Analysis of deviations from local thermal equilibrium in thermal spray plasma jet generated by a DC torch

A direct current atmospheric plasma spray torch was operated at different power levels and flow rates of argon plasma gas. The characteristic of the plasma jet was studied by using optical emission spectroscopy and enthalpy probe. In this paper, the intensity ratio of Ar atom spectrum lines was used to estimate the electron excited temperature of the thermal plasma jets, at the same time the temperature of the thermal plasma jet was determined using enthalpy probe. The temperature difference between them was investigated with the changes of current intensity and Ar flow rate. The results show that the electron temperature from emission spectroscopy measurements is always higher than the temperature of the plasma jet from enthalpy probe measurements under the same condition, and deviations from local thermal equilibrium exist in the plasma spray jets. Finally, non-equilibrium characterization of such turbulent thermal plasma jets was analyzed.