Gas-solids Pipe Flow Research Articles

Tribo-charging of binary mixtures composed of coarse and fine particles in gas–solid pipe flow

Experiments were conducted to investigate the effect of adding fines on the tribo-charging of coarse glass beads. Four types of fines, i.e., copper, stainless steel, uncoated and silver-coated fine glass beads, mixed with 240–830μm glass beads were conveyed by air through a stainless-steel spiral pipe acting as a tribo-charger. Regardless of the type or electrical conductivity of the fine particles tested, adding small amounts of fines (up to 10wt%) to coarse glass beads resulted in a sharp increase in the mass and surface charge densities of the particles. In general, the profiles of the mass and surface charge densities of the fine–coarse particle mixtures as a function of the mixture composition were determined by the relative magnitude of contact potential differences and the total surface areas of all the components. The dominant particle tribo-electrification mechanism switched from coarse particle–wall contacts to fine particle–wall contacts when the fines weight percentage in the mixture exceeded 10%. A model was developed to predict the mass charge density of binary mixtures as a function of the mixture composition.

Direct measurement of particle size and 3D velocity of a gas-solid pipe flow with digital holographic particle tracking velocimetry.

The 3D measurement of the particles in a gas-solid pipe flow is of great interest, but remains challenging due to curved pipe walls in various engineering applications. Because of the astigmatism induced by the pipe, concentric ellipse fringes in the hologram of spherical particles are observed in the experiments. With a theoretical analysis of the particle holography by an ABCD matrix, the in-focus particle image can be reconstructed by the modified convolution method and fractional Fourier transform. Thereafter, the particle size, 3D position, and velocity are simultaneously measured by digital holographic particle tracking velocimetry (DHPTV). The successful application of DHPTV to the particle size and 3D velocity measurement in a glass pipe's flow can facilitate its 3D diagnostics.

Euler–Lagrange simulation of gas–solid pipe flow with smooth and rough wall boundary conditions

Numerical simulation of upward turbulent particle-laden pipe flow is performed with the intention to reveal the influence of surface roughness on the velocity statistics of the particle phase. A rough wall collision model, which models the surface as being sinusoidal, is proposed to account for the wall boundary condition ranging for smooth surfaces to very rough surfaces. This model accounts for the entire range of possible surface roughness found in pipes and industrial pneumatic equipment from smooth plastic pipes over machined steel pipes to cast iron surfaces. The model is based on a geometric interpretation of the wall collision process where the particle restitution coefficient is based on the data presented by Sommerfeld and Huber [1]. Simulations are performed using the Eulerian–Lagrangian methodology for the dilute one-way coupling regime. Results are reported for 3 different sizes of glass spheres: 50μm, 200μm and 550μm and evaluated using the data by Mathisen et al. [2]. The results reveal the dependence of the particle concentration, particle mean and particle RMS velocity profiles on the surface roughness. Significant differences can be seen for the particle RMS velocity profiles as the mean motion changes from motion mainly in the axial direction for the smooth surface condition to bouncing motion between the pipe sides for the fully rough surface condition.

An investigation of particle behavior in gas–solid horizontal pipe flow by an extended LDA technique

An extended Laser Doppler Anemometry (LDA) technique has been developed to measure the distributions of particle velocities and particle number rates over a whole pipe cross-section in a dilute pneumatic conveying system. The first extension concentrates on the transform matrix for predicting the laser beams’ cross point in a pipe according to the shift coordinate of the 3D computer-controlled traverse system on which the probes of the LDA system were mounted. The second focuses on the proper LDA sample rate for the measurement of gas–solid pipe flow with polydisperse particles. A suitable LDA sample rate should ensure that enough data is recorded in the measurement interval to precisely calculate the particle mean velocity or other statistical values at every sample point. The present study explores the methodology as well as the fundamentals of measurements, using a laser facility, of the cross-sectional distributions of solid phase. In the horizontal gas–solid pipe flow (glass beads less than 110μm), the experimental data show that the cross-sectional flow patterns of the solid phase can be classified by annulus-like flow describing the axial particle velocity contours and stratified flow characterising particle number rate distribution over a cross-section. Thus, the cross-sectional flow pattern of the solid phase in a horizontal pipe may be annular or stratified dependent on whether the axial particle velocity or particle number rate is the phenomenon studied.

