Comparative Assessment of Turbulence Models for Prediction of Flow-Induced Corrosion Damages

2011 ◽  
Author(s):  
Kaushik Das ◽  
Debashis Basu ◽  
Todd Mintz
Keyword(s):  
Corrosion Rate ◽  
Cross Sections ◽  
Volume Fraction ◽  
Solid Phase ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Continuous Phase ◽  
Comparative Assessment ◽  
Solid Particles ◽  
Protective Film

The present study makes a comparative assessment of different turbulence models in simulating the flow-assisted corrosion (FAC) process for pipes with noncircular cross sections and bends, features regularly encountered in heat exchangers and other pipeline networks. The case study investigates material damage due to corrosion caused by dissolved oxygen (O2) in a stainless steel pipe carrying an aqueous solution. A discrete solid phase is also present in the solution, but the transport of the solid particles is not explicitly modeled. It is assumed that the volume fraction of the solid phase is low, so it does not affect the continuous phase. Traditional two-equation models are compared, such as isotropic eddy viscosity, standard k-ε and k-ω models, shear stress transport (SST) k-ω models, and the anisotropic Reynolds Stress Model (RSM). Computed axial and radial velocities, and turbulent kinetic energy profiles predicted by the turbulence models are compared with available experimental data. Results show that all the turbulence models provide comparable results, though the RSM model provided better predictions in certain locations. The convective and diffusive motion of dissolved O2 is calculated by solving the species transport equations. The study assumes that solid particle impingement on the pipe wall will completely remove the protective film formed by corrosion products. It is also assumed that the rate of corrosion is controlled by diffusion of O2 through the mass transfer boundary layer. Based on these assumptions, corrosion rate is calculated at the internal pipe walls. Results indicate that the predicted O2 corrosion rate along the walls varies for different turbulence models but show the same general trend and pattern.

scholarly journals CFD-based numerical simulation of cyclone separator for separating stigmas from petals of saffron

2020 ◽  
Author(s):  
Javad Nemati ◽  
Babak Beheshti ◽  
Ali Mohammad Borghei
Keyword(s):  
Separation Efficiency ◽  
Solid Phase ◽  
Equations Of Motion ◽  
Fluid Phase ◽  
Reynolds Stress Model ◽  
Continuous Phase ◽  
Solid Particles ◽  
Inlet Section ◽  
Ansys Fluent ◽  
Discrete Phase

This study numerically modeled the flow of a fluid (air) and solid particles (saffron flower) inside a cyclone using the finite volume method (FVM) in ANSYS Fluent. The continuous phase was simulated under steady state conditions, as the initial condition, using the Reynolds Stress Model (RSM) for turbulence at three constant inlet air velocities of 1.5 m/s, 2.5 m/s, and 3.5 m/s over the inlet section. One-way coupling was assumed to govern all numerical analyses. The fluid phase and particles were treated as the continuous medium (within a Eulerian framework) and discrete phase (within a Lagrangian framework), respectively. The equations governing the gas phase included the compressible Navier–Stokes and the conservation of mass. The discrete phase equations included the equations of motion for three different particles including petals, stigmas, and anthers. According to the numerical results, the cyclone separation efficiency was calculated, and the static pressure and velocity contours were plotted. The results showed the capability of the CFD-based simulation for an accurate demonstration of the behavior of the fluid–solid phase. Accordingly, it can be used to predict the efficiency of stigma separation from petals of saffron using airflow in the cyclone. According to the results, the highest cyclonic separation efficiency of 89% was achieved at an inlet air velocity of 3.5 m/s, which was very close to the experimental data.

Application of Wray-Agarwal turbulence model for numerical simulation of gas-solid flows in CFB risers

2021 ◽  
pp. 1-25
Author(s):  
Yali Shao ◽  
Ramesh K. Agarwal ◽  
Xudong Wang ◽  
Baosheng Jin
Keyword(s):  
Turbulence Model ◽  
Circulating Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Solid Volume Fraction ◽  
Turbulence Models ◽  
Two Phase ◽  
Efficient Simulation ◽  
Pressure Profiles ◽  
First Time

Abstract In recent decades, increasing attention has been focused on accurate modeling of circulating fluidized bed (CFB) risers to provide valuable guidance to design, optimization and operation of reactors. Turbulence model plays an important role in accurate prediction of complex gas-solid flows. Recently developed Wray-Agarwal (WA) model is a one-equation turbulence model with the advantages of high computational efficiency and competitive accuracy with two-equation models. In this paper for the first time, Eulerian-Eulerian approach coupled with different turbulence models including WA model, standard κ-ε model and shear stress transport (SST) κ-ω model is employed to simulate two-phase flows of gas phase and solid phase in two CFB risers, in order to assess accuracy and efficiency of WA model compared to other well-known two-equation models. Predicted gas-solid flow dynamic characteristics including the gas-solid volume fraction distributions in radial and axial directions, pressure profiles and solid mass flux distributions are compared with data obtained from experiment in detail. The results demonstrate WA model is very promising for accurate and efficient simulation of gas-solid multiphase flows.

