Solid Particle Velocity Research Articles

A comparative study on hydrodynamics of circulating fluidized bed riser and downer

Hydrodynamics in a 76mm i.d., 10.2m high circulating fluidized bed (CFB) riser and a 76mm i.d., 5.8m high CFB downer were studied for superficial gas velocities ranging from 2 to 5m/s and solid circulation rates up to 100kg/(m2s). Solid holdup, particle velocity and solid flux profiles in the radial and axial positions were presented. Under these operating conditions, axial solid holdup profiles in the riser and the downer could be approximated by an exponential decay function. The radial gradients of the solid holdup profiles in the riser were much higher than those in the downer, showing that the downer had much more uniform solid distribution. The average solid holdup for the entire riser was about 1.5 times higher than the predicted value from Gs/(ρpUg). However, for the downer reactor this ratio dropped to 0.45–0.98 which increased with increasing superficial gas velocity and decreasing solid circulation rate. Solid flow developed much slower in the riser than in the downer. Negative particle velocity was observed in the near-wall region for nearly the entire height of the riser. The average particle velocity for the entire riser was 0.8–0.96 times higher than the superficial gas velocity, and increased with increasing superficial gas velocity and decreasing solid circulation rate. However, in the downer the average particle velocity was 1.13–2.13 times higher than the superficial gas velocity, and increased with both superficial gas velocity and solid circulation rate. High local solid fluxes were observed in the near wall region of the CFB riser and downer reactor. Over-estimation of the calculated cross-sectional average solid flux over the solid circulation rate in the CFB riser was attributed to the fluctuations of the solid holdup and particle velocity.

Measurement of velocity of solid/air two phase fluid using electrostatic sensors and cross correlation technique

In this paper, application of the cross correlation method for estimating the velocity of air/solid fluid is explained. Electrostatic sensors are used as the primary sensors for this measurement and by using the cross correlation of signals from two electrostatic sensors, the speed of air/solid fluid is calculated. In calculating cross correlation, a truncated version of cross correlation is considered in order to perform cross correlation in an on-line mode. Also, to improve the accuracy of truncated cross correlation, it is performed only when a particle passes across the sensors. MATLAB is selected as the programming tool for performing the cross correlation algorithm. Different tests have been performed, in which the distance between two electrostatic sensors is set at various specified values, and the calculated velocities of solid particles are compared. It is shown that the results of these measurements are very similar, which is proof of the correctness of the results.

3E2 相互相関法により得られる超音速流中の固体粒子の速度に関する研究(<OS4・2>熱流体フロンティア(圧縮性流体))

3E2 相互相関法により得られる超音速流中の固体粒子の速度に関する研究(<OS4・2>熱流体フロンティア(圧縮性流体))

Spatial Selectivity of Linear Electrostatic Sensor Arrays for Particle Velocity Measurement

The signal quality and accuracy of the spatial filtering method for solid particle velocity measurement based on a linear electrostatic sensor array (LESA) are dependent on the spatial filtering characteristics of the LESA and particle distribution in a pneumatic conveying pipeline. In this paper, the charge induced on a circular LESA with different geometric sizes from a single particle having a unity charge is mathematically modeled. Furthermore, a dimensionless computation model of the sensitivity of the LESA is suggested based on a fitted cosine function to the finite-element calculation results of the mathematical model, and the spatial filtering characteristics and spatial selectivity of the LESA are quantitatively investigated based on the computation model. Experimental work was performed on a purpose-built particle flow test rig to verify the dimensionless computation model and the modeling results. Results obtained reveal that the LESA acts as a narrow-bandpass filter in the temporal and spatial frequency domains, and its spatial selectivity is closely related to the number, spacing, and width of the electrode. These results provide an important basis for the performance improvement and optimized design of the LESA for particle velocity measurement.

Comparative study of gas–solids flow patterns inside novel multi-regime riser and conventional riser

A novel CFB riser integrated with an enlarged bottom section was presented in this paper, with the aim to increase overall solids concentration, improve local flow structure and intensify gas–solids contact in the bottom region. Detailed measurements of the flow patterns indicated a multi-regime flow was achieved in this novel riser with a dense-phase bottom region and a dilute upper region. Compared with non-uniform radial profiles of solids concentration and particle velocity presented at the high-density bottom region of a conventional riser, high cross-sectional averaged solids concentration with limited radial gradient was observed in the diameter-enlarged section of this novel riser. Local flow structures in the bottom regions of both risers were also depicted. Better gas–solids contact over the conventional riser was confirmed by the analysis of transient signals and probability distribution of solids concentration. Finally, key flow features of the both risers were summarized.

