Mechanical properties and morphologies of polypropylene with different sizes of glass bead particles

A commercial grade of isotactic polypropylene (PP) was used to study the mechanical properties and morphologies of the PP composites filled with four sizes of glass bead particles. The glass bead particles used were with average particle sizes of 15 μm (GB15), 10 μm (GB10), 5 μm (GB5), and 2.5 μm (GB2.5), respectively. It was clear that the glass bead size was an important factor on the determination of mechanical properties of the composites. As a whole, in view of the scatter in the data, under the condition of same filler content, the yield strength and impact strength of the composites filled with smaller glass bead particles was higher than those of the composites filled with bigger ones. And the flexural strength and modulus of the composites filled with GB10, GB5, or GB2.5 particles could be regarded as the same. The flexural strength and modulus of the composites filled with GB15 particles were higher than those of the composites filled with other three sizes of particles. Among four sizes of glass bead particles, GB2.5 had the best toughening effect to improve the impact strength of PP matrix. And the major toughening mechanism of the PP/GB2.5 composites was the pinning effect introduced by GB2.5. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effect of particle characteristics on particle pickup velocity

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.     

Influence of powder size on characteristics of air plasma sprayed silicon coatings

Silicon powders with different medium sizes (114 μm, 79 μm and 31 μm, respectively) were used to fabricate coatings by air plasma spraying. The velocity and temperature of in-flight silicon particles during plasma spraying were determined. The composition and microstructure of the coatings were characterized and some physical properties of the coatings were measured. The obtained results showed that the size of silicon particles had great influence on their velocity and temperature in plasma flame. The oxidation of silicon particles in the spraying process was observed and is higher for particles of smaller sizes. Areas of silicon oxide in micrometer size are embedded and randomly distributed in the coating. The surface roughness and void content of silicon coatings increase with an increase in the particle size of the powders. The microhardness and oxygen content of coatings decrease with an increase in the particle size. However, the size of silicon particles has little impact on the deposition efficiency of silicon under the same deposition conditions.     

Entrance effects at a multi-orifice distributor in gas-fluidised beds

The behaviour of multi-orifice distributors in gas-solids fluidised beds has been studied with particular regard to the height of the entrance effect and the mechanics of gas-solids flow in the region immediately above the distributor plate. A model is proposed to predict the height of the entrance effect for a given distributor and gas-solids system at various fluidising flow-rates, and good agreement has been found with experiment. Experiments have been carried out with (a) a two-dimensional air-fluidised bed using three sizes of sand particles (d_p: 137, 263, and 350 μm) and four distributors (orifice diameters: 0.001 m, 0.002 m; orifice spacings: 0.025 m, 0.05 m); and (b) a three-dimensional air-fluidised bed, 0.3 m square in cross-section, using 350 μm sand particles on a distributor with 0.003 m diameter orifices at a spacing of 0.04 m. The principal factors influencing the height of the entrance effect were found to be the incipient fluidising velocity, mean particle size, orifice spacing and gas flow-rate. The model has been used to estimate the minimum ratio of distributor pressure drop to bed pressure drop to bring about an even distribution of gas at the bottom of the bed.     

Transport of Airborne Particles from an Unobstructed Cough Jet

This article presents analytical and experimental results for the velocity distribution and transport of expiratory particles from an artificial cough. The stream-wise penetration distance and velocity field of the cough jet were determined through a combination of dimensionless analysis and experimental techniques. The experiments were conducted in a well-controlled environmental chamber with simplified thermal manikins to simulate human coughs and buoyant thermal plumes, and involved flow visualization, velocity measurements employing high and low velocity hot-wire anemometers, and particle size and concentration measurement. The study analyzed three particle sizes—0.77, 2.5, and 7 μm—to examine the impact of particle size on particle transport in the cough jet region and in the vicinity of a receiver occupant positioned in close proximity to the coughing source. The results indicate that the cough jet has a lower axial velocity but higher span-wise expansion rate than a steady jet with an identical discharge velocity. The particles of three sizes have a similar trajectory when considering the transport in the cough jet region. However, particle concentration distributions of the three size particles show that size is an important factor for particle transport in the vicinity of the receiver occupant where airflow velocity decays to the room background air velocity. Furthermore, the results suggest that a cough jet is able to overcome the buoyant human thermal plume and travel further ahead in the region behind the receiver occupant.

