Fraction Of Large Particles Research Articles

Rainfall effects on vertical profiles of airborne fungi over a mixed land-use context at the Brazilian Atlantic Forest biodiversity hotspot

Whilst fungi are a large fraction of primary biological aerosol particles (PBAPs) and their impact on global climate has been widely recognised, few studies have empirically assessed fungal vertical profiles and diversity relating those with rainfall. Here, we show the results of fungal PBAPs before and after a rainfall event during a fieldwork campaign using a hot-air balloon over a mixed land-use context at the Brazilian Atlantic Forest biodiversity hotspot. Four flights of c. 1 hour each were performed in the early morning from 8th until 11th of March 2022, and data were collected at three sampling heights (0, 150 and 300 m). Rainfall estimation using IMERG data indicated the precipitation event was of 15–20 mm and ERA5/ECMWF data highlighted that most of the airborne samples were taken above the boundary layer height. After the rainfall, the concentration of fungal spores at the ground level remained unchanged, whereas it was reduced to between 2- and 2.5-fold for the 150 and the 300 m heights, respectively. This was also accompanied by a reduction in the number of Pink-CFU, indicating a major drop in fungal PBAPs at higher altitudes associated with the rain. In addition, total spore concentration indicated Cladosporium sp. as dominant at all sampling heights, accounting for more than 80% of all spores, whereas Aspergillus/Penicillium-like represented less than 20%. Our results show the effects of rainfall and altitude on the concentration of fungal PBAPs, indicating how wet removal impacts fungi vertical profiles which has knock-on-effects on cloud and precipitation formation.

Stratified and gradient films by evaporation-induced stratification of bimodal latexes. Potential of confocal and scanning electron microscopy for compositional depth profiling

In the field of bimodal latex film's formation, finding methods to quantify particle concentration profiles within the film thickness is a challenge. Herein the advantages and limitations of confocal fluorescence microscopy (CFM) and scanning electron microscopy (SEM) are presented. Films are prepared from a bimodal fluorescent acrylic mixture of large non-deformable particles and small deformable particles having high Péclet numbers. A fixed volume fraction of large particles (ΦL) in the dispersion is used with increasing volume fractions of small particles latex (ΦS). At low ΦS, a surface stratification of large particles occurs with thicknesses up to several micrometers, allowing detection by both CFM and SEM. Small particles form a stratified surface layer above a threshold ΦS value. Its thickness of less than 500 nm is evidenced only by SEM due to the resolution limit of the confocal scan. SEM is also able to reveal concentration gradients of large particles below the “small-on-top” stratified layer.

Spray dried tigecycline dry powder aerosols for the treatment of Nontuberculous mycobacterial pulmonary infections

Nontuberculous mycobacterial (NTM) pulmonary infections are a global health concern and a significant contributor to lung disease. Systemic therapies of a cocktail of antibiotics administered over a long period often lead to adverse reactions and/or treatment failure. NTM pathogens, such as Mycobacterium abscessus (Mabs), are notoriously difficult to treat due to resistance to many traditional antibiotics. However, the antibiotic tigecycline has demonstrated efficacy in vitro and in vivo against Mabs strains varying in drug susceptibility. Tigecycline exhibits instability in aqueous medium, posing delivery challenges, and has caused severe adverse gastrointestinal effects following intravenous administration, requiring treatment discontinuation. To mitigate both of these concerns, inhalation therapies using dry powder aerosols are proposed as an alternative administration route and means of delivery. Tigecycline dry powder formulations were prepared, characterized, and optimized to develop a therapeutic aerosol with low moisture, high dispersibility, and a large fraction of particles in the respirable size range (1–5 μm). The addition of lactose, leucine, and phosphate buffer salts was investigated to achieve additional stability, dispersibility, and tolerability. Preliminary delivery of the dry powders to Mabs-infected mice for 30 min per day over 7 d demonstrated a 0.91-log (87.7%) decrease in lung bacterial burden.

