Search

Copyright of Polymer Materials Science & Engineering is the property of Sichuan University, Polymer Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microplastics and other microscopic debris are a concern in the coastal environment but measurements in the water column and sediment are often problematic and rely on non-standardised and highly variable methodologies. To this end, we explore the potential of different species of temperate-cold marine macroalgae as passive biomonitors of anthropogenic microparticles at three contrasting locations in southwest England. Specifically, fronds from samples of fucoids and Ulva lactuca (n = 9 in total, and three from each location) have been sectioned and analysed directly under a microscope and anthropogenic microparticles counted and subsequently characterised for chemical composition. Microparticles were heterogeneously distributed throughout sections from the same sample. However, on a dry weight basis, combined microparticle concentrations for each sample ranged from about 7.5 g-1 to 110 g−1, and from about 0.2 cm−2 to 0.9 cm−2, and for a given species were higher in samples from a semi-enclosed harbour and urban beach than in samples from a protected beach facing the open sea. These values compare with published concentrations of microplastics and microfibres reported for the regional water column on the order of 0.1 m-3. Most particles were cellulosic (e.g., rayon) and petroleum-based (mainly polyester and polyethylene terephthalate) fibres but plastic fragments were also present on most samples. Glass retroreflective beads derived from road markings were also present at up to 18 g−1 on fucoids from the urban beach because of its proximity to a stormwater effluent. Most microparticles were adhered to the smooth parts of the macroalgal surface but some displayed wrapping around edges and creases or entrapment by appendages. The practical and environmental implications of macroalgae passively capturing significant quantities of anthropogenic microparticles are discussed. [Display omitted] • Fucoids and Ulva lactuca from three locations in SW England accumulated microplastics and fibres. • Infrared analysis revealed both cellulosic (e.g., rayon) and petroleum-based materials. • Retroreflective glass beads also accumulated on fucoids in the vicinity of a stormwater drain. • Total particles numbers attached to the surface ranged from about 7.5 to 110 per g dry weight. • Macroalgae can be used as biomonitors and, potentially, bioremediators of microdebris. [ABSTRACT FROM AUTHOR]

A new component of the combined finite-discrete element method (FDEM) is employed to estimate the effects of geometrical features, friction and energy dissipation parameters on the bulk properties of rigid pellet packs. This work constitutes the first systematic validation of the Solidity FDEM code for rigid particles. The experimental and numerical axial and radial packing density profiles and orientation distributions have been compared, confirming that the numerical simulations of packing of cylindrical catalyst supports, glass beads and trilobe pellets deposited in a cylindrical container match the corresponding emergent bulk properties obtained from X-Ray CT scans. The presented results are a first confirmation of the applicability of FDEM based methods to the simulation of this class of multi-body problems. The assessment of the accuracy of the simulated topology of the pellet pack that is established in this work is encouraging for further investigations of the multi-physical engineering systems of interest for catalyst pellets involving hydro-thermo-mechanical, fracturing and fragmentation interactions using coupled FDEM formulations. Unlabelled Image • A combined finite-discrete element method (FDEM) is used in packing simulations. • The mesh, contact, friction, damping parameters influence on packs is shown. • FDEM packs of cylinders, beads, trilobes match X-Ray scans emergent properties. [ABSTRACT FROM AUTHOR]

The mixing and separating process of different-sized particles in a self-designed rotating drum were explored, where the glass beads were taken as particles. The power consumption of rotating drum under different operating parameters were measured. The results show that the particle separation is more evident when the drum is operated at high fill level, where the small particles surrounded by large particles are mostly observed. When the filling rate is low, it is unobvious for the particle separation of the similar size particles at different rotating speeds. The larger difference of the particle size, the more particle separation occurs. With the increasing rotational speed and fill level, the power consumption increases, while the power consumption is relatively less sensitive to the particle size ratio. [ABSTRACT FROM AUTHOR]

In the present work, the particle-laden coaxial turbulent jet flow is studied using large-eddy simulation (LES). An Eulerian–Lagrangian framework is used to study the interaction between the continuous phase (air) and the discrete phase (glass bead particles). The solver is validated, using single-phase and particle-laden simulations, with reference data from experiments. A good match is observed between the present results and the reference data, for centerline velocity decay and radial profiles of axial velocity. Simulations are performed for three co-flow velocity ratios of 0, 1, and 1.5. The results pertaining to particle characteristics are presented for three different particle size-classes. The effect of the co-flow velocity ratio on the particle size–velocity correlation and velocity statistics of both phases are studied with an emphasis on understanding the differences in the particle dispersion due to co-flow around the central jet. It is observed that the particle size–velocity correlation is negative in the potential core region, and it becomes positive as one moves downstream. For heavy particles, the axial distance required to attain the same velocity as that of air increases with an increase in the co-flow velocity ratio. The size-conditioned particle number density profiles along the axial and radial directions of coaxial jets showed some interesting trends that could be explained based on the particle Stokes number effect. Significant radial dispersion of particles is realized when the corresponding Stokes number (StL), defined based on large-scale turbulent eddies, is of the order of one. The axial evolution of the characteristic particle size exhibited non-monotonic trends for all co-flow ratios. Overall, the present work demonstrates potential application of LES for an in-depth study of dispersion of poly-disperse particles in turbulent coaxial jets. [ABSTRACT FROM AUTHOR]

Materials capable of ultrasonic imaging in vivo are essential for the development of ultrasound visualized interventional catheters. In the present research, hollow glass beads (HGB) were added to polyurethane as ultrasonic image‐enhancing agent to obtain composite with improved ultrasonic visibility within body tissues. The experimental results show that with the increase of the volume percentage of HGB (VHGB) in the composites, the clarity of the ultrasonic images of the composite samples gradually improves. For ultrasonic imaging, a proper VHGB would be 6% to 10%. The particle size (25‐65 μm) of the HGB has almost no effect on the imaging of the composites at the same loading level of the glass beads. The result obtained in the experiments conducted in pig body confirmed that TPU/HGB composite sample could provide significant enhanced ultrasonic imaging compared with pure polyurethane sample and the commercial interventional catheter sample used. Medical safety of the composite was briefly investigated as well by testing the extraction solution of the composite sample. [ABSTRACT FROM AUTHOR]

