Atmospheric Corona Discharge Research Articles

Nanoscale Discharge Electrode for Minimizing Ozone Emission from Indoor Corona Devices

Ground-level ozone emitted from indoor corona devices poses serious health risks to the human respiratory system and the lung function. Federal regulations call for effective techniques to minimize the indoor ozone production. In this work, stable atmospheric corona discharges from nanomaterials are demonstrated using horizontally suspended carbon nanotubes (CNTs) as the discharge electrode. Compared with the conventional discharges employing micro- or macroscale electrodes, the corona discharge from CNTs could initiate and operate at a much lower voltage due to the small electrode diameter, and is thus energy-efficient. Most importantly, the reported discharge is environmentally friendly since no ozone (below the detection limit of 0.5 ppb) was detected for area current densities up to 0.744 A/m(2) due to the significantly reduced number of electrons and plasma volume generated by CNT discharges. The resulting discharge current density depends on the CNT loading. Contrary to the conventional wisdom, negative CNT discharges should be used to enhance the current density owing to the efficient field emission of electrons from the CNT surface.

Increasing the efficiency of deep photocatalytic oxidation of organic vapors under the action of negative atmospheric corona discharge

The influence of atmospheric corona discharge on the photocatalytic oxidation of acetone (83 ppm), acetaldehyde (108 ppm), and toluene (12–46 ppm) vapors on TiO2 under the action of soft UV light in a closed chamber has been studied. Corona discharge was created around the wire of the charging unit of an electric filter at the inlet of a photocatalytic reactor. The rate of the removal and deep oxidation of substances to CO2 increased considerably and reached maximum for acetaldehyde. The concentrations of inter-mediates in the course of experiments did not exceed 1 ppm. In the presence of corona discharge, the rate of deep oxidation per unit of consumed electric power increased by a factor of 1.2–3.6. The results show that combined photocatalytic and plasmochemical oxidation is promising for the purification of released gases.

The effect of atmospheric corona treatment on AA1050 aluminium

The effect of atmospheric corona discharge on AA1050 aluminium surface was investigated using electrochemical polarization, SEM-EDX, FIB-SEM, and XPS. The corona treatment was performed with varying time (1, 5, and 15 min) in atmospheric air. A 200 nm oxide layer was generated on AA1050 after the 15 min air corona treatment. A significant reduction in anodic and cathodic reactivities was observed starting from 1 min exposure, which further decreased with prolonged exposure (15 min) and after delayed testing (after 30 days). The reduction in surface reactivity is due to the formation of thicker and denser oxide film.

An investigation into the biocidal effect of high voltage AC/DC atmospheric corona discharges on bacteria, yeasts, fungi and algae

A newly developed, low cost plasma system that works at atmospheric pressure and operates with both DC or AC high voltage power supplies was presented. This system was tested for its biocidal effect on a wide range of micro-organisms in water. Optimal killing parameters such as time, temperature and AC and DC high voltage power levels were tested for bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus mutans, Bacillus subtilis), yeast ( Candida albicans), fungi ( Aspergillus niger) and green algae. Results show this system to have a very efficient biocidal effect on most bacteria, algae and fungi in water.

Optical properties and chemical behavior of Laser-dye Coumarin-500 and the influence of atmospheric corona discharges

Structure elucidation of Coumarin-500 Laser-dye in cyclohexane at room temperature has been studied by UV–Vis, Raman, and FTIR spectroscopic techniques. Optical properties and chemical behavior under the influence of atmospheric positive electric pulsed corona discharges were also examined. The effects of UV–Vis irradiation changed some optical parameters, such as decrease in optical density on the absorption spectrum and formation of photoproducts, due to the chromaticity removal. No significant optical changes were observed in the light absorption upon UV-irradiation but large changes in absorption spectrum were observed after positive electric corona discharge treatments, FTIR and Raman spectra in non-polar solvent are recorded and interpreted.

A comparative assessment of two optical fibre techniques for measuring the speed of the electric wind in a negative polarity, atmospheric corona discharge**This paper was presented at the 13th International Conference on Sensors and their Applications, held in Chatham, Kent, on 6–7 September 2005.

Two optical fibre anemometers, one based on a Mach–Zehnder interferometer (OFIA) and another a novel laser-optical fibre Bragg grating sensor (FBGA) have been constructed to measure the speed of the convective air flow generated in the point-plane gap of a negative corona discharge in atmospheric air. In both configurations the sensing section of the optical fibre anemometers is subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localized heating and convective cooling by the corona wind results in an optical signal that is directly calibrated to the speed of the wind. Both the OFIA and FBGA successfully measured the speed of the corona wind in the discharge gap, with wind speeds ranging from 0 to 0.7 m s−1 observed at different locations in the discharge gap. However, the FBGA, due primarily to the ability to average sensor response over many measurements, exhibited an order of magnitude higher sensitivity than the OFIA (Δv ≈ 4 × 10−3 m s−1 compared to 3 × 10−2 m s−1). Both sensors yielded measurements of wind speed that were an order of magnitude lower than similar measurements using laser Doppler anemometry (LDA), indicating that the seed particles introduced as part of the LDA system are providing false reading of wind speed due to acceleration by the gap electric field.

Treatment of a perfluorocarbon using nonthermal plasma produced by atmospheric streamer corona discharge

A nonthermal plasma produced by streamer corona discharge at atmospheric pressure was investigated for the treatment of perfluorocarbon gas. The effectiveness of fluorocarbon treatment was investigated using mixture gases of Ar or N with CF/sub 4/. A maximum decomposition rate of 86% and a maximum energy efficiency of 0.6 g/kWh were achieved using the mixture gas of CF/sub 4/ (1%) and Ar (99%).

Image evaluation of atmospheric corona discharge applied for road tunnel high-velocity electrostatic precipitator

Electrostatic precipitator (ESP) applied to road tunnel ventilation is required to treat high air velocity and large volume because it should install very limited space in road tunnel. Strong corona discharge can ionize particles and realize this high performance ESP. We evaluate the corona discharge using wire and saw edge electrode with and without zigzag edge by discharge images.

Using an optical fibre anemometer to measure the speed of the electric wind in a negative polarity, atmospheric corona discharge

Coronas are partial discharges that occur in regions of non-uniform electric fields adjacent to conductors stressed to high voltages. Negative, Trichel-pulse coronas in air occur when a dc, negative-polarity, high voltage is applied to a conductor. Trichel pulses in atmospheric air generate significant amounts of ozone as well as electrical and acoustic noise. Under the right conditions these coronas can be a precursor to complete electrical breakdown of the air gap due to a reduction in the density of neutral molecules resulting from a combination of localised heating and convective air flow generated by the movement of negative ions. An optical fibre anemometer, based on a Mach-Zehnder interferometer has been constructed to measure the speed of the wind generated in the point-plane gap of a negative, Trichel-pulse corona discharge in atmospheric air. The sensing arm of the fibre interferometer is subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localised heating and convective cooling by the corona wind results in fringe shifts which are directly calibrated to the speed of the wind. This paper reports on the nature of the calibration process and presents some radial profiles of wind speed in the corona gap.

Application of atmospheric corona discharge for PES fabric modification

Polyester fabrics belong to often and regularly used materials in the textile industry. Traditional, mostly chemical methods of their processing often join with undesired environmental problems. The ecological requirements oblige to search and explore new and environmentally safer methods or technologies. One of them might be the cloth surface modification by means of atmospheric corona discharge. Paper presents connection between modification characteristics such as corona power input, duration of action, electrode optimisation and cloth sorption. It shows that the corona-modified cloth has an increased sorption and, probably, the touch.

