Binary gas mixture outflow into vacuum through an orifice

Abstract

The results of a numerical study of a binary gas mixture outflow from a source with specified stagnation parameters into vacuum through a round orifice are presented. Silver and helium atoms (with a mass ratio of 26.95) are selected as a mixture species. The near free-molecular, transitional, and near-continuum regimes of the flow are considered with the direct simulation Monte Carlo method used for the computations. The results of simulations show that the rarefaction degree and the mole composition of the mixture have a significant impact on the spatial variation of flow parameters and the flow rates through the orifice. At all degrees of rarefaction, the variation in the dimensionless flow rate (related to the free-molecular flow rate) of the mixture is a non-monotonic function of the mole fraction of the species with a maximum/minimum (for the mass/particle flux). The presence of a light carrier gas (helium) leads to the acceleration, axial focusing, and increase in the flow rate of the heavy species (silver). The velocity slip of light and heavy species is observed at all degrees of rarefaction under consideration. The effect of the increasing density of heavy species near the orifice plane is revealed. The spatial variation of mole fractions of species on the degree of rarefaction is studied. The results of the study are compared to available analytical and experimental data, and the simulation results of pure gas outflow obtained by other authors.