Resulting Particle Size Distribution Research Articles

THERMAL BEHAVIOR PREDICTION OF FOOD PARTICULATES UNDER AMBIENT AND CRYOGENIC CONDITIONS

ABSTRACT This article describes experiments to quantitatively characterize the thermal effects of solid food particulates in terms of temperature increment as a function of particle size under ambient and cryogenic conditions using turmeric (Curcuma longa L.) as a model material. The log‐normal function was used to characterize the thermal behavior. Cylindrical specimens of turmeric were impacted diametrally, and the resulting particle size distributions and cumulative volume fraction were measured by computerized inspection particle size analyzer. The various model parameters estimated under the said conditions, such as surface‐volume ratio, energy density and combined strength parameter, were found to be in the range of 3.5 × 103–1.14 × 106 (m−1), 2.4 × 105–6.6 × 107 J/m3 and 174.1–229.5 J/m2, respectively. The temperature change ΔT (C) was calculated in terms of log‐normal parameters and material properties such as the specific heat and local energy density. The calculated ΔT was plotted as a function of size of particles. Local temperature rise up to 114.5 and 67.2C was found for the particle size of 12 µm or lower for ambient and cryogenic conditions, respectively. A novel mathematical model has been proposed to correlate the size distributions of solid particles under fracture to the temperature changes.PRACTICAL APPLICATIONSDuring the size reduction of solid food materials, intensive energy degradation into heat takes place during fracture before resulting into fragments. Because fracture is a rate process with random fluctuation of stresses, the thermal effects cannot be calculated from classical approaches. The article describes a novel approach to quantitatively characterize the thermal effects of solid food particulates in terms of temperature change as a function of particle size under different treatment conditions. These characterizations can serve as a principled basis for modeling effects in a field where classical approaches are not applicable. The proposed approach can also be extended to nanoparticle and molecular characterization, which otherwise necessitates the usage of expensive instrumentation and also in biological processing such as in cancer research wherein if the cell size and its material properties are known, it may be possible to control the temperature induced during cell division.

A study on stability and thermophysical properties (density and viscosity) of Al2O3 in water nanofluid

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles (obtained from different sources) in water have been analyzed. The differences arising from different dispersion techniques, the resulting particle size distribution, and time stability among the different samples are evaluated. Then the volumetric behavior up to high pressures (25 MPa) and atmospheric pressure viscosity were experimentally determined. It has been found that the influence of particle size in density is subtle but not negligible, but the differences in viscosity are very large and must be taken into account for any practical application. These viscosity differences can be rationalized by considering a theory describing the aggregation state of the nanofluid.

Surface Area Effects on the Response Mechanism of Ion Optodes: A Preliminary Study

The relationship between the surface-to-volume ratio and the response mechanism of polymeric ion probes (ion optodes) is not well understood. In this work, the surface-to-volume ratio of ion optodes was systematically increased in an attempt to characterize this relationship. Several different batches of ion-selective optodes were fabricated via the solvent displacement method using sodium ionophore X, BME-44, and ETH 1001 for sodium-, potassium-, and calcium-selective optodes, respectively. Dilution of the membrane cocktail with varying amounts of an organic solvent provided a convenient tool to control the resulting particle size distribution. Specifically, ion optodes of five different size distributions were fabricated. An apparent shift of the response function on the pH scale was observed for optodes with identical composition that differed in terms of size. There was a strong correlation between the calculated specific surface area and the apparent ion-exchange constant for all three types of ion optodes. However, there was an indication that selectivity does not substantially correlate with the optode size. We hypothesize that the observed effect is caused by surface phenomena which contribute to the overall optode response. The results reported here may raise a word of caution about the application of established response models, which were developed for macroscopic ion optodes, toward probes at micrometer and submicrometer scales.

Electrospray versus Nebulization for Aerosolization and Filter Testing with Bacteriophage Particles

Aerosolization of bacteriophage MS2 virions by nebulization and charge-reduced electrospray were compared during testing of three filter media. Sample swatches were taken from a surgical mask, N95 filtering-facepiece respirator (FFR), and N100 FFR for use in repeated, short-duration (15 min) penetration tests with bacteriophage MS2 aerosolized by nebulizer and electrospray. Evaluated were (1) the virus suspension preparation protocol, (2) resulting particle size distribution, count stability, and count variability, and (3) the ability to generate culturable MS2 virions. While preparation of the electrospray bacteriophage suspension required additional purification and concentration steps and took more time than the nebulization protocol, it resulted in a much higher titer suspension. The nebulizer produced a polydisperse aerosol; conversely, the electrospray produced a relatively monodisperse aerosol with a count peak at the mobility size of the single virion. The nebulized aerosol particle count was 2.8 ...

