声凝并中颗粒间相互作用研究进展

声凝并是细颗粒物(PM2.5)排放控制的重要技术途径,其通过外加声场作用促进PM2.5发生碰撞凝并,使得颗粒数目减少、粒径增大,从而提高后续除尘装置的效率。对声凝并中颗粒间的相互作用机理,包括同向相互作用、声尾流效应、互辐射压力效应、互散射效应的相关研究进行总结和评述,结合声凝并技术在PM2.5排放控制中的应用,指出已有研究在理论模型和实验观测上存在的问题,进而提出今后的研究应在实验方法上进行创新,发展出能够跟踪微米和亚微米尺度PM2.5颗粒或颗粒团相互作用过程细节信息的实验手段,为理论模型的实验验证提供数据支撑;同时应进一步发展理论模型,从而在模型验证的基础上,充分发挥数值模拟的优势,全面识别声凝并中颗粒间相互作用的动力学行为。     

水基铁磁流体磁致凝聚行为的三维耗散粒子动力学研究

用耗散粒子动力学方法对铁磁流体在外加恒定磁场作用下的凝聚行为进行了三维模拟.基于Flory-Huggins相混理论得到包括磁性颗粒珠子间的通常意义上的相互作用参数;利用Ewald方法把单磁畴结构的磁性颗粒长程的磁性相互作用转换成短程加和形式,从而得到磁偶极子的磁性相互作用参数.模拟结果表明,外加磁场强度是形成凝聚结构的...     

CFD simulations of droplet and particle agglomeration in an industrial counter-current spray dryer

In this study, CFD simulations of particle and droplet agglomeration in an industrial counter-current spray dryer are presented. For this purpose, a modified form of the stochastic collision agglomeration model is proposed. This model takes into account droplet–droplet collision as well as wet and dry particle interaction. These events are coupled with heat, mass and momentum transfer. A comprehensive moisture evaporation model based on the concept of characteristic drying curve (CDC) was applied to predict the drying kinetics of the detergent slurry. Due to high instability in air flow inside the drying chamber, simulations were carried out under transient condition. A comparison between time-averaged simulation results and measurements, which were performed on an industrial spray drying installation, shows a good agreement. This finding proves the correctness of the developed agglomeration and drying models. The presented methodology of CFD simulations of agglomeration can be used to design or optimise spray-drying installations and to predict the final particle size distribution of the product.     

Effect of turbulent flow field properties on improving the removal of coal-fired fine particles in chemical-turbulent agglomeration

Chemical-turbulent agglomeration is a promising coupling agglomeration method to improve the removal of fine particles, in which the turbulent flow field plays an important role on the collision of chemical droplets and fine particles. However, there is no specific study about the effect of turbulent flow field properties on the agglomeration and removal of fine particles. In this work, three kinds of turbulent vortex sheets with different structures were designed to generate vortexes with different scales and generation dimensions, the particle agglomeration effect and characteristics, as well as the particle removal effect by ESP with different turbulence generators were investigated. The results demonstrated that the turbulence generator with large-scale and two-dimensional vortexes in flow field had the best effect on improving the agglomeration and removal of fine particle. Besides, the motion trajectories and the turbulent agglomeration kernel of chemical droplets and fine particles were calculated to further explore the interaction mechanism of particle agglomeration and flow field properties. The results proved that the turbulent flow field containing large-scale and two-dimensional vortexes can effectively enlarge the capture area of fine particles by chemical droplets and promote the collision probability of them, thus improving the agglomeration and removal of fine particles.     

Use of non-negative constraint in Tikhonov regularization for particle sizing based on forward light scattering

Abstract

The set of linear equations in the inversion of particle size distribution (PSD) based on forward light scattering is an ill-posed problem. In order to solve the inverse problem of this kind, a number of inversion algorithms have been proposed. The regularization algorithm can reconstruct the PSD, but in usual case, the solution may contain negative values and is strongly oscillating. Owing to the natural reason, the solution should be non-negative and smooth. In this paper, a simple non-negative constraint (NNC) is used with a combination of the Tikhonov regularization. Simulations and experiments show that the regularization with NNC can achieve more reasonable results.     

