Direct Current Corona Research Articles

Direct Current Corona Characteristics of Innovative Portable High Voltage dc to dc Booster Device in Corona Charging Setup

In the present work an experimental investigation has been carried out to study the corona characteristics of a portable high voltage dc to dc booster device proposed and used by us for the first time as an innovation in corona charging of electrets. The experiments were conducted in a point-to-plane system to measure the corona current I as a function of applied corona voltage V and inter-electrode separation. Obtained results have been analyzed and discussed successfully in the light of cited works and show that both positive and negative corona produced by this device is consistent with the Townsend Relation adapted for point-to-plane geometry. This device is suitable and effective in applications where the local corona is required.

Experimental study on toluene removal by a two-stage plasma-biofilter system

Volatile organic compounds (VOCs) are typical pollutants that affect air quality. Discharge plasma is thought to be a potential method that can remove VOCs from flue gas. In this experiment, pulsed corona discharge plasma combined with a biological tower was carried out to remove the benzene series, and toluene was selected as the typical VOC. The results indicated that the removal efficiency of toluene by pulsed corona plasma was slightly higher than that of direct current (DC) corona plasma, while its energy efficiency was much higher than DC corona plasma. Under the optimal experimental conditions of pulse voltage 8.5 kV, initial toluene concentration 1400 mg m−3, and toluene flow rate of 12 l h−1, the toluene removal efficiency reached 77.11% by the single method of pulsed corona discharge plasma, and the energy efficiency was up to 1.515 g/(kW·h) under the pulse voltage of 4.0 kV. The trickling biofilter was constructed by using the screened and domesticated Acinetobacter baumannii, and the highest toluene removal efficiency by the pulsed corona discharge plasma combined with the trickling biofilter rose up to 97.84%. Part of the toluene was degraded into CO2, H2O, and some intermediate products such as o-diphenol under the influence of Acinetobacter baumannii. When the remaining waste gas passed through the discharge plasma reactor, the benzene ring structure could be directly destroyed by the collision between toluene and plasma. Meanwhile, O·, OH·, and some other oxidizing radicals generated by the discharge also join into the oxidative decomposition of toluene and its intermediate products, thereby further improving the removal efficiency of toluene. Therefore, the two-stage plasma-biofilter system not only showed a high toluene removal efficiency, but also had a good energy efficiency. The results of this study will provide theoretical support and technical reference for industrial VOC treatment.

Microscopic analysis of Trichel's pulse characteristics and the effect of air pressure and temperature

The negative direct current corona discharge experiment under the needle-plate electrode is conducted, and the typical Trichel pulse waveform is obtained. Furthermore, to analyze the microscopic process of corona discharge, a plasma-fluid discharge simulation model, including air chemical reactions, is established, and a Trichel pulse waveform is obtained, which is consistent with the experimentally obtained waveform. Thus, the chemical reaction that plays a dominant role in the generation and disappearance of charged particles as well as the spatiotemporal distribution and quantitative variation of charged particles during the discharge process are clarified. On this basis, the variation of the microscopic and macroscopic parameters in the discharge process under different air pressure and temperature conditions is studied. The results show that microscopic parameters, such as charge density and electric field intensity, are negatively associated with air pressure and positively associated with temperature, while macroscopic parameters, such as Trichel pulse average current, average peak current, and discharge frequency, are positively associated with the microscopic parameters.

Investigation of negative corona discharge Trichel pulses for a needle-plane geometry via two numerical 2D axisymmetric models

Trichel pulses for negative direct current corona discharge in a pin plate configuration under open dry air conditions are investigated using two numerical models. The first well known general model takes electrons and positive and negative ions into consideration. The second model, a more detailed one, takes electrons and other 16 nitrogen and oxygen species into consideration. Both models are able to capture the general evolution of the electrical discharge. However, the detailed model is able to also show the effect of behavior and contribution of specific species on the discharge. The results show that negative oxygen ions play a key role in the development of Trichel pulses. Furthermore, O2− and O3− ions develop in the interlayered spatial layers in the discharge gap, with the number of layers corresponding to the number of Trichel pulses. It is also shown that nitrogen ions are mostly generated in front of the negatively biased (−5.5 kV) pin.

