Effects of relative humidity and particle and surface properties on particle resuspension rates

Wind tunnel experiments examined the coupled effects of relative humidity (RH) and surface and particle properties on aerodynamically induced resuspension. Hydrophilic glass spheres and hydrophobic polyethylene spheres ～20 μm in diameter, with nanoscale surface features, were resuspended from hydrophilic glass, hydrophobic chemical agent resistant coating (CARC), and gold surfaces. Roughness of the glass and gold surfaces was on the nanoscale, whereas CARC surfaces had microscale roughness. Different particle–surface combinations yielded van der Waals interactions that varied by a factor of 4, but these differences had a relatively minor effect on resuspension. Wind tunnel RH was varied between 7% and 78%. Overall, RH affected the resuspension of hydrophilic particles on hydrophilic surfaces most strongly and that of hydrophobic particles on hydrophobic surfaces the least. For each particle–surface combination there was a threshold RH value below which resuspension rates were essentially constant and in good agreement with a dimensionless model of particle resuspension.

Copyright © 2016 American Association for Aerosol Research     

Influence of carbon content and particle dispersion on radiation properties of coal chars

Thermal radiation dominates the heat transfer in coal gasification or combustion furnaces operated at high temperatures. This study is to evaluate the radiation properties of coal char or ash particles, which are necessary to predict the behavior of heat transfer of a multiphase flow in the furnace. The monochromatic extinction of the sample particles dispersed in liquid paraffin wax was measured by the FT-IR spectroscopic analysis at a room temperature. Carbon containing in char particles influences significantly extinction efficiency as a radiation property. The normalized extinction efficiency was correlated by an exponential function of carbon content if the sample was prepared appropriately although the spectra depended on the preparation method of the samples.     

Numerical methods for retrieving aerosol size distributions from optical measurements of solar radiation

Retrieving aerosol size distributions from ground measurements is an ill-posed problem. Several methods have been developed to “regularize” it, giving a stable approximation of its solution. The aim of this paper is to review the techniques usually adopted and present some new approaches. The case of solutions retrieved both in their parametric and non-parametric form is considered. For all the considered methods the problem of choosing an optimal level of regularization is also discussed. Finally, numerical results comparing some inversion techniques in a real case are presented.     

水泥粒度分布对其性能的影响

0引言 水泥的粒度分布是其重要的物理指标之一,对水泥的性能有着极其重要的影响。特别是水泥胶砂强度检验方法改用ISO法后,多数水泥企业采取提高粉磨细度的方法,使水泥强度达到标准要求。     

Effects of particle type on thermal and mechanical properties of polyoxymethylene nanocomposites

The effects of particle size of titanium dioxide (TiO₂) on mechanical, thermal, and morphological properties of pure polyoxymethylene (POM) and POM/TiO₂ nanocomposites were investigated and compared with the results for nanoparticle ZnO in the same matrix, reported in a previous paper. POM/TiO₂ nanocomposites with varying concentration of TiO₂ were prepared by the melt mixing technique in a twin screw extruder, the same method that used for blending the homogeneous ZnO nanocomposites. The dispersion of TiO₂ particles in POM nanocomposites was studied by scanning electron microscopy (SEM). The agglomeration, as observed by the mechanical properties of TiO₂ particles in the polymer matrix, increased with increasing TiO₂ content, a result not found for ZnO even at lower particle sizes. Increasing the filler content of POM/TD32.4 and POM/TD130 (130 nm) nanocomposites resulted in a decrease in tensile strength. The Young modulus, stress at break and impact strength of TiO₂ nanocomposite did not improve with increasing filler contents, in opposition to the better agglomeration conditions of ZnO nanocomposite even at lower particle sizes. Because of agglomeration, the POM/TD32.4 nanocomposites had lower mechanical properties and lower degradation temperature than the POM/TD130 ones. The sizes of nanoparticles determined the agglomeration, but however, the agglomeration also depended on the type of nanoparticles, even when using the same matrix (POM) and the same mixing method. TiO₂ nanoparticles were more difficult to mix and were more agglomerated in the POM matrix as compared to ZnO nanoparticles, regardless of the size of the nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modelling the effect of particle size on dust explosions

