Properties of dry air at atmospheric pressure

Temperature

°C

Density

kg m^-3

Dynamic Viscosity

Pa s

Kinematic Viscosity

m² s^-1

Conductivity

W m^-1 K^-1

Specific Heat

J kg^-1 K^-1

Thermal Diffusivity

m² s^-1

Prandtl Number

Notes

This calculator gathers several correlations to estimate the thermodynamic and transport properties of dry air at atmospheric pressure, for the range 200 - 400 K. All correlations deviate by less than 0.15 % from tabulated values.

Density follows a simple inverse relationship (ideal gas) with a small correction term:

\[\rho \: \mathrm{[kg \: m^{-3}]} = \frac{351.99}{T} + \frac{344.88}{T^2}\]

Viscosity and thermal conductivity can be estimated using Sutherland’s equation:

\[\mu \: \mathrm{[10^{-6} Pa \: s]} = \frac{1.4592 T^{1.5}}{109.10 + T}\]

\[\nu \: \mathrm{[m^2 s^{-1}]} = \frac{\mu}{\rho}\]

\[k \: \mathrm{[W m^{-1} K^{-1}]} = \frac{2.3340 \times 10^{-3} T^{1.5}}{164.54 + T}\]

Specific heat follows a quadratic relationship:

\[C_p \: \mathrm{[J \: kg^{-1} K^{-1}]} = 1030.5 - 0.19975 T + 3.9734 \times 10^{-4} T^2\]

Thermal diffusivity is calculated from the definition:

\[\alpha \: \mathrm{[m^2 s^{-1}]} = \frac{k}{C_p \rho}\]

Alternatively, it can be estimated by:

\[\alpha \: \mathrm{[10^{-6} m^2 s^{-1}]} = -4.3274 + 4.1190 \times 10^{-2} T + 1.5556 \times 10^{-4} T^2\]

Prandtl number is calculated by:

\[Pr = \frac{C_p \mu}{k}\]

References

B.E. Poling, J.M. Prausnitz, J.P. O'Connell. Properties of Gases and Liquids, 5th Edition, McGraw-Hill, 2001.