minicooprc Posted May 14, 2014 Share Posted May 14, 2014 say i have 500 cfm flowing thru 2" pipe and i have an adapter to 3" pipe will that change the cfm or velocity or both and what equation(s) would i use to calculate the pipe diameter change? Link to comment Share on other sites More sharing options...
minicooprc Posted May 14, 2014 Author Share Posted May 14, 2014 i have a constant source that produces 500CFM out of a 1.5 pipe and need to expand to 2.5"pipe. i need to know how to calculate the amount of pressure dropped and or velocity. Link to comment Share on other sites More sharing options...
studiot Posted May 14, 2014 Share Posted May 14, 2014 (edited) what equation(s) would i use to calculate the pipe diameter change? [math]\Delta \Phi [/math] = [math]\frac{{2\tan \theta }}{L}[/math] Where delta_phi is the pipe diameter change, theta the flare angle of the adapter and L the pneumatic length of the adapter. Is this what you really want or would you like to explain your needs further? Edited May 14, 2014 by studiot 1 Link to comment Share on other sites More sharing options...
swansont Posted May 14, 2014 Share Posted May 14, 2014 ! Moderator Note Similar questions merged. Link to comment Share on other sites More sharing options...
minicooprc Posted May 14, 2014 Author Share Posted May 14, 2014 yeah that was way over my head... ok i think i got everything figured out but what is the pneumatic length and that doesnt really help me with change in cfm and velocity of the air Link to comment Share on other sites More sharing options...
studiot Posted May 14, 2014 Share Posted May 14, 2014 You cannot change the volumetric flow rate (cuft/min) by changing the pipe size or air would accumulate somewhere (or worse appear out of nowhere). The volumetric flow rate Q = Area cross section times the velocity. Note for your units the area is in square feet and the velocity in ft/min. Your second question, what is the diameter change from a 2" pipe to a 3" pipe is surely (3"- 2") = 1"? You cannot calculate the flow within the adapter or about 3 diameters upstream or downstream by these methods. Link to comment Share on other sites More sharing options...
minicooprc Posted May 14, 2014 Author Share Posted May 14, 2014 so the cfm would be the same no matter what size the pipe? Link to comment Share on other sites More sharing options...
studiot Posted May 14, 2014 Share Posted May 14, 2014 so the cfm would be the same no matter what size the pipe? Within limits, yes. If you tried to force the air into too small a pipe, say 1/16", you would probably not be able to do it - the resistance would be too great. And if you opened out the pipe too far. say 72", it would become a chamber and air would start to circulate as in the atmosphere. Link to comment Share on other sites More sharing options...
minicooprc Posted May 14, 2014 Author Share Posted May 14, 2014 so given the formula q=av solving for v and converting to mph i get only 3mph this cannot be right Link to comment Share on other sites More sharing options...
studiot Posted May 14, 2014 Share Posted May 14, 2014 Try the arithmetic again. 500 cfm = 500 x 60 cuft/hour = 30,000 cfh v = 30000/(pi x (1/12)2) =ft per hour divide this by 5280 to get to mph. Link to comment Share on other sites More sharing options...
minicooprc Posted May 14, 2014 Author Share Posted May 14, 2014 where does 1/12 come from Link to comment Share on other sites More sharing options...
studiot Posted May 15, 2014 Share Posted May 15, 2014 A 2" pipe has a 1" radius and 1" is 1/12 feet, yes? Link to comment Share on other sites More sharing options...
minicooprc Posted May 15, 2014 Author Share Posted May 15, 2014 thanks for your help i think i got it ok so i believe i got this right for a 1.5" pipe flowing 500cfm, velocity would be 463 mph and thru a 3" pipe 115.75 mph right? Link to comment Share on other sites More sharing options...
studiot Posted May 15, 2014 Share Posted May 15, 2014 I haven't checked the arithmetic but your figures are the right sides of the value I got for a 2" pipe. However do you not think your value for the 1.5" pipe is telling you that that flowrate is impractical for such a pipe? Link to comment Share on other sites More sharing options...
minicooprc Posted May 15, 2014 Author Share Posted May 15, 2014 well how does pressure relate to all this Link to comment Share on other sites More sharing options...
BloGGer004 Posted May 28, 2014 Share Posted May 28, 2014 say i have 500 cfm flowing thru 2" pipe and i have an adapter to 3" pipe will that change the cfm or velocity or both and what equation(s) would i use to calculate the pipe diameter change? I Don't think this will change the velocity of the "air Flow" through the pipe ; but if so please tell me why I am wrong ; and explain how this will work Please and thanks Link to comment Share on other sites More sharing options...
studiot Posted May 28, 2014 Share Posted May 28, 2014 but if so please tell me why I am wrong It's called the continuity equation. https://www.google.co.uk/search?hl=en-GB&source=hp&q=continuity+equation&gbv=2&oq=continuity+eqa&gs_l=heirloom-hp.1.0.0i10.1172.5203.0.7703.14.13.0.1.1.0.188.1624.1j12.13.0....0...1ac.1.34.heirloom-hp..0.14.1656.ekvxV8MoHaw Link to comment Share on other sites More sharing options...
minicooprc Posted May 29, 2014 Author Share Posted May 29, 2014 ok i think we are getting away from what i need...another example if you have a leaf blower that creates 300 cfm what changes if you increase the pipe size it flows thru??? pressure volume air speed...etc Link to comment Share on other sites More sharing options...
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