The recent concept of inherent safety uses the properties of a material or process to eliminate or reduce the risk thus removing or minimizing the hazard at the source as opposed to accept the hazard and looking to mitigate the effects. In this framework the control of particle size in dust explosion prevention and mitigation is recognized as a major inherent safety methodology. Indeed, the increase of particle size may allow significant reduction of particle reaction rate eventually reducing the risk.In this paper a novel model is developed to quantify the effect of particle size on dust reactivity in an explosion phenomenon. The model takes into account all of the steps involved in a dust explosion: internal and external heating, devolatilization reaction and volatiles combustion. Varying the dust size can establish different regimes depending on the values of the characteristic time of each step and of several dimensionless numbers (Damköhler number, Da; Biot number, Bi; thermal Thiele number, Th). Results from the model are reported in terms of the deflagration index (K_St) as a function of dust diameter in all regimes and at varying Da, Th and Bi. Comparison with experimental data from polyethylene explosion tests shows promising results. Finally, the results of the model are presented in the form of a dust explosion regime diagram, which is helpful to make a draft evaluation of the role of dust size on explosion behavior and severity.     

Effects of radiation type and dose on the properties of selected polymers

Using ionizing radiation to sterilize medical and health care products is a widespread and well established approach, as products can be treated in their final shipping container without any residuals. During irradiation, the product materials will undergo some changes due to the absorbed energy, which have to be assessed during product qualification in order to specify a maximum allowable dose for the product. However, there is a lack of a systematic approach studying polymers in regard to dose ranges encountered and all types of ionizing radiation. Therefore, the aim of this work was to investigate the influence of radiation dose and source on the resulting properties of various polymers, which were already brought into final shape via injection molding, and to compare these effects found in the mechanical and rheological properties as well as their appearance. We found, that the mechanical properties of most investigated polymers are not influenced, except for polypropylene, but that yellowing was a pronounced effect in all the cases. The differences in polymer properties due to the radiation sources are small, only some materials exhibit more degradation by gamma irradiation due to the lower dose rate applied in comparison to x-ray and e-beam irradiation.     

Effects of zinc oxide particle shape on properties of a prevulcanized latex

Iranian Polymer Journal - From a zinc precursor of zinc nitrate hexahydrate and a precipitating agent of sodium hydroxide, zinc oxide (ZnO) was hydrothermally synthesized. Using different...     

不同粒度金刚石微粉对PCD微结构与性能的影响

在烧结温度为1550℃、合成压力为5.7士0.1GPa、烧结时间180s时,采用国产六面顶压机进行了微米级聚晶金刚石的合成试验,研究不同粒度(10μm、5μm、2μm,1μm)的金刚石微粉对合成的PCD微结构与性能的影响.分别采用了SME、XRD和Raman对合成的PCD样品的微结构进行表征,并测试其耐磨性和耐热性.结果表明,PCD试样中均形成了D-D结合,且当金刚石原料粒度为2μm时,样品中存在石墨;随着金刚石原料粒度的减小,Co元素的扩散更加均匀,合成PCD样品的磨耗比越小,耐热温度越低.     

Effects of radiation on mechanical properties of polybutadiene/polystyrene blends

Blends containing 3 wt % low molecular weight polybutadiene (PB) in a polystyrene (PS) matrix were prepared via a precipitation technique that yielded spherical, submicron pools of PB. Tensile specimens made from these blends were then irradiated with high energy electrons in air at dose levels from 0 to 70 Mrads. The blends, which previously showed high levels of toughness approaching that of high impact PS, lost all enhanced toughness when irradiated above 10 Mrads. Analysis of pure PS specimens irradiated over the dose range from 0 to 45 Mrads showed no appreciable dependence of mechanical behavior on dose level. Molecular weight studies of the polybutadiene demonstrated only a very modest increase in molecular weight in the dose range studied here; therefore, reduced mobility of the PB in the blends was not the reason for the dramatic drop in toughness with radiation dose. It was concluded that radiation-induced scission of the PS near the surface of the blends resulted in a significant local reduction in molecular weight. This degraded layer led to premature craze failure and hence a low level of toughness. It was demonstrated that the absence of oxygen during the irradiation process or the removal of the scissioned surface layer via mechanical abrasion resulted in a recovery of toughness. © 1995 John Wiley & Sons, Inc.     

