text: In the ideal regime, the usual ideal-gas behavior is qualitatively recovered. For an ideal gas, in fact, the value of the fundamental derivative reduces to the constant value , where  is the heat capacity ratio. By definition,  is the ratio between the constant pressure and the constant volume specific heats, so it is larger than 1, leading to a value of  larger than 1 too.
  In this regime, only quantitative differences with respect to the ideal model are encountered. The flow evolution in fact depends on total, or stagnation, thermodynamic conditions. For example, the Mach number evolution of an ideal gas in a supersonic nozzle depends only on the heat capacity ratio (namely on the fluid) and on the exhaust-to-stagnation pressure ratio. Considering real-gas effects, instead, even fixing the fluid and the pressure ratio, different total states yield different Mach profiles.
  Typically, for single-phase fluids made of simple molecules, only the ideal gasdynamic regime can be reached, even for thermodynamic conditions very close to saturation. It is for example the case of diatomic or triatomic molecules, such as nitrogen or carbon dioxide, which can only experience small departure from the ideal behavior.