Letteratura scientifica selezionata sul tema "Discharge decomposition"

The paper deals with the influence of avalanche streamer discharges on aqueous solutions of organic substances such as phenols, methyl-orange and simulating amino acid and protein compounds. Studies have shown the possibility of universal water purification when using gas-discharge decontamination technologies. Complex impact of discharge phenomena, physical and chemical factors, radiation at different frequencies of avalanche streamer discharge lead to degradation of organic and inorganic substances in water impurities. The most frequently used discharges for water purification are electrolyte (discharge in liquid), glow, corona, microwave-frequency discharge excitation in several GHz, barrier discharge and avalanche streamer discharge. It is shown that application of avalanche streamer discharges allows to undertake the decomposition of organic matter in water with decomposition in carbon compounds, gaseous components and water more efficiently and with low cost energy. Applying of a discharge technology is a promising direction of water treatment and industrial wastewater disposal technology development. Energy electric shock changes chemical characteristics of the treated water, affects its Ionic composition, structure of dissolved organic matter, viability of the microorganisms in water without additional chemical reagents.

This review examines the processes of degradation of organic dyes in their aqueous solutions under the action of atmospheric pressure discharges. These processes are important for solving the environmental problem associated with the purification of water from organic pollution. A brief description of the types of discharges used for these purposes is given - dielectric barrier discharge, pulsed corona discharge, gliding arc discharge, direct current glow discharge, diaphragm discharge, and contact glow discharge electrolysis. The results are given on the degree of degradation of more than 30 types of dyes in different types of discharges. The features of comparing different types of discharges in terms of their energy efficiency of the degradation process - the energy spent on the decomposition of one gram of dye - are discussed. The kinetic regularities of the decomposition process and the influence on them of various factors - the initial concentration of the dye, the discharge power, and the pH of the solution are considered. Possibilities of accelerating degradation using homogeneous and heterogeneous catalysts are discussed. Possible mechanisms of the ongoing processes and the participation in them of active particles formed in solution under the action of a discharge (OH, HO2 and ozone radicals) are analyzed.

The task of CO2 decomposition is one of the components of the problem associated with global warming. One of the promising directions of its solution is the use of low-temperature plasma. For these purposes, different types of discharges are used. Microwave discharge in liquid hydrocarbons has not been studied before for this problem. This paper presents the results of a study of microwave discharge products in liquid Nefras C2 80/120 (petroleum solvent, a mixture of light hydrocarbons with a boiling point from 33 to 205 °C) when CO2 is introduced into the discharge zone, as well as the results of a study of the discharge by optical emission spectroscopy and shadow photography methods. The main gas products are H2, C2H2, C2H4, CH4, CO2, and CO. No oxygen was found in the products. The mechanisms of CO2 decomposition in the discharge are considered. The formation of H2 occurs simultaneously with the decomposition of CO2 in the discharge, with a volumetric rate of up to 475 mL/min and energy consumption of up to 81.4 NL/kWh.

Partial discharge detection is an important means of insulation diagnosis of electrical equipment. To effectively suppress the periodic narrowband and white noise interferences in the process of partial discharge detection, a partial discharge interference suppression method based on singular value decomposition (SVD) and improved empirical mode decomposition (IEMD) is proposed in this paper. First, the partial discharge signal with periodic narrowband interference and white noise interference x(t) is decomposed by SVD. According to the distribution characteristics of single values of periodic narrowband interference signals, the singular value corresponding to periodic narrowband interference is set to zero, and the signal is reconstructed to eliminate the periodic narrowband interference in x(t). IEMD is then performed on x(t). Intrinsic mode function (IMF) is obtained by EMD, and based on the improved 3σ criterion, the obtained IMF components are statistically processed and reconstructed to suppress the influence of white noise interference. The methods proposed in this paper, SVD and SVD + EMD, are applied to process the partial discharge simulation signal and partial discharge measurement signal, respectively. We calculated the signal-to-noise ratio, normalized correlation coefficient, and mean square error of the three methods, respectively, and the results show that the proposed method suppresses the periodic narrowband and white noise interference signals in partial discharge more effectively than the other two methods.

The effect of gas rate on the plasma discharge stability and energy values of hydrogen sulfide decomposition has been established in plasma chemical reactor. Processes taking place in a swirling flow of hydrogen sulfide during its plasmolysis have been analyzed. Plasmotrone basic hydrodynamic model has been suggested.

