直流电弧等离子体炬的特性研究

介绍了局部热力学平衡下描述直流电弧等离子体炬的磁流体力学模型，采用数值模拟方法研 究了等离子体炬内等离子体的传热和流动特性、湍流对等离子体炬内等离子体特性的影响， 以及等离子体炬运行参数对等离子体特性的影响.将数值模拟结果与已有的实验结果进行了 比较. 关键词： 等离子体炬 磁流体力学 数值模拟     

超音速等离子体炬的数值模拟

介绍了描述大气压下超音速等离子体炬内等离子体特性的磁流体力学模型，在二维近似下，对会聚-扩展型喷口等离子体炬进行了数值模拟，获得了等离子体炬内等离子体速度、温度、压力以及马赫数的分布.结果表明超音速等离子体炬内的流场特性可以分为亚音速、跨音速和超音速三个明显的区域. 关键词： 等离子体炬 磁流体力学 数值模拟     

大气压等离子体炬电子密度的光谱诊断

利用空心针-板放电装置产生了大气压等离子体炬,采用光谱法测量了其内部及表面的电子密度. 向空心针中通入氩气,在大气环境中产生了长度为1cm的等离子体炬.实验分别测量了Hα谱线和ArⅠ(696.54nm)谱线,通过反卷积方法分离出其相应的Stark展宽,并由此计算了电子密度.结果发现,采用Hα谱线和ArⅠ(696.54nm)谱线Stark展宽计算得到的等离子体的电子密度分别为1.0×10¹⁵cm^－3和3.78×10^{15关键词： 等离子体炬 电子密度 气体温度 Stark展宽}     

超声速等离子体射流的数值模拟

基于可压缩的全Naiver-Stokes方程，利用PHOENICS程序对由会聚 辐射阳极形状等离子体炬产生的超声速等离子体射流进行了数值模拟.考虑了等离子体的黏性、可压缩性以及变物性对等离子体射流特性影响.研究了超声速等离子体射流的流场结构特性以及不同环境压力对等离子体射流产生激波结构的影响.结果表明，超声速等离子体射流在喷口附近形成的周期性激波结构是其和环境气体相互作用的结果. 关键词： 等离子体炬 超声速等离子体射流 PHOENICS     

等离子体气流量对ICP光源工作状态及分析性能的影响

本文从ICP形成的难易程度、炬管的冷却效果,ICP工作状态的变化,分析性能的差异等方面,观察和讨论了等离子体气流量的影响。一、前言 ICP光源的工作状态和分析性能与实验参数的选择有着密切的关系。Fassel认为:如果能够合理选取频率、炬管尺寸和气流模式以保证样品有效地注入等离子体的中心通道,那么剩下来的主要的工作参数就是功率、载气流量和观测高度。以前我们曾对上述三个工作参数进行过实验,但关于等离子体气流的影响并未进行过详细的观察。     

常压针-板放电等离子体密度演化

分别采用Stark展宽法、图像法诊断等离子体电子密度,研究常压针-板放电等离子体电子密度随放电参数的演化.实验结果表明,降低电源的脉冲频率,减小等离子体的电极间距和采用细径电极,都有助于提高等离子体密度.利用全局模型分析影响电子密度变化的因素可知,随着脉冲频率的下降,等离子体放电体积减小,导致电子密度上升.在电极间距减小的过程中,电子密度变化则是降低等离子体吸收功率与减小放电体积共同作用的结果,其中放电体积的减小起到了更为主导的作用,导致电子密度上升.此外,采用细径电极也可以使等离子体放电体积减小,从而有利于获得较高的电子密度.     

大功率长寿命电弧等离子体炬的研制

通过对大功率长寿命等离子体炬的基本特性的深入了解,得到了一套完整的等离子体炬运行参数.制成的等离子体炬功率在80～250kW之间可任意调节,弧电压最高达到490V,热效率最高达到73%,等离子体射流长度大于40cm.研制的等离子体系统运行稳定,性能可靠,阴极烧损量仅为4.1ng.C-1.该等离子体炬已成功地应用于三废处理实验中,运行时间已超过100h.     

