CHARACTERISTICS OF NON-EQUILIBRIUM ARC PLASMA IN PLASMATRON NOZZLE CHANNEL

摘要

A mathematical model was developed for processes of energy, pulse, mass and discharge transfer in non-equilibrium plasma of electric arc, burning in cylindrical channel with water-cooled walls being blown out by laminar flow of plasma inert gas. The model is based on multi-fluid equations for nonisothermal, ionization non-equilibrium arc plasma, considering double ionization of atoms of the plasma gas written in a drift-diffusion approximation. Such an approach allows uniform description of the processes taking place in central region of the channel (in arc column plasma) as well as near-wall region (in plasma ionization layer) up to interface of space charge layer directly adjacent to channel wall. Consideration of the processes taking place in collisionless layer of space discharge and determination of characteristics of thermal and electric interaction of arc plasma with channel wall is carried out using corresponding boundary conditions on interface of the indicated layer. Besides, if presence of doubly charged ions in arc plasma is taken into account, it is possible to calculate its characteristics in a wide range of values of arc current and channel radius. Numerical solution of equations of the proposed model is carried out by finite volume method. Corresponding software is developed for computer realization. Detailed numerical analysis is given to radial distribution of characteristics of argon arc plasma in the cylindrical channels of direct plasmatron nozzle as well as intensity of longitudinal electric field in arc plasma and heat flow from plasma to channel wall at different values of arc current, channel radius and consumption of plasma gas. It is shown that in contrast to the central regions of the channel, where arc plasma is virtually equilibrium, a significant thermal and ionization non-equilibrium of plasma is realized in the near-wall region. It is also shown that increase of arc current and reduction of channel radius requires consideration of the doubly charge ions present in arc plasma. Comparison of results of modelling of characteristics of the non-equilibrium argon arc plasma in the plasmatron nozzle channel with available experimental data was carried out.