真空电弧等离子射流蒸发法沉积超微粉

在真空电弧等离子喷涂设备上设计安装了超微粉的制备装置。制备出 Fe,Si,Ni,Mo,TiAl,Ti_3Al 和 Si_3N_4等超微粉。通过控制真空室工作压力和等离子弧电流,超微粉的粒度可分别为5,10,20和50nm。观察了粉的形状、分布,测试了沉积速率。     

ISOTHERMAL PREDICTION OF PARTICLE AND GAS FLOW IN A COAL-FIRED REACTOR

The steady, turbulent gas flow with entrained coal particles in a laboratory-scale axisymmetric coal gasification reactor is numerically analyzed. The reactor is designed to provide rapid mixing and heatup of the coal in a configuration which results in a nearly isothermal and uniform flow in the main reaction chamber so as to allow controlled study of coal gasification. A detailed knowledge of the reactor dynamics is required in order to interpret experimental results. The nonreacting, isothermal flow pattern is first presented as a base case. Calculations are performed with an iterative, implicit scheme suitable to the elliptic nature of the gas flow equations in an Eulerian frame-work. The turbulent motion is resolved using the eddy-viscosity concept with the standard k-ε turbulence model. Coal particle trajectories are then calculated using the Lagrangian form of the momentum equations. The influence of solid particles on the gas phase is neglected. Particle trajectories and residence time distributions are presented for a variety of particle sizes and particle inlet locations. The influence of the inlet conditions, turbulent diffusion, and gravity on the particle motion, are investigated. Implications of the predictions, with respect to the design of the reactor, are discussed.     

圆柱谐振腔式MPCVD装置中氢、氩微波等离子体分布规律的数值模拟

在使用简化的等离子体放电模型的基础上,模拟了圆柱谐振腔式微波等离子体沉积室中,不同金刚石膜生长条件下微波等离子体的分布状态。在模拟中,针对纳米金刚石的生长环境,就纯氩气反应气体中,不同的输入功率、不同气体压力条件下,沉积室中形成的等离子体分布的变化规律进行了模拟,将其与一般氢气气氛下的相应模拟结果相对比。模拟所获得的结果,对微波等离子体方法沉积金刚石膜的操作环境的优化,有着一定的指导意义。     

用于制备YBCO薄膜的光辅助MOCVD反应器内流动现象的数值研究

对一种制备YBCO薄膜的光辅助MOCVD反应器内的流动现象进行了三维数值模拟研究.在模拟计算中,分别改变基座与进口的相对角度(Φ)、反应器顶壁倾斜角度(Ψ),得出反应器中流场的相应变化.根据对模拟结果的分析,发现当基座平面与进气口轴线之间的夹角Φ=22.5°及反应器顶壁倾角ψ=30°时,基片表面气流速度大小合适,分布均...     

柱形靶电弧离子镀系统的研究

柱形靶电弧离子镀系统是在吸收了平面靶电弧离子镀系统高电离率、高沉积速率等优点的基础上,又综合了柱型磁控溅射系统装炉量大、设备结构简单等优点而研制出的一种新型镀膜技术。柱形阴极靶置于真空室的中央,弧斑在绕柱靶表面高速旋转的同时,可人为地控制弧斑沿柱靶表面往复运动。因而靶面刻蚀均匀,镀膜均匀区宽。通过控制弧斑的移动速率,可细化膜层组织,减少熔滴。被镀工件置于阴阳极之间,只作自转,无需公转。不仅简化了工件架的结构,而且对不同尺寸的工件可以混装。在制备氮化钛超硬薄膜时,沉积速率可达4～8μm/h。     

用于气体流量控制的压电陶瓷阀的温度特性

采用PEV-1型压电陶瓷阀作为溅射气体Ar流量输出的驱动元件,用于真空磁控溅射镀膜中溅射气体恒压力控制.应用过程中发现压电陶瓷阀本身的迟滞特性和温度特性对气体输出流量有较大影响.试验分析得到压电陶瓷阀偏振电压变化过程中,气体输出流量的迟滞曲线.当压电陶瓷阀环境温度升高时,该迟滞特性会减弱,气体输出流量随偏振电压变化速率变大.     

