基于DEM模拟液固流化床粒度级配对颗粒流动特性的影响

采用离散单元方法(DEM)对三维液固流化床进行数值模拟。考虑润滑力的作用,对比二元混合、窄级配和宽级配3种粒度级配方式对颗粒分布、速度、温度波动和混合程度的影响。分析结果表明:大颗粒有向床层下部运动的趋势,而小颗粒则有向床层上部聚集的趋势;与窄级配相比,二元混合和宽级配的轴向速度在不同高度上差异较明显,且颗粒温度波动也较小,颗粒更加容易出现偏析;2种颗粒粒径差距越大,越容易分离,而粒径越接近,越难分离,混合程度越好。     

Influence of particle size and particle size distribution on MICA filled nylon 6 composite

Particulate reinforced thermoplastic composites are designed to improve the properties and to lower the overall cost of engineering plastics. In this study the effects of particle size and particle size distribution on the properties of mica filled nylon-6 was investigated. Composites of nylon-6 with varying concentrations (viz. 5 to 40 wt%) of mica were prepared by twin screw extrusion. The composite showed improved mechanical, thermal as well dielectric properties on addition of filler.     

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.     

Mechanical,thermal and friction properties of rice bran carbon/nitrile rubber composites: Influence of particle size and loading

Four types of rice bran carbon (RBC) with different particle sizes were compounded with nitrile rubber (NBR) in a laboratory size two-roll miller. The obtained RBC/NBR composites were characterized using Field Emission Scanning Electron Microscopy (FE-SEM) and tensile tests. Experimental results showed the RBC with lowest particle size exhibited best dispersion state and superior reinforcement ability. Then, we investigated the influence of RBC loading on the morphology, vulcanization characteristics, mechanical, thermal and friction properties of NBR composites. Experimental results indicated that the incorporation of RBC resulted in higher torque values, longer curing time, but shorter scorch time. The addition of RBC remarkably improved the mechanical properties of NBR composites. However, when the RBC loading exceeded 60 phr, the improvement in the tensile strength was not significant due to the poor dispersion state and weak interfacial bonding between RBC and NBR matrix, which were confirmed by Mooney–Rivlin stress–strain curves and FE-SEM observations. The thermal stabilities of RBC/NBR composites were largely improved as the loading of RBC increased. Friction tests revealed that under a certain concentration, the presence of RBC increased the static friction coefficient of NBR composites, suggesting the anti-skid role of RBC in the NBR composites. The overall results demonstrated that RBC could act as ideal filler for NBR composites providing both economic and environmental advantages.     

The effects of particle size, density and shape on margination of nanoparticles in microcirculation

In the recent past, remarkable advances in nanotechnology have generated nanoparticles of different shapes and sizes, which have been shown to exhibit unique properties suitable for biomedical applications such as cancer therapy and imaging. Obviously, all nanoparticles are not made equal. This becomes evident when we consider their transport behavior under blood flow in microcirculation. In this work, we evaluated the effect of critical physical characteristics such as the particle shape, size and density on a nanoparticle's tendency to marginate towards the vessel walls in microcirculation using an in vitro model. The wall deposition of nanoparticles was tested in a fibronectin-coated microfluidic channel at a physiologically relevant flow rate. Different classes of nanoparticles (liposome, metal particles) of different sizes (60-130 nm), densities (1-19 g ml(-1)) and shapes (sphere, rod) displayed significantly different deposition as a result of different margination rates. The smaller-sized and the oblate-shaped particles displayed a favorable behavior as indicated by their higher margination rates. Notably, the particle density showed an even more essential role, as it was observed that the lighter particles marginated significantly more. Since nanoparticles must escape the flow in order to approach the vascular bed and subsequently extravascular components for meaningful interactions, the design of nanoparticles strongly affects their margination, a key factor for their ultimate in vivo effectiveness.     

Simultaneous measurements of individual ambient particle size, composition, effective density, and hygroscopicity

The interaction between atmospheric particles and water vapor impacts directly and significantly the effect that these particles exert on the atmosphere. The hygroscopicity of individual particles, which is a quantitative measure of their response to changes in relative humidity, is related to their internal compositions. To properly include atmospheric aerosols in any model requires knowledge of the relationship between particle size, composition, and hygroscopicity. Here we demonstrate the capability to conduct in real time the simultaneous measurements of individual ambient particle hygroscopic growth factors, densities, and compositions using a humidified tandem differential mobility analyzer that is coupled to an ultrasensitive single-particle mass spectrometer. We use as an example the class of particles that are composed of sulfate mixed with oxygenated organics to illustrate how multidimensional single-particle characterization can be extended to yield in addition quantitative information about the composition of individual particles. We show that the data provide the relative concentrations of organics and sulfates, the density of the two fractions, and particle hygroscopicity.     

