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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)

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    $\begingroup$ 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. $\endgroup$ – Chet Miller Apr 12 at 14:06
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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 $p=0.5\ \mathrm{bar}$.

Note that the absolute value of enthalpy at a single state point is meaningless; it is only the difference between two different state points that matters.

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  • $\begingroup$ Thanks, I need to find the difference between the enthalpy of nitrogen at two different set-points [(T = 295.15, P = 1 bar) and (T = 308.46, P = 0.5 bar)]. I do not have access to the NIST database. So I tried to look up the values from Perry's Engineering Handbook. I have the table for the enthalpy values but it only gives me values at certain conditions. I obtained the enthalpy for (T = 295.15, P = 1 bar), which is 306.168 kJ/kg. It would be really helpful if you could check the enthalpy at (T = 308.46, P = 0.5 bar) $\endgroup$ – Tammy Chong Apr 15 at 10:06
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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.

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