FRVT - Artículos en Revistas Internacionales
Permanent URI for this collectionhttp://48.217.138.120/handle/20.500.12272/396
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Item Ambient Species Density and Gas Temperature Radial Profiles Derived from a Schlieren Technique in a Low Frequency Non-thermal Oxygen Plasma Jet.(2017) Chamorro, Juan Camilo; Prevosto, Leandro; Cejas, Ezequiel; Kelly, Héctor; Mancinelli, Beatriz; Fischfeld, GerardoA quantitative interpretation of the schlieren technique applied to a non-thermal atmospheric-pressure oxygen plasma jet driven at low-frequency (50 Hz) is reported. The jet was operated in the turbulent regime with a hole-diameter based Reynolds number of 13,800. The technique coupled to a simplified kinetic model of the jet effluent region allowed deriving the temporally-averaged values of the gas temperature of the jet by processing the gray-level contrast values of digital schlieren images. The penetration of the ambient air into the jet due to turbulent diffusion was taken into account. The calibration of the optical system was obtained by fitting the sensitivity parameter so that the oxygen fraction at the nozzle exit was unity. The radial profiles of the contrast in the discharge off case were quite symmetric on the whole outflow, but with the discharge on, relatively strong departures from the symmetry were evident in the near field. The time-averaged gas temperature of the jet was relatively high, with a maximum departure of about 55 K from the room temperature; as can be expected owing to the operating molecular gas. The uncertainty in the temperature measurements was within 6 K, primarily derived from errors associated to the Abel inversion procedure. The results showed an increase in the gas temperature of about 8 K close to the nozzle exit; thus suggesting that some fast-gas heating (with a heating rate *0.3 K/ls) still occurs in the near field of the outflow.Item An Interpretation of Langmuir Probe Floating Voltage Signals in a Cutting Arc.(2009) Prevosto, Leandro; Kelly, Héctor; Mancinelli, BeatrizAn experimental study of the electrostatic probe floating voltage signals in a cutting arc and its physical interpre tation in terms of the arc plasma structure is reported. Sweeping electrostatic probes have been used to register the local floating potential and ion current at 3.5 mm from the nozzle exit in a 30-A arc generated by a high energy density cutting torch with a nozzle bore radius of 0.5 mm and an oxygen mass flow rate of 0.71 g · s−1. It is found that the floating potential signal presented a central hump with duration almost similar to that corresponding to the ion current signal but having also lateral wings with much larger duration. Capacitive coupling between the probe and the conducting body of the nozzle and arc as a source for the float ing potential signal was discarded. It is assumed that the hump in these probe voltage signals results from the presence of an electrostatic field directed in the radial direction outward the arc axis that is caused by thermoelectric effects. The probe floating voltage signal is inverted using the generalized Ohm’s law together with the Saha equation, thus obtaining the radial profiles of the temperature, particle densities, radial electric field, and potential of the plasma at the studied section of the arc. The resulting temperature and density profiles derived from our interpretation are in good agreement with the data published elsewhere in this kind of high-pressure arcs. There is not a straightforward connec tion between the measured hump amplitude in the floating signal (≈4 V) and the derived increase in the plasma potential between the arc edge and the arc center (≈10 V), due to the global zero cur rent balance condition established by the finite size of the probe. It is shown, however, that the probe takes a floating potential value close to that corresponding to the plasma temperature at the probe center.Item Calculation of harmonic losses and ampacity in low-voltage power cables when used for feeding large LED lighting loads.