In this paper, lignite and glass beads with different particle size were selected as experimental materials. These powder materials were discharged from hoppers in the situations of without insert (No In), with confined insert (Con In) and with unconfined insert (Ucon-In), respectively. The discharge processes were first discussed in detail and consequently, the solid flow rate of powders was obtained and analyzed. The flow zones in hoppers were divided based on the radial flow model of powder flow and the effects of inserts on the flow zone evolution were revealed. Experimental results show that both confined and unconfined inserts are beneficial to the increase of the solid flow rate, especially for the weaker flowability powders. The lignite, with the worst flowability, shows the largest increment of solid flow rate giving a value of 58% under Con In. Considering characteristics of the inserted hopper structure as well as the development of flow zones, a modified model derived from the minimum energy theory was developed. The model was able to predict the solid flow rate through both the traditional hoppers and the inserted hoppers, with the deviation below than 10%. Unlabelled Image • Special flow phenomena in insert-hopper were described. • Con-In and Ucon-In improved the solid flow rate. • Insert had a better effect on powders with weaker flowability. • A novel solid flow rate prediction method was proposed. [ABSTRACT FROM AUTHOR]

• Pneumatic conveying of glass particles with charges in the range of -10 to 10 n C. • U pu increased with particle initial charge for the positively charged particles. • U pu decreased with charge magnitude of negatively charged particles. • Correlation mis-predicted U pu by up to 10 % for charged monodisperse particles. • Correlation mis-predicted U pu by up to 40 % for charged binary-size systems. Pneumatic conveying experiments involving monodisperse and binary-size mixtures of glass beads with charges in the range of −10 to 10 n C have been carried out. The mass loss method was adopted, with the minimum pickup velocity (U p u) determined as the minimum velocity at which entrainment occurred. Similar to previous studies on minimum fluidization velocity, the U pu 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 U pu decreased with charge magnitude. Therefore, for the particle initial charge range investigated (−10 to 10 nC), U pu increased monotonically with particle initial charge, and the correlations available (Kalman et al., 2005; Tay et al., 2012) mis-predicted U pu 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. [ABSTRACT FROM AUTHOR]

Hoppers and silos are widely used in storing powders in various industries, such as agricultural, chemical, food and pharmaceutical industries. It is of practical importance to design hoppers and silos to ensure smooth discharge of bulk solids from these devices, and to minimise the occurrence of arching, blockage and build-up of materials around the walls. However, due to the complex nature of bulk solids, arching behaviour of bulk solids in silos and hoppers is still not well understood. In this study, a combined experimental and numerical study was performed to explore the transition from non-flow to flow of bulk solids from a flat bottom hopper. Glass beads of various sizes were considered and the minimal orifice size through which these materials can be discharged was determined experimentally using a Flodex™ tester and numerically with discrete element modelling (DEM). The dependency of the minimal orifice size on the particle size was explored. Both the experimental and numerical results showed that the minimal orifice size is a function of the particle size, which can be well described using a modified Beverloo equation. It was also interesting to find that, even for spherical particles, dead zones could be formed during the discharge from the flat bottom hopper. Moreover, mono-layered dead zones were created when large particles were used. Unlabelled Image • Monolayer dead zones were observed for hopper discharge with large particles. • The effects of orifice size and particle size on the discharge rate and the dead zone profile were investigated. • A modified Beverloo equation was proposed to predict both the discharge rate and the critical orifice size. [ABSTRACT FROM AUTHOR]

• A quasi-2D visualization hopper was used to study flow of mixed granular systems. • The rotation of elongated particles would lead to local secondary flow. • Local secondary flow increased the flowing layer thickness. • A method of torque estimation is proposed to explain the increase in discharge rate. Previous study has reported that adding elongated particles to cohesive granular matters can significantly improve their flowability. In this study, the mechanism of how the elongated particles work to this system was experimentally investigated. The experimental system included a quasi-two-dimensional visualization hopper and a high speed camera to record the flow behavior of the mixed granular systems consisting of glass beads and elongated particles during hopper discharge. Experiments revealed that the discharge rate first increased and then decreased as the mass fraction of elongated particles increased. It was observed that during the discharge flow, the elongated particles rotated and caused local secondary flow of the glass beads. This resulted in a significant increase in flowing layer thickness. Consequently, the effect of elongated particles rotation on discharge flow was discussed. Finally, the estimation of rotational torque of elongated particles was proposed to quantitatively describe the increase of discharge rate. [ABSTRACT FROM AUTHOR]

Few studies have focused on the influence of particle shape on the mechanical properties of cemented sand. To address this lack of information, this study investigated the influence of the cement content and particle shape on the strength and deformation of cemented sand based on a series of unconfined compression tests of mixed specimens. Cemented specimens were prepared with cement contents ranging from 4 to 8% and different mixing ratios of angular glass beads (AGBs) and rounded glass beads (RGBs). A shape parameter (overall regularity O R ) was proposed to quantitatively evaluate the shape of the particles. Mixed specimens were examined using scanning electron microscopy (SEM) analysis to illustrate the properties of the bonds with different mixing ratios of AGBs and RGBs. The test results indicated that the strength and stiffness increased as the cement content increased and the O R decreased. The trend of particle shape on the strength and stiffness was found to be independent of the cement content. The SEM images showed that the effective cementation area between angular particles is larger than that between rounded particles and that between angular and rounded particles, which resulted in increased strength and stiffness of the cemented sand. [ABSTRACT FROM AUTHOR]

