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     

氩气电弧等离子体炬提纯大鳞片石墨研究

石墨材料作为一种工业原料,特别是纯度在99.9%以上的高纯石墨被应用在各大高科技领域,现有物理法和化学法的石墨提纯技术成本高、酸碱对设备和环境破坏严重、工艺流程复杂,因此开发一种优良有效的石墨提纯技术,已成为近年来国内外研究的热点。建立了一种利用非转移电弧等离子体炬提纯大鳞片石墨的方法,利用电弧可快速产生高温的特性,对黑龙江省鸡西市纯度为94.18%的大鳞片石墨样品进行高温处理。研究显示在本文电弧装置下提纯石墨的最佳放电参数范围气流量为25 L/min、电流为400 A、功率为10 kW,此时的电弧表面温度高达3350 ℃,利用扫描电子显微镜等对电弧处理前后石墨样品的微观结构对比发现石墨样品出现粉碎、断裂等特点,根据石墨化学分析方法国家标准GB/T 3521 2008对石墨纯度及其杂质进行研究分析,经电弧处理后石墨纯度提高到99.21%。     

放射性废物玻璃固化专用等离子体炬的数值模拟与实验研究

采用了数值模拟与实验结合的方法研究了用于模拟放射性固体废物玻璃固化的非转移弧型等离子体炬的电、热特性。基于包括电弧室和开放空间在内的3D 模型得到了电弧等离子体和等离子体射流的温度场。根据计算结果,电弧室内的最高温度位于第一阳极内,达到1.77×10⁴ K;弧电压的计算值高于实测值,二者之间的差异随着电流强度的增大而逐渐减小。采用该等离子体炬熔融模拟废物的实验发现,所确定的等离子体炬到炉底的距离能够满足废物熔融的要求,与计算的结果相符合。上述结果表明,数值模拟的结果可以作为等离子体炉工程设计的依据,并可以用作进一步分析等离子体炉炉膛内工艺过程的输入条件。     

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采用了数值模拟与实验结合的方法研究了用于模拟放射性固体废物玻璃固化的非转移弧型等离子体炬的电、热特性。基于包括电弧室和开放空间在内的3D 模型得到了电弧等离子体和等离子体射流的温度场。根据计算结果,电弧室内的最高温度位于第一阳极内,达到41.77×10 K;弧电压的计算值高于实测值,二者之间的差异随着电流强度的增大而逐渐减小。采用该等离子体炬熔融模拟废物的实验发现,所确定的等离子体炬到炉底的距离能够满足废物熔融的要求,与计算的结果相符合。上述结果表明,数值模拟的结果可以作为等离子体炉工程设计的依据,并可以用作进一步分析等离子体炉炉膛内工艺过程的输入条件。     

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对感应耦合氩气热等离子体的速度分布特性以及各操作参数对等离子体速度分布的影响进行了细致的研究。研究结果表明,与直流电弧热等离子体相比,感应耦合热等离子体速度小,弧流集中,速度峰值出现在等离子体炬下游,在线圈段上游出现明显的回流现象。此外,送气流量、感应电流等操作参数对等离子体速度分布有明显影响。研究结果可为等离子体球化粉末颗粒及其他应用提供理论指导。     

The behavior of nitrogen excited in an inductively coupled argon plasma

An inductively coupled argon plasma, working at atmospherique pressure, was used as an excitation source for nitrogen gas. Excitation of atomic lines of N and of molecular bands of N₂ and N⁺₂ were observed. Two lines (389.2 and 388.8 nm) which were not previously described, are attributed to atomic nitrogen. Using the first negative system of N⁺₂, several temperature-measurement methods were used according to the resolving power of the monochromator. Good agreement is found between the rotational (4500–5000 K) and excitation temperatures (4500–5100 K) of elements injected into the plasma.     

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为了提高等离子体废物处理效率,根据磁流体动力学理论,利用计算流体力学软件FLUENT,采用磁矢量势的方法对直流双阳极非转移型电弧等离子体炬进行了二维轴对称数值模拟。计算中采用了SIMPLE算法。数值模拟得到了等离子体的温度、速度等分布。结果表明,等离子体的温度随着轴向距离的增加而减小,随弧电流增加而增加;其速度随着轴向距离的增加而先增大后减小,随弧电流增加而增加;等离子体炬出口处的温度和速度随着径向距离的增加而减小。这些结果与实验结果基本相符。     

Numerical studies on velocity, temperature history and heat transfer to the particles injected into the argon plasma

A new approach to study the particle velocity in a thermal plasma in relation to input parameters (power, gas flow rate, injection velocity of the particle and particle size) and nozzle dimensions (nozzle length and diameter) has been made. Injected particle's temperature and thermal history were calculated for particles of three different materials (alumina, tungsten and graphite) in argon plasma. Allowable powder feed rate was calculated for the particles. Heat transfer per particle injected in to the plasma is reported. Liquid fraction of the particle after it reached the melting point is also reported. Particle velocity is found to increase with increase in power, gas flow rate and injection velocity and decrease with increase in particle size, nozzle length and nozzle diameter. Thermal histories of the particles in relation to the plasma temperature and particle diameter are presented. Particle's residence time is found to increase with increase in diameter of the particle. Allowable powder feed rate for complete melting of the particle is higher at higher percentage utilisation of the plasma power. Powder feed rate is seen to decrease with increase in particle size and it is higher for tungsten and lower for graphite particle. Heat transfer rate from plasma to particle is seen to decrease with increase in time and the same is higher for plasmas of higher temperature and smaller sized particle. Received 4 May 2000 and Received in final form 15 March 2001     

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.     

