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《等离子体物理论文集》2017,57(2):58-66
Plasma jets from conventional non‐transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non‐transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device. 相似文献
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Levitan Y.S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(1):30-33
Friction factor and wall heat-transfer data for axially symmetric flow in a wall-stabilized arc analysis are given. Heat transfer results revealed three significant modes: laminar flow with an unstable arc, laminar flow with a wall-stabilized arc, and turbulent flow with a wall-stabilized arc. It was shown that the critical Reynolds number increases, in comparison with the case of the flow without Joule heating. A friction factor from Reynolds-number dependence peculiarities was not discovered for laminar to turbulent flow transition 相似文献
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A detailed observation of an arc in a model puffer-type SF6 gas circuit breaker in the current range between 10 and 50 kA (rms) has been carried out. It was found that the arc column remained stable on the center axis during the high-current region, then became turbulent near current zero. It was found that the time interval during which the turbulent arc was observed decreased with increasing values of the peak current. These phenomena indicated that the thermal effects of high-current arcs remain even at current zero. It also was observed that the arc diameter at the nozzle throat outlet was smaller than that at the throat (29 mm), even at a current as high as 70 kA (instantaneous), and that the boundary of gas flow at a downstream region had a very large diameter when the arcs were present. However, around current zero the boundary diameter became as small as that without arc. 相似文献
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《等离子体物理论文集》2017,57(9):395-403
An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry. 相似文献
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The gas dynamics in a discharge chamber for arc production of fullerenes in the inert gas atmosphere is analyzed for the first
time. A turbulent fanlike jet due to the carbon flow from the discharge gap is shown to be a crucial factor in the gasdynamic
pattern formation. The dependence of the fraction of fullerenes extracted from the chamber on the total amount of the product
is constructed, with the gas flow rate, as well as the radius and length of the chamber, being adjustable parameters. Tangential
twisting of the gas, a way of improving the fullerene extraction efficiency, is considered. 相似文献
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The conservation equations of mass, momentum, and energy in differential form, Ohm's law, and the experimentally determined dependence of the interruption capability of the arc on current shape are employed to obtain similarity relations for high pressure electric arcs in forced axial flow around current zero. The similarity relations are then applied to assess the validity of laminar and turbulent flow models for the arc by comparing model predictions with experiment. It is found that the laminar flow model quite often predicts arc behavior contrary to experiment, while the turbulent flow model predictions are much more consistent with experiment. Moreover, the similarity relations should also be useful in exploring arc behavior under circumstances not discussed in this work. 相似文献
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Flow phenomena occurring in repetitively pulsed gas-flow spark gaps have been investigated experimentally and compared with theory. Optical flow diagnostics were obtained after the current pulse using schlieren photography, a flashlamp, and a framing image converter camera (ICC). Experimental results reveal nearly spherical arc-generated shocks propagating symmetrically with respect to the arc debris center. Supersonic shocks rapidly weaken into acoustic disturbances. Heated arc debris convects at the undisturbed gas velocity, while turbulent debris spreading causes a linear growth of the heated gas region radius at a velocity of 10-40 m/s. At low flow velocity (15 m/s), the upstream edge of the heated arc debris remains at a constant streamwise position until 700 ?s after the arc, and then moves downstream at constant velocity. This delay time before downstream motion begins is reduced to 38 ?s for gas velocities of 35 m/s. Numerical results qualitatively agree with experiments, where heated gas is predicted to convect at the undisturbed gas velocity. The shocks, which initially propagate at high Mach number, rapidly slow to acoustic speed. 相似文献
