For an ideal gas, the volumetric (isobaric) thermal expansion depends on the type of process in which temperature is changed. Two simple cases are isobaric change, where pressure is held constant, and adiabatic change, where no heat is exchanged with the environment. In case of isobaric thermal expansion, the coefficient is the inverse of the temperature $T_{gas}$.
Values and equation for air are taken from the engineering toolbox .
| $2{\cdot}{10}^{-13} {\theta_{gas}}^4-2{\cdot}{10}^{-10} {\theta_{gas}}^2+5{\cdot}{10}^{-8} {\theta_{gas}}^2-{10}^{-5}\theta_{gas}+0.0037$ | air @ 1 bar |
| $\left(\theta_{gas}+\theta_{abs}\right)^{-1}$ | Gas-temperature in Celsius |
| ${T_{gas}}^{-1}$ | general formula for gases |
| Gas | Pressure | -50°C | -25°C | 0°C | 25°C | 50°C | 60°C | 80°C | 100°C | 125°C | 150°C |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Air | 1 bar | 0.00455 | 0.00408 | 0.00369 | 0.00338 | 0.00312 | 0.00302 | 0.00285 | 0.0027 | 0.00251 | 0.00233 |
