Comparison of Reynolds average Navier-Stokes turbulence models in numerical simulations of the DC arc plasma torch

Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.

Characteristics and Temperature Measurement of a Non-Transferred Cascaded DC Plasma Torch

Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The potential structure inside the torch and its dependence on the plasma current and gas flow rate are also investigated. The arc voltage is seen to exhibit negative characteristic for a current below 150 A and positive characteristic above that current value. The voltage drop near the electrodes is found to decrease with the increase in plasma current. 25~ of the total voltage is dropped near the cathode at a plasma current of 50 A and a argon plasma gas flow rate of 10 liter per minute （LPM）, and it decreases to 12% with the current increasing to 300 A, and to 17% with a gas flow rate of 25 LPM. The variation in the torch efficiency with the gas flow rate and plasma current is also reported. The efficiency of the torch is found to be between 36% and 48%. In addition, the plasma gas temperature at various positions of the reactor and for different currents and voltages are measured by calorimetric estimation with a heat balance technique.

Optical characterization of single-crystal diamond grown by DC arc plasma jet CVD

Optical centers of single-crystal diamond grown by DC arc plasma jet chemical vapor deposition(CVD) were examined using a low-temperature photoluminescence(PL) technique. The results show that most of the nitrogen-vacancy(NV) complexes are present as NV-centers, although some H2 and H3 centers and B-aggregates are also present in the single-crystal diamond because of nitrogen aggregation resulting from high N_2 incorporation and the high mobility of vacancies under growth temperatures of 950–1000°C. Furthermore, emissions of radiation-induced defects were also detected at 389, 467.5, 550, and 588.6 nm in the PL spectra. The reason for the formation of these radiation-induced defects is not clear. Although a Ni-based alloy was used during the diamond growth, Ni-related emissions were not detected in the PL spectra. In addition, the silicon-vacancy(Si-V)-related emission line at 737 nm, which has been observed in the spectra of many previously reported microwave plasma chemical vapor deposition(MPCVD) synthetic diamonds, was absent in the PL spectra of the single-crystal diamond prepared in this work. The high density of NV-centers, along with the absence of Ni-related defects and Si-V centers, makes the single-crystal diamond grown by DC arc plasma jet CVD a promising material for applications in quantum computing.

Diagnosis of Electron,Vibrational and Rotational Temperatures in an Ar/N2 Shock Plasma Jet Produced by a Low Pressure DC Cascade Arc Discharge

In this paper, a low pressure Ar/N2 shock plasma jet with clearly multicycle al- ternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis. Plasma emission intensity, electron, vi- brational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones. The results indicate that the ranges of the measured electron temperature, vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV, 0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV, respectively, and it is found for the first time that the vibrational and rota- tional temperatures increase while the electron temperature decreases in the compression zones. The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma effects. Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.

Design and characteristics of a new type laminar plasma torch for materials processing

Laminar plasma jet(LPJ)generated by laminar plasma torch(LPT)has a favorable temperature and velocity distribution.Thus,it is superior to the turbulent plasma jet in material processing.However,most of the reported LPTs usually operate at a relatively low output power with a relatively low arc voltage and thermal efficiency,which limits its capabilities.In this context,this paper attempts to design a new type of high-power LPT with a relatively low arc current and a high thermal efficiency.In the first section,the design principle of the main components is studied and discussed in detail,and a new high-power LPT is proposed.Then,the experimental characteristics of the proposed high-power LPT are examined.Experimental results reveal the following characteristics of the proposed LPT.(1)The max jet length of the proposed LPT reaches at 540 mm.(2)Its mean arc voltage is higher than 290 V when the LPT works with arc currents lower than 200 A.leading to an output power greater than 50 kW.(3)The mean thermal efficiency is higher than 509f.Lastly,the proposed LPT has been applied to spheroidize the aluminum oxide powers.The experiment results for the production of spherical powders show that the proposed LPT hits a good characteristic for material processing.

Prediction of Weld Bead Geometry in Plasma Arc Welding using Factorial Design Approach

The effect of various process parameters like welding current, torch height, welding speed and plasma gas flow rate on front melting width, back melting width and weld reinforcement of plasma arc welding on aluminum alloy is investigated by using factorial design approach. Variable polarity plasma arc welding is used for welding aluminum alloy. Trail experiments are conducted and the limits of the input process parameters are decided. Two levels and four input process parameters are chosen and experiments are conducted as per typical design matrix considering full factorial design. Total sixteen experiments are conducted and output responses are measured. The coefficients are calculated by using regression analysis and the mathematical models are constructed. By using the mathematical models the main and interaction effect of various process parameters on weld quality is studied.

