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Pickup (critical) velocity of particles

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Abstract

This work presents experimental results on pickup velocity (critical velocity) measurements for a variety of particulate solids. The present experiments together with previously published experiments of a number of researchers encompass about 100 measurements of 24 materials for a wide range of particle sizes, shapes and densities. Based on the experimental results, three zones are defined by establishing simple relationships between the Reynolds and Archimedes numbers. The empirical relationships were further modified by taking into account the pipe diameter and particle shape (sphericity). The three-zone model was shown to reasonably correlate to Geldart's classification groups.

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... To estimate the potential for the removal of process by-products of various process gases, the particle pickup velocity u pu can be utilized. Kalman et al. [29] proposed an empirical model for the calculation of u pu based on the dimensionless particle Reynolds number Re p and the Archimedes number Arch. Following this model, u pu depends on both the gas and ...
... These two numbers describe particle movements in a fluid and account for gravitational as well as drag forces [30]. The calculation of Re p is divided into three zones, which leads to a stepwise function for u pu according to Arch can be calculated with the particle shape modification factor K Φ (set to 0.9 in this study [29]) by Zone (I) is valid for large particles, where gravitational forces dominate. Zone (III) applies to very fine particles, where mostly inter-particular forces have an effect on the particle cohesion. ...
... Their experimental results using Ar as a process gas showed a good agreement with the model calculations for a variety of powder materials (e.g., 316L stainless steel). For further details on the model calculation, the reader is referred to [29] and [31]. ...
Article
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The powder bed fusion of metals using a laser beam (PBF-LB/M) is increasingly being utilized in industrial applications. This is due to several advantages over conventional manufacturing processes when it comes to the fabrication of complex part designs. However, the process still poses various challenges that have to be overcome. One of these challenges is the formation of a significant amount of spatters and fumes. These could attenuate the laser beam or decrease the powder reusability. To lower their negative impact on the process and the mechanical properties of the parts, a process gas flow is used in PBF-LB/M to remove these by-products from the processing zone. This study was, therefore, dedicated to investigating the potential of various gases on the removal of spatters. The focus was placed on argon, helium, and their mixtures. After theoretical considerations determining the range of applicable gas flow velocities, the experimental results unveiled the real spread of spatters over the powder bed and their characteristics. Whilst the removal of spatters was found to be worse for an argon–helium gas mixture at comparable gas flow velocities, increasing the velocity turned out to be a proper measure to enhance the removal for low-density gases. At this flow condition, the use of the argon–helium gas mixture led to a similar removal of spatters and the creation of a lower spatter mass in total (reduced to 40%) compared to argon.
... With the help of a specially adapted device for measuring the collection rate of particles, and by altering the particle composition and assimilation port diameter [21,22], the factors affecting the velocity of particles on the road surface can be identified. Kalman et al. [23] determined the effect of the lifting force of the particles and the rotation speed on the removal rate during particle collection. Through an experimental study of dust removal efficiency, Hu et al. [24] found that changes in the dust structure affect the suction efficiency. ...
... The starting velocity of the dust particles was determined in a horizontal circular tube. For a single dust particle [21,23,32,51]: ...
... It is assumed that the suction velocity is defined by the vertical drawdown (vertical force equilibrium) and is found that [21,23,52]: ...
Article
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The influence of variable operational conditions affects the performance of particle collection and separation of a regenerative air vacuum sweeper. Therefore, the purpose of this paper was to numerically investigate the factors affecting the particle suction efficiency of the pick-up head. Using computational fluid dynamics (CFD), a model of an integrated pick-up head was developed based on the particle suction process to evaluate the particle removal performance. The realizable k-ε and discrete particle models were utilized to study the gas flow field and solid particle trajectories. The particle structure, sweeping speed, secondary airflow, pressure drop, and distance between the particle suction port and the road surface, as factors that affect the particle removal efficiency, were investigated. The results indicate that the particle suction efficiency increases with decreasing sweeper speed. Furthermore, the particle overall removal efficiency increased with a reduction in the distance between the suction port and the road surface as well as the control of the secondary airflow in the system. By increasing the airflow rate at the suction port, high efficiencies were achieved at a high sweeper speed and high particle densities. At a sweeper speed of 6–10 km/h, the results showed that the secondary airflow recirculation varied between 60 to 80 %, while the high-pressure drop ranged from 2200 to 2400 Pa, and the particle suction efficiency recorded was 95%. The numerical analysis results provide a better understanding of the particle suction process and hence could lead to an improvement in the design of the pick-up head.
... Dasani [11] measured the pickup velocity of three glass spheres in water and compared the pickup velocity trends under various particle properties for similar gas-solid phase systems. Kalman [12] presented 100 measurements of the pickup velocity of 24 materials having various particle sizes, shapes, and densities and established simple relationships of three zones between the Reynolds and Archimedes numbers (see Figure 1). However, these studies mainly involved micron-sized powder particles. ...
... They inferred the pickup velocity of particles inversely by measuring the height of the stabilized particle group and made the airflow velocity when the mass of particles picked up was larger than zero be the pickup velocity of materials. Kalman et al. [12] defined the mass loss of particles within 30 s in one test, and the pickup velocity was identified as the airflow velocity when the material mass loss was not zero. Rabinovich [27] and Zhou [12] defined the airflow velocity when the picking mass of the particle was 50% as the pickup velocity. ...
... Kalman et al. [12] defined the mass loss of particles within 30 s in one test, and the pickup velocity was identified as the airflow velocity when the material mass loss was not zero. Rabinovich [27] and Zhou [12] defined the airflow velocity when the picking mass of the particle was 50% as the pickup velocity. To reduce the influence of random factors on the pickup velocity, this paper tended to measure the pickup velocity qualitatively, the pickup velocity of pebble particles was determined by drawing the function relationship between the airflow and the entrainment of particles, measuring the intersection point of measurement point and vertical coordinate as well, the pickup velocity was treated as the airflow velocity when the picking mass was 50%. ...
Article
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Pneumatic conveying is widely used in coal mining. As the lowest conveying velocity of materials, the pickup velocity is the key to the study of gas–solid two-phase flow. In this study, the pickup velocity of pebble particles was experimentally investigated. When the particle size is 3–9 mm, the airflow velocity was found to suitably describe the results as a function of the pickup velocity and have a high correlation. When the swirl number is 0.2, the optimal swirl number was found for which the highest particle pickup ratio was observed. Based on four different methods, namely, visual observation, mass weighing, coefficient of difference analysis, and determination of the peak-average ratio of the pressure drop in the flow field to measure the pickup velocity of the spraying material, the results showed that the accuracy of the particle pickup velocity obtained through visual observation was the lowest, and when the mass–loss rate of the particle was selected as the measurement index of the pickup velocity, the accuracy was the highest. The results will help to realize the long-distance transportation of spraying materials in inclined roadway under the shaft.
... This type of detailed data recording is one of the advantages of computer simulation techniques. Referring to the work of Kalman et al. [39] Processes 2020, 8,1597 8 of 16 provides a means of comparison for the particle flow characteristics between the proposed simulation and current empirical models. Kalman et al. [39] described a three-zone model that correlates the Reynolds number and Archimedes number to the type of granular material flow regime. ...
... Referring to the work of Kalman et al. [39] Processes 2020, 8,1597 8 of 16 provides a means of comparison for the particle flow characteristics between the proposed simulation and current empirical models. Kalman et al. [39] described a three-zone model that correlates the Reynolds number and Archimedes number to the type of granular material flow regime. Granular materials that are part of group D, such as field peas, fall within Zone 1. ...
