FRVT - Artículos en Revistas Internacionales
Permanent URI for this collectionhttp://48.217.138.120/handle/20.500.12272/396
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Item Interpretation of Voltage Measurements in Cutting Torches.(2015) Prevosto, Leandro; Kelly, Héctor; Minotti, Fernando Oscar; Mancinelli, BeatrizAnode-cathode and nozzle-cathode voltages, plenum pressure and gas mass flow measurements in a low current (30 A) cutting torch, operated with oxygen gas, are used as inputs for an electrical model coupled to a simplified fluid model, in order to infer some properties of the plasma-gas structure that are difficult to measure.Item Numerical modeling of the gas breakdown development in the space–charge layer inside the nozzle of a transferred arc torch(2012) Mancinelli, Beatriz; Prevosto, Leandro; Minotti, Fernando OscarDouble–arcing is a phenomenon that occurs when a transferred arc, flowing inside an electrically insulated nozzle, breaks into two separate arcs: one that connects the cathode with the nozzle, and another that connects the nozzle with the anode. Experimental evidence suggests that the reason for double–arcing is a Townsend like breakdown occurring in the thin space–charge layer, which separates the plasma from the metallic nozzle, due to the high voltage drop across it. Breakdown phenomena in a gas between metallic electrodes have been extensively studied; however the present case involves breakdown of a high–temperature gas between one electrode (the nozzle) and a plasma boundary. A 1–D model of the gas breakdown development in the space–charge layer contiguous to the nozzle of a cutting arc torch operated with oxygen is reported. The dynamics of the discharge is analyzed. The kinetic scheme includes processes of ionization of heavy particles by electron impact, electron attachment, electron–ion recombination and ion–ion recombination.Item On the dynamic behavior of the anode–arc–root at the nozzle surface in a non-transferred plasma torch(2012) Prevosto, Leandro; Risso, Marcelo Natalio; Infante, Damián Leandro; Cejas, Ezequiel; Kelly, Héctor; Mancinelli, BeatrizThe dynamic behavior of the anode–arc–root at the nozzle surface of a plasma torch was experimentally investigated in this work. A gas (N2) vortex–stabilized non–transferred arc torch with a thoriated tungsten rod (2wt %) cathode (3.2 mm diameter) and a coaxial anode (5 mm diameter, 30 mm length) was used in the experiment. By using a sweeping Langmuir probe in floating condition, the voltage of the plasma jet outside the nozzle was inferred. Arc voltage waveforms were also obtained. Data have been obtained for an arc current of 100 A and a gas flow rate of 30 Nl min-1. A typical sawtooth shape (i.e., restrike mode) (with a fluctuating level of º 25 %) and a dominant frequency of º 6.5 kHz was observed in the arc voltage waveforms, which is attributed to anode–arc–root movements along the anode surface followed by a restrike at a certain point close to the cathode. By performing a time correlation between the probe and arc voltage oscillograms together with simple estimations, the amplitude of the movement of the arc–root along the anode surface as well its velocity were inferred.Item Investigation of the relevant kinetic processes in the initial stage of a double-arcing instability in oxygen plasmas.(2018) Mancinelli, Beatriz; Prevosto, Leandro; Chamorro, Juan Camilo; Minotti, Fernando; Kelly, HéctorA numerical investigation of the kinetic processes in the initial (nanosecond range) stage of the double-arcing instability was developed. The plasma-sheath boundary region of an oxygen operated cutting torch was considered. The energy balance and chemistry processes in the dis charge were described. It is shown that the double-arcing instability is a sudden transition from a diffuse (glow-like) discharge to a constricted (arc-like) discharge in the plasma-sheath boundary region arising from a field-emission instability. A critical electric field value of 107 V/m was found at the cathodic part of the nozzle wall under the conditions considered. The field-emission instability drives in turn a fast electronic-to-translational energy relaxation mechanism, giving rise to a very fast gas heating rate of at least 109 K/s, mainly due to reactions of preliminary dissocia tion of oxygen molecules via the highly excited electronic state populated by electron impact. It is expected that this fast oxygen heating rate further stimulates the discharge contraction through the thermal instability mechanism.Item Improvement of growth and yield of soybean plants through the application of non-thermal plasmas to seeds with different health status.(2019) Pérez Pizá, María; Prevosto, Leandro; Grijalba, Pablo; Zilli, Carla; Cejas, Ezequiel; Mancinelli, Beatriz; Balestrasse, KarinaSoybean (Glycine max (L.) Merrill) is a globally important crop, providing oil and protein. Diaporthe/Phomopsis complex includes seed-borne pathogens that affect this legume. Non-thermal plasma treatment is a fast, cost-effective and environmental-friendly technology. Soybean seeds were exposed to a quasi stationary (50 Hz) dielectric barrier discharge plasma operating at atmospheric pressure air. Different carrying gases (O2 and N2) and barrier insulating materials were used. This work was performed to test if the effects of non-thermal plasma treatment applied to healthy and infected seeds persist throughout the entire cycle of plants. To this aim, lipid peroxidation, activity of catalase, superoxide dismutase and guaiacol peroxidase, vegetative growth and agronomic traits were analysed. The results here reported showed that plants grown from infected seedsdid not trigger oxidative stress due to the reduction of pathogen incidence in seeds treated with cold plasma. Vegetative growth revealed a similar pattern for plants grown from treated seeds than that found for the healthy control. Infected control, by contrast, showed clear signs of damage. Moreover, plasma treatment itself increased plant growth, promoted a normal and healthy physiological performance and incremented the yield of plants. The implementation of this technology for seeds treatment before sowing could help reducing the use of agrochemicals during the crop cycle.Item Plasma Cutting of Concrete: Heat Propagation and Molten Material Removal From the Kerf.(2019) Chamorro, Juan Camilo; Prevosto, Leandro; Cejas, Ezequiel; Milardovich, Natalio; Mancinelli, Beatriz; Fischfeld, GerardoAn experimental investigation of heat propagation in the case of plasma cutting of concrete is reported. The experiments were carried out by using a high-enthalpy nitrogen plasma jet generated in a dc vortex-stabilized nontransferred arc torch. Concrete plates of different thicknesses up to 52 mm and with and without steel reinforcement were used. The plates were placed horizontally while cutting. The heat conduction losses inside the material were estimated by comparing thermocouple measurements and theoretical temperatures obtained with an analytical model of the heat propagation in the material. The influence of the molten concrete layer that separates the plasma to the solid material due to the high viscosity of the liquid concrete was accounted for. The power losses below the material in the extinguishing plasma have also been determined from calorimet ric measurements. For different plate thicknesses and cutting velocities, a complete power balance of the process is performed with the calculation of the cutting efficiency on the basis of various relevant power terms. In addition, the hydrodynamics of the molten concrete layer in the kerf is analyzed. For a mean power level of 11.2 kW and a nitrogen gas flow rate of 25 Nl/min, the torch is able to cut a concrete plate of 52 mm in thickness with a speed of 20 mm/min and a whole efficiency of about 30%. The viscosity force is the main limiting factor on the cutting velocity in thick plates.Item Glow Discharge in a High-Velocity Air Flow: The Role of the Associative Ionization Reactions Involving Excited Atoms.