Originally Posted by
John Coloccia
I disagree that you maintain the same flow when you transition to 4".
That was never stated...at least by me. Please re-read my earlier response.
The statement that I was responding to was that "adding a 4" duct at the end of a 6" run makes the run behaves like it is all made up of 4". That is simply not the case whether calculated or properly measured. Rather, it makes the run behave less than an entire 6" duct run but more than an entire 4" duct run.
By the way, air is indeed an ideal gas (PV=nRT), but that's irrelevant in the discussion here. That's because there are no density changes at these low pressure differentials (i.e., systems typically operate with a differential pressure of less than 1 psi) and are therefore considered an incompressible gas at these low pressures (i.e., P & V remain constant). Also, the temperature (T) doesn't change significantly from start to finish. So, nothing changes in the ideal gas equation of PV=nRT and it can be ignored.
Jeff
Last edited by Jeffrey Makiel; 01-22-2011 at 6:17 PM.
Reason: Gramma'
Thank goodness for SMC and wood dough.