scholarly journals ANALYSIS OF NUMERICAL MODELLING OF TURBULENCE IN A CONICAL REVERSE‐FLOW CYCLONE

2010 ◽  
Vol 18 (4) ◽  
pp. 321-328 ◽  
Author(s):  
Petras Vaitiekūnas ◽  
Inga Jakštonienė
Keyword(s):  
Numerical Modelling ◽  
Swirling Flow ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Equation System ◽  
Reynolds Stress Model ◽  
Cylindrical Part ◽  
Solid Particles ◽  
System Modelling

This paper aims to analyse the problem of numerical modelling of the airflow in a conical reverse‐flow (CRF) cyclone with tangential inlet (equipment for separation of solid particles from gaseous fluid flow). A review of experimental and theoretical papers that describe cyclones with very complex swirling flow is performed. Three‐dimensional transport differential equations for incompressible turbulent flow inside a cyclone are solved numerically using finite volume‐based turbulence models, namely, the Standard k–ϵ model, the RNG k–ϵ model and the Reynolds stress model (RSM). The paper describes the numerical modelling of the airflow in the CRF cyclone, the height of which is 0.75 m, diameter ‐ 0.17 m, height of cylindrical part ‐ 0.255 m, height of conical part ‐ 0.425 m, inlet area is 0.085×0.032 m2. Mathematical model of airflow in a cyclone consisted of Navier‐Stokes (Reynolds) three‐dimensional differential equation system. Modelling results, obtained from the numerical tests when inlet velocity is 4.64, 9.0 and 14.8 m/s and flow rate is, respectively, 0.0112, 0.0245 and 0.0408 (0.0388) m3/s, have demonstrated a reasonable agreement with other authors’ experimental and theoretical results. The average relative error was ± 7.5%. Santrauka Nagrinejama duju aerodinamikos kūginiame grižtamojo srauto (KGS) ciklone (irenginys kietosioms dalelems atskirti iš oro srauto) su tangentiniu srauto itekejimu skaitinio modeliavimo problema. Trimates nespūdžiojo turbulentinio srauto ciklono viduje pernašos diferencialines lygtys skaitiškai sprestos baigtiniu tūriu metodu taikant standartini k–ϵ, RNG k–ϵ ir Reinoldso itempiu (RIM) turbulencijos modelius. Atliktas skaitinis oro srauto judejimo KGS ciklone modeliavimas. Ciklono aukštis – 0,75 m, skersmuo ‐ 0,17 m, cilindrines dalies aukšti ‐ 0,255 m, kūgines ‐ 0,425 m, itekejimo angos plotas 0,085×0,032 m2. Oro srauto judejimo ciklone matematinis modelis – Navje ir Stokso (Reinoldso) trimačiu diferencialiniu lygčiu sistema. Modeliavimo rezultatai, kai itekejimo greitis 4,64, 9,0 bei 14,8 m/s ir debitas – 0,0112, 0,0245 ir 0,0408 (0,0388) m3/s, neblogai sutapo su kitu autoriu eksperimentiniais rezultatais. Vidutine santykine paklaida ‐ ± 8 proc. Резюме Анализируется проблема аэродинамики газового потока в коническом возвратного потока (КВП) циклоне (оборудование для отделения твердых частиц от газового потока) с тангенциальной подачей газа. Произведен обзор экспериментальных и теоретических работ в циклонах такого типа, в которых образуется сложное вихревое течение потока. Для моделирования использованы трехмерные дифференциальные уравнения переноса, численно решаемые методом конечных объемов с использованием следующих моделей: стaндартной k–e, RNG k–e и рейнольдсовой модели турбулентности напряжений. Произведено численное моделирование движения потока воздуха в циклоне КВП, высота которого 0,75 м, диаметр – 0,17 м, высота цилиндрической части – 0,255 м, конической части – 0,425 м, площадь входного отверстия – 0,085×0,032 м 2 . Математическую модель движения потока воздуха в циклоне составила система трехмерных дифференциальных уравнений Навье-Стокса и Рейнольдса. Анализ результатов, произведенный при скоростях втекания в циклон 4,64, 9,0 и 14,8 м/с (дебит – 0,0112, 0,0245 и 0,0408 м 3 /c) и для модели рейнольдсовых напряжений, показал приемлемую согласованность с результатами других исследователей – со средней относительной погрешностью ± 7,5 проц.

