Gas-solid Particle Flow Research Articles

Twin-array capacitance sensor for multi-parameter measurement of gas-solid particle flow based on BP-Adaboost

The measurement of gas-solid particle flow is a complex and error-prone task due to the intricacies of the flow process. To address the limitations associated with Electrical Capacitance Tomography (ECT) such as the complexity of hardware structure and the computational demands of imaging algorithms, this study proposes a novel TAC measurement method that utilizes the BP-Adaboost algorithm. The proposed method utilizes TAC to measure multiple parameters of the gas-solid particle flow under several working conditions and calibrate the measured flow rate with gravity sensors. At first, we conduct experiments to identify the working conditions that have the least impact on the measurements of concentration and velocity, offering valuable insights for subsequent two-phase flow measurement. The BP-Adaboost algorithm is then utilized to classify the flow pattern based on capacitance data obtained from the TAC sensor. Finally, the pattern, concentration, and velocity are used as inputs for BP-Adaboost neural network to optimize the mass flow rate and improve the measuring accuracy. Experimental results demonstrate the effectiveness of the method, with an accuracy of 83.3% for two-phase flow pattern classification and a mass flow rate error of 6.71%. Additionally, BP-Adaboost algorithm, an ensemble learning technique, effectively avoids overfitting, leading to good generalizability.

Experimental measurements of gas-particle flows in large-scale strippers

Measurements of gas–solid particle flow in a large-scale stripper unit are reported. The experiments target industrial (pilot) scale measurements of gas-particle flow that can be used to validate numerical methods for modeling multiphase flows, such as computational fluid dynamics coupled to the discrete element method (CFD-DEM). Specifically, experiments were performed with Geldart Group B (533 µm) glass beads in a stripper unit. In general, previous CFD-DEM validation datasets were performed in benchtop experimental systems and limited to O(105) particles. Here, the number of particles in the isolated section of the stripper is O(107) for all tests. Measurements are reported for a ∼2 m tall section of the ∼1 m diameter stripper. Radial mass flux profiles measured at five axial positions and three axial pressure drop measurements are reported for six operating conditions.

Identifying Laser-Induced Plasma Spectra of Particle in Gas-Solid Flow Based on the Standard Deviation of Pixel Intensities

A new method which schemes of conditional data processing named standard deviation (SD) method is present and evaluated for identifying spectral data of gas-solid particle flow based on laser-induced plasma spectroscopy. The SD method is also compared with two conditional analysis methods called the SNR method and the absolute intensity method. First, the effect of three methods identifying the spectral data of the same fly ash sample is compared. Then, the threshold stability of the three methods under different conditions was observed by screening the spectral data of a set of 12 coal samples. The rejection rate, error rejection rate (or error rejection) and missing rejection rate (or missing rejection) were used to evaluate these three different approaches. And probability of false hits is determined by evaluating various conditional processing thresholds. The characteristic peaks used for the analysis of fly ash and coal samples are selected as Si 288.16 nm and C 247.86 nm, respectively. The result shows that for all approaches the SD method has the minimum rejection rate and error rejection (both 0%) when the SD threshold value is 120, the total rejection rate of the SD method is also the lowest of the three under this condition, which is 37.67%. It means that true data and false data could be completely and accurately identified by using the SD method. Moreover, for different samples and experimental conditions, the thresholds of absolute intensity method and SNR method fluctuate in the range of 83 - 135 counts and 2.05 - 4.00, respectively, while the threshold of the SD method has been stable at 55. Compared with other two methods, the SD method is more universal when faced with variable detection conditions. So it has more advantages in the rapid detection and analysis of power plants.

