Wide Range Of Particle Diameters Research Articles

Evaluation of chemical mechanical planarization slurry dispersion using a combined scanning mobility particle sizer-optical particle sizer system

A combined scanning mobility particle sizer-optical particle sizer (SMPS-OPS) system was evaluated for measuring the dispersion of a chemical mechanical planarization (CMP) slurry. The dilution rate of one particle per droplet was confirmed to minimize agglomeration. The SMPS and OPS measurements showed similar particle size distributions of 400 nm polystyrene latex particles. The particle size distributions of settled ceria and silica slurries were measured using the SMPS-OPS system. The settled commercial ceria slurry showed a decrease in the number concentration in the top layer. In the bottom layer, increases in the concentration of active particles and in the number of large particles were observed. This indicates that large particles were formed during settling of the slurry. In the silica slurry, there was a change in concentration with depth and little change in number of large particles with settling time. The SMPS-OPS system was able to analyze CMP slurries across a wide range of particle diameters for both active and large particles. Therefore, this system can be helpful for analysis of CMP slurry size.

Seasonal variability in size-resolved hygroscopicity of sub-micron aerosols over the Western Ghats, India: Closure and parameterization

Hygroscopicity of atmospheric aerosol primarily depends on the size and chemical composition of the particle and is important for estimating anthropogenic aerosol radiative forcing. There is limited information exists over the Indian region on size segregated aerosol hygroscopicity (κ) in different seasons. This study presents ‘κ’ as derived from a Humidified Tandem Differential Mobility Analyzer (HTDMA) over a High Altitude Cloud Physics Laboratory (HACPL) in the Western Ghats, India for more than a year (from May 2019 to May 2020). The average hygroscopicity values of aerosol particles of diameters 32, 50, 75, 110, 150, 210 and 260 nm at 90 % RH condition are 0.19, 0.18, 0.16, 0.17, 0.18, 0.20, 0.21 respectively during the entire observation period. κ was observed to decrease with an increase in size in the Aitken mode regime (32–75 nm) and an increase in the accumulation mode (110–260 nm). Seasonal variation of hygroscopicity for a wide range of particle diameters is reported which is highly demanding as there is a change in the air mass flow pattern in each of the seasons. The diurnal cycle of hygroscopicity showed a prominent peak during the midnight to early morning hours followed by a decrease in the forenoon hours and a secondary peak in the afternoon hours. κ is found to be higher in pre-monsoon compared to winter season as Chl is approximately 3 % higher in pre-monsoon and NH4Cl is highly hygroscopic among the assumed chemical composition. Hygroscopicity derived through chemical speciation observations assuming internal and external mixing of aerosols i.e. κinter and κexter are overestimating as compared to κHTDMA. However, the bias between kexter and kHTDMA is relatively lower as external mixing type of aerosol is evident through the growth factor data sets measured by HTDMA. Utilizing the hygroscopicity measurements available for discrete diameters by HTDMA, a parameterization of hygroscopicity with the dry diameter of sub-micron particles is developed.

Effect of Soil Particle Size on the Accuracy of Tactile Pressure Sensors

This paper investigates the effects of soil particle size on the measurement accuracy of single-point type tactile pressure sensors when used for measuring soil contact stresses. Sensors with two different diameters (Dsens) are integrated into an oedometer cell. Granular materials with a wide range of particle diameters (D50) and angularities (from rounded to irregular shaped) are evaluated, resulting in a wide range of ratios of Dsens/D50 from 2.6 to 105.8. The test results show that the soil particle size significantly affects and exponentially correlates with the measurement accuracy of the sensor. A threshold Dsens/D50 of 10.5 is identified for the sensor, beyond which the error is less than 5%. It is also shown that even for ratios of Dsens/D50 as large as 40, an error of approximately 2% can be observed, which is intrinsic to the sensor.

