Distribution Of Particles In Flow Research Articles

Particle Flow Distribution in a Fluidized-Particles Multitube Solar Receiver

A fluidized-particles two-tube solar receiver was tested at ambient temperature at PROMES Laboratory to investigate the influence of an inhomogeneous solar flux density on the particle mass flow rate between the tubes. The principle of this 3rd generation solar receiver is to fluidize the particles in a container, called dispenser, in which the tubes’ bottom are immersed. The fluidized particles are flowing upward the tubes by applying an overpressure in the dispenser. Air velocities are changed inside the tubes, thanks to air mass flow controllers, to represent temperature heterogeneity between the tubes. Air velocities from 0.05 up to 0.52 m/s were tested, both in homogeneous and heterogeneous conditions. In the heterogeneous ones, the differences in air velocity between the tubes aim to mimic a difference in temperature from 20 to 100 % with homogeneous air flow rates injected. The following conclusions were drawn. First, the particle mass flux in the tubes are the same with homogeneous air velocities, each one following a calibration map previously obtained. Second, different air velocities lead to different particle mass flux. Third, the rise of the total particle mass flux diminishes the pressure in the dispenser. Four, this diminution of pressure leads to a decrease of the particle mass flow rate of the tube with the lower air velocity. This influence can lead in some cases to the stop of the fluidized bed circulation in the affected tube.

Heavy inertial particles in rotating turbulence: Distribution of particles in flow and evolution of Lagrangian trajectories.

We revisit the problem of heavy particles suspended in homogeneous box turbulence flow subjected to rotation along the vertical axis, which introduces anisotropy along the vertical and horizontal planes. We investigate the effects of the emergent structures due to rotation, on the spatial distribution and temporal statistics of the particles. The distribution of particles in the flow are studied using the joint probability distribution function (JPDFs) of the second and third principle invariants of the velocity gradient tensor, Q and R. At high rotation rates, the JPDFs of Lagrangian Q-R plots show remarkable deviations from the well-known teardrop shape. The cumulative probability distribution functions for times during which a particle remains in vortical or straining regions show exponentially decaying tails except for the deviations at the highest rotation rate. The average residence times of the particles in vortical and straining regions are also affected considerably due to the addition of rotation. Furthermore, we compute the temporal velocity autocorrelation and connect it to the Lagrangian anisotropy in presence of rotation. The spatial and temporal statistics of the particles are determined by a complex competition between the rotation rate and inertia of the particle.

A Continuous Microfluidic Concentrator for High-Sensitivity Detection of Bacteria in Water Sources.

Water contamination is a critical issue that threatens global public health. To enable the rapid and precise monitoring of pathogen contamination in drinking water, a concentration technique for bacterial cells is required to address the limitations of current detection methods, including the culture method and polymerase chain reaction. Here we present a viscoelastic microfluidic device for the continuous concentration of bacterial cells. To validate the device performance for cell concentration, the flow characteristics of 2-μm particles were estimated in viscoelastic fluids at different concentrations and flow rates. Based on the particle flow distributions, the flow rate factor, which is defined as the ratio of the inlet flow rate to the outlet flow rate at the center outlet, was optimized to achieve highly concentrated bacterial cells by removal of the additional suspending medium. The flow characteristics of 0.5-, 0.7-, and 1.0-μm-diameter particles were evaluated to consider the effect of a wide spectrum of bacterial size distribution. Finally, the concentration factor of bacterial cells, Staphylococcus aureus, suspended in a 2000-ppm polyethylene oxide solution was found to be 20.6-fold at a flow rate of 20 μL/min and a flow rate factor of 40.