衝突帯電による粒子の表面電荷の制御

The control of electrostatic charge on particles in gas-solids pipe flow has been studied experimentally and theoretically. Alumina particles of 3.3μm in mass median diameter were dispersed in airflow and pneumatically transported in dilute phase. Five different materials were used for the transport pipes, and the relationships between the particle charge and the pipe length were obtained. The polarity and the amount of particle charge were found to depend on the pipe material and the length. In order to control the particle charge, a system combining two different pipe materials was proposed depending on the particle charging characteristics. The particle charge controlled by this method was in good agreement with the theoretical calculation, in which the distribution of particle charge as well as the average was well estimated.

315 振動条件下での静電気による粉体粒子の流量測定

This paper is concerned with a newly developed measurement technique of particle flow-rate in gas-solids pipe flow based on the static electrification of particles. The method is found to be feasible to detect the flow-rate as small as 0.5 g/s for large alumina particles of 0.3mm in mass median diameter. Here we investigated the effect of sensor vibration on the detection sensitivity to get fundamental data for practical applications of the sensor in various particulate processes such as sand blasting. Jet tests with alumina particles were carried out using a vibration exciter under various frequencies and amplitudes. According to the experiments, it was found that the detection sensitivity was increased by the vibration and the sensor could be applied even if the vibration was as large as 30G. It was also found that the resonance of the sensor vibration had no serious effect on the measurement of particle flow-rate.

1512 静電気センサーを用いた増粘着材噴射のモニタリング(OS0,6,8,OS0,6,8交通・物流一般,メンテナンス・信頼性・モニタリング・環境,TRANSLOG 2006)

This paper is concerned with a newly developed monitoring technique of particle flow-rate in gas-solids pipe flow based on the static electrification of particles. The method is found to be feasible to detect the flow-rate as small as 0.5g/s for large alumina particles of 0.3mm in mass median diameter. Here we investigated the effect of vibration on the detection sensitivity of the sensor to obtain fundamental data for practical applications of the sensor in various particulate processes such as sand blasting. In order to obtain one of the fundamental data to apply the sensor, it was found that the detection sensitivity was increased by the vibration and the sensor could be applied even in a condition such as the vibration was as large as 30G. It was also found that material or length of transport pipe had serious effect on the sensitivity of particle flow-rate.

Influence des collisions dans un écoulement gaz–solide anisotherme en conduite verticale et horizontale

An Eulerian–Lagrangian approach is used to study the effect of particle–particle and particle–wall collisions upon the thermal properties of a gas–solid pipe flow. The effects of the nature of particle–wall collisions, as well as the influence of interparticle collisions, which are known to be important on the dynamical point of view, are observed to have notable consequences on the temperature profiles and on the suspension Nusselt number. Such significant modifications are due to the collision induced alteration of the velocity and concentration profiles. In particular, a strong effect of the irregular character of particle–wall collisions is found. At rather high loading ratio m, the question may arise of the possible effect of conductive heat transfer during collisions, therefore this point is also examined. The results obtained up to m=20 confirm that this heat transfer mechanism is negligible.

Test of an Eulerian–Lagrangian simulation of wall heat transfer in a gas-solid pipe flow

An Eulerian–Lagrangian model is proposed to numerically predict the heat transfer between a vertical pipe wall and a turbulent gas-solid suspension. The whole problem lies in the combined solution of mass, momentum, and energy equations written for each phase. Closure equations devoted to turbulence and heat transfer simulation are also needed for the continuous phase. This problem is treated using a k–ε model and a turbulent Prandtl number model for the gaseous phase. The coupling terms standing for the fluid–particle interactions are taken into account. The simulation of the dispersed phase dynamics is addressed using a Lagrangian model, taking the particle–wall and particle–particle interactions into account. Additionally, the temperature of each particle is tracked using a model for the convective heat exchange between the two phases. The accuracy of the thermal and dynamic solutions has been tested for particles of diameter 200 and 500 μm, and for a wide range of loading ratios (0–20). Corresponding velocity and turbulent kinetic energy profiles are presented for the dynamic modelling validation, while Nusselt numbers are calculated for the study of the thermal problem.