Plasma chemistry is a rapidly growing field to develop and exploit the great potential of plasma to perform chemical reactions. This thesis deals with the oxidation of organic pollutants in air and water promoted by the action of air non-thermal plasma (NTP). Such plasmas, which are conveniently produced by electric non-thermalizing discharges like corona and dielectric barrier discharges in air at atmospheric pressure and ambient temperature, provide highly reactive oxidizing environments comprising electrons, excited molecules, atomic and radical species (O, OH), ions (O2+, N2+, NO+, O–, O2–, O3–), O3 and NO. Despite the numerous successful applications of NTP in processes of environmental and commercial relevance, the chemistry of organic compounds within air non-thermal plasmas is still not well characterized, both as far as products and mechanisms are concerned. This thesis developed as a contribution to this field of research along three lines dealing, respectively, with plasma processing of: volatile organic compounds (VOCs) in air with plasma alone; VOCs in air with plasma plus an heterogeneous catalyst; organic pollutants in aqueous solutions above which an air plasma is generated. All three projects had a common focus in the mechanistic characterization of the oxidation processes within these very complex and highly reactive systems. The study of VOC oxidation in air NTP was carried out with a large prototype corona reactor developed at the Department of Chemical Sciences in Padova, which can be energized with DC or pulsed high voltage of either polarity. Comparative studies were carried out to evaluate the response of selected model VOCs to different corona regimes (+DC, −DC and +pulsed). The VOCs considered include two alkanes (n-hexane and i-octane), toluene and two halogenated methanes, dibromomethane (CH2Br2) and dibromodifluoromethane (CF2Br2, halon 1202). Remarkably, all these different VOCs, including the highly inert halon, can be oxidized to CO2 at room temperature with efficiencies which depend on VOC type (despite their high reactivity NTPs display some selectivity), on VOC concentration (the efficiency increases linearly with the reciprocal of VOC concentration) but also on the way energy is given to the plasma. Thus, for all VOCs examined the efficiency decreases in the order: +pulsed > -DC > +DC corona. This means that any given amount of energy produces an extent of VOC conversion ([VOC]/[VOC]0) which depends on the corona regime and decreases in the order +pulsed > –DC > +DC. The greater efficiency of +pulsed corona is due to the higher mean electron energy achieved, for any given input of energy, with this type of power supply with respect to DC high voltage. The mean electron energy of the plasma under the different corona regimes was experimentally determined in our reactor by emission spectroscopy measurements following a published procedure. Another important variable tested was the humidity in the air, which is known to produce the strongly oxidizing OH radicals via electron induced dissociation or via reaction with O2+ and N2+ ions. Thus, the greater efficiency in humid with respect to dry air observed for the oxidation of hydrocarbons and of CH2Br2 with –DC and +pulsed corona was attributed to reaction with OH radicals. Surprisingly, in experiments with + DC the same VOCs undergo less efficient oxidation in humid air than in dry air, despite the presence of OH radicals. Analysis of the plasma ionized species, performed by APCI-MS (Atmospheric Pressure Chemical Ionization – Mass Spectrometry), coupled to the determination of current/voltage characteristics of DC coronas, led to the proposal that in the case of +DC corona the oxidation of hydrocarbons and of CH2Br2 is initiated by reactions with ions (O2+, H3O+ and their hydrates, NO+) both in dry as well as in humid air. In contrast, with –DC and +pulsed corona in humid air, OH radicals are involved in the initial stage of hydrocarbons and of CH2Br2 oxidation. Consistent with its very low reactivity with the OH radical, the oxidation of CF2Br2 in humid air proceeds less efficiently with both +DC and –DC corona. It was thus proposed that the oxidation of CF2Br2 occurs via a common mechanism under all corona regimes tested, the initial step being electron induced C-Br dissociation. The process efficiency is lower in humid air because the mean electron energy is lowered due to reaction of the electrons with water molecules. The two halomethanes also form different products: FTIR analysis of post-discharge gas has shown that CH2Br2 produces both CO2 and CO, whereas CF2Br2 forms CO2 and F2C=O. The latter product is a longlived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however very rapidly hydrolized to CO2 and HF as shown by combined ion chromatography and FT-IR analysis of the solution and of the exhaust gas obtained after a water scrubbing step. Other non-carbon containing products of the discharge were analyzed by FT-IR analysis, including ozone, HNO3 and N2O. In experiments with both halomethanes evidence was found for brominesustained catalytic ozone destruction cycles, responsible also for increased conversion of NOx into HNO3. Efficiency and, especially, product selectivity can be improved by the combined action of plasma and heterogeneous catalysts which usually result in synergic effects. The nature and origin of this synergy was the focus of the research I carried out in my second year in graduate school during a stage at the Advanced Industrial Science and Technology Institute (AIST) in Tsukuba (Japan), in the group of dr. Hyun-Ha Kim. As molecular probe to compare the effects of plasma alone and plasma plus catalyst we selected the O-scrambling reaction to form 16O18O starting from a mixture of 16O2 and 18O2. Four different reactors were used and various catalysts, including TiO2, MS-13X and gAl2O3 also containing a few % of Ag. It was possible to conclude that, in the absence of a catalyst the O-exchange reaction occurs in the gas phase and not on the electrodes surface. It was also possible to use the results of these experiments to estimate, for any given energy input the average concentration of O atoms within the plasma. This is a most interesting outcome of these studies since the traditional method for obtaining O atom density involves sophisticated laser spectroscopy instrumentation and procedures. As for the catalyst/plasma interaction, using again a labelled molecular probe, 18O2, it was possible to conclude that the plasma induces oxygen fission on the catalyst surface and that this oxygen is then used in the oxidation of VOCs. The third project dealt with the plasma induced oxidation of phenol in aqueous solution. For these studies two prototype reactors were developed and tested, both characterized by application of electric discharges in the air above the solution. The first is a dielectric barrier discharge reactor which afforded the efficient removal of phenol from the aqueous solution according to an exponential decay as a function of treatment time at constant power. A qualitative analysis of the intermediate and final products of phenol oxidation was performed and the major reactive species formed upon the application of the discharge in air were identified and determined. It is concluded that the decomposition of phenol is initiated by reactions with ozone, taking place on the surface of the solution, and with hydroxyl radicals, both at the surface and within the bulk of the solution. An interesting and most convenient result is the better efficiency of phenol removal in tap water than in milliQ water. After ruling out possible effects due to conductivity, to Fenton’s reaction due to Fe2+ and to active chlorine, it was concluded that the efficiency increase is due to the higher pH of the solution mantained by the presence of bicarbonate salts. The second developed reactor allowed us to perform some interesting comparisons since it can be powered by different types of high voltage for the generation of plasma. The possibility to apply this technology to the treatment of waste water depends on many factors: the process efficiency, the final composition of the treated solution, the general applicability of the system to the organic pollutants. The data obtained so far are very promising due to the efficient oxidation all the way to CO2 and to the absence of any hazardous organic byproduct after a proper treatment time. The results of this thesis confirm that plasma processing is a promising highly efficient means for the advanced oxidation of organic pollutants both in air and in aqueous solution.
