大气压低温等离子体射流甲醇直接合成乙二醇新技术实验教学研究

利用激光诱导荧光(LIF)及发射光谱(OES)对大气压CH_3OH/Ar等离子体射流放电进行了详细地诊断研究,主要考察了不同CH_3OH/Ar体积比对射流中OH自由基的密度时空分布的影响。研究结果表明,仅少量的甲醇蒸气掺入到工作气体氩气中时(CH_3OH/Ar体积比为0.05%),有利于OH自由基的产生。发射光谱测量结果中发现存在含碳的特征活性粒子,如CN、CH、C2等。对大气压CH_3OH/Ar等离子体放电中甲醇的分解机制进行了详细的探讨。通过实验数据及进一步的探讨分析,评估了大气压低温等离子体射流中甲醇直接合成乙二醇技术的关键性外界工作参数。

基于大气压低温等离子射流处理的材料亲水性实验教学研究

通过大气压下低温等离子体射流对材料表面进行处理,可以极大地提高材料表面的亲水性。该方法有别于传统的共混、表面接枝和界面聚合等方法对膜材料亲水性改性,利用悬浮电极射流源产生的等离子体化学活性强、气体温度低,而且操作简单、成本低廉。通过水接触角测量仪测量射流处理前后材料表面的水接触角,从而表征材料表面亲水性改性。该实验可以吸引学生的注意力,帮助学生加深了解材料及物理等交叉学科基本知识,培养学生运用材料物理基础理论知识和实验技能进行材料研究开发的基本能力,可为中国大学材料及物理相关专业的本科实验教学提供参考和启示。

基于介质阻挡放电实现高分子薄膜与金属层间有机黏合实验方法

提出一种新型的金属与聚乙烯薄膜层间有机黏合方法,能够实现薄膜层之间的有机黏合。该方法基于大气压Ar/O2介质阻挡放电对聚乙烯薄膜表面改性预处理,利用射频电感耦合等离子体增强非平衡磁控溅射系统在预处理的聚乙烯薄膜表面镀铜膜。研究结果表明,介质阻挡放电处理聚乙烯薄膜表面,引入了氧原子功能团(C—O,C=O,O—C=O等),导致薄膜表面自由能的增加。此外,这种方法得到的薄膜层之间黏着强度为1.5 MPa;而铜膜与未进行等离子体预处理聚乙烯之间的黏着强度仅为0.8 MPa。此外,SEM照片也显示,经过等离子体预处理后聚乙烯表面的电镀铜膜晶粒较小且分布更均匀。

场发射冷阴极微栅孔阵列制备技术

实现了一种采用聚苯乙烯纳米球自组装技术和微机械制造技术加工的场发射阴极用亚微米栅极微孔阵列。设计了一套完整的工艺实验方案,首先采用微球自组装技术获得了亚微米级金属网孔掩膜,然后通过反应离子刻蚀技术获得了亚微米栅极孔阵列,从而实现了集成度高、分布均匀的周期性亚微米孔洞阵列的制备,微孔集成度达到108cm-2。实验研究了氧气刻蚀聚苯乙烯微球的规律。采用金属掩膜,四氟化碳干法刻蚀二氧化硅,获得了深度为500nm的微孔。实验结果证明该工艺方案是一种获得大面积、均匀分布、集成度高的场发射冷阴极栅孔阵列的有效方法。

离子初始速度对等离子体鞘层厚度的影响

本文从理论上研究了离子初始速度对等离子体鞘层厚度的影响,建立了理论计算公式和数值模拟方法,考察了离子初始速度对鞘层厚度的影响因子。在离子初始能量为3.2eV情况下,用粒子模拟程序进行了数值模拟,模拟与理论计算得到的空间电场分布十分接近。