... The simulation resulted in average particle velocities and Reynold's numbers that were inside the boundaries of the non-pickup regime ( * = 6912). This confirmed the observed stratified smooth flow to be in agreement with the model proposed by Kalman et al. [39]. The simulation was qualitatively evaluated by examining the seed flow characteristics. ...
Article
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Air seeding equipment consists of various machine components that rely on pneumatic conveying of seeds (granular material) for its operation. However, studying air seeder dynamic features in detail is difficult through experimental measurements. A simulation was performed to study seed motion in a horizontal tube section of an air seeder distributor system. The simulation incorporated two-way coupling between discrete element modeling (DEM) and computational fluid dynamics (CFD). Simulated particles were assigned material properties corresponding to field peas. Air velocity was assigned values of 10, 15, 20, and 25 m/s. The solid loading ratio (SLR) in this study included values between 0.5 and 3 to describe typical seed metering rates used in air seeding. The different pneumatic conveying conditions were studied to determine their overall effect on the average seed velocity and seed contact force. The simulation was validated through the comparison of average seed velocity data from the literature and current pneumatic conveying theory. The effect of SLR on the average seed velocity was found to be not significant for the simulated SLR values. The CFD-DEM simulation was able to capture seed collisions between seeds and the surrounding boundaries. The seed contact force increased with the air velocity, and the number of seed collisions increased with the SLR.
... The pickup velocity is relevant in wide range of applications. For example, some pharmaceutical industries are focused on dry powder inhalers for drug delivery, the movement of sand dunes and soil deposition in river and ocean flows (Kalman et al., 2005). ...
... It can be seen also the influence of density in the pickup velocity, i.e. higher densities demands a greater fluid velocity for entrainment of particles. th Brazilian Congress of Thermal Engineering and Sciences Copyright © 2008 by ABCM November 10-14, 2008 In order to evaluate the accordance of the correlation developed by us, the pickup velocity was calculated and plotted against the experimental result of Cabrejos and Klinzing (1994), Hayden et al. (2003), Kalman et al. (2005) and Gomes and Mesquita (2006). The predicted values with the use of present correlation showed a very good agreement with the experimental data (Figs. ...
... More studies must be made to verify this inconsistency. However, the results obtained for particles with sizes ranging from 30 to 4000 µm are in good concordance with experimental measures carry out by Cabrejos and Klinzing ( 1992), Hayden et al. ( 2003), Kalman et al (2005) and Gomes and Mesquita (2006). ...
Conference Paper
The project of a pneumatic transport system must consider parameters as the pressure drop, the gas velocity, particles velocity, the wall roughness, the particle-particle interaction, among others. One aspect of great importance in the operational stabilization of a pneumatic transport system is the transport of particulates materials at minimum possible velocity. In this work, a semi-empirical correlation is developed for the pickup velocity of particles in rest at the bottom of pipeline. This new technique proposed for prediction of pickup velocity was developed based on a model for incipient motion of a single particle in a vertical direction and the Archimedes number. This correlation presents good results for particles with sizes ranging from 30 to 4000 µm.
... The particle pickup speed, a threshold above which the gas flow picks up loose particles, can be used as a good reference to set the upper limit. Extensive work on particle pickup has been done in fields of pneumatic powder conveying and fluidized powder beds [11][12][13][14][15][16][17][18] . An empirical model developed by Kalman et al. 12 achieved good agreement with experimental data. ...
... Extensive work on particle pickup has been done in fields of pneumatic powder conveying and fluidized powder beds [11][12][13][14][15][16][17][18] . An empirical model developed by Kalman et al. 12 achieved good agreement with experimental data. This model uses two non-dimensional parameters to correlate pickup speed with powder properties: 12 ...
... A characteristic diameter is required to account for a gas flow profile different from the baseline gas flow setup (a 50-mm pipe) used to develop the model. 12 A modified Reynolds number is used to account for different characteristic diameters. The Archimedes number is also modified to account for the particle sphericity: 12 ...
Article
Using gas flow to reduce laser plume attenuation is critical in the process control of laser powder bed fusion (LPBF) of metal powders. First, this work investigated Hastelloy X (HX) samples built at different gas flow speeds. Higher porosity with lack of fusion defects was found in the samples built at lower gas flow speeds, which indicates a significant influence of laser plume attenuation. Then, particle pickup experiments were conducted to investigate the limit of further increasing the gas flow speed without disturbing the powder bed. Eight different powders of four alloys (Al, Ti, steel, and Ni) with mean sizes ranging from 25 µm to 118 µm were studied. A model was introduced to predict the pickup speeds of different powders. Lastly, a method based on porosity and particle pickup speed was proposed for the reference of setting the lower and upper limits of gas flow speed in LPBF.
... The chart is defined by Reynolds number (operating conditions) as a function of Archimedes number (solid properties). The chart predicts the flow type for any material at any air velocity, whether to be packed bed, fluidized, bubble flow or slug flow (in the range of fluidization) or fast (Rabinovich and Kalman, 2008a), saltation and minimum pressure Kalman, 2008b, 2010) and pick-up (Kalman et al., 2005) velocities, among others. In most of the cases, Re was modified to take into account the pipe diameter and Ar was modified to take into account various affecting parameters, such as particle sphericity, coefficient of restitution, friction coefficient and volumetric concentration. ...
... A comprehensive research of Kalman et al. (2005) analyzed almost hundred experiments of their own and others found in the literature to present power relationships between Re and Ar in three zones. The pick-up velocity was defined for an air stream over a stationary layer of particles, as visualized in Fig. 3a and presented in Fig. 3b. ...
... pipe. Other pipe diameters and particle shapes are converted by the functions presented by Kalman et al. (2005) to the values of Fig. 3b. However, in the following equations and flow regime chart, the pick-up velocity for a 2-in. ...
Article
Dense phase pneumatic conveying is preferred by industry over dilute phase flow due to its advantages. Models enabling to calculate pressure drop are worthless for a designer if he is unable to predict in advance the mode of conveying. Therefore, this research is focused on developing a new flow regime chart. Based on hundreds of experiments all required threshold velocities are defined by Reynolds number as a simple power function of Archimedes number. This work, revealed two new kind of plugs unknown before. Using the threshold functions a new flow regime chart was plotted By comparing the results to previously published models characterizing only the material properties revealed that the feeder is probably have a major role controlling the final mode of flow. Taking into account the findings in this paper, one might have ideas of how to improve the feeders in order to fully fulfill the flow potential.
... Although this simplification might be valid for PC, it is firstly not correct and certainly not valid for HC. Hence, some recent works on various threshold velocities (mainly for PC, but in some cases, also including HC) showed that the Archimedes number (Ar) is more appropriate [9][10][11][12]. Later, by considering the various forces affecting some threshold velocities, it was confirmed that the Re and Ar affect the velocities for both PC or HC [10,[13][14][15]. ...
... For instance, it was shown that the pick-up velocity from a layer of particles can be described as the Re as a power function of the Ar. The function is common to both fluids, air and water, for large particles [9]. For small particles, there is a difference, since the Van der Waals force acts on dry fine particles and is almost negligible for particles immersed in water. ...
... where Re* is the Reynolds number modified by the effect of the pipe diameter (Re à ¼ ρUpud μ ) and Ar* is the Archimedes number modified by the particle shape (Ar ¼ ρ f ðρ p −ρ f Þgd 3 μ 2 0:03 expð3:5αÞ) [9] where D50 is the diameter of a 2-in. pipe (50 mm) and α is the particle sphericity. ...
