多针-网电极离子风激励器推力与推功比的实验研究

本文搭建了一种无摩擦气垫悬浮测试平台测量了19针和31针-网电极离子风激励器产生的推力特性, 为多针-网电极离子风激励器作为新型动力源提供动力控制方法. 通过研究多针-网间隙、针-针间距、针尖曲率半径和电晕电压电流对离子风激励器推力特性的影响, 提出了在低功耗下产生较大推力的方法, 改善离子风激励器对低功耗与大推力的需求不能同时满足的现状. 关键词： 多针-网电极 离子风 推力 推功比     

低气压离子风推进器仿真与实验

离子风动力具有无需机械旋转部件、低功耗及低噪声等优点, 在平流层飞艇和太阳能飞机上具有重要的应用潜力。模拟临近空间的低气压环境, 采用"线-柱"电极结构电晕放电装置产生离子风, 实验测量不同放电条件下离子风推进器产生的推力和推功比, 研究了气压、放电电压、电极间隙对离子风动力的影响。仿真和实验结果表明, 气压的降低会导致推进器推功比的下降, 具体表现为: 当电极间隙为2.0 cm, 最大推功比由1 atm (1 atm＝101325 Pa)时的17.70 mN/W降低至0.02 atm时的0.24 mN/W; 而推功比的损失可以通过增大电极间隙来补偿, 当电极间隙增加至14 cm, 在0.02 atm的气压环境下, 推功比由0.24 mN/W升至0.70 mN/W。通过优化离子风推进器结构, 增加电极间隙, 离子风动力具备低气压环境下的应用潜力。      

石蜡液面离子风的研究

研究了常压空气中针-石蜡液面 50Hz 交流电晕放电离子风特性。交流电晕离子风能够引起液体石蜡 显著变形,随着电压升高,变形从漏斗状发展到盆状。在石蜡层厚度为 5mm 时,盆状变形最大,深度达到 5.3mm, 最大作用范围半径 18.8mm,变形产生的压强达到 48.9Pa,远远超过直流针-水电晕放电情况。随着电压升高,从 电晕放电过渡到流注放电时盆状变形依然存在,这一点明显不同于直流针-水电晕放电。研究表明交流电晕离子风 具有优良的驱动绝缘液体介质的巨大潜力。     

声脉冲法空间电荷测量系统的研究

气体中空间电荷的分布与电晕放电的机理紧密相关, 获取电晕放电过程中空间电荷分布对深入研究电晕放电起始、自持过程有着重要作用, 但是如何准确获得电晕放电过程中的空间电荷分布一直是国际上尚未解决的难题. 本文基于声脉冲法提出一种电场信号解耦算法, 推导了空间电荷在声场中被调制产生的电场信号与声脉冲信号和空间电荷密度之间的数值关系, 讨论了不同测量情况下声发射系统的设计要求; 搭建了一套可用于实时测量针板电极电晕放电空间电荷分布的非接触式测量系统, 该系统主要包括声脉冲发生模块、空间电荷模块及电场信号解耦算法模块. 运用该系统实现了声脉冲激发作用下电场信号的测量, 通过提出的电场信号解耦算法得到了空间电荷密度, 对其测量结果与电晕电流法测量结果进行比较, 验证了电场信号解耦算法的有效性. 该算法可以应用于空间电荷一维、二维和三维测量系统中.     

离子风强化平板对流传热的数值模拟

本文应用多物理场耦合计算软件COMSOL对离子风作用下强化平板对流换热的过程进行了数值模拟.研究了空气在高压电场下的对流换热现象,得到线-板电极模型相应的流场和温度场分布,并与文献中的实验结果进行了对比,验证了多物理场耦合数值方法的准确性。通过研究不同电压下传统风扇风冷、离子风和离子风与风扇共同作用下的对流换热系数变化规律,发现空气放电强化传热较传统方式有明显优势。还研究了不同极板距与板长比和不同板长情况下对流换热系数的变化规律.     

