DC Corona Discharge In Air Research Articles

Capacitance Calculation Model in Corona Discharge Case

The (I-V) characteristic pattern of the corona discharge case is very different from the pattern of ordinary electric circuits, so it is interesting to investigate. Several previous studies involved the concept of Maxwell's equations on several physical case models such as coaxial cylinder, electrohydrodynamic, and the electric wind. In this study, we use a capacitance calculation model for positive dc corona discharge in air, especially in calculating the (I-V) current-voltage characteristics of an electrode configuration model, often referred to as capacitively coupled plasma (CCP). The configuration model comprises active and passive electrodes, with the active electrode in the form of a pentagonal with the sharp end (in the middle) facing downwards in an upright position. The passive electrode under the active electrode has a large rectangular shape in a lying place. This configuration model is named The Chisel Eye and Midpoint-Plane (CEM-P). The analytical calculation of the (I-V) characteristics uses the geometric properties of the active electrode, which will produce a large corona current flow at the pointed electrode. These properties in analytical calculation manifest with the emergence of the corona flow multiplication factor at the sharp active electrode’s integration boundary condition called the shape sharpness factor k. The Python GUI Programming simulation program makes graphic simulations, Standard Deviation (SD), t-tests, and calculating the factor k (fitting curve value) between numerical calculations and research data. The values of the SD, the t-tests, and the Percentage of tangent points meet the requirements for a high level of accuracy for the four CEM-P configuration models of the (I-V) characteristics simulation graph with the graph has a relatively large percentage of tangent points values (82.35% – 94.44%).

The Current-Voltage Characteristics for Electrode Geometry Model of Positive DC Corona Discharge in Air

Research on corona plasma discharges from plasma reactors has been carried out using the Point and Semicircular-Plane (PSC-P) electrode configuration in the air. The purpose of this study is to compare the suitability level of the current-voltage (I-V) characteristics curve from the results of experimental data and numerical simulation calculations of the electrode geometry function based on the variation of three electrode configuration sizes (small plate, medium plate, and large plate) and two variations of the distance between the two electrodes in each electrode configuration size. The results of the study prove that there is a high degree of conformity between numerical calculations with experimental data through calculations from the Python GUI Programming by taking a fitting value from the certain k-shape sharpness factor. The calculation location of the k-shape sharpness factor lies on the electrode tip sharp surface which will produce the largest plasma flow in the plasma reactor equipment.

Experimental study on electrostatic removal of high-carbon particle in high temperature coal pyrolysis gas

A high-temperature electrostatic precipitator (ESP) presents a good solution for hot gas cleaning, which can remove fly ash from pyrolysis gas at temperatures higher than the tar dew point. In this paper, the characteristics of negative DC corona discharge in air and simulated coal pyrolysis gas were studied. The removal of coal pyrolysis furnace fly ash (ash A) was investigated and compared with that of coal-fired power plant fly ash (ash B) in ESP with a temperature ranging from 300 K to 900 K. The current density of simulated gas was higher than that of air under the same discharge voltage and at different temperatures. The simulated gas also had a higher spark voltage and a lower onset voltage compared with air. The fractional collection efficiency of ash A was lower for particles with diameters of larger than 0.1 µm at high temperature, compared with ash B. A lower collection efficiency in simulated gas was obtained for particles with diameters of less than 0.1 µm compared with air. The collection efficiency of submicron particles in simulated gas was usually higher than it in air, especially for particles with diameters of less than 0.04 µm. In simulated gas, the overall collection efficiency of ash A was obviously lower than that of ash B, especially at high temperature. From 300 K to 700 K, the collection efficiencies of both ash samples were as high as above 93%, but the collection efficiency of ash A in simulated gas decreased to 78.7% at 900 K.

Trichel Pulse in Negative DC Corona discharge and Its Electromagnetic Radiations

We investigate in this paper the radiated electromagnetic waves together with the discharge characteristics of Trichel pulse of negative DC corona discharge in air in pin-to-plate and wire-to-plate configurations. The feature of the current pulse and the frequency spectrum of the electromagnetic radiations were measured under various pressures and gas gaps. The results show that the repetition frequency and the amplitude of Trichel pulse current depend on the discharge conditions, but the rising time of the pulse relates only to the radius of needle or wire and keeps constant even if the other conditions (including the discharge current, the gas gap and the gas pressure) change. There exists the characterized spectrum of electromagnetic waves from negative corona discharge in Trichel pulse regime. These characterized radiations do not change their frequency at a given cathode geometry even if the averaged current, the gas gap or the air pressure changes, but the amplitude of radiations changes accordingly. The characterized electromagnetic radiations from Trichel pulse corona relate to the formation or the rising edge of current pulse. It confirms that the characterized radiations from Trichel pulse supply information of discharge system and provide a potential method for detecting charged targets.

