General approach to transient flows of rarefied gases through long capillaries

•A general approach to model transient flows of gas through long capillaries is proposed.•The approach is based on numerical results obtained previously.•As an example, a transient flow through a long circular tube is calculated.

An approach to model a transient flow of rarefied gas through a long capillary based on numerical data for flow rate previously obtained from the linearized and stationary kinetic equation was proposed. As an example, non-steady flow through a long circular tube connecting two reservoirs is considered. Pressures in the reservoirs and flow rates in the inlet and outlet are obtained as a function of time. It is shown that the behaviors of these quantities vary by changing the gas rarefaction from the free-molecular regime to hydrodynamic one. The typical time to reach the equilibrium state is calculated.