共查询到20条相似文献,搜索用时 31 毫秒
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Boswell R.W. Vender D. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(2):141-143
A particle-in-cell (PIC) code with nonperiodic boundary conditions, including ionization and ion motion, is used to simulate the approach to equilibrium and the decay in the postdischarge of model electropositive and electronegative plasmas in a symmetric RF diode. In the electropositive plasma the density decreases to 1/e in ~10 μs. The electronegative ion plasma density is about four times higher and decreases to 1/e in ~50 μs, with the electron temperature and density decreasing to zero in a few microseconds. During this latter time scale, a weak field is set up to drive the negative ions to the boundaries at the same rate as the ion diffusion velocity. In the postdischarge this is close to thermal, hence some hundreds of microseconds are required to remove most of the negative ions from the system. As negative ions are thought to be the precursors for particulate formation, plasmas pulsed at around 1 kHz will severely decrease the lifetime of the negative ions and thereby reduce the possibility of particulate growth 相似文献
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The most challenging objective in the electronic industries is to develop materials that demonstrate a tunable thermal property with today's microelectronic devices. The development of composite material with balanced thermal properties is highly appreciated and currently competing the traditional monolithic conductive material. However, the tailored thermal properties of the composite are significantly influenced by the composites constituents and their fabrication routes. This article presents a review of thermal properties of particulate as well as fiber-reinforced composite proportional to matrix microstructure, reinforcement architecture. The processing techniques used to fabricate composites have been addressed with an objective to achieve suitable thermal properties. The developments in the analytical and numerical simulation approach to predict the thermal conductivity and CTE of the developed composites have been critically reviewed. Lastly, future work needs attention is summarized. 相似文献
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《Proceedings of the Combustion Institute》2023,39(3):3467-3477
Co-firing ammonia in coal units is a promising approach for the phasedown of coal power. In this paper, we demonstrate the feasibility of burning ammonia with coal and biomass in a 25- kW down-fired furnace with a swirl-stabilized burner. Ammonia is injected from the central tube at thermal ratios ranging from 0 to30% and can be completely burnt out in most co-firing cases. We investigate the NOx emission, unburnt carbon in fly ash, particulate matter formation and ash deposition behaviors when co-firing NH3 with either SH lignite coal or the coal/biomass blend. With a fixed air staging ratio, the NOx emission increases linearly with the NH3 fuel ratio. By increasing the percentage of secondary air, the emitted NOx can be reduced to 300 ppm with an NH3 thermal ratio of 30%. The unburnt carbon is affected by NH3 addition in a complex manner. With a 30% (thermal) NH3 addition, the unburnt carbon increases from 0.4% to 5.6% for the SH coal mainly due to a temperature drop, but decreases from 2.2% to 0.7% for the SH coal/biomass blend. As for the ash-related issues, the addition of NH3 to either coal or coal/biomass blend is found to alleviate both the fouling intensity and the ultrafine particulate matter formation ability. This is a major advantage over biomass combustion. 相似文献
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《Composite Interfaces》2013,20(1):43-66
Fly ash (FA)-general purpose unsaturated polyester resin (GPR) particulate composites have been made. The effect of surface treatment of FA with two different silane coupling agents (CAs) on the mechanical properties like tensile, flexural, impact strength and hardness, thermal properties like thermal stability and morphological properties (SEM) of FA-GPR composites are studied. The properties of FA-CA-GPR are also compared with that of GPR and CaCO3 -GPR. An enhancement in the tensile, flexural, and impact strength and moduli are observed when FA is surface treated with CA. Hardness is also found to increase with CA-treated FA-filled GPR. A suitable mechanism for the chemical reaction taking place at the interface in the presence of CAs is proposed. 相似文献
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The trend in magnetic recording media is towards higher frequencies and larger storage capacities. Base film technology has developed in a manner analogous to corresponding demands on particulate and thin-film media, i.e. in the direction to reduced thickness, smoother surfaces, and very high uniformity. Key elements for the success of polyester films as substrates for all kinds of flexible media are new concepts for pigmentation and surface design. Future digital video recording systems and thin-film media will require new substrates with higher mechanical strength and thermal stability. Trends in base film development including dual-surface films and alternative polymer substrates are discussed. 相似文献
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Measurements of the attenuation of 1.5 to 7 MHz ultrasound in milks and creams, aqueous solutions of milk proteins and milk fat demonstrated that the attenuation due to the fat component was proportional to the fat concentration (at low volume fractions, less than 4%) and was caused by two effects: losses arising from its particulate nature and intrinsic attenuation (mass attenuation coefficient 1.1 cm2 g−1 at 7 MHz in pure milk fat). Comparison with theoretical equations showed that absorption by thermal conduction dominated the particulate losses and increased with decreasing fat globule size, over the range 1.5 to 7 MHz. This was confirmed by examining milks homogenized to different degrees. The losses in the non-fat components were mainly due to the protein components which also probably dominated the shape of the attenuation titration curves for skimmed milk, producing peaks in attenuation in the range pH 4–4.5 and about pH 11.3. 相似文献
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采用所建立的四方程线性弹性-阻尼离散单元模型,同时考虑了液桥力的作用,对填充量为40%、含液量为3%的水平薄滚筒内S型(不同直径颗粒)二元湿颗粒体系混合过程进行了数值模拟,并与同等操作条件下不含液的干颗粒体系的混合行为进行了比较,分析了液体对颗粒体系混合行为的影响. 同时还将计算结果与文献中的实验结果进行了比较. 结果表明,由于湿颗粒间液桥力的牵引作用使不同性质的颗粒不易分离,使部分颗粒聚结成团,减弱了离析作用的影响,使得滚筒内湿颗粒的混合程度高于相同条件下的干颗粒体系,且接触力的分布较干颗粒体系更加均匀. 通过对混合过程的模拟,直观地反映了混合过程中颗粒的微观运动特性和内部的力学结构,为研究湿颗粒体系混合过程机理提供了依据和参考.
