Turbulent Gas-solid Flow Research Articles

Effect of particle diameter and void fraction on gas–solid two-phase flow: a numerical investigation using the Eulerian–Eulerian approach

AbstractSudden expansion pipes are crucial in fluid dynamics for studying flow behavior, turbulence, and pressure distribution in various systems. This study focuses on investigating the behavior of a two-phase flow, specifically a gas–solid turbulent flow, in a sudden expansion. The Eulerian–Eulerian approach is employed to model the flow characteristics. The Eulerian–Eulerian approach treats both phases (gas and solid) as separate continua, and their interactions are described using conservation equations for mass, momentum, and energy. The study aims to understand the complex phenomena occurring in the flow, such as particle dispersion, turbulence modulation, and pressure drop. The governing equations are solved using house developed code called FORTRAN, a widely used programming language in scientific and engineering simulations. The results of this study will provide valuable insights into the behavior of gas–solid two-phase flows in sudden expansions, which have important applications in various industries, including chemical engineering, energy systems, and environmental engineering. A parametric study of the impact of particles diameters (20, 120, 220, 500 µm), the solid volume loading ratios $$(0.005, 0.008, 0.01)$$ ( 0.005 , 0.008 , 0.01 ) and area ratios (2.25, 5.76, 9) effect of sudden expansion on the streamlines, local skin friction, pressure, velocity, turbulent kinetic energy, and separation zone.

Stochastic Lagrangian wall deposition model for RANS prediction of deposition in turbulent gas–solid flows

In industrial-scale Reynolds Averaged Navier–Stokes (RANS) simulations, a wall-modeled approach is often employed, specifically choosing a dimensionless wall-cell height much greater than one. However, in gas–solid flows, a coarse description of the boundary layer may lead to inaccurate results in terms of particle dispersion and deposition. In this study, we conducted an investigation on stochastic RANS dispersion models with deposition on smooth walls using a wall-modeled approach. These models were applied to turbulent channel flows in both vertical and horizontal orientations. The modeling approach involved the adoption of the Euler–Lagrange formalism and the RANS k−ϵ turbulence model in OpenFOAM®. To assess particle behavior first, a simple homogeneous isotropic stationary turbulence (HIST) case was examined. Fluid elements were also tracked in an inhomogeneous turbulence for dispersion analysis. These tests gave the good formulation for the dispersion model to be used for particle tracking coupled with turbulent channel flow simulation. However, the deposition results in turbulent channel using such stochastic dispersion model in the wall-cell were found to be consistently overestimated across various scenarios for low-inertia particles. To address these limitations arising from the coarse description of the boundary layer, we examined, implemented, and evaluated a Lagrangian stochastic wall deposition model. The activated deposition model demonstrated good agreement with experimental data.

Predicting reattaching turbulent gas-solid flow with a strong pressure gradient

In this study, the focus is on examining how the flow characteristics are influenced by particle density in the context of downward turbulent gas-solid flow through a sudden expansion pipe. The Eulerian-Lagrangian approach is performed to simulate the gas and the solid phases. A self-written FORTRAN code is developed based on the finite volume technique with a hybrid scheme in a staggered grid to simulate the problem. Experimental measurements and numerical simulations are employed to study the flow dynamics. After comparing the outcomes with previously published experimental findings, the current code demonstrates favorable results that provide encouragement for the authors to expand their theoretical work and explore various parameters. The sudden expansion performance is studied at different particle materials (sodium, sand, aluminum, copper, and gold) and Reynolds numbers. In light of the computational results, the particle material has a significant influence on the flow behavior. As the particle density increases from sodium to gold, the solid phase becomes more concentrated and exhibits different flow patterns. The particle density also affects the pressure distribution, velocity profiles, and turbulent kinetic energy in the flow. The particle size significantly influences both the flow behavior and the loss coefficient.

