Characterizing Effects of the Shape of Screw Conveyors in Gas–Solid Fluidized Beds Using Advanced Numerical Models

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Qingang Xiong ◽  
Soroush Aramideh ◽  
Alberto Passalacqua ◽  
Song-Charng Kong
Keyword(s):  
Numerical Study ◽  
Numerical Models ◽  
Fluid Model ◽  
Operating Conditions ◽  
Screw Conveyor ◽  
Blade Thickness ◽  
Computational Mesh ◽  
Computational Fluid Dynamics Cfd ◽  
Two Fluid Model ◽  
Screw Pitch

A numerical study of the effects of the shape of an enclosed screw conveyor on the mixing and heat transfer in a horizontal gas–solid fluidized bed was conducted using computational fluid dynamics (CFD). A two-fluid model (TFM) was employed to model the gas and solid phases as continua through mass, momentum, and energy conservations. The motion of the screw conveyor was simulated by using a rotating reference frame (RRF) such that the computational mesh was free from dynamic reconstruction. The diameters of the screw flight and shaft, the pitch, and the blade thickness were varied in the parametric study. Under the operating conditions studied, it was found that the increase in the diameter of the screw flight results in the enhancement of the solid mixing and conveyance. The increase in the diameters of the screw shaft and the screw blade thickness lead to the enhanced solid mixing but reduced conveyance. The variation in the screw pitch gives rise to rather complex behaviors in the solid mixing and conveyance. As the screw pitch is decreased, the solid mixing increases initially but then decreases before it increases eventually. The solid conveyance capability was found to first increase and then decrease. Explanations to the effects of the shape of the screw conveyor were discussed in this work.

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.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

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

Simulation Study of Gas-Solid Macro-Mixing Characterization in Small Fixed-Fluidized Bed Reactor

2011 ◽  
Vol 236-238 ◽  
pp. 1537-1545
Author(s):  
Wen Jing Liu ◽  
Hui Zhao ◽  
Chao He Yang ◽  
Hong Hong Shan
Keyword(s):  
Fluidized Bed ◽  
Raw Materials ◽  
Fluid Model ◽  
Structural Parameters ◽  
Flow Behavior ◽  
Fluidized Bed Reactor ◽  
Operating Conditions ◽  
Laboratory Evaluation ◽  
Two Fluid Model ◽  
Two Fluid

In fixed-fluidized bed reactor, laboratory evaluation of different catalyst, raw materials and process parameters can be implemented, so it has wide applications in the refining process. In this study, we focused on small fixed-fluidized bed reactor, using Eulerian-Eulerian two-fluid model, simulated the gas-solid flow behavior in it. Gas residence time distribution was measured in order to characterize macro-mixing. At the same time, by changing the reactor structure and operating conditions, we studied their effects on gas-solid macro-mixing characterization. The results show that the effects of structural parameters are larger than operating conditions, and different parameters have different effects. Different parameters can be adjusted to change the gas-solid macro-mixing characterization in small fixed-fluidized bed reactor. Therefore, the small fixed-fluidized bed reactor can provide better results in more application areas.

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.

scholarly journals Numerical Study on Performance Characteristics of Draft Tube of Mixed Flow Hydraulic Turbine

2012 ◽  
Vol 10 ◽  
pp. 48-52
Author(s):  
Ruchi Khare ◽  
Vishnu Prasad
Keyword(s):  
Coming Out ◽  
Draft Tube ◽  
Numerical Study ◽  
Flow Simulation ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Mixed Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Overall Performance

Draft tube is an important component of the hydraulic reaction turbine and affects the overall performance of turbine to a large extent. The flow inside the draft tube is complex because of the whirling flow coming out of runner and its diffusion along the draft tube. The kinetic energy coming out of runner is recovered in draft tube and part of recovery meets the losses. In the present work, the computational fluid dynamics (CFD) has been used for flow simulation in complete mixed flow Francis turbine for performance analysis for energy recovery, losses and flow pattern in an elbow draft tube used in Francis turbine at different operating conditions. The overall performance of the turbine at some typical operating regimes is validated with the experimental results and found to be in close comparison.DOI: http://dx.doi.org/10.3126/hn.v10i0.7103 Hydro Nepal Vol.10 January 2012 48-52

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.

Hydrodynamics of Multiple Size Particles in a Liquid Fluidized Bed Classifier

2003 ◽  
Author(s):  
Dinesh Gera ◽  
Madhava Syamlal ◽  
Thomas J. O’Brien
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Fluid Model ◽  
Operating Conditions ◽  
Particle Sizes ◽  
Two Fluid Model ◽  
Predicted Values

A two fluid model is extended to an N-phase, multi-fluid model, in which each particulate phase represents a collection of particles with identical diameter and density. The current N-phase model is applied to a fluidized bed classifier with six different particle sizes to investigate the effects of different operating conditions—fluidizing liquid flow rate, feed voidage, and particle size distribution in the feed stream—on the particle size distribution inside the classifier and the discharge streams. The predicted volume fraction of different particle sizes is compared with the experimental data reported by Chen et al. (2002) for two columns, 191 mm and 292 mm in diameter, each having different geometries and containing glass beads of different sizes fluidized with water. A fairly good agreement is observed between the measured and predicted values for mono- and poly-dispersed systems.

scholarly journals Numerical Study of Particle Interaction in Gas-Particle and Liquid-Particle Flows: Part I Analysis and Validation

2009 ◽  
Vol 1 (3) ◽  
pp. 217-244
Author(s):  
K. Mohanarangam ◽  
J. Y. Tu
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Fluid Model ◽  
Particle Interaction ◽  
Sudden Expansion ◽  
Liquid Particle ◽  
Particle Flows ◽  
Dispersed Phases ◽  
Two Fluid Model

A detailed study into the turbulent behaviour of dilute particulate flow under the influence of two carrier phases namely gas and liquid has been carried out behind a sudden expansion geometry. The major endeavour of the study is to ascertain the response of the particles within the carrier (gas or liquid) phase. The main aim prompting the current study is the density difference between the carrier and the dispersed phases. While the ratio is quite high in terms of the dispersed phase for the gas-particle flows, the ratio is far more less in terms of the liquid-particle flows. Numerical simulations were carried out for both these classes of flows using an Eulerian two-fluid model with RNG based k- emodel as the turbulent closure. An additional kinetic energy equation to better represent the combined fluid-particle behaviour is also employed in the current set of simulations. In the first part of this two part series, experimental results of Fessler and Eaton (1995) for Gas-Particle (GP) flow and that of Founti and Klipfel (1998) for Liquid-Particle (LP) flow have been compared and analysed. This forms the basis of the current study which aims to look at the particulate behaviour under the influence of two carrier phases. Further numerical simulations were carried out to test whether the current numerical formulation can used to simulate these varied type of flows and the same were validated against the experimental data of both GP as well LP flow. Qualitative results have been obtained for both these classes of flows with their respective experimental data both at the mean as well as at the turbulence level for carrier as well as the dispersed phases.

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