Copyright 2014 American Association for Aerosol Research     

Retracted: Effects of the Operating Conditions and Geometry Parameter on the Filtration Performance of the Fibrous Filter

The gas‐solid two‐phase flows in fibrous filters were simulated by computational fluid dynamics (CFD) technology. The pressure drops and filter efficiencies with different operating conditions and geometry parameter, including face velocity, particle size, and solid volume fraction (SVF) were calculated. The effects of the operating conditions and geometry parameter on the filter performance of the fibrous filter were obtained. The results indicate that the pressure drop increases linearly with the face velocity and the predicted values of the pressure drops are in excellent agreement with the experimental correlation. Filtration efficiency decreases with the face velocity for submicrometer particles (0.1 μm) and, for larger particles (1 μm) the tendency is just the opposite. The filtration mechanism is different for different particle sizes. For the filter in this paper, when the particle size is smaller than 0.2 μm, Brownian diffusion plays a significant role in the filtration process. When the particle size is greater than 0.5 μm, inertial impaction becomes an important capture mechanism. For particle sizes in the range of 0.2–0.5 μm, the Brownian diffusion and inertial impaction are both relatively weak and, therefore, the filtration efficiency has the least value in this range. Additionally, the SVF distribution is an important geometry parameter in the filter. The filtration efficiency of the filter with a decreased SVF (geometry B) along the thickness of the filter is higher than that of the filter with the even SVF (geometry A), while maintaining a low pressure drop.     

Physicochemical Factors Influencing Colloidal Particle Transport in Porous Media

Abstract

The mobilization/immobilization of colloidal-sized particles which have high surface areas per unit mass is an important process occurring in groundwater flow systems. Association of contaminants with mobile colloidal particles may enhance the transport of adsorbed pollutants, or deposition of colloidal particles in porous media may decrease permeability and reduce contaminant transport. The general objective of this work was to elucidate physical and chemical factors affecting colloidal particle (Brownian and non-Brownian) transport in porous media under typical groundwater flow velocities. The most critical chemical factor influencing Brownian particle (0.1 and 1.0 μm) transport in a packed column was found to be pH. The next most critical factor was electrolyte concentration (calcium ion and sodium ion concentration). Gravitational force was found to be an important factor for non-Brownian particle (10 μm) transport. The non-Brownian particle transport was observed to be independent of solution chemistry. Increases in superficial velocity (from 0.9 to 2.7 m/day) resulted in different types of behavior for Brownian and non-Brownian particle transport under different conditions. The Brownian particle throughputs at a superficial velocity of 0.9 m/day were mainly controlled by the surface interaction forces, that is, hydrodynamic action was not important. The difference in Brownian diffusivity between 0.1 and 1.0 μm particles caused opposite results in particle throughputs in all experimental columns regardless of solution chemistries. Particles of 0.1 μm produced the maximum transport in the column filled with the smallest glass beads, while 1.0 μm particles produced the maximum transport in the column packed with the largest glass beads.     

Modeling Dry Deposition of Aerosol Particles onto Rough Surfaces

Dry deposition is a primary mechanism by which suspended particles are transported from gas onto surfaces. Prediction of this transport rate is needed in a vast range of applications, including environmental, industrial, and engineering, and in studying the impacts of aerosols. Besides air flow characteristics and properties of aerosol particles, the dry deposition velocity depends greatly on surface properties. However, existing models describe rough surfaces with only one parameter, the surface roughness height, and are therefore of limited accuracy. Here, we introduce a new, and yet simple, physical approach to account for the influence of surface roughness on the dry deposition velocity. The approach relies on a hybrid parameter that combines the surface roughness height and the peak-to-peak distance between roughness elements. Our new approach is able to predict the deposition velocity accurately, being superior to many of the earlier models, which overpredict deposition velocities by a factor as high as 25. In addition, our approach is more general and covers a wide size range of aerosol particle diameter (0.001–100 μm).

