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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 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 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 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 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 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 Non-thermal plasma application improves germination, establishment and productivity of Gatton panic grass (Megathyrsus maximus) without compromising forage quality.(2022) Pérez Pizá, María Cecilia; Clausen, Liliana; Cejas, Ezequiel; Ferreyra, Matías; Chamorro, Juan Camilo; Fina, Brenda; Zilli, Carla; Vallecorsa, Pablo; Prevosto, Leandro; Balestrasse, KarinaMegathyrsus maximus (Gatton panic) is a tropical grass highly valued both for its use as forage and for its biofuel potential. A major constraint in establishing pastures of this cultivar is the low viability and germination ofseeds and the poorinitialseedling establishment. We used non-thermal plasma (NTP, partially ionised gas) as a novel technology to treat seeds of this grass, aiming to improve their quality (i.e. germination traits). We also followed the performance of seedlings grown from NTP-treated seeds under field conditions by assessing seedling establishment, biomass production and forage quality during the first regrowth period, which is the critical period for pasture establishment. Two NTP treatments were performed through dielectric barrier discharges employing N2 as carrier gas. Non-treated seeds served as the control. Results showed that the viability of NTP treated seeds was, on average, 1.5-fold higher than the control, and that germination energy and germination percentage of treated seeds was superior to the control by 2.1-fold and 2.2-fold, respectively. A field experiment showed that seedling establishment parameters (dynamics of cumulative emergence, emergence coefficient, and weighted average emergence rate) and pasture early productivity (represented by shoot dry matter) were enhanced by NTP treatment (phenolic sheet–polyester film barrier and 3 min exposure), showing 1.4–2.6-fold higher values than the control, confirming the results of the laboratory assays. Although NTP markedly increased the shoot dry matter production of the pasture, which was related to higher tiller population density and greater tiller weight, it did not affect the forage quality of the plants grown in the field. We conclude that NTP technology is suitable to improve seed germination of Gatton panic, in turn leading to improvements in seedling establishment and biomass production under field conditions without compromising forage quality.Item Non-thermal plasma as emerging technology for Tribolium castaneum pest-management in stored grains and flours.(2022) Zilli, Carla; Pedrini, Nicolás; Prieto, Eduardo; Girotti, Juan Roberto; Vallecorsa, Pablo; Ferreyra, Matías; Chamorro, Juan Camilo; Cejas, Ezequiel; Fina, Brenda; Prevosto, Leandro; Balestrasse, KarinaThe red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a major secondary pest on wheat stored in metal bins, silo-bags and is also frequently found in wheat products such as flour. Non-thermal plasmas (NTPs) are (quasi-neutral) partially ionized gases that may be produced by a variety of electrical dis charges. We propose the use of an atmospheric pressure dielectric barrier discharge (DBD) as an emerging technology in post-harvest integrated pest management. To this aim, a series of experiments were performed in order to test the lethality of such plasmas on three life stages of T. castaneum by measuring insect mortality and their impacts on physiological and biochemical parameters affecting insect fitness. The different NTP treatments were performed by increasing the time of exposure to either O2 or N2 used as carrier gases. After 24 hours, high levels of mortality (30–100%) were reached for each applied treatment, in both larval and adult populations. Mortality seems to be related to a significant water content loss and redox imbalance. Atomic force microscopy (AFM) scanning of the prothoracic surface showed that nitrogen causes more severe damage than oxygen. As a consequence of the cuticle damage, the quinone-containing secretions of the prothoracic and abdominal glands were affected. We also carried out experiments on egg-containing flours to test the ovicidal activity of NTP. The flours were evaluated at three and twelve weeks after treatments. A 3-min nitrogen treatment showed ovicidal properties, while the remaining NTPs partially killed the eggs and delayed the emergence of larvae and adults. In conclusion, we propose an inexpensive physical treatment, which controls the entire life cycle of a major grain pest, avoiding chemical residues.Item Non‑Thermal Plasmas Afect Plant Growth and DNA Methylation Patterns in Glycine max.(2021) Pérez Pizá, María Cecilia; Ibañez, Verónica; Varela, Anabella; Ferreyra, Matías; Chamorro, Juan Camilo; Zilli, Carla; Vallecorsa, Pablo; Fina, Brenda; Prevosto, Leandro; Marfil, Carlos; Cejas, Ezequiel; Balestrasse, KarinaNon-thermal plasmas (NTP) are partially ionized gases that represent a promising technology for seed treatment to enhance seed health while promoting germination and vigor in a fast, cost-efective, and eco-friendly way. The seed treatment with NTP generates phenotypic variations in plants that could be related to changes in DNA methylation. This work analyses the efects of two diferent NTP: nitrogen for 3 min (PMN3) and oxygen for 2 min (PMO2) applied to soybean (Glycine max) seeds. Growth parameters of plants grown from treated and untreated seeds were evaluated at two growth stages: 6 and 20 days after sowing (DAS). MSAP (Methylation Sensitive Amplifed Polymorphism) markers were assayed to evaluate epigenetic changes induced by NTP treatments. Plants obtained from PMN3 and PMO2-treated seeds were phenotypically similar to each other: exhibited a superior growth at both stages. At 6 DAS root and shoot length and fresh weight surpassed the Control, while at 20 DAS root length and fresh and dry weight were higher than Control. PMN3 and PMO2 induced DNA methylation changes with respect to the Control plants, with higher diferentiation at 20 DAS than at 6 DAS. The epigenetic variability and the phenotypic variability correlated only at 20 DAS (R2=0.5). The observed phenotypic diferences among Control and NTP-treated plants could not be explained by overall changes in the methylation levels, but both demethylation and methylation changes at specifc loci appear to be operating in response to NTP treatments.Item Numerical Simulation of the Voltage–Current Characteristic of an Atmospheric Pressure Discharge: The Glow‑to‑Arc Transition.