Pressure Arc Plasma Research Articles

Improvements in Surface Properties of Polypropylene, Polycarbonate and Polyurethane by Nonthermal Atmospheric Pressure Plasma Arc Jet in Air

Improvements in Surface Properties of Polypropylene, Polycarbonate and Polyurethane by Nonthermal Atmospheric Pressure Plasma Arc Jet in Air

NOx production in a rotating gliding arc plasma: potential avenue for sustainable nitrogen fixation

An atmospheric pressure plasma arc reactor operating in two distinct modes shows substantially different NOx concentrations; one mode produces record NOx concentrations (up to 5.5%) with an energy consumption of 2.5 MJ mol−1.

КЛАССИФИКАЦИЯ ТЕХНОЛОГИЙ УПРОЧНЕНИЯ, НАНЕСЕНИЯ ПОКРЫТИЙ И ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ ТОПЛИВНОЙ АППАРАТУРЫ ДИЗЕЛЬНЫХ ДВИГАТЕЛЕЙ

During operation, any technical product with friction units, as parts wear out, loses its working capacity and as a result cannot perform the specified functions with the parameters, established by the requirements of technical documentation. Today, the technological capabilities of manufacturing various machines and mechanisms have been exhausted throughout the world without noticeable wear on the mating surfaces of friction units. Depreciation is practically impossible to exclude. Therefore, a search for new ways to extend the life of technical devices by exposing them to friction surfaces is an urgent task. These requirements apply to the fuel equipment of automotive and combine diesel engines. In this paper, we analyze the known covering technologies for hardening and restoration of fuel equipment parts. The methodology of choosing the optimal covering process with the aim of hardening and restoration of parts of fuel equipment is formulated. In accordance with this concept of choosing a technology to increase the durability of fuel equipment parts, plasma finish hardening with the application of multilayer wear-resistant coatings is a promising technology. The paper presents the results of a study of the physicomechanical properties of diamond-like coverings of the DLCPateks type (a-C:H/a-SiOCN) obtained on friction surfaces by transporting an atomic and molecular stream of particles of liquid chemical compounds by a plasma jet of an atmospheric pressure plasma arc torch. The layer formed on the working surfaces is a non-metallic amorphous multilayer covering with a low coefficient of friction, increased microhardness, chemical inertness, hydrophilicity, high heat resistance and dielectric characteristics. In order to minimize possible defectiveness of the base material at the final stage of manufacturing parts of fuel equipment, it is proposed to apply thin-film coatings on them.

Heating of the cathode with a conical tip by atmospheric-pressure arc plasma

PurposeIn this study, the authors performed a numerical investigation on the heating of a hot cathode with a conical tip by atmospheric arc, taking into account of the two temperature sheath effect for the first time.Design/methodology/approachThe Schottky effect at cathode surface is considered, which is based on the analytic solution of a one-dimensional sheath model. The unified model allows one to predict the cathode-plasma heat transfer.FindingsThe total heat flux to cathode surface is smaller than its components’ heat flux due to electron back diffusion is as large as that due to ion flux with the increase of cathode length the total heat transported to the cathode body has an obvious decrease.Originality/valueIt is found that two kinds of solution exist for the cathode with a 140° conical tip; however, only one stable solution exists when the conical angle is reduced to 130°.

Characterization of the surface topography of arc-treated aluminum alloys by fractal geometry

Abstract An atmospheric pressure plasma arc discharge creates a complex structure on an aluminum (Al) surface that is a challenging task to characterize by conventional techniques. The solution could be in applying the principles of fractal geometry to characterize the arc-treated aluminum surface while studying profiles obtained by an optical profilometer and SEM (scanning electron microscope) images. The fractal dimension (FD) is determined along with the other conventional surface characteristic parameters (Ra, Rq, Sa, and Sq). The influence of the arc process parameters such as the arc current (I) and plasma torch velocity (v) on the fractal dimension is explored.

RLC-Induced Current Oscillations in Convoluted Arcs With Independently Activated Magnetic Fields

Experimental results on atmospheric-pressure arc plasma convolutes in air around a polytetrafluoroethylene cylindrical shroud containing a magnetic field ( B-field) producing coil are presented. In this paper, the B-field coil is energized by a current separate from that flowing through the arc, and a separate RLC circuit was connected across the arc gap. Thus the magnitude and time duration of the B-field are independent of the arc current and the high-frequency current oscillations produced by the parallel RLC circuit. Experimental results for the time variation of the current through and voltage across the arc plasma for these different conditions are presented, along with high-speed photographs of the oscillating current arc. The effects of varying the B-field upon plasma pulsations formed by the independent B-field and RLC current oscillations are discussed.

