Compressibility Charts

[ksb24]

I understand how to use them but my book gives very exact answers that I feel I could only estimate. Is there a formula used when your P(reduced) and T(reduced) aren't nice numbers to work with?
For example a Pr of .977 and a Tr of 1.038. My compressibility chart has a large gap between Tr of 1 and 1.05 in that region so I don't know how the book got an answer of Z=.56

 

[25362]

The graph in the attached link justifies the book:

http://www.et.byu.edu/~rowley/ChEn2...Single_Phase_Systems/Corresponding_States.htm

 

[katmar]

You can calculate an estimate for the compressibility factor using the appropriate Equation of State. Calculating to a higher precision does not automatically make the answer more accurate.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[ksb24]

@25362
That is the same graph that i use. I understand how you could estimate the Pr easily but not the Tr because they are curves.

 

[25362]

Katmar is absolutely right.
The article gives an example and clearly says Tr was interpolated.

 

[georgeverghese]

As Pr approaches 1.0, Tr approaches 1.0, the error in predicting z increases to about 30% according to the narrative in Perry, which is probably why the graph stops in this area. If you need some ballpark values on this through a numerical expression, you could try using the Redlich Kwong EOS or other similar EOSs; which you can find in physical chem uni textbooks or chem engg texts ( else Perry Chem Engg Handbook also gives you a few methods on this).