Thermodynamic Data for Nitrogen

[boneh3ad]

Does anyone have a good source of saturation data for nitrogen at low pressures? By low pressures, I mean something along the lines of 0.01 atm.

Thanks,

 

[Mech_Engineer]

I was going to recommend NIST's Themophysical Properties of Fluid Systems database, but their saturation data for Nitrogen only goes down to about .125atm.

Still, judging by the shape of the curve you might consider interpolation if you can't find anything else. Keep in mind we're talking about seriously cryogenic temperatures at those low pressures, probably less than 10K!

 

[boneh3ad]

Right. I ran into the same problem as the NIST web book is typically my go-to source as well.

Extrapolating may provide a reasonable estimate. The point of my query is that for supersonic wind tunnels you can achieve static temperatures that low and if you don't pay attention to the saturation temperature of your gas, you can see liquefaction occur. I am planning on writing a homework problem based on this but was trying to make sure the data was readily available first. Maybe I'll just stick to helium. That is more commonly used anyway.

 

[Mech_Engineer]

Well since the saturation temperature of Nitrogen at that low of a pressure is <10K, you shouldn't need to worry about condensation unless you're doing tests in a wind tunnel near absolute zero...

 

[boneh3ad]

Again, you can easily get down into that range in a wind tunnel if you have a high enough Mach number. For example, in a Mach 10 wind tunnel, if you started with your reservoir at room temperature (300K) you would have a static temperature in your test section of 14K. This is why wind tunnels operating at high Mach numbers must have the flow preheated.

 

[Mech_Engineer]

It looks like Helium's saturation temperature will be very low, less than 2K if we believe the quick and dirty power series fit interpolation from Excel.

Looking at the data sets side by side Nitrogen is more difficult to predict than I expected because it's unclear how its properties change at very low pressures. It seems that it would have to asymptotically approach (0.000 K , 0.000 atm) but a simple power series fit doesn't do a very good job representing that... so basically don't listen to me ;-)

 

[boneh3ad]

Haha, yeah. NIST has data sufficient for helium so I will just use that. Helium is actually used in wind tunnels more often that pure nitrogen anyway, so it is probably a more "relevant" problem.