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Study of airflow induced by regular particles in freefall through tubes
Abstract
Airflow induced by falling particles can be a significant factor in causing dust emission during the conveyance of bulk materials. Heretofore, there have been few experimental studies on the effect of the particle size and the diameter of the tubes through which they are falling on the induced airflow. This study involved the experimental analysis of the correlation between those two factors and the induced airflow. The results were as follows: within the range of the total drag coefficient (0.62–0.94) of the experimental setup, the induced airflow velocity increased with an increment of the mass flow rate of the particles and drop height, and the power exponents of a fitted curve were approximately 0.35 and 1.29, respectively. Within the particle diameter range of 3.247–9.223 mm, the power coefficients and power exponents of a fitted curve for induced airflow velocity increased from 0.224 and 0.269 to 0.458 and 0.384, respectively, with the increase in particle size. As the tube diameter decreased from 200 mm to 120 mm, both the induced airflow velocity and the quantity of specific induced airflow increased, while the quantities decreased when the tube diameter decreased from 120 mm to 75 mm. The semi-empirical equation of the induced airflow velocity was established to predict the quantity of induced airflow under various operation conditions.
... Logachev et al. [18] considered the drag of particles with different sizes using a probabilistic approach and proposed a new model to compute the flow rate of entrained air for a polydisperse loose material. Wan g and Li [19] derived a semi-empirical equation for entrained airflow velocity calculations with the consideration of the effect of particle sizes and tube diameters. Besides, Duan et al. [20] experimentally investigated the first and second fugitive dust generation rates with changing drop heights, hopper outlet diameters and material temperatures, while Wang et al. [21] mainly focused on the effect of the drop height and divided particle flow into three regimes including the stable, transitive and dispersive regimes. ...
... (4) Entrained airflow rate per unit mass flow rate According to the work done by Wang and Li [19], the entrained airflow rate per unit mass flow rate was analysed in this study. Similar to the method adopted by Uchiyama [8,9], the entrained airflow rate per unit mass flow rate for each DHS was calculated by integrating the airflow velocities over the area. ...
Dust pollution related to the discharge of hoppers has drawn the attention from industries dealing with bulk solids handling. This paper presents an experimental setup to measure the dust concentration of dust suppression hoppers (DSHs) with various geometries and investigate the dust influencing factors. To understand the interactions of the bulk solids and entrained air during discharge, a coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) method is developed. The behaviour of the bulk solid particles and airflow is studied numerically. Results show that DSHs with a central plug of the bulk solid suppress dust by minimising the air entrainment within the particle flow, compacting the particle flow and reducing the velocities of the particles and airflow. Moreover, hopper geometries including the hopper half angle, outlet opening and outlet diameter can have significant influences on the performance of dust suppression.
... The current research results mainly focus on the following dimensions: for high skidding unloading, the influence of different factors on the impact airflow and dust distribution characteristics is mainly studied. Xu Shengdong, Jiang Zhongan et al [4][5][6][7] took mass flow rate, unloading height, and the sealing degree of the chute into consideration, and confirmed that both of them also have a large influence on the dust distribution characteristics; Henmon et al [8][9][10][11] derived the formula for the volume of air volume of coiled suction in the process of free-falling through calculations, and continuously revised it; Sun Hongfa et al [12][13][14] used experimental means to illustrate the relationship between induced airflow and each material, the angle of outflow, the outflow velocity, the velocity of the outflow, and the dust distribution characteristics. Sun Hongfa et al [12][13][14] used experimental means to illustrate the close degree of induced airflow and each material outflow angle, outflow speed, discharge height and other factors. ...
Based on the one-factor method (with different mass flow rates), experiments were carried out on the diffusion phenomenon of particle flow, diffusion diameter, transport velocity and dust concentration to derive the relationship between mass flow rate and each field quantity. The results show that: with the increase of mass flow rate, the particle flow diffusion phenomenon is more obvious under the influence of tangential friction and horizontal resistance, and is accompanied by the generation of vortex; the diffusion diameter, transport velocity and dust concentration all show a tendency to increase with the increase of mass flow rate, and the duration of the high concentration of dust at 0.152kg/s reaches 10s, and the dust transport velocity does not increase any more when the height of the downward drop is increased to 0.33m. When the drop height increased to 0.33m, the dust transport velocity no longer increased.