(2014) Milardovich, Natalio; Prevosto, Leandro; Lara, MarcelaA numerical investigation on the harmonic disturbances in low-voltage cables feeding large LED loads is reported. A frequency domain analysis on several commercially available LEDs was performed to investigate the signature of the harmonic current injected into the power system. Four-core cables and four single-core cable arrangements (three phases and neutral) of small, medium, and large conductor cross sections, with the neutral conductor cross section approximately equal to the half of the phase conductors, were examined. The cables were modelled by using electromagnetic finite-element analysis software. High harmonic power losses (up to 2.5 times the value corresponding to an undistorted current of the same rms value of the first harmonic of the LED current) were found. A generalized ampacity model was employed for re-rating the cables. It was found that the cross section of the neutral conductor plays an important role in the derating of the cable ampacity due to the presence of a high-level of triplen harmonics in the distorted current. The ampacity of the cables should be derated by about 40 %, almost independent of the conductor cross sections. The calculation have shown that an incoming widespread use of LED lamps in lighting could create significant additional harmonic losses in the supplying low-voltage lines, and thus more severe harmonic emission limits should be defined for LED lamps.Item Cathode-sheath model for field emission sustained atmospheric pressure discharges(2021) Cejas, Ezequiel; Prevosto, Leandro; Minotti, Fernando; Ferreyra, Matías; Chamorro, Juan Camilo; Fina, BrendaThe cathode-sheath region of a discharge in atmospheric pressure air with a flat copper cathode is numerically investigated by using a simple fluid model that takes into account non-local ionization. The effects of the cathode temperature are considered. Results are obtained in a wide current density range of 1–102 A/cm2 , which spans from normal glow discharge, through abnormal glow discharge, up to the early stages of the arcing transition. It is shown that the glow-to-arc transition arises from a field-emission instability at the cathode when the cur rent density is larger than 10 A/cm2 , i.e., when the cathode field exceeds a critical value of about 45 V/lm for the conditions considered. It is also shown that the cathode temperature significantly influences the cathode-sheath region. The proposed model is validated by comparing the numerical results with available experimental data.Item Cathode-sheath model for field emission sustained atmospheric pressure discharges.(2021-03-16) Cejas, Ezequiel; Prevosto, Leandro; Minotti, Fernando Oscar; Ferreyra, Matías; Chamorro, Juan CamiloThe cathode-sheath region of a discharge in atmospheric pressure air with a flat copper cathode is numerically investigated by using a simple fluid model that takes into account non-local ionization. The effects of the cathode temperature are considered. Results are obtained in a wide current density range of 1–102 A/cm2 , which spans from normal glow discharge, through abnormal glow discharge, up to the early stages of the arcing transition. It is shown that the glow-to-arc transition arises from a field-emission instability at the cathode when the cur rent density is larger than 10 A/cm2 , i.e., when the cathode field exceeds a critical value of about 45 V/lm for the conditions considered. It is also shown that the cathode temperature significantly influences the cathode-sheath region. The proposed model is validated by comparing the numerical results with available experimental data.Item Correlation methods in cutting arcs(IOPscience, 2011-05-25) Prevosto, Leandro; Kelly, HéctorThe present work applies similarity theory to the plasma emanating from transferred arc, gas-vortex stabilized plasma cutting torches, to analyze the existing correlation between the arc temperature and the physical parameters of such torches. It has been found that the enthalpy number significantly influence the temperature of the electric arc. The obtained correlation shows an average deviation of 3 % from the temperature data points. Such correlation can be used, for instance, to predict changes in the peak value of the arc temperature at the nozzle exit of a geometrically similar cutting torch due to changes in its operation parameters.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.Item Determination of plasma velocity from light fluctuations in a cutting torch.(2009) Prevosto, Leandro; Kelly, Héctor; Mancinelli, BeatrizItem Diagnostics of cutting arc plasmas.(2014) Prevosto, Leandro; Kelly, HéctorAn over-view of several remote and invasive diagnostics to characterize cutting arcs at the nozzle exit-anode gap as well as inside the nozzle is reported. A briefly description of the experimental set-ups, together with the main results obtained in a 30 A high-energy density cutting torch (including the calculation assumptions) are given.Item Effect of in–package cold plasma treatments on the quality of minimally processed apples.