脉冲电磁驱动低温螺旋流注放电机理

特定脉冲放电参数条件下,原来沿直线传播的低温等离子体射流放电通道会在脉冲电磁驱动下发生放电模式转换,形成螺旋形态的流注通道.与传统的螺旋波放电不同,实验中并没有外加恒定磁场等破坏介质管极向对称性的因素,而且螺旋的手性方向会随放电参数变化.为深入了解等离子体射流中螺旋结构的电磁作用机理,探索其导致螺旋形态和决定手征性的极向电场来源及影响因素,本文通过建立完备自洽的等离子体理论模型,对螺旋流注的手性方向、螺距变化、分叉等复杂放电特性和电磁机理进行分析.研究发现击穿时极向电场波模的初始相位对螺旋流注的手性选择存在影响,电子密度对螺旋流注的螺距参数存在影响,放电的脉冲重复频率对螺旋流注分叉的分叉点位置存在影响.以上放电特性及其影响因素对探明电磁波与等离子体的相互作用机制具有重要科学意义,同时也为低温等离子体的手性应用提供实验和理论支撑.

大气压非平衡等离子体甲烷干法重整零维数值模拟

大气压非平衡等离子体由于其独特的非平衡特性,可为甲烷和二氧化碳稳定温室气体分子活化和重整提供非热平衡和活化环境.本文采用了零维等离子体化学反应动力学模型,考虑了详细的CH_(4)/CO_(2)等离子体化学反应集,重点研究了反应气体CH_(4)/CO_(2)摩尔分数(5%—95%)对大气压非平衡等离子体甲烷干法重整制合成气和重要含氧化合物的影响.首先,给出了进料气体不同体积比时电子密度和温度随时间的演化规律,结果表明初始甲烷摩尔分数的提高有利于获得较高的电子密度和电子温度.随后,讨论了主要自由基和离子数密度在不同的甲烷摩尔分数下随着时间的变化规律,并给出了反应气体的转化率、合成气体和重要含氧化合物的选择性.此外,还明确了合成气和含氧化合物主要生成和损耗的化学反应路径,发现甲基和羟基是合成含氧化合物的关键中间体.最后,归纳总结给出了主要等离子体粒子之间的总体等离子体化学反应流程图.

Atmospheric Pressure Cold Argon/Oxygen Plasma Jet Assisted by Preionization of Syringe Needle Electrode

An atmospheric pressure nonequilibrium argon/oxygen plasma jet assisted by the preionization of syringe needle electrode discharge is reported. With the syringe needle plasma as its pre-ionization source, the hybrid barrier-jet was shown to generate uniform discharge with a lower breakdown voltage and a relatively low gas temperature varying from 390 K to 440 K, even when the vol.% oxygen in argon was up to 6%. Utilizing the actinometry method, the concentration of atomic oxygen was estimated to be about in an orders of magnitude of 10^17 cm^-3. The argon/oxygen plasma jet was then employed to clean out heat transfer oil, with a maximum cleaning rate of 0.1 mm/s achieved.

Numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium–air plasma jet

A numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium-air plasma jet is presented. The generation and loss mechanisms of the OH radicals in a positive half-cycle of the applied voltage are studied and discussed. It is found that the peak OH density increases with water content in air （varying from 0% to 1%） and reaches 6.3 x 10^18 m-3 when the water content is 1%. Besides, as the water content increases from 0.01% to 1%, the space-averaged reaction rate of three-body recombination increases dramatically and is comparable to those of main OH generation reactions.

Effect of pulse voltage rising time on discharge characteristics of a helium-air plasma at atmospheric pressure

In this paper,the influence of voltage rising time on a pulsed-dc helium-air plasma at atmospheric pressure is numerically simulated.Simulation results show that as the voltage rising time increases from 10 ns to 30 ns,there is a decrease in the discharge current,namely 0.052 A when the voltage rising time is 10 ns and 0.038 A when the voltage rising time is 30 ns.Additionally,a shorter voltage rising time results in a faster breakdown,a more rapidly rising current waveform,and a higher breakdown voltage.Furthermore,the basic parameters of the streamer discharge also increase with voltage rise rate,which is ascribed to the fact that more energetic electrons are produced in a shorter voltage rising time.Therefore,a pulsed-dc voltage with a short rising time is desirable for efficient production of nonequilibrium atmospheric pressure plasma discharge.

