Calculating Air Pipe Flow System Rates & Velocities

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To calculate flow rates and velocities in a suction system with a main branch diameter of 30" and a total capacity of 30,000 CFM, the flow in each sub-branch can be determined using the ratio of the cross-sectional areas of the branches. Assuming minimal head loss of about 5%, the flow distribution can be proportional to the areas of the branches. For instance, if one branch has twice the area of another, it would receive two-thirds of the flow from the main branch. It is important to confirm the total CFM figure to ensure accurate calculations. Understanding these principles is essential for effective fluid dynamics analysis in engineering applications.
matt1996
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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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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?
 
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?
 
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