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

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Résumé

Electrical equipment, such as circuit breakers, often encounters operational issues, such as short-circuit failures. These malfunctions can be attributed to the deposition of aerosols containing aluminium oxide (Al2O3), calcium oxide (CaO), ferric oxide (Fe2O3), and silica (SiO2) on the devices. Previous studies have examined the influence of dust particles, such as silica, on the performances of circuit breakers. Silica significantly modifies molar fractions, leading to the formation of solid and liquid phases of SiO2 that condense on the surfaces of the gas generator. This results in changes to the dynamic viscosity of the arc, its motion and speed. However, these recent studies did not consider the combined effects of various species, including Fe2O3, CaO, Al2O3, and CO, which can be present in dust deposits depending on regional environmental conditions. To enhance the protection of circuit breakers from dust, this study investigates the effect of aerosols on the transport coefficients of air plasma in local thermodynamic equilibrium (LTE), for atmospheric pressure and temperatures ranging from 2,000 K to 30,000 K. Transport coefficients are calculated using the Chapman-Enskog method. The findings reveal alterations in the transport properties of the electric arc plasma during the circuit-breaking process. A reduction in thermal conductivity, and dynamic viscosity with
increasing temperature is observed. However, thermal conductivity increases at 4,000 K, respectively, and both the mass density and electrical conductivity of the plasma increase with temperature. Consequently, the presence of these aerosols within the circuit breaker during the cutoff phase adversely affects its performance, potentially leading to leakage currents post-operation or even to fire hazards in cases of unsuccessful circuit interruption.

Mots-clés

Electrical, Thermal, Conductivity, Viscosity, Plasma, Circuit Breaker