(2023) Denoya, Gabriela Inés; Polenta, Gustavo Alberto; Apóstolo, Nancy Mariel; Cejas, Ezequiel; Fina, Brenda; Chamorro, Juan Camilo; Ferreyra, Matías; Prevosto, Leandro; Vaudagna, SergioCold plasma technology is being increasingly used for food preservation and, incipiently, for minimal processing of fruit. Therefore, the objective of this work was to study the effect of in-package cold plasma (generated in atmospheric–pressure air by a low–frequency -50 Hz- dielectric barrier discharge operated at 30 kV) on the quality of minimally processed apples during refrigerated storage. Apple slices were subjected to the different treatments following a completely randomized design with 3 x 3 factorial arrangement. The independent variables were the exposure time (0, 1, 3 min) and the storage times (1, 4, 7 days). Cold plasma treatments preserved the quality of the fruit, maintaining the tissue structure. Plasma treatment applied for 1 min rendered apple slices with the highest antioxidant content but only at day 1. Even though polyphenoloxidase activity was reduced by the treatment, it was not sufficient to stabilize the antioxidant content during storage.Item Effects of non-thermal plasma technology on Diaporthe longicolla cultures and mechanisms involved.(2021-01-05) Pérez Pizá, María Cecilia; Grijalba, Pablo Enrique; Cejas, Ezequiel; Chamorro, Juan Camilo; Ferreyra, Matías; Zilli, Carla; Vallecorsa, Pablo; Yannarelli, Gustavo; Prevosto, Leandro; Balestrasse, Karina; Santa Cruz, DiegoBACKGROUND: The Diaporthe/Phomopsis complex (D/P) is a group of soybean seed-borne fungi. The use of chemical fungicides, either for seed treatment or during the crop cycle, is the most adopted practice for treating fungal diseases caused by this complex. Worldwide, there is a search for alternative seed treatments that are less harmful to the environment than chemicals. Non-thermal plasma (NTP) is a novel seed treatment technology for pathogen removal. This research aimed to evaluate the effects of NTP on the in vitro performance of pure cultures of Diaporthe longicolla and elucidate the mechanisms underlying these effects. RESULTS: Active D. longicolla mycelium, growing in vitro, was exposed to different NTP treatments, employing a dielectric bar rier discharge arrangement with different carrier gases (N2 or O2). Fungal growth, fresh biomass and colony appearance were negatively affected by plasma treatments (TN3 and TO3). Lipid peroxidation and antioxidant activities were higher in plasma treated colonies comparison with non-exposed colonies (control). Fungal asexual spores (conidia) were also exposed to NTP, showing high susceptibility. CONCLUSION: Exposure of D. longicolla colonies to NTP severely compromised fungal biology. Ozone production during treat ment and lipid peroxidation of fungal cell membranes appeared to be involved in the observed effects. © 2020 Society of Chemical IndustryItem Effects of non–thermal plasmas on seed-borne Diaporthe/Phomopsis complex and germination parameters of soybean seeds.(2018) Pérez Pizá, María Cecilia; Prevosto, Leandro; Zilli, Carla; Cejas, Ezequiel; Kelly, Héctor; Balestrasse, KarinaDiaporthe/Phomopsis (D/P) is a complex of seed-borne fungi that severely affects soybean (Glycine max (L.) Merrill), one of the most important crops worldwide. Non-thermal plasma treatment is a fast, economic and ecological friendly technology that can destroy seed-borne fungi and improve seed quality. Soybean seeds were exposed for 1, 2 and 3 minutes 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. In this work we focused on the ability of plasma to control D/P in soybean seeds and to enhance seed quality. To support these results, different antioxidant enzymes (catalase, superoxide dismutase and guaiacol peroxidase), lipid peroxidation and phytohormones (ABA and AIA) content in seeds were evaluated. The results demonstrated reductions of 29% in catalase activity and increments of 30% in glutathione content after plasma treatment, reversing the oxidative damage caused by D/P fungi. This eco-friendly technology improved soybean seed quality and, for the first time, its efficiency in controlling soybean seed-borne pathogen fungi that colonize the inside of seeds was demonstrated.Item Effects of the Plasma-Activated Water on the Quality and Preservation of Fresh-Cut Lettuce.