# Thermal conductivity for gas

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$^{\circ}$C are taken from encyclopedia.airliquide.com
• Equation 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$^{\circ}$C', 2007
• Equation for dry air is taken from paper by T.F. Irvine and P. Liley: 'Steam and gas tables with computer equations', 1984
• Equation 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
• Equations 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 .
• Equation for CO2 is a linear interpolation of the values between 240 and 400 K.
• Equation for O2 is a linear interpolation of the values between 240 and 400 K.

Symbol
$k_{gas}$
Unit
W/(m.K)
Formulae
 $- 3.322412767 \cdot 10^{-11} \theta_{air}^{4} - 1.351703529 \cdot 10^{-9} \theta_{air}^{3} - 1.788037411 \cdot 10^{-7} \theta_{air}^{2} + 7.278410162 \cdot 10^{-5} \theta_{air} + 0.0240073953$ humid air @ 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 @ 1 bar (Dumas&Trancossi2009) $\frac{0.002334 T_{air}^{1.5}}{T_{air} + 164.54}$ air @ 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) $2.43 E + 6.63 \cdot 10^{-5} \theta_{gas} - 2$ N2 (Vermeer1983) $1.17 E + 6.2 \cdot 10^{-5} \theta_{gas} - 2$ SF6 (Vermeer1983) $\frac{0.0241059 T_{gas}^{3} + 77.7891 T_{gas}^{2} - 18539.4 T_{gas} + 1461860}{T_{gas}^{2} + 505.67 T_{gas} + 29661.7}$ SF6 (Assael2012) $8.075 \cdot 10^{-5} T_{gas} - 0.007302$ CO2 (linear interpolation) $7.836 \cdot 10^{-5} T_{gas} - 0.002991$ O2 (linear interpolation)
Related
$T_{air}$
$T_{gas}$
$\theta_{air}$
$\theta_{gas}$
Gas temperature [$^{\circ}$C]
Used in
$\alpha_{gas}$
$h_{encl}$
$h_{tr}$
$\mathrm{Pr}_{gas}$
$T_{conv_{ce}}$
Choices
GasPressure0$^{\circ}$C15$^{\circ}$C25$^{\circ}$C200 K240 K250 K300 K320 K340 K350 K360 K400 K450 K500 K
Air1 bar0.024360.0254990.026247
N21 bar0.0240010.0251080.0258350.021480.025970.027390.028790.030150.03281
N210 bar0.02190.026290.03304
SF61 bar0.0116270.0127010.013412
CO21 bar0.0146750.0158440.0166430.012240.016790.018420.020090.021770.02514
CO210 bar0.012940.017250.018840.020470.022120.02546
CO1 bar0.024740.025790.026478
O21 bar0.024350.025550.026340.01820.02260.02680.03070.03460.03830.0417
H21 bar0.172580.180050.18488
NH31 bar0.0229160.0240730.024934
SO21 bar0.0084340.0090920.00954
He1 bar0.14620.151690.15531
Ar1 bar0.0164830.0172450.017746
Kr1 bar0.0086520.0090820.009363
Xe1 bar0.0051070.0053650.005535