An Increase in the Density and Flow Rate of the Heavy Species under Rarefied Gas Mixture Outflow into Vacuum
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rease in the Density and Flow Rate of the Heavy Species under Rarefied Gas Mixture Outflow into Vacuum N. Yu. Bykova* and V. V. Zakharovb a
Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia b Institute for Space Astrophysics and Planetology, Rome, Italy *e-mail: [email protected] Received April 2, 2020; revised April 2, 2020; accepted April 13, 2020
Abstract—A numerical study of the gas dynamics of the processes of the outflow of a rarefied binary gas mixture with a large ratio of the species mass from the source into vacuum is carried out. The calculations are performed by the direct simulation Monte Carlo method. The effect of increasing the density of the heavy species in the vicinity of the outlet of the source is revealed . A significant effect of the light species on the gas dynamics of the mixture is shown, leading to an increase in flow rate and an enhancement of the effect of axial focusing of the heavy species. Keywords: rarefied gas dynamics, binary gas mixture, outflow into vacuum, gas flow rate, gas-jet technologies. DOI: 10.1134/S1063785020080040
The processes of the outflow of the gas mixture with a large difference in the mass of the species are widely used in various technical applications. Among the latter, one can note the technology of deposition of nanostructured films and synthesis of nanoclusters in the nanosystem industry [1, 2]. For example, the technology of vacuum gas-jet deposition (VGJD) of cluster films of noble metals involves the outflow of silver (gold) vapor from a crucible together with helium carrying gas. In this case, the mass ratio of the metal/helium atoms is 26.95 for silver and 49.24 for gold. The VGJD method is characterized by low stagnation pressure of the mixture in the source [3]. The outflow into vacuum occurs, as a rule, in a transition regime with respect to the Knudsen number (0.001 < Kn = λ/D < 1, λ is the mean free path of particles in the mixture, D is the diameter of the outlet) and effects related to small number of mutual collisions of particles of light and heavy species are expected. A large number of works have been devoted to the study of rarefied gas flows through short channels with a large pressure difference in communicating reservoirs. However, these studies have concerned the case of the flow of a single gas or air with a small mass ratio of the main species. This work is devoted to studying the outflow of rarefied silver–helium binary mixture from a source into vacuum through an orifice in an infinitely thin wall. The calculations were performed by the direct simulation Monte Carlo method [4]. Collisions of particles were considered according to the model of hard spheres with diameters d1 = 2.9 × 10–10 m, d2 = 2.19 ×
10–10 m, d12 = (d1 + d2)/2 (d1, d2, d12 are silver–silver, helium–helium, and silver–helium collision diameters, respectively) [5, 6]. Hereinafter, index 1 refers to silver, 2 refers to helium, and 0 corresponds to the conditions in the source. The stagnation temperature of the mixture in the sou
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