... Based on the diffusion mechanism of dusty airflow and the energy dissipation theory, the geometric structure of the transport chute was improved, and a composite straight-arc chute dust suppression device was proposed. In studies [21][22][23][24], according to the motion characteristics of the induced airflow during the transfer of loose materials in a chute, a return flow structure was set in the material-guide chute to form eddy currents to promote the internal airflow hedge, and thus reduce the induced airflow speed. In addition, a dust curtain was set in the dust removal area of the maze to further consume the kinetic energy of the airflow and allow the dust carried by the dusty air to settle to suppress the dust. ...
Aiming at addressing the problem of dust generated when grab is unloaded, the flow field characteristics of fugitive dust in an open space were studied and reflected its unstable and complex nonlinear dynamic process. Using coal, sand, and flour as research objects, an experimental model and measurement system for grab unloading were built, and the dust diffusion range, diffusion speed and direction, settling time, dust concentration, and induced wind velocity at different measurement points were compared. The computational fluid dynamics–discrete element method (CFD-DEM) coupling method was adopted, the discrete phase model (DPM) of dust was established, the interaction of the particle, dust, and airflow fields during the unloading process of the grab was further studied, and the distribution and diffusion laws of the induced airflow and dust were obtained. The acquisition of flow field characteristics is of great significance for controlling and guiding the orderly deposition of dust.
... Theoretical friction coefficient and air resistance (Eq. (3.2)) [10] is used in numerical experiments, and particles induced air motion is considered. ...
In the Thesis a new method is developed for optimising the shape of mechanical elements by considering the interaction of these elements with a multiphase uncertainty environment whose approximation model achieves a significant number of degrees of freedom (DOF). The Thesis analyses the process of dust formation during the handling of granular material. Different experimental designs are used to derive metamodels and to analyse the segregation of granular material in the silo discharge depending on the oscillation frequency, amplitude, and geometrical characteristics of the silo.
... ВВЕДЕНИЕ П роцессы загрузки сыпучих материалов сопровождаются значительным пылевыделением, что негативно сказывается на окружающей среде, здоровье человека [1,2], долговечности оборудования и может привести к взрывам и пожарам [3]. Причинами образования и распространения пыли являются как процесс эжекции воздуха сыпучим материалом [4,5], так и вторичное пылеобразование при взаимодействии потока с поверхностью [6,7].Одним из способов снижения пылеобразования является снижение расхода эжектируемого воздуха [8,9]. Методам расчета расхода эжектируемого воздуха [10][11][12], а также изучению процессов увлечения воздуха сыпучим материалом посвящено много научных работ [13][14][15]. ...
Расчетным путем показана целесообразность веерной загрузки бункеров порошкообразным сыпучим материалом. Предложена конструкция кольцевого загрузочного устройства, использующего эффект Коанда, для снижения пылеобразования. Численно и экспериментально определены рациональные конструктивно-технологические параметры разработанного устройства.
... Сравнение осевых максимальных скоростей при удалении от крышки бункера показало, что пылеобразующая способность веерной струи значительно ниже, чем в случае осесимметричной и плоской струй (рис. 2), что важно для за-ÝÊÎËÎÃÈß * Часть 1 статьи опубликована в журнале «Новые огнеупоры» № 2 за 2021 г. дач совершенствования систем аспирации [1,2] и обеспыливания при загрузке сыпучих материалов [3,4] в бункеры силосного типа. ...
On the basis of the obtained analytical dependencies, the expediency of fan loading of bunkers with powdery bulk material has been proved. The design of an annular charging device, which reduces dust formation, using the Coanda effect is proposed. The rational design and technological parameters of the developed device are numerically and experimentally determined.
... Li et al. 16 studied the induced airflow velocity of falling materials in a semiclosed transfer station and discussed the nonlinear characteristics of induced airflow velocity with the mass flow, falling height, and the resistance coefficient of the shell. Li et al. also studied the airflow induced by regular particles in free fall through tubes, 17,18 Jalaal et al. 19 used a similar experimental device to Li's to study the influencing factors of induced airflow, and they considered all factors more fully. Chen et al. 20,21 studied the induced airflow and dust emission in the belt conveyor transfer by numerical simulation and proposed several scale models to reduce dust emission. ...
