Air density at high pressure 2

[mecheng66]

I'm looking for a formula to estimate the density of air (approx 20C at 60-100psi). Do the ideal gas laws still apply at these pressures?

 

[israelkk]

Yes

 

[insult2injury]

Take a look at a compressibility chart.

I2I

 

[katmar]

A generalized compressibilty chart will quickly give you a good "feel" for where you can apply the ideal gas law. Have a look at the figure on page 6 of the document

http://courses.chem.psu.edu/chem453-544/summaries/summary_2.pdf

For air at 20 deg C your reduced temperature is about 2.2. From this chart I would estimate that the ideal gas law will give you answers to within 2 or 3% all the way up to 2,000 psi.

While the chart is the best way to quickly get an overall feel for the situation, you can also use a simple Equation of State like Peng Robinson to estimate the compressibility. If PR gives an answer close to 1.0 then you know ideal behavior is a reasonable assumption. You can download the free units converter program "Uconeer" from my web site (see signature below) and use the Peng Robinson calculator built into it to estimate densities of common gases.

Of course it depends on why you need the density. If you are sizing air lines then you do not need extreme accuracy. The data you use must suit the application.

Harvey

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Tunalover]

For altitudes up to 7 miles,
absolute pressure at altitude=
abolute pressure at sea level
times: [(288-.00198z)/288]^4.256
where z=altitude in feet.


Tunalover

 

[Tunalover]

Note also that [(density at altitude)/(density at sea level)]=[(288-.00198z)/288]^4.256 where z=altitude in feet.

A lot simpler to use than a pile of charts, tables, and graphs!



Tunalover