CFD MODELING OF SO2 CAPTURE USING LIMESTONE IN INDUSTRIAL SCALE CIRCULATING FLUIDIZED BED BOILER

The unsteady state computational fluid dynamics model for gas-solid particle flow in industrial scale circulating fluidized bed boiler combining with combustion and desulfurization (using limestone solid sorbent) chemical reactions, both homogeneous and heterogeneous, was developed in this study. The effects of solid sorbent feeding position and solid sorbent particle size on sulfur dioxide concentration were investigated. The results showed that both the solid sorbent feeding position and solid sorbent particle size had an effect on the sulfur dioxide capture. Entering solid sorbent at the upper secondary air position gave lower sulfur dioxide concentration than the one at the lower secondary air position and fuel feed position, respectively. This can be explained by the influence of suitable temperature at the upper secondary air position for desulfurization chemical reaction. About the solid sorbent particle size, the sulfur dioxide capture was the lowest when using the largest solid sorbent particle size due to the system hydrodynamics.

A study on the gas-solid particle flows in a needle-free drug delivery device

Different systems have been used over the years to deliver drug particles to the human skin for pharmaceutical effect. Research has been done to improve the performance and flexibility of these systems. In recent years a unique system called the transdermal drug delivery has been developed. Transdermal drug delivery opened a new door in the field of drug delivery as it is more flexible and offers better performance than the conventional systems. The principle of this system is to accelerate drug particles with a high speed gas flow. Among different transdermal drug delivery systems we will concentrate on the contour shock tube system in this paper. A contoured shock tube is consists of a rupture chamber, a shock tube and a supersonic nozzle section. The drug particles are retained between a set of bursting diaphragm. When the diaphragm is ruptured at a certain pressure, a high speed unsteady flow is initiated through the shock tube which accelerates the particles. Computational fluid dynamics is used to simulate and analyze the flow field. The DPM (discrete phase method) is used to model the particle flow. As an unsteady flow is initiated though the shock tube the drag correlation proposed by Igra et al is used other than the standard drag correlation. The particle velocities at different sections including the nozzle exit are investigated under different operating conditions. Static pressure histories in different sections in the shock tube are investigated to analyze the flow field. The important aspects of the gas and particle dynamics in the shock tube are discussed and analyzed in details.

Effects of the variation of mass loading and particle density in gas–solid particle flow in pipes

The method of two dimensional Reynolds Averaged Navier–Stokes (RANS) equations has been employed for the simulation of turbulent particulate flow. This approach was fitted with appropriate closure equations that take into account all the pertinent forces and effects on the solid particles, such as: particle–turbulence interactions; turbulence modulation; particle–particle interactions; particle–wall interactions; gravitation, viscous drag and lift forces. The flow domain in all cases was a cylindrical pipe and the computations were carried for upward pipe flow. The finite volume technique was used for the numerical solution of the governing and closure equations. The results show the effect of loading and particle density on the profiles of the velocity, the turbulence intensity and the solids concentration.

NUMERICAL SIMULATION OF UPRISING GAS-SOLID PARTICLE FLOW IN CIRCULATING FLUIDISED BED

Concentration of solid particles of ash and inert material present in the combustion chamber of a circulating fluidised-bed boiler is very high, giving rise to some disadvantages. At the same time, the required temperature level in the combustion chamber is guaranteed by circulation of solid particles. In this work numerical simulation of gas-solid particle flow has been performed in the frame of a two-fluid model, namely the Eulerian approach for the dispersed phase, for conditions of the circulating fluidised bed, ranging from moderate to high mass ratios of the flow. An incorporated original model of closure of transport equations of the dispersed phase permitted to account the interparticle collisions which might be indispensable to proper numerical simulation of the process in the circulating fluidised bed under discussion. The results of this work would help to improve the processes occurring in the combustion chamber of the circulating fluidised-bed boiler.