(2023) Chamorro, Juan Camilo; Denoya, Gabriela Inés; Santamaría, Brenda; Fina, Brenda; Ferreyra, Matías; Cejas, Ezequiel; Rodriguez, Anabel; Vaudagna, Sergio; Prevosto, Leandro— The effect of the application of plasma-activated water (PAW) on the quality and preservation of fresh-cut lettuce is reported in this article. PAW was produced by using a liquid cathode air discharge. The average (bulk) water temperature was kept at ∼22 ◦ C during the activation procedure and stored at 4 ◦ C for up to five days. The pH value, electrical conductivity, and concentrations of H2O2 and NO− in liquid at day 1 were 2.81, 1492µS/cm, and 77.8 and 223.4 mg/L, respectively, with slight variations over the whole storage time. No measurable amounts of NO− 10 2 were found. Twenty pieces of lettuce leaves were washed for 1 and 5 min in 1 L of PAW and stored for one and five days. PAW treatments were compared to tap water treatments. The lettuce samples were stored at 4 ◦ C and analyzed on days 1, 3, and 7. The chromatic parameter results suggest that PAW treatments significantly reduce the degradation of lettuce chlorophyll from day 3 of refrigerated storage. The lettuce firmness was not significantly modified. The microbiological results of aerobic mesophilic, enterobacteriaceae, and psychrotrophs populations have shown that lettuce treated with PAW after three days of storage exhibited the strongest inactivation efficiency. Psychrotrophs counts were maintained for up to seven days. Similar inactivation efficiencies were found regardless of the PAW storage time. PAW treatments also favored both the antioxidant capacity FRAP, ABTS, and DPPH, and the total phenolic.Item Enhancement of soybean nodulation by seed treatment with non–thermal plasmas(2020-03-18) Pérez Pizá, María Cecilia; Cejas, Ezequiel; Zilli, Carla; Prevosto, Leandro; Mancinelli, Beatriz; Santa Cruz, Diego; Yannarelli, Gustavo; Balestrasse, KarinaSoybean (Glycine max (L.) Merrill) is one of the most important crops worldwide providing dietary protein and vegetable oil. Most of the nitrogen required by the crop is supplied through biological N2 fxation. Non-thermal plasma is a fast, economical, and environmental-friendly technology that can improve seed quality, plant growth, and crop yield. Soybean seeds were exposed to a dielectric barrier discharge plasma operating at atmospheric pressure air with superimposed fows of O2 or N2 as carrying gases. An arrangement of a thin phenolic sheet covered by polyester flms was employed as an insulating barrier. We focused on the ability of plasma to improve soybean nodulation and biological nitrogen fxation. The total number of nodules and their weight were signifcantly higher in plants grown from treated seeds than in control. Plasma treatments incremented 1.6 fold the nitrogenase activity in nodules, while leghaemoglobin content was increased two times, indicating that nodules were fxing nitrogen more actively than control. Accordingly, the nitrogen content in nodules and the aerial part of plants increased by 64% and 23%, respectively. Our results were supported by biometrical parameters. The results suggested that diferent mechanisms are involved in soybean nodulation improvement. Therefore, the root contents of isofavonoids, glutathione, auxin and cytokinin, and expansin (GmEXP1) gene expression were determined. We consider this emerging technology is a suitable pre-sowing seed treatment.Item Experimental Characterization of a Low-Current Cutting Torch.(2004) Kelly, Héctor; Mancinelli, Beatriz; Prevosto, Leandro; Minotti, Fernando; Márquez, AndrésAn experimental characterization of a low-current (30-40 A) cutting torch is presented. To avoid contamination of the plasma arc by removed anode material, a rotating steel cylinder was used as the anode and the arc was anchored onto the cylinder lateral surface. The cathode-anode and cathode-nozzle voltage drops, together with the gas pressure in the plenum chamber were registered for different values of the mass flow rate injected into the plenum chamber. By employing an optical system with a large magnification (≈ 15 X), the arc radius at the nozzle exit was also determined with a digital optical camera. The obtained experimental quantities were used to evaluate several flow properties at the nozzle exit (hot arc plasma and cold gas temperatures, arc and gas velocities, etc.) by employing a simplified theoretical model for the plasma flow in the nozzle. The obtained results are in reasonable agreement with the data reported in the literature by other authors. Explanations of the origin of the clogging effect and the nozzle voltage are also presented.