Copyright 2012 American Association for Aerosol Research     

Effect of sound on the fluidization of group B particles

The behaviour of several kinds of group B particles ranging from 100 μm to 600 μm was studied in a sound wave vibrated fluidized bed (SVFB). The fluidized bed consists of a transparent Plexiglas tube that is 54 mm i.d. × 1 m high. A speaker mounted at the top of the bed was supplied by a function generator with square waves and was used to generate the sound as the source of vibration of the fluidized bed. The influence of the particle size, density of particles and sphericity of particles on the minimum fluidization velocity, pressure fluctuations and bubble rise velocity in the SVFB was investigated. The minimum fluidization velocity decreased as the sound energy increased. When the sound energy was strong enough and greater than the critical power, the minimum fluidization velocity would approach the same value regardless of the degree of resonance (DOR) value if the particles were in spherical shape. For non-spherical shape particles the minimum fluidization velocity was the function of the DOR value if the power was greater than the critical power. For the middle particle size range, the standard deviation of pressure fluctuations in an SVFB became lower than the one without the effect of sound in high superficial gas velocity range, but the result was reverse for the low superficial velocity; for the large particle size range, the standard deviation of pressure fluctuations in an SVFB was larger than the one without the effect of sound. The sound could also reduce the bubble rise velocity in an SVFB.     

Effect of Small-Scale Obstructions and Surface Textures on Particle Deposition from Natural Convection Flow

ABSTRACT

To increase knowledge of particle dynamics in indoor environments, we have conducted experiments on the effects of small surface discontinuities and roughness on deposition from natural convection flow. Measurements were made in a half-height (1.22 m) aluminum test chamber and in a full-scale experimental room. In the test chamber, air flow was induced by uniformly heating the floor and one wall while cooling the ceiling and opposite wall to a constant temperature difference of 3 K. In the full-scale room, one wall was heated and the opposite wall was cooled to a constant wall-to-wall temperature difference of 3 or 7 K. Other surfaces in both experiments were approximately adiabatic. Near-monodispersed fluorescent particles (diameters 0.1, 0.5, or 1.3 μm in the half-height experiments and 0.2 or 1.0 μm in the full-scale experiments) were injected into the chamber. Following an exposure period, the mass of fluorescent particles deposited on sections of the walls and/or plates mounted on the walls were extracted and measured by fluorometry. The effect of surface discontinuities was explored by comparing deposition onto the walls or onto flush-mounted plates with deposition onto thin, smooth, surface-mounted plates. The effect of surface roughness was investigated by measuring deposition onto textured plates (finely scratched, a rectangular array of 2.4 mm balls, or skip-coat drywall texture). Deposition of the smallest particles (0.1 and 0.2 μm) was relatively insensitive to surface obstructions and texture, but the effect of roughness increased with particle size. For 1.3 μm particles, deposition to the roughest surface was as much as five times greater than deposition to a smooth wall. The effect of surface roughness was greater for vertical surfaces than horizontal and for warm surfaces than cool. Deposition velocities measured with a 3 K temperature difference are fairly consistent between the full-scale room and the half-height chamber. Overall, surface roughness of the type commonly found indoors can significantly impact deposition rates, and, therefore, many real surfaces cannot be assumed to be smooth when analyzing particle deposition in indoor environments.     

Particle Shape and Size Effects on Anisotropic Shrinkage in Tape-Cast Ceramic Layers

The particle shape of a commercial low-temperature cofired ceramic (LTCC) composite powder was determined quantitatively in the as-received and milled state using a new particle image analyzer. All grades of the milled powder with average particle sizes of 3.0, 2.4, and 1.8 μm, respectively, exhibit a considerable stretched particle shape, because 40% of their particles have circularity values below 0.95. On the basis of the fast particle image analyzer, the influence of the raw materials on particle alignment during tape casting was investigated using "design of experiments" (DOE). In the cast LTCC green tapes, the degree of particle orientation was measured and correlated with the information from the particle shape analyses and with other material and process factors from the DOE. The results showed that the degree of particle alignment correlates significantly with the measured particle shape and size; more than 80% of the particles were oriented in the casting direction if their shape factor was below 0.5. The particle orientation causes shrinkage anisotropy. The use of a coarser LTCC powder with an average particle size d ₅₀ of 3.0 μm instead of 1.8 μm increased the sintering anisotropy factor of LTCC tapes and laminates significantly from 1.0% to 1.85% and from 3.6% to 7.6%, respectively. The use of more binder or less solvent led to higher shrinkage anisotropies too. The casting velocity showed only a minor effect on the degree of particle orientation and sintering anisotropy, which is due to the shorter shearing period in which particle rotation can take place.     