Lo studio di processi chimici indotti da plasmi sta suscitando un notevole interesse per il grande potenziale che questi sistemi possono sviluppare. Questa tesi riguarda l’ossidazione di inquinanti organici in aria e in soluzione acquosa promossa dall’interazione con plasma non-termico (NTP). Questi plasmi, che sono convenientemente generati da scariche elettriche non termalizzanti, principalmente scariche corona e a barriera di dielettrico, in aria a temperatura e pressione ambiente, costituiscono ambienti di reazione molto reattivi e fortemente ossidanti per la presenza di elettroni, molecole eccitate, specie atomiche e radicali (O, OH), ioni (O2+, N2+, NO+, O–, O2–, O3–), O3 e NO. Nonostante siano numerose le applicazioni tecnologiche di questi plasmi in processi di rilevanza ambientale e commerciale, la chimica dei composti organici in questi sistemi è tuttora non ben nota sia per quanto riguarda i prodotti che i meccanismi di reazione. Questa tesi è uno studio meccanicistico che si è sviluppato lungo tre linee di ricerca riguardanti l’ossidazione di: i) composti organici volatili (VOC) in aria con solo plasma; ii) VOC in aria con plasma e un catalizzatore eterogeno; inquinanti organici in soluzioni acquose poste a contatto con plasma non termico in aria. I tre progetti hanno un obiettivo comune che riguarda la caratterizzazione dei meccanismi di ossidazione che operano in questi sistemi di enorme complessità chimica. Lo studio dell’ossidazione di VOC in plasmi non termici in aria è stato condotto utilizzando un reattore prototipo a scarica corona sviluppato presso il Dipartimento di Scienze Chimiche a Padova, che può essere alimentato da alta tensione DC o ad impulsi di polarità sia positiva che negativa. Sono stati svolti studi comparativi per valutare la risposta di alcuni modelli di VOC a diversi regimi di scarica corona, precisamente +DC, -DC e +pulsed. I composti studiati sono due alcani (esano ed iso-ottano), il toluene e gli alometani dibromometano (CH2Br2) e dibromodifluorometane (CF2Br2, halon 1202). E’ notevole il fatto che tutti questi VOC, compreso l’halon notoriamente molto inerte, possono essere ossidati a CO2 in questi plasmi a temperatura ambiente con un’efficienza che dipende dal tipo di VOC (nonostante la loro elevata reattività questi plasmi presentano comunque un certo grado di selettività), dalla concentrazione del VOC (l’efficienza aumenta linearmente col reciproco della concentrazione iniziale del VOC) e dal modo in cui l’energia viene fornita al reattore. Infatti, per tutti i VOC considerati, l’efficienza del trattamento aumenta nell’ordine: +DC < -DC < +pulsed. Questo significa che il grado di conversione ([VOC]/[VOC]0) prodotto da una certa quantità di energia fornita al sistema dipende dal tipo di scarica utilizzato, che a sua volta determina la composizione e natura del plasma e quindi la sua reattività. La maggiore efficienza del corona ad impulsi rispetto al corona DC è attribuibile alla maggiore energia media degli elettroni in questo regime di scarica. L’energia media degli elettroni è stata determinata sperimentalmente nel nostro reattore nelle diverse condizioni di scarica mediante esperimenti di spettroscopia di emissione utilizzando un metodo pubblicato in letteratura. Un’altra importante variabile di questi processi è il grado di umidità dell’aria, che determina la formazione di maggiori o minori concentrazioni del radicale OH. Questo radicale si forma dall’acqua attraverso reazione con elettroni ad alta energia o reazione con gli ioni O2+ and N2+. La maggior efficienza dell’ossidazione di idrocarburi e del CH2Br2 osservata con -DC in aria umida rispetto all’aria secca è stata quindi attribuita alla reazione con radicali OH. Sorprendentemente, con +DC l’umidità produce un effetto opposto per gli stessi VOC, nonostante la presenza in aria umida di radicali OH. L’analisi degli ioni del plasma, effettuata mediante spettrometria di massa APCI-MS (Atmospheric Pressure Chemical Ionization – Mass Spectrometry), accoppiata allo studio della caratteristica corrente/tensione del corona DC, ha portato a concludere che nel caso del corona +DC l’ossidazione degli idrocarburi e del dibromometano è iniziata da reazione con ioni (O2+, H3O+ e i loro idrati, NO+) sia in aria secca che in aria umida. Al contrario, nel caso del corona –DC e del corona +pulsed la principale reazione di attacco a questi VOC risulta essere quella del radicale OH. Per quanto riguarda invece l’halon CF2Br2, sia con +DC che con –DC l’ossidazione in aria umida risulta meno efficiente che in aria secca, un risultato coerente con la nota scarsa reattività di questo