Geometry and electronic properties of Cu2(n≤9)

The equilibrium geometries and the atomization energies of Cu_n(n≤9) clusters have been calculated using the B3LYP/LANL2DZ method. It is shown that the clusters do not copy the bulk structures and undergo significant geometrical changes with size and the atomization energy per atom increases monotonically with size. By analysing the energy level distribution, the Fermi level, HOMO－LUMO gaps, the electron affinities and the ionization potentials are calculated and the results are in reasonable agreement with experiment. These electronic properties are found to be strongly structure dependent, which can be used to determine which of the low-lying structures is observed experimentally.     

Separated flow modelling and interfacial transport phenomena

A physical explanation of the different types of interfacial waves that appear in stratified and annular gas-liquid flows is presented. The role of waves in affecting process performance is discussed. Particular attention is paid to interfacial drag, gas absorption, the initiation of slug flow and atomization.This paper was presented at the Shell Conference on Computational Fluid Dynamics in Apeldoorn, December, 1989.     

Comprehensive determination of trace elements in human saliva by ETA-AAS

A method is described for the comprehensive determination of a series of trace and ultratrace elements (Fe, Mn, Zn, Cu, Sr, Cr, Al and Si) in human saliva by atomic absorption spectrometry with electrothermal atomization and Zeeman-effect background correction. Procedures for sampling of total mixed saliva and its treatment including centrifugation and mineralization by HNO₃ are described in detail. To avoid the use of matrix modifiers, element standards with an artificial saliva matrix were used to construct calibration curves. Instrumental precision, tested by repeated analyses of natural salivas, is good (error less than 5%) for most elements. Lower precision was obtained for elements like Al and Si present in concentrations close to the detection limit. The analysis of some natural salivas clearly shows the influence of the sampling and treatment procedures on the reliability of the data. An accurate standardization of these procedures is thus recommended.     

高速气流中横向液体射流雾化研究进展

在涡轮燃烧室和以液态碳氢燃料为工质的超燃冲压发动机中,高速气流中横向液体射流雾化是一个重要而复杂的过程.雾化过程进行的好坏直接关系到燃料的掺混和燃烧,进而影响发动机的性能. 针对高速气流中横向射流雾化的特点,对现阶段的实验和数值模拟研究进展进行了综述.实验方面结合国内外现状,阐明了一次、二次雾化的机理和雾化过程中的波现象,对穿透深度的确定方法及其影响因素进行了概括总结,分析了气液混合区的结构性质, 并列举和分析了常用的测量手段.数值模型研究介绍了现阶段的一次雾化和二次雾化常用的计算模型.最后提出了存在的问题和未来的研究方向.      

纳米硫化铜近红外吸收材料

采用新型超声喷雾法技术,把摩尔分数都为0.5%的Cu(NO3)2和Na2S水溶液分别作为初始反应溶液,调节溶液体系的pH值在6～8,把经过超声雾化后的Cu(NO3)2溶液逐步加入到处于强力搅拌的Na2S水溶液中,经陈化过滤后获得纳米半导体硫化铜(CuxS,1≤x≤2)粉体。分析了不同热处理温度与原料配比对获得的硫化铜纳米颗粒化学成分的影响,用X射线粉末衍射仪表征了纳米硫化铜粒子的晶相与化学组成,并采用扫描电镜观察了相应化学组成的粒子晶相形貌,测定了不同化学组分纳米硫化铜粒子从可见到近红外胶体状的吸收和透射光谱。研究表明不同化学组成的纳米硫化铜对近红外光都具有显著的吸收效应,这是由于电子在硫化铜半导体纳米粒子能带中的跃迁所致,同时这些半导体粒子对可见光具有很高透过性,但其可见光透射率随着纳米粒子从Cu2S趋向CuS而略有下降。     

