Thermodynamic Properties of Non-equilibrium Plasmas

Abstract

This chapter is devoted to the analysis of thermodynamic properties of thermal plasmas under nonequilibrium conditions. In the course of the development of thermal plasma technology, the assumption of local thermodynamic equilibrium (LTE) in the hot regions of the plasma has been generally accepted. However, over the past years there has been increasing evidence that the existence of LTE in thermal plasmas is rather the exception than the rule. Therefore, it is important to quantify the effects of deviations from LTE in order to provide guidance for computer simulation of flow, temperature, and particle concentrations in plasma reactors. This can only be achieved through a fundamental understanding of the basic phenomena involved and their influence on the plasma properties. The presentation of this chapter is divided into two main sections. The first section deals with two-temperature plasmas, calculation of the partition function and of the plasma composition, and their influence on the corresponding thermodynamic properties. The second section deals with deviations from local chemical equilibrium introducing the concepts of steady-state kinetic calculations, state-to-state approach, and pseudo-equilibrium calculations. Examples are given mostly for argon and nitrogen plasmas at atmospheric and higher pressures. These are complemented by other gaseous systems including argon–hydrogen, or nitrogen–oxygen, and CO2 mixtures.