Effect of power supply parameters on discharge characteristics and sterilization efficiency of magnetically driven rotating gliding arc

Plasma sterilization is a new generation of high-tech sterilization method that is fast,safe,and pollution free.It is widely used in medical,food,and environmental protection fields.Home air sterilization is an emerging field of plasma application,which puts higher requirements on the miniaturization,operational stability,and operating cost of plasma device.In this study,a novel magnetically driven rotating gliding arc(MDRGA)discharge device was used to sterilize Lactobacillus fermentation.Compared with the traditional gas-driven gliding arc,this device has a simple structure and a more stable gliding arc.Simulation using COMSOL Multiphysics showed that adding permanent magnets can form a stable magnetic field,which is conducive to the formation of gliding arcs.Experiments on the discharge performance,ozone concentration,and sterilization effect were conducted using different power supply parameters.The results revealed that the MDRGA process can be divided into three stages:starting,gliding,and extinguishing.Appropriate voltage was the key factor for stable arc gliding,and both high and low voltages were not conducive to stable arc gliding and ozone production.In this experimental setup,the sterilization effect was the best at 6.6 kV.A high modulation duty ratio was beneficial for achieving stable arc gliding.However,when the duty ratio exceeded a certain value,the improvement in the sterilization effect was slow.Therefore,considering the sterilization effect and energy factors comprehensively,we chose 80%as the optimal modulation duty ratio for this experimental device.

A Novel Explanation of the Origin of the Magnetic Field of Stars and Planets

Today, the origin of the magnetic field of stars and planets is explained by the dynamo effect. Since Cowling’s anti-dynamo theorem has forbidden a purely axisymmetric dynamo, scientists are all convinced today that the fluid flow in the core of a star cannot be laminar, so it is turbulent. However, we will see in this study that the configuration in which the conductive fluid contained in the core of a star is in rapid rotation around an axis of symmetry is the one that best explains the origin of the magnetic field of stars and planets. It also explains why certain types of stars have very intense magnetic fields. Indeed, we will show here that the magnetic field of stars and planets is created by the electric current generated by the rotational movement of charged fluid particles as in an electromagnet. The lines of this magnetic field are channelled by the solid paramagnetic seed which plays the role of magnetic core in the cores of planets and stars. The seed is composed mainly of Iron and Nickel on the planets and of solid helium-3 in the stars. In this work, we will use this model of rapidly rotating fluids to introduce a new way to ionize a neutral gas and maintain it in a plasma state for indefinitely large time scales, to present a new technique for generating very intense magnetic fields, to establish a new magnetic nucleation process and to propose a new type of nuclear fusion reactor in which the plasma is perpetually rapidly rotating.

Numerical simulation of low-current vacuum arc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma,cathode spots(CSs)play an important role on the behaviors of the vacuum arc.Their characteristics are affected by many factors,especially by the magnetic field.In this paper,the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field(AMF)are studied.A multi-species magneto-hydro-dynamic(MHD)model is established to describe the vacuum arc.The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model.The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet.When the external AMF is high enough,a bright spot appears on the anode surface.This is because with a higher AMF,the contraction of the diffused arc becomes more obvious,leading to a higher energy flux to the anode and thus a higher anode temperature.Then more secondary plasma can be generated near the anode,and the brightness of the‘anode spot’increases.During this process,the arc appearance gradually changes from a cone to a dumbbell shape.In this condition,the arc is in the diffuse mode.The appearance of the plasma jet calculated in the model is consistent with the experimental results.

Comparative Observation of Ar,Ar-H_2 and Ar-N_2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.