CFD simulation of the high shear mixing process using kinetic theory of granular flow and frictional stress models

In order to enhance process understanding and to develop predictive process models in high shear granulation, there is an ongoing search for simulation tools and experimental methods to model and measure the velocity and shear fields in the mixer. In this study, the Eulerian–Eulerian approach to model multiphase flows has been used to simulate the mixer flow. Experimental velocity profiles for the solid phase at the wall in the mixer have been obtained using a high speed camera following the experimental procedure as described by Darelius et al. [2007a. Measurement of the velocity field and frictional properties of wet masses in a high shear mixer. Chemical Engineering Science, 62, 2366–2374]. The governing equations for modelling the dense mixer flow have been closed by using closure relations from the kinetic theory of granular flow (KTGF) combined with frictional stress models. The free slip and partial slip boundary conditions for the solid phase velocity at the vessel wall have been utilized. The partial slip model originally developed for dilute flows by Tu and Fletcher [1995. Numerical computation of turbulent gas–solid particle flow in a 90 ∘ bend. A.I.Ch.E. Journal, 41, 2187–2197] has been employed. It was found that the bed height could be well predicted by implementing the partial slip model, whereas the free slip model could not capture the experimentally found bed height satisfactorily. In the simulation, the swirling motion of the rotating torus formed was over-predicted and the tangential wall velocity was under-predicted, probably due to the fact that the frictional stress model needs to be further developed, e.g. to tackle cohesive particles in dense flow. The advantage of using the Eulerian–Eulerian approach compared to discrete element methods is that there is no computational limitation on the number of particles being modelled, and thus manufacturing scale granulators can be modelled as well.

Numerical computation of turbulent gas-particle flow in a 90 degree bend: comparison of two particle modelling approaches

A numerical study into the physical characteristics of dilute gas-particle flows over a square-sectioned $90^\circ$~bend is reported. Two approaches, namely the Lagrangian particle tracking model and Eulerian two fluid model are employed to predict the gas-particle flows. Renormalization Group based $k$-$\epsilon$ model is used as the turbulent closure for both the approaches; however, for the Eulerian model, additional transport equations are solved to account for the combined gas-particle interactions and the turbulence kinetic energy of the particulate phase. In comparison to both Eulerian-Eulerian and Eulerian-Lagrangian approaches the former was found to yield closer agreement with the measured values. The Eulerian-Lagrangian approach obtains finer details of the behaviour of particles, while Eulerian-Eulerian model can be used for industrial scale problems. All the simulated results are compared against the experimental finding of Kliafas and Holt (1987). References J. A. C. Humphrey, J. H. Whitelaw, and G. Yee. Turbulent flow in a square duct with strong curvature. J. Fluid Mech., 103:443--463, 1981. doi:10.1017/S0022112081001419. Y. Kliafas and M. Holt. Ldv measurements of a turbulent air-solid two-phase flow in a 90 degree bend. Exp. Fluids, 5:73--85, 1987. doi:10.1007/BF00776177. J. D. Kulick, J. R. Fessler, and J. K. Eaton. Particle response and turbulence modification in fully developed channel flow. J. Fluid Mech., 277:109--134, 1994. doi:10.1017/S0022112094002703. Z. F. Tian, J. Y. Tu, and G. H Yeoh. Numerical simulation and validation of dilute gas- particle flow over a backward-facing step. Aerosol Sci. Technol., 39:319--332, 2005. doi:10.1080/027868290930961. J. Y Tu. Computational of turbulent two-phase flow on overlapped grids. Numer. Heat Transfer Part B Fundam, 32:175?195, 1997. doi:10.1080/10407799708915004. J. Y. Tu and C. A. J. Fletcher. An improved model for particulate turbulence modulation in confined two-phase flows. Int. Commun. Heat Mass Transfer, 21(6):775--783, 1994. doi:10.1016/0735-1933(94)90031-0. J. Y. Tu and C. A. J. Fletcher. Numerical computation of turbulent gas-solid particle flow in a 90 degree bend. AIChE Journal, 41(10):2187--2197, 1995. doi:10.1002/aic.690411003. A. Adeniji-Fashola and C. P. Chen. Modelling of confined turbulent fluid-particle flows using eulerian and lagrangian schemes. Int. J. Heat Mass Transfer, 3(4):691--701, 1990. doi:10.1016/S0307-904X(98)00007-9. F. Durst, D. Milojevic, and B. Schonung. Eulerian and lagrangian predictions of particulate two-phase flows :a numerical study. Appl. Math. Model, 8(2):101--115, 1984. doi:10.1016/0307-904X(84)90062-3. J. R. Fessler and J. K. Eaton. Particle response in a planar sudden expansion flow. Expl Thermal and Fluid Sci, 15:413--423, 1997. doi:10.1016/S0894-1777(97)00010-1. J. R. Fessler and J. K. Eaton. Turbulence modification by particles in a backward-facing step flow. J. Fluid Mech, 394:97--117, 1999. http://journals.cambridge.org/action/displayAbstract?aid=15369.

