text: In general, equation (2) is applicable only for incompressible flows. It can be modified by introducing the expansibility factor, (also called the expansion factor)  to account for the compressibility of gasses.
   is 1.0 for incompressible fluids and it can be calculated for compressible gases using empirically determined formulae as shown below in computation.
  For smaller values of β (such as restriction plates with β less than 0.25 and discharge from tanks), if the fluid is compressible, the rate of flow depends on whether the flow has become choked. If it is, then the flow may be calculated as shown at choked flow (although the flow of real gases through thin-plate orifices never becomes fully choked By using a mechanical energy balance, compressible fluid flow in un-choked conditions may be calculated as:
  or
  Under choked flow conditions, the fluid flow rate becomes:
  or