(2024) Cejas, Ezequiel; Prevosto, Leandro; Minotti, FernandoThe glow-to-arc transition of a convection-stabilized atmospheric pressure air discharge is numerically investigated. Two separate models are considered: a one-dimensional axisym metric time-dependent fuid model of the positive column, describing the thermal-instabil ity, and a sheath model of a cold cathode describing the feld-emission instability, which must then be properly matched together. The fuid model considers the most important chemical reactions in air plasma, including thermal ionization in atomic collisions. The radial electric feld in the plasma is obtained from the Poisson equation. The voltage–cur rent characteristic of the discharge is simulated for a time-varying current up to 300 mA. It is found that at some critical value slightly above 200 mA, the contraction of the positive column arises from a vibrational–translational energy relaxation. The subsequent increases in the discharge current density in the positive column drive in turn a feld-emission insta bility in the cathode, which is accompanied by a large voltage drop. Simulation results are validated against available experimental data.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 On the physical processes ruling an atmospheric pressure air glow discharge operating in an intermediate current regime(2015-02-06) Prevosto, Leandro; Kelly, Héctor; Mancinelli, Beatriz; Chamorro, Juan Camilo; Cejas, EzequielLow-frequency (100 Hz), intermediate-current (50 to 200 mA) glow discharges were experimentally investigated in atmospheric pressure air between blunt copper electrodes. Voltage–current characteristics and images of the discharge for different inter-electrode distances are reported. A cathode-fall voltage close to 360V and a current density at the cathode surface of about 11 A/cm2, both independent of the discharge current, were found. The visible emissive structure of the discharge resembles to that of a typical low-pressure glow, thus suggesting a glow-like electric field distribution in the discharge. A kinetic model for the discharge ionization processes is also presented with the aim of identifying the main physical processes ruling the discharge behavior. The numerical results indicate the presence of a non-equilibrium plasma with rather high gas temperature (above 4000 K) leading to the production of components such as NO, O, and N which are usually absent in low-current glows. Hence, the ionization by electron-impact is replaced by associative ionization, which is independent of the reduced electric field. This leads to a negative current-voltage characteristic curve, in spite of the glow-like features of the discharge. On the other hand, several estimations show that the discharge seems to be stabilized by heat conduction; being thermally stable due to its reduced size. All the quoted results indicate that although this discharge regime might be considered to be close to an arc, it is still a glow discharge as demonstrated by its overall properties, supported also by the presence of thermal non-equilibrium. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4907661]Item Physicochemical Properties and Time Stability of Plasma Activated Water by a Liquid-Cathode Glow-Type Discharge in Air: The Effect of Air Confinement.(2023) Santamaría, Brenda; Ferreyra, Matías; Chamorro, Juan Camilo; Cejas, Ezequiel; Fina, Brenda; Prevosto, LeandroNonthermal discharges in atmospheric pressure air in contact with water produce large amounts of reactive species in the gas phase that can enter into the water by diffusion, thus inducing the formation of secondary reactive species in the liquid phase, including those long-lived species such as NO2 NO3, and H2O2. Depending on the controllable parameters of the discharge, the plasma activated water (PAW) may acquire differ 8 ent physicochemical properties, resulting in various applications. Physicochemical measurements of PAW obtained by means of a water-cathode glow-type discharge in atmospheric pressure air operating in open and closed reactor conditions are reported. The discharge was operated in a millisecond pulsed-dc regime at an rms current value of 100 mA and a power of 100 W. A large volume of 1 L of distilled water was treated for 30 min. In both cases, low pH values of ∼2.5 and very high levels of NO3(up to 250 mg/L) in PAW were obtained; however, in the closed system, no H2O2 was found and high concentrations of nitrite (120 mg/L) were measured, while in the open system, large levels of H2O2 were observed (45 mg/L) and no NO 2 was found. Likewise, the electrical conductivity value for the closed reactor (≈2000 µS/cm) was significantly higher than for the open reactor (≈1000 µS/cm). The reasons for these different behaviors in terms of PAW chemistry are discussed. Also, the time stability of PAW was measured.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 Quantitative Schlieren Diagnostic Applied to a Nitrogen Thermal Plasma Jet.(2018) Chamorro, Juan Camilo; Prevosto, Leandro; Cejas, Ezequiel; Kelly, Héctor— A quantitative interpretation of the schlieren technique applied to an atmospheric pressure, vortex-stabilized nitrogen thermal plasma jet generated in a direct-current nontransferred arc plasma torch (nitrogen gas flow rate of 25 NL/min, power level of 15 kW), discharging into ambient air is reported. A Z-type, two-mirror schlieren system was used in the research. The technique allowed inferring the temporally averaged values of the temperatures and densities of different species present in the plasma jet in a wide range of radial and axial distances. Deviations from kinetic equilibrium in the calculation of the plasma refractive index were accounted for, but maintaining the assumption of the local chemistry equilibrium. The influence of several assumptions on the accuracy of the measurements was considered. The results have shown that for a distance of 3.5-mm downstream from the nozzle exit, the kinetic equilibrium is realized (being both electron and gas temperatures values around 11 000 K), but noticeable deviation from kinetic equilibrium appears toward the jet border. On the other hand, a marked deviation from the kinetic equilibrium was found in the whole far field of the plasma jet, where the electron temperature remains still quite high (about 10 000 K at 30-mm downstream of the nozzle exit), well decoupled from the gas temperature (about 7000 K at the same distance). The obtained results are in reasonable good agreement with those previously reported by some of the authors by using a double floating probe method in the same plasma torch.