... For example, larger particles demand a greater velocity at the pickup head, and vice versa. The critical pickup velocities of particles were experimentally studied by Kalman et al. [11] to evaluate the performance of the pickup head for varying particle shapes, sizes, and densities. It was observed that for large particles, the pickup velocity increased as the diameter increased, owing to the increase in gravitational force. ...
... The effect of structural changes in the particles during the operation of road cleaners on the initial velocity of the particles is shown in Figure 14. Because the size of the particles on the road surface is not always small, when studying the size of the particles encountered in real conditions, it was found that the initial velocity of high-density particles is relatively high [10,11]. The starting velocity of the removal of 3 mm sized wood particles was 7.4 m/s, while the starting velocity of sand particle removal was 12.3 m/s. ...
Article
Full-text available
In a regenerative air sweeper, airflow and dust particles entering the system are filtered and recirculated within the system. The uncirculated portion of the exhaust air in the system spreads to the ambient air, and PM2.5 dust in the air can poison the environment and adversely affect human health. The development of an airflow control system to reduce road dust emissions and improve air quality was the main contribution of this study. A regenerative air sweeper airflow control system is designed to direct the air from the centrifugal fan back into the pickup head to fully absorb the dust particles and balance the positive and negative air pressures inside the pickup head. The modeling and analysis of the dust control system were performed using an experimental test rig system. A mathematical model of the fundamental parameters of the regenerative air sweeper and dust control system was established. Computational fluid dynamics (CFD) ANSYS was used for the analysis to determine the direction of airflow via the suction and inlet ducts. The discrete particle model (DPM) accurately predicted particle trajectories and measured the suction efficiency of particles of different shapes and types. By controlling the circulating harmful air flow in the system, the amount of PM2.5 released into the atmosphere was reduced by 90%. The suction efficiency of the 200 μm sized sand particles was higher than 95%. The results provide theoretical and methodological assistance for the development of improved road sweeper dust control systems.
... Consequently, critical acceleration for 59 detachment decreases as the roughness increases 60 Ahmadi, 1994a, 1994b Valenzuela also belongs to the surname. NAME: Karina de los Ángeles SURNAME: Valenzuela Aracena K.d.l.Á.V. Aracena et al. / Particuology xxx (2020) xxx-xxx To initiate increased movement of particles that were deposited 62 on a layer of fixed particles, experiments to determine the pickup 63 velocity (critical velocity) for a wide variety of particulate solids 64 in a wind tunnel have been presented by Hubert and Kalman 65 (2004), and Kalman, Satran, Meir, and Rabinovich (2005). The inter-66 est resides in the fact that a prediction of the minimum conveying 67 velocity is related closely to an understanding of the saltation and 68 pickup mechanisms during pneumatic conveying system operation 69 (Hubert & Kalman, 2004). ...
... The particle pickup velocity has been found to depend on the 71 initial configuration, is different for coarse and fine particles and is 72 higher than the saltation velocity (Hubert & Kalman, 2004). Three 73 zones were defined for the pickup mechanism by establishing sim-74 ple relationships between the Reynolds and Archimedes numbers 75 (Kalman et al., 2005). ...
Article
We performed experiments to determine the critical moment for movement initiation of a millimeter bead on a rotating rough surface. The corresponding critical angular velocities were measured for glass and stainless-steel ball bearings over two different rough surfaces with glued glass beads. A basic theoretical analysis was developed to explain the observed results. Although the expectation of a simple approach with the presence of the obstacles offered by a rough surface could be sufficient to describe the problem, we prove here that the sole consideration of these obstacles, and even friction, are insufficient to explain the results in the range of a few-millimeter glass particles. Where the thermodynamic work of adhesion between surfaces is significant, the adhesion forces must be considered in the force balance for particle detachment. This effect is a determinant for describing theoretically and numerically the dynamics of millimeter particles.
... The pickup velocity is defined as the gas velocity necessary to suspend the particles initially at rest at the bottom of the pipeline or it may be defined as the gas velocity required to initiate sliding motion, rolling and suspension of particles. To determine the pickup velocity of particles, the empirical correlations are proposed in the axial flow field [31,32]. The diameter and density of particles and particle shape are the crucial factors in the determination of pickup velocity of particles [33]. ...
... The diameter and density of particles and particle shape are the crucial factors in the determination of pickup velocity of particles [33]. Fig. 22 shows the calculated pickup velocities using Cabrejos and Klinzing [31] and Kalman et al. [32]. From numerical simulations, the radial and tangential velocities of gas at the surface of the bed is obtained, and the gas velocities u g,cd entering the cylindrical domain is determined at the cylindrical domain x/R = 1.0. ...
Article
The draft fan is used to generate a controlled transportation of particles to enhance entrainment of gas and particles from the particles bed. Present investigations show the entrainment behavior of particles induced by an axial 4-blade draft fan hovering over the particles bed. The distributions of velocities and volume fractions of gas and particles are simulated using Euler-Euler two-fluid model (TFM) with kinetic theory of granular flow (KTGF) at different hovering heights and rotational speeds of the draft fan. The dense region with high solids volume fraction and low particles velocity and the dilute region with low solids volume fraction and high particles velocity exist beneath the draft fan along hovering heights. The entrainment of particles increases with the decrease of hovering height and increase of rotational speed of the draft fan. Present numerical simulations confirm that the gas-solid TFM with the kinetic theory of granular flow and multiple reference frame model can be effectively applied to analysis for entrainment of particles induced by draft fan.
... Using, instead, the pick-up velocity, gives higher velocities and an additional factor of safety. A number of correlations can be found in the literature describing both threshold velocities, Kalman et al. (2005), Rabinovich & Kalman (2007, 2008. Knowing the relevant threshold velocity enables to define the required fluid flow rate. ...
... 2. A simple centrifugal pump can be used without erosion since it pumps clear water. 3. The mass flow rate can be measured at two locations along the pipe for clear water and for the mix. ...
... When the airflow speed reaches a certain level, the particles will be transported by the airflow, that is, the suspension speed [28]. There are many formulas for calculating the suspension speed [29][30][31] of particles in pneumatic conveying. The regional suspension velocity formula and its applicable particle size method are the most extensive, the specific formula is as follows: ...
Article
Full-text available
Pneumatic conveying technology is an efficient, energy-saving and environmentally friendly means of solid feed conveying. In the process of pneumatic conveying, wind speed has a decisive influence on conveying characteristics. Here, computational fluid dynamics coupled with a discrete element method simulation and experiment were combined, and the conveying wind speed was used as the experimental variable to study the conveying characteristics of the conveying material in the tube, such as particle distribution state, solid phase mass concentration, coupling force on solid feed, average speed and pressure drop of solid feed in the pipe. The results show that when the conveying wind speed increases from 18 m/s to 20.6 m/s, the solid feed changes from sedimentary flow to suspended flow, the particle accumulation gradually decreases and the conveying efficiency is significantly improved. The particle slug greatly reduces the collision and friction between the internal particles and the pipe and reduces the crushing rate to a certain extent. When the conveying wind speed is about 23.2 m/s, there are almost no trapped particles in the pipeline, which can achieve rapid feed delivery, and conveying efficiency is greatly improved. Therefore, this paper provides a good theoretical basis for improving conveying efficiency and reducing crushing rate in the process of pneumatic conveying.
... The CFD-DEM model considers buoyance, gravity, and viscous drag and was verified against the analytical solutions derived by Kalman et al. (2005) before its application to field conditions. The model setup and boundary conditions are shown in Fig. 2a, and results in Fig. 2b, c. ...