CFD Study on must of Grapes Separation in a Hydrocyclone

2013 ◽  
Vol 837 ◽  
pp. 645-650
Author(s):  
Petru Cârlescu ◽  
Ioan Tenu ◽  
Marius Baetu ◽  
Radu Rosca
Keyword(s):  
Cfd Simulation ◽  
Reynolds Stress Model ◽  
Continuous Phase ◽  
Solid Particles ◽  
Advanced Degree ◽  
Separation And Purification ◽  
Discrete Phase Model ◽  
Flow Rates ◽  
Discrete Phase ◽  
Simulation And Experiment

Abstract. Hydrocyclones are increasingly used in the food industry for various separation and purification. In this paper, an optimization was made to design a hydrocyclone model using CFD (Computational Fluid Dynamics). CFD simulation is performed with FLUENT software by coupling the Reynolds Stress Model (RSM) for must of grapes flow with Discrete Phase Model (DPM) for solid particles trajectory. Coupling of discrete phase (particles) and continuous phase (must of grapes) in the mathematical model is set so that the continuous phase to influence discrete phase. Tracking particles traiectory in this hydrocyclone allows advanced degree is separation so obtained to the maximum particle size approaching the size of a yeast cell 10 μm, without separating them. Hydrocyclone dimensional designed simulation was performed and analyzed on an experimental pilot plant for three different must flow rates supply. Introduced particle flow rates simulation and experiment does not exceed 10% of the must flow rates. The degree of separation obtained is in agreement with experimental data.

Three-Dimensional Numerical Simulation of Convective Melting of Solid Particles in a Fluid

1999 ◽  
Author(s):  
Y. L. Hao ◽  
Y.-X. Tao
Keyword(s):  
Volume Fraction ◽  
Solid Phase ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Phase Changes ◽  
Solid Particles ◽  
Preliminary Calculation ◽  
Two Phase ◽  
Closed Set ◽  
Gravity Effects

Abstract A physical model of two-phase flow and heat-mass transfer with the phase changes based on the theory of interacting continua is proposed. All terms in the conservation equations are analyzed and the constitutive equations are presented. A closed set of governing equations describing the convective melting of solid particles in a fluid is obtained. The numerical method is developed for the solution of velocity, temperature, and volume fraction of solid phase for the three-dimensional melting in a rectangular cross-section channel. Preliminary calculation, including gravity effects, shows that the result is reasonable. This study provides a basis for the theoretical and experimental investigation of convective melting of solid particles in a fluid.

The nonlinear dynamics of solidification of a binary melt with a quasi-equilibrium mushy region

1990 ◽  
Vol 68 (9) ◽  
pp. 790-793 ◽  
Author(s):  
Yu. A. Buyevich ◽  
L. Y. Iskakova ◽  
V. V. Mansurov
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Volume Fraction ◽  
Solid Phase ◽  
Internal Heat ◽  
Solid Particles ◽  
Mushy Region ◽  
Parameter Method ◽  
Quasi Equilibrium ◽  
Phase Volume Fraction

A mushy region (a two-phase zone) between the solid and liquid phases occurs often in the process of solidification of a binary melt. An analysis of the structure of the mushy region, which includes the liquid, solid particles, and dendrites extending from the bulk solid surface, is suggested. The processes of heat and mass transfer in the mushy region are considered on the basis of the small parameter method. The analysis leads to equations governing unsteady heat and mass transfer with internal heat, and mass sources within the mushy region, and it includes the condition for the absence of supercooling (the condition for the zone quasi-equilibrium), convection being neglected. The temperature, concentration of solute, and solid phase volume fraction are found. On the basis of this solution a new model of the process is formulated. Within the scope of this model the mushy region is replaced by a liquid–solid interface with discontinuous boundary conditions.

Effect of Rolling-Remelting SIMA Process on Semi-Solid Microstructure of ZCuSn10 Alloy

2014 ◽  
Vol 217-218 ◽  
pp. 418-425 ◽  
Author(s):  
Jia Wang ◽  
De Hong Lu ◽  
Han Xiao ◽  
Rong Feng Zhou ◽  
Rong Zhou ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Deformation Process ◽  
Volume Fraction ◽  
Solid Phase ◽  
Solid Particles ◽  
Deformation Degree ◽  
Fine Grain ◽  
Sima Process ◽  
Semi Solid ◽  
Sharp Corners