In this paper, a coupled computational fluid dynamics and discrete element method (CFD-DEM) is used to numerically simulate the energy transfer of the ore falling process and the change law of impact airflow velocity under different influencing factors. The results are as follows: the total drag force is an important factor that determines the impact airflow velocity. The greater the total drag force, the greater the impact airflow velocity. The impact airflow velocity increases with the increase of mass flow rate and discharge height and decreases with the increase of ore size, and it is found that the discharge height has the greatest impact on the impact airflow velocity, the ore size is the second, and the mass flow rate is the smallest. Therefore, in the allowable range of mine production, the discharge height should be appropriately reduced. The mathematical model of the impact airflow velocity is obtained by multivariate nonlinear regression on the experimental results of orthogonal experiments.
Vehicle unloading causes dust emission during the fall of raw materials in a semi-open industrial building. The dust is further dispersed around buildings via natural wind, which has rarely been investigated. This study examines the effects of approaching wind and induced airflow on wind and pollutant fields around a semi-open industrial building during vehicle unloading. Four influencing factors are assessed, namely, the induced airflow velocity, continuity, proportion of induced airflow, and direction of approaching wind. Turbulence model and numerical methods are applied after validations with benchmark wind tunnel experiments, and the correlation coefficients are above 0.83. The personal intake fraction (P_IF) is utilized to quantify human exposure risk. Results indicate that both the induced airflow velocity and proportion of airflow are positively related to the pollutant dispersion ranges. Unloading at different positions as a continuity variation also affects the concentration distributions. Specifically, unloading at the central position more effectively dilutes pollutants than does unloading at the outer position of the building. Pollutant dispersion extends up to 10H under a 90° wind direction, whereas the maximum average P_IF occurs under a 135° wind direction. The findings provide a useful reference for further building design to reduce pollutant dispersion around semi-open industrial buildings.
Transshipment of compacted soybean is characterized by labor-intensive processes, long operating times, and a great amount of dust that cannot be collected by sealed devices. This dust significantly reduces air quality of the workshop and represents a great threat to human health. Solving this problem has been a great challenge in the soybean storage industry. For this reason, in the present study the concept of a transshipment system for soybean clearance was proposed. This system can simultaneously achieve real-time transshipment of falling materials and air curtain control of fugitive dust. The main factors influencing the performance of the air curtain dust control system were investigated using numerical simulation, and the effects of the exhaust-to-pressure ratio K and air curtain outlet velocity V on dust control efficiency were determined. Results showed that the width of the dust-collecting paths increased with increasing K and V values. We also found out that dust-escape paths were mainly concentrated in the transition height between the complete air curtains and local air curtains. At the beginning of the process, dust control efficiency rapidly increased and the increment rate became slower as K increased. When K = 1.5 and V = 5–6 m/s, dust control efficiency reached values up to 94.03–97.73%. Based on numerical simulation results, the prototype transshipment system for soybean clearance was developed, and the effectiveness of air curtain dust control was validated via smoke tracing experiments. After the application of the developed system, occupational lung disease can be significantly reduced, and transshipment efficiency per clearance can be enhanced by approximately 67% (about 50,113￥ can be saved in terms of energy consumption and labor resources). An extra granary can be saved after using the newly developed system for 36.5–52.1 clearances.
On the basis of the obtained analytical dependences, the expediency of fan loading of bunkers with a powdery bulk material has been proved. The design of an annular loading device which reduces dust generation using the Coanda effect is proposed. The rational design and technological parameters of the developed device have been determined numerically and experimentally.
By means of a calculation, the expediency of fan loading of bunkers with powdery bulk material is shown. The design of an annular loading device using the Coanda effect to reduce dust generation is proposed. The rational design and technological parameters of the developed device have been determined numerically and experimentally.
The effects of three factors (i.e., drop height h, hopper outlet diameter d0, and material temperature T) on the dust generation rate derived from a free falling particle stream were investigated via full factorial experiments. The correlation between the three factors and dust generation rate was also analysed. Results show that T and h affect the first fugitive dust rate largely, whereas the second fugitive dust rate is mainly dominated by h and d0. Through analysing the first fugitive dust percentage data, it is found that h and T should be considered first for higher temperatures and lower flow rates, whereas h and d0 can be considered under contrasting conditions, and h should be controlled in the remaining two sets of conditions. Relationships between the influencing factors and total and first fugitive dust rates were developed via multiple regression to quantify the dust emission rates for different contact surfaces (rigid or water).
