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This paper is dedicated to the calculation of the radiative properties of 82%argon-18%CO2 thermal plasmas with the addition of metallic vapors (iron, in the present case, due to workpiece and wire erosion), this mixture being representative of metal active gas (MAG) arc welding processes. These radiative properties are obtained in the frame of the net emission coefficient (NEC) theory, using the recent and accurate “line by line” method. All significant radiative contribution mechanisms are taken into account in the calculation: atomic lines, atomic continuum (radiative attachment, radiative recombination, and bremsstrahlung), molecular bands for diatomic and polyatomic molecules, and molecular continuum. Broadening phenomena (Doppler and pressure effects) are also carefully treated for bound-bound transitions (atomic lines and molecular bands). Regarding 82%Ar-18%CO2 plasma, the results obtained demonstrate the key role of molecular bands at low temperatures (T < 4 kK), whereas the atomic line and continuum prevailed at intermediate and high temperatures. With the addition of a few percentages of iron vapor, it was shown that the total NEC is significantly increased (especially at low temperatures) and that the atomic and ionic lines become dominant in all the studied temperature ranges (3–30 kK). This theoretical study will constitute a groundwork to build a diagnostic method (based on the calculation of partial NECs for accurately chosen spectral intervals) for the determination of plasma temperature and iron vapor concentration in welding arcs.

Multi-wire welding has received much attention in the machinery industry due to its high efficiency. The aim of this study was to investigate a novel pulse gas metal arc welding (GMAW) that has circular triple-wire electrodes. The effect of the pulse phage angle on arc stability was particularly studied. Research showed that for typical phase angles the arc stability from low to high is 180&deg, 0&deg, and 120&deg, and the arcs are very stable at 120&deg, The triple-wire welding was used to weld a 9 mm thick Q960E steel, which is typically used for the arm of construction machinery. When the welding heat input was controlled at 1.26&ndash, 1.56 kJ/mm, the weld zone was dominated by acicular ferrite, and the coarse-grained zone of the heat-affected zone was a mixed structure of lath martensite and lath bainite. The tensile strength of the welded joint reached 85% of the base metal and the impact toughness was above 62 J, which can meet the requirements of construction machinery. This indicates that the triple-wire welding has great potential to achieve efficient and high-quality welding for the construction machinery.

This tutorial is intended to provide a basic overview of non-equilibrium phenomena for thermal plasmas. Thermal plasmas (TPs) mainly issued from electrical discharges are often assumed to be in ≪ equilibrium ≫ as opposed to ≪ non-equilibrium plasmas ≫ where non-equilibrium phenomena are more pronounced. As a first approximation it can be shown that TPs are close to a local thermodynamic equilibrium (LTE) which is often taken as their reference state. However, in many situations, deviations from LTE can clearly exist. The main goal of this brief tutorial is to explain to interested scientists the main phenomena, mechanisms and characteristics associated to TPs or quasi-TPs. Then we introduce the different laws of the thermodynamic equilibrium applied to these plasmas and show that not all of them are valid in TPs, which lead us to define the LTE. However, even if the transport phenomena are non-equilibrium mechanisms, we show with illustrations that they are studied and estimated within the framework of the LTE. The next sections focus on phenomena named ‘departures from equilibrium’ for thermal plasmas. For convenience and educational reasons, we split them into the departures from the chemical and the thermal equilibria respectively. In each case we present and clearly define the mechanisms that promote equilibrium and those that tend to create departures. We present not only experimental setups that highlight these deviations but also the basis for the mathematical models that allow them to be simulated, before concluding the tutorial with the outlooks and challenges currently under research.

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SF6 is widely used in the industrial field due to its stable structure and excellent properties. It is mainly used in electrical insulation equipment. Due to the boiling point of SF6, its use in extremely cold regions has been limited. It is harmful to the health of practitioners due to the toxicity of decomposition products. The gas has limited its wider use because of its strong greenhouse effect. As a result, researchers and electrical equipment manufacturing companies around the world are gradually searching for new environmentally friendly gases and have conducted research and exploration on theory and experiment. In this paper, the current status and existing problems of SF6 are summarized. The research contents and research methods of SF6 alternative gas direction are reviewed from the aspects of insulation performance, interrupter performance, and decomposition performance. The existing research results of the natural gas, SF6 mixed gas, perfluorocarbons, and CnFmX gas are summarized, and the future development trend of alternative gas for SF6 in the electrical industry is proposed.