Comparison of micron- and nano-particle transport in the human nasal cavity with a focus on the olfactory region

Intranasal administration of drugs serves as a promising, noninvasive option for the treatment of various disorders of the central nervous system and upper respiratory tract. Predictive, ie, realistic and accurate, particle tracking in the human nasal cavities is an essential step to achieve these goals. The major factors affecting aerosol transport and deposition are the inhalation flowrate, the particle characteristics, and the nasal airway geometry. In vivo and in vitro studies using nasal cavity casts provide realistic images regarding particle-deposition pattern. Computational Fluid-Particle Dynamics (CF-PD) studies can offer a flexible, detailed and cost effective solution to the problem of direct drug delivery. The open-source software OpenFOAM was employed to conduct, after model validation, laminar and turbulent fluid-particle dynamics simulations for representative nasal cavities. Specifically, micron particles and nanoparticles were both individually tracked for different steady airflow rates to determine sectional deposition efficiencies. For micron particles, inertial forces were found to be the dominating factor, resulting in higher deposition for larger particles, mainly due to impaction. In contrast, diffusional effects are more important for nanoparticles. With a focus on the olfactory region, the detailed analysis of sectional deposition concentrations, considering a wide range of particle diameters, provide new physical insight to the particle dynamics inside human nasal cavities. The laminar/turbulent Euler-Lagrange modelling approach for simulating the fate of nanoparticles form a foundation for future studies focusing on targeted drug delivery. A major application would be direct nanodrug delivery to the olfactory region to achieve large local concentrations for possible migration across the blood-brain-barrier.

Jamming probability of granular flow in 3D hopper with shallow columns: DEM simulations

We performed a numerical study of the jamming that stops the flow of granular material from a three-dimensional hopper discharging due to gravity. When the hopper outlet is not much larger than the particles, granular material clogs the hopper outlet due to the formation of an arch or dome. For a wide range of particle diameters, we obtained the size distribution of the “avalanche,” defined as the number of particles that fall before jamming. We repeated this process through a discrete element method model verified with a simple experiment. From these distributions, we determined the probability of the flow jamming before N particles pass through the hopper. As the ratio between the hopper outlet diameter and the particle diameter increases, the probability that an arch will block the outlet decreases. We show here that the probability of one particle passing through the hopper is not constant when there are not sufficient particles. Then, we propose a new model that can quantify changes in particle passing probability. Using this model, we derive the particle passing probability in a hopper with shallow columns and confirm that the probability of one particle passing through the hopper is closely related to the pressure acting on the bottom of the hopper.

Experimental Study on Gas-Solid Flow in the Spouted Bed under Longitudinal Vortex Effect.

To strengthen the particles radial movement and mixing, the longitudinal vortex generator of a sphere was adopted in the spouted bed in this study. To find the influence of the longitudinal vortex and particle properties on axial and radial velocities of particles in a 152 mm-diametered spouted bed, particle image velocimetry (PIV) was employed. The experimental results show that the addition of the longitudinal vortex generator caused the vortex movement of high-speed gas and induced a considerable secondary fine vortex in the cross section of the spouted bed, and the existence of longitudinal vortex significantly improved the radial velocity of particles, compared with that of the conventional spouted bed. Due to the effect of longitudinal vortex on particles, the phenomenon of early dropping of particles was increasingly obvious with the rise in bed height, and the value of axial velocity of particle phase was negative. With the decrease in the particle diameter, the longitudinal vortex effect of gas-driven particle movement would be enhanced. The longitudinal vortex could enhance particle velocity under a wide range of particle diameters, and the enhancement factor η decreased with the rise in the particle diameter and gradually approaches to 1.