Bulk materials handling operations involving falling streams of the bulk material are common throughout industry. Proper design of any fugitive dust control system servicing such operations requires knowledge of the behaviour of the free-falling stream in terms of the air entrained by the falling material and the concentration of dust liberated. In this paper results of experiments on alumina powder free-falling from a hopper are presented. It was found that the material stream initially contracts in cross-section as it accelerates and a boundary layer of dusty air develops around the core stream of bulk material. Results of air entrainment per unit mass of parent material are also given. The authors describe a simple analytical model of the complex air entrainment process by treating the falling stream of material as a negatively buoyant plume of dusty air fully miscible with the ambient air. The experimental data are successfully correlated using this approach. The plume model provides a more realistic description for the situation considered here than previous theoretical treatments based on air movement induced by isolated particles independently falling through quiescent air.
We experimentally and numerically examine the flow characteristics of powder jet and entrained air. A phase-Doppler anemometer is used for the measurement of axial velocity profiles of particle and entrained air. It is found that the axial velocity profile of the entrained air takes a maximum at the center-line and decreases toward outer edge. A flow region of the entrained air extends transversely into a particle free region. The center-line velocity of entrained air at first increases with increasing distance from the orifice outlet and then decreases after it remains a plateau. The transverse dispersion of the entrained air is very small as compared with that of a single-phase turbulent jet. The numerical simulation is performed based on the Lagrangian modeling for particles and Eulerian modeling for air flow. We consider particle-particle collision, gravity force, drag force and transverse force due to the particle spin and to the velocity gradient of airflow, and apply a k-ε model. The present simulation qualitatively explains our measurement in terms of velocity profiles and dispersion ofparticle and air.
† This report was originally printed in J. Soc. Powder Technology, Japan. 37(3), 160-167 (2000) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Dust generation in solids handling involving free fall of bulk materials and impacts on a stockpile can cause many problems in industry and be a great danger for operators health. This paper describes an experimental set up to characterize the dust plume formed in free fall of powders from a hopper and investigates the influence of various outlet geometries on the dust plume. For this purpose an image analysis technique was developed to quantify the characteristics of the dust plume.
The characteristics of a free falling powder jet of glass beads are investigated in terms of axial velocity profile at several distances ranging between 1 to 1500 mm from different orifices using a laser-Doppler velocimeter. The free falling velocity of a particle in the powder jet is larger than that of the single particle in an unbounded fluid vs and increases with increasing mass flow rate. A uniform profile exists near the orifice. At a long distance from the orifice, the velocity profiles of powder jet are like those of a single-phase free turbulent jet, provided that the outer edge of the powder jet does not extend past the radius where the velocity is slightly greater than vs. The diffusion of the powder jet is very small as compared with that of a single-phase jet.
In this paper the problem of dust emission from belt conveyor transfer points is thoroughly examined. Different formulas and current design methods are reviewed, compared and analyzed. The sensitivity of exhaust volume requirements to the pertinent parameters is demonstrated. An analytical tool for exhaust volume calculations is offered. A discussion on the importance of a number of factors on dust enclosure designs is also presented.
The dust generation occurring during the handling of bulk materials in free falls or at the impact on a stockpile can be a source of danger for the operators health. Proper design of control systems of fugitive dust requires knowledge of the behavior of the free falling powder, the air it entrains, and the concentration of dust liberated. This paper presents first a simple model for a free falling column of bulk solids and compares it with relevant previous research. This two phase model predicts the particle and air velocities, and especially the volumetric flow of induced air in the column without dependence on any empirical constant like the entrainment constant used in the plume model. For small drop heights, the predictions of the theory appear to be in qualitative agreement with the available data for the quantity of air entrained, but the theory needs to be extended in the case of large drop heights, when the expansion of the jet of particles is large. in a second part, the description of an expanded jet of particles is experimentally studied with PIV measurements. The data obtained are well fitted by the model by Liu, when the entrainment constant is taken as the angle of expansion of the jet obtained from the velocity field.
