CFM flow rate with different inlet and outlet areas

[JohnPinnacle]

Hello,

Here are the knowns:
Inlet open area = 17 inches^2
Outlet open area = 30 inches^2
Internal Fans = 270 cfm (3 fans @ 90 cfm each)

What is the CFM through the system and what's the equations used to figure this out?

Thanks a ton!
John

 

[russ_watters]

The answer appears to be given in the problem statement: 270 cfm.

 

[JohnPinnacle]

The fan spec is 90cfm per fan. That doesn't mean that 270cfm (3 fans) is what will exhaust out the rear of the unit. If I have a huge fan inside a box and a very little inlet or outlet, the fan will be choked and pressure will build due to the open air restriction.

 

[russ_watters]

You'll need to look at fan curves and estimate pressure drop through your system then.

Do you have a sketch you can upload?