La première partie de ce travail présente une nouvelle méthode qui permet de détermination rapidement de la température et de la concentration en fer d'un plasma d'arc MAG utilisé dans la technologie de soudage par plasma. Le plasma est un mélange [Ar-CO2] en présence de fer, avec un rapport molaire entre Ar et CO2 constant de 82%-18%. La seconde partie s'intéresse au rayonnement d'un plasma d'argon utilisé dans la technologie soudage GTAW et pouvant conduire à des dangers photobiologique. Dans le chapitre 1, le contexte et la motivation de ce travail sont présentés. Les travaux déjà effectués et publiés dans ces deux axes scientifiques sont passés en revue. Dans le chapitre 2, les compositions à l'équilibre sont calculées par la méthode de la minimisation de l'énergie libre de Gibbs. Les densités et fonctions de partitions obtenues pour chaque espèces présente dans le plasma sont ensuite utilisées pour déterminer les pertes radiatives des plasmas [Ar-CO2]-Fe via la méthode du coefficient d'émission net (CEN). Cette estimation des pertes ne peut se faire sans le calcul préalable du coefficient d'absorption spectral que nous avons réalisé finement par la méthode " raie par raie ". Tous les mécanismes radiatifs prédominants dans le plasma ont été pris en compte: continua atomique et moléculaire, raies atomiques et moléculaires. Cette partie constitue la base de cette étude sur laquelle se fonde notre nouvelle méthode de diagnostic destinée à déterminer à la fois la température et la concentration en fer d'un plasma d'arc de soudage. Le chapitre 3 est dédié à l'étude expérimentale d'un plasma d'arc MAG constituée d'une analyse spectroscopique permettant de remonter au profil de température et tester l'hypothèse de l'Équilibre Thermodynamique Local. La température d'excitation est obtenue par la méthode de Boltzmann tandis que la mesure d'élargissement de Stark pour les raies de fer et d'argon permet de remonter à la température et la densité des électrons. / This PhD thesis introduces a method that allows the fast determination of temperature and iron concentration for MAG-P Arc. The MAG-P Arc is in fact [Ar-CO2]-Fe mixtures, with a constant molar ratio between Ar and CO2 [82%Ar-18%CO2]. In a second time, this thesis presents a study of the optical radiation associated to photobiological hazards for argon GTAW Arc. In chapter 1, the background and motivation of this work is introduced. The previous works published in this field are reviewed. In chapter 2, the equilibrium compositions are calculated firstly using the minimization of Gibbs free energy. Then the radiative properties of [Ar-CO2]-Fe plasmas are obtained in the frame of the net emission coefficient (NEC) approach, using the accurate "line by line" method. All significant radiative contribution mechanisms are taken into account in the calculation. This study will constitute a groundwork to build the diagnostic method that allows determination of temperature and iron concentration profiles in welding arc. In chapter 3, spectroscopic investigation of the LTE hypothesis across the MAG-P Arc is made. Excitation temperature is obtained with Boltzmann plot method while iron and argon lines Stark broadening measurements are used to get electron temperature and electron density. LTE hypothesis validity across the arc is discussed considering the agreement between the two temperatures, the electron density and iron content. Results show supporting evidence for the main part of the plasma, along radial and axial directions. Discrepancies occur only at the fringe of the arc, where the two temperatures differ by more than 2000 K. In chapter 4, a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase is introduced. This method consists in measuring the plasma spectral radiation of the arc with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570-590 nm and 606-627 nm respectively; calculating theoretically the dependence of the absolute emissivity e570-590 nm and relative emissivity e570-590 nm/e607-627 nm versus the plasma temperature and the iron concentration. This method has also been validated for a layer of plasma by adopting other existing diagnostics such as Stark broadening, which demonstrates the effectiveness of this new method. In chapter 5, a theoretical investigation of the UV (180-400 nm), UVA (315-400 nm) and blue light (300-700 nm) radiation associated with the photobiological hazards to workers for argon GTAW arcs is presented. The radiative properties of argon plasma are calculated for the three spectral regions, and a two-dimensional model of a GTAW arc is then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment. Finally, a general conculsion is given in chapter 6.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

This thesis contains a brief summary of the theoretical applications of plasma discharges, and a description of the principle Gliding Arc plasma source. The practical part is focused on the research of the influence ofcereal seed treatment using plasma discharge on their nutritional value (dry matter, ash, protein and fiber). In the conclusion of this thesis is evaluation of the whole experiment.