Semi-solid billet of ZCuSn10 (Wt%: 88.25Cu, 10.48Sn) alloy is prepared by strain induced melt activated (SIMA) method which including rolling and remelting process. Firstly, ZCuSn10 alloy is casted, and rolling samples are cut from ingot casting. Secondly, the rolling samples are two pass or four pass rolled after holding 15 minutes at 450°C, then samples with 10% and 20% pre-deformation degree are obtained. The remelting samples are cut from pre-deformed samples. Lastly, the remelting samples are reheated up to 850°C or 875°C, water quenching after holding for 15 minutes. Then semi-solid microstructure of ZCuSn10 alloy is prepared. The semi-solid microstructure of ZCuSn10 alloy is observed and compared with annealed microstructure and microstructure of ZCuSn10 alloy directly remelted after casting. The results indicate that semi-solid microstructure of ZCuSn10 alloy by rolling-remelting SIMA process is uniform and fine grain, and spheroidization level of solid particle is well. The optimum semi-solid microstructure is obtained when alloy with pre-deformation 20% is remelted at 875°C for 15 minutes, the average grain diameter is about 75.80μm, shape factor is 1.62, and volume fraction of liquid phase reaches about 17.28%. Pre-deformation process plays a crucial role in grain refinement and spheroidization during SIMA process for preparing the semi-solid ZCuSn10 alloy, as pre-deformation degree and remelting temperature increases, volume fraction of liquid phase increases, the solid particles in semi-solid microstructure are smaller and rounder. The main mechanism of SIMA process preparing semi-solid billet of ZCuSn10 alloy is that pre-deformation breaks dendrites and stores energy of deformation into alloy, and promotes dendrites fusing through remelting process. Meanwhile, liquid phase occupies sharp corners of solid particles by Sn element diffusing from liquid phase into α solid phase, so that fine and uniform and globular α solid particles are gained.

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.

Discrete Particle Study of Turbulence Coupling in a Confined Jet Gas-Liquid Separator

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Wayne Strasser
Keyword(s):  
Liquid Phase ◽  
Gas Phase ◽  
Volume Fraction ◽  
Liquid Droplet ◽  
Reynolds Stress Model ◽  
Continuous Phase ◽  
Liquid Entrainment ◽  
Induced Flow ◽  
Flow Effects ◽  
Liquid Separator

A 3D computational fluid dynamics investigation of particle-induced flow effects and liquid entrainment from an industrial-scale separator has been carried out using the Eulerian–Lagrangian two-way coupled multiphase approach. A differential Reynolds stress model was used to predict the gas phase turbulence field. The dispersed (liquid) phase was present at an intermediate mass loading (0.25) but low volume fraction (0.05). A discrete random walk method was used to track the paths of the liquid droplet releases. It was found that gas phase deformation and turbulence fields were significantly impacted by the presence of the liquid phase; these effects have been parametrically quantified. Substantial enhancement of both the turbulence and the anisotropy of the continuous phase by the liquid phase was demonstrated. It was also found that a large number (⩾1000) of independent liquid droplet release events were needed to make conclusions about liquid entrainment. Known plant run conditions and entrainment rates validated the numerical method.

Numerical Simulation and Test Research on the Wear of Back Blades in Slurry Pumps

2016 ◽  
Author(s):  
Yi Tao ◽  
Shouqi Yuan ◽  
Jianrui Liu ◽  
Fan Zhang ◽  
Jianping Tao
Keyword(s):  
Optimization Design ◽  
Volume Fraction ◽  
Solid Phase ◽  
Wear Test ◽  
Solid Particles ◽  
Particle Model ◽  
Optimized Design ◽  
Trailing Edge ◽  
Blade Number ◽  
The Impact

Back blades are usually assembled on the outside surface of impeller back shroud as a sealing device in centrifugal slurry pumps. The presence of solid particles in slurry leads to an obvious problem about the abrasion of the flow components of pump. Especially, the life of sealing devices, like the back blades, the oil seals and the shaft sleeve, is only a quarter or less of other components. Hence, an important engineering significance lies in the research on the abrasion of back blades. In this paper, a single-stage horizontal type centrifugal pump was chosen as the main study model. The 3D model of the entire flow field was meshed by hexahedral structured grids. Based on the Particle model, which is an Eulerian multiphase method, the internal two-phase flow in the centrifugal slurry pump was simulated by using ANSYS CFX software. Six optimized design cases with the variation of back blades were analyzed to study the influence of vane profile and blade number of back blades on the abrasion characteristic and sealing performance. The main conclusions obtained are as follows: the volume fraction of solid phase achieved by simulation is in good agreement with the test results; the effect of vane profile on the flow of particles in the passages and the pressure on the seal is small; the usage of less back blade number will lower the flow constraint of blades on the particles and increase the area of axial vortex in each single passage, which means that the impact velocity of particles towards the pressure side grows and the pressure on the seal increases significantly. Based on the simulation mentioned above, two better cases were selected and manufactured for trial. Then, a wear test rig was set up to study the wear pattern of impeller during the operation of pump. Through the comparison of these two impellers after the wear test, it is found that: the back blades with the back forward shape can effectively reduce the abrasion of back blades at the pressure sides near the trailing edge; thickening the trailing edge of back blades to increase the life of back blades is feasible in practical application. The optimization design of back blades was preliminarily achieved which could provide some reference for the optimization design of back blades in centrifugal slurry pumps.

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