two-phase flow-like landslides are both highly mobility. (2) During a two-phase flow-like landslide, the mobility ability of the liquid-phase material is stronger than that of the solid-phase material; when the liquid slide volume fraction is sufficiently large, the liquid phase exerts a drag force on the solid phase. (3) Various liquids exert different drag effects on the solid; the solid-liquid velocity difference and the liquid viscosity determine the drag intensity and the mobility and depositional characteristics of the landslide.

A Nonlinear Rail Vehicle Dynamics Computer Program SAMS/Rail: Part 1—Theory and Formulations

2009 ◽  
Author(s):  
Khaled E. Zaazaa ◽  
Brian Whitten ◽  
Brian Marquis ◽  
Erik Curtis ◽  
Magdy El-Sibaie ◽  
...  
Keyword(s):  
High Speed ◽  
Dynamic Performance ◽  
Three Dimensional ◽  
Contact Element ◽  
Contact Forces ◽  
Simulation Code ◽  
Vehicle Performance ◽  
Normal Contact ◽  
Advantages And Disadvantages ◽  
High Speed Trains

Accurate prediction of railroad vehicle performance requires detailed formulations of wheel-rail contact models. In the past, most dynamic simulation tools used an offline wheel-rail contact element based on look-up tables that are used by the main simulation solver. Nowadays, the use of an online nonlinear three-dimensional wheel-rail contact element is necessary in order to accurately predict the dynamic performance of high speed trains. Recently, the Federal Railroad Administration, Office of Research and Development has sponsored a project to develop a general multibody simulation code that uses an online nonlinear three-dimensional wheel-rail contact element to predict the contact forces between wheel and rail. In this paper, several nonlinear wheel-rail contact formulations are presented, each using the online three-dimensional approach. The methods presented are divided into two contact approaches. In the first Constraint Approach, the wheel is assumed to remain in contact with the rail. In this approach, the normal contact forces are determined by using the technique of Lagrange multipliers. In the second Elastic Approach, wheel/rail separation and penetration are allowed, and the normal contact forces are determined by using Hertz’s Theory. The advantages and disadvantages of each method are presented in this paper. In addition, this paper discusses future developments and improvements for the multibody system code. Some of these improvements are currently being implemented by the University of Illinois at Chicago (UIC). In the accompanying “Part 2” and “Part 3” to this paper, numerical examples are presented in order to demonstrate the results obtained from this research.

Some notes on a volume fraction mixture theory and a comparison with the kinetic theory of gases

1991 ◽  
Vol 29 (5) ◽  
pp. 561-573 ◽  
Author(s):  
A.C. Hansen ◽  
R.L. Crane ◽  
M.H. Damson ◽  
R.P. Donovan ◽  
D.T. Horning ◽  
...  
Keyword(s):  
Kinetic Theory ◽  
Volume Fraction ◽  
Mixture Theory ◽  
Kinetic Theory Of Gases ◽  
Fraction Mixture
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