Research on the Simulation Method for HVDC Continuous Positive Corona Discharge

Corona current is one of the most direct parameters to describe corona discharge. Accurate simulation for corona current is very important for studying the physical process and characteristics of corona discharge. It can provide the theoretical basis for solving electromagnetic environment problems and optimizing transmission lines. A simulation method for high voltage direct current (HVDC) continuous positive corona discharge is presented in this article. First, based on the experiments of continuous positive corona discharge under the different voltages, the regularity of time intervals between adjacent current pulses is obtained. Then, a two-dimensional simulation model of the positive continuous corona discharge process is established with the obtained regularity, which is used to imitate the electron re- emission in the simulation. Finally, the correctness and validity of the method are verified by the experimental results. Since the proposed model is more in line with the actual situation than the existing equal-time interval model, the change and motion process of various ions in the discharge process will also be more realistic. The results are helpful to further understand the corona discharge process and provide a theoretical reference for the design of HVDC transmission lines.

Removal of air pollutant by a spike-tubular electrostatic device: Multi-stage direct current corona discharge enhanced electrostatic precipitation and oxidation ability

In this work, a spike-tubular electrostatic device was developed for effectively removing particulate matter (PM) and VOCs, based on multi-stage electric field enhancement and expanded arc interface ratio of corona discharge. In the experiment, it was equipped with a portable 12 V D.C. power supply module and a fan module; PM from moxa smoke, mainly composed of submicron particles with a high penetrate rate, and HCHO were employed to test its electrostatic precipitation and oxidation ability, respectively. Additionally, CFD numerical simulation was adopted to investigate the characteristics of the electric field, the flow field, and the ozone generation. Experimental results showed that the electrostatic device could remove 99% of the fine particles at 2 m/s. Meanwhile, it could also remove HCHO of 2.14 × 103-1.07 × 104 μg/m3 concentration with 100% efficiency. By comparison, its oxidation capacity could be about 80 times that of ozone oxidation, revealing the enhanced oxidation ability of other short-living reactive species. Simulation results proved that the promising purification performance resulted from the locally enhanced electric field strength, up to 2 × 107 V/m in the central region, and sufficient contact between pollutants and the corona discharge region. Finally, as verified by the airtight chamber cycle experiment and case comparison, the device owns feasible purification ability and promising energy yield (0.79 g/kWh) in the application. Moreover, prospects and strategies for the device's practical application in air purification and disinfection were proposed, which may provide helpful enlightenment for air purification.

Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer.

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in the form of miniaturized instrument. Analytes may exist in the form of positively or negatively charged ions according to their chemical composition and ionization condition, and therefore require both polarity of electric field for the detection. In this work the polarity switching of a drift-time ion mobility spectrometer based on a direct current (DC) corona discharge ionization source was investigated, with novel solutions for both the control of ion shutter and the stabilization of aperture grid. The drift field is established by employing a switchable high voltage power supply and a serial of voltage regulator diode, with optocouplers to drive the ion shutter when the polarity is switched. The potential of aperture grid is stabilized during the polarity switching by the use of four diodes to avoid unnecessary charging cycle of the aperture grid capacitor. Based on the proposed techniques, the developed DT-IMS with 50 mm drift path is able to switch its polarity in 10 ms and acquire mobility spectrum after 10 ms of stabilization. Coupled with a thermal desorption sampler, limit of detection (LoD) of 0.1 ng was achieved for ketamine and TNT. Extra benefits include single calibration substance for both polarities and largely simplified pneumatic design, together with the reduction of second drift tube and its accessories. This work paved the way towards further miniaturization of DT-IMS without compromise of performance.

Removal of ethyl acetate in air by using different types of corona discharges generated in a honeycomb monolith structure coated with Pd/γ-alumina

A method based on the corona discharge produced by high voltage alternating current (AC) and direct current (DC) over a Pd/γ-Al2O3 catalyst supported on a honeycomb structure monolith was developed to eliminate ethyl acetate (EA) from the air at atmospheric pressure. The characteristics of the AC and DC corona discharge generated inside the honeycomb structure monolith were investigated by varying the humidity, gas hourly space velocity (GHSV), and temperature. The results showed that the DC corona discharge is more stable and easily operated at different operating conditions such as humidity, GHSV, and gas temperature compared to the AC discharge. At a given applied voltage, the EA conversion in the DC honeycomb catalyst discharge is, therefore, higher compared with that in the AC honeycomb catalyst discharge (e.g., 96% of EA conversion compared with approximately 68%, respectively, at 11.2 kV). These new results can open opportunities for wide applications of DC corona discharge combined with honeycomb catalysts to VOC treatment.