VOC con il radicale OH. E’ stata quindi avanzata l’ipotesi che l’ossidazione di questo halon proceda attraverso un meccanismo comune, indipendentemente dal regime di scarica applicato, che comporta la dissociazione iniziale del legame C-Br indotta da interazione con elettroni del plasma. Il processo è meno efficiente in aria umida probabilmente perché la reazione di dissociazione dell’acqua provoca una riduzione dell’energia media degli elettroni rispetto a quella in aria secca. L’ossidazione dei due alometani in aria secca dà prodotti diversi: l’analisi FT-IR del gas in uscita dal reattore ha individuato sia CO2 che CO fra i prodotti di CH2Br2 mentre nel caso di CF2Br2 i prodotti sono CO2 e F2C=O. Quest’ultimo è un intermedio di ossidazione con tempo di vita sufficientemente lungo da poter essere rivelato in quanto notoriamente poco reattivo nelle reazioni con radicali. E’ tuttavia idrolizzato molto velocemente a CO2 e HF come dimostrato da analisi integrate di cromatografia ionica e FT-IR della soluzione e del gas ottenuti dopo gorgogliamento del gas trattato in acqua. Altri prodotti di questi trattamenti rivelati e quantificati mediante spettroscopia FT-IR sono l’ozono, l’acido nitrico e l’ossido N2O. Con entrambi gli alometani si è osservato l’intervento di cicli catalitici di distruzione dell’ozono in cui il bromo atomico è la specie propagatrice. Gli stessi cicli sono inoltre responsabili della conversione degli NOx in HNO3. L’efficienza e la selettività dei processi di ossidazione al plasma possono essere migliorati attraverso l’azione combinata del plasma e di catalizzatori eterogenei. Ne deriva un effetto sinergico, la cui origine e natura sono tuttora in fase di studio. Di questo problema mi sono occupato durante un soggiorno presso l’Advanced Industrial Science and Technology Institute (AIST) a Tsukuba (Giappone), presso il gruppo del Prof. Hyun-Ha Kim. Per confrontare gli effetti di solo plasma e plasma più catalizzatore abbiamo utilizzato come sonda molecolare la reazione di scambio di ossigeno che produce 16O18O partendo da miscele di 16O2 e 18O2. Sono stati utilizzati diversi reattori al plasma con diverse alimentazioni elettriche e parecchi catalizzatori fra cui TiO2, MS-13X e gAl2O3 contentente varie modeste percentuali di Ag. Questi studi hanno permesso di concludere che, in assenza di catalizzatore, la reazione di scambio di ossigeno avviene in fase gas e non sulle superfici degli elettrodi. I risultati di questi esperimenti sono stati utilizzati per sviluppare un metodo basato sulla reazione di scambio isotopico al fine di determinare la concentrazione di ossigeno atomico in questi plasmi. Questo è un risultante importante che si propone come alternativa al metodo tradizionale per la determinazione della concentrazione di ossigeno atomico con strumentazioni ottiche laser e procedure piuttosto sofisticate. Per quanto riguarda l’interazione catalizzatore/plasma, è stato possibile concludere, sempre utilizzando la sonda molecolare 18O2, marcata isotopicamente, che il plasma determina la fissazione dell’ossigeno sulla superficie del catalizzatore e che questo ossigeno è quindi trasferito al VOC nel processo di ossidazione. Infine, il terzo progetto ha riguardato l’ossidazione del fenolo in soluzioni acquose esposte all’azione di plasma non-termico in aria. Per questi studi sono stati sviluppati due prototipi di reattore caratterizzati entrambi dall’applicazione di scariche elettriche nell’aria sovrastante la soluzione da trattare. L’ossidazione del fenolo nel primo reattore, che utilizza scariche a barriera di dielettrico, procede efficacemente fino a CO2 seguendo un decadimento esponenziale in funzione del tempo di trattamento a potenza applicata costante. Dall’analisi dei prodotti ed intermedi di ossidazione nonché dalla determinazione delle principali specie reattive è emerso che la decomposizione del fenolo avviene per reazione con l’ozono sulla superficie della soluzione a contatto con il plasma, e con il radicale OH, sia sulla superficie che all’interno della soluzione. Un risultato molto interessante e utile in vista di applicazioni pratiche di questi processi riguarda la maggiore efficienza dell’ossidazione del fenolo in acqua di rubinetto rispetto all’acqua milliQ. Dopo aver escluso che all’origine di questo fenomeno potessero esserci effetti dovuti alla conduttività maggiore, alla presenza di ioni Fe2+ capaci di indurre la reazione di Fenton, e alla presenza di cloro attivo nell’acqua potabile, è stato verificato che l’effetto tampone esercitato dallo ione bicarbonato mantiene un pH elevato e consente al processo di procedere velocemente.