Article
Full-text available
A field case is described to show the first application of a sliding sleeve sandface completion without sand control in a moderately competent sand-prone reservoir formation. This type of sandface completion consists of blank pipe segments, isolation packers, and sleeves in between serving as flow ports. This geometrical configuration renders a unique sanding mechanism. Due to a large opening in the annulus, the rock starts to disaggregate at a low reservoir pressure depletion, but its aggregates tend to be blocky and thus favorable in lowering sanding risk as bigger aggregates have a higher frictional resistance and require a higher fluid velocity to transport. Also, annular fluid flow is accumulative, and its velocity is zero at the packer and the highest at the sleeve. An effective practical measure to lower sanding risk, therefore, is to optimize the number and locations of packers and sleeves in relation to reservoir formation strength and sandface flow contributions. The sanding mechanism and practical ramifications are illustrated through historical sanding responses in 11 wells in an oil field in the UK North Sea. Most wells have experienced watercut and the flowrate in some wells is high. Sanding to date, however, is below the design tolerance. A method was developed to estimate the annular fluid velocity. Through cross-referencing historical sanding responses within the sanding mechanism framework, empirical relationships between sand mass per meter length and annular fluid velocity were established to help optimize sandface completion design in future wells and production and interventions in existing wells.
... Liu et al. [3] studied the influence of lateral vibrations on the ballast pick-up velocity in vertical pipelines and concluded that the ballast pick-up velocity significantly impacts the pipeline system's stability, safety, and energy consumption rate. Several studies [4][5][6] have investigated the ballast pick-up velocity in horizontal pipes by building a pneumatic conveying platform and analysing the influences of the pipe diameter, ballast shape, and stacking height. Other studies [7][8][9] have determined the ballast pick-up velocity using the weighing method and the image method, based on the pipeline experiment platform. ...
... Particle resuspension, that is the re-entrainment of particles initially at rest on the ground into the flow [31], is here assumed to occur when the friction velocity u * at the wall exceeds a critical velocity u * c [32,33], also called threshold or pick-up velocity. A general difficulty associated with the resuspension of micron particles in a large domain lies in evaluating these two velocities u * and u * c . ...
Article
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Air pollution caused by particle resuspension is a growing public health problem in many cities. Pollen and anthropogenic pollutants, such as heavy metal particles and micro-plastics debris, settle onto urban ground surfaces. Prolonged urban heat waves are propitious for heavy and continuous deposition. Particles in the submillimeter size range eventually resuspend by urban winds within seconds, may be inhaled, cause allergic reactions and escape the city’s boundaries. Here, the resuspension and subsequent dispersion of generic particles ranging from 10 to 100 \upmu μ m in size are simulated. The city area “Bayerischer Bahnhof” in Leipzig, Germany, has been chosen as a practical example. To track the resuspended particles, a Lagrangian model is used. Taking advantage of graphics processing unit, turbulent flow simulations at different wind speeds are performed in almost real time. The results show that particle resuspension starts, when the inlet wind speed beyond the canopy, that is at a height of 40 m, exceeds 7 m/s. At wind speed beyond 14 m/s, resuspension occurs in almost all city parts. At moderate wind speed, high-risk areas are identified. The effect of green infrastructures on both the flow field and particle resuspension is also investigated.
... For targeting using powder layer disturbance, there are several factors at play. For instance, the characteristics of the powder itself, such as the size, shape, density, and flowability, influence the degree to which the gas flow velocity can change the powder layer profile [26,46]. Additionally, the distance between the part and the gas inlet will determine the gas flow velocity above the part. ...
... [194] Together they can be assessed through the particle Reynolds number and Archimedes number. [195] In general, the U pu can be written in the form of [180,194,196] ...
Article
The design freedom offered by additive manufacturing (AM) enables the fabrication of components with internal surfaces that are challenging to access post-manufacture. This is of concern, as the surface condition can markedly deteriorate fatigue performance. Additionally, the adaptation of surface finishing methods for AM components with topologically optimised designs can be a costly practice. It is therefore desirable to consider deploying AM parts with no or minimal surface processing for targeted applications. This requires an in-depth understanding of the formation of various types of AM surfaces, including the variation in surface condition and controlling factors, and their influence on mechanical performance. The last few years have seen significant research advances in these aspects. Ti-6Al-4V is the most extensively studied alloy for AM. The research data available now allows an informative treatment of this topic for both practical applications and future research. Using laser powder bed fusion (LPBF) of Ti-6Al-4V as a model AM−alloy system, this article examines (i) the characteristics of various types of LPBF surfaces including horizontal, vertical, inclined, upward, downward, internal isolated, and slotted surfaces; (ii) the design features and LPBF variables that affect the surface topography; (iii) the capabilities of existing post-AM surface processing methods; and (iv) the influence of AM surface topography on mechanical properties by focusing on the fatigue performance. On this basis, design considerations are recommended for AM of consistent surfaces, and priority surface-related research issues are identified. The purpose is to establish an essential knowledge base for improved commercial designs for LPBF for suitable dynamically loaded applications, with no or minimal surface processing. While centring on LPBF of Ti-6Al-4V, the insights derived are expected to be applicable to other AM processes or metallic materials.
... Although an even faster flow may be beneficial [25][26][27]30,31], at a certain velocity the gas flow will begin to disturb the powder bed below, which is undesirable. To this end, Shen et al. [28], building upon earlier work by Kalman et al. [32], modeled and validated the upper bound velocity that will not disturb the powder bed. Therefore, a first step in our design process was to determine a target gas velocity for flow within the HPLM chamber. ...
Article
Metal additive manufacturing (AM) by laser powder bed fusion (L-PBF) builds upon fundamentals established in the field of laser welding which include the influence of gas and plume dynamics on weld depth and quality. L-PBF demands a thorough investigation of the complex thermophysical phenomena that occur where the laser interacts with the metal powder bed. In particular, melt pool turbulence and evaporation are influenced by the ambient gas chemistry and pressure. This paper presents the design and validation of high pressure laser melting (HPLM) testbed; this accommodates bare metal plate samples as well as manually-coated single powder layers, and operates at up to 300 psig. The open architecture of this testbed allows for full control of all relevant laser parameters in addition to ambient gas pressure and gas flow over the build area. Representative melt tracks and rasters on bare plate and powder are examined in order to validate system performance, and preliminary analysis concludes that pressure has a significant impact on melt pool aspect ratio. The HPLM system thus enables careful study pressure effects on processing of common L-PBF materials, and can be applied in the future to materials that are challenging to process under ambient pressure, such as those with high vapor pressures.
... Although an even faster flow may be beneficial [25,30,31,26,27], at a certain velocity the gas flow will begin to disturb the powder bed below, which is undesirable. To this end, Shen et al. [28], building upon earlier work by Kalman et al. [32], modeled and validated the upper bound velocity that will not disturb the powder bed. Therefore, a first step in our design process was to determine a target gas velocity for flow within the HPLM chamber. ...
Preprint
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Metal additive manufacturing (AM) by laser powder bed fusion (L-PBF) builds upon fundamentals established in the field of laser welding which include the influence of gas and plume dynamics on weld depth and quality. L-PBF demands a thorough investigation of the complex thermophysical phenomena that occur where the laser interacts with the metal powder bed. In particular, melt pool turbulence and evaporation are influenced by the ambient gas chemistry and pressure. This paper presents the design and validation of high pressure laser melting (HPLM) testbed; this accommodates bare metal plate samples as well as manually-coated single powder layers, and operates at up to 300 psig. The open architecture of this testbed allows for full control of all relevant laser parameters in addition to ambient gas pressure and gas flow over the build area. Representative melt tracks and rasters on bare plate and powder are examined in order to validate system performance, and preliminary analysis concludes that pressure has a significant impact on melt pool aspect ratio. The HPLM system thus enables careful study pressure effects on processing of common L-PBF materials, and can be applied in the future to materials that are challenging to process under ambient pressure, such as those with high vapor pressures.
