Fundamental process of thermal plasma flow

摘要

The physical and chemical characteristics of thermal plasmas were examined for spraying process. Plasma jets consist of partially ionized gas with high velocity and high temperature higher than 10{sup}4K. In the first part of this paper, basic concepts as well as transport and thermophysical properties of thermal plasmas were described for estimation of heat and momentum transfer of sprayed particles. The second part was devoted to structure of plasma jets, including electrode phenomena, turbulence and instability. Plasma jets used for plasma spraying show strong fluctuations owing to fluid dynamic motion as well as instability induced by the arc motion on the anode. An engulfment-type entrainment mechanism takes place in turbulent plasma jets. The instability of plasma jets is one of the most important parameters for heating of sprayed particles. Therefore the instability can be used as the indicator for control of the coating quality.