Thermophysical properties calculation of C4F7N/CO2 mixture based on computational chemistry — A theoretical study of SF6 alternative

An SF6 alternative gas, C 4 F 7 N mixed with CO 2 , has attracted great attention in recent years. The related experimental reports show that it has good insulation, thermal dissipation, switching performances and other characteristics. In theoretical research area, the thermophysical properties of plasma are of great significance to study the arc behaviour. However, for C 4 F 7 N, due to its complicated molecular structure, the decomposition process during the arc process is still unknown. Also for the particles generated as the temperature increases, the spectral parameters are not available. Therefore, the studies on the thermophysical property of C 4 F 7 N are rarely reported. In order to obtain the decomposition process, we assumed that the decomposition of C 4 F 7 N molecules is in the form of covalent bond cleavage. Then the main decomposition path and decomposition products of C 4 F 7 N can be obtained by analyzing the molecular bond energy. The relevant parameters of gas particles were calculated from the molecular structure using computational chemistry software. Based on the composition results assuming local thermodynamic equilibrium, the transport properties including viscosity, thermal conductivity and electrical conductivity of C 4 F 7 N-CO 2 were calculated in the temperature range from 300 to 30000 K and at the pressures between 0.1 and 16 atm, using Chapman enskog method. For the collision integrals, the phenomenological potential was adopted.