<div> <p>The electric arc furnace (EAF) is one of the most widely-used steelmaking process recycling the scrap as the raw material. Electric arc furnace steelmaking is a material-dependent and energy-consuming process. The electricity is utilized as the main heat source to melt the scrap by the electric arc discharging from the graphite electrodes. Since the plasma arc weld has the very similar heat transfer mechanism and melting phenomenon comparing with the scrap melting in EAF process, the model development for the free-burning arc, the arc-metal heat transfer, and the metal melting will refer to the research of plasma arc weld field and start with a relatively small scale. In this study, a comprehensive computational dynamics (CFD) model was developed to predict the heat transfer from the electric arc to the metal anode, which is composed of the DC electric arc model, solidification and melting model, and the arc-metal heat transfer model. The validation of the CFD models has been conducted utilizing the experimental data and simulation results in other literature. The commercial software, ANSYS FLUENT^®, was employed with the User-Defined Function scripts and the User-Defined Scalar to model the magnetic field, comprehensive flow field, and high temperature field. Furthermore, the parametric studies for the process of the anode melted by the plasma arc were performed to investigate the effects of the arc current and the initial anode temperature on the anode melting. The results reveal that the value of the arc current has a positive correlation with the arc temperature and velocity but has negative correlation with the penetration time of the anode. Meanwhile, with the increase of anode initial temperature, the metal penetrate time will decrease.</p> </div> <br>

Dans le domaine des dépôts réalisés par projection thermique, les dernières recherches ont permis de développer des dépôts nanostructures par projection de suspensions (SPS) ou de solutions de précurseurs (SPPS). L’injection de liquide est une technique prometteuse qui a le potentiel pour devenir industriellement viable. Cependant, un meilleur contrôle des interactionsplasma/matériaux est nécessaire. En effet, les torches à courant continu mono-cathodes génèrent un plasma fortement fluctuant qui modifie les transferts thermiques et dynamiques vers les gouttelettes injectées, entraînant un traitement non-homogène de ces dernières. Cela influence directement les microstructures des dépôts obtenus et leurs propriétés. Des travaux antérieurs ont montrés les origines de ces instabilités. Une alternative à l’atténuation de ces instabilités est proposée : le renforcement et la modulation. L’ajustement des paramètres opératoires a permis d’obtenir un plasma pulsé laminaire avec modulation de ces propriétés. Une torche à courant continu modulé de faible puissance est utilisée avec de l'azote pur comme gaz plasmagène. Ce dispositif est synchronisé avec un système d'injection jet d’encre Drop-On-Demand pour reproduire les mêmes conditions d'interactions plasma / matériau pour chaque gouttelette injectée. Des solutions et des suspensions sont injectées pour réaliser des dépôts homogènes avec une microstructure contrôlée. Les objectifs de ces travaux sont d'abord de caractériser et de comprendre les transferts thermiques et dynamiques plasma / gouttelettes. Deuxièmement, de mettre en évidence l'influence de la synchronisation et des paramètres opératoires sur les dépôts obtenus. / In the field of thermal spray coating processes, research has led to the development of nanostructured coatings by suspension plasma spraying (SPS) and precursor solution plasma spraying (SPPS). Liquid injection are promising techniques with the potential to become industrially viable. However, a better control of plasma/material interactions is necessary. Mono-electrode DC torches indeed generate strongly fluctuating plasma that modifies the thermal and dynamic transfers to the injected droplet, resulting in an inhomogeneous treatment of the latter. This directly influences the texture and microstructure of deposits and subsequently their properties. Previous works have shown the origins of these instabilities. As an alternative to instabilities attenuations, a new approach is proposed: the reinforcement and modulation of the instabilities. The adjustment of process parameters has allowed obtaining a pulsed laminar plasma with a modulation of its properties. A low powered home-made modulated DC torch is used and operates with pure nitrogen as plasma forming gas. This device is synchronized with a Drop-On-Demand injection system to reproduce the same conditions of plasma/material interactions for each injected droplet. Solutions and suspensions are injected to make homogeneous coatings with controlled microstructure. The objectives of this work are firstly to characterize and understand plasma / droplet heat and dynamics transfers. Secondly, to highlight the influence of the synchronization and operating parameterson the coatings obtained.

