In the context of propulsion, the specific heat ratio (γ) is a thermodynamic property of the working fluid (usually air or exhaust gases) and is used to describe how the specific heat at constant pressure (Cp) relates to the specific heat at constant volume (Cv). It is a crucial parameter in the analysis of compressible flows and thermodynamic processes within propulsion systems like jet engines, rocket engines, and gas turbines.
The specific heat ratio (γ) is defined as:
Where:
- γ is the specific heat ratio.
- Cp is the specific heat at constant pressure (in Joules per kilogram per Kelvin, J/(kg·K)).
- Cv is the specific heat at constant volume (in Joules per kilogram per Kelvin, J/(kg·K)).
For dry air, which is a common working fluid in many propulsion systems, γ is approximately 1.4. This value is widely used in aerodynamics and propulsion analyses. However, for different gases and gas mixtures, γ may have different values.
In the SI (International System of Units) system, γ is a dimensionless quantity, as specific heat is measured in J/(kg·K). The formula is dimensionless because it is a ratio of two specific heat values with the same units.