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空气中的大气压辉光放电通常因放电易过渡到火花状态而难以产生。在静态大气压空气针-板等离子体发生器中，采用阻容耦合负反馈方法控制等离子体放电发展过程，成功地抑制了辉光放电向火花放电的过渡，产生了稳定的交流辉光放电。研究了电压、电极间距等参数变化对放电的影响。     

大气压微波等离子体炬的仿真设计与实验

设计了一个低成本、高稳定性的基于BJ22矩形波导的微波等离子体炬源。整个系统由1～10 kW主频2.45 GHz的磁控管微波功率源、环形器、调谐器和微波反应腔体组成。通过特殊设计的调谐装置,在气体喷嘴处产生高幅值的电场强度,使工作气体电离形成大气压开放式微波等离子体炬。对影响电场强度的几个关键因素进行了仿真,得出各个参数对场强的影响规律;根据仿真参数设计了微波反应腔体,该系统可以在大气压下激发和维持开放的稳定氩气、氦气、氮气和空气等离子体炬。对等离子体炬的基本特性和基本参数进行了研究,验证了设计参数的正确性,讨论了其可扩展性及潜在的工业应用。     

高频感应热等离子体中粉末颗粒的运动行为研究

建立了高频电感耦合等离子体炬的二维轴对称模型,利用商用软件FLUENT对钛粉颗粒在纯氩热等离子体内的运动轨迹进行了模拟,研究了前驱体粒径及载气流量的变化对粉末颗粒受力过程的影响。研究结果表明,粒径小的颗粒受炬内回流作用的影响较大,颗粒运动轨迹杂乱,而粒径大的颗粒受回流的影响则很小;降低载气流量可以使钛粉的受热更加充分,使得更多的颗粒被加热至熔化,可提高粉末的球化率。     

直流纯氩层流等离子体射流的长度变化

采用主要由阴极、阳极以及介于阴极和阳极之间的中间段组成的直流非转移式电弧等离子体发生器,在大气压条件下,比较系统地研究了纯氩层流等离子体射流的长度随着弧电流、气体流量以及发生器结构而变化的规律。结果表明:层流射流的长度随弧电流和工作气流量的增加而增长;层流向湍流流动转变的临界气流量值随弧电流增大而提高;在发生器的伏安特性呈大梯度变化的情况下,射流长度随弧电流的变化幅度增大。     

反向载气注入下等离子体反应器二维数值模拟

本文对有反向载气注入条件下等离子体反应器内的传热与流动特性进行了二维数值模拟.数值计算结果表明,由于反向载气的注入,在等离子体发生器喷嘴出口与载气喷口之间的空间区域会形成一个滞止层,而且该滞止层的位置随着反向注入的载气速度(流量)的增加向等离子体发生器出口移动,数值模拟结果与实验观察结果定性一致.     

直流非转移弧热等离子体喷枪加热效率分析

利用计算机模拟技术,采用有限容积方法,针对自制的低能耗、高效率内送粉等离子喷涂设备,对喷枪内部影响喷涂热效率的因素进行了分析。研究结果表明通过适当提高进气流量、提高混合气体中的氮气或氢气含量和减少喷枪通道长度,均能提高等离子喷枪热效率。而电流的大小以及喷枪的通道直径对热效率无显著影响。     

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介绍了自行研制的直流非转移弧等离子体炬的结构和工作原理。运用相似理论,研究了该等离子体炬的电热特性与运行参数,比如气体流量、弧功率的关系,并将计算值与实验结果进行了比较。结果表明,计算值与实验结果吻合较好,可以利用获得的公式来对炬进行结构改进和参数优化。     

外磁场对直流等离子体炬放电特性的影响

介绍了新研制的磁约束直流等离子矩设备,计算了螺旋管线圈的磁场分布,通过实验研究了磁场变化对等离子体矩放电特性和伏安特性的影响。     

Plasma generation for the plasma cutting process

This study is an attempt to estimate the overall properties, viz. the thermal power and force, of an intense plasma jet produced by a plasma cutting torch, and to relate the properties of the plasma to the diameter of the nozzle of the plasma torch and the flow rate of plasma-forming gas. For cutting metallic plates using a thermal plasma, a narrow plasma jet is produced by means of a transferred electric are between an electrode in a plasma torch and the material to be cut. The power density and pressure exerted by the plasma jet on the material at the region of cut needs to be high so that a straight cut, without dress at the bottom of the plate, can be obtained. A simple theory to describe the behavior of the arc in a plasma cutting torch has been developed to predict the are radius, pressure, and arc voltage at the nozzle exit as a function of are current for a range of nozzle sizes and air flow rates. The results obtained are in good agreement with the measured values for an air plasma cutting torch nominally rated for 100-A operation. The relationships between the mass flow rate of plasma gas, plasma power, and arc force have been discussed in the light of design of plasma torches for plasma cutting     

