Equations for Calculating the Gas Flow Rate through a Cylindrical Tube in Various Flow Regimes

The characteristics of the gas flow changes depending on the diameter and the length of the cylindrical tube, pressure, gas spices, and temperature. There are at least six flow regimes to explain the characteristics of the gas flow, such as molecular flow (also called free molecular flow) ; continuum flow including viscous laminar flow, turbulent flow, critical flow (sonic flow or choked flow), and subcritical flow (subsonic flow or non-choked flow) ; and their intermediates (intermediate flow, transition flow, or slip flow). This review paper summarized equations to calculate the gas flow rate through a cylindrical tube for each flow regime.