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Modeling of rarefied gas flows in vacuum systems is based on two main approaches: direct simulation Monte Carlo (DSMC) method and solution of the kinetic Boltzmann equation. The principal idea of the first approach is a consideration of a huge number of particles simulating the interaction between them and their interaction with surfaces. This method has many advantages. It is easy to apply it to complicated geometrical configuration. The CPU time is not very sensitive to many generalizations such as gaseous mixtures, polyatomic gases, molecular dissociation etc. In the open literature one can find numerical codes based on the DSMC methods that can be directly used in practice. That is why the method is widely used in practical calculations and constantly improved. However, it has some restrictions and shortcomings, e.g. in some situation the statistical scattering can be significant. The second approach is based on the kinetic equation. The main advantage of this method is the absent of the statistical noise, but it is not so easy to apply this method to complicated systems. In the final report a comparison between the two approaches will be performed and recommendations on their applications will be given. |