Rheological behavior of magnetic colloids in the borderline between ferrofluids and magnetorheological fluids

Magnetic colloids were formulated by dispersion of magnetic oxide spheres in water. Their rheological behavior was investigated for a wide range of particle diameters covering in detail the magnetic single-multidomain transition and therefore spanning the gap between ferrofluids and conventional magnetorheological fluids. The magnetoviscous effect (i.e., the ratio between the viscosity increment under field and the viscosity value in the absence of field) was found to reach a maximum for a critical particle size in the single-multidomain transition region. The observations were explained in terms of magnetization changes with particle size. The results obtained are applicable to any magnetic material (not only iron oxides) and therefore constitute a new route to enhance the magnetorheological effect. For very small particle sizes (in the superparamagnetic region), thermal motion plays a crucial role and the dimensionless viscosity scales with the Peclet number as expected for Brownian Hard Spheres. For larger particle sizes and λ>1, the dimensionless viscosity scales with the Mason number and closely follows the structural viscosity model under the mean magnetization approximation.

Design, simulation, and characterization of a radial opposed migration ion and aerosol classifier (ROMIAC)

We present the design, simulation, and characterization of the radial opposed migration ion and aerosol classifier (ROMIAC), a compact differential electrical mobility classifier. We evaluate the performance of the ROMIAC using a combination of finite element modeling and experimental validation of two nearly identical instruments using tetra-alkyl ammonium halide mass standards and sodium chloride particles. Mobility and efficiency calibrations were performed over a wide range of particle diameters and flow rates to characterize ROMIAC performance under the range of anticipated operating conditions. The ROMIAC performs as designed, though performance deviates from that predicted using simplistic models of the instrument. The underlying causes of this non-ideal behavior are found through finite element simulations that predict the performance of the ROMIAC with greater accuracy than the simplistic models. It is concluded that analytical performance models based on idealized geometries, flows, and fields should not be relied on to make accurate a priori predictions about instrumental behavior if the actual geometry or fields deviate from the ideal assumptions. However, if such deviations are accurately captured, finite element simulations have the potential to predict instrumental performance. The present prototype of the ROMIAC maintains its resolution over nearly three orders of magnitude in particle mobility, obtaining sub-20 nm particle size distributions in a compact package with relatively low flow rate operation requirements.

Long Working-Distance Optical Trap for in Situ Analysis of Contact-Induced Phase Transformations.

A novel optical trapping technique is described that combines an upward propagating Gaussian beam and a downward propagating Bessel beam. Using this optical arrangement and an on-demand droplet generator makes it possible to rapidly and reliably trap particles with a wide range of particle diameters (∼1.5-25 μm), in addition to crystalline particles, without the need to adjust the optical configuration. Additionally, a new image analysis technique is described to detect particle phase transitions using a template-based autocorrelation of imaged far-field elastically scattered laser light. The image analysis allows subtle changes in particle characteristics to be quantified. The instrumental capabilities are validated with observations of deliquescence and homogeneous efflorescence of well-studied inorganic salts. Then, a novel collision-based approach to seeded crystal growth is described in which seed crystals are delivered to levitated aqueous droplets via a nitrogen gas flow. To our knowledge, this is the first account of contact-induced phase changes being studied in an optical trap. This instrument offers a novel and simple analytical technique for in situ measurements and observations of phase changes and crystal growth processes relevant to atmospheric science, industrial crystallization, pharmaceuticals, and many other fields.

Flow characteristics of biomass particles in a horizontal stirred bed reactor: Part I. Experimental measurements of residence time distribution

The horizontal stirred bed reactor (HSBR) is a prevalent biomass pyrolysis reactor due to its effective seal, excellent control of temperature and residence time, and capacity to handle a wide range of particle diameters. This paper focused on the effects of various parameters on residence time distribution (RTD) and particle flow behavior in the HSBR. The RTD of biomass particles in a custom-built HSBR was measured using the impulse response method. The effects of operational parameters (including flow rate and agitator rotation rate), material flow properties (characterized by the angle of repose), and design parameters (including the number of blades and blade angle) on solid hold-up, mean residence time (MRT) and relative variance of residence time were investigated. The solid hold-up was affected by the rotation rate, flow rate, blade number, blade angles and material flow properties. The flow rate and material flow properties had a significant influence on the MRT while the effect of the other three parameters on the MRT was minimal. The relative variance was primarily influenced by the flow rate, rotation rate, blade number and material flow properties. The effect of the flow properties on the relative variance was irregular. The inter-particle mixing mainly resulted from agitator stirring. Hence, the inter-particle mixing was enhanced with the increase of the rotation rate and blade number. As such, it is essential to further examine the effect of material flow properties on inter-particle mixing using a modeling approach.