For many powder processes, the particle size distribution (PSD) is a key quality attribute of the flow properties of the process powders. This paper presents a method for estimating the PSD with acoustic emissions (AE) by implementing a time domain-based threshold approach followed by the extraction of the amplitude mean from each set threshold and correlation to particle size. The experiments were carried out using a powder-free fall experimental rig, and a set of glass beads, while the acquired data were analyzed with a designed signal analysis method. The results of the experiments showed that the PSD of the particle mixtures being investigated could be identified with an average absolute error of 10%. The main advantage of the designed signal analysis method was identified as the requirement for a low hardware complexity due to a simpler algorithm than its predecessors. In an attempt to benchmark the performance of the system, the performance of the designed approach was compared to a wavelet-based analysis designed by Ren et al. From this it was seen that the approach used by Ren et al. is reliant on a tuning process to aid the algorithm in making the size estimation, suggesting that Ren's approach would prove to be inefficient in a process where powder segregation occurred due to poor mixing. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) methods have been proposed for on-line size measurement of pneumatically conveyed particles in recent years. However, there is limited research on the fundamental mechanism of the AE-based particle sizing technique. In order to achieve more accurate measurement of particle size, the impact between particles and a waveguide should be described in a more realistic way. In this paper, an improved model based on the Stronge impact theory is presented to establish the relationship between the resulting AE signal and the particle size being measured. The improved model is validated with experiments on a single-particle test rig. A total five sets of glass beads with a mean diameter of 0.4, 0.6, 0.8, 1.0 and 1.2 mm, respectively, are used as the test particles with an impact velocity ranging from 22 m/s to 37 m/s. It is proven that the Stronge impact theory is more accurate to describe the collision process than the Hertzian impact theory and is thus more suitable for the particle size inversion, which is validated by comparing the inversion results using these two impact theories. Meanwhile, a good agreement is observed between the measured and reference particle sizes under different experimental conditions. The mean relative error between the measured and reference diameters is mostly within 12%. Unlabelled Image • An on-line particle sizing approach considering plastic deformation is presented. • Experiments were conducted on a single-particle test rig. • The particle collision process is modelled using the Stronge impact theory. • The Stronge impact theory is applied to particle size inversion. [ABSTRACT FROM AUTHOR]

The multigene genetic programming (MGGP) technique based hydrodynamics models were developed to predict the solids holdups of a liquid-solid circulating fluidized bed (LSCFB) riser. Four different particles were considered to investigate the effects of particle size, shape and density on hydrodynamics behavior of the LSCFB riser. In this regard, two spherical shape glass bead particles (500 and 1200 μm), two irregular shape lava rock particles (500 and 920 μm) were employed as solid phase and water as liquid phase. The MGGP models were developed, relating the solids holdup ( ε s ${\varepsilon _s}$ , output parameter) with eight input parameters. The developed models were first validated by comparing the model predicted and experimental data of solids holdups. The average solids holdups decreased with the increase of net superficial liquid velocity ( U l − U t ${U_l} - {U_t}$) and normalized superficial liquid velocity U l U t $\left({\frac{{{U_l}}}{{{U_t}}}} \right)$. Uniform axial solids holdups observed in axial locations (H) except close to the liquid-solid distributor of the riser. The radial non-uniformity of solids holdup observed all radial positions (r/R). In the central region almost flat but increased toward the wall region. The radial profiles of the solid holdup are approximately identical at a fixed average cross-sectional solid holdup for all of the three LSCFB systems of this study. The statistical performance indicators such as the mean absolute percentage error and correlation coefficient are also found to be within acceptable range. All these findings of suggest that the MGGP modeling approach is suitable for predicting effect of particle size and shape on hydrodynamics behavior of the LSCFB system [ABSTRACT FROM AUTHOR]

Highlights • Development of a multicamera shadowgraphy system for solid phase investigations. • Local examination of the size, position and velocity of particles inside the zigzag channel. • Identification of characteristic particle trajectory directions. • Determination of particle velocities and particle fluctuation energies. Abstract A multicamera shadow imaging (shadowgraphy) system is developed to simultaneously capture particle dynamics at multiple locations inside a so called zigzag air separator which is used for separating fine from coarse particle fractions. The adaption of the shadowgraphy system to the specific requirements of the separator apparatus to measure particle sizes and velocities including calibration and particle size correction strategies is described. Measurements reveal the behaviour of glass beads ranging from 1 to 4 mm in diameter with variable particle mass loadings and air flow rates inside the zigzag channel. From the processing of the shadow data, particle flow morphologies and characteristic particle trajectories inside the channel stages are obtained. Furthermore, it is shown that particle mean velocities and particle fluctuation energies depend on the particle mass loading, the air flow rate and the location inside the zigzag channel. The results reveal novel quantitative insights into particle velocities in such an air separator which can be used to better understand the underlying particle mechanisms and foster the development of refined process models. [ABSTRACT FROM AUTHOR]

A method of measuring the refractive index of a particle is presented from a glare-point image. The space of a doublet image of a particle can be determined with high accuracy by using auto-correlation and Gaussian interpolation, and then the refractive index is obtained from glare-point separation, and a factor that may influence the accuracy of glare-point separation is explored. Experiments are carried out for three different kinds of particles, including polystyrene latex particles, glass beads, and water droplets, whose measuring accuracy is improved by the data fitting method. The research results show that the method presented in this paper is feasible and beneficial to applications such as spray and atmospheric composition measurements. [ABSTRACT FROM AUTHOR]

A series of triaxial compression tests were performed on the methane hydrate-bearing sands formed with rounded glass beads and natural sands to examine their mechanical properties. The effect of particle characteristics on the mechanical response of methane hydrate-bearing sands with regard to the exertion of bonding force and de-bond mechanism between grains is explained from the grain-scale viewpoint. In comparison with the natural sand, methane hydrate-bearing glass beads owns a similar initial stiffness and rapidly attains the peak shear strength at a smaller axial strain. The obvious post-peak strain-softening behaviour of methane hydrate-bearing glass beads which differs from the tender post-peak strain-softening tendency of methane hydrate-bearing natural sand is observed. It is attributed to almost simultaneous exfoliation of hydrate mass from the glass beads with smooth surface within the straightly sheared layers. The substantial resource of shear strength enhancement for methane hydrate-bearing glass beads is the cohesion but the shear strength of methane hydrate-bearing natural sand was jointly governed by the cohesion and angle of internal friction. In contrast to the increasing tendency of difference of shear strength with the level of effective confining pressure for methane hydrate-bearing natural sand, the methane hydrate-bearing glass beads exerts a stronger effect of bonding force on the difference of shear strength at relatively lower pressures but this effect decreases at higher pressures. [ABSTRACT FROM AUTHOR]