Surface Quality Prediction of Atmospheric Pressure Plasma Arc Cleaning Based on Least Square Support Vector Machine

The theory of Least Squares Support Vector Machines was applied to metal surfaces cleaning by atmospheric pressure plasma arc. An intelligent predictive model of the non-linear relationship between cleaning quality and process parameters was established with the k-fold cross training of sample data. An orthogonal experiment was conducted to assess the effect of processing parameters on surface quality. The experimental results and predicted values show that the atmospheric pressure plasma arc (APPA) cleaning is effective in reducing considerably the amount of lubricant. Furthermore, it is feasible to apply LS-SVM in forecasting the cleaning quality and determining processing parameters, and the mean absolute percent error eMAPE between predictive value and experimental value of water contact angle is 6.09%. Otherwise, the eMAPE of working current is 4.46%.

Effects of External Transverse Alternating Magnetic Field on the Heat Flux Density Distribution of Atmospheric Pressure Plasma Arc

A theoretical analysis was carried out to investigate the characteristics of atmospheric pressure plasma arc injected transverse to a transverse alternating magnetic field and a mathematical model was developed to describe the heat flux density distribution of the plasma arc. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the heat flux density distribution of plasma arc were also analyzed. The results show that it is feasible to adjust the heat flux density of the plasma arc by the transverse alternating magnetic field, which can expand the region of plasma arc thermal treatment and flatten the heat flux density upon the workpiece. With the magnetic flux density enhancing, the heat flux density gradient upon the workpiece decreases. Under the same magnetic flux density, the more gas flow rate and arc current, the more heat flux density peak increase. Contrarily, more distance from nozzle outlet to workpiece descends the heat flux density peak.

Effects of External Transverse Alternating Magnetic Field on the Oscillating Amplitude of Atmospheric Pressure Plasma Arc

A mathematical model was developed to describe the oscillating amplitude of the plasma arc injected transverse to an external transverse alternating magnetic field. The characteristic of plasma arc under the external transverse alternating magnetic field imposed perpendicular to the plasma current was discussed. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the oscillation of plasma arc were also analyzed. The results show that it is feasible to adjust the shape of the plasma arc by the transverse alternating magnetic field, which expands the region of plasma arc thermal treatment upon the workpiece. Furthermore, the oscillating amplitude of plasma arc decreases with decrease of the magnetic flux density. Under the same magnetic flux density, more gas flow rate, more arc current, and less standoff cause the oscillating amplitude to decrease. The researches have provided a deeper understanding of adjusting of plasma arc characteristics.

Mode Transition of an Atmospheric Pressure Arc Plasma Jet Sustained by Pulsed DC Power

An atmospheric pressure arc plasma jet sustained using pulsed DC power is studied by examining its appearance using a high-speed camera and measuring current and voltage waveforms at the powered electrode using current and high-voltage probes. Given the seemingly uniform in time visual appearance, the high-speed camera images show that the plasma jet undergoes some transition within each power cycle. Current and voltage waveform characteristics suggest that such a transition is most likely due to a glow-to-arc mode transition. The occurrence of this transition is controlled by the plasma physics rather than by the duty cycle of the pulsed power.

Modeling of reactive kinetics in the metal surface contaminant cleaning using atmospheric pressure plasma arc

Atmospheric pressure plasma arc (APPA) cleaning is a newly developed method of metal surface cleaning. In this paper, a mathematical model of reactive kinetics in the metal surface contaminant cleaning using APPA has been developed. Based on the analysis of APPA cleaning mechanism and the feature of cleaning interface, a governing equation was established with heat transfer equation and energy conservation on the moving interface. Using fourth-order Rounge–Kutta method, above equation was solved and removal percentages of the cleaning contaminant at different time were obtained. In virtue of reactive kinetics theory, a reactive kinetics model of metal surface cleaning using APPA was established on the base of above calculation results. Afterwards, reactive kinetics parameters such as activation energy and pre-exponential factor were calculated. Cleaning lubricant was taken as an example, the results indicated that predictive values of lubricant removal percentages gotten from this established reactive kinetics model show good consistent with experimental data at the same time. Furthermore, the ambient temperature on the cleaning lubricant surface affects the removal rate strongly. The removal rate increases with the increase of the ambient temperature. To avoid the damage of metal substrate surface because of higher temperature and ensure the removal rate of the lubricant, the appropriate temperature which lies between the lubricant decomposition temperature and damage temperature of metal substrate under given calculation conditions should be determined.

