Numerical-simulation of ac plasma-arc thermodynamics

A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequency range of 10-10(2) Hz which includes most industry ac arc frequencies. (C) 1994 Academic Press, Inc.

Stress-distribution at the rigid circular-arc inclusion end

The elastic plane problem of a rigid co-circular arc inclusion under arbitrary loads is dealt with. Applying Schwarz's reflection principle integrated with the analysis of the singularity of complex stress functions, the general solution of the problem is found and several closed-form solutions to some problems of practical importance are given. Finally, the stress distribution at the arc inclusion end is examined and a comparison is made with that of the rigid line inclusion end to show the effect of curvature.

Evolution of ideal micro-crack system

The ideal micro-cracks are treated with the number-density function; the characteristics of their evolution are investigated; a deterministic model is applied to the discussion of their extension. It is discovered that under certain conditions saturation may occur in the number-density. The main features of the statistical formulation are illustrated by several examples and compared with those observed in experiments.

Impact of cathode evaporation on a free-burning arc

A free-burning, high-intensity argon arc at atmospheric pressure was modelled during the evaporation of copper from the cathode. The effect of cathode evaporation on the temperature, mass flow, current flow and Cu concentration was studied for the entire plasma region. The copper evaporates from the tip of the cathode with an evaporation rate of 1 mg s-1. The copper vapour in the cathode region has a velocity of 210 m s-1 with a mass concentration of above 90% within 0.5 mm from the arc axis. The vapour passes from the cathode toward the anode with a slight diffusion in the argon plasma. Higher temperatures and current densities were calculated in the core of the arc caused by the cathode evaporation.

钢基铝镀层转化为陶瓷层的演变规律研究

热浸镀铝钢经等离子体电解氧化（Plasma Electrolytic Oxidation,PEO）处理后,表面铝镀层转化为陶瓷层.实验对阳极电压变化、陶瓷层生长规律、涂层截面形貌和成分等进行了研究.结果表明：在PEO初期,热浸铝试件的阳极电压变化趋势与纯铝试件相同,在PEO后期电压有下降趋势.铝镀层消耗和陶瓷层厚度增长近似为线性变化.当铝镀层完全陶瓷化后,FeAl层参与PEO反应,但陶瓷层生长速率变慢,在界面处出现大量裂纹;陶瓷层主要成分为Al、Si、O元素,相结构主要为γ-Al_2O_3与莫来石相,在PEO后期出现α-Al_2O_3相.复合陶瓷层硬度呈区域性分布,陶瓷层最高硬度可达HV1800.

热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al2O3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能，采用扫描电镜（SEM）观察了纳米压痕形貌，并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响．结果表明：等离子体电解氧化（PEO）陶瓷层中包含许多微米和亚微米尺度的细小孔洞，陶瓷层弹性模量约为226．4 GPa，纳米硬度约为19．6 GPa．当纳米压入深度为250nm时，所测得陶瓷层的力学参数分散性较大．与FeAl层比较，PEO陶瓷层具有较高的裂纹扩展阻力．FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹；而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹．

Comparative Observation of DC Arc Plasma Jets and Their Arc Root Behaviors at Reduced Pressure

Experimentally observed, results are presented for the DCarcplasmajets and theirarc-rootbehaviors generated atreduced gas pressure and without or with an' applied magnetic field. Pure argon, argon -hydrogen or argon-nitrogen mixture is used as the plasma-forming gas. A specially designed copper mirror is constructed and used for better observing the arc-root behavior on the anode surface of the DC non-transferred arcplasma torch. It is shown that for the cases without applied magnetic field, the laminar plasmajets are stable and approximately axisymmetrical. The arc-root attachment on the anode surface is completely diffusive when argon is used as the plasma-forming gas, while the arc-root attachment often becomes constrictive when hydrogen or nitrogen is added into the argon. When an external magnetic field is applied, the arcroot tends to rotate along the anode surface of the non-transferred arcplasma torch.

Edge and Size Effects in Micro Composite Structure

Because of the load transfer effect of interface layer, the stress distribution inside the composite structure of film/substrate can be very different from the Timoshenko's model. In this paper, we give the derivation and analysis of such load transfer effect of shear-lag (S-L) model. The micro-structure size (boundary conditions) effect together with interface load transfer effect becomes more and more important as the microstructure size including the three dimensions of thickness, width and length shrinks. The microstructure size is also responsible for the so-called edge-induced stress. The edge effect and difference of S-L model and Timoshenko model are also demonstrated.

The Droplet Group Micro-Explosions, Viscosity and Atomization Characteristics of W/O Emulsions

The spray of emulsified fuel, composed of diesel fuel, water and methanol can make micro-explosion under high temperature conditions, and the viscosity and the atomization characteristics of emulsion have significant effects on the micro- explosion of emulsions. To clarify the combustion mechanism of water-in-oil emulsion sprays, combustion bomb experiments were carried out, and the droplet group micro- explosions in W/O fuel emulsion sprays in a high-pressure, high-temperature bomb were observed clearly by a multi-pulsed, off-axis, image-plane ruby laser holocamera and continuously by a high-speed CCD camera.The viscosity and atomization characteristics of emulsions were also studied experimentally. The experimental results show that the higher concentration of the aqueous phase (water-methanol) (<50%) increases the viscosity of the emulsions, especially for higher agent concentration, and higher aqueous phase concentration and higher viscosity results in lager Sauter Mean Diameter (SMD). The experiment results also show that the different kinds of emulsifying agents, with different Hydrophile-Lipophile Balance (HLB) values, have significant influence on the viscosity of the emulsions.

Monte Carlo Modeling of Micro Scale Gas Flows

An information preservation (IP) method has been used to simulate many micro scale gas flows. It may efficiently reduce the statistical scatter inherent in conventional particle approaches such as the direct simulation Monte Carlo (DSMC) method. This paper reviews applications of IP to some benchmark problems. Comparison of the IP results with those given by experiment, DSMC, and the linearized Boltzmann equation, as well as the Navier-Stokes equations with a slip boundary condition, and the lattice Boltzmann equation, shows that the IP method is applicable to micro scale gas flows over the entire flow regime from continuum to free molecular.