air flow

[minicooprc]

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?

[minicooprc]

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.

[studiot]

 

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

[swansont]

!

Moderator Note

Similar questions merged.

[minicooprc]

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

[studiot]

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.

[minicooprc]

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

[studiot]

 

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.

[minicooprc]

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

[studiot]

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.

[minicooprc]

where does 1/12 come from

[studiot]

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

[minicooprc]

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?

[studiot]

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?

[minicooprc]

well how does pressure relate to all this

[BloGGer004]

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

[studiot]

 

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

[minicooprc]

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