Numerical simulation on ionic wind in circular channels* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0406000) and the National Natural Science Foundation of China (Grant No. 51676036).

Ionic wind induced by direct-current corona discharge has attracted considerable interest because of its low energy consumption, low noise emission, flexible designs, and lack of moving parts. The purpose of this study is to investigate the configuration parameters to improve the velocity of the ionic wind. Accordingly, this study develops a three-dimensional (3D) model of circular tube with multi-needle-to-mesh electrode configurations, in this model, the influences of various parameters were explored such as the mesh gap, the distribution of needle electrodes, the number of needle electrodes, and the radius of the circular channel. The numerical research results showed that the mesh gap, the distribution of needle electrodes, and the radius of the circular tube significantly affected the velocity of the ionic wind. When mesh gap is 12 mm, which indicates that there is an optimal mesh gap which can enhance the velocity of the ionic wind. What is more, changing the distribution of needle electrodes and increasing the number of needle electrodes can effectively improve the velocity of the ionic wind, the optimum distribution α of needle electrodes is 0.7–0.9, which greatly increase the velocity of the ionic wind. However, for multi-needle-to-mesh structure, the improvement of the radius of the circular channel is conducive to enhance the velocity and improve the velocity distribution.

Inexpensive Ultrasonic Nebulization Coupled with Direct Current Corona Discharge Ionization Mass Spectrometry for Liquid Samples and Its Fundamental Investigations.

The concept of direct mass-spectrometric analysis, especially exploited by ambient desorption/ionization (ADI) methods, provides numerous means for convenient sample analysis. While many simple and versatile ionization sources have been developed, challenges lay in achieving efficient sample introduction. In previous work, a sample introduction method employing direct current corona discharge (CD) coupled to a surface acoustic wave nebulization (SAWN) device enhanced sampling performance for both polar and nonpolar analytes by up to 4 orders of magnitude. In fact, the SAWN-CD method generated a multiply charged peptide ion signal comparable to that of conventional ESI. Unfortunately, the high cost of the SAWN devices themselves limits their accessibility. Herein, we report on an analogous implementation of CD with an inexpensive ultrasonic nebulizer (USN) on the basis of a commercial room humidifier demonstrating equivalent exemplary performance. We subsequently compare the two methods of SAWN-CD and USN-CD in a screening application of milk for the detection of two antibiotic drugs, ciprofloxacin and ampicillin. Finally, we further investigate the relative softness of these CD-coupled acoustic nebulization methods in comparison to that of ESI using a survival yield study of the thermometer ion nitrobenzylpyridinium.

Corona Discharge-Induced Water Droplet Growth in Air

In natural clouds, water droplets grow by condensation in a supersaturated environment. Under subsaturated conditions, water droplets normally keep evaporating until they eventually disappear. In this article, we study the effect of corona discharge on water droplet growth under both supersaturated and subsaturated conditions. It is shown that the formation of mist visible to the naked eyes could be induced by direct current (dc) corona discharge under supersaturated conditions. Furthermore, we find that corona discharge could promote the growth of water droplets even under subsaturated conditions. Possible mechanisms are discussed, and the results suggest that the droplet growth enhancement is supported by the synergetic effects of droplet surface charge, external electric field, and ionic wind generated by the corona discharge.

Design and Experimental Evaluation of Innovative Wire-to-Plane Fins’ Configuration for Atmosphere Corona-Discharge Cooling Devices

Electro-fluid-dynamic cooling devices (EFAs) are being recognized due to their enormous advantages for their application in several industrial sectors, their performance benefits from generated ionic winds and their singular features, which make them competitive with conventional fans and heatsinks. Due to the problems in the electronics industry, where traditional refrigeration systems are not effective due to their dimensions, this study analyzes an innovative arrangement based on wire-to-plane fins by direct current (DC) positive corona discharge in atmospheric air for applications. The paper focuses on optimizing the multicriteria geometry of the electrodes. Several parameters are analyzed such as the gap between emitter and ground electrodes, the electrode materials and geometry, the diameter of the high-voltage electrode and the influence of the dielectric barriers located near the corona electrode to improve heat exchange. Experimental validation shows the potential of this arrangement related to weight, volume, non-mobile parts and silence.