Testing Barley Samples for Potential Insect Infestations with a Conductance Mill

Highlights The conductance mill successfully detected seeds infested with large larvae, over 80% in barley and wheat. Barley seeds, infested with medium larvae, were detected at a lower rate than wheat; ~40% for barley vs. ~65% for wheat. The feed-rate of barley samples was slower than the wheat and the resulting ground barley material contained higher fractions of large particles, over #20 mesh sieve. Abstract. A laboratory mill was developed by Pearson and Brabec (2007) which typically detects 50% to 80% of infested kernels of wheat, brown rice, or popcorn. Barley is another cereal grain of similar size as wheat. Barley is normally sold with its hull attached to the seed, which makes detection of insect infestations more difficult. The objective of this study was to determine the potential of using the conductance mill to detect barley kernels infested by the lesser grain borer, Rhyzopertha dominica (F.), in comparison to detection in wheat. As in previous studies, these experiments found that the conductance mill could detect infested kernels of wheat containing large and medium larvae at a rate of ~90% and ~65%, respectively. For barley, the detection of infested kernels was over ~80% for large larvae and ~40% for medium larvae. Also, we showed that adults that were freely moving throughout the grain mass could also be detected. Approximately ~65% of the adults were detected in wheat while that percentage was reduced to ~35% in barley. The hull on the barley seems to function as an insulator during the conductance measurement and thus reduces detections. Also, the hull seems to affect the feed rate of material through the mill. The feed-rate for wheat was 500 g in 50 s, while the feed-rate for barley was 500 g in ~80 s. Despite these pitfalls, the conductance mill could still be considered as a useful tool with inspecting barley sample, because there was significant detection of insects in the samples and 1000 g sample of barley could be processed in ~4 min. Keywords: Barley, Detection, Rhyzopertha dominica, Sampling, Wheat, X-ray.

Shear thickening in dense bidisperse suspensions

Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from δ=1.4 (nearly monodisperse) to δ=4, and the large particle fraction of the total solid loading with values ζ=0.15, 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction ϕJ with shear stress σ are reported. At a fixed volume fraction ϕ, bidispersity decreases the suspension relative viscosity ηr=ηs/η0, where ηs is the suspension viscosity and η0 is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at ζ≈0.5, but instead decreases with further increase of ζ to 0.85. The second normal stress difference N2 acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosity ηr of bidisperse rate-dependent suspensions can be predicted by a power law linking it to ϕJ, ηr=(1−ϕ/ϕJ)−2 in both low and high shear stress regimes. The agreement between the power law and experimental data from literature demonstrates that the model captures well the effect of particle size distribution, showing that viscosity roughly collapses onto a single master curve when plotted against the reduced volume fraction ϕ/ϕJ.

Gradient Structure of the Transfer Layer in Friction Stir Welding Joints.

Despite a thirty-year history of friction stir welding, some basic aspects still remain unclear. In particular, questions arise about mass transfer and the formation of transfer layers. It is not clear why there are visible boundaries between the layers. The structure of the transfer layer has been studied very little. These issues are not considerably important from the viewpoint of obtaining high-quality welds, but they can help to a better understanding of the welding process. In this paper, the structural evolution in the transfer layer of 2024 aluminum alloy welds produced under various loads and with ultrasonic assistance is discussed. Structural studies revealed a gradient structure in the transfer layer. The grain size, the volume fraction and size of large intermetallic particles decrease towards the center of the layer, while the volume fraction of semi-coherent secondary particles increases. As a result, the microhardness is higher in the center of the transfer layer. A mass transfer mechanism is proposed based on the experimental results: the rotating tool transfers the material back layer by layer during welding; the contacting layers rub against each other and generate heat, due to which the structure at the layer boundary changes. With increasing axial force on the tool, the grain size also increases due to higher heat generation. Ultrasound has almost no effect on the grain structure, but it reduces the volume fraction and size of secondary particles and microhardness.

Sources and processes of water-soluble and water-insoluble organic aerosol in cold season in Beijing, China