Dans ce travail de thèse de doctorat, des études expérimentales et théoriques sont réalisées sur les caractéristiques de décomposition du mélange gazeux C5F10O/N2/O2 à l'interface gaz-solide de matériaux métalliques et sous l'action d'une décharge électrique dans un appareil de coupure électrique. La faisabilité et la sécurité de son utilisation sont évaluées en combinaison avec la biosécurité du gaz C5F10O et des produits de décomposition du gaz plasmagène. Compte tenu du contact long entre le mélange gazeux C5F10O/N2/O2 et les matériaux internes de l'équipement de coupure électrique pendant son fonctionnement, la stabilité de l'interaction gaz-solide du mélange gazeux avec les métaux couramment utilisés (cuivre, aluminium et argent), à l'intérieur de l'équipement est caractérisé, et le mécanisme d'interaction gaz-solide entre le mélange gazeux C5F10O et les matériaux métalliques est précisé. Un défaut thermique peut également se produire pendant le fonctionnement de l'équipement. Les caractéristiques typiques de la décharge et de la décomposition par défaut thermique du mélange gazeux C5F10O/N2/O2 contenant différentes concentrations d'oxygène sont identifiées. La composition et les processus de création des produits de décomposition du mélange gazeux sont obtenues, et la corrélation entre les types et le contenu des produits de décomposition caractéristiques et les types de défaut, ainsi que la réaction de l'oxygène vers les produits de décomposition du mélange gazeux C5F10O et le mécanisme d'inhibition de la précipitation des produits solides sont analysés. Sur la base de ce travail, nous proposons un schéma d'optimisation de la stabilité de la couche protectrice argent- cuivre est proposé pour le cuivre avec une faible stabilité gaz-solide du gaz C5F10O/N2/O2. Nous avons défini les produits caractéristiques de la décharge et du défaut thermique du mélange gazeux, ce qui constitue une référence pour la surveillance en ligne des défauts. Nous avons testé la biosécurité du C5F10O et des produits de décomposition par arc. Sa sécurité d'application a été évaluée en fonction des caractéristiques de décharge et de décomposition thermique du mélange gazeux, et des mesures et de protection ciblées et des suggestions sont proposées
In this doctoral thesis work, experimental and theoretical studies are carried out on the decomposition characteristics of C5F10O/N2/O2 gas mixture at the gas-solid interface of metal materials and under the discharge and thermal action, and the feasibility and safety of its application are evaluated in combination with the biosafety of C5F10O gas and arc decomposition products of C5F10O/N2/O2. Considering the long-term contact between C5F10O/N2/O2 gas mixture and the internal materials of the equipment during normal operation, the gas-solid interaction stability of C5F10O/N2/O2 gas mixture with commonly used metal copper, aluminum and silver inside the equipment is evaluated, and the mechanism of gas-solid interface interaction between C5F10O gas mixture and metal materials is clarified. Discharge and thermal fault may also occur during the long-term operation of the equipment. The failure decomposition mechanism of C5F10O/N2/O2 gas mixture is studied through experiments and simulations. The typical discharge and thermal fault decomposition characteristics of C5F10O/N2/O2 gas mixture containing different concentrations of oxygen are revealed. The composition and generation rules of decomposition products of the gas mixture under the faults are obtained, and the correlation between the types and contents of characteristic decomposition products and the fault types, as well as the regulation of oxygen to C5F10O gas mixture decomposition products and the inhibition mechanism of solid product precipitation are analyzed. In conclusion, based on the simulation and experimental results, we proposed the stability optimization scheme of silver-plated protective layer on copper surface for metal copper material with poor gas-solid stability of C5F10O/N2/O2 gas. We extracted the characteristic products characterizing the discharge and thermal fault of C5F10O/N2/O2 gas mixture, which provided a reference for the on-line fault monitoring based on the decomposition components. We tested the biosafety of C5F10O and its arc decomposition products, and evaluated its application safety based on the discharge and thermal fault decomposition characteristics of C5F10O/N2/O2 gas mixture, and proposed targeted safety protection measures and suggestions

The current persistent drought and changes in the climate system have raised water managers expert questions about how to manage water resources in the future. The manifestation of climate change in hydrological series and their influence on the magnitude of threats to the storage functions of reservoirs are more often investigated. Already today, long-term shortages of storage capacity in reservoirs lead to the introduction of special manipulations on water structures. The aim of the thesis is to perform the analysis of time series, respectively decomposition of hydrological series average annual and monthly discharges. Create extended hydrological bases using synthetic discharge series generators and develop a comprehensive analysis of storage volume without considering losses even with the introduction of losses from the water surface vapor in the UNCE RESERVOIR program. The created discharge series are compared and evaluated on the basis of statistical characteristics and reservoir storages results with the real discharge series. The practical app is conducted on the Vranov reservoir in the Dyje River Basin.