The effect of arrangement in multi-cyclone filters on performance and the uniformity of fluid and particle flow distribution

In this research, a design algorithm of a multi-cyclone filter box based on available volume is proposed. The influence of arranging cyclones in the box and the uniformity of fluid and particle flow distribution is also studied. After introducing domain physics, used governing equations are expressed. Grid generation and validation of the numerical solution are then examined. Design of the quantity, diameter, and performance parameters of the cyclone in the filter set is performed by presenting an algorithm. This study shows that adding only 10% to the volume of the filter box reduces the pressure drop by 40 to 50%. For filters consisting of many cyclones, the optimized arrangement of cyclones next to each other is introduced which can improve the standard deviation of flow distributions by 27.5%. Increasing the inlet flow rate can make the distribution of larger diameter particles among cyclones non-uniform by up to 85%.

Parametric Study on the Flow Profiles of Vertical Sinter Cooling Bed Using the DEM and Taguchi Method for Waste Heat Recovery

To comprehensively understand the effectiveness of external factors on flow characteristics and realize particle flow distribution evenly in bulk layers is an essential prerequisite for improving the performance of heat transfer in vertical sinter cooling beds (VSCBs). The numerical discrete element method (DEM) was applied to investigate external geometric and operational factors, such as the aspect ratio, geometry factor, half hopper angle, normalized outlet scale, and discharge velocity. Using the Taguchi method, a statistical analysis of the effect of design factors on response was performed. In this study, we focused more on external factors than granular properties, be remodelling the external factors was more useful and reliable for actual production in industries. The results showed that the most important factor was the aspect ratio, followed by the geometry factor, normalized outlet scale, half hopper angle, and discharge velocity for the dimensionless height of mass flow. In terms of the Froude number, the most influential factor was the normalized outlet scale with a contribution ratio of 33.81%, followed by the aspect ratio (22.86%), geometry factor (17.73%), discharge velocity (17.73%), and half hopper angle (11.83%).

Low-rank coal gasification using a bubbling fluidized bed reactor at low operating temperature

Coal gasification is one of coal utilizations that produces less CO2 emission than coal combustion. Coal gasification technology that has been used in Indonesia is generally a fixed bed gasification. Fixed bed is designed for high-rank coal and the majority of Indonesian coal is of a low-rank. Low ash and high moisture content of the Indonesian coal in a fixed bed can affect mechanical and thermal fragmentation, pressure drop, gas and particle flow distribution. The operation of gasifier may cause unstable condition. Another gasification technology is bubbling fluidized bed, which is operated above 1,200°C, so ash can melt. High operating temperature causes agglomeration and makes unstable gasification process. Therefore, in this study, low-rank coal is gasified in bubbling fluidized bed reactor at low operating temperature. The purpose of this study is to determine the optimal conditions of bubbling fluidized bed gasification. The research was conducted in bubbling fluidized bed coal gasification Process Development Unit (PDU) at Coal Utilization Technology Centre of R&D Centre of tekMIRA, Palimanan. Coal was fed continuously as many as 20 kg/hour into a gasifier then was gasified to produce gas using air as a gasifying agent and silica sand as a bed material at 850- 950°C. The produced gas from the gasification was analyzed using the Orsat Analyzer. A simulation using a ChemCAD 7.1 CC steady state was applied to validate the experiment result. From the analyzed result of yield gas composition, the produced CO and CO2 were about 10-15 wt%. Gas compositions that are close to criteria of producer gas, no agglomeration, and stable process condition during study indicate that bubbling fluidized bed gasification at low operating temperature is suitable to be applied as gasification technology for Indonesian low-rank coal.

Operating technical characteristics on asymmetrical arrangement of six cyclones in a 600 MW supercritical CFB boiler

In order to obtain the operating characteristics of the first 600 MW supercritical circulating fluidized bed (CFB) boiler with six cyclones in an asymmetrical arrangement, the gas-solid flow information and temperature distribution of six circulating loops were measured and analyzed. The experimental results indicate that bed temperature in the furnace presents an S-type distribution pattern along the furnace height direction, for three cyclones of the same side, the temperature in the middle cyclone is high and the temperature on both side cyclones is low. At high boiler loads (450–600 MW), the temperature distribution of six cyclones and the gas-solid flow uniformity along the furnace height direction is more uniform, the temperature distribution uniformity in dense phase zone of furnace and three circulating loops on the right side wall are superior to those of the left side wall. The calculation results indicate that the particle flow distribution of six cyclone inlets is relatively uniform, the calculated results are consistent with the test results. The gas-solid flow asymmetry phenomenon of six circulating loops on both sides of the furnace is found, and the relative standard deviation of six cyclones inlet temperature does not exceed 4.30%, the back pass structure needs further optimization.

