Effect Of Particle Size Variation Research Articles

An Experimental Analysis of Lean Binary Mixture Segregation in a Continuous Liquid Fluidized Bed

This study examined the phenomenon of particle segregation in lean-phase binary mixtures, with a specific focus on the effect of particle size variations while flowing over a continuous liquid fluidized bed (LFB). The experimental configuration included a cylindrical column with a 72 mm internal diameter and 3 m vertical height. The binary mixture considered for this investigation was made up of solid materials that were rich in flotsam and jetsam. The study encompassed various factors, including liquid velocity, solid feed rate, and feed composition, in order to examine the separations containing flotsam and jetsam. A segregation index was calculated for each of the various combinations. On the other hand, the fluidization of the blend consisting of two solid components displayed notable differences in its behavior when compared to the reported effects of particle separation in any of the mixtures. Empirical correlations have been employed to establish relationships between variables, particularly with respect to solid entrainment and top and bottom product purity levels.

Combined Light Extinction and Scattering Measurement for Measuring a Low-Particulate-Mass Concentration with a White Cell-Based Optical System

Based on a white cell optical system coupled with two wavelengths of 638nm and 520nm, a combined extinction-scattering method was developed to alleviate the effect of particle size variation on mea...

Laser Alloying Advantages by Dry Coating Metallic Powder Mixtures with SiOx Nanoparticles.

Up to now, minimizing segregation of free-flowing, microscale metal powder mixtures driven by different mass density is an open challenge. In this work, effects of particle size variation on homogeneity of Al-Cu mixtures, with a density ratio of 3.3, are examined. Dry coating Al particles with 0.3 wt% fumed silica SiOx nanoparticles significantly decreases interparticle attraction. This enlarges the range of free-flowing Al particle sizes to < 20 µm. Powder mixture homogeneity is examined optically in vibrated bulk powder and thinly spread layers. From various powder mixtures, solid samples are built layer by layer with the Additive Manufacturing (3D printing) technology Laser Beam Melting in metal powder bed (LBM). Chemical homogeneity of solids is evaluated via energy-dispersive X-ray spectroscopy, backscattered electron microscopy, metallographic analysis and tensile tests. Persistent homogeneity of Al-Cu powder mixtures and LBM solids is found only with particles < 20 µm dry coated with SiOx nanoparticles. Observed segregation phenomena are explained with a decrease in particle mobility at increasing local concentration and the decreasing effectiveness of mass in smaller particles. The main effects are based on geometry, so they are expected to be transferrable to other nanoparticles, alloying components and powder bed technologies, e.g., binder jetting.

Particle separation by phase modulated surface acoustic waves.

High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution.

Novel cellular perlite-epoxy foams: Effects of particle size

The micro-structure and mechanical properties of lightweight porous foams synthesized by dispersing expanded perlite particles (expanded siliceous volcanic glass) in a matrix of epoxy resin were examined. Foams were fabricated with three distinct particle size ranges and, within each size, samples covered a density range of 0.15–0.45 g/cm3. The effects of particle size variation on compressive strength, effective elastic modulus, and modulus of toughness were investigated. An upper and a lower bound were estimated for the elastic modulus of particles in EP/epoxy foams. EP/epoxy foams showed Reuss-like behaviour similar to metals but atypical of non-plastic materials. In addition, results illustrated the significant contribution of the expanded perlite particles in the effective elastic modulus of the foams. Micro-structure of expanded perlite particles was examined and related to their macroscopic properties via two geometrical relationships. Post-test microscopic observations coupled with macroscopic observations taken during the test were used to understand the effect of particle size on the behaviour of the foams under compressive load. Observations revealed the presence of three different failure modes for all foams regardless of their particle size and density; however, the strain to activate each mode was different for each foam type.

Effect on particle size on the compaction mechanism and tensile strength of tablets.

The effect of particle size variation on tablet tensile strength for spray-dried lactose, Sta-Rx 1500 and Avicel PH-101 was investigated. Decreasing the particle size of spray-dried lactose and Sta-Rx 1500 resulted in stronger compacts whereas the tablet tensile strength of Avicel PH-101 was unaffected by particle size variation. The Heckel relationship, at two different contact times, was used to examine the predominant compaction mechanism. This was independent of the size fractions studied for all three materials. Angle of repose and Hausner ratio measurements indicated a correlation between the internal forces of friction and cohesion of the sized powders and the tensile strength of compacts formed from them.

