The LTE Thermofluid Simulation of Ar/SF₆ Gas-Blast Arcs in a Nozzle Space in an Arc Device

Abstract

The present paper describes numerical thermofluid simulation results of SF₆, Ar, and Ar/SF₆ arcs in a nozzle space at atmospheric pressure on the assumption of local thermodynamic equilibrium (LTE) condition. It is crucial to investigate fundamentals on arc extinction phenomena by numerical simulation approach as well as experimental approach. Two-dimensional temperature distributions in SF₆, Ar, Ar/SF₆ gas-blast arcs were calculated in a steady state at a direct current of 50A. Furthermore, transient temperature distributions in these arcs were computed under free recovery condition for a fundamental study. We investigated dependences of the gas mixture ratio of SF₆ to Ar and the gas flow velocity on the arc temperature and the arc voltage. The calculated arc voltage in the steady state and the transition of electron density under free recovery condition were compared with those obtained by laser Thomson scattering method in our experiments. As a result, the increasing admixture ratio of SF₆ to Ar and the increasing gas flow velocity shrinks the arc plasma around nozzle throat inlet, leading to the higher arc resistance. Under free recovery condition, the arc plasma decay more rapidly there. Comparison in electron density shows the similar dependence on SF₆ and Ar, while there is still some difference in the absolute value of electron density between the calculation results and experimental results.