A Coarse-Grained Two-Fluid Model for Gas-Solid Fluidized Beds

Due to increasing computer power the numerical simulation of fluidized and moving beds has become feasible. However, while kinetic theory based CFD (Computational Fluid Dynamics) has become a valuable design tool for modeling pilot plant scale gassolid fluidized bed reactors, a fully resolved simulation of industrial scale reactor is still nearly unfeasible. It is, therefore, common to use sub-grid models to account for the effect of the small unresolved structures on large resolved scales when using coarse grids. It is generally agreed that the influence of these small scales on the drag force is a key parameter in the prediction of the hydrodynamics of fluidized beds. We present a sub-grid drag modification dealing with the influence of heterogeneous structures on the drag force. It is assumed that these structures appear as distinct clusters of particles within an interstitial dilute particle phase. The clusters and the dilute phase itself consist of homogeneously distributed particles enabling the application of a homogenous drag correlation to these structures. In contrast to the established sub-grid drag modification EMMS (Energy-Minimization Multi-Scale Method), the presented model distinguishes between resolved and unresolved clusters by computing the expectation value of the diameter of the unresolved clusters. This reveals a grid and slip velocity dependent drag modification, which recovers the homogenous drag law as the solids volume fraction approaches the maximum packing of frictional spheres. The presented model is validated on the one hand, in case of industrial scale bubbling and turbulent fluidized beds. On the other hand, the model is applied to the coarse grid simulation of a riser flow. The numerical results obtained on a coarse gird demonstrate that our model reveals fairly good agreement with experimental data of bed expansion and solids volume fraction distributions. Thus, the results proof that the presented drag modification is applicable to a wide range of particle diameters (Geldart A, B and D group particles) and different fluidization regimes.

PHOTOCHEMISTRY IN TERRESTRIAL EXOPLANET ATMOSPHERES. II. H2S AND SO2PHOTOCHEMISTRY IN ANOXIC ATMOSPHERES

Sulfur gases are common components in the volcanic and biological emission on Earth, and are expected to be important input gases for atmospheres on terrestrial exoplanets. We study the atmospheric composition and the spectra of terrestrial exoplanets with sulfur compounds (i.e., H2S and SO2) emitted from their surfaces. We use a comprehensive one-dimensional photochemistry model and radiative transfer model to investigate the sulfur chemistry in atmospheres ranging from reducing to oxidizing. The most important finding is that both H2S and SO2 are chemically short-lived in virtually all types of atmospheres on terrestrial exoplanets, based on models of H2, N2, and CO2 atmospheres. This implies that direct detection of surface sulfur emission is unlikely, as their surface emission rates need to be extremely high (>1000 times Earth's volcanic sulfur emission) for these gases to build up to a detectable level. We also find that sulfur compounds emitted from the surface lead to photochemical formation of elemental sulfur and sulfuric acid in the atmosphere, which would condense to form aerosols if saturated. For terrestrial exoplanets in the habitable zone of Sun-like stars or M stars, Earth-like sulfur emission rates result in optically thick haze composed of elemental sulfur in reducing H2-dominated atmospheres for a wide range of particle diameters (0.1-1 micron), which is assumed as a free parameter in our simulations. In oxidized atmospheres composed of N2 and CO2, optically thick haze, composed of elemental sulfur aerosols (S8) or sulfuric acid aerosols (H2SO4), will form if the surface sulfur emission is 2 orders of magnitude more than the volcanic sulfur emission of Earth. Although direct detection of H2S and SO2 by their spectral features is unlikely, their emission might be inferred by observing aerosol-related features in reflected light with future generation space telescopes.