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对大气压直流滑动弧等离子体的电参数和发射光谱进行了测量,比较研究了不同气体种类下滑动弧等离子体电压的特性.以氮气滑动弧为例,分析了其在一个周期内电弧电压、电流、电阻和功率的变化特性.通过对电弧电压信号进行快速傅里叶变换频谱分析,研究了气体种类、气体流量和外部电阻值对滑动弧等离子体脉动特性的影响.结果表明随着气流量或外部电阻值的增加,其主要脉动频率变高,电弧周期变小.利用光谱法检测了氮气、氧气和空气滑动弧等离子体的主要自由基种类,并研究了外部电阻值对发射光谱强度的影响和沿电极中轴线在337.1 nm(N关键词:
滑动弧等离子体
非平衡等离子体
脉动特性
发射光谱 相似文献
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Stability of the combined flow of liquid film and turbulent gas is studied theoretically for an arbitrary angle between the directions of gas flow and gravity force. The three-dimensional wave flow of the film is described on the basis of integral approach and quasilaminar model of the turbulent gas flow. Increment and phase velocity of waves are calculated for the case of a vertical film and horizontal gas flow depending on the direction of their propagation. According to calculations, the cross gas flow increases the instability area significantly as well as the range of directions for propagation of the fast growing perturbations on the film surface. 相似文献
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Classification and performance capability of electric are linear plasmatrons are presented. The results of investigation into convective and radiative heat transfer in the discharge channel of a plasmatron are reported. The radiative heat transfer dominates both in the structure of heat losses and in the formation of discharge volt-ampere characteristic at the initial region of the flow. Relations to calculate heat losses by radiation are given. Radiative convective interaction at the arc boundary is shown to play a substantial role for high-current discharges stabilized by axial vortex gas flow. It is shown that the calculation of convective heat transfer at the turbulent region of the flow may be carried out by flow averaged parameters. 相似文献
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使用空心针板放电装置,以氩气作为导入气体,在大气环境下产生了1.6~3 cm波长的等离子体炬。利用发射光谱法,研究了等离子体炬弧根和弧梢处的气体温度和振动温度,以及它们随气体流量的变化。等离子体气体温度通过对OH基309 nm附近的谱带进行拟合得到,等离子体振动温度由氮分子第二正带系C3Πu—B3Πg计算得到。实验发现弧根和弧梢处的气体温度相等,并随着气体流量的增大而下降。当气体流量从3.0 mL.min-1增大到6.5 mL.min-1时,气体温度由350 K下降到300 K。当气体流量较小(如3.0 mL.min-1)时,弧梢处的振动温度(1 950 K)高于弧根处的振动温度(1 755 K)。随着气体流量的增大,弧梢处与弧根处的振动温度均下降,但弧梢处下降速率较快。当气体流量较大时,二者趋于相等。 相似文献
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N. N. Simakov 《Technical Physics》2013,58(4):481-485
To investigate the influence of a strongly turbulent incoming flow on the hydrodynamic drag of a body and occurrence of the early crisis of drag, a numerical experiment is conducted in which a free gas flow about a sphere is simulated for two cases, namely, for a laminar flow and for a strongly turbulent flow. Turbulence is simulated by assuming a high kinematic coefficient of turbulent viscosity. Calculation data lead us to conclude that the early crisis of drag at Reynolds numbers near 100, which shows up as a considerable (four-to sevenfold) decrease in the hydrodynamic force and the drag coefficient of the body, can be explained by the strong turbulence of the incoming flow. 相似文献
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H. P. Graf H. P. Meili E. Fischer H. J. Schoetzau 《Applied physics. B, Lasers and optics》1985,36(1):33-40
The increase of the interrupting capability of modern SF6 puffer breakers demands a better knowledge of the interaction of the arc with the gas flow. During the current interruption in an SF6 breaker the arc temperature in the stagnation zone is of decisive importance. The temporal evolution of the arc temperature and the diameter is studied by means of interferometry and emission spectroscopy. Experimental results are presented which show the influence of the current slope and the gas pressure on the arc decay. These results are compared with a theoretical model describing the temperature decay after current interruption. 相似文献
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针对活性剂等离子弧焊焊接过程,利用光谱分析方法对活性剂等离子弧焊焊接电弧进行光谱分析,采用红外热像伪着色法测定活性剂等离子弧焊焊接电弧温度场,并建立活性剂等离子弧焊焊接电弧热流密度径向分布模型,对焊接电弧的成分及焊接电弧温度场进行了研究。研究结果表明,常规等离子焊焊接电弧以氩原子和氩一次电离离子的谱线为主,金属蒸气谱线不突出,焊接电弧以气体粒子为主,属于气体电弧;活性剂等离子弧焊焊接电弧的光谱中氩原子及氩一次离子谱线的辐射强度增强,Ti,Cr,Fe金属谱线大量涌现;活性剂等离子弧焊焊接电弧的温度分布比较紧凑,温度场外形窄,温度分布范围较集中,电弧径向温度梯度较大;电弧径向温度分布呈现正态Gauss分布模式。 相似文献
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本文应用强旋湍流气一固两相流动和煤粉燃烧的数学模型,对新型涡旋燃烧炉内的流动、传热和燃烧过程进行了系统的模拟和分析,得到了与实验相符合的结果。结果表明,涡旋燃烧炉内的湍流空气动力场分布具有强旋、回流和正在发展流的特点。水冷壁总吸热量随燃烧热负荷的增大成比例地增加。煤粉颗粒在炉内的平均停留时间随初始粒径的增大而加长。炉内可实现煤粉的低温、强旋、高效率和高强度燃烧。 相似文献