Activation process of Pd/Al 2O 3 catalysts for CH 4 combustion by reduction/oxidation cycles in CH 4-containing atmosphere

In this work, the effect of a conditioning process, consisting of several alternated CH 4-lean combustion/CH 4-reducing pulses at 350 °C, was investigated over Pd/Al 2O 3 catalysts with different Pd loadings (1, 2 and 4 w/w%) prepared from Cl-free precursors. Such a treatment resulted in a one order of magnitude activity enhancement and in the achievement of stable catalytic performances in all the investigated systems. The activity enhancement was associated with an increase in PdO reducibility, as revealed by the comparison of CH 4-TPR profiles before and after the conditioning process. Characterization studies showed that negligible or minor (for the 1% w/w Pd sample) modifications of Pd dispersion occurred upon conditioning, thus ruling out a significant effect of particle size variations on the observed activity enhancement. TPR, FT-IR and XRD measurements showed that palladium is completely oxidized upon conditioning, PdO is less crystalline than in the fresh catalyst likely due to the low oxidation temperature in the conditioning cycles but high activity was retained upon re-crystallization of PdO at 600 °C. FT-IR characterization revealed that conditioning results in a weakening of Pd–support interactions, which possibly originated from the interaction of the acidic Pd precursor with basic hydroxyls of the alumina surface, which acts as germination center during the impregnation step. Such a weakening of Pd–support interactions is likely responsible for the observed activity/reducibility enhancement.

Effect of particle size of fly ash on recycled poly (ethylene terephthalate) / fly ash composites

This study deal with the effect of particle size variation of fly ash, as filler with different concentration (5–40%, wt/wt), on various properties of recycled polyethylene terepthalate (RPET). The mechanical, rheological, electrical and thermal properties of the composite material were evaluated and microstructure was investigated through scanning electron microscopy (SEM). It was seen that micro particle inclusion increased the mechanical properties of the system. From the SEM, it was observed that good dispersion and also very good interaction of fly ash particle—polymer matrix occurred.

Effect of particle size variations of gypsum bonded investment powders on metallurgical quality of investment castings

In the present work, the effect of particle size distribution parameters of investment powder on the metallurgical characteristics of castings produced by flask mould investment casting process was investigated. The main aim of this study is to establish the relationships between the casting quality and investment powder characteristics. For this purpose, models for tensile, density and surface roughness specimens were prepared in accordance with the standards and these models were moulded by gypsum bonded investment powders. Specimens of sterling silver (92·5Ag–7·5Cu alloy) were subsequently cast into these moulds by centrifugal casting process. After the completion of solidification process, the specimens were tested and results were analysed. The preliminary results illustrate that fineness of investment powders play an important role in determining the metallurgical quality of castings produced by investment casting process.

Effect of particle size variation of Ag nanoparticles in Polyaniline composite on humidity sensing

The results of synthesis of Ag-Polyaniline nanocomposite along with an investigation of optical fiber based humidity sensor using evanescent wave absorption spectroscopy are discussed. The sensor was fabricated using Ag-Polyaniline nanocomposite deposited on an optical fiber clad and tested in the range of 5-95% relative humidity (RH). Optimization of clad length (2-8mm) was done and then particle size (15-30 nm) variation of silver nanoparticles in Polyaniline composite was studied for better performance of sensor. The effect of particle size on sensing humidity was investigated. The reduction of particle size, leads to a dramatic improvement in sensitivity and speed of response. The optimized clad length of 6mm exhibits the better results for 15 nm particle size of Ag nanoparticles dispersed in Polyaniline. The sensor response is fully reversible having almost 1% of standard deviation. Response time of the sensor is 30s with a slow recovery of 90 s.

Strength of the H2O near‐infrared absorption bands in hydrated minerals: Effects of particle size and correlation with albedo

We use laboratory experiments and radiative transfer modeling to study how the 1.9‐ and 3‐μm H2O absorption bands are affected by variations of mineral particle size and albedo. A consistency between results of physical experiments and numerical simulations demonstrates that the studied effects are well described by the theory of radiative transfer in particulate media. Band strengths show different relationships with particle size, depending on the absolute intensity of the absorption and the criterion used to calculate band strength (band depth, area, ESPAT function, etc.). Various mixing processes used to vary sample albedo reveal a strong dependence of band strengths with albedo. For the 1.9‐μm band, those effects result in variations of the hydrated minerals detection limit by more than 1 order of magnitude. However, the shape of the relationship between the 1.9‐μm band strength and albedo could be used to get information on the mixing mode (intimate, granular, or geographic) between hydrated and nonhydrated minerals. For the 3‐μm band, we found a strong linear correlation between the integrated band area and the continuum reflectance that opens a promising way to isolate the effect of albedo on planetary surfaces and retrieve spatial variations of material hydration state. When this spectral criterion is used for the 3‐μm band, the effects of particle size are very limited for particles larger than 150 μm but remain important below this value. Therefore, an independent way to derive particle size from remote sensing appears necessary to address the effects of particle size variations where small particles are present.

