Comparative study for rarefied gas flow into vacuum through a short circular pipe

The problem of rarefied gas flow into vacuum through a short circular pipe is studied numerically by solving the Boltzmann kinetic equation. Comparison of the results obtained with the exact and S-model collision integrals is presented across a large range of Knudsen numbers. Computed values of mass flow rate are also compared against the DSMC results and experimental data from existing literature.