Current-voltage characteristics of dc corona discharges in air between coaxial cylinders

This paper presents the experimental measurement and numerical analysis of the current-voltage characteristics of dc corona discharges in air between coaxial cylinders. The current-voltage characteristics for both positive and negative corona discharges were measured within a specially designed corona cage. Then the measured results were fitted by different empirical formulae and analyzed by the fluid model. The current-voltage characteristics between coaxial cylinders can be expressed as I = C(U − U0)m, where m is within the range 1.5–2.0, which is similar to the point-plane electrode system. The ionization region has no significant effect on the current-voltage characteristic under a low corona current, while it will affect the distribution for the negative corona under a high corona current. The surface onset fields and ion mobilities were emphatically discussed.

Analysis of current-voltage characteristics in the wires-to-planes geometry during corona discharge

The behaviour of DC corona discharge in air that is free of particulate matter with the wires-to-plane geometry was analysed in this work. The formulae I = KV ( V − V 0 ) and I = A ( V − V 0 ) m commonly used for the current-voltage characteristics were used to determine the various corona parameters for the two polarities of the corona discharge. Using curve fitting, it has been shown that the geometric factors K and A and the exponent m are strongly affected by the number n of the discharging wires. However, the corona inception voltage determined from the measurements is weakly influenced when n is small, and it remained constant for n > 5 discharging wires. As for the breakdown voltage of the discharge, it is practically independent of the number n . Furthermore, it was verified that the two formulae above can be used for both negative and positive corona in multiple wires-to-plane geometries.

On the negative corona and ionic wind over water electrode surface

Abstract The DC corona discharge in air and the induced ionic wind were investigated in the needle-to-water system at atmospheric pressure. The water deformation was measured under various conditions, and wind pressure and active areas were estimated accordingly. The effects of applied voltage, gap spacing and tip radius on the corona ionic wind were studied and the qualitative analysis was provided. Self-rotation of corona discharge was observed in experiments. The results show that higher voltage or electric field strength results in a stronger ionic wind. The active area increases with applied voltage below a voltage threshold. There is an optimal gap distance for a wider as well as stronger ionic wind and blunter needle we used leads to an enhancement on both the active area and the wind strength. The wind velocity reaches 7 m/s at optimized condition in the present system. The rotation of corona discharge helps to improve the active area and uniformity of the treating area which may be associated with the chemical reaction of the water surface.

Electrohydrodynamic force produced by a wire-to-cylinder dc corona discharge in air at atmospheric pressure

Wire-to-cylinder corona discharges are studied to better understand the electrohydrodynamic (EHD) phenomena that govern the performances of electric propulsion systems. First, theory associated with EHD thrusters is presented in order to be compared with experimental results. Secondly, direct thrust measurements are carried out to optimize the electrical and geometrical parameters of such devices. The main results are as follows: (1) the discharge current I is proportional to the square root of the grounded electrode diameter and to 1/d2 where d is the electrode gap; (2) for d ⩽ 20 mm, the mobility of negative ions is higher than that of positive ions while the mobility of both ions is equal for higher gaps; (3) therefore, for gap ⩾30 mm, positive and negative coronas results in the same current-to-thrust conversion; (4) the current-to-thrust conversion is equal to 33 N A−1 per centimetre of gap, and it is proportional to the gap; (5) the thruster effectiveness θ increases with , decreases with the square root of thrust and reaches about 15 N kW−1 for d = 40 mm; (6) the force computed from experimental velocity profiles is overestimated compared with the values measured with a balance, showing that this method cannot be used for thrust determination.

Onset conditions for positive direct current corona discharges in air under the action of photoionization

This paper presents a numerical model for the inception of positive dc corona discharges in air near cylindrical anodes, which plays a bridge role between the classic positive corona onset criterion and the photoionization model considering the effective radiation wavelength. The predicted onset voltages agree well with Peek’s experimental data in a wide range of conductor radii and relative air densities. The influence of the collisional quenching of emitting excited states on the surface onset field is significant with low air density or small conductor radius. Within the effective radiation wavelength, numerical expressions for the photon absorption coefficient in air and Townsend’s second coefficient due to photoionization are deduced on the basis of the new model. A different perspective on the classic coefficients is given.

