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cp values for really low temperature

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Old   May 13, 2013, 07:41
Default cp values for really low temperature
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My problem is that i need them for really low temperature. I have max Mach Number of about 8 so may temperture are pretty low about 20 K which model should i use?

is janaF still valid in this temperatures?

and how to get the values?

Best Regards

Henning
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Old   May 14, 2013, 03:15
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Christian Lucas
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Hi,

have a look at the paper where the janaF data comes from. In the paper, a temperature range is stated.

Are you sure that the fluid is still a gas (perfect gas) at 20 K?

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Christian
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Old   May 14, 2013, 08:56
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Thanks for the response


the pressure is pretty low as well about 700 Pa, which is under the triple point for nitrogen. these conditions are only reached for a really short period about 0.1 ms so only a small part of the fluid will become solid.

So the perfect gas should be still valid

what do you think?

the problem is that the janaf coefficients are usually valid until 200 K (i think haven't seen a different case).
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Old   May 15, 2013, 03:17
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Christian Lucas
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Hi,

at the working conditions your describing, I would also say that the perfect gas law can't be used anymore. You can find a real gas implementation in OpenFOAM 1.6 ext. here, which might be better suited near the vapor dome.

Real Gas EOS

The question is, if you really need to use "correct" thermodynamics in this small local area where the low temperatures occurs or if you should only insure that your thermodynamics return reasonable results (e.g. positive specific heat).

Kind Regards
Christian
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