... According to the relative sizes between the thickness of the viscous sublayer and the particle diameter, Rabinovich and Kalman [13] , Cabrejos and Klinzing [8] classified the particles into two groups: the large particles with the diameter bigger than the thickness of the viscous sublayer and the smaller particles with the diameter smaller than the thickness of the viscous sublayer. Kalman et al. [25] established a three-region model (Table 5) by modifying the Reynolds and Archimedes number to clarify the effect of particle size on the dominant force and critical velocity of the particles. increases with the increase of particle size. ...
Conference Paper
Sand deposition and transportation in pipelines has become one of the major concerns for flow assurance in petroleum industry. However, research in this field is still in its infancy. This study describes the current development of sand deposition and sand transport in pipeline. The mechanism of particles deposition is described. The effects of particle properties, fluid properties and pipeline structure on the carrying capacity of single-phase and multiphase flow carrying sand are introduced, with emphasis on factors such as particle size, liquid viscosity, flow regime and pipeline inclination. As for modeling studies, the sand transport models can be classified to three categories based on the approach used to develop them: empirical, mechanistic, and semi-mechanistic. The methods for developing and extending models are illustrated in this study. Based on the experimental data, the prediction accuracy of four multiphase models for critical velocity in stratified flow is verified. Further researches should focus on the mechanisms and the establishment of the accurate model for sand flow pattern transformation boundary.
... In any case, at superficial velocities higher than approximately 2 m/s, the results of all five tested materials coincide with each other. Fig. 11 also presents the pick-up velocity [41,42] of the two sands. The pick-up velocities of the other materials are higher (not shown). ...
Article
For the plug flow mode of dense-phase pneumatic conveying, three different types of plugs have been defined, and models for predicting the pressure drop in conveying pipeline have been established. In literature, the model for Plug-2 pressure drop is mechanistic and depends on several properties of the materials forming the plug. Therefore, modification of the model with experimentally corrected material properties is considered in this study. The parameters tested in this study are plug velocity, particle velocity, and the stationary layer height. Using the new functional relationships, the Plug-2 pressure drop model is modified and its predictions are compared with experimentally measured pressure drops obtained in conveying Plug-2. It is found that the modified Plug-2 pressure drop model matches experimental values well within the variation range of ±20%. Further, a detailed analysis of various types of related velocities is presented and a new type of plug, called ‘Plug-2*’, is developed.
... The report provides algebraic correlations and charts to estimate this parameter. Ural suggested an alternative empirical algebraic relationship, based on the Kalman et al, work for predicting the minimum threshold velocity for poly-dispersed dust with a broad particle size distribution [8,10]. In applications where dust particles are expected to be removed as agglomerates, Ural suggested that substituting the particle density with its bulk density may be more appropriate [8]. ...
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An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust. The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply. If the concentration of the dispersed rock dust is sufficient, the flame will stop propagating. Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health (NIOSH) Lake Lynn Experimental Mine (LLEM) to measure the dynamic pressure history and the post-explosion dust scour depth. The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process. This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions. Keywords: Underground, Coal dust, Explosion, Dust sampling
... In any case, at superficial velocities higher than approximately 2 m/s, the results of all five tested materials coincide with each other. Fig. 11 also presents the pick-up velocity [41,42] of the two sands. The pick-up velocities of the other materials are higher (not shown). ...
Conference Paper
Three different types of plugs of particulate materials were defined in the past. First type (Plug-1) is the one in which the plug covers the whole pipe wall and does not leave any stationery particle behind. In second type (Plug-2) of plugs a stationary layer of particles exist between moving plugs. Whereas, third type of plugs (Plug-3) are small plugs which move over a stationary bed of particles. This presentation is focused on Plug-2, although other plugs will also be related. For Plug-2 analysis particle and plug velocities and stationary layer height are required. For Plug-2 in steady-state the particle velocity should always be lower than the plug velocity due to the stationary layer (for constant plug length). In order to use the velocities in the pressure drop model they were defined as functions of the superficial air velocity. Also the stationary layer height was defined as a function of the superficial air velocity. In addition, since we conducted experiments with a number of materials, Archimedes number was used to generalize the models to all materials. Finally, various ratios and parameters were analysed to show existence of two more kind of plugs, which were never defined in the past. These findings were strengthen by both graphs of various measured parameters and high-speed video visualization.
Article
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To study the effect of swirl intensity on the picking speed of wheat particles, a test bench for the transportation status of bulk grain particles was developed, and a theoretical model for the picking speed of wheat particles transported by swirl was established. Firstly, the critical conveying speed is determined through theoretical analysis and budgeted using the C&K model. Then, experiments are conducted to pick up loose grain particles in different flow fields. The particles in the swirling field are gradually rolled up from the windward end and sequentially pushed backwards to be picked up and transported. The picking speed of loose grain particles shows a trend of first increasing and then decreasing with the increase of swirling intensity. Using dimensionless swirl intensity as a variable, a predictive model for the effect of swirl intensity on particle picking speed during swirl conveying of wheat particles is derived. Practical applications When conveying bulk grain particles through a swirling flow, the intensity of swirling flow is closely related to the picking speed of bulk grain particles. This is extremely important for setting the wind speed of the conveying system, as it directly affects the energy consumption, particle crushing, and conveying efficiency of the entire system. Therefore, it is extremely important to predict the picking speed of bulk grain particles under different swirling strengths to control the corresponding wind speed. Therefore, this study conducts in‐depth research on this issue.
Chapter
According to the deposition law of hydrate particles in the deepwater undulating pipe, this paper analyzed the stress of hydrate particles in the undulating pipe, established the force model and critical deposition velocity model of hydrate particles. Based on the analysis of individual hydrate particle, the coalescence between hydrate particles was analyzed, and the force and critical sedimentation flow rate of hydrate particles after coalescence were studied. Based on the critical deposition velocity model of hydrate particle, the effects of hydrate particle diameter, gas density, pipe wall roughness and different pipe inclination on the critical deposition velocity of hydrate particles were analyzed. The results show that the critical deposition velocity of hydrate particle decreases with the increase of hydrate particle size; With the increase of fluid density in the pipe, the critical deposition velocity of hydrate particle decreases; The critical velocity of hydrate particle increases with the increase of pipeline roughness; In the upwardly inclined pipe section, the critical deposition velocity of hydrate particle first increases and then decreases with the increase of pipe inclination; In the downwardly inclined pipeline, with the increase of the inclination angle of the pipeline, the critical deposition velocity of hydrate particle gradually decreases, and the hydrate particles are more easily separated from the pipe wall, so it is easier to form hydrate deposition and blockage at the connection between the downwardly inclined pipeline section and the straight pipeline section.
Preprint
The Apollo 12 lunar module (LM) landing near the Surveyor III spacecraft at the end of 1969 has remained the primary experimental verification of the predicted physics of plume ejecta effects from a rocket engine interacting with the surface of the moon. This was made possible by the return of the Surveyor III camera housing by the Apollo 12 astronauts, allowing detailed analysis of the composition of dust deposited by the LM plume. It was soon realized after the initial analysis of the camera housing that the LM plume tended to remove more dust than it had deposited. In the present study, coupons from the camera housing have been reexamined. In addition, plume effects recorded in landing videos from each Apollo mission have been studied for possible clues. Several likely scenarios are proposed to explain the Surveyor III dust observations. These include electrostatic levitation of the dust from the surface of the Moon as a result of periodic passing of the day-night terminator; dust blown by the Apollo 12 LM flyby while on its descent trajectory; dust ejected from the lunar surface due to gas forced into the soil by the Surveyor III rocket nozzle, based on Darcy's law; and mechanical movement of dust during the Surveyor landing. Even though an absolute answer may not be possible based on available data and theory, various computational models are employed to estimate the feasibility of each of these proposed mechanisms. Scenarios are then discussed which combine multiple mechanisms to produce results consistent with observations.
