Gas Specific Heat

[mielke]

Can anyone help me with understanding how gas properties (espicially specific heat) are affected by pressure. I am looking for only quantitative help (ie equations relating thermophysical properties to gas pressure).

If anyone can help or refer me to something i greatly appriciate it.

 

[dcasto]

for hydrocarbons, as pressure goes up Cp goes up slightlty. C.C. Li produced a report on heat capacities as did API, NIST (Refprop), NBS (81), I've looked into them as the change in Cp (Cv) is typically low as the pressure changes. The temperature has a large effect.

This should get going in the right direction.

 

[zdas04]

I'm with dcasto, I don't think that any of the old correlations ever worked very well, and the EOS approach in something like REFPROP is far more reliable. If it is something you need in a program or for an ongoing calculation you can run a hundred data points in RefProp for your specific gas and input it as a table.

David

 

[mbt22]

I keep coming back to "The Properties of Gases and Liquids" by Poling, Prausnitz and O'Connell. Not necessarily for data, but to refresh myself on what to expect and what the limits of applicability of the various methods are.

 

[25362]

([∂]Cp/[∂]P)_T = -T([∂]²V/[∂]T²)_P

and integrating between, say, 1 atm absolute and P, at constant temperature one can obtain:

[Δ]Cp = - T[∫][∂]²V/[∂]T²)_PdP.

And,

([∂]Cv/[∂]V)_T = T([∂]²P/[∂]T²)_V

Therefore, applying equations of state for real gases, these molar values can be estimated.

 

[dcasto]

From "Elements of the Theory of Gases" here is a quote.

The most astonishing consequence of the table of Cv in the CRC handbook is the absence of significant contributions due to vibrational motion of atoms.

This is why there is little change in Cv in gases.

 

[ginsoakedboy]

NIST Chemistry Webbook

 

[FOURe]

When considering species behaving as ideal gas, specific heat is either constant or just depends on temperature -- there is no pressure dependency ...

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