Ok, I think I have some results now. I studied up on this for what seems like about the last 8 hours (probably closer to 2 hours in reality though) so I hope I did this right and I hope the results are helpful to the discussion.
Ok, above the orange line is a random pic of a Moody diagram. Never seen this thing before so I'm not sure I'm qualified to read it correctly.
Below the orange line is the results of a random air flow simulator. Duct is simulated as PVC with 2 inch diameter, 90 inch length.
I wasn't sure what to enter for cfm so I used a couple different velocity to flow (m/s to cfm) calculators to make sure the results match each other (as I usually do with simulators and calculators when I don't know the underlying math.)
Both these calculators say 10 m/s through a 2 inch diameter hole = 42.894 or 42.946 cfm (slightly different results in each), so that's what I entered. This seems to make sense because the calculated velocity is 1966.2 fpm, which is roughly 10 m/s, as expected.
Then I used the calculated Reynolds number and the calculated friction factor to plot out where this design falls on the Moody chart (at the point where my design is pushing exactly 10 m/s) with a big red X.
I'm not sure if I'm reading the Moody chart right but it appears that when my design is at pushing exactly 10 m/s the red X is almost exactly midway between the completely laminar flow line and the completely turbulent line.
I think this proves my point, but like I said I'm not sure I'm reading the graph right. The Reynolds number is pretty high but I'm not sure what that means on it's own. A Reynolds number of 4000 indicates the onset of turbulence as far as I can tell from my quick research, but I have no idea how this calculated Reynolds number as shown in the pic translates to compression or chuffing.
So I would appreciate some input on this but I'm assuming that if anyone knew what this meant exactly they would have brought up the Moody diagram, Reynolds number and friction factor a long time ago.
As always, I will still be quite happy if this info proves me wrong as long as I end up with the correct answer in the end.Edited by diy speaker guy - 12/11/12 at 11:29pm