Influence of heat input/multiple passes and post weld heat treatment on strength/electrochemical characteristics of friction stir weld joint

The V-95 and D-19 precipitation hardened Russian aluminum alloys are widely used in the Russian aircraft industry and these alloys are not weldable by conventional fusion weld techniques. This paper intends to evaluate the effect of spindle and weld speed on joint strength characteristics of a single pass (SP) and double pass (DP) friction stir lap weld through a common heat index and to analyze the effect of retrogression and re-ageing treatment (RRA) on joint strength and corrosion characteristics. The strength characteristics were analyzed by welding and shear testing of specimens and corrosion susceptibility of joint through immersion in EXCO solution as per ASTM G34. The trials revealed that the joint strength of the welded alloy is inversely proportional to the heat index and the DP weld provided significantly higher strength than an SP weld. The heat affected zone of the joint was found most sensitized to corrosion. The RRA treatment was found to improve the strength of the joints welded with higher heat input while it slightly degraded the joint strength for low heat input welds. The corrosion characteristics of the welded joint is also significantly improved by the post weld RRA treatment.     

Influence of stream vorticity on friction and heat exchange in application to the case of a supersonic jet impinging on an obstacle

The flow in the neighborhood of the stagnation point of a stationary plane stream of viscous incompressible fluid with harmonic components superposed on the velocity components is investigated. Such a flow corresponds to a stream containing periodic eddies perpendicular to the flow plane. The results of the investigation can be applied to estimate thermal fluxes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 4, pp. 633–638, October 1969.     

粒径对煤泥絮团特性及沉降效果的影响

为研究添加絮凝剂后不同粒径原煤形成的絮团微观特性和沉降效果,利用光学显微镜观察煤泥絮团结构,使用Image J软件提取面积与周长数值,计算絮团大小、分形维数值、密度和强度值;添加不同剂量的絮凝剂,以沉降速度与上清液透射比为因素考查絮团的絮凝沉降效果。结果表明:每吨干煤泥絮凝剂用量为200 g时,粒径为0.250~0.125 mm煤粒沉降速度和上清液透射比达最大值,分别为78.40 cm/min和83.6%,絮团粒径最大值为1.380 mm,强度最大值为280.01×10-19 N,密度最小值为1 033.95 kg/m3,分形维数最小值为1.361。     

Heat exchange and friction in a subsonic vapor flux of high-temperature heat pipes

The influence of forced vapor convection on heat transport in heat pipes is examined on the basis of the solution of the energy and motion equations. It is shown that radial heat flux due to molecular heat conduction of the vapor in the evaporator is negligible.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 3, pp. 397–402, March, 1976.     

Study of heat exchange between a model particle and a fluidized bed

An experimental study is made of heat exchange between an unsecured model particle and a fluidized bed. The test data is generalized with a dimensionless relation.     

Influence of dispersant size on rheology of non-aqueous ceramic particle suspensions

The surface of alumina, which is hydrophilic in general, was made hydrophobic either by adsorption of polymer (phys-adsorption) or by an alkylation reaction with alcohol (chem-adsorption) to enable dispersion in dodecane. Hypermer A70 (8.2 nm) was used as the polymer and 1-octanol (1.2 nm), 1-decanol (1.5 nm) and 1-hexadecanol (2.5 nm) were used as the alcohol (values in brackets are the approximate thickness of the steric barrier). Rheological measurements of ceramic suspensions indicate that it is possible to achieve a high solid loading (50 vol.%) with relatively low viscosity (0.25 Pa s at 100 s^?1, the typical shear rate for pumping of liquids in pipes) as long as the stabilising molecule is large enough. The observed rheological behaviour fitted the Quemada viscosity model quite well when excluded volume effects were taken into account. Addition of 2.8 wt.% of Hypermer A70 with respect to weight of alumina was enough to stabilise the particles.     

