I am using the gas dynamics library to simulate a simple adiabatic compression of a volume of nitrogen. Using the "ideal gas" computation. Just wondering if the ratio of specific heats changes during the calculation as the temperature changes.
The Gas Dynamics (GD) “Ideal Gas” model treats Cp as a function of temperature. Hence gamma = Cp(T)/[Cp(T) – R] will also be a function of temperature. It is a weaker function of temperature than Cp, since Cp appears in both the numerator and denominator.
The “Perfect Gas” model treats Cp and gamma as constants.
Except for initial estimations in iterative calculations, there are very few components that use gamma in the calculations when the “Ideal Gas” model is selected. So you will not get exactly the same results with the GD “Ideal Gas” model as you will with hand calculations based upon constant gamma.
Please refer to Chapter 4 of the Gas Dynamics User Guide. For an adiabatic compression of a closed system the GD library calculates the temperature and pressure by simultaneously solving Equations 4-1 and 4.8 for Pdot and Tdot. In that case all of the mass flow terms are zero, as is the heat transfer and condensation terms in Equation 4.8.
