International Journal of Computer Applications (0975 – 8887) Volume 86 – No 14, January 2014 6 Modelling the Influence of the Oxygen Concentration in the Gas Mixture (N2/O2) at Thermodynamic Equilibrium O. Zeggai Research Unit of Materials and Renewable Energies (URMER), University Abou Bakr Belkaïd, B.P. 119, Tlemcen, Algeria A. Ould-Abbas Research Unit of Materials and Renewable Energies (URMER), University Abou Bakr Belkaïd, B.P. 119, Tlemcen, Algeria H.Zeggai Research Unit of Materials and Renewable Energies (URMER), University Abou Bakr Belkaïd, B.P. 119, Tlemcen, Algeria ABSTRACT Knowledge of the chemical composition of plasma is required for calculations and modeling in thermal plasmas. Indeed, from the knowledge of this composition can be calculated thermodynamic properties, transport coefficients and the radiative properties of a plasma environment. In this work, we propose to study the influence of thermodynamic equilibrium concentration of oxygen in a gas mixture N2/O2. Particularly we study the evolution of the species density in the plasma created according to the temperature and pressure variables for O2 mixtures. A thermodynamic equilibrium, when you want to take into account a large number of species, two main methods are usually employed, one is based on the law of mass action and the other on minimization of the Gibbs. We decided in our study to the law of mass action and the method of Newton-Raphson. The results show that when the plasma is in thermodynamic equilibrium densities of the different species present in plasma that are functions of temperature and pressure. They are not independent because they are bound by certain laws of thermodynamic equilibrium Keywords Plasma, heat transfer, law of mass action, thermodynamic equilibrium, N2/O2 1. INTRODUCTION Nowadays, the pollution of the atmosphere has become a major environmental issue due to the rapid growth of industrial and technological development that requires high energy consumption. In the case of fossil fuels, this necessarily leads to an increase of emissions by industry, automotive, housing, etc ... gaseous air pollutants such as volatile organic compounds (VOCs) and various oxides (NOx , SOx, ozone, etc ...). In this work we are interested in modeling the chemical composition at thermodynamic equilibrium of a gas mixture (N2/O2). Thus the law of mass action (law Saha and Guldberg and Waage law) allows the thermodynamic equilibrium to determine the concentrations of different species (N, N2, electrons). We analyze in particular the influence of the concentration of oxygen (O2) (1, 10, 50, 90 and 99% of (O2)) and pressure (0.01 bar 1bar -10 bar) on the evolution of density of the two species: N, N2, the mixture was subjected to a power ranging from 1000 to 20000K. 2. MODELLING Plasmas are home to a large number of chemical reactions that can be written as: (1) Where ( ) are the stoichiometric coefficients of the inverse and direct reactions, N is the number of chemical species present in the mixture ( ) is the symbol of the chemical species (j). If the external conditions the plasma (pressure, temperature) are kept constant, for example by atmospheric pressure and by the electric field, then the chemical equilibrium is reached when the state functions are invariable. Therefore, we can write for the free energy: (2) ( ) is the variation in the number of species (i). For reaction (1) we have (3) By introducing the chemical potential, the relation (2) becomes: (4) We have seen that the chemical potential ( ) is expressed in terms of the chemical potential calculated at the reference pressure (P0): At thermal equilibrium: (5) . With a thermal disequilibrium: (8) We note that the thermal equilibrium we find the formula (7). These two relationships are the mass action laws governing the balance of the constituents of a chemical reaction in thermal equilibrium and thermal non-equilibrium. If we apply the formula (8) to the ionization A + +e - A (9) We find the law of Saha (10) Where (E i ) is the ionization energy Similarly, if we apply the formula (8) to the dissociation of the type: A+B AB (11)