Browsing by Author "Prevosto, Leandro"

Now showing 1 - 20 of 56

Algoritmo que genera las competencias del ingeniero electromecánico, en la aplicación de software de modelado numérico y simulación titulo de trabajo.
(UTN FRVT, 2021) Papa, Mara Jaquelina; Prevosto, Leandro; Giraudo, Germán
En el presente trabajo se ha investigado el algoritmo que genera las competencias del ingeniero electromecánico, en la aplicación de software de modelado numérico y simulación. Se fundamenta este estudio en el impulso de la educación basada en competencias en Argentina, situación que se presenta en los estudiantes de ingeniería electromecánica, quienes necesitan adquirir las competencias para aplicarlas durante su carrera y cuando se reciben como ingenieros en su vida profesional. Junto a esto las Tecnologías de la Información y Comunicación (TIC) cambian o evolucionan continuamente, ofreciendo la oportunidad de modificar las formas de enseñar y aprender, innovando, incorporando softwares, entre tantos otros recursos educativos. Junto a ello, los desarrollos tecnológicos día a día en la industria generan diferentes softwares que ha de aplicar un ingeniero electromecánico. El estudio tuvo como objetivo desarrollar un algoritmo para la adquisición de competencias de uso de software de modelado numérico y simulación, en la carrera de ingeniería electromecánica de la facultad regional Venado Tuerto, de la Universidad Tecnológica Nacional. Desde una perspectiva cualitativa, bajo un estudio etnográfico descriptivo, se han realizado observaciones grabadas y entrevistas a informantes clave, para el análisis se utilizó el software cualitativo Atlas.ti. Los resultados revelan que existe un algoritmo genérico para la adquisición de la competencia, que tiene dos elementos claves como: la decisión del software a utilizar y el método a aplicar. La investigación sustenta, entre otras implicaciones la necesidad de integrar las competencias como diferentes saberes en el proceso de enseñanza y aprendizaje.
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, Gerardo
A 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.
An Interpretation of Langmuir Probe Floating Voltage Signals in a Cutting Arc.
(2009) Prevosto, Leandro; Kelly, Héctor; Mancinelli, Beatriz
An 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.
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, Marcela
A 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.
Cathode-sheath model for field emission sustained atmospheric pressure discharges
(2021) Cejas, Ezequiel; Prevosto, Leandro; Minotti, Fernando; Ferreyra, Matías; Chamorro, Juan Camilo; Fina, Brenda
The 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.
Cathode-sheath model for field emission sustained atmospheric pressure discharges.
(2021-03-16) Cejas, Ezequiel; Prevosto, Leandro; Minotti, Fernando Oscar; Ferreyra, Matías; Chamorro, Juan Camilo
The 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.
Correlation methods in cutting arcs
(IOPscience, 2011-05-25) Prevosto, Leandro; Kelly, Héctor
The 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.
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, Beatriz
A 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.
Descargas en contacto con líquidos: caracterización eléctrica de una descarga corona pulsada.
(2021) Milardovich, Natalio; Ferreyra, Matías; Chamorro, Juan Camilo; Prevosto, Leandro
La gran cantidad de trabajos publicados en los últimos años sobre descargas no-térmicas en (y en contacto con) líquidos,evidencia el creciente interés en este particular campo de las descargas eléctricas debido al gran número de aplicacio-nes tecnológicas. En particular, una de las aplicaciones emergentes de mayor crecimiento es el tratamiento de agua,tanto para su potabilización como para su activación, con vistas a realizar el tratamiento indirecto de alimentos y semi-llas con descargas no-térmicas; sin el agregado de sustancias químicas. En este trabajo, se presenta la caracterizaciónexperimental de una descarga corona en contacto con agua operando en régimen pulsado. Se usó una geometría tipoalambre-plano con el electrodo plano sumergido en agua. La descarga fue alimentada a través de una fuente pulsadatipo capacitiva, capaz de proveer un tren periódico de pulsos de alto voltaje (∼15 kV) y corta duración∼100 ns), conuna frecuencia de repetición de 40 pulsos/s. Se reportan y discuten resultados de las mediciones de voltaje y corrientede la descarga para diferentes condiciones de operación, y se infieren la potencia instantánea y la energía disipada en elplasma generado. Se muestran además fotografías con largos tiempos de exposición de la descarga pulsada. The large number of works published in recent years on non-thermal discharges in (and in contact with) liquids, showsthe growing interest in this particular field of electric discharges due to the large number of technological applications.In particular, one of the fastest growing emerging applications is the treatment of water, both for its purification andfor its activation, with a view to carrying out the indirect treatment of food and seeds with non-thermal discharges;without the addition of chemicals. In this work, the experimental characterization of a corona discharge in contact withwater operating in a pulsed regime is presented. A flat-wire type geometry was used with the flat electrode immersedin water. The discharge was powered through a pulsed capacitive type source, capable of providing a periodic train ofhigh voltage pulses (∼15 kV) with short duration (∼100 ns), with a repetition frequency of 40 pulses/s. The resultsof discharge voltage and current measurements are reported and discussed for different operating conditions, and theinstantaneous power and energy dissipated in the generated plasma are inferred. Photographs in the visible with longexposure times of the pulsed discharge are also shown.
Determination of plasma velocity from light fluctuations in a cutting torch.
(2009) Prevosto, Leandro; Kelly, Héctor; Mancinelli, Beatriz
Diagnostics of cutting arc plasmas.
(2014) Prevosto, Leandro; Kelly, Héctor
An 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.
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, Sergio
Cold 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.
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, Diego
BACKGROUND: 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 Industry
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, Karina
Diaporthe/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.
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.
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, Karina
Soybean (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.
Evaluación basada en Competencias de la enseñanza de Modelado Numérico y Simulación en Mecánica de Fluidos.
(UTN FRVT, 2020) Papa, Mara Jaquelina; Giraudo, Germán; Prevosto, Leandro
Se presenta una propuesta preliminar de evaluación, bajo un enfoque basado en competencias, del tópico modelado numérico y simulación, en el marco de cátedra Mecánica de Fluidos de la Carrera Ingeniería Electromecánica de la Universidad Tecnológica Nacional, Facultad Regional Venado Tuerto. La evaluación por competencias requiere la reestructuración sistémica de la cátedra, incluyendo su planificación, las estrategias didácticas en la práctica áulica y del proceso de evaluación. Se describen los elementos de la planificación, poniendo énfasis en la competencia de Modelado numérico y Simulación del flujo de un fluido y los requisitos de los saberes cognitivos, procedimentales y actitudinales que la componen. Se definen las estrategias de enseñanza-aprendizaje empleadas y se presentan los instrumentos de evaluación propuestos.
Experimental Characterization of a Low-Current Cutting Torch.
(2004) Kelly, Héctor; Mancinelli, Beatriz; Prevosto, Leandro; Minotti, Fernando; Márquez, Andrés
An 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.
Glow Discharge in a High-Velocity Air Flow: The Role of the Associative Ionization Reactions Involving Excited Atoms.
(2019) Cejas, Ezequiel; Mancinelli, Beatriz; Prevosto, Leandro
A 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.
Hydrodynamic Model for the Plasma-Gas Flow in a Cutting Torch Nozzle.
(2004) Kelly, Héctor; Minotti, Fernando; Prevosto, Leandro; Mancinelli, Beatriz
We 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.

Browsing by Author "Prevosto, Leandro"

SECRETARÍAS

ENLACES UTN

ENLACES EXTERNOS