Rapid desorption of low-volatility compounds in liquid droplets accompanied by the flash evaporation of solvent below the Leidenfrost temperature.

The objective of this work is to study the interaction of methanol droplets with the heated surface for the improved detection of low-volatility and thermally labile compounds by the flash evaporation that occurs below the Leidenfrost temperature. 5 μL solutions of low-volatility compounds in methanol were introduced into the heated tube. Desorbed analytes were ionized in the sealed atmospheric pressure chemical ionization (APCI) source by direct current (DC) corona discharge using air as the reagent gas. The rapid desorption of low-volatility compounds accompanied by the flash evaporation of methanol solvent was observed in the temperature range of 60-100°C. Linear relationships between the signal intensities and the solute concentrations in the range of 0.01-5 ppm for morphine, cocaine, methamphetamine, and amphetamine were obtained at 95°C. The observed rapid desorption of low-volatility compounds below the Leidenfrost temperature would provide useful information in many fields, e.g., the interaction of liquid droplets with heated matter, liquid sample introduction into the injection port of a gas chromatograph, coupling of the flash evaporation with pulse valve operated miniaturized mass spectrometer, etc.

Stability of Corona Discharge in High Pressure Nitrogen

The study of corona discharge is important for successful development of various electrostatic technologies. The current study is directed at investigating the stability of a negative polarity direct current corona discharge in high pressure nitrogen. Experiments were carried out at test set-up equipped with a high temperature high pressure (HTHP) corona discharge ionizer which has star-shaped disk high voltage electrodes installed inside of a cylinder grounded electrode. The “direct” and “indirect” current–voltage characteristics (CVCs) were measured for various gas pressure values without and with a gas flow through the HTHP set-up casing and without external heating of the ionizer grounded electrode. An increase of gas pressure results in an increase of a “CVC-direct” onset voltage and in a decrease of the corona current at a constant value of the applied voltage. A hysteresis effect is observed for the corona discharge CVCs at a high gas pressure when corona currents for the “CVC-indirect” are measured at voltages lower than the “CVC-direct” onset voltage. The area of the “hysteresis window” increases with an increase of gas pressure.

A dielectric barrier discharge ion source increases thrust and efficiency of electroaerodynamic propulsion

Electroaerodynamic (EAD) propulsion, which produces a thrust force by electrostatic means, has been proposed as a method of electric airplane propulsion which is solid-state and nearly silent and produces no combustion emissions. Previous work demonstrated that EAD is capable of sustaining flight of heavier-than-air airplanes. The most successful EAD propulsion devices have thus far used a direct current (DC) corona discharge to produce ions and the same DC field to accelerate them. However, these corona discharge EAD devices are subject to a performance trade-off where increasing thrust reduces efficiency (thrust-to-power ratio). This is a key barrier to practical adoption. Here, we show that by using a dielectric barrier discharge (DBD) instead of a corona discharge to produce ions, while still using a DC field to accelerate them, higher thrust and thrust-to-power can be achieved. We identify operating regimes for this thruster, optimize the electrical characteristics of the DBD ion source, and find that the thrust-to-power can reach up to 20 N/kW at a thrust of 50 mN/m and up to 10 N/kW at 150 mN/m—in both cases, approximately twice that of the equivalent corona discharge devices. With lower power draw for the same thrust, DBD enhanced EAD propulsion devices could increase the endurance of EAD airplanes and begin to enable the design of practically useful solid-state aircraft.