It was reported that a sheet-like or cone-like shock forms when a granular jet, composed of spherical glass beads impacts a fixed target. The discrete element method (DEM) was employed to simulate this process using elliptical particles, which were approximated by using the glued-particle method (GPM). In comparison with circular particles, our simulations show that the aspect ratio does not affect the open angle. However, in comparison with circular particles, using elliptical particles leads to the stagnation zone in front of the target with higher area fraction and lower granular temperature. As a validation of GMP, a simple simulation of a binary collision is presented at the end of this article. [ABSTRACT FROM AUTHOR]

The capture of a falling particle at a horizontal gas–liquid interface (film flotation) is determined by the particle impact velocity and the subsequent motion of the three phase contact line (TPCL) as the particle penetrates into the liquid. In this study, the three phase contact lines were observed experimentally using high speed video camera for a number of different particle liquid systems. The particles comprised hydrophilic glass bead particles with and without surface hydrophobicity treatment. The liquid comprised water, and NaCl, sucrose and hexadecyltrimethylammonium bromide (CTAB) aqueous solutions with different concentrations. Previous modelling of Liu et al. (2010a) was extended to include the advancing velocity of TPCL on dynamic contact angle. The critical fall height predictions by the modified model compared favourably with experimental measurements. [ABSTRACT FROM AUTHOR]

A model, which allows analyzing compression isotherms of mono- and multi layered films formed with particles at the air–water or oil–water interface is here proposed. The number of contacts established between particles in the layer was linked to surface pressure. The parameters used in the model permit calculating the energy of layer formation, and area per particle in the mono- or multi-layered films. These data reflect particle–particle and particle-subphase interaction and, consequently, particle organization in the film. The model was tested with micrometric glass beads and used for calculating the diameters of particles formed at the interface. The excellent representation of the experimental compression isotherms shows that the model can be used for constructing films with defined properties. [ABSTRACT FROM AUTHOR]

The Abductive Network (AN), a group method data handling (GMDH) algorithm-based self-organizing model, was applied to study the solids holdup distribution of a liquid-solid circulating fluidized bed (LSCFB) system. At first, the AN model was trained with experimental data sets obtained from a pilot scale LSCFB operated with spherical glass beads and irregularly shaped lava rock particles as solid phases, and water as liquid phase. In the model training the effects of various auxiliary and primary liquid velocities and superficial solids velocities on radial phase distribution at different axial positions were considered. The developed AN model was employed to predict the solids holdups at various locations of the LSCFB riser under different operating conditions. The competency of the developed AN model was confirmed by comparing the model-predicted and experimental solids holdups of the LSCFB system. Both the experimental and model-predicted outputs showed that under different superficial liquid velocities the solids holdup was higher for the glass beads than the lava rocks. The solids holdup decreased with increasing liquid velocity at all axial locations. The radial non-uniformity distributions of solids holdup in the central region decreased toward the wall. The higher drag force acting on the spherical-shaped particles was likely responsible for this variation of the solids holdups. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate the influences of particle migration lengths as well as the sizes of the weighing bar and vessel on the particle size distribution measured by the buoyancy weighing-bar method, we experimentally measured the size distribution of hollow glass beads as floating particles. The buoyancy weighing-bar method, microscopy, and laser diffraction/scattering method give similar particle size distributions. The variation coefficient of the buoyancy weighing-bar method is close to the value determined by the laser diffraction/scattering method. Moreover, the accuracy of the buoyancy weighing-bar method is equal to that of the laser diffraction/scattering method. For vessels with identical sizes, the particle sizes measured by the buoyancy weighing-bar method increase when the weighing bar is too thick or too thin. Additionally, the influence of the weighing bar length on the particle size distribution is not confirmed in the case of the hollow glass beads. Thus, to effectively employ the buoyancy weighing-bar method, the sectional area ratio of the rod/vessel must be 0.02–0.2. [Copyright &y& Elsevier]

Electric tweezers are a touchless positioning apparatus that employs dielectrophoresis and electroorientation to arbitrarily position cellsized particles. In this paper, we develop an algorithm which enables electric tweezers to operate on multiple particles. Furthermore, we probe the limits of this technique in simulation, examining the range of electric field magnitudes and forces that can be applied.We then demonstrate this new functionality on two particles. The device can apply forces on any particle of non-zero polarizability and here this is highlighted by manipulating negatively polarized glass beads. Additionally, we demonstrate that negligibly polarized particles can also be manipulated through mechanical forces applied by other particles [ABSTRACT FROM AUTHOR]

Abstract: Experiments involving monodisperse Geldart Group B particles have been carried out in a pilot-scale riser of a circulating fluidized bed (CFB). Several combinations of superficial gas velocity (U s ), solid flux (G s ), average particle diameter (d ave ), and particle material density (ρ s ) were investigated. Surprisingly, the experiments reveal the presence of a reverse core-annulus profile (i.e., a dense core with a dilute annulus) under certain conditions. Specifically, for the large glass beads (d ave =650μm, ρ s =2500kg/m3), the reverse core-annulus profile was observed near the top of the riser for all U s and G s combinations examined. For high-density polyethylene (HDPE) pellets (d ave =650μm, ρ s =900kg/m3) of the same d ave , reverse core-annulus was observed at the top of the riser only at relatively low G s . However, for the smaller glass beads (d ave =170μm, ρ s =2500kg/m3), the traditional core-annulus profile was observed for all U s and G s combinations. Although previous work provides possible explanations for this behavior (gas-phase turbulence, etc.), the evidence obtained in this system suggests a novel dominant factor for reverse core-annulus flow: the particle Stokes number (St). Lower-St particles are more apt to follow the gas exiting the riser, while higher-St particles have a longer relaxation time and thus are more likely to re-enter the riser after collision with the roughened rounded-elbow exit. Accordingly, the re-direction of particles from the rounded-elbow exit and back into riser due to large-scale roughness along the elbow is greater for higher-St particles. [Copyright &y& Elsevier]

