Net emission coefficients of radiation were calculated for isothermal plasmas of air and SF 6 as a function of the plasma temperature 5,000-30,000 K and the arc radius (0.01-10 cm) at various plasma pressures. Calculations take into account continuum and line radiations, special attention has also been taken to influence of molecular species in case of the air plasmas. It has been found that the molecular bands of O 2 , N 2 , N 2 ? , NO and NO ? have very strong effect on the net emission coefficients at low temperatures (below 10,000 K). In case of SF 6 , effect of PTFE admixture on the net emission coefficients was also studied. It follows from the calculations that the net emission coefficients vary very little with various admixtures of PTFE. Values of net emission coefficients if SF 6 plasma calculated for various spectral regions were compared.

This paper presents a numerical investigation of characteristics and processes in the worldwide unique type of thermal plasma generator with combined stabilization of arc by argon flow and water vortex, the so-called hybrid-stabilized arc. The arc has been used for spraying of ceramic or metallic particles and for pyrolysis of biomass. The net emission coefficients as well as the partial characteristics methods for radiation losses from the argon–water arc are employed. Calculations for 300–600 A with 22.5–40 standard litres per minute (slm) of argon reveal transition from a transonic plasma flow for 400 A to a supersonic one for 600 A with a maximum Mach number of 1.6 near the exit nozzle of the plasma torch. A comparison with available experimental data near the exit nozzle shows very good agreement for the radial temperature profiles. Radial velocity profiles calculated 2 mm downstream of the nozzle exit show good agreement with the profiles determined from the combination of calculation and experiment (the so-called integrated approach). A recent evaluation of the Mach number from the experimental data for 500 and 600 A confirmed the existence of the supersonic flow regime.

Abstract. The paper deals with net emission coefficients of radiation of air thermal plasmas with admixtures of copper and tungsten as a function of the plasma temperature up to 25 000 K and the arc radius (0.01 to 10 cm) at various pressures. The net emission coefficients are calculated for various equilibrium compositions (mole fractions of Cu and W) of the plasma. Calculations take into account continuum and line radiations, special attention has also been taken to the fraction of radiation that is below threshold of 120 nm. From the results follows that presence of metallic vapour increases net emission coefficients even at low temperatures below 10 000 K.

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