Numerical study of species separation in rarefied gas mixture flow through micronozzles using DSMC

Abstract

This work investigates the species separation in the rarefied flow of the argon-helium mixture through convergent-divergent micronozzles. Imposing a molecular mass ratio in the order of 10, the flow of this mixture can lead to the formation of serious nonhomogeneous phenomena such as the species separation. This study is performed in the ranges of 2.0–4.0 for the geometrical expansion ratio, 200–400 K for the wall temperature, and 0.003–1.454 for the inlet Knudsen number. The effects of these parameters are examined on the separative performances of micronozzle. The direct simulation Monte Carlo method is selected as the solution method because it can provide reliable solutions in the current rarefied flow regime study. The current study reveals two important separative effects in the mixture flow through micronozzles. The first effect is the lateral species separation, which results in the enrichment of heavier species near the centerline. The second effect is the streamwise separation, which leads to the enrichment of one species, mostly the lighter one, as the mixture passes through the micronozzle. The current results show that increasing the expansion ratio will enhance the lateral separation monotonically. However, there are specific wall temperature and Knudsen values, which can result in optimum lateral separative effects. In addition, it is observed that the expansion ratio has little effect on the streamwise separation. However, increasing either the wall temperature or the Knudsen number will enhance the streamwise separation, albeit with a limiting value at very high Knudsen numbers.

Femtosecond Laser-micromachining of Glass Micro-chip for High Order Harmonic Generation in Gases

“…It should be noticed that the nozzle flow behavior in the considered conditions deviates from the classical one, as described by inviscid theory. Although the inlet pressure is high enough to avoid rarefaction effects, viscous forces are very pronounced (the nozzle throat Reynold's number is about 300) and delay the supersonic transition within the divergent section whose effective area is strongly reduced by a thick boundary layer [17]. So far, the best nozzle configuration consists of a simple double cone geometry with an inlet diameter of 220 μm, a 60 μm throat diameter and a 90 μm exit diameter, whose size is the largest as possible which preserves the guiding characteristics of the hollow waveguide.…”

Femtosecond Laser-Micromachining of Glass Micro-Chip for High Order Harmonic Generation in Gases

“…It should be noticed that the nozzle flow behavior in the considered conditions deviates from the classical one, as described by the inviscid theory. Although the inlet pressure is high enough to avoid rarefaction effects, viscous forces are very pronounced (the nozzle throat Reynold's number is about 300) and delay the supersonic transition within the divergent section whose effective area is strongly reduced by a thick boundary layer [18]. So far, the best nozzle configuration consists of a simple double cone geometry with an inlet diameter of 220 µm, a 60 µm throat diameter, and a 90 µm exit diameter, whose size is the largest as possible which preserves the guiding characteristics of the hollow waveguide.…”

A direct relaxation process for particle methods in gas kinetic theory

“…The multi-scale mechanism from the continuum flow to the rarefied flow (or from the macroscopic flow to the microscopic flow) is crucial for the force and heat loaded on nearspace and reentry vehicles, the control of spacecraft by thrusters 1,2 , the propelling and cooling of Micro-Electro-Mechanical System (MEMS) 3,4 , etc. Since the continuum flow and rarefied flow often exist simultaneously in a singe multi-scale flow field, the modeling and prediction become complicated: The continuum flow is governed by the Navier-Stokes (N-S) equation, and the rarefied flow is governed by the Boltzmann equation, while there is no multi-scale governing equation for the transitional flow between continuum and rarefied ones.…”