Abstract. Water-soluble and water-insoluble organic aerosol (WSOA and WIOA) constitute a large fraction of fine particles in winter in northern China, yet our understanding of their sources and processes are still limited. Here we have a comprehensive characterization of WSOA in cold season in Beijing. Particularly, we present the first mass spectral characterization of WIOA by integrating online and offline organic aerosol measurements from high-resolution aerosol mass spectrometer. Our results showed that WSOA on average accounted for 59 % of the total OA and comprised dominantly secondary OA (SOA, 69 %). The WSOA composition showed significant changes during the transition season from autumn to winter. While the photochemical-related SOA dominated WSOA (51 %) in early November, the oxidized SOA from biomass burning increased substantially from 8 % to 29 % during the heating season. Comparatively, local primary OA dominantly from cooking aerosol contributed the major fraction of WSOA during clean periods. WIOA showed largely different spectral patterns from WSOA which were characterized by prominent hydrocarbon ions series and low oxygen-to-carbon (O/C = 0.19) and organic mass-to-organic carbon (OM/OC = 1.39) ratios. The nighttime WIOA showed less oxidized properties (O/C = 0.16 vs. 0.24) with more pronounced polycyclic aromatic hydrocarbons (PAHs) signals than daytime, indicating the impacts of enhanced coal combustion emissions on WIOA. The evolution process of WSOA and WIOA was further demonstrated by the triangle plot of f44 (fraction of m/z 44 in OA) vs. f43, f44 vs. f60, and the Van Krevelen diagram (H/C vs. O/C). We also found more oxidized WSOA and an increased contribution of SOA in WSOA compared with previous winter studies in Beijing, indicating that the changes in OA composition due to clean air act have affected the sources and properties of WSOA.

Scaling Analysis of Shear Thickening Suspensions

Dense suspensions of particles in viscous liquid often demonstrate the striking phenomenon of abrupt shear thickening, where their viscosity increases strongly with increase of the imposed stress or shear rate. In this work, discrete-particle simulations accounting for short-range hydrodynamic, repulsive, and contact forces are performed to simulate flow of shear thickening bidisperse suspensions, with the packing parameters of large-to-small particle radius ratio δ = 3 and large particle fraction ζ = 0.15, 0.50, and 0.85. The simulations are carried out for volume fractions 0.54 ≤ ϕ ≤ 0.60 and a wide range of shear stresses. The repulsive forces, of magnitude FR, model the effects of surface charge and electric double-layer overlap, and result in shear thinning at small stress, with shear thickening beginning at stresses σ ∼ FRa−2. A crossover scaling analysis used to describe systems with more than one thermodynamic critical point has recently been shown to successfully describe the experimentally-observed shear thickening behavior in suspensions. The scaling theory is tested here on simulated shear thickening data of the bidisperse mixtures, and also on nearly monodisperse suspensions with δ = 1.4 and ζ = 0.50. Presenting the viscosity in terms of a universal crossover scaling function between the frictionless and frictional maximum packing fractions collapses the viscosity for most of the suspensions studied. Two scaling regimes having different exponents are observed. The scaling analysis shows that the second normal stress difference N2 and the particle pressure Π also collapse on their respective curves, with the latter featuring a different exponent from the viscosity and normal stress difference. The influence of the fraction of frictional contacts, one of the parameters of the scaling analysis, and its dependence on the packing parameters are also presented.

Effect of Spectral Variability of Aerosol Optical Properties on Direct Aerosol Radiative Effect

Aerosol optical properties depend on wavelength as well as both mixing ratios and size distributions of components that make up a particular type of aerosol. This study examines impacts on direct aerosol radiative effect (DARE) for desert, clean maritime, and polluted maritime aerosol types over the ocean when their optical properties are determined by various combinations of observations made by active (i.e., lidar) and passive (e.g., shortwave spectrometer) satellite sensors. Spectral optical properties are perturbed by altering mixing ratios of components that define aerosol types with assumptions that components within an aerosol type are fixed and only one aerosol type is present in the atmosphere. When 532 nm depolarization ratio from the lidar is used to identify desert aerosol, the uncertainty in the mean DARE due to spectral optical property variabilities is 10%. When the 532 nm depolarization and lidar ratios are used to identify clean and polluted maritime aerosols, uncertainties in mean DARE are, respectively, 4 and 18%. When scattering optical thicknesses are also known to within ± 3% at four passive imager wavelengths (340 nm, 546 nm, 966 nm, and 1,657 nm), uncertainty in the polluted maritime DARE decreases to 8%. Uncertainties in the instantaneous top-of-atmosphere (TOA) reflected irradiances derived from observed broadband radiances and angular distribution models are also estimated. When TOA irradiances are derived solely from the nadir view, their uncertainties can be reduced if aerosol type can be identified and aerosol type dependence is considered in the radiance to irradiance conversion. This is especially so for aerosols with a large fraction of nonspherical particles, such as desert aerosols.

Coal Structure Characteristics in the Northern Qinshui Basin and Their Discrimination Method Based on the Particle Size of Drilling Cuttings.