直流电弧等离子体炬数值模拟与诊断

直流电弧等离子体炬内部物理过程复杂且具动态性,较难对其进行准确描述与深入研究,且其工作温度较高,其状态参数难以使用常规方式测量。针对直流电弧等离子体炬,建立流动、传热和电磁相互耦合的数值模型,基于Fluent软件对直流电弧等离子体炬进行三维数值模拟和特性分析,设计并搭建了一套热焓探针实验系统,完成对直流电弧等离子体炬射流参数的测量分析。结果表明:建立的数值模型模拟结果与实验测量结果吻合较好,误差在10%以内;炬内温度与速度最大值与工作气流量呈正相关,均出现在靠近阴极区域,且沿轴线逐渐降低;等离子体炬内高温区与高电流密度区重合。

直流电弧等离子体喷射(DCPJ)法在沉积金刚石膜上的应用

直流电弧等离子体喷射法是制备金刚石膜的一项很有前途的技术。综述了直流电弧等离子体喷射法的原理、进展状况、工艺上的改进和建立机理模型上的努力。

在DC-PCVD阴阳极上沉积氮化硅薄膜

置于直流等离子体化学气相沉积（ＤＣＰＣＶＤ）装置的阴极或阳极的２０、２０Ｃｒ、ＧＣｒ１５及２Ｃｒ１３钢，以及单晶硅材料的试样均可沉积获得以Ｓｉ３Ｎ４成分为主要成分的非晶态的绝缘薄膜。这种膜有一定制作条件，讨论了阴阳极上试样都能获得这种膜的原因。

大容量直流电弧炉接入对电网谐波的影响分析

大容量直流电弧炉是高功率的非线性负荷,运行时会产生大量谐波,影响电网的电能质量。基于某钢铁集团130t直流电弧炉配电网架构及参数,建立了含治理装置的大容量直流电弧炉的动态仿真模型,分析了大容量直流电弧炉的谐波发射特性及其影响因素。通过现场实测和仿真结果,分析了大容量直流电弧炉接入电网后的谐波特性,验证了静止无功补偿器(SVC)的滤波效果,为直流电弧炉接入电网后的监督和治理提供了参考。

直流（DC）电弧炉技术的发展动态

大电流可控硅整流电源的发展和炉底电极这一难题的解决促使直流（ＤＣ）电弧炉的迅速发展，近几年大部分新建电弧炉为ＤＣ炉并将一些已有的交流（ＡＣ）电弧炉改成ＤＣ电弧冶炼。

直流电弧等离子体炬的数值模拟

等离子体炬内部的物理场是影响等离子体性能及等离子体炬设计等方向的重要信息。受等离子体炬内部小空间、高能量密度及高电荷密度等因素的影响,无法通过常规手段进行测量。为了得到等离子体炬内部的温度、速度场分布情况,本文使用COMSOL建立了一台30 kW直流等离子体炬的二维轴对称模型。为了验证模型的可靠性,搭建了包括等离子电源、等离子体炬在内的实验平台,并使用热焓探针对该等离子体炬出口处的温度场进行诊断。将等离子体炬的模拟结果与实验测得的数据进行对比,发现模拟结果能够较好的吻合实际情况。改变模型阴极的电流输入,对等离子体炬内部的流场及温度场变化情况进行了系统模拟研究,得出了等离子体炬内部的发展模式,以及热量传递的薄弱点,可以为今后等离子体炬的优化方向提供参考。

热等离子体裂解低碳烃制备石墨烯研究进展

石墨烯是一种新型二维碳纳米材料,因其特殊的二维结构而具有卓越的力学、电学、光学、热力学等性质,在储能、电子、环境等方面具有广阔的应用前景。然而,现有的制备方法还难以实现高品质石墨烯的低成本、大规模的制备,阻碍了石墨烯的产业化广泛应用。文章综述了近年来石墨烯的各种制备方法,介绍了不同制备方法的特点,重点介绍了热等离子体法裂解低碳烃制备石墨烯的研究进展,主要包括射频热等离子体法和直流电弧放电热等离子体法,并对该领域存在的问题和发展方向进行了总结和展望。

甲烷等离子体法制氢气和碳材料研究进展

传统甲烷制氢技术会伴随大量的二氧化碳排放,甲烷等离子体法裂解技术将甲烷中的碳元素直接转化为固体碳材料,过程无二氧化碳排放,并有效提高了甲烷的利用价值。通过文献调研方式回顾和分析了甲烷等离子体法裂解技术在国内外的发展现状。研究结果表明:(1)甲烷等离子体法裂解中等离子体的类别主要分为热等离子体和冷等离子体,冷等离子体中主要的活性粒子是高能电子,热等离子体中的活性物质为高能电子和重粒子;(2)冷等离子体的产生方式主要有电晕放电、介质阻挡放电、滑动电弧放电等,所需功率较低;热等离子体的产生方式主要为直流电弧放电、直流-射频耦合放电,所需功率较高;(3)甲烷在等离子体中的转化率和氢气的产率与工作气体类别、工作气体与甲烷物质的量比、气体电解功率大小、电极构型、反应腔体结构等工艺参数都有直接关系;(4)通过调整工艺参数和电极结构设计,甲烷在等离子体中可裂解生成如炭黑、碳纳米管、石墨烯纳米薄片等不同形貌的固体碳材料,产品多样。结论认为,甲烷等离子体法裂解技术不仅可以降低温室气体排放,还是甲烷高附加值利用的一个重要方向;提高甲烷等离子体法制氢的能量利用效率和生成碳材料的选择性是该技术的发展方向。