SiC陶瓷纤维先驱体设计原则及合成研究进展

总结阐述了SiC陶瓷纤维先驱体的设计原则,对国内外SiC陶瓷纤维先驱体的主要合成方法进行了总结.在设计原则的指导下,比较了各种合成方法的优缺点,包括先驱体的产率、杂元素含量、分子形态、分子量及其分布等结构参数,先驱体可纺性以及制备的SiC纤维的性能;并根据设计原则和研究进展提出,降低先驱体中杂元素含量,提高陶瓷产率并兼顾可纺性、稳定性要求是SiC陶瓷纤维先驱体分子设计的方向;指出国内SiC陶瓷纤维的发展要立足于创新,通过不同途径制备出符合要求的陶瓷先驱体。     

氢等离子电弧法半连续制备单壁纳米碳管

用氢气到代拟气作为缓冲气体,适当改进电弧反应装置并掺加一种生长促进剂可以有效地提高单壁纳米碳管的产量和质量。氢电弧法制备出的单壁纳米碳管堆积成膜状或网状,电镜下可见产物主要由相互缠绕的单壁纳米碳管束构成,纯度较高;激光拉曼分析结果表明制得的单壁纳米碳管直径较大。单壁纳米碳管产物在形貌和结构上的上述特征与氢气和生长促进剂的作用密切相关。     

A STUDY OF PLASMA PROPERTIES FOR VARIOUS MAGNETIC FIELDS IN A MICROWAVE MULTIPOLAR ECR PLASMA

A sputtering-type microwave multipolar ECR plasma processing for preparing thin films, is built with Nd-Fe-B magnets and 2.45 GHz, TE_(10) mode microwave. The plasma distributions in the axial direction, which is important for preparing thin films, are found to be very sensitive to the magnetic potential fields in plasma chamber. The plasma parameters are also influenced by the background gas pressure.     

SIC COATING OF SMALL PARTICLES IN A FLUIDIZED BED REACTOR

Silicon carbide was chemically vapor deposited on the small particles in the fluidized bed reactor. Methyltrichlorosilane and hydrogen were used as reactants and in some cases argon was added as a fluidizing gas. Thirty-one coating runs were carried out where coating temperature, methyltrichlorosilane concentration and fluidizing gas composition were varied systematically. The deposit composition was found to be beta-SiC or mixture of beta-SiC and silicon by X-ray diffractometry. The coating temperature affected the deposit composition. From the results of the coating experiment, the model of the CVD processes was presented, which was based on the mass transfer mechanism. This model explained the experimental results fairly well.     

ESTIMATING FILM FLOW RATE IN A VENTURI SCRUBBER

An empirical design correlation has been developed to predict the fraction of liquid flowing on the wall as a film in a Venturi scrubber. This correlation takes into account primary operating variables such as Liquid to Gas Ratio, and Throat Gas Velocity and design variables such as nozzle diameter and Venturi throat width in the direction of liquid injection. Data for the design correlation were obtained on a pilot plant scale Venturi scrubber using operating variables ranges that are normally encountered with industrial size units.     

一种跨音速伺服气动弹性分析方法

基于CFD技术,运用系统辨识方法,建立了基于模态坐标的跨音速气动力降阶模型(ROM)。耦合气动状态方程、结构状态方程和伺服状态方程,建立了一个适合跨音速伺服气动弹性分析的数学模型。算例首先通过对比基于ROM技术的分析结果和直接仿真结果,以证明该模型的正确性和精度。在保证精度的同时,其计算效率比直接耦合CFD技术的仿真方法高1个～2个数量级。算例还研究了传感器安放位置和结构陷幅滤波器对该导弹伺服气动弹性特性的影响,结果显示结构陷幅滤波器的引入可以显著地降低开环气动弹性系统和控制系统的耦合。     

SiC晶须增强LD2铝复合材料的时效

本文利用显微硬度和透射电镜研究了SiC晶须增强LD2铝(SiCw/LD2)的时效。结果表明,在150℃和170℃下时效时,SiCw/LD2复合材料及LD2合金的析出相为G.P.区。SiCw/LD2复合材料的时效过程比LD2合金略有提前。     

