Parametric Study on Arc Behavior of Magnetically Diffused Arc

A model coupling the plasma with a cathode body is applied in the simulation of the diffuse state of a magnetically rotating arc.Four parametric studies are performed:on the external axial magnetic field (AMF),on the cathode shape,on the total current and on the inlet gas velocity.The numerical results show that:the cathode attachment focuses in the center of the cathode tip with zero AMF and gradually shifts off the axis with the increase of AMF;a larger cathode conical angle corresponds to a cathode arc attachment farther away off axis;the maximum values of plasma temperature increase with the total current;the plasma column in front of the cathode tip expands more severely in the axial direction,with a higher inlet speed;the cathode arc attachment shrinks towards the tip as the inlet speed increases.The various results are supposed to be explained by the joint effect of coupled cathode surface heating and plasma rotating flow.     

Numerical Analysis of the Arc Plasma in a Simplified Low-voltage Circuit Breaker Chamber with Ferromagnetic Materials

This paper is devoted to the simulation of the arc plasma in a simplified low-voltage circuit breaker chamber. Based on a group of coupled governing equations, a three-dimensional （3-D） arc plasma model is built and solved by a modified commercial code. Firstly, this paper presents a solution of the stationary state of the arc plasma and discusses the distribution of some parameters throughout the chamber. Secondly, with the ferromagnetic materials included, the balance of the stationary state is broken and a transient course is calculated. In light of the simulation results, the temperature distribution sequence, the arc motion and the plasma jet are then described and analyzed in detail.     

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics (MHD) model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.     

Characterization of a 3-Phase a.c. Free Burning Arc Plasma

A 3-phase a.c. arc plasma reactor with large volume plasma has been developed for the synthesis of new carbon nano-structures. One of the main characteristics of the plasma system is related to the absence of a fixed neutral point. This gives rise to a rich and complex phenomenology related to instabilities and arc motion since the arcs are ＂burning＂ freely in the gas flow between the three electrodes. This paper is dedicated to the analysis of the behavior of such a system under typical conditions using argon and nitrogen as plasma gases. A classification of are configuration, arc commutating, arc interaction, arc motion and arc instabilities are discussed based on ultra high-speed cine camera analysis. A simple model describing the time evolution of the system is also presented and compared with the experimental measurements. The results show that an adequate control could allow the improvement of the overall system.     

Nonequilibrium modeling study on plasma flow features in a low-power nitrogen/hydrogen arcjet thruster

Gasdynamic flow features in an electrothermal arcjet thruster with a mixture of 1:2 nitrogen/ hydrogen as the working gas have been studied by a two-temperature numerical simulation.Seven species and 17 kinetic processes are included in the chemical kinetic model used to represent dissociation,ionization,and the corresponding recombination reactions in this nitrogen/hydrogen mixture system.Based on the gas flow characteristics inside the arcjet nozzle,a new method is introduced to define the edge of the cold boundary layer,which is more convenient to analyze the evolution and development of plasma flow in an arcjet thruster.The results show that the arcjet thruster performance is determined largely by the exchange of energy and momentum between the low-density,high-temperature arc region and the high-density,coolttow region near the nozzle wall.A significant thermal nonequilibrium is found in the cold boundary layer in the expansion portion of the nozzle.The important chemical kinetic processes determining the distribution of hydrogen and nitrogen species in different flow regions are presented.It has been shown that the reaction rate of hydrogen species ionization impacted by electrons is much higher than that of nitrogen species ionization in the center of the constrictor of the arcjet thruster.This indicates that hydrogen species is very important in the conversion of applied electric energy into thermal energy in the constrictor region of the arcjet thruster.     

基于LB方法的管内流动沸腾传热模拟

为研究竖直管内流动沸腾的传热情况及气泡行为学,采用格子玻尔兹曼（LB）方法,利用改进后的伪势模型和热模型分别模拟流动和传热过程。为验证模型的合理性,对模拟结果与经验关系式进行了定量对比。之后对气泡行为对沸腾传热系数的影响进行了研究,结果表明,随着气泡的核化、生长、滑移和脱离,传热系数呈现周期性波动。最后考察了重力加速度对气泡行为和沸腾传热的影响,重力越大,气泡生长周期越短,沸腾传热系数越大。     

Numerical Solution Method for Prediction of Heat Transfer in Tube Bundles of Large-Size Intermediate Heat Exchangers in FBR Plants

A study was made of uranium contamination in (a) the coating layers of TRISO particles (a-1) before compacting and (a-2) separated from once-compacted fuel heat-treated at 1,400 or 1,800°C, and (b) in the matrix material of the same compacts. The contamination in the pyrocarbon layers of the coating was determined, after mechanically separating the coating layers, by a procedure of neutron activation, burn-off and ¹³³Xe trapping. For the silicon carbide coating layer, the fragments of coating left from the above procedure were fused into alkaline melt, and the ¹³³Xe released at each heating step was trapped. For the matrix material, the fuel compacts were deconsolidated electrolytically or mechanically, followed by activation analysis. The results of the foregoing measurements proved the uranium contamination in pyrocarbon and silicon carbide coating to be at most of the order of 10^?4 in reference to uranium content in kernel, while the corresponding value for particles sampled from fuel compacts heat-treated at 1,800°C were appreciably higher. The corresponding values found for the matrix material were of the order of 10^?5.     

