Free air/gas (or undissolved)

Single component physical properties: Free air/gas

Regardless to the type of fluid properties chosen, the free air/gas has a polytropic equation of state, and then the free air/gas bulk modulus is directly computed from Equation 5:

The density of the undissolved air/gas is equal to the density of the dissolved air/gas.

The hydraulic reference conditions for the air/gas are taken at Patm and 273 K. The equation of state for an ideal gas gives the density from T0 to T at constant pressure Patm:

And a polytropic change from Patm to the current pressure P gives:

Equation 8: Air/gas density at P and T

If we consider the total air/gas, we obtain the air/gas volume at P and T: