# Thermal conductivity and enthalphy data for nitrogen gas

I am struggling to find the data for thermal conductivity and ethalphy of nitrogen gas at reduced pressure (500 mbar). Most of the information is for nitrogen gas at 1 bar or above. Does anyone know where I can find this information? Specifically, I need to know the thermal conductivity and enthalphy of nitrogen at 295.15 K (22 degrees) and pressure of 0.5 bar (500mbar)

• Transport Phenomena, Bird, Stewart, and Lightfoot. Certainly, under these conditions, N2 can be treated as an ideal gas. The data at 1 bar are adequate, and the values are not significantly different. Apr 12, 2019 at 14:06

By way of comparison, using NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) – NIST Standard Reference Database 23, Version 9, I have got a specific enthalpy of $$h=306.26\ \mathrm{kJ/kg}$$ and thermal conductivity of $$\lambda=25.601\ \mathrm{mW/(K\ m)}$$ for nitrogen at a temperature of $$T=295.15\ \mathrm K$$ and a pressure of $$p=0.5\ \mathrm{bar}$$.
The thermal conductivity is largely independent of pressure. Values for nitrogen gas at 1 atm. are (in units of $$10^{-2}$$ W/m/K ) 1.59 at 173.2 K, 2.40 at 273.2 and 3.09 at 373.2 K.
The values are independent of pressure because conductivity is, from kinetic theory of gases, $$\kappa = n\bar v s k_B \lambda_m/6$$ where $$n$$ is the number density of molecules, $$s$$ the number of translational degrees of freedom, 3, $$\bar v$$ the mean speed of the gas and $$\lambda_m$$ the mean free path. (This equation can be re-written as $$\displaystyle \kappa=\frac{\bar v sk_B}{6\sqrt{2}\pi r^2}$$ where $$r$$ is the molecular radius which shows that $$\kappa$$ has no pressure dependence )
The conductivity will be greatest when there are more molecules to carry the energy (large $$n$$) and when they can travel unrestricted through the gas, large $$\lambda_m$$. However, these two terms are in inverse relationship and exactly cancel one another and hence thermal conductivity is largely independent of pressure. The range turns out to be from about $$10^3 \to 10^6$$ Pa.