Uneven distribution of particle flow in RFCC reactor riser

The uneven distribution of particle flow, i.e., a different particle mass flow rate in each outlet of the riser in residue fluidized catalytic cracking (RFCC) processes, is one major problem associated with commercial RFCC processes. This problem affects the formation of carbonaceous deposits in the secondary reactor cyclone, which incurs serious catalyst carryover in the fractionators. This study analyzes particle-fluid flow patterns in the riser, and diagnoses the uneven distribution of particle flow using a computational particle fluid dynamics (CPFD) method to solve this real industrial problem. Through this analysis, the effect of the number of feed injectors is investigated. The CPFD method, which has been developed to complement the Eulerian-Eulerian and Eulerian-Lagrangian methods, applies the Navier-Stokes equation for fluid phase and multi-phase-particle-in-cell (MP-PIC) models for particle phase. The particle flow distribution was found to vary by 15.5–18.7% at different outlets in the 1 injector case, which implies that the solid loading ratio in each cyclone is different, thereby affecting the separation efficiency of the cyclone and the formation of carbonaceous deposits. The uneven distribution of particle flow phenomena was identified, and the standard deviations of particle mass flow rates were evaluated for the cases of 1, 2, 4, 6, 8 and 12 injectors, and were found to be 7.52, 4.07, 2.66, 1.78, 2.85 and 3.82, respectively. From these results, the 6 injectors case was found to have a largely even particle flow distribution.

A DEM-based approach for analyzing energy transitions in granular and particle-fluid flows

Granular and particle-fluid flows are widely observed in nature and in industry. Their behaviors are determined by the injection of energy and the subsequent cascade of energy. This work presents a DEM-based approach for the analysis of energy transitions in such flows. The approach can consider the energy injection, dissipation and conversion due to driving forces such as particle-fluid interactions and the gravitational force, particle-particle/wall collisions and frictions. The effectiveness is demonstrated in two systems respectively and the transient and averaged energy transitions are discussed. The results reveal the connection between the formation of a cluster and the variation of energy in fluidized beds. From the viewpoint of energy transition, the results also illustrate the minimization of energy dissipation, the startup of fluidization and the particle flow distribution. Furthermore, the correlation of the contact between particles and the energy transition is demonstrated. The findings should be useful for the understanding of structure formation in fluidized beds and for industrial applications.

Influence of a laminarizer at the inlet on the classification performance of a cyclone separator

Abstract A laminarizer consisting of a bank of 15 tubes was assembled at the entrance of a cyclone. Experiments and numerical simulations were performed to examine the influence of the laminarizer on the pressure drop across the cyclone, partial separation efficiency, gas tangential velocity distribution, particle distribution at the entrance, and 50% cut size. Using the laminarizer slightly increased the pressure drop across the cyclone and slightly reduced the gas tangential velocity. The laminarizer altered the air mass flow rate and particle flow distribution at the entrance. It increased the air mass flow rate through the outer part of the entrance. At an inlet gas velocity of 11 m/s, installing the laminarizer reduced the number of particles flowing through the inner part of the entrance by 20.2%. Higher particle concentrations were found at the outer part of the entrance, where the particles were more easily captured after entering the main body. At an inlet gas velocity of 11 m/s, using the laminarizer increased the pressure drop across the cyclone by 8.1% and reduced the 50% cut size of the cyclone from 2.04 μm to 1.89 μm.

