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 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.

 

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, 201411 yr by studiot

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Moderator Note

Similar questions merged.

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

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.

so the cfm would be the same no matter what size the pipe?

 

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.

so given the formula q=av solving for v and converting to mph i get only 3mph this cannot be right

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.

where does 1/12 come from

A 2" pipe has a 1" radius and 1" is 1/12 feet, yes?

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?

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?

well how does pressure relate to all this

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

 

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

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