Conversion of coalbed methane surrogate into hydrogen and graphene sheets using rotating gliding arc plasma

The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surrogate.Based on a previous investigation of discharge properties,product distribution and energy efficiency,the operating parameters such as CH4 concentration,applied voltage and gas flow rate can effectively affect the CH4 conversion rate,the selectivity of H2 and the properties of solid generated carbon.Nevertheless,the basic properties of RGA plasma and its role in CH4 conversion are scarcely mentioned.In the present work,a 3D RGA model,with a detailed nonequilibrium CH4/Ar plasma chemistry,is developed to validate the previous experiments on CBM conversion,aiming in particular at the distribution of H2 and other gas products.Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection,electron migration and electron diffusion,and is prominently determined by the variation of the gas flow rate and applied voltage.Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction,taking into consideration the formation and loss pathways of crucial targeted substances(such as CH4,C2H2,H2 and H radicals)and corresponding contribution rates.Additionally,the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM)and Raman spectroscopy.The results show that increasing the applied voltage and decreasing CH4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets,while the size of the graphene sheets is slightly affected by the change in gas flow rate.

旋转电弧焊接技术研究进展

熔焊焊接时会不可避免地出现侧壁不熔、咬边、晶粒粗大等问题,导致接头性能较低。为更好地解决焊接中存在的问题,提出旋转电弧焊接技术。相对于普通焊接,旋转电弧中的旋转电弧耦合力在焊接时对熔池的搅拌破碎效应能加速焊缝中的传质传热,并细化晶粒减小焊缝残余应力,能解决焊接中常见问题,获得优质焊缝并提高焊接接头的使用寿命。主要综述了基于外加磁场、非对称钨极旋转电弧、缆式焊丝熔化极旋转电弧的研究现状,指出目前旋转电弧焊接技术还存在的问题,并对相关技术的应用前景进行展望。

Simulation of Arc Rotation and Its Effects on Pressure of Expansion Volume in an Auto-Expansion SF_6 Circuit Breaker

A 3D Magnetohydrodynamics （MHD） arc model in conjunction with an arc move- ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The rotation of the arc driven by an external electromagnetic force is simulated in the case with 200 kA of the short circuit current and 16 ms of arc duration. The arc rotating process and the speed of arc rotation have been obtained in the simulation. A comparison of the pressure in the expansion volume with and without an external magnetic field has been carried out based on the calculation results of two cases. The results of the simulation reveal that the arc rotation, which causes more energy exchange between the arc and its sur- rounding gas, can evidently bring about the pressurization in the expansion volume, which would contribute to more effective arc quenching at current zero and further reducing operation power.

Direct Current Interruption with RLC Circuit-convoluted Arc Interaction

Investigations are reported into the use of an electromagnetically convoluted arc,external to a magnetic field(B-field)producing coil,in combination with a parallel R,L,C resonant circuit for interrupting quasi-steady currents.In order to elucidate the complex interactions between the arc,B-field and R,L,C circuit,the B-field producing coil is energised independently from the current to be interrupted and the R,L,C circuit.Experimental results are presented for the time variation of the currents flowing through the arc gap,the B-field coil and the parallel R,L,C circuit,along with the voltage across the arc gap.An insight is gained into the role of various effects,which are produced by the complex interactions and which might be used to advantage for direct current interruption.

场反构型无电极洛伦兹力推力器研究进展

场反构型洛伦兹力推力器利用旋转磁场驱动等离子体产生场反构型等离子体团(Filed Reversed Configuration-FRC),并利用洛伦兹力将其加速产生推力。由于该推力器不使用栅极加速,故不存在栅极溅射问题,大大延长推力器工作寿命。该技术借鉴自磁约束核聚变技术,推力密度大、功率扩展性好(MW级),在未来的深空探测和星际航行中具有广泛的应用前景。文章对场反构型洛伦兹力推力器发展现状进行了综述,并对工作原理、计算模型和技术瓶颈问题作了介绍,为中国等离子体推力器技术发展提供参考。

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。

电极间距对真空电弧电压及阳极熔池旋转速度影响的实验研究

在可拆卸真空灭弧室中对纯铜杯状纵向磁场电极分别进行了间距10,16,20mm的大电流(有效值为10,20kA)燃弧实验,用高速摄影仪拍摄电极间的电弧形态及阳极表面熔池的旋转运动,并测量了电弧电压波形。以实验测量为基础,分析研究了真空电弧在不同间距下的电弧电压特性、阳极表面熔池旋转运动。实验结果表明,随着电极间距的增大,电弧逐渐向不稳定态发展并且电弧电压逐渐增大。阳极表面熔池半径及金属液体旋转速度随着电极间距的增大而增大。电极间距10mm的熔池旋转线速度大约为0.664m/s,熔池半径大约为14.5mm;而电极间距16mm的熔池旋转线速度为1.204m/s,熔池半径大约为15.6mm。