A comprehensive solution is offered to the problem of dust emissions at belt conveyor transfer points. Details of enclosure design are discussed and a straightforward procedure for calculating required dust control exhaust volume is presented. Many design variables are taken into account which heretofore have been commonly ignored or inadequately considered. These include belt widths, belt speeds, enclosure openings, material flow rate, material bulk densities, material lump sizes, height of material fall, material temperature, and ambient air temperature.
Dust generation mechanisms are discussed in terms of basic theory, particularly the theory of induced air flow, derived from the frictional drag imposed by air on the falling or projected particles. Methods of quantifying the dust generation mechanism are derived. Example calculations concerning a typical enclosed conveyor-to-conveyor transfer operation illustrate the key parameters determining the magnitude of the induced air flow which must be controlled. Good transfer chute design practice is discussed. (D.W.T.)
The flow regimes in a free falling particle stream and the dust emission rate are experimentally explored in this paper. The results show that the particle stream could be divided successively into the stable regime, the transitive regime and the dispersive regime. The length of each regime is quantitatively identified. In our testing range, the dust emission rate (ηr) increases monotonically with Z and the gratitude gradually increases when the particle stream impacts onto the rigid surface in the transitive regime. The dust generation rate shows linear to the dimensionless drop height. However, the rate decreases slightly monotonically with the drop height (Z) when the particle stream impacts onto the surface in the dispersive regime. The dust generation rate presents an exponent relation with the dimensionless drop height. The empirical equation about ηr is derived. It is found that the second fugitive dust still emits under the condition that the particle stream impacts into the water surface when the hopper outlet diameter is from 1 to 8 mm. It is considerably important that reducing the impaction intensity of the particle flow and the particle flow expanding level when the contact surface is in the transitive regime and the dispersive regime, respectively.
This paper is concerned with the numerical analysis of particulate jet generated by solid particles falling from a slit orifice into an unbounded quiescent air. A two-dimensional vortex method, proposed for the simulation of particle-laden free turbulent flow in prior papers, is employed for the analysis. The falling particles induce complicated air jet involving large-scale eddies around the jet. The air takes its maximum velocity at the center line of the jet. The particle velocity is higher than the free falling velocity of a single particle. The effects of the diameter and density of the particle on the velocity distributions of the air and particle are investigated. The entrained air flow rate is favorably compared with the value predicted by an analytical model.
Present paper presents a research of the air velocity distributions, particle diffusion and particle movement characteristic of free-fall particles with non-uniform particle diameter based on DPM-CFD model. The simulation results well matched the experimental and theoretical data. The research found that air jet forms in the axis, and vortex is produced around axis. The axis line air velocity is at a maximum, increased as the axial increasing. Besides, with the radial distance increasing, the airflow velocity increases firstly and then decreases and then increases again. The particle concentration decreases along the radial direction, and the diffusion radius increases with decreasing particle size. The particle velocity rapidly increases in the initial phase, and then gradually flatten; With the particles falling down, the increasing amount of particle velocity become smaller and smaller, and then gradually flattens; Terminal velocity of small-size particles decreases, mixed with large-size particles. ©, 2015, Xi'an Jianzhu Keji Daxue Xuebao/Journal of Xi'an University of Architecture and Technology. All right reserved.
In many industries across the world, the topic of dust control is a major concern. Within the bulk material handling process the action of material free fall is generally unavoidable. In this case, the adjacent air surrounding the free falling stream is induced into the stream of bulk material as the particles naturally dilate, which results in generation of dust upon subsequent compaction of the stream. Obtaining a better understanding of the way air is induced into the stream of bulk material, and the quantity of the induced air, will assist in the design of more efficient dust control systems.
In this paper the interaction between the particles and the air is reviewed. A series of computer simulations and physical experiments have been carried out. The particle image velocimetry (PIV) technique has been employed to measure the fluid velocity within a free falling stream of coarse material. Each experiment was also simulated using Ansys CFX. Particle and air velocities as well as air entrainment readings from simulation have been compared with experimental measurements and theoretical formulas. The experimental programme was designed and conducted to classify the effect of particle diameter and particle density independently. This paper presents several distinct sections that detail the experimental and simulation results as well as a comparison of these two methods while also including a discussion of existing theories.