Empirical correlations for heat transfer and flow friction characteristics of herringbone wavy fin-and-tube heat exchangers

This study presents an empirical correlation describing the airside performance of herringbone wavy fin pattern. A total of 61 samples containing approximately 570 data points are used in the regression analysis. The proposed heat transfer correlation can describe 91% of the test data within ±15% with a mean deviation of 6.98% while the proposed friction correlation can describe 85% of the database within ±15% with a mean deviation of 8.82%.     

Selective particle size analysis in binary submicron particle mixtures using density dependent differential sedimentation

Particle size characterization of heterogeneous mixtures is a challenging task, as it is not feasible to assign the measured signals to the individual components. Within this framework, the study proposes a method that applies the working principle of differential centrifugal sedimentation (DCS) in order to simultaneously separate and measure the denser component within a binary material mixture of submicron particles. The method was validated using a model system consisting of polyvinyl chloride (PVC) and diamond particles in a size range of 0.5 – 1.5 µm. The results proved that by applying a proper density gradient fluid, the diamond particles can be selectively analyzed by hindering the sedimentation of the lighter PVC component. Furthermore, a very promising application could be found with respect to wet fine grinding processes in stirred media mills. In fact, the approach was utilized to individually determine the particle size distribution of the grinding media wear within an ultrafine organic product. Despite the low quantity of wear particles, it was possible to separate them from the organic product under appropriate density conditions. The size distributions of both the wear and the product particles were validated with SEM images, confirming the feasibility of the method.     

热处理对刨花板力学性质的影响

为了探索提高刨花板力学性质的途径，采用全因素试验方法，对12mm刨花板进行热处理研究。结果表明：在热处理过程中，处理时间对刨花板的静曲强度（MOR）和弹性模量（MOE）影响比较明显，而对内结合强度（IB）影响比较弱；处理温度对刨花板的内结合强度影响显著，而对静曲强度和弹性模量影响不显著。经过热老化处理，获得了力学性质明显改善的优质刨花板。     

Heterogeneous ignition and extinguishing of a particle with consideration of radiant heat exchange

I. I. Mechnikov State University, Odessa. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 3, pp. 435–442, March, 1992.     

Influence of dispersion method on particle size and dissolution of grisgofulvin-silicon dioxide tripurations

Dissolution rate and particle size distribution of griseofulvin were determined after simple blending or solvent deposition using colloidal silicon dioxide. Griseofulvin deaggregation in simple blends and micro-particulate drug dispersion in solvent deposited samples, both determinants of drug dissolution rate, were a function of silicon dioxide content. Solvent deposited samples scored impressively highly initial dissolution rates compared to corresponding simple blends. However, dissolution data thereafter were not encouraging. Drug particle size enlargment in griseofulvin rich samples and incomplete drug recovery from silicon dioxide rich samples were notable drawbacks in solvent deposition systems. Viscosity effects of silicon dioxide dispersion on griseofulvin dissolution were demonstrated. Simple blending with silicon dioxide was recommended as a means of promoting dissolution rate of griseofulvin. Limitation of average particle size data determined by methods which do not discriminate between drug and insoluble carrier is discussed.     

Influence of dispersion method on particle size and dissolution of grisgofulvin-silicon dioxide tripurations

Abstract

Dissolution rate and particle size distribution of griseofulvin were determined after simple blending or solvent deposition using colloidal silicon dioxide. Griseofulvin deaggregation in simple blends and micro-particulate drug dispersion in solvent deposited samples, both determinants of drug dissolution rate, were a function of silicon dioxide content. Solvent deposited samples scored impressively highly initial dissolution rates compared to corresponding simple blends. However, dissolution data thereafter were not encouraging. Drug particle size enlargment in griseofulvin rich samples and incomplete drug recovery from silicon dioxide rich samples were notable drawbacks in solvent deposition systems. Viscosity effects of silicon dioxide dispersion on griseofulvin dissolution were demonstrated. Simple blending with silicon dioxide was recommended as a means of promoting dissolution rate of griseofulvin. Limitation of average particle size data determined by methods which do not discriminate between drug and insoluble carrier is discussed.     

Influence of particle size on the magnetocaloric and dielectric properties of GdCrO3

Journal of Materials Science: Materials in Electronics - In this paper, the GdCrO3 polycrystalline samples with different particle sizes were prepared by the sol–gel method and the structure,...