Size and composition distribution dynamics of alloy nanoparticle electrocatalysts probed by anomalous small angle X-ray scattering (ASAXS)

Anomalous small angle X-ray scattering (ASAXS) is shown to be an ideal technique to investigate the particle size and particle composition dynamics of carbon-supported alloy nanoparticle electrocatalysts at the atomic scale. In this technique, SAXS data are obtained at different X-ray energies close to a metal absorption edge, where the metal scattering strength changes, providing element specificity. ASAXS is used to, first, establish relationships between annealing temperature and the resulting particle size distribution for Pt25Cu75 alloy nanoparticle electrocatalyst precursors. The Pt specific ASAXS profiles were fitted with log-normal distributions. High annealing temperatures during alloy synthesis caused a significant shift in the alloy particle size distribution towards larger particle diameters. Second, ASAXS was used to characterize electrochemical Cu dissolution and dealloying processes of a carbon-supported Pt25Cu75 electrocatalyst precursor in acidic electrolytes. By performing ASAXS at both the Pt and Cu absorption edges, the unique power of this technique is demonstrated for probing composition dynamics at the atomic scale. These ASAXS measurements provided detailed information on the changes in the size distribution function of the Pt atoms and Cu atoms. A shift in the Cu scattering profile towards larger scattering vectors indicated the removal of Cu atoms from the alloy particle surface suggesting the formation of a Pt enriched Pt shell surrounding a Pt-Cu core. Together with XRD and TEM, ASAXS is proposed to play an increasingly important role in the mechanistic study of degradation phenomena of alloy nanoparticle electrocatalysts at the atomic scale.

3‐D Modeling of Shock‐induced Precursor Decomposition and Nano‐Particle Growth

AbstractIn the ongoing joint project “Gasdynamically induced nano–particles” (PAK 75/1) a novel method of gas–phase synthesis of nano–particles is being developed [1]. This project is supported by the Deutsche Forschungsgemeinschaft (DFG), the pilotfacility is erected in collaboration with Evonik Degussa, Hanau, Germany. The key features of the new method are the static temperature increase across a stationary shock to provide ignition conditions of the precursor and the subsequent gasdynamic quenching of the particle growth when the desired particle diameter of 10−8m is reached. In this work the decomposition of the precursor, the reactive heat release and the particle growth are coupled with the 3–D transonic flow inside the particle reactor. The simulation results show the effect of shock/boundary layer interactions on the decomposition reaction as well as the effects of the reactive heat release on the shock location and the resulting particle size distribution. The Reynolds number at the shock location is Rex=9·106, the boundary layer thickness is δ=2.2 mm and the pre–shock Mach number is M=1.58. The complex transonic reactive flow within the particle reactor requires a high mesh resolution to resolve the local details of the internal flow problem. In addition, an efficient particle model is required. The formation and growth of the particles are modeled by three separate reactions. The primary reaction is the decomposition of the precursor and the production of monomers. It is modeled by a one step reaction described by an Arrhenius equation. The secondary reaction, the formation of critical nuclei is in our case negligible, because of the high supersaturation ratio of the order of 103 instantly after the primary reaction, where the monomers are already critical nuclei. The tertiary reaction is the particle growth by surface condensation, coagulation and single–aggregation. To simulate the particle growth we apply a local monodisperse bimodal formulation. Thereby, the monodisperse model of Kruis et al. [2] is extended by an additional discrete monodisperse mode for the critical nuclei. This method describes the local particle size due to turbulent mixing, coagulation and coalescence. The coagulation starts in the Knudsen regime Kn ≫ 1 and reaches the continuum regime with particle diameters of the order of 10−8m and a mean free path of the same order of magnitude. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous 3D observation of different kinetic subprocesses for precipitation in a T-mixer

A coupled direct numerical simulation (DNS)—population balance equation (PBE)–DLVO approach is presented to calculate the product properties of particles originating from precipitation in a T-mixer. A special focus is given to the coupling of different subprocesses such as mixing, nucleation, growth, stabilization and aggregation for a rapid precipitation process. Based on the predictive computation of the resulting particle size distributions (PSD) full 3D-field information of all transient parameters are accessible, e.g., supersaturations, nucleation rates, particle sizes and stabilities. By interpolating the kinetic data, relevant subprocesses can be visualized and studied separately in the mixer. The resulting PSDs are predicted for different conditions where aggregation can be neglected. For unstable conditions aggregation and transient stabilization effects are determined by the DLVO theory. The size of the particles, their surface potential and the ionic strength of the solution vary extensively during the solid formation process. The dynamic evolution of the particle stability leads to a better description of the PSD based on the DNS–PBE–DLVO approach for unstable conditions and allows to develop strategies how to better stabilize particles. This approach is verified for barium sulphate precipitation but can be transferred to any other ionic system for which the relevant material specific data are known.

