The Virial Effect—Applications for SF6 and CH4 Thermal Plasmas

International audienceA tool based on the mass action law was developed to calculate plasma compositions and thermodynamic properties for pure gases and mixtures, assuming a local thermodynamic equilibrium for pressures of up to 300 bar. The collection of the data that was necessary for tool calculation was automated by another tool that was written using Python, and the formats for the model were adapted directly from the NIST and JANAF websites. In order to calculate the plasma compositions for high pressures, virial correction was introduced. The influences of the parameters that were chosen to calculate the Lennard-Jones (12-6) potential were studied. The results at high pressure show the importance of virial correction for low temperatures and the dependence of the dataset used. Experimental data are necessary to determine a good dataset, and to obtain interaction potential. However, the data available in the literature were not always provided, so they are not well-adapted to a large pressure range. Due to this lack, the formulation provided by L. I. Stiel and G. Thodos (Journal of Chemical and Engineering Data, vol. 7, 1962, p. 234-236) is a good alternative when the considered pressure is not close to the critical point. The results may depend strongly on the system studied: examples using SF 6 and CH 4 plasma compositions are given at high pressure

EXPERIMENTAL STUDY OF A PLASMA BUBBLE CREATED BY A WIRE EXPLOSION IN WATER

International audienceAn experimental setup is developed to study the bubble dynamic created by a wire explosion in a liquid. This arrangement can be encountered in many configurations and processes and differs by the level and frequency of the applied energy and of the liquid nature. In our study the wire explosion is due to a current intensity around one thousand amps during 10ms in a water medium and a distance between the electrodes of few millimeters. By fast imaging the bubble radius is determined versus time depending on the applied energy. The results indicate that the maximum radius of the bubble versus the applied energy leads to a linear variation of 2.3 cm/kJ roughly. A modification of the Rayleigh model is proposed to consider not an empty bubble but pressure variation inside. The experimental results coupled with the Rayleigh model allow determining the maximum bubble radius, the bubble dynamic and to evaluate its mean temperature. For electrical arc energy of 846 J and an inter-electrode distance of 1 mm, the bubble presents an expansion and a collapse. A maximal radius is reached near 4 cm before 1.5 ms the end of the half current period, due to the leak of energy to feed the bubble

A Pressure Based Compressible Solver for Electric Arc-plasma Simulation

The electric arc discharge in a liquid medium is used in several applications such as the sterilization of the liquid by UV radiation, the fracturing of rocks by shock wave, the circuit breakers in oil bath or the forming of mechanical parts. Thus, describing the physics of the arc in a liquid and in particular its interaction with a liquid interface is an important issue to better characterize this type of configuration. However, such a challenging task requires to couple high-fidelity solver for compressible two-phase flows with liquid phase change and a plasma solver to describe the plasma and its interaction with the bubble. To study this type of medium, we use a compressible formulation of the fluid equations. For this purpose, a pressure based solver has been developed for the computation of the energy conservation equation. Moreover, our numerical model uses the immersed boundary method to simulate the solid electrodes. The numerical model is briefly described in this paper and the first results of the electric arc discharge in steam water are presented. To our knowledge this pressure based model has never been used to describe plasmas and electric arc discharge

Heat Transfer in the Solid Cathode of a Hollow Cathode Plasma Torch

After recalling the working principle of hollow cathode plasma torches, we evaluate the heat flux profile on the cathodic arc root. This evaluation takes into account the physics of the cathode sheath. Particular attention is devoted to electron emission from the cold copper cathode. This heat flux profile is then used as a moving boundary condition to obtain the temperature field in the solid cathode with a heat conduction study, with the aim of discussing the problem of its erosion

Interpretation of Stark broadening measurements on a spatially integrated plasma spectral line

