Advanced Thermal Plasma Modelling

Basic knowledge on radiative and transport properties to begin in thermal plasmas modelling

“…According to relation (4), the crucial point of the study is the treatment of the lines' intensities which depends on the lines' profiles and consequently on the broadenings effects: Doppler, Van der Waals, resonance and Stark broadenings. [41][42][43][44] The treatment of the lines is thus a complex and long step since they are numerous in thermal plasmas (15150 lines for SF 6 47 as examples. In this case, we need more than 300000 wavelengths to obtain a fine and correct description of the spectra (between 1 and 3 million wavelengths are needed if the molecular bands have to be considered; 37,48,49 the spectral resolution of the absorption coefficient cannot be taken as constant and depends on the nature of the species mixed in the plasmas (from 10 −3 nm to 10 −1 nm for SF 6 -C 2 F 4 plasmas; 48 the lines' profiles must be calculated on spectral ranges being more than 100 times the half width at half maximum.…”

“…An example of the divergence of the flux is shown in Fig. 5 in the case of pure SF 6 High Voltage Circuit Breaker. 45 The results were obtained with the Net Emission Coefficient (NEC), with the P1 model using the mean absorption coefficients deduced from the Rosseland or the Planck approximations, and compared to a fine resolution of the equation (3) for a given temperature profile (see the work of Randrianandraina et al 45 ) for the definition of the mean absorption coefficients, for the discretisation and the temperature profile).…”

“…With the rise of the pressure, the maximum increases and its position is shifted towards higher temperatures. -the thermal conductivity is dominated by the internal and heavy translational terms at low temperatures (except for SF 6 ), then by the reactional and heavy translational terms at intermediate temperatures (3kK<T<20kK), and finally by reactional and electron translational terms for higher temperatures. The most important step is to well describe the peaks corresponding to the ionisation and dissociation reactions.…”

“…), metallurgy (plasma welding, plasma cutting) petrochemistry, medical applications (treatment of tumours), protection of humans and electrical installations, or in the environment (syngas production, applications for waste treatments). Depending on the application, we use various technologies which often imply: non transferred arcs (used in plasma torches for spraying, with Ar, H 2 or He gases, their mixtures Ar/H 2 , Ar/He, Ar/H 2 /He, contaminated or not by iron, copper or aluminium particles); transferred arcs (used in plasma torches for plasma cutting, with Ar, O 2 , N 2 or Air gases, their mixtures Ar/O 2 and Ar/N 2 , with or without metallic vapours Fe, Al, Cu, Ag, or Si for welding); the circuit breakers with SF 6 , CO 2 or Air mixed with organic and/or metallic vapours C 2 F 4 , Cu, W, Ag, Al); the wall-stabilized arcs (Ar, H 2 , He and their mixtures Ar/H 2 , Ar/He); the plasmas created by laser impact (LIBS) used to analyse materials or to detect pollutants in liquids (H 2 O + alkaline salts NaCl, MgCl 2 , CaCl 2 ); the short-circuit arcs (phenomena of arc tracking with mixtures of Air-Al or Air-Fe for example); the arc lamps for which the visible radiation represents the efficiency of the process (the main objective consists in obtaining an effective, pleasant and long life luminosity with a low energy consumption; these lamps can work at low or high pressure); the spectro-analysis, the treatment or the synthesis of materials where radio frequency torches (RF) are mainly used (a gas is excited by RF under a pressure often close to the atmospheric pressure as in the case of the inductive coupling plasma torches (ICP), the corresponding plasmas are often thermal plasmas with high volumes, high purity, but the energy densities are generally weaker than those of some arc plasmas leading to a weaker influence of the radiation); the plasmas reactors to synthesize nanopowders such as fullerenes or carbon nanotubes (but the most important region of the process is not really affected by the radiation of the gas). Whatever the fields of applications, the scientific studies concern the modelling of the energy transfers (inside the plasma or outside considering the surrounding materials) usually dominated by the thermal radiation and the transport phenomena.…”

Three-dimensional modelling of arc behaviour and gas shield quality in tandem gas–metal arc welding using anti-phase pulse synchronization

“…To take all the effects into account would require treating the transport and reactions of each plasma species separately. This would inevitably introduce inaccuracies because of the lack of available reaction data and uncertainties about appropriate calculation of thermodynamic and transport properties [27,28].…”