The effect of varying the volume fraction of 650 μm glass beads in a poly(vinyl butyral) matrix on the level of debonding in the particulate composites at a given applied tensile stress was investigated. Both clean beads and ones surface treated with the adhesion promoter 3-aminopropyltriethoxysilane were used. A model was developed to predict the observed behavior, based on Goodier's analytical solution for the stress concentration developed by a single sphere in an infinite matrix and the superposition of stress concentrations. By increasing the volume fraction of glass beads the average interparticle distance is decreased, leading to an increase of the overlap of the stress concentration fields surrounding the beads, thus causing debonding at a lower applied stress. The use of an adhesion promoter increased the maximum local stress required to cause debonding, but had no effect on the interparticle stress fields so the same trends, at higher applied stress, were observed. The model, although quite simple, showed good agreement with the experimental results for the dependence of the particle-matrix debonding behavior on the volume fraction of beads. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present work was to develop 3D discrete element models capable of simulating the observed flow of glass beads (simple glass spheres) and maize grains (represented as a combination of spheres) during their discharge from a small model silo. A preliminary model for each material was constructed based on values for variables measured in the laboratory or taken from the literature. The ability of the models to predict the flow of these materials was then tested by comparing their results with observed discharge flows. Three variables were recorded for this: the mean bulk density at the end of the filling phase, the discharge rate and the flow pattern. The comparison of the results for the last of these variables required the discharge process be filmed using a high speed camera in order to more easily recognise the details of the flow. The preliminary model for the glass beads made very reasonable predictions, but that for the maize grains required calibration. This involved modifying the values of the friction properties of the material until a model capable of making acceptable predictions was obtained. The results obtained highlighted the influence of friction properties on the characteristics of the discharge flow. Finally, some of the numerical results provided by the models were analysed in order to describe the flow characteristics and the behaviour of the discharge rate in more detail. [Copyright &y& Elsevier]

Abstract: In this study, the discrete element method (DEM) was used to investigate the influence of particle shape and interparticle friction on the bulk friction in a Jenike direct shear test. Spherical particle and non-spherical particles using two overlapping sphere giving particle aspect ratio of up to 2 and a full range of interparticle contact friction coefficient were studied numerically. These were compared with physical Jenike shear tests conducted on single glass beads and paired glass beads. To separate the influence of sample packing density from interparticle contact friction on the bulk shearing response, the same initial packing was used for each particle shape in the simulations. The interplay between contact friction and particle interlocking arising from geometric interaction between particles to produce the bulk granular friction in a direct shear test is explored and several key observations are reported. The results also show that particle interlocking has a greater effect than packing density on the bulk friction and for each particle shape; DEM can produce a good quantitative match of the limiting bulk friction as long as similar initial packing density is achieved. [Copyright &y& Elsevier]

Abstract: The effect of air humidity on flow properties of two different cuts of fine glass beads was experimentally studied by means of shear tests. The moisture content of powder samples was conditioned by humid air at relative humidities between 13% and 98% in a fluidization column. In spite of the very low moisture contents in the powder (<0.2%) obtained by this technique, a significant change in the powder cohesion was observed, while the effect on the angle of internal friction was limited. A model based on the Kelvin equation and the Laplace–Young equation was applied to describe the capillary condensation between touching asperities found on the surface of neighbouring particles and to estimate the relevant interparticle forces. This result was used to derive the powder tensile strength following the Rumpf approach and compare it with values derived from shear experiments. A single value of the unknown capillary bridge gap was chosen on the basis of the observed dependence of interparticle cohesive forces. This gap was able to provide quantitative agreement between model predictions and experimental results at relative humidity lower than 80%. Comparison between the total moisture content and the amount of water in liquid bridges indicated that water mainly condenses on rough surfaces of the particles and only a small portion of this condensed humidity contributes to change the powder flow properties by interparticle capillary forces. [ABSTRACT FROM AUTHOR]

Abstract: The mixing of a wetted insoluble granular medium was experimentally investigated focusing on the variation of the specific intensity consumption of mixing with addition of liquid in the granular bulk. Preliminary results showed the influence of the particle average diameter of glass beads and calcites (CaCO3), on the intensity consumption which decreased with the increase of the particles size (for the capillary and funicular states). However, an exception was observed at the level of the funicular state of the calcite, for which there was no particle size influence on the intensity consumption (for particles sizes inferior to 150μm). The effect of an inhomogeneous liquid distribution was not clearly demonstrated. However, the funicular intensity consumption was linked with the compacity of the medium. By stopping the liquid flow at the end of the funicular state, and by continuing the mixing of a calcite, the funicular state intensity consumption and the measured granular compacities were increased. Moreover, this compacity measured during the funicular state, decreased with the particle size. [ABSTRACT FROM AUTHOR]

Abstract: The elastic properties of 400μm polyethylene powders and 335μm glass beads in a vibrator were dynamically determined using the apparent mass method, the top cap method and the energy dissipation method. The particle assembly resonance frequencies determined using these three methods were of the similar values. The average resonance frequency of 400μm polyethylene powder bed of 0.015m in height is 340Hz with the standard deviation of 32.2Hz. The average resonance frequency of 335μm glass bead bed of 0.015m in height is 165.7Hz with the standard deviation of 13.5Hz. Although all three methods can be utilized to determine the particle assembly resonance frequencies, the top cap method is recommended because this method can determine the particle assembly stiffness constant and the particle assembly damping constant in the same experimental run. [Copyright &y& Elsevier]

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The impact strength of V-notched U-notched and non-notched specimens of hollow glass bead filled polypropylene composite (PP/HGB) were measured by using Charpy impact tester, and the directed gray relational grade (GRG) between the HGB size distribution and the impact strength of the composites was determined by means of gray relational analysis (GRA) in order to investigate the influence of the HGB size distribution on the impact strength of the composites. The results indicated that the particles with size range from 0.00 to 24.7 µm have a positive influence on the impact strength of the composites, and the particles with size ranging from 18.90 to 24.7µm have a greater positive influence than that of the particles with size range from 0.00 to 18.9 µm. While the particles with size ranging from 24.72 to 256.0 µm have a negative influence, especially the particles with size in a range from 100.60 to 256.0 µm. That is, the impact strength of the composites could be enhanced by increasing the particle content in the tested fillers with size range from 0.00 to 27.72 µm especially the particles with size ranging from 18.90 to 24.7 mm, whereas decreasing the particles content with size range from 24.72 to 256.0 µm, especially the particles with size range from 100.60 to 256.0 µm. [ABSTRACT FROM AUTHOR]