Different Exit Effects between a Combined Riser with Variable Exit Constraints and a Conventional Riser with Weak Exit Constraints

A large-scale cold model experimental setup of combined riser with variable constraint exit (CRVCE) was established. The axial and radial distributions of solids holdup and particle velocity, under different operating conditions, were investigated experimentally, and the results were compared with conventional riser (CR). Experimental results showed that, the exit restrictive effect of combined riser with variable constraint exit was weak when particle circulation flux and static bed height in upper fluidized bed were lower, while it turned to be strong when superficial gas velocity and static bed height in upper fluidized bed were higher. Under the same conditions, averaged cross-sectional solids holdup of CRVCE was characterized by C type distribution when article circulation flux was higher, while that of CR with weak constraint exit was characterized by linear distribution. In axial direction, averaged cross-sectional particle velocity of CRVCE changed in order: acceleration-constant-decrease velocity, while that of CR changed in another: acceleration-constant velocity. The maximum of local solids holdup value of CRVCE appeared at the dimensionless radius position r/R=0.7, while that of CR appeared in the wall region. Their local particle velocities were similar in the core region, while local particle velocity of CRVCE was lower than that of CR in the annular region.

CFD-DEM simulation of spouting of corn-shaped particles

Three dimensionally coupled computational fluid dynamics (CFD) and discrete element method (DEM) were used to investigate the flow of corn-shaped particles in a cylindrical spouted bed with a conical base. The particle motion was modeled by the DEM, and the gas motion by the k-ɛ two-equation turbulent model. A two-way coupling numerical iterative scheme was used to incorporate the effects of gas–particle interactions in terms of momentum exchange. The corn-shaped particles were constructed by a multi-sphere method. Drag force, contact force, Saffman lift force, Magnus lift force, and gravitational force acting on each individual particle were considered in establishing the mathematical modeling. Calculations were carried out in a cylindrical spouted bed with an inside diameter of 200mm, a height of 700mm, and a conical base of 60°. Comparison of simulations with experiments showed the availability of the multi-sphere method in simulating spouting action with corn-shaped particles, but it depended strongly on the number and the arrangement of the spherical elements. Gas–solid flow patterns, pressure drop, particle velocity and particle concentration at various spouting gas velocity were discussed. The results showed that particle velocity reaches a maximum at the axis and then decreases gradually along the radial direction in the whole bed. Particle concentration increases along the radial direction in the spout region but decreases in the fountain region, while it is nearly constant in the annulus region. Increasing spouting gas velocity leads to larger pressure drop, remarkably increased speed of particle moving upward or downward, but decreased particle concentration.

Theoretical modelling of slurry erosive wear testing of HVOF thermally sprayed Inconel-Titania coatings

Material loss due to slurry erosion is a serious problem in many industrial applications like hydraulic turbines, slurry pumps, pipe lines, etc. where the ideal choice of engineering materials is a real challenge. Lightweight aluminum alloys are finding wi de applications in the field of aerospace automobile, defence, etc. due to improved physical, mechanical and tribology properties. HVOF (High velocity oxy fuel ) Sprayed coatings provide protection against corrosion, erosion and wear. Inconel-718 is a metallic coating which has good wear and erosion resistance. This was sprayed on to mild steel substrate and then subjected to slurry erosive wear tests. It is observed that the slurry wear rates of mild steel decreased on coating the substrate material with-718. The tests were conducted in a slurry erosive wear tester at varying spindle speeds (500 -1500rpm) at different intervals of time .The wear loss was recorded experimentallycompared with theoretical values and graphs are plotted to check accuracy. For this comparison, various parameters such as impinging particle size, velocity of solid particles, concentration of slurry bath, h ardness of mild steel, time are correlated to o btain a theoretical formulation. A non -dimensional analysis is also done to reduce the number of parameters influencing the wear rate.

Experimental investigation of the effects of particle properties on solids holdup in an LSCFB riser

The effects of particle properties (density and size) on solids holdup (ɛs) in the riser of a Liquid–Solid Circulating Fluidized Bed (LSCFB) were investigated experimentally based on three parameters: the superficial liquid velocity (Ul), the normalized superficial liquid velocity (Ul/Ut) and the excess superficial liquid velocity (Ul−Ut). The results showed that the excess superficial liquid velocity (Ul−Ut) among those three parameters is a more appropriate parameter to evaluate the effects of the particle properties on the solids holdup (ɛs), facilitating general and direct comparisons for different types of particles. A discussion on the force balance of the particles revealed that the excess superficial liquid velocity (Ul−Ut) is approximately equivalent to the average particle velocity (V¯P) when the solids holdup (ɛs) is less than 0.1. Also the solids holdup (ɛs) is a function of superficial solids velocity (Us) and particle velocity (Vp), expressed quantitatively in terms of average value as ε¯s=Us/V¯P=Us/(Ul-Ut) when ε¯s<0.1.