雷云电场作用下长地线表面正极性辉光电晕放电的仿真研究

在雷云电场的缓慢作用下, 一种无流注的正极性辉光电晕在接地物体表面起始, 向周围空间注入大量正极性空间电荷, 从而改变雷电先导对雷击目的物的选择. 本文对雷云电场作用下起始于长地线表面的正极性辉光电晕放电进行了仿真研究; 考虑了正极性离子与其他离子的附着与碰撞作用, 建立了一种精确的二维正极性辉光电晕模型; 并通过在实验室内开展高压电晕放电试验, 测量了不同背景电场下的电晕电流; 与本文所建模型的仿真结果进行对比, 对模型的正确性进行了验证. 基于上述模型, 对正极性辉光电晕在雷云感应作用下的起始发展过程与电晕特性进行了仿真模拟, 得到了该电晕的电晕电流、正离子密度分布规律以及正离子迁移规律. 发现在雷云电场作用下, 电晕放电产生的正离子在迁移初期于垂直于地线的平面内基本呈圆对称状均匀分布, 但随着离子逐渐远离地线其分布不再均匀, 呈拉长的椭圆形分布, 多数离子最终分布于地线上方区域并逐渐向雷云方向迁移; 由于正离子在地线上方迁移区聚集形成的正空间电荷背景对行进电子束具有衰减和消耗作用, 抑制了电子崩的形成, 并降低了电子崩转化为流注的概率, 阻止了新的电子崩对流注的不断注入, 同时正空间电荷背景使气体的碰撞面增大, 增加了与电子的复合概率, 引起大量电子的消耗, 最终抑制了电子崩的形成与流注的发展, 地线表面的上行先导得到抑制.     

氩气/空气等离子体助燃激励器的实验研究

为了获得氩气/空气等离子体助燃激励器的特性,首先在空气中加入少量氩气的条件下,对条状、王状和网状三种不同电极形状的等离子体助燃激励器的放电特性进行对比,实验结果表明电极形状对激励器放电特性影响不大。然后对条形电极在纯空气和10%氩气/90%空气两种条件下的放电特性和发射光谱进行研究,发现加入氩气后,放电参数变化趋势与纯空气相似,但电流脉冲增多,放电均匀度增加,起始放电电压由27kV降低到24kV,并且介质阻挡放电发射光谱增强。     

离子风作用下LED光热关联特性研究

LED芯片结温对其光电性能影响很大,因此需要一种有效的热管理方式。设计一种"针-网"式离子风散热器,通过实验研究了电晕放电产生离子风在LED前照灯冷却中的应用,探讨了热学和光学性能之间的关联机理。结果表明,使用离子风散热技术可以有效降低LED芯片结温,削弱色度坐标的红移,减缓光通量的衰减速度;LED光源的两个重要颜色指标相关色温(CCT)和显色指数(CRI)在离子风作用下均不会有明显变化;当放电功率为2 W时,将获得更加对称和均匀的光分布。验证了离子风散热技术用于大功率LED前照灯散热的可行性。     

基于电晕放电的大功率LED散热研究

针对大功率LED芯片的散热问题,提出了一种基于电晕放电原理的离子风散热方案。通过试验,研究了电晕放电的电学性能,同时探寻了放电电压对制冷效果的影响以及温降随电晕放电功率的变化规律。结果表明,放电间距相同时,对发生器施加负电晕能够在较低的电压下产生离子风,降温效果显著。电晕电流平方根与放电电压呈线性关系。电晕放电功率为1.5 W、放电间距为10 mm时,散热效果最好。     

实验研究大气压多脉冲辉光放电的模式和机理

采用稍不平行电极进行大气压He气介质阻挡多脉冲辉光放电实验,通过增强电子耦合器件相机短时曝光照片,研究大气压多脉冲辉光放电在不同时刻的放电模式.通过气隙放电电流、表面电荷计算,理论分析了表面电荷、空间电荷、外加电压与气隙电场强度的关系,研究大气压辉光放电形成多脉冲的机理.实验结果表明,放电首先在间隙稍窄的电极左端开始;在第一个脉冲电流峰值,电极右端也开始放电;第一个电流脉冲经历了Townsend放电到辉光放电的过程;电流脉冲之间的时间内,间隙一直维持着微弱的辉光放电;随后的每个电流脉冲均是辉光放电.理论分析表明,大气压辉光放电的多个电流脉冲是表面电荷、空间电荷与外加电压共同演化的结果;除放电伊始出现Townsend放电外,同一半周期内的放电电流脉冲中不会再出现Townsend放电.     