Model of Heat and Mass Transfer in Atmospheric Pressure Plasma Arc (APPA) Cleaning Metal Surface

According to analyzing the principle of atmospheric pressure plasma arc (APPA) cleaning metal surface, a model of heat and mass transfer is put forward with using transient-state heat transfer equation about interior heat source and Arrhenius equation of chemical reaction kinetics theory. With finite volume method, the one dimensional control differential equation is transformed into discrete control equation, which is calculated numerically and analyzed with the using of implicit scheme. Taken cleaning lubricant film as an example and analyzed temperature distribution of cleaning film on metal surface, the result indicates that the temperature of film has a strong effect on its removal rate which improves with increasing temperature. In order to both avoid damaging the workpiece surface owing to higher temperature and ensure removal rate of the film, there exists an appropriate temperature under given calculation conditions.

Instabilities in the anode region of atmospheric pressure arc plasmas

To understand the origin of the multiple arc–anode attachments in the anode region of high intensity arcs, a linear stability analysis of a non-uniform argon plasma consisting of electrons, argon neutrals and singly ionized argon ions and an arc–anode interface instability analysis are performed and presented. Plasma conditions typical of the anode region of high intensity argon arcs are emphasized. The calculations have shown that small-amplitude fluctuations presented in the plasma excite two different wave modes, space-charge relaxation mode and electron thermal mode, on a time scale shorter than the one in which the multiple-attachment mode forms. The space-charge relaxation mode has been found to be stable and not affected by the non-uniformity of the plasma. The electron thermal mode can be unstable, depending on the distributions of the current flow, the electric field, the electron temperature and the electron density. The analysis, together with a consideration of the evaporation–ionization instabilities at the arc–anode interface, has been applied to previous experimental data. The observed multiple-attachment mode, consisting of several constricted attachment spots in the arc fringes, can be explained by this analysis.

Sweeping electrostatic probes in atmospheric pressure arc plasmas-Part II: temperature determination

In a previous paper, it was shown that only the ion portion of the probe characteristics curve (V-I) can be used to estimate the temperature from probes sweeping in the column of a flowing atmospheric pressure arc plasma. Methods relating the measured ion current directly to the temperature can be used, if a particle density-temperature relationship is available. However, several sources of disturbance need to be considered in the application of these methods. The main focus of this paper is in establishing how the experimental data permit an identification of the correct model taking into account these limitations. It is shown that some previously published criteria for the establishment of cooling induced by probes in atmospheric pressure arc plasmas and of recombination in the perturbed region are inadequate and their modification is consistent with the gathered data. Because of the thin and collisionless sheath, the temperatures reconstructed by probes belong to the edge of a sheath which is fully embedded in a perturbation region (PR) and not to the bulk of the plasma. A range of arc currents is studied and comparison with data from emission spectroscopy is used to assess and quantify the degree of depression shown by the probe determined temperatures. The consideration of flow velocity within the expressions for the probe currents shows that ad hoc corrections, in absence of direct experimental evidence on flow velocity distributions, do not lead to substantial benefit for the temperature corrections. Cooling mechanisms are considered and between ion energy loss and ion-electron recombination, the first dominates at temperatures below about 7500 K, whereas the latter dominates within the PR in the temperature range 9-13 000 K. For higher temperatures, the two contributions are very close to each other. Despite the severe interpretation difficulties, the practical reproducibility of the results and their empirical relationships with spectroscopic values assumed exact, permits the reconstruction of reasonable electron temperature by the probe method in these plasmas even if experimental data on flow velocity distribution are not available.

Origin of fluctuations in atmospheric pressure arc plasma devices.

Fluctuations in arc plasma devices are extremely important for any technological application in thermal plasma. The origin of such fluctuations remains unexplained. This paper presents a theory for observed fluctuations in atmospheric pressure arc plasma devices. A qualitative explanation for observed behavior on atmospheric pressure arc plasma fluctuations, reported in the literature, can be obtained from the theory. The potential of the theory is demonstrated through comparison of theoretical predictions with reported experimental observations.