A computational modeling study on the helium atmospheric pressure plasma needle discharge

A two-dimensional coupled model of neutral gas flow and plasma dynamics is employed to investigate the streamer dynamics in a helium plasma needle at atmospheric pressure. A parametric study of the streamer propagation as a function of needle tip curvature radius and helium gas flow rate is presented. The key chemical reactions at the He/air mixing layer which drive the streamer propagation are the direct ionization via collision with electrons, the Penning effect being not so crucial. With increasing the gas flow rate from 0.2 standard liter per minute（SLM） to 0.8 SLM, however, the emissions resulting from reactive oxygen and nitrogen species change from a solid circle to a hollow profile and the average streamer propagation velocity decreases. Air impurities（backdiffusion from ambient air） in the helium jet result in a significant increase in the streamer propagation velocity. Besides, with decreasing the tip curvature radiusfrom 200 μm to 100 μm,the electron avalanche process around the near-tip region is more pronounced. However, the spatially resolved plasma parameters distributions（electron, helium metastables, ground state atomic oxygen, etc.） remain almost the same, except that around the near-tip region where their peak values are more than doubled.

LIF diagnostics of hydroxyl radical in a methanol containing atmospheric-pressure plasma jet

In this paper, a pulsed-dc CH;OH/Ar plasma jet generated at atmospheric pressure is studied by laser-induced fluorescence（LIF） and optical emission spectroscopy（OES）. A gas–liquid bubbler system is proposed to introduce the methanol vapor into the argon gas, and the CH3OH/Ar volume ratio is kept constant at about 0.1%. Discharge occurs in a 6-mm needle-to-ring gap in an atmospheric-pressure CH;OH/Ar mixture. The space-resolved distributions of OH LIF inside and outside the nozzle exhibit distinctly different behaviors. And, different production mechanisms of OH radicals in the needle-to-ring discharge gap and afterglow of plasma jet are discussed. Besides, the optical emission lines of carbonaceous species, such as CH, CN, and C;radicals, are identified in the CH;OH/Ar plasma jet. Finally, the influences of operating parameters（applied voltage magnitude, pulse frequency, pulsewidth） on the OH radical density are also presented and analyzed.

A two-dimensional model of He/O_2 atmospheric pressure plasma needle discharge

In this paper, a computational modeling study of stream propagation in the atmospheric-pressure helium plasma in ambient atmosphere（oxygen） is presented. A coupled fluid model between time-dependent plasma dynamics and steady state neutral gas flow is employed to provide a fundamental insight into the evolution of the streamers. The obtained simulation results showing that the sheath forms near the dielectric surface and shields the axial stream propagation. The stream front propagates with axial velocity in a range of 10^4m/s–10^5m/s. And, the increasing accumulated surface charge should be responsible for reducing the propagation velocity of the streamer front in the axial direction. Besides, when the gas flow rate is 1.1 standard liter per minute（SLM）, we find that the concentration of oxygen drastically increases at a larger radial position near a treated surface. Therefore, Penning ionization by helium metastables and oxygen peaks at an off-axis position, corresponding to the ring-shaped emission profile in cylindrical coordinates. In this case, the simulated results show the ring-shaped ground atomic oxygen density profile near the treated surface（z = 0.5 mm） at a large gas flow rate of 1.1 SLM, which is consistent with the observation in a similar experiment.

Modeling of the Distinctive Ground-State Atomic Oxygen Density Profile in Plasma Needle Discharge at Atmospheric Pressure

A two-dimensional coupled model of neutral gas flow and plasma dynamics is presented to explain the two distinctive patterns of ground-state atomic oxygen density profiles that have been observed experimentally in the helium plasma needle discharge. When the gas flow rate is 0.25 standard liter per minute （SLM）, the discharge is substantially sustained by the electron impact ionization of air near a dielectric surface, corresponding to the radial density peaks along the axis of the symmetry. However, as the flow rate is 1.1 SLM, Penning ionization between helium metastables and surrounding air dominates the ionization reactions and peaks at an off-center position （r = 0.9 mm）, which indicates the ring-shaped density distribution. The critical feeding gas flow rate is found to be around 0.4SLM. The peak density is on the order of 1020 m-3 in our case. Previous reports of a flow-dependent bacterial killing pattern and ground-state atomic oxygen measurement support our simulation results.