横向旋转磁场对TIG焊焊缝成形的影响

设计了一种横向旋转磁场发生装置，利用载波和高频调幅波分别控制励磁电流（0～15A）和励磁频率（50～1000Hz）的大小。将该磁场应用于TIG焊，利用磁场的旋转带动TIG焊接电弧的旋转，并以奥氏体不锈钢0Cr18Ni12M02Ti为研究对象，重点考察了磁场参数对其焊缝成形的影响规律。分析了横向旋转磁场作用下TIG焊电弧瞬时形态的特点，并根据旋转电弧对工件作用区域的变化特征，论述了横向旋转磁场影响焊缝成形的机理。结果表明，合理设置横向旋转磁场的磁参数可简便、有效地控制焊缝成形，能够满足不同场合的焊接要求。

滑动弧促进甲烷干重整电弧图像及电参数分析

为充实旋转滑动弧促进甲烷干重整技术的相关研究,利用高速摄影和示波器,研究了磁场和气流协同驱动的滑动弧的物理特性。通过电弧图像和电参数图像,分析滑动弧CO2放电随磁场有无、流量变化的关系,并对总体积流量6 L/min下,甲烷干重整随CH4/CO2比例变化时滑动弧的物理特性进行了分析。研究表明:磁驱动可以提高滑动弧旋转速度,增大等离子体区域和非平衡态程度;总进气体积流量6 L/min,甲烷体积分数为30%时,干重整反应剧烈,电弧弧长周期性变化,电弧与电极有多触点现象,且会发生触点漂移。

磁控电弧旋转磁场发生装置的设计

基于逆变电路脉冲宽度调制技术和三相步进电机原理,以智能功率模块IPM作为开关器件,研制了一种旋转磁场发生装置。通过改变励磁线圈的励磁转换频率和励磁电流大小来调节磁场的旋转频率和磁场强度,产生一个转速和场强连续可调的空间旋转磁场,并利用此旋转磁场来控制焊接电弧。试验证明,该装置产生的旋转磁场可以很好地控制焊接电弧,并能使焊接电弧以不同的速率稳定地旋转。

磁旋滑动弧促进甲烷部分氧化重整制氢

与传统的甲烷催化制氢技术相比,低温等离子体技术具有能耗低、无需催化剂、启停迅速、可在常温常压下运行等优点,具有良好的应用前景。为此,研究了空气载气下磁旋滑动弧放电等离子体的物理特性,并开展了甲烷部分氧化重整制氢实验。结果表明:空气体积流量分别为2 L/min、8 L/min、16 L/min时,电弧均可稳定旋转,转速最高为111 r/s,且存在固定的放电周期;而与传统刀片滑动弧不同的是,磁旋滑动弧在2 L/min的体积流量下依然可以维持稳定的运行和较长的电弧长度,从而有利于反应的充分进行;电弧长度和直径对放电电压、电流、功率、电流密度、电场强度和电导率等参数有直接影响。在甲烷部分氧化重整制氢实验中,CH_4的转化率和H_2的选择性均随过量空气系数的增加而先升后降,CH_4的转化率最高可达100%,H_2的选择性最高为42.42%,效果远好于传统的刀片式滑动弧。此外,微富氧的环境有利于甲烷的完全转化。研究结果证明磁旋滑动弧能够促进甲烷部分氧化重整制氢。