Ionic wind generation by a wire-cylinder-plate corona discharge in air at atmospheric pressure

A wire-cylinder-plate electrode configuration is presented to generate ionic wind with a dc corona discharge in air at atmospheric pressure. The objective of the work is to maximize the power supplied to the flow in order to increase acceleration while avoiding breakdown. Thus, the proposed experimental setup addresses the problem of decoupling the mechanism of ion generation from that of ion acceleration. Using a wire-plate configuration as a reference, we have focused on improving the topography of the electric field to (1) separate the ionization and acceleration zones in space, and (2) guide the trajectory of charged particles as parallel to the median axis as possible. In the proposed wire-cylinder-plate setup, a dc corona discharge is generated in the space between a wire and two cylinders. The ions produced by the corona then drift past the cylinders and into a channel between two plates, where they undergo acceleration. To maximize the ionic wind it is found that the geometric configuration must be as compact as possible and that the voltage applied must be right below breakdown. Experimentally, the optimized wire-plate reference setup provides a maximum flow velocity of 8 m s−1, a flow rate per unit electrode length of 0.034 m2 s−1, and a thrust per unit electrode length of 0.24 N m−1. The wire-cylinder-plate configuration provides a maximum flow velocity of 10 m s−1, a flow rate per unit electrode length of 0.041 m2 s−1, and a thrust per unit electrode length of 0.35 N m−1. This 46% increase in thrust is obtained by increasing the electric power per unit electrode length by only 16% (from 175 to 210 W m−1), which confirms the gain in efficiency obtained with the decoupled system. In comparison with a simple wire-wire corona configuration, the wire-cylinder-plate configuration increases the ionic wind velocity by up to a factor of 3, and the thrust by an order of magnitude.

Impedance-stabilized positive corona discharge and its decontamination properties

The point-to-plane DC corona discharge in air at atmospheric pressure was stabilized by a serially connected ballast impedance. The ballast impedance was implemented by a resistor-capacitor group connected in parallel. In the case of connecting the serial impedance into the electric circuit of a negative corona, the transition into a spark takes place at parameters similar to those of a non-stabilized discharge. In contrast, in the case of a positive corona, the discharge does not undergo a transition into a spark, but rather into a mode of periodic streamers. We measured the bactericidal effect of the stabilized discharge. The experiments showed that after a 2-minute exposure the quantity of surviving bacteria decreased from 95% for a non-stabilized discharge down to 5% for a stabilized one.

Atmospheric pressure dc corona discharges: operating regimes and potential applications

The operating regimes and the structures of dc corona discharges in air, nitrogen, helium and hydrogen–methane mixtures are studied for a point to plate electrode configuration. The characteristics of the dc negative corona discharge are investigated. In addition to the bright glow at the cathode (pin) region, a uniform diffuse glow is observed near the anode (plate) surface for the negative corona. This diffuse glow is observed in air and hydrogen–methane discharges only and not in nitrogen discharges. The presence of a glow near the planar anode is perhaps due to the increased electric field caused by a negative ion sheath formed only in electronegative gases. Optical emission spectroscopy (OES) was used to obtain species, spatially resolved temperature measurements and electric field estimations for the corona discharges in air. For the negative corona, the presence of a weak glow indicates an active plasma region near the positive planar electrode which may be useful for processing techniques such as plasma enhanced chemical vapor deposition. The dc negative corona discharge was observed to deposit films on the anode surface for air and methane.

Ozone production by a dc corona discharge in air contaminated by n-heptane

Beneficial purposes of ozone such as elimination of odours, harmful bacteria and mildew can be used for transportation of food, fruits and vegetables with the aim to extend their storage life. To date the main technique used for this purpose in the transportation of these commodities, e.g. by trucks, was cooling. Here a combination of cooling together with the supply of ozone into containers with these commodities is considered. For these purposes we studied the effect of air contamination by n-heptane (part of automotive fuels) and humidity on ozone production by a dc hollow needle to mesh corona discharge.We found that, for both polarities of the needle electrode, addition of n-heptane to air (a) decreases ozone production; (b) causes discharge poisoning to occur at lower current than for air; (c) does not substantially influence the current for which the ozone production reaches the maximum. Finally the maximum ozone production for the discharge in air occurs for the same current as the maximum ozone production for the discharge contaminated by n-heptane. We also found that humidity decreases ozone production from air contaminated by n-heptane irrespective of the polarity of the coronating needle electrode. This dependence is stronger for the discharge with the needle biased positively.

Conditions for inception of positive corona discharges in air

Conditions for inception of dc corona discharges in air near spherical and cylindrical anodes are considered. The parameter K (ionization integral) in the standard discharge inception criterion is evaluated for a wide range of electrode radii and air densities.

A critique of the Deutsch assumption

The field equations of a small-scale point-plane negative DC corona discharge in air have been solved in a particular case by the authors. The technique was to use a finite-element method for solving Poisson's equation, and an algorithm for finding the charge density from a current-continuity relation. A single mobility coefficient was adopted and the methods were used alternately until convergence was obtained. Boundary conditions for this technique are the potentials of the electrodes and the measured current distribution. Geometric convergence occurs before arithmetic convergence, with the accuracy of the latter being better than 1% for the electric field (typically 0.5% everywhere except at the tip of the active electrode). The uncertainty in the solution because of the unknown charge distributions in the small glow region has been accurately quantified by using two extreme models. Geometrical and numerical differences between these models have been shown to be very small.