<p>The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electrodes and burners. The migration to EAF steelmaking has accelerated in the steel industry over the past decade owing to the consistent growth of the scrap market and the goal of "green" steel production. The EAF production already hit a new high in 2018, contributing to 67% of total short tons of U.S. crude steel produced. The EAF steelmaking process involves dynamic complex multi-physics, in which electric arc plasma and coherent jets coexist resulting in an environment with local high temperature and velocity. Different heat transfer mechanisms are closely coupled and the phase change caused by melting and re-solidification is accompanied by in-bath chemical reactions and freeboard post-combustion, which further creates a complicated gas-liquid-solid three-phase system in the furnace. Therefore, not all conditions and phenomena within the EAF are well-understood. The traditional experimental approach to study the EAF is expensive, dangerous, and labor-intense. Most of the time, direct measurements and observations are impossible due to the high temperature within the furnace. To this fact, the numerical model has aroused great interest worldwide, which can help to gain fundamental insights and improve product quality and production efficiency, greatly benefiting the steel industry. However, due to the complexity of the entire EAF steelmaking process, the relevant computational fluid dynamics (CFD) modeling and investigations of the whole process have not been reported so far. </p> <p><br></p> <p>The present study was undertaken with the aim of developing the modeling methodologies and the corresponding comprehensive EAF CFD models to simulate the entire EAF steelmaking process. Two state-of-the-art comprehensive EAF CFD models have been established and validated for both the lab-scale direct current (DC) EAF and the industry-scale alternating current (AC) EAF, which were utilized to understand the physical principles, improve the furnace design, optimize the process, and perform the trouble-shootings.</p> <p><br></p> <p>For the lab-scale DC EAF, a direct-coupling methodology was developed for its comprehensive EAF CFD model which includes the solid steel melting model based on the enthalpy-porosity method and the electric arc model (for lab-scale DC arc) based on the Magneto Hydrodynamics (MHD) theory, so that the dynamic simulation of the steel ingot melting by DC arc in the lab-scale furnace can be achieved, which considered the continuous phase changing of solid steel, the ingot surface deformation, and the phase-to-phase interaction. Both stationary DC arc and the arc-solid steel interface heat transfer and force interaction were validated respectively against the experimental data in published literature. For the given lab-scale furnace, the DC arc behavioral characteristics with varying arc lengths generated by the moving electrode were analyzed, and the effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were revealed.</p> <p><br></p> <p>For the industry-scale AC EAF, an innovative integration methodology was proposed for its comprehensive EAF CFD model, which relies on the stage-by-stage approach to simulate the entire steelmaking process. Six simulators were developed for simulating sub-processes in the industry-scale AC EAF, and five models were developed for the above four simulators, including the scrap melting model, the electric arc model (for industry-scale AC arc), the coherent jet model, the oxidation model, and the slag foaming model, which can be partially integrated according to the mass, energy, and momentum balance. Specifically, the dual-cell approach and the stack approach were proposed for the scrap melting model to treat the scrap pile as the porous medium and simulate the scrap melting together with its dynamic collapse process. The statistical sampling method, the CFD-compatible Monte Carlo method, and the electrode regulation algorithm were proposed for the electric arc model to estimate the total AC arc power delivery, the arc radiative heat dissipation, and the instantaneous electrode movement. The energetic approach was proposed to determine the penetration of the top-blown jet in the molten bath based on the results from the coherent jet model. The source term approach was proposed in the oxidation model to simulate the in-bath decarburization process, where the oxidation of carbon, iron, and manganese as well as the effect of those exothermic reactions on bath temperature rising was considered. Moreover, corresponding experiments were performed in the industry-scale EAF to validate the proposed simulators. The quantitative investigations and analyses were conducted afterward to explore and understand the coherent jet performance, the AC arc heat dissipation, the burner preheating characteristics, the scrap melting behavior, the in-bath decarburization efficiency, and the freeboard post-combustion status.</p> <p><br></p>

This thesis focuses on an experimental study of the anode area of the hybrid water- gas DC arc plasma torch that is used in many industrial applications, including plasma spraying, hydrocarbon reforming, pyrolysis, and organic waste gasification. The effects of ambient pressure and plasma generation conditions on the torch's plasma jet were studied, with particular focus on the torch's anode area. Movement of the anode arc attachment is described in detail, including its speed, range of its motion on the anode surface, restrike periods, and the frequency of its many sudden decelerations and re-accelerations. It was found that the anode erosion can be compared relatively simply by quick processing of high-speed camera videos. The anode erosion was also measured directly. Many electric probe measurements were made in the anode area of this plasma torch for the first time. By using these electric probes, shock waves, turbulent vortices, and plasma potential fluctuations were studied directly. It was found that a mean plasma electric field and a mean plasma electrical conductivity in the anode area can be satisfactorily estimated also non-intrusively by quick processing of high-speed camera videos. Moreover, schlieren videos of the plasma jet in the anode area were created. 1