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Full-text available
Aiming at the problems of high energy consumption and particle breakage in the pneumatic conveying process of large-scale breeding enterprises, in this paper, based on the theoretical calculated value of particle suspension velocity, a computational fluid model and a discrete element model are established based on computational fluid dynamics (CFD) and discrete element method (DEM). Then, through the numerical simulation of gas-solid two-phase flow, the influence of four factors of conveying wind speed, particle mass flow rate, pipe diameter, and particle size on the velocity distribution of particles in a horizontal pipe, dynamic pressure change in the pipe, pressure drop in the pipe, and solid mass concentration are studied. The results show that the k-ε turbulence model can better simulate the movement of gas-solid two-phase flow, and through the analysis of the simulation, the influence of four different factors on the conveying characteristics is obtained, which provides a scientific basis for the construction of the conveying line.
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Studying solids settling under sheared conditions is important for designing and operating slurry transportation pipelines. Electrical resistance tomography (ERT) is used for the first time to determine solids settling velocity under sheared conditions in a rheometer. The settling velocity of glass particles descending in 90 vol% glycerol solution located in the annular space between the ERT rheometer cup and bob was evaluated from conductivity data tracking particles' downward movement. The shear rate was varied from 5 to 125 s⁻¹ by changing the bob rotational speed. Solids concentration ranged from 5 to 25 vol%. Settling velocity decreased with increasing solids concentration, slurry viscosity and shear rate. An empirical settling velocity correlation was developed using a modified Richardson-Zaki model incorporating the effects of solids concentration, slurry viscosity and shear rate. This correlation could be adopted as the basis for determining solids settling velocity for slurry transport in laminar flow in a pipe.
Article
The purpose of this study is to apply the oscillation flow induced by a combination of a circular cylinder and non-uniform soft fins to gas–solid two-phase flows to reduce the transport gas velocity and power consumption in a horizontal pipe. In order to evaluate the oscillation flow, several different sizes of square and circular cylinders are used to combine four pieces of soft fins with non-uniform lengths, which are mounted on the horizontal central plane in front of the particle supply. The test pipe comprises a horizontal acrylic pipe with a length of 5 m and an inside diameter of 80 mm. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m³ were used as the test particles. The average gas velocity was 9–16 m/s, and the solid mass flow rate was 0.11–0.51 kg/s. It is found that the combination of a circular cylinder or square cylinder of L = 10 mm with non-uniform soft fins causes the lowest pressure drop and highest velocity fluctuation in the oscillation flow based on single-phase flow (gas only) measurement. Compared to conventional gas–solid two-phase flows, the reduction in the minimum transport velocity, pressure drop, power consumption, and additional pressure drop were obtained using a combination of circular cylinders with non-uniform soft fins. This combination provides the highest reduction rates in the minimum conveying velocity and an additional pressure drop by approximately 10.0% and 34.1%, respectively. Based on particle image velocimetry measurements, the time-mean particle velocity and particle fluctuating velocity of a circular cylinder with non-uniform soft fins were higher than those of conventional flows near the bottom part of the pipe, thus easily accelerating and suspending particles near the pipe bottom, even at lower gas velocities.
Article
In some engineering applications, the inlet velocity of cyclones for gas-solid separation varies periodically with time. This investigation is based on a push chain concrete spraying machine, measures and trigonometrically characterises the inlet periodic air velocity. Four standard cyclones and a design cyclone have been simulated to investigate performance under inlet periodic velocity. The simulation of the particle and fluid phases of the cyclone was carried out using the Reynolds Stress Model (RSM) using Computational Fluid Dynamics (CFD). The designed cyclone was used to verify the simulation results, the simulation and experimental data were in good agreement. The results of the study show that the 1D3D/w cyclone is optimal for the gas-solid separation of push chain concrete spraying machine. The effect of cyclone inlet size on separation performance under periodic velocity is significant. Furthermore, the concept of hysteresis time is defined by the difference between the time corresponding to the peak number of escaped particles and the time corresponding to the inlet velocity peak. Inlet periodic velocity can lead to situations where particles enter the cyclone and then return to the inlet duct or even escape by the inlet.
Article
The angle of repose, angle of tilting, and Hausner ratio are frequently used to estimate the flowability of particulate materials. In addition, free and tapped densities are commonly used for the design and operation of systems for handling particulate solids. In this study, these properties were determined for mono-sized and particle size distributions of three non-spherical particle materials. Based on previous and additional new measurements with new size fractions of mono-sized particles, it was found that mono-sized properties can be described as simple new functions (replacing the previous correlations) of the Archimedes number. Mixtures with wider size distributions were defined using logistic functions based on the median size and distribution parameter. Normalizing the measured property by the median size and assuming it to be mono-sized enabled finding a simple relation to the distribution parameter, equivalent to that found for spherical particles. Thus, the appropriate properties can be predicted based on the size distribution.
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Nanoparticles have broad application prospects, but their poor flowability poses a challenge to the handling and transportation. Here, we experimentally demonstrate that modulated pulsed aeration can destroy the consolidation of nano powder and achieve a breakthrough in silo discharge from clogging to flow. We confirm the multi-level arch structure in the silo discharge of nano powders: free-fall arch and cohesive arch. And the location of multi-level arch can be determined by the yield stress of material. Furthermore, the method of combined pulsed aeration was proposed to enhance the discharge flow. Specifically, the influence of modulation of pulsed airflow including frequency and duty cycle and aeration location configuration on nanoparticles silo discharge flow was explored. And the optimal combination method of double pulsed aeration was determined to eliminate the cohesive arch and greatly increase the discharge rate, which is close to the hypothesis liquid-like flow rate.
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It is a key and difficult problem to find the optimal powder-feeding technique in the study of powdered engines. In this paper, the feeding of powder in powder engines at different gas-solid ratios was experimentally investigated. Working characteristics of the classic piston-driven powder feeding system were obtained. A high linear tendency between powder mass flow rate and the minimum throttle channel area is observed from the experiment. The solid-gas mass ratio to maintain a stable powder feeding is approximately valued in range of 34.4–54.6 under different throttle channel areas. The least deviation in the relative powder mass flow rate for the tests is −15% to +8%. Due to the high uncertainty of the gas-solid flow structures at different gas-solid ratios, obvious low-frequency oscillations and high-frequency oscillations exist during the powder feeding process. The frequencies of low-frequency oscillations are mainly 1–3 Hz, while those of high-frequency oscillations are 20–30 Hz and 30–45 Hz in different tests.
