Calculation and Analysis of the Thermodynamic Properties of Air-Aerosols Mixtures

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Résumé

Circuit breakers and other electrical equipment are often exposed to opera- tional challenges caused by dust contamination, particularly short-circuit failures. These issues are frequently linked to the deposition of aerosols containing compounds such as aluminium oxide (Al2O3), calcium oxide (CaO), iron oxide (Fe2O3), and silicon dioxide (SiO2) on critical components. While previous research has examined the influence of individual dust species—especially silica—on circuit breaker performance, these studies primarily focused on isolated effects, neglecting the combined thermodynamic impact of multiple aerosol constituents. In reality, environmental dust often comprises a mixture of
species, including Al2O3, CaO, Fe2O3, and CO, which can vary significantly depending on the geographical context. This study aims to assess the influence of such aerosols on the thermodynamic properties of air plasma under atmos- pheric pressure and local thermodynamic equilibrium conditions, across a temperature range of 2000 K to 30,000 K. The properties, including mass enthalpy, specific heat at constant pressure, sound velocity, and mass density, are computed directly from the population densities of the relevant species. Results reveal that the presence of aerosol mixtures alters the thermodynamic behaviour of the arc plasma during circuit interruption. Notably, reductions
in mass enthalpy, specific heat, and sound velocity are observed with increasing temperature, while specific heat increases at temperatures below 7000 K. Additionally, mass density is found to increase with temperature. These findings suggest that aerosol contamination during the interruption phase can de-
grade circuit breaker performance, potentially resulting in residual leakage currents or fire risks due to incomplete arc quenching.

Mots-clés

Composition, Density, Enthalpy, Plasma, Heat, Sound, Aerosol