The dimensionless parameters of a pipe flow’s Reynolds number (Re), mass flow-rate number (mp/(μD)), specific induced airflow number (ρp·(ugD2/mp)), height number (h/D), and granular-flow number (Gr) were obtained by using the Pi theorem. The influences of mp/(μD), ρp·(ugD2/mp), and h/D to the Re were explored by similitude experiments. Finally, the semi-empirical model of induced airflow velocity was established through the Gr and Re. The conclusions are as follows: in the semi-closed transfer station, the Re value increased with the increase of the mp/(μD) value. Due to the interaction among the particles and change of the specific flow space of the blanking tube on the specific induced air flow, the ρp·(ugD2/mp) value was found to be proportional to the mp/(μD) value raised to the power of approximately −0.73. Due to limitations of drop heights, particles should be in the acceleration phase from beginning to end, when the resistance drag of the particles is less than the gravity of itself. It was also discovered that the Re value is proportional to the h/D value raised to the power of approximately 0.88. Additionally, similitude experiment results revealed that the Re value is proportional to the Gr value raised to the power of approximately 0.27. On this basis, the semi-empirical model for induced airflow velocity was established. The model can forecast actual values accurately with a deviation of the calculated values limited to plus or minus 10%. These research results can benefit industries in their transfer station dust control systems and in the design of ventilation systems.
The dust generation occurring during the handling of bulk materials in free falls or at the impact on a stockpile can be a source of danger for the operators health. Proper design of control systems of fugitive dust requires knowledge of the behavior of the free falling powder, the air it entrains, and the concentration of dust liberated. This paper presents first a simple model for a free falling column of bulk solids and compares it with relevant previous research. This two phase model predicts the particle and air velocities, and especially the volumetric flow of induced air in the column without dependence on any empirical constant like the entrainment constant used in the plume model. For small drop heights, the predictions of the theory appear to be in qualitative agreement with the available data for the quantity of air entrained, but the theory needs to be extended in the case of large drop heights, when the expansion of the jet of particles is large. In a second part, the description of an expanded jet of particles is experimentally studied with PIV measurements. The data obtained are well fitted by the model by Liu, when the entrainment constant is taken as the angle of expansion of the jet obtained from the velocity field.
This article explores the hypothesis that the amount of dust generated by an industrial process that handles granular material depends on (a) the size distribution of the granules and (b) the ratio of impaction to cohesion. Here, impaction characterizes particle separation forces caused by energy input from the process, and cohesion characterizes interparticle binding forces within the material itself. A mathematical model based on this hypothesis is presented and evaluated using 441 data sets from an industrial- scale apparatus designed to measure dust generation. Dust generation was characterized in experiments using titanium dioxide, limestone, glass beads, and lactose with moisture contents ranging from 0% to 6% and size distributions of d < 5 μm, 5 < d < 25 μm, and d > 25 μm in aerodynamic diameter, dropped from heights of 0.25, 0.7, and 1.25 m at material flows of 0.1, 0.3, and 0.6 kg/sec. Results are presented in equations for impaction, cohesion, and dust generation as a function of particle size. The equation for dust generation was validated by comparing its predictions with 147 additional data sets. Cohesion due to material properties affected dust generation more than impaction due to the material handling process; the size distribution of the granular material was not as important as either cohesion or impaction. Results suggest that the equations presented can be used with reasonable confidence to predict dust generation, especially for the materials and process investigated in this study.