Measuring solid particles in sand-carrying gas flow using multiscale vibration response statistics and deep learning algorithms

A method to quantitate sand particles in turbulent gas flow that combines the multiscale triaxial vibration response and deep learning algorithms is proposed. First, an optimized adaptive wavelet-empirical mode decomposition (EMD) denoising method is proposed based on multifrequency coherent and statistical analysis. Second, complex gas–solid turbulent flow information under multiple gas–particle coupling is characterized based on Hilbert-Huang transform (HHT), Hurst analysis, EMD entropy, etc. In addition, a deep learning algorithm that integrates multiscale flow information to determine sand content that includes two independent branches, a pure deep convolutional neural network (CNN) model driven by microscale triaxial response and a shallow long short-term memory (LSTM) network with regularization driven by mesoscale triaxial response, is proposed. Finally, a quantitative model to characterize sand-carrying turbulent gas flow based on the entropy weight effect of the triaxial vibration response is constructed as follows: Csand=A·p.∑i=xzSiQi. Experimental validation indicates that the proposed deep learning algorithm has recognition and prediction accuracy of 97.8% and 96.97% for sand particle size and the power spectrum, respectively, which are higher than those of the existing intelligent models to characterize sand information. Moreover, the quantitative sand content model based on the multiscale response and deep learning algorithm has a maximum error of only 1.56% under strong turbulence.

Research on the Deposition and Orientation Characteristics of Cylindrical Particles in a Gas-solid Two-phase Turbulent Flow Through a Curved Tube

Research on the Deposition and Orientation Characteristics of Cylindrical Particles in a Gas-solid Two-phase Turbulent Flow Through a Curved Tube

Research on Deposition and Orientation Characteristics of Cylindrical Particles in Gas-Solid 2-Phase Turbulent Flow in Curved Tubes

Research on Deposition and Orientation Characteristics of Cylindrical Particles in Gas-Solid 2-Phase Turbulent Flow in Curved Tubes

Investigation on ultralight particle dispersions in dense two-phase flow using a kinetic friction stress model

The graphite particle dispersion characteristics with irregular shapes of dense gas-solid turbulent flow in downer reactor is numerically investigated using an improved kinetic friction stress model and a adopted drag coefficient describing momentum transfer between gas and non-spherical particles. Hydrodynamic predictions are in better line with experimental results. Redistributions of Reynolds normal and shear stresses with strongly anisotropic dispersions are captured. Comparisons to glass bead, ultralight particles elongate the second acceleration length, gather the concentration peaks at near wall region, and weak the maximum dense ring. Maximum kinetic energy at fully development region is approximately 1.2 times larger than that of second acceleration region. Lower particle sphericities are contribution to the enhancement of particle velocity, particle concentration, particle shear stress, particle collision frequency, and granular temperature, except for the reduction of turbulent kinetic energy. The negative amplitudes of shear stresses at fully development regions are approximately 4.0 times larger than those of second acceleration regions.

Unsteady CFD simulation on ash particle deposition and removal characteristics in tube banks: Focusing on particle diameter, flow velocity, and temperature

This study establishes a numerical deposition and removal model coupled with unsteady gas–solid turbulent flow to predict transport, impaction, sticking, and removal (or rebounding) characteristics of ash particles with high alkali metals based on Ansys Fluent software extended by user–defined functions. Dynamic mesh analytical strategy is employed to adjust the grid on the interface of flue gas and deposition layer to illustrate ash deposit growth characteristics. In this study, the effects of particle size, flow velocity, and inlet gas temperature on formation and distribution of ash deposits are studied. The results indicate that ash deposit distribution has significant particle size dependence. Larger particles tend to deposit on the windward side of first–row tubes, and account for the greatest share of total deposited mass. Smaller particles may deposit on the leeward side of the tube surfaces. Variation in impaction rates with time are influenced by the thermophoretic force and enlarged deposition area. With the increase in flow velocity, total deposited mass increases gradually. The influence of flow temperature on impacting rates is mainly embodied in the effect of flow temperature on thermophoretic force. However, the increase in inlet gas temperature has little effect on the sticking efficiency and ash deposit distribution. Nevertheless, the total deposited mass shows an increasing trend with inlet flue gas temperature.

