Estimating pressure drop of air in pipes
Estimating pressure drop of air in pipes
(OP)
Anyone have a good source to estimate pressure drop of air (atmospheric pressure) flowing through pipes (3" to 6" diam). My flowrates are only about 10-15 SCFM. TIA





RE: Estimating pressure drop of air in pipes
http://www.lmnoeng.com/moody.htm
As a nice resource, The Engineering Toolbox has an entire page on fluid mechanics. The selection above was from one of the links on this page:
http://ww
Specific charts and tables have been developed for HVAC ductwork, and can be found in ASHRAE or SMACNA literature.
RE: Estimating pressure drop of air in pipes
Do you think the ASHRAE or SMACNA literature (where can I find it?) has a simple chart I can get a ballpark number from?
RE: Estimating pressure drop of air in pipes
One of the nicest free pressure drop calculators I know of is simply called "dP" and is available from http://www.xs4all.nl/~kostermw/dP/index.htm The only drawback is that it works only in metric units. But I am sure that if you Google for "free liquid pressure drop software" you will get dozens of hits.
In the example you give, the velocities are very low (15 SCFM in a 3" pipe = 5 ft/sec) which is probably why the online calculator you tried choked on the data.
Using my own "home rolled" software and checked with "dP" I get a pressure drop of around 0.0025 PSI per 100 ft of 3" pipe with a flow of 15 SCFM. This is VERY low, and confirms that it was OK to treat the air as an incompressible liquid.
regards
Harvey
RE: Estimating pressure drop of air in pipes
They also have an electronic version available.
http://www.lorencook.com/About/destools.shtml
RE: Estimating pressure drop of air in pipes
Interestingly, that pressure drop is a general midrange value along the line of 500 fpm, a very common HVAC velocity. 15 cfm in a 3" duct is actually 305 fpm, which is not that unusual - just that the flow rates are so small. (Katmar is still right about that one: 5 ft/s x 60 sec/min ~ 300 fpm)
Unfortunately, I have seen real applications where this airflow and duct size is critical.
I apologize for not actually running the numbers (another lesson) when I gave you the first links. However, it is still true that the ASHRAE and Loren Cook charts are magnified versions of the laminar section of the Moody chart. It is linear when plotted on a log-log scale.
Thanks to Walkes for the references.
RE: Estimating pressure drop of air in pipes