氩气等离子体射流诱导水生成OH自由基的研究

·OH在众多领域中具有非常重要的作用,在国际上引起了广泛关注,而大气压等离子体射流由于不需要真空、装置简单易于携带,且具有高浓度活性粒子、高电子温度、低射流温度等优点,具有极强的应用前景,成为气体放电领域的重要研究课题。特别是如何诱导等离子体射流中·OH的产生已成为等离子体射流领域一个新的研究热点。国外率先报道了将水蒸汽以一定的比例混入等离子体射流工作气体中以诱导产生大量·OH的研究,然而当含水量较高时,射流会剧烈摆动,放电变得十分不均匀、不稳定。为此,本文设计了一种大气压双环电极氩气等离子体射流诱导水产生·OH的装置,通过引入超声雾化装置增加等离子体羽周围的湿度以提高·OH含量,重点研究了不同电压、流量下诱导水生成OH(A2Σ+)的生成规律;利用发射光谱法测试了装置产生·OH的含量;并利用810.41和811.48nm这两条Ar原子光谱线,计算了等离子体羽中的电子温度。结果表明等离子体羽可以诱导周围的水产生·OH,且随电压从20kV增大到28kV时,OH(A2Σ+)的产量逐渐增大;而当氩气流量从100L·h-1增大到200L·h-1时,·OH产量随着流量的增大而增大,但是当氩气流量从200L·h-1增大到600L·h-1时,·OH产量随着流量的增大而不断减小。OH(A2Σ+)的产量和电子温度变化趋势完全一致,证明了·OH的产量主要受电子温度的影响。

三种波形激励的大气压等离子体射流的比较研究

本文采用了棒-环结构的氩气等离子体射流装置,在正弦波、三角波和方波三种激励下均产生了锥形的大气压等离子体羽.利用电学方法,发现三种波形激励的放电,其放电脉冲均出现在电压正半周期内,而负半周期内没有放电脉冲.并且放电脉冲个数均随着电压峰值的增加而增加.对于多脉冲放电,正弦波和三角波激励的放电脉冲强度在电压上升沿内逐渐增加,而方波激励的脉冲强度在电压的正半周期内保持不变.此外,方波激励的相邻放电脉冲的时间间隔要比正弦波和三角波的大.利用高速影像研究发现正弦波和三角波激励的等离子体羽均由击穿阶段(流光发展)和余辉阶段组成.通过分析放电过程,对以上现象进行了定性解释.

Degradation of the Emission Current from the Field Emitter Caused by Ion Bombardment

In field emission devices, the emission current sometimes degrades with the time. The mechanism of the current degradation is complicated. In this paper, a program is used to simulate the movement of the electron beam from a field emitter. According to the current distribution and the trajectories of the primary electron beam, it is shown that the residual gas is ionized and the ion pairs are generated. The trajectories of the positive ions are simulated. With the different locations and kinetic energy of i...

Combustion characteristics of supersonic strut-cavity combustor under plasma jet-assisted combustion

Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.

Development of an Emulator for the Plasma Process Control

This work aims at developing an automatic system for the control of the APS （air plasma spraying） plasma process in which some instability phenomena are present. APS is a versatile technique to produce coatings of powder material at high deposition rates. Using this technique, powder particles are injected into a plasma jet, where they are melted and accelerated towards a substrate. The coating microstructures and properties depend strongly on the characteristics of the plasma jet, which can be controlled by the adjustment of the process parameters. However, the imeractions among the spray variables, render optimization and control of this process are quite complex. Understanding relationships between coating properties and process parameters is mandatory to optimize the process technique and the product quality. We are interested in this work to build an on-line control model for the APS process based on the elements of artificial intelligence and to build an emulator that replicates the dynamic behavior of the process as closely as possible.

The Pulsed Plasma-Liquid Systems at Cylindrical Geometry with Possibility of Convergent Acoustic Waves Efficient Generation

This research investigates the possibility of convergent acoustic waves generation in the liquid by means of the sotmd waves reflection from the solid cylindrical surface, emerged in the pulsed electric discharge. The spectra of pulse discharge plasma emission in the water and in the air-water mixture were obtained. The temperature of cuprum and oxygen atoms electronic excitation levels and the temperature tendencies during the discharge current existence were calculated.

Laser-driven plasma collider for nuclear studies

A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D ＋D → n＋3He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to - 7.6 ×105 neutrons had been observed. This new type of ＂plasma collider＂ could provide an innovative tool to study nuclear reactions under astrophysical conditions.

Effect of pressure on the performance of plasma synthetic jet actuator

The effects of the ambient air pressure level on the performance of plasma synthetic jet actuator have been investigated through electrical and optical diagnostics.Pressures from 1 atm down to 0.1 atm were tested with a 10 Hz excitation.The discharge measurement demonstrates that there is a voltage range to make the actuator work reliably.Higher pressure level needs a higher breakdown voltage,and a higher discharge current and energy deposition are produced.But when the actuator works with the maximum breakdown voltage,the fraction of the initial capacitor energy delivered to the arc is almost invariable.This preliminary study also confirms the effectiveness of the plasma synthetic jet at low pressure.Indeed,the maximum velocities of the precursor shock and the plasma jet induced by the actuator with maximum breakdown voltage are independent of the ambient pressure level;reach about 530 and 460 m/s respectively.The mass flux of the plasma jet increases with ambient pressure increasing,but the strength of the precursor shock presents a local maximum at 0.6 atm.

Aerodynamic control of NACA 0021 airfoil model with spark discharge plasma synthetic jets

Spark discharge plasma synthetic jets(SPJs) have been used for the active flow control study on an NACA 0021 straight-wing model in a wind tunnel. The model forces and moments were measured using a six-component sting balance at a 20 m/s wind speed. The aim was to explore the SPJ's effect on airfoil aerodynamic by examining SPJ generators' position along the chordwise and the jet flow direction about the chord. Near the wing leading edge, two SPJ generators raised the stall angle by 2° and increased the maximum lift coefficient by 9%. The drag coefficient was decreased by 33.1%, and the lift-drag ratio was increased by 104.2% at an angle of attack above 16°. The rolling-moment coefficient was modified by 0.002, and the yawing-moment coefficient was changed by 0.0007 at angles of attack in the range of 0°–16°. The results showed that SPJs can control wing aerodynamic forces at a high angle of attack and moments at a low angle of attack.

The effect of actuation frequency on the plasma synthetic jet

The flow induced by plasma synthetic jet actuator was simulated through solving the Reynolds-averaged Navier-Stokes equations augmented by body force phenomenological plasma model.The effect of actuation frequency on the plasma synthetic jet was examined by case study.The numerical results present that with the actuation frequency increasing,the stream-wise distance of the adjacent vortex pairs induced by the actuator decreases monotonically,which is the same as the situation of the velocity fluctuations field caused by the vortex pairs.When the actuation frequency is 60 Hz,the vortex pairs formed during the adjacent actuation periods merge together quickly,and the flow structure in the downstream region is more close to that of the steady case.The actuation frequency has no visible influence on the time-averaged flow field of plasma synthetic jet.However,when the actuation frequency is relatively low(f<40 Hz),the momentum flux close to the actuator increases with the actuation frequency increasing,which is contrary to the situation in the far field from the wall.