Measurement of mass flow rate of polymer powder based on static electrification of particles

Measurement of mass flow rate of polymer powder in a gas-solids pipe flow was investigated theoretically and experimentally. The measurement was based on the static electrification of the flowing particles. In the system, two current detecting pipes made of different materials were used and mass flow rates were calculated from the two generated currents. Since polymer powder formed a stiff coating layer on the hard surface of metallic pipes by particle collision, several polymer materials were examined as to the detecting pipes and the performance of the current detection was evaluated by changing the powder flow rate. It was found that electrically conductive polymers containing carbon had superior stability for the current detection. It was also found that the mass flow rate of polymer powder could be measured by use of two different conductive polymers for the detecting pipes.

Numerical Simulation and Experimental Study of Two-Phase Flow in a Vertical Pipe

ABSTRACT The fully developed flow of air and solid particles in a vertical pipe was calculated using a modified model for particle-eddy interaction in two-phase turbulent flows, which is developed from the particle-source-in-cell model. This model was proposed to account for the effects of the fluctuation frequency spectrum of turbulent gas flow on the motion of particle phase and the influence of particles on the gas turbulent flow. In order to validate this modified model, the flow characteristics of a turbulent upward gas-solid pipe flow was studied both numerically and experimentally. Various combinations of loading and particle diameter were investigated. Velocities of both phases, turbulence intensities, and volume fraction distributions were obtained. The predictions were compared with experimental data measured by the use of a laser Doppler anemometer showing that the overall agreement is good.

管内固気二相流における微粉体の帯電現象

The electrification of fine particles in a gas-solids pipe flow is investigated theoretically and experimentally. Flowing particles are charged through their collisions with a pipe wall. When a part of the pipe is electrically isolated and grounded, the charge transferred from the particles to the wall is detected as an electric current from the wall. The current generated and the electric charge of fine particles(fly-ash: Dp50=3.4 and 12μm) and relatively large particles (quartz sandDp50=320μm are measured. The relationship between the current per unit powder flow rate I/Wp and charge-to-mass ratio (q/mp)0 is represented by a linear equation irrespective of particle diameter as long as the mass flow ratio is below 0.0058. However, the absolute value of I/Wp of fine particles decreases with increasing mass flow ratio m when m exceeds 0.011. It is found that the current I/Wp is represented by a quadratic equation of(q/mp)0. The fact is well explained by introducing the concept of electrification efficiency.

静電気を利用した高分子系粉体の質量流量計測

Measurement of the mass flow rate of a polymer powder in a gas-solids pipe flow was investigated theoretically and experimentally. The measurement was based on the static electrification of the flowing particles. In the system, two current detecting pipes made of different materials were used, and mass flow rates were calculated from the two generated currents.Since the polymer powder formed a stiff coating layer on the hard surface of metallic pipes due to particle impaction, several polymer materials were examined as the detecting pipes, and the performance of the current detection was evaluated by changing the powder flow rate. It was found that electric conductive polymers containing carbon showed superior stability in current detection. It was also found that the mass flow rate of the polymer powder could be measured by the use of two different conductive polymers in the detecting pipes.