Gas–Solid Particle Flow in Horizontal Channels: Decomposition of the Particle-Phase Flow and Interparticle Collision Effects

This paper examines the turbulent flow of heavy particles in horizontal channels and pipes. Calculations for the fluid are performed within an Eulerian frame of reference, while the particulate phase is considered as several continuous polydisperse media, each constituting a separate phase. The interparticle collisions include two mechanisms: collisions with sliding friction and collisions without sliding friction. The collisions of particles are accounted for, by collisions due to the difference in the average and fluctuating velocities of the several particulate fractions. This work introduces an original model for the closure for the mass and momentum equations based on the collisions as well as an original description of the particle motion in a horizontal channel, by introducing the decomposition of the particle-phase motion into two types of particle phases: falling and rebounding particles. The decomposition allows the correct calculation of the influence of the wall on the motion of particles.

Effect of a Dispersed Admixture on the Flow Pattern and Heat Transfer in a Supersonic Dusty-Gas Flow Around a Cylinder

A mathematical model of two-phase (gas-solid particle) flow which takes into account particle-particle collisions and the feedback effect of the admixture on the gas parameters is proposed. The dispersed phase is described by a kinetic equation of the Boltzmann type and the carrier gas by modified Navier-Stokes equations. Using this model, a supersonic uniform dusty-gas flow past a cylinder is calculated. The fields of the macroparameters of the admixture and the carrier medium are obtained. The dependence of the heat transfer at the stagnation point on the relative particle size and the free-stream admixture concentration is studied in detail. The ranges of these parameters on which particle collisions and the feedback effect of the admixture on the carrier-gas flow are important are found.

Simulation of gas–solid particle flows by boundary domain integral method

A novel numerical scheme based on the boundary domain integral method (BDIM) for the numerical simulation of gas–solid particle flows is presented. A program is being developed to model the hydrodynamics of fluidized bed systems by using the Eulerian approach in terms of velocity–vorticity variable formulation. Both phases are treated as separated, incompressible, continuous and fully interpenetrating fluids. Each phase is described by a modified Navier–Stokes equation including interphase momentum exchange. With the vorticity vector ω p i representing the curl of the velocity field v p i , computation scheme of both phases motion is partitioned into its kinematic and kinetic aspects. Therefore, the additional equation from the drift flux theory is necessary to compute volume fraction. Main advantage of the proposed BDIM scheme is the reduced number of additional physical models derived from the kinetic theory of granular flows for the description of the solid phase. Numerical scheme has been tested first on a single-phase test examples. Two-phase two-component results are studied on two-phase gas–solid particles vertical channel flow.

Eulerian Simulation of Gas-Solid Particle Flow by BDIM

The numerical scheme based on the boundary domain integral method (BDIM) for the numerical simulation of twophase two-component flows is presented. A program is being developed to model the hydrodynamics of fluidized bed systems by using the Eulerian approach in terms of velocity-vorticity variables formulation. With the vorticity vector both phases motion computation scheme is partitioned into its kinematic and kinetic aspect. Influence of the drag coefficient on the two-phase two-component flow field is studied on the two-phase gas-solid particles vertical channel flow.

BDIM For Two-phase Two-componentFlows

A novel numerical scheme based on the boundary domain integral method (BDIM) for the numerical simulation of gas-solid particle flows is presented. Eulerian approach in terms of velocity-vorticity variables formulation is used. Each phase is described by a modified Navier-Stokes equation including interphase momentum exchange. With the vorticity vector w,j representing the curl of the velocity field v~ both phases motion computation scheme is partitioned into its kinematic and kinetic aspect. The additional equation from the drift flux theory is necessary to compute volume fraction. Main advantage of the proposed BDIM scheme is reduced number of physical models derived from the kinetic theory of granular flows for description of the solid phase. Two-phase two-component results are studied on twc~ phase gas-solid particles vertical channel flow.