Gas tungsten arc welding (GTAW), a widely used industrial process, is one of the most intense artificial sources of optical radiation. This paper presents 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. The radiative properties of argon plasma were calculated and discussed for the three spectral regions of interest at temperatures from 5000–25,000 K and atmospheric pressure. A two-dimensional model of a GTAW arc was then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This model is also used to study the influence of the welding parameters (current intensity and arc length) on the radiative properties and the effective irradiances. The permissible exposure durations for skin and eyes were further evaluated according to the radiation exposure standard of the Directive 2006/25/EC for the three spectral intervals. It is found that the UV radiation is most hazardous among these spectra. Indeed, it is shown that the UV permissible exposure duration is very short, e.g. from 5.89 s to 9.8 min at the distances from 0.5 m to 5 m for a typical GTAW arc (200 A and 5 mm arc length). This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment.

This work concerns the calculation of electron-impact excitation and ionisation cross sections and reaction rate coefficients for carbon, nitrogen and oxygen atoms. Several analytical formulas proposed in the literature are used to calculate cross sections and rate coefficients for excitation of optically allowed and parity/spin forbidden transitions and for ionisation from electronic levels of the atoms. Theoretical calculations are then compared with each other and confronted to available experimental cross sections in order to deduce the most accurate analytic rate coefficient formula, which will be used in the implementation of Collisional-Radiative (CR) model for C-N-O-containing plasmas. The cross section and the reaction rate database created will be used in the development of a multi-temperature CR model allowing the determination of the population number densities inside an electric arc generated between two graphite electrodes and dedicated to the synthesis of carbon nanoparticles.

This work is devoted to the study and comparison of theories to calculate densities of chemical species in a SF6 plasma in thermal non equilibrium conditions. The limits of the 2T law of mass action are shown. Then, the reaction rates are studied for several types of processes and they are implemented in a chemical kinetic model to acess the composition of the plasma. Finally, a comparison with the densities obtained with the law of mass action is performed and the results are discussed.

International audience; This paper focuses on the 3D MHD modeling of a very high-pressure (20 bar) arc plasma at industrial level; the torch is a 'Kvaerner-type' one, made of two concentric graphite electrodes and where spots are displaced with an external magnetic field. Different phenomenologies in arc movement were observed, ranging from a gliding arc on electrodes surfaces to hopping arc foots and notably impacting electrodes erosion and the overall efficiency in the plasma process. Besides those dynamics which are indebted to torch configuration, current and flow rates, arc stability is also investigated with a theoretical model based on an energy principle. This research work provides new insight on the dynamics and stability of the arc inside the Kvaerner-type torch along with an unprecedented understanding of the very high pressure arc under concentric-electrodes-configuration, highlighting strong deformations due to pressure-driven instabilities for the high power arc.

A time-saving method is proposed to evaluate the arc quenching ability for a gas by combining the 1-D hydrokinetic modeling and Boltzmann equation analysis. In this method, the arc decaying process is divided into three stages, i.e., thermal recovery, predielectric recovery, and postdielectric recovery stages. The parameters, namely, thermal recovery rate, predielectric recovery rate, and postdielectric recovery rate are calculated to feature the characteristics of the corresponding stages. By using these parameters different gases are easy to be compared. We demonstrate this method by comparing the arc quenching performance of SF6, CO2, CF4, and air. It is found that the orders of the arc quenching ability for the four gases in different stages are as follows: 1) thermal recovery stage: SF6 > CF4 > CO2 > air; 2) predielectric recovery stage: SF6 >CO2 > CF4 > air; and 3) postdielectric recovery stage: SF6 > CF4 > air > CO2.

