Heat capacity of air at low temperatures

In summary, the tabular values for heat capacity and ratio gamma are available for air at low pressures and temperatures, but only for high pressure values. For low pressure and low temperature calculations, the Engineering Toolbox has tabular values. For high pressure calculations, a computer database can be used.
  • #1
jpo
47
0
Hello,

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

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

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

Many thanks in advance.
 
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  • #3
Thank you, nasu

these are at p = 1 atmosphere

I have been trying to find data for low pressures and temperatures
 
  • #4
This is what I also found:

http://www.nist.gov/data/PDFfiles/jpcrd581.pdf

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
 
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  • #5
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
Q_Goest,

thank you very much indeed

Perhaps this is the formula you were referring to
 

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  • #7
jpo said:
Thank you, nasu

these are at p = 1 atmosphere

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

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

Thank you all for your replies
 

Related to Heat capacity of air at low temperatures

1. What is heat capacity?

Heat capacity is the amount of heat energy required to raise the temperature of a substance by 1 degree Celsius. It is typically measured in units of joules per degree Celsius (J/°C).

2. How does heat capacity change with temperature?

Heat capacity generally increases with temperature. This is because at higher temperatures, molecules have more thermal energy and are able to store more heat energy for a given temperature change.

3. Why does the heat capacity of air decrease at low temperatures?

The heat capacity of air decreases at low temperatures because the molecules are moving less and have less thermal energy. This means that they are less able to store heat energy, resulting in a lower heat capacity.

4. How is the heat capacity of air at low temperatures measured?

The heat capacity of air at low temperatures can be measured using a calorimeter, which is a device that measures the amount of heat required to raise the temperature of a substance. The calorimeter is filled with air and the temperature change is recorded as heat is added to the system.

5. Why is the heat capacity of air at low temperatures important?

The heat capacity of air at low temperatures is important in understanding how heat is transferred and stored in the atmosphere. It also plays a role in weather patterns and climate, as changes in heat capacity can affect the temperature and density of air, which can impact the movement of air masses and the formation of weather systems.

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