A low-cost, noninvasive, three-dimensional (3D), particle tracking velocimetry system was designed and built to investigate particle movement in match-index-refraction porous media. Both a uniform load of the glass beads of the same diameter and a binary load of the glass beads of two diameters were used. The purpose of the experiments is to study the effect of the two loads on the trajectories, velocity distribution, and spreading of small physical particles. A total of 35 particles were released and tracked in the uniform load and 46 in the binary load. The 3D trajectory of each particle was recorded with two video camcorders and analyzed. It is found that the particle’s velocity, trajectory, and spreading are very sensitive to its initial location and that the smaller pore size or heterogeneity in the binary load increases the particles’ velocity and enhances their spreading as compared with the uniform load. The experiments also verified the previous finding that the distribution of the particle velocities are lognormal in the longitudinal direction and Gaussian in two transverse directions and that the particle spreading is much larger along the longitudinal direction than along the traverse directions. [ABSTRACT FROM AUTHOR]

In this article, the shrinkage and density variations of cylindrical fresh green beans were investigated in a fluidized bed dryer with energy carriers. A pilot-scaled fluidized bed dryer was set up for performing the drying experiments. Glass bead particles were used as inert materials. The drying experiments were done with fresh green beans of several lengths using hot air as a heating agent with the temperature range of 30–50C, and the effects of various parameters, such as the presence of inert materials, temperature and sample length, were investigated. It was found that the shrinkage or volume changes, and radial and axial contractions of fresh green beans could be well correlated as linear functions of moisture content during drying. Calculated and experimental values were in good agreement with mean absolute errors (MAE s) of 3.56, 2.48 and 1.22 for volume changes, and axial and radial contractions, respectively. By considering that the change in the volume of the samples was equal to the volume of evaporated water, mathematical models were proposed for volume and density variations. Comparison of the predicted values for volume and density by the proposed model with experimental date showed that the uniform model of shrinkage could explain the shrinkage and density variations of fresh green beans with MAE s of 5.190 and 4.250 for volume and density variations, respectively. The shrinkage coefficients were evaluated by considering their measurement uncertainties. PRACTICAL APPLICATIONS Any attempt to characterize drying behavior must inevitably address the physical parameters of the material such as shrinkage and density. The shrinkage phenomenon occurring during the drying process affects the physical properties of the solids, as well as the transport phenomena properties. The shrinkage of vegetables during drying is important not only from the viewpoint of material end use but also for simulation problems. [ABSTRACT FROM AUTHOR]

The entrainment of heterogeneous particles in a gas-fluidized bed for particle mixtures of categories A and B according to the Geldart classification was conducted in this study. The experiments were carried out in an acrylic column of 0.092 m diameter. The distributors were perforated plates of up to 5.9% free area fraction. Measurements of pressure gradients were made using 24 pressure taps. Glass beads with particle diameters from 60 to 400 μm were used. The mixtures were described using the Rosin-Rammler-Bennet granulometric distribution model. The transport disengaging height (TDH) heights were obtained using the Geldart methodology. A 25 experimental design was applied relating the dispersion index, mean diameter, solid mass, superficial gas velocity, and free area fraction of the distributor to obtain the TDH heights. Slugging and transition for turbulence regimes characterized the behaviors of fluidized beds. The results showed that TDH heights for heterogeneous particles were dependent on the solid mass and superficial gas velocity. [ABSTRACT FROM AUTHOR]

Recent decades have witnessed considerable research effort in the development and application of the discrete element method (DEM) for modeling granular materials. One key aspect that appears to have not been addressed adequately is the choice or determination of the DEM model parameters to produce satisfactory quantitative predictions. In many DEM studies, the input parameters were often not measured and the values were sometimes assumed without any proper justification. This article describes a careful validation study in which DEM was used to model confined compression of spherical (glass beads) and nonspherical (corn grains) particles. The key properties of the particles were independently measured. The experimental data on the bulk compressibility and the corresponding load transfer to the cylindrical wall and the bottom platen provide quantitative information for direct comparison with the DEM results. Initial particle packing structure is expected to influence the bulk behavior of the assembly, so several methods of particle generation were used to investigate the sensitivity of particle generation in DEM. An investigation of the influence of interparticle friction and particle stiffness in DEM simulations provided an insight into the bulk response of the granular assemblies under confined compression. Comparison between the simulations and the experiments revealed several useful observations, including the roles of these model parameters in the predicted bulk responses. [ABSTRACT FROM AUTHOR]

The notched Izod impact properties of polypropylene (PP) filled with hollow glass beads (HGB) have been measured at room temperature to identify the effects of the particle contents, size and its distribution on them in the present paper. The mean diameters of the particles were 11, 35, and 70 μm, and named TK10, TK35 and TK70 respectively. The surface of the particles was pretreated with silane coupling agent. The results showed that the notched Izod impact strength ( σ I) of the filled systems increased gently with increasing the volume fraction ( φ f) of the fillers when φ f was less than 15%, and then it decreased. When φ f was 10%, σ I decreased with an increase of the mean diameter of the particles. Furthermore, the impact fracture surface of the specimens was observed by using a scanning electron microscope (SEM). The improvement of the impact toughness of the composites might be mainly attributed to the shear yielding first of the matrix around the beads to absorb relevant deformation energy under impact load. [ABSTRACT FROM AUTHOR]

Particle breakthrough can occur by either the breakoff of previously captured particles (or flocs) or the direct passage of some influent particles through the filter. Filtration experiments were performed in a laboratory-scale filter using spherical glass beads with a diameter of 0.55 mm as collectors. A single type of particle suspension (Min-U-Sil 5) and three different destabilisation methods (pH control, alum and polymer destabilisation) were used to destabilise particles. The filtration velocity of 5 m/h was similar to that used in standard media filtration practice. To assess the possibility of particle detachment during normal filtration, a hydraulic shock load (20% increase of flow rate) was applied after 4 h of normal filtration. The magnitude of particle detachment was proportional to the particle size for non-Brownian particles. At the same time, less favourable particles, i.e. particles with larger surface charge, were easily detached during the hydraulic shock load. Therefore, proper particle destabilisation before filtration is crucial for maximum particle removal, as well as minimum particle breakthrough. [ABSTRACT FROM AUTHOR]

