Thermal conductivity of a substance is an intensive property that indicates its ability to conduct heat.

Air and other gases are generally good insulators, in the absence of convection. Light gases, such as hydrogen and helium typically have high thermal conductivity. Dense gases such as xenon have low thermal conductivity. An exception, sulfur hexafluoride, a dense gas, has a relatively high thermal conductivity due to its high heat capacity. Argon, a gas denser than air, is often used in double paned windows to improve their insulation characteristics.

The sources are:

- Values for 0, 15, and 25°C are taken from encyclopedia.airliquide.com
- Formula for humid air is taken from paper by P.T. Tsilingiris: 'Thermophysical and transport properties of humid air at temperature range between 0 and 100°C', 2007
- Formula for dry air is taken from paper by T.F. Irvine and P. Liley: 'Steam and gas tables with computer equations', 1984
- Formula for air is taken from paper by A. Dumas and M. Trancossi: 'Design of Exchangers Based on Heat Pipes for Hot Exhaust Thermal Flux, with the Capability of Thermal Shocks Absorption and Low Level Energy Recovery', 2009. They are calculated from polynomial curve fits to a data set for 100 K to 1600 K in the SFPE Handbook of Fire Protection Engineering, 2nd Edition Table B-2. You may find a free air property calculator from Pierre Bouteloup
- Formulae for N2 and SF6 are taken from paper by J. Vermeer: 'A simple formula for the calculation of the convective heat transfer between conductor and sheath in compressed gas insulated (CGI) cables', 1983 as published in Elektra 87
- Second formula for SF6 is taken from paper by M.J. Assael at al: 'Reference Correlation of the Thermal Conductivity of Sulfur Hexafluoride from the Triple Point to 1000 K and up to 150 MPa', 2012
- Values for N2 for 240–400 K are taken from the engineering toolbox .
- Values for CO2 for 240–400 K are taken from the engineering toolbox .
- Formula for CO2 is a linear interpolation of the values between 240 and 400 K.

$k_{\mathrm{gas}}$

W/m.K

$- 3.322412767 \cdot 10^{-11} \theta_{\mathrm{air}}^{4} - 1.351703529 \cdot 10^{-9} \theta_{\mathrm{air}}^{3} - 1.788037411 \cdot 10^{-7} \theta_{\mathrm{air}}^{2} + 7.278410162 \cdot 10^{-5} \theta_{\mathrm{air}} + 0.0240073953$ | humid air at 1 atm (Tsilingiris2007) |

$1.5207 \cdot 10^{-11} T_{air}^{3} - 4.8574 \cdot 10^{-8} T_{air}^{2} + 0.00010184 T_{air} - 0.00039333$ | air at 1 bar (Dumas&Trancossi2009) |

$\frac{0.002334 T_{air}^{1.5}}{T_{air} + 164.54}$ | air at 1 bar (UW/MHTL 8406, 1984) |

$2.47663035 \cdot 10^{-17} T_{air}^{5} - 1.066657 \cdot 10^{-13} T_{air}^{4} + 1.73550646 \cdot 10^{-10} T_{air}^{3} - 1.4815235 \cdot 10^{-7} T_{air}^{2} + 0.00012598485 T_{air} - 0.002276501$ | dry air at 1 atm (Irvine&Liley1984) |

$2.43 E + 6.63 \cdot 10^{-5} \theta_{\mathrm{gas}} - 2$ | N2 (Vermeer1983) |

$1.17 E + 6.2 \cdot 10^{-5} \theta_{\mathrm{gas}} - 2$ | SF6 (Vermeer1983) |

$\frac{0.0241059 T_{\mathrm{gas}}^{3} + 77.7891 T_{\mathrm{gas}}^{2} - 18539.4 T_{\mathrm{gas}} + 1461860}{T_{\mathrm{gas}}^{2} + 505.67 T_{\mathrm{gas}} + 29661.7}$ | SF6 (Assael2012) |

$8.075 \cdot 10^{-5} T_{\mathrm{gas}} - 0.007302$ | CO2 (linear interpolation) |

$\theta_{\mathrm{air}}$

$\theta_{\mathrm{gas}}$

Gas temperature [°C]

$F_{\mathrm{pt}}$

$h_{\mathrm{c}}$

$h_{\mathrm{encl}}$

$h_{\mathrm{tr}}$

Heat transfer coefficient [W/K.m^{2}]

$\mathrm{Pr}_{\mathrm{gas}}$

$T_{\mathrm{conv_{\mathrm{ce}}}}$

Gas | Pressure | 0°C | 15°C | 25°C | 240 K | 300 K | 320 K | 340 K | 360 K | 400 K |
---|---|---|---|---|---|---|---|---|---|---|

Air | 1 bar | 0.02436 | 0.025499 | 0.026247 | ||||||

N2 | 1 bar | 0.024001 | 0.025108 | 0.025835 | 0.02148 | 0.02597 | 0.02739 | 0.02879 | 0.03015 | 0.03281 |

N2 | 10 bar | 0.0219 | 0.02629 | 0.03304 | ||||||

SF6 | 1 bar | 0.011627 | 0.012701 | 0.013412 | ||||||

CO2 | 1 bar | 0.014675 | 0.015844 | 0.016643 | 0.01224 | 0.01679 | 0.01842 | 0.02009 | 0.02177 | 0.02514 |

CO2 | 10 bar | 0.01294 | 0.01725 | 0.01884 | 0.02047 | 0.02212 | 0.02546 | |||

CO | 1 bar | 0.02474 | 0.02579 | 0.026478 | ||||||

O2 | 1 bar | 0.02435 | 0.02555 | 0.02634 | ||||||

H2 | 1 bar | 0.17258 | 0.18005 | 0.18488 | ||||||

NH3 | 1 bar | 0.022916 | 0.024073 | 0.024934 | ||||||

SO2 | 1 bar | 0.008434 | 0.009092 | 0.00954 | ||||||

He | 1 bar | 0.1462 | 0.15169 | 0.15531 | ||||||

Ar | 1 bar | 0.016483 | 0.017245 | 0.017746 | ||||||

Kr | 1 bar | 0.008652 | 0.009082 | 0.009363 | ||||||

Xe | 1 bar | 0.005107 | 0.005365 | 0.005535 |