Feasibility study of artificial rainfall system using ion seeding with high voltage source

A non-linear computational modelling of ions from the ground station for electrifying the atmosphere to make feasibility study of artificial rainfall system is proposed and analyzed. The model considers generation of intermediate ions and ionized airflow velocity. The governing electro hydrodynamic (EHD) equations of the model shows that the space charge density, electric field intensity and velocity of the ionized airflow are function of high input voltage applied to generate the ions. The number of ions generated and their velocity is proportional to the applied ion generator voltage.These artificial ions will be introduced in the atmosphere which will act in a similar manner as cosmic rays. These ions will ionize the aerosols and catalyze nucleation processes and thus electrify the atmosphere which will form cloud droplets to get artificial rain. The mathematical model to study the feasibility of artificial rainfall is also validated under favourable conditions.     

Effect of air flow on corona discharge in wire-to-plate electrostatic precipitator

This paper analyses corona discharge in ambient air with laboratory-scaled wire-to-plate electrostatic precipitator (WPESP). The electric field is behind the electro hydrodynamic (EHD) flow in air. Its measurements provide complementary results for the corona discharge study because the classical theory based on the current and voltage data is unsatisfactory. Taking into account the dynamic air flow velocity is perpendicular to the active wires, measurement method of the positive and negative DC corona current density and electric field, has been introduced. It has been shown also that the dynamic air flow velocity modifies the current density and the electric field distributions on the planes surfaces of the WPESP.     

闪电放电通道等离子体成分及相关特性的研究

以无狭缝摄谱仪获得了青海和西藏地区的云对地闪电回击过程的光谱,依据谱线波长和相对强度等信息,结合等离子体相关理论,得到了放电通道温度和电子密度;在此基础上,根据Saha方程、电荷守恒方程和粒子数守恒方程计算了闪电通道主要元素各级电离的离子数密度,进而得到通道质量密度、压强及平均电离度, 并分析了不同强度闪电放电通道的电离度、粒子数密度及其分布特征。结果表明：回击通道接近于完全电离,一次电离离子占主要地位,且NⅡ离子数密度最高;不同强度的闪电放电通道中,NⅡ和OⅡ离子的相对浓度值变化不大;计算过程中考虑带电离子间库仑相互作用以后,原子电离能的计算值降低,中性原子以及一次电离离子数密度的计算值变小,高次电离离子数密度的计算值变大。     

3-D numerical analysis of EHD turbulent flow and mono-disperse charged particle transport and collection in a wire-plate ESP

The present study attempts to develop a detailed numerical approach and a simulation procedure to predict the motion of gas, ions and particles inside a simple parallel plate channel containing a single corona wire. A hybrid Finite Element (FEM)-Flux Corrected Transport (FCT)-Finite Volume (FVM) method is used: the FEM–FCT numerical algorithm is applied for modeling the steady-state corona discharge, while the turbulent gas flow and the particle motion under electrostatic forces are modeled using the commercial CFD code FLUENT. Calculations for the gas flow are carried out by solving the Reynolds-averaged Navier–Stokes equations and turbulence is modeled using the k–? turbulence model. An additional source term is added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations using User-Defined Functions (UDFs). The particle phase is simulated based on the Lagrangian approach, where a large number of particles is traced with their motion affected by the gas flow and electrostatic forces using the Discrete Phase Model (DPM) in FLUENT. The developed model is useful to gain insight into the particle collection phenomena that take place inside an ESP.     

Modeling of ionization–recombination processes in the atmospheric surface layer

The electrical structure of non-stationary horizontally-homogenous surface layer with multi-charged aerosol particles was mathematically modeled in the approximation of turbulent electrode effect. The profiles of positive and negative small ions and nuclei, electric field, polar air conductivity, current density and space charge density were computed in different time periods and various physical conditions. The mathematical model of non-stationary horizontally homogenous surface layer with aerosol particles was made regarding turbulent mixing and convective transport. The space-time distributions of positive and negative small ions and nuclei, electric field, electrical conductivity, current density and space charge density for various physical conditions (aerosol concentrations, turbulent mixing, convective transport, air ionization rate, electric field strength near surface, aerosol particles size) were received. Experimental data of electrical and meteorological parameters were measured and analyzed. It was received that theoretical results are in a good agreement with experimental data.     