Empirical preprocessing methods and their impact on NIR calibrations: a simulation study

AbstractThe extraction of chemical information from dense particulate suspensions, such as industrial slurries and biological suspensions, using near‐infrared (NIR) spectroscopic measurements is complicated by sample‐to‐sample path length variations due to light scattering. Empirical preprocessing techniques such as multiplicative scatter correction (MSC), extended MSC and derivatives have been applied to remove these effects and in some cases have shown promise. While the performance of these techniques and other related approaches is known to depend on the nature and extent of the variations and on the measurement configuration, detailed investigations into the efficacy of these approaches under various conditions have not been previously undertaken. The main obstacle to carrying out such investigations has been the lack of, and the difficulty in obtaining, an accurate and comprehensive experimental data set. In this work, simulations that generate ‘actual’ measurements were carried out to obtain ‘experimental’ spectroscopic data on particulate systems. This was achieved by solving the exact transport equation for light propagation. A model system comprising four chemical components with one consisting of spherical submicron particles was considered. Total diffuse transmittance and reflectance data generated through simulations for moderate particle concentrations were used as the basis for examining the effect of particle size variations and measurement configurations on the efficacy of a number of preprocessing techniques in enhancing the performance of partial least squares (PLS) models for predicting the concentration of one of the non‐scattering chemical species. Additionally, a form of extended multiplicative signal correction based on considerations arising from fundamental light scattering theory is proposed and found to perform better than the other techniques for the cases considered in the study. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Modeling the gas absorption in a spray scrubber with dissolving reactive particles

The absorption of a gaseous species into a spherical slurry droplet with internal circulation that contains reactive, sparingly soluble microparticles is studied. The droplet recirculation is assumed to be similar to Hill's vortex flow, and the chemical reaction is assumed to be either instantaneous or of second order. Reactive gas species diffusion, chemical reaction and particle dissolution are numerically modeled using droplet recirculation streamlines as a coordinate. Parametric calculations are performed, and are utilized to assess the adequacy of the widely used film theory, and to examine the effect of particle size variation on the absorption rate. A transient model is also developed that utilizes the aforementioned quasi-steady droplet mass transfer and reaction models and calculates the time variation of the average solid particle size in the droplet. Parametric calculations are presented that confirm the importance of particle size and its variation as a result of dissolution. Transient parametric calculations show a declining total absorption rate with time as a result of the shrinkage of the average particle size. The results are everywhere sensitive to droplet internal circulation, however. Partial suppression of droplet internal circulation leads to significant reduction in absorption rate, even with a high concentration of particles. The calculation results thus demonstrate that several parameters should be considered for optimal design of a slurry spray scrubber.

Factors affecting the prediction of organic matter Digestibility of grass silage by near infrared reflectance spectroscopy

Earlier studies (Barber et al., 1990) showed the superiority of near infrared reflectance spectroscopy (NIRS) for predicting the organic matter digestibility (OMD) in vivo of grass silage over fibre and in vitro procedures. However, during routine application occasional erroneous values were predicted for which there were no obvious reasons. Baker and Barnes (1990) reported that the likely sources of the problems contributing to the errors were instrumental and environmental noise, sample particle size effects and variable moisture content of the samples. These authors also reported that standard normal variate - detrend (SNV-D) scatter correction procedure of Barnes et al. (1989) could be used to reduce the effects of particle size variation and they also emphasised the need to test NIRS calibrations for repeatability. The purpose of the present work was to evaluate the use of the SNV-D scatter correction procedure, the techniques for reducing the sensitivity of calibrations to residual moisture and methods to improve the repeatability of the predicted OMD in vivo values of grass silage. In addition, a further objective was to compare three calibration methods, namely modified stepwise regression (MSR), modified partial least squares (MPLS) and principal component analysis (PCA).