Coal structure, including primary coal, cataclastic coal, granulated coal, and mylonitized coal, is one of the key factors controlling coal and gas outburst, and it also determines the efficiency of coalbed methane (CBM) extraction. Therefore, it is significant to identify the characteristics of coal structures and to predict them in advance. In this work, the spatial distribution, mechanical properties, and microscopic morphology of the four coal structures from the No. 3 coal seam of the Xinyuan Mine in the northern part of the Qinshui Basin were investigated through the in situ observation in the roadway, the hardness coefficient (f) test, and the scanning electron microscope analysis. Moreover, the drilling cuttings from the gas pressure releasing holes were sampled and sieved, and then, the correspondence between different coal structures and the particle size of the cuttings was analyzed quantitatively based on the Rosin–Rammler model. The result shows that the spatial distribution of the coal structure has strong heterogeneity in the vertical and lateral directions. The f value decreases successively with the increase in coal structure deformation, which indicate that f can directly characterize the coal structure. Furthermore, the relations between f and drilling cutting average particle size (d0), crushability indicator (n), crushing degree index (λ), and the median diameter (d50) were established. Specifically, the coal deformation degree is positively correlated with the mass fraction of large particles in the cuttings under the same drilling parameters. Overall, as f increases, d0 and d50 decrease, and n and λ increase. However, parameters d0, d50, and λ of granulated coal are inconsistent with other coal structures, and mylonitized coal is inconsistent with other coal structures in n, as a result of the coal structure broken characteristics itself and the difference in the stress state between the coal and the drill bit during the rock breaking process. Ultimately, the coal structures determined by the surface CBM well logging curve and the cuttings particle size method were compared, and they have a high degree of coincidence in the distinction between primary coal and tectonic coal.

Effect of dispersion particles and precipitates on the corrosion properties of ODS-Cu, Cu-Cr-Zr and Cu-Cr alloys in Na2SO4 solutions

• Corrosion resistance of Cu alloys in a 0.1 M Na 2 SO 4 solution was evaluated. • In ODS-Cu, oxide particles degraded protective performance of the passivation film. • Precipitation hardened Cu alloys showed good corrosion resistance. • Cu-Cr-Zr alloy showed corrosion due to the coarse columnar Cr precipitates. Precipitation-hardened Cu-Cr-Zr alloy is proposed as a heat sink material for various components of the ITER (blanket first wall, divertor, electrical straps and others) owing to its high strength, high conductivity and superior resistance against neutron irradiation. ODS-Cu (Oxide Dispersion Strengthened Copper) is also selected as a candidate material. Corrosion properties of alumina-dispersed copper alloys (GlidCop® CuAl15, CuAl25), aevaluated by electrochemical methods in 0.1 M and 0.01 M sodium sulfate (Na 2 SO 4 ) solutions. In open circuit potential (OCP) measurement in 0.1 M Na 2 SO 4 solution, the potential of all alloys decreased immediately after immersion and then gradually decreased. CuAl15 showed good corrosion resistance in the OCP measurement with little potential drop. In the polarization curve measurements, a difference was observed for each material in the cathode region. The corrosion current densities tended to be higher for CuAl25 and Cu-Cr-Zr, and the corrosion potential was also low in both solutions. In these alloys, the surface observation after the polarization curve measurements showed variations in the thickness of the Cu 2 O passivation film, and there were large areas where the film was thought to be thin. In Cu-Cr-Zr, coarse columnar Cr precipitates and segregation of Zr at the precipitate/matrix interface are thought to deteriorate corrosion resistance. In the case of CuAl25, it is suggested that dissolution of the passivation film is enhanced due to large volume fraction of alumina particles.

Strengthening mechanisms and tensile properties of 20Cr2Mn2Mo processed by laser shock peening and vacuum carbonitriding

The effects of laser shock peening and vacuum carbonitriding on strength and plasticity of 20Cr2Mn2Mo were investigated. Uniaxial tension tests were carried out and the microstructures were analyzed by optical microscope, scanning electron microscope, electron backscatter diffraction, and transmission electron microscope. The phase composition was characterized by X-ray diffraction. The results revealed that the yield strength and ultimate tensile strength of samples were increased by 10.63% and 4.15%, respectively, after compound treatment due to the formation of large volume fraction of grain boundaries, high-density dislocations, and second-phase particles. However, the plasticity was only decreased by 0.99%, which was benefited from gradient structures induced by laser shock peening. The improvement of strength was mainly attributed to Orowan strengthening and dislocation strengthening. The grain refinement had little influence on the improvement of strength.