Three-dimensional analysis of electrohydrodynamic flow in a spiked electrode-plate electrostatic precipitator

A three-dimensional numerical model has been created to evaluate the electrical and electrohydrodynamic characteristics of a single spiked wire-plate electrostatic precipitator. The hybrid Finite Element – Flux Corrected Transport numerical technique is used for solving the Poisson and current continuity equations to estimate the electric potential and ion charge density distributions in the precipitation channel. The fully three-dimensional turbulent airflow distribution is calculated using the commercial FLUENT software assuming a standard k–? turbulence model. A non-uniform corona discharge is assumed, as it is produced along the electrode in the form of a flat tape with some number of spikes. The EHD secondary flow pattern and its interaction with the main airflow in different planes along the precipitation channel are examined for different voltages applied to the corona spiked electrode. The numerical results are compared with experimental data published in the literature.     

强流电子束源阴极等离子体的粒子模拟

 模拟了强流电子束源阴极表面附近区域数密度约1014 cm-3的等离子体的膨胀过程,观察到等离子体膨胀速度约为1 cm/μs。通过观察不同时刻阴极附近电子和离子的相空间分布、数密度分布和轴向电场分布,分析了等离子体膨胀过程。结果表明:等离子体的产生使得阴极表面电场增强,进而增大阴极的电流发射密度,电流密度增加使得空间电荷效应增强,并使等离子体前沿处的电场减小,当等离子体前沿处的电场减小到零时等离子体向阳极膨胀。讨论了等离子体温度、离子质量、束流密度和离子产生率对等离子体膨胀速度的影响。结果表明:等离子体的膨胀速度随着等离子体温度升高而增大,随离子质量增大而减小,但膨胀速度不等于离子声速;等离子体产生率越小,等离子体膨胀速度越小。     

Improved model for the analysis of back corona in pulse energised electrostatic precipitators

Formation of back corona and its effect on the voltage–current characteristics, etc., have been analysed by several authors. It has also been examined how the harmful effect of back corona can be reduced, for example by the application of pulse energisation. However, to find an optimal solution, modelling of the back corona effect is necessary. Different back corona models were created to estimate the time of its development, the change in current–voltage characteristics, the decrease in particle charge and finally, the collection efficiency of the ESP with back corona. In this paper the authors present an improved numerical ESP model that is capable of determining the parameters of back corona in such cases, when pulse energisation is applied for the power supply of the electrostatic precipitator. Based on the modular structure of the model, different modules calculate the distribution of gas velocity, electric field intensity, particle charging and particle movement. All these parameters are important to determine the properties of back corona while it feeds back on these parameters; therefore iteration is necessary to obtain reliable result. The harmful effects of back corona can be characterised with the help of the evaluation of calculated results.     

Theory of positive corona in SF6 due to a voltageimpulse

A theoretical examination is made of the mechanism of corona formation for a positive point-plane gap in SF₆ at 100 kPa. The impulse voltage applied has a rise time of 15 ns and peak value of 200 kV. Seed electrons are released 1 ns after the start of the voltage rise. For a 0.5-cm diameter positive sphere located 6.5 cm from a negative plane, the calculated circuit current initially consists of subnanosecond corona onset pulses, and then the current steadily rises to a maximum, as the voltage reaches a maximum, followed by a rapid fall in current. During the current rise a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field where ionization equals attachment. The light output during the discharge is predicted to be a maximum at the anode with only a minor pulse of light at the streamer head, making it hard to detect. After the current maximum, recombination rapidly reduces the numbers of positive ions, negative ions, and electrons, but the net charge density remains constant and thus so does the electric field. The electric field is E~E* in the streamer trail, but has a sharp maximum, E≫E* at the head of the streamer trail. The origin of mid-gap precursors, observed when the streamer channel reilluminates after some 100 ns, is attributed to this field maximum in the remnant electric field. The evolution of positive ions, negative ions, and electrons is described by one-dimensional continuity equations, with the space-charge electric fields determined by the disk method. The effects of ionization, attachment, recombination, electron diffusion, and photoionization are all included. New numerical methods allow resolution of the streamer head and the anode fall region to be obtained with a 1-μm mesh, while following the streamer propagation for ~2 cm     