Effects of Water Temperature on Chlorophyll-a Concentration Stratification in the Tributary Bay of Three Gorges Reservoir

AbstractThis study aims to quantitatively investigate the formation mechanism of concentration stratification for chlorophyll-a in thermal-stratified water bodies. A well-validated, three-dimensional hydrodynamic-water temperature model was established and applied to simulate the water temperature distribution in Xiangxi Bay (XXB), a representative tributary bay of the Three Gorges Reservoir in China. The numerical results show that temperature stratification with stable vertical temperature profiles seasonally occurred in XXB. Based on these findings, the effect of water temperature stratification on the vertical transport of suspended solids was discussed. Using theoretical derivation and analysis of the relationship between water temperature and the settling velocity of a single spherical solid particle, the settling velocity of suspended solids was significantly affected by temperature under weak turbulence. Therefore, the suspended solids tended to accumulate in the epilimnion or thermocline regions,...

A spatial filtering velocimeter for solid particle velocity measurement based on linear electrostatic sensor array

A novel spatial filtering velocimeter for solid particle velocity measurement in gas-solid flow system is presented based on a Linear Electrostatic Sensor Array (LESA) in the paper. The fundamental spatial filtering principle of the LESA is theoretically described, and a differential filter based on two LESAs is further proposed to remove the pedestal component of the output signal from the LESA. Thus solid particle velocity can be measured by determining the central frequency of the periodic output signal of the differential filter. A spatial filtering velocimeter consisting of a measurement head, seven-channel differential amplifiers and a computer-based data acquisition and processing system is designed and its performance is evaluated on a purpose-built gravity-fed particle flow rig and a belt rig, respectively. Experimental results show that the system repeatability is within ±5.4% over the velocity range of 1.72–3.91 m/s for a particle concentration range 0.011–0.163 m3/m3.

Non-uniform distribution of gas–solid flow through six parallel cyclones in a CFB system: An experimental study

In large-scale circulating fluidized bed (CFB) boilers, it is common to use multiple cyclones in parallel for the capture of solids, assuming that gas–solid flow to be the same in the cyclones. This article presents a study investigating gas–solid flow through six parallel cyclones in a CFB cold test rig. The six cyclones were located asymmetrically on the left and right walls of the riser. Solid volume fraction and particle velocity profiles at the riser outlets and in the horizontal ducts were measured using a fiber optical probe. Cyclone pressure drop and solid circulating rate were measured for each individual cyclone. Measurements showed good agreement as to the non-uniform distribution of the gas–solid flow, which occurred mainly across the three cyclones on one side: the middle cyclones on both sides had higher particle velocities. Conversely, the solid volume fractions, solid fluxes and solid circulating rates of the middle cyclones were lower than those of the other four cyclones. The apparent reason for the flow non-uniformity among the cyclones is the significant flow non-uniformity at the riser outlets. Under typical operating conditions, the solid volume fractions at the riser outlets had a deviation of up to 26% whereas the solid circulating rates at the stand pipes, 7%. These results are consistent with most other studies in the literature.

Study on the Group Settling Velocity of Non-Viscous Solid Particle

Based on the view of relative movement, the group settlement was considered as a movement of current moving up in the suspended particle layer. The expressions of Reynolds number and drag coefficient were set up by the analysis of dimension and stress of dynamic equilibrium state. The theoretic formulae on group settlement of uniform sediment in the laminar region and turbulent region are proposed. It is verified by measured data, and shown that the calculated value by the theoretic formula and measured value agree with each other fairly well.

