Thermodynamic Data for Nitrogen

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Discussion Overview

The discussion revolves around the search for saturation data for nitrogen at low pressures, specifically around 0.01 atm. Participants explore the implications of low saturation temperatures in the context of applications like supersonic wind tunnels, where such conditions may lead to liquefaction of gases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant requests sources for saturation data for nitrogen at low pressures, indicating a specific interest in values around 0.01 atm.
  • Another participant mentions that NIST's database provides saturation data only down to approximately 0.125 atm and suggests interpolation as a possible solution.
  • A participant notes that extrapolation might yield reasonable estimates for nitrogen's behavior at low pressures, particularly in the context of supersonic wind tunnels where static temperatures can drop below 10K.
  • Concerns are raised about the potential for liquefaction of nitrogen at low pressures, especially in high Mach number wind tunnel tests.
  • One participant highlights that helium has a lower saturation temperature than nitrogen and suggests that it may be a more suitable gas for wind tunnel applications.
  • Another participant expresses uncertainty about the predictability of nitrogen's properties at very low pressures, indicating that simple models may not accurately represent its behavior.

Areas of Agreement / Disagreement

Participants express a general consensus that helium is often preferred over nitrogen in wind tunnel applications due to its lower saturation temperature. However, there is no consensus on the availability of reliable saturation data for nitrogen at the requested low pressures, and multiple viewpoints on the predictability of nitrogen's properties remain unresolved.

Contextual Notes

Participants acknowledge limitations in the available data for nitrogen at low pressures and the challenges in modeling its behavior accurately. The discussion also highlights the need for careful consideration of temperature and pressure conditions in experimental setups.

Who May Find This Useful

This discussion may be of interest to researchers and engineers working in fluid dynamics, cryogenics, and related fields, particularly those involved in wind tunnel testing and the use of gases at low temperatures.

boneh3ad
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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,
 
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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!
 
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.
 
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...
 
Last edited:
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.
 
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 ;-)
 

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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.
 

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