Erodent size effect on the erosion of polyphenylene sulfide composite

The effect of erodent particle size on solid particle erosion of randomly oriented short glass fiber and mineral particle reinforced polyphenylene sulfide (PPS) was investigated. To examine the effect of erodent size on the erosion resistance of the PPS composite, aluminum oxide particles at three different sizes, namely, 300–425 μm, 150–212 μm, and 45–75 μm, were used. The erosion tests were performed at six different contact angles of 15°, 30°, 45°, 60°, 75°, and 90°, respectively. The results showed a strong relationship between the erodent particle size and erosion rates of PPS composite. Maximum erosion rate for the erodent particles with sizes of 45–75 μm and 150–212 μm occurred at contact angle of 30°, on the other hand maximum erosion rate for particles having 300–425 μm size occurred between 45° and 60°. The morphologies of eroded surfaces were characterized by the scanning electron microscopy (SEM). Possible erosion mechanisms were discussed. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Characterizing the effect of substrate surface roughness on particle-wall interaction with the airflow method

The effect of surface roughness on particle-wall interaction was studied by the airflow method. Five kinds of monodispersed spherical particles (D_p50 = 11-41 μm) and six test pieces with different surface roughness (Ra = 0.01-1.64 μm) were used in the experiments. The particles were dispersed on the test pieces to form a monolayer, and entrained in a rectangular air channel. The air velocity increased at a constant rate, and the entrained particles were detected with a laser dust monitor. Microscopic observations showed that particle entrainment occurred in discrete and intermittent events during experiment, thus a statistical parameter, i.e. the particle entrainment efficiency as a function of the air velocity, was defined for evaluating the particle-wall interaction force distribution. The experimental results showed that the air velocity for particle entrainment decreases with the increase of the surface roughness within submicron-scale and reaches a lower limit, while increases to some extent for micron-scale surface roughness. It was also found that the effect of the substrate surface roughness depends on the particle diameter.     

Analysis of the efficiency of reverse flow cyclones

The efficiency of a 152 mm cyclone was determined for inlet velocities in the range 6.1 — 15.5 m/s, for particle sizes from 0.6 μm to 4.7 μm, using monodisperse methylene blue-uranine aerosol particles. The efficiency of a geometrically similar 76 mm cyclone was also measured for a few conditions of inlet velocity and particle size. These data and others were correlated by linear regression analyses on a function of cyclone Stokes number and cyclone Reynolds number. It was concluded that in the range of variables spanned by the experimental data, the flow fields within the cyclones depended on Reynolds number, and hence that contrary to the assumptions of most theoretical models, cyclone efficiency is not exclusively a function of Stokes number.     

The use of latex rubber-modified polystyrene as a model system for HIPS: Effect of particle size

The effect of particle size in high-impact polystyrene (HIPS) is difficult to determine because of a size polydispersity and changes in particle morphology during the HIPS synthesis process. In this study, poly(n-butyl acrylate) rubber core/polystyrene shell particles were made by emulsion polymerization methods such that the only difference was in particle diameter, which ranged from 0.4 to 6.2 μm. The latexes were subsequently incorporated into a polystyrene matrix to form a toughened composite that acted as a simple model for HIPS. Charpy impact energies (notched and unnotched) of the composites showed that there was no toughening for particle sizes less than 2μm in diameter. The optimal impact energy was obtained with particle diameters in the region of 2–3 μm at 8 wt % rubber loading. The results imply that craze stabilization is the most important aspect of the toughening process. A simple toughening model based on the crack opening displacement of craze breakdown between adjacent rubber particles is suggested, with interparticle distance as the most important variable. © 1993 John Wiley & Sons, Inc.     

