# 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°C are taken from encyclopedia.airliquide.com
• Values for 50, 75, and 100°C are taken from nist.gov
• Values for 50, 75, and 100°C for SF6 and SO2 have been interpolated from values from engineersedge.com
• Values for 50, 75, and 100°C for dry air have been calculated using the equation from Irvine & Liley, 1984.
• 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°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 100, 200, 300, 400, and 500 K are taken from engineeringsedge.com .
• Additional and more precise values for N2 for 240–400 K are taken from the engineering toolbox .
• Additional and more precise 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 O22 is a linear interpolation of the values between 240 and 400 K.

Symbol
$k_{gas}$
Unit
W/(m.K)
Formulae
 $2.40073953{\cdot}{10}^{-2}+7.278410162{\cdot}{10}^{-5} \theta_{gas}-1.788037411{\cdot}{10}^{-7} {\theta_{gas}}^2-1.351703529{\cdot}{10}^{-9} {\theta_{gas}}^3-3.322412767{\cdot}{10}^{-11} {\theta_{gas}}^4$ humid air @ 1 atm (Tsilingiris2007) $1.5207{\cdot}{10}^{-11} {T_{gas}}^3-4.8574{\cdot}{10}^{-8} {T_{gas}}^2+1.0184{\cdot}{10}^{-4} T_{gas}-3.9333{\cdot}{10}^{-4}$ air @ 1 bar (Dumas&Trancossi2009) $\frac{2.334{\cdot}{10}^{-3} {T_{gas}}^{\frac{3}{2}}}{164.54+T_{gas}}$ air @ 1 bar (UW/MHTL 8406, 1984) $-2.276501{\cdot}{10}^{-3}+1.2598485{\cdot}{10}^{-4} T_{gas}-1.4815235{\cdot}{10}^{-7} {T_{gas}}^2+1.73550646{\cdot}{10}^{-10} {T_{gas}}^3-1.066657{\cdot}{10}^{-13} {T_{gas}}^4+2.47663035{\cdot}{10}^{-17} {T_{gas}}^5$ dry air @ at 1 atm (Irvine&Liley1984) $2.43e-2+6.63{\cdot}{10}^{-5} \theta_{gas}$ N2 (Vermeer1983) $1.17e-2+6.2{\cdot}{10}^{-5} \theta_{gas}$ SF6 (Vermeer1983) $\frac{1461860-18539.4T_{gas}+77.7891{T_{gas}}^2+0.0241059{T_{gas}}^3}{29661.7+505.67T_{gas}+{T_{gas}}^2}$ SF6 (Assael2012) $-7.302{\cdot}{10}^{-3}+8.075{\cdot}{10}^{-5} \left(\theta_{gas}+\theta_{abs}\right)$ CO2 (linear interpolation) $-2.991{\cdot}{10}^{-3}+7.836{\cdot}{10}^{-5} \left(\theta_{gas}+\theta_{abs}\right)$ O2 (linear interpolation)
Related
$T_{gas}$
$\theta_{abs}$
$\theta_{gas}$
Used in
$\alpha_{gas}$
$h_{conv,c}$
$h_{conv,encl}$
$h_{tr}$
$\mathrm{Pr}_{gas}$
$T_{conv,ce}$
Choices
GasFormula0°C15°C25°C50°C75°C100°C
Air78%N2+21%O2+minor0.024360.0254990.0262470.0277340.0295010.031224
N2N20.0240010.0251080.0258350.0273850.028990.030557
SF6SF60.0116270.0127010.0134120.0147480.0166480.018548
CO2CO20.0146750.0158440.0166430.0186850.0207690.022875
COCO0.024740.025790.0264780.0281630.0298040.031411
O2O20.024350.025550.026340.0285180.305240.32531
H2H20.172580.180050.184880.196780.209390.22142
NH3NH30.0229160.0240730.0249340.027390.0302410.033443
SO2SO20.0084340.0090920.009540.0106810.0118560.013031
HeHe0.14620.151690.155310.16420.17290.18141
ArAr0.0164830.0172450.0177460.0188370.0200150.021161
KrKr0.0086520.0090820.0093630.0100440.0107110.011357
XeXe0.0051070.0053650.0055350.00595790.00637480.0067862
NeNe0.0454120.0470260.0480840.0506730.0531880.055638