À l’échelle mondiale, des enjeux socio-économiques majeurs reposent sur les systèmes karstiques, tant pour l’alimentation en eau potable des populations que pour l’exploitation des gisements auxquels ils sont associés. Ces systèmes sont définis, par De Marsily (1984), comme des milieux dans lesquels « l’hétérogénéité atteint son paroxysme » : les modelés physiques caractérisant le karst sont particulièrement variés et les réponses hydrodynamiques sont indéniablement complexes et non-linéaires. Aujourd’hui, il n’est toujours pas possible de définir précisément l’organisation des hétérogénéités de ces aquifères bien que de nombreuses études aient été menées sur leur fonctionnement global. Ces dernières s’appuient sur les seules informations généralement disponibles sur ces systèmes : les précipitations sur le bassin versant étudié, les débits relevés à l’exutoire, des suivis ponctuels de niveau d’eau, de concentration ou de turbidité, et des estimations locales de propriétés hydrodynamiques telles que la conductivité hydraulique de l’aquifère ou le coefficient d’emmagasinement. Dans ce contexte, les méthodes d’analyse de séries temporelles hydrologiques enregistrées à des exutoires karstiques ont été largement exploitées dans le but d’interpréter le fonctionnement hydro(géo)logique de ces hydrosystèmes. Ce travail de thèse a exploré les potentialités de ces méthodes d’analyse du signal hydrologique comme aide à l’interprétation et à l’inférence des caractéristiques physiques et hydrogéologiques (géométries de réseaux karstiques, échanges entre réseaux et matrice poreuse environnante, modes de recharge diffus ou concentré). L’étude a été basée sur le couplage entre la modélisation directe d’écoulements sur des systèmes karstiques synthétiques, et le traitement statistique et spectral des signaux simulés. Les domaines modélisés ont été construits avec différents degrés de complexité : depuis des cas arbitraires très simples à des cas complexes correspondant à des systèmes réalistes. Les écoulements dans ces réseaux synthétiques ont été simulés avec le modèle hydrogéologique à base physique développé par le BRGM, MARTHE (Thiéry, 2015), et plus particulièrement grâce au module « Drains-Conduits » permettant de coupler matrice, conduits karstiques et échanges entre ces deux entités. Les méthodes de traitement du signal utilisées ont permis de comparer les propriétés statistiques et spectrales d’un signal climatique (précipitations) avec celles des débits simulés, et de comprendre comment celles-ci sont dépendantes des propriétés hydrauliques et physiques imposées dans les domaines. Même si les fonctions d’auto- ou d’inter-corrélation peuvent présenter des comportements globalement similaires (e.g. « effets-mémoire » ou temps de décorrélation similaires pour des géométries karstiques ou propriétés d’échanges matrice-conduits différentes), des différences en apparence subtiles et statistiquement significatives permettent de distinguer les comportements plus ou moins karstiques des domaines modélisés. En domaine spectral, tous les modèles se différencient par leur comportement scalaire et notamment par différentes gammes d’invariance d’échelle temporelle. Celles-ci traduisent les différentes modalités de filtrage du signal d’entrée par l’hydrosystème, et caractérisent donc différentes modalités d’écoulement. L’utilisation de méthodes de décomposition par ondelettes discrètes permet finalement de reconstruire la variabilité hydrodynamique associée à ces modalités d’écoulement, achevant ainsi une décomposition statistique de l’hydrogramme à l’exutoire
Globally, major socio-economic challenges lie on karst systems, both for drinking water supply to populations and for deposits exploitation. Karst systems are defined, by De Marsily (1984), as environments in which "heterogeneity reaches its paroxysm": the physical patterns characterizing karst domains are particularly varied and the hydrodynamic responses are undeniably complex and non-linear. Today, it is still not possible to precisely define the heterogeneities organization of these aquifers although many studies have been carried out on their overall functioning. These studies are based on the only information generally available on these systems: precipitation on the studied watershed, flow rates recorded at the outlet, well-located monitoring of water levels, concentrations or turbidity, and local estimated hydrodynamic properties such as the hydraulic conductivity of the aquifer or the storage coefficient. In recent years, several works have shown the interest of applying correlative and spectral analyzes on time series recorded on karst systems in order to interpret them hydro(geo)logical functioning. This thesis work explored the potential of this hydrological signal analysis methods as an aid to the interpretation and inference of physical and hydrogeological characteristics (karst networks geometry, exchanges between conduit networks and the surrounding porous matrix, recharge mode including diffuse and point-source one). This study was based on a coupling approach of direct modeling flows through synthetic karst systems, and the statistical and spectral processing of these simulated signals. The modeled domains were built according to different complexity degrees: from very simple arbitrary cases to complex cases corresponding to realistic systems. The flows in these synthetic networks were simulated with the physics-based hydrogeological model developed by the BRGM, MARTHE (Thiéry, 2015), and more particularly thanks to the “Drains-Conduits” package allowing to couple matrix, karst conduits and exchanges between these two entities. The employed signal processing methods compared the statistical and spectral properties of a climatic signal (precipitations) with those of the simulated discharges. They also give an understanding of how these properties vary according to changes in the domains hydraulic and physical characteristics. Even if the auto- and cross-correlation functions may exhibit almost similar behaviors (i.e. similar “memory effects” or decorrelation times, for different karst networks or matrix/conduit exchange properties), subtle but statistically significant differences allow the distinction between the karstification degree of the modeled domains. The scalar behaviors, and more particularly the different ranges of time scale invariance, can be used to distinguish the models in the spectral domain. These spectral properties reflect the possible filtering of the input signal by the considered hydrosystem, and therefore express different flow kinetics. Using discrete wavelet decomposition methods ultimately allows to reconstruct the hydrodynamic variability associated with these flow kinetics, completing thus a statistical decomposition of the hydrograph at the outlet

