Graphite condensation and thermophysical properties of nonequilibrium C 4 F 7 N–CO 2 –O 2 arc plasma mixed with PTFE ablation vapour

Abstract The C 4 F 7 N–CO 2 –O 2 mixture has emerged as one of the most promising environmentally friendly alternatives to SF 6 and is gradually being adopted in high-voltage circuit breakers. Under the intense ablation of the nozzle by switching arcs, both C 4 F 7 N and polytetrafluoroethylene (PTFE), as carbon–fluorine compounds, inevitably undergo graphite condensation during arc extinction—a process which often significantly deviates from the assumption of local thermodynamic equilibrium. In order to accurately elucidate the effects of non-equilibrium conditions and graphite formation, a novel method was employed to calculate the composition and thermophysical properties of a multi-temperature [C 4 F 7 N–CO 2 –O 2 ]-PTFE mixture. The results indicate that graphite condensation markedly alters the species composition and thermophysical parameters in the low-temperature plasma, and that the admixture of PTFE vapour has a substantial impact on solid carbon formation. The multi-temperature model affects the thermodynamic and transport properties of the plasma by modifying both heavy-particle energy and chemical reaction progression, particularly under strongly non-equilibrium conditions. These results provide essential baseline data for the non-equilibrium arc modelling of C 4 F 7 N-based gas mixtures.