| AVS 56th International Symposium & Exhibition | |
| Vacuum Technology | Wednesday Sessions |
| Session VT-WeM |
| Session: | Partical and Theoretical Aspects of Gas Dynamics |
| Presenter: | O. Sazhin, Ural State University, Russia |
| Correspondent: | Click to Email |
A rarefied gas flow through a short channel into a vacuum presents a complex task due to significant non-equilibrium. Therefore, it is possible to find a good number of empirical formulas in open literature for calculating flow rate in this case. Correct approach to solving this problem should be based on the Boltzmann equation [1]. The difficulties of numerical solutions for this equation, caused by a large number of independent variables and a complex structure of a non-linear collision integral, are well-known. In our opinion, direct simulation Monte Carlo (DSMC) method [2], which is customarily viewed as a stochastic solution for Boltzmann equation, is preferable for use in tasks with strong non-equilibrium. DSMC method is an effective tool to solve problems of rarefied gas dynamics from free molecular to viscous regimes. An approach based on using DSMC method allows to take into account several factors, such as strong non-equilibrium, as well as to use various models of the gas-surface scattering and the gas molecule-molecule interactions. Therefore, it is appropriate to use DSMC method to study the rarefied gas flow through a short channel into a vacuum.
Practical application of the results of such research can be in the development and creation of such devices as micro- and nanoseparators, micropumps, microshutters, microgyroscopes, micro- and nanosatellites, and other micro- and nanoelectromechanical systems (MEMS/NEMS) [3]. The flow of gas in MEMS/NEMS, depending on device size and gas pressure, can be viscous, transitional or free molecular.
In this study, the mass flow rate through the channel into a vacuum is calculated over the wide range of gas rarefaction as function of channel’s length. To study the gas molecule–molecule interaction influence, we used the variable hard sphere and variable soft sphere models defined for inverse–power–law potential and also the generalized hard sphere model defined for the Lennard–Jones potential. Maxwell, Cercignani–Lampis and Epstein models were used to simulate the gas–surface scattering. This study demonstrates that the gas molecule–molecule interaction and the gas–surface scattering can have a significant influence on the rarefied gas flow through a short channel into a vacuum. The analysis of the flow field, both within the channel as well as in upstream and downstream containers, is presented.
REFERENCES
1. C. Cercignani, The Boltzmann Equation and its Application, Springer, New York (1988).
2. G.A. Bird, Molecular Gas Dynamics and the Direct Simulation of Gas Flow, Oxford University Press, Oxford (1994).
3. Encyclopedia of Microfluidics and Nanofluidics, ed. by Dongqing Li, Springer, New York (2008).