Article
This study is focused on reducing the pressure drop, conveying velocity, and power consumption in a horizontal gas–solid flow. Four types of lattice models, which are fixed in the particle inlet, are proposed to easily generate the oscillation of the wake flow to easily convey the gas–solid two-phase flow. A horizontal pipeline with an inner diameter of 80 mm and length of approximately 5 m was used. Polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m³ were employed as conveying solid materials. The experimental ranges of the average gas velocity and solid mass flow rate were 10–16 m/s and 0.10–0.47 kg/s, respectively. Compared to the nonlattice gas–solid flow, reductions in the total pressure drop, conveying gas velocity, power consumption, and additional pressure loss were achieved in the range of lower gas velocity when using the lattice model. The highest reduction rates of the minimum conveying velocity and additional pressure drop were approximately 5.12% and 15.2%, respectively. In the acceleration region, the particle concentration in the flows with the lattice model was larger than that in the nonlattice flow near the upper part of the pipe and lower than those in the nonlattice flows in the lower part of the pipe. The time-mean axial particle velocity and particle fluctuating velocity in all lattice model flows were higher than those in the nonlattice flow, according to particle image velocimetry measurements, particularly in the upper part of the pipe.
Article
The pick-up velocity is a threshold velocity that is considered when designing hydraulic or pneumatic conveying systems. Defining the conveyed particles as ‘settling’ or ‘non-settling’ affects the calculation method of the pressure drop over a hydraulic conveying system. Rheometers are commonly used to measure the dynamic viscosity of liquids and suspensions. In this work, a unique method of using a rheometer is presented. The method enables simple measurement of the pick-up velocity by increasing the rotational speed of the rheometer. In addition, characterizing the particles as non-settling is achieved by decreasing the rotational speed. The results of this work correlate well with previously published results, confirming that these two parameters can be found by conducting very simple and quick measurements.
Article
This paper presents an analysis of all forces affecting the void fraction (VF) and density of a particulate bed. The bulk density of many materials, both spherical and non-spherical, with a variety of properties, including particle size and density, were measured in air and various liquids. The Archimedes number (Ar) was found to be an appropriate representation of the particle behavior that considered the van der Waals forces. The effects of buoyancy and viscous forces, as components of Ar, on the VF were shown by experiments in various liquids. Additional forces, such as friction, impact, and tapping were discussed quantitatively and qualitatively. Furthermore, the effect of the particle shape on the VF was considered. Finally, general equations for VF and density were developed for practical use. The major effects of the moisture content and compression pressure on the VF will be discussed in a following paper.
Article
Any scientific behavior is best represented by nondimensional numbers. However, in many cases, for pneumatic conveying systems, dimensional equations are developed and used. In some cases, many of the nondimensional equations include Reynolds (Re) and Froude (Fr) numbers; they are usually defined for a limited range of materials and operating conditions. This study demonstrates that most of the relevant flow types, whether in horizontal or vertical pipes, can be better described by Re and Archimedes (Ar) numbers. Ar can also be used in hydraulic conveying systems. This paper presents many threshold velocities that are accurately defined by Re as a simple power function of Ar. Many particulate materials are considered by Ar, thereby linking them to a common behavior. Using various threshold velocities, a flow regime chart for horizontal conveying is presented in this paper.
Article
To reduce the pickup velocity, the pickup characteristics of lump non-spherical particles in oscillating airflow were numerically studied on the basis of experimental verification. Five typical shapes of lump coal particles schistose, strip, cobble, block, and irregular block with diameters of 5-7 mm were modelled and numerically calculated in oscillating airflow, including rectangular wave airflow and sinusoidal wave airflow. The impact of the oscillating amplitudes and the frequencies were discussed. In addition, the oscillating number was first defined to quantitatively examine the oscillating intensity. A synthetic examination of pickup velocity variation in both swirling airflow and rectangular airflow was conducted. Two points are worth highlighting: (1) the increase in the particle pickup ratio caused by the strength interaction intensity mostly prioritized of the particle pickup process in oscillating airflow. Particles were liable to be entrained, but this process was weakened in the continuous pickup process in high frequency rectangular wave airflow. The 10 Hz to 100 Hz range is an appropriate oscillating frequency pan. (2) A significant consistent regression relationship was observed in both the swirling airflow and oscillating airflow, in which the particle pickup velocity increases at first and then decreases with both oscillating number and swirling number. This regular relationship was well fitted by a cubic polynomial function.
Article
A design concept to feed dry coal from a hopper to a 100 kWt pressurized oxy-coal reactor using CO2 at 2 MPa was developed using transient CFD simulations and bench-scale measurements. The feed system was required to maintain a steady flow of gas and solids at a coal flow rate of approximately 3.8 g/s and a CO2-to-coal mass ratio in the range 1-2. A 5.08-cm diameter vertical coal hopper feeding into a 0.635-cm diameter horizontal pipe was used to represent key elements of the feed system. A fluidized bed concept was found capable of providing the desired coal flow rate and CO2-to-coal flow ratio. Use of separate fluidization and dilution flows allowed the coal flow rate and CO2-to-coal flow ratio to be controlled independently. The amount of coal transported from the hopper was dependent on the net CO2 flow in the hopper but independent of the CO2 dilution flow. Pipe exit coal flow rates were found to fluctuate at levels acceptable for steady burner operation. Tests from a bench-scale apparatus using Pittsburgh 8 coal with a median particle diameter of 50 um and moisture content of 6% confirmed the feasibility of the fluidization design. However, for a given CO2 fluidization flow rate, experimental coal flow rates were lower than predicted coal flow, in part due to simplifying assumptions of dry, spherical coal particles and smooth piping in the simulations.
Article
Pneumatic conveying experiments involving monodisperse and binary-size mixtures of glass beads with charges in the range of −10 to 10 nC have been carried out. The mass loss method was adopted, with the minimum pickup velocity (Upu) determined as the minimum velocity at which entrainment occurred. Similar to previous studies on minimum fluidization velocity, the Upu increased with particle initial charge for the positively charged particles (0–10 nC). Surprisingly, however, negatively charged particles exhibited an opposite trend such that the Upu decreased with charge magnitude. Therefore, for the particle initial charge range investigated (−10 to 10 nC), Upu increased monotonically with particle initial charge, and the correlations available (Kalman et al., 2005; Tay et al., 2012) mis-predicted Upu by up to 10 % for monodisperse systems and up to 40 % of binary-size systems. This underscores the necessity to account for particle initial charge in such correlations, particularly for polydisperse particle systems.
Article
Powder propellant feeding system is the key part of powder engine, and the powder fluidization process is quite complex due to the comprehensive effects of intake type, piston and compressible dense gas-solid flow in tank. In order to explore the regimes and fluidization characteristics at high pressure, in this paper, visualization technique with pressure transducer are applied, and the pressure signals have been analyzed by using standard deviation and wavelet transform methods. It is found that in powder tank the fluidization regime will be changed with the increase of pressure: from partial powder fluctuation at low pressure (0.4 MPa) to steady gas-solid interface at high pressure (2.5 MPa), and the regime phenomenon can be explained roughly by standard deviation analysis of pressure signals. Meanwhile, the flow representations of pressure sub-signals were redistricted through wavelet energy method based on ten-level decomposition: the approximation sub-signal a10 (0–4.88 Hz) represents the fluidized gas intake, sub-signals d8–d10 (19.53–39.0625 Hz) represent the powder flow structure changing, gas-solid interaction is represented by d6–d7(39.0625–156.25.Hz), and sub-signals d1–d5 (156.25–5000 Hz) can be used for gas turbulence flow representation. Where gas turbulence and powder fluctuation were determined as the main contributions to pressure fluctuation in the tank. Otherwise, the wavelet energies of sub-signals except for approximation decrease with pressure increase, but there exist large differences for that with the increase of particle mean diameter with different leading force, and the easier entrainment for different size powder, the slighter effects of gas turbulence and gas-solid interaction.
