THERMODYNAMIC AND TRANSPORT-PROPERTIES OF AR-H2 AND AR-HE PLASMA GASES USED FOR SPRAYING AT ATMOSPHERIC-PRESSURE .1. PROPERTIES OF THE MIXTURES

The transport properties of argon/helium and argon/hydrogen mixtures used for plasma spraying were calculated according to the Chapman-Enskog theory with the following approximations: third for electrical conductivity and for electron translational thermal conductivity, second for heavy species translational thermal conductivity and internal thermal conductivity, and first for reactional thermal conductivity and viscosity. The results are as follows: for electrical conductivity for T < 14, 000 K, that of Ar/H-2 is almost unaffected by the mole percent H-2, while that of Ar/He is almost that of Ar up to 80 mole % He. for viscosity, that of Ar-H2 is between those of pure Ar and pure H-2, while for Ar-He mixtures an "anomalous" behavior is observed with higher values of the mixture viscosity compared to those of the components, in the temperature range 6000-10,000 K. Such behavior is due to the value of the Ar-He interaction potential proposed and experimentally verified by Aziz et al. The simplified mixing rule of Wilke must be used very cautiously especially for Ar-He where it predicts higher values for the mixture. The addition of hydrogen or helium to argon increases its thermal conductivity drastically. When considering the mean integrated thermal conductivity, the addition of hydrogen results in a step variation when dissociation occurs, while the increase is more regular when adding He.