Air pipe flow system

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1. May 19, 2015

matt1996

I'm working in an engineering internship after my first year and we haven't covered fluid dynamics in my program yet. I've been assigned to find flow rates and velocities in several branches of a suction (dust collection) system in our factory. The main branch has a diameter of 30" and is attached to a suction system "sucking" 30 000 cfm total, and there are several other branches and sub-branches with varying diameters ultimately attached to machines which create the dust to be sucked up (rough diagram attached, colour-coded for different diameters.) How can I find the cfm and velocity in each branch? Do I need more information?
Thanks

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2. May 21, 2015

Staff: Mentor

Welcome to PF!

If you are sure the total is 30,000 CFM, you can just use the ratio of the areas of the branches...

...but I suspect you actually aren't sure the total is 30,000 CFM. Where did you get that number?

3. May 22, 2015

matt1996

Thanks for the reply. the fan draws (approximately) 30 000 cfm at full capacity according to the manufacturer. So since the head loss due to the pipe lengths and minor sources is minimal (I calculated it to be about 5% or so for the entire system) I can just assume the flow drawn through each sub-branch is proportional to its area relative to the areas of other sub-branches on the same main branch? For example in the diagram if FL4 sander's pipe has twice the area of FL4 finisher's, 2/3 of the flow from branch 3 will come from the sander?