This Diploma thesis is focused on physical and chemical effects which contribute to the decomposition of organic dyes by diaphragm discharge generated in water solutions. Due to the application of DC high voltage source in continuous regime, there is an effect of electrolysis contributing to the dye decomposition by diaphragm discharge. The aim of this work was to find out when the electrolysis is running (or when is the moment of discharge breakdown) and which factors influence the breakdown. The other goal was decomposition of selected textile and food organic dyes by electrolysis itself. In the theoretical part, theory about creation of electrical discharges in aqueous solutions is noted and various types of underwater discharges are described. Background researches about underwater electrical discharges used in the world are mentioned as well as the use of diaphragm discharges and various ways how to remove organic dyes from wastewater. Finally, theories of electrolysis, UV-VIS spectroscopy and basis of other analytical methods useful for detection of organic molecules are described. Experimental part is oriented to experiment procedure which was carried out in a reactor with separated electrode areas. Separation was made by dielectric diaphragm with a pinhole in the centre. Its initial diameter was 0.4 mm. Used chemicals and course of experiments are described in this part, too. First, the breakdown moment in the reactor was investigated (i. e. determination, when only electrolysis was operating) by formation of hydrogen peroxide and measurement of dynamic (time resolved) electrical characteristics. Next, decomposition of selected dyes by electrolysis was carried out. As the decomposition was related to decolorization of the solution, UV-VIS spectroscopy in the range of 350–700 nm was used for determination of dye concentration. Next part focused on results presents various factors which had an effect on breakdown of diaphragm discharge. These factors are kind of used electrolyte, initial conductivity of solution, kind of dye, temperature of solution and type of reactor (or solution volume). From the result, the most important factor is initial solution conductivity. After the determination of the breakdown moment, the electrolysis of organic dyes was performed. The applied current was 10 mA, initial conductivity was 500 µS/cm and used electrolyte was NaCl. Moreover comparison of dye decomposition in dependence on the different applied power was realized. From this comparison one can assume, there is no significant contribution of electrolysis (the efficiency is approximately 15 %) to the diaphragm discharge in aqueous solution.

Au cours des dernières décennies, les plasmas créés par une décharge micro-ondes ont de plusen plus attiré l’attention de la communauté scientifique aérospatiale sur le sujet du contrôled’écoulements. En effet, il a été démontré expérimentalement que le dépôt d’énergie obtenu parle plasma peut modifier les propriétés aérodynamiques de l’écoulement autour d’un objet telleque la trainée de frottement. Or, la conception et l’optimisation de ces actionneurs plasma entant que technique de contrôle d’écoulements nécessitent une compréhension approfondie de laphysique sous-jacente que les seules expériences sont incapables de fournir.Dans ce contexte, nous nous intéressons à la modélisation numérique de l’interaction desondes électromagnétiques avec un plasma et le gaz afin de mieux comprendre la nature desdécharges micro-ondes et leur applicabilité. La modélisation de ces phénomènes présente desdifficultés importantes en raison du couplage multi-physique et donc de la multitude des échellesspatiales et temporelles qui apparaissent. Ce travail de thèse traite des questions de physiqueet de mathématiques appliquées soulevées par la modélisation numérique de ces plasmas.La première partie du travail se focalise sur les questions de validité du modèle physique duclaquage micro-onde fondé sur l’approximation de champ effectif local. En raison des gradientsde densité du plasma très élevés, la validité du concept de champ effectif local peut être misen doute. Pour cela, un modèle fluide du second ordre est développé en incluant une equationd’énergie électronique non-locale. Cette modélisation permet de décrire de façon plus précisele dépôt d’énergie par plasma induisant la formation d’ondes de choc dans le gaz. Une analysedimensionnelle du système d’équations fluide permet de caractériser la non-localité en espace dubilan d’énergie électronique en fonction du champ électrique réduit et de la fréquence de l’onderéduite. Une discussion est également menée sur d’autres approximations des coefficients detransport électronique. Dans une deuxième partie, la construction et l’analyse d’une méthode multi-échelles derésolution numérique du problème de propagation des ondes électromagnétiques dans le plasmasont réalisées. Il s’agit du couplage entre les équations de Maxwell dans le domaine temporel avecune équation de quantité de mouvement pour les électrons. L’approche s’appuie sur la méthodede décomposition de domaine de type Schwartz, basée sur une formulation variationnelle duschéma de Yee et utilisant deux niveaux de grilles Cartésiennes emboitées. Une grille locale,appelée patch, est utilisée pour calculer de manière itérative la solution dans la région du plasmaoù une meilleure précision est requise. La méthode proposée permet le raffinement local etdynamique du maillage spatial tout en conservant l’énergie du système. Une analyse théorique dela convergence de l’algorithme pour les résolutions temporelles explicite et implicite est égalementréalisée. Dans la dernière partie, des simulations numériques sur le claquage micro-ondes et la formation de structures filamentaires de plasma sont conduites. Les effets de différents types d’approximations sur le modèle physique du plasma sont analysés. Puis, ces expériences numériques démontre la précision et l’efficacité, en terme de temps de calcul, de la méthode multi-échelleproposée. Enfin, on étudie les effets de chauffage du gaz sur la formation et l’entretien de structures filamentaires dans l’air à pression atmosphérique. Pour cela, le modèle micro-onde-plasma développé est couplé avec les équations de Navier-Stokes instationnaires pour les écoulements compressibles. Les simulations montrent des caractéristiques intéressantes de la dynamique deces structures plasma pendant le processus de chauffage du gaz, qui sont en accord étroit avec les données expérimentales