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将等离子体作为磁流体,考虑其流体属性和电磁属性,介绍了利用FLUENT软件包并将其进行二次开发,解算电磁场方程、质量连续性方程、动量守恒方程、以及能量守恒方程的数值模拟方法,得到了以磁矢势为表达形式的电磁场分布、温度分布和速度分布.数值模拟了粉末球化所用的感应耦合等离子体炬电磁场分布、温度分布、速度分布.分析了温度分布、速度分布产生的物理原因,为感应耦合等离子体炬球化粉末颗粒提供理论性指导.     

外粒子源注入下气体放电过程的模拟研究

利用Geant4程序建立外源注入式、低气压气体开关物理模型,通过模拟计算电子增益与极板间电场强度、电子增益与极板间隙距离的函数关系验证了模型的正确性。计算了气体种类、气体压强对电子增益的影响,分析得到形成自持放电所需最小入射电子数,计算结果表明：在相同的气压及电场条件下,氮气的电子增益远大于氦气,这与氦气的高电离能性质相吻合; 随气压增大,电子增益呈非线性增长; 为实现自持放电,外源注入电子数面密度为1×10⁵~2×10⁵ /cm²。     

Modelling of an argon plasma flow

One-fluid MHD equations are numerically solved for an axisymmetric flow of argon inside and outside a discharge chamber of a cascaded plasma torch. Arc currents of 100 and 150 A, flow rates of 10 and 30 slpm, and two different optical thicknesses are assumed. The flow is shown to be only weakly compressible, of the Mach number below 0.3. The calculated torch powers range from 3 to 7 kW, the energy lost by radiation is (1–3) kW. Axial velocities of (200–600) m/s and temperatures of (12 500–14 400) K are found at the torch nozzle exit and compared with available experimental data. Inside the chamber, several recirculation zones are predicted. The physical model and the chamber shape used can readily be extended for a hybrid plasma torch with the simultaneous stabilization of the electric arc inside the chamber by argon and, e.g., water swirl.Dedicated to Professor Jií Horáek on the occasion of his 60th birthday.     

Observations of acoustic-wave-induced superluminescence in an argon plasma

It is shown that in an argon discharge plasma it is possible to obtain overpopulation of certain electronic levels of atomic argon under the influence of acoustic waves. When the specified threshold is exceeded, then a superluminescence (in the form of light flashes) from the overpopulated electronic levels of atomic argon is observed.     

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。     

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。     

Time-resolved imaging of anodic arc root behavior duringfluctuations of a DC plasma spraying torch

The fluctuating behavior of a Sulzer Metco F4 DC plasma gun has been investigated by simultaneous measurement of the time dependencies of the are voltage and of images from the nozzle interior. An end-on imaging arrangement using a mirror and a mask in the optical path from the are to the camera allows visualization of the anodic arc attachment by strongly attenuating the bright emission from the are column. With the torch operating in the restrike mode, sequences of images have been acquired in synchronization with several typical features of the are voltage fluctuations showing that the attachment nature changes during a restrike cycle. Multiple attachments which coexist at least during the 1 μs exposure time of the camera have been evidenced and are interpreted as a continuous process of creation/vanishing of successive arc roots with a smooth transfer of the current from one to the other. The anode wear is shown to have a strong effect on the root position over the anode periphery, with a preference for attachment in eroded regions. The effects of operation parameters such as current, gas flow and injector type on the attachment nature and position are also presented     

不同振动模式下颗粒分离行为的数值模拟

利用三维离散元法对垂直方向上的直线、圆和椭圆振动模式颗粒分离过程进行了数值模拟研究,对直线振动时上层大颗粒的波动及圆和椭圆振动时出现的聚集、循环等现象的形成机理进行了分析,并讨论了振动强度对各振动模式下颗粒分离形态的影响规律. 研究表明,综合运用空隙填充、侧面驱动的颗粒运动和能量非均匀分布三种机理,并结合颗粒群的速度矢量分布情况能够较好地解释各振动模式下的颗粒分离行为. 振动强度对圆和椭圆振动模式的分离形态具有显著的影响,并在振动强度约为3时,各种振动模式均具有良好的颗粒分离效果和稳定的颗粒运动状态. 关键词： 振动模式 颗粒分离 离散元法 数值模拟     

不同振动模式下颗粒分离行为的数值模拟

利用三维离散元法对垂直方向上的直线、圆和椭圆振动模式颗粒分离过程进行了数值模拟研究,对直线振动时上层大颗粒的波动及圆和椭圆振动时出现的聚集、循环等现象的形成机理进行了分析,并讨论了振动强度对各振动模式下颗粒分离形态的影响规律. 研究表明,综合运用空隙填充、侧面驱动的颗粒运动和能量非均匀分布三种机理,并结合颗粒群的速度矢量分布情况能够较好地解释各振动模式下的颗粒分离行为. 振动强度对圆和椭圆振动模式的分离形态具有显著的影响,并在振动强度约为3时,各种振动模式均具有良好的颗粒分离效果和稳定的颗粒运动状态.     

Experimental study for the optimization of plasma torch operations

In this paper the electric and efficiency attributes of a low-powered dc plasma torch has been investigated. Torch operations require reproducibility, reliability and economicity to be attained. The characterisation allowed to scope operative ranges on the basis of minimum voltage fluctuations and maximum thermal efficiency levels for different gas flow rates, anode dimensions, arc current and two process gases (Ar, N₂){\rm (Ar, N_2)}.     

Analytical treatment of plasma injected into an illuminated photoconductor

An analytical treatment of optically generated carriers in a double injection structure is given. The quasineutrality approximation is used, and both recombination through traps (constant lifetime) and bimolecular recombination are considered.