Phosphatidylcholine (18:0/20:4), a potential biomarker to predict ethionamide-induced hepatic steatosis in rats.

Ethionamide (ETH), a second‐line drug for multidrug‐resistant tuberculosis, is known to cause hepatic steatosis in rats and humans. To investigate predictive biomarkers for ETH‐induced steatosis, we performed lipidomics analysis using plasma and liver samples collected from rats treated orally with ETH at 30 and 100 mg/kg for 14 days. The ETH‐treated rats developed hepatic steatosis with Oil Red O staining‐positive vacuolation in the centrilobular hepatocytes accompanied by increased hepatic contents of triglycerides (TG) and decreased plasma TG and total cholesterol levels. A multivariate analysis for lipid profiles revealed differences in each of the 35 lipid species in the plasma and liver between the control and the ETH‐treated rats. Of those lipids, phosphatidylcholine (PC) (18:0/20:4) decreased dose‐dependently in both the plasma and liver. Moreover, serum TG‐rich very low‐density lipoprotein (VLDL) levels, especially the large particle fraction of VLDL composed of PC containing arachidonic acid (20:4) involved in hepatic secretion of TG, were decreased dose‐dependently. In conclusion, the decreased PC (18:0/20:4) in the liver, possibly leading to suppression of hepatic TG secretion, was considered to be involved in the pathogenesis of the ETH‐induced hepatic steatosis. Therefore, plasma PC (18:0/20:4) levels are proposed as mechanism‐related biomarkers for ETH‐induced hepatic steatosis.

Development and evolution of an anomalous Asian dust event across Europe in March 2020

Abstract. This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over southern Europe in late March 2020 (27–30 March 2020). This event was associated with an anomalous circulation pattern leading to several days of PM10 (particulate matter with an aerodynamic diameter less than 10 µm) exceedances in connection with a dust source located in central Asia; this is a rare source of dust for Europe, which is more frequently affected by dust outbreaks from the Sahara Desert. The synoptic meteorological configuration was analyzed in detail, and the aerosol evolution during the transit of the dust plume over northern Italy was assessed at high time resolution by means of optical particle counting at three stations, namely Bologna, Trieste, and Mt. Cimone, allowing for the revelation of the transport timing among the three locations. Back-trajectory analyses supported by Copernicus Atmosphere Monitoring Service (CAMS) maps allowed for the location of the mineral dust source area in the Aralkum region. Therefore, the event was analyzed by observing the particle number size distribution with the support of chemical composition analysis. It is shown that the PM10 exceedance recorded is associated with a large fraction of coarse particles, which is in agreement with mineral dust properties. Both the in situ number size distribution and the vertical distribution of the dust plume were cross-checked using lidar ceilometer and aerosol optical depth (AOD) data from two nearby stations and showed that the dust plume (in contrast to those originating from the Sahara Desert) traveled close to the ground (up to a height of about 2 km). The limited mixing layer height caused by high concentrations of absorbing and scattering aerosols caused the mixing of mineral dust with other locally produced ambient aerosols, thereby potentially increasing its morbidity effects.

Probing criticality with deep learning in relativistic heavy-ion collisions

Systems with different interactions could develop the same critical behavior due to the underlying symmetry and universality. Using this principle of universality, we can embed critical correlations modeled on the 3D Ising model into the simulated data of heavy-ion collisions, hiding weak signals of a few inter-particle correlations within a large particle cloud. Employing a point cloud network with dynamical edge convolution, we are able to identify events with critical fluctuations through supervised learning, and pick out a large fraction of signal particles used for decision-making in each single event.

Analysis of grinding in a spiral jet mill. Part 2: Semi-batch grinding

The breakage and classification of particles in a spiral air jet mill, operated in a semi-batch mode, is studied for varying operating conditions. The particle size distributions of the product leaving the mill and the material inside the mill are measured, along with the mass in the mill. The median particle size of the product is found to be unchanged with inlet jet pressure at about 5 μm but increases with holdup to about 7.5 μm. At low pressures and high holdups, the classification is imperfect and a significant fraction of large particles, in the size range 150–350 μm, exit in the product. The mass flux from the mill increases with both pressure and holdup and an empirical expression is given to calculate it. A population balance model is presented, which predicts size distributions, mean sizes and mass flux from the mill, in agreement with the measurements.