Powders and granulated solids are widely used in industrial bulk solids storage, handling, and transportation systems. Such bulk materials handling operations frequently involve a falling stream of material. During such a process, the surrounding air is induced to flow with the falling particle stream, forming a particle-driven plume. Herein, experimental research results are reported on this fundamental problem, focusing in particular on the velocity profile of air entrained by the free-falling particles. This investigation shows that the velocity profile of the induced air can be modeled as a Gaussian distribution. The radius of the particle plume is found to increase linearly with increasing drop height, and it also increases with increasing bulk solid mass flow rate. Comparisons are made with other entrainment flows, such as jets and plumes, and it was found that air entrainment and hence the angle of spread of the particle-driven plumes was much less than for the other entrainment flows. The angles of spread of the particle-driven plumes were found to be in the range 1.3°
Jet of particles falling from a hopper under gravity have been investigated experimentally. In general they consist of a rather sparse cloud of particles surrounding a tapering central core. The mechanism of formation of the cloud is discussed and it is shown to be caused by interparticle collisions at the orifice; particles moving radially towards and through the orifice form the central core, although the rapid convergence of particle trajectories is prevented by collisions. Bagnold's concept of “dispersive pressure” of particles under shear is used to explain and quantify the effects of collisions on the trajectories. Introducing a concurrent flow of air through the hopper outlet sometimes caused a periodic instability which is tentatively ascribed to Helmholtz resonance. Flow of particles through an array of baffles, and a baffle design to promote dispersion, are described.
This paper is concerned with the numerical simulation of the particulate jet generated by solid particles falling from a slit orifice into an unbounded quiescent air. A two-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in prior papers, is employed for the simulation. The falling particles induce complicated air flow involving eddies with a wide variety of scales. The air takes its maximum velocity at the jet centerline. The particle velocity is higher than the free falling velocity of a single particle. The effects of the diameter and density of the particle on the flow are investigated. The entrained air flow rate is favorably compared with the value predicted by an analytical model.
The particulate jet generated by solid particles falling from a circular orifice into an unbounded quiescent air is simulated. The three-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in a prior study, is employed for the simulation. It is found that the falling particles induce complicated three-dimensional unsteady air flow involving large-scale eddies. The air takes its maximum velocity at the jet centerline, and the velocity profile satisfies the self-similarity around the centerline. The effect of particle diameter on the velocity distribution for the two phases is investigated. The entrained air flow rate is favorably compared with the value predicted by the analytical models.
Dust generation during solids handling, principally from the free falling of bulk materials and their impact on stockpiles, can be a health threat for operators and a cause of dust explosions. The proper design of a dust emission control system requires knowledge of the behaviour of the free falling jet, in particular the amount of air entrained by the falling powder and the concentration of dust liberated. The focus in this present paper is on the effect of drop height of a free falling jet on segregation by particle size, particle velocity, changes in particle concentration and entrained air in the dust plume. This gives a quantification of the important parameters and the concentration of dust emitted during a free fall.
A method is presented to examine factors that affect the amount and size distribution of dust generated by falling granular material in still air. This work was conducted by using an apparatus with separate dust generating and dust measuring sections. The dust generated by a falling material was carried into an elutriation column equipped with a slotted Sierra high-volume impactor at the top. This apparatus can measure dust generation rates for particles between 0.4 and 25 microns in aerodynamic diameter as well as the amount of air entrained by the falling material. Four granular materials were tested, and a simple model was developed to describe the dust generation rate of these materials as a function of particle size, drop height, material flow, and moisture content. Moisture content strongly influenced the interparticle binding forces and the amount of dust generated. Drop height and material flow influenced the material separation forces and also significantly influenced the amount of dust generated.
- D Wang
- X Li
D. Wang, X. Li / Advanced Powder Technology 31 (2020) 169-180
Hemeon's Plant and Process Ventilation: New Edition of the Classic Industrial Ventilation Text
- W C L Hemeon
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Emission characteristics of dust generation from falling powder materials
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Generation characteristics of inhalable particles of free falling powder materials, Chin
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- Z J Wang
G.Q. Zhang, Z.C. Liu, Z.J. Wang, Generation characteristics of inhalable particles
of free falling powder materials, Chin. J. Environ. Eng. 1 (2) (2007) 82-87.
Emission characteristics of fugitive dust generation of falling material and its model
- G Q Zhang
- Z C Liu
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G.Q. Zhang, Z.C. Liu, H. Wilhelm, Emission characteristics of fugitive dust
generation of falling material and its model, J. Shandong Agricul. Univ. (Nat.
Sci.) 39 (1) (2008) 114-118.
Primary investigation of air entrainment in free falling particle plumes
- Y L Zhao
- Z C Liu
- J H Zhao
Y.L. Zhao, Z.C. Liu, J.H. Zhao, Primary investigation of air entrainment in free
falling particle plumes, J. Zhengzhou Univ. (Eng. Sci.) 28 (3) (2007) 72-75.
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