Article
Over the past years, experimental research on both pickup and sanitation mechanisms has been conducted in our laboratory. Both pickup and saltation mechanisms of solid particles have been examined in relation to the prediction of the minimum conveying velocity required in horizontal pneumatic transport systems that operate in dilute-phase. Several experiments have been carried out to determine pickup, saltation, and particle velocity of a wide variety of materials. The use of dimensional analysis and the experimental findings led to simple correlations useful to predict pickup and saltation velocity of coarse particles (above 100 μm). Noteworthy is the effect of pipe diameter on the pickup mechanism, an important result to be considered in scale-up procedures. The pickup and saltation mechanisms of solid particles have been related with the aid of a novel diagram, opening new avenues to fully understand the complex behavior of gas-solids suspensions flowing inside pipes.
Article
Determination of saltation velocity is one of the key design parameters in pneumatic conveying systems. The aim of this work is to study the mechanism of saltation. Experimental results of measurements of saltation velocity in wind tunnel with very dilute flow are presented. Experiments were carried out with alumina spheres, glass beads, metal balls, sand, potassium sulphate and potash. The relationship between saltation velocity and the maximum conveying length (saltation length) is shown. The boundary saltation velocity was defined as the saltation velocity at which particulate solids can be conveyed for significant (long) distances. The influence of the feeding method (forced or gravitational feeding) and conditions on saltation velocity and length was investigated.
Article
Attrition during pneumatic conveying is a problem faced by the industry for a long time. This paper first evaluates a few experimental test rigs and procedures and then presents extensive experimental investigation with most of the parameters affecting attrition. The parameters are categorized into material strength, operation parameters and bend structure. It is shown that air velocity, loading ratio, bend flexibility and number of collisions are the main factors influencing the rate of attrition. Most of them are in the hands of the designer and operator to control the attrition.
Article
Particle entrainment is investigated by measuring the velocity required to pick up particles from rest, also known as pickup velocity. Pickup velocity is a function of individual particle characteristics and interparticle forces. Although 5–200 μm particles are investigated, the work presented here focuses on the pickup of particles in a pile in the size range of 5–35 μm. These smaller particle sizes are more typical for pharmaceutical and biomedical applications, such as dry powder inhalers (DPIs). Pickup velocities varied from 3.9 to 16.9 m/s for the range of particle sizes investigated.There is a strong correlation between particle size and the dominating forces that determine the magnitude of the pickup velocity. Preliminary data investigating pickup velocity as a function of particle size indicate the existence of a minimum pickup velocity. For larger particle sizes, the mass of the particle demands a greater fluid velocity for entrainment, and for smaller particle sizes, greater fluid velocities are required to overcome particle–particle interactions. Pickup velocity remains relatively constant at very small particle diameters, specifically, less than 10 μm for glass spheres and 20 μm for nonspherical alumina powder. This can be attributed to the negligible changes in London–van der Waals forces due to a hypothesized decrease in interparticle spacing. At intermediate particle diameters, electrostatic forces are dominant.
Article
The minimum velocities required to convey single particles in horizontal flow are correlated with Reynolds number in terms of the conventional drag coefficient. Experimental data obtained in 1 1/4-inch and 2 1/2-inch pipe agree with measurements of sand movements in the open desert. The results have practical significance in establishing the lowest limit of velocity in pneumatic conveying without saltation. The minimum velocities necessary for saltation-free conveying of mixed size materials under various degrees of solids loading are correlated with the single particle saltation velocity of the most difficultly transported size in the mixture. A parameter in this correlation is a constant characterizing the size and spread of sizes of the particles in the mixture. This constant is calculable from the particle size analysis and, in combination with the saltation velocity correlation, can be used as a criterion for distinguishing between materials more feasibly transported in dilute or in dense phase.
Article
This study presents a mechanistic model that predicts the critical velocity, which is required to initiate the movement of solid bed particles. The model is developed by considering fluid flow over a stationary bed of solid particles of uniform thickness, which is resting on an inclined pipe wall. Sets of sand bed critical velocity tests were performed to verify the predictions of the model. An flow loop with recirculation facilities was constructed to measure the critical velocities of the sand beds. The tests were carried out by observing the movement of the bed particles in a transparent pipe while regulating the flowrate of the fluid. Water and aqueous solutions of PolyAnoinic Cellulose were used as a test fluid. The critical velocities of four sand beds with different particle size ranges were measured. The model was used to predict the critical velocities of the beds. The model predictions and experimentally measured data show satisfactory agreement. The results also indicated that the critical velocity is influenced by the properties of the fluid, flow parameters, and particle size.
Article
This work presents experimental results of the pickup velocity measurements for variety of particulate solids. The experiments were carried out in a horizontal wind tunnel. The influence of three initial arrangements of particle(s) on pickup velocity was investigated. Particle(s) were placed either on the bottom surface of the tunnel or on the horizontal layer of particles or the heaps of particles with various heights were created in the wind tunnel. A high-speed video camera was used to visualize the particle entrainment. However, the pickup velocity was defined in a qualitative manner by extrapolating the carried weight of particles as a function of air velocity. Comparison between the saltation velocity in dilute phase flow and the pickup velocity, both measured in the horizontal wind tunnel, provide an insight and guideline how the minimum operating air velocity in a pneumatic conveying line could be defined and determined.
Article
A technique for finding the minimum pickup velocity of solid particles in horizontal pneumatic conveying has been developed. A general semi-empirical correlation based on the Archimedes number which is valid over a range of particle size from 10 to 1000 μm is presented for the prediction of the minimum gas velocity required to pick up particles. Experiments have been carried out with fine particles (glass beads, alumina and coal) in a 52 mm i.d. transparent pipeline. Noteworthy is the existence of a minimum point in the curves of minimum pickup velocity as a function of particle diameter for particle diameters of approximately 100 μm. Maximum conveyability is expected to occur at this particle size. Above and below this minimum point, higher gas velocities are required to pick up particles lying on the bottom of a pipe. Experiments in an actual pneumatic conveying system clarify the practical significance and usefulness of the minimum pickup velocity. Thus, it is suggested that the proposed test procedure be used as a unified technique in determining the minimum transport velocity of solid particles in horizontal pneumatic conveying systems.
Article
Both pickup and saltation mechanisms of solid particles have been examined from an experimental viewpoint, in relation to the prediction of the minimum conveying velocity required in horizontal pneumatic transport systems that operate in dilute-phase. Several experiments were carried out to determine pickup, saltation, and particle velocity of a wide variety of materials using different techniques. The use of dimensional analysis and the experimental findings led to a simple correlation useful to predict pickup velocity of coarse particles (above 100 μm). Noteworthy is the existence of a pipe diameter effect on the pickup mechanism, an important result to consider in scale-up procedures.For the first time in pneumatic transport, pickup and saltation mechanisms of solid particles in horizontal pipelines have been related, with the aid of branching and stability analysis. These ideas open new avenues to full understanding of the complex behavior of particles conveyed pneumatically through pipelines.
The effect of sphericity on the Archimedes number
  • Ar
  • Ar
  • Sphericity
  • H Fig
  • Kalman
Ar * /Ar Sphericity, φ Fig. 14. The effect of sphericity on the Archimedes number. H. Kalman et al. / Powder Technology 160 (2005) 103 – 113
Incipient rolling, sliding and suspension of particles in horizontal and inclined turbulent flow
  • Hallow
J. Hallow, Incipient rolling, sliding and suspension of particles in horizontal and inclined turbulent flow, Chemical Engineering Science 28 (1978) 1 -12.
  • K S Hayden
  • K Park
  • J S Curtis
K.S. Hayden, K. Park, J.S. Curtis, Effect of particle characteristics on particle pickup velocity, Powder Technology 131 (2003) 7 – 14.