Characterization of the accuracy of the fast multipole method in particle simulations

The fast multipole method (FMM) is a fast summation algorithm capable of accelerating pairwise interaction calculations, known as N‐body problems, from an algorithmic complexity of ??(N²) to ??(N) for N particles. The algorithm has brought a dramatic increase in the capability of particle simulations in many application areas, such as electrostatics, particle formulations of fluid mechanics, and others. Although the literature on the subject provides theoretical error bounds for the FMM approximation, there are not many reports on the measured errors in a suite of computational experiments that characterize the accuracy of the method in relation with the different parameters available to the user. We have performed such an experimental investigation, and summarized the results of about 1500 calculations using the FMM algorithm, applied to the 2D vortex particle method. In addition to the more standard diagnostic of the maximum error, we supply illustrations of the spatial distribution of the errors, offering visual evidence of all the contributing factors to the overall approximation accuracy: multipole expansion, local expansion, hierarchical spatial decomposition (interaction lists, local domain, far domain). This presentation is a contribution to any researcher wishing to incorporate the FMM acceleration to their application code, as it aids in understanding where accuracy is gained or compromised. Copyright © 2009 John Wiley & Sons, Ltd.     

Use of digital image correlation to measure strain recovery in particle toughened thermoset resins

A methodology for finding the yield point of epoxy resins, both neat and particulate toughened, is described. Trends of the effect that particulate filling has on the time dependent response of these materials were constructed from observations made with stereo‐based digital image correlation (3D–DIC), namely, creep and stress relaxation at constant load. The use of 3D–DIC also enabled the observation of differences in deformation mechanisms resulting from the particle addition. The focus is put on the technique's potential to characterise materials and produce clear relationships between composition and mechanical strain response. The methodology proposed herein allows the observation and study of multiple deformation mechanisms from a single test, and thus can potentially minimise the number of specimens needed for a comprehensive test campaign.     

Use of plasma impedance monitoring for the determination of SF6 reactive ion etch process end points in a SiO2/Si system

It is shown here that plasma impedance monitoring can be used successfully to determine the end point of reactive ion etching of a SiO₂ layer lying on a Si substrate in SF₆ plasma. The usefulness of this technique is demonstrated using a commercial Plasma Impedance Monitoring (PIM) system. The end point conditions are tested by monitoring changes in the fundamental and the first four harmonic components of the RF current, RF voltage, phase between RF voltage and current, RF discharge power and RF impedance. The best process monitoring parameter found in this work is modeled as a polynomial equation of RF input power, chamber pressure and gas flow rate, from which the end point can be predicted with good precision and easily detected by the PIM. The end point conditions are confirmed by both Fourier Transform Infrared Spectroscopy (FTIR) measurements and via observation of plasma color changes. Received:15 June 2001 / Accepted: 18 June 2001     

Effects of main particle diameter on improving particle flowability for compressed packing fraction in a smaller particle admixing system

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the mechanisms by which this technique improves flowability are not yet fully understood. In this study, we examined compressed packing in a particle bed, which is affected by particle flowability. To estimate the mechanism of improvement, we investigated the effects of the main particle diameter on the improvement of compressed packing fractions experimentally.The main particles were 397 and 1460 nm in diameter and the admixed particles were 8, 21, 62, and 104 nm in diameter. The main and admixed particles were mixed in various mass ratios, and the compressed packing fractions of the mixtures were measured. SEM images were used to analyze the coverage diameter and the surface coverage ratio of the admixed particles on the main particles. The main particle packing fraction was improved as the diameter ratio (=main particles/admixed particles) increased. This was explained by a linked rigid-3-bodies model with leverage. Furthermore, the actual surface coverage ratio at which the most improved packing fraction was obtained decreased with increasing main particle diameter. This was explained by the difference in the curvature of the main particle surface.     

Characterization of tunnel-oxide degradation due to plasma field oxide recess in flash memory devices

This paper presents the characterization of degradation of tunnel oxide during plasma recess of field oxide films for Shallow Trench Isolation (STI) in sub 30 nm flash memory devices. Simple plasma charge damage monitor wafers with Metal-Oxide-Semiconductor (MOS) capacitor structures were used to analyze the mechanisms of degradation of tunnel oxide due to process-induced charging damage. We characterized the gate leakage currents and breakdown voltages of MOS capacitors with area antennas after performing the plasma process for field oxide recess of STI with various etching conditions in a dual-frequency capacitively coupled plasma reactor. The results showed that the degradation was strongly dependent on plasma non-uniformity, which could be improved by optimizing the radio-frequency and biasing power. Especially, we found that RF biasing power caused stress-induced leakage currents due to dielectric breakdown by the leakage current originating from the electrostatic chuck.     

