# Heat capacity of air at low temperatures

1. Jul 12, 2011

### jpo

Hello,

would someone know where can one find tabulated values for the heat capacity of air $c_{p}$ or the ratio $\gamma = c_{p}/c_{v}$?

I need those at low temperatures and pressures, e.g. tending towards zero.

So far I was only able to find $\gamma$ tabulated for high pressures in Perry's Chemistry Handbook.

Many thanks in advance.

2. Jul 12, 2011

### nasu

3. Jul 13, 2011

### jpo

Thank you, nasu

these are at p = 1 atmosphere

I have been trying to find data for low pressures and temperatures

4. Jul 13, 2011

### jpo

This is what I also found:

http://www.nist.gov/data/PDFfiles/jpcrd581.pdf [Broken]

But the low temperature/pressure data is only on the dew/bubble lines where air becomes liquid...

I need data for air in the gas phase

Last edited by a moderator: May 5, 2017
5. Jul 13, 2011

### Q_Goest

Here's a source where you can determine Cp and Cv for the individual components (ie: N2, O2, Ar, etc...) for any pressure and temperature, though it doesn't combine those gasses in the form of air. I'm not absolutely sure but I would assume the overall Cp and Cv would simply be some function of the partial pressures.
http://webbook.nist.gov/chemistry/fluid/

Maybe someone else can provide a function for how they get combined.

If you can't get an answer or need to check the values, I have a computer database that can output Cp and Cv for air at any pressure and temperture.

6. Jul 13, 2011

### jpo

Q_Goest,

thank you very much indeed

Perhaps this is the formula you were referring to

#### Attached Files:

• ###### hc.jpg
File size:
18.5 KB
Views:
396
7. Jul 15, 2011

### klimatos

Although gamma is a dimensionless number, its two components are not dimensionless. They are usually expressed in units of energy per unit of mass. As such, they are largely independent of pressure.

Specific heat at constant volume is obviously independent of pressure. Specific heat at constant pressure has the same value for a pressure of 50 hPa as for a pressure of 1000 hPa.

I think that you may safely use the tabular values in the Engineering Toolbox for your low pressure and low temperature calculations. Within the accepted limits of scientific accuracy and precision, of course.

8. Aug 7, 2011

### jpo

I was able to find the book "Thermodynamic properties of air" and it will do

Thank you all for your replies