Sensitivity of Lagrangian Particle Tracking Based on a 3D Numerical Model

The aim of the paper is to investigate in detail the sensitivity of particles displacement based on method of Lagrangian particle tracking in combination with a 3D Eulerian numerical model that was developed by the first author, namely FSUM. The characteristic parameters used for this research include the possibilities of random movement, settling velocity of solid particle, horizontal and vertical diffusion coefficients and condition of particle fixed with a constant distance under water surface. The first part is on the fluid flow model. It includes 3D Navier-Stokes equations together with the initial and boundary conditions that were numerically solved with the finite difference method and coded with FORTRAN 90/95 using parallel technique with OpenMP. A semi-Lagrangian treatment of the advective terms was used. The second part is related to Lagrangian particle tracking model and was solved with the fourth Runge-Kutta method. Model was applied for Strait of Johor and has been calibrated by using measured data on water level and velocity at one station. Eight cases of simulations with many different options were carried out. Through computed cases it shows that random term and settling velocity are very important factors for the behavior of particle trajectory. Although the random diffusion is minor in comparison with flow velocity, but it can rearrange the initial distribution of particles then the cluster of particles become more dispersive during the process of movement. In addition, introducing settling velocity of particle makes a big change on the trajectory of particle that becomes more suitable to sediment transport. The study gave a comprehensive picture on particle movement. The model also showed its possibilities of multiform applications in simulation and prediction for the different problems in practice.

A modified correlation to calculate solid friction factor for horizontal dilute phase pneumatic conveying

The calculation accuracy of solid friction factor ( f p ) is important for the prediction of pressure drop, gas–solid drag force and particle velocity in a horizontal dilute phase pneumatic conveying system. In this study, some modifications were applied to the commonly-used f p correlation developed by Yang. First, the data processing to implicitly correlate f p was improved. Unlike the method used Yang's derivation, the solid volumetric concentration, the ratio of the particle's radial velocity to axial velocity and the ratio of inertial force to gravity force of the fluid were separately used instead of combining together. In addition, the sphericity of the particles was considered such that the correlation can be valid for the non-spherical particles. Experiments were also conducted to validate the correction of the modified correlation. Compared with the experimental data, the modified correlation has remarkably better accuracy on f p prediction than the existing correlation. Moreover, the correlations of solid velocity and pressure drop based on the newly proposed f p correlation were derived. The predictions of the derived correlations agree well with the present and literature experimental data.

삼상유동층 공정에서 수력학적 Similarity 해석

삼상유동층에서 수력학적 유사성을 규모인자(scaling factor)를 이용하여 해석하였다. 규모인자는 직경이 다른 두 종류의 삼상유동층간의 기체, 액체, 그리고 고체입자의 체류량과 단위면적당 유효부피흐름속도를 기준으로 정의하였다. 두 종류 삼상유동층의 직경은 각각 0.102 m와 0.152 m이었다. 여과된 압축공기, 물 그리고 밀도가 2,500 kg/<TEX>$m^3$</TEX>인 유리구슬을 각각 기체, 액체 그리고 유동고체입자로 사용하였다. 각 삼상유동층에서 각 상들의 체류량은 정압강하법에의해 결정하였다. 기체 및 액체의 유속 그리고 고체유동입자의 크기가 각 상들을 기준으로한 규모인자와 유효부피흐름속도를 기준으로한 규모인자에 미치는 영향을 검토하였다. 직경이 다른 두 삼상유동층에서 기체 체류량의 편차는 기체와 액체의 유속이 증가함에 따라 감소하였으나 유동입자의 크기가 증가함에 따라 증가하였다. 직경이 다른 두 종류 삼상유동층에서 액체 체류량 편차는 기체와 액체 그리고 고체유동입자의 크기가 증가함에 따라 감소하였다. 두 종류 삼상유동층에서 고체입자 체류량 편차는 기체유속과 유동입자의 크기가 증가함에 따라 증가하였으나 액체의 유속이 증가함에 따라 감소하였다. 직경이 다른 두 종류 삼상유동층에서 유효부피흐름속도를 매개로 한 규모인자는 기체유속과 유동입자의 크기가 증가함에 따라 감소하였으나 액체의 유속이 증가함에 따라 증가하였다. 본 연구에서 정의된 규모인자는 삼상유동층 공정의 수력학적 유사성을 해석하는데 효과적으로 사용될 수 있었다. Hydrodynamic similarity was analyzed by employing scaling factor in three phase fluidized beds. The scaling factor was defined based on the holdups of gas, liquid and solid particles and effectivity volumetric flux of fluids between the two kinds of fluidized beds with different column diameter. The column diameter of one was 0.102 m and that of the other was 0.152 m. Filtered compressed air, tap water and glass bead of which density was 2,500 kg/<TEX>$m^3$</TEX> were used as gas, liquid and solid phases, respectively. The individual phase holdups in three phase fluidized beds were determined by means of static pressure drop method. Effects of gas and liquid velocities and particle size on the scaling factors based on the holdups of each phase and effective volumetric flux of fluids were examined. The deviation of gas holdup between the two kinds of three phase fluidized beds decreased with increasing gas or liquid velocity but increased with increasing fluidized particle size. The deviation of liquid holdup between the two fluidized beds decreased with increasing gas or liquid velocity or size of fluidized solid particles. The deviation of solid holdup between the two fluidized beds increased with increasing gas velocity or particle size, however, decreased with increasing liquid velocity. The deviation of effective volumetric flux of fluids between the two fluidized beds decreased with increasing gas velocity or particle size, but increased with increasing liquid velocity. The scaling factor, which was defined in this study, could be effectively used to analyze the hydrodynamic similarity in three phase fluidized processes.