Study of erosion prediction of turbulent gas-solid flow in plugged tees via CFD-DEM

In many industrial applications, sand erosion wear is the main cause of equipment failure, particularly in the transferring pipeline fittings. In order to reduce the adverse consequences of erosion in bends, in this study the potential usage of plugged tees instead of standard elbows under a wide range of flow conditions is examined. A computational fluid dynamics (CFD) model coupled with discrete element method (DEM) was used and the particle-laden flows with different fluid velocities in the corresponding geometries carrying various entrained particle mass loadings were simulated. The reliability of selected turbulence models as well as rebound and erosion models were verified by comparing the model predictions with the available experimental data. The final simulation model included the E/CRC erosion model, and the Grant and Tabakoff rebound model. The DEM used in the computational model includes the effects of particles rotation and collisions between the particles. The study also considered the effect of modifications of the plugged length of the tee geometries. The simulation results indicated that, as the particle mass loading increases, the effectiveness of plugged tee compared to the standard elbow increases. Moreover, although increasing the plugged length will generally reduce the erosion rate due to the cushioning effect, the rate of reduction depends on mass loading.

Numerical simulation of turbulent gas–solid flow using an approximate deconvolution model

In our prior study (Schneiderbauer and Saeedipour, Phys. Fluids, 2018; 30:023301), an a-priori analysis on the spatially-filtered two-fluid model (TFM) was presented for turbulent gas–solid flows, where the unresolved terms were modeled by an approximate deconvolution model (ADM). With such an approach, an approximation of the unfiltered solution is obtained by repeated filtering allowing the determination of the RSFS (resolved sub-filter scales) contribution of unclosed terms of the filtered equations directly. In the present study, this ADM-TFM approach is implemented in an a-posteriori manner for the coarse grid simulation of a fluidized bed of Geldart type B particles and is verified against highly-resolved TFM simulations. Furthermore, different regularization methods, which account for the sub-filter scale (SFS) contribution, are presented and discussed with respect to their predictiveness and stability. It is shown that employing an appropriate rheological model for the solid phase considerably improves stability without removing too much energy from the resolved scales. Finally, the ADM-TFM predictions are in fairly good agreement with the fine grid reference case and do not show a notable grid-dependency. Compared to TFM simulations using the same grid resolution, the ADM-TFM approach does only require marginally more computational resources.

Modeling of Particle-Laden Cold Flow in a Cyclone Gasifier

Isothermal transient Eulerian–Lagrangian simulation of the turbulent gas–solid flow in a cyclone gasifier with two inlet tubes at 890 °C has been performed. The single-phase gas flow is modeled using SSG Reynolds stress turbulence model. Ten thousand representative solid particles of different sizes are injected from each inlet continuously at every second of simulation time. Particles are finally stopped as soon as they arrive at the outlet or reach the bottom plate of the gasifier. The effect of particle-to-gas coupling on the pressure and velocity of the flow and particles motion inside the gasifier is studied. The numerical approach can reasonably predict the impact of particle load on the gas flow as presented in the experimental results. Single particles are traveled throughout the transient gas flow field by using Lagrangian approach. High temperature of the gas flow inside the gasifier has significant effects on the swirl intensity reduction, damping the turbulence in the core region, pressure, and particle behaviors. However, the presence of solid particles does not have a notable influence on the swirl intensity and turbulence.

Experimental and numerical study of the effects of pre-drying of S-PVC using a pneumatic dryer

ABSTRACT Pneumatic conveying drying (PCD) has been widely used in industrial processes because it is regarded as a highly efficient technique in heating, and mass transfer of product operation. Despite the fact that the use of multi-stage drying techniques is now justifiable, many industrial complexes still use older single-stage systems. The purpose of this article is to investigate the effects of using a pneumatic dryer as a pre-dryer in PVC suspension production line at Bandar Imam Petrochemical Complex (BIPC). The current operating system in PVC suspension production line is fluidized bed drying. In the present work, computational fluid dynamics (CFD) is utilized to predict the hydrodynamics and drying mechanisms of a three-dimensional, dilute-phase, gas-solid turbulent flow in the laboratory-scale. The experimental study is carried out in two pilot-scale spiral pneumatic conveying dryers of diameter 5 cm and 13.45 m length and diameter 10 cm and 7.2 m length. As the main goals of this research, the influence of diameter and length of the dryer are investigated in two pilot-scale vertical pneumatic conveying dryers. In addition, the effects of gas velocity and temperature, particle temperature, mass flow rate and initial moisture content on the dryer performance are examined. The variations in the air velocity, air temperature, air pressure and particle moisture content are investigated along the length of the dryer. The results of energy analysis show that by using the pneumatic dryer as a pre-dryer, the specific energy consumption is reduced about 23.1%.