Non‐thermal plasma‐induced apoptosis in yeast Saccharomyces cerevisiae

The effect of non‐thermal plasma generated by the direct current (DC) corona discharge in the mode of transition spark is studied on a yeast Saccharomyces cerevisiae. The exposure to plasma increases production of reactive oxygen species (ROS) in cells, possibly causing the induction of apoptosis. To clarify the mechanism of apoptosis, its induction is tested not only on a wild strain of S. cerevisiae, but also on mutant strains: A deletion mutant Δyca1 without yeast metacaspase proves that in S. cerevisiae the apoptosis occurs partly by the caspase‐independent pathway. A petite strains with mutation in the mitochondria do not show pronounced ROS formation, but in spite of this, apoptosis is detected. Hence, mitochondrial ROS probably do not play an important role in induction of apoptosis.

Disinfection by HO2 Radicals Generated by Negative Corona Discharge on Acidic Solution

An oxygen-supplied negative direct current (dc) corona discharge on acidic solution is studied to reduce the odor associated with conventional disinfectants, such as ClO - , HClO, O 3 , and ClO 2 . The discharge system provided an odorless bactericide of hydroperoxyl (HO2) radicals, generated from the reaction of discharge-generated O 2 - with H + in the acidic solution. A 2.5-log reduction of Escherichia coli (E. coli) was observed under the conditions of pH 2.8, dc -4.8-kV dc, and -17 μA, where the concentration of ozone and hydrogen peroxide was too low to inactivate the E. coli. At a pH of 5.6 or by adding a superoxide dismutase, which is a scavenger of HO 2 , negligible inactivation was observed.

One-Dimensional Simulation of Synergistic Desulfurization and Denitrification Processes for Electrostatic Precipitators Based on a Fluid-Chemical Reaction Hybrid Model

Non-thermal plasma (NTP) technologies can be used to treat a variety of gaseous pollutants, and extensive research has been carried out worldwide because of its high purification efficiency, low dependence on temperature, and other advantages. NO and SO2 are the main gaseous pollutants in coal-fired flue gas. The plasma dynamics for desulfurization and denitrification is a hot topic in the field of NTP pollutant control technologies. In this paper, a one-dimensional fluid model for the simultaneous desulfurization and denitrification of flue gas by negative direct current (DC) corona discharge was established based on the traditional zero-dimensional chemical kinetic model. The simplified wire-cylindrical electrodes configuration and numerical simulation conditions are similar to the working process of electrostatic precipitators. The results obtained by the finite element method show that the removal efficiency of NO and SO2 is remarkable in the region with a radius of less than one centimeter around the high-voltage electrode, and the effective purification area expands with the increase of the discharge voltage. There are different removal pathways for NO at different positions in the removal region, while the removal of SO2 is mainly dependent on the oxidation by OH.

Comparative Study of AC and Positive and Negative DC Visual Corona for Sphere-Plane Gaps in Atmospheric Air

Due to the expansion of high-voltage direct current (HVDC) power systems, manufacturers of high-voltage (HV) hardware for alternating current (ac) applications are focusing their efforts towards the HVDC market. Because of the historical preponderance of ac power systems, such manufacturers have a strong background in ac corona but they need to acquire more knowledge about direct current (dc) corona. Due to the complex nature of corona, experimental data is required to describe its behavior. This work performs an experimental comparative analysis between the inception of ac corona and positive and negative dc corona. First, the sphere-plane air gap is analyzed from experimental data, and the corona inception voltages for different geometries are measured in a high-voltage laboratory. Next, the surface electric field strength is determined from finite element method simulations, since it provides valuable information about corona inception conditions. The experimental data obtained are fitted to an equation based on Peek’s law, which allows determining the equivalence between the visual corona surface electric field strength for ac and dc supply. Finally, additional experimental results performed on substation connectors are presented to further validate the previous results by means of commercial high-voltage hardware. The results presented in this paper could be especially valuable for high-voltage hardware manufacturers, since they allow determining the dc voltage and electric field values at which their ac products can withstand free of corona when operating in dc grids.

A novel method to predict current voltage characteristics of positive corona discharges based on a perturbation technique. I. Local analysis

A novel method to compute current-voltage characteristics (CVCs) of direct current positive corona discharges is formulated based on a perturbation technique. We use linearized fluid equations coupled with the linearized Poisson’s equation. Townsend relation is assumed to predict CVCs apart from the linearization point. We choose coaxial cylinders as a test problem, and we have successfully predicted parameters which can determine CVCs with arbitrary inner and outer radii. It is also confirmed that the proposed method essentially does not induce numerical instabilities.