Nonequilibrium Processes in Supersonic Jets of N2, H2, and N2 + H2 Mixtures: (I) Zone of Silence

Number density and rotational temperature in the zone of silence of supersonic jets of N-2, H-2, and their mixtures N-2 + 2H(2) and 2N(2) + H-2, at p(0) = 1 bar and T-0 = 295 K, have been measured by Raman spectroscopy. Translational temperature in the jets has been derived from the experimental data assuming isentropic flow. The density along the jet axis decays at a rate depending on the composition of the expanded gas, which can be explained by the variation of its effective heat capacity ratio. Measurements across the jet axis do not support numerical off-axis density modeling from the literature. A strong nonequilibrium between the rotational degrees of freedom of both species is observed, even between the two spin species ortho-H-2 and para-H-2. From the corresponding rotational temperature data, a relationship between rotational cross sections for the inelastic collisions of the different species is established. In the expansions of the mixtures, an enrichment of N-2 is measured on the axis, which is compared with the predictions from the theory of diffusive separation in jets.