Experimental and Numerical Study of Dilute Gas-Solid Flow inside a 90° Horizontal Square Pipe Bend

A pneumatic test rig is built to test a curved 90° square bend in an open-circuit horizontal-to-horizontal suction wind tunnel system. Sand particles are used to represent the solid phase with a wide range of particle diameters. Velocity profiles are constructed by measuring the gas velocity using a 3-hole probe. Flow patterns inside the bend duct are introduced using sparks caused by burning sticks of incense with the air flow inside the piping system for flow visualization purpose. Numerical calculations are performed by Lagrangian-particle tracking model for predicting particle trajectories of dispersed phase, and standard k-ε model for predicting the turbulent gas-solid flows in bends. Comparisons made between the theoretical results and experimental data for the velocity vectors and particle trajectories show good agreement.

Inertial impaction behavior of fuel particles under severe accident scenario in pool type sodium cooled fast reactor

During a highly unlikely event of energetic core disruptive accident in sodium cooled fast reactor (SFR), a high temperature and high pressure volume is formed due to neutronic excursion and expands rapidly (∼ms) into the sodium pool in the form of a fuel vapor bubble. This fuel vapor bubble further rises into the cover gas space, carrying radioactive materials along with it, which will contribute to the radiological source term in reactor containment building. In relation to this, a computer code PTRACK has been developed to describe the motion of an expanding and oscillating bubble and to evaluate trajectories of particles inside the bubble. The code considers adiabatic process for bubble expansion and solves particle momentum equation for evaluating the particle trajectories. PTRACK code has been validated against FAUST-1A benchmark experiments and the code predictions are in fairly good agreement with experimental results. Subsequently, a parametric analysis has been carried out to evaluate particle trajectories in a typical pool type SFR with initial fuel vapor bubble pressure of 1, 2 and 4MPa and for various particle diameters from 3 to 500μm. From this study, it has been observed that during fuel vapor bubble expansion, fuel particles are effectively retained by the sodium pool due to the inertial impaction behavior over a wide range of particle diameters and initial pressures. A parameter (inertial impaction parameter) has been defined to explain the above mentioned phenomenon. Results show that the fuel particle removal from the oscillating fuel vapor bubble due to inertial impaction phenomenon becomes significant when the inertial impaction parameter is close to unity.

Architecture-driven aqueous stability of hydrophobic, branched polymer nanoparticles prepared by rapid nanoprecipitation

The first nanoprecipitation study of hydrophobic branched vinyl polymers is presented with control across a wide range of particle diameters (approximately 60–800 nm) from control of degree of polymerisation and precipitation parameters. In contrast to linear polymers of identical primary chain length, the formation of stable nanoparticles in aqueous media appears to be architecture driven with a contribution from oligomeric chain-ends with measureable water-solubility. The aqueous nanoparticles dispersions are robust and stable to dilution, solvent addition, sonication and temperature. The addition of small amounts of NaCl led to a destabilisation indicating charge stabilisation is also a major contributor to stability.

Validation of EMMS-based drag model using lattice Boltzmann simulations on GPUs

Interphase momentum transport in heterogeneous gas–solid systems with multi-scale structure is of great importance in process engineering. In this article, lattice Boltzmann simulations are performed on graphics processing units (GPUs), the computational power of which exceeds that of CPUs by more than one order of magnitude, to investigate incompressible Newtonian flow in idealized multi-scale particle–fluid systems. The structure consists of a periodic array of clusters, each constructed by a bundle of cylinders. Fixed pressure boundary condition is implemented by applying a constant body force to the flow through the medium. The bounce-back scheme is adopted on the fluid–solid interfaces, which ensures the no-slip boundary condition. The structure is studied under a wide range of particle diameters and packing fractions, and the drag coefficient of the structure is found to be a function of voidages and fractions of the clusters, besides the traditional Reynolds number and the solid volume fractions. Parameters reflecting multi-scale characters are, therefore, demonstrated to be necessary in quantifying the drag force of heterogeneous gas–solid system. The numerical results in the range 0.1 ≤ Re ≤ 10 and 0 < ϕ < 0.25 are compared with Wen and Yu's correlation, Gibilaro equation, EMMS-based drag model, the Beetstra correlation and the Benyahia correlation, and good agreement is found between the simulations and the EMMS-based drag model for heterogeneous systems.