On-line characterization of gaseous and particulate organic analytes using atmospheric pressure chemical ionization mass spectrometry

A modified atmospheric pressure chemical ionization ion source is applied for direct analysis of volatile or low volatile organic compounds in air. The method is based on the direct introduction of the analytes in the gas phase and/or particle phase into the ion source of a commercial ion-trap mass spectrometer. Two methods are employed for the production of primary ions at atmospheric pressure, photoionization and corona discharge. It is shown that in the presence of a dopant, photoionization can be a highly efficient ionization method also for real-time analysis with detection limits for selected analytes in the lower ppt-range. Using corona discharge for the production of primary ions, which is instrumentally easier since no additional chemicals have to be added to the sample flow, we demonstrate the analytical potential of on-line atmospheric pressure chemical ionization mass spectrometry for reaction monitoring experiments. To do so, an atmospherically relevant gas phase reaction is carried out in a 500 l reaction chamber and gaseous and particulate compounds are monitored in the positive and negative ion mode of the mass spectrometer.

Onset voltages of atmospheric corona discharges on plants

In this article, experimental studies of the onset voltages and of the low current region of negative atmospheric corona discharge on trees are presented. Recent experiments show that the corona discharges on natural biological objects often differ from the classical discharges with metal electrodes. The onset voltage values lie in a wide range around the expected value. It has been found that the negative corona onset voltage of multiple point (such as the top of a coniferous tree) is higher than that of a single point. VA characteristics of multiple point coronas lie below those for a single point from the onset until a critical value is reached. From this point, the slope of the characteristics is steeper for the multipoint geometry. The effect of the multiple point configurations depends mainly on separation of needles. When the needles are closed together-the case of the needles of spruce or pine-the needles behave as a single needle. The difference may be caused by the presence of complex hydrocarbons released from the plants and the changes in the surrounding atmosphere.

The positive corona in air: A simplified analytic approach

The stable positive corona in air is analyzed; the coaxial cylindrical geometry is considered in detail. The analysis separates the corona into two physical regions, corresponding to the absence or presence of significant electron impact ionization. Continuity of electric field and carrier flux across the boundary between these regions gives rise to the criterion for the stable discharge. Electron attachment and detachment are included in the analysis, in an approximate manner. Three secondary-electron-generation processes are considered: secondary emission at the cathode wall due to positive ion impact, photoemission of electrons from the cathode wall, and photoionization in the volume of the air. Comparison of the analysis with experimental data suggests that secondary processes associated with the cathode wall play a minor role in the atmospheric positive corona discharge in cylindrical geometry. Evidence is shown that photoionization of the air is a viable candidate to be the leading secondary-electron-generation process in the discharge.

Energy yields for hydrogen cyanide and formaldehyde syntheses: the HCN and amino acid concentrations in the primitive ocean.

Prebiotic electric discharge and ultraviolet light experiments are usually reported in terms of carbon yields and involve a large input of energy to maximize yields. Experiments using lower energy inputs are more realistic prebiotic models and give energy yields which can be used to estimate the relative importance of the different energy sources on the primitive earth. Simulated prebiotic atmospheres containing either CH4, CO or CO2 with N2, H2O and variable amounts of H2 were subjected to the spark from a high frequency Tesla coil. The energy yields for the synthesis of HCN and H2CO were estimated. CH4 mixtures give the highest yields of HCN while H2CO is most efficiently produced with the CO mixtures. These results are a model for atmospheric corona discharges, which are more abundant than lightning and different in character. Preliminary experiments using artificial lightning are also reported. The energy yields from these experiments combined with the corona discharge available on the earth, allows a yearly production rate to be estimated. These are compared with other experiments and model calculations. From these production rates of HCN (e.g. 100 nmoles cm-2 yr-1) and the experimental hydrolysis rates, the steady state concentration in the primitive ocean can be calculated (e.g., 4 X 10(-6) M at pH 8 and 0 degrees). A steady state amino acid concentration of 3 X 10(-4) M is estimated from the HCN production rate and the rate of decomposition of the amino acids by passage through the submarine vents.