Calculation of Thermodynamic Physical Properties of C4F7N-CO2 Mixed Gas

摘要

Recent studies have shown that a mixture of C4F7N-CO2 can be used as an environmentally friendly alternative to SF6. In this paper, the saturated vapor pressure of C4F7N-CO2 mixed gas is calculated by Antoine vapor pressure equation and gas-liquid equilibrium law, and the liquefaction temperature of the mixed gas in different states is obtained. According to the molecular structure characteristics, the C4F7N-CO2 mixed gas compression factor, constant pressure specific heat capacity and viscosity were calculated by P-R (Peng Robinson) equation of state, Joback group contribution method and Thodos method, respectively. The calculation results show that if the liquefaction temperature of the insulating medium is not higher than 253K when the GIS and GIL are operated at 0.5MPa, the proportion of C4F7N in the mixed gas should not exceed 10, the ratio of the GWP (Global Warming Potential) of the mixed gas is 694, which is about 2.95% of SF6, and the corresponding compression factor is close to 1, and the mixed gas tends to be in an ideal gas state. The constant pressure specific heat capacity and viscosity of C4F7N-CO2 mixed gas increase with the increase of temperature at the same pressure, and increase with the increase of pressure at the same temperature. At the same pressure and temperature, the specific pressure specific heat capacity and viscosity of the mixed gas are less than SF6, such as the specific heat capacity and viscosity of 5% C4F7N-95% CO2 at 273K and 0.5MPa are about 43.37% and 85.62% ofSF6, respectively.