Query - Compressed air line sizing using nomograph 1

[chemks2012]

Hello all,

I have one query for compressed air line sizing. Please find the attached file for quick calcs and summary of this post.

Problem

http://www.engineeri...ssure-d_36.html

A plant receives compressed air at 25Nm3/min and 7barg. Please size the line for compressed air intake. [Assumption: assume given nomograph is for the supply pressure of 7barg]

Query

What is the 'Free Air Flow (cfm)' in the Nomograph? Is it the flowrate at actual conditions [at 20deg C and 7barg] or standard conditions [15degC and atmospheric pressure]

If we select 3" pipe at actual flowrae of 119.92 cfm, the pressure drop is about 0.08psi/100ft

If we select 3" pipe at standard flowrae of 930.66scfm, the pressure drop is about 0.6psi/100ft

Regards,
KS

 

[Latexman]

A gas volume or volumetric flow rate without a reference temperature and pressure is useless. That web page and nomograph is not perfectly clear to me on the definition of "free air". It does a pretty good job on SCFM, but it leaves you wondering the relationship between "free air" and SCFM. I suspect "free air" = SCFM, but it really should be clear.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[chemks2012]

Thanks Latexman.

 

[katmar]

"free air" is the term used by compressor manufacturers to specify the inlet conditions of the air. It would usually be in the region of 15 to 20 degrees C and 1 atm abs, but it needs to be specified for the actual ambient conditions. Anyone who has ever worked at high altitude will have experienced the never-ending confusion this causes when your atmospheric pressure is only 12 or 13 psia.

The lines you have drawn on the nomograph are wrong. The 119.9 cfm line is drawn at about 280 cfm, and the 930 cfm is drawn at about 800 cfm. 119.9 cfm is not free air flow - it is the actual flow rate. You should be sizing for the 930 cfm of free air flow.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[chemks2012]

Hi Katmar,

Thanks for all your input and help.
Ooops!.. I got wrong values on x axis…
Thanks
KS