Abstract: Effects of sound field on the fluidization of fine particles have been comprehensively examined by using fine powders (4.8–65 μm average in size) including Al2O3, TiO2, glass beads and FCC catalyst. It is found that the fluidization quality of fine particles can be enhanced with the assistance of a sound field, resulting in higher pressure drops and a lower u mf. The effect of sound on the fluidization of fine particles is strongly dependent on the particle properties (Geldart type and particle size) as well as the parameters of the sound field such as sound pressure level (or intensity) and frequency. Given a fixed sound frequency, the effect becomes more significant at a higher sound pressure level. For the present sound-aided fluidized bed system, there is a resonant frequency at about 100–110 Hz, at which the effectiveness of the sound wave in improving fluidization of fine particles is most remarkable. In addition, based on the different attenuation features of sonic waves in the gas–solid suspension of group C and A particles, a novel acoustic method is explored to distinguish group C from group A particles. [Copyright &y& Elsevier]

A technique has been developed to determine the charge distribution around single rising bubbles in a two-dimensional fluidized bed. Four induction probes positioned flush with the outside wall of the column and connected to charge amplifiers record induced charge signals as bubbles pass. The charge distribution surrounding a single bubble is then reconstructed with the assumption that the bubble is symmetrical and that the charge around the bubble remains constant as it rises. The emulsion phase far from the bubble in a two-dimensional fluidized bed of glass beads was found to be charged negatively and, contrary to our previous assumptions, the charge density decreased gradually toward the bubble-dense phase interface, with a nearly zero charge density inside the bubble. The wake of the bubble is more negatively charged than the emulsion phase, supporting our previous speculations. [ABSTRACT FROM AUTHOR]

Vacuum contact drying kinetics of a model system consisting of nonporous glass beads and water has been experimentally measured on a laboratory scale. A methodology for determination of drying curves from experimental data in a statistically robust way has been developed. The effects of jacket temperature, head-space pressure, particle bed depth, vessel diameter, and particle size on drying rate during constant and falling rate periods have been studied. It was found that in the range of parameters investigated, drying rate does not depend on the means of realization of the driving force (by temperature or pressure); drying rate in the constant-rate period decreases with increasing bed depth while the overall heat-transfer rate increases due to increased surface area. A very strong dependence of drying rate and regime on particle size was observed; the constant-rate period disappeared for small particles. [ABSTRACT FROM AUTHOR]

Granular segregation in a rotating tumbler occurs due to differences in either particle size or density, which are often varied individually while the other is held constant. Both cases present theoretical challenges; even more challenging, however, is the case where density and size segregation may compete or reinforce each other. The number of studies addressing this situation is small. Here we present an experimental study of how the combination of size and density of the granular material affects mixing and segregation. Digital images are obtained of experiments performed in a half-filled quasi-2D circular tumbler using a bi-disperse mixture of equal volumes of different sizes of steel and glass beads. For particle size and density combinations where percolation and buoyancy both contribute to segregation, either radial streaks or a “classical” core can occur, depending on the particle size ratio. For particle combinations where percolation and buoyancy oppose one another, there is a transition between a core composed of denser beads to a core composed of smaller beads. Mixing can be achieved instead of segregation if the denser beads are also bigger and if the ratio of particle size is greater than the ratio of particle density. Temporal evolution of these segregated patterns is quantified in terms of a “segregation index” (based on the area of the segregated pattern) and a “shape index” (based on the area and perimeter of the segregated pattern). [ABSTRACT FROM AUTHOR]

Experimental data on the effects of the velocity slip and mass loading on a grid-generated turbulence in gas-solid particles flow are presented. Glass beads (700 µm) were used as the dispersed phase. Velocities of both phases were measured with a Laser Doppler Anemometer. Turbulence decay curves, obtained for different grids, show that particles enhance turbulence for small grids and attenuate it for the large ones. Turbulence enhancement and attenuation are intensified with the increase of the flow mass loading. The particles effect on turbulence changes from turbulence attenuation for a small velocity slip to its enhancement for a large velocity slip. A criterion for the evaluation of turbulence modification in gas-solid particles flow is proposed. [ABSTRACT FROM AUTHOR]

The predictive capabilities of CFD techniques as applied to solid-liquid stirred vessels are investigated. The distribution of solid particles was simulated in three baffled stirred tanks agitated with single and multiple impellers. Suspensions of glass beads of different diameters and average concentration up to 6 vol. % in water were studied. The simulations of solid-liquid suspensions in the stirred vessels were performed by using fully predictive approaches, Eulerian multiphase models were adopted for modelling the solid-liquid flow, coupled with three different extensions of the standard k-ϵ model to the case of multiphase flows. The simulated particle axial concentration profiles are compared with experimental data and critically discussed. The most successful simulation strategy and one possible implementation are described. [ABSTRACT FROM AUTHOR]

Studies were carried out on coating glass beads with fine hematite particles by use of the theta composer, a newly developed high-shearing-type mixer. Topics of study included the effects of rotational speed of the rotor, Nr, (i.e., tangential velocity of the rotor tip, vr), and a gap width between the rotor and the wall of the vessel, l, on the coating process. The amount of hematite particles deposited on glass beads was plotted versus a parameter $\varepsilon (= \roundv^2_r t/l)$ that relates a cumulative shear force acting on particles over a coating period t. All experimental data could be fitted by a single curve, and the parameter ε was found to describe the coating process in the theta composer. Compression of core particles by the rotor was also analyzed using a 3-D DEM simulation. Average contact force by the rotor was found to be proportional to vr and inversely proportional to l. Thus, a cumulative shear force acting on a core particle is proportional to (vr/l)(vr t) after the particle passes through the gap Nrt times. Reasonable agreement was found between the experimental results and those of simulation. The coating process can be properly described by the parameter ε. [ABSTRACT FROM AUTHOR]