International audience; This paper focuses on the 3D MHD modeling of an arc plasma at industrial level; the torch is a 'Kvaerner-type' one, made of two concentric graphite electrodes and where spots are displaced with an external magnetic field. Different phenomenologies in arc movement were observed, ranging from a gliding arc on electrodes surfaces to hopping arc foots, agreeing with previous experimental works at atmospheric pressure. These dynamics have non-negligible consequences in the plasma process: the hopping mode induces more erosion due to a higher heat flux at the electrodes surfaces in comparison to the gliding arc; the latter mode results also in a strong gas swirling inside the torch, thus longer particles residence time is predicted.

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International audience; This paper is focused on the state-of-the-art and challenges concerning the thermophysical properties of thermal plasmas used in numerical modelling devoted to high voltage circuit breakers. For Local Thermodynamic Equilibrium (LTE) and Non-Local Thermodynamic (NLTE) and/or Chemical Equilibrium (NLCE) plasmas, the methods used to calculate the composition, thermodynamic, transport and radiative properties are presented. A review of these last data is proposed and some comparisons are given for illustrations.

In metallurgic applications of thermal plasmas the presence of metal vapour, even in small proportion tends to increase the electron number density and to modify some basic properties such as the electrical conductivity and the radiation emission. In this paper we focus on the influence of these vapours on the radiation properties. After the definition of some necessary and basic functions and laws we briefly present the mechanisms responsible for emission and absorption of radiation in thermal plasmas. Then an important section is devoted to the role of metal vapours on the net emission coefficient which is the most popular parameter used to evaluate the radiation power losses in general models. It is shown that metal vapours increase the emission especially at low and intermediate temperatures (T

Vortex-stabilized water-wall arc lamps are used in rapid thermal processing applications. A key issue is to develop more accurate models so that better control is achieved of the temporal radiation exiting the lamp. The current problem is the lack of a practical means of incorporating radiative transfer. This paper shows that it is possible to obtain a good qualitative understanding of the arc and reasonable quantitative agreement with experiments using the net emission coefficient method to model the isothermal core region of the plasma and a modified version of the mean absorption method to model the surrounding colder regions of the plasma.

International audience; The c-C4F8 gas is considered to have great potential as a gaseous medium for gas-insulated equipment, due to its good insulation properties and its relatively low greenhouse gas potential (GWP) relative to SF6. However, the decomposition is an important indicator of its use in equipment. In this paper, the decomposition characteristics of c-C4F8 and the influence by oxygen have been explored through experiments and theoretical calculations. Firstly, the breakdown test of mixed gas was carried out and the precipitated elements of the electrodes and breakdown products of gas mixture were analyzed by X-ray photoelectron spectroscopy (XPS) and gas chromatography mass spectrometry (GC-MS). At the same time, the differences in decomposition products have also been studied when a small amount of O2 was present. The path and mechanism of c-C4F8 decomposition is then discussed, based on density functional theory (DFT). The results show that the black powdery substance descends on the electrode surface after the breakdown of the mixture of c-C4F8/N2 gas containing O2, and its main constituent elements are C, O and F. O2 can promote the decomposition of c-C4F8. The mixture with O2 produced a large number of additional toxic and corrosive COF2 in addition to generating more CF4, C2F4, C2F6, C3F6 and C3F8. The GWP values of the products are lower than SF6. Comprehensive insulation properties and decomposition characteristics, c-C4F8 should not be mixed with dry air for use, and the oxygen content should be strictly controlled in c-C4F8 mixed gas.