2.5-D poroelastic wave modelling in double porosity media

SUMMARY To approximate seismic wave propagation in double porosity media, the 2.5-D governing equations of poroelastic waves are developed and numerically solved. The equations are obtained by taking a Fourier transform in the strike or medium-invariant direction over all of the field quantities in the 3-D governing equations. The new memory variables from the Zener model are suggested as a way to represent the sum of the convolution integrals for both the solid particle velocity and the macroscopic fluid flux in the governing equations. By application of the memory equations, the field quantities at every time step need not be stored. However, this approximation allows just two Zener relaxation times to represent the very complex double porosity and dual permeability attenuation mechanism, and thus reduce the difficulty. The 2.5-D governing equations are numerically solved by a time-splitting method for the non-stiff parts and an explicit fourth-order Runge-Kutta method for the time integration and a Fourier pseudospectral staggered-grid for handling the spatial derivative terms. The 2.5-D solution has the advantage of producing a 3-D wavefield (point source) for a 2-D model but is much more computationally efficient than the full 3-D solution. As an illustrative example, we firstly show the computed 2.5-D wavefields in a homogeneous single porosity model for which we reformulated an analytic solution. Results for a two-layer, water-saturated double porosity model and a laterally heterogeneous double porosity structure are also presented.

Experimental study on the solid velocity in horizontal dilute phase pneumatic conveying of fine powders

The calculation reliability of pressure drop and gas–solid drag force in horizontal dilute phase pneumatic conveying strongly depends on the accuracy of gas–solid velocity correlation. However, there are limited studies on the solid velocity in horizontal dilute phase pneumatic conveying and it is important to further validate suitability of existing correlation of gas–solid velocity, especially for fine particles (such as pulverized coal). Consequently, in this paper, a negative pressure pneumatic conveying test rig is set up and two kinds of powders with different sizes are adopted. Optical fiber probe (OFP) was used to measure the volumetric solid concentration and particle velocity. The volumetric solid concentration was also calculated by using the measured particle velocity. The results show that the solid concentrations obtained by the two methods have good agreement, and discrepancy is within ± 20%. It was found the particle velocities are different in the upper and lower part of the cross-section in the horizontal pipe. However, the difference is generally no more than 2 m/s. The velocity difference will decrease with the increasing gas velocity, and increases with the solid mass flow rate. In the experimental condition of 0.06 mm < d s < 0.35 mm, 1400 kg/m 3 < ρ s < 2600 kg/m 3, the implicit correlation based on Yang's Unified Theory gives the best prediction of particle velocity among existing studies but still with noticeable discrepancy with the comparison of the present experimental data. By modifying the solid friction factor, an improved correlation of the particle velocity was obtained, which agrees better with the experimental data given in the present and literature studies.

Solid-Liquid Two-Phase Flow Measurement Using an Electromagnetically Induced Signal Measurement Method

An electromagnetically induced signal measurement method is presented to measure solid-liquid two-phase flows in the present study. The method is validated by comparing visualization results for three flow patterns of “pseudo-homogenous flow,” “heterogeneous flow” and “heterogeneous and sliding-bed flow.” The present method has demonstrated a promising capability of measuring concentration and velocity of solid particles simultaneously with good accuracy.

Experiments and simulations of gas–solid flow in an airlift loop reactor

The hydrodynamics in a gas–solid airlift loop reactor was investigated systematically using experimental measurements and CFD simulation. In the experiments, the time averaged parameters, such as solid fraction and particle velocity, were measured by optical fiber probe. In the simulation, the modified Gidaspow drag model accounting for the interparticles clustering was incorporated into the Eulerian–Eulerian CFD model with particulate-phase kinetic theory. Predicted values of solid fraction and particle velocity were compared with experimental results, validating the drag model and the simulation. The results show that the profiles of particle velocity and solid fraction are uniform in annulus. However, the core-annulus structure appears in other three regions (draft tube region, bottom region and particle diffluence region), which presents the similar heterogeneous feature of aggregative fluidization usually occurred in normal fluidized beds. Simulated profiles of particle residence time distribution indicate that the airlift loop reactor should be characterized by near perfect mixing.