Piezoelectric particle counter using the resonance vibration modes of a circular plate

In the field of environmental measurements, robust and simple sensors with no electric power supply are required. In the river, the size distributions of sand and small stones in river-bed are important factor for river disaster prevention. In this report, a passive piezoelectric sensor for measurement of the particle distribution in flow was investigated. The sensor consists of an aluminum circular plate (diameter: 50 mm; thickness: 2 mm) and an annular piezoelectric transducer (inner radius: 5 mm; outer radius: 10 mm). Alumina spheres with several diameters (φ = 3, 5, and 8 mm) were employed as small particles. When the particles hit the surface of the sensor, the flexural vibration is excited on the circular plate and the electric power is generated through the piezoelectric effect. Two main peaks at 16.3 and 66.7 kHz appeared in the output signal, and the ratio of these peaks depended on the particle size. From the finite element analysis, it was found that these frequencies of 16.3 and 66.7 kHz correspond with the fundamental and second resonance vibration modes. These results indicate that the particle size can be determined from the frequency spectrum of the output signal.

Preferential concentration of heavy particles in compressible isotropic turbulence

Numerical simulations of particle-laden compressible isotropic turbulence with Taylor Reynolds number Reλ ∼ 100 are conducted by using a high-order turbulence solver, which is based on high-order compact finite difference method in the whole flow domain and localized artificial diffusivities for discontinuities. For simplicity, only one-way coupling (i.e., the influence of fluid on particles) between the carrier flow and particles is considered. The focus is on the study of the preferential concentration of heavy particles in dissipative scale of turbulence and the underlying mechanisms. Firstly, the effect of Stokes number (St) on the particle distribution in flow of Mach 1.01 (referred to as high-Mach-number case in this study) is investigated as a necessary supplementation for the previous studies in incompressible and weakly compressible flows. It turns out that heavy particles with Stokes number close to unity exhibit the strongest preferential concentration, which is in agreement with the observation in incompressible flow. All types of heavy particles have a tendency to accumulate in high-density regions of the background flow. While all kinds of particles dominantly collect in low-vorticity regions, intermediate and large particles (St = 1 and St = 5) are also found to collect in high-vorticity regions behind the randomly formed shocklets. Secondly, the impact of turbulent Mach number (Mt) (or the compressibility) of the carrier flow on the spatial distribution of the particles with St = 1 is discussed using the simulated compressible flows with Mt being 0.22, 0.68, and 1.01, respectively. In low-Mach-number flow, particles tend to concentrate in regions of low vorticity due to the centrifuge effect of vortices and particle concentration decreases monotonically with the increasing vorticity magnitude. As Mach number increases, the degree of particle clustering is slightly weakened in low-vorticity regions but is enhanced in high-vorticity regions, which only account for a small fraction of the flow domain. This observation as well as the anomalous correlation between the fluid density and vorticity can be ascribed to the appearance of randomly distributed shocklets in high-Mach-number turbulence, which enhance the vorticity and density (pressure) immediately behind them. Finally, the effects of the forcing and cooling schemes on the properties of flow and particles are also discussed.

Hadronization properties in   e e annihilation at S  60GeV centre of mass energy

The hadronic events from the experimental data , as well as the PYTHIA Monte-carlo data at the 60 GeV centreof mass energies are studied.We present the general properties of multihadron final states produced by e e   .Globalshape, inclusive charged-particle, and particle-flow distributions are presented. Our measurements are comparedwith QCD + fragmentation models that use either leading-logarithmic parton-shower evolution or QCD matrixelements at the parton level, and either string or cluster fragmentation for hadronization. Possible explanations forourcompariaon are presented in this paper.

Electric propulsion plasma plume interaction with “Phobos-Soil” spacecraft structural components

Assessment was made by calculations for the possible consequences of the effect of plasma plume injected by the solar electric propulsion system (SEPS) on the structural components of “Phobos-Soil” spacecraft (SC). Propulsion system comprises three SPT-140 thrusters, two of which should secure the required total thrust impulse during 8000 hours of operation approximately. Variation of the solar panel (SP) properties as a result of their surface contamination with the products of erosion of thruster and SC structural components is the primary negative consequence of plasma plume effect on the SC. Calculation study for the processes of erosion, particle flow distribution, and contaminating coating formation on the SP surface was made for different SEPS arrangements. It is shown that power reduction for the landing module SP sections, which are subjected to the contaminating coating deposition to the most extent, will not exceed 5% of the nominal level.