Theory of Dynamic Behavior in Atmospheric Pressure Arc Plasma Devices: Part I: Theory and System Behavior

Fluctuations in atmospheric pressure arc plasma devices play important role in plasma processing applications. A full knowledge and control over such fluctuations can effectively lengthen lifetime and drastically improve performance and reliability. Dynamical analyses of associated experimental fluctuating signals established existence of chaotic dynamics in such devices. However, the origin of such fluctuations remained unexplained so far and no theoretical investigation is carried out to explore underlying physics behind such phenomena. This work addresses development of a general theory for such fluctuations in atmospheric pressure arc plasma devices in terms of various nondimensional parameters using basic governing equations and presents the result of application of the theory to various important experiments reported in literature. Various aspects of dynamic behavior have been investigated through the study of coefficients appearing in the nonlinear amplitude equation. It has been shown that the theory supports arc current and gas flow rate as the major externally available controlling parameters in agreement with experiment. Theory exhibits period doubling route to chaos under variation of control parameter as observed experimentally. System includes catastrophic behavior for some operating range. The whole work is divided into two parts. This paper presents part I: development of theory for such fluctuations using basic equations of the dynamics and study of system behavior.

Theory of Dynamic Behavior in Atmospheric Pressure Arc Plasma Devices: Part-II: Validation of Theory With Experimental Data

The results of an application of the developed nonlinear theory for atmospheric pressure arc plasma instability to various experiments are presented in this paper. Most of the important experiments on atmospheric pressure arc plasma instability reported in literature are addressed. In all cases, a good match has been observed between experiment and theory. General nature of the theory to explain observed instability features is brought out in this paper.

Thomson scattering diagnostics of thermal plasmas: Laser heating of electrons and the existence of local thermodynamic equilibrium.

A number of assessments of electron temperatures in atmospheric-pressure arc plasmas using Thomson scattering of laser light have recently been published. However, in this method, the electron temperature is perturbed due to strong heating of the electrons by the incident laser beam. This heating was taken into account by measuring the electron temperature as a function of the laser pulse energy, and linearly extrapolating the results to zero pulse energy to obtain an unperturbed electron temperature. In the present paper, calculations show that the laser heating process has a highly nonlinear dependence on laser power, and that the usual linear extrapolation leads to an overestimate of the electron temperature, typically by 5000 K. The nonlinearity occurs due to the strong dependence on electron temperature of the absorption of laser energy and of the collisional and radiative cooling of the heated electrons. There are further problems in deriving accurate electron temperatures from laser scattering due to necessary averages that have to be made over the duration of the laser pulse and over the finite volume from which laser light is scattered. These problems are particularly acute in measurements in which the laser beam is defocused in order to minimize laser heating; this can lead to the derivation of electron temperatures that are significantly greater than those existing anywhere in the scattering volume. It was concluded from the earlier Thomson scattering measurements that there were significant deviations from equilibrium between the electron and heavy-particle temperatures at the center of arc plasmas of industrial interest. The present calculations indicate that such deviations are only of the order of 1000 K in 20 000 K, so that the usual approximation that arc plasmas are approximately in local thermodynamic equilibrium still applies.

Electrical characterization of atmospheric pressure arc plasmas

The properties of atmospheric pressure arcs are investigated by means of electric exploration of plasma column and anode region. For the electrostatic probe technique, where the level of collisionality distorts the characteristic curve, data interpretation is difficult because no comprehensive underlying theory exists for the non-homogeneous electric arcs used in industry. Results are presented from an extended study of Langmuir probes applied to short, point-plane arcs. A multi-wire apparatus, operating for arc currents in the range 50-200 A is described and ion current densities and temperature maps are shown. The reduction of the probe determined temperature with respect to emission spectroscopy values is discussed and the “cooling” is ascribed to ion-electron recombination within the perturbation region formed around the probe. This region is investigated by means of emission spectroscopy and the extension found agrees both with numerical estimations and fast speed camera photographs. Diamond Like Carbon (DLC) partially coated wires can address data inversion problems and the role of arc flow directionality on charge capture and preliminary observations are shown. Charge capture and anode fall structure can be investigated using a “split-anode” technique. A prototype of a modified apparatus is described and preliminary results on the collected current are given.

Estimation of dynamic properties of attractors observed in hollow copper electrode atmospheric pressure arc plasma system

Understanding of the basic nature of arc root fluctuation is still one of the unsolved problems in thermal arc plasma physics. It has direct impact on myriads of thermal plasma applications being implemented at present. Recently, chaotic nature of arc root behavior has been reported through the analysis of voltages, acoustic and optical signals which are generated from a hollow copper electrode arc plasma torch. In this paper we present details of computations involved in the estimation process of various dynamic properties and show how they reflect chaotic behavior of arc root in the system.