Flow distribution and pressure of air due to ionic wind in pin-to-plate corona discharge system

An electrohydrodynamic investigation has been carried out in a pin-to-plate gas discharge system to clarify the mechanism of repulsive force generation between a pin and plate electrode at corona discharge. Numerical calculations have been conducted in two steps. First, the axi-cylindrical static corona discharge field was calculated with the finite-element method to deduce the Coulombic body force ρ E applied to the air, where ρ is the charge density and E is the electric field, and then the induced ionic wind was calculated with the finite differential method. The calculated pressure distribution on the plate electrode was on the order of 10 Pa which was in good agreement with the measured pressure distribution. The calculated air velocity at the center was several m/s and was confirmed by a time-of-flight experiment and the velocity distribution near the pin electrode also agreed with measurements using a laser Doppler velocimeter. Pressure and wind velocity were increased at high-applied voltage. These results confirm that the ionic wind is the cause of the repulsive force to the pin electrode at the corona discharge.     

Modelling of corona discharge in cylinder-wire-plate electrode configuration

Numerical computation of the electric field strength and ionic space charge density in electrode systems consisting of ionizing wire and non-ionizing cylinder, connected to the same DC high-voltage supply and facing a grounded plate, is a difficult problem, which is of interest to several electrostatic processes applications. In a previous study a simple numerical method has been proposed to calculate the spatial distributions of electric field and ionic space charge in a case of a continuum and uniform corona discharge originating at the surface of the wire. The aim of the present paper is to improve the physical model of the corona discharge in this particular electrode configuration, by assuming a more realistic law of charge injection on the wire circumference. The computations were carried out for an ionizing wire of radius r=0.1 mm, located at different distances h from a metallic tubular support of radius R=13.4 mm.The initial conditions of the corona discharge took into account the non-uniformity of the charge injection around the ionizing wire electrode. The computational results were compared with those obtained under the assumption of uniform corona discharge. The comparison pointed out that neither the non-uniformity of the electric field nor that of the charge injection can be neglected. They depend on the geometry of the electrode system and affect the distribution of the electric field and of the space charge density in the inter-electrode gap.     

An empirical model for ionic wind generation by a needle-to-cylinder dc corona discharge

We present the results of an experimental study on ionic wind generation by a needle-to-cylinder dc corona discharge. A strong electrical field in the air generates air flow driven by the motion of ionized gas molecules along electric field lines. We measured the ionic wind velocity and discharge current with respect to various electrode geometries, distances between electrodes, and applied voltages. Our measurements suggest an empirical model for the ionic wind velocity as a function of the geometric factors of the collector electrode and the applied electric potential, which is useful for designing ionic wind cooling systems for small electronics.     

Characteristics and underlying physics of ionic wind in dc corona discharge under different polarities

During a dc corona discharge, the ions' momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind.The characteristics of corona discharge and the induced ionic wind are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration.The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode.Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage.The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition.The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model.The ionic wind of negative corona is mainly affected by negative ions.The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area.The ionic wind of positive corona is mainly affected by positive ions.The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.     

Analysis of geometric scaling of miniature,multi-electrode assisted corona discharges for ionic wind generation

The assisted corona discharge is a unique discharge configuration that utilizes multiple collecting electrodes to minimize the voltage required to initiate a corona discharge and to generate an ionic wind. In this work, the geometric parameters that govern the formation of the assisted corona discharge and subsequent ionic wind are evaluated. Flow velocity measurements suggest that the geometry of the electrode spacings is optimized for ionic wind generation when the current flowing to the collector electrode is maximized, and that as the electrode gap is decreased to microscale dimensions, ionic wind production is inhibited.     

Positive discharge from a grounded electrode toward negatively charged particles cloud

In order to understand electrostatic discharges occurring between a grounded electrode and a space charge cloud, the positive discharges were experimentally caused by negatively charged particles cloud. The discharges were initiated by locating a grounded sphere electrode at the inside or outside of the charged powder particles blown by an air flow. The luminous aspect and the discharge current were observed for the grounded sphere electrode with various diameters. Positive streamer corona discharges extended from it. The luminous aspect, peak value of the discharge current and the interval of the discharge significantly depend on the diameter of the grounded sphere electrode as well as its position.