Un modèle numérique d’un arc électrique diffus dans un disjoncteur à vide à champ magnétique axial (AMF) a été développé dans le but de mieux comprendre à terme la transition d’un mode de fonctionnement diffus de l’arc vers un mode plus concentré. Le comportement du plasma d’arc a été simulé depuis la sortie de la zone de mélange cathodique jusqu’à l’entrée de la gaine anodique. Le modèle bidimensionnel est basé sur un système d’équations hydrodynamiques à deux fluides non magnétisés (ions et électrons), incluant les équations de conservation d’énergie ionique et électronique. Il est démontré que les processus d’ionisation et de recombinaison et les effets visqueux sont négligeables. Les transferts radiatifs ne sont pas considérés en première approximation. Outre les forces dues au champ AMF, le modèle inclut les forces dues aux trois composantes du champ magnétique induit par l’arc. Deux régimes d’écoulement des ions, supersonique (aux faibles densités de courant) et subsonique (aux fortes densités de courant), sont considérés. Près de la cathode, les conditions aux limites sont spécifiées à partir de résultats de la littérature. A proximité de l’anode, elles sont basées sur une description simplifiée de la gaine anodique. Les résultats de simulation présentés mettent en évidence une constriction du courant et un comportement différent des ions aux faibles et aux fortes densités de courant, et renseignent sur l’influence de divers paramètres (intensité du courant, distance interélectrode). Ce travail présente également une étude expérimentale, basée sur des visualisations par vidéo rapide de l’arc et des mesures pyrométriques de la température de la surface de l’anode / A model of a diffuse arc in a vacuum circuit breaker with an axial magnetic field (AMF) has been developed with the ultimate aim to better understand the transition of the arc from a diffuse mode to a more confined mode. The interelectrode plasma is simulated from the exit of the mixing region on the cathode side to the entrance of the anode sheath. The two-dimensional model is based on the solution of a system of two-fluid (ions and electrons) hydrodynamic equations, including in particular the energy balance equations relative to both the ions and the electrons, which are treated as non-magnetized particles. It is demonstrated that ionisation and recombination processes, as well as viscous effects, can be neglected. Radiation losses are not taken into account in a first approximation. In addition to the forces due to the AMF, the model considers the forces created by the three components of the magnetic field induced by the arc current. The possibility of both supersonic (at low current density) and subsonic (at high current density) ionic flow regimes is considered. On the cathode side, the boundary conditions are specified using results from the literature. On the anode side, they are based on a simplified description of the anode sheath. The simulation results presented show a constriction of the current lines, emphasize the differences in the behaviour of the ions at low and high current densities, and provide some insight on the influence of various operating parameters (arc current, gap length). The present work comprises also an experimental study, based on high-speed camera visualisations of the arc and measurements of the temperature at the anode surface

Hlavním cílem práce je studium radiačního přenosu energie v termálním plazmatu pomocí aproximační metody sférických harmonických funkcí (PN-aproximace). Práce má teoretický charakter. Pozornost je věnována především P1-aproximaci. Spektrální závislost absorpčních koeficientů byla zpracována pomocí multigroup aproximace. Byl vytvořen výpočetní program pro výpočet radiačních charakteristik v izotermickém válcovém plazmatu a ve válcovém plazmatu s daným teplotním profilem, a vypočteny radiační charakteristiky pro plazma vzduchu a směsí SF6 a PTFE. Získané výsledky umožňují zahrnout radiační ztráty energie do celkové energetické bilance plazmatu elektrického oblouku. Jsou využívány v matematických modelech elektrického oblouku, které vytváří naši spolupracovníci z Ústavu fyziky plazmatu AV ČR v Praze a také ze zahraničních pracovišť (ABB Corporate Research ve Švýcarsku a Siemens AG Corporate Technology v Německu).

This master´s thesis si focused on determinig methodology of optical diagnostics of the switching arc using the high-speed camera Photron SA-X2. The thesis contains basic rules for proper setup of the measurement system and the rules to adjust the camera exposure. The experiments were performed on the prototype of a parametric switching chambre, while the majority of source materials was derived from the requirements of another study which was aimed on the movement of the electode spots. The process of the first adjustment of the camera, a record edit options for the presentation purposes and the process of the 3D model design of the switching arc in SketchUp software was stated. Paper contains a comparsion of the spectral filter effect and neutral density filter effect on the final record as well. The part of the work outputs are the 3D model of the switching arc and the supporting record editing software. The paper results show a degree of the inaccuracies in a optical diagnostics made from only one direction caused by the lack of the information about third dimension.