(2019) Cejas, Ezequiel; Mancinelli, Beatriz; Prevosto, LeandroA kinetic scheme for non-equilibrium regimes of atmospheric pressure air discharges is developed. A distinctive feature of this model is that it includes associative ionization with the participation of N(2D, 2P) atoms. The thermal dissociation of vibrationally excited nitrogen molecules and the electronic excitation from all the vibrational levels of the nitrogen molecules are also accounted for. The model is used to simulate the parameters of a glow discharge ignited in a fast longitudinal flow of preheated (T0 = 1800–2900 K) air. The results adequately describe the dependence of the electric field in the glow discharge on the initial gas temperature. For T0 = 1800 K, a substantial acceleration in the ionization kinetics of the discharge is found at current densities larger than 3 A/cm2 , mainly due to the N(2P) + O(3P) → NO+ + e process; being the N(2P) atoms produced via quenching of N2(A3P u +) molecules by N(4S) atoms. Correspondingly, the reduced electric field noticeably falls because the electron energy (6.2 eV) required for the excitation of the N2(A3P u +) state is considerably lower than the ionization energy (9.27 eV) of the NO molecules. For higher values of T0, the associative ionization N(2D) + O(3P) → NO+ + e process (with a low–activation barrier of 0.38 eV) becomes also important in the production of charged particles. The N(2D) atoms being mainly produced via quenching of N2(A3P u +) molecules by O(3P) atoms.Item Modelling of an Atmospheric–Pressure Air Glow Discharge Operating in High–Gas Temperature Regimes: The Role of the Associative Ionization Reactions Involving Excited Atoms.(2020) Cejas, Ezequiel; Prevosto, Leandro; Mancinelli, BeatrizA model of a stationary glow-type discharge in atmospheric-pressure air operated in high-gas-temperature regimes (1000 K < Tg < 6000 K), with a focus on the role of associative ionization reactions involving N(2D,2P)-excited atoms, is developed. Thermal dissociation of vibrationally excited nitrogen molecules, as well as electronic excitation from all the vibrational levels of the nitrogen molecules, is also accounted for. The calculations show that the near-threshold associative ionization reaction, N(2D) + O(3P) → NO+ + e, is the major ionization mechanism in air at 2500 K < Tg < 4500 K while the ionization of NO molecules by electron impact is the dominant mechanism at lower gas temperatures and the high-threshold associative ionization reaction involving ground-state atoms dominates at higher temperatures. The exoergic associative ionization reaction, N(2P) + O(3P) → NO+ + e, also speeds up the ionization at the highest temperature values. The vibrational excitation of the gas significantly accelerates the production of N2(A3P u +) molecules, which in turn increases the densities of excited N(2D,2P) atoms. Because the electron energy required for the excitation of the N2(A3P u +) state from N2(X1P g +, v) molecules (e.g., 6.2 eV for v = 0) is considerably lower than the ionization energy (9.27 eV) of the NO molecules, the reduced electric field begins to noticeably fall at Tg > 2500 K. The calculated plasma parameters agree with the available experimental data.Item Schlieren technique applied to the arc temperature measurement in a high energy density cutting torch.(2010) Prevosto, Leandro; Artana, Guillermo; Kelly, Héctor; Mancinelli, BeatrizPlasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes.Item Departures from local thermodynamic equilibrium in cutting arc plasmas derived from electron and gas density measurements using a twowavelength quantitative Schlieren technique.(2011) Prevosto, Leandro; Artana, Guillermo; Kelly, Héctor; Mancinelli, BeatrizA two-wavelength quantitative Schlieren technique that allows inferring the electron and gas densities of axisymmetric arc plasmas without imposing any assumption regarding statistical equilibrium models is reported. This technique was applied to the study of local thermodynamic equilibrium (LTE) departures within the core of a 30 A high-energy density cutting arc. In order to derive the electron and heavy particle temperatures from the inferred density profiles, a generalized two-temperature Saha equation together with the plasma equation of state and the quasineutrality condition were employed. Factors such as arc fluctuations that influence the accuracy of the measurements and the validity of the assumptions used to derive the plasma species temperature were considered. Significant deviations from chemical equilibrium as well as kinetic equilibrium were found at elevated electron temperatures and gas densities toward the arc core edge. An electron temperature profile nearly constant through the arc core with a value of about 14 000–15 000 K, well decoupled from the heavy particle temperature of about 1500 K at the arc core edge, was inferred.