直流电弧等离子体炬物理场的数值模拟研究

直流电弧等离子体炬内部温度较高,物理场情况复杂,较难进行实验研究,因此对等离子体炬内部物理场的研究一般采用基于磁流体动力学模型的数值模拟研究。以一种直流电弧等离子体炬为研究对象,在给定的电流大小以及工作气体流量条件下对其温度场、速度场等物理场进行了数值模拟研究,研究结果表明:在电流大小200 A、工作气体流量0.0014 kg/s的工作模式下,直流电弧等离子体炬射流在出口处中心温度可达到13000 K,出口最大流速可达到2400 m/s。高温等离子体的温度分布主要与电流密度的分布有关,其能量来源主要是电弧产生的焦耳热。台阶形的阳极结构主要对等离子体射流的流速产生影响。

直流电弧炉无功超短期滚动预测及控制

为提升直流电弧炉系统SVC装置动态补偿性能,提出了一种直流电弧炉无功超短期滚动预测及控制方法。首先,分析并揭示了直流电弧炉的控制原理及无功特性;其次,建立了直流电弧炉超短期无功滚动预测模型,基于AIC信息准则和历史冶炼数据实现了预测模型的定阶;然后,基于预测模型提出了直流电弧炉无功超短期滚动预测控制方法;最后,对预测及控制效果进行了仿真验证。与传统控制方法相比,采用预测控制算法后,瞬时闪变降低了31.16%。所提预测控制算法对直流电弧炉系统SVC装置的闪变抑制效果改善显著。

Optical emission spectroscopy diagnosis of energetic Ar ions in synthesis of SiC polytypes by DC arc discharge plasma

硅碳化物是有合适的 bandgaps (2.4-3.3 eV ) 和唯一的光性质的尺侧皮的陶艺。有不同形态学，尺寸，和水晶类型的 SiC@C monocrystal nanocapsules 经由快、灵巧的直接水流(DC ) 被综合弧分泌物血浆方法。nanocrystal 的形成上的 Ar 空气的影响原文如此， polytypes 被光排放光谱学(OES ) 调查在弧分泌物血浆上诊断。Boltzmanns 阴谋被用来估计作为 10,582 K 包含不同 Ar 集中的血浆的温度(在 2 ??唓 吗？？

外部磁场对直流电弧等离子体放电特性的影响及其机理

通过外部磁场驱动电弧旋转产生相对均匀的等离子体是一种可能的改进等离子体放电特性的有效手段。利用高速摄像技术和虚拟仪器技术,观察并测量了大气条件下、非均匀磁场驱动的直流电弧等离子体阳极弧根运动以及电弧电压波动。结果发现:相比无外部磁场,非均匀外部磁场驱动下的直流电弧等离子体在旋转力和稳弧力的作用下阳极弧根旋转,均匀性提高;其电弧电压波动幅度增大,放电模式发生改变;伏安特性曲线向上平移,电弧等离子体炬放电功率提高。另外,由于等离子体射流的高速运动而引起的等离子体射流在喷口处径向扩张,使等离子体射流横截面扩大,进一步提高了射流的均匀性。从结果中可以看出,外部磁场改善了直流电弧等离子体炬的基本特性,对直流电弧等离子体炬应用效率的提高具有重要的意义。

直流污秽放电对硅橡胶表面特性破坏过程

为研究直流电弧烧蚀作用下硅橡胶材料表面特性的变化,利用直流斜面法装置,从憎水性丧失和恢复特性、泄漏电流变化、生成物质特性3个方面对硅橡胶材料进行漏电起痕实验。实验发现,污秽放电过程分4个发展阶段,分别为随机初始电弧、电弧集中烧蚀、憎水性物质形成及电弧终止。在每个阶段,硅橡胶烧蚀部分的憎水性分布具有典型特征,泄漏电流随硅橡胶表面破坏速度和范围的变化同步发展。不同试品在电弧烧蚀过程中,均会产生具有憎水性的白色粉末,该物质的出现会阻碍电弧的发展。实验结束后将试品于恒温箱中放置48h,发现硅橡胶材料在电弧烧蚀破坏部分静态接触角可达到136.6°,憎水性得到很好的恢复,好于新的硅橡胶样品。

改进型地铁用直流断路器

直流断路器是地铁供电系统中切除故障的关键设备。目前,我国地铁供电系统中采用的直流断路器多为强制拉弧,故障电流可高达数万安培,从而导致直流断路器烧毁。该文首先在分析电弧数学模型的基础上,结合Matlab软件中的Mayr模型,建立了传统直流断路器的仿真模型,仿真结果表明,因断路器电流过大从而导致传统直流断路器易损坏。针对传统直流断路器的不足,文中提出了传统直流断路器的改进方案,给出了电路结构,并建立了仿真模型。仿真结果表明,改进型直流断路器具有良好的熄弧特性,不易遭受损坏,具有良好的应用前景。