Transient flow of rarefied gas through a short tube

A transient rarefied gas flow through a short tube is studied on the basis of the direct simulation Monte Carlo method. The mass flow rates through both inlet and outlet cross sections are calculated as a function of the time in the free-molecular, transitional and hydrodynamic regimes with respect to the gas rarefaction. Two values of the pressure ratio, i.e. 0.1 and 0.5, and two values of the aspect ratio, i.e. 1 and 5, are considered. A characteristic time equal to that needed to cross the tube radius with the most probable molecular speed is defined. A typical interval of time to establish the steady flow rates was calculated. It was found that this time is about ten and forty characteristic times for the shorter and longer tubes, respectively. The flow field for the longer tube is analyzed in details.

► A transient rarefied gas flow through a short tube is studied.
► Mass flow rates through inlet and outlet cross sections are calculated as a function of time.
► The time needed to establish the steady flow is calculated.
► The variation of flow fields in time is analyzed.