Monodisperse ultrafine polystyrene nanoparticles prepared by a semicontinuous microemulsion polymerization

Monodisperse ultrafine polystyrene nanoparticles have been successfully prepared under low levels of surfactant through a novel semicontinuous microemulsion polymerization, in which the first part of monomer (Sti) is added dropwise while the subsequent supply to the polymerizing system is delivered in one potion. Polystyrene nanoparticles with number-average diameter of 17.4 nm and polydispersity index of 1.06 were obtained using low level of surfactant/monomer weight ratio of 0.20. Influencing of parameters including amount of St 1 , solid content, initiator, reaction temperature, and cosurfactant on the resultant particle size and size distribution were investigated. The mechanism of nucleation and particle growth was discussed as well.

Mass, Number and Surface Area Concentrations of α‐Quartz Exposures of Refractory Material Manufacturing Workers

This study set out to assess the respirable mass, surface area, and number concentrations of the alpha-quartz content particles (C(r-m), C(r-s) and C(r-n)) to which workers were exposed in six different exposure groups, the raw material handling (n=10), crushing (n=12), mixing (n=12), forming (n=10), furnace (n=10), and packaging (n=10), in a refractory material manufacturing plant. For C(r-m), the exposure values in sequence were found as: mixing (68.1 microg/m3)>packaging (55.9 microg/m3)>raw material handling (53.3 microg/m3)>furnace (31.0 microg/m3)>crushing (29.8 microg/m3)>forming (22.4 microg/m3). We also found that ~21.2-68.2% of the above Cr-m exceeded the current TLV-TWA for the alpha-quartz content (50 microg/m3) suggesting a need for initiating control strategies immediately. We further conducted particle size-segregating samplings in four workplaces: crushing (n=3), mixing (n=3), forming (n=3), and furnace (n=3). We found that all resultant particle size distributions shared a quite similar geometric standard deviation (sigma(g); =2.24-2.92), but the process area, associated with higher mechanical energy (i.e., crushing process), contained finer alpha-quartz content particles (mass median aerodynamic diameter; MMAD=3.22 microm) than those areas associated with lower mechanical energy (i.e., mixing, forming, and furnace; MMAD=6.17, 5.95, and 8.92 microm, respectively). These results gave a ratio of C(r-m) in the above four exposure groups (i.e., crushing: mixing: forming: furnace=1.00: 2.30: 0.753: 1.04) which was quite different from those of C(r-s) (1.00: 1.74: 0.654: 0.530) and C(r-n) (1.00: 1.27: 0.572: 0.202). Our results clearly indicate the importance of measuring particle size distributions for assessing workers' free silica exposures.

Factors influencing the particle size distribution of flaked meat. II. Effect of aperture size, number of cutting stations, rotational speed and impeller design

Summary Diced steer flank and brisket were flaked at a nominal temperature of -4.0°C to investigate the effects of rotational speed (3360 or 5250 r.p.m.), two different impeller designs, aperture size (1.5, 6.1 and 19.0mm) and number of cutting stations on the resulting particle size distribution, measured using video image analysis. Changes in ice content and enthalpy were also calculated from measurements of temperature before and after flaking. The amount of ice which melted, and the corresponding enthalpy change, was significantly greater for the smaller aperture sizes, and the higher speeds. Of the four factors investigated, the most important influence on particle size was that of aperture size. However, under some conditions, the number of cutting stations and the rotational speed also influenced the resulting particle size characteristics, most notably in producing thinner particles.