基于微秒脉冲激励的飞翼模型等离子体流动控制试验研究

为了改善飞翼布局的大迎角气动特性,采用飞翼全模和半模分别在低速和跨声速风洞中开展了微秒脉冲介质阻挡放电等离子体流动控制的试验研究。通过流动显示和测力的试验方法研究了等离子体流动控制的主要作用机制和激励频率与激励电压等对飞翼模型失速特性的影响规律,验证了微秒脉冲介质阻挡放电等离子体流动控制技术从低速到亚声速的有效性,有效的试验最高马赫数Ma达到0.6、雷诺数Re达到3.05×10⁶。试验研究表明：微秒脉冲介质阻挡放电等离子体通过非定常微尺度压缩波扰动的形式作用于翼面流场,通过频率耦合机制减弱模型的前缘分离涡、抑制翼面的流动分离;无量纲频率F⁺是影响等离子体流动控制效果的重要参数;在低速风洞试验风速V=30 m/s时,无量纲频率F⁺=0.35～1.06的控制效果较好,可将模型的最大升力系数提高25%以上、失速迎角推迟4°;在跨声速风洞试验马赫数Ma=0.6时,无量纲频率F⁺=0.22和F⁺=0.44的控制效果较好,可将模型的最大升力系数分别提高4.72%、4.77%,失速迎角分别推...     

高频等离子体阳极氧化铝膜的特性

将真空蒸发沉积的铝膜 ,在一台高频等离子体辉光放电的装置中进行阳极氧化。铝膜表面氧化层的特性用XRD、XPS、AES和四探针法测定。结果表明 ,铝膜表面氧化层结构是γ -Al2O3 ,晶格常数ao =0.79124nm。室温电阻为6.56～0 .11Ω/□或1256.4～4.81Ω/□ ,低温电阻(77～273K)为0.18～0 .38Ω/□。     

微管道内湍流转捩的实验研究

研究旨在确定微管道内流动从层流到湍流转捩的临界雷诺数。利用微观粒子图像测速技术(Micro-PIV)研究了去离子水在内径为230μm的圆形截面玻璃微管道内的流场结构,得到了从层流到充分发展湍流各流动状态下的轴向平均速度分布和湍流度分布,实验雷诺数为1020~3145,同时研究了微管道内的流动阻力特性。平均速度场和脉动速度场的实验结果表明微管道内从层流到湍流的转捩发生在Re=1800~1900左右,与流动阻力的测量结果一致,与宏观流动比较,并未发现微管道内的流动转捩有明显提前。实验结果还显示,当Re>2700时,微管道内的平均流速分布和相对湍流度分布呈现典型的充分发展湍流状态特征。     

A STUDY OF PARTICLE MOTION IN TURBULENT SHEAR FLOW OF A SUSPENSION

ABSTRACT

A report is made on the measurement of turbulent shear flows of a two-phase suspension of particles in a carrier fluid by the recently developed laser-Doppler anemometry particle sizing techniques, one for small particles (smaller than 240 μm) and one for large particles (larger than 240 μm). A good deal of insights of the dynamics at the individual particle level has thus been gained which defy the explanations offered by the conventional macroscopic theories.

These new experimental findings have stimulated the development of a series of new theoretical approaches which are based on the individual particle's dynamical frequency response characteristics in a turbulent flow. These new theories provide explanations to the measured peculiar features of flow behavior as well as a better understanding of the physics of such flows.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

A STUDY OF PARTICLE MOTION IN TURBULENT SHEAR FLOW OF A SUSPENSION

A report is made on the measurement of turbulent shear flows of a two-phase suspension of particles in a carrier fluid by the recently developed laser-Doppler anemometry particle sizing techniques, one for small particles (smaller than 240 μm) and one for large particles (larger than 240 μm). A good deal of insights of the dynamics at the individual particle level has thus been gained which defy the explanations offered by the conventional macroscopic theories.

These new experimental findings have stimulated the development of a series of new theoretical approaches which are based on the individual particle's dynamical frequency response characteristics in a turbulent flow. These new theories provide explanations to the measured peculiar features of flow behavior as well as a better understanding of the physics of such flows.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

ABSTRACT

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-? turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.