In thermal plasma spectroscopy, Stark broadening measurement of hydrogen spectral lines is considered to be a good and reliable measurement for electron density. Unlike intensity based measurements, Stark broadening measurements can pose a problem of interpretation when the light collected is the result of a spatial integration. Indeed, when assuming no self-absorption of the emission lines, intensities simply add up but broadenings do not. In order to better understand the results of Stark broadening measurements on our thermal plasma which has an unneglectable thickness, a Python code has been developed based on local thermodynamic equilibrium (LTE) assumption and calculated plasma composition and properties. This code generates a simulated pseudo experimental (PE) H$\alpha$ spectral line resulting from an integration over the plasma thickness in a selected direction for a given temperature profile. The electron density was obtained using the Stark broadening of the PE spectral line for different temperature profiles. It resulted that this measurement is governed by the maximum electron density profile up until the temperature maximum exceeds that of the maximum electron density. The electron density obtained by broadening measurement is 70% to 80% of the maximum electron density.Comment: European Physical Journal: Applied Physics, EDP Sciences, 202

Etudes expérimentale et numérique d’un arc électrique dans l’eau

Les arcs électriques dans les liquides sont présents dans de nombreux procédés. Cependant, la problématique de la formation et de la dynamique de la phase gazeuse qui entoure l’arc n’est que très peu abordée dans la littérature. De plus, parmi les résultats existants, les analyses peuvent être différentes selon les énergies et les temps de décharge mis en jeu. Afin d’étudier le comportement et de mieux comprendre la dynamique de la bulle, un dispositif expérimental instrumenté et un modèle numérique sont proposés. Dans cette étude un courant AC de quelques kA est appliqué sur 10ms. Il existe un bon accord entre la taille de la bulle donnée par les résultats du modèle et les résultats expérimentaux. Pour une distance inter électrode de 3mm et une énergie appliquée de 1kJ la température dans la bulle à 2,5ms est estimée à 12kK

Compositions chimiques et propriétés thermodynamiques à l’ETL d’un mélange air-CH4

Cet article présente nos travaux relatifs à la détermination de la composition chimique et des propriétés thermodynamiques d’un mélange air-CH4 à l’équilibre thermodynamique local. Le calcul est réalisé dans un intervalle de température de 300 K à  60 kK, et une gamme de pression comprise entre 1 bar et 300 bars. Les corrections de la pression au premier ordre de Debye-Hückel et au second ordre du viriel sont prises en compte pour assimiler le gaz au comportement d’un fluide réel. Les résultats sont confrontés avec ceux de l’air pur. Les différences importantes sur l’enthalpie et la chaleur spécifique à pression constante de ces deux gaz sont mises en évidence

Etude d'un arc de découpe par plasma d'oxygène (modélisation - expérience)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

EXPERIMENTAL STUDY OF A PLASMA BUBBLE CREATED BY A WIRE EXPLOSION IN WATER

International audienceAn experimental setup is developed to study the bubble dynamic created by a wire explosion in a liquid. This arrangement can be encountered in many configurations and processes and differs by the level and frequency of the applied energy and of the liquid nature. In our study the wire explosion is due to a current intensity around one thousand amps during 10ms in a water medium and a distance between the electrodes of few millimeters. By fast imaging the bubble radius is determined versus time depending on the applied energy. The results indicate that the maximum radius of the bubble versus the applied energy leads to a linear variation of 2.3 cm/kJ roughly. A modification of the Rayleigh model is proposed to consider not an empty bubble but pressure variation inside. The experimental results coupled with the Rayleigh model allow determining the maximum bubble radius, the bubble dynamic and to evaluate its mean temperature. For electrical arc energy of 846 J and an inter-electrode distance of 1 mm, the bubble presents an expansion and a collapse. A maximal radius is reached near 4 cm before 1.5 ms the end of the half current period, due to the leak of energy to feed the bubble

Overview of Current Research into Low-Voltage Circuit Breakers

International audienceThe low-voltage circuit breaker has been used for many years for network and persons protection. The review papers existing on these devices generally deal with electrical aspects or macroscopic information on the arc but fewconcern the “fine” understanding of arc behaviour from its ignition between the opening contact to the current limitation stage due to its presence in the splitter plates. In this paper, we focus our attention on this point. We firstly describe the working of such devices, their limitations and the different phenomena occurring during breaking. Then, the difficulties involved with understanding the behaviour of the arc are identified and discussed in two main sections: physical arc characteristics and the study of arc movement during the breaking process. A review of the papers dealing with these subjects is proposed: both experimental and theoretical results from the literature are confronted and discussed and technical difficulties identified