Rarefied gas flow through a thin slit at an arbitrary pressure ratio

Rarefied gas flow through a thin slit is studied on the basis of the direct simulation Monte Carlo method. The flow rate and flow field are calculated over the whole range of gas rarefaction for various values of the pressure ratio. It is found that at all values of the pressure ratio a significant variation of the flow rate occurs in the transition regime between the free-molecular and hydrodynamic regimes. In the hydrodynamic regime, the flow rate tends to a constant value. In the case of finite pressure ratio, the flow field qualitatively differs from that for outflow into vacuum, namely, vortices appear in the down-flow container in the vicinity of the hydrodynamic regime. Then, in the hydrodynamic regime the gas flow forms a strong jet.