磁旋转电弧中热阴极弧根形态的实验研究

阴极弧根形态对电弧状态和电极损耗有着重要影响。在同轴电极磁旋转电弧等离子体发生器中,利用高速CCD观察了阴极弧根斑点形态随外加轴向磁场的演化过程,采用双波长法从CCD影像得到阴极端面温度分布;利用水冷电探针对近阴极区等离子体参数进行诊断,得到了阴极附近电子温度及阴极区位降。实验结果表明:(1)在50 A电弧电流下,随着轴向磁场从0.01 T增加到0.02 T,阴极端面最高温度下降,阴极弧根斑点增大,阴极附近等离子体电子温度逐渐降低,阴极弧根为收缩模式;(2)在100 A电弧弧电流下,轴向磁场从0.01 T增加至0.015T,阴极状态变化趋势与前相同;(3)在100 A电弧弧电流下,当轴向磁场增大到0.02 T时,弧根斑点弥散均匀,阴极区位降明显升高,阴极弧根模式由收缩模式转变为扩散模式。分析认为,磁旋转电弧中弧根模式的转变是一个突变的过程。

轴向磁场对焊接电弧作用的数值模拟研究

采用耦合阴极模型模拟轴向磁场对焊接电弧的作用,分析了轴向磁场对焊接电弧位形的作用机制。计算结果显示,随轴向磁场增加:阴极弧根收缩;阴极附近等离子体温度升高,高温核心径向增大,弧柱收缩程度增加;阳极附近弧柱径向张开,中心温度降低;阳极表面电流密度和压力分布呈环状结构;阳极加热面增大,极值温度降低,出现温度平顶;电弧对阳极的传热量增加。分析认为,轴向磁场与电弧径向电流间的Lorentz力作用使近阳极区电弧旋转流动,产生磁抽吸作用,使阴极弧根和近阴极弧柱收缩,而阴极弧根收缩增强了阴极射流,并且抑制近阳极区电弧扩张。

多模式旋转磁场对电弧离子镀弧斑放电的影响分析

电弧离子镀工艺中,弧斑的放电形式、运动速率、运动方式的控制对于减少以至消除大颗粒的发射至关重要。本文采用自主研发的机械式旋转磁控弧源,围绕三种不同模式的旋转磁场下弧斑的放电行为及规律进行了研究,并从弧斑放电的物理机制出发,分析讨论了不同模式的旋转磁场对阴极斑点运动的影响机理。研究结果表明,多模式旋转磁场可以有效提高弧斑的运动速度、扩大放电面积、降低放电功率密度、减少大颗粒的发射,同时还能够大幅度提高靶材的利用率,拓展电弧离子镀的应用。

磁控状态下Fe90堆焊层显微组织对力学性能的影响

为了研究直流横向磁场对Fe90堆焊层组织和性能的影响,在Fe90自熔堆焊合金的等离子弧堆焊过程中引入直流横向磁场,采用洛氏硬度仪、磨损试验机对不同规范下试样的硬度、耐磨损性进行测试,采用OM及SEM对堆焊层进行显微组织分析,进而揭示外加磁场对堆焊层性能的作用机理.结果表明,施加磁场的堆焊层要比无磁场作用的堆焊层硬度高、耐磨性好;当堆焊电流为I=180A,磁场电流为Im=3 A时,堆焊层性能取得最佳值,其磨损量为0.421 8 g,表面硬度HRC为72.1.外加磁场提高堆焊层性能的主要原因是电弧和熔池在磁场作用下运动状态发生改变,改善了堆焊层组织,使堆焊层的组织由柱状晶转化为等轴晶并细化晶粒,进而提高堆焊层的综合力学性能.

电弧离子镀的旋转横向磁场弧源设计

电弧离子镀工艺中电弧蒸发产生的大颗粒污染严重影响了所沉积涂层的性能。为了从源头上解决大颗粒难题,本文提出了一种新的旋转横向磁场的设计思路,通过频率和强度可调且覆盖整个靶面的旋转横向磁场控制弧斑的运动。通过有限元模拟磁场的分布,对旋转横向磁场控制的电弧离子镀弧源进行了优化设计。并根据方案制作了旋转磁场发生装置及其电源,使该弧源的旋转磁场具有多模式可调频调幅的功能,用以改善弧斑的放电形式,提高靶材刻蚀均匀性和靶材利用率,减少靶材大颗粒的发射,用以制备高质量的薄膜以及功能薄膜,以拓展电弧离子镀的应用范围。