Experimental study on the interface of core-annulus flow in the riser of a circulating fluidized bed

An experimental study on the interface of the core-annulus flow in the riser of a circulating fluidized bed has been carried out in a lab-scale circulating fluidized bed. The dual-stem differential probe, which was developed for the measurement of differential pressure along axial direction in a dense, vertical gas-solids pipe flow has been employed in the experiment. The solid cluster velocity in the riser was obtained statistically by applying cross-correlation analysis to the pressure drop signals obtained from two probes. The interface of the core-annulus flow inside a riser was revealed by the profiles of the solid cluster velocity. The experimental study also indicated that the interface of the core-annulus flow in the riser of a circulating fluidized bed varied with the height above the distributor and the operating conditions. The high solids circulation rate led to a thicker, downward moving particle layer near the wall of the pipe. An S-shaped profile of the core-annulus interface along the riser was observed in the experiments.

Measurements of powder flow rate in gas-solids pipe flow based on the static electrification of particles

A New measuring method of powder flow rate in gas-solids pipe flow was developed and investigated both theoretically and experimentally. The method is based on the static electrification of particles by their impaction on the inside wall. The powder flow rate was successfully calculated by use of the electric currents generated from the wall to the ground. It was found that the effect of initial charge of particles on the measurement could be eliminated by using two metallic pipes whose inner-surfaces were coated with different materials. It was also found that the powder flow rate and the mean particle charge could be measured simultaneously.

Simulation of particle-to-particle interactions in gas solid flows

A Lagrangian simulation technique of a non-dilute gas—solid suspension flow is presented. The method is based on the introduction of simulated particle-to-particle collisions during the trajectory calculation of a particle, with a probability which is predicted through an iterative process, since it depends on the local concentration and velocities. This simulation makes it possible to predict dense gas—solid flows, without having to compute simultaneous trajectories. After a description of the simulation principle, we examine the dynamics of a binary collision between spherical particles, including rotation effects. As a test case, a horizontal gas solid pipe flow was investigated at loading ratios up to 20. Results concerning velocity and concentration profiles, as well as pressure losses, are presented. Comparisons are made with the case of dilute flow simulation, revealing that particle-to-particle interactions play a non-negligible role as soon as the loading ratio exceeds unity.

Solid Phase Contribution in the Two-Phase Turbulence Kinetic Energy Equation

This paper presents a multiphase turbulence closure employing one transport equation, namely, the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A double-time averaging approach for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less restrictive assumptions comparative to the previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.

Measurements of powder flow rate in gas-solids pipe flow based on the static electrification of particles

A new measuring method of powder flow rate in gas-solids pipe flow was developed and investigated both theoretically and experimentally. The method is based on the static electrification of particles by their impaction on the inside wall. The powder flow rate was successfully calculated by use of the electric currents generated from the wall to the ground. It was found that the effect of initial charge of particles on the measurement could be eliminated by using two metallic pipes whose inner-surfaces were coated with different materials. It was also found that the powder flow rate and the mean particle charge could be measured simultaneously.

Analysis of Turbulent Gas-Solid Suspension Flow in a Pipe

The mixing length theory is extended to close the relevant momentum equations for two-phase turbulent flow at a first-order closure level. It is assumed that the mass fraction of the particles is on the order of unity, that the particle size is so small that the particles are fully suspended in the primary fluid, and that the relaxation time scale of the particles is sufficiently small compared with the time scale of the energy containing eddies so that the suspended particles are fully responsive to the fluctuating turbulent field. Bulk motion of the particles is treated as a secondary fluid flow with its own virtual viscosity. The proposed closure is applied to a fully developed gas-solid pipe flow in which the particles are assumed to be uniformly distributed across the pipe section. Predicted velocity profiles and the friction factors are in good agreement with available experimental data.

The static electrification of particles in gas-solids pipe flow

A theoretical model for the charging of solid particles through their collisions with the pipe wall in gas-solids pipe flow is discussed. The model is based both on a flow adopted from the fluid mechanics and on the electrification model adopted from the electrodynamics. Particular attention is given to the turbulent diffusion of particles in steep concentration gradient regions. The motion of particles is predicted upon Eulerian pressure-velocity formulation of the gas flow equations, and the Lagrangian formulation of the particle motion equation.