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.