In recent decades, microwave discharge plasmas have attracted increasing attention of aerospace scientific community to the subject of aerodynamic flow control because of their capability of sub- stantially modifying the properties of the flow around bodies by effective energy deposition. The design and optimization of these plasma actuators as flow control technique require a compre- hensive understanding of the complex physics involved that the sole experiments are incapable to provide.In this context, we have interest in the numerical modeling of the mutual interaction of elec- tromagnetic waves with plasma and gas in order to better understand the nature of microwave discharges and their applicability. A challenging problem arises when modeling such phenomena because of the coupling of different physics and therefore the multiplicity of spatial and tempo- ral scales involved. A solution is provided by this thesis work which addresses both physics and applied mathematics questions related to microwave plasma modeling.The first part of this doctorate deals with validity matters of the physical model of microwave breakdown based on the local effective field concept. Because of large plasma density gradients, the local effective field approximation is questionable and thus a second-order plasma fluid model is developed, where the latter approximation is replaced by the local mean energy approximation. This modeling approach enables to take into account the non-locality in space of the electron energy balance that provides a more accurate description of the energy deposition by microwave plasma leading to the shock waves formation into the gas. A dimensionless analysis of the plasma fluid system is performed in order to theoretically characterize the non-locality of the introduced electron energy equation as function of the reduced electric field and wave frequency. It also discusses other approximations related to the choice and method of calculation of electron transport coefficients.Concerning the mathematical aspects, the thesis work focuses on the design and the analysis of a multiscale method for numerically solving the problem of electromagnetic wave propagation in microwave plasma. The system of interest consists of time-dependent Maxwell’s equations coupled with a momentum transfer equation for electrons. The developed approach consists of a Schwartz type domain decomposition method based on a variational formulation of the standard Yee’s scheme and using two levels of nested Cartesian grids. A local patch of finite elements is used to calculate in an iterative manner the solution in the plasma region where a better precision is required. The proposed technique enables a conservative local and dynamic refinement of the spatial mesh. The convergence behavior of the iterative resolution algorithm both in an explicit and implicit time-stepping formulation is then analyzed.In the last part of the doctorate, a series of numerical simulations of microwave breakdown and the filamentary plasma array formation in air are performed. They allow to study in detail the consequences of the different types of physical approximations adopted in the plasma fluid model. Then, these numerical experiments demonstrate the accuracy and the computational efficiency of the proposed patch correction method for the problem of interest. Lastly, a numerically investigation of the effects of gas heating on the formation and sustaining of the filamentary plasma array in atmospheric-pressure air is carried out. For doing this, the developed microwave-plasma model is coupled with unsteady Navier-Stokes equations for compressible flows. The simulations provide interesting features of the plasma array dynamics during the process of gas heating, in close agreement with experimental data

The aim of this thesis was to elaborate the issue of the decomposition of volatile organic compounds in the Gliding Arc plasma discharge at atmospheric pressure. Technologies based on nonthermal plasma could offer a good alternative to conventional techniques for the decomposition of volatile organic compounds, such as thermal and catalytic oxidation. Gliding Arc discharge (GidArc) is a widely exploited nonthermal plasma source used for many industrial applications, such as air-pollution control. The energy efficiency, reaction selectivity or production of specific species may be achieved in this kind of plasma, and thus for various chemical processes it can be much more effective then in conventional techniques. Presented experiments are linked to the previous results published in diploma thesis, which gave us the basics for construction of new reactor and optical emission spectroscopy measurements have been done to characterize the plasma. Toluene (aromatic, unsaturated), cyclohexane (aromatic, saturated) and hexane (aliphatic, saturated) were used as the model compounds for these experiments in the concentration range from hundreds to thousands ppm. Results focused on the electrical parameters of the reactor were carried out, with the aim to operate the system at a lower energy cost. In order to get the time-resolved diagnostics of the moving plasma channel, the evolution of the plasma channel was recorded continuously by using a high-speed video camera. In next part of the work, some results concerning generation of low molecular products like nitric oxide, nitrogen dioxide, hydrogen and carbon monoxide on the discharge conditions are presented. In combustion process, undesirable mixture of toxic highmolecular by-products can be formed. Samples were therefore analysed in gas chromatograph linked to mass spectrometer, to characterize the chemical transformation pathway of VOC in plasma.

Abstract Simulations and experiments are conducted to model, simulate, test and demonstrate the effect of plasma discharges on decomposition of carbon dioxide (CO2). A pin-to-plane discharge is employed in gas samples containing CO2. A high voltage plasma system is used which was previously shown to be able to decrease CO2 concentration in gas samples. The discharge is modeled and described, including monitoring electrical parameters such as current and voltage. The present study investigated plasma decomposition of carbon dioxide experimentally, and through simulation. A plasma micro-discharge was utilized to better understand plasma-CO2 interactions. Enhancements are suggested to help increase the efficiency and yield of the plasma-CO2 decomposition process. Gas samples are analyzed over time using a CO2 meter.