International audience

The c-C4F8 gas is considered to have great potential as a gaseous medium for use in gas-insulated equipment due to its good insulation properties and its relatively low greenhouse gas potential (Global warming potential, GWP) relative to SF6. In this paper, the breakdown characteristics of c-C4F8/N2 gas mixtures are explored through the experimental and theoretical calculations and the influence of a small amount of oxygen in the mixtures is discussed. The breakdown tests were conducted under AC voltage. With the mixing ratio of c-C4F8 at 15%, the breakdown voltage of different oxygen contents was tested at 0.15 MPa. At the same time, the self-recovery performance of gas mixture was tested by several times breakdown test, and the breakdown voltage of mixed gas was calculated according to the Townsend self-sustaining discharge condition. The results show that the addition of O2 significantly reduced the breakdown voltage of the c-C4F8/N2 mixed gas, and the self-recovery characteristics of the mixed gas containing 3% O2 are significantly lower than that of the c-C4F8/N2 without O2. The calculation results of breakdown voltage are consistent with the test results. It is considered that the content of oxygen in the mixed gas of c-C4F8 should be strictly controlled.

C4F8-CO2 mixtures are one of the potential substitutes to SF6 in high-voltage circuit breakers. However, the arc quenching ability of C4F8-CO2 mixtures is still unknown. In order to provide the necessary basic data for the further investigation of arc quenching performance, the compositions, thermodynamic properties, transport coefficients, and net emission coefficients (NEC) of various C4F8-CO2 mixtures are calculated at temperatures of 300–30 000 K in this work. The thermodynamic properties are presented as the product of mass density and specific heat, i.e., ρCp. The transport coefficients include electrical conductivity, viscosity, and thermal conductivity. The atomic and molecular radiation are both taken into account in the calculation of NEC. The comparison of the properties between SF6 and C4F8-CO2 mixtures is also discussed to find their differences. The results of compositions show that C4F8-CO2 mixtures have a distinctive advantage over other alternative gases e.g., CF3I and C3F8, because the d...

This paper deals with the calculation of net emission coefficients (NECs) for CO–H2 thermal plasmas. This task required the elaboration of a complete spectroscopic database including atoms and molecules formed by carbon, oxygen and hydrogen elements. We have used a systematic line by line method to calculate all the main radiative contributions which are the atomic and molecular continua, the atomic lines and the molecular (diatomic and polyatomic) lines. The main diatomic electronic systems for CO–H2 plasmas and the triatomic molecular bands were considered. We present some variations of the net emission coefficient versus temperature, for various pressures and for two relative proportions of the components. The role of the diatomic molecules is important at temperatures lower than 5000 K whereas the net emission coefficient presents an unusual peak at temperature around 1000 K, due to the presence of the CO2 molecule presenting a strong infrared radiation. Finally, the results show that the NEC slightly depends on the relative proportion of CO and H2.

This work is devoted to the calculation of the composition for a monoatomic plasma (argon in the case presented) for which the assumption of thermal equilibrium is not realized. The plasma composition is obtained from a CR model, taking into account free electrons and a great number of electronic levels of Ar atoms and Ar+ ions. This model is based on a large set of transition probabilities and reaction rate coefficients for radiative processes (spontaneous emission and radiative recombination) and on an extended database of direct and reverse reaction rate coefficients for collisional processes (excitation/de-excitation and ionization/recombination mechanisms). Assuming Maxwellian energy distribution functions for electrons and heavy chemical species, detailed balance equations are determined for all kind of reactions in the frame of the micro reversibility principle. From these balance equations, reverse rate coefficients are calculated as a function of direct reaction rates and of electrons and heavy particles translation temperatures (T e and T h respectively). Particular attention is paid to problematic chemical reactions with electrons involved on one side and only heavy species on the other side such as: Ar + Ar → Ar + Ar+ + e. The detailed balance relations obtained for ionization/recombination processes demonstrate the non-uniqueness of the multi-temperature Saha-Eggert law (i.e. non-uniqueness of the multi-temperature law of mass action). Multi-temperature argon plasma compositions obtained in the present work exhibit abrupt density variations. These sharp variations are characteristic of the transition between the domination of heavy particle reactions (at low temperature) and the predominance of electron collisions (at high temperature).