Numerical modelling of a direct current non-transferred thermal plasma torch for optimal performance

A laminar steady-state 2D axisymmetric model of a direct current (DC) thermal plasma torch using a magneto-hydrodynamic approach has been developed. The model takes into account the entire torch system comprising the plasma gas injection, the inner region of the torch, and the jet exiting into the ambient environment. Numerical results are obtained for two different power inputs chosen from published experimental data. The temperature predictions at the torch exit are found in good agreement with experimental results. Velocity analysis of the plasma jet has been presented and the impact of electromagnetic force on jet velocity is analysed. The Lorentz force arising due to the coupling of fluid motion and electromagnetic forces shoots up the jet velocity to significantly high values near the cathode tip. Temperature and velocity profiles are in good agreement with the characteristics of a long laminar plasma jet. An operating value of heat transfer coefficient (h) has been suggested for optimal torch operation, thus ensuring a low anode erosion rate and acceptable thermal efficiency. The argon torch has the maximum temperature and longest jet length among the plasma gases considered.     

RF discharges at atmospheric pressure

The described plasma source is based on the RF torch discharge. The powered RF electrode of the torch discharge plasma source is made from the thin metal pipe with an inner diameter of 1–2 mm and with a length of several cm. The working gas (argon pure or with an admixture of reactive components) flows through the RF electrode as the nozzle. The electrode is connected through the matching unit to the RF generator of the frequency of 13.56 MHz.The advantage of this described plasma source consists in the fact that the torch discharge remains stable up to the atmospherical pressure of the working gas even in the liquid environments. Up to now the torch discharge has been used only for treatment in liquid environment only for archaeological artefacts. For further applications it is necessary to additional study of this phenomenon. While in previous papers we presented a measurement of different temperatures from spectra emitted by plasma, there is drawn attention to equiintensity maps inside the nozzle.     

Numerical analysis of nitrogen-mixed argon plasma characteristicsand injected particle behavior in an ICP torch for ultrafine powdersynthesis

A numerical model is presented for the analysis of plasma characteristics of an ICP torch and gas mixing effects on the plasma when a nitrogen gas is added into the argon plasma as a carrier or sheath gas at the torch inlet, The fluid equations describing the plasma flow and temperature fields and the diffusions between two different gases are solved along with a magnetic vector potential equation for electromagnetic fields. The trajectory and the temperature change with time for a particle injected into the plasma are also investigated by a plasma-particle interaction model to find out optimum injection conditions for the synthesis of ultrafine nitride ceramic powders, It is found from the calculations that the nitrogen-mixed argon plasma with a nitrogen sheath gas is more favorable than the plasma with a nitrogen carrier gas for the reaction kinetics of nitride synthesis. It is also found that the radial injection through the holes of the tube wall Is preferable to the axial injection at the torch inlet for the complete evaporation of injected particle and the effective chemical reaction of reactant vapor with nitrogen. For the radial injection in an ICP torch of 20 cm in axial length, the optimum injection locations and initial velocities of 50 μm aluminum particles are found for synthesizing aluminum nitride are in the range of 6~12 cm apart from the torch inlet and over 15 m/s, respectively     

Effect of powder loading on the excitation temperature of a plasma jet in DC thermal plasma spray torch

A DC non-transferred mode plasma spray torch was fabricated for plasma spheroidization. The effect of powder-carrier gas and powder loading on the temperature of the plasma jet generated by the torch has been studied. The experiment was done at different input power levels; the temperature of the jet was within 5000–7000 K argon was used as plasma gas and powder-carrier gas. Nickel powder particles in the size range from 40 to 100 μm were processed. The temperature of the jet was estimated after flowing powder-carrier gas only into the plasma jet and with powder-carrier gas feeding powder into the flame. On introduction of powder-carrier gas and powder loading the temperature of the jet was found to decrease appreciably down to 11%. The temperature of the plasma jet was estimated using the Atomic Boltzmann plot method.