A hierarchical approach to simulate the packing density of particle mixtures on a computer

In many fields of materials science it is important to know how densely a particle mixture can be packed. The “packing density” is the ratio of the particle volume and the volume of the surrounding container needed for a random close packing of the particles. We present a method for estimating the packing density for spherical particles based on computer simulations only, i.e. without the need for additional experiments. Our method is particularly suited for particle mixtures with an extremely wide range of particle diameters as they occur e.g. in modern concrete mixtures. A single representative sample from such mixtures would be much larger than can be handled on present standard computers. In our hierarchical approach the diameter range is therefore divided into smaller intervals. Samples from these limited diameter intervals are drawn and their packing density is estimated from a simulated packing. The results are used to “fill” the interstices in the sample from the next larger particle interval. To account for the interaction between particles of different sizes we include larger particles into the sample of smaller ones. The larger ones act as part of the boundary during the packing. Thus we obtain more realistic estimates of how dense a fraction of particles can be packed within the whole mixture. The focus of this paper is on the divide-and-conquer approach and on how the simulation results from the fractions can be collected into an overall estimate of the packing density. We do not go into details of the simulation technique for the single packing. We compare our results to some experimental data to show that our method works at least as good as the classical analytical models like CPM without the need for any experiments.

Modeling Study of the Vortex and Short Circuit Flow Effect on Inclusion Removal in a Slab Tundish

AbstractA mathematical model was developed to study effects of the vortex and the short circuit flow phenomena during tundish operation on the inclusion removal for a wide range of particle diameters. The model was solved using FLUENT® commercial software; for the particle tracking the Lagrangian discrete phase model was employed. Even when the vortexes drag about 50% of the inclusions, the most detrimental phenomenon for inclusion removal is the short circuit flow. It is important to stress that for the global inclusion behavior the removal rate decreases as the tundish level increases. It can be concluded that when increasing the tundish capacity without any flow control device adjustment, the steel cleanliness is deteriorated significantly.

Macrophage Responses to Silica Nanoparticles are Highly Conserved Across Particle Sizes

Concerns about the potential adverse health effects of engineered nanoparticles stems in part from the possibility that some materials display unique chemical and physical properties at nanoscales which could exacerbate their biological activity. However, studies that have assessed the effect of particle size across a comprehensive set of biological responses have not been reported. Using a macrophage cell model, we demonstrate that the ability of unopsonized amorphous silica particles to stimulate inflammatory protein secretion and induce macrophage cytotoxicity scales closely with the total administered particle surface area across a wide range of particle diameters (7-500 nm). Whole genome microarray analysis of the early gene expression changes induced by 10- and 500-nm particles showed that the magnitude of change for the majority of genes affected correlated more tightly with particle surface area than either particle mass or number. Gene expression changes that were particle size-specific were also identified. However, the overall biological processes represented by all gene expression changes were nearly identical, irrespective of particle diameter. Direct comparison of the cell processes represented in the 10- and 500-nm particle gene sets using gene set enrichment analysis revealed that among 1009 total biological processes, none were statistically enriched in one particle size group over the other. The key mechanisms involved in silica nanoparticle-mediated gene regulation and cytotoxicity have yet to be established. However, our results suggest that on an equivalent nominal surface area basis, common biological modes of action are expected for nano- and supranano-sized silica particles.

Magnetization reversal process in FePt L10 nanoparticles

We have studied the magnetization reversals of FePt L10 particles. Lithographically fabricated single FePt particles and well isolated epitaxial FePt L10 nanoparticles have been investigated for a wide range of particle diameters D. Careful analyses of the experiments have revealed that for particles larger than 20 nm the magnetization reversal behaviors are governed by either nucleation or expansion of a reversed domain depending on the temperature, and the coherent rotation mode becomes dominant for D<20 nm.