关键词:
湿颗粒体系
混合
分离
离散单元法 相似文献
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Giuseppe Bonifazi Franco Francini Vanni Guarnieri Giuseppe Longobardi Paolo Massacci Marco Recinella 《Particle & Particle Systems Characterization》1995,12(6):318-323
The guidelines which are at the base of the definition of a system capable of operating on a slurry containing the solid particulate for its characterization are described. All the considerations have been developed with particular reference to the case of a granular heterogeneous material in particular, the different research problems, making a comparison with the case of static images, acquired under laboratory conditions, are pointed out. Attention was focused on problems of acquisition and digital image processing to obtain information which is clean from noise and errors. The considerations and procedures analysed show general validity and can be applied to a large number of problems linked to the “on-line” morphological characterization of particulate solids materials. Some results for morphological characteristics of lead sulphide (PbS) samples are reported. 相似文献
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《Current Applied Physics》2007,7(5):547-554
A bioactive and biodegradable composite material consisting of hydroxyapatite (HA) and polyhydroxybutyrate (PHB) was investigated for bone tissue repair. A fabrication process involving the use of injection moulding was developed for manufacturing the HA/PHB composite which contained up to 40% by volume of particulate HA. The processing parameters for composite manufacture were optimized through thermal analyses of HA/PHB composite produced and production trials. The microstructure and properties of the composite were evaluated using various techniques. Form the results obtained, it is shown that good quality HA/PHB composite products could be manufactured via the established production route. 相似文献
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Particulate gels are known to be formed by bovine β-lactoglobulin near the isoelectric point when partial unfolding is allowed
to occur under heating. The aggregation process of the protein has been investigated within the context of a nucleation and
growth process by preparing gels under precisely controlled thermal histories. This was achieved using a Differential Scanning
Calorimeter (DSC) to provide controlled heating rates, and known final temperatures and incubation times. The resulting particulate
gels were characterized by their particle size and polydispersity using Environmental Scanning Electron Microscopy (ESEM),
which permits hydrated samples to be observed. Particle size was found to decrease with increasing final temperature, with
the aggregation taking longer to reach completion for lower temperatures. Particle size was also found to decrease with increasing
heating rate. This system could be modelled as evolving via nucleation and growth by taking into account the fact that the
concentration of the aggregating species was varying as a function of temperature as well as time. The intrinsic tryptophan
fluorescence as a function of temperature was used as a guide to the fraction of unfolded protein in solution, thereby permitting
successful comparisons between the model predictions and the particle sizes to be made.-1 相似文献
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Winske D. Jones M.E. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(4):454-464
The forces on and resulting dynamics of particulate contaminants near the plasma-sheath boundary in a one-dimensional, steady-state glow discharge are examined. Various expressions for the electric force, including the effects of nonneutrality and particulate spacing on the charge state, are considered, and several different ways to compute the ion drag force are compared. The properties of the particulate traps that result from the interplay of these forces are studied. The effects of the gravitational, neutral drag, and polarization forces are also considered. Time-dependent motion of the particulates, including the effects of a temporally varying, spatially localized particulate density, is also investigated. While some uncertainties exist in the individual expressions for the various forces and in the properties of the discharge, the particulate traps are fairly well defined and consistent with experiments and other analyses 相似文献
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EAST超导托卡马克冷屏结构与受力分析 总被引:3,自引:2,他引:1
EAST是一个全超导磁体系统的托卡马克实验装置,超导纵场和极向场磁体工作在4K温区下。在磁
体和其它发热部件之间布置有冷屏系统,以减少作用到所有低温冷质部件上的热载,将其保持在最低水平。该系
统包括真空室冷屏(内冷屏)和外真空杜瓦冷屏(外冷屏)两部分。在分析了冷屏低温运行时所受热应力以及等离
子体破裂时所受电磁载荷的基础上,运用大型有限元分析程序NASTRAN,对其不同载荷状况进行了数值计算,为其
结构设计与优化提供了理论依据。 相似文献
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The efficiency of reactors fed with particulate mixtures is often reduced by segregation of solids. Placing continuous mixers directly ahead of a reactor may be a solution to this problem. The performance of such mixers can be monitored for appropriate binary solids systems with an optical in-line measuring system. The tracer concentration (SiC or Irgalite) in Al(OH)3 was registered with high time resolution, thus making possible an extended statistical analysis of mixing processes using the power density spectrum. Experimental mixers with a maximum -throughput of 300 kg/h were fed with a fluctuating tracer concentration and the variance reduction ratios were determined. A model was developed that takes into account feeding constancy, residence time distribution and the limited homogeneity of particulate mixtures. Diagrams for continuous solids mixing processes are derived therefrom. They demonstrate the importance of high-accuracy feed-rate control. 相似文献
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Three aspects of the rheological behavior of PVC are considered. These are (a) particulate flow, which occurs below the true crystal-line melting point, (b) true melting flow, which occurs at or above the melting point, and (c) the flow of PVC compounds. The effect of structural differences resulting from different polymerization temperatures employed in preparing different molecular weight polymers on the melt viscosity and flow activation energy is re-examined, and new data a r e presented to unconfound the effect of syndiotacticity and molecular weight. The three types of flow behavior of PVC are shown to be represented by three distinct flow regions. Because of thermal instability, the true melt flow region is achieved only with difficulty. However, in commercial operations this latter state is seldom, i f ever, achieved in rigid formulations. The effect of compounding additives, especially lubricants and plasticizers, and the importance of thermal and mastication history on the flow behavior are discussed with reference to the flow mechanism. 相似文献