Transport and thermodynamic properties of SF6 gas contaminated by PTFE reinforced with Al2O3 and BN particles

The computational approach in which time-dependent balance equations of mass, momentum, and energy are solved numerically is becoming an important technique for analyzing electric arcs in a gas circuit breaker (GCB) or gas-insulated switchgear (GIS). In this paper, the transport and thermodynamic properties of SF₆ gas necessary for this approach as basic data are calculated under multimixed condition by PTFE(-C₂F₄-) reinforced with alumina (-Al₂ O₃-) or BN particles. Calculations are carried out for a wide range of temperatures from 1500 to 30000 K, of pressures from 0.1 to 0.4 MPa, and of concentration ratios from 0 to 50%. The results show that the change of electron density is significant for alumina-reinforced PTFE, but insignificant for BN-reinforced PTFE contamination. Henceforth, the electrical conductivity varies only for alumina-reinforced PTFE contamination. The thermal conductivity, however, changes distinctly by mixing alumina-reinforced PTFE as well as by mixing BN-reinforced PTFE. Up to three characteristic peaks (T<3600 K), the thermal conductivity decreases, but above this temperature, augmented thermal conductivity is noticed until 7000 K for alumina and until 12000 K for BN. All thermodynamic properties and viscosity vary only at a higher level of contamination, at or above 10% admixture ratio