Studies on the preparation and properties of particle boards made from bagasse and PVC. I: Effects of operating conditions

Under study were the mechanical properties of particle boards comprised of ground sugarcane bagasse, PVC, and poly{methylene (polyphenyl isocyanate)} [PMPPIC]. The effects of different parameters, e.g. mixing temperature, molding conditions - platen temperature, time and pressure, particle size of bagasse, concentration of PVC and PMPPIC, as well as dilution of PMPPIC, on the mechanical properties of the resulting particle boards were also investigated. In general, the properties of particle boards change with the variation of mixing and molding conditions. A mixing temperature of 175°C and molding conditions [platen temperature, 190°C; time, 10 min; and pressure, 3.8 MPa] were believed to be optimal conditions of compounding particle boards. Both the mechanical properties and the density of particle boards of bagasse with a mesh size of 60, improved up to 20 weight % of PVC and 10 weight % of PMPPIC.     

Effects of particle sizes and shapes of zinc metal on the properties of anticorrosive coatings

The paper deals with a study of the zinc particle sizes and shape effects on the anticorrosive coating properties. As a binder the epoxyester resin is used. The zinc particle size and shape effects are discussed from the mechanical coating properties, film permeabilities to water vapor and above all the pigment anticorrosion protection efficiency points of view. The connection between the spherical particle sizes and the coating anticorrosive efficiency was found. The smaller particle sizes mean better anticorrosive coating properties. The lamellar zinc particles exhibit the highest anticorrosion efficiency at a concentration around 20 vol.%.     

硼矿粉尘物化性质研究

对我国辽东地区硼镁矿加工过程中产生的硼矿粉尘的化学与矿物成分及其粒度分布、真密度、粘附性、浸润性、吸湿性等物理性质进行了全面的分析测定,并与燃煤飞灰等进行了对比分析,在此基础上对焙烧后硼矿粉尘的有效收尘提出了建议。     

Effects of exponentially decaying and growing concentrations on particle size distribution from a scanning mobility particle sizer

Abstract

A scanning mobility particle sizer (SMPS) is one of the most widely used instruments to obtain size distribution for atmospheric particles. In an SMPS measurement, a voltage scanning process on a differential mobility analyzer is required, and it typically takes 30?s to 120?s to obtain one entire size distribution. A size distribution obtained by an SMPS measurement might have significant deviations from actual values due to the scanning process when the measured particle concentrations change over time. In this study, we introduce an analytical approach for estimating particle size distribution under exponentially decaying and growing particle concentrations. The analytical SMPS results are validated by performing experiments using exponentially decaying particle concentrations under the same conditions. Furthermore, the effects of a decay parameter, initial size distribution, and scan time are evaluated, and the deviations from actual (real or true) size distributions obtained by an exact solution are analyzed. Geometric mean diameters and standard deviations of the size distributions from SMPS results increase or decrease with exponentially decaying or growing concentrations, respectively, and total concentrations estimated by the analytical SMPS approach are significantly underestimated or overestimated compared to real total concentrations. While SMPS measurements have been widely employed in various applications such as atmospheric particle characterization in highly variable particle concentrations versus time, very few studies on the influence of changing concentrations on SMPS measurements have been conducted. Therefore, the introduced analytical approach and findings provide valuable insight into the importance of accurate SMPS measurements with changing particle concentrations.

Copyright © 2020 American Association for Aerosol Research     

板状刚玉粒度和加入量对高铁镁砂-烧结刚玉复合材料性能的影响

以粒度为3~1、≤1、≤0.088 mm的高铁镁砂,≤0.088 mm的高纯镁砂为主要原料,分别研究了不同加入量(质量分数分别为3%、6%、9%、12%、15%)和不同粒度(3~2、2~1、≤1 mm)的烧结板状刚玉对试样性能的影响,并分析其物相组成和显微结构。结果表明:当烧结板状刚玉细粉加入量为6%(w)时,试样的显气孔率16%,体积密度2.99 g·cm-3,常温耐压强度80.9 MPa,荷重软化温度1 609℃,抗热震性达到20次,综合性能最好;改变加入刚玉的粒度,可以控制刚玉反应速度,同时影响高铁镁砂中Fe的扩散;铁在方镁石中固溶度大,高铁镁砂的引入可以起到方镁石改性的作用;由于铁氧化物的存在,高铁镁砂-刚玉体系在高温下易于促进镁铝尖晶石和铁铝尖晶石固溶体的形成。     

