How to determine duct sizes from calculated pressure drops?
How to determine duct sizes from calculated pressure drops?
(OP)
I'm trying to redesign a pneumatic transport system, so I know that the optimum velocity to move my product is 5000 fpm and i know our production rates, my question is how do i know if the current duct sizes are suitable for the new air volume that i assumed.





RE: How to determine duct sizes from calculated pressure drops?
http://www.me.ua.edu/me407/f04/E-Ductulator.xls
If you know the duct dimensions, you know cfm, and pressure drop can be obtained from the ductulator.
e.g.,
12" round would be 3,927 cfm with 2.17 in. w.c. pressure drop per 100 linear feet;
10" x 10" would be 3,472 cfm with 2.43 in. w.c. drop per 100 feet;
24" x 24" would be 20,000 cfm with 0.85 in. w.c. drop per 100 feet.
What are the current duct sizes?
RE: How to determine duct sizes from calculated pressure drops?
Thank you
RE: How to determine duct sizes from calculated pressure drops?
In fact, the pipe is a little smoother.....
I'll guess your flow is turbulent.
RE: How to determine duct sizes from calculated pressure drops?
The flow through your 26" x 26" duct would be 23,470 cfm, but pressure drop will vary based on the duct: galvy or spiral would be .31 in. w.c. in the 40 foot run; PVC or aluminum .30; 'smooth liner' .42; fiber liner .57; flex duct .49.
They don't seem to vary tremendously, probably because it's a pretty big duct and the bulk of the stream would be unhindered by friction. Maybe use the fiber liner model as a conservative approach (assume a pressure drop of 0.6 in. w.c.).
RE: How to determine duct sizes from calculated pressure drops?
thanks
RE: How to determine duct sizes from calculated pressure drops?
1. Particle size matters.
2. You're asking 205 lb/min of air (density 0.075 lb/ft3) to move 125 lb/min of product (density in maybe the 40-80 lb/ft3 range?). Is that practical or do you need a bigger duct moving more air? I anticipate the product would fill up and dam the duct in short order.
3. We get 2.7" pressure loss in the duct from friction, considering air density alone. What about the pressure loss associated with forcing the air and product into the cyclone? Does the cyclone manufacturer have a spec for inlet pressure required to be effective?
RE: How to determine duct sizes from calculated pressure drops?
You will find an excellent article on pneumatic conveying system design from the link below.
http://www.cheresources.com/pnuconvey.shtml