Turbulent dispersion of particles in self-generated homogeneous turbulence

Turbulent dispersion of particles in their self-generated homogeneous turbulent field was studied both experimentally and theoretically. Measurements involved nearly monodisperse spherical glass particles (nominal diameters of 0.5, 1.0 and 2.0 mm) falling with uniform particle number fluxes in a nearly stagnant water bath. Particle Reynolds numbers based on terminal velocities were 38, 156, and 545 for the three particle sizes. The flows were dilute with particle volume fractions less than 0.01%. Measurements included particle motion calibrations, using motion-picture shadowgraphs; and streamwise and cross-stream mean and fluctuating particle velocities, using a phase-discriminating laser velocimeter. Liquid-phase properties were known from earlier work. Particle properties were predicted based on random-walk calculations using statistical time-series methods to simulate liquid velocities along the particle path.Calibrations showed that particle drag properties were within 14% of estimates based on the standard drag correlation for spheres, however, the particles (particularly the 1.0 and 2.0 mm diameter particles) exhibited self-induced lateral motion even in motionless liquid due to eddy-shedding and irregularities of shape. Particle velocity fluctuations were primarily a function of the rate of dissipation of kinetic energy in the liquid since this variable controls liquid velocity fluctuations. Streamwise particle velocity fluctuations were much larger than cross-stream particle velocity fluctuations (2–5:1) largely due to varying terminal velocities caused by particle size variations. Cross-stream particle and liquid velocity fluctuations were comparable owing to the combined effects of turbulent dispersion and self-induced motion. Predicted mean and fluctuating particle velocities were in reasonably good agreement with the measurements after accounting for effects of particle size variations and self-induced motion. However, the theory must be extended to treat self-induced motion and to account for observations that this motion was affected by the turbulent environment.

An Energy Based Approach Toward Determining Part Shape Change During the Sintering of Ceramic Parts

Part distortion during sintering results from nonhomogeneous and nonisotropic shrinkage. Shrinkage is highly dependent on density and particle size distributions within a part, thus, “shrinkage factors” are not constant and may vary throughout the part. An energy based approach is presented which can be used to form accurate shrinkage laws for eventual use in a finite element solution of part shape change. This energy method can be easily modified to include the important effects of particle size variations, contact forces and irregular particle shape in the formation of accurate of shrinkage laws. Linear particle shrinkage and rotations due to contact stresses are examined using simple two particle geometries to test the validity of the approach. Energy methods give results which agree well with observation and the direct application of the diffusion equation, however, the advantage of this formulation over traditional diffusion based analysis will be fully realized in the eventual task of specifying time dependent shrinkage laws of realistic multi particle models.

Coated Drug Cores in Multiple Unit Preparations Influence of Particle Size

The influence of the size of barrier-coated drug cores was investigated using a special experimental design. It was shown that the release rate is directly proportional to the surface area of the coated cores. This means, for example, that four times more coating solution should be needed to maintain the release properties if the particle size is reduced to half of its original value. This large effect of particle size variations is important both concerning product quality and production economy.

Near infra‐red analysis of grass silage by principal component analysis of transformed reflectance data

AbstractMost of the observed variation between n.i.r. spectra in any sample collection is due to particle size variation; in addition, absorbance readings are highly inter‐correlated. Application of multiple linear regression techniques to such spectral data produces a multiplicity of solutions which vary in the wavelengths selected and in predictive accuracy. Evaluation of all or most of these calibrations requires a significant amount of time. In the present study, alternative data treatment methods are described which reduce the effect of particle size variations, select only those wavelengths which contain significant information, and overcome the problem of inter‐correlation by means of principal component analysis. These methods were applied to the analysis of dried silage for crude protein (CP) and in vitro dry matter digestibility (IVDMD); accuracy of the novel data treatments (best standard error of prediction of CP and IVDMD equal to 0.63 and 2.7, respectively) was better than that generally achieved by more conventional statistical techniques.

Entrainment of Sediments and Dredged Materials in Shallow Lake Waters

Results of recent laboratory experiments concerned with the entrainment and deposition of sediments in lakes are reported. From these experiments and other recent work, quantitative descriptions and parameterizations of entrainment and deposition processes are made. In the interpretation of the experimental results, the effects of particle size variation and cohesion of particles are significant. The laboratory results are also compared with previous observations of turbidity in the western basin of Lake Erie and good agreement is obtained.

Quantitative determination of crystalline silica in respirable-size dust samples by infrared spectrophotometry.

A direct differential scanning infrared spectrophotometric method is described for the determination of crystalline silica in respirable-size atmospheric dust samples from a wide range of industrial environments. The test atmosphere is drawn through a cyclone elutriator, fitted with a membrane filter, at 1.9 l min–1 for, typically, 1–4 h. The filter, without further preparation, is scanned from 1500 to 400 cm–1 and the atmospheric concentration of crystalline silica determined from the intensity of the quartz (799, 780 and 695 cm–1), together with, when present, cristobalite (796 and 621 cm–1) absorption bands. Generation of standard crystalline silica atmospheres using a portable dust chamber is described. The effect of particle size variation on the absorbance intensity, together with sample re-radiation and mineral interference effects, are examined.