Effects of particle shape and size on devolatilization of biomass particle

Experimental and theoretical investigations indicate particle shape and size influence biomass particle dynamics, including drying, heating rate, and reaction rate. Experimental samples include disc/flake-like, cylindrical/cylinder-like, and equant (nearly spherical) shapes of wood particles with similar particle masses and volumes but different surface areas. Small samples (320 μm) passed through a laboratory entrained-flow reactor in a nitrogen atmosphere and a maximum reactor wall temperature of 1600 K. Large samples were suspended in the center of a single-particle reactor. Experimental data indicate that equant particles react more slowly than the other shapes, with the difference becoming more significant as particle mass or aspect ratio increases and reaching a factor of two or more for particles with sizes over 10 mm. A one-dimensional, time-dependent particle model simulates the rapid pyrolysis process of particles with different shapes. The model characterizes particles in three basic shapes (sphere, cylinder, and flat plate). With the particle geometric information (particle aspect ratio, volume, and surface area) included, this model simulates the devolatilization process of biomass particles of any shape. Model simulations of the three shapes show satisfactory agreement with the experimental data. Model predictions show that both particle shape and size affect the product yield distribution. Near-spherical particles exhibit lower volatile and higher tar yields relative to aspherical particles with the same mass under similar conditions. Volatile yields decrease with increasing particle size for particles of all shapes. Assuming spherical or isothermal conditions for biomass particles leads to large errors at most biomass particle sizes of practical interest.     

Impacts of wind velocity on sand and dust deposition during dust storm as inferred from a series of observations in the northeastern Qinghai-Tibetan Plateau, China

The monthly sand and dust deposition flux and modern dust storms were monitored in the northern Qaidam Basin of the Qinghai-Tibetan Plateau. The monthly sand and dust flux varied between 0.57 and 18.12 mg cm^− 2 month^− 1 from June 2003 to April 2005, and was well correlated with the monthly extreme wind velocity (V_extr) (r² = 0.60, n = 23). Sand and dust was mainly deposited in spring and early summer in the study area. The weight of settled sand and dust collected during dust storms exhibited a positive correlation with the mean 10-min wind velocity (r² = 0.60, n = 16) during the dust storms. For the typical dust storms, the weight and flux of settled sand and dust will linearly increase with the increasing wind strength and fluctuation amplitude of wind velocities. The coarse fraction (> 63 μm) also increases with them, in contrast, the fine-grained fraction (< 63 μm) decreases. It is plausible to assume that most of the fine-grained dust particles are lifted and transported far from the region under dust storm conditions, especially under the stronger and more variable wind conditions. The results demonstrate that the wind regime (strength and variability) is a key control on the sand and dust deposition during dust storm; dust can be emitted from the Qaidam Basin as one of dust source areas in China.     

Wind tunnel study and numerical simulation of dust particle resuspension from indoor surfaces in turbulent flows

Particle resuspension from flooring is an important source of air pollution in the indoor environment. In this work, resuspension of monolayer, polydisperse, irregularly shaped dust particles from various types of floorings was studied via a series of wind tunnel experiments. The range of free-stream velocity needed for resuspension of dust particles was evaluated as a function of particle size and material of particles and surfaces. In addition, a Monte Carlo simulation for predicting the resuspension of dust particles was developed. The resuspension model took into account the effects of particle irregularity, particle surface roughness, and flow characteristics. The dust particle resuspension from different floorings for several particle sizes was evaluated. The model predictions for resuspension fractions were compared with the experimental data and good agreement was observed. The study provided information on the role of airflow velocity on irregular dust particle resuspension from common floorings.     

乳化粒子大小对烷基糖苷乳化体系性能的影响

通过不同的制备工艺制备出不同乳化粒子大小的乳状液,研究了乳化粒子大小对烷基糖苷乳化体系液晶形成、离心稳定性、流变性能以及高温稳定性的影响。结果表明,随着乳化粒子尺寸的减小,体系的液晶结构越来越不明显,离心稳定性逐渐增强,存储状态下的黏度逐渐升高,高温稳定性越来越好。