Fully resolved numerical simulation of interphase heat transfer in gas–solid turbulent flow

We use a ghost-cell based high-order immersed boundary method (IBM) to study the thermal interaction between entrained solid spherical particles and a turbulent velocity- and temperature-carrying flow. The sphere diameter (D) is about eight times the Kolmogorov scale (η). The ambient turbulent field is isotropic, and the Taylor microscale Reynolds number is 50. The inflow turbulent velocity intensity varies from 0.05 to 0.1, and the intensity of temperature fluctuation varies from 0.1 to 0.4. The particle volume fractions are 0.01 and 0.02, and particle-to-fluid density ratios are 1.2, 10.0, and 100.0. It is observed that the particle-to-fluid density ratio affects the Nusselt number the most, followed by the solid volume fraction and turbulence intensity, while the effect of the intensity of temperature fluctuation is relatively small. It is also shown that correlations that have been proven to be valid for a single stationary particle can deviate significantly from the exact value obtained by directly integrating the dimensionless temperature gradient over the surface of the particle. Better estimates can only be gained by also taking the local flow and thermal conditions into consideration, in addition to the particle Reynolds number.

Erosion of natural gas elbows due to rotating particles in turbulent gas-solid flow

This work investigates the erosion of an elbow pipe due to the gas-solids turbulent pipe flow using computational fluid dynamics (CFD) with special attention to the effect of particle rotational motion on erosion. The gas-solid flow is solved by employing two-way coupled Eulerian-Lagrangian approach while enhanced wall treatment is used for modeling the flow behavior close to the walls and in boundary layer. Effects of key erosion parameters such as gas velocity, particle diameter and particle mass flow rate on the erosion rate was evaluated and discussed. Simulation results are verified with experimental data with concept of percent bias. Results show that the erosion rate is strongly affected by the particle rotation. The particles rotation has a considerable effect on the particle motion path and consequently the erosion pattern of the elbow. Particle trajectories show that particles have reverse motion due to rotation which plays a significant role on erosion pattern due to the more collision to the elbow wall.

The game theoretical approach for multi-phase complex systems in chemical engineering

This paper explores the application of noncooperative game theory together with the concept of Nash equilibrium to the investigation of some basic problems on multi-scale structure, especially the meso-scale structure in the multi-phase complex systems in chemical engineering. The basis of this work is the energy-minimization-multi-scale (EMMS) model proposed by Li and Kwauk (1994) and Li, et al. (2013) which identifies the multi-scale structure as a result of ‘compromise-in-competition between dominant mechanisms’ and tries to solve a multi-objective optimization problem. However, the existing methods often integrate it into a problem of single objective optimization, which does not clearly reflect the ‘compromise-in-competition’ mechanism and causes heavy computation burden as well as uncertainty in choosing suitable weighting factors. This paper will formulate the compromise in competition mechanism in EMMS model as a noncooperative game with constraints, and will describe the desired stable system state as a generalized Nash equilibrium. Then the authors will investigate the game theoretical approach for two typical systems in chemical engineering, the gas-solid fluidization (GSF) system and turbulent flow in pipe. Two different cases for generalized Nash equilibrium in such systems will be well defined and distinguished. The generalize Nash equilibrium will be solved accurately for the GSF system and a feasible method will be given for turbulent flow in pipe. These results coincide with the existing computational results and show the feasibility of this approach, which overcomes the disadvantages of the existing methods and provides deep insight into the mechanisms of multi-scale structure in the multi-phase complex systems in chemical engineering.

Experimental investigation of the particle distribution of gas-solid turbulent flow in the boundary layer

By the three-dimensional and no-contact optical technique digital holography, the particle distributions of a turbulent gas-solid boundary layer were studied in a fully developed horizontal channel, and the velocity field of the gas phase was obtained by particle image velocimetry (PIV) with main upstream speeds of Uh=2.1ms−1, 5.2ms−1, and 8.74ms−1. Carborundum powders with diameters of 38μm and 60μm were used as the particle phase and titanium dioxide nanoparticles were used as ghost particles. It was found that the peak of the particle distribution occurs in a logarithmic region. With an increase of particle size, the peak shifts toward the wall. As the velocity increases, the peak shifts toward the channel center. The gravity and sweeps have influence on the particle motion toward the wall; particle–wall collisions, ejections and the Magnus lift force have influence on the particle motion toward the channel center. Through analysis of the velocity field and shear strain distribution in the gas boundary layer, the existence of sweeps and ejections caused by quasi-flow vortices has been confirmed. Meanwhile, it was found that the peak of shear strain occurred near the wall and that wall-normal fluctuation and shear strain under high flow rate were significantly higher than at low flow rate; these characteristics were consistent with the distribution of particles in the boundary layer.