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 Hydrodynamic Model for the Plasma-Gas Flow in a Cutting Torch Nozzle.(2004) Kelly, Héctor; Minotti, Fernando; Prevosto, Leandro; Mancinelli, BeatrizWe present a simple hydrodynamic model to obtain the profiles of the relevant physical quantities along a nozzle of arbitrary cross-section in a cutting torch. The model uses a two-zone approximation (a hot central plasma carrying the discharge current wrapped by a relatively cold gas which thermally isolates the nozzle wall from the plasma). Seeking for a solution with sonic conditions at the nozzle exit, the model allows expressing all the profiles in terms of the externally controlled parameters of the torch (geometry of the torch, discharge current, mass flow of the gas and plenum pressure) and the values of the arc and gas temperatures at the nozzle entrance. These last two values can be estimated simply appealing to energy conservation in the cathode-nozzle region. The model contains additional features compared with previous reported models, while retaining simplicity. The detailed consideration of an arc region coupled to the surrounding gas dynamics allows determining voltage drops and consequent delivered power with less assumptions than those found in other published works, and at the same time reduces the set of parameters needed to determine the solution.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 Indigo Carmine Degradation in Water Induced by a Pulsed Positive Corona Discharge in Air: Discharge and Postdischarge Effects.(2022) Ferreyra, Matías; Fina, Brenda; Milardovich, Natalio; Chamorro, Juan Camilo; Santamaría, Brenda; Balestrasse, Karina; Prevosto, LeandroIn recent years, one of the fastest growing technological applications in the field of nonthermal plasmas is the degradation of organic contaminants of water. In this work, the degradation of indigo carmine (IC) in water induced by a pulsed positive corona discharge operating in ambient air is reported. Degradation levels in different volumes of IC in solution with distilled water treated with different plasma exposure times immediately after discharge (0 h), and in the postdischarge up to 24 h were examined. To explain the IC discoloration in the postdischarge phase, a chemical model was developed. The stability of the reactive species in solution nitrate (NO3 −), nitrite (NO2 −) and hydrogen peroxide (H2O2 ), as well as the properties of the solution (electrical conductivity, pH) were also measured. The results suggest that the hydroxyl radical (OH˙) as well as ozone (O3 ) are the main oxidizing species during the discharge phase, being primarily formed in the gas phase through plasma-mediated reactions and then transferred to the liquid by diffusion, while the OH˙ production in the bulk liquid through the decomposition of peroxinitrous acid (O=NOOH) plays a major role in the IC degradation during the postdischarge. These results are associated with a noticeably increase in the energy-yield values observed at 24 h post-treatment.Item Influencia de las dimensiones de la sección transversal sobre la resistencia a flexión en madera aserrada de Populus Deltoides cultivado en Argentina.(2016) Guillaumet, Alfredo Aníbal; Manavella, Roberto; Acuña Rello, Luis; Piter, Juan CarlosEn el artículo se analiza el efecto de las dimensiones de la sección transversal sobre la resistencia a flexión en piezas de madera aserrada de Populus deltoides ‘Australiano 129/60’ y ‘Stoneville 67’, cultivados en el delta del río Paraná, Argentina. El programa experimental se llevó a cabo según las normas europeas sobre un total de 820 cuerpos de prueba separados en 5 muestras exhibiendo las dimensiones estructurales usuales. Los resultados mostraron que el aumento de la altura de la sección fue acompañado de una tendencia decreciente de la tensión de rotura en flexión, pero no permiten afirmar que esa relación está vinculada a la calidad de la madera. Se confirmó que puede despreciarse una correlación entre la resistencia y el ancho de la sección. El análisis puso en evidencia que la relación entre la altura de la sección y la resistencia del material investigado está adecuadamente expresada por el criterio europeo, el cual fue adoptado por la normativa de Argentina.
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