Measurements and calculations of mean and rms of fluctuations of particle velocities and concentration and cross-correlation coefficients of two particle velocity components and concentration fluctuations in a horizontal plane shear layer laden with glass beads with mean diameters 55 and 90 μm are presented. The particles were injected at the low speed side of the flow, which is different from previous studies, and enhances the influence of gravity on particle dispersion. The ranges of Stokes numbers, based on the time scale of the large eddies, were 0.2–0.6 and 0.6–1.4 for 55 and 90 μm respectively. The particle gravitational settling parameter, due to gravity acting normal to the main flow direction at the low speed side of the shear layer, was for the mean flow 0.2 and 0.5 and for the turbulent flow 0.5 and 1 for 55 and 90 μm respectively. Velocity measurements were obtained by particle image velocimetry (PIV) and instantaneous particle concentration by counting the number of particles in each interrogation cell of the PIV images. The effect of interrogation cell size on instantaneous particle concentration was assessed and an appropriate interrogation cell size was chosen to quantify the non-random contribution of particle concentration fluctuations. The intensity of spatially-resolved non-random concentration fluctuations varied between 0.6 and 0.9 of the local mean concentration at the edge of the shear layer, where particles dispersed only due to centrifuging by fluid flow large scale structures and between 0.15 and 0.35 in the central region of the shear layer, where particles are convected by the flow or arrive due to centrifuging from the fluid eddies and gravitational effects and, as a consequence, random contributions on particle concentration become more important. The contribution of various fluid flow structures and gravity on concentration fluctuations was quantified and explained by quadrant analysis of the cross-correlation between measured particle streamwise velocity and concentration. The calculations of the fluid flow in the shear layer were based on the discrete vortex method and the discrete phase motion was calculated by Lagrangian particle tracking. The calculations showed fluid velocity fluctuations frequency spectra with −5/3 decay, as measured in the experiments, and the simulated particle mean and rms velocities and cross-correlation coefficients of particle concentration and velocity fluctuations agreed qualitatively with the measurements. Remaining discrepancies in the absolute values were due to the omission of gravity in the calculations and the resulting narrower range of fluid flow eddy sizes predicted by the calculations relative to experiments. The consequences of current findings on the operation of light detection and ranging (LIDAR) systems for measurements of atmospheric turbulence due to vortices of the wake of airplanes are discussed and improvements in the data processing are suggested. [Copyright &y& Elsevier]

A particle–bubble attachment apparatus, similar to that used by Whelan and Brown [Bull. Inst. Min. Met. Trans. 65 (1956) 181] is developed to study free falling glass beads (dp=131 μm) with different surface treatment attaching to a stationary air bubble (db=3 mm). The entire process of the particle–bubble attachment is photographically recorded using a high framing-rate camera and analyzed frame by frame. It is found that the hydrophilic particle slides on the top half of the bubble, and then the particle leaves the bubble, as anticipated. The particle sliding velocity increases with increasing angular position on the bubble surface. For the hydrophobic particle, it was found that the particle slides over the entire bubble surface without detaching from the bubble. The sliding velocity, however, reaches a maximum at an angular position of 90–100°, and then slows down to zero. A smaller sliding velocity is obtained for the hydrophobic particle than that of the hydrophilic particle at a given angular position. The attachment efficiency for the hydrophobic particle reduces with increasing initial angular positions, suggesting that the hydrophobicity alone does not directly guarantee the attachment to a bubble. Adding surfactant (sodium dodecyl sulfate [SDS]) to the test solution makes the hydrophobic particle become less hydrophobic or even hydrophilic, thereby decreasing the attachment efficiency. A much longer induction time is obtained in our present work than that reported in the literature. A simplified particle sliding velocity and attachment model is developed, and a good agreement between the theoretical prediction and experimental measurement is obtained. [Copyright &y& Elsevier]

• Influence of the flight design on the temperature drop during cooling is measured. • Higher number of flights can decrease the cooling time by one third. • Increasing flight length ratio (FLR) up to 1 leads to better cooling. • Exceeding FLR of 1 worsens the cooling. • Particle motion-based explanations are given for the described influences. An experimental parameter study in an indirectly heated rotary drum (L = 1.76 m, D = 0.5 m) with L-shaped flights was conducted. The influence of the flight design parameters as the flight length ratio (0.375–2.0) and the number of flights (6–18) on the temperature-time profile and the temperature drop are analyzed. Therefore, the rotary drum is filled with glass beads as reference material and heated in batch operation while contact heat transfer is the main heat transfer mechanism. After reaching an upper temperature of 330 °C, the system is cooled by forced convection as ambient air is sucked through the drum. Type k-thermocouples in three axial and six radial positions are used to measure the time evolution of the temperature. The thermocouples are mounted to a flight, such that they rotate with the drum and also capture the circumferential temperature distribution. [ABSTRACT FROM AUTHOR]

• The GBs can increase the mechanical properties and energy-absorption capacity of polymer foams. • The novel simulation strategy enables to model both cells and GBs explicitly. • The numerical predictions show good agreements with experimental and analytical results. • The numerical results indicated the hardening stress increased with the decrease of GBs size. Particle reinforced (PR) polymer foams are promising materials for lightweight structures. In this research, compression tests were conducted on glass beads (GBs) reinforced linear low-density polyethylene (LLDPE) foams. The experimental results indicated that embedding GBs could increase the yield strength, elastic modulus and energy absorption capacity of bulk material. Analytical predictions of GBs reinforced foams were also used to compare with experimental results. To investigate the micromechanics of neat foams and glass PR foams under compression, the finite element (FE) simulations were conducted. The analysis of neat foams indicated that the strain localization occurred at right and left sides of hollow cells during the plateau stage. For GBs reinforced foams, the foam matrix around the particle reinforcements was nearly densified while the foam matrix without GBs remained undensified due to the stabilisation of glass particles. The parametric studies reasonably explained why hardening stress of foam increases with the decrease of particle size. [ABSTRACT FROM AUTHOR]