Behavior of downward turbulent gas–solid flow through sudden expansion pipe

The effects of solid-particles on downward turbulent-air flow through a pipe with sudden expansion are simulated by Eulerian–Lagrangian approach. Reynolds averaged Navier Stokes equations associated with standard k-ε turbulence model are used. Source terms are included to represent the effects of fluid–particle interactions and particle–particle collisions assuming non-deformed spherical shape particles. A FORTRAN code is developed based on the finite volume discretization with hybrid scheme to simulate the problem. Based on comparisons with published experimental work, the present code introduces good results that encourage the authors to extend the theoretical work considering different parameters. The performance of sudden expansion in the form of loss coefficient is studied at different particle sizes, mass loading ratios and Reynolds numbers. In light of the computational results, the finest particles can improve the performance of the sudden expansion, while the size of separation bubble increases.

The influence of secondary flow in a two-phase gas-solid system in straight channels with a non-circular cross-section

The paper considers two-phase gas-solid turbulent flow of pneumatic transport in straight horizontal channels with a non-circular cross-section. During turbulent flow, a specific flow phenomenon, known as secondary flow, occurs in these channels in the cross-sectional plane. The existence of strong temperature gradients in the cross-sectional plane of the channel or the cases of curved channels result in the appearance of the secondary flow of the first kind. However, in straight channels with a non-circular cross-section, in the developed turbulent flow mode, a secondary flow, known as Prandtl?s secondary flow of the second kind, is induced. The paper presents a numerical simulation of a developed two-phase turbulent flow by using the PHOENICS 3.3.1 software package. Reynolds stress model was used to model the turbulence. The paper provides the data on the changes in turbulent stresses in the channel cross-section as well as the velocities of solid particles transported along the channel.

Modeling the electrostatic effect on the hydrodynamic behavior in FCC risers: From understanding to application

A CFD simulation was proposed to investigate the electrostatic effect on the hydrodynamic behavior of turbulent gas–solid flow in FCC risers. The simulation was first verified using the open experimental data with expected electrostatic effects observed in FCC risers. The influences of several operating parameters on the degree of electrification in FCC risers were analyzed, such as surface charge densities, pressure, gas velocity. It was noted that the gas velocity played a highly significant role compared with solid flux, while the effect of pressure was relatively weak. Further analysis showed that a much stronger electrostatic effect was found in small-scale FCC risers than their large-scale counterparts, and in addition, the major regions affected by the electrostatic charge depend on the scale of the riser. Finally, an external electric field was applied to optimize the flow field distribution in the FCC riser. The results of the electrostatic effects on the hydrodynamic behaviors in FCC risers are of great use in providing a reference for the optimization of FCC risers and their scaling.

Computation of wall to suspension heat transfer in vertical pipes

ABSTRACTIn this article, turbulent gas-solid flow in a vertical pipe is investigated for predicting the heat transfer from the heated wall to the suspension. The Eulerian-Eulerian model is used, incorporating a four-way coupling; i.e., considering inter-particle collisions as well as particle-wall collisions. Both the phases are simulated based on Reynolds averaged Navier-Stokes equations (RANS) with a two-equation k − ϵ turbulence model for the gas phase and a granular temperature equation for the solid phase. The closure of the granular temperature (kinetic energy associated with the random motion of the particles) equation is done by the use of kinetic theory of granular flows. The main objective of the study is to investigate the variations of two-phase heat-transfer coefficient and Nusselt number with flow parameters like flow Reynolds number, particulate loading, and particle size. In comparison to single-phase flow, heat transfer is found to be significantly increased with the increase in Reynolds number and particulate loading. This happens because of the presence of the solid particles in a gas flow, which bring changes to the heat-transfer characteristics of the gas phase. Heat transfer increased by adding solid particles for particulate loading in the range of 1 to 20 and particle size in the range of 30 to 50 µm.