Particle interaction with the wall surface in two-phase gas–solid particle flow

Solid-particle impact interaction with material wall surfaces is a problem in many multiphase flow industrial devices. This interaction affected by flows around curved surfaces (aerodynamic effects) is analysed in this paper for generic wall geometry and carrier gas flow. The focus of this paper is to quantify the incidence and reflection of small (near-Stokesian) particles. Particle reflection threshold is found, and depends on both particle Stokes number and carrier gas flow near the wall surface. The analytical results are illustrated and compared with the computational results for cylindrical wall surfaces. The boundary layer theory is employed to predict the key model parameter. The analytical prediction agrees well with the computational results.

Simulation of gas–solid particle flows over a wide range of concentration

Simulation of gas–solid particle flows over a wide range of concentration

Simulation of gas-solid particle flows over a wide range of concentration

SUMMARY A two-fluid model of gas‐solid particle flows that is valid for a wide range of the solid-phase volume concentration (dilute to dense) is presented. The governing equations of the fluid phase are obtained by volume averaging the Navier‐Stokes equations for an incompressible fluid. The solid-phase macroscopic equations are derived using an approach that is based on the kinetic theory of dense gases. This approach accounts for particle‐particle collisions. The model is implemented in a control-volume finite element method for simulations of the flows of interest in two-dimensional, planar or axisymmetric, domains. The chosen mathematical model and the proposed numerical method are applied to three test problems and one demonstration problem. © 1998 John Wiley & Sons, Ltd.

A control-volume finite element method for dilute gas-solid particle flows

The formulation of a co-located equal-order Control-Volume-based Finite Element Method (CVFEM) for the solution of two-fluid models of 2-D, planar or axisymmetric, incompressible, dilute gas-solid particle flows is presented. The proposed CVFEM is formulated by borrowing and extending ideas put forward in earlier CVFEMs for single-phase flows. In axisymmetric problems, the calculation domain is discretized into torus-shaped elements and control volumes: in a longitudinal cross-sectional plane, or in planar problems, these elements are three-node triangles, and the control volumes are polygons obtained by joining the centroids of the three-node triangles to the midpoints of the sides. In each element, mass-weighted skew upwind functions are used to interpolate the convected scalar dependent variables and the volume concentrations. An iterative variable adjustment algorithm is used to solve the discretized equations. The capabilities of the proposed CVFEM are illustrated by its application to two test problems and one demonstration problem, using a simple two-fluid model for dilute gas-solid particle flows. The results are quite encouraging.

Gas and solid flow in the freeboard of a fluidized bed combustor

The transport phenomena in the freeboard of a fluidized bed combustor are particularly influenced by the behaviour of the gas—solid particle flow. In order to describe the flow field, data on particle and gas velocities are needed. A laser—Doppler—velocimetry- and-particle-sizing system has been used in a commercial scale fluidized bed combustor. The measuring technique and experimental data from the unit will be presented. In addition a numerical model of the fluid dynamics in the freeboard based on particle trajectory calculations has been developed. Computational and experimental results are compared and discussed. It is shown that gas turbulence in the freeboard has almost no effect on entrainment rates, but is significant for the explanation of the measured particle velocities. A particle trajectory model including gas turbulence provides quantitative information on the gas—solid flow field in the freeboard.

Stability of two-phase gas-solid particle flow in a boundary layer

The stability of a boundary layer above a flat plate with a pressure gradient in the case when a gas flow carries suspended particles of an admixture is considered on the basis of the equations for the aeromechanics of heterogeneous media [1, 2]. The investigation is carried out in the framework of the same assumptions as in [3], where the stability of Poiseuille flow in a channel was studied. The velocity profile of the unperturbed flow is selected from the Falkner-Skan family. The Chebyshev spectral element method is used for the calculations.