Reactivity and sintering kinetics of Au/TiO2(110) model catalysts: particle size effects

We review here our studies of the reactivity and sintering kinetics of model catalysts consisting of gold nanoparticles dispersed on TiO2(110). First, the nucleation and growth of vapor-deposited gold on this surface was experimentally examined using x-ray photoelectron spectroscopy and low energy ion scattering. Gold initially grows as two-dimensional islands up to a critical coverage, θ cr, after which 3D gold nanoparticles grow. The results at different temperatures are fitted well with a kinetic model, which includes various energetic parameters for Au adatom migration. Oxygen was dosed onto the resulting gold nanoparticles using a hot filament technique. The desorption energy of Oa was examined using temperature programmed desorption (TPD). The Oa is bonded ~40% more strongly to smaller (thinner) Au islands. Gaseous CO reacts rapidly with this Oa to make CO2, probably via adsorbed CO. The reactivity of Oa with CO increases with increasing particle size, as expected based on Bronsted relations. Propene adsorption leads to TPD peaks for three different molecularly adsorbed states on Au/TiO2(110), corresponding to propene adsorbed on gold islands, to Ti sites on the substrate, and to the perimeter of gold islands, with adsorption energies of 40, 52 and 73 kJ/mol, respectively. Thermal sintering of the gold nanoparticles was explored using temperature-programmed low-energy ion scattering. These sintering rates for a range of Au loadings at temperatures from 200 to 700 K were well fitted by a theoretical model which takes into consideration the dramatic effect of particle size on metal chemical potential using a modified bond additivity model. When extrapolated to simulate isothermal sintering at 700 K for 1 year, the resulting particle size distribution becomes very narrow. These results question claims that the shape of particle size distributions reveal their sintering mechanisms. They also suggest why the growth of colloidal nanoparticles in liquid solutions can result in very narrow particle size distributions.

Modelling dust distributions in the atmospheric boundary layer on Mars

A time and height dependent eddy diffusion model is used to investigate possible scenarios for the size distribution of dust in the lower atmosphere of Mars. The dust is assumed to either have been advected from a distant source or to have originated locally. In the former case, the atmosphere is assumed to initially contain dust particles with sizes following a modified gamma distribution. Larger particles are deposited relatively rapidly while small particles are well mixed up to the maximum height of the afternoon boundary layer and are deposited more slowly. In other cases, a parameterization of the dust source at the surface is proposed. Model results show that smaller particles are rapidly mixed within the Martian boundary layer, while larger particles (r > 10 μm) are concentrated near the ground with a stronger diurnal cycle. In all simulations we assume that the initial concentration or surface source depend on a modified gamma function distribution. For small particles (cross-sectional area weighted mean radius, reff = 1.6 μm) distributions retain essentially the same form, though with variations in the mean and variance of the area-weighted radius, and the gamma function can be used to represent the particle size distribution reasonably well at most heights within the boundary layer. In the case of a surface source of larger particles (mean radius 50 μm) the modified gamma function does not fit the resulting particle size distribution. All results are normalised by a scaling factor that can be adjusted to correspond to an optical depth for assumed particle optical scattering properties.

Emission potential of condensable suspended particulate matter from flue gas of solid waste combustion

Condensable suspended particulate matter, condensable SPM, is generated during the cooling process of flue gas by mixing with the atmosphere. Condensable SPM from stationary sources, such as power plants, waste incinerators and factories, is rather difficult to evaluate since dust sampling from exhaust gas is usually performed downstream of dust collectors, which are maintained at relatively high temperatures. In this study, in order to discuss the emission mechanism of condensable SPM from waste incinerators, model flue gas comprised Cd and Pb was produced by the sublimation of pure CdCl 2 and PbCl 2 in gas stream. Model flue gas was cooled in a diluter after separation of particulates by a bag filter kept at operational temperatures common to commercial plants. Particle size distribution of generated condensable SPM after a diluter was measured by a differential mobility analyzer (DMA). The composition of the model gases was determined based on our experiments carried out on fueled refuse derived fuel (RDF) in a laboratory-scale fluidized bed combustor. The effect of the CdCl 2 and PbCl 2 sublimation temperature, filtration temperature, and bag filter ash layering on the resulting particle size distribution of SPM was examined. The emission possibility of condensable SPM from solid waste incinerators is discussed based on experimental results and thermodynamic calculation.

Population Balance Model for Emulsion Polymerisation Under Pseudo‐Bulk Conditions: Combined Particle Size Distribution and Molecular Weight Distribution

AbstractA comprehensive model for emulsion polymerisation is presented, accounting for particle size distribution (PSD) and molecular weight distribution (MWD). The PSD information is incorporated through a population balance framework. A mechanistic formulation is adopted in modelling the average number of radicals/particle under pseudo‐bulk compartmentalisation conditions. The method of moments is adopted to simplify the MWD equations over each discrete size class. The impact of the pseudo‐bulk assumption on the PSD and MWD results is assessed. An identification of potential manipulated variables for control of PSD and MWD is done through sensitivity analysis.

Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles

AbstractRecent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.

Multiplicity and contiguity of ablation mechanisms in laser-assisted analytical micro-sampling

Laser ablation is implemented in several scientific and technological fields, as well as a rapid sample introduction technique in elemental and trace analysis. At high laser fluence, the ejection of micro-sized droplets causes the enhancement of the surface recession speed and depth resolution degradation as well as the alteration of the sampling stoichiometry. The origin of such large particles seems to be due to at least two different processes, phase explosion and melt splashing. Experimental evidence for both was found in metallic matrices, whereas non-metallic samples showed more complex phenomena like cracking. The spatial distribution of the beam energy profile is responsible for significant differences in the ablation mechanism across the irradiated region and for heterogeneous sampling. Under Gaussian irradiance distribution, the center of the crater, where the irradiance is the highest, experienced a fast heating with rapid ejection of a mixture of particles and vapor (spinodal breakdown). The crater periphery was subjected to more modest irradiation, with melt mobilization and walls formation. The overall resulting particle size distribution was composed of an abundant nano-sized fraction, produced by vapor condensation, and a micro-sized fraction during melt expulsion.

ポリマー粒子の最前線 ソープフリー乳化重合による単分散ポリマー粒子の合成

Current research on soap-free emulsion polymerization is described together with fundamental aspects concerning the mechanism of this polymerization. Conventional methods of soap-free emulsion polymerization were only applicable to the synthesis of monodisperse submicron-sized polymer particles. Previous work, however, pointed out that resultant particle size distributions are strongly dependent on particle coagulation that can be controlled by electrostatic interaction between particles. This basic concept for the particle formation has led to development of a new type of soap-free emulsion polymerization that employs an amphoteric initiator in combination with pH control. This method has enabled the production of highly monodisperse polystyrene particles up to 3μm in a single stage polymerization. Larger particles can be produced with a simple method of monomer addition to polymerization system after the formation of particles. The soap-free emulsion polymerization is also applicable to the polymerization of methyl methacrylate. Currently, soap-free polymerization methods are widely applied to the synthesis of monodisperse composite particles. The examples given are magnetic polymer latex, silica/polystyrene core-shell particles, bell-shaped hollow core-shell particles and multilayered gold/silica/polystyrene core-shell particles.

Comparação de Modelos Matemáticos para o Traçado de Curvas Granulométricas de Sedimentos do Leito de Rios

Knowledge about particle-size distribution of riverbed sediments is essential to use indirect methods for calculating the total fluvial sediment discharge in a river cross-section, as well as for other hydro-sedimentological studies. In general, the techniques used to determine the particle-size distribution of a sample result in point values, requiring subsequent interpolation to fit the complete particle-size distribution curve and to obtain specific characteristic diameter values. The transformation of discrete points into continuous functions can be performed by mathematical models. Thus, the objective of this paper was to evaluate and recommend the best model or group of models for fitting particle-size distribution curves of riverbed sediments. Using the particle-size distribution results of 30 riverbed sediment samples, 14 different models were tested. The parameter used to compare the models was the sum of the square errors between the measured and calculated values, obtained in the adjustment of each model. The results showed that the Lima & Silva 3P model is best for fitting particle-size distribution curves of riverbed sediments

Predictive simulation of nanoparticle precipitation based on the population balance equation

Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulation with a Lagrangian particle tracking strategy is applied in combination with the coupled population balance–micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation.

NaCl particle interaction with 193-nm light: Ultraviolet photofragmentation and nanoparticle production

The interaction of nanoscale NaCl particles with 193-nm photons is studied to better understand particle disintegration and production by ultraviolet photofragmentation. The particles are irradiated in a constrained air stream with laser fluences from 0.08to0.23J∕cm2 with single and multiple pulses striking the particles. The resulting particle size distributions are measured with a scanning mobility particle sizer and the morphology is analyzed qualitatively by scanning electron microscopy (SEM). Photofragmentation of NaCl particles at 193nm produces gas-phase species as well as small solid-phase fragments without significantly heating the particles or creating a plasma. The irradiated particles have a mean diameter from 20to55nm (depending on the photon energy) and a number concentration an order of magnitude higher than the 118-nm mean diameter nonirradiated particles. The SEM images before and after 193-nm irradiation reveal that the irradiated particles are less fractal and more spherical.