Thermal characteristics of non-transferred DC plasma torches under various combinations of pure and mixture gases

The thermal characteristics of two nontransferred DC plasma torches have been investigated for operating powers between 10 and 80 kW for various combinations of Ar, N/sub 2/, H/sub 2/, O/sub 2/ and CO/sub 2/ gas mixtures. The Acurex torch contained an axially struck, flow-stabilized plasma arc roughly 10-cm long and a removable mixing section. The MWR-1 torch contained a radially struck plasma arc 0.5-2-cm long but no mixing section. Typical radial temperatures profiles of the MWR-1 torch indicate the rapidity with which the plasma quenches on entering the reaction chamber. The Acurex torch was much less efficient than the MWR-1 torch (typically 50% versus 75%). The thermal efficiency of the torches was significantly affected by the fraction of N/sub 2/, air, Ar, and H/sub 2/ in the plasma gas. The Acurex torch with the mixing plenum in place was able to achieve much better mixing of the plasma gas than the MWR-1 torch. Side injection of gas tended to raise the downstream temperature of the plasma. Increasing concentrations of H/sub 2/ in the Ar-H/sub 2/ plasma decreased the temperature near the exit of the torch and increased the temperature further downstream. >