The field dependence of the thermal conductivity: Evidence for nodes in the gap

The increased thermal conductivity below T_c in YBa₂Cu₃O_7–x (YBCO) is shown to agree with the microwave electrical conductivity, affirming that increase is due to quasiparticle conduction The field dependence, particularly in the conducting plane permits us to separate phonon and quasiparticle contributions for both YBCO and T₂Ba₂CuO₆ single crystals.     

Sensitivity enhancement of laser absorption spectroscopy for atomic oxygen measurement in microwave air plasma

A high sensitive laser absorption spectroscopy system has been developed for the detection of atomic oxygen in a microwave plasma. Firstly, the sensitivity of this system was evaluated by ring-down time measurement. The effective absorbing pass length was extended up to 640 times as long as that of the conventional laser absorption spectroscopy. Then, the system was applied to the air plasma diagnostics. As a result, the absorption signal from the meta-stable atomic oxygen at 777.19 nm could be observed at the input enthalpy range from 0.93 MJ/kg to 467 MJ/kg. The detected minimum number density was 1.6 × 10¹¹ m⁻³ with temperature of 388 K, which correspond to the center fractional absorption of 1.4 × 10⁻²% in the LAS.     

A vacuum plasma surface pretreatment for refining seeding of Co in electroless copper plating

In this work, various vacuum plasma types, generated by either single gaseous sources (N₂ or H₂) or mixed sources (N₂-H₂) are incorporated into an aqueous-solution electrochemical seeding process to pre-treat the surfaces of SiO₂ dielectric layers. Under the optimal plasma atmosphere (monitored by optical emission spectroscopy), the dielectric surfaces can be modified to terminate by hydrophilic bonds, accelerating the adsorption of a crowd of catalytic seeds as small as 3 nm. Such a seeding refinement allows for the growth of a Co-based barrier layer with thickness as thin as 10 nm using electroless plating. Moreover, the capacity of integrating the plasma surface pretreatment with the seeding and electroless-plating process steps to deposit an ultrathin copper-stacked metallization layer in a selective and sequential manner on blanket wafers will be demonstrated by the fabrication of copper-gated and barrier-interposed capacitors. Finally, a tentative work of filling the seeds and the barrier layer into trenches of a patterned wafer was carried out, demonstrating the potential of the reported technique for advanced technology nodes of 60 nm or less.     

等离子体基离子注入菱形靶鞘层扩展的流体动力学模拟

利用流体动力学模型,研究了围绕菱形靶的等离子体鞘层扩展,通过改变靶的形状,考察了不同角度外角对鞘层的时空演化及等离子体参量的影响。结果表明,外角愈尖锐,鞘层扩展速度愈慢,而参考平面处鞘层扩展速度最快,因而使鞘层有向圆柱形扩展的趋势,尽管尖锐的外角处电荷密度高,会吸引较多的离子轰击该处,但非垂直入射会显著降低离子入射剂量。     

Effect of nano-silver particles in bonding material on field emission properties for carbon nanotube cathodes

Effects of bonding materials in a screen-printing paste on field emission properties were investigated for carbon nanotube (CNT) cathodes. The CNT cathodes were characterized for their dependence on current density in terms of the sintering behavior of the bonding material. As the diameter of the Ag particles in the bonding material decreased from 1000 nm to 10 nm, the current density of the CNT cathode increased. The sintering temperature of bonding materials was decreased for small silver (Ag) particles in bonding material. The higher current density for a CNT cathode fabricated with smaller Ag particles was primarily due to the lower sheet resistance of the bonding material after heat treatment.     

用可压缩流涡方法模拟叶轮机动静叶的相互作用

本课题组发展了一种扰动涡方法,用以研究叶轮机内动、静叶相互作用。其优点是物理图画清楚,计算收敛快。它采用了一个重要假设：扰动胀量为零,从而大大简化 了计算过程。文章的目的是研究此假设的影响,并取消此假设,使扰动涡方法建立在完全严格的数学基础上。由于取消了“扰动胀量为零的假设,需要耦合求解扰动质量方程、扰动涡量输运方程和扰动能量输运方程。这是文章与文献[1,2]的主要区别。     

电感耦合等离子体质谱法测定饮用水中微量元素

采用电感耦合等离子体质谱法快速测定饮用水中的微量元素 ,样品处理简便 ,检出限低 ,重现性好 ,分析速度快。方法检出限为 (0 0 0 7～ 0 911) μg L ,精密度达到 0 73%～ 4 87%。