Optimisation of sputnik distributor using numerical method

A coal distributor is necessary to mix and split raw coal for subsequent processing in a parallel module coal preparation plant. The sputnik hydraulic distributor, a static device with two internal chambers and tangential water pipes, is widely employed for this purpose. Biased properties in the discharging slurry streams may lead to many problems. It is useful to develop a mathematical model to aid the design, control and optimisation of the operation. For this purpose, we have recently developed a computational fluid dynamics (CFD) model which uses homogeneous two-phase flow method to solve the three-dimensional distribution of water flow and its volume fraction and a discrete element method (DEM) to describe the motion of coal particles in the distributor. In this article, extensive numerical experiments based on the CFD model are conducted and the detailed fluid flow pattern is analysed to understand the main causes for water maldistribution inside a 12-way coal distributor, aiming to identify the optimum operational condition and design for practice. Variables considered include water flow rate and velocity, layout of water inlets, size and position of the inserted table, geometry of orifice slots and outlet size. The initial momentum of tangential inlet jet is found to be most important to minimise biased mass flow rate among outlets. Three mechanisms, namely, geometric distribution, swirl distribution and gravity distribution, are found to be responsible for the water distribution. To test the outcomes, the flow of coal particles is also simulated using DEM. Several cases with different operational conditions are considered to clarify the influence of water flow on particle flow and the relationship between water distribution and particle flow distribution at the outlets. The findings should be useful in the development of a better understanding of this complicated gas-liquid-particle flow system or new designs and control strategies for coal distributors.

中心装入粒子の密度や摩擦特性が高炉内固体粒子流れと炉芯挙動に与える影響の数値解析

A center coke charging method from the top of blast furnace is known for a novel approach to burden distribution and coal combustion. This method is considered as one of the key technologies for keeping gas permeability of deadman in the lower part of blast furnace and producing iron liquid with a stable furnace operation. In recent years, the center charging method is also expected as improving the unsteady behavior with bridging/slipping of solid bed in low reducing agents operation of blast furnace. In the present study, a center charging method with different particle density or friction coefficients is carried out numerically by using a 3-dimensional Discrete Element Method (DEM). Before the numerical analysis, an experimental approach using a two-dimensional cold model is also examined. Alumina sphere was used as representative particle of coke/ore packed bed and the glass sphere was for the center charge. From the experiment, it was found that the height of deadman is reduced dramatically by using the center charging method with the glass sphere. This experimental result was compared with the numerical approach, although the gas flow was not considered in the numerical method. In the numerical results, the void fraction was calculated more precisely compared to the previous numerical two-dimensional calculation. Almost uniform particle flow distribution called a piston flow pattern was fairly maintained by the numerical center charging method, and as the result, the height of deadman was also confirmed reduced numerically compared to the alumina bed only. This result was qualitatively coincident with the experimental flow pattern except for the particle velocity descending faster in the experimental center-charging region, which could be available for the operation of deadman control.

Numerical Simulation of Effect of Tuyere Angle and Wall Scaffolding on Unsteady Gas and Particle Flows Including Raceway in Blast Furnace