Effect of relative humidity on current–voltage characteristics of monopolar DC wire-to-plane system

This paper deals with the DC monopolar corona discharge in wire-to-plane geometry under variable humid air conditions. The classical formulas of Townsend commonly used for the current–voltage characteristics were used to determine the various corona parameters for the both polarities of the corona discharge. A circular biased probe has been adapted to the plane and is used to measure the ground plane current density and electric field during the monopolar corona discharge. A new approach to the problem of corona discharge in transmission system has been described in this paper. The effect of varying the humidity and wires diameter is also investigated. The values of the electric field and the current density are maximum beneath the corona wire and decrease when moving away from them and the current–voltage characteristics follow the quadratic Townsend's law. The experimental results show that the monopolar corona discharge is strongly affected by the air humidity. The current density and the electric field are measured and compared with the computed values. The agreement between the calculated values and those obtained experimentally is satisfactory. The per unit electric field and current density are also represented by a unique function.     

Three-dimensional simulation of electric field and space charge in the advanced hybrid particulate collector

The advanced hybrid particulate collector (AHPC) is an efficient hybrid system that combines the electrostatic precipitator (ESP) and the bag filter in a unique approach. In this study, an unstructured finite volume method (FVM) is used to compute the three-dimensional distributions of the electric field and the space charge density in an AHPC setup for two cases: without the perforated plate and with the perforated plate. The current–voltage characteristics of the AHPC setup are measured. The current on the bag plate has a mean value 7.82 μA without the perforated plate and 0.08 μA with the perforated plate for the measured voltages. The total currents are used to calculate the charge density at the corona wire according to the Peek's formula. For both cases, the numerical predictions of the current–voltage relations of the plates of the model AHPC agree well with the measurements. When the AHPC has the perforated plate, numerical results show that the electric field and space charge density distributions on the perforated plate have the same number of peaks corresponding to the holes. The electric field on the bag plate surface is lower than that of the top plate and the perforated plate. Though the bag plate has low current, its surface still has high space charge density. When the AHPC has no perforated plate, the electric field is higher than six times and the space charge density is higher than three times that of the case with the perforated plate on the bag plate surface.     

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.     

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.     

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.     

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.     

Numerical simulation and experimental validation of direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage– current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.     

Numerical simulation and experimental validation of a direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage-current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.     

Effect of a corona discharge on the gasdynamical flow rate

We have shown experimentally that the application of an electric field to an air stream blowing over a corona point has the additional effect of increasing the air velocity. This result is derived from the interaction of two factors. We have developed a model of the phenomenon which is based on electrostatic and hydrodynamic equations. The model provides an equation which relates the additional air velocity to the basic corona discharge parameters. The resulting function agrees with the experimental results.     

EPR studies of changes in the charge state of Cr over a cross section of dislocation pipes in ZnS crystals

Short-term high-temperature annealing of ZnS crystals in a zinc atmosphere is shown to cause rapid Zn diffusion through dislocation pipes along growth-dislocation lines. As a result, the impurity ions of divalent chromium localized in Cottrell atmospheres outside Read cylinders become singly ionized. Plastic deformation of such ZnS crystals or the passing of an electric current through them under a voltage higher than a certain threshold value leads to a decrease in the number of univalent chromium ions. This decrease can be explained by an increase in the radius of Read cylinders as growth dislocations leave Cottrell atmospheres and by an increase in the linear density of their electric charge.     

Electrostatic potential and field near the boundary between space charge and no charge regions within a cylindrical pipe

In electronic industries, a corona ionizer is widely used for the elimination of electrostatic charge on the material. Although the high frequency AC ionizer proved the effectiveness of its performance, the corona ions must be sent through a metal pipe to reach targeting area. In order to analyze the behavior of ions in elimination process, the potential and electric field within a pipe must be known. Since the potential and field distribution near the boundary between space charge and no charge regions are extremely important, the analytical solution for this problem was sought by using Bessel functions. Analytical solution showed that even in no charge region, there exists potential distribution within a pipe. Numerical calculation of electric field on the inner pipe surface indicated useful information to estimate the charge density in the pipe. Furthermore, some mathematical formulae were obtained by using Bessel functions.