The first formula for air in tunnel at atmospheric pressure is taken from IEC 60287-2-3.
The formulas for dry air at different pressures ate taken from paper by Daniel L. Carrol at al: 'Thermal Conductivity of Gaseous Air at Moderate and High Pressures', 1968
| $2.42{\cdot}{10}^{-2}+7.2{\cdot}{10}^{-5} \theta_{at}$ | IEC 60287-2-3 @ 1 atm. |
| $24.545+0.0765\theta_{gas}-5{\cdot}{10}^{-5} {\theta_{gas}}^2$ | dry air @ 1 bar (Carroll1968) |
| $24.762+0.075\theta_{gas}-4{\cdot}{10}^{-5} {\theta_{gas}}^2$ | dry air @ 5 bar (Carroll1968, interpolated) |
| $24.979+0.0734\theta_{gas}-3{\cdot}{10}^{-5} {\theta_{gas}}^2$ | dry air @ 10 bar (Carroll1968, interpolated) |
| $25.586+0.0692\theta_{gas}-4{\cdot}{10}^{-6} {\theta_{gas}}^2$ | dry air @ 25 bar (Carroll1968) |
| $27.222+0.0635\theta_{gas}-4{\cdot}{10}^{-5} {\theta_{gas}}^2-5{\cdot}{10}^{-7} {\theta_{gas}}^3+{10}^{-8}{\theta_{gas}}^4$ | dry air @ 50 bar (Carroll1968) |
| Gas | Pressure | 0°C | 15°C | 25°C | 50°C | 75°C | 100°C |
|---|---|---|---|---|---|---|---|
| Air | 1 bar | 0.024545 | 0.025681 | 0.026426 | 0.028245 | 0.030001 | 0.031695 |
| Air | 5 bar | 0.024762 | 0.025878 | 0.026612 | 0.028412 | 0.030162 | 0.031862 |
| Air | 10 bar | 0.024979 | 0.026073 | 0.026795 | 0.028574 | 0.030315 | 0.032019 |
| Air | 25 bar | 0.025586 | 0.026623 | 0.027314 | 0.029036 | 0.030754 | 0.032466 |
| Air | 50 bar | 0.027222 | 0.028164 | 0.028781 | 0.030297 | 0.031865 | 0.033672 |