Organic Coating Reduces Hygroscopic Growth of Phase-Separated Aerosol Particles

A large fraction of secondary aerosol particles are liquid-liquid phase-separated with an organic shell and an inorganic core. This has the potential to regulate the hygroscopicity of such particles, with significant implications for their optical properties, reactivity, and lifetime. However, it is unclear how this phase separation affects the hygroscopic growth of the particles. Here, we showed a large variation in hygroscopic growth (e.g., 1.14-1.32 under a relative humidity (RH) of 90%) of particles from the forest and urban atmosphere, which had different average core-shell ratios. For this reason, a controlled laboratory experiment further quantifies the impact of the organic shell on particle growth with different RH values. Laboratory experiments demonstrated that (NH4)2SO4 particles with thicker secondary organic shells have a lower growth factor at an RH below 94%. Organic shells started to deliquesce first (RH > 50%) and the phase changes of sulfate cores from solid to liquid took place at an RH higher than 80% as deliquescence relative humidity of pure (NH4)2SO4. Our study provides the first direct evidence on an individual particle basis that hygroscopic growth behavior of phase-separated particles is dependent on the thickness of organic shells, highlighting the importance of organic coating in water uptake and possible heterogeneous reactions of the phase-separated particles.

Nutritional composition and physicochemical properties of oat flour sieving fractions with different particle size

Nutritional constituents, hydration, pasting, and thermal properties of oat flour sieve fractions (74–180 μm) and the relationship between composition and characteristics were studied. Starch constituents, protein components (except for albumins), and saturated fatty acids (SFA) were mostly distributed in small particle fractions, while total protein, albumin, dietary fiber (DF), lipids, and unsaturated fatty acids (UFA) were abundant in large particle fractions. Amino acids (except for Tyr and Gly) of group Ⅰ, Ⅱ, and Ⅲ were significantly lacking in S2 (150–180 μm), and Cys decreased from 2.51% to 1.50% with the decrease in sieving particle sizes. The largest particles showed the highest water solubility index (WSI, 9.90%), the medium particles (100–132 μm) exhibited the highest pasting viscosities (final viscosity of 4148 cP), and the smallest particles had the maximum gelatinization enthalpy (ΔH, 3.2 J/g). Correlation analysis demonstrated that except for the basic components, Glu, Cys, Iso, Phe, C16:0, C18:0, and C18:2n6c also significantly affected the WSI and pasting properties of oat flour, while amylose, Gly, Ala, Val, Met, and C20:1 were highly correlated with thermal properties. The results are useful for oat processing and the development of oat-based products with specific particle size range to achieve desirable characteristics.

Properties of a powder metallurgy low-alloy steel with varying fractions of large iron particles

ABSTRACT Interiors of coarse iron particles in blends used in powder metallurgy may not be adequately alloyed during sintering. Relatively low concentrations of alloying elements reduce the hardenability of these regions, which may not transform to martensite during quenching. Since an actual microstructure (martensite, pores and pearlite) may differ from the desired microstructure (martensite and voids), it is reasonable to speculate that large and relatively soft pearlitic inclusions may worsen mechanical properties. This conjecture was tested, and it was experimentally found that unless the fraction of coarse particles exceeded a certain threshold, the properties of a medium-density powder metallurgy steel did not vitiate significantly. It also was observed that when the fraction of large particles dropped below a certain limit, apparent density, compressibility and flowability degraded to an extent rendering the corresponding mixtures unusable.A contradiction between a visual perception and a verdict of a statistical analysis is commented upon.

External heat-exchange in a quasi-bidisperse granular fluidized bed

This paper presents the results of an experimental study of the external heat-exchange with a tube bundle in a bidisperse fluidized bed with marked bimodality of particle size distribution. The dependence of the maximum heat-transfer coefficient on the rate of air filtration was determined. The influence of the mass fraction of large particles on the heat-transfer coefficient in a mixture has been established. An interpolation dependence for calculating the optimal filtration rate of the investigated mixtures has been obtained. It is recommended to use the average surface diameter of the polydisperse particles mixture as the equivalent diameter when calculating the heat-exchange. A method for calculating the maximum heat-transfer coefficient and the optimal filtration rate for a quasi-bidisperse fluidized bed has been developed. The method is based on the use of heat transfer coefficients and optimal filtration rates of individual components of the bidisperse mixture. The equations for calculating the maximum heat-transfer coefficient and the optimal filtration rate in the bidisperse mixture has been obtained.