A Rational Basis for National Ambient Air Standards for Particulate Matter

The aspiration of large particles (18–30.5 μm) in the human nose was studied to determine the inhalation efficiency as a function of particle size, and to evaluate the upper size cutoff for inhalable particles in still air. Under these conditions, the ability of a particle to be inhaled is dependent on the inhalation velocity entering the nose and the particle terminal settling velocity. Nasal inhalation of radiolabeled pollen and wood dust aerosols was measured in four subjects at normal resting breathing rates. The efficiency of nasal aspiration was found to decrease as the square of the particle size. The upper size cutoff for inhalability was estimated to be approximately 39 μm in still air.     

Evaluation of an optical particle sensor to determine the effect of nozzle shape on counting efficiency

The optical particle sensor (OPS), using light scattering from particles, is widely used in clean-rooms and in atmospheric environmental monitoring. However, parameters that affect the particle counting of the OPS have been less explored previously. The present study examines the effect of the nozzle shape on particle counting performance of the OPS. Experiments and simulation studies were carried out for four different nozzle shapes in conjunction with three different particle sizes. The effect of nozzle shape is evaluated not only by experiments analyzing the intensity of scattered light and particle velocity but also by simulation. Fluent was used to simulate the flow field and particle trajectories. We observed that particle velocity and trajectory are strongly dependent on the input nozzle shape, which in turn has an effect on the particle counting performance. Using these results, the design of OPS can be optimized to provide higher counting efficiency.     

多效旋风分离器性能的实验研究

多效旋风分离器通过采用2级螺旋管预分离含尘气体、螺旋形顶盖板导流、筒体中心稳流锥稳流和吸气回流系统防止粉尘返混等措施,解决了在旋风流场中分离微米及亚微米级颗粒的难题。文中通过实验研究了直径为0.25 m的多效旋风分离器的压降、分离效率和进口风速的关系,实验物料粒径范围为0.1—23μm,平均粒径为7.59μm。结果表明:在10—14 m/s入口风速时,对0.1—3μm颗粒的分离效率大于90%,对大于5μm颗粒的分离效率接近100%,压降在500—1 000 Pa。风速大于16 m/s时,对0.1—2μm颗粒的分离效率大于75%。     

The Effects of Bluntness and Orientation on Two-Dimensional Samplers in Calm Air

This article uses numerical simulation to investigate the effect of sampler bluntness, particle size, and sampler orientation on aspiration efficiency in calm air. The procedure is to first numerically solve the velocity field around the sampler in calm air and then to trace the particle trajectories and calculate the the aspiration efficiency. Two samplers are studied: a two-dimensional parallel plate and a two-dimensional blunt cylinder. The variation of aspiration efficiency with particle size shows two minima between two asymptotic values. When the samplers are facing upward, the asymptotic values are 1 for very small particles and the ratio of particle settling velocity to suction velocity for very large particles. At other orientations, the horizontal-facing and the downward-facing, the asymptotic value for large particles is 0. The sampler bluntness has an important effect in the region of particle size where there is competition between the particle inertia and the fluid drag force (i.e., 5 μm < d > 100 μm in our case). A blunt sampler always has higher aspiration efficiency than does a sharp-edged sampler in this region of particle sizes. For very small particles and very large particles, the aspiration efficiencies approach asymptotic values and the sampler bluntness has little effect. The results also show that the sampler orientation affects the predicted aspiration efficiency     

Comparison of Three Approaches to Model Particle Penetration Coefficient through a Single Straight Crack in a Building Envelope

In this study, we present three approaches to predict particle penetration coefficients through a single straight crack in building envelops. The three approaches are an analytical approach, an Eulerian approach, and a Lagrangian approach, respectively. The particle penetration coefficient through an idealized straight crack (smooth inner surfaces) and a strand board crack (rough inner surfaces) were modeled by the three presented approaches. The calculated results were compared with the literature results. The comparison shows that for the idealized smooth crack, the modeled results by the Eulerian approach match the experiments best for the entire range of particle sizes studied among the three approaches. The predicted results by the analytical approach also match the experiments reasonable well. Results modeled by the Lagrangian approach are less satisfied for fine particles (d _p < 0.1 μm). Overall, all the three approaches agree well with the experiments for particle sizes ranging from 0.4–1.2 μm. For cracks with rough inner surfaces, the results agree better with the measurements for all the three approaches by adjusting the boundary conditions to incorporate the “intercept” effect of roughness on particle deposition in the cracks.