Fractal analysis of atomizing liquid flows

The work reported in this paper questions the relevance of using fractal concept to study liquid primary atomization process by characterizing the shape of the continuous liquid flow from the nozzle exit to the end of the atomization process. First, three fractal methods were tested on synthetic images in order to define the best adapted protocol to the objective of the study. It appeared that the Euclidean distance mapping was the best appropriate method. Second, this technique was applied to analyze series of images of atomizing liquid flows obtained for several working conditions. This application demonstrates that atomizing liquid flows are fractal objects and that primary atomization can be reasonably seen as fractal processes. The appropriateness of fractal concept was also demonstrated by the fact that fractal characteristics such as textural or structural fractal dimension and inner cutoff scale are physically representative of the process investigated here.     

The breakup and atomization of a viscous liquid jet

Based on the linear analysis of stability, a dispersion equation is deduced which delineates the evolution of a general 3-dimensional disturbance on the free surface of an incompressible viscous liquid jet. With respect to the spatial growing disturbance mode, the numerical results obtained from the solution of the dispersion equation reveal that a dimensionless parameterJ _e exists. AsJ _e>1, the axisymmetric disturbance mode is most unstable; and whenJ _e<1, the asymmetric disturbances come into being, their growth rate increases with the decrease, ofJ _e, till one of them becomes the most unstable disturbance. The breakup of a low-speed liquid jet results from the developing of axisymmetric disturbances, whose instability is produced by the surface tension; while the atomization of a high-speed liquid jet is brought about by the evolution of nonaxisymmetric disturbance, whose instability is caused by the aerodynamic force on the interface between the jet and the ambient gas. The project supported by the National Natural Science Foundation of China     

Detailed simulation of primary atomization mechanisms in Diesel jet sprays (isolated identification of liquid jet tip effects)

In this study, the atomization characteristics of Diesel jet front tip have been investigated to elucidate the physical mechanisms by detailed numerical simulation. The computations are carried out with the finest grid resolutions ever that can resolve the final droplet generation by surface tension. The numerical methods are based on level-set interface tracking. The methods were validated by test cases and the grid resolution survey shows that the resolutions for the present study are sufficient. The present flow setup excludes nozzle disturbances to investigate how the disturbances from the liquid jet front would lead to atomization where the liquid jet impacts against the quiescent gas. The liquid jet front becomes an umbrella-like shape. From the front umbrella tip edge, ligament breakup first occurs. Ligament breakup is strongly correlated with the gas motion in the vicinity. The gas region behind the front is highly disturbed by atomization. By the gas recirculation motion here, air and some droplets are entrained and mixed. Also, the disturbances are fed back to the front umbrella by this motion and become synchronized with the breakup. Droplet pinch-off is mainly in the short-wave mode, but some ligaments are elongated by local gas stretch to finally have a long-wave mode shape, namely a mode shift occurs. The above findings of liquid jet front umbrella formation, atomization at the umbrella edge, mixing and atomization loop in the recirculation flow region and droplet generation mode give an insight to the modeling of droplet generation in actual sprays.     

柴油混合闪蒸喷雾的探索研究

基于同时降低柴油机中的NOx和微粒的想法，作者提出混合闪蒸喷雾的设想，井建立了混合闪蒸试验台，以证实这种设想在喷雾阶段是否能实现．试验证实了混合闪蒸雾化改善柴油雾化的机理．文中分析了水油比、水的温度、压力对雾束形状、油滴平均直径的影响，对混合闪蒸用于实际柴油机的潜力做了估计．     

Interpretation of atomization rates of the liquid film in gas-liquid annular flow

For vertical gas-liquid annular flow the fraction of the liquid in the gas is controlled by the rate of atomization of the liquid film flowing along the wall and the rate of deposition of droplets entrained in the gas. Measurements of the rate of atomization are interpreted by a Kelvin-Helmholtz mechanism. Small wavelets on the liquid film are visualized to be entrained when wave-induced variations in the gas pressure cannot be counterbalanced by surface tension effects.