The Properties of the Rectangular Arc Ion Plating with Magnetic Filtering Shutter

A major obstacle to the broad application of cathodic arc plasma deposition is the presence of macroparticles. In this paper, the properties of the large rectangular arc ion plating with a magnetic filtering shutter system to filter macroparticles are studied. It is proposed that the macroparticles in the plasma beam are effectively removed with the magnetic filtering shutter system, and the quality of the deposited films is improved.     

Effect of Gas Introduction on Temperature Distribution for Tube Flow with Internal Heat Sources

An experimental study has been conducted to investigate the effect of gas introduction on the heat transfer characteristics for turbulent flow of a heat generating liquid in an adiabatic tube 20 mm in inside diameter. Heat generation within the fluid was brought about by passing an alternating current through the working fluid, which was an aqueous solution of sodium chloride mixed with air bubbles. The superficial liquid Reynolds number ranged 3,700–11,000. The quality was varied from 2.6×10^?5 to 3.3×l0^?3. Measurements were made of the temperature distributions in the fluid as well as on the tube wall. The experimental results were compared with theoretical analyses.

In bubbly flow; the introduction of air into liquid brought forth a flat temperature distribution due to a considerable increase of turbulence and a saddle-shaped void distribution, which had a maximum near the tube wall. In slug flow, however, the void distribution changed to a dome-shaped profile with a maximum at the tube center and the rate of heat generation was higher near the wall than in the center region, resulting in a steep temperature distribution.     

液态金属钠在圆管和环管内流动时放热问题的数值解

液态金属因导热系数很高,与普通流体相比,其传热规律独特。特别是由于湍流放热机理复杂,纯理论研究不能或难于给出精确解析解,但是借助数值计算法则可得到满意的结果。本文中广泛比较了影响 Nu 值的各种因素的关系式,验证了它们的适用性,而且用数值法研究了等热流边界条件下液态金属圆管和环管放热问题,所得结果与实验及他人理论计算结果符合得较好。     

液态金属钠在圆管内传热特性数值模拟研究

为研究液态金属钠在不锈钢材料表面流动时的湍流传热特性,在已有实验研究的基础上,提出了k-ε模型下的湍流普朗特数Pr_t模型,并使用Fluent程序对圆管内的液态金属钠在不锈钢材料表面流动时的传热特性进行了计算。理论设计值与已有实验结果进行对比,二者符合较好。根据本文提出的Pr_t模型,可较为精确地计算液态金属钠在不锈钢材料表面流动时的传热特性。     

阴极端面旋转弧根的数值分析

辅助电弧的阴极弧根在管状钨阴极端面旋转时，随着阴极弧根旋转频率的增加，在阴极端面形成一圈温度较高的区域；区域中各点的温度（除弧根处温度）趋于均匀，从而为主电弧的阴极弧根在这个区域中分裂成多弧根或形成扩散型弧根模式提供了必要的温度条件；弧根处的阴极端面温度随旋转频率的增加而下降并趋于一个稳定的值。本文利用三维热传导方程对此进行了分析。     

竖直圆管通道内超临界水传热实验及数值模拟研究

为了对超临界水冷堆概念设计参数范围内超临界水的传热特性有进一步的了解,通过实验和数值模拟的方法对竖直上升圆管通道内超临界水的传热特性开展了研究,用实验数据对现有传热关系式和CFD计算模型进行了评估。通过实验数据与现有经验关系式的对比,发现现有大多数超临界传热关系式能够对本实验的壁温进行预测。使用实验数据对CFD模型进行了评估,结果表明在本实验参数条件下SST模型和RNG k-ε 模型的计算壁温与实验数据趋势基本一致。     

Numerical simulation of the effects of protrusion on DC arc anode attachment

The attachment of the DC arc on the anode is usually affected by surface morphology such as protrusions due to ablation or melting deformation.A three-dimensional thermodynamic and chemical non-equilibrium model is used to numerically simulate the effect of artificially assumed surface protrusions on the arc anode attachment.The numerical simulation results show that the arc deflects toward the protrusions on the anode and attaches to them in a constricted mode,resulting in an increase in the temperature of the arc attachment region.The analysis shows that the presence of protrusion on the anode surface changes the electric field distribution,intensifies the degree of thermodynamic and chemical non-equilibrium in its vicinity,further influences the chemical kinetic process of the plasma around it,which is the main reason for the deflection of the arc toward the protrusions and the arc anode attachment in a constricted mode.In order to verify the numerical simulation results,verification experiments are also performed using similar size scale anode protrusion,and the results showed that the presence of protrusion can indeed cause the deflection of the arc and even cause the ablation of the protrusion.     