We have performed the numerical simulation for the particle and gas flows in the raceway region in a blast furnace of which dimension is almost the same as that of the commercial blast furnace using Distinct Element Method for the computation of the multi-body interaction among coke particles, Hard Sphere Model for two body interaction of powder particles based on Direct Simulation of Monte-Carlo Method, and Finite Difference Method for the numerical analysis of Navier–Stokes equations with the interaction terms between gas and particles for the gas flows. In the present simulation we have calculated the particle and gas flows in the raceway regions in which tuyere angles are 0, 3, 7 and 11 degree downward. The downward inclination of tuyere means that the air injects to the higher pressure side. This would stabilize the air flow and the raceway would become stable. However if the inclination angle is too high, the flow becomes unstable by various conditions near the bottom of blast furnace. The coke particle flow rate from the center region of blast furnace and its flow width increase with increasing the tuyere downward angle from the horizontal and attains the maximum value at near 7 degree. It means that the coke particle flow becomes widely uniform at about 7 degree tuyere angle except the region near the furnace wall.We have also calculated the effect of scaffolding on the furnace wall on the particle and gas flows. The coke particle flow distributions with scaffolding on the wall become narrower. The scaffolding is nearer to the raceway, the effect of that becomes stronger. The raceway is not spherical and becomes unstable in cases with scaffolding on the wall. The coke particle velocity becomes higher by the narrow coke particle flow distribution caused by the existence of the scaffolding on the wall and it concentrates coke particles on the upper part of raceway near the furnace wall. The coke particle flow is dammed by the scaffolding and the wide area in which the coke particle velocity is very low is formed on the scaffolding. The gas flow distribution with scaffolding becomes non-uniform, particularly in the area between the softening melting cohesive zones and the scaffolding due to their interaction. The gas flow is also dammed up by the scaffolding and softening melting cohesive zones. The existence of scaffolding near softening melting cohesive zones strongly affects the gas flow.

Colour reconnection effects in WW production at LEP

Preliminary results from the search for colour reconnection effects by the four LEP experiments and a first combination of their measurements of the inclusive particle flow distributions in four-jet events are presented. Data are compared with predictions of various models with and without colour reconnection. The extreme scenario of the SKI model, where almost all events are reconnected, is ruled out and a limit on the model parameter, controlling the fraction of reconnected events, is set.

Studies of colour reconnection effects in hadronic W pair decays at LEP

The main results obtained from studies of colour reconnection effects in hadronic decays of W pairs produced in e + e − annihilation are reviewed. This includes results on charged particle multiplicity and momentum distributions as well as investigations using a new method based on particle-flow distributions.

Particle dispersion for suspension flow

Particle dispersion is the flow-induced long-time collective particle diffusion. It is different from the short-time or long-time self-diffusion of particles (Brady 1994) for there is no particle dispersion in a suspension at rest. The contradiction of the dispersivity among different experimental settings reported in the literature is resolved. Applying volume-and-time averaging concepts in analyzing suspension flow, we are able to relate the particle dispersion with bulk flow velocity field. Non-uniformity in particle force dipole strength gives rise to particle collision-deflection induced particle migration or shear-induced particle migration (dispersion). In addition, bulk flow itself and the rotation of particles also cause particle random movement in concentrated suspensions. Thus, there is a pure bulk flow-induced particle dispersion. A constitutive equation for computing particle concentration and velocity profiles is proposed. The model parameters are drawn from fluidization, flow in porous media, sedimentation and granular flow down a rectangular channel. The model predictions agree well with experimental data for suspension flows in concentric cylinders. The particle concentration distribution in a flow field is greatly influenced by the particle size d s and average concentration in addition to the details of the flow field. The two parts of the particle dispersion, flow-induced dispersion and shear-induced particle migration, have opposing effects on particle concentration distribution. Shear-induced particle migration causes particles to concentrate in the low shear region, while flow-induced particle dispersion causes particles to spread evenly in the flow field. The shear-induced particle migration is proportional to d 2 s . The two parts in the flow-induced particle dispersion, particle dispersion due to translational flow and particle dispersion due to rotational flow, have different degrees of dependence on the particle size. The particle dispersion due to translational flow is directly proportional to d s and the particle dispersion due to rotational flow is proportional to d 2 s . Thus, suspension of smaller particles tends to have more even distribution of particles in flow. Since the particles cannot concentrate more than the random packing limit, the average particle concentration also influences the particle concentration distribution.