A numerical simulation study on active species production in dense methane-air plasma discharge

Recently, low-temperature atmospheric pressure plasmas have been proposed as a potential type of ＇reaction cartier＇ for the conversion of methane into value-added chemicals. In this paper, the multi-physics field coupling software of COMSOL is used to simulate the detailed discharge characteristics of atmospheric pressure methane-air plasma. A two-dimensional axisymmetric fluid model is constructed, in which 77 plasma chemical reactions and 32 different species are taken into account. The spatial density distributions of dominant charged ions and reactive radical species, such as ＋ ＋ ＋ ＋ CH4, CH3,N2,02, H, O, CH3, and CH2, are presented, which is due to plasma chemical reactions of methane/air dissociation （or ionization） and reforming of small fragment radical species. The physicochemical mechanisms of methane dissociation and radical species recombination are also discussed and analyzed.

针板缺陷位形下局部放电击穿特性实验教学研究

电介质的局部放电现象是输电线路和配电系统故障检测的重要内容,也是电气工程专业高电压技术课程教学的难点和重点。为了让学生对这一问题有更加形象具体的理解,文章在大气压下使用针板缺陷放电装置和高压脉冲电源进行了针板放电实验教学。通过改变针板间隙距离并使用逐步升压法来测量分析空气间隙的击穿特性,并通过建立针板仿真模型计算不同间距针板间隙被击穿时的电场强度,得出最大电场强度与针板间距的关系曲线。进而与Mason公式的理论计算值进行了比较和分析,验证了Mason公式的有效性,增强了学生的动手实践能力和数值模拟仿真能力。

N_2 Mole Fraction Dependence of Plasma Bullet Propagation in Premixed He/N_2 Plasma Needle Discharge at Atmospheric Pressure

In this work, a computational modeling study on the mechanism of the acceleration behavior of a plasma bullet in needle-plane configuration is presented. Above all, in our model, two sub-models of time-dependent plasma dynamics and laminar flow axe connected using a oneway coupled method, and both the working gas and the surrounding gas around the plasma jet are assumed to be the same, which are premixed He/N2 gas. The mole fractions of the N2 （NMF） ingredient are set to be 0.01%, 0.1% and 1% in three cases, respectively. It is found that in each case, the plasma bullet accelerates with time to a peak velocity after it exits the nozzle and then decreases until getting to the treated surface, and that the velocity of the plasma bullet increases at each time moment with the peak value changing from 0.72×10^6 m/s to 0.80×10^6 m/s but then drops more sharply when the NMF varies from 0.01% to 1%. Besides, the electron impact ionizations of helium neutrals and nitrogen molecules are found to have key influences on the propagation of a plasma bullet instead of the penning ionization.

低气压条件下氢气潘宁放电的模拟分析

为更好地理解低气压、弱电离条件下潘宁离子源放电过程中离子和电子的动力学行为,通过建立二维轴对称模型,采用粒子模拟与蒙特卡罗相结合(PIC/MCC)的方法,考虑了电子与氢气之间的弹性碰撞、激发、电离以及氢原子、离子之间的弹性碰撞和电荷交换等过程,对微型氢气潘宁离子源放电和引出过程进行了数值研究.考察了磁场位形、壁面二次电子发射系数、引出电压和充气压力对放电过程的影响,得到了实验中难以诊断得到的放电腔内电子与离子数密度分布,阳极电流、引出极离子电流、单原子氢离子比例和双原子氢离子比例等宏观参数与实验结果相一致.通过仿真使得对氢气潘宁放电机制的研究从定性过渡到定量,这对于潘宁离子源的设计和改进具有重要意义.