Modelling Study to Compare the Flow and Heat Transfer Characteristics of Low-Power Hydrogen, Nitrogen and Argon Arc-Heated Thrusters

A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters (arcjets) for three different propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthalpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.     

The Effect of High-Pressure Arc Discharge Plasma on the Degradation of Chlorpyrifos

A study is conducted to determine the effect of a kind of high-pressure arc discharge plasma on the degradation rate and kinetic equations of chlorpyrifos in different solvents with the treated times and concentrations as variables. The degradation rate was sorted in different solvents as water, methanol, acetone and then acetoacetate. The tendencies of the degradation rates with treated time in water and methanol were optimally fitted with first-order kinetics equations while those in acetone and acetoacetate were fitted with zeroth-order kinetics equations. The difference was attributed to the stronger polarity of water and methanol. The weak correlation of the degradation rates with time was mainly because the high-temperature of the arc discharge tube and the chemically-active species generated by the discharge. The degradation half-life was extended with increase of chlorpyrifos concentration. A degradation half-life less than 3 min was achieved for chlorpyrifos in water and methanol when the initial concentration was less than 300 μg/ml.     

直流蒸汽发生器全范围流动与传热数值模拟

以BW公司实际运行的直流蒸汽发生器为原型,采用两流体三流场数学模型数值模拟直流蒸汽发生器二次侧单相液对流换热区、核态沸腾区、蒸干后区域、过热区(即全范围)的流动沸腾换热现象。结果表明:本文采用的模型可较好地预测直流蒸汽发生器全范围的流动与传热特性,数值模拟结果与运行数据符合较好;蒸干后质量含汽率低于热平衡质量含汽率,结合壁温变化趋势表明直流蒸汽发生器运行过程中蒸干后区域存在一定程度的热力非平衡;随着流动换热的发展,表面传热系数迅速上升,蒸干的发生导致传热性能急剧下降,在蒸干后区域及过热蒸汽区表面传热系数缓慢上升。     

Radial and Angular Resolved Langmuir Probe Diagnosis of a Pulsed Vacuum Arc Plasma

Vacuum arc ion sources are known for delivering high currents of ion beams in many technological applications. There is a great need in the present ion accelera...     

横摇运动下U型管内流动与传热数值分析

利用Fluent软件分析了横摇运动下U型管内湍流流体摩擦阻力系数f和努塞尔数Nu随时间的变化。计算结果表明:横摇运动下U型管内流体f和Nu随着时间周期性波动,波动周期与横摇周期相同,波动幅度随着横摇周期的减小和横摇振幅的增大而增大;f和Nu的平均值、最大值与横摇振幅和横摇角频率近似呈线性关系;横摇增大了U型管内流体流动阻力和传热系数;横摇对U型管内流体流动传热的影响与直管明显不同。     

Behavior of an indigenously fabricated transferred arc plasma furnace for smelting studies

The utilization of industrial solid waste for metal recovery requires high-temperature tools due to the presence of silica and alumina, which is reducible at high temperature. In a plasma arc furnace, transferred arc plasma furnace(TAP) can meet all requirements, but the disadvantage of this technology is the high cost. For performing experiments in the laboratory, the TAP was fabricated indigenously in a laboratory based on the different inputs provided in the literature for the furnace design and fabrication. The observed parameters such as arc length, energy consumption, graphite electrode consumption, noise level as well as lining erosion were characterized for this fabricated furnace. The nitrogen plasma increased by around 200 K(200 ℃) melt temperature and noise levels decreased by ~10 d B compared to a normal arc.Hydrogen plasma offered 100 K(100 ℃) higher melt temperature with ~5 d B higher sound level than nitrogen plasma. Nitrogen plasma arc melting showed lower electrode and energy consumption than normal arc melting, whereas hydrogen plasma showed lower energy consumption and higher electrode consumption in comparison to nitrogen plasma. The higher plasma arc temperature resulted in a shorter meltdown time than normal arc with smoother arcing. Hydrogen plasma permitted more heats, reduced meltdown time, and lower energy consumption, but with increased graphite consumption and crucible wear. The present study showed that the fabricated arc plasma is better than the normal arc furnace with respect to temperature generation, energy consumption, and environmental friendliness. Therefore, it could be used effectively for smelting-reduction studies.