A phenomenological picture of pulsed electrical discharge in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying ~350 μs long 100 to 220 V pulses (values of current from 400 to 1000 A, respectively) between the point-to-point copper electrodes submerged into the non-purified tap water. Plasma channel and gas bubble occur between the tips of the electrodes, which are initially in contact with each other. The study includes detailed experimental investigation of plasma parameters of such discharge using the correlation between time-resolved high-speed imaging, electrical characteristics, and optical emission spectroscopic data. Radial distributions of the electron density of plasma is estimated from the analysis of profiles and widths of registered Hα and Hβ hydrogen lines, and Cu I 515.3 nm line, exposed to the Stark mechanism of spectral lines’ broadening. Estimations of the electrodes’ erosion rate and bubbles’ size depending on the electrical input parameters of the circuit are presented. Experimental results of this work may be valuable for the advancement of modeling and the theoretical understanding of the pulse electric discharges in water.

Arc tracking tests have been carried out between two voluntarily damaged aeronautic cables. Copper or aluminum conductors have been exposed to short circuits under alternating current. Various data have been recorded (arc voltage and current, radiated power and ablated mass), enabling to determine a power balance, in which every contribution is estimated. The total power is mainly transferred to the cables (between 50 and 65%, depending on the current and the cable type), and causes the melting and partial vaporization of the metallic core and insulating material, or is conducted or radiated. The other part is deposited into the arc column, being either radiated, convected or conducted.

International audience; This work is devoted to the calculation of the energy balance associated with the formation of an electric arc between the bolt shank and an inner structural part of the fuselage during a lightning strike. Assessment of the pressure build-up in the confined volume around the bolt fastener has also been performed. This pressure rise comes from the temperature increase and from the mass density increase (melting and vaporisation of materials). Previous electrical measurements performed by Airbus Group during a lightning test campaign have been used to calculate the total available electrical energy. The energies necessary for melting and vaporisation of bolt and rib are derived from thermodynamic properties of aluminium and titanium. A numerical code has been developed to determine the chemical composition (under the local thermodynamic equilibrium [LTE] assumption) and the internal energy of the plasma for air-Al/Ti mixtures. Plasma and material radiation losses and heat conduction losses have also been evaluated. Finally, an analytical model has been implemented to determine the overpressure as a function of the deposited electrical energy, the energy involved in the arc formation, the energy necessary for melting and the plasma composition and mass density. With this approach, maximum pressure values are in the range 200–330 bars.

International audience; This paper focuses on the modeling of a hydrogen arc column at very high pressure (20 bar). The problem is solved from Elenbaas-Heller equation where the radiation is carefully considered with the net emission coefficient. The absorption spectrum requires the integration of background continuum, molecular bands, and line spectra. This work directly aims to predict the electric current-voltage characteristics which is key for the design of new processes. We propose also a new analytic solution which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the energy balance. The presented formalism allows a better determination of the plasma thickness parameter Rp for net emission coefficient method in cylindrical arcs and gives satisfactory results in comparison to earlier experimental works on high pressure hydrogen plasma.

A method based upon the weighted total cross section (WTCS) theory is proposed to calculate the photo-ionisation cross sections and the radiative recombination rate coefficients between the fundamental level of CO and the main electronic states of its corresponding ion. Total photo-ionisation cross sections and radiative recombination rate coefficients are determined from the calculation of elementary vibrational photo-ionisation cross sections. Transitions between CO+(X, A and B) and CO(X) are considered. Total photo-ionisation cross sections and recombination coefficients are computed in the temperature interval 500–15000 K.

This paper focuses on the calculation of the radiative transition probabilities for the main diatomic molecules contributing to the discrete radiation of CO–H2 syngas plasma. We propose extensive tables of rovibrational transition probabilities for the main electronic systems of OH, CH, CH+, CO and CO+. The rotational dependence of the nuclear wave-functions was included in our calculations to take into account the coupling between the rotational and vibrational motions. References are also given to data for O2, C2 and H2 molecules already published in the literature. The calculations were performed using the Rydberg–Klein–Rees (RKR) inversion procedure for the reconstruction of the potential-energy curves and an improved Numerov-type method was used to obtain the rovibrational wave-functions by solving the radial Schrodinger equation. We rigorously selected the most up-to-date equilibrium spectroscopic constants for the RKR procedure and the most accurate electronic transition moment functions (ETMF) available in the literature. The results obtained with this procedure were systematically validated by comparison with available experimental observations.

SF6 is widely used in electrical equipment as an insulating medium. However, SF6 is a serious greenhouse gas. CF3I is considered as one of its potential alternatives. This study verifies whether free metal particle (Cu, Al, or Fe) defects adversely affect CF3I insulation and investigates the incidence from different types and numbers of metal particles. This study is also devoted to calculating specific heat at constant pressure and electrical conductivity of CF3I–metal mixtures. The calculation results prove that with the increase of metal ions, temperature rises faster in the CF3I–Cu plasma or in the CF3I–Fe plasma than in the CF3I plasma without metal absorbing the same energy. The fast development of ionization can promote the increase of free electrons and the rise of electric conductivity. On the basis of the experiments and theoretical analysis, the influence of Cu and Al on the insulating capacity of CF3I is greater than that of Fe.

CO2-N2 mixtures are often used as arc quenching medium (to replace SF6) in circuit breakers and shielding gas in arc welding. In such applications, copper vapour resulting from electrode surfaces can modify characteristics of plasmas. This paper therefore presents an investigation of the effects of copper on thermophysical properties of CO2-N2 plasma. The equilibrium compositions, thermodynamic properties (including mass density, specific enthalpy, and specific heat), transport coefficients (including electrical conductivity, viscosity, and thermal conductivity), and four kinds of combined diffusion coefficients due to composition gradients, applied electric fields, temperature gradients, and pressure gradients respectively, were calculated and discussed for CO2-N2 (mixing ratio 7:3) plasma contaminated by different proportions of copper vapour. The significant influences of copper were observed on all the properties of CO2-N2-Cu mixtures. The better ionization ability and larger molar mass of copper and larger collision integrals related to copper, should be responsible for such influences.

As the first part of this series of papers, a new calculation method for composition and thermodynamic properties of 2-temperature plasma considering condensed species under local chemical equilibrium (LCE) and local phase equilibrium assumption is presented. The 2-T mass action law and chemical potential are used to determine the composition of multiphase system. The thermo-physical properties of CO2–CH4 mixture, which may be a possible substitution for SF6, are calculated by this method as an example. The influence of condensed graphite, non-LTE effect, mixture ratio and pressure on the thermo-physical properties has been discussed. The results will serve as reliable reference data for computational simulation of CO2–CH4 plasmas.

The metallic vapours (i.e., copper, iron, and silver in this paper) resulting from walls and/or electrode surfaces can significantly affect the characteristics of air plasma. Different from the previous works assuming local thermodynamic equilibrium, this paper investigates the influence of metallic vapours on two-temperature (2 T) air plasma. The 2 T compositions of air contaminated by Cu, Fe, and Ag are first determined based on Saha's and Guldberg–Waage's laws. The thermodynamic properties (including mass density, specific enthalpy, and specific heat) are then calculated according to their definitions. After determining the collision integrals for each pair of species in air-metal mixtures using the newly published methods and source data, the transport coefficients (including electrical conductivity, viscosity, and thermal conductivity) are calculated for air-Cu, air-Fe, and air-Ag plasmas with different non-equilibrium degree θ (Te/Th). The influences of metallic contamination as well as non-equilibr...

In the field of lighting and for devices such as big panels, leds remain less interesting compared with the high-pressure lamps which are preferred for their high illumination coupled to a correct IRC index and lifetime. For these lamps, the challenges consist in illuminating most efficiently in the visible spectral region and in reducing mercury inside the lamps. Among the solutions, we can put in additives having a high power radiation (calcium, sodium, dysprosium, thallium, and strontium), and\or find free mercury gases (mercury being usually mixed with pure argon). For such mixtures at high pressure, the radiative spectrum goes from UV to IR radiations. The UV radiations can be very important and could be absorbed and converted by phosphors in order to increase the visible light and reduce the skin diseases. Unfortunately, adding phosphors leads to expensive post-treatments. A theoretical study of the radiative spectrum seems more adapted and cheaper to estimate the radiation emitted in the IR, visible and UV regions. This radiative energy is often deduced according to simplified approaches1. Here, we propose a more accurate method, usually applied to evaluate the divergence of the radiative flux in thermal plasma modeling: the Net Emission Coefficient2. This method allows a good and rapid estimation of the total power emitted by the center of the lamp, by keeping a good description of the radiative mechanisms in the different spectral intervals (IR, visible and UV). The lamps we are studying work with a primary gas between 10–500 mbar, 5–40 mg/cm3 mercury, and metallic additives between 1 and 30 mg/cm3. The partial pressures are 200 mbar for Ar, 10 bar for Hg and 1 bar for metallic species with maximal temperatures around 5500K in the center of the lamp and plasma size of 1mm. We present the radiation emitted in the three spectral regions for different mixtures: 89%Hg-2%Ar-9% additives, the binary mixture 98%Hg-2%Ar often used in lamps, and a ficticious binary free mercury mixture at 11.2bar. The results show the radiation proportion emitted in each spectral interval (IR, visible and UV), and allow us to evaluate the UV part that can be converted in visible light. We also show the increase of the radiative power due to the presence of the metallic species and particularly in the visible and UV regions. The free mercury mixture is studied in order to evaluate the capacity of free mercury lamps to be good candidates.

In the field of the electrical installation protection, and more particularly for high voltage circuit breakers, one of the most important challenges is to find new gases to replace SF6 and reduce the greenhouse effects. Among the several candidates such as CO2, air, vacuum or g31, the recent studies on CF3I highlight interesting electrical and thermal properties2 for this gas. Unfortunately, these studies only consider pure CF3I gas or CF3I mixed with other gases such as N2, air, CO22. Yet, during the creation of an electrical arc between the two electrodes, several metallic vapors issued from the electrodes' erosion and mixed with pure CF3I gas strongly modify the electrical ad thermal properties of the initial gas. This work proposes to study the influence of the copper, iron or aluminum metallic vapors on the thermal properties of CF3I for a pressure of 6 bar, temperatures from 300K to 30000K and concentrations of vapors between 0% and 50%. The mass density and specific heat at constant pressure are directly deduced from the population number densities of the species, their partition functions and their enthalpies of formation. Electrical conductivity, thermal conductivity and viscosity are obtained according to the Chapman-Enskog method2 and using the collision integrals calculated from theoretical expressions or given in the literature. The results show that few proportions of metallic vapors (less than 1%) strongly increase the electrical conductivity at low temperature, modify the thermal conductivity around 5–7kK and the viscosity around 10kK for proportions higher than 20%. We compare the transport properties for the three metallic vapors and highlight the strong effect of the species having the lowest ionization potential on the electrical conductivity. Coupled with the electrical properties and the radiation losses, these database will enable us to estimate the interruption capability of CF3I in presence of metallic vapors and consequently, to conclude on the use of CF3I as a good alternative to replace SF6 in high voltage circuit breakers.

International audience; This computational fluid dynamics work is dedicated to the study of heat and mass transfer in a new 100-kW three-phase ac/50 Hz plasma torch operating with air. The transient behavior of the arc is simplified using time-averaged heat and momentum source inputs in a stationary source volume whose form was chosen according to the results from a separate magnetohydrodynamic calculation. A parametric study of source volume and momentum intensity is conducted and shows a little influence on the overall temperature and velocity fields. Radiation from gas and walls is taken into account using the discrete ordinate model. Air radiation data consider both atomic and molecular contributions in the temperature range between 300 and 30 000 K and for the wavelengths from 0.209 \mu text{m} to the far infrared. The results show a huge impact of radiation on wall temperature and heat losses. Two different methods, Planck and Rosseland, are used for the calculation of mean absorption coefficients. Although Planck’s average is recommended in this case, the absolute temperature difference between both averages is below 13%. Finally, this paper allows checking that the temperature of different components of plasma torch remains below the physical limits of the selected materials.