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The flow of a rarefied gas through a short tube connecting two containers is investigated based on the Direct Simulation Monte Carlo method. The pressure at the upstream container varies, while the pressure at the downstream container is taken always equal to zero. The solution of the problem is determined in terms of two parameters, namely the Knudsen number defined at the inlet of the tube and the dimensionless length of the tube. When the flow is in the transition and hydrodynamic regimes the particle distribution functions at the inlet and outlet of the tube can not be considered as Maxwellians and therefore, the flow field under investigation includes the tube and the two containers. The gas-surface interaction is modeled by the Cercignani-Lampis scattering kernel, while the hard sphere and the variable hard sphere models have been used for the intermolecular potential. The implemented computational grid is not uniform. It is divided into several subregions with various cell sizes. In general, the cell size is decreased in regions characterized by large gradients in the flow quantities, which usually occur close to the boundaries. This is achieved by dividing each cell into sub-sells. Potential collision partners are chosen from same sub-cell. Also, weighting factors are introduced to ensure uniform distributions of particles in the whole computational domain. Thus, statistical scattering is significantly reduced, while the same number of model particles is maintained. The results include the mass flow rates through the tube, which is the main quantity of practical interest, as well as velocity, pressure and temperature distributions throughout the flow domain in the whole range of the Knudsen number. The variation of the flow characteristics and quantities between the limiting cases of the free molecular and hydrodynamic flows is significant and it is studied in a detailed manner. As the length of the tube is decreased the present results tend to agree with the corresponding results recently obtained for flow through an orifice. |