Numerical studies of arc plasma generation in single cathode and three-cathode plasma torch and its impact on plasma spraying

Abstract

This paper is to study the characteristics of arc plasma torch generated by single cathode and three-cathode structure and their potential impact on plasma spraying. A comprehensive physical model is developed, which is capable of describing plasma generation, compressible reacting flow and its interaction with particles involving heat, momentum and mass transfer as well as particle melting and re-solidification. A computational scheme is also developed to solve the Navier–Stokes equations, Maxwell’s equations and equations of particles’ momentum, heat and mass transfer with plasma jet and particles’ phase change. This scheme is applied to simulate thermal spraying processes using both single cathode and three-cathode plasma guns. Results show that plasma torch from the single cathode plasma gun shifts to one side, while that from the three-cathode plasma gun is axisymmetric along the jet axis with triangular structure on the jet cross sections. Temperature and velocity along the center axis are lower than those away from the jet axis in the three-cathode plasma torch. The regime with high temperature and velocity in the three-cathode plasma jet is larger than that in the single cathode plasma jet. By choosing a suitable injection position, the in-flight particles in the three-cathode plasma jet can be uniformly distributed within the high temperature and velocity region